LIBRARY 
 
 ANNEX 
 
 2 
 
 m'^ 
 
 S<rY' 
 
 WtM 
 
 )!iY-6'l 
 
New York 
 
 State College of Agriculture 
 
 At Cornell University 
 
 Ithaca, N. Y. 
 
 The 
 
 Professor Dwight Sanderson 
 
 Rural Sociology 
 
 Library 
 
Cornell University Library 
 QE 26.L48 1905 
 
 Elements of geology; a text-book for coll 
 
 924 002 983 645 
 
Cornell University 
 Library 
 
 The original of tiiis book is in 
 tine Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924002983645 
 
ELEMENTS OF 
 GEOLOGY 
 
 A TEXT-BOOK FOR COLLEGES AND FOR 
 THE GENERAL READER 
 
 BY 
 
 JOSEPH LE CONTE 
 
 AUTHOR OF RELIGION AND SCIENCE ; SIGHT : AN EXPOSITION OF THE 
 PRINCIPLES OF MONOCULAR AND BINOCULAR VISION ; EVOLU- 
 TION IN ITS RELATION TO RELIGIOUS THOUGHT, ETC. 
 
 REVISED AND PARTLY REWRITTEN BY 
 
 HERMAN LE ROY FAIRCHILD 
 
 PROFESSOR OF GEOLOGY IN THE UNIVERSITY OF ROCHESTER 
 
 FIFTH EDITION, REVISED AND ENLARGED 
 WITH NEW PLATES AND ILLUSTRATIONS 
 
 NEW YORK 
 
 D. APPLETON AND COMPANY 
 
 1905 
 
fJA, ^Tl 
 
 Copyright, 1877, 1882, 1891, 1896, 1903, 
 By D. APPLETON AND COMPANY. 
 
EEVISER'S PREFACE. 
 
 The growth of geologic science makes it imperative in a work 
 like this, designed as a general treatise and for advanced students, 
 to discuss some of the current problems and the new theories. Just 
 now this is especially true, as changing views on the physical side of 
 the science relating particularly to the earth's origin are unsettling 
 some long-accepted theories (see pp. 88, 296). The teacher should 
 not blame the book if he finds .that a few interrogations have taken 
 the place of supposed facts. The theory of earth-genesis is funda- 
 mental to so many physical problems that the change in that impor- 
 tant theory will mark a new epoch in the development of the science. 
 
 It has been necessary to largely rewrite some sections of the book 
 and to insert several new topics. Pew changea, however, have been 
 made in the text where not required by advancing knowledge ; and the 
 spirit and style of the revered author have been held as the model. 
 
 Acknowledgment of assistance on special subjects is due to many 
 friends, especially as follows : To John M. Clarke, Palaeozoic inverte- 
 brates; David White, Palseozoic and Triassic plants; T. W. Stanton, 
 Postpalseozoic invertebrates ; C. E. Eastman, fishes ; F. E. Lucas, rep- 
 tiles and mammals; C. E. Button, earthquakes; C. K. Van Hise, 
 metamorphism ; T. C. Chamber lin, earth-genesis, etc. 
 
 For new illustrations thanks are tendered to many individuals, 
 to whom credit is generally given in the titles; to Macmillan & Co. 
 for the use of several figures from the works on PalsBontology by 
 A. S. Woodward and Karl A. von Zittel; to A. P. Brigham and 
 G. K. Gilbert for contribution of illustrations from Brigham's Text- 
 Book of Geology and Gilbert and Brigham's Physical Geography. 
 
 Herman L. Faiechild. 
 
 Jwie, 1903. iii 
 
PREFACE TO THE FOURTH EDITION. 
 
 In' this new edition of my Elements of Geology, while the form, 
 and largely the matter, of the third edition are retained, the changes 
 necessitated by the rapid advance of geological science are so numer- 
 ous and important as to require a complete resetting of the whole work. 
 I have striven, however, to keep the work within the limits necessary 
 for a text-book. The changes have been partly by replacement, partly 
 by modification of statement, and partly by addition of new matter. 
 But while more than sixty new figui'es and many new paragraphs are 
 introduced, yet the actual increase in the number of figures is only 
 twenty, and of pages twenty-five. 
 
 The most important additions are a fuller discussion of the difficult 
 subject of earthquakes, in the light of the , recent investigations of 
 Milne, Button, Seebach, and Schmidt ; a brief account of the origin of 
 varieties of igneous rocks ly differentiation of rock-magmas, made ne- 
 cessary by the writings of Iddings and others ; a greater emphasis on 
 the Cambrian as a subdivision of the Palaeozoic ; -the latest results of 
 Walcott, Matthew, and Beecher on the structure and affinities of Trilo- 
 hites J the latest results of Marsh, Cope, Osborn, Scott, and Wortman 
 on the structure and affinities of Mesozoic reptiles and Mesozoic and 
 Tertiary mammals ; some clearer statement on the subject of the 
 causes of the glacial climate ; and a brief discussion of the causes of 
 geological climates in general. 
 
 I wish to acknowledge my obligations to many American geologists 
 for help in preparing this edition, but especially to Profs. Marsh, 
 Beecher, and Pirsson for many valuable suggestions. 
 
 Joseph Le Cokte. 
 
 August 10, 1896. 
 
PEEFACE TO THE FIRST EDITION. 
 
 Ik preparing the following work I have not attempted to make an 
 exhaustive manual to be thumbed by the special student ; for, even if 
 I felt able to write such a work, Prof. Dana's is already in the field, 
 and is all that can be desired in this respect. I have endeavored only 
 to present clearly to the thoroughly cultured and intelligent student 
 and reader whatever is best and most interesting in Geological Science. 
 I have attempted to realize what I conceive to be comprised in the 
 word elements, as contradistinguished from manual. I have attempted 
 to give a really scientific presentation of all the departments of the 
 wide field of geology, at the same time avoiding too great multiplica- 
 tion of detail. I have desired to make a work "which shall be both 
 interesting and profitable to the intelligent general reader, and at the 
 same time a suitable text-book, for the higher classes of our colleges. 
 In the selection of material and mode of presentation I have been 
 guided by long experience, as to what it is possible to make interesting 
 to a class of young men, somewhat advanced in general culture and 
 eager for knowledge, but not expecting to become special geologists. 
 In a word, I have tried to give such knowledge as every thoroughly 
 cultured man ought to have, and at the same time is a suitable founda- 
 tion for the further prosecution of the subject to those who so desire. 
 The ivork is the substance of a course of lectures to a senior class; 
 organized, compacted, and disencumbered of too much detail, by re- 
 presentation for many successive years, and now for the first time 
 reduced to writing. 
 
 Most text-books now in use in this country are, in my opinion, 
 either too elementary on the one hand, or else adapted as manuals for 
 the specialists on the other. I wish to fill this gap — to supply a want 
 felt by many intelligent students and general readers, who desire a 
 
viii PREFACE TO THE FIRST EDITION. 
 
 reallj' scientific general knowledge of geology. Lyell's Elements 
 comes nearest to supplying this want ; but there are two objections to 
 this admirable work : 1. The principles (dynamical geology) are sepa- 
 rated from the elements (structural and historical geology), and treated 
 in a diilerent work ; 2. Its treatment of American geology is of course 
 meager. 
 
 I have treated several subjects in dynamical and structural geology 
 — e. g., rivers, glaciers, volcanoes, geysers, earthquakes, coral-reefs, 
 slaty cleavage, metamorphism, mineral veins, mountain-chains, etc. — 
 more fully than is common. I feel hopeful that many geologists and 
 physicists will thank me for so doing. I am confident that I give 
 somewhat fairly the present condition of science on these subjects. 
 
 In the historical part I have found much more difiiculty in being 
 scientific without being tiresome, and in being interesting without 
 being superficial and wordy. I have attempted to accomplish this difii- 
 cult task by making evolution the central idea, about which many of 
 the facts are grouped. I have tried to keep this idea in view, as a 
 thread running through the whole history, often very slender — some- 
 times, indeed, invisible — but reappearing from time to time to give 
 consistency and meaning to the history. 
 
 If this work have any advantage over others already before the 
 public, it is chiefly in the two points mentioned above, viz., in a fuller 
 presentation of some subjects in dynamical and structural geology, and 
 in the attempt to keep evolution in view, and to make it the central 
 idea of the history. Another advantage, I believe, is that it does not 
 seek to compete with the best works now before the public, but occu- 
 pies a distinct field and supplies a distinct want. 
 
 I have confined myself mostly, though not entirely, to American 
 geology, especially in , giving the distribution of the rocks and the 
 physical geography of the different periods. In only one case have I 
 made American geology subordinate, viz., in the Jura-Trias period, and 
 that only because of the meagerness of the record of this period in this 
 country. 
 
 In a science so comprehensive and many-sided as geology, it is 
 simply impossible, as every teacher knows, to avoid anticipations in 
 one part of what strictly belongs to a subsequent part. It is for this 
 reason that the order of presentation of the different departments, and 
 of the various subjects under each department, is so different in the 
 
PREFACE TO THE PIEST EDITION. ix 
 
 hands of difEerent writers. The order which I have adopted I know is 
 not free from objection on this score, but it seemed to me, on the 
 whole, the best. 
 
 In preparing the work I have, of course, drawn largely from many 
 sources, both text-books and works of original research ; for whatever 
 of merit there be in a work of this kind must consist not so much in 
 the novelty of the matter as in the selecting, grouping, and presenta- 
 tion. • - Such obligations are acknowledged in the pages of the work. 
 I can not forbear, however, making here a special acknowledgment of 
 my indebtedness, in the historical part, to the invaluable Manual of 
 Prof. Dana. I must also acknowledge especial indebtedness to Profs. 
 Marsh, Newberry, and Cope, and the geologists and paleontologists of 
 the United States Surveys, in charge of Prof. Hayden and Lieutenant 
 Wheeler, not only for valuable materials, but also for much personal 
 aid. 
 
contents; 
 
 PAGES 
 
 Introduction ......... o. . 1-2 
 
 PART I. 
 DYNAMICAL GEOLO&T. 
 
 CHAPTER 
 
 I. — Atmospheeic Agencies . 3-9 
 
 II. — Aqueous Agencies . . . . , 9-84 
 
 Sec. 1. Rivers, 9 ; Estuaries, 32 ; Lakes, 33. 
 " 3. Ocean, 34. 
 
 " 3. Ice, 45 ; Glaciers, 45 ; Icebergs, 72o. 
 " 4. Chemical Agencies of Water, 74. 
 
 III. — Igneous Agencies 84-146 
 
 Sec. 1. Interior Heat, 84. 
 •" 3. Volcanoes, 89 ; Geysers, 103. 
 " 3. Earthquakes, 113. 
 
 IV. — Okganic Agencies 146-169 
 
 Sec. 1. Vegetable Accumulations, Peat, 147. 
 " 2. Bog-Iron Ore, 150. 
 " 3. Lime Accumulations, 151. 
 " 4 Phosphate Deposits, 169. 
 " 5. Siliceous Deposits, 169. 
 
 PART II. 
 STRUCTURAL QEOLOGY. 
 I. — General Form and Structure of the Earth .... 170-178 
 
 II. — Stratified or Sedimentary Rocks 178-209 
 
 III. — Unstratified or Igneous Rocks 210-228 
 
 IV. — Metamorphic Rocks 328-235 
 
 V. — Structure Common to all Rocks 235-284 
 
 Sec. 1. Joints and Fissures, 336 ; Faults, 388. 
 " 3. Mineral Veins, 243. 
 " 3. Mountains, 360. 
 
 VI. — Denudation or General Erosion ....... 384-289 
 
 xi 
 
xii CONTENTS. 
 
 PART III. 
 HISTORICAL GEOLOGY. 
 
 CHAPTBK PAGES 
 
 I. — Gkneral Principles 390-396 
 
 II. — Akch^an and Alqonkian Ages 396-300 
 
 III.— Paleozoic Bra 301-430 
 
 Sec. 1. Cambrian and Silurian, 307. 
 " 3. Devonian, 340. 
 
 " 3. Carboniferous, 358; Coal, 366; Climate, 393; Petro- 
 leum and Rock Gas, 401. 
 
 IV.— Mesozoio Era 430-519 
 
 Sec. 1. Triassic, 431. 
 " 3. Jurassic, 441. 
 " 3. Jura-Trias in America, 467. 
 " 4. Cretaceous, 485. 
 
 v.— Cenozoic Era 519-639 
 
 Sec. 1. Tertiary, 531. 
 " 3. Quaternary, 568; Glacial, 569; Champlain, 579; Cli- 
 mate, 613. 
 
 VI.— PsTCHozoic Bra 639-648 
 
 Sec. 1. Antiquity of Man, 633. 
 " 2. Character of Primeval Man, 646. 
 
 Appendix 649 
 
INTEODUOTOEY. 
 
 DEFINITION OF QEOLOGY, AND OF ITS DEPARTMENTS. 
 
 Geology is the physical history of the earth and its inhabitants, 
 as recorded in its structure. It includes an account of the changes 
 through which they have passed, the laws of these changes, and their 
 causes. In a word, it is the history of the evolution of the earth and 
 its inhabitants. 
 
 The fundamental idea of geology, as well as its principal sub- 
 divisions and its objects, may be most clearly brought out by compar- 
 ing it with organic science. We may study an organism from three 
 distinct points of view : 1. We may study its general form, the parts 
 of which it is composed, and its minute internal structure. This is 
 anatomy. It is best studied in the dead body. 2. We may study the 
 living body in action, the function of each organ, the circulation of the 
 fluids, and the manner in which all contribute to the complex phenom- 
 ena of life. This is physiology. 3. We may study the living and 
 growing body, by watching the process of development from the egg 
 to the adult state, and striving to determine its laws. This is embry- 
 ology. 
 
 So, looking upon the earth as an organic unit, we may study its 
 form, the rocks and minerals of which it is composed, and the manner 
 in which these are arranged ; in other words, its external form and in- 
 ternal structure. This is the anatomy of the earth, and is called struct- 
 ural geology. Or, Tve may study the earth under the action of physical 
 and chemical forces, the action and reaction of land and water, of earth 
 and air, and the effects of these upon the form and structure. This is 
 the physiology of the earth, and is called dynamical geology. Finally, 
 we may study the earth in the progress of its development, from the 
 earliest chaotic condition to its present condition as the abode of man, 
 and attempt to determine the laws of this development. This is the 
 embryology of the earth, or historical geology. 
 
 Principal Departments, — The science of geology, therefore, nat- 
 urally divides itself into three parts, viz. : 1. Structural geology, or 
 
2 INTRODDCTOEY. 
 
 geognosy. 2. Dynamical geology, or physical and chemical geology. 
 3. Historical geology, or the history of the earth. 
 
 But there are two important points of difference between geology 
 and organic science. The central department of organic science is 
 physiology, and both anatomy and embryology are chiefly studied to 
 throw light on this. But the central department of geology, to which 
 the others are subservient, is history. Again : in case of organisms 
 — especially animal oi;ganisms-^the nature of the changes producing 
 development is such that the record of each previous condition is suc- 
 cessively and entirely obliterated ; so that the science of embryology is 
 possible only by direct observation of each successive stage. If this 
 were true also of the earth, a history of the - earth would, of course, be 
 impossible. But, fortunately, we find that each previous condition of 
 the earth has left its record indelibly impressed on its structure. 
 
 Order of Treatment. — The prime object of geology is to determine 
 the history of the earth, and of the organisms which have successively 
 inhabited its surface. The structure and constitution of the earth are 
 the materials of this history, and the physical and chemical changes 
 now going on around us are the means of interpreting this structure 
 and constitution. Evidently, therefore, the only logical order of pre- 
 senting the facts of geology is to study, first, the causes, physical and 
 chemical, now in operation and producing structure ; then the structure 
 and constitution of the earth which, from the beginning, have been 
 produced by similar causes ; and, lastly, from the two preceding to un- 
 fold the history of the earth. 
 
 G-eoIogy may be defined, therefore, as the history of the earth and 
 its inhabitants, as revealed in its structure, and as interpreted by 
 causes still in operation.* 
 
 There is no other science which requires for its full comprehension 
 a general knowledge of so many other departments of science. A 
 knowledge of mathematics, physics, and chemistry, is required to under- 
 stand dynamical geology ; a knowledge of mineralogy and lithology is 
 required to understand structural geology ; and a knowledge of zoology 
 and botany is required to understand the affinities of the animals and 
 plants which have successively inhabited the earth, and the laws which 
 have controlled their distribution in time. 
 
 * The great importance of studying "causes now in operation" as a basis of scien- 
 tific geology was first brought out by llutton, but it was through the writings of Sir 
 Charles Lyell that it became generally accepted. 
 
PART I. 
 DYNAMICAL GEOLOGY. 
 
 The agencies now in operation, modifying the structure of the sur- 
 face of the earth, may be classed under four heads, viz., atmospheric 
 agencies, aqueous agencies, igneous agencies, and organic agencies. 
 These agencies haVe operated from the beginning, and are still in 
 operation. We study their Operation now, in order that we may un- 
 derstand their effects in previous epochs of the earth's history — i. e., 
 the structure of the earth. 
 
 While all geologists agree that the nature of the agencies which 
 have operated in modifying the earth's surface has remained the same 
 from the beginning, they differ in their views as to the energy of their 
 operation in different periods. Some believe that theif energy has been 
 much the same throughout the whole history of the earth, while others 
 believe" that many facts in the structure of the earth require much 
 greater operative energy than how exists. We will attempt to show 
 hereafter that neither of these extreme opinions is probably true, but 
 that some of these agencies have been decreasing, while others have 
 been increasing, with the progress of time. It is the constant change 
 Of balance between these which determines the development of the 
 earth. 
 
 CHAPTER I, 
 
 ATMOSPBERW AGENCIES. . 
 
 The general effect of atmospheric agencies is the disintegration of 
 rocks and the formation of soils. The atmosphere is composed of nitro- 
 gen and oxygen, with small quantities of watery vapor and of carbonic 
 acid. There are but few rocks which are not gradually disintegrated 
 ujider the constant, chemical action of the atmosphere. The chemical 
 agents of these changes are oxygen, carbonic acid, and watery vapor, 
 the nitrogen being inert. To these must be added, where vegetation 
 
4 ATMOSPHERIC AGENCIES. 
 
 is present, the products of vegetable decomposition, especially ammo- 
 nia and humus acids. 
 
 Atmospheric agencies graduate so insensibly into aqueous agencies 
 that it is difficult to define their limits. Water, holding in solution 
 carbonic acid and oxygen, may exist as invisible vapor; or, partially 
 condensed as fogs ; or, completely condensed, as rain falling upon and 
 percolating the earth. In all these forms its chemical action is the 
 same, and, therefore, can not be separated and treated under different 
 classes ; and yet the same rain runs off from and erodes the surface of 
 the earth, comes out from the strata and forms springs, rivers, etc., all 
 of which naturally fall under aqueous agencies. We shall, therefore, 
 treat of the chemical effects of atmospheric water in the disintegration 
 of rocks, and the formation of soils, under the head of atmospheric 
 agencies ; and the mechanical effects of the same, in eroding the surface 
 and carrying away the soil thus formed, under the head of aqueous 
 agencies. In moist climates vegetation clothes and protects soil from 
 erosion, but favors decomposition of rocks and formation of soil.* 
 
 Atmospheric agencies are obscure in their operation, and, therefore, 
 imperfectly understood. Yet these are not less important than aque- 
 ous agencies, since they are the necessary condition of the operation of 
 the latter. Unless rocks were first disintegrated into soils by the 
 action of the atmosphere, they would not be carried away and depos- 
 ited as sediments by the agency of water. These two agencies are, 
 therefore, of equal power and importance in geology, but they differ 
 very much in the conspicuousness of their effects. Atmospheric agen- 
 cies act almost equally at all times and at all places, and their effects, 
 at any one place or time, are almost imperceptible. Aqueous agen- 
 cies, on the contrary, in their operation are occasional, and to a great 
 extent local, and their effects are, therefore, more striking and easily 
 studied. Nevertheless, the aggregate effects of the former are equal 
 to those of the latter. 
 
 Soils. — All soils (with the trifling exception of the thin stratum 
 of vegetable mold which covers the ground in certain localities) are 
 formed from the disintegration of rocks. Sometimes the soil is 
 
 * Terminology. — The generic term for the entire sheet of roclc waste which corers 
 land surfaces, of whatever origin or character — is mantle rock, or mantle. The product 
 of rock decay, in situ, is geest, and this word replaces " soil " as generally used in this 
 book. In the strict sense soil applies only to the superficial layer of mantle rock which 
 is adapted to the support of plant life. Materials deposited by stream action are allu- 
 vium, of which siU is the finest, forming the muddy bottoms of lakes and bays. The 
 term drift includes that part of the mantle which is the product of glacial action, while 
 loess is the fine unstratified deposit formed wholly or partly by wind action. Detritus is 
 a general term applied to any material from rock destruction in the process of removal 
 or transportation. 
 
ROCK DECAY. 5 
 
 formed in situ, and, therefore, rests on its parent rock. Sometimes it 
 is removed as fast as formed, and deposited at a distance more or less 
 remote from the parent rock. The evidence of this origin of soils is 
 clearest when the soil is formed in situ. In such cases it is often easy 
 to trace every stage of gradation between perfect rock and perfect soil. 
 This is well seen in railroad cuttings and in wells in the gneissie or 
 so-called primary region of our southern Atlantic slope. On examin- 
 ing such a section, we find near the surface perfect soil, generally red 
 clay; beneath this we find the same material, but lighter colored, 
 coarser, and more distinctly stratified ; beneath this, but shading into 
 it by imperceptible gradations, we have what seems to be stratified 
 rock, but it crumbles into coarse dust in the hand ; this passes by imper- 
 ceptible gradations into rotten rock, and finally into perfect rock. 
 There can be no doubt that these are all different stages of a gradual 
 decomposition. But closer observation will make the proof still 
 clearer. In gneissie and other metamorphic regions it is not uncom- 
 mon to find the rock traversed, in various directions, by veins of 
 quartz or flint. Now, in sections such as those mentioned above, it 
 is common to find such a quartz-vein running through the rock and 
 upward through the superincumbent soil, until it emerges on the sur- 
 face. In the slow decomposition of the rock into soil, the quartz- 
 vein has remained unchanged, because quartz is not commonly 
 affected by atmospheric agencies. 
 
 The depth to which soil will thus accumulate depends partly on the 
 nature of the rock and the rapidity of decomposition, partly on the 
 slope of the ground, and 
 
 partly on climate. In Bra- rf/i TV 
 
 zil, undisturbed soils are 
 found three hundred feet 
 deep. When the slope is! 
 considerable, as at d (Fig- 
 1), the rocks are bare, not 
 
 because no soil is formed, ' j.'.^^ \_lj^,^, seciio'n, Ih^wing Eock parsing into soa' 
 
 but because it is removed 
 
 as fast as formed; while at a the soil is deep, being formed partly by 
 decomposition of rock in situ, and partly of soil brought down from d. 
 Wherever perfect soil is found resting on sound rock, the soil has 
 been shifted. 
 
 If rocks were solid and impervious to water, this process would be 
 almost inconceivably slow ; but we find that all rocks, for reasons to be 
 discussed hereafter, are broken by fissures into irregular prismatic 
 blocks, so that a perpendicular cliff of rock usually presents the appear- 
 ance of rude gigantic masonry. These fissures, or joints, increase im- 
 mensely the surface exposed to the action of atmospheric water. 
 
ATMOSPHERIC AGENCIES. 
 
 Again, on closer inspection, we find even the most solid parts of rocks, 
 i. e., the blocks themselves, penetrated with capillary fissures which 
 allow water to reach every part. Thus the rock is decomposed, or 
 
 Fi8. 8 -Erosion Forms in Granite, near Harney Peak, South Dakota. (Photograph by Em. 
 
 Barbour.) 
 
 becomes rotten, to a great depth below the surface. But, while the 
 rock is gradually changed into soil the soil may be carried away by 
 wind and rain, and the unequal erosion produces a great variety of 
 erosional forms, some of which are repre- 
 sented in Figs. 2 and 3. 
 
 In the process of disintegration the orig- 
 inal blocks lose their prismatic form, and be- 
 come more or less rounded, and are then 
 called lowlders of disintegration. When of 
 great size and resisting decomposition better 
 than the surrounding rocks, they often form 
 huge perched blocks. These must not be 
 confounded with true bowlders and rocking- 
 stones which are brought from a distance, 
 by agencies which we will discuss hereafter, 
 and which are, therefore, entirely different from the subjacent or 
 country rock. 
 
 General Explanation. — The process of rock-disintegration may be 
 explained, in a general way, as follows : Almost all rocks are composed 
 partly of insoluble materials, and partly of materials which are slowly 
 dissolved by atmospheric water. In the process of time, therefore, 
 these latter are dissolved out, and the rock crumbles into an insoluble 
 dust, more or less saturated with water holding in solution the soluble 
 ingredients. To illustrate : common hardened mortar may be regarded 
 as artificial stone; it consists of carbonate of lime and sand; the car- 
 bonate of lime is soluble in water containing carbonic acid (atmospher- 
 ic water), while the sand is quite insoluble. If, therefore, such mor- 
 tar be exposed to the air, it eventually crumbles into sand, moistened 
 with water containing lime in solution. Again, to take a case which 
 
 Via. 3— Balanced K ck. Garden 
 of the Gods, Colorado. 
 
ROCK DECAY. f 
 
 often occurs in Nature, it is not uncommon to find rock through which 
 iron pyrites, FeSj, is abundantly disseminated. This mineral is insol- 
 uble; but under the influence of water containing oxygen (atmospher- 
 ic water) it is slowly oxidized, and changed into sulphate of iron, or 
 copperaSj which, being soluble, is washed out, and the rock crumbles 
 into an insoluble dust or soil, saturated with a solution of the iron 
 salt. We have given these only as illustrative examples. We now pro- 
 ceed to give examples of the principal kinds of rocks, and of the soils 
 formed by their disintegration. 
 
 Granite, Gneiss, Volcanic Rocks, etc. — Granite and gneiss are mainly 
 composed of three minerals, quartz, feldspar, and mica, aggregated 
 together into a coherent mass. Quartz is unchangeable and insoluble 
 in atmospheric water. Mica is also very slowly affected. Feldspar is, 
 therefore, the decomposable ingredient. But feldspar is, itself, a 
 complex substance, partly soluble and partly insoluble. It is essen- 
 tially a silicate of alumina, united with a silicate of potash or soda, 
 although it often contains also small quantities of iron and lime. 
 Now, while the silicate of alumina is perfectly insoluble, the other 
 silicates are slowly dissolved by atmospheric water, with the formation 
 of carbonates, and the silicate of alumina is left as Tcaolin or clay. 
 But, since we may regard the original rock as made up of quartz and 
 mica, bound together by a cement of feldspar, the disintegration of 
 the latter causes the whole rock to lose its coherence, and the final 
 result of the process is a mass of clay containing grains of sand and 
 scales of mica, and moistened with water containing a potash salt. 
 If there be any iron in the feldspar, or if there be other decompo- 
 sable ingredients in the rock containing i^on, such, for example, as 
 hornblende, the clay will be red. This is precisely the nature of the 
 soil in all our primary regions. Volcanic roclcs decompose into clay- 
 soils often, though not always, deeply colored with iron. 
 
 ■ Limestone.— Pure limestone may be regarded as composed of gran- 
 ules of carbonate of lime, cohering by a cement of the same. The 
 dissolving of the cement by atmospheric water forms a lime-soil, 
 moistened with a solution of carbonate of lime (hard water), im- 
 pure limestone is a carbonate of lime, more or less mixed with sand 
 or clay; by disintegration it forms, therefore, a marly soil. 
 
 Sandstones. — Sandstones consist of grains of quartz cemented to- 
 gether by carbonate of lime or peroxide of iron. Where peroxide of 
 iron is the cementing substance, the rock is almost indestructible, 
 since this substance is not changed by atmospheric water: hence the 
 great value of red sandstone as a building material. But, when car- 
 bonate of lime is the cementing material, this substance, being solu- 
 ble in atmospheric water, is easily washed out, and the rock rapidly 
 disintegrates into a sandy soil. 
 
8 ATMOSPHERIC AGENCIES. 
 
 Slate. — In a similar manner slate-rocks disintegrate into a pure 
 clay soil by the solution of their cementing material, which is often a 
 small quantity of carbonate of lime. 
 
 There can be no doubt that all true soils (geest), formed in situ, 
 are produced by decay of the underlying rocks. The best examples 
 in the United States are found in the uplands of the Southern 
 States, especially in regions of crystalline rocks. In the recently 
 glaciated area of the Northern States the old soil has been removed 
 or worked over by glacial ice and water, and the renewal of the soil- 
 making process has only just begun. 
 
 Everywhere the mantle is moving seaward, creeping down the 
 land slopes until seized by streams and borne away. The silt or 
 alluvium of valleys and river , bottoms is only the transported and 
 assorted material derived from rock destruction. 
 
 Mechanical Agencies op the Atmosphere. 
 Frost. — The effects of freezing water are most conspicuous in cold 
 climates and in mountain-regions, where piles of rock rubbish form 
 at the base of steep cliffs (Fig. 4). Such a pile of materials, the 
 
 Pig. 4.— Cliff and Talus, Ravine of Genesee River. 
 
 ruins of the cliff above, is called a talus. In mountainous regions 
 frost is a powerful agent in disintegrating the rocks, and in deter- 
 mining the outlines of mountain-peaks. 
 
 WmAs.—Eolian Deposits. —The effect of winds is seen in the phe- 
 nomenon of shifting sands called Dunes. At Cape Cod, for instance, 
 the sands thrown ashore by the sea are driven by the winds inland, 
 and thus advance upon the cultivated lands, burying them and 
 
RIVERS. 9 
 
 destroying their fertility. The sands from the heaeh on the Pacific 
 coast near San Francisco are driven inland in a similar manner, and 
 are encroaching upon the better soil. Ancient cities and monuments 
 of Egypt have been buried by the encroachments of the Sahara 
 Desert. Dunes two hundred feet in height are piled by winds on the 
 shores of Lake Michigan. On exposed coasts and in arid regions 
 wind-blown sand has some effect in cutting and polishing bare rocks, 
 and the fantastic forms of rock sculpture in the Western States are 
 partly due to this agency. 
 
 In China and central Asia are vast deposits of a brownish, soft, 
 structureless earth which is regarded, in part at least, as the accumu- 
 lation,- through long ages, of wind-borne dust. These are named 
 Loess J after similar deposits in the Ehine Valley. In China they cover 
 thousands of square miles to varying depths up to two thousand feet. 
 The fine-grained deposits over great areas of the Mississippi basin, 
 from Iowa southward, are also regarded as partly of eolic origin. 
 Eolian deposits must contain no rock materials which wind ig incom- 
 petent to carry. The subject is further discussed on page 583. 
 
 CHAPTEE II. 
 
 AQUEOUS AGENCIES. 
 
 The agencies of water are either mechanical or chemical. The 
 mechanical agencies of water may be treated under the threefold aspect 
 of erosion, transportation, and sedimentary deposits. We will consider 
 them under the heads of Rivers, Oceans, and Ice. Under chemical 
 agencies we will consider the phenomena of chemical deposits in 
 Springs and Lakes. 
 
 Section 1. — Eiveks. 
 
 Under the head of river agencies we include all the effects of circu- 
 lating meteoric water from the time it falls as rain until it reaches the 
 ocean : i. e., all the eifects of Rain and Rivers. 
 
 Water, in the form of vapor, fogs, or rain, percolating through the 
 earth, slowly disintegrates the hardest rocks. Much of these percolating 
 waters, after accomplishing the work of soil-making, already treated in 
 the preceding chapter, reappears on the surface in the form of springs, 
 and gives rise to streamlets. A large portion of rain-water, however, 
 never soaks into the earth, but runs off the surface, forming n'ZZs, which 
 by erosion produce furrows. The uniting rills form rivulets, which 
 excavate gullies. The rivulets, uniting with one another and with the 
 streamlets issuing from springs, form torrents, which in their course 
 excavate ravines, gorges, and canons. The uniting torrents, finally issu- 
 
10 AQUEOUS AGENCIES. 
 
 ing from their mountain-home upon the plains, form great rivers, which 
 deposit their freight partly in their course and partly in the sea. Such 
 is a condensed history of rain-water on its way to the ocean whence it 
 came. Our object is to study this history in more detail. 
 
 Erosion of Rain and Rivers. 
 
 The whole amount of water falling on any land-surface may be 
 divided into three parts: 1. That which rushes immediately ofE the 
 surface, and causes the iloods of the rivers, especially the smaller 
 streams ; 3. That which sinks into the earth, and, after doing its 
 chemical work of soil-making, reappears as springs, and forms the 
 regular supply of streams and rivers ; and, 3. That which reaches the 
 sea wholly by subterranean channels. Of these, the first two are the 
 grand erosive agents, and these only concern us at present. Of these, 
 the former predominate in proportion as the land-surface is bare ; the 
 latter in proportion as it is covered with vegetation. 
 
 HydrograpMcal Basin. — An hydrographical basin of a river, lake, 
 or gulf, is the whole area of land the rainfall of which drains into that 
 river, lake, or gulf. Thus the hydrographical basin of the Mississippi 
 Eiver is the whole area drained by that river It is bounded on the 
 east and west by the Alleghany and Rocky Mountains, and on the 
 north by a low ridge running from Lake Superior westward. The 
 whole area of continents, with the exception of rainless deserts, may be 
 regarded as made up of hydrographical basins. The ridge which sepa- 
 rates contiguous basins is called the divide. It is evident that every 
 portion of the land, with the exception of the rainless tracts already 
 mentioned, is subject to the erosive agency of water, and is being worn 
 away and carried into the sea. There have been various attempts to 
 estimate the rate of this general erosion. 
 
 Rate of Erosion of Continents. — This is usually estimated as follows : 
 Some great river, such as the Mississippi, is taken as the subject of 
 experiment. By accurate measurement during every portion of the 
 year, the average amount of water discharged into the sea per second,, 
 per hour, per day, per year, is determined. This is a matter of no 
 small difficulty, as it involves the previous determination of the average 
 cross-section of the river and the average velocity of the current. The 
 average cross-section X average velocity = the average discharge per 
 second : from which may be easily obtained the annual discharge. Next, 
 by experiment during every month of the year, the average quantity of 
 mud contained in a given quantity of water is also determined. By an 
 easy calculation this gives us the annual discharge of mud, or the whole 
 quantity of insoluble matter removed from the hydrographical basin in 
 one year. This amount, divided by the area of the river-basin, will give 
 the average thickness of the layer of insoluble matter removed from the 
 
EROSION OF KAIN AXD KIVERS. H 
 
 basin in one year. To this must be added the soluble matters, which 
 are about one sixth as much as the insoluble. 
 
 Estimates of this kind have been made for two great riyers, viz., the 
 Ganges and the Mississippi. The whole amount of sediment annually- 
 carried to the sea by the Ganges has been estimated as 6,368,000,000 
 cubic feet. This amount, spread over the whole basin of the Ganges 
 (400,000 square miles), would make a layer ^^^ of a foot thick. The 
 Ganges, therefore, erodes its basin one foot in 1,751 years.* The area 
 of the Mississippi basin is 1,244,000 square miles. The annual dis- 
 charge of sediment, according to the recent and accurate experiments 
 of Humphreys and Abbot, is 7,471,411,300 cubic feet, a mass sufficient 
 to cover an area of one square mile, 368 feet deep.f This spread over 
 the whole basin would cover it j^ij^ of a foot. Therefore, this river 
 removes from its basin a thickness of one foot in 4,640 years. The 
 cause of the great difference in favor of the Ganges is, that this river 
 is situated in a country subject to very great annual fall of water, the 
 whole of which falls during a rainy season of six months. The rains 
 are therefore very heavy, and the floods and consequent erosion propor- 
 tionately great. The erosive power of this river is still further increased 
 by the great slope of the basin, as it takes its rise in the Himalaya, the 
 highest mountains in the world. 
 
 Now, since continents may be regarded as made up of hydrographi- 
 cal basins, the average rate of their erosion may be determined either by 
 making similar experiments on all the rivers of the world, or, since this 
 is impracticable, by taking some river as an average. "We believe the 
 Mississippi is much nearer an average river than the Ganges. It can 
 hardly be less than the average, for a considerable portion of the earth 
 — as rainless deserts — is not subject to any erosion. It is probable, 
 therefore, that the whole surface of continents is eroded at a rate not 
 exceeding one foot in 4,640 years. For convenience we will call it one 
 foot, in 5,000 years. We will use this estimate when we come to speak 
 of the actual erosion which has occurred in geological times. 
 
 Law of Variation of Erosive Power. — The erosive power of water, or 
 its power of overcoming cohesion, varies as the square of the velocity of 
 the current {p a v'). The velocity depends upon the slope of the bed,, 
 the depth of the water, and many other circumstances, so numerous and 
 complicated that it has been found impossible to reduce it to any simple 
 law. The angle of slope, however, is evidently the most important cir- 
 cumstance which controls velocity, and therefore erosive power. In the 
 upper portions of great rivers, like the Mississippi, the erosion is very 
 great ; while in the plains near the mouth there may be no erosion, but, 
 
 * Philosophical Magazine, vol. v, p. 261. 
 
 t Humphreys and Abbot, Report on Mississippi River, pp. 148-160. 
 
12 
 
 EROSION. 
 
 on the contrary, sedimentary deposit. The high lands, therefore, espe- 
 cially mountain-chains, are the great theatres of erosion. Pure water, 
 however, erodes very slowly, the main agents of erosion being the gravel 
 and sand carried along by the current. The general effect of erosion is 
 leveling. If unopposed, the final effect would be to cut down all lands 
 to the level of the sea, at an average rate of about one foot in five thou- 
 sand years. But the immediate local effect is to increase the inequalities 
 of land-surface, deepening the furrows, gullies, and gorges, and increas- 
 ing the intervening ridges and peaks up to a certain limit, after which 
 it again decreases. The effect, therefore, is like that of a graver's tool, 
 constantly cutting at every elevation, but making trenches at every 
 stroke, although the final effect is to bring all to one level. 
 
 Thus land-surfaces everywhere, especially in mountain-regions, are 
 cut away by a process of sculpturing, and the debris carried to the low- 
 lands and to the sea. The smaller lines and more delicate touches are 
 due to rain, the deeper trenches or heavier chiselings to rivers proper. 
 The effects of the former are more general and far greateit^m the aggre- 
 gate, but the effects of the latter are far more conspicuous. It is only 
 under certain conditions that rain-sculpture becomes conspicuous. 
 These conditions seem to be a bare soil and absence of frost. Beautiful 
 examples are found in the arid regions of southern Utah. 
 
 Examples op Great Erosion now going on: Waterfalls. 
 
 The erosive power of water is most easily studied in ravines, gorges, 
 canons, and especially in great waterfalls. One of the most interest- 
 ing of these is Niagara. 
 
 Fig. 5.— Bird's-eye View of the Niagara River. 
 
 Niagara : General Description. — The plateau on which stands Lake 
 Erie {P N, Fig. 6) is elevated about three hundred feet above that 
 
WATERFALLS. I3 
 
 of Lake Ontario, and is terminated abruptly by an escarpment about 
 three hundred feet high (P). Prom this point a narrow gorge with 
 nearly perpendicular sides, and two hundred to three hundred feet 
 
 L.CT/E. 
 
 - "^ -^ - ~ •^^^ 
 
 Fig. 6.— Ideal Longitudinal Section through Niagara Kiver from Lake Erie to Lake Ontario. 
 
 deep, runs backward through the higher or Erie plateau as far as 
 the falls (N). The Niagara River runs out of Lake Erie and upon 
 the Erie plateau as far as the falls, then pitches a hundred and sixty- 
 seven feet perpendicularly, and then runs in the gorge for seven miles 
 to Queenstown (Q), where it emerges on the Ontario plateau. Long 
 observation has proved that the position of the fall is not stationary, 
 but slowly recedes at a rate which has been variously estimated at from 
 three to five feet per annum. The process of recession has been care- 
 fully observed, and the reason why it maintains its perpendicularity 
 is very clear. The surface-rock of Erie plateau is a firm limestone (a). 
 Beneath this is a softer shale (&). This softer rock is rapidly eroded 
 by the force of the falling water, and leaves the harder limestone pro- 
 jecting as table-rocks. From time to time these projecting tables are 
 loosened and fall into the chasm below. This process is facilitated by 
 the joint structure spoken of on page 5. 
 
 Recession of the Falls. — Now, there is every reason to believe that 
 the fall was originally situated at Queenstown, the river falling over 
 the escarpment at that place, and that it has worked its way backward 
 seven miles to its present position by the process we have just de- 
 scribed. These reasons are as follows: 1. The general configuration 
 of the country as already described forcibly suggests such an explana- 
 tion to the most casual observer. 3. A closer examination confirms it 
 by showing that the gorge is truly a valley of erosion, since the strata 
 on the two sides correspond accurately (see Fig. 7). The falls have 
 receded during the last fifty years at a rate of about five feet a year. 
 The portion of the gorge thus formed under our eyes does not differ in 
 any essential respect from other portions farther down the stream. 
 Facts relating to the geology of the region make the evidence conclu- 
 sive that the gorge was formed by the present river during the present 
 geologic epoch. 
 
 Other Falls. — The evidence is completed by examination of other 
 great falls. In almost all perpendicular falls we find a similar arrange- 
 ment of strata followed by similar results. The Falls of St. Anthony, 
 in the Mississippi Eiver, are a very beautiful illustration. Here we 
 
14 
 
 AQUEOUS AGENCIES. 
 
 find a configuration of surface very similar to that in the neighbor- 
 hood of Niagara. Above the falls the Mississippi Eiver runs on a 
 plateau which terminates abruptly at the mouth of Minnesota Eiver 
 by an escarpment about a hundred feet high. From this escarpment, 
 backward through the upper plateau, runs a gorge with perpendicular 
 sides nearly a hundred feet high for eight miles to the foot of the falls. 
 The river above the falls runs on a hard, silurian limestone rock, only 
 
 Fig. 7.- 
 
 - Whirlpool Eapids, Niagara Gorge, looking Down-Stream (NorthJ. 
 
 Bishop.) 
 
 (Photograph by I. P. 
 
 a few feet in thickness. Beneath this is a white sandstone, so soft that 
 it can be easily excavated with the fingers.. This sandstone forms the 
 walls of the gorge as far as the escarpment. The recession of the falls 
 by the undermining and falling of the limestone is even more .evident 
 than at Niagara. Tributaries running into the Mississippi just below 
 the falls are, of course, precipitated over the margin of the gorge. 
 Here, therefore, the same conditions are repeated, and hence are 
 formed subordinate gorges, headed by perpendicular falls. Such are 
 the falls and gorge of Minnehaha Eiver, which runs into the Missis- 
 sippi about two miles above the mouth of the Minnesota Eiver. 
 
 Another admirable illustration of the conditions under which per- 
 pendicular falls recede is found in the falls of the numerous tributaries 
 of Columbia Eiver where the great river breaks through the Cascade 
 Eange. The Columbia Eiver gorge is 3,500 to 3,000 feet deep. The 
 walls consist of columnar basalt underlain near the water-level by a 
 softer conglomerate. Every tributary at this point emerges from a 
 deep gorge, headed two or three miles back by a perpendicular wall, 
 
WATERFALLS. IS 
 
 over which is precipitated the water of the tributary as a fall 300 to 
 300 feet high. 
 
 The wonderful falls of the Yosemite Valley, of which there are six 
 in a radius of five miles, one of them 1,600 feet, three 500 to 700 feet, 
 and two 300 to 400 feet high, seem to be an exception to the law given 
 above. Their perpendicularity seems to be the result of the compara- 
 tive recency of the evacuation of the valley by an ancient glacier, and 
 therefore the shortness of the time during which the rivers have been 
 falling, combined with the hardness of the granite rocks. The Yo- 
 semite gorge was not made by the present rivers during the present 
 epoch. 
 
 Time necessary to excavate Niagara Gorge. — All attempts to esti- 
 mate accurately the time consumed in excavating Niagara gorge must 
 be unreliable, since we do not yet know the circumstances which con- 
 trolled the rate of recession at different stages of its progress. Among 
 these circumstances, the most important are the volume of water and 
 the precise relations of the hard and soft strata. The present posi- 
 tion of the falls is apparently favorable for rapid recession, and the 
 rate is about five feet per year. At this rate it would require about 
 7,000 years. But it appears from recent studies that there have been 
 two episodes in the history of Magara when the upper Great Lakes 
 drained directly east, by the Trent River Valley and by the Ottawa 
 Eiver. During these phases Niagara carried only 'the drainage of the 
 Erie basin, and the diminished volume was less effective in gorge- 
 cutting. Emphasizing this factor of the problem, estimates have made 
 the life of Niagara as much as 70,000 years. But whether we adopt 
 the one or the other estimate, this time must not be confounded with 
 the age of the earth. The work of excavating the Niagara chasm be- 
 longs to the present epoch, and the time is absolutely insignificant in 
 comparison with the inconceivable ages of which we will speak in the 
 subsequent parts of this work. The Falls of St. Anthony recedes about 
 five feet per annum, and has made its gorge in about 8,000 years. 
 
 Ravines, Gorges, Canons. — We have already seen (page 12) that 
 ravines, gorges, etc., are everywhere produced in mountain-regions by 
 the regular operation of erosive agents. Nowhere are examples more 
 abundant or more conspicuous than in our own country, and espe- 
 cially in the Western portion. On the Pacific slope, the most remark- 
 able are the gorges of the Fraser and of the Columbia Rivers, fifty 
 miles long and several thousand feet deep; those of the North and 
 South Forks of the American River, 2,000 to 3,000 feet deep in solid 
 slate; the canon of the Tuolumne Eiver, with its Hetchhetchy Valley; 
 the canon of the Merced,'with. its Yosemite Valley, with nearly vertical 
 .granite cliffs, 3,000 to nearly 5,000 feet high ; and, deepest of all, the 
 grand canon of King's Eiver, 3,000 to 7,000 feet deep, in hard granite. 
 
16 
 
 AQUEOUS AGENCIES. 
 
 Some of these great caflons have been forming, ever since the forma- 
 tion of the Sierra Range — i. e., since the Jurassic period. It is possible, 
 also, that in some of them the erosive agents have been assisted by 
 
 Fig. 8. — Lava-Stream cut throngh by Rivers: a a, Basalt: b d. Volcanic Ashes; c e, Tertiary; d d^ 
 Cretaceous Bocks. (From Whitney.) 
 
 antecedent igneous agencies, producing fissures, which have been en- 
 larged and deepened by water and by ice. But there are some, at least, 
 which may be proved to have been produced wholly by erosion, and , 
 that during the present or at least during very recent geological times. 
 We refer especially to those which have been cut through lava-streams. 
 In Middle and Northern California are found lava-streams which 
 have flowed from the crest of the Sierra. By means of the strata on 
 which they lie, these streams are known to have flowed after the end of 
 the Tertiary period. Yet the present rivers have since that time cut 
 great caflons through the lava and into the underlying rock, in some 
 cases at least 2,000 feet deep. Such facts impress us with the immen- 
 sity of geological times. This important point is discussed more fully 
 in a subsequent part of this work. 
 
 FiQ. 9.— Mesa of Shinarump, Southwestern Utah. (Photograph by W. M. Davis.l 
 
 But nowhere in this country, or in the world, are the phenomena of 
 canons exhibited on so grand a scale, and nowhere are they so obviously 
 the result of pure erosion, as in the region of the Grand Plateau of 
 
CANONS, GORGES, ETC. 
 
 11 
 
 Utah, Arizona, New Mexico, and Colorado. This plateau is elevated 
 7,000 to 8,000 feet above the sea, and composed entirely of nearly hori- 
 zontal strata, comprising nearly the whole geological series from the 
 Tertiary downward. Through this series all the streams have cut their 
 way downward, forming narrow canons with almost perpendicular 
 walls several thousand feet deep, so that in many parts we have the 
 singular phenomenon of a whole river-system running almost hidden 
 far below the surface of the country, and rendering the country en- 
 tirely impassable in certain directions (see Fig. 11a). N"or is the 
 
 Fig. 10.— Cailon of the Colorado. (Photogr^h from United States Geological Survey.) 
 
 erosion confined to caiions ; for the rain-erosion has been so thorough 
 and general that much of the upper portion of the plateau has been 
 wholly carried away, leaving only isolated turrets (buttes) or isolated 
 level tables with cliil-like walls (mesas) to indicate their original 
 height. The explanation of these deep and narrow canons is prob- 
 ably to be found in the predominance of stream-erosion over gen- 
 eral disintegration and rain-erosion, which is characteristic of an 
 arid climate. 
 
 Chief among these caiions is the Grand Canon of the Colorado, 
 300 miles long and 3,000 to 6,300 feet deep, forming the grandest 
 natural geological section known. Into this the tributaries enter by 
 side-canons of nearly equal depth, and often of extreme narrowness. 
 Fig. 11 represents the natural proportions of such a canon. 
 
18 
 
 AQUEOUS AGENCIES. 
 
 Time. — These remarkable cations have evidently been cut wholly 
 by the streams which now occupy them, and which are still continuing 
 the work. The work, probably commenced in the early Tertiary with 
 the emergence of this portion of the continent, became more rapid in 
 the latter portion of the Tertiary with the great elevation of the plateau, 
 
 and has continued to the present time. 
 Thus, causes, now in operation are identi- 
 iied with geological agencies. 
 
 In the Appalachian chain gorges and 
 valleys of erosion are abundant, but the 
 evidences of present action are less obvi- 
 ous, and therefore we defer their treat- 
 ment to Part II, for we are now discussing 
 agencies still in operation. Among the 
 more remarkable narrow gorges in this 
 region, we may mention, in passing, the 
 Tallulah Eiver gorge, several miles long 
 and nearly 1,000 feet deep, in Eabun 
 County, Georgia, and the gorge of the 
 French Broad in North Carolina. The 
 general effects of erosion will be more 
 fully treated under Mountain Sculpture 
 (page 278). 
 
 Transportation and Distrilution of 
 
 Fio. 11.— Section of the Virgen River 
 (after Gilbert). 
 
 The specific gravity of most rocks is 
 about 2-5. Immersed in water, they there- 
 fore lose nearly half their weight. This 
 fact greatly increases the transporting 
 power of water. The actual transporting 
 power of water is determined partly by 
 experiment and partly by reasoning on the general laws of force. By 
 experiment we determine the transporting power under a given set of 
 circumstances : by general reasoning we determine its law of variation, 
 and apply the data given by experiment to every possible case. 
 
 Experiments.— It has been found by experiment that a current, 
 moving at the rate of three inches per second, will take up and carry ' 
 along /ree clay; moving six inches per second, will carry fine sand • 
 eight inches per second, coarse sand, the size of linseed ; twelve inches 
 gravel ; twenty-four inches, pebbles; three feet, angular stones of the 
 size of an egg. It will be seen that the carrying power increases much 
 more rapidly than the velocity. For instance, a current of twelve 
 inches per second carries gravel, while a current of three feet per 
 
TBANSPOKTATION AND DISTRIBUTION OP SEDIMENTS. 
 
 19 
 
 second, only three times greater velocity, carries stones many hun- 
 dred times larger. By mathematical analysis the law is determined. 
 
 Fia llo —Bird's-eye View of Marble Ciifii'ii fiom itn' \ c riiijluni Oliffie, near the Mouth of the 
 Paria In the distance the Colorado Biver is seen to rarn lo ine west, where its gorge divides 
 the Twin Plateaus. On the right are seen the Eastern Kaibab Displacements appearing as 
 folds, and farther in the distance as faults." ' . ' 
 
s 
 
 s 
 
 s 
 
 ^ 
 
 s 
 
 
 
 
 s 
 
 
 
 
 
 
 
 
 Fig. 12. 
 
 2Q AQUEOUS AGENCIES. 
 
 That is, the transporting power of a current or the weight of the largest 
 fragment it can carry, varies as the sixth poioer of the velocity. This 
 seems so extraordinary a result that, before accepting it, we will try to 
 make it still clearer by an example. 
 
 Let a (Pig 12) represent a cubic inch of stone, which a current of 
 a certain velocity will just move. Now, the proposition is that, if the 
 
 velocity of the current be doubled, it will 
 move the stone S, sixty-four times as large. 
 That it would do sa is evident from the 
 fact that the opposing surface of I is sixteen 
 times as great as that of «, and the moving 
 force would be increased sixteen times from 
 this cause. But the velocity being double, 
 as we have already seen, the force against 
 
 \ every square inch of I will now be four times 
 that previously against a, and, therefore, the 
 whole force from these two causes would 
 ■ *■ be 16 X 4 = 64 times as great. But the 
 weight is also sixty-four times as great; 
 therefore, the current would be just able to move it. We may accept 
 it, therefore, as a law, that the transporting power varies as the sixth 
 power of the velocity. If the velocity, therefore, be increased ten 
 times, the transporting power is increased 1,000,000 times. 
 
 We have seen that a current running three feet per second, or about 
 two miles per hour, will move fragments of stone of the size of a hen's 
 egg, or about three ounces' weight. It follows from the above law that 
 a current of ten miles an hour will carry fragments of one and a half 
 ton, and a torrent of twenty miles an hour will carry fragments of 100 
 tons' weight. We can thus easily understand the destructive efEects of 
 mountain-torrents when swollen by floods. 
 
 The transporting power of water must not be confounded with its 
 erosive power. The resistance to be overcome in the one case is weight, 
 in the other cohesion ; the latter varies as the square, the former as the 
 sixth power of the velocity. In many cases of removal of slightly co- 
 hering material the resistance is a mixture of these two resistances, 
 and the power of removing material will vary at some rate between 
 v* and v". 
 
 There are certain corollaries which follow from the above law : 
 A. If a current bearing sediment have its velocity checked by any 
 cause, even in a slight degree, a comparatively large portion of the sedi- 
 ment is immediately deposited. But if, on the other hand, the velocity 
 of a current be increased by any cause, in never so small a degree, it 
 will again take up and carry on materials which it had deposited ; in 
 other words, it will erode its bed and banks ; and these efEects are sur- 
 
STRATIFICATION. 
 
 21 
 
 prisingly large on account of the great change in erosive and trans- 
 porting pojver, with even slight changes of velocity. 
 
 B. Water, whether still or running, has a wonderful power of sort- 
 ing materials. If heterogeneous material, such as ordinary earth, con- 
 sisting of grains of all sizes, from pebbles to the finest clay, be thrown 
 into still water, the coarse material sinks first to the bottom, and then 
 the next finer, and the next, and so on, until the finest clay, falling 
 last, covers the whole. In running water the same sorting takes place 
 even more perfectly, only the different kinds of materials are not 
 dropped upon one another, but successively farther and farther down 
 the stream in the order of their fineness. This operation we call the 
 sorting power of water. Advantage is often taken of this principle 
 in the arts to separate materials of difEerent sizes or specific gravities. 
 By this means grains of gold are separated from the gravel with 
 which it is mingled, and emery or other powders are separated into 
 various degrees of fineness. 
 
 1 . — Stratification. 
 
 We have seen that heterogeneous material thrown into still water 
 is completely sorted. This is not stratification, since the various 
 degrees of fineness graduate insensibly into one another. But, if we 
 
 l^^^p,l^j,,j0atl««0i«ti«^,^^ 
 
 Fis. 12a.— stratification in Fine Sand, with Subsequent Faulting. 
 
 repeat the experiment, the coarsest material will fall upon the finest 
 of the previous experiment, and then graduate similarly upward. If 
 we examine the deposit thus made, we observe a distinct line of junc- 
 3 
 
22 AQUEOUS AGENCIES. 
 
 tion between the first and the second deposit. This is stratification, or 
 lamination. For every repetition of the experiment a distinct lamina 
 is formed. To produce stratification it is evident that there must 
 be some variation in the grade of materials or in the deposition proc- 
 ess. Such variability is always a factor in the work of shore currents 
 of seas and lakes, as well as of rivers. Wherever products of land 
 waste are carried out into standing water they are deposited at varying 
 rates, and the least variation or interruption in the process produces 
 aplane of stratification, or even of separation (seam), in the consoli- 
 dated beds (see page 39). 
 
 The velocity of every river-current varies not only very greatly 
 in different portions of the year, as in seasons of low water and seasons 
 of flood, but also (from the constant shifting of the subordinate cur- 
 rents of the stream) from day to day, from hour to hour, and even 
 from moment to moment. It follows, therefore, that deposits in run- 
 ning water are also always stratified. Sometimes extreme beauty and 
 distiactness of stratification in the deposits of large rivers are due to 
 the fact that the several tributaries have their floods at different sea- 
 sons, and bring down differently colored sediments. 
 
 We may, therefore, announce it as a law, that all sedimentary de- 
 posits are stratified; and, conversely, that all stratified masses in 
 which the stratification is the result of sorted material are sedimentary 
 in their origin. Upon this law is founded almost all geological rea- 
 soning. 
 
 2. — Relation of Current-Velocity to Erosion and Sedimentation. 
 
 The force of a current is consumed in two ways, viz., by transpor- 
 tation and erosion. If the current is full-loaded, its whole force is 
 consumed in transportation and none is left over for erosion. Such a 
 river will neither erode nor deposit. If under-loaded, the river wil-l 
 erode; if overloaded, it will deposit. Thus a current of pure water 
 will erode but little, because it carries no graving-tools. If we add 
 sand and gravel, the erosion will increase to a maximum, beyond which 
 it again decreases, because more and more force is consumed in carry- 
 ing, and less and less is left over for erosion ; until finally, in the full- 
 loaded stream, erosion ceases and sedimentation begins. Thus the 
 Platte and Colorado Elvers have about the same slope and velocity; 
 but while the Colorado is deepening its channel, the Platte, on the 
 whole, remains about the same level, sometimes cutting, sometimes 
 depositing. The Colorado is under-loaded, the Platte full-loaded. 
 Again : the Feather Eiver, duririg floods, is overloaded, and builds up 
 by deposit. During low water it scours out what was previously de- 
 posited, even though its velocity is much less. 
 
RIVERS AS INDICATORS OF CRUST-MOVEMENTkS. 23 
 
 3. — Rivers as' Indicators of Crust-Movements. 
 
 The level of the ocean is the general base level toward which erosion 
 tends to reduce land surfaces. This base level should be conceived as 
 the permanent, universal, geometric surface passing beneath all the 
 land masses. Elvers seek to plane their valleys to that base level, 
 without ever accomplishing the task. Local and temporary base levels 
 are established in the courses of streams by barriers or lakes; and 
 trunk streams serve as base levels to their tributaries. 
 
 A mature stream is one which has found adjustment between its 
 power (velocity) and the work it has to do : in other words, its slope 
 is proportioned to its load. A river or a section of a river which has 
 cut down, and filled up, all inequalities in its channel so as to have 
 a uniform slope is said to be graded. A full-loaded stream requires 
 a steeper grade than one with little load. The Platte Eiver is graded 
 on a steep slope because of its heavy load. 
 
 In every graded stream the lowest point is coincident with its 
 base level, and the river work throughout the graded reach is corre- 
 lated with the lower part. Thus it is that any relative change in base 
 level, produced usually by up and down (diastrophic) movement of 
 the land, affects the flow of all streams graded to the base level. If 
 the land area be lifted the graded streams are rejuvenated — that is, 
 their grade and power are increased (see page 31). Eivers thus be- 
 come indicators of the up and down movements of land-surfaces. 
 
 In valley-making two processes are at work, down-cutting by the 
 stream and widening out by weathering. The shape or proportions 
 of a valley depends on 
 the relative effect of 
 these two processes. 
 Wide valleys and low di- 
 vides are characteristic 
 
 of old toTlotTaTlhv V- Fio. 13.— Ideal Section across Grand Cafion (after Dutton): 
 wj. v/iu. i/u^ugicijjiijr, r o a, inner gorges 46, outer cafion walls. 
 
 shaped valleys of youth- 
 ful streams (see page 31). The terraces and broad upper part of the 
 Colorado canon (Fig. 13, & 6) have been regarded as the work of the 
 river while the plateau was long poised at a lower level and the river 
 was well graded. Since then the region has been lifted and the river 
 rejuvenated so that it has cut down another 3,000 feet, making the 
 narrow gorge a a; and it is still cutting. 
 
 On the other hand, a land area by sinking diminishes the grades of 
 its mature streams. The flattened slopes check the velocities of the 
 currents, and the rivers immediately begin to build up, or aggrade, 
 their channels by deposition, until they attain steeper grades, giving 
 velocities sufficient to carry their loads. For example, in the Missis- 
 
24 
 
 AQU50US AGENCIES. 
 
 sippi Eiver the following events are recorded : 1. A higher condition 
 of land, during which it reached gradation, and formed the broad 
 trough r'' r" r" . 2. A subsidence of land and a building up by sedi- 
 
 PiQ. 14.— Generalized Section across the Mississippi River : r" r" r", old bed ; r' r', second bed ; 
 r, present bed ; d' d', old deposits ; d, d, present deposits. , 
 
 mentation d' to the level II. 3. A partial re-elevation and a cutting 
 down 200 feet, to the level r' r'. 4. A resinking and building by- 
 alluvial deposit d of about 50 feet. Thus, while on coast-lines, old 
 sea-margins are indicators of crust movements, in the interior of 
 continents river-channels may be used for the same purpose. 
 
 4. — Winding Course of Rivers. — Meanders. 
 
 The winding course of rivers is due partly to erosion and partly to 
 sedimentary deposits.- It is most conspicuous and most easily studied 
 in rivers which run through extensive alluvial deposit. If the chan- 
 
 Fio. 15.— Meanders and Lakes by " Cut^ofE." 
 
 nel of such a river be made perfectly straight by artificial means, very 
 soon some portion of the bank a little softer than the rest will be ex- 
 
MEANDERS AND FLOOD-PLAINS. 25 
 
 cavated ; this will reflect the current obliquely across to the other side, 
 which will become similarly excavated. Thus the current is reflected 
 from side to side, increasing the excavations. In the mean time, while 
 erosion is progressing on the outer, or tangential, side of the curves, 
 because the current is swiftest there, deposit is taking place on the 
 inner or radial side, because there the current is slowest : thus, while 
 the outer curve extends by erosion, the inner curve extends, pari passu, 
 by deposit (Fig. 16), and the winding continues to increase, until, 
 under favorable circumstances, contiguous curves on the same side 
 
 i-A 'T»'*"»*r(n 
 
 Pig. 16.— Meandering Stream, Eock Creek, Wyoming. (Photograpli by E. H. Barbonr.) 
 
 run into each other, and a loop is cut off and deserted. Thus are 
 formed the crescentic lakes or lagoons so common in the swamps of 
 great rivers. They are abundant in the swamps of all the Gulf rivers, 
 especially the Mississippi. They are old beds of the river, thrown out 
 and silted up in the manner indicated above. 
 
 5. — Flood-Plain Deposits. 
 
 All great rivers annually flood portions of level land near their 
 mouths, and cover them with sedimentary deposits. The whole area 
 thus flooded is called the flood-plain. These flood-plains are very 
 extensive, and the deposits very large, in the case of rivers rising in 
 lofty mountains and flowing in the lower portion of their course 
 through extensive tracts of flat country. In the lofty mountains the 
 current runs with great velocity, and gathers abundant sediment ; on 
 reaching the flat country the velocity is checked, the river overflows, 
 and the sediment is deposited. The flood-plain of the Mississippi 
 Eiver is 30,000 square miles. 
 
 The flood-plain of a river may be divided into two parts, viz., the 
 river-plain and the delta. The river-plain is that part which was 
 originally land-surface ; the delta, that part which has been reclaimed 
 from the sea or lake by the river. 
 
26 AQUEOUS AGENCIES. 
 
 The extent of such river-plains is sometimes very great. That of 
 the Nile constitutes the whole fertile land of Egypt above the delta. 
 That of the Mississippi Eiver, or its flood-plain exclusive of the delta, 
 extends from iifty miles above the mouth of the Ohio to the head of 
 the delta, a distance of about five hundred miles; its average width 
 is over thirty miles, and it includes an area of 16,000 square miles. 
 It is bounded on either side by high bluffs belonging to a previous 
 geological period. 
 
 Pig. 17.— Diagram of Valley, Bhowing Flood-plains terraced by down-cnttmg (after Davis). 
 
 Natural Levees. — These are found along all rivers _ subject to 
 regular overflows. In times of flood the whole flood-plain is cov- 
 ered with water moving slowly seaward. Through the midst of this 
 wide expanse of water runs the rapid current of the river. Now, on 
 either side, just where the rapid current of the river comes in con- 
 tact with the comparatively still water of the flood-plain, and is 
 checked by it, a line of abundant sediment is determined, which forms 
 the natural levee. 
 
 Artificial Levies.— These are constructed for the purpose of con- 
 fining the river within its banks, and thus reclaiming the fertile 
 lands of the fiood-plain. As the bed of the river continues to 
 rise by deposit, the levees must be constantly elevated in propor- 
 tion. Thus, under the combined effect of human and river agencies 
 contending for mastery, an ever-increasing embankment is formed, 
 until finally the river runs in an aqueduct elevated far above the sur- 
 rounding plain. This is very remarkably the case with the river Po, 
 which is said to run in a channel that has been thus elevated above the 
 tops of the houses in the town of Ferrara. It is easy to see that the 
 destructive effects of overflow from accidental crevasses become greater 
 and greater with the elevation. The Po has thus several times broken 
 through its levees and deserted its bed, destroying several villages. 
 The best examples of rivers successfully leveed are those of Italy and 
 Holland. The Mississippi has never been successfully leveed. 
 
 Terraces. — When a stream, from any cause, cuts slowly down 
 through soft materials, frequently its own earlier deposits or valley 
 filling, it forms successively lower and lower flood-plains, while rem- 
 nants of its higher, deserted plains appear along the valley sides as 
 a series of platforms or terraces. Throughout the glaciated region 
 
DELTAS. 
 
 2Y 
 
 these are common and conspicuous features, as the preglacial valleys 
 were deeply filled with drift from the ice-sheet, which has been only 
 partially removed by the present streams (see Pig. 17, and further 
 description, page 581). 
 
 6.— Deltas* 
 
 Deltas are portions of land situated at the mouths of rivers, and 
 reclaimed from the sea by their agency. Over the flat surface of the 
 delta the river runs by inverse ramification, and empties by many 
 mouths. They are usually of irregular triangular form, the apex of 
 the triangle pointing up the stream. The delta of the Nile (Fig. 18) - 
 
 Fig. 18.— Delta of the Nile. 
 
 is perhaps the best example of the typical form. As seen in the figure, 
 at the head of the delta the river divides into branches, and communi- 
 cates with the sea by many mouths. The area of land thus made va- 
 ries with the size of the river, the proportion of sediment in its water, 
 and the time it has been making sedimentary accumulations. The 
 delta of the Nile is 100 miles long and 200 miles wide at its base; that 
 of the Ganges and Brahmapootra is 230 miles long and 200 miles wide 
 at its base, comprising an area of 20,000 square miles. The delta of 
 the Mississippi (Fig. 19) is very irregular in form, and is an admirable 
 
 * The diverging branches of a stream over its delta are called distributaries. At the 
 mouths of steep ravines or mountain valleys where torrents drop their burdens, deposits 
 are built on the land which are comparable to deltas in water. These are called detriial 
 cones or alluvial fans. 
 
28 
 
 AQUEOUS AGENCIES. 
 
 illustration of the manner in which each mouth pushes its way into 
 the sea. Its area is estimated at 12,300 square miles. The materials 
 of which deltas are composed are usually the finest sands and clays, all 
 the coarser materials having been deposited higher up the stream. 
 
 Deltas are formed only in lakes and tideless or nearly tideless seas. 
 In tidal seas, the sediments brought down by the rivers are swept 
 away and carried to sea by the retreating tide ; and instead of the land 
 encroaching upon the domain of the sea by the formation of deltas, 
 the sea encroaches upon the land by the erosive action of the tides, and 
 
 Fie. 19.— Delta ot the Mississippi. 
 
 forms' bays or estuaries. Thus in tideless seas or lakes the rivers empty 
 by many slender mouths, while in tidal seas they empty by wide bays : 
 thus, for example, all the rivers emptying into the great Canadian 
 lakes, and all the rivers emptying into the Gulf of Mexico, form 
 deltas, while all the rivers emptying into the Atlantic in both North 
 and South America form estuaries. In Europe all the rivers emptying 
 into the Black, the Caspian, the Mediterranean, and the Baltic, form 
 deltas, while those emptying into the Atlantic form estuaries. 
 
 Process of Fonnatioa. — The process of formation of a delta may 
 be best studied by observing it on a small scale, in the case of stream- 
 lets running into ponds. In such cases we observe always a sand or 
 mud flat at the mouth of the streamlet, evidently formed by the sand 
 
DELTAS. 29 
 
 and clay brought down by the current. As soon as the current strikes 
 the still water of the pond, its velocity is checked, and its burden of 
 sediment is deposited. In all such cases of streams ilowing into 
 ponds or lakes, the stream flows in muddy, but flows out comparatively 
 clear, having deposited its sediment in the pond or lake. Evidently 
 if this process continues without interruption, the pond will eventually 
 be filled up, after which, of course, the sediment will be carried far- 
 ther down the stream. In this manner small mountain-lakes are often 
 entirely filled up. The Ehone flows into Lake Geneva a turbid stream, 
 but flows out beautifully transparent. The whole of its sediment is 
 deposited where it enters the lake, and it has there formed a delta six 
 miles long. We may confidently look forward to the time, though 
 
 Pig. 20.— Delta in Ancient Glacial Lake, near DansTille, N. Y. 
 
 many thousand years distant, when this lake will be entirely filled up. 
 After leaving the lake the Ehone again gathers sediment from tribu- 
 taries flowing in below the lake, and forms another delta where it 
 empties into the Mediterranean. Many examples of lakelets partially 
 filled, or entirely filled and converted into meadows, are found among 
 the Sierra Mountains. If lakes are drained away or dried away, old 
 deltas are found on the slopes at the level of their old margins. Many 
 such are seen about Great Salt Lake, and in the basins of the Lauren- 
 tian lakes (see Fig. 20). These might be called fossil deltas. 
 
 In Fig. 21 is shown the structure of a delta consisting of coarse 
 materials, which implies a rapid stream. The steeply inclined beds 
 are called foreset beds. The finer beds at the bottom, deposited in 
 advance of, and later buried under, the foreset beds, are called bottom- 
 
30 
 
 AQUEOUS AGENCIES. 
 
 set beds. The coarser, horizontal beds at the top, consisting of the 
 laggard materials, are called iopset beds. In large deltas of great 
 
 WATLK SURnCE 
 
 Fig. 21.— Diagram of Delta Structure. 
 
 rivers, which are composed of the finest sediment, the stratification 
 is Tery regular and quite horizontal. 
 
 Rate of Growth. — There have been several attempts to estimate the 
 rate of growth of deltas, in order to base thereon an estimate of their 
 age. The delta of the Ehone in Lake Geneva has advanced at least 
 one and a half mile since the occupation of that country by the Eo- 
 mans; for the ancient town Portus Valesise (now Port Valais), which 
 stood then on the margin of the lake, is now one and a half mile inland. 
 The delta of the same river at its mouth in the Mediterranean is said 
 to have advanced twenty-six kilometres, or sixteen miles, since 400 
 B. c, or thirteen miles during the Christian era. The delta of the Po 
 has advanced twenty miles since the time of Augustus ;. for the town 
 Adria, a seaport at that time, is now twenty miles inland. But the 
 most elaborate observations have been made on the Mississippi. This 
 river, as seen in Fig. 19, has pushed its way into the Gulf in a most 
 extraordinary manner. According to Thomassy, and also Humphrey 
 and Abbot, the rate of advance is about one mile in sixteen years. The 
 rate of progress in the deltas mentioned has, however, probably not 
 been uniform. There are special reasons for their more rapid advance 
 at the present time. In the ease of the Po, the successful leveeing of 
 this river has transferred to the sea the whole of the sediment which 
 would otherwise have been spread over the flood-plain. In the case of 
 the Mississippi, for many centuries the principal portion of the deposit 
 has been confined to a narrow strip but a few miles wide, and the ad- 
 vance has been proportionately rapid. For this reason the river has 
 run out to sea for more than fifty miles, confined only by narrow strips 
 of land, the continuation of the natural levees. These marginal ridges 
 are continued as submarine banks even much beyond the present 
 mouths of the river. The rate of advance of the Wile delta seems to 
 be much slower. 
 
 ' Age of River-Deposits. — The age of river-plain deposits may be 
 estimated by determining their absolute thickness and their rate of 
 increase. The river Nile is peculiarly adapted for estimates of this 
 
EVOLUTION OF DRAINAGE. 31 
 
 kind, because we have on its alluvial deposits the seat of the oldest 
 civilization and the oldest Imovirn monuments of human art. These 
 monuments, the ages of which are approximately known, are many 
 of them more or less buried in the river-deposit. At Memphis, the 
 foundation of the colossal statue of Eameses II, over 3,000 years old, 
 was found in 1854, buried about nine feet in river-deposit. This 
 makes the rate of increase of the deposit three and a half inches per 
 century. Experiments at Heliopolis bring out nearly the same result. 
 The whole depth of the alluvial deposit at Memphis was found to be 
 about forty feet, which, at the above raje, would make the age of the 
 deposit at this point about 13,500 years. But this all belongs to the 
 human epoch, for bricks have been found beneath the lowest part. 
 The alluvial deposit of the Nile is much thicker at some points than 
 forty feet; but, on the other hand, the rate of increase for different 
 places is probably variable. 
 
 Life of Rivers— Evolution of Drainage. — Like organisms, streams 
 have their phases of infancy, youth, maturity, and old age. These 
 terms apply with equal force to the land-surfaces on which the streams 
 lie — that is, they designate stages of topographic evolution. The 
 infancy of a region is characterized by sluggish drainage, numerous 
 lakes, absence of well-marked divides, with evaporation at its maxi- 
 mum. This is the condition over much of the northern part of the 
 glaciated area — Canada and Minnesota, for example — from whence 
 the glacier has only recently withdrawn. The youthful stage is indi- 
 cated by ravines or narrow valleys, cataracts, larger lakes, and high 
 topographic relief. In the mature stage the valleys have become 
 broad and open, the streams are of steady slope or graded, the whole 
 area is dissected and well drained, and the run-off is at its maximum. 
 In old age there is a return through long erosion to low relief, slug- 
 gish drainage, but without lakes or cliffs or cataracts, and with evapo- 
 ration again in excess. 
 
 While the lower stretches of many river-valleys and limited coastal 
 areas are near base level, it is doubtful if the entire cycle of erosion is 
 illustrated in any continental area to-day, as land-surfaces may not 
 be sufficiently stable. Any diastrophic effect (elevation or subsidence) 
 interferes with the uniform development by changing the relation of 
 drainage to base level. Great areas have probably approached base 
 level during past geological ages and have become peneplains. The 
 plateaus of southern New York and northern Pennsylvania and of 
 western New England, where the hill summits have a comparatively 
 uniform height, are believed to represent ancient peneplains, since 
 uplifted and dissected. 
 
 In the adjustment of streams to their environment, or the evolu- 
 tion .of drainage, the following classes of streams are recognized by 
 
32 AQUEOUS AGENCIES. 
 
 the physiographers: Consequent streams have their courses deter- 
 mined by (in consequence of) the topography. All streams are con- 
 sequent at first. Streams which are secondary to the original drain- 
 age — that is, are produced wholly by erosion — are called subsequent. 
 They develop especially along belts of weak strata, and conform more 
 than other classes of streams to geological structure. By headward 
 cutting they may rob or " behead " other streams, thus causing migra- 
 tion of divides, and greatly change the river system of a region. The 
 Appalachian highlands hold many examples of these phenomena. An 
 antecedent stream is one which antedates the present topography or 
 relief of its area. A vigorous river might cut as a saw through a fold 
 that was slowly rising across its path, and thus keep its right of way. 
 The Green River with a gorge across the Uinta range has been 
 regarded as an example. The numerous " gaps " along the Susque- 
 hanna and neighboring rivers, through ridges of inclined strata, are 
 not examples of antecedent streams, but illustrate the adjustment of 
 rivers in the lowering of a land-surface by erosion, or the etching-out 
 process on hard and soft strata. The crests of the ridges in which 
 the gaps occur are believed to represent the ancient surface of a 
 peneplain which the revived streams have dissected. 
 
 Several other terms are in use by the physiographers which are 
 significant of geologic processes. The term superimposed applies to 
 a stream whose course does not now conform to the rock structure on 
 which it lies, because its course had been initiated on some higher 
 deposits which have been eroded. Streams in the glaciated region 
 may become superimposed by the removal of the drift mantle which 
 determined their courses. Streams are revived when they are given 
 a greater fall, enlivened by uplift of their valleys or by downthrow 
 of their base level. Drowned applies to portions of rivers which have 
 been carried below sea-level, like the Hudson, Delaware, and Susque- 
 hanna. A stream is dismembered when cut off from its trunk stream 
 by the drowning of the latter — for example, the Potomac, which must 
 have been a tributary of the Susquehanna before the latter was drowned 
 as Chesapeake Bay. On the contrary, a stream is engrafted when 
 made tributary to another river by the uplift of a submerged area. 
 The terms longitudinal and transverse apply to the attitude of streams 
 with reference to strata folds or mountain-ridges. 
 
 7. — Estuaries. 
 
 We have already seen that rivers which empty into tideless seas 
 communicate with the sea by numerous branches traversing an alluvial 
 flat, formed by the deposits of the river; while rivers emptying into 
 tidal seas communicate by wide mouths or bays, formed by the erosive 
 
ESTUARIES. 
 
 32a 
 
 action of the flowing and ebbing tide. Such bays are called estuaries. 
 We have fine examples of estuaries in the Amazon and La Plata Elvers, 
 in the Delaware and Chesapeake Bays, in the friths of Scotland and the 
 fiords of Norway ; in fact, at the months of all the rivers emptying into 
 the Atlantic on our own coast as well as on the European coast. The 
 mouth of the Columbia Eiver is a good example on the Pacific coast. 
 The phenomena of a delta and an estuary are sometimes combined in 
 the same river. This is the case to some extent in the Ganges. 
 
 Mode of Formation. — Estuaries are often formed by the erosive 
 action of the inflowing and outflowing tide. Their shape, narrow 
 above and widening toward the 
 sea, gives great force to the tidal 
 current, which, entering below 
 and concentrated in the ever- 
 narrowing channel, rushes along 
 with prodigious velocity and 
 rises to an immense height. In 
 the Bay of Pundy the tide rises 
 seventy feet, and at Bristol, 
 England, it rises forty feet; in 
 Puget Sound twenty-five feet. 
 Sometimes, from obstructions at 
 the mouth of the river, the tide 
 enters as one or more immense 
 waves, rushing along like an 
 advancing cataract. This is 
 called an eagre or hore. The 
 finest examples are perhaps in 
 the Amazon and Tsien-tang 
 Elvers. In the eagre of the Ama- 
 zon "the tide passes up in the 
 form of three great waves, thir- 
 teen to twenty-three feet high." 
 In the Tsien-tang, a single wave 
 plunges along at the rate of 
 twenty-five miles an hour, with 
 perpendicular' front, like an ad- 
 vancing cataract, four or five 
 miles wide and thirty feet high. 
 In the river Severn also we have a remarkable example of an eagre. 
 According to the laws already developed (pp. 18 and 30), the erosive 
 and transporting power of such currents must Ijp immense. 
 
 But estuaries are also in many cases the result of subsidence of the 
 land and invasion of the lower courses of the rivers by the sea. They 
 
 Fig. 22.— Estuaries of Atlantic Coast. 
 
325 AQUEOUS AGENCIES. 
 
 are drowned river valleys. All broad estuaries, those most commo- 
 dious and important for commerce, are of this character. Examples 
 are seen in all the bays of the Atlantic coast from New York south 
 to Florida. 
 
 Deposits in Estuaries. — The larger portion of the materials thus 
 eroded is carried out to sea by the retreating tide, and will be again 
 spoken of under " Sea-deposits." Many estuaries are occupied alter- 
 nately, during the wet and dry seasons, by fresh and brackish or salt 
 water, and the deposits in them are therefore alternately fresh-water 
 and salt-water deposits. These alternations are highly characteristic 
 of estuary-deposits in all geological periods ; in fact, of all deposits at 
 the mouths of rivers where river and ocean agencies meet. Estuarine 
 deposits may contain a few of either marine or fresh-water fossils, 
 but they are poor in fossils, as comparatively few organisms can live 
 in brackish water and under the rapidly changing conditions. 
 
 8.— Bars. 
 By the term iars we mean the shoals or ridges of sand built by 
 currents and waves. These are formed in accordance with the law 
 already given as controlling all current deposits — that is, if the ve- 
 
 Fia. 23.— Land Erosion by tranegreesion of Lake, West Shore of Lake Huron.- (PhotoeraDh bv 
 
 C. H. Gordon.) e, f j 
 
 locity of any current be checked its burden is dropped. Eiver bars 
 are frequent in the course of a stream, but are very changeable. The 
 more permanent one is»at the mouth of the river or at the head of the 
 estuary, where the river flow is checked by the opposing current of the 
 inflowing tide. In the case of the Hudson this bar is 140 miles up 
 
LAKES. 
 
 33 
 
 the river, and only a few miles below Albany. Strong bars arp. fnnnr^ 
 at the mou thg_o f rivers ini ideless s ea.s, and at the mouths of estuaries, 
 where the outflow of the tide meets the open sea. They frequently 
 interfere with navigation, and can not usually be permanently 
 
 M 
 
 Pio. 24.— Wave-bnilt Bar, Sodas Bay, Lake Ontario. 
 
 removed. These outer bars are part of the sand structures — em- 
 banhmentSj harriers^ and spits — ^which are formed along all shores 
 by the combined work of waves and shore currents. They will be dis- 
 cussed in the succeeding chapters. 
 
 9. — Lakes. 
 
 Lakes may be regarded as expansions of streams. As such they 
 act as reservoirs, regulating the flow, and as catchment basins for 
 sediment. In serving the latter function they ultimately come to 
 an end by filling (see page 39), unless they are earlier drained away 
 by down-cutting of their outlets. Geologically speaking, lakes are 
 ephemeral features, and practically are not found in regions of old 
 drainage, as the Southern States. Like the ocean, they modify the 
 climate of adjacent land. To the geological student they are most 
 instructive subjects of study, and give to those living inland a minia- 
 ture of the sea. All forms of shore phenomena may be studied in 
 lakes as well as in the sea, although the work of waves and shore cur- 
 rents is less effective, due to the lighter gravity of the water. Like the 
 sea, lakes cut away headlands and use the debris Jio build barriers 
 across embayments, thus straightening the shore-line, or giving smooth, 
 
34 
 
 AQUEOUS AGENCIES. 
 
 curving lines. Cliffs and terraces, deltas and estuaries, spits and 
 bars, may be seen in perfection. In Utah and Nevada are remains 
 of great "fossil lakes" which have dried up (see Gilbert's Lake 
 Bonneville and Eussell's Lake Lahontan), while in the basins of 
 the Laurentian great lakes are numerous shore-lines of ancient gla- 
 cial lakes. According to the origin of their basins, lakes are of 
 many kinds, but space will not permit description here. The reader 
 is referred to Eussell's Lakes of North America. 
 
 Section 3. — Ocean. 
 Waves and Tides. 
 
 Waves. — Waves produce no current, and therefore no geological 
 effect in deep water. The erosive effect of this agent is almost entirely 
 confined to the coast-line, but at this point is incessant and powerful. 
 The average force of waves on the west coast of Scotland for the 
 summer months is estimated by Stevenson at 611 pounds per square 
 foot, and for the winter months at 2,086 pounds per square foot. In 
 violent storms the force is estimated at 6,000 pounds per square foot, 
 and fragments of rock of many hundred tons' weight are often hurled 
 
 to a considerable distance on 
 the land. These fragments 
 hurled against the shore ar& the 
 principal agent of wave-erosion. 
 The rapidity of the erosion of 
 a coast-line by the action of 
 waves is determined partly by 
 the softness and partly by the 
 inclination of the strata. If 
 the strata turn their faces to 
 the- waves, particularly if in- 
 clined at a small ang;le, the 
 effect of the waves is compara- 
 tively slight; but, if the edges 
 of the strata are exposed to the 
 waves, the erosion is much 
 greater. For instance, if the 
 strata be horizontal, as in Pig. 
 26, then the strata are under- 
 FiG. 25.-waTe-cutting, Lake champiain. mined and form overhanging 
 
 table-rocks, which from time 
 to time fall into the sea; if the strata are vertical or highly inclined 
 and their edges turned to the sea, then an exceedingly irregular coast- 
 
WAVES AND TIDES. 
 
 35 
 
 line is formed and the erosion is very rapid, as the force of the waves 
 is concentrated upon the re-entering angles. 
 
 Waves, cutting ever at the shore-line only, act like an horizontal 
 saw (Fig. 26). The receding shore-cliff, therefore, leaves behind it 
 an ever-increasing sub- 
 aqueous platform which 
 marks the amount of re- 
 cession. The steep slope 
 of erosion is the sea-cliff; 
 the subaqueous platform 
 of erosion is the wave- 
 cut terrace. The exten- 
 sion of the platform sea- 
 ward by the materials 
 derived from cliff cut- 
 ting is the wave-built 
 terrace. These are all 
 shown in Fig. 38. Level 
 platforms terminated by 
 cliffs, therefore, when 
 found inland, indicate the position of old shore-lines. If the land 
 should be subsequently elevated, these remain and mark the former 
 margins of the sea. 
 
 Tides. — The tide is a wave of immense base, and three or four feet 
 in height in the open ocean, produced by the attractive force of the 
 moon and sun on the waters of the ocean. The velocity of this wave 
 
 Fia. 26.— Wave-cutting in Horizontal EocliB, 
 Lake Champlain. 
 
 FiQ. 27.— Erosion Cliff of the Glacial Lake Warren, Alabama, N. Y. 
 
 is very great, since, if unobstructed, it would travel around the earth in 
 twenty-four hours. In the open ocean it produces very little current, 
 only a slow transfer of the water back and forth, too slow to produce 
 any geological effect ; but in shallow water, where the progress of the 
 wave is impeded, it piles up in some cases forty to fifty feet in height. 
 
36 
 
 AQUEOUS AGENCIES. 
 
 and gives rise to currents of great velocity and immense erosive power. 
 By this means bays and harbors are formed^ and straits and channels 
 are scoured out and deepened. Tides also act an important part in as- 
 sisting the action of waves upon the whole coast-line. The action of 
 waves on exposed cliffs quickly forms accumulation of debris at their 
 base, composed of sand, mud, shingle, or rocky fragments (Pig. 26), 
 which receive first and greatly diminish the shock of 
 the waves upon the cliff. The incessant beating of 
 
 Fig. 88.— Diagram of Sea-Cliff, Wave-cut Terrace, and Wave-built Terrace. 
 
 the waves upon this debris reduces it to a finer and finer condition, 
 and the retreating waves bear much of it seaward ; so that, even with- 
 out the assistance of any other agent, the protection is incomplete, 
 and the erosion therefore progresses. But if strong tidal currents 
 run along the coast, these effectually remove such debris and leave 
 the cliff exposed to the direct action of the waves. 
 
 In lakes the small tides are obscured by the greater and irregular 
 changes in water-level due to winds, etc. In Lake Michigan the tides 
 have a maximum range of three inches, but the local variations pro- 
 duced by winds may amount to several feet. Frequent tide-like oscil- 
 lations of level occur, called seiches, which are caused by changes in 
 barometric pressure; the passage of a cyclonic storm producing an 
 impulse that is continued as a long series of oscillations. 
 
 Examples of the Action of Waves and Tides. — The coasts of the 
 United States show many examples of the erosive, action of waves and 
 tides. The form of the whole New England, coast is largely deter-, 
 mined by this cause. The softer parts are worn away into harbors by 
 the waves and scoured out by the tides, while the harder parts reach 
 out like rocky arms far into the sea. Sometimes only small rocky 
 islands, stripped of every vestige of earth, mark the position of the 
 former coast-line. Boston Harbor and the rocky points and islands in 
 its vicinity are good examples. The process is still going on, and its 
 progress may be marked from year to year. 
 
 On the Southern coast examples of a similar process are not want- 
 ing. At Cape May, for instance, the coast is wearing away at a rate 
 
WAVES AND TIDES. 37 
 
 of about nine feet per annum. The more exposed portions about 
 Charleston Harbor, such as Sullivan's Island, are said to be wearing 
 away even more rapidly. As a general fact, however, the low, sandy, 
 or muddy shores of the Southern coasts are receiving accessions more 
 rapidly than they are wearing; while, on the contrary, the New Eng- 
 land coast, as proved by its rocky character, is losing much more than 
 it gains. The shores of Lake Superior (Fig. 29) furnish many beauti- 
 ful examples of the action of waves — in this case, of course, unassisted 
 by tides. The general form of the lake along its south shore is deter- 
 mined by the varying hardness of the rock; the two projecting pro- 
 montories La Pointe (a) and Keweenaw Point (c) being composed of 
 hard, igneous rocks, while the intervening bays h and d are softer sand- 
 stone. On the south shore, about e, between La Pointe and Fond du 
 Lac (f), the conditions of rapid erosion are beautifully seen. The 
 shores are sandstone cliffs, with nearly horizontal strata. These have 
 been eroded beneath by the waves, in some places for hundreds of feet, 
 forming immense overhanging table-rocks, supported by huge sand- 
 stone pillars of every conceivable shape. Among these huge pillars, 
 and along these low arches and gloomy corridors, the waves dash with 
 a sound like thunder. From time to time these overhanging table- 
 rocks, with their load of earth and primeval forests, fall into the lake. 
 
 Fig. 29.— Lake Superior. 
 
 The coasts of Europe furnish examples on a more magnificent 
 scale, and have been more carefully studied. The cliffs of Norfolk are 
 carried away at a rate of three feet, and those of Yorkshire six feet, 
 annually. The church of the Eeculvers, on the coast of Kent, near 
 the mouth of the Thames, stood, in the time of Henry VIII, one mile 
 inland. Since that time the sea has steadily advanced until, in 1804, 
 a portion of the churchyard fell in, and the church was abandoned as 
 a place of worship. The church itself, ere this, would have been under- 
 mined and fallen in, had it not been protected by artificial meanSi 
 
38 
 
 AQUEOUS AGENCIES. 
 
 Fig. 30. — Wick, Scotland. 
 
 There are many instances in the German Ocean of islands which have 
 been entirely washed away during the historic period. 
 
 The tidal currents through the British and Irish Channels, along 
 the western coasts of Ireland and Scotland, among the Orkneys aad 
 Hebrides, and especially along the coast of Norway, are very powerful. 
 
 Along this latter coast it 
 r forms the celebrated Mael- 
 
 I j strom. The erosive effects of 
 
 the sea are, therefore, very 
 
 conspicuous. On the south 
 
 and east coast of England the 
 
 erosion is now progressing 
 
 _l^^_ rapidly. On the west coast of 
 
 k. 1 J^H^A Ireland and Scotland the 
 
 ' ^—^■fl^P' ' ^^H^^H J ^^^^^ i^ '^^^ ^^^ ^^ great, be- 
 
 ^^^^VH^^ .^^^SSRi^^k^ .^sjd^ cause the softer material is all 
 
 removed, but the configura- 
 tion of the coast shows the 
 waste which it has suffered. 
 A glance at a good map of 
 Ireland shows a deeply-indented western coast, composed entirely 
 of alternating rocky promontories and deep bays. On the western 
 .coast of Scotland, and especially on the Orkney, Shetland, and 
 Hebrides Islands, the wasting effect of the sea has been still 
 greater. Not only have we here the same character of coast as al- 
 ready described (as seen in the friths of Scotland), but many 
 small islands have been 
 eroded, until only a nucelus ' 
 of the hardest rock is left; 
 and even these have been 
 worn until they seem but 
 the ghastly skeletons of once 
 fertile islands. Pigs. 30 and 
 31 will give some idea of the 
 appearance of these spectral 
 islands. 
 
 The coast of Norway con- 
 sists entirely of deep fiords al- 
 ternating with jutting head- ^^^H^^B^HI^^P \A 
 lands of hardest rock several pig. 3i.-skye, Scotland, 
 thousand feet high. Along 
 
 this intricately-dissected coast there runs a chain of high, rocky isl- 
 ands, which in an accurate map is scarcely distinguishable from the 
 coast itself, being separated only by narrow, deep fiords. Toward the 
 
WAVES AND TIDES. 
 
 39 
 
 northern part of the coast the crest of the Scandinavian' chain seems to 
 run directly along the jutting promontories of the coast-line, for these 
 headlands are the most elevated part of the country ; in fact, in some 
 parts it would sefem that the original crest was at one time still farther 
 west, along the line of coast-islands. If so, then the sea has not only 
 carried away the whole western slope, but has broken through the main 
 axis, leaving only these isolated rocky islands as monuments of its 
 former position, and is even now carrying its ravages far inland on the 
 eastern slope. In the case of Norway, however, and probably in case, 
 of nearly all bold, rocky coasts, the intricacy of the coast-line is not 
 due wholly or even principally to the action of waves and tides, but also 
 to other causes, mainly subsidence, to which we shall refer hereafter. 
 
 Transporting Power. — The transporting power of waves is immense- 
 ly great, often taking up and hurling on shore masses of rock hundreds 
 of tons in weight ; but, being entirely confined to the coast-line, the dis- 
 tance to which they carry is necessarily very limited. There are some 
 instances, however, of materials carried to great distances by the inces- 
 sant action of waves. Thus, according to Prof. Bache, coast-sand is 
 carried slowly farther and farther south by the action of waves, and 
 siliceous sand is found at Cape Sable on the extreme southern point of 
 Florida, although the whole Florida coast as far as St. Augustine is 
 composed of coral limestone alone. He accounts for this by supposing 
 that the trend of the United States coast is such that waves coming 
 from the east strike the coast obliquely and fall off toward the south, 
 carrying each time a little sand with them. A similar phenomenon 
 has been obsei"ved on Lake Michigan ; the sands are carried steadily 
 toward the south end, where they accumulate. 
 
 Deposits. — The invariable effect of waves, chafing back and forth 
 upon coast debris, is to wear off their angles and thus to form rounded 
 fragments and granules. Thus, pebbles, shingle, and round-grained 
 sand, though produced by all currents, are especially characteristic of 
 wave-action.. Ripple-marhs are also characteristic of current-action 
 in shallow water. They are, therefore, always formed on shore by the 
 action of waves and tides. By means of these characteristics of shore 
 deposit, many coast-lines of previous geological epochs have been deter- 
 mined. 
 
 We have seen that waves usually destroy land. In many cases, 
 however, they also make land. This is the case whenever other agen- 
 cies, such as river or tidal currents, drop sediment in shallow water, 
 and therefore within reach of wave-action. We shall again speak of 
 these under the head of Land formed by Ocean Agencies. 
 
40 AQUEOUS AGENCIES. 
 
 Oceanic Currents. 
 
 The ocean, like the atmosphere, is in constant motion, not only on 
 its surface, but throughout its whole mass. The general direction of 
 the currents in the two cases is also similar, but there are disturbing and 
 complicating causes peculiar to each, which interfere with the regularity 
 and simplicity of the phenomena. If the currents of the atmosphere 
 are more variable on account of the greater levity of the fluid, oceanic 
 currents have also their peculiar disturbing causes in the existence of 
 impassable barriers in the form of continents. In both atmosphere and 
 sea, currents may also be deflected by submarine ianhs, for mountain- 
 chains are the banks of the aerial ocean. 
 
 Theory of Oceanic Currents.— By some distinguished physicists, 
 oceanic currents have been attributed entirely to the action of the trade- 
 winds.* There can be no doubt that this is a real cause ; yet it seems 
 probable, nay, almost certain, that the great and controlling cause of 
 currents of the ocean, as of the air, is difference of temperature between 
 the equatorial and polar regions. 
 
 General Course of Oceanic Circulation.— We leave it for physicists 
 to determine the true theory of oceanic currents. Suffice it to say that 
 on either theory the general course of circulation would be much the 
 same. An equatorial current stretches across both the great oceans 
 from east to west, impinges against the continent, turns northward and 
 southward to about 45° or 50° latitude, then eastward, then southward 
 and northward to form again the equatorial current (Fig. 32). The 
 details of their courses may be made more complex by the configura- 
 tion of continental margin and of sea-bottom. We take as example the 
 
 Gulf Stream. — Currents coming from the north and south on the 
 African coast {b V, Fig. 32) unite to form an equatorial current, c c', 
 which stretches across the Atlantic until, striking against the coast of 
 South America, it turns north and south, a a'. The southern branch 
 turns gradually eastward, d', and forming a grand circle in the south- 
 ern Atlantic joins again the South African current I'. The northern 
 branch, a, runs along the coast of South America, through the Carib- 
 bean Sea and into the Gulf of Mexico, from which emerging it runs 
 with great velocity through the narrow straits of Florida and thence 
 under the name of the Gulf Stream along the coast of North America, 
 turning more and more eastward in obedience to the law already men- 
 tioned, until it becomes an eastward current, d, about 50° latitude; 
 and then stretches across to the coast of Europe, and turns again south- 
 ward to join the equatorial current. A portion of it, however, in its east- 
 ward course turns northward, e, and returns as a cold polar current, e", 
 
 * Herschel, Physical Geography, p. 13 ; and CroU, Climate and Time. 
 
OCEANIC CURRENTS. 
 
 41 
 
 hugging the shore of North America as a cold wall to the Gulf Stream, 
 and thus passes south. 
 
 Geological Agency of Oceanic Currents.— The velocity of oceanic 
 currents is generally small, although, in the case of the Gulf Stream, 
 at the Florida Straits, it reaches almost the velocity of a torrent, 
 viz., three and a half to five miles per hour. The volume of water 
 carried by them is almost inconceivably great; it is estimated that 
 the Gulf Stream alone carries many times more water than all the 
 
 Fig. 32.— General Course of Oceanic Currents. 
 
 rivers of the globe. According to CroU, it is equal to a current fifty 
 miles wide and one thousand feet deep, running at a rate of four miles 
 an hour. 
 
 The chief function of oceanic currents is the distribution of heat, 
 as the " drift " in the north Atlantic carries mild climate to the Brit- 
 ish Islands, but they have a minor function of carrying sediments. 
 By far the larger part of the debris of the land is dropped near the 
 shore, and marginal sea-bottoms everywhere are the great theatres 
 of sedimentation. But through the agency of currents some of the 
 finest material is carried out far from land. 
 
 Oceanic Deposits. — These may be classified as littoral, or shore 
 deposits, shallow-water deposits, and deep-sea deposits, the latter at 
 depths over 600 feet, or beyond the continental shelves. Another 
 classification, based on character of the materials, is as follows : Ter- 
 rigenous or land-derived sediments include not only rubble and peb- 
 
42 . AQUEOUS AGENCIES. 
 
 ble along shore and the vast stretches of sand, but also the clays or 
 " muds " which are found in some seas up to a depth of over 16,000 
 feet. The most important is the "blue mud," which is estimated 
 to cover over 14,000,000 square miles of sea-bottom. Organic sedi- 
 ments include the limestones of shallow waters and the " oozes " of 
 the deep ocean. The latter are derived from a variety of organisms, 
 and are both calcareous and siliceous. Of the calcareous ooze the 
 foraminiferal is the most widely distributed, especially in the Atlan- 
 tic, and is estimated to cover 50,000,000 square miles. A modifica- 
 tion of this is the pteropod ooze. Of the siliceous deposits, the 
 radiolarian ooze covers over 3,000,000 square miles of bottom in the 
 Pacific and Indian Oceans, at depths of 14,000 to nearly 27,000 feet, 
 and the diatom ooze occupies nearly 11,000,000 square miles in the 
 Antarctic Ocean at depths up to ] 2,000 feet. In the abyssal depths 
 of the ocean is found only a " red clay," which seems to be the re- 
 siduum from volcanic, organic, and meteoric materials. It occupies 
 over 51,000,000 square miles, its greatest field being the Pacific Ocean. 
 The organic materials, which probably fall in the abyssal depths as 
 well as the lesser depths of the ocean, seem to be nearly all dissolved 
 in the profound abysses. 
 
 The only deposit in the strata of the continental areas which has 
 any resemblance to the deep-sea deposits is the chalk of cretaceous 
 time, which resembles the foraminiferal ooze, but was probably formed 
 in the moderate depth of continental seas. This fact has a bearing 
 on the question of the comparative permanence of continental and 
 oceanic areas. 
 
 Some Effects of the Co-operation of the Preceding Agencies— Sub- 
 marine Banks. — These are usually accumulations of material dropped 
 by currents. They are formed under conditions similar to those 
 which determine the formation of bars; i. e., either by the meeting 
 of opposing sediment-laden currents or else by such a current coming 
 in contact with still water. In fact, the outer bar is a true submarine 
 bank. The currents may be either tidal or oceanic or river. Admira- 
 ble examples of both those modes of formation are found in the Ger-^ 
 man Ocean. The tidal wave from the Atlantic strikes the British Isles, 
 passes round in both directions, and enters this ocean from the north 
 around the north point of Scotland, and from the south through the 
 British Channel and Straits of Dover (Fig. 33). These two currents 
 coming from opposite directions meet and make'still water, and there- 
 fore deposit their sediment and form banks. Again, the tidal current 
 is concentrated in the British Channel, and runs with great velocity, 
 scouring out this channel, and in addition gathering abundant sediment 
 from the rivers emptying into the channel. Thus loaded with sedi- 
 ment it rushes through the narrow Straits of Dover, and, coming in 
 
OCEAJ^IC CURRENTS. 
 
 43 
 
 contact with the still water of the German Sea, forms eddies on either 
 side, and deposits its sediments. Besides the banks thus formed, there 
 are, of course, bars formed at the mouths of the rivers emptying into 
 this shallow sea. By a combination of all these causes, we explain the 
 numerous banks which render the navigation of this sea so dangerous. 
 
 Fia. 33 — Tides of the Qerman Ocean. The curved lines represent snccessive positions^ of the 
 ' advancing tide. 
 
 But great banks far away from shore are usually formed by oceanic 
 currents. Thus the Banks of Newfoundland are evidently formed, 
 partly at least, by the meeting of the polar current (e", Fig. 32), bearing 
 icebergs loaded with earth, and the warm current of the Gulf Stream, 
 perhaps also bearing its share of fine sediment. Again, the Gulf 
 Stream, rushing at high velocity (four miles per hour) through the 
 narrow Straits of Florida, coming in contact with the still water of 
 the Atlantic beyond and forming eddies on each side, and depositing 
 sediment, has certainly contributed to form, if it has not wholly formed, 
 the Bahama Banks on one side, and the bank on which the Florida 
 reefs are built on the other. It is probable that many other peculiari- 
 
44 
 
 AQUEOUS AGENCIES. 
 
 ties of the Atlantic bottom in the course of the Gulf Stream may be 
 similarly accounted for.* 
 
 Land formed by Ocean Agencies.— Upon submarine banks, however 
 these may be produced, are gradually formed islands. These islands 
 are always formed by the immediate agency of waves. As soon as the 
 submarine bank rises so near the surface that the waves touch bottom, 
 and form breakers, these commence to throw up the sand or mud until 
 an island is formed, which continues to grow by the same agency, until 
 it becomes inhabited by plants and animals, and finally by man. The 
 
 height of such islands above the sea 
 will depend upon the height of the 
 tides and the force of the waves. 
 They are seldom more than fifteen 
 feet above high water. Thus we 
 find that extensive banks are always 
 dotted over with islands. In this 
 manner are formed the low islands 
 so common about the mouths of 
 harbors and estuaries, also the nar- 
 row sand-spits all along our South- 
 ern coast, separating the harbors 
 and sounds from the ocean. Pig. 
 34, which is a map of the North 
 Carolina coast, will give a good idea 
 of these sand-spits. In the course 
 of time such sounds, being protected 
 in some measure by the sand-spits 
 from the scouring action of the 
 tides, are gradually filled up with 
 sediments brought down by the 
 rivers, leaving only narrow passages 
 for the flow of the tide. In this 
 manner were formed the sea-islands 
 all along our Southern coast, sepa- 
 rated from the mainland only by narrow tidal inlets. These tidal 
 inlets may become filled up, and the whole coast-line transferred farther 
 seaward. 
 
 A large portion of the coasts of the»world is thus bordered by wave- 
 formed islands. We have already seen, however, that on some coasts, 
 e. g., Norway, Scotland, etc., islands are formed by the destructive ac- 
 tion of waves. Bordering islands, so common along all coasts, are 
 therefore of twd classes, and formed by two opposite effects of waves — 
 
 Fia. 34.— Coast of North Carolina. 
 
 * pee the author's views on this subject, American Journal of Science, vol. xxiii, p. 
 46, ISSY; Nature, vol. xxii, p. 558, 1880; Science, vol. ii, p. 764, 1883. 
 
GLACIERS. . ~ 
 
 45 
 
 the one land-destroying, the other land-forming. The islands of one 
 class are high and rocky, of the other low and sandy or muddy the 
 former are the scattered remains of an old coast-line, the latter the 
 commencing points of a new coast-line. 
 
 Section 3. — Ice. 
 The agency of ice will be considered under the heads of Glaciers 
 and Icebergs ; the effects of frost in disintegrating rocks having been 
 already treated of under Atmospheric Agencies. It is only compara- 
 tively recently that the great importance of ice as a geological agent 
 has been recognized. To Agassiz is due the credit of having first fully- 
 recognized this importance. 
 
 Glaciers. — General Principles. 
 Deflnition.— In many parts of the earth, where the mountains reach 
 into the region of perpetual snow, and other favoring conditions are 
 present, we find that the mountain-valleys are occupied by masses of 
 compact ice, connected with the snow-cap above, but extending far 
 below the snow-line into the region of cultivated fields, and moving 
 slowly but constantly down the slope of the valley. Such valley-pro- 
 longations of the perpetual snow-caps are called glaciers. The exist- 
 ence of glaciers and their motion are -necessitated by the great law of 
 circulation, so universal in Nature. For in those countries where 
 glaciers existi the waste of perpetual snow by evaporation is small in 
 comparison with the supply by the fall of snow. There would be no 
 limit, therefore, to the accumulation of snow on mountain-tops, if it 
 did not run off, down the slope, by these ice-streams, and thus return 
 into the general circulation of meteoric waters. Glaciers extend not 
 only far below the snow-line, but even far below the mean line of 32°. 
 In the Alps the snow-line is about 9,000* feet above the sea-level, 
 while some of the glaciers extend down to within 3,225 feet (Prest- 
 wich) of the same level, i. e., more than 5,000 feet below the snow-line. 
 Necessary Conditions. — The conditions necessary to the formation 
 of glaciers are : 1. The mountain must rise into the region of perpetual 
 snow, for the snow-cap is the fountain of glaciers. 2. There must be 
 considerable changes of temperature, and therefore alternate thawings 
 and freezings. This condition seems necessary to the gradual compact- 
 ing of snow into glacier-ice. The want of this condition is apparently 
 the cause of the non-existence, or small development, of glaciers in 
 tropical regions. 3. A moist atmosphere is favorable to their produo- 
 
 * Glaciers may be regarded as the icicles which drain away the snow from the roofs 
 of the mountains. 
 
46 
 
 AQUEOUS AGENCIES. 
 
GLACIERS. 
 
 47 
 
 tion, for the moister the climate the greater is the snow-fall, and the 
 smaller is the waste by evaporation, and therefore the greater the 
 excess which must run off by glaciers. This is an additional reason 
 why glaciers are not formed under the equator ; for the great capacity 
 for moisture of the air in this zone increases the waste while it decreases 
 the fall of snow. This is also the reason of the scanty formation of 
 glaciers in the Sierra Mountains, and their abundance and magnitude 
 in the Alps. 
 
 Bamifications of Glaciers. — We have said glaciers are valley-prolon- 
 gations of the ice-cap. Now, mountain-valleys are of two kinds, viz., 
 1. The deeper and larger longitudinal valleys, between parallel ranges; 
 and, 2. The transverse or radiating valleys, transverse in case of ridges, 
 and radiating in case of peaks. The longitudinal valleys may be formed 
 either by erosion or by igneous agencies folding the crust of the earth ; 
 but the transverse or radiating valleys are always formed ly erosion. 
 It is these valleys of erosion which are occupied by glaciers. In coun- 
 tries where there are no glaciers they are occupied, of course, by 
 streams. We have already shown (p. 9) how these valleys commence 
 near the top of the mountain as furrows, which, uniting, form gullies, 
 and these, in their turn, forming ravines and gorges,, thus becoming less 
 and less numerous, but larger as we api^roach the base of the mountain. 
 In the same manner, therefore, as streams ramify, so also do glaciers. 
 The onfy difference is the degree of ramification. Streams ramify 
 almost infinitely, while glaciers seldom have taore than three or four 
 tributaries. Fig. 35 is a map of the Mont Blanc glacier region. By 
 inspection of this map it will be seen that the Mer de Glace, m, receives 
 four tributaries, marked t, I, g, etc. On page 55 is an enlarged view 
 of the same glacier with its tributaries. 
 
 Motion of Glaciers. — Again, we have said in our definition that gla- 
 ciers are in constant motion. By the law of circulation, constant down- 
 Tfard motion is as necessary to the idea of a glacier as it is to that of a 
 river, since both the glacier and the river carry away the excess of sup- 
 ply over evaporation. But a glacier, though in constant motion, never 
 passes beyond a certain point, where the slow downward motion is 
 exactly balanced by the melting of the ice by sun and air. This point 
 is called the lower limit of the glacier. As long as conditions remain 
 unchanged, the lower end of the glacier remains exactly at the same 
 point, although 'the substance of the glacier moves always downward. 
 But if external conditions change, the point of the glacier may move 
 upward or downward. There are two opposing conditions which de- 
 termine the position of the point of the glacier, viz., the rate of mo- 
 tion and the rate of melting. Thus, during a succession of cool, damp 
 years, the melting being less rapid, the point of the glacier moves 
 slowly down, sometimes invading cultivated fields and overturning 
 
48 
 
 AQUEOUS AGENCIES. 
 
 huts, until it finds a new point of equilibfium. During a succession of 
 warm and dry years, on the contrary, the melting being more rapid, 
 the point retreats, to find a new point of equilibrium higher up the 
 mountain. Again, during a cycle of years of heavy snow-fall, the gla- 
 cier is flooded, its motion increased, and its point advances; while 
 
 Fig. 36.— a Glacier of the Cascade Eange in Northern Washington. (Photograph by Bailey Willis.) 
 
 during a cycle of smaller snow-fall its dimensions shrink, its motion 
 is retarded, and its point retreats. But, whether the point be station- 
 ary, or advance or recede, the substance of the glacier is ever moving 
 steadily onward. It may be compared to those rivers, in dry, sandy 
 
GLACIERS. 
 
 49 
 
 countries, which run ever toward the sea, but never reach beyond a 
 certain point, being absorbed by the sand. 
 
 Of these two factors of advance and retreat, the second is probably 
 the greater; for, in the same region and under the same climatic- con- 
 ditions, some glaciers may be advancing and some retreating. The 
 reason is as follows : As in small streams the iloods quickly follow the 
 rain, while in long rivers like the Mississippi the flood at the mouth 
 may be delayed a week or ten days; so in short glaciers the ice-flood 
 may reach the point in five or ten years, while in long glaciers it may 
 take fifty or more years.* 
 
 Line of the Lower Limit of Glaciers.— We have said, again, that the 
 glacier reaches below the snow-line. There are three lines, or rather 
 spheroidal surfaces, running above the surface of the earth, which are 
 apt to be confounded 
 with one another, and 
 must, therefore, be now 
 defined. These are the 
 line of perpetual snow, 
 the mean line of 32°, 
 and the line of the 
 lower limit of glaciers. 
 The line of perpetual 
 snow, at the equator, is 
 about 16,000 to 17,000 ^ 
 feet above the sea-lev- 
 el. As we approach the 
 poles it gradually ap- 
 proaches the sea-level, 
 until it touches at or 
 near the poles, form- 
 ing thus a spheroid 
 more oblate than the 
 earth itself (Pig. 37). 
 Next follows the mean line of 32°. This commences at the equator, E, 
 coincident with the snow-line (it may be even above it — Dana), but 
 diverges as we pass toward the pole, and finally touches the sea-level 
 at about 66° north and south latitude, at I h. Below this, again, is 
 the line of lower limit of glaciers, which, commencing again nearly 
 coincident with the two preceding, at the equator, approaches and' 
 touches the sea-level at about 50° latitude, or, under favorable cir- 
 cumstances, at even lower latitudes. The difference between these 
 lines is often several thousand feet. In the Alps, the line of 33° is 
 
 * At the present time most of the glaciers of the world are retreating, but there are 
 a few striking exceptions. 
 
 Fia. 37.— General Eelatior of Limit of Glaciers to Snow-Line. 
 
50 AQUEOUS AGENCIES. 
 
 3,000 feet, and the line of lower limit of glaciers 5,000 feet, below 
 the snow-line. In some parts of the arctic region, the line of 33° 
 is 3,500 feet below the snow-line, and in Norway the lower limit of 
 glaciers is 4,000 feet below the line of 33° (Dana). For the sake of 
 simplicity we have represented the surfaces, of which these lines are 
 the sections, as regular spheroids ; but, in fact, they are very irregu- 
 lar, being much influenced by climate. Their intersection with the 
 sea-level will, therefore, not be along lines of latitude, but will be 
 irregular, like isotherms. As the line a c marks the lower limit of 
 glaciers in difEerent latitudes, it is evident that at c glaciers will touch 
 the sea, and beyond this point will run far into the sea. It is in this 
 manner, as we will see hereafter, that icebergs are formed. In Chili, 
 glaciers touch the sea-level at 46° 40' south latitude. 
 
 General Description — Glacial Field. — A glacial field may be defined 
 as a perpetual snow-covered area from which flow glaciers in many 
 directions. The field best known is that of the Alps. In the region 
 about Mont Blanc (Pig. 35) and Pinsteraarhorn alone there are about 
 400 glaciers, varying in length from 5 to 15 miles, in width from one 
 half to 3 miles, and in thickness from 300 to 800 feet. In the Hima- 
 layas the snow-field is far more extensive and the glaciers much larger 
 — 40 miles long and 1,000 feet thick. On the Pacific coast of North 
 America glaciers begin to appear as little isolated glacierets in the 
 Sierra of Middle California, become of respectable size {2\ miles long) 
 on Mount Shasta, almost rival those of the Alps (8 to 10 miles long) 
 on Mount Tacoma, and reach grand proportions, running into the sea 
 and forming icebergs in Alaska. Por example, the Muir Glacier is a 
 complex system of ice-streams altogether more than 100 miles long. 
 The Malaspina Glacier is a great Mer de Glace, covering an area of 
 1,500 square miles, fed by many ice-streams coming down from the 
 Mount St. Elias group.* 
 
 Continental Ice-Sheet. — But it is only in arctic and antarctic regions 
 that we find ice action on a scale which gives us any adequate idea of 
 its agency in the Glacial period. Greenland is a continental mass 1,300 
 miles long and 600 miles wide. This whole area of 600,000 square 
 miles is buried 3,000 to 3,000 feet deep under a continuous mass of 
 snow and ice which moves bodily with slow glacier motion seaward in 
 all directions, and finally through the great fiords into the sea to form 
 icebergs. The antarctic ice-sheet is much larger; it covers an area 
 of 4,000,000 to 8,000,000 square miles to a supposed depth of 10,000 
 feet. This great mass moves in all directions with slow glacial 
 motion, and runs out many miles to sea to break off there and form 
 icebergs. 
 
 * It is taken as the type of the class of glaciers aaSleA jnedmont. 
 
GLACIERS. 
 
 51 
 
 An Individual Glacier.— A typical glacier may be divided into two 
 parts : a great amphitheatral part in which the snows are gathered ; 
 and an icy tongue pr glacier proper, which runs from the amphi- 
 theater or cirque down the valley. Or we may regard water as exist- 
 ing in four conditions: first, as light snow; then, as we go down, as 
 mve or granular snow— half snow, half ice ; then as solid glacier ice ; 
 and, finally, as a river. The river which flows from the snout of every 
 glacier is formed partly by the natural drainage of the hydrographical 
 basin, but mainly by the melting of the glacier by sun and air. The 
 thickness removed (ablation) during a single summer is 18 to 25 feet. 
 The surface of a glacier is therefore covered with rushing rills. These 
 do not run the whole length, but soon fall into crevasses, find their way 
 to the bottom, and generally come out beneath the sneut of the 
 glacier. 
 
 ^il^=^ 
 
 Fio. 38.— Ice-Pillars on Parker Creek Glacier, California (after Eussell). 
 
 We are apt to suppose that the surface of a glacier must be smooth. 
 This is, however, very far from being true. On the contrary, the ex- 
 treme roughness of the ice-surface renders the ascent along the glacier 
 extremely difficult. This inequality of surface is due partly to unequal 
 melting and partly to crevasses, or fissures. The unequal melting is 
 produced as follows : A stone, lying on the surface of a glacier, pro- 
 tects the surface beneath from the rays of the sun. Meanwhile the 
 surrounding ice is melted, until finally the slab of stone stands on a 
 column of ice often several feet in height (Fig. 38). A slab seen 
 by Forbes measured 33 feet long, 17 feet wide, and 3^ feet thick, 
 and rested on a column 13 feet high. In such cases the stone finally 
 falls' off, leaving a sharp pinnacle, and another column commences to 
 form under the stone. In this manner are formed what are called 
 5 
 
52 
 
 AQUEOUS AGENCIES. 
 
 needles. When we consider that there are immense numbers of stones 
 on the glacier-surface, we can easily see that these needles will multi- 
 
 FlG. i 
 
 -Ice-Blades on Hallet Glacier, Mummy Mountain, Colorado (from Photograph hy Chapin). 
 
 ply indefinitely. If, on the other hand, a thin stratum of earth stains the 
 surface of the glacier in spots, these spots will racM faster than the sur- 
 rounding ice, because more absorbent of heat, and thus form deep holes. 
 An admirable illustration of extreme inequality of the surface of 
 ice is seen in the case of the small residual glacier still remaining on 
 Mount Lyell, Sierra Nevada.* On the top of Mount Lyell there is an 
 immense amphitheater {cirque), filled with snow and ice. In August 
 the surface of this ice-field is set with ice-blades, three to four feet 
 ■high and only two feet apart, as shown in Fig. 39, which, however, 
 represents the phenomenon in another glacier. They are pi'obably 
 
 * See paper by the writer, American Journal of Science, vol. v, p. 333, 1873. 
 
GLACIERS. 
 
 53 
 
 formed as follows : In winter, when the snow is deep and light, it is 
 blown into wind-ripples on a large scale. These soon become fixed by 
 surface melting and freezing, and then the greater action of the sun in 
 the troughs, partly by the reverberation of heat and partly by accumu- 
 lation of dust there, causes these to become deeper and deeper. It is 
 necessary to remember that there is little snow or rain in this region 
 after about the first of May until November. 
 
 Again, fissures or crevasses, often of great size, ten to twenty feet 
 wide, one hundred feet deep, and sometimes running entirely across the 
 glacier, are very abundant. As the surface of the glacier is often cov- 
 ered with snow, and the fissures thus concealed, they form the most 
 dangerous feature connected with Alpine travel. The law which gov- 
 erns their formation will be discussed hereafter ; suffice it to say that 
 the great transverse fissures are formed by the glacier passing over an 
 angle formed by a sudden change in the slope of the bed. Streams, 
 produced by the melting of ice, running on the surface of the glacier, 
 plunge into these fissures with a thundering noise, and hollow out im- 
 mense wells, called moulins, and magnificent ice- caves. Although the 
 glacier moves, the great crevasses and the wells with their falls remain 
 stationary, precisely as the position of a rapid or breaker remains sta- 
 
 FiG. 40, — Ice-ueedlee, asicent of Mont BJanc. 
 
 tionary, although the river runs onward; and for the same reason, 
 viz., that it is reformed always on the same spot. 
 
 From all these causes the surface of a glacier is often studded over 
 with conical masses and projecting points of every conceivable shape. 
 This is well shown in the accompanying figure (Fig. 40). These in- 
 
g^ AQUEOUS AGENCIES. 
 
 equalities are, of course, the result of differential melting. The whole 
 melting (ablation) is much greater, even as much as twenty-five feet 
 in the course of the summer.* 
 
 Earth and Stones, etc.— The surface of a glacier is, morever, largely 
 covered with earth and stones gathered in its course from the crumbling 
 
 Fio. 41.— Zermatt Glacier (Agassiz). 
 
 cliffs on either side. These are often so abundant as almost to cover 
 the surface. More usually, however, they are distributed in two or 
 more rows, called moraines. Fig. 41 is a view of a glacier, with its 
 moraines and lateral crevasses. 
 
 Such is a general description of the appearance of a glacier. There 
 are, however, several points which, by their importance and interest, 
 require special notice. These are : 1. Moraines ; 3. Glaciers as a geo- 
 logical agent ; 3. Glacier-motion j and 4. Glacier-structure. 
 
 Moraines. 
 
 There are four kinds of moraines described by writers, viz., lateral 
 moraines, medial moraines, terminal moraines, and ground moraines. 
 Lateral moraines are continuous lines of earth and stones, arranged 
 on either margin of the glacier and evidently formed from the ruins of 
 
 * Prestwich, Geology, vol. i, p. 176. 
 
MORAINES. 
 
 65 
 
 the crumbling cliffs of the inclosing valley. This debris does not fall 
 from every part of the valley-sides, but generally only from certain 
 bold, projecting cliffs. It is converted into a continuous line by 
 the motion of the glacier, just as light materials thrown constantly 
 into a river at one point would appear as a continuous line on the 
 stream. 
 
 Medial moraines are similar lines of debris, occupying the central 
 portions of the glacier. Sometimes there is but one ; sometimes two, 
 or more ; sometimes the whole surface of the glacier is almost covered 
 with them. The true explanation was first pointed out by Agassiz. 
 They are formed by the coalescence of the interior lateral moraines of 
 tributary glaciers, carried down the main trunk by the motion of the 
 ice-current. The accompanying map (Fig. 42) of the Mer de Glace 
 and its tributaries shows clearly 
 the manner in which these mo- 
 raines are formed. Both lateral 
 and medial moraines are gener- 
 ally situated on a ridge of ice, 
 sometimes fifty to eighty feet 
 high, evidently formed by the 
 protection of the ice, in this 
 part, from the melting power of 
 the sun. The fragments of rock 
 brought down by glaciers are 
 often of enormous size. One 
 described by Forbes contained 
 244,000 cubic feet. 
 
 The ground moraine is the 
 mass of debris carried between 
 the glacier and its bed. It is 
 derived partly from erosion of 
 the bed, and partly from top 
 material (lateral and medial mo- 
 raines) ingulfed and carried 
 down to the bottom. 
 
 Everything which falls upon 
 the surface of the glacier is 
 slowly and silently carried down- 
 ward by this ice-stream, and 
 finally dropped at its point. 
 
 Much finely- triturated matter is also pushed along beneath the gla- 
 cier, and finds its way to the same point. In the course of time an 
 immense accumulation is formed, of somewhat crescentio shape, as 
 seen in Fig. 43. 
 
 Fio. 42.— Mer de Glace. 
 
56 
 
 AQUEOUS AGENCIES. 
 
 This accumulation is called the terminal moraine. It is the delta 
 of this ice-river. The existence of moraines is a constant witness of 
 the motion of the glaciers. 
 
 Glaciers as a Geological Agent. 
 
 Glaciers, like rivers, erode the surface over which they move, carry 
 the materials gathered in their course often to great distances, and 
 finally deposit them. 
 
 Erosion. — When we consider the weight of glaciers and their un- 
 yielding nature as compared with water, it is evident that they may 
 have some efEect of abrasion. Fragments of stone between the glacier 
 and its bed are the graving-tools. The glacier is a rasp, with stone 
 teeth. But on the other hand, on account of their slow motion, gla- 
 cier-erosion is by force of pressure, while that of water is by force of 
 impact. The effects of glacier-erosion differ entirely from those of 
 water: Water, by virtue of its perfect fluidity, wears away the 
 softer spots of rock, and leaves the harder standing in relief; while 
 
 Fig. 4.3.— Roches Moutonn^es of an Ancient Glacier, Colorado (after Hayden). 
 
 a glacier, like an unyielding rubber, grinds both hard and soft. Gla- 
 ciers, for reasons to be discussed hereafter, conform to large and gentle 
 inequalities of their beds, though not to small ones, acting thus like 
 a very stiffly viscous body. Thus their beds are worn into very remark- 
 able and characteristic smooth and rounded depressions and eleva- 
 tions called roches moutonnees (Fig. 43). 
 
GEOLOGICAL WORK OF GLACIERS. 
 
 5Y 
 
 Fia. 44. — Glacial Scorings on Bed-Eock, Niagara Limestone, 
 Kochester, N. Y. 
 
 Thus, smooth, gently-billowy surfaces, marked with straight, paral- 
 lel scratches, are very characteristic of glacial action. We will call 
 
 such surfaces glaci- 
 ated, and the process 
 glaciation. 
 
 The turbidity of 
 ordinary rivers is 
 usually yellowish, 
 the turbidity of gla- 
 cial rivers is always 
 milky. The one is 
 due to sediments de- 
 rived from soil, and 
 therefore oxidized ; 
 the other is due to 
 ground-up sound 
 rock or rock-meal. 
 
 Transportation. — 
 The transporting 
 power of glaciers 
 follows no law similar to that pointed out under rivers — in fact, it 
 has no relation at all to velocity. The reason is, that the stone rests 
 on the surface as a floating body. There is, therefore, no limit to 
 the transporting power. Bowl- 
 ders of 250,000 cubic feet are 
 carried with the same ease and 
 the same velocity as the finest 
 dust. 
 
 Erratics — Balanced Stones.— 
 A water-current carrying stones 
 bruises and rounds their corners, 
 and deposits them always in the 
 most secure positions; but gla- 
 ciers often deposit huge angular 
 fragments of rock in the most 
 insecure positions — so nicely bal- 
 anced, sometimes, that a touch 
 of the hand will dislodge thera. 
 The reason is, they are set down 
 by the gradually melting ice with 
 inconceivable gentleness. Thus 
 balanced stones, rocking-stones, etc., are common in glacial regions 
 In using these as a sign of glacial action, however, we must recollect 
 that a bowlder dropped by any agent, or even a bowlder of dismte- 
 
 Fig 45 —A Perched Bowlder, " erratic " 20 feet 
 across. Mono Valley, California. 
 
58 
 
 AQUEOUS AGENCIES. 
 
 gration (p. 6), may in time become a rocking-stone, by slow but 
 irregular disintegration changing the position of the center of grav- 
 ity. But angular erratics in insecure positions are very characteristic 
 of glacial action. 
 
 Material of the Terminal Moraine.— The material of the terminal 
 moraine is very characteristic: 1. It consists of fragments of every 
 conceivable size, from huge bowlders down to fine earth, mixed together 
 into a heterogeneous mass entirely different from the neatly-sorted de- 
 posits from water. It is, therefore, entirely unsorted and unstratified, 
 and without organic remains. 2. The mass consists of two parts, viz., 
 that which is carried on the top of the glacier, and that which was 
 forced out beneath (ground moraine). The first consists of loose 
 
 Fig. 46. — Terminal Moraine, near Dansville, N. Y. 
 
 material containing angular, unworn fragments; the other of fine 
 compact material containing fragments worn and polished, and 
 scratched with straight, parallel scratches, but in both cases entirely 
 different from water-worn pebbles. In all respects, therefore, the 
 action of glaciers is characteristic and can not be confounded with 
 that of water. 
 
 Evidences of Former Extension of Glaciers. — The present glaciers 
 of the Alps are small compared to their former size. The proofs of 
 their greater extension in ancient time are their tracks or records, 
 which are found far down their valleys and high on the valley sides. 
 Terminal (retreatal) moraines, roche moutonnee^ striated rock sur- 
 faces, and perched blocks are found many miles below the present 
 glaciers, and lateral moraines are found stranded on the valley walls 
 even 3,000 feet above the present ice-level (see p. 595). 
 
 Similar proofs of glacier invasion are found as far south as the 
 Ohio and Missouri Eivers, and over western Europe and Great Brit- 
 
GLACIER MOTION. 
 
 59 
 
 ain. There can be no possible doubt of this, since glacial records are 
 peculiar and unmistakable. 
 
 Glacial Lakes.— This name strictly applies only to lakes which owe 
 their existence to barriers of glacier ice. The Merjelen See, lying 
 against the east side of the Aletsch glacier, is a living example. 
 
 In America many glacial lakes, some of vast size, existed during 
 the recession of the ice-sheet. As the front of the glacier retreated, 
 to the north of the divide the waters were held between the high land 
 on the south and the ice-front on the north. 
 
 The thousands of lakes, lakelets, and tarns which remain as yet 
 undestroyed in the Northern States and Canada are mostly morainal 
 lakes, because lying in depressions blocked by morainal drift. Doubt- 
 less a very few lakelets lie in shallow ice-eroded rock-basins, and 
 should be called rock-basin lakes. 
 
 Motion of Glaciers and its Laws. 
 
 Evidences of Motion. — That glaciers move slowly down their val- 
 leys was long known to Alpine hunters. Kude experiments of the 
 first scientific explorers confirmed this popular notion. Hugi in 
 1827 built a hut upon the Aar glacier. This hut was visited from year 
 to year by scientific explorers and its change of position measured. 
 In 1841 Agassiz found that it had moved 1,438 metres in fourteen 
 years, or about 100 metres (330 feet) per annum. The ruins of 
 Agassiz's hut (Hotel Neuchatelois), built in 1840, were found in 
 1884. They had moved in forty-four years 7,900 feet. Numerous 
 other observations from year to year by Agassiz and others, on the 
 position of conspicuous bowlders lying on the surface of glaciers, 
 confirmed these results and placed the fact of glacier-motion beyond 
 doubt. But the most important observations determining both the 
 rate and the laws of glacier-motion were made in 1842 by Prof. 
 Agassiz on the Aar glacier, and Prof. Forbes on the Mer de Glace. 
 By these experiments, carefully made by driving stakes into the gla- 
 cier, in a straight row from one side to the other, and observing the 
 change in the relative position of the stakes, it was determined that 
 the center of the glacier moved faster than the margins. This differ- 
 ential motion is the capital discovery in relation to the motion of gla- 
 ciers. It is claimed by both Agassiz and Forbes. It had, however, 
 been previously distinctly stated, though not proved, by Bishop Eendu. 
 
 Laws of Glacier-Motion. — The term differential motion is a con- 
 densed expression for all the laws of glacier-motion. It asserts that 
 the different parts of a glacier do not move together as a solid, but 
 move among themselves in the manner of a fluid. A glacier moves like 
 a fluid, though a very stiff, viscous fluid ; its motion may therefore be 
 
60 
 
 AQUEOUS AGENCIES. 
 
 f 3 
 
 -q—o 
 
 :<3 
 
 rightly called viscoid. We will mention some of the most important 
 laws of fluid-motion, and show that glaciers conform to them : 
 
 1. The Velocity of the Central Parts is greater than that of the 
 Margins. — This well-known law of currents, the result of friction of 
 the fluid against the containing banks, was completely proved in the 
 case of glaciers by the experiments of Agassiz and 
 Forbes, and recently confirmed in the most perfect 
 o. ~L c tC 6 f 3 manner by Tyndall. A line of stakes, a 5 c(?e/^, 
 placed in a straight row across a glacier, becomes 
 every day more and more curved, as seen in Fig. 
 47. The exact rate of motion for each stake is 
 easily measured by the theodolite. The rate of 
 the center is often many times greater than that 
 of the margins. 
 FiQ. 47. 2. The Velocity of the Surface is greater than 
 
 that of the Bottom. — This law of currents, which 
 is the necessary result of friction on the bed, is more diflBcult to 
 prove in the case of glaciers, because it is difficult to get a vertical 
 section. The necessary observation was, however, successfully accom- 
 plished by Prof. Tyndall in 1857. We have already said (page 57) 
 that glaciers conform to large but not to small inequalities of their 
 channels ; a glacier, therefore, passing by a narrow side-ravine will 
 expose its whole thickness on the side. Prof. Tyndall, having found 
 such a side exposure more than 140 feet vertical, placed three pegs in 
 a vertical line, one near the top, one near the middle, and one at the 
 bottom (Pig. 48, a b o). The vertical line became more and more 
 inclined daily. The daily motion 
 at top was six inches, in the middle 
 4"5 inches, and at the bottom 3-5 
 inches. Thus, glaciers, like rivers, 
 slide on their beds and banks, pro- 
 ducing erosion ; but, also, the sev- 
 eral layers, both horizontal and ver- 
 tical, slide on each other. 
 
 3. The Velocity increases with 
 the Slope.— Y\g. 49 represents the surface-slope of the glacier Du GSant, 
 Gj the Merde Glace, M ; and the glacier DeBois, B; and their daily 
 motion. The increase of velocity with the slope is evident. 
 
 4. The Velocity increases with the Fluidity.— The dally motion of 
 glaciers is greater in summer, when the ice is rapidly melting, than in 
 winter ; and in mid-day than at night. 
 
 5. The Velocity increases with the Depth. — In the Alps, where the 
 thickness is 200 to 300 feet, the mean daily motion is one to three feet; 
 but in Greenland, where the thickness is 2,000 to 3,000 feet, the daily 
 
 FiQ. 48.— The exposed side of a glacier, show- 
 ing successive positions of the pegs abc. 
 The arrow shows the direction of motion. 
 
THEORIES OF GLACIER MOTION. 
 
 61 
 
 motion, in spite of the much lower temperature, is in some cases 60 
 feet* or even 99 feet.f The Muir Glacier in Alaska, according to 
 Wright, moves 70 feet a day ; but the later results of Ried make it 
 only 7 to 10 feet.J 
 
 Fig. 49. 
 
 Fig. 50. 
 
 6. Fluid Currents conform to the Irregularities of their Channel— 
 Glaciers, like water-currents, conform to the inequalities of the bottom 
 and sides of their channels. They have 
 
 their shallows and their deeps, their nar- 
 rows and their lakes, their cascades, their 
 rapids, and their tranquil portions. Fig. 
 50 shows a glacier running through a nar- 
 row gorge into a wide lake of ice, and again 
 through another gorge. There is this 
 difference, however, between a glacier and 
 a water-current, viz., that, while the latter 
 conforms to even the minutest and sharp- 
 est outlines, the former conforms only to 
 the. larger or more gentle. In this, a gla- 
 cier acts like a stiiJ, viscous fluid. 
 
 7. The Line of Swiftest Motion is more sinuous than the Channel. 
 — We have already seen that this is true of rivers (page 34); The line 
 
 of swiftest current is reflected from side to side, in- 
 creasing the curves by erosion. The same has been 
 proved by Tyndall to be the case with glaciers. Fig. 
 51 represents a portion of a sinuous glacier, like the 
 Mer de Glace : the dotted line represents the line of 
 swiftest motion. 
 
 8. The existence of partial currents up and down 
 and side to side determined by inequalities of bed 
 
 and banks. 
 
 Theories of Glacier Motion. 
 
 There are few subjects connected with the physics 
 of the earth which have excited more interest than 
 that of glacier-motion. The subject is one of exceed- 
 ing Jbeauty, and not without geological importance. 
 Passing over several very ingenious theories which 
 have now been abandoned, the first theory which was 
 
 Fig. 51. 
 
 * Helland, Journal of Geological Society, vol. xxxiii, p. 142 et seq. 
 
 \ Science, vol. xi, p. 259, 1888. X American Geologist, vol. ii, p. 276, 1893. 
 
62 AQUEOUS AGENCIES. 
 
 conceived in the true inductive spirit, and which explains the differ- 
 ential motion, is that of Prof. James Forbes. 
 
 Viscosity Theory of Forbes. 
 
 Statement of the Theory.— According to Forbes, ice, though appar- 
 ently so hard and solid, is really, to a slight extent, a viscous body. 
 In small masses this property is not noticeable, but in large masses 
 and under long-continued pressure it slowly yields, and will flow like 
 a stiffly viscous fluid. In large masses like a glacier, this steady, 
 powerful pressure is furnished by the immense weight of the super- 
 incumbent ice. 
 
 Argument. — It is evident that this theory completely accounts for 
 all the phenomena of glacier motion, even in their minutest details. 
 A glacier, beyond all doubt, moves like a viscous body, but it is still a 
 question whether it does so by virtue of a property of viscosity. The 
 proposition that ice is a viscous substance seems at first palpably ab- 
 surd. It is necessary, therefore, to show that this proposition is not so 
 absurd as it seems. 
 
 The properties of solidity and liquidity, though perfectly distinct 
 and even incompatible in our minds, nevertheless, in Nature, shade 
 into one another in the most imperceptible manner. Malleability, 
 plasticity, and viscosity are intermediate terms of a connecting series. 
 The idea which underlies all these expressions is that of capacity of 
 riiotion of the molecules among themselves without rupture : the differ- 
 ence among them being the greater or less resistance to -that motion. 
 In the case of malleable bodies, like the metals, great force is required 
 to produce motion ; in plastic bodies, like wax or clay, less force is re- 
 quired ; in viscous bodies, like stiff tar, motion takes place spontane- 
 ously but slowly ; while in liquids it takes place freely and with little 
 or no resistance. In all these cases, if the pressure be sufficient, the 
 body will change its form without rupture — in other words, will/ow. 
 Now, by increasing the mass we may increase the pressure to any ex- 
 tent. Therefore, all malleable, ductile, plastic, or viscous bodies, if in 
 sufficiently large masses, will flow like water. Thus, a mass of lead, 
 sufficiently thick, would certainly flow under the pressure of its own 
 weight. 
 
 But solid bodies may be divided into two great classes, viz., bodies 
 which are malleable, plastic, or viscous, and bodies which are brittle ; 
 the very idea of brittleness being that of total incapacity of motion 
 among the particles without rupture. Now, ice belongs to the class of 
 brittle bodies. Forbes attempts to remove this difficulty by showing 
 that many apparently brittle bodies will also flow under their own 
 weight ; for instance, pitch, so hard and brittle that it flies to pieces 
 under a blow of the hammer, will, if the containing barrel be removed, 
 
REGELATION THEORr OF TYNDALL. go 
 
 flow and spread itself in every direction. So, also, molasses-candy 
 made quite hard and brittle, will still flow by standing. A remarkable 
 pitch-lake, about three miles in circumference, occurs in Trinidad. 
 The pitch is described as in constant, slow-boiling motion, coming up 
 in the center, flowing over to the circumference, and again sinking 
 down. Yet this pitch in small masses, would be called solid and 
 brittle. Struck with a hammer, it flies to pieces like glass. In fact, 
 the essential peculiarity of a stiif, viscous body, in which it differs 
 from malleable or plastic bodies, is, that it yields only to slowly-applied 
 force. 
 
 Forbes, therefore, thinks that glacier-ice is an exceedingly stiff, vis- 
 cous substance, which, though apparently brittle in small quantities and 
 to sudden force, yet, under the slow-acting but powerful pressure of 
 its own weight, flows down the slope of its bed, squeezing through 
 narrows and spreading out into lakes, conforming to all the larger and 
 gentler inequalities of bed and banks, but not to the sharper ones. 
 The velocity of motion is small in the same proportion as the viscous 
 mass is stiff. The descent of the Mer de Glace from the cascade of 
 the Glacier du Geant to the point of Glacier de Bois, a distance of 
 ten miles, is 4,000 feet. Water, under these circumstances, would rush 
 with fearful velocity. The glacier moves but two feet in twenty-four 
 hours. 
 
 Such viscosity of ice as supposed by Forbes is now proved by ex- 
 periments. Ice-boards supported at the two ends bend into an arc 
 under their own weight. Cylinders of snow compacted into ice may 
 be bent in the hand to a semicircle without rupture,* and bars of ice 
 may even be stretched by slow pulling. f 
 
 Regelation Theory of Tyndall. 
 
 If ice be indeed a viscous body, then there seems no reason why it 
 should not yield to pressure even in small masses, if the pressure be 
 sufBciently slowly graduated. In the hands of a skillful experiment- 
 alist it ought, to exhibit this property. Prof. Tyndall tried the ex- 
 periment. Masses of ice of various forms were subjected to slowly- 
 graduated, hydrostatic pressure. In every case, however slowly grad- 
 uated the pressure, the ice broke; but if the broken fragments were 
 pressed together, they reunited into new forms. In this manner, ice 
 in the hands of Prof. Tyndall proved as plastic as clay : spheres of 
 ice (fl. Fig. 52) were flattened into lenses (5), hemispheres (c) were 
 changed into bowls («?), and bars (e) into semi-rings (/). He even 
 
 * Aitkin, American Journal of Science, vol. v, p. 305, third series, 1873. 
 ■f American Journal of Science, vol. xxxiv, p. 149, 188Y; and Nature, vol. xxxix, p. 
 203, 1888. 
 
64 
 
 AQUEOUS AGENCIES. 
 
 asserts that ice may be molded into any desirable form ; e. g., into vases, 
 statuettes, rings, coils, knots, etc. Here, then, we have a power of being 
 molded such as was not dreamed of before ; but this power was not de- 
 
 B 
 
 G 
 
 T<=>r 
 
 mjf 
 
 Fig. 52.— j1 B C, molds; ace, original forms of the ice; b df, the forms into which they 
 
 were molded. 
 
 pendent on a property of viscosity, but upon another property long 
 known, but only recently investigated by Faraday, viz., the property of 
 regelation. 
 
 Regelation. — If two' slabs of ice be laid one atop of the other, they 
 soon freeze into a solid mass. This will take place not only in cold 
 weather, but in midsummer, or even if boiling water be thrown over 
 the slabs. If a mass of ice be broken to pieces, and the fragments be 
 pressed or even brought in contact with one another, they will quickly 
 unite into a solid mass. Snow pressed in the warm hand, though con- 
 stantly melting, gradually becomes compacted into solid ice. This 
 very remarkable but imperfectly understood property of ice completely 
 explains the phenomena of molding ice by experiment. By this prop- 
 erty the broken fragments reunite in a new form as solid as before. 
 We may possibly call this property of molding under ^kssvltq plasticity 
 (although it is not true plasticity, since it does not mold without rupt- 
 ure, but by rupture and regelation) ; but it can not in any sense be 
 called viscosity, for the true definition of viscosity is the property of 
 yielding under tension — the property of stretching like molasses-candy, 
 or melted glass ; but ice in the experiments, according to Tyndall, did 
 not yield in the slightest degree to tension. In the experiment, if, in- 
 stead' of placing the straight bar at once into the curved mold, it had 
 been placed successively in a thousand molds, with gradually-increased 
 curvature, or, still better, if placed in a straight mold, and this mold, 
 while under pressure, curved slowly, then there would have been no 
 sudden visible ruptures, but an infinite number of small ruptures and 
 regelations going on all the time. The ice would have behaved pre- 
 cisely like a viscous body. Now, this is precisely what takes place in a 
 glacier. 
 
STEUOTURE OF GLACIERS. 65 
 
 Application to Glaciers. — A glacier, on accouiit of its immense 
 mass, is, in its lower parts, under the heavy pressure of its own weight 
 tending to mold it to the inequalities of its own bed, and in every part 
 under a still more powerful pressure — a pressure proportioned to the 
 height of the head of the glacier — urging it down the slope of its bed. 
 Under the influence of this pressure the mass is continually yielding 
 by fracture of all sizes, but, after changing the position of its parts, 
 again uniting by regelation. By this constant process of crushing, 
 change of form, and reunion, the glacier behaves like a plastic or vis- 
 cous body ; though of true plasticity or true viscosity there is, accord- 
 ing to Tyndall, none. In fact, we have in the phenomena of glaciers 
 the most delicate test of viscosity conceivable ; but we find the glaciers 
 will not stand the test. For instance, the slope of the Mer de Glace at 
 one point changes from 4° to 9° 35', and yet the glacier, although 
 moving but two feet a day, can not make this slight bend without 
 rupture; for at this point there are always large transverse fissures 
 which heal up below by pressure and regelation. In another place 
 the glacier is similarly broken by passing an angle produced by a 
 change of slope of only 2°. It seems almost impossible that a body 
 having the slightest viscosity should be fractured under these circum- 
 stances. Tyndall concludes, therefore, that the motion of glaciers is 
 viscoid, but the body is not viscous — the viscoid motion being the re- 
 sult, not of the property of viscosity, but of fracture, change of posi- 
 tion, and regelation. 
 
 CroU's Theory. — This attempts a physical explanation of the vis- 
 cosity of ice by assuming that heat is transferred downward from 
 molecule to molecule, and that the alternate melting and refreezing 
 gives rise to a movement similar to viscosity. 
 
 Thomson's Theory. — This assumes that the ice yields at points of 
 greatest pressure, hy melting. According to Tyndall's theory differ- 
 ential motion is by fracture, change of motion, and regelation. Ac- 
 cording to Thomson's theory it is by melting, change of position, and 
 regelation. 
 
 Eecent experiments by Miigge indicate that the apparent viscosity 
 of glaciers is the result of shearing along the cleavage planes of the 
 crystalline granules of the ice. The granular structure of glacier ice 
 is a fact of prime importance. It now seems likely that movement 
 of the granules, either by cleaving or by sliding over each other, will, 
 when taken in connection with regelation, give the most acceptable 
 theory of glacier motion. 
 
 Structure of Glaciers. 
 There are two points connected with the structure of glaciers 
 which require notice, viz., the 'veined structure and the fissures. 
 
66 
 
 AQUEOUS AGENCIES. 
 
 Veined Structure. — The ice of glaciers is not homogeneous, but 
 consists of white vesicular ice (white because vesicular) banded, often 
 very beautifully, with solid transparent blue ice (transparent blue 
 because solid), the banding sometimes so delicate that a hand-specimen 
 looks like striped agate. These blue veins are not continuous planes, 
 but apparently very flat lenticular in shape, varying in thickness from 
 a line to several inches, and in length from a few inches to several 
 feet. Their direction being parallel to one another, they give a strati- 
 fied or cleavage structure to the glacier, and, in melting, the glacier 
 often splits or cleaves along these planes. 
 
 Fissures. — These are marginal, transverse, and longitudinal. The 
 marginal fissures are shown in Fig. 41; they are always at right 
 angles to the marginal veins. 
 
 Theories of Structure. 
 
 Fissures. — There can be no doubt that the great fissures or crevasses 
 are produced by tension or stretching, and that their direction is 
 always at right angles to the line of greatest tension. Thus the trans- 
 verse fissures are produced by the stretching of the glacier in passing 
 over a salient angle. The marginal fissures are produced by the drag- 
 ging or pulling of the swifter central portions upon the slower mar- 
 ginal portions. It has been proved by Hopkins, the English physicist 
 and geologist, that the line of greatest tension from this cause would 
 be inclined 45° with the course of the glacier, as shown by the arrows 
 (Fig. 53). The fissures should be at right angles to these lines, and, 
 
 Fia. 53. 
 
 Fig. 54. 
 
 therefore, also inclined 45° with the margin, and running upward and 
 inward. The longitudinal fissures are best seen where a glacier runs 
 through a narrow gorge out on an open plain. The lateral spreading 
 of the glacier causes it to crack longitudinally (Fig. 54). 
 
 Theory of Veins. — Tyndall has shown conclusively that veins are 
 always at right angles to the line of greatest pressure, and that, there- 
 fore, they are produced by pressure. Thus fissures and veins, being 
 
CLASSES OF GLACIERS. 
 
 67 
 
 produced by opposite causes — one by tension and the other by pressure 
 — are formed under opposite conditions. As transverse fissures are 
 produced by the longitudinal stretching of a glacier passing over a 
 salient angle, so transverse veins are formed by the longitudinal com- 
 pression of a glacier passing over a re-entering angle. 
 
 Again, as marginal fissures are produced by the pulling of the cen- 
 tral portions upon the lagging margins behind, so the marginal veins 
 are produced by the crowding or pushing of the swifter central parts 
 on the slower marginal parts in front (Fig. 55). The marginal veins 
 
 fed 
 
 Fio. 55. 
 
 Fig. 56. 
 
 Fig. 57. 
 
 are, therefore, inclined to the margin about 45°, but pointing inward 
 and downward, and, therefore, at right angles to the crevasses. The 
 relation of these to one another is shown in Fig. 56. 
 
 Finally, as longitudinal fissures are produced by lateral spreading 
 (Fig. 55), so longitudinal veins are produced by lateral compression. 
 This is best seen where two tributaries meet at a high angle (Fig. 57) 
 — for instance, where the Glacier du Geant and the Glacier de Leehaud 
 form the Mer de Glace (Fig. 42). All these facts have been experi- 
 mentally illustrated by Tyndall. 
 
 Classes of Glaciers. 
 
 Thus far the discussion of glaciers has referred especially to 
 stream glaciers, and the facts and illustrations have been drawn from 
 alpine studies. However, the physics and phenomena of alpine gla- 
 ciers do not wholly apply to the great glaciers of Alaska and Green- 
 land, and even less to the vast ice-sheets which invaded the United 
 States and western Europe. It is now in order to briefly discuss 
 glaciers in a comparative way. 
 
 Glaciers are now classified as alpine, piedmont, and continental 
 Alpine glaciers are the streams of ice which occupy mountain-valleys. 
 During and following the glacial invasion of the United States there 
 were alpine glaciers in the higher mountains, as the White Mountains, 
 Eocky Mountains, and Sierras, and they still linger in the high sierras 
 of California and Oregon. 
 6 
 
68 AQUEOUS AGENCIES. 
 
 The Malaspina glacier, in Alaska, is the type of the piedmont 
 class. It is a plateau of glacier ice, some 15,000 square miles in 
 area, formed by the confluence of huge stream glaciers from the Mount 
 St. Elias alps. Being a " lake " of ice, produced by union of alpine 
 
 Fig. 68.— Banding of Glacier, South Point Glacier, Greenland. (Photograph hy T. C. Ohamberlin ) 
 
 glaciers, its movement is less pronounced, and portions of the border 
 are stagnant, where a thickness of even 1,000 feet is buried under 
 moraine debris and extensive forests. 
 
 Continental glaciers are represented to-day only by the Greenland 
 and Antarctic ice-caps, but as they are the living illustrations of the 
 vast ice-bodies vrhich once covered western Europe and parts of North 
 America they are of special interest and importance to geologists. 
 
 Worlc of the Ice-Sheet. 
 
 Within the limits reached by the ice-sheet in the United States it 
 covered practically all heights of land and spread a mantle of drift 
 over the entire surface. Eroding action was not confined to the 
 valleys, as in alpine glaciers, although it was often more pronounced 
 in large valleys parallel to the ice movement. DifEerential flow was 
 not so emphatic as in alpine glaciers, and crevassing could not have 
 been so common. .A large part of the drift mantle was produced 
 from the geest and decayed rock of the millions of years of pre- 
 glacial weathering, which the ice-sheet seized and worked over, but in 
 
FORMS OF DRIFT. 
 
 69 
 
 many pPaces did not entirely remove. In some places the glacier cut 
 into the live rock, but it did not greatly change the larger topography 
 of any region, although it tended to plane off the saliences. Its 
 'greater effect was to fill transverse depressions with the drift. In 
 general it had a smoothing effect upon the country, and over great 
 areas the minor topography is a result of the ice work. This leads 
 us to consideration of the drift. 
 
 Forms of Drift. 
 
 Excepting moraines, the forms of glacial drift described below 
 are not exemplified in the work of alpine glaciers. This was one rea- 
 son why the American geologists of half a century ago did not readily 
 accept the new explanation of the drift. Indeed some special forms 
 of the drift have never been seen in the process of formation, and our 
 knowledge of their genesis is inferential. On that account, however, 
 they are no less interesting, and perhaps even more valuable for pur- 
 poses of study. ' 
 
 The Till — ^Up to the middle of the last century the mantle of 
 rock rubbish which covers the glaciated territory was attributed to 
 
 Till, on Niagara Limestone, Rochester, N. Y. 
 
 overwhelming floods of water from the north, and the term " drift " 
 is an inheritance from that discarded theory. We now use the term 
 in a broad sense to include not only the unassorted materials, depos- 
 
YO AQUEOUS AGENCIES. 
 
 ited directly by the mechanical action of the ice, the till, but also 
 for the assorted materials, sand and gravel, spread by the glacial 
 waters far beyond the ice-front, and termed modified drift, or water- 
 laid drift. The student should appreciate the fact that all the ice 
 of the immense glacier, thousands of feet in thickness, became water, 
 and he must be prepared to find a large amount of water-laid drift 
 associated with the till. 
 
 The till-sheet is theoretically divided into subglacial, interglacial, 
 and superglacial till. The first of these, often called bowlder clay, 
 or ground moraine (hard-pan of the farmers), is the consolidated 
 product of grinding and pressure beneath the ice. It is rock-flour, 
 with striated stones, often resting directly on striated rock.' The 
 continental glacier, unlike the alpine glaciers, had little or no super- 
 glacial drift, except near the border of the glacier where the inter- 
 glacial material became superglacial by ablation (removal by melting 
 and evaporation) of the surface of the glacier. The superglacial till 
 may be distinguished by its less compact state and its included stones 
 being more angular and less striated. 
 
 In the upper Mississippi basin several distinct sheets of till have 
 befen recognized, with separating beds of interglacial and warm-cli- 
 mate epochs. This fact will appear again when we discuss the history 
 of the Glacial Period (see p. 569). 
 
 Moraines. — The morainal drift left by the continental glaciers,in 
 America and Europe are mostly in the form of extensive terminal 
 or peripheral moraines. Lateral arid medial moraines are charac- 
 teristic of" alpine but not of continental glaciers, as rock masses 
 are required at or above the glacier surface. A few peaks of rock, 
 "nunataks," project up through the borders of the Greenland 
 ice-cap, but even such were probably wanting from our ice-sheets. 
 During the ice retreat some lobes of the glacier front may have 
 extended down valleys so as to simulate stream glaciers, and lateral 
 moraines should be searched for on the sides of strong north-and- 
 south valleys. 
 
 Moraines are typically composed of till, but in places where the 
 glacial drainage was concentrated the material m^y be mostly sand 
 and gravel, or kames. The characteristic morainal topography is 
 mound-and-basin, or knob-and-kettle. Pits or bowls — "kettles" — 
 are peculiar to glacial drift. If in till they produce lakelets or tarns, 
 but in pervious drift they are naturally dry. Many kettles are be- 
 lieved to have been made by the melting away of buried masses of 
 ice, allowing the drift cover to fall in. Basins in valley drift, often 
 far from any moraine, are also regarded as ice-block kettles. 
 
 The extreme limits of the ice action and the location of the great 
 terminal moraines are described later in this work, in discussion of 
 
FORMS CF DRIFT. 
 
 71 
 
 the Glacial Period (see pp. 569 et seq.). The latest of the ice advances 
 has left the 'most pronounced moraines. In the basins of the Great 
 Lakes these are disposed in series of great loops, convex southward, 
 indicating that the border of the ice-sheet was decidedly lobate. 
 This fact shows that the ice pushed farther down the valleys than it 
 did on the ridges. In some cases the lobation was so pronounced 
 that lobes met, and the consequent blending of the terminal moraines 
 produced massive moraines of pBculiar relationship, which Chamberlin 
 has aptly called interlobate moraines. A very striking one lies west 
 of Lake Michigan. The student should not confuse these with medial 
 moraines. The looped moraines lie in concentric series, marking 
 pauses in the recession of the ice-front. The inner moraines are 
 called recessional or retreatal moraines (see Figs. 948a, 949). 
 
 Drumlins. — These are hills composed of till and having strikingly 
 smooth, curving, convex outlines, quite unlike the irregular hum- 
 mocky surfaces of morainic hills. Drumlins are sometimes mammil- 
 lary, but usually either oval or elongated as ridges, but always with the 
 
 FiQ. 60.— Drumlins, Wayne County, N. T. 
 
 longer axis in the direction of the ice movement. They are the best 
 indices of the direction of glacial flow. In any particular, region they 
 are liable to have a prevailing form. Those of Massachusetts are 
 more likely to be oval or short, while those of New York are decidedly 
 elongated, many being one or two miles in length. In size they range 
 froni mere knolls up to 100 or 200 feet in height, and in many locali- 
 ties they are the most conspicuous elevations. They were formed 
 beneath the waning border of the ice-sheet, along the zone where the 
 ice became incompetent to carry its burden. They are subglacial 
 heapings of the ground-moraine, perhaps comparable to the longitudi- 
 nal sand-bars in the bed of a river. However, they are exceptional 
 phenomena, and the entire absence of them from most of the drift 
 area is a more striking fact than their occurrence. Three areas of 
 special development are Wisconsin, eastern Massachusetts, and Kew 
 
72 
 
 AQUEOUS AGENCIES. 
 
 York. Practically every hill seen along the !N"ew York Central Eail- 
 road between Eoehester and Syracuse is a drumlin. The name is 
 from Ireland, and signifies a little hill. 
 
 Kames. — These are mounds of water-laid drift, sand, or gravel, 
 rather poorly stratified, and built at the ice margin by the glacial 
 drainage. Kames may occur as single, isolated mounds, or in groups, 
 or as extensive kame-areas. In the latter form they have the same 
 mound-and-basin topography as true moraines. Indeed, they are a 
 form of morainal drift, in that they are terminal accumulations. 
 
 Fig. 61.— Kames, Monroe County, N. Y. 
 
 Moraines are frequently partly water-laid, and such deposits may be 
 called " kame-moraine." 
 
 Eskers. — Eskers are long, sinuous ridges of coarse sand or gravel, 
 sharp-crested, with steep slopes, and of height 10 to 20 fget, rarely 
 as much as 50 feet. They are frequently broken or interrupted, 
 becoming even a series of kame knolls. The typical esker was depos- 
 ited in the bed of an overloaded glacial stream, which flowed between 
 ice-walls, either in a tunnel beneath the ice, or more probably in a 
 trench or canon cut down from the surface of the glacier by bottom 
 melting. The peculiar ridged form is supposed to be due to the 
 crumbling down of the sides of the deposit when the retaining ice- 
 walls disappeared. The direction of eskers, like drumlins, is gener- 
 ally parallel with the ice movement. They occur most commonly in 
 valleys, but sometimes they run up and down over hills, with little 
 reference to topography, being apparently superimposed. They are 
 especially developed in Maine. The name is Irish. In Scandinavia 
 they are called Osar (singular Os). 
 
FLOATING ICE— ICEBEEGS. 
 
 na 
 
 The following generalization will aid the student: In composi- 
 tion, moraines and drumlins are ice-laid ; kames and eskers are water- 
 laid. In location, moraines and kames are peripheral or marginal 
 
 Fig. 62.— Esker, Monroe County, N. Y. 
 
 to the ice-body and transverse to tlie ice movement. Drumlins and 
 eskers are axi-radiant to the ice-body, or parallel to the ice movement. 
 
 Floating Ice — Icebergs. 
 
 We have already seen (p. 50) that at-a certain latitude, varying 
 
 from 46° in South America to about 65° in Norway, glaciers touch the 
 
 . surface of the ocean. Beyond this latitude, they run out to sea often to 
 
 Fig. 63.— Formation of Icebergs. 
 
 great distances. By the buoyant power of water, assisted by tides and 
 waves, these projecting floating masses are broken off, and accumulate 
 as immense ice-barrier's in polar seas, or are drifted away by currents 
 
72& 
 
 AQUEOUS AGENCIES. 
 
 S 
 
 si 
 
 Fig. 836.^Vertical Section through End of Muir Glacier and Glacier Bay. Scale, 1 inch = 3,500 feet. 
 
 (After Gilbert.) 
 
FLOATING ICE-ICEBERGS. 72e 
 
 toward the equator. Such floating fragments of glaciers are called ice- 
 bergs. Pig. 63 is an ideal section, through a glacial valley, in which 
 ag\s the glacier, b the clitls beyond, I s the sea-level, and i an iceberg. 
 The principal source of the icebergs of the north Atlantic is the 
 coast of Greenland. This country is an elevated table-land, sloping 
 in every direction to a coast deeply indented like Norway, with alter- 
 nate deep fiords and jutting headlands. The whole table-land is com- 
 pletely covered with an ice-sheet, probably several thousand feet thick, 
 moving slowly seaward, and discharging through the fiords as immense 
 glaciers,* which, as already explained, form icebergs. In this remarka- 
 ble country no water falls from the atmosphere except in the form of 
 snow, and all the rivers are glaciers. The geological effects of such a 
 moving ice-sheeb may be easily imagined. The whole surface of the 
 country rock must be polished and scored, the general direction of the 
 striae being parallel over large areas. 
 
 The antarctic continent is probably similarly, and even more thick- 
 ly, ice-sheeted, for the humid atmosphere of that region is very favorable 
 to the accumulation of snow and ice. Captain Wilkes found an impen- 
 etrable ice-barrier, in many places 150 to 200 feet high, for 1,200 miles 
 along that coast. From this ice-barrier, icebergs separate and are 
 drifted toward the equator. 
 
 The formation of icebergs in polar regions, and their drifting into 
 warmer latitudes, to be melted there, are evidently a necessary conse- 
 quence of the great laiv of circulation, for otherwise ice wonld accumu- 
 late without limit in these regions. But, by glacial motion, the excess 
 is brought down to the sea, broken off as icebergs, carried southward 
 by currents, and there melted and returned into the general circulation 
 of meteoric waters. 
 
 General Description. — The number of icebergs accumulated about 
 polar coasts is almost inconceivable. Scoresby counted 500 at one 
 view. Kane counted 380 of the first magnitude at one view. They 
 are often 200 and sometimes even 400 feet high, and the mass above 
 water 66,000,000 cubic yards (Dr. Eink). As the specific gravity of 
 ice is 0-918, if these were solid ice, there would be about one twelfth 
 above water ; but as glacier-ice is somewhat vesicular, there is about 
 one seventh above water. The thickness of some of these icebergs 
 must therefore be 2,000 to 3,000 feet, and their volume near 500,000,000 
 cubic yards, which is about equivalent to a mass one mile square and 
 500 feet thick. Under the influence of the melting power of the sun 
 unequally affecting different parts, they assume various and often 
 strange forms. The accompanying figure (Fig 64) gives the usual ap- 
 pearance in the northern Atlantic. Those separated from the antarctic 
 
 * Dr. Rink, Archives des Sciences, vol. xxvii, p. 1S6. 
 
1U 
 
 AQUEOUS AGENCIES. 
 
 barrier present, before they have been much acted upon by the sun, a 
 much more regularly prismatic appearance. Fig. 65 gives the appear- 
 ance of one of these prismatic blocks or tables, 180 feet high, seen Jby 
 Sir James Boss in the antarctic seas. 
 
 r 
 
 Fig. 64.— North Atlantic Iceberg. (Photograph by Walcott.) 
 
 Icebergs as a Geological Agent— Erosion. — The polishing and scor- 
 ing effects of the ice-sheets and of their discharging glaciers must, of 
 course, extend over the sea- bottoms about polar coasts as far as the 
 glaciers touch bottom, which, considering their immense thickness, 
 must be for considerable distances (Fig. 63, a to g). This, however, is 
 glacier agency rather than iceberg stgency. On being separated they 
 float away, and are carried by currents with their immense loads of 
 
 Fio. 65. 
 
 earth and bowlders, amounting often to 100,000 tons or more, as far 
 as 40° or even 36° latitude, where, being gradually melted, they drop 
 their burden. If the water be not sufficiently deep, they ground, and 
 being swayed by waves and tides they chafe and score the bottom in a 
 somewhat irregular manner; or, packing together in large fields, and 
 
MECHANICAL AGENCIES OF WATER. Y3 
 
 urged onward by powerful currents, they may possibly score the bot- 
 tom over considerable areas somewhat in the manner of glaciers. A 
 large iceberg will ground in water 3,000 and 3,500 feet deep ; they 
 have been found by James Ross actually aground in 1,560 feet of water 
 off Victoria Land. A true glaciated surface, however, can not be pro- 
 duced by icebergs. 
 
 Deposits. — The bottom of the sea about polar shores is found deeply 
 covered with the materials brought down by glaciers and dropped by 
 icebergs (Fig- 63). Again, similar materials are carried by icebergs as 
 far as these are drifted by currents, and spread on the bottom of the 
 sea everywhere in the course of these currents. Where stranded ice- 
 bergs accumulate, as on the banks of Newfoundland, large quantities 
 of such materials are deposited. These banks are in fact supposed to 
 have been formed, in part at least, in this way. Such deposits have 
 not been suflBciently examined ; they are probably somewhat similar to 
 those of glaciers, exhibiting, however, some signs of the sorting power 
 of water. Balanced stones or bowlders in insecure positions can hardly 
 be left by icebergs. 
 
 8hore-Ice. 
 
 In cold climates the freezing of the surface of the water forms 
 sheets of ice many inches or even feet thick, and of great extent, about 
 the shores of rivers, bays, and seas. They often inclose stones and 
 bowlders of considerable size, and when loosened in spring from the 
 shore they bear these away, and again drop them at considerable dis- 
 tances from their parent rock. Also such sheets packed together in 
 large masses, and driven ashore by river and tidal currents, and chafed 
 back and forth by waves, produce effects on the shore-rocks somewhat 
 similar to the scoring, polishing, and even the roches moutonnees of 
 glacier-action. On a rising or on a subsiding coast such scorings and 
 polishings may extend over wide areas, and thus simulate true glacial 
 action. These effects are well seen on the shores of the St. Lawrence 
 River and Gulf. 
 
 The importance of the study of ice-agencies will be seen when we 
 come to explain the phenomena of the Drift or Glacial period. 
 
 Comparison of the Different Forms of the Mechanical Agencies of 
 
 Water. 
 Rivers and glaciers are constantly cutting down all lands, bearing 
 awav the materials thus gathered, and depositing them on the sea- 
 margins. Acting alone, therefore, their effect must be to diminish the 
 height and to extend the limits of the land. Ocean agencies, on the 
 other hand, by tides and currents bear away to the open sea the mate- 
 rials brought down from the land, and thus tend to prevent marginal 
 
/j-^ AQUEOUS AGENCIES. 
 
 accumulations ; and by waves and tides constantly eat away the coast- 
 line, and thus strive to extend the domain of the sea. Thus, while 
 river and ocean agencies are in conflict with one another at the coast- 
 line, the one striving to extend the limits of the land, and the other 
 of the sea, yet they co-operate with each other in destroying the in- 
 equalities of the earth's surface, and are therefore called leveling agen- 
 cies. Moreover, it is evident that the erosion of the land and the fill- 
 ing up of the seas are correlative, and one is an exact measure of the 
 other. Now, we have seen (page 11) that the probable rate at which 
 all continents are being cut down by rivers is about one foot in 4,500 
 to 5,000 years. But since the ocean is about three times the extent of 
 the land, this spread evenly over the bottom of the sea would make a 
 stratum about four inches thick. . Therefore, we conclude that, neg- 
 lecting the destructive effects of waves and tides on the coast-line, 
 which, according to Phillips, are small in amount compared with gen- 
 eral erosion of the land-surface, we may say that stratified deposits are 
 now forming, or the ocean-bed filling up, at the average rate over the 
 whole bottom of about four inches in 5,000 years. 
 
 Section 4. ^Chemical Agencies oe Water. 
 
 Underground Waters and the Origin of Springs. 
 
 As we have already seen (page 10), of the rain which falls on any 
 hydrographical basin, a part runs from the surface, producing universal 
 erosion. A second part sinks into the earth, and, after a longer or 
 shorter subterranean course, comes up as springs, and unites with the 
 surface-water to form rivers; while a third portion never comes up at 
 all, but continues by subterranean passages to the sea.* This last por- 
 tion is removed from observation, and our knowledge' concerning it is 
 very limited. But there are numerous facts which lead to the convic- 
 tion that it is often very considerable in amount. In many portions of 
 the sea near shore, springs, and even large rivers, of fresh water, are 
 known to well up. Thus, in the Mediterranean Sea, " a body of fresh 
 water fifty feet in diameter rises with such force as to cause a visible 
 convexity of the sea-surface." Similar phenomena have been ob- 
 served in many other places in the same sea, and also in the Gulf of 
 Mexico near the coast of Florida, among the West India Isles, andnear 
 the Sandwich Islands. Besides the last mentioned, there is still another 
 portion of subterranean water existing permanently in every part of 
 the earth far beneath the sea-level, filling fissures and saturating sedi- 
 ments to great depths, and only brought to the surface by volcanic 
 
 * A fourth portion escapes by evaporation. In arid regions this is the major part of 
 the total rainfall. 
 
SUBTEIiKANEAN WATERS, SPRINGS, ETC. 
 
 75 
 
 forces. This, in contradistinction from the constantly-circulating me- 
 teoric water, may be called volcanic water. 
 
 Perpetual Ground- Water. — Passing from the surface downward the 
 ground contains more and more water until it becomes saturated and 
 the water movable. This region of movable water rises and falls with 
 the season, but never below a certain level depending upon the climate. 
 
 Fia 66.— Diagram of Perpetual Ground-Water: s s, surface of ground; w w, ground-water; spsp, 
 
 hill-eide springs. 
 
 The highest level at which water is always movable is called the level 
 of " perpetual ground- water." It is deepest on the hill-tops and comes 
 nearer the surface toward the valleys, where under favorable conditions 
 it may issue on the surface as springs, as in Fig. 66. 
 
 Springs. — The appearance of subterranean waters upon the surface 
 constitutes springs. They occur in two principal positions, viz. : 1. 
 Upon hill-sides, just where porous, water-bearing strata such as sand 
 outcrop, underlaid by impervious strata like clay ; 3. On fissures pene- 
 trating the country rock to great depth. 
 
 Most of the small springs occurring everywhere belong to the first 
 class. The figure (Fig. 67) represents a section of a hill composed 
 mostly of porous strata, i, but underlaid by impervious clay stratum, c. 
 Water falling upon the surface sinks through b until it comes in contact 
 with c, and then by hydrostatic pressure moves laterally until it emerges 
 at a. Sometimes this is a geological agent of considerable importance, 
 modifying even the forms of mountains, and producing land-slips, etc. 
 Thus the Lookout and Raccoon Mountains, in Tennessee, are table- 
 
 FiG. 67.— Hill-side Spring. 
 
 FiQ. 68. 
 
 mountains of nearly horizontal strata, separated by erosion-valleys. 
 These mountains are all of them capped by a sandstone stratum about 
 100 feet thick, underlaid by shale. The water which falls upon the 
 mountain emerges in numerous springs all around where the sandstone 
 cap comes in contact with the underlying shale. The sandstone is 
 
76 
 
 AQUEOUS AGENCIES. 
 
 gradually undermined, and falls from time to time, and thus the clifE 
 remains always perpendicular (Fig. 68). 
 
 Large springs generally issue from fissures. Water passing along 
 the porous stratum I, perhaps from great distance, and prevented from 
 rising by the overlying imper- 
 
 FlG. 
 
 Fiseure-Spring. 
 
 ■vious stratum c, coming m con- 
 tact with a fissure, immediately 
 rises through it to the surface 
 at a (Fig. 69). 
 
 Artesian Wells.— If subter- 
 ranean streams have their ori- 
 gin in an elevated region, a d, composed of regular strata dipping 
 under a lower flat country, c, then the subterranean waters passing 
 along any porous stratum as a (Fig. 70), and confined by two imper- 
 meable strata, b and d, will be under powerful hydrostatic pressure, and 
 •will, therefore, rise to the surface, perhaps with considerable force, if 
 the stream be tapped by boring at c. Borings by which water is 
 obtained in this manner are called Artesian wells, from the French 
 province Artois,, where they were first successfully attempted. The 
 source of the water may be 100 miles or more distant from the well. 
 Some of these wells are very deep. The Grenelle Artesian in Paris is 
 
 2,000 feet deep. At the 
 moment of tapping the 
 stream, a powerful jet was 
 thrown 112 feet high. One 
 in Westphalia, Germany, is 
 2,385 feet deep ; one at St. 
 Louis, 3,843 feet; one at 
 Louisville, Kentucky, 2,852; 
 one near Berlin, 4,173 feet ; 
 one near Pittsburg, Pa., 4,625 ; and one near Leipsic, 5,735 feet.* 
 In parts of Alabama and California the principal supply of water for 
 agricultural purposes is drawn from these wells, 
 
 Thus there is on all coasts a constant flowing of water, both super- 
 ficial and subterranean, into the sea. _ Their relative amount it is impos- 
 sible to determine. Much depends upon the configuration of the coun- 
 try and the nature of the strata. The heavy hydrostatic pressure to 
 which subterranean ^water is subjected, especially in elevated countries, 
 brings the larger portion of it to the surface as springs. But, in lime- 
 stone regions (this rock being aSected with frequent and large fissures, 
 and open subterranean passages, as will be hereafter explained), large 
 subterranean rivers often exist, and these even after coming to the sur- 
 face are often re-engulfed, and finally reach the sea by subterranean 
 
 * These deep borings are not all " artesian " in.the fonse of having a flow of water. 
 
 Fio. 70.— Artesian Well. 
 
LIMESTONE CAVES. 
 
 Y7 
 
 passages. The same is true also of regions covered with recent lava-^ 
 flows; for these also are full of caves and galleries (page 94). The 
 largest springs, therefore, generally occur either in limestone or in 
 volcanic countries. From the Silver Spring, in Florida, issues a 
 stream navigahle for small steamers up to the very spring itself. The 
 country for sixty miles around is entirely destitute of superficial 
 streams, the whole drainage being subterranean, and coming up in this 
 spring. About Mount Shasta all the streams head in great springs. 
 
 Chemical Effects of Subterranean Waters. — ^We have already seen 
 (page 6) how atmospheric water disintegrates" rocks, dissolving out 
 their soluble parts, and reducing their unsoluble parts to soils. 
 Springs, ^:heref ore, always contain the soluble matters. In granite 
 regions they contain potash; in limestone regions they contain lime, 
 and are called hard; in other eases they contain salt, and are brack- 
 ish; when the saline ingredients are unusual in quantity or in kind, 
 they are called mineral waters. 
 
 Limestone Caves. — In limestone regions, percolating waters dis- 
 solve the limestone, hollow out open passages, and form immense 
 
 Fis. 71.— stalactites and Stalagmites, Marengo Cave, Indiana 
 
 caves. Water charged with limestone, dripping from the roofs, de- 
 posit their limestone by evaporation, and form stalactites and stalag- 
 mites. Subterranean waters may hollow out passages by solution or 
 
Y8 AQUEOUS AGENCIES. 
 
 fill them up by deposit according as its waters are under-saturated or 
 over-saturated with mineral matter. 
 
 There are many other- effects of subterranean waters of the greatest 
 importance, such as the formation of fossils, the filling of mineral 
 veins, the metamorphism of rocks, etc. ; but these will be taken up 
 each in its appropriate place. 
 
 Chemical Deposits in Springs. 
 
 Depositsof Carbonate of Lime.— We have just seen that ordinary 
 subterranean waters in limestone districtsrand, therefore, containing 
 small quantities of carbonate of lime, deposit this substance only very 
 slowly by drying, as stalactites and stalagmites; but in carbonated 
 springs in limestone districts a very rapid deposit of lime carbonate 
 often occurs. 
 
 Explanation.— In order tg understand this, it is necessary to re- 
 member : 1. That lime carbonate is insoluble in pure water, but soluble 
 in water containing carbonic acid ; 2. That the amount of carbonate 
 dissolved is, up to a limit, proportionate to the amount of carbonic acid 
 contained ; 3. That the amount of carboniov acid which may be taken 
 in solution by water is proportionate to the pressure. 
 
 Now, there are two sources of carbonic acid, viz., atmospheric and 
 subterranean. All water contains carbonic acid from the atmosphere, 
 and will, therefore, dissolve limestone, but this deposits only slowly by 
 drying, as already explained. But in many districts, especially in vol- 
 canic districts, there are abundant subterranean sources of carbonic 
 acid. If subterranean waters come in contact with such carbonic acid, 
 being under heavy pressure, they will take up a large quantity of this 
 gas ; and if such water comes to the surface, the pressure being re- 
 moved, the gas will escape in bubbles. This is a carbonated spring. 
 If, further, the subterranean waters, thus highly charged with carbonic 
 acid, come in contact with limestone rocks, or rocks of any kind con- 
 taining lime carbonate, they will dissolve a proportionately large amount 
 of this carbonate ; arid when they come to the surface, the escape of 
 the carbonic acid causes the lime carbonate to deposit abundantly. 
 Thus around carbonated springs in limestone districts, and along the 
 course of the streams which issue from thepi, are generally found ex- 
 tensive deposits of this substance. Being found mostly in volcanic 
 regions, these springs are commonly hot. 
 
 Kinds of Materials.— The material thus deposited is usually called 
 travertine, but is very diverse in appearance. If the deposit is quiet, 
 the material is dense; if tumultuous, the material is spongy ; if no 
 iron is present, it is white like marble ; but if iron be present, its oxida- 
 tion colors it yellow, brown, or reddish, If the amount of iron be vari- 
 able, the stone is beautifully striped. If objects of any kind, branches, 
 
CHEMICAL DEPOSITS IN SPRINGS. 
 
 79 
 
 twigs, leaves, are immersed in such waters, they are speedily incrusted, 
 often in the most beautiful manner. At the baths of San Filippo, 
 Beautiful facsimiles of medallions, coins, etc., are formed by placing 
 these objects of art in the spray of an artificial cascade. 
 
 A well-known example is the beautiful deposit of basins and ter- 
 races still in process of formation at the Mammoth Hot Springs, in 
 the Yellowstone National Park (Fig. 73). The precipitation of lime 
 is at least partly due to the agency of algae, which give the bright 
 colors to the surf aces where deposition is active. The material weathers 
 white. In California, about the shores of Lake Mono, abundance of 
 beautiful and strangely branched coralline forms are found, and 
 about Pyramid Lake, in Nevada, are abundant deposits in strange and 
 
 Fia. 72.— Travertine Deposits, Mammoth Hot Springs, Yellowstone Park. 
 
 remarkable shapes. A vast deposit near ancient Tibur (modern 
 Tivoli) supplied the stone for many buildings of ancient Eome. The 
 name " travertine " is derived from the name of the old village. The 
 so-called Mexican onyx, or " onyx marble," is a compact, banded vari- 
 ety from Pueblo, Mexico. Lime deposits are not confined to thermal 
 springs, but may occur frequently in limestone regions. At Mum- 
 ford, N. Y., a church and other buildings are constructed of a porous 
 tufa quarried from a recent deposit in a neighboring swamp. 
 
 Deposits of Iron.— Iron carbonate, like lime carbonate, is to some 
 
 extent soluble in water containing carbonic acid. Subterranean waters, 
 
 therefore, which always contain atmospheric carbonic acid, when they 
 
 meet this carbonate, will take up a small quantity in solution. Such 
 
 7 
 
80 AQUEOUS AGENCIES. 
 
 waters are called chalybeate. On coming to the surface the iron gives 
 up its carbonic acid, is peroxidized, becomes insoluble, and is deposited. 
 As the presence of organic matter is usually necessary to bring the iron 
 into a soluble condition, the full discussion of this very interesting sub- 
 ject is reserved until we take up organic agencies. 
 
 Deposits of Silica. — Silica is soluble in alkaline waters, especially if 
 the waters be hot. Such waters, reaching the surface and cooling, de- 
 posit the silica in great abundance, often at first in a gelatinous con- 
 dition, but drying to a white porous material called siliceous sinter. 
 Examples of such deposits are found in all geysers, as in those of 
 Iceland, and in the Steamboat Springs in Nevada, and especially in 
 the wonderful geysers of Yellowstone Park. Such deposits are con- 
 fined to volcanic regions, the volcanic rocks furnishing both the 
 alkali and the heat. We will discuss these again under Igneous 
 Agencies. 
 
 Deposits of Sulphur and Gypsum. — Springs containing sulphide of 
 hydrogen (HgS), usually called sulphur-springs, sometimes deposit 
 sulphur by oxidation of the hydrogen (HgS+O^HaO-f-S), and some- 
 times gypsum. This latter deposit is caused by the more complete oxi- 
 dation of the sulphide of hydrogen, forming sulphuric acid (H3S-I-4O 
 =HgS04), and the reaction of this acid on lime carbonate held in solu- 
 tion in the same water. 
 
 Chemical Deposits in LaTces. 
 
 Salt Lakes and Alkaline Lakes. — Salt lakes may be formed either 
 ^1. By the isolation of a portion of sea-water in the elevation of sea- 
 bottom into land ; or, 2. By indefinite concentration of river-water in 
 a lake without an outlet. Thus, the Dead Sea, Lake Elton, and the 
 brine-pools of the Russian steppes, are usually supposed to be concen- 
 trated remains of isolated portions of the sea,* for their waters are 
 highly concentrated mother-liquors of sea-water, having a composition 
 very similar to the mother-liquors of the salt-maker. \ The Caspian 
 Sea, on the other hand, although elevated lake-margins show that much 
 of its waters has dried away, is still much fresher than sea- water. This 
 fact, together with the composition of its waters, is usually supposed 
 to indicate that it has been formed by the simple concentration of the 
 waters of a once fresh lake. J Yet there are some evidences, as we shall 
 see hereafter (p. 596), of this sea having been once connected with the 
 Black Sea and with the Arctic Ocean. It is probable that the Caspian 
 
 * Bisehof, Chemical and Physical Geology, vol. i, p. 396. 
 
 f And yet the presence of fresh water shells on the elevated old margins of the Dead 
 Sea seem to indicate that it may have been a fresh lake emptying through the Arabah 
 valley into the Gulf of Akabah (Rice). 
 
 X Bisehof, Chemical and Physical Geology, vol. i, p. 91. 
 
CHEMICAL DEPOSITS IN LAKES. gj 
 
 was first isolated from the ocean as a salt lake, then freshened by an 
 outlet, and finally re-concentrated to its present conditions. The com- 
 position of the waters of the Great Salt Lake of Utah would seem to 
 indicate its origin in the isolation of sea-water ; but there are evidences 
 of its once having had an outlet ; in which case it must have been 
 fresh.* 
 
 Alkaline lakes can only be formed by the second way. Both salt 
 and alkaline lakes, therefore, may be formed by indefinite concentra- 
 tion of river-water in a lake without outlet. Whether the one or the 
 other is formed depends on the composition of the river-water. If al- 
 kaline chlorides predominate, a salt lake will be formed ; but if alkaline 
 carbonates, an alkaline lake. Such alkaline lakes are found in Hun- 
 gary, in Lower Egypt, and in Persia. In our own country, Lake Mono, 
 fifteen miles long, and twelve miles wide, and Lake Owen, of at least 
 equal dimensions, are examples of alkaline lakes. The waters of Lake 
 Mono consist principally of a strong solution of carionate of soda and 
 chloride of sodium, with a little carbonate of lime and borate of soda.f 
 Borax lakes, which are found in California and a few other countries, 
 can. be formed only by the concentration of the water of springs of 
 exceptional composition. 
 
 Conditions of Salt-Lake Formation. — Spring and river waters always 
 contain a small quantity of saline matter derived from the rocks and 
 soils. Suppose, then, we have a lake supplied by rivers: 1. If the 
 supply of water by rivers is greater than the loss by evaporation from 
 the lake-surface, then the water will rise until, finding an outlet in the 
 rim of the lake-basin, it flows into the sea. In this case the lake will 
 remain fresh, or the quantity of saline matter will be inappreciable. 
 But if, on the other hand, the loss by evaporation is greater than the 
 supply by rivers, the lake will decrease in extent, and therefore in evap- 
 orating surface, until an equilibrium is established. Now all the saline 
 matters constantly leached from the earth accumulate in the lake with- 
 out limit ; the lake, therefore, must eventually become saturated with 
 saline matter, and afterward begin to deposit salt. It is evident, then, 
 that whether a lake is fresh or salt depends upon whether or not it has 
 an outlet, and this latter depends upon the relation of supply by rivers 
 to loss by evaporation. Lakes are mostly fresh, because much more 
 water falls on continents than evaporates from the same surface, the 
 excess running back to the sea by rivers. It is only in certain parts 
 of the continents, where the climate is very dry, that there is no such 
 
 * Gilbert, Wheeler Report for 1872, p. 49. 
 
 t The probability of Great Salt Lake baring been produced by simple evaporation of 
 riyer-water is increased by the difference in the composition of the waters of lakes in 
 this general region. Where sedimentary rocks prevail, as in Utah, they are salt ; where 
 volcanic rocks prevail, as about Mono and Owen, they are alkaline. 
 
82 AQUEOUS AGENCIES. 
 
 excess. In these regions alone, therefore, can salt lakes exist. Such 
 regions occur in the interior of Asia, on the plateau of Mexico, in the 
 basin of Utah, and in several other places. • 
 
 Even in case a salt lake is originally formed by the isolation of a 
 portion of sea-water, whether it remains a salt lake or gradually be- 
 comes fresh will depend upon the conditions we have already men- 
 tioned. For example : if the Mediterranean should be separated from 
 the Atlantic at the straits of Gibraltar, it would not only remain a salt 
 lake, but would diminish in area, and finally deposit salt. This we 
 conclude, because the water of the Mediterranean seems to be a little 
 more salt than that of the Atlantic. If, on the contrary, the Black 
 Sea were separated from the Mediterranean, or the Baltic from thd At- 
 lantic, or the bay of San Francisco from the Pacific, the supply by 
 rivers, in the case of these inland seas being greater than their loss by 
 evaporation, they would rise until they found an outlet, and then would' 
 be gradually rinsed out, and become fresh. Lake Ohamplain was, in 
 very recent geological time, an arm of the sea. When first isolated it 
 was salt. It has become fresh by this process. 
 
 Saltness of the Ocean. — It is obvious that only the last reservoir is 
 salt. Thus Lake Tahoe runs into Pyramid"Lake, but only the latter is 
 salt ; Lake Utah, a fresh lake, runs into Great Salt Lake ; the Sea of 
 Galilee, a fresh lake, empties into the Dead Sea, a salt lake. Now, 
 the ocean is, of course, the last reservoir of circulating waters. Is its 
 saltness to be similarly accounted for ? Not exactly ; salt lakes receive 
 their salt largely from strata deposited in the ocean and salted thereby, 
 but the ocean preceded all stratified rocks. Nevertheless the ocean, 
 too, received its salt from the rocks. Throughout the whole geological 
 history of the earth there has been a progressive differentiation of the 
 soluble and the insoluble parts of the original rocks, the one accumu- 
 lating in the ocean, the other forming derivative rocks and soils. 
 
 Deposits in Salt Lakes. — The nature of the chemical deposits in 
 salt lakes will depend upon the manner in which these lakes have been 
 formed. We will take the simplest case, viz., that of a lake formed by 
 the isolation of sea-water, and its concentration by evaporation. In 
 this case the substance first deposited would be gypsum ; for this sub- 
 stance is insoluble in a saturated brine, and therefore always deposits 
 first in the artificial evaporation of sea-water in salt-making. Upon 
 the gypsum would be deposited salt. Meanwhile, however, the rivers 
 during their flood-season would bring down sediments. During the 
 flood-season, the supply of water being greater than loss by evaporation, 
 the deposit of salt or gypsum would cease ; while during the dry season 
 the deposit of sediment would cease, and the evaporation being now in 
 excess, the deposit of salt would recommence. Thus the deposits in the 
 bottom of salt lakes probably consist of alternations of salt and sedi- 
 
CHEMICAL DEPOSITS IN SEAS. 33 
 
 ment, the whole underlaid by layers of gypsum. These yiews have been 
 confirmed by observation. During the dry season Lake Elton deposits 
 annually a considerable layer of salt. Wells dug near the margin of 
 this lake revealed a hundred alternations of salt and mud, the salt-beds 
 being many of them eight or nine inches thick. Most of the salt has 
 already deposited ; fot the water of this lake is an almost pure bittern. 
 The great predominance of chloride of magnesium in Dead Sea water 
 shows that it is a mother-liquor, from which immense quantities of 
 common salt have already been deposited. Similar alternations, there- 
 fore, no doubt exist in the bottom of this sea. The Great Salt Lake, 
 in Utah, is also a saturated brine depositing salt, as is proved by the 
 incrustations of salt about its margin in dry seasons ; but the deposit 
 has not progressed so far in this case as in the preceding. The great 
 extent to which the waters of this lake have dried away and become 
 concentrated is further shown by old lake-margins far beyond the 
 limits, and several hundred feet above the level, of the present shore- 
 line. Similar phenomena are observed about other salt lakes, especially 
 about the Caspian Sea (Murchison).* 
 
 In the case of salt lakes, either formed entirely, or modified, by 
 river-water, the deposits are probably much more complex and various 
 — sometimes salt, sometimes carbonate of lime, and sometimes sulphate 
 of lime. Immense deposits, mostly of carbonate of lime, are found 
 about the salt lakes of Nevada. They form a conspicuous feature of 
 the scenery about Pyramid Lake. 
 
 Deposits are also sometimes formed in lakes which are not salt. 
 For example : the Solfatara Lake, Italy, is formed by the accumulation 
 of the water from warm carbonated springs, similar to those of San 
 Filippo and San Vignone. In this lake, therefore, deposits of traver- 
 tine are forming. Although these deposits take place in a lake, they 
 properly belong to deposits from springs, since they do not take place 
 entirely by concentration, but partly also by escape of carbonic acid. 
 
 Chemical Deposits in Seas. 
 
 Concerning these little is known. It is certain, however, that all 
 rivers carry to the sea carbonate of lime in solution, and some of them 
 in considerable quantities. There is scarcely any river-water which 
 contains less carbonate of lime than sea-water; many rivers contain 
 four times as much. This carbonate of lime thus constantly carried 
 into the sea must eventually deposit in some form. Usually, however, 
 sea- water is kept below the saturating point for this substance, by its 
 constant withdrawal by shells and corals, as will be explained under 
 
 * See page 590 for the history of Lake Bonneville, the predecessor of Great Salt 
 Lake. 
 
84 IGNEOUS AGENCIES. 
 
 Organic Agency. But in shallow bays nearly cut ofiE from the sea, or 
 in salt lagoons on the sea-margin near the mouths of rivers in dry 
 climates, and subject to occasional overflows by the sea and floodings 
 by rivers, carbonate of lime and sulphate of lime may deposit by evapo- 
 ration. At the mouths of many rivers, whose waters contain much 
 carbonate of lime, as, for instance, the Ehine, the delta deposit is 
 cemented into hard rock by means of this substance. On shores of 
 coral seas, as npon the Keys of Florida, the coast of the West India 
 Islands, and the islands of the Pacific, shore-material is consolidated 
 into hard rock by the same means. On many shores in tropical regions 
 the waves, being driven up on flat beaches far inland, leave sea- water 
 inclosed in shallow pools, which by evaporation give rise to calcareous 
 deposits which are increased by the frequent alternate influx and evapo- 
 ration of sea-water. Conglomerate rocks are thus forming at the pres- 
 ent time in the Canaries and many other places. 
 
 CHAPTER III. 
 
 lONSOUS AQENCIES. 
 
 The agencies thus far considered tend to reduce the inequalities of 
 the earth by cutting down the continents and filling up the seas. 
 Their final effect, if unopposed, would be to bring the whole surface to 
 one level, and thus to make the empire of the sea universal. This is 
 prevented by igneous agencies, which tend, by elevation of land and 
 depression of sea-bottoms, to increase the inequalities of the earth- 
 surface, and thus to increase the area and the height of the land. 
 These two opposing agencies have entirely different sources. The one 
 is external, or sw/i-derived ; the other internal, or ear^A-derived. The 
 one gives the great outlines of earth-features ; the other sculptures 
 these into forms of beauty. The one rough hews ; the other shapes. 
 The actual forms of earth at any time is the result of the state of 
 balance between them. All the different forms of igneous agency are 
 connected with the interior heat of the earth. This must, therefore, 
 be first considered. 
 
 Section 1.— Intebioe Heat of the Earth. 
 
 Stratum of Invariable Temperature.— The mean surface tempera- 
 ture of the earth varies from 80° at the equator to nearly 0° at the 
 poles. The rate of decrease in passing from the equator to l;he poles 
 
INTERIOR HEAT OF THE EARTH. 
 
 85 
 
 is not the same in all longitudes; the isotherms, or lines joining places 
 of equal mean temperatures, are therefore not parallel to the lines of 
 latitude, but quite irregular. The mean temperature of the whole 
 earth-surface is about 58°. There is also in every locality a daily and 
 an annual variation of temperature. As we pass below the surface 
 both the daily and annual variations become less, until they cease al- 
 together. The stratum of no daily variation is but a foot or two 
 beneath the surface; but the stratum of no annual variation, or 
 stratum of invariable temperature in temperate climates, is about sixty 
 to seventy feet deep. The temperature of the invariable stratum 
 is nearly the mean temperature of the place. The depth of the in- 
 variable stratum depends upon the amount of annual variation ; it is, 
 therefore, least at the equator, and increases toward the poles. At the 
 equator it is only one or two feet beneath the surface ; * in middle 
 latitudes about sixty feet, and in high latitudes probably more than a 
 hundred feet.f It is, therefore, a spheroid more oblate than the earth 
 itself. The temperature of the earth everywhere within this spheroid 
 is unaffected by external changes. 
 
 Increasing Temperature of the Interior of the Earth. — Beneath the 
 invariable stratum the temperature of the earth everywhere increases, 
 for all depths to which it has been penetrated, at an average rate of 
 
 Pig. 73. 
 
 Fio. 74. 
 
 about 1° for every 53 feet. This very important fact has been de- 
 termined by numerous observations on the temperature of mines and 
 
 * Humboldt, Cosmos, Sabine's edition, vol. i, p. 165. 
 
 \ In polar regions, or the region ot perpd^ml grmind-ke, the stratum of mvanable 
 temperature probably again rises nearer the surface, on account of the property of ice of 
 retaining its temperature by melting. 
 
gg IGNEOUS AGENCIES. 
 
 of Artesian wells in almost every part of the earth. All the facts thus 
 far stated are graphically illustrated in the accompanying figure (Fig. 
 73), in which the line a b represents depth below the surface, and the 
 diverging line c d'the increasing heat; m the invariable stratum; n 
 the line of no daily variation ; the curves jt? e, c e, o e, the temperatures 
 in summer, autumn, and winter, respectively ; the space ceo the an- 
 nual swing of temperature; and the smaller curves meeting on the 
 the line n, the daily variation or swing of temperature. 
 
 We have given the rate of increase as about 1° in 53 feet. It 
 varies, however, in different places, from 1° in 30 feet to 1° in 90 feet. 
 Except in the vicinity of volcanic action, this difference is probably 
 due to varying conductivity of the rocks. The lines, or rather sur- 
 faces, which join places in the interior of the earth, having equal tem- 
 peratures, may be called isogeotherms. If the rate of increase were 
 everywhere the same, the isogeotherms would be regularly concentric ; 
 but, as this is not the case, they are irregular surfaces (Fig. 74), rising 
 nearer the earth-surface and closing upon one another where the con- 
 ductivity is poor, and sinking deeper and separating where the con- 
 ductivity is greater. 
 
 Constitution of the Earth's Interior. — From the facts given above 
 it is probable that the temperature of the interior of the earth is very 
 great. A rate of increase of 1° for every 53 feet would give us, at the 
 depth of twenty-five or thirty miles, a temperature sufficient to fuse 
 most rocks. Hence it has been confidently concluded by many that 
 the earth, beneath a comparatively thin crust of thirty miles, must be 
 liquid. A crust of thirty miles on our globe is equivalent to a crust of 
 less than one tenth of an inch in a globe two feet in diameter. There 
 are, however, many objections to this conclusion. The question of the 
 interior constitution of the earth is one of extreme difficulty and com- 
 plexity, and science is not yet in a position to solve it completely. 
 Nevertheless, it can be proved that the solid crust must be much 
 thicker than is usually supposed, if, indeed, there be any general 
 interior fluid at all. 
 
 The argument for the interior fluidity of the earth, beneath a crust 
 of only thirty miles, proceeds upon two suppositions, viz. : 1. That the 
 interior temperature increases at the same rate for all depths ; and, 2. 
 That the fusing-point of rocks is the same for all depths. Now, neither 
 of these can be true. 
 
 1. Rate of Increase not Uniform.— Altl;ough we have spoken of 1° 
 for every 30 feet or 50 feet or 90 feet, yet it must not be supposed that 
 observation -gives a uniform rate of increase at any place. On the con- 
 trary, the rate is sometimes faster and som'etimes slower, depending on 
 the conductivity of the rock penetrated, and on other causes little 
 understood. The rate given is always an average. In other words, 
 
INTERIOR HEAT OF THE EARTH. g^ 
 
 observation gives the fact of increase, but not the law. We are thus 
 thrown back on general reasoning. 
 
 If two bars, one a good conductor, like metal, and the other a bad 
 conductor, like charcoal, be heated red hot at one end, and the rate of 
 decreasing temperature — fall of heat — toward the other be observed, 
 it will be found that the rate is very rapid in the case of the charcoal, 
 so that a temperature of 60° is reached at the distance of two or three 
 inches i while in the case of the metal the rate of decrease is much 
 slower, and 60° is only reached at a distance of several feet. Con- 
 versely, the rate of increase, or rise, in passing toward a source of 
 heat, is rapid in the case of the bad conductor, and slow in the cast; of 
 the good conductor. Now, the average density of materials at the sur- 
 face of the earth is about 3*5, but the average density of the whole 
 earth is more than 5"5 ; therefore the density of the central portions 
 must be much more than 5"5. It has been estimated at 16'37. There 
 can be no doubt, therefore, that the density of the earth increases 
 toward the center,- and as this increase is probably largely the result 
 of piressure, it is probably somewhat regular. Whatever be the cause 
 the effect would be to increase the conductivity for heat, and therefore 
 to diminish the rate of increasing temperature. Thus it follows that, 
 though in a homogeneous globe the melting-point of rocks (3,000°) 
 would be reached at the depth of thirty miles, yet, in a globe increas- 
 ing in density toward the center, we must seek this temperature at 
 a greater depth. 
 
 3. Fusing-Point not the same for all Depths.— Nearly all substances 
 expand in the act of melting, and contract in the act of solidifying. 
 Only in a few substances, like ice, is the reverse true. Now, the fusing- 
 point of all substances which expand in the act of fusing must be 
 raised by pressure, since the expanding force of heat, in this case, 
 must overcome not only the cohesion, but also the pressure. That 
 this is true, has been proved experimentally for many substances by 
 Hopkins. But granite and other rocks have been proved to expand 
 in fusing; therefore the fusing-point of rocks is raised by pressure, 
 and must be greatly raised by the inconceivable pressure to which 
 they are subjected in the interior of the earth. For this reason, 
 therefore, we must again go deeper to iind the interior fluid. The 
 pressure of fifty miles of rock would certainly greatly raise the 
 fusing-point. Suppose it is thus raised to 3,500°: to find this we 
 must go still deeper, perhaps seventy miles in depth. But the 
 increased pressure would again raise the fusing-point; and thus, in 
 this chase of the increasing heat after the flying fusing-point, where . 
 the former would overtake the latter, or whether it would overtake it 
 at all, science is yet unable to answer. However, it seems most prob- 
 able that the earth is wholly solid. 
 
88 IGNEOUS AGENCIES. 
 
 Astronomical Reasons. — There is another and entirely different 
 line of reasoning which has led some of the best mathematicians and 
 physicists to the same result. According to the thin-crust theory, the 
 earth is still substantially a liquid globe, and therefore under the at- 
 tractive influence of the sun and moon it ought to behave like a yield- 
 ing liquid. Now, according to Hopkins, Thomson, and others, the 
 earth in all its astronomical relations behaves like a rigid solid — a 
 solid more rigid than a solid globe of glass — and the difference between 
 the behavior of a liquid globe and a solid globe could easily be detected 
 by astronomical phenomena. A complete exposition of the proof 
 would be unsuitable to an elementary work. Suffice it here to say 
 that the force of these arguments has led some geologists to the con- 
 clusion that the earth must be regarded as a substantially solid and 
 very rigid globe ; and that, therefore, the theories of igneous phenom- 
 ena must be constructed on the basis of a substantially solid, not a 
 substantially liquid, earth. 
 
 There are many phenomena, however, especially the great lava- 
 floods to be described hereafter and the instability of the crust-level 
 under increase and decrease of weight by sedimentation and erosion, 
 which seem to require a mobile layer at no great distance beneath 
 the surface. Many geologists, therefore, find a compromise in the 
 view that there exists, between the solid crust and a solids nucleus, a 
 layer of greatest instability, i. e., liable to fusio^ by relief of pressure. 
 This seems the most probable condition. Taken as a whole, however, 
 the earth must be regarded as substantially solid. 
 
 The idea of interior fluidity of the earth, or at least of an inter- 
 mediate layer, was a natural and quite necessary conception following 
 the belief in the nebular theory of the earth's origin. But it is now 
 more than doubtful if our planet was ever, as a separate globe, in a 
 state of incandescence, either gaseous or fluid. Eecent studies dis- 
 credit the nebular hypothesis in its application to the origin of the 
 planets, and favor instead a modified form of the meteoroidal theory 
 (see writings of Prof. Chamberlin in the Journal of Geology). Ac- 
 cording to the " Planetesimal " hypothesis, the earth, and the moon 
 as well, have grown by slow accretion, or infall, of small, cold, dis- 
 crete particles (planetesimals) which formed the earth-moon ring or 
 zone. The ocean and the atmosphere have slowly accumulated from 
 the gases originally held in the planetesimals, being forced to the 
 earth's surface by interior consolidation due to gravity. The heat of 
 the earth's interior is, under this theory, due to gravitational com- 
 pression, similar to the production of the sun's heat. 
 
 It seems most probable that the enormous amount of steam 
 required to operate volcanoes is derived from the gases primarily 
 resident within the earth, and that their exhalation is still a part of 
 
VOLCANOES. 39 
 
 the long process of ocean-making and atmosphere-formation. While 
 the earth's interior heat may be increasing, it is possible that vul- 
 
 Fio. 75.— Eruption of Vesuvius, April 26, 1878. 
 
 eanism may be diminishing, on account of the reduction in amount 
 of the available gases within the earth. 
 
 The interior heat of the earth manifests itself at the surface in 
 three principal forms, viz., volcanoes, earthquahes, and gradual oscil- 
 lations of the earth's crust. 
 
 Section- 2. — Volcanoes. 
 
 Definition. — A volcano is usually a conical mountain, with a funnel- 
 shaped, or pit-shaped, or cup-shaped opening at the top, through which 
 are ejected materials of various kinds, always hot, and often in a fused 
 condition. The activity of volcanoes is sometimes constant, as in the 
 case of Strombolijin Italy, and Kilauea,in Hawaii, but more commonly 
 intermittent, i. e., having periods of eruption alternating with periods 
 of more or less complete repose. Volcanoes which have not been 
 known to erupt during historic times are said to be extinct. It is im- 
 possible, however, to draw the line of distinction between active and 
 extinct volcanoes. Vesuvius, until the great eruption which overthrew 
 the ancient cities of Herculaneum and Pompeii, was regarded as an 
 
90 IGNEOUS AGENCIES. 
 
 extinct volcano. Since that time it has been very active. Krakatoa, 
 after a silence of 200 years, burst out in 1883 in the greatest eruption 
 known. 
 
 Size, Number and Distribution.— Some volcanoes are among the 
 loftiest mountains on our globe. Aconcagua, in Chili, is 33,000 feet, 
 Cotopaxi, in Peru, 19,660 feet in height. These volcanic cones, how- 
 ever, are situated on a high plateau ; their height, therefore, is not due 
 to volcanic eruptions entirely. But Mauna Loa, in Hawaii, nearly 
 14,000 feet, and Mount Etna, 11,000 feet high, seem to be due entirely, 
 and Mount Shasta, California, 14,440 feet. Rainier, State of Washing- 
 ton, 14,444, almost entirely to this cause. The crater of Mauna Loa 
 is two and a half miles across; that of Kilauea three miles across 
 and 1,000 feet deep. 
 
 The numler of known volcanoes, according to Humboldt, is 407, 
 and of these 300 to 350 are known to have been active in the last 160 
 years. The actual number is, however, probably much greater. It 
 has been estimated that, in the archipelago about Borneo alone, there 
 are 900 volcanoes.* The distribution of volcanoes is remarkable. 
 (a) They are almost entirely confined to the vicinity of the sea. Two 
 thirds of them are found on islands in the midst of the sea, and the 
 remainder, with the exception of a few in the interior of Asia, are near 
 the sea-coast. Those on the islands in the sea, probably commenced, 
 most of them, at the bottom of the sea, the islands having been formed 
 by their agency. New islands have been suddenly formed under the 
 eye of observers in the Mediterranean and in the Pacific Ocean. The 
 basin of the Pacific is the great theatre of volcanic activity, nearly 
 seven eighths of all known volcanoes being situated on its coasts or on 
 islands in its midst, (b) Volcanoes are, moreover, distributed in groups 
 (as the Hawaiian volcanoes, the Mediterranean volcanoes, the Icelandic 
 volcanoes, the West Indian volcanoes, the volcanoes of Auvergne, etc.), 
 or along extensive lines as if connected with a great fissure of the 
 earth's crust. The most remarkable linear series of volcanoes is that 
 which belts the Pacific coast. Commencing with the Fuegian vol- 
 canoes it runs along the whole extent of the Andes, then along the 
 Cordilleras of Mexico, the Rocky Mountains, then along the Aleutian 
 chain of islands, Kamtchatka, the Kurile Islands, Japan Islands, 
 Philippines, New G-uinea, New Zealand, to the antarctic volcanoes 
 Mounts Erebus and Terror, thence back by Deception Island to Fuegia 
 again, thus completely encircling the globe, (c) Volcanoes are gen- 
 erally formed in comparatively recent strata. This seems to be con- 
 nected with their relation to the sea; for recent strata are abundant 
 about the sea-coast, and the most recent are now forming in the bed 
 
 * Herschel, Physical Geology, p. 113. 
 
VOLCANOES. 
 
 91 
 
 of the sea. The extinct volcanoes of France and Germany are in 
 tertiary regions. Possibly the retiring of the sea has extinguished 
 them. In the oldest strata volcanic activity has apparently died out 
 long ago. 
 
 Phenomena of an Eruption.— The phenomena of an eruption are very 
 diverse. Sometimes there is a gradual melting of the floor of the crater, 
 and then a. rising and boiling of the liquid contents until they quietly 
 overflow and form immense streams. of lava extending flfty to sixty 
 miles. After the eruption, the melted lava again sinks and cools, and 
 solidifies, to form the floor of the crater until another eruption. This 
 is the case with the Hawaiian and many other volcanoes in the South 
 Seas. In other cases, as in the Mediterranean volcanoes, and especially 
 in many in the Indian Ocean, the eruption is fearfully explosive. In 
 such cases the eruption is usually preceded by premonitory earthquakes 
 and sounds of subterranean explosions; then the bottom of the crater 
 is blown out with a violent explosion, throwing huge rocky fragments 
 to great distances, often many miles ; then the melted lava rises and 
 overflows in streams running down the side of the mountain. The 
 rise and overflow of lava are accompanied with violent explosions of 
 gas which throw up immense quantities of ashes and cinders 6,000 and 
 even 10,000 feet above the crater. The fine ashes from Krakatoa. are 
 said to have been carried, by the uprush of gas and vapors, to the 
 amazing height of 17 miles. In the great eruption of Tomboro, in 
 the island of Sumbawa near Java, in 1815, these explosions were heard 
 in Sumatra, 970 miles distant. Explosions of Kraiatoa were heard 
 3,000 and even 3,000 miles. The emission of gas usually continues 
 after all other ejections cease. Violent storms and heavy rain accom- 
 pany the eruption,, and when the mountain reaches into the region of 
 perpetual snow, as in many of the South American volcanoes, the 
 fearful deluges produced by the sudden melting of the snows are 
 often the most destructive phenomenon connected with the eruption. 
 
 Volcanic eruptions, therefore, may be divided into two great types, 
 viz., the quiet and»the explosive. .In the one, lava-flows predominate ; 
 in the other, scoriae and dust, and steam and gas. The Hawaiian vol- 
 canoes are perhaps the best examples of the former, and the Javanese 
 volcanoes, especially Krakatoa, of the latter. The Mediterranean and 
 most other volcanoes are mixtures of these two types in varying pro- 
 portions. 
 
 the quantity of materials ejected during an eruption is sometimes 
 almost inconceivable. During the great eruption of Tomboro, already 
 mentioned, ashes and cinders were ejected sufficient to make three 
 Mont Blancs, or to cover the whole of Germany two feet deep, or equal 
 to 37 cubic miles. In the eruption of Krakatoa, August, 1883, 4| cubic 
 miles of material were blown into dust so fine that it was carried by the 
 
92 IGNEOUS AGENCIES. 
 
 gas-current 17 miles high, and some of it remained suspended for two 
 or three years. The lava which streamed from Skaptar Jokull, Ice- 
 land, in 1783, has been computed to be equivalent to about twenty-one 
 cubic miles, or to the whole quantity of water poured by the Nile into 
 the sea Ln one year ! These were, however, very extraordinary erup- 
 tions. In the greatest eruptions of Vesuvius the quantity of lava 
 poured out was not more than 600,000,000 cubic feet := one square 
 mile covered twenty-two feet deep. 
 
 Great destruction of life is often produced by volcanic eruptions. 
 The overflow of Herculaneum and Pompeii by ejections from Vesu- 
 vius is well known. The great eruption of Skaptar JokuU destroyed 
 1,300 human lives and 150,000 domestic animals. The eruption of 
 Etna, in 1669, overwhelmed fourteen towns and villages. In the prov- 
 ince of Tomboro, out of a population of 13,000, only twenty-six per- 
 sons escaped the great eruption of 1815. 
 
 One of the greatest catastrophes in history, and by the most singu- 
 lar eruption, was the destruction of the city of St. Pierre, on the 
 island of Martinique, West Indies, on the morning of May 8, 1903. 
 A huge cloud of red-hot dust and vapor swept down from the crater 
 of Mount Pelee with hurricane velocity, and in a moment destroyed 
 the entire city, with 30,000 people. Only one person, a colored man 
 in the city prison, was rescued, although terribly burned. (See Nat. 
 Geogr. Mag. for July and December, 1903.) 
 
 Monticules. — Eruptions occur not only from the summit-crater, but 
 also frequently from fissures in the side of the mountain. By the 
 immense upheaving force necessary to raise lava to the mouth of the 
 crater of a lofty volcano, the mountain is fissured by cracks radiating 
 from the crater in all directions. These cracks are filled with lava, 
 which on hardening form radiating dikes which intersect the succes- 
 sive layers of ejections, and bind them into a stronger mass (Fig. 78, 
 p. 96). Through these fissures the principal streams of lava often 
 pass. During an eruption of Mauna Loa, in 1853, the immense pres- 
 sure of the lava in the principal crater fissured the side of the moun- 
 tain, and a fiery fountain of liquid lava, 1,000 feet long, was projected 
 upward through the fissure to the height of 700 feet, and continued 
 to play for several days. Upon these fissures subordinate craters, and 
 finally cones, are formed. Thdse subordinate cones about the base, 
 and upon the slopes of the principal cone, are called monticules. 
 There are about 600 monticules on Etna — one over 700 feet high. 
 
 Materials erupted. — As we have already stated, the materials 
 erupted are stones, lava-streams, scoricB, dust, and gases. 
 
 Stones. — In explosive eruptions the solid floor of the crater is often 
 blown out with violence, and rock-fragments, sometimes of vast size, 
 are thrown to great distances. 
 
VOLCANOES. 93 
 
 Lava. — The term lava is applied to the liquid matter poured from 
 a volcano during eruption, and also to the same when it has hardened 
 into rock. 
 
 Liquidity of Lava. — At the time of eruption the liquidity of lava 
 varies very much, depending partly upon the heat, partly on the fusi- 
 bility of the material, and partly upon the hind of fusion. In the 
 Hawaiian volcanoes the lava is a melted glass almost as thin as honey. 
 In Kilauea this lava, by the attenuation of steam vesicles when the sur- 
 face is agitated by the sinking of crusts, is drawn out into long threads 
 like spun glass, which is carried by the winds, and collects in places as 
 a soft, brownish, towy mass, called " Pele's hair." 
 
 Physical Conditions of Lava.— Completely fused lava, when cooled 
 rapidly, forms volcanic slag or volcanic glass (obsidian) ; but if cooled 
 slowly, so that the several minerals of which it is composed have time 
 to separate and crystallize, forms stony lava. If it is full of gas-bubbles 
 (rock-froth) and hardens in this condition, it forms vesicular or scori- 
 aceous lava. If the quantity of gas and steam be very great, the whole 
 liquid mass may swell into a rock-froth, which rises to the lip of the 
 crater, and outpours much as porter or ale from a bottle when the cork 
 is drawn. Or the rock-froth may be thrown violently into the air, and, 
 hardening there, may fall again in cindery or scoriaceous masses ; or, 
 thrown with still greater violence, the rock-froth may be broken into 
 fine rock-spray, and fall as volcanic sand and ashes. Ashes, when con- 
 solidated by time and percolating water, or when deposited in water 
 form tufa. Thus, there are four physical conditions in which we find 
 lava — viz., stony, glassy, scoriaceous, and tufaceous. 
 
 Again, the liquidity of lava and its character depend much on the 
 hind of fusion. Daubr^e has shown that all siliceous rocks and glass 
 mixtures, in the presence of superheated water even in small quantities, 
 and under pressure, will become more or less liquid, at temperatures far 
 below that necessary to produce true fusion. At 400° Pahr., such rocks 
 become pasty, at 800° completely liquid. The same change takes place 
 at even lower temperatures if a little alkali be present. To distinguish 
 this liquidity from that of true igneous fusion, which requires a tem- 
 perature of 2,500° to 3,000°, it has been called aqueo-igneous or hy- 
 drothermal fusion. Now, very much lava at the time of eruption is in 
 this condition. Such lava, when the pressure is suddenly removed by 
 breaking up of the floor of the crater, and the contained water suddenly 
 changed into steam, is blown into the finest dust, which is then carried 
 to great height by the out-rushing steam, and falls again as volcanic 
 ashes, which may consolidate into tufa. If the heat be not sufficient to 
 produce complete aqueo-igneous fusion, the lava is outpoured as a kind 
 of rock-iroth consisting of unfused particles in a semifused mass, which 
 concretes into an earthy kind of rock. Or the material may pour out 
 
94 IGNEOUS AGENCIES. 
 
 only as hot mud, which concretes into a kind of tufa. In fact, every 
 variety of fusion and semifusion, depending on the degree of heat and the 
 quantity of water, may be traced, from perfect igneous fusion through 
 various grades of aqueo-igneous fusion, to the condition of hot mud. 
 
 It is evident that, of the two hinds of eruption mentioned above, 
 *the quiet type is characterized by igneous fusion, the explosive type by 
 aqueo-igneous fusion. In the former the heat is great, but the amount 
 of water is small ; while in the latter the heat is less, but the amount 
 of water far greater. 
 
 The rapidity of the flow of a lava-stream depends on its fluidity. In 
 the Hawaiian volcanoes the Isjiva, where it issues from the crater, has 
 been seen to flow with a velocity of iifteen miles an hour ; while 
 Vesuvian lava seldom flows at a rate of more than two or three miles 
 an hour. Lava, like glass, passes through various grades of viscous 
 fluidity in cooling. It gradually becomes so stiff that it may flow only 
 a few feet per day. The froth or scum which covers the surface of a 
 lava-stream quickly cools and hardens into a crust of vesicular lava, 
 which may even be walked upon while the interior is still flowing be- 
 neath. In this way are often formed long galleries. Also the running 
 together of the contained gas-bubbles and steam-bubbles forms huge 
 blisters in the viscous mass, which, on hardening, form cavities often 
 of great size. Thus, recent lavas have often a cavernous and galleried 
 structure, like limestone (page 77), but from a different cause. 
 
 Classification of Lavas. — Mineralogically, lava consists essentially of 
 feldspar, augite, and magnetite, either their constituents chemically unit- 
 ed, as in glassy lava, or aggregated into more or less distinct particles or 
 crystals, as in the stony varieties. Now, feldspar is a light-colored mineral, 
 having a specific gravity of about 2-5, while augite and magnetite are usu- 
 ally very dark-colored minerals, having specific gravities of about 3-5 to 5. 
 It is evident, therefore, that in proportion as feldspar predominates, the 
 lava is lighter colored and of less specific gravity ; and in proportion 
 as augite and magnetite predominate, the rock is darker and heavier. 
 Chemically, feldspar is a silicate of alumina and alkali, with excess of 
 silica (acid silicate). The alkali may be either potash, and then it is 
 called potash feldspar, or orthoclase ; or else it is soda and lime, and 
 then it is called soda-lime feldspar, or plagioclase. Of these two the 
 former is the more acid. Augite is a silicate of lime, magnesia, and 
 iron, with excess of base (basic silicate). Therefore, lava may be di- 
 vided into two classes — acidic lavas and lasic lavas. In the former, 
 feldspar predominates, in the latter augite. Moreover, in the one the 
 form of feldspar is orthoclase, in the other plagioclase. Further, it is 
 seen that all lavas are multiple silicates, like glass : they are, therefore, 
 true glass-mixtures. Now, the acidic lavas are a more difficultly fusi- 
 ble, the basic lavas a more easily fusible glass-mixture. Either of these 
 
VOLCANOES. 95 
 
 two kinds of lava may exist in any of the conditions mentioned above 
 — viz., as stony, glassy, vesicular, or tufaceous lava. Trachyte is an ex- 
 ample of acidic lava, and basalt of basic lava in a stony condition. 
 Pumice is a peculiar vesicular variety of feldspathic lava. 
 
 It is not improbable that the fusion and subsequent cooling of 
 granite, or gneiss, or even of the purer varieties of mixed sandstones 
 and clays, would make a trachytic lava ; while the fusion and cool- 
 ing of impure slates and shales and limestones would produce basaltic 
 
 Gas, Smoke, and Flame. — The gases emitted by volcanoes are prin- 
 cipally steam, sulphurous vapor (S and SOg), hydrochloric acid, and 
 carbonic acid. By far the most abundant of these is steam. In violent, 
 explosive eruptions, which eject principally cinders and ashes, it is 
 probable that water, mostly in the form of steam, is one of the most 
 abundant of all the ejected materials. In quiet lava-eruptions, like 
 those of the Hawaiian volcanoes, the quantity of steam and gases is 
 small. It is worthy of notice, in connection with the position of vol- 
 canoes near the sea, that the gases ejected are such as might be formed 
 from sea- water and from limestone. The so-called smoke und flame of 
 volcanoes have no connection with combustion. The condensed vapors 
 and the ashes suspended in the air, often in such quantities as to make 
 midnight-darkness at high noon, form the smoke ; and the red glare 
 of the same, reflecting the light from the incandescent lava beneath, ' 
 forms the apparent flame. 
 
 All volcanic ejections, except the gases, accumulate about the crater, 
 and continue to increase with every successive eruption, forming a sort 
 of stratified deposit. Sometimes the cone is made up of successive 
 layers of lava, as in Hawaiian volcanoes ; sometimes it is made up of 
 successive layers of cinders or tufa ; sometimes of alternate layers of 
 lava and tufa. Stratified materials of this kind, 'however, can not 
 be confounded with those produced by the action of water. In the 
 former case the stratification is not the result of the sorting of the 
 materials. 
 
 Kinds of Voleanic Cones. — Volcanic cones and craters have been 
 divided into two kinds — viz., cones of elevation and cones of eruption. 
 A cone of elevation is formed by interior forces lifting the crust of the 
 earth at a particular point until the latter breaks and forms a crater, 
 through which eruptions take place. It is an earth-blister, which 
 swells and breaks at the top. A cone of eruption, on the other hand, 
 is formed by the accumulation around a crater of its own ejection. 
 There has been much discussion among physical geologists as to 
 whether existing volcanic cones are formed mostly by the one method 
 or the other. We will not enter into this discussion. It seems prob- 
 able, however, that most cones are principally cones of eruption, 
 8 
 
96 
 
 IGNEOrS AGENCIES. 
 
 although their height and size have been increased somewhat also by 
 elevating forces. 
 
 Mode of Formation of a Volcanic Cone. — A volcano commences — 1. 
 As a simple opening in the earth's crust, in most cases with little or no 
 
 Fig. 76.— Section across Hawaii. 
 
 elevation. Through this opening or crater are ejected, from time to 
 time, lava, cinders, ashes, etc., which accumulate immediately about the 
 
 crater, and continue to increase, by 
 successive layers, with every eruption. 
 Ejections of pure lava, particularly if 
 the lava is very fluid, form a cone of 
 broad base and low inclination. This 
 is the case with the Pacific volcanoes. 
 Fig. 76 is a section through Hawaii, 
 showing the slope of the pure lava- 
 cones of Mauna Loa (i), nearly 14,000 feet high, and of Mauna Kea 
 (K). Tufa-cones and cinder-cones (Fig. 77) take a much higher angle 
 
 Fig. 77. -Section of Cinder-Cone. 
 
 FiQ. 78.— Dikes at the Base of the Serra del Solflzio, Etna. 
 
VOLCANOES. 
 
 97 
 
 of slope. 2. With every eruption the powerful internal forces fissure 
 the mountain, in lines radiating from the crater. These fissures are 
 filled with liquid lava, which, on hardening, forms radiating dikes, in- 
 tersecting the layers of ejections, and binding them into a more solid 
 mass. By erosion these stand out from the sides of the mountain like 
 buttresses. Fig. 78 shows how these dikes, rendered more visible by 
 erosion, intersect the strata. 3. After a time, when the mountain has 
 grown to considerable height, the force necessary to raise liquid lava 
 to the lip of the crater becomes so great that it breaks in preference 
 through the fissured sides of the mountain. The secondary craters 
 thus formed immediately commence to make accumulations around 
 
 FiQ. 79.— Section of Volcano, showing Monticules. 
 
 themselves, and thus form secondary cones (Fig. 79, c'), or monti- 
 cules, about the base and on the sides of the primary cone. If a 
 secondary cone becomes extinct, it is finally buried (Fig. 79, c") in 
 the layers of the primary cone. 4. Finally, in volcanoes of the explo- 
 sive type, during great eruptions the whole top of the mountain is 
 often blown off, and in volcanoes of the quieter type is melted and 
 falls in — in either case forming an immense crater, within which, by 
 subsequent eruptions, another smaller cone of eruption is built up, and 
 in this latter often a still smaller cone is again built. This cone-within- 
 
 Pieseut outline of Vesuvius and Soiuma. 
 
 Outline of the volcano before the greaf eruption of 79. 
 
 Outline of the cone during the sixteenth and seventeenth centuries. 
 
 Outline of the cone after the great eruption of 1832. 
 
 Fig. 80.— Outlines of Vesuvius, showing its form at different periods of its history (after Judd). 
 
 cone structure is well illustrated by the present condition, and still 
 better by the history, of Vesuvius. Vesuvius is a double - peaked 
 mountain, with a deep, semicircular valley between the peaks. The 
 present active cone of Vesuvius is encircled by a rampart, very high 
 
98 
 
 IGNEOUS AGENCIES. 
 
 on one side, and called Mount Somma, but traceable to some degree all 
 around, and having the same structure as Vesuvius itself. This ram- 
 part is the remains of a great crater, many miles in diameter. This 
 
 Fia. 81. — Mount Vesuvius in 1756 {after Scrope). 
 
 is further and beautifully illustrated by the history of this mountain, 
 which records the repeated destruction and rebuilding of these cones 
 within cones. Many other volcanoes are known which have similar 
 circular ramparts made up of layers of volcanic ejections. 
 
 Craters by Subsidence— Calderas. — Volcanic cones are construc- 
 tional features, formed from the ejectamenta, and the ordinary cra- 
 ters at the summits of cones are the product of explosion, or outthrow. 
 
 Fig. 82— Bird's-eye View of Crater Lake, Oregon (alter Gilbert). 
 
 But there is another class of large so-called craters which have a 
 different genesis, .being produced by subsidence, or the drawing away 
 of the lava from below. These are called calderas. An example is 
 the basin of Crater Lake, Oregon, described by Diller (Fig. 82). 
 The circular basin is iive to six miles in diameter, and the walls 900 
 to 3,200 feet above the lake. The latter is 6,000 feet above the sea, 
 
THEORY OF VOLCANOES. 99 
 
 and about 3,000 feet deep. The basin therefore has a depth of some 
 4,000 "feet. This was formed by the recent engulf ment of a great 
 volcanic peak. The ramparts about the basin, with vertical inner 
 walls and sloping outer walls, are the lower portions of trenched and 
 glaciated slopes. The great cone which only recently towered over 
 the present caldera was comparable to Mount Shasta, and is named 
 Mount Mazama. 
 
 Fio. 83.— Caldera of Kilauea, Hawaii (after Duttpn). 
 
 The huge crater of Kilauea, in Hawaii (Fig. 83), is of the caldera 
 class. The circular depressions on the moon have the form of calde- 
 ras, bu.t they also have the singular attitude of lying below the gen- 
 eral surface of the sphere. The basin of Coon Butte, Arizona, has 
 the same character, but some geologists think that it may have been 
 produced by impact of a meteorite. 
 
 Estimate of the Age of Volcanoes. — The date of origin, may be 
 told by the relationship to the sedimentary strata. Etna belongs to 
 the most recent geological epoch, for it has broken through, and is 
 built upon, the newer tertiary strata. But Etna had already attained 
 very nearly its present size and shape 3,500 years ago, when it was 
 observed by the early Greek writers. The lava-stream which stopped 
 the Carthaginians in their march against Syracuse, 396 years before 
 Christ, may still be seen at the surface, not yet covered by subsequent 
 eruptions. 
 
 Theory of Volcanoes. 
 
 In the theory of volcanoes there are two things to be accounted 
 for, viz.: 1. The force necessary to raise melted lava to the lips of 
 the crater, and even to project it with violence high into the air; 
 2. The heat necessary to fuse rocks and form lava. 
 
100 IGNEOUS AGENCIES. 
 
 Force. — The specific gravity of lava being about 25 to 3, it would 
 require the pressure of one atmosphere, or fifteen pounds to the square 
 inch, for every eleven or twelve feet of vertical elevation of the liquid 
 mass. The following table gives the pressure in atmospheres for four 
 well-known volcanoes, assuming the point of hydrostatic equilibrium 
 to be at the sea-level : 
 
 NAME. 
 
 Height. 
 
 Pressure in atmospheres. 
 
 Vesuvius 
 
 3,900 feet 
 11,000 " 
 13,800 '' 
 19,660 " 
 
 325 
 
 Etna 
 
 920 
 
 Mauna Loa 
 
 1,150 
 
 
 1,638 
 
 
 The lava is often, however, in a frothy or vesicular condition. In 
 such cases the pressure necessary to produce overflow would be much 
 less. But, on the other hand, the force in most cases is not only suf- 
 ficient to lift lava to the top of the crater, but to project it thousands 
 of feet into the air. A rock-mass of over 2,700 cubic feet was pro- 
 jected from the crater of Cotopaxi to a distance of nine miles (Lyell). 
 The agent of this prodigious force is evidently gas and vapors, es- 
 pecially steam. The great quantity of steam issuing from all volcanoes, 
 but especially from those of the explosive type, is sufficient proof. 
 Thus far theorists generally agree, but from this point opinions diverge 
 into the most opposite directions. 
 
 The Heat. — There are many and diverse opinions as to the source of 
 the heat associated with volcanic eruptions. Two prominent views, 
 however, may be said to divide geologists. According to the one, the 
 heat is the remains of the primal heat of the once universally incandes- 
 cent earth ; according to the other, the heat is produced by chemical 
 or mechanical action. 
 
 Internal Fluidity Theory.— This theory supposes that the earth, 
 from its original incandescent condition, slowly cooled and formed a 
 surface-crust; that this surface-crust, though ever thickening by ad- 
 ditions to its interior surface, is still comparatively very thin, and 
 beneath it is still the universal incandescent liquid; that by move- 
 ments of the surface the solid crust is fissured, and water from the sea 
 or from other sources finds its way to the incandescent liquid mass, 
 and develops elastic force sufficient to produce eruption. 
 
 By this view the focus of volcanoes is situated at the lower limit of 
 the solid crust. The theory seems clear and simple enough, but when 
 closely examined there are many objections to it. 
 
 Objections.— The objections to this view are: 1. That the crust, as 
 already shown, must be far thicker than this theory requires, probably 
 hundreds of miles thick, if, indeed, there be any general liquid interior 
 at all; but volcanoes are evidently very superficial phenomena. Under 
 
THEORY OF VOLCANOES. ■ IQl 
 
 the pressure of this difficulty these theorists have been driven to the 
 acknowledgment of local thinnings of the solid crust in the region of 
 volcanoes. 
 
 2. Pressure on a general interior liquid from any cause at any place 
 would, by the law of hydrostatics, be transmitted equally to every part 
 of the crust, which would, therefore, yield at the weakest point, 
 wherever that may be, even though it be on the opposite side of the 
 globe ; but the force of volcanic eruption is evidently just beneath the 
 volcano. 
 
 3. Volcanoes belonging to the same group, and therefore near 
 together, often erupt independently, as if each had its own reservoir of 
 liquid matter. The pressure of these two objections has driven many 
 to the admission of a sort of honey-combed remains of the interior 
 liquid inclosed in the solid crust, and now isolated both from the in- 
 terior liquid and from each other. 
 
 4. Advancing knowledge gives less and less countenance to the 
 idea of internal fluidity from primal heat (see discussion on p. 89), 
 or from any other cause. And there is an objection which seems 
 fatal to all theories that require the entrance of surface water to the 
 zone of vulcanism. Volcanoes have an enormous water supply. It 
 would seem 'to be impossible for sufficient water to penetrate to the 
 layer of potential tluidity. It could not be through fissures from the 
 ocean bottom, and in opposition to the much greater hydrostatic 
 pressure of the lava in the volcanic column, for instead of the water 
 entering, the lava would run out. 
 
 Chemical Theory. — Whether or not the earth consist of solid crust 
 covering an interior liquid, it almost certainly consists of an oxidized 
 crust covering an unoxidized interior. Now, the oxidizing agents are 
 water and air, and therefore the limit of the oxidized crust is the limit 
 of volcanic water. Therefore, the oxidizing agent and the unoxidized 
 material are in close proximity, and the former ever encroaching on 
 the latter, and therefore liable at any moment to set up chemical 
 action, the intensity of which would vary with the nature of the mate- 
 rial. If the action be intense, heat may be formed sufficient to fuse 
 the rocks and to develop elastic force necessary to produce eruption. 
 
 In this general form, the chemical theory seems plausible, but 
 many have attempted to give it more definiteness, and to explain the 
 special forms of oxidation which cause volcanoes. The most cele- 
 brated of these definite forms is that of Sir Humphry Davy, who 
 attributed it to the contact of water with metallic potassium, sodium, 
 calcium, and magnesium, in the interior of the earth. In such defi- 
 nite forms the theory seems far too hypothetical. 
 
 Recent Theories.— l- Aqueo-igneous TAeor?/.— Accumulation of 
 sediment on sea-bottoms would necessarily produce corresponding rise 
 
JQ2 IGNEOUS AGENCIES. 
 
 of isogeotherms, and thus the interior heat of the earth would invade 
 the sediments with their contained waters. The lower portion of 
 sediments 10,000 feet thick would be raised to a temperature of about 
 260° Pahr., and of 40,000 feet thick (sediments of this thickness and 
 more are known) to that of 860°. This temperature, or even a less 
 temperature if alkali be present, would be sufficient in the presence of 
 the contained water of the sediments to produce complete aqueo- 
 igneous fusion, and probably to develop elastic force sufficient to pro- 
 duce eruption. This view was first brought forward by John Herschel. 
 Observe that this temperature and the corresponding force would be 
 gradually developed as the accumulation progressed, until sufficient to 
 produce these effects. Observe, again, that in this case the water does 
 not seek the heat by descending (the difficulties in the way of this 
 are insuperable), but the heat seeks the already imprisoned water by 
 ascending. 
 
 It seems very probable that cases of eruption of hot mud and of 
 aqueo-igaeously fused lavas may be accounted for in this way, but the 
 temperature would not be sufficient to account for true igneous fusion, 
 nor would the force be suflacient to break up the crust of the earth 
 and produce eruption. It is possible, however, that this, may be com- 
 bined with the next theory. 
 
 3. Mechanical Theory.— As we shall explain hereafter (p. 277), 
 there is much reason to believe that the interior of the earth is con- 
 tracting more rapidly than the exterior, and that the exterior is thus 
 necessarily thrust upon itself by irresistible horizontal pressure. Ac- 
 cording to Mr. Mallet, the crushing of the rocky crust in places under 
 this pressure develops heat sufficient to fuse the rocks, and to produce 
 eruption. But it is at least doubtful whether the heat thus generated 
 would alone be sufficient for this purpose. 
 
 3. Issuing of Superheated Gases. — Rev. 0. Fisher has advanced a 
 view which deserves attention. He thinks volcanoes are vents through 
 which issue from the earth's interior superheated steam and gases, 
 melting the rocks in their course and ejecting them by their pressure. 
 According to this view, the water is not derived from the surface, but 
 is original and constituent. This view is independent of the conditiou 
 of the earth's interior, whether solid or liquid ; for a temperature 
 which would permit solidity at great depths would produce fusion 
 under less pressure near the surface.* The sun may be regarded as a 
 globe in an earlier and more active stage of vulcanism. From its in- 
 terior gases are seen to issue in great quantity, and almost constantly. 
 
 4. PrestwicKs Theory. — If we assume the existence of a sub-crust 
 layer of liquid matter, then lateral crushing of the earth's crust, such 
 
 * See page 89 for approval of this theory. 
 
GEYSERS. 103 
 
 as undoubtedly occurs ia mountain-making, would squeeze the liquid 
 upward into and through fissures to the surface, producing the quieter 
 lava-eruptions ; or else, coming in contact in its upward course with 
 subterranean waters, especially abundant in the fissured and cavernous 
 structure of recent lavas, would develop steam and therefore violent 
 explosive eruptions. 
 
 5. Fusion ly relief of Pressure. — We have already seen that there 
 is probably a sub-crust layer, which if not fused is nearest the fusing- 
 point, and therefore liable to become fused not by. increase of heat, but 
 by relief of pressure. Such relief of pressure may be produced either 
 by erosion, which often cuts away miles of thickness, or by a fissure, 
 or by lateral pressure such as elevates mountain-ranges. In the last 
 case the same lateral crush, which by relief of pressure produced the 
 fusion, would also squeeze out the liquid matter thus formed. 
 
 Suiordinate Volcanic Phenomena. 
 
 These are hot springs, carbonated springs, solfataras, fumaroles, 
 mud-volcanoes, and geysers. They are all secondary phenomena, i. e., 
 formed by the percolation of meteoric water through hot volcanic ejec- 
 tions. Or perhaps in some cases the heat may be produced by slow rock- 
 crushing by horizontal pressure, as explained above, or else by local 
 chemical action. 
 
 General Explanation. — Thick masses of lava outpoured from vol- 
 canoes remain hot in their interior for an incalculable time. Water 
 percolating through these acquires their heat, and comes lip again as 
 hot springs ; or, if in addition it contains lime, as lime-depositing 
 springs ; or, if it contains carbonic acid, as carbonated springs ; or, if 
 it contains sulphurous acid and sulphureted hydrogen, as solfataras. 
 If condensible vapors issue in abundance so as to make an appearance 
 of smoke, they are called fumaroles. If the hot water brings up with 
 it mud which accumulates about the vent, then it is a mud-spring or 
 a mud-volcano. If the heat is very great, so that violent eruption of 
 water takes place periodically, then it becomes a geyser. We have 
 already spoken of carbonated lime-depositing springs (p. 78). We 
 shall again, under the head of the theory of mineral veins (p. 243), 
 speak of solfataras. The only one which need detain us now is geysers. 
 
 Geysers. 
 
 A geyser may be defined as a periodically eruptive spring. Geysers 
 
 are found only in Iceland, in the Yellowstone Park of tjie United 
 
 States, and in New Zealand. The so-called geysers of California are 
 
 . rather fumaroles. Those of Iceland have been long studied ; we will, 
 
 therefore, describe these first. 
 
104 
 
 IGNEOUS AGENCIES. 
 
 Iceland is a volcanic plateau, with a narrow marginal habitable 
 region sloping gently to the sea. The interior plateau is the seat of 
 eyery species of volcanic action, viz., lava-eruptions, solfataras, mud- 
 
 volcanoes, hot springs, and geysers. There are several hundred vents 
 of all kinds in comparatively small space, among which are many 
 geysers. One of these, the Great Geyser, has long attracted atten- 
 tion. 
 
GEYSERS. 
 
 105 
 
 Description. — The Great Geyser is a basin or pool fifty-six feet in 
 diameter, on the top of a mound thirty feet high. From the bottom 
 of the basin descends a funnel-shaped pipe eight or ten feet in 
 diameter, and seventy-eight feet deep. Both the basin and the tube 
 are lined with silica, evidently deposited from the water. The natural 
 inference is, that the mound is built up by deposit from the water, in 
 somewhat the same manner ._ 
 
 £^ - 
 
 as a volcanic cone is built 
 up by its own ejections. 
 In the intervals between the 
 eruptions the basin is filled 
 to the brim with perfectly 
 transparent water, having a 
 temperature of about 170° 
 to 180°. 
 
 Phenomena of an Erup- 
 tion, — 1. Immediately pre- 
 ceding the eruptions sounds 
 like cannonading are heard 
 beneath, and bubbles rise 
 and break on the surface of 
 
 the water. 2. A bulging of the surface is then seen, and the water 
 overflows the basin. 3. Immediately thereafter the whole of the water 
 in the tube and basin is shot upward one hundred feet high, forming 
 a fountain of dazzling splendor. 4. The eruption of water is imme- 
 diately followed by the escape of steam with a roaring noise. These 
 last two phenomena are repeated several times, so that the fountain 
 
 85.— (After Hayden.) 
 
 Fig. 86.— The Turban (after Hayden). 
 
 continues to play for several minutes, until the water is sufficiently 
 cooled, and then all is again quiet until another eruption. The level 
 of the water after an eruption is seven or eight feet in the tube. The 
 
106 
 
 IGNEOUS AGENCIES. 
 
 frequency of the eruptions is slowly diminishing. In 1804 it was once 
 every hour ; now several days often elapse.* Throwing large stones 
 into the tube has the effect of bringing on the eruption more quickly. 
 
 FiQ. 87.— Qastle Geyser in Action. (Pliotograpli by ¥. J. Haynes.) 
 
 Yellowstone Geysers.— In magnificence of geyser displays, however, 
 Iceland is far surpassed by the geyser basin of Firehole River. This 
 
 * Daubrfie, Archiyes des Sciences, vol. xix, p. 425, 1888. 
 
GEYSERS. 
 
 107 
 
 wonderful geyser region is situated in the northwest corner of Wyo- 
 ming, on an elevated volcanic plateau near the head-waters of the 
 Madison Eiver, a tributary of the Missouri, and of the Snake Eiver, a 
 tributary of the Columbia. The basin is only about three miles wide. 
 About it are abundant evidences of prodigious volcanic activity in 
 
 Fig. 88,— Bee-Hive Geyser in Action. (Photograph by F. J. Haynes.) 
 
 former times, and although primary volcanic activity has ceased, sec- 
 ondary volcanic phenomena are developed on a stupendous scale and 
 of every kind, viz. : hot springs, carbonated springs, fumaroles, mud- 
 volcanoes, and geysers. In the Yellowstone Park itself there are at 
 least 3,000 vents of all kinds, and of these more than sixty are erup- 
 
108 
 
 IGNEOUS AGENCIES. 
 
 tive geysers. In some places, as on Gardiner's River, the hot springs 
 are mostly lime-depositing (page 78) ; in others, as oh Firehole River, 
 they are geysers depositing silica. 
 
 In the upper geyser basin the valley is covered with a snowy deposit 
 from the hot geyser-waters. The surface of the mound-like, chimney- 
 like, and hive-like elevations (Fig. 89), immediately surrounding the 
 vents, is, in some cases, ornamented in the most exquisite manner by 
 deposits of the same, in the form of scalloped embroidery set with 
 pearly tubercles ; in others the siliceous deposits take the most fantastic 
 forms (Figs. 84, 85, 86). In some places the silica is deposited in large 
 quantities,- three or four inches deep, in a gelatinous condition like 
 
 starch-paste. Trunks and branches of 
 trees immersed in these waters are 
 speedily petrified. It has been shown 
 by Mr. Weed that the process is greatly 
 assisted by the growth of certain algae.* 
 We can only mention a few of the 
 grandest of these geysers : 
 
 1. The " Grand Geyser," according 
 to Hayden, throws up a column of water 
 six feet in diameter to the height of 300 
 feet, while the steam ascends 1,000 feet 
 or more. The eruption is repeated every 
 thirty-two hours, and lasts twenty min- 
 utes. In a state of quiescence the tem- 
 perature of the water at the surface is 
 about 150°. 
 
 2. The " Giantess " throws up a large 
 column twenty feet in diameter to a 
 height of sixty feet, and through this 
 great mass it shoots up five or six lesser 
 jets to a height of 250 feet. Its eruptions 
 are fitful but last sometimes several hours. 
 
 3. The "Giant" (Fig. 87) throws a 
 column five feet in diameter 140 feet high, 
 and plays continuously for three hours. 
 
 4. The "Bee -Hive" (Fig. 88), so 
 called from the shape of its mound, 
 
 shoots up a splendid column two or three feet in diameter to the 
 height by measurement of 319 feet, and plays fifteen minutes. 
 
 5. " Old Faithful," so called from the frequency and regularity of its 
 eruptions, throws up a column six feet in diameter to the height of 100 
 to 150 feet about once an hour, and plays about fifteen minutes. 
 
 Fig. 89.— Forms of Geyser-Craters 
 (after Hayden). 
 
 * Am. Jouv., vol. xxxvii, p. 351, 1889; Ninth An. Eep. U. S. Geol. Surv., p. 613. 
 
GEYSERS. 
 
 109 
 
 Theories of Geyser-Eruption. — The water of geysers is not volcanic 
 water, but simple spring- water. A geyser is not, therefore, a volcano 
 ejecting water, but a true spring. There has been much speculation 
 concerning the cause of their truly wonderful eruptions. 
 
 Mackenzie's Theory. — According to Mackenzie, the eruptions of the 
 Great Geyser may be accounted for by supposing its pipe connected by 
 a narrow conduit with the lower part of a subterranean cave, whose 
 walls are heated by the near vicinity of volcanic fires. Pig. 90 repre- 
 sents a section, through the basin, tube, and supposed cave. Now, if 
 meteoric water should run into the cave through fissures more rapidly 
 than it can evaporate, it would accumulate until it rose above, and 
 therefore closed, the 
 opening at a. The 
 steam, now having no 
 outlet, would condense 
 in the chamber i until 
 its pressure raised the 
 water into the pipe, and 
 caused it to overflow the 
 basin. The pressure 
 still continuing, all the 
 water would be driven 
 out of the cave, and 
 partly up the pipe. Now, 
 the pressure which sustained the whole column a d would not only 
 sustain, but eject with violence, the column c d. The steam would 
 escape, the ejected water would cool, and a period of quiescence "would 
 follow. If there were but one geyser in Iceland, this would be rightly 
 considered a very ingenious and probable hypothesis, for without 
 doubt we may conceive of a cave and conduit so constructed as to 
 account for the phenomena. But there are many eruptive springs in 
 Iceland, and it is inconceivable that all of them should have caves and 
 conduits so peculiarly constructed. This theory is therefore entirely 
 untenable. • 
 
 Bunsen's Investigations.— The investigations of Bunsen and his 
 theory of the eruption and the formation of geysers are among the 
 mo'st beautiful illustrations of scientific induction which we have in 
 geology. We therefore give it, perhaps, more fully than its strict 
 geological importance warrants. 
 
 Bunsen examined all the phenomena of hot springs in Iceknd. 1. 
 He ascertained that geyser-water is meteoric water, containing the 
 soluble matters of the igneous rocks in the vicinity. He formed 
 identical water by digesting Iceland rocks in hot rain-water. 2. He 
 ascertained that there are two kinds of hot springs in Iceland, viz., acid 
 
 Pig. 90.— Mackenzie's Theory of Eruption. 
 
110 IGNEOUS AGENCIES. 
 
 springs and alkaline-carbonate springs, and that only alkaline-car- 
 bonate springs contain any silica in solution. The reason is obvious ; 
 alkaline waters, especially if hot, are the natural solvents of silica. 3. 
 He ascertained that only the silicated springs form geysers. Here is 
 one important step taken — one condition of geyser-formation dis- 
 covered. Deposit of silica is necessary to the existence of geysers. 
 The tube of a geyser is not an accidental conduit, but is built up by 
 its own deposit. 4. Of silicated springs, only tJiose with deep tubes 
 erupt — another condition. 5. Contrary to previous opinion, the silica 
 in solution does not deposit on cooling, but only by drying. This 
 would make the building-up of a geyser-tube an inconceivably slow 
 process, and the time proportionally long. 6. The temperature of the 
 water in the basin was found to be usually 170° to 180°, and that in the 
 tube to increase rapidly, though not regularly, with depth. Moreover, 
 the temperature, both at the surface and at all depths, increased 
 regularly as the time of eruption approached. Just before the erup- 
 tion it was, at the depth of about forty-five feet, very near the boiling- 
 point /or that depth. 
 
 Theory of Geyser-Eruption — Principles. — 1. It is well known that 
 the boiling-point of water rises as the pressure increases. This is 
 shown in the adjoining table. 2. It follows 
 from the above that if water be under strong 
 pressure, and at high temperature, though 
 below its boiling-point for that pressure, and 
 the pressure be diminished sufficiently, it 
 will immediately flash into steam. 3. Water 
 heated beneath, if the circulation be unim- 
 peded, is very nearly the same temperature, throughout. That it is 
 never the same temperature precisely is shown by the circulation itself, 
 which is caused by difference of temperature, producing difference iii 
 density. The phenomenon of simmering is also a well-known evidence 
 of this difference of temperature, since it is produced by the collapse 
 of steam-bubbles rising into the cooler water above. 4. But if the cir- 
 culation be impeded, a.sgiv'hen the water is contained in long, narrow, 
 irregular tubes, and heated with great rapidity, the temperature may 
 be greater below than above to any extent, and the boiling-point may ■ 
 be reached in the lower part of the tube, while it is far from this point 
 in the upper part. 
 
 Application to Geysers.— We will suppose a geyser to have a 
 simple but irregular tube, without a cave, heated below by volcanic 
 fires, or by still hot volcanic ejections. Now, we have already seen 
 that the temperature of the water in the tube increases rapidly with 
 the depth, but is, at every depth to which observation extends, short 
 of the boiling-point for that depth. There is no doubt, therefore. 
 
 Pressure in 
 Atmospheres. 
 
 Boiling-Point. 
 
 1 Atm03. 
 
 2 " 
 
 3 " 
 
 4 " 
 
 212° 
 250° 
 275° 
 293° 
 
GEYSERS. 
 
 Ill 
 
 that, at the moment of eruption, at some point below the reach of 
 observation, the boiling-point for that depth is actually reached. As 
 soon as this occurs, a quantity of water would be changed into steam, 
 
 Fig. 91.— Old Faithful Geyser, Yellowstone Park. 
 
 and the expanding steam would lift the overlying column of water, 
 and cause the water in the basin to bulge and overflow. As soon as 
 the water overflowed, the pressure would be diminished in every part 
 9 
 
112 
 
 IGNEOUS. AGENCIES. 
 
 of the tube, and consequently a large quantity of water, before very 
 near the boiling-point, would flash into steam and produce an erup- 
 tion. The premonitory cannonading beneath is evidently produced 
 by the collapse of large steam-bubbles rising through the cooler water 
 of the upper part of the tube ; in other words, it is simmering on a 
 huge scale. An eruption is hastened by throwing stones into the 
 throat of the geyser, because the circulation is thus more effectually 
 impeded. A similar effect is produced by throwing soap down the 
 tube, as it increases the density and tension of the water. 
 
 The theory given above is substantially that of Bunsen for the 
 eruption of the Great Geyser, but modified to make it applicable to 
 all geysers. In the Great Geyser, as already stated, Bunsen found a 
 point forty-five feet deep, where the temperature was nearer the boil- 
 ing-point than at any within reach of observation. This point, forty- 
 five feet deep, plays an important part in Bunsen's theory. But it 
 
 Fib. 92.— Crater of Grotto Geyser. (Photograph from United States Geological Survey.) 
 
 ,is extremely unlikely that this condition should exist in all geysers, 
 neither is it at all necessary in order to explain the phenomenon of 
 an eruption. 
 
 To prove beyond question the truth of this theory, Bunsen con- 
 structed an artificial geyser. The apparatus consisted of a tube of 
 
GEYSERS. 
 
 113 
 
 tinned sheet-iron about ten feet long, expanding into a disk above 
 for catching the erupted water. It may or may not be expanded 
 belDw for the convenience of heating. It was heated, also, a little 
 below the middle, by an encircling charcoal chauffer, to represent the 
 point of nearest approach to the boiling-point in the geyser-tube. 
 
 Fig. 93.— Excelsior Geyeer in Action. (Pliotograpli by F. J. Haynes.) 
 
 When this apparatus was heated at the two points, the phenomena 
 of geyser-eruption were completely reproduced : first, the violent ex- 
 plosive simmering, then the overflow, then the eruption, and then the 
 state of quiescence. In Bunsen's experiment, the eruptions occurred 
 about every thirty minutes. 
 
 Theory of Geyser-Formation. — According to Bunsen, a geyser 
 does not find a cave, or even a perpendicular tube, ready made, but, 
 like volcanoes, makes its own tube. 
 
 It is evident, however, that Bunsen's theory of geyser-eruption is 
 independent of his theory of geyser-formation. A tube or fissure of 
 any kind, and formed in any way, if long enough, would give rise 
 to the same phenomena. The Yellowstone geysers have low mounds 
 
114 
 
 IGNEOUS AGENCIES. 
 
 or chimney-like cones, but it is certain that the whole length of their 
 eruptive tubes has not been built up by siliceous deposit. 
 
 Eecent experimentation * has improved on the simple apparatus 
 of Bunsen by adding a reservoir so as to simulate the subterranean 
 water supply of the geysers. The experiments indicate that, like all 
 springs, the geysers and geyser-springs are subject to the laws of 
 hydrostatics, and that the varied behavior of geysers is due to difEer- 
 
 Fio. 94.— The 
 
 ' Mud Puffs " or " Giant Paint-Pots," Fountain Group of Geysers. 
 E. H. Barbour.) 
 
 (Photograph by 
 
 ences m the hydrostatic conditions. Jaggar has shown that a dis- 
 tinction should be made between two types of geysers. The type rep- 
 resented by Old Faithful has no overflow or escape of fluids except 
 by eruption^ and is comparatively regular. In the class represented 
 by Excelsior there is continuous outflow, and the eruptions are very 
 irregular. The Excelsior was not known to be a geyser until 1881, 
 and has not been seen in eruption since 1888. The length of each 
 eruption depends on several conditions — the quantity of water, depth 
 of reservoir, irregularity in size and direction of the tube, and the 
 capacity of the bowl at the top of the tube, which may catch the fall- 
 ing water and pour it back upon the ascending fluid. The interval of 
 eruption is dependent on the balance of the several hydrostatic con- 
 ditions. 
 
 * Jaggar, Am. Jour. Sci., vol. v, 1898, p. 323. 
 
EARTHQUAKES. n^ 
 
 Some geologists have thought that the geyser phenomena of the 
 Yellowstone Park showed general decline. Changes are certainly- 
 taking place, and in time there must be extinction, but it is not 
 evident that activity has lessened in thirty years.* Some of the 
 greater geysers of former time are apparently extinct, or nearly so, 
 as the Castle and the Giant. Others are new, as the Excelsior, which 
 is probably the most powerful of living geysers. The famous geyser 
 and beautiful deposits of Eotomahana, New Zealand, were destroyed 
 by volcanic disturbance in 1886. 
 
 The siliceous sinter deposited by the geysers is called geyserite. 
 While the waters of all known geysers are siliceous it does not fol- 
 low that all silica-bearing springs are eruptive. There are hun- 
 dreds of thermal, siliceous springs scattered among the geysers and 
 elsewhere, which are not explosive. As a rule, springs with continu- 
 ous outilow are not eruptive, and the form of the pools is some- 
 what characteristic (Figs. 85-86), the deposition occurring through 
 the agency of algae instead of by evaporation. In the waters of the 
 Yellowstone Park algs flourish in temperatures up to 185° P. On 
 the other hand, the deposition by the geysers is mainly by evaporation, 
 and they build low cones or mounds (see Figs. 87-89, 91, 92). The 
 rate of deposition has been estimated at one inch in thirty years. Such 
 mounds as the Castle and the Giant must have required many thou- 
 sands of years. 
 
 Section 3. — Eaethquakes. 
 
 During the last half century our knowledge on the subject of earth- 
 quakes has taken scientific form. This slovmess of advance has 
 arisen not from any want of materials, but from the great complexity 
 of the phenomena, their origin deep within the bowels of the earth, 
 and therefore removed from observation, and, more than all, from the 
 surprise and alarm usually produced unfitting the mind for scien- 
 tific observation. For these reasons, until about 1850, the state of 
 knowledge on this subject was much the same as it was 3,000 years 
 ago. And yet now, we think, our knowledge of earthquakes is even 
 more advanced than that of volcanoes. 
 
 Frequency. — Mallet, in his earthquake catalogue, has collected the 
 records of 6,830 earthquakes as occurring in 3,456 years previous to 
 1850 ; but, of that number, 3,240, or nearly one half j occurred in the 
 
 * Arnold Hague says : " It is not true that the geysers show any eridence of declining 
 within historical time (since the advent of white men, about thirty-fire years). - Geolog- 
 ically speaking, it is probably true that they are slowly declining. The eridence goes to 
 show that they were more powerful in former times than at present. There are constant 
 changes talcing place, but in my judgment there is no diminution of real force." — Letter 
 of February, 1903. 
 
116 
 
 IGNEOUS agencies; 
 
 last fifty years ; not because earthquakes were more numerous, but be- 
 cause tile records were more perfect. According to the more complete 
 catalogue of Alexis Perrey, from 1843 to 1872, inclusive, there were 
 17,249, or 575 per annum. In Japan alone there are, on an average, 
 three to four shocks per day. It seems probable, therefore, that, con- 
 sidering the fact that even now the larger number of earthquakes 
 are not recorded, occurring in mid-ocean or in uncivilized regions, the 
 earth is constantly quaking in some portion of its surface. 
 
 Connection with Igneous Agency. — The close connection of earth- 
 quakes with volcanoes is undoubted. Volcanic eruptions, especially 
 those of the explosive type, are usually preceded and accompanied by 
 earthquakes. Examination of Prof. Mallet's earthquake-map shows 
 that the distribution of earthquake-centers is much the same as that 
 
 Fig. 94a. — Street Scene in Charleston after the Earthquake, 
 United States Geological Survey.) 
 
 (Photograph from 
 
 of volcanoes already given (page 90). It may be regarded as almost 
 certain, therefore, that the forces which generate some earthquakes 
 are closely allied with those which produce volcanic eruptions. 
 
 Again, the connection of earthquakes with bodily movements of 
 great areas of the earth's crust, by elevation or depression, is equally 
 close. In 1835, with a great earthquake, which shook the coast of 
 South America over an area of 600,000 square miles, the whole coast- 
 line of Chili and Patagonia was elevated from two to ten feet above 
 sea-level. Again, in 1822, in connection with a similar earthquake in 
 
EAETHQDAKES. j^jY 
 
 the same region, the coast-line was elevated from two to seven feet 
 Now, m this very region, old beach-marks, 100 feet to 1,300 feet above 
 the sea-level, and extending 1,200 miles along the coast on each side of 
 the southern end of this continent, plainly show that, in very recent 
 geological times, the whole southern end of South America has been 
 bodily raised out of the sea to that extent. It is impossible to doubt 
 that the force which produced this continental elevation was also the 
 cause of the accompanying earthquakes. Again, in 1819, with a 
 severe earthquake, which shook the whole region about the mouth of 
 the Indus, a large tract of land of 2,000 square miles was sunk and 
 became a salt lagoon; while another area, fifty miles long and ten to 
 sixteen miles wide, was elevated ten feet. In commemoration of this 
 wonderful event, the raised portion was called Ullah Bund, or the 
 Mound of God. Again, in 1811, a severe earthquake shook the valley 
 of the Mississippi. In the region about the mouth of the Ohio, where 
 it was severest, large tracts of land were sunk bodily several feet below 
 their former level, and have been covered with water ever since. It is 
 now called the " Sunk Country." The Inyo earthquake of 1872 was 
 accompanied by a fissure of forty miles in length and a slip or fault of 
 twenty-five feet. In the Sonora earthquake of 1887 there was a 
 fissure for a hundred miles and a vertical slip of eight feet. In the 
 Japan earthquake of 1891, there was a fissure seventy miles long and 
 a slip of twenty feet. We might multiply examples if necessary. 
 Fearly all earthquakes, if carefully studied, have shown such fissures 
 and slips. Fissures and faults, formed in previous geological times, 
 are found intersecting the earth in all directions. We see them, in 
 these cases, formed under our eyes, and in connection with earthquakes. 
 Cause of Earthquakes. — The connection of earthquakes with the 
 volcanic forms of igneous agency naturally suggested these as a pos- 
 sible cause. Preceding and accompanying volcanic eruptions, espe- 
 cially of the explosive type, occur subterranean explosions, which are 
 often heard hundreds of miles. Such eruptions are also accompanied 
 with escape of immense quantities of steam and gas. These facts, 
 together with the association of earthquakes with volcanoes, have sug- 
 gested the idea that the sudden formation or the sudden collapse of 
 vapor is the cause of earthquakes. According to this view, an earth- 
 quake is, on a grand scale, a phenomenon similar to the jar produced 
 by the explosion of a keg of gunpowder buried in the earth. 
 
 But the association of earthquakes with bodily movements of the 
 earth's crust over large areas, suggests another and far more probable 
 cause. It is well known that there are operating, in the interior of 
 the earth, forces tending to elevate or depress or to crush together 
 laterally the earth's crust. We shall discuss the nature of these forces 
 hereafter. Suffice it to say now that in this way mountain-ranges are 
 
j^lg IGNEOUS AGENCIES. 
 
 formed and continents elevated. One effect of these forces is to break 
 the earth's crust into great blocks many miles in length and breadth 
 and several miles in thickness. These blocks do not remain in their 
 original position, but are always slipped one on another, producing 
 displacement often thousands of feet. Such great crust-blocks sepa- 
 rated by profound fissures, and slipped onp on another, are found 
 everywhere. They are, in fact, among the commonest of geological oc- 
 currences. They will be described in Part II. Some of these fissures 
 are doubtless now forming ; many of them are still slipping. Suppose, 
 then, a subterranean force, tending to elevate a portion of the earth's 
 crust, and gradually increasing but resisted by the rigidity of the crust. 
 It is evident that the time would finally come when the crust would 
 break, by a fracture extending perhaps hundreds of miles in length 
 and through several miles in depth of solid rock. Such a fracture 
 would certainly cause an earth-jar great enough to produce all the 
 •dreadful efEects of an earthquake. But, again, the enormous crust- 
 blocks thus formed would inevitably from time to time settle, or read- 
 just themselves to new positions. Every such readjustment would also 
 produce an earthquake. We conclude, therefore, that by far the most 
 common cause of earthquakes is either the formation of a great fissure 
 or else the readjustment of the walls of such a fissure. Even in the 
 case of the tremors accompanying volcanic eruptions, it is probable 
 that their true cause is the fracturing of the mountain by the erup- 
 tive forces and the readjustment of the broken parts. 
 
 Proximate Cause. — But whatever be our view of the ultimate cause 
 of earthquakes, there can be no doubt that the proximate or immediate 
 cause of the observed effects is the arrival of an earth- jar — the emer- 
 gence, on the earth-surface, of a succession of elastic earth-waves, 
 produced by a violent concussion of some kind in the interior. Evi- 
 dently, therefore, the discussion of earthquake-phenomena is nothing 
 more than the discussion of the laws of propagation and the effects 
 of elastic earth-waves occurring under peculiar and very complex con- 
 ditions. 
 
 Application to Earthquakes. — Suppose, then, a concussion of any 
 kind to occur at a considerable depth (x, Pig. 95), say ten or twenty 
 miles, beneath the earth-surface, S S. Taking, for simplicity sake, 
 the origin as a point, a series of elastic spherical waves, similar to 
 sound-waves, will be generated, consisting of alternate compressed and 
 rarefied shells, the whole expanding with great rapidity in all directions 
 until they reach the surface at a. Erom this point of first emergence 
 immediately above the focus x, the still-enlarging spherical shells 
 would outcrop in rapidly-expanding circular waves, b" i", c" c", d" d" 
 (Pig. 95), similar in form to water-waves, but very different in char- 
 acter. This we will call the surface-wave. The circles here drawn 
 
EARTHQUAKES. 
 
 119 
 
 would equally represent a series of waves, or the same wave in succes- 
 sive degrees of enlargement. 
 
 This surface-wave would not be a normal wave propagating itself 
 like a water-wave. It would be only the outcropping or emergence of 
 the ever-widening spherical wave on the earth-surface. Both its 
 velocity of transit along the surface, and the direction of its vibration 
 in relation to the surface, will vary continually according to a simple 
 law. The direction of vibration, being along the radii x a, x b, x c, 
 etc., will be perpendicular to the surface at a, and become more in- 
 clined until it finally becomes parallel with the surface at an infinite 
 distance. The velocity of its transit will be infinite at a, aiid then 
 gradually decrease until, if we regard the surface as a plane surface, at 
 an infinite distance it reaches its limit, which is the velocity of the 
 spherical wave. Between these two extremes of infinity at a, and the 
 velocity of the spherical wave at infinite distance, the velocity of the 
 surface-wave varies inversely as the cosine, or directly as the secant, of 
 the angle of emergence xba,xca, etc. 
 
 Fio. 95.— Section and Perspective View of a Portion of tlie Earth's Crust shaken by an Earthquake, 
 showing the origin, a:, sections of the spherical waves, a, b, c, d, etc., and perspective of surface- 
 wave, b", c", d", etc. 
 
 For, it aa,bb,cc,d d, etc. (Fig. 95), be successive positions of the 
 spherical wave, then the radii xa,xb,xc, would be the direction both of 
 propagation and of vibration. Now, when the wave-front is at b, 
 while the spherical wave moves from b' to c, the surf ace- wave would 
 move from b io c; when the spherical wave moves from c' to d, the 
 surface-wave moves from c to d, etc. If, therefore, b c,c d, etc., be 
 taken very small, so that bb' c,c c' d, may be considered right-angled 
 triangles, then in every position the surface-wave moves along the 
 hypotenuse, while the spherical wave moves along the base of the 
 small triangles bb' c,c c' d, etc. Letting v = velocity of the spherical 
 wave, and v' that of the surface-wave, and E the angle of emergence 
 {xba,xca, etc., Fig. 95), we have the proportion—?; : v' : : 1 : sec. E, 
 and v' — V. sec. E, or if v is constant v' <x sec. E. Therefore, at a, the 
 point of first emergence, E being a right angle and sec. E= infinity, 
 v' =infinity. At an infinite distance from a the angle E becomes 0, 
 
120 
 
 IGNEOUS AGENCIES. 
 
 and the secant = 1, and v' = v. 1 = v. That is, at the point of first 
 emergence the velocity of the surface-wave is infinite ; from this point 
 
 FiQ. 96. 
 
 it decreases as the secant of the angle of emergence decreases, until 
 finally at an infinite distance it becomes equal to the velocity of the 
 spherical wave. 
 
 On a spherical surface (Fig. 96) it is evident that H never becomes 
 0, and therefore v' never reaches the limit v. If we conceived the 
 wave to pass through the whole earth (Fig. 97), then the velocity of 
 the surface-wave would decrease to a certain point where iS* is a mini- 
 mum, say about c, and then would again increase to infinity on the 
 other side of the earth, p, where F becomes again a right angle. If x 
 be near the surface, v' would become nearly equal to v at some point 
 of its course ; but as x approaches the center, C, the limit of v' would 
 be greater and greater, until, if x is at the center, v' would become in- 
 finite everywhere ; i. e., a shock at the center would reach the surface 
 everywhere at the same moment. We are indebted to Hopkins for 
 this discussion of the relation of the velocity of the surface- wave to 
 that of the spherical wave. It may therefore be called Hopkins 
 law. 
 
 We have thus far taken the earth as homogeneous and of equal 
 elasticity at all depths. But the earth certainly increases in density 
 (p. 87), and therefore in elasticity as we ap- 
 proach the center. This fact would seriously 
 affect the form of the earth-wave and, in a 
 remarkable way, the velocity of its outcrop on 
 the surface — i. e., the surface-wave. This has 
 been worked out in a masterly way by Schmidt.* 
 If, as before, s s (Fig. 98), represent the sur- 
 face of the earth and x the centrum of the 
 earthquake, then the earth-wave would come 
 from X to the epicentrum, a, without devia- 
 tion, but with decreasing velocity, as shown 
 by the decreasing spaces between the co-seis- 
 mals. In all other directions, however, the waves would be refracted 
 by passing from a denser to a rarer medium. The form of the wave, 
 therefore, would not be perfectly spherical, but ellipsoidal, with the 
 
 * Nature, vol. ii, p. 631, 1895. 
 
EARTHQUAKES. 
 
 121 
 
 centrum in one focus of the ellipsoid. The radii — always normal to 
 the wave-front — would be curved, with the concavity upward. Under 
 these conditions it is evident that, as before, the velocity of the surface- 
 wave would be infinite at the epicentrum, a, then decrease as before, 
 but by a different law and more rapidly, would reach a minimum which 
 would be equal to the velocity at the centrum, and thenceforward again 
 increase to infinity at infinite distance. This is shown by the gradual 
 approach of the radii to a position normal to the earth surface. This 
 may be called " Schmidfs law." It undoubtedly explains many other- 
 wise inexplicable phenomena of varying velocity of earthquake-waves 
 as will be shown in the proper place. 
 
 Pio. 98.— Diagram illustrating Schmidt's Law. 
 
 Experimental Determination of the Velocity of the Spherical Wave. 
 
 —On the supposition that earthquakes are really produced by the 
 emergence on the surface of a series of elastic earth-waves, Mallet 
 undertook to determine experimentally the velocity of such waves. 
 Two stations were taken about a mile or more apart, and connected by 
 telegraphic apparatus ; a keg of gunpowder was buried at one, and at 
 the other was placed an observatory, in which was a clock, a mercury 
 mirror, and a light, the image of which reflected from the mercury 
 mirror, was thrown on a screen. The slightest tremor communicated 
 
122 IGNEOUS AGENCIES. 
 
 to the mercury surface of course caused the image to dance. The 
 moment of explosion was telegraphed ; the moment of arrival of the 
 earth-tremor was observed. The difference gave the time of transit: 
 the distance, divided by the time, gave the velocity per second. .In 
 this manner Mallet found the velocity in sand 825 feet per second, or 
 nearly nine and one half miles per minute; in slate 1,235 feet per 
 second, or fourteen miles per minute; and in granite, 1,665 feet per 
 second, or nineteen miles per minute. 
 
 More recent experiments have given much higher velocities. In a 
 series of very careful experiments Fouque found in sand a velocity of 
 984 feet, in carhoniferous sandstone about 7,400 feet, and in granite 
 about 9,300 feet per second. The explosion at Hallett's Point gave 
 5,000 to 8,000 feet per second, and that of Flood Rock, 4,500 to 
 20,000 feet per second (Abbot). These agree well with the observed 
 velocity of some earthquakes. It should be remembered that all these 
 experiments give only the velocity of the spherical wave, because oji 
 account of the very small depth of the focus the velocity of the spheri- 
 cal and surface waves are practically identical. 
 
 Theory requires that all waves of elasticity should travel in the 
 same medium with the same velocity. The velocity of sound in 
 granite is from 15,000 to 18,000 feet per second. The discrepancy 
 in the above figures is partly due to inaccuracy of the observations. 
 But waves from artificial shocks are in the broken, discontinuous, 
 superficial rocks which, lacking homogeneity, can not carry larger 
 waves at the theoretical velocity. 
 
 The Charleston earthquake was probably the first one that has 
 ever yielded a close approximation to the true velocity of the deep- 
 seated wave. This greater precision is due to the use of a standard 
 time-system over the country affected, and to the general habit of 
 accurate time-keeping. From a vast amount of sifted data. Major 
 Button determined that the Charleston earthquake had a velocity of 
 5,184 metres per second, with a possible error of plus or minus 80 
 metres. This is 190 miles per minute. Determinations by Prof. 
 Milne have given 130 miles per minute for the average velocities of 
 shocks, and 180 miles for tremors. 
 
 Character of the Earth-Wave. — In elastic solids, there are two 
 kinds of waves, with different rates of progression — ^namely, the nor- 
 mal and the transverse. The former are waves of compression, the 
 latter of distortion. The vibrations which are felt at the earth's sur- 
 face are waves which have been modified by passage through the rock 
 strata, and are very complex, consisting of both normal and transverse 
 waves with superposition of smaller vibrations on the larger (see 
 Fig. 109). Fig. 99 pictures a model (" Sekiya's wires") represent- 
 ing, by bent wire, the path of an earth-particle during an earthquake.. 
 
EARTHQUAKES. 123 
 
 The path of the particle is plotted by combining the records of the 
 seismograph (Figs. 108, 109). 
 
 Isoseismals and Coseismals. — Isoseismal lines are lines drawn 
 through points on the ground surface where the intensity of the 
 earthquake-shock is equal. Coseismal lines mark points of simulta- 
 neous arrival of the earth vibration (see Fig. 110). Very accurate 
 
 Fig. 99.— Model showing the Path of a Particle during an Earthquake (after Sekiya). 
 
 time observations are probably the most valuable data, but they are 
 rare in the absence of astronomical and seismologieal observatories, 
 and slight inaccuracies in time data lead to disproportionate errors 
 in the calculations. Intensity observations, or isoseismals, are prac- 
 tically of great value. Their advantage is that even very rough esti- 
 mates if sufficiently numerous may give fair approximations in the 
 deduced results. 
 
 Index - Circle. — This is the name given by Button to the line 
 which marks the points, on radii from the epicentrum, where the 
 surface intensity of shock diminishes with greatest rapidity. In other 
 words, it is the circular locus of maximum variation whose center is 
 the epicentrum. If far different in shape from a circle, it may be 
 called the index-circuit. In locating the index-circle, it is assumed 
 that the intensity is manifested in accordance with the law of the 
 inverse square of the distance, and that it is not materially obscured 
 by local inequalities of the ground surface. From the index-circle 
 the depth of focus is determined. The radius of the index-circle is 
 proportional to depth of focus, the latter being the product of the 
 radius multiplied by the square root of 3. The position of the 
 epicentrum need not be determined by independent evidence, as it is 
 the center of the index-circle. 
 
 As the position of the index-circle is not affected by the origi- 
 nal intensity of the shock, no absolute standard of measurement is 
 
124 IGNEOUS AGENCIES. 
 
 required. But in order to collect data relating to intensity, and to 
 determine the index-circle, some relative standard or scale of intensity 
 must be applied. No unit of intensity has been established, nor has 
 any accurate method of estimating the varying intensity been devised. 
 It is therefore necessary to employ some arbitrary scale. That of 
 Eossi-Forel ranges through ten degrees, 1 marking the faintest per- 
 ceptible vibrations, and 10, great disasters. 
 
 The application of the principle of the index-circle will be found 
 on pages 136, 137.* 
 
 ' Earthquake-Phenomena. — Earthquakes have been wrongly divided 
 into three kinds, viz., the explosive, the horizontally progressive, and 
 the vorticose. But there is only one kind of earthquake. There can 
 be no " explosive " or " vorticose " earthquakes, but simply difEer- 
 ences of movement of the surface earth-particles, wholly due to the 
 different conditions under which the waves emerge on the surface. 
 The three kinds of surface movements are, in fact, often united in 
 the same earthquake. 
 
 The most remarkable example of explosive movement is that 
 which destroyed Eiobamba in 1797. In this dreadful earthquake, the 
 shock came suddenly, like the explosion of a mine. N'ot only was the 
 earth broken up and rent in various places, but objects lying on the 
 surface of the earth were thrown violently upward; bodies of men 
 were hurled several hundred feet in the air, and afterward were found 
 across a river and on the top of a hill. In movements of this kind — 
 1. The impulse is very powerful and sudden, so as to make a high 
 but not a long wave, or, in other words, the velocity of vibration 
 or of the shock is very great; and, 2. The focus i§ not deep, so 
 that the velocity of the shock-motion does not become small before 
 it reaches the surface. At Eiobamba the velocity of the shock-mo- 
 tion was still very great when the wave reached the surface. From 
 the distance bodies were thrown. Mallet supposes the velocity of 
 the shock-motion could not have been less than eighty feet per sec- 
 ond (Jukes). 
 
 The horizontally progressive movement may be regarded as the 
 ordinary type; it is in fact the spreading surface-wave already ex- 
 plained. If the elasticity of the earth, and therefore the velocity of 
 the waves, is the same in all directions, the surface-wave will spread 
 in concentric circles; but if the elasticity, and therefore the velocity 
 of the waves, be greater in one direction than in another, as, for 
 example, north and south than east and west, or the converse, then 
 the form of the outcrop will be elliptical. In some rare cases the 
 
 * Major Dutton's discussion of isoseismals and the Index-circle method of determin- 
 ing the depth of focuB will be found in his report on the Charleston earthquake in Ninth 
 Annual Report of the U. S. Geological Survey, 1889. 
 
EAIITHQUAKES. 
 
 125 
 
 shock seems to mn along a line. Thus progressive movements have 
 been subdivided into circular, elliptical, and linear progressive. The 
 linear progression usually follows mountain-chains, and may be theo- 
 retically explained as the passage of waves along a granitic axis, as 
 illustrated in Figs. 100, 101. 
 
 X 
 
 ill -r^M^ 
 
 V-rr* 
 
 Fig. 100.— Diagram illustrating Linear Earthquakes. 
 
 '^ i c 
 
 FiQ. 101. 
 
 In vorticose movement the ground is twisted or whirled round 
 and back, or sometimes ruptured and left in a twisted condition. 
 The most conspicuous examples of this kind of motion occurred in 
 the earthquake of Eiobamba and in the great Calabrian earthquake 
 of 1783. In this latter earthquake the blocks of stone forming obe- 
 lisks were twisted one on another j the earth was broken and twisted, 
 so that straight rows of trees were left in interrupted zigzags. Phe- 
 nomena similar to some of these were observed also in the California 
 earthquake of 1868. Chimney-tops were separated at their Junction 
 with roofs, and twisted around without overthrow; wardrobes and 
 
 \ 1 
 
 Fio. 103. — Diagram of Pier driven down- 
 ward by the Charleston Earthquake. 
 
 Fig. 103.— Fissnre and Fault produced by Earth- 
 quake in Arizona. 
 
 bureaus turned about at right angles to the wall, or even with their 
 faces to the wall. 
 
 Some of these effects — such as twisting of obelisks and chimney- 
 tops, and turning about of bureaus, etc. — may be explained without 
 any twisting motion of the earth at all, as merely the effects of the 
 backward-and-forward motion common to all earthquakes. 
 
126 IGNEOUS AGENCIES. 
 
 But there are other eases of undoubtedly real vorticose motion ; as, 
 for example, straight rows of trees changed into interrupted zigzags 
 by fissures and displacement. All such cases of real twisting are 
 probably explicable on the principle of concurrence and interference 
 of waves. 
 
 Minor Phenomena. — These are all explained by application of the 
 wave-theory. 
 
 1. Sounds. — These are usually described as a hollow rumhling, 
 rolling, or grinding; sometimes as clashing, thundering, or cannona- 
 ding. They are probably produced by rupture of the earth at the 
 origin, and by the passage of the wave through the imperfectly elastic 
 rocky medium breaking the medium and grinding the brohen parts 
 together. But what is especially noteworthy is, that these sounds 
 precede as well as accompany the shocks. In every earthquake there 
 are transmitted waves of every variety of size. The great waves are 
 sensible as shocks, or Jars, or tremors ; the very small waves, too small 
 to be appreciated as tremors, are heard as sounds. But, as already 
 explained, these last run with greater velocity in an imperfectly 
 coherent medium like the earth, and therefore arrive sooner than the 
 great waves, which constitute the shock. The same was observed in 
 Mallet's experiments. 
 
 3. Motion. — As to direction, the observed motion is sometimes 
 vertically up and down, sometimes horizontally back and forth, and 
 sometimes oblique to the' horizon. Almost always a roching motion, 
 i. 6., a leaning of tall objects first in'one direction and then 'in the 
 other, is observed. As to violence or velocity of motion, this is some- 
 times so great that objects are thrown into the air, and whole cities 
 are shaken down as if they were a mere collection of card-houses; 
 while in other cases only a slow swinging, or heaving, or gentle rock- 
 ing, is observed.* 
 
 If we confine our attention to the principal or normal wave, the 
 difference in direction is wholly due to the position of the observer. 
 At the epicentrum it is of course vertical, and thence it becomes 
 more and more oblique, until at great distances it is usually horizontal. 
 The violence of the shock or velocity of ground-motion depends 
 partly upon the violence of the original concussion, and partly 
 on the distance from the origin or focus. This velocity of the 
 ground-motion must not be confounded with the velocity of the 
 wave already discussed. The latter is the velocity of transit from 
 place to place; the former is the velocity of oscillation up and down, 
 or back and forth. The velocity of oscillation has no relation to the 
 
 * The physicist would now use the term acceleration in place of the expression " vio-. 
 lence " or " velocity of ground motion.'' 
 
EARTHQUAKES. 
 
 127 
 
 velocity of transit, but depends only on the height of, the wave, which 
 constantly diniinishes and becomes finally very small, though the 
 velocity of trai;sit remains the same, and always enormously great. 
 The rocking-motion is also easily explained. A series of waves, some- 
 what similar in form to water-waves (though differing in nature), 
 actually passes beneath the observer. Of course, when an object is on 
 the /row^sZope, it will lean in the direction of transit; and when on 
 the hind-slope, in the contrary direction. 
 
 3. Circle of Principal Destruction. — In some earthquakes a certain 
 zone at considerable distance from the point of first emergence (epicen- 
 trum) has been observed, within which the destruction by overthrow is 
 very great, and beyond which it speedily diminishes. This has been 
 called the circle of principal destruction or overthrow. It is thus ex- 
 plained: The overthrow of buildings depends not so much on the 
 amount of oscillation as upon the horizontal element of the oscillation. 
 E"ow, the whole amount of oscillation is greatest at the point of first 
 emergence, and decreases outward ; but the horizontal element is 
 nothing at a, and increases as the cosine of the angle of emergence. 
 Therefore, under the influence of these two conditions, one decreasing 
 the whole oscillation, 
 
 the other increasing **■' tJ 
 
 the horizontal element 
 of that oscillation, it is 
 evident that there will 
 be a point on every 
 side, or, in other words, 
 a circle, where the bori- 
 zontal element will be 
 a maximum. This is 
 shown in Fig. 104, in 
 which a a', i h', c c', 
 etc., are the decreasing oscillation, and b b", c c", are the horizontal ele- 
 ment. This reaches a maximum at c. It has been found by mathemati- 
 cal calculation, based upon the supposition that the whole oscillation 
 varies inversely as the square of the distance from JT, that the hori- 
 zontal element will be a maximum when the angle of emergence is 54° 
 44'. By determining by observation the circle of principal disturbance, 
 it is easy to calculate the depth a X of the .focus, for it will be the 
 apex of a cone whose base is that circle, and whose apical angle is 70° 
 32'.* 
 
 4. Shocks more severely felt in Mines. — It has been sometimes ob- 
 served that shocks are distinctly felt in mines which are insensible at 
 
 Fig. 104.— Diagram illustrating Circle of Principal Disturbance. 
 
 * Mallet's Keport for 1858, p. 101. 
 10 
 
 ax : ac :: 'v/2 ; 
 ax — ao X 1'41. 
 
 1 : : 1.41 : 1. 
 
128 
 
 IGNEOUS AGENCIES. 
 
 Fig. 105.— Shocks in Mines. 
 
 the surface. This is probably explained as follows : Let 8 S (Fig. 105) 
 be the surface of the ground : and let a i represent hard, elastic strata, 
 covered with loose, inelastic materials, c c. Now, if a series of waves 
 
 come in the direction 
 of the arrows d d, and, 
 passing through a b 
 on their way to the 
 surface, strike upon 
 the lower surface of 
 c c, a portion would 
 reach the surface by 
 refraction, but a por- 
 tion would be reflect- 
 ed and return into a h, concurring and interfering with the advancing 
 waves, and producing great commotion in these strata. 
 
 5. Shocks less severe in Mines. — This case is probably more com- 
 mon than the last. It was notably the case in the earthquake of 1872 
 in Inyo County, California. While the surface was severely shaken, 
 many houses destroyed, and large fissures formed in the earth, the 
 miners, several hundred feet below the surface in the hard rock, 
 scarcely felt it at all. This is probably, at least partly, explained as 
 follows : As long as the wave travels within the earth, motion of the 
 particles is restrained by the work of elastic compression ; but, as soon 
 as the surface is reached, the motion becomes free, and the velocity of 
 shock is far greater than before, often so great as to throw bodies high 
 in the air. The phenomenon is exactly like that in the familiar ex- 
 periment of the ivory balls : when the first in the series is struck, an 
 elastic wave of compression passes through all, but only the last one 
 moves. 
 
 6. Bridges. — In a manner somewhat similar are to be accounted 
 for the phenomena of bridges. In the earthquake regions of South 
 America there are 
 
 certain favored spots, 
 often of small ex- 
 tent, which are par- 
 tially exempt from 
 the shocks which in- 
 fest the surrounding 
 country. The earth- 
 quake-wave seems to 
 pass under them as under a bridge, to reappear again on the other 
 side. The mere inspection of Fig. 106 will explain the probable cause 
 of this exemption, viz. : reflection from the under surface of an isolated 
 mass of soft, inelastic strata, c c. 
 
 Fig. 106. 
 
EARTHQUAKES ORIGINATING BENEATH THE OCEAN. 129 
 
 7. Fissures. — The ground-fissures, so commonly produced by earth- 
 quakes, are sometimes of the nature of the great fissures of the crust, 
 which are the probable cause of earthquakes. Such great fissures are 
 usually wholly beneath the surface at great depth, but sometimes may 
 break through and appear on the surface. This is certainly the case 
 when decided faults occur with elevation or depression of large tracts 
 of land. But the surface-fissures so frequently described, small in 
 size, very numerous, and running in all directions, have an entirely 
 different origin. They are evidently produced by the shattering of the 
 softer, more incoherent, and inelastic surface-soil, and by the passage 
 of the earth-wave. Even the more elastic underlying rock is broken 
 by the same cause, but to a much less extent. 
 
 Earthquakes originating beneath the Ocean. 
 
 We have thus far spoken of earthquakes originating beneath the 
 land-surface. But three fourths of the earth-surface is covered by the 
 sea ; and we have already seen that other forms of igneous agency are 
 most abundant in and about the sea. As we might expect, therefore, the 
 greater number of earthquake-shocks (eighty-four per cent) occur be- 
 neath the sea-bed. It is worthy of remark that this is especially true of 
 the sea-hed immediately bordering the continents, and still more espe- 
 cially if the slope of bottom is steep. In such, the phenomena already 
 described are often complicated by the addition of the " Great Sea- 
 Wave.'' 
 
 Suppose, then, an earthquake-shock to occur beneath the sea-bed ; 
 the following waves will be formed : 1. As before, a series of elastic 
 spherical waves will spread from the focus, until they emerge on the 
 sea-bed. 2. As before, a series of circular surface-waves, the outcrop 
 of the spherical waves, will spread on the sea-bottom until they reach 
 the nearest shore, and perhaps produce destructive effects there. 3. 
 On the back of this submarine earth- wave is carried a corresponding 
 sea-wave. This is called the "forced sea-wave," since it is not a free 
 wave, but a forced accompaniment of the ground-wave beneath. It 
 reaches the shore at the same time as the earth-wave. It is of little 
 importance. 4. In addition to all these is formed the great sea-wave ; 
 or tidal wave, as it is sometimes, but wrongly, called. 
 
 Great Sea -Wave.— This common and often very destructive accom- 
 paniment of earthquakes is formed as follows : The sudden upheaval 
 of the sea-bed lifts the whole mass of superincumbent water to an 
 equal extent, forming a huge mound. This movement of the sea-bed 
 is not due to the mere emergence of the earth-wave, for this is far too 
 small to produce such effects ; but is due to bodily movement of the 
 earth-crust by displacement of a fissure which, as we have seen, is the 
 usual cause of earthquakes. The falling again of this water as far 
 
130 IGNEOUS AGENCIES. 
 
 below as it was before above its natural level generates a circular wave 
 of gravity, which spreads like other water-wares, maintaining its 
 original wave-length, but gradually diminishing its wave-height until 
 it becomes insensible. Usually, a series of such waves is formed. 
 These waves are often 100 to 200 miles across their base (wave-length) 
 and fifty to sixty feet high at their origin. Their destructive effects 
 may be inferred from the enormous quantity of water they contain. In 
 the open sea they create no current, and are not even perceived ; but, 
 when they touch bottom near shore, they pile up and rush forward as 
 great breakers fifty or sixty feet high, sweeping away everything in 
 their course. 
 
 Being waves of gravity, their velocity, though very great on account 
 of their size, is far less than that of the earth-waves, and they reach 
 the neighboring shore, therefore, some time later, and often complete 
 the destruction commenced by the earth-waves. 
 
 Examples of the Sea-Wave. — In the great earthquake which de- 
 stroyed Lisbon in 1755, the epicentrum was on the sea-bed fifty or 
 more miles off the coast of Portugal. From this point the surface 
 earth-waves spread along the sea-bottom until they reached shore. 
 It was the arrival of these waves which destroyed Lisbon. About a 
 half-hour later, when all had become quiet, several great sea-waves, one 
 of them sixty feet high, came rushing in, deluging the whole coast and 
 completing the destruction commenced by the earth-waves. This 
 wave was thirty feet high at Cadiz, eighteen feet at Madeira, and five 
 feet on the coast of Ireland. It was sensible on the coast of Norway, 
 and even on the coast of the West Indies, after having crossed the 
 whole breadth of the Atlantic. 
 
 In 1854 a great earthquake shook the coast of Japan. Its focus 
 was evidently beneath the sea-bed some distance off the coast, for, in 
 about a half-hour, a series of water-waves thirty feet high rushed upon 
 shore and completely swept away the town of Simoda. Prom the 
 same center the waves, of course, spread in the contrary direction, 
 traversed the whole breadth of the Pacific, and in about twelve and a 
 quarter hours struck on the coast of California at San Francisco, and 
 swept down the coast to San Diego. These waves were thirty feet 
 high at Simoda, fifteen feet high at Peel's Island, about 1,000 miles 
 off the coast of Japan, 0-65 feet, or eight inches, high at San Francisco, 
 and six inches at San Diego.* 
 
 On the 13th of August, 1868, a great earthquake desolated the 
 coast of Peru. Its focus was evidently but a little way off shore, lor m 
 less than a half-hour a series of water-waves fifty or sixty feet high 
 rushed in and greatly increased the devastation commenced by the 
 
 ' Report of Coast Survey for 1862. 
 
EARTHQUAKES ORIGINATING BENEATH THE OCEAN. 
 
 131 
 
 earth-waves. These waves reached Coquimbo, 800 miles distant, in 
 three hours; Honolulu, Sandwich Islands, 5,580 miles, in twelve 
 hours ; the Japan coast, over 10,000 miles, the next day. They were 
 also observed on the coast of California, Oregon, and Alaska, over 
 G,000 miles in one direction, and on the Australian coast, nearly 8,000 
 miles in another direction. This series of waves was distinctly sensible 
 at a distance of nearly half the circumference of the earth. Had it 
 not been for the barrier of the South American Continent, it would 
 have encircled the globe.* 
 
 Many other earthquake sea- waves have been observed and recorded 
 by tidal gauges, especially those of the Iquique earthquake of May, 
 1877, and the waves caused by the great eruption of Krakatoa, August, 
 1883. In Fig. 107 we give the record of the Iquique earthquake taken 
 by the tidal gauge at San Francisco. 
 
 Pio 107 —Record of Waves of the Iquique Earthquake (after Milne). The cross, x , marks the time 
 
 of occurrence at Iquique. 
 
 There are several points in the above description which we must 
 very briefly explain : 
 
 1. The velocity of these great sea-waves, though less than that of 
 the earth-waves, is still very great in comparison with ordinary sea- 
 waves. The waves of the Japan earthquake crossed the Pacific to San 
 Francisco, a distance of 4,535 miles, in a little more than twelve hours, 
 and therefore at a rate of 370 miles per hour, or over six miles per 
 minute. The waves of the South American earthquake of 1868 ran to 
 the Hawaiian Islands at a rate of 454 miles per hour. This amazing 
 velocity is the result of the great size of these waves ; for the velocity 
 of water-waves varies as the square root of the wave-length (v a. |/l). 
 
 * Report of Coast Surrey for 18Q9. 
 
132 IGNEOUS AGENCIES. 
 
 2. The size of these great waves is determined by multiplying the 
 time of oscillation by the velocity, on the well-known principle that 
 every kind of wave runs its own length during the time of one com- 
 plete oscillation. The velocity is obtained by observing the time at 
 diiferent points. The time of oscillation is determined by means of 
 tidal gauges. The tidal gauges established by the Coast Survey on the 
 Pacific coast showed that the time of oscillation of the larger waves of 
 the Japan earthquake was about thirty-three (thirty-one to thirty-five) 
 minutes. This would give a wave-length of a little over 200 miles. 
 It is probable that the wave-length in the case of the South American 
 earthquake was at least equally great. , 
 
 3. The distance to which the sea-waves run is far greater than that 
 of the earth- waves. The former is distinctly sensible for 10,000 miles ; 
 the latter very rarely more than a few hundreds. There are two 
 reasons for this: 1. All waves diminish in oscillation (wave-height) as 
 they spread from the origin, because the quantity of matter successively 
 involved in the oscillation constantly increases. But in the one case 
 the matter involved lies in the circumference of a circle ; in the other, 
 in the surface of a sphere ; therefore, the one increases as the distance, 
 the other as the square of the distance. Therefore, the decrease of 
 oscillation (height of wave) is far less rapid for water-waves than for 
 elastic spherical waves. 3. A still more effective reason is this : Water- 
 waves run in a perfectly homogeneous medium, and therefore diminish 
 only according to the regular law just stated ; but the earth-waves run 
 in an heterogeneous, imperfectly elastic, and imperfectly coherent 
 medium, and therefore they are rapidly quenched and dissipated by 
 repeated refractions and reflections, and by repeated fractures of the 
 medium and thus changed into other forms of force, as heat, elec- 
 tricity, etc. Were it not for this, the destructive effects of earthquakes 
 would be far more extensive. 
 
 4. We have said the wave-length remains unchanged. This length, 
 therefore, represents the diameter of the original water-mound, and 
 therefore of the original sea-bottom upheaval. In the Japan earth- 
 quake this was 200 miles across. This shows the grand scale upon 
 which earthquake-movements take place. 
 
 5. Earthquake sea-waves differ from all other sea-waves in that 
 their great size makes them drag bottom even in open deep sea. In 
 their case, therefore, the velocity depends not only on the wave-length, 
 but also on the depth of the sea. Knowing the size (wave-length) of 
 these waves, and therefore what ought to be their /ree velocity, and also 
 knowing their actual velocity by observation, the difference gives the 
 retardation by dragging ; and by the retardation may be calculated 
 the mean depth of the ocean traversed. In this way it has been de- 
 termined that the mean depth of the Pacific between Japan and San 
 
DEPTH OF EARTHQUAKE-FOCUS. 
 
 133 
 
 Francisco is 13,000 feet, and between Peru and Honolulu, Sandwich 
 Islands, 18,500 feet. The great importance of such results is obvious. 
 
 Depth of Earthquake- Focus. 
 
 The great obscurity which hangs about the subject of the in.terior 
 condition of the earth and the ultimate cause of igneous agencies 
 renders any positive knowledge on these subjects of peculiar interest. 
 There can be little doubt that the phenomena of earth quake- waves, 
 their form, their velocity, their angle of emergence, etc., if once 
 thoroughly understood, would be a most delicate index of this con- 
 dition, and a powerful means of solving many problems which now 
 seem beyond the reach of science. Among problems of this kind none 
 is more important, and at the same time more capable of solution, than 
 the depth of the 
 origin of earth- 
 quakes, and there- 
 fore presumably of 
 volcanoes. 
 
 Seismographs.— 
 The most direct 
 way of determining 
 the depth of an 
 earthquake-focus is 
 by means of well- 
 constructed seismo- 
 graphs. These are 
 instruments for re- 
 cording earthquake- 
 phenomena. They 
 are of infinite varie- 
 ty of forms, depend- 
 ing partly upon the 
 facts desired to be 
 recorded, and partly 
 upon the mode of 
 record. As exam- 
 ples we will mention 
 only two : 
 
 An excellent in- 
 strument for recording slight tremors is one invented and used by 
 Prof. Palmieri, of the'Vesuvian Observatory. It consists of a tele- 
 graphic apparatus with the usual paper-slip and stile.' The paper- 
 slip, accurately divided into hours, minutes, and seconds, travels at 
 a uniform rate by means of clock-work. The battery-circuit is closed 
 
 FiQ 108 — Ewine's Seismograph : a and 6, horizontally oscillating 
 Dendnlum: c. vertically oscillating pendulum; d, driving clock; 
 «, time-recording clock. (Taken from a photograph of one at the 
 University ol California.) 
 
134 
 
 IGNEOUS AGENCIES. 
 
 and opened, and the recording stile worked by the shaking of a metal- 
 lic bob, hung by a delicate spiral spring above a mercury-cup; the 
 shaking of the bob being determined by the tremor of the earth. 
 Such an instrument records the exact mom,ent of occurrence of earth- 
 quake-shocks, however slight; also, the moment of passage of every 
 wave and its time of oscillation;, and if there be more than one such 
 instrument, the moment of occurrence at different places gives the 
 velocity of the surface- wave v'. 
 
 If we desire to record not only the time but also the character of 
 the earth-movement, then a different kind of seismograph is necessary. 
 The principle of all these is the principle of a pendulum. If we have 
 a pendulum with a heavy bob swinging freely, when an earthquake 
 arrives, the bob will stand still, while the earth moves beneath it. 
 This relative movement of the pendulum may be recorded by suitable 
 device. But an ordinary /reeZt/ swinging pendulum moves often too 
 largely, and continues its movement after the cessation of the cause. 
 What we want is a pendulum which will stand indifferently in any 
 position (astatic). One of the best forms of instrument yet devised is 
 that of Prof. Ewing (Fig. 108). It consists essentially of three pendu- 
 lums swinging in the manner of a bracket or a gate, and placed in 
 
 three rectangular planes: (1) vertical, 
 north and south, a ; (3) vertical, east 
 and west, &; and (3) horizontal, c. The 
 horizontal one is retained in position by 
 sensitive spiral springs. Stiles are fixed 
 to these pendulums in such wise as to 
 record on a circular smoked glass plate 
 rotating in a horizontal plane. No. 1 
 records the east-and-west movement. No. 
 2 the north-and-south movement, and 
 No. 3 the up-and-down movement. A 
 clock is set agoing by the arrival of the 
 earth- wave, and afterward marks seconds 
 on the revolving smoked glass disk. Pig. 
 109 represents a portion of such record. 
 These three records may be combined so 
 as to show the actual amount and direc- 
 tion of the earth-movement (Fig. 99, p. 
 121). 
 
 The important facts recorded by this 
 instrument are : 1. The instant of tran- 
 sit ; 2. The direction of transit ; 3. The direction of oscillation, or 
 angle of emergence; 4. The arnount of oscillation. From these ele- 
 ments (if we have several seismographs scattered about the country) 
 
 Fia. 109.— Record of a Ewing's Seismo- 
 graph: a, east-and-west motion; *, 
 north-and-south motion; c, up-and- 
 down motion (after Sekiya). 
 
DEPTH OF EAKTHQUAKE-POCUS. 
 
 135 
 
 may be calculated : 1. The velocity of transit ; 2. Tha position of the 
 focus J 3. Perhaps the form of the focus, whether point or fissure ; 4. 
 The force of the original concussion. The most important of these 
 are the position and depth of the focus. 
 
 The Detennination of the Epicentrum. — A good seismograph, or a 
 number of these, will give the direction of transit of the surface- wave. 
 If in this way, or even by rougher methods, we get a number of these 
 
 surface-lines of transit, by 
 following these back we get 
 the epicentrum at their inter- 
 section. This is Mallet's 
 method. Or if, by means of 
 many seismographs giving 
 time of transit, or even by 
 observatories or stations of 
 any kind with accurate clocks, 
 we get several points of simul- 
 taneous arrival of the wave, 
 then by drawing a curve 
 through these points we have 
 a coseismal curve. A perpen- 
 dicular drawn from the mid- 
 dle point of the line joining 
 any two of these points will pass through the epicentrum, and two 
 such perpendiculars would determine its position. Fig. 110 rep- 
 resents coseismal curves, and h, c, d, three points on the curve; a 
 is the epicentriim. This is Seebach's method, which might give 
 good results if the curves were regular, but generally it is not prac- 
 ticable. 
 
 Determination of the Focus. — Mallet's Method. — The normal wave 
 is a wave of longitudinal oscillation. The direction of oscillation, 
 therefore, is the same as the direction of transmission (wave-path). 
 
 Fig. 110. — Coseismal Lines. 
 
 WtltllttlnjiM^^ 
 
 H#^W||||^^ 
 
 Fig. 111.— Railway Track bent by Charleston Earthquake. 
 
 which is the radius of the agitated sphere. If, therefore, the direction 
 of the ground-motion be followed into the earth,, it carries us back 
 along the wave-path to its origin, the focus. Two such wave-paths 
 
136 
 
 IGNEOUS AGENCIES. 
 
 by their intersection would determine its position. As the direction 
 of the normal wave can not be ascertained the method is impracticable. 
 Seebach's Method. — Mallet's experiments (page 119) were under- 
 taken in the hope that the relation of the velocities of the surface and 
 spherical waves would at once, by simple calculation, give the depth of 
 
 v' 
 the focus, for by Hopkins's law sec. U= —. It would do so if v were 
 
 constant. But this is not true, and thus the method is valueless. But 
 although it is impossible thus to find the depth directly, it may be 
 found indirectly, as Seebach has shown, by the rate of decrease of the 
 velocity of the surface-wave v', the rate being slower for deep 
 earthquakes in proportion to the depth of their centrums. The rate 
 of decrease by Hopkins's law follows the law of a hyperbolic curve, as 
 shown in Fig 112, in which equal times are plotted on vertical, and 
 
 FiQ. 112.— Diagram illustrating Hopkins's Law and Seebach's Method of Determining Focus of 
 
 Eartliquake. 
 
 spaces passed over in equal times on horizontal co-ordinates. In this 
 hyperbolic curve horizontality, as at a, represents infinite velocity, and 
 the velocity decreases as the angle increases up to 45°, when the velocity . 
 reaches its limit of equality with the velocity of the spherical wave v. 
 The asymptote of the hyperbola passes through the foci^s of the earth- 
 quake. This method requires very accurate time data. 
 
 Button's Method. — There is still another method, used by Major 
 Dutton in his admirable discussion of the Charleston earthquake, and 
 claimed by him as the most accurate of all. The intensity of the 
 
DEPTH OF EARTHQUAKE-FOCUS. 
 
 137 
 
 shock decreases from the epicentrum according to a certain law. The 
 distance from the epicentrum of the place of most rapid decrease 
 depends on the depth of the focus. If s s (Fig. 113) represent the sur- 
 
 S-r- 
 
 Fio. 113.— Diagram illustrating Button's Method of Determining Focus of Earthquake. 
 
 face of the earth, x the centrum, and a the epicentrum of an earth- 
 quake, then the curve i i' i" will represent the law of variation of the in- 
 tensity of the shock. Its height, as is seen, is greatest at the epicen- 
 trum and decreases in all directions. But at a certain distance, d, just 
 where the curvature changes from convexity to concavity, the descent is 
 steepest — i. e., the decrease is most rapid. This distance ad : the 
 depth a X : : 1 : V^: : 1 : 1-73. If the distance, ad, is known we 
 easily find the depth, ax (see pp. 120, 131). 
 
 We have assumed the earth-waves as normal We are justified in 
 so doing, because this is the most decided wave, and soon outruns the 
 transverse wave. 
 
 Although seismometers, such as we have described, are necessary 
 for accurate results from few observations, yet by multiplying the ob- 
 servations, even by rough methods, approximative results may be ob- 
 tained. We will mention several examples of determinations by these 
 various methods. 
 
 In 1857 a terrible earthquake shook the territory of Naples, de- 
 stroying many towns and villages and killing about 10,000 people. The 
 scene of destruction was visited soon after by Mr. Mallet. By careful 
 examination of overthrown objects, many lines of transit of the surface- 
 wave were determined, which, protracted, carried him with consider- 
 able certainty to the epicentrum ; similarly many lines of emergence, 
 or paths of the spherical wave, protracted back, conducted to the focus. 
 
138 - IGNEOUS AGfENCIBS. 
 
 This focus was determined to be not a point, but a fissure, nine miles 
 long and through three miles of solid rock. The center of this rent 
 was about six miles beneath the surface.* By somewhat similar 
 methods the focus of the Japan earthquake of February 33, 1880, 
 was found by Milne to be only three to five miles deep.f By his new 
 method, viz., the law of decrease of intensity of the shock-motion, the 
 focus of the Charleston earthquake of August, 1886, was found by 
 Captain Button to be about twelve miles deep. J All of these earth- 
 quakes also seem to have originated in a fissure. 
 
 In 1874 a not very severe earthquake shook central Germany. It 
 has been thoroughly investigated by Seebach. The epicentrum was 
 determined with great precision by erecting perpendiculars to the 
 bisected chords of the coseismal curves. The focus was determined by 
 his method as a rent through four miles of rock, the center of the 
 rent being nine or ten miles in depth.* 
 
 The velocity of transit of the waves of the Ifaples earthquake was 
 860 feet per second, or between nine and ten miles per minute ; that 
 of the earthquake of middle Germany was about twenty-eight miles per 
 minute. The velocity of transit in the case of the Charleston earth- 
 quake is estimated as high as one hundred and ninety miles per 
 minute. 
 
 All these methods for depth assume Hopkins's law, and are there- 
 fore vitiated by the important modifications introduced by Schmidt. 
 By Schmidt's law the varying velocity of the surface-wave must be 
 represented not by a simple hyperbolic curve, as Seebach supposes 
 (Pig. 113), but by a double curve, as shown in the upper part of Fig. 
 98. We have already seen (page 119) that the velocity of the surface- 
 wave is indeed infinite at the epicentrum and then decreases, but it 
 soon reaches a minimum at d, and then increases again without limit. 
 Therefore the curve representing it is at first horizontal, then rises 
 gradually to a maximum inclination, and again more and more ap- 
 proaches horizontality. 
 
 It is evident, then, that our knowledge is not yet sufficient to de- 
 termine the depth of the centrum with any high degree of accuracy. 
 With more perfect knowledge, however, we may hope not only to 
 determine this, but even to sound the interior of the earth, gauge its 
 density, and determine its general constitution. 
 
 Meet of the Meon on Earthquake-Occurrence. — By an extensive 
 comparison of the times of occurrence of several thousand earthquakes 
 
 * Mallet, Principles of Seismology. 
 
 f Seismological Society of Japan, vol. i, Part II, p. 1. 
 X Science, vol. ix, p. 489, IBS'?. 
 
 * Seebach, Das Mittel Deutsche Erdbeben. 
 
DEPTH OF •EARTHQUAKE-FOCUS. ]39 
 
 with the positions of the moon, Alexis Perrey has made out with some 
 probability the following laws : 1. Earthquakes are a little more fre- 
 quent when the moon is on the meridian than when she is on the 
 horizon. 3. They are a little more frequent at new and full moon 
 (svzygies) than at half-moon (quadratures). 3. They are a little more 
 frequent when the moon is nearest the earth (perigee) than when she 
 is farthest off (apogee). Now, if these laws are really true, it would 
 seem that there is a slight tendency for earthquakes to follow the law 
 of tides : for the first law gives the time of flood-tide, aud the second 
 and third the times of highest flood-tide. It would seem, therefore, 
 that the attraction of the sun and moon has a perceptible effect in de- 
 termining the time of occurrence of earthquakes. Many geologists 
 regard these laws, if established, as conclusive proof of the general 
 fluid condition of the earth beneath a comparatively thin crust. This 
 interior liquid they suppose to be influenced by the tide-generating 
 forces of the sun and moon ; but, if this were true, the effect ought to 
 be far greater than we find it — i. e., the shock would occur always at 
 high tide. Whatever be the interior condition of the earth, the effect 
 of the moon on the meridian would be to assist, and on the horizon 
 to repress, any force whatsoever tending to break up the crust of the 
 earth and to produce an earthquake. 
 
 Relation of Earthquake- Occurrence to Seasons and Atmospheric 
 Conditions — By extensive comparison of earthquake-occurrence with 
 the seasons, it has been shown that they are a trifle more frequent in 
 winter than in summer. Constructing a curve representing the annual 
 variation of earthquake intensity, this curve rises to its maximum in 
 January and sinks to its minimum in July. But the difference is 
 small. 
 
 Prof. Knott has recently suggested what seems a possible expla- 
 nation of this, at least for Japan, where this relation is quite marked. 
 During winter, there is high barometer— i. e., great atmospheric pressure 
 over the whole of Northern Asia (Siberia), and low barometer over 
 equatorial Pacific. In addition to this, the heavy winter snow-fall 
 greatly increases the pressure over Siberia. In summer, the condition 
 of things is reversed— the barometer is low and the snow is removed 
 over Siberia, and the barometer is high over mid-Pacific. This 
 change of excess of pressure from a large land-area to a large ocean- 
 area back and forth, must tend to fracture the earth-crust, or to pro- 
 duce readjustment of previous fractures, along their dividing line, i. e., 
 along the margin of the sea-basin. This is known to be the place of 
 origin of most of the Japanese earthquakes. This would take place 
 mainly in winter, if the tendency of the earth-forces producing earth- 
 quakes were to produce readjustment by subsidence of land or elevation 
 of sea-bottom. 
 
140 IGNEOUS AGENCIES. 
 
 There is an almost universal popular belief in earthquake-regions 
 that the occurrence is preceded by a stilly oppressive state of the air. 
 Although no scientific investigations have confirmed this impiession, 
 yet it seems quite possible and even probable that diminished atmos- 
 pheric pressure, indicated by a low state of the barometer, may act as 
 a determining cause of earthquake-occurrence, precisely as the position 
 of the moon on the meridian. A fall of one inch is equivalent to a 
 lifting of 1,000,000 tons per square mile from the surface pressure. 
 In both cases, however, we must regard these not as true causes of 
 earthquakes, but only as causes determining the moment of occurrence. 
 
 Section 4. — Gradual Elevation' and Depkession oe the 
 Earth's Ceust. 
 
 Of all the effects of igneous agencies these are by far the most im- 
 portant. Although not violent and destructive like volcanoes and 
 earthquakes, although indeed so little conspicuous as to be generally 
 unobservable except to the eye of science, yet acting not paroxysmally 
 but constantly, not in isolated spots but over wide areas and affecting 
 whole continents, their final result in modifying the crust of the earth 
 and making history is far greater than that of all other igneous agen- 
 cies put together. It is probable that the same causes which are now 
 at work gradually raising or depressing the earth's crust have during 
 geological times formed the continents and the seas. 
 
 Elevation or Depression during Earthquakes.— We have already 
 spoken (pages 114 and 115) of sudden elevations or depressions of great 
 areas of country at the time of earthquake-occurrence in Hindostan, 
 in the valley of the Mississippi Eiver, and especially of the southern 
 part of South America It is not probable, however, that much is accom- 
 plished in this paroxysmal way. These cases are referred to in order 
 to show the close connection of such sudden bodily movements, and 
 therefore presumably, also, of the slower movements about to be de- 
 scribed, with the causes and forces which produce earthquakes. 
 
 Movements not connected with Earthquakes— South America.— Be- 
 sides the sudden elevation of Chili and Patagonia by earthquakes, the 
 same countries show evidences of gradual elevation on a stupendous 
 scale. The evidences are old sea-beaches, full of shells of species now 
 living in the adjacent sea, far above the present water-level. These 
 " raised beaches " have been traced 1,180 miles on the eastern shore 
 and 3,075 miles on the western, and at different levels from 100 to 1,300 
 feet above the sea. More recently Alexander Agassiz has traced them 
 by means of corals still sticking to the rocks to the height of nearly 
 3,000 feet.* It is not probable that all this movement took place dur- 
 
 * Proceedings of the American Academy of Sciences, vol. xi, p. 287, M'lG. 
 
ELEVATION AND DEPRESSION OF EARTH'S CRUST. 
 
 141 
 
 ing the present geological epoch, but it is the more instructive on that 
 very account, since it shows the identity of geological causes with causes 
 now in operation. 
 
 Italy.— The most carefully-observed instance of gradual depression 
 and elevation is that of the coast of Naples. Fig. 114 is a map and 
 
 Fig. 115 a section of the coast of the bay of Baise, near Naples. Be- 
 tween a a a, the present coast-line, and the cliff llh, which marks 
 the position of the former coast-line, there is a nearly level plain called 
 the Starza. Now, there is perfect evidence that at one time the land 
 was depressed until the sea beat against the cliff h b, and that both the 
 depression and the re-elevation to its present condition took place since 
 the period of Koman greatness. The evidence is as follows : 
 
 • 1. There are certain shells abundant in the Mediterranean and in 
 many other seas, called Uthodomus {\i6o<i, a stone ; domus, a house), 
 from the habit of boring for themselves holes in the rocks near the 
 water-line. Such borings, often with the dead shells in them, are 
 found all along the base of the cliff b b, twenty feet above the present 
 sea-level. 2. The level plain called Starza is composed of strata con- 
 taining shells of the Mediterranean and Eoman works of art. 3. On 
 this plain, near the present sea-margin, are the ruins of a Roman tem- 
 ple dedicated to Jupiter Serapis. The floor and three of the columns 
 d of this beautiful work are still 
 almost perfect (Fig. 115). When 
 first discovered the floor and the 
 lower part of the columns were 
 covered by the materials of the 
 plain. Above the part thus cov- 
 ered the columns were bored with 
 Uthodomi to a height of twenty feet. This temple was, of course, above 
 the sea-level during the Eoman period. After that period it sank 
 
 Fio. 115. 
 
142 IGNEOXTS AGENCIES. 
 
 until the sea-level stood at s' (Pig. 115), twenty feet above the base. 
 Since that time it rose to sea-level and is now again subsiding. These 
 changes were so gradual that they were entirely insensible, and, in fact, 
 unknown to the inhabitants. The upright position of the columns 
 also shows that it could not have been produced by convulsive action. 
 
 4. Italian historians state that in 1530 the sea beat against the clifE bb. 
 
 5. Evidences of similar changes, in some cases depression and in others 
 elevation, are seen in many places along the coast of Italy, Oandia, and 
 Greece. 
 
 In all the cases thus far mentioned, but especially that of the tem- 
 ple of Serapis, the near vicinity of volcanoes (Fig. 114) suggests that 
 these effects were probably in some way connected with volcanic ac- 
 tion. But there are many instances in which no such connection can 
 be traced. 
 
 Scandinavia. -^The best-observed instance of this kind is that of the 
 coasts of Sweden. Careful observations on the coasts of the Baltic 
 and Polar Seas have proved that nearly the whole of Norway and 
 Sweden is rising slowly, and has been rising for thousands of years. 
 South of Stockholm there is no elevation, but, on the contrary, slight 
 depression ; but north of Stockholm the -^yhole coast is rising at a rate 
 which increases as we go north until it attains a maximum of five to 
 six feet per century. These observations were made under the direc- 
 tion of the Swedish Government by means of permanent marks made 
 at the sea-level, and examined from year to year. That similar 
 changes have been in progress for thousands of years, and have greatly 
 increased both the height and the extent of these countries, is proved, 
 by the fact that old sea-beaches, full of shells of species now living in 
 the neighboring seas, are found fifty to seventy miles inland, and 100, 
 300, and even 600 feet above the present sea-level on both sides of the 
 Scandinavian peninsula.* In some places, the country rock, when un- 
 covered by removing superficial deposit of beach-shells, is found stud- 
 ded with barnacles like those which mark the present shore-line (Jukes). 
 
 The rising area is about 1,000 miles long north and south, and of 
 unknown breadth. It may embrace a considerable portion of Kussia. 
 Lyell estimates the average rate as not more than two and a half feet 
 per century. At this rate, to rise 600 feet would require 24,000 years, f 
 Similar raised beaches are found in nearly all countries. We give 
 these as examples of an almost universal phenomenon, which will be 
 again more perfectly described in the chapter on the Quaternary. 
 
 Greenland. — For obvious reasons, evidences of elevation are much 
 more conspicuous than evidences of depression. One of the best ob- 
 
 * De Geer, Bulletin of the Geological Society of America, vol. iii, p. 65, 1892. 
 f Lyell'a Antiquity of Man, p. 58. 
 
ELEVATION AND DEPKESSION OF EARTH'S CEUST. I43 
 
 served instances of the latter is that of the coast of Greenland. This 
 coast is now sinking along a space of 600 miles. Ancient buildings 
 on low rock-islands have been gradually submerged, and experience 
 has taught the native Greenlander never to build his hut near the 
 water's edge. 
 
 Deltas of Large Rivers.— In the deltas of the Mississippi, the 
 Ganges, the Po, and many other large rivers, there are unmistakable 
 evidences of gradual depression. These evidences are fresh-water 
 shells, and planes of vegetation, or dirt-leds, far below the present 
 level of the sea. A section of the delta deposits of the Mississippi 
 River reveals the fact that these deposits consist of river sands and 
 clays, s cl, (Fig. 116), cont&ming fresh-water sAeZfe, with now and then 
 an intercalated stratum of 
 marine origin, I, containing 
 marine shells, and at uncer- 
 tain intervals distinct lines 
 of turf or vegetable soil,g' g,", 
 each with the stumps and 
 roots of cypress-trees as they 
 originally grew. Each one 
 of these turf-lines is a sub- 
 merged forest-ground, except 
 
 the uppermost, which is the fio. ne. 
 
 present forest-ground. Pre- 
 cisely similar"phenomena have been observed in other large deltas. The 
 deltas of the Ganges and the Po have been penetrated more than 400 
 feet without reaching bottom. In both the deposit is made up of fresh- 
 water strata alternating with dirt-beds or forest-grounds. These 
 facts are of great importance in geology, and will be again referred 
 to in the following pages (see pages 147-150, 387-393). 
 
 Southern Atlantic States. — Evidence of a similar kind proves that 
 a large portion of the coasts of our Southern Atlantic States is slowly 
 subsiding at the present time, though there are also evidences, in the 
 form of raised beaches, of elevation immediately preceding the present 
 subsidence. The evidences of subsidence are most conspicuous along 
 the coast of South Carolina and Georgia, where cypress-stumps may be 
 seen in position below the present tide-level. The New Jersey coast 
 is sinking at the rate of two feet a century. Past subsidence has 
 drowned the ancient' river valleys, producing the estuaries of the 
 Atlantic seaboard (see Fig. 22). The drowned channel of the Hud- 
 son extends out -under the ocean for 100 miles beyond Sandy Hook, 
 and the broad tidal flats near New York are peat-marshes of great 
 depth that have accumulated at sea-level. 
 
 These facts seem to point to the conclusion that subsidence is 
 11 
 
144 IGNEOUS AGENCIES. 
 
 going on in nearly all places where large deposits of sediment are 
 accumulating. 
 
 Pacific Ocean. — But by far the grandest example of subsidence 
 known is that which has been going on for thousands, probably hun- 
 dreds of thousands, of years, and is still going on in the mid-Pacific 
 Ocean. The subsiding area is situated under the equator, and is 
 about 6,000 miles long by about 3,000 to 3,000 miles wide. The evi- 
 dence of the subsidence and its rate is entirely derived from the study 
 of coral-reefs in this region. The further discussion of the subject 
 will be deferred until we take up the coral-reefs. 
 
 Continents. — These examples are taken from the vicinity of coast- 
 lines, the sea-level being used as datum. In the interior of conti- 
 nents, and in the midst of the sea where there are no islands, this 
 means of detecting changes fails us, yet it is precisely there, i. e., in 
 the middle of the rising or subsiding area, that the. changes are prob- 
 ably the greatest. In the case of continents, however, we have two 
 evidences of crust-movements. One is the behavior of rivers. As 
 explained on page 33, rivers in a rising area are revived and rapidly 
 deepen their channels, while in a subsiding area they fill their beds 
 and flow at higher levels. From this fact we know that the plateau 
 and Sierra regions have greatly risen in comparatively recent time, 
 and are still rising. Another test is the deformation of water planes. 
 Good examples are found in the basins of the Great Lakes, where the 
 high beaches of the glacial lakes (see p. 580) have lost their original 
 horizontality and now rise toward the northeast. The changes of 
 level of the present Great Lakes with reference to their north and 
 south shores prove that tilting is still going on. Following the re- 
 moval of the glacier, Ontario was an arm of the sea, and the Thou- 
 sand Islands have been raised about 300 feet in post-glacial time. 
 Apparently the Laurentian area is in the zone of canting, on the 
 southern side of a rising area. 
 
 The reader will now be prepared to appreciate the proofs of 
 erustal movements in ancient geologic time. One of the most evi- 
 dent is the great thickness of shallow-water sediments (sandstones, 
 shales, and limestones) over the greater portions of all the continents, 
 which represent eras of slow subsidence; and the great breaks or 
 unconformities between series of strata, which represent eras of uplift 
 and atmospheric erosion. 
 
 Diastrophism. — The forces which produce movements of the 
 earth's surface are called diastropMc. These are of two classes. The 
 movements which involve broad, or continental, areas are termed 
 epeirogenic (Greek epeiros, continent), while those which have to do 
 with the uplift and crushing of belts of land, producing mountain- 
 ranges, are called orogenic (Greek oroSj, mountain). 
 
THEORIES OF ELEVATION AND DEPRESSION. 145 
 
 Theories of Elevation and Depression. 
 
 It is evident that observation only determines changes of relative 
 position of sea and land. The popular mind naturally attributes them 
 to the rise and fall of the sea, as the more unstable element. But, 
 by the principle of hydrostatic level, it is clearly impossible that the 
 'ocean should rise or fall permanently at one place without being 
 similarly affected everywhere. It is certain, therefore, that the 
 changes we have described above, being in different directions in dif- 
 ferent places, must be due to movements of the solid crust. Neverthe- 
 less, it is also true that any increase in the height and extent of the 
 whole amount of land on the globe must be attended with a cprre- 
 sponding depression of the sea-bottoms, and therefore an actual sub- 
 sidence of the sea-level everywhere. Hence, if it be true, as is gener- 
 ally believed, that the continents have been, on the whole, increasing 
 in extent and in height, in the course of geological history, then it is 
 true also that the seas have been subsiding, and that therefore the 
 relative changes are the sum of these two. 
 
 Admitting, however, that the actual increase of land at the present 
 time is imperceptible, or at least very small in comparison with the 
 oscillatory movements described above, we may look upon the sea-level 
 as fixed ;'ihis statement being sufHciently correct when regarding the 
 subject from the physical point of view, though untenable when re- 
 garded from the geological point of view. Admitting, then, the fixed- 
 ness of the sea-level, what are the causes of the gradual movements of 
 the solid crust? 
 
 Babbage's Theory. — Babbage believed that, in the vicinity of volca- 
 noes, the rise and fall of ground were due to the expansion and eon- 
 traction of rocks by heating and cooling. The re-elevation of the 
 temple of Serapis occurred apparently soon after the eruption which 
 formed Monte Nuovo (Fig. 114). It is not improbable that this re- 
 elevation was the result of the heating and vertical expansion of the 
 rocks to great depth, caused by the eruption of the interior heat at 
 this point. A very small elevation of temperature of rocks several 
 miles thick would be sufficient to produce a vertical expansion of 
 twenty feet. 
 
 Herschel's Theory. — Sir John Herschel assumes, as a general law 
 — what has been proved in a great number of instances — that areas of 
 great accumulation of sediment are areas of subsidence. He agrees 
 with Babbage, that accumulation of sediments must cause an upward 
 movement of the isogeotherms, bu': he differs from Babbage in believ- 
 ing that this invasion of sediments by the interior heat would produce 
 subsidence instead of elevation. For, according to Herschel, the inva- 
 sion of sediments by the interior heat would produce chemical changes, 
 
146 ORGANIC AGENCIES. 
 
 and sometimes even aqueo-igneous fusion. These chemical changes, 
 whatever other effects they produce, would certainly change loose sedi- 
 ments into denser crystalline rocks (metamorphism), thus producing 
 contraction instead of expansion. 
 
 General Theory. — The theory of Babbage accounts with great prob- 
 ability for the rise of ground in the vicinity of volcanoes, and Her- 
 schel's theory accounts, perhaps, for the subsidence of deltas and other 
 places where great accumulation of sediment occurs; and this latter 
 theory has the additional advantage of accounting for metamorphism, 
 and perhaps, also, for volcanic phenomena. But it is evident that 
 some other and more general theory is necessary to account for those 
 great inequalities of the earth's crust which form land and sea-bottom. 
 For example : although loading with sediment may cause sea-bottoms 
 to sink; and lightening by erosion may cause, land-surf aces to rise, 
 yet this does not at all explain how sea-bottoms and land-surfaces came 
 to be such. These great inequalities must be originated by some 
 other cause ; loading and lightening only tend to maintain them. The 
 formation of these must be a phenomenon somewhat different from 
 those local oscillations which alone have been the subject of direct 
 observation. Such general changes can only be the result of some 
 general cause affecting the earth as a whole, as, for example, gradual 
 unequal contraction of the whole earth consequent upon gravitation. 
 The further discussion of this theory, however, belongs properly to 
 the second part of this work. 
 
 CHAPTEE IV. 
 ORGANIC AGENCIES. 
 
 The geologic work of organisms is both destructive and construc- 
 tive. The most general destructive effect is the decay of rocks by 
 organic acids, derived from plant decomposition. Branner has shown 
 that a similar effect is produced in the tropics by the myriads of ants. 
 Earthworms and all burrowing animals facilitate rock decay. Some 
 marine animals bore into stone, particularly Pholas and Lithodomus 
 among moUusks. The roots of growing plants are effective in dis- 
 placing rocks, especially on cliff faces. 
 
 Plants have also a protective influence. Forests and turf pre- 
 vent the erosion of slopes, while willows and other plants save banks 
 from stream and wave-cutting. Grasses on dunes tend to hold 
 the sand. Other minor conservative effects will occur to the observ- 
 ing student. 
 
PEAT-BOGS AND PEAT-SWAMPS. 147 
 
 The more important constructive work of organic agencies will 
 now be described. 
 
 Sectiok 1. — Vegetable Accumulations. 
 
 Peat-Bogs and Peat-Swamps. 
 
 Description. — In humid climates, in certain places, badly drained 
 and overgrown with moss and shrubs, a black carbonaceous mud accu- 
 mulates often to great depths. This siibstance is called peat or turf, 
 and such localities peat-bogs. The thick mass of vegetation which 
 covers their surface, with its interlaced roots often forms a crust upon 
 which a precarious footing may be found, but beneath this is a tremu- 
 lous, semi-lluid quagmire, sometimes twenty to forty feet deep, in 
 which men and animals, venturing in search of food, are often lost. 
 These bogs are most numerous in northern climates. One tenth of the 
 whole surface of Ireland, and large portions of Scotland, England, and 
 France, are covered with peat. The bog of the Shannon Eiver is fifty 
 miles long and three miles wide ; that of the Loire in Francfe is 160 
 miles in circumference. Extensive bogs exist also in the northern por- 
 tions of our own country. The amount of peat in Massachusetts alone 
 has been estimated at more than 15,000,000,000 cubic feet (Dana). In 
 California, an imperfect peat covers large areas about the mouth of the 
 San Joaquin Eiver and elsewhere (tule-lands). In more southern cli- 
 mates, where the condition of humidity is present, immense accumula- 
 tions of peat also occur — not, however, in bogs overgrown with moss 
 and shrubs, but in extensive szvamps covered with large trees.* 
 
 Composition and Properties of Peat.— Peat is disintegrated and 
 partially decomposed vegetable matter. It is composed of carbon, with 
 small and variable quantities of hydrogen, oxygen, and nitrogen. It is, 
 therefore, vegetable matter which has lost a part of its gaseous con- 
 stituents, and in which,' therefore, the carbon is greatly in excess. In 
 more recent peat, the vegetable nature and structure are plainly detect- 
 able by the eye, but in older peat only by the microscope. In all coun- 
 tries where it occurs, it is dried and used as a valuable domestic fuel. 
 By powerful pressure it may be converted into a substance scarcely 
 distinguishable from some varieties of coal, and, thus changed, is now 
 extensively used for all purposes for which coal is used, and has there- 
 fore become an important article of commerce. 
 
 Peat possesses a remarkable antiseptic property. This property is 
 probably due to the presence of humic acid and of hydrocarbons anal- 
 ogous to bitumen, which are formed only when vegetable matter is 
 decomposed in presence of excess of water. The bodies of men and 
 
 * TKe principal peat-making plant in cool climates is a peculiar moss called sphagnum. 
 
148 ORGANIC AGENCIES. 
 
 animals have been found in bogs in a good state of preservation, which 
 must have been buried many hundred years. In 1747, in an English 
 bog, the body of a woman was found, with skin, nails, and hair, almost 
 perfect, and tvith sandals on her feet. In Ireland, under eleven feet of 
 peat, the body of a man was found clothed in coarse hair-cloth. Several 
 other instances of bodies of men and animals, and innumerable in- 
 stances of skeletons of animals, preserved in bogs where they have per- 
 ished, might be mentioned. Large trunks of trees are often so per- 
 fectly preserved that they are used as timber, and stumps similarly 
 preserved are found with their roots firmly fixed in the under-soil of 
 the bog as if they had grown on the original soil on which the bog was 
 accumulated. 
 
 Mode of Growth. — Plants take the greater portion of their food from 
 the air, and give it, by the annual fall of leaf and finally by their own 
 death, to the soil. Thus is formed the humus or vegetable mold found 
 in all forests. This substance would increase without limit were it not 
 that its decay goes on pari passu with its formation. But in peat-bogs 
 and swamps the excess of water, and, still more, the antiseptic property 
 of the peat itself, prevent complete decay. Thus each generation takes 
 from the air and adds to the soil continually and without limit. The 
 soil which is made up entirely of this ancestral accumulation continues 
 to rise higher and higher, until the bog often becomes higher than the 
 surrounding country, and, when swollen by unusual rains, bursts and 
 floods the country with black mud. A bog is therefore composed of 
 the vegetable matter of thousands of generations of plants* It repre- 
 sents so much matter withdrawn from the atmosphere and added to 
 the soil. In some cases, besides the material deposited from the 
 growth of vegetation in situ, the accumulation may be partly also the 
 result of organic matter drifted from the surrounding surface-soil. 
 
 Rate of Growth. — The rate of peat-growth must be very variable, 
 since it depends upon the vigor of the vegetation and upon the manner 
 of accumulation, whether entirely by growth of plants in situ, or partly 
 by driftage. Many of the European bogs are evidently the growth of 
 not more than eighteen hundred years, for they were forests in the 
 time of the Eomans, or even later. The felling of these forests, as a 
 military measure to complete the subjugation of the country, and the 
 consequent impediments to drainage thus produced, have changed 
 them into bogs. At their bottoms, and covered with eight to ten feet 
 of peat, are found the trunks and the stumps of the original forests, 
 the axes and coins of the Eoman soldiers, and the roads of the Roman 
 army. The rate of accumulation has been variously estimated, from 
 one or two inches to several feet per century. In all cases of simple 
 growth in situ, however, and therefore always in great peat-swamps, 
 the increase is very slow. 
 
PEAT-BOGS AND PEAT-SWAMPS. 149 
 
 Conditions of Growth. — The conditions usually considered necessary 
 for the formation of peat are cold and moisture; and of these the 
 former is considered the more important, as without cold it is supposed 
 vegetable matter would be destroyed by decay. In proof of this it is 
 stated that peat-bogs are more numerous in cold climates. But it is 
 more probable that excess of moisture is the only important condition. 
 This condition may be rarer in warm climates on account of the greater 
 capacity of the air for moisture in these climates ; but when it is pres- 
 ent, immense accumulations of peat occur in extensive swamps. The 
 Great Dismal Swamp is a good illustration. This swamp, situated 
 partly in North Carolina and partly in Virginia, is forty miles long by 
 twenty-five miles wide. It is covered with a dense forest of cypress 
 and other swamp trees, by the annual fall of whose leaves the peat is 
 formed. These trees, by means of their long tap-roots and their wide- 
 spreading lateral roots, maintain a footing in the insecure soil, but are 
 often overthrown, and add their trunks and branches to the vegetable 
 accumulation. The original soil, upon which the accumulation was 
 formed, must have been lower in the center, but the surface of the peat 
 rises very gently toward the center, which is twelve feet higher than 
 the circumference (Pig. 117). Near the center there is a lake of clear, 
 
 Pig. 117.— Ideal Section throagh Central Portion of Dismal Swamp and Lake Drummond. 
 
 wine-colored water, seven miles across and fifteen feet deep, the banks 
 and bottom of which are composed of pure peat. 
 
 In the Mississippi Eiver swamps there are also large areas where 
 pure peat has been accumulating for age?, and is still accumulating, by 
 growth of trees in situ, though subject to the annual floods of the river. 
 The pureness of the peat in these cases is due to the fact that the mud- 
 dy waters of the river are strained of all their sedimentary matter by 
 passing through the dense jungle-growth of cane and herbage which 
 surrounds these favored spots. Thus only pure water reaches them.* 
 Similar peat-swamps are found at the mouths of the Ganges, the Niger, 
 and other great rivers. 
 
 Alternation of Peat with Sediments. — We have already stated (page 
 136) that a section of the delta-deposit of many great rivers, such as 
 the Mississippi, Granges, and Po, reveals alternate layers of fresh-water 
 and marine sediments, with thin layers of vegetable mold containing 
 stumps. In some cases these layers of vegetable mold amount to con- 
 siderable thickness of turf or peat. Layers of peat two feet thick have 
 
 * Lyell's Elements of Geology, fifth edition, p. 386. 
 
150 OKGANIO AGENCIES. 
 
 been found between layers of river-mud in the delta of the Ganges 
 (Lyell's Principles of Geology). Similar layers have been found in 
 the delta of the Po. They are evidently submerged peat-swamps. 
 These facts are of great importance in the explanation of the accumu- 
 lation of coal. 
 
 Drift- Timber. 
 
 Great rivers in wooded countries always bring down in large num- 
 bers the trunks of trees torn from the soil of their banks. These 
 trunks lodging near their mouths, where the current is less swift, and 
 accumulating from year to year, form rafts at great extent. The great 
 raft of the Atchafalaya, which was removed in 1835 by the State of 
 Louisiana, was a mass of tiniber ten miles long, seven hundred feet 
 wide, and eight feet thick. It had been accumulating for more then 
 fifty years, and at the time of its removal was covered with vegetation, 
 and even with trees sixty feet high. Similar accumulations of drift- 
 wood are described as occurring in the Eed Kiver, the Mackenzie Kiver, 
 and in Slave Lake. Such rafts become finally imbedded in river-mud, 
 and undergo a slow change into lignite or imperfect coal. Beds of 
 partially-formed lignite are therefore found in sections of the delta-de- 
 posit of almost all great rivers. We will use these facts in speaking of 
 the theories of the coal. 
 
 Section 2. — BoG-lBOiir Oeb. 
 
 At the bottom of peat-bogs is often found a " hard pan " of iron- 
 ore, sometimes one to two feet thick. The same material often collects 
 in low spots, even when there is no decided bog. The manner in which 
 this iron-ore accumulates is very interesting, and in a geological point 
 of view very important. 
 
 Peroxide of iron exists very generally diffused as the red coloring- 
 matter of soils and rocks. In this form, however, it is insoluble, and 
 therefore can not be washed out by percolating waters. For this pur- 
 pose the agency of decomporing organic matter, present in all percolat- 
 ing waters, is necessary. Decomposition of organic matter is a process 
 of oxidation. In contact with peroxide of iron (ferric oxide) it deoxi- 
 dizes and reduces it to protoxide (ferrous oxide). The acids, especially 
 carbonic acid, produced by decomposition of the organic matter, then 
 unite with the protoxide, forming carbonate of iron. The carbonate, 
 being soluble in water containing excess of carbonic, acid, is washed 
 out, leaving the soils or rocks decolorized, and the iron-charged waters 
 come up as chalybeate springs. But the ferrous carbonate rapidly 
 oxidizes again in the presence of air, by exchanging its carbonic^ acid 
 for oxygen, and returns to its former condition of ferric oxide, and is 
 deposited. Thus all about iron springs, and in the course of the 
 
CORAL KEEFS AND ISLANDS. 151 
 
 streams which flow from them, and in low places where their waters 
 accnmulate, we find reddish deposits of hydrated ferric oxide. This 
 is the most common but not the only form. For if the iron-waters 
 accumulate and the iron be deposited in the presence of excess of 
 , organic matter, as peat, then the iron is not (for in the presence of 
 this reducing agent it can not be) reoxidized, but remains in the. form 
 oi ferrous carbonate. 
 
 Thus there are two forms in which iron leached out from the soils 
 and rocks may accumulate, viz., ferric oxide and ferrous carbonate : the 
 former is accumulated where the organic matter is in small quantities, 
 and consumes itself in doing the work of dissolving and carrying ; the 
 latter where the organic matter is in excess. • 
 
 Many familiar phenomena may be explained by the principles given 
 above : 1. Clay containing both iron and organic matter is never red, 
 but always blue or slate-colored, because the iron is in the form of 
 ferrous carbonate and ferrous sulphate ; but the same clay will make 
 good red brick, because by burning the organic matter is destroyed and 
 the iron peroxidized. 2. In red-clay soils, such as those of our primary 
 regions, the surface-soil, especially in forests, is always decolorized, the 
 coloring of peroxide of iron being washed out and carried deeper by 
 water containing organic matter derived from the vegetable mold. 
 3. In sections of red clay, at the sides of gullies or railroad-cuttings, 
 along every fissure or crevice through which superficial waters per- 
 colate, the clay is bleached. The marbled appearance of red clays is 
 also probably due, in a great measure, to the irregular percolation of 
 superficial waters containing organic matter. 4. The under clay or 
 sand of peat-bogs is usually decolorized. 
 
 We will hereafter make use of these facts and principles in the ex- 
 planation of beds of iron-ore. 
 
 Section- 3. — Lime Accumulation's. 
 
 Coral Reefs and Islands. 
 
 Interest and Importance. — The subject of corals and coral reefs is 
 one of much popular as well as scientific interest. The strange forms 
 and often splendid colors of the living animals ; the number and ex- 
 treme beauty of the coral islands which gem the surface of certain 
 seas ; the large amount of habitable land which owes its existence to 
 the agency of these minute animals ; the fact that a large area, prob- 
 ably several thousand square miles, has been thus added to our own 
 territory ; the great dangers connected with the navigation of coral 
 seas, strikingly displayed on our own coast by the fact that the consid- 
 erable town of Key West is almost wholly dependent on the wrecking 
 
152 ORGANIC AGENCIES. 
 
 business for its existence — these and many other facts invest the 
 subject with popular interest, while the great importance of corals 
 as a geological agent gives the subject a scientific interest no less 
 strong. 
 
 Coral Polyp. — The animal which secretes coralline stone is no 
 insect, as generally supposed, but belongs to one of the lowest divisions 
 of the animal kingdom, viz., the class of polyps. Like most of the 
 lowest animals, it is composed of soft, gelatinous, and almost trans- 
 parent tissue. The animal, however, has the power of extracting 
 carbonate of lime from sea-water, and depositing it within its own 
 body. The lime carbonate is deposited only in the lower portion of 
 the animal, leaving thus the upper part and the tentacles free to move. 
 The radiated structure of the polyp is perfectly reproduced in the 
 coralline axis. This is a purely vital function, having no more con- 
 nection with volition than the secretion of the shell of an oyster or the 
 bones of the higher animals. The limestone thus deposited within the 
 animal constitutes 90 to 95 per cent of its whole weight. 
 
 Compound Coral, or Corallum.— A single coral polyp is very small, 
 but, like many of •the lower animals, it has the power of multiplying 
 indefinitely by buds and branches. Thus are formed compound corals. 
 These may branch profusely, and then may be called coral-trees ; or 
 may grow in hemispherical masses, and are then called coral-heads. 
 Coral-trees are sometimes six or eight feet high, and coral-heads" fifteen 
 to twenty feet in diameter. They consist of millions of individual 
 . coral polyps. Only the upper and outer portions of a coral-tree, and 
 outer portion of a coral-head, are living ; the lower and interior por- 
 tions consist only of coralline lime-stone without life. 
 
 Coral Forests. — Coral polyps, however, reproduce not only by bud- 
 ding, but also by eggs. These eggs have the power of locomotion. 
 As soon as they are extruded, they swim and float away, and, if they 
 fall on sea-bottom favorable for their growth, they soon form first a 
 coral polyp, and finally a coral-tree or coral-head. Thus from one 
 coral-tree other ooral- trees spring up all around and form a coral 
 forest, which spreads in every direction where they find conditions 
 favorable. 
 
 Coral Reef.— Finally, the limestone accumulation of thousands of 
 successive generations of coral forests growing and dying on the same 
 spot, together with the shells of mollusks and the bones of fishes which 
 live in swarms preying on the corals, the whole, of course, crowned 
 with the living forest of the present generation, constitute the coral 
 reef. It is evident, then, that a reef is formed somewhat after the 
 manner of a peat-bog. As a peat-bog represents so much matter 
 taken from the air, so a coral reef represents so much matter taken 
 from the sea- water. As each generation adds itself to the ancestral 
 
CORAL REEFS AND ISLANDS. I53 
 
 funeral-pile, the ground upon which the corals grow steadily rises until 
 it becomes elevated far above the surrounding sea-bottom. 
 
 Coral Islands. — These are due to the action of waves upon the 
 coral reefs. We have already seen how low islands are formed on sub- 
 marine banks by this 
 
 agency. N^ow, reefs are ^ ^.,<<^'^'vtV- ■.'■':':■ ['.'^-'TP-^-^ ^ 
 also a kind of subma- 
 rine bank. On these, 
 
 therefore, islands are ™' "*' 
 
 also formed by waves. Pig. 118 represents an ideal section across a 
 reef, as it would be if no wave-action interfered, 1 1 being the sea-level. 
 But by the action of the beating waves during storms large masses of 
 reef-rock, often six or eight feet in diameter,'or great coral-heads, are 
 broken off from the outer or seaward side of the reef and rolled over 
 to the leeward side. These form a nucleus about which collect similar 
 or smaller fragments, and among these still smaller fragments, and 
 these again are filled in and made firm with coral-sand, and the whole 
 cemented into solid limestone rock (breccia) by the carbonate of lime 
 in the sea-water. 
 
 Islands thus formed, like all wave-formed islands, are low (twelve 
 to fifteen feet high) and narrow (one quarter to one half mile wide), 
 but long_in the direction of the reef. They are at first perfectly bare, 
 
 but become in time cov- 
 ered with vegetation, and 
 even teeming with popula- 
 tion. They are celebrated 
 for their gem-like beauty. 
 The final result is shown 
 in ideal section in Fig. 
 119, in which the dotted portion is reef-rock, the strong waving line 
 the surface of the living reef, and the shaded portion the island. 
 
 Conditions of Coral Growth. — Reef -building corals do not grow in 
 all seas, nor over the whole bottom of the sea indiscriminately, but are 
 confined to certain seas, and in these to certain spots and lines. The 
 conditions of the growth are : 
 
 1. A Winter Temperature of 68°. — This condition confines them 
 almost entirely to the torrid zone. The most marked exception to 
 this is on the Florida coast and the Bahamas, where corals extend to 
 28° north latitude, and in the Bermudas to 33° north latitude. This 
 extension of the usual limits of reef-building corals is due to the warm 
 tropical watei's carried northward by the Gulf Stream. 
 
 2. A Depth of not more than One Hundred Feet. — This condition 
 confines them to submarine banks, and especially to the shores of con- 
 tinents and islands. 
 
 Fig. 119. 
 
154 
 
 ORGANIC AGENCIES. 
 
 3. Clearness and Saltness of the Water. — On account of this condi- 
 tion corals will not grow on muddy shores, nor off the mouths of 
 rivers, being destroyed by the fresh and muddy water. 
 
 4. Free Exposure to Waves. — Some species of corals grow in still 
 water, but the strongest reef-building species delight in the dash of the 
 surf. They will even flourish and build an almost perpendicular wall 
 in breakers which would wear away the hardest rock. The reason is, 
 that the immense profusion of life on a reef rapidly exhaust's the water 
 of the oxygen necessary for respiration, and of the carbonate of lime 
 necessary for their stony structure, and therefore constant change of 
 water is necessary. 
 
 All the conditions mentioned above apply only to reef-building 
 species. Some corals live in temperate regions, some in very deep 
 water, and some in sheltered places. 
 
 Pacific Reefs. — The reefs of the Pacific Ocean are of three general 
 kinds, Viz., fringing reefs, barrier reefs, and circular reefs or atolls. 
 We will describe these in the order mentioned. 
 
 Fringing Reefs. — In the tropical Pacific every high island or previ- 
 ously-existing land of any kind is surrounded by a reef which attaches 
 itself to the shore-line, and extends outward on every side just beneath 
 the water-level, as far as 
 the condition of depth 
 will allow, thus forming 
 a submarine platform 
 bordering the island or 
 other land. At the outer 
 margin of this platform ^'^- ^^°- 
 
 the bottom drops off very suddenly, forming a slope of 50° to 60°, and 
 sometimes almost perpendicularly. The position and extent of the 
 coral platform is indicated to the eye of the observer by a white sheet 
 of breakers which surrounds the island like a snowy girdle, and ex- 
 tends some distance from the shore-line (Fig. laO). The section Pig. 
 131 will give a clear idea of the contour of land and sea-bottom. In 
 this and the following sections the dotted parts represent coral forma- 
 tion. If the island is large, and considerable rivers flow into the sea, 
 breaks in the reef platform will occur opposite the mouths of the 
 
 rivers, the corals 
 in these places 
 being destroyed 
 by the fr'esh, 
 muddy waters. 
 In the case of 
 fringing reefs no islands are formed by the action of waves, but only 
 a shore-addition to the original island, as shown at a a in the section. 
 
 Fra. 121. 
 
CORAL REEFS AND ISLANDS. 
 
 155 
 
 Pro. 123. 
 
 Fio. 123. 
 
 Barrier Reefs.— In many cases besides the fringing reef there is 
 another reef surrounding the island like a submarine rampart at the 
 distance of from ten to fifty miles. As the reef rises nearly to the 
 
 ^_^ surface of the sea, 
 
 its position is indi- 
 cated by a snowy gir- 
 dle of breakers sur- 
 rounding the island 
 at a distance, and 
 this snowy girdle is 
 gemmed with wave- 
 formed green islets. Within this girdle, and between the rampart and 
 the island, there is a ship-channel twenty or thirty fathoms deep (Pig. 
 122). Through breaks in the coral rampart ships enter this channel 
 and find secure harbor 
 in a stormy sea. The 
 section Fig. 123 will 
 give a clear idea of 
 the conformation of 
 bottom. On the land- 
 ward side of the coral rampart the slope of the bottom is gentle, but 
 on the seaward side it is very steep, so that it is almost unfathomable 
 at a short distance from the reef. 
 
 Circular Reefs or Atolls.— These are the most wonderful of the 
 
 reefs of the Pacific. In 
 a circular reef there is 
 no volcanic island or 
 other visible land to 
 which the reef is at- 
 tached. Imagine a cir- 
 cular line of breakers 
 like a snow-wreath on the sea, indicating a circular submarine ridge 
 (the coral reef) gemmed as before with wave- formed islets ; and within 
 the circle a lagoon of 
 placid water twenty 
 or thirty or even 
 sixty * fathoms deep 
 (Fig. 124). It is a 
 submarine urn stand- 
 ing in unfathomable 
 water, as seen in the 
 ships enter the 
 
 Pis. 124. 
 
 Fig. 125. 
 
 section Fig. 125. Through breaks in the reef 
 charmed circle and find safe harbor. By means of 
 
 ' Sollas, Nat., 48, 575, 1893. 
 
156 
 
 ORGANIC AGENCIES. 
 
 Fig. 126.— View of Whitsunday Island. 
 
 sounding it is found that on the interior or lagoon side the slope 
 of the bottom is very gentle, but on the outer or seaward side is 
 very steep, often 50° to 60°, and sometimes in places almost perpen- 
 dicular to very 
 great depth. 
 Pig. 136 gives 
 a perspective 
 view, and Fig. 
 137, fl, a map 
 view, of an 
 atoll, showing 
 the irregular 
 circular form of 
 the reef and the 
 little islands 
 which gem its 
 surface. 
 
 Small Atolls and Lagoonless Islands.— Besides the atolls already 
 described, there are others, evidently of similar origin, but much 
 smaller, in which the land is continuous. Sometimes the continuous 
 line is open on one side 
 (Fig. 127, i), and the lagoon 
 is still in connection with 
 the open sea. Sometimes 
 the circle of land is com- 
 plete, and the lagoon is iso- 
 lated from the sea (Fig. 
 137, c). Sometimes the 
 lagoon closes up, and a la- 
 goonless island is the result 
 (Fig. 137, d). These dif- 
 ferent forms graduate into 
 one another and into the 
 typical atoll. 
 
 Theories of Barrier and Circular Reefs. 
 
 Fringing reefs require no theory. Corals attach themselves to the 
 shore-line because they find there the depth necessary for their growth, 
 and they extend outward until they are limited by the increasing 
 depth. But there is a real difficulty in explaining barriers, for they 
 seem to rise from water too deep for coral-growth ; and the difficulty 
 becomes still greater in the case of circular reefs or atolls, for these 
 seem to have no connection with any pre-existing land, but to grow up 
 from an unfathomable bottom. These latter, by their singularity and 
 
 Fia. 127. 
 
THEORIES OF BAUEIER AND CIRCULAR REEFS. 157 
 
 extreme beauty, have always attracted the attention and excited the 
 wonder of Pacific "travelers; and to their explanation theories have 
 been principally addressed. 
 
 Crater Theory. — This theory supposes that an atoll is an extinct 
 submarine volcano, the lagoou being the crater and the reef the lip or 
 margin of the crater ; that corals finding on this circular rim the con- 
 ditions of depth necessary for their growth, occupy and build upon it 
 to the surface of the water, after which, of course, waves finish the work 
 by beating up the islets. The incredible supposition that thousands of 
 these volcanoes should have come within 100 feet of the surface, and 
 yet none of them appear above the surface, is not necessary ; for we 
 may suppose that many of them were originally above the surface, 
 but, being composed of ashes and cinders, have been washed down by 
 the waves. In 1831 a volcano burst forth in the Mediterranean and 
 quickly formed an island of cinders and ashes, called Graham's Island. 
 In a few months this island was entirely washed away by the waves, 
 and only a circular submarine bank remained. If corals grew in the 
 Mediterranean, there seems no reason why a circular reef should not 
 have been formed. 
 
 Objections — Even in its most plausible form, however, this theory 
 is very improbable as a general explanation of atolls : 1. The great size 
 of some of these atolls — thirty, sixty, and even ninety miles in diam- 
 eter ; and, 2. The high angle of the slope of these submarine mount- 
 ains — 50° to G0° or more — seems inconsistent with their volcanic origin. 
 3. This theory offers no explanation of the barrier reefs, and yet it is 
 possible to trace every stage of gradation between barriers and atolls, 
 showing that they are due to similar causes. 
 
 Subsidence Theory of Darwin. — This theory explains not only atolls; 
 but also barriers, and connects both in a satisfactory manner with 
 fringing reefs. It supposes that the sea-bottom, where atolls and 
 barriers occur, has been for ages subsiding, but at a rate not greater 
 than the upward building of the coral-ground ; that every reef com- 
 mences as a fringing reef, but, in the progress of subsidence, was con- 
 verted first into a barrier and finally into an atoll. For, as the vol- 
 canic island went down, the corals would build upward on the same 
 spot ; and as the island would become smaller and smaller, and the 
 corals would grow faster on the outer side of the reef, where they are 
 exposed to the breakers, it is evident that the reef would become 
 separated from the island by a ship-channel, and thus become a bar- 
 rier. Finally, when the island disappears entirely, the reef, still build- 
 ing upward, would become an atoll. These changes are represented in 
 the accompanying section (Fig. 128). As the changes are relative, 
 they may be represented either by the land sinking or the sea-level ris- 
 ing ; for the sake of convenience we use the latter. In the figure, f l" 
 
158 
 
 ORGANIC AGENCIES. 
 
 represents the sea-level when the reef was a fringe, V V when it was a 
 harrier, and 1 1 the present sea-level, when it has become an atoll. The 
 ship-channel and the lagoon, though always lower, rise pari passu with 
 the reef proper. This is the result partly of the growth of placid- 
 water species of corals, and partly of the drifting of coral debris from 
 the reef, and detritus from the volcanic island. It is seen that the 
 corals do not build a vertical wall, and therefore that the atoll is always 
 smaller than the coast-line of the original island. Consequently, if the 
 
 suhsidence continues, a typical atoll is changed into a small closed 
 lagoon, and, finally, into a lagoonless island. These, therefore, indicate 
 the deepest subsidence. 
 
 Evidences. — 1. This theory accounts for all the more obvious phe- 
 nomena of atolls, such as their irregular circular form, their size, the 
 steepness of their outer slopes, etc. 2. Every stage of gradation be- 
 tween the fringing reef on the one hand, and the atoll on the other, 
 has been traced by Dana, strongly suggesting that they are all different 
 stages of development of the same thing. We have , in the Pacific 
 some high islands, which are surrounded by a pure fringing reef; 
 others in which the reef is a fringe on one side and a barrier on the 
 other ; others in which the barrier is one mile, two miles, five miles, 
 ten miles, twenty, or thirty miles distant ; others which are called 
 atolls, but the point of the original volcanic island is still visible in 
 the middle of the lagoon ; others which are perfect atolls, but, by 
 sounding, the head of the drowned volcanic island is still detectable. 
 The next step in the series is the perfect atoll, then the small atoll, 
 and, finally, the lagoonless coral island. These last kinds show that 
 the original island has gone down deeply. 3. By grappling-hooks 
 dead coral-trees have been broken off and brought up from the 
 ground where they once grew, now far below the limiting depth of 
 coral-growth. The evidence of subsidence in this case is of the 
 same kind and force as that derived from the submerged forest- 
 ground (page 143). The corals have been carried below their depth 
 and drowned. 4. The remarkable distribution of the various kinds of 
 reefs brought to light by Dana is satisfactorily explained by this 
 theory, and therefore is an argument in its favor. In the middle of 
 
THEORIES OF BARRIER AND CIRCULAR REEFS. 159 
 
 the atoll region of the Pacific there is a blank area, 2,000 miles long 
 and 1,000 or more miles wjde, where there are no islands. Next about 
 this is an area in which small atolls predominate ; about this again the 
 region of ordinary atolls ; beyond this the region mostly of barriers, 
 and finally of fringes. Now, by this theory this distribution is thus 
 explained : The sea-bottom in the blank area has gone down so fast 
 that the corals have not been able to keep pace, and have therefore 
 been drowned, and left no monument of their existence. In the next 
 region the corals have been able to keep within living distance of the 
 surface, but the original islands have not only disappeared, but gone 
 down to great depths. In the next the original high islands have 
 disappeared, but not gone down so deep ; in the next they have sunk 
 only to the middle. The fringing reefs stand on the margin of the 
 sinking area. Outside of this again there is in some places even evi- 
 dence of upheaval instead of subsidence. Eaised beaches in th,e form 
 of fringing-reuf rocks are found clinging to the sides of high islands 
 many feet above the present sea-level. 5. In some places this sub- 
 sidence seems to be still in progress. On certain coral islands sacred 
 structures of stone made by the natives are now standing in water, and 
 the paths worn by the feet of devotees are now passages fdr canoes 
 (Dana). According to this view, thrrefore, an atoll is the site of a 
 drowned island. 
 
 Murray's Theory. — Eecently serious doubts have been cast on Dar- 
 win's subsidence theory, at least as a universal explanation of barriers 
 and atolls.* Mr. Murray, from his observations during the voyage of 
 the Challenger, believes that barriers and atolls may be explained with- 
 out subsidence of the sea-floor. An outline of his views may be thus 
 stated : 1. Suppose submarine banks formed in any way, either (a) built 
 up by accumulating sliells of successive generations of marine animals, 
 until within the reach of coral-growth ; or (5) by volcanic cinder cones 
 cut down by the waves so as to form suitable banks. 2. The bank thus 
 formed, taken possession of by corals, is built up to the sea-level, and 
 thus forms a small island. 3. The coral-growth is confined to, or at 
 least most rapid on, the outer margin, because exposed to the action of 
 the sea. Thus arises a ring with blank space within. 4. The action of 
 waves beats these rings into a series of islets. 5. Meanwhile the scour- 
 ing action of currents and the solvent action of sea-water scoops out the 
 blank area into a more or less deep lagoon. 6. The action of waves 
 breaking the living coral and the reef -rocks forms a de6ns-pile or talus, 
 
 with steep outward slope, on which the corals continue to grow sea- 
 
 • 
 
 * The author of this volume believes that he was the first who showed, in the case of 
 the Florida reefs, how barriers may be formed without subsidence. American Journal of 
 Science and Art, vol.' xxiii, p. 46, January, 1857. 
 
 20 
 
160 ORGANIC AGENCIES. 
 
 ward into deep water. Thus the coral ring continues to spread, 
 like a fairy ring, by growing seaward in every direction and dying 
 behind. 7. According to Darwin, atolls grow continually smaller; 
 according to Murray, they grow continually larger. According to 
 the one, the lagoonless islands are the last remnants of drowning 
 islands; according to the other, they are the beginnings of new 
 islands. ~ 
 
 Barriers are similarly explained. They commence as fringes, which 
 grow seaward as far as depth will allow. Then the corals die near 
 the shore, and this part is scoured out into a channel. Meanwhile the 
 i-eef' extends seaward on its own talus, and the channel is pari passu 
 widened. 
 
 Perhaps the chief objection to Murray's views is the depth of some 
 lagoons and channels. It seems improbable that the solvent and 
 scouring action of the sea should extend to such depth. On the con- 
 trary, the lagoons are more apt to fill up than to deepen unless by 
 subsidence. , 
 
 In the present condition of the question it is probable that there 
 are more ways than one in which barriers and atolls may be formed, 
 but Darwin's view seems still to hold its own as a general, though not 
 as a universal theory. 
 
 On Darwin's view, of course, every atoll marks the site of a sunken 
 • volcanic island. It will be interesting, therefore, to make some esti- 
 mates based on this view. 
 
 Area of Land Lost.^ — Probably several hundred thousand square 
 miles of habitable high land has been lost by this subsidence. The 
 actual extent of atolls known is at least 50,000 square miles. But this 
 is far less than the loss of high land. For — 1. It is certain that the 
 area of an atoll is always less than that of the original fringe or base 
 of the original high island, for the outer wall of an atoll is not per- 
 pendicular. The contraction continues as the subsidence progresses, 
 until small atolls or only lagoonless islands remain. 2. An immense 
 lost area is represented by the space between barriers and their high 
 islands. The great Australian barrier extends along that coast 1,100 
 miles, at an average distance of thirty miles, with a ship-channel be- 
 tween of thirty to sixty fathoms deep. This single barrier, therefore, 
 represents a lost land-area of 33,000 square miles. 3'. In the blank 
 area already spoken of, probably many islands went down, and left no 
 record behind. 
 
 The large amount of high land thus lost has been replaced only 
 to a small extent by the wave-formed coral islets on the-reefs-. 
 
 Amount of Vertical Subsidence.— The amount of subsidence may be 
 estimated by the distance of barriers, from their high islands, or by 
 
THEORIES OF BARBIEE AND CIRCULAR REEFS. 161 
 
 soundings off atolls, to ascertain the height of these coral mounds, 
 or by the average height of the high islands of the Pacific. 1. The 
 average slope of the high islands of the Pacific is about 8°. Now, as- 
 suming this slope (Fig. 129), a barrier, d, at the distance of five miles 
 
 Pio. 139. 
 
 would be 3,700 feet thick, and would represent a subsidence nearly to 
 that extent (Rad. : tan. 8° : : ad: dV); a distance of ten miles would 
 represent a vertical subsidence of 7,400 feet. Many barriers are at 
 much greater distance. 3. Off Keeling atoll, 6,600 feet, a line of 
 7,300 feet found no bottom (Darwin). Near other atolls a depth of 
 3,000 feet has been found (Dana). 3. The average height of the 
 high islands of the Pacific can not be less than 9,000 feet (Dana) ; 
 some of them reach nearly 14,000 feet. It is very improbable that, 
 among the hundreds of atolls known, not one of their high islands 
 should have reached the average elevation of 9,000 feet. Yet these 
 have entirely disappeared, and not only so, but the small atolls and 
 lagoonless islands, and more especially the blank area, would seem to 
 indicate that they have disappeared to great depths. For these 
 reasons, it is almost certain that the extreme subsidence has been at 
 least 9,000 feet. We will take 10,000 feet as the most probable ex- 
 treme subsidence. 
 
 Rate of Subsidence. — The rate of subsidence may have been to any 
 degree less, but can not have been greater, than the rate of coral 
 ground-rising j for otherwise the corals would have been carried be- 
 low their depth and drowned. It is difficult to estimate the rate of 
 coral ground-rising, but the only basis of such estimate is the rate of 
 coral-growth. Of the observations on this point we select two, one of 
 them on the head-coral (-meandrina), the other on the staghorn-coral 
 (madrepore) : 
 
 1. On the walls of the fort at the Tortugas, Florida, meandrina 
 commenced to grow, and in fourteen years the crust had become only 
 one inch thick. Agassiz takes one inch in eight years as a probable 
 rate under favorable circumstances. This would be one foot in a cen- 
 tury. .As this is a head-coral, the coral-growth maybe taken as the 
 measure of the reef ground-rising. 
 
 3. In examining the reefs about the Tortugas in the winter of 1851, 
 an extensive grove of madrepore was found in the comparatively still 
 water on the inside of the outer reef, in which the thick-set prongs 
 had grown, year after year, to the same level, and were successively 
 
162 ORGANIC AGENCIES. 
 
 killed. The mean level of the water here is lower dtiring the winter, 
 by about a foot, than during the summer. The falling of the water 
 annually clips this grove at the same level. Now all the prongs at 
 this level were dead for about three inches. Evidently, therefore, this 
 is the annual growth of madrepore-prongs.* But in brahching corals 
 the rate of point-growth is very different from the 'rate of ground- 
 rising. If all the points of a madrepore be cut off three inches, then 
 ground into powder, and the powder strewed evenly over the ground 
 shaded by the coral-tree, the elevation thus produced would correctly 
 represent the annual rate of reef ground-rising for this species. A 
 quarter of an inch would probably be a full estimate. This would 
 make two feet for a century. One foot to two feet per century is, 
 therefore, probably about the rate at which coral ground rises. As 
 already stated, the rate of subsidence may be less, but can not be 
 greater, than this. 
 
 Time involved. — At this rate 10,000 feet of vertical subsidence would 
 require 500,000 to 1,000,000 years. How much of this belongs to the 
 present geological epoch it is impossible to say. Dead corals, indentical 
 with those still living on the reefs, have been brought up from a depth 
 of 350 feetj but, as this is only 150 feet below the limit of coral-growth, 
 it would require only 75 to 150 centuries. The process probably com- 
 menced in previous geological epochs, and has continued to the pres- 
 ent time. This is, therefore, an admirable example of geological agen- 
 cies still at work. 
 
 Geological Application. — The facts brought out in the preceding 
 pages are of great importance in geology. 
 
 1. We have here the most magnificent example of subsidence still 
 in progress. The subsiding area has not been accurately defined, but 
 it probably covers nearly the whole of the intertropical Pacific. Ac- 
 cording to Dana, estimated by the atolls alone, it is 6,000 miles long 
 and 2,000 miles wide ; but if we take into account also barriers, which 
 are equally certain evidences of subsidence, it extends east and west 
 from the extreme of the Paumotu group on the one side to the Pelews 
 on the other, and north and south from the Hawaiian group to the 
 Peejees, making an area of not less than 20,000,000 square miles. 
 Now, it is evident that there must have been, as a correlative of this 
 extensive and permanent downward movement, an equally extensive 
 permanent elevation of the earth's crust somewhere else. Dana thinks 
 its correlative is found in the extensive elevations of the Glacial epoch, 
 and therefore that the whole work was accomplished since the Ter- 
 tiary. But it is more probable that this correlative is found in the 
 
 • See full account of these observations in American Journal of Science and Arts, 
 vol. X, p. 34. 
 
KEEFS OF FLORIDA. 
 
 163 
 
 gradual bodily upheaval of the whole western side of the continent, 
 especially in the Rocky Mountain region, which commenced after the 
 Cretaceous. 
 
 2. We have here the formation of limestone rocks of various kinds 
 going on before our eyes over immense areas and several thousand feet 
 in thickness, and we learn thus that limestones are of organic origin. 
 
 3. The character of the rocks thus formed is very interesting to 
 the geologist. In some places, as we have already seen, it is a coarse 
 conglomerate, or breccia, composed of fragments of all sizes cemented 
 together [island-rock) ; in some places it is made up eutirely of rounded 
 granules of coralline limestone (coral-sand), cemented together {shore- 
 rock), and forming a peculiar oolitic rock (tSov Aii9os, egg-stone). But 
 the larger portion of the reef ground is a fine compact limestone, made 
 up of comminuted coralline matter {coral mud), cemented together 
 {lagoon-rock). This fine coral mud is carried by waves and tides into 
 the lagoon, and serves to raise its bottom : it is also carried by currents 
 and distributed widely over the neighboring sea-bottoms. Soundings 
 in coral seas bring up everywhere this final coral mud, showing that 
 compact limestone is now forming over wide areas in coral seas. 
 The reef -rock, as 
 already stated, has 
 been found clinging 
 to the sides of high 
 islands, having been 
 elevated many feet 
 above sea-level; in 
 other cases atolls 
 have been elevated 
 350 feet above the 
 sea-level. The struc- 
 ture of the reef- rock 
 has thus been ex- 
 posed to view. In 
 some places it con- 
 tains imbedded re- 
 mains of corals and 
 shells, but in other 
 parts it is entirely 
 
 destitute of these Fig. ISO.— Map of Florida with its Keys and Reefs : a. Boutbern 
 coast; a', keys; a", living reef; e. Everglades; «', shoal water; 
 remains. «", shlp-channel; ff £r;8, Gulf Stream. 
 
 Reefs of Florida. 
 The reefs of Florida deserve a brief separate notice, both because 
 they are different from, those of the Pacific, having been formed under 
 
164 
 
 ORGANIC AGENCIES. 
 
 different conditions, and because they are much more efficient agents 
 in land-making, and illustrate in a striking manner how different 
 agencies co-operate for this purpose. The process has been accurately 
 observed. 
 
 Description of Florida. — Fig. 130 is a map of Florida, with its reefs 
 and keys, and Fig. 131 is a section along the line N S. The southern 
 coast (a a) is ridge, elevated twelve to fifteen feet above the sea-level, 
 within which is the Everglades (e) an extensive fresh- water swamp 
 only two or three feet above sea-level, and dotted over with small 
 islands called hummochs. Between the southern coast {a a) and the 
 
 Fia. 131.— Section of same along line N S. Letters indicate the same. The dotted lines show sup- 
 posed previous conditions. 
 
 line of keys {a' a') the water (e') is very shallow, only navigable to 
 smallest fiishing-craft, and dotted over with small low mangrove islands. 
 A considerable portion of this area, in fact, forms mud-flats at low tide. 
 Between the line of keys (a' a') and the living reef {a" a") there is a 
 ship-channel {e") five to six fathoms deep. Outside the reef {a" a") the 
 bottom slopes rapidly into the almost unfathomable abyss of the Gulf 
 Stream ((?^<S'). 
 
 General Process of Formation. — Now, Agassiz * has proved that 
 not only the living reef but the keys, the southern coast, and the pen- 
 insula, certainly as far north as the north shore of the Everglades 
 {d d), and probably on the east side as far north as St. Augustine {d'), 
 have been formed by coral agency. The evidence of this important 
 conclusion is that the rock in all these parts is identical with the reef- 
 rock already described, and with what is even now forming under our 
 eyes on the living reef («" a"). It is, moreover, almost certain that 
 the peninsula of Florida has been progressively elongated by the for- 
 mation of successive barrier reefs, one outside of the other, from the 
 
 * Coast Survey Keport for 1851, p. 145 et seq. 
 
REEFS OF FLORIDA. 165 
 
 north toward the south, and the successive filling up of the inter- 
 vening ship-channels, probably by coral debris from the reef and 
 sediments from' the mainland. 
 
 Mangrove Islands. — Mangrove-trees co-operate in an interesting 
 manner with corals in the process of land-formation. These trees 
 form dense jungles on the low, muddy shores of tropical regions. 
 They are very abundant on the shores of Florida. They have the re- 
 markable power of throwing out aerial roots from their trunks and 
 branches, thus forming subordinate connections with the ground or 
 with the bottom of shallow water. From these may spring other 
 trunks, which throw out similar roots, etc. Thus an inextricable en- 
 tanglement of roots and branches continues to extend far beyond the 
 actual shore-line. These form a nidus for the detention of sediments 
 and protect them from the action of waves; and the shore-line thus 
 steadily advances. 
 
 Florida Reefs compared with other Reefs. — In comparing the reefs 
 just described with other reefs, it will be seen that the former are 
 unique in two respects. 
 
 1. No other reefs continuously make land. In fringing reefs there 
 is a small accretion about the shore-line of the "previously-existing 
 land, but this process is quickly limited. In barriers and atolls, 
 according to Darwin, there is always loss oi land, only a small fraction 
 of which is recovered by coral and wave agency. But under these 
 agencies Florida has steadily advanced southward more than 100 
 miles, and the area thus added to the continent is at least 10,000 square 
 miles. It seems utterly impossible to account for this, except by 
 supposing some other agency at work preparing the ground for the 
 growth of successive reefs. 
 
 Probable Agency of the Gulf Stream.— There is no evidence of 
 subsidence on the coast or keys of Florida. On the contrary, the 
 height of these parts is precisely the usual height of wave-formed 
 islandSj although no longer exposed to their action. It follows, there- 
 fore, that the corals must have built upon an extensive submarine 
 bank, produced by some other agency. Furthermore, since the reefs 
 were formed successively one beyond another, it is evident that there 
 must have been a progressive formation of this bank from the north 
 toward the south. The dotted lines (Fig. 131) show successive posi- 
 tions of the bank of the reefs.- 
 
 At one time it was supposed that the bank was formed and 
 extended by mechanical sediments brought by the Gulf Stream, and 
 deposited on the inner side of its curve ; but Alexander Agassiz has 
 shown that the sediments are more probably organic, and the bank 
 was formed partly by such sediments brought by the Gulf Stream 
 from other coral banks in the Caribbean Sea, but mostly built up in 
 
IQQ OEGANIC AGENCIES. 
 
 situ by the accumulation of shells of successive generations of deep- 
 sea animals, the Gulf Stream bringing only the conditions of rapid 
 growth in the form of warmth and abundant food. 
 
 It is probable, therefore, that the southern portion of the peninsula 
 of Florida is due to the co-operation of four or five different agencies, 
 viz. : 1. The Gulf Stream building up a submarine bank to the dotted 
 line n' n', Fig. 131, within 100 feet of the surface; 2. Then corals 
 building up to the surface; 3. Then waves raising it twelve to fifteen 
 feet above the surface ; 4. And, finally, debris from the peninsula, on 
 the one side, and the reef and keys on the other, filling up the inter- 
 vening channels, and afterward raising the level of the swamps or 
 Everglades thus formed; 5. In this last process the mangrove-trees 
 have assisted. 
 
 Ancient Coral-Beefs. 
 
 Ancient reefs, formed from polyp corals and from Bryozoa or 
 other reef-builders, are found in thp rock strata of former geologic 
 ages. Fig. 131a represents a section of an ancient Devonian coral- 
 
 Fiu. 131a.— Section of Coral-Eeef, Alpena, Mich, (after Grabau). 
 
 reef in Michigan, and Fig. 131& is a photograph of a reef, chiefly 
 constructed of Bryozoan" coral, in the Clinton (Silurian) strata of 
 western New York. 
 
 Crinoidal Limestone. 
 
 The group of marine animals known as Crinoids (Encrinites) , 
 now nearly extinct, lived in ancient times in such variety and numbers 
 that they were an important agent in limestone formation. While 
 not producing branching masses or colonies, like the corals, yet their 
 bodies consisted so largely of calcareous plates that locally they were 
 reef-builders. Their skeletons seem to have been usually added to 
 the coral debris, but not infrequently the limestone mass appears to 
 have been chiefly derived from erinoid -stems and plates. 
 
 Molluscan Limestone and Shell-Marl. 
 
 When living in immense numbers near shore and on submarine 
 banks, leaving their dead shells generation after generation, the mol- 
 
ANCIENT CORAL-REEFS. 
 
 167 
 
 lusks sometimes form pure deposit? and frequently shelly deposits 
 mingled with sediments from other sources. When exposed to the 
 action of breakers the shells may be broken into coarse fragments, 
 or comminuted, and cemented into limestone. Such shell limestone 
 is forming to-day on the coasts of Florida and the Bahamas from a 
 bivalve called " Coquina." Buildings at St. Augustine are constructed 
 
 Fig. 131 J.— Section of Ooral-Reef in Niagara Gorge (after C. J. Sarle). 
 
 from coqiiina limestone. When shells or other skeletons are reduced 
 to rounded grains the rock is called Oolite (roe stone) . (See p. 442.) 
 The several species of small gasteropods (snails) which live in 
 fresh water have sometimes flourished in such multitudes that the 
 decomposed shells form white, soft, structureless deposits, often many 
 feet in depth, called shell-marl. These deposits are specially well 
 developed in the glaciated area, in swamps, overlain with peat, and 
 representing iilled-up lakes. The material is in demand as a con- 
 stituent of " Portland " cement. 
 
 Nummulitic Limestone. 
 
 In southern Europe and northern Africa and eastward to India 
 are limestone rocks of vast extent and thousands of feet in thickness, 
 which were formed from the tests of giant Foraminifera called Num- 
 mulites (Latin, nummulus, a coin). The pyramids of Egypt are 
 
168 
 
 ORGANIC AGENCIES. 
 
 partly built of nummulitic limestone, a specimen of which is the 
 plinth of Cleopatra's Needle, in Central Park, New York (see pp. 
 531, 532). 
 
 Chalk. 
 
 Belonging to the same animal group as the nummulites, but of 
 microscopic size, are the shells or tests which form the greater mass 
 of the calcareous ooze of the deep sea. This is a white, sticky ooze, 
 composed of the lime shells of Foraminifera (see Fig. 132), and of 
 microscopic plants (coccospheres). Some of these seem to be living, 
 or recently dead; some dead and empty, but still perfect; but most 
 of them completely disintegrated. On account of the great abun- 
 dance of one form of foraminifera this soft, white mud is called 
 
 Fig. 132.— Shells of Living J^oramwf/era.' a, Orbulina universa, in its perfect condition, showing 
 the tubular spinus which radiate from the surface of the shell ; 6, OlolAgerina bulloides, in its 
 ordinary condition, the thin hollow spines which are attached to the shell when perfect having 
 been broken off ; c, Texiularia variabilis ; d, Peneroplis planatns ; e, Motalia amcamerata ; f, 
 CHstellaria subarcitatula. Fig. a is after Wyville Thomson ; the others are after Williamson. 
 AH the figures are greatly enlarged (after Nicholson). 
 
 Glohigerina ooze. Mingled in considerable numbers among the cal- 
 careous shells are others of silica. These are also partly animals 
 (Radiolaria) and partly plants (Diatoms). The resemblance of this 
 deep-sea ooze, in both chemical and biologic characters, to the chalk- 
 beds of England and France leaves no room for doubt that chalk was 
 formed in a similar manner, though not necessarily in very deep ocean. 
 
PHOSPHATE DEPOSITS. 169 
 
 In Kansas and Iowa are chalky beds of the same nature (see pp. 487- 
 488). The chalk deposits give distinguishing character to the Cre- 
 taceous period (Latin, creta, chalk), which was a time of remarkable 
 development of the minute foraminifers in continental seas, as the 
 later Eocene time was of the giant forms, the nummulites. 
 
 Section 4. — Phosphate Deposits. 
 
 The most important deposits of pTiosphatic materials are the 
 beds of Guano, formed from the excrements of birds in arid regions, 
 as on the coast of Peru. In some cases leaching has concentrated the 
 soluble salts in the underlying rocks as calcium phosphate. Guano 
 is also formed in caves, by bats. 
 
 Some limestones consist partly of phosphate of lime, which may 
 be concentrated in nodules. Such limestones occur in South Caro- 
 lina, Florida, Arkansas, and Tennessee. The nodules are sometimes 
 gathered into stream channels from the weathered rocks, and are 
 known as "pebble phosphate." It is supposed that the rock phos- 
 phate may be derived from the shells of certain braehiopods, which 
 are largely calcium phosphate instead of calcium carbonate; also 
 from the tests of crustaceans, and possibly to some extent from the 
 bones of vertebrates. 
 
 Section 5. — Siliceous Deposits. 
 
 Eeference was made on page 43 to the vast areas of siliceous 
 ooze on the ocean bottom, derived from radiolarians and from dia- 
 toms. The latter also abound everywhere in fresh waters, cold or hot. 
 The beautiful siliceous skeletons of these microscopic algae form 
 deep deposits in some lakes. In Nevada, for example, beds are found 
 200 to 300 feet thick, of the white,-porous diatomaceous earth called 
 " tripolite.'' Diatoms live in great abundance in the hot springs of 
 California, Nevada, and the Yellowstone Park, in temperatures up 
 to 185° F. Large areas in the Yellowstone Park are buried under 
 several feet of sinter derived from diatoms. See pages 539-530 for 
 a further account of ancient deposits. 
 
 It has already been stated (p. 168) that the calcareous ooze of 
 the sea-bottom holds some siliceous material. The indurated ooze 
 called chalk has its siliceous content gathered into concretions or 
 nodules of flini. This is derived from a variety of. silica-secreting 
 organisms, as sponges, radiolarians, diatoms, etc. It is to be ex- 
 pected that many limestones should contain much siliceous matter, 
 which if concentrated is known as chert or hornstone. The Cornifer- 
 ous limestone is so called from its characteristic abundance of horn- 
 stone (Latin, cornu, horn). 
 
PAET II. 
 STRUCTURAL GEOLOGY. 
 
 Thus far we have studied the operation of geologic forces and 
 agencies, or the processes and principles of earth dynamics. We now 
 come to the study of earth structure, or the effects and products of 
 geologic forces working through all time. Structural geology con- 
 siders the materials of the earth's crust, and the form, position, and 
 arrangements of rock masses. As a branch of geology it is largely 
 descriptive, but for explanation of structure the dynamical processes, 
 must be frequently invoked. 
 
 CHAPTEE I. 
 GENERAL FORM AND STRUCTURE OF THE EARTH. 
 
 1. Form of the Earth. 
 
 The general form of the earth is that of an oblate spheroid flat- 
 tened at the poles, or, more definitely, an ellipsoid of revolution on the 
 minor axis. The polar diameter is less than the equatorial diameter 
 by about twenty-six miles, or about -j^ of the mean diameter.* The 
 highest mountains, being only five miles high, do not interfere greatly 
 with the general form. 
 
 This form, being precisely that which a fluid body revolving freely 
 would assume, has been regarded by many of the most distinguished 
 physicists as conclusive evidence of the former fluid condition of the 
 earth. The argument may be stated as follows: 1. A fluid body 
 standing still, under the influence only of its own molecular or gravi- 
 tating forces, would assume a perfectly spherical form ; but, if rotating, 
 the form which it would assume, as the only form of equilibrium, is 
 that of an oblate spheroid, with its shortest diameter coincident with 
 the axis of rotation. Wow, this is precisely the form not only of the 
 
 * More exactly ijrsV.l) Philosophical Magazine, vol. x, p. 121, 1880. 
 170 
 
FORM OF THE EARTH. 171 
 
 earth, but, as far as known, of all the planetary bodies. 3. In an ob- 
 late spheroid of rotation the oblateness increases with the rapidity of 
 rotation. Now, Jupiter, which turns on its axis in ten hours, is much 
 more oblate than the earth. The flattening of the earth is only about 
 5^-j of its diameter, while that of Jupiter is about tV- 3. The forms 
 of the earth and of Jupiter agree with theoretical calculation. 
 
 The force of this argument, however, has been, to say the least, 
 greatly exaggerated. The oblateness of the earth and planets only 
 proves that they have assumed their form under the influence of rota- 
 tion — that they are spheroids of rotation — but not that they have ever 
 been in a fluid condition. For since a rotating body, whatever be its 
 form, always tends to assume an oblate spheroid form, and since the 
 materials on the surface of the earth are in continual motion, being 
 shifted hither and thither under the influence of atmospheric and 
 aqueous agencies, it is evident that the flnal and total result of such 
 motions must be in the course of infinite ages to bring the earth to the 
 only form of equilibrium of a rotating body, viz., an oblate spheroid. 
 If, for example, the earth were a rigid sphere, standing still and cov- 
 ered with water, and then set rotating, the waters would gather into 
 an equatorial ocean, and the land be left as polar continents. But this 
 condition would not remain ; for atmospheric and aqueous agencies, if 
 unopposed, would eventually cut down the polar continents and de- 
 posit them as sediments in the equatorial seas, and the solid earth or 
 lithosphere would thus become an oblate spheroid. 
 
 The form of the earth, therefore, must not be assumed as demon- 
 strative proof of original fluid condition, since a similar form would 
 be produced by causes now in operation on the earth-surface, whatever 
 may have been its original form and condition. Moreover, it is evi- 
 dent that the exact original form, however determined, can not have 
 been retained; for there are causes in operation which have tended 
 constantly to modify it. If abrasion can produce, it can also modify 
 the form of the earth. If the form of the earth is a form, of equilib- 
 rium, then a change in the rate of rotation will produce a change in 
 the degree of oblateness or ellipticity. Now, if the earth first solidi- 
 fied from an incandescent liquid condition, it had a certain degree of 
 ellipticity determined by its rate of rotation ; but this rate of rotation 
 wcftild not be constant. The earth, from that time until now, would 
 have been cooling and contracting; and contraction would tend to 
 accelerate rotation and increase ellipticity. But, also, ever since an 
 ocean was first formed, tides have been formed by the moon and the 
 sun, and the friction of the dragging tides would tend to retard rota- 
 tion and decrease ellipticity. 
 
 Under the planetesimal hypothesis of earth-genesis, as formulated 
 by Chamberlin (see p. 88), the two factors noted above as directly 
 
172 
 
 GENERAL FORM AND STRUCTURE OP THE EARTH. 
 
 affecting the rate of rotation and indirectly the oblateness of the 
 globe, also apply after the earth had grown to such size that its gravi- 
 tational attraction was competent to retain an atmosphere and form 
 the ocean. Fluid water could not exist on the earth until there was 
 sufficient atmosphere to retain the sun heat. The increase in size 
 of the growing earth did not reduce rotational velocity because the 
 added material contributed its due proportion of momentum. Under 
 this hypothesis contraction of the earth is a greater factor than under 
 the nebular hypothesis, while tidal friction was nothing at first, but 
 has been an increasing factor with the growth of the ocean. Under 
 either hypothesis contractional acceleration may have prevailed at 
 first, tending to increase the oblateness, but now tidal retardation 
 probably prevails, thus reducing the ellipticity. Geologically this is 
 not an important effect. 
 
 The figure of the earth is not a true or perfect spheroid. Geo- 
 detic studies indicate that it is somewhat irregular in form, while 
 pendulum experiments show that the density is not uniform. These 
 facts favor the planetesimal hypothesis. 
 
 2. Density of the Earth. 
 
 The mean density of the earth, as determined by several inde- 
 pendent methods, is about 5'6. The density of the materials of the 
 earth-surface, leaving out water, is only about 2'5. It is evident, 
 therefore, that the density of the central poi'tions must be much 
 more than 5"6. This great interior density may be the result — 1. Of 
 a difference of material. It is not improbable that the surface of the 
 earth has become oxidized by contact with the 
 atmosphere, and that at great depths the earth 
 may consist largely of metallic masses. Or the 
 great interior density may be the result — 2. Of 
 condensation by the immense pressure of the 
 superincumbent mass. In either case the ten- 
 dency of increasing heat would be to diminish 
 the increasing density. But how much of the 
 greater density is due to difference of material, 
 and how much to increasing pressure, and how 
 much these are counterbalanced by expansfon 
 due to increasing heat, it is impossible to deter- 
 mine. 
 
 The increase of density has been somewhat arbitrarily assumed to 
 follow an arithmetical law. Under this condition a density equal to the 
 mean density would be found at J radius from the surface, and taking 
 the surface density at 2-5, and the mean density at 5-6, the central 
 density would be nearly 15. In the diagram (Pig. 133), if a c = 
 
 Pig. 133 — Diagram illustra- 
 ting the Increasing Densi- 
 ty oj the Earth. 
 
THE CRUST OF THE EARTH. 
 
 173 
 
 radius, the ordinate ax^ surface density = 3-5, and i y =■ mean 
 density = 5'6, then C2, the central density, will be = 14-9. 
 It is needless to say that this result (Plana's) is unreliable. 
 
 3. The Crust of the Earth. 
 
 The surface of the earth undoubtedly differs greatly in many re- 
 spects from its interior, and therefore the exterior portion may very 
 properly be termed a crust. It is a cool crust, covering an incandescent 
 interior ; a stratified crust, covering an unstratified interior ; probably 
 an oxidized crust, covei'ing an unoxidized interior ; and many suppose 
 a solid crust, covering a liquid interior. This last idea, although very 
 doubtfur(p. 86), has probably given rise to the term crust. The term, 
 however, is used by all geologists, without reference to any theory 
 of interior condition, and only to express that portion of the exterior 
 which is subject to human observation. The thickness which is' ex- 
 posed to inspection is about ten to twenty miles. 
 
 Means of Geological Observation. — The means by which Tve are 
 enabled to inspect the earth below its immediate surface -are: 1. Arti- 
 
 FiG. 134. 
 
 flcial sections, such as mines, artesian wells, etc. These, however, pene- 
 trate only to the insignificant depth of half a mile, or rarely of a mile 
 (p. 76). 2. Natural sections., such as cliffs, ravines, caflons, etc. These, 
 as we have already seen (p. 17), sometimes penetrate 5,000 to 6,000 
 feet. 3. Folding, and subsequent erosion of the crust, by which strata 
 from great depths have their edges exposed. Thus, in passing along the 
 surface from s to a (Fig. 134), lower and lower rocks are successively 
 brought under inspection. The dotted lines show how much has been 
 cut away, and therefore the depth of strata exposed. In this way often 
 ten miles depth of strata are brought into view. This is by far the 
 most important means of observation; without it the study of 
 geology would be almost impossible. 4. Volcanoes bring np to the 
 surface materials fr6m unknown but probably very great depths. 
 
 Ten miles seems an insignificant fraction of the earth's radius, 
 being in fact equivalent to less than one thirtieth of an inch in a globt 
 
174 GENERAL FORM AND STRUCTURE OF THE EARTH. 
 
 two feet in diameter. It may seem at first sight an insufficient basis 
 for a science of the earth. We must recollect, however, that only this 
 crust has been inhabited by animals and plants— on this crust only 
 have operated atmospheric, aqueous, and organic agencies — and there- 
 fore on this insignificant crust have been recorded all the most im- 
 portant events in the history of the earth. 
 
 4. General Surface Ponfigtiration of the Earth. 
 
 The surface inequalities of the solid earth or lithosphere are of two 
 general kinds, which may be called greater and lesser. The one is 
 due to interior, ihQ other io exterior causes; the one io igneous, the 
 other to aqueous or erosive agencies. The lesser inequalities we wjU 
 treat under the head of forms of sculpture (p. 378). Our discussjgn 
 now is limited to the greater. Again, these are of two orders of great- 
 ness, viz., those which constitute land-masses and ocean basins, and 
 those which constitute mountain-ranges and intervefling valleys. 
 These latter we shall treat fully hereafter (p. 360) ; we are therefore 
 specially concerned ngw with the former. 
 
 Nearly three quarters of the whole surface of the earth is covered 
 by the ocean.* The mean height of the continents, according to the 
 most recent results, is as follows: Europe, 984 feet; Asia and Africa, 
 1,640 feet; America, Forth' and South, 1,083 feet; Australia, 830 feet. 
 The mean height of all land is given as about 1,378 feet.f These 
 figures are considerably greater than those given by Humboldt and 
 heretofore adopted. 
 
 The mean depth of the ocean is probably 13,000 to 15,000 feet 
 (Thompson). There is probably water enough in the ocean, if the 
 inequalities of the earth's surface were removed, t6 cover the earth to a 
 depth of about two miles. 
 
 The extreme height of the land above the sea-level is five miles, 
 and the extreme depth of the ocean is at least as much. The extreme 
 relief of the lithosphere is therefore not less than ten miles. 
 
 Cause ofLand-Surfaces and Sea-Bottoms.— The discarded idea among 
 geologists as to the general constitution of the earth has been that the 
 earth is still essentially a liquid mass, covered by a solid shell of twen- 
 ty-five to thirty miles in thickness; and that the great inequalities,* 
 constituting land-surfaces and ocean-bottoms, are produced by the up- 
 bending and down-bending of this crust into convex and concave 
 arches, as shown in Fig. 135. The clear statement of this view is 
 sufficient to refute it ; for, when it is remembered that the arches with 
 which we are here dealing have a span of nearly a semi-circumference 
 
 * Land : water : : 1 : 2-63 (Wagner, 1896). 
 
 f Krummel, American Naturalist, vol. xiii, p. 464, 1879. More, recent estimates make 
 it a little over 2,000 feet.— Jour. Geol., vol. i, p. 422, 1893. 
 
GENERAL SURFACE CONFIGURATION OF THE EARTH. 
 
 1Y5 
 
 Fig. 135. 
 
 of the earth, it becomes evident that no such arch, either above or below 
 the mean level, could sustain itself for a moment: for the pressure 
 would be thirty 
 times the crush- 
 ing strength of 
 steel and 500 
 times the crushing 
 strength of granite.* The only condition under which such inequali- 
 ties could sustain themselves on a supporting liquid is the exist- 
 ence of inequalities on the under surface of the crust next the liquid, 
 similar to those on the upper surface, but in reverse, as shown in 
 Pig. 136. And these lower or under-surface inequalities would have 
 to be repeated not only for the largest inequalities, viz., continental 
 surfaces and ocean-bottoms, but also for great mountain plateaus. 
 And thus the hypothesis seems to break down with the weight of its 
 own assumption.f 
 
 Besides, we have already given good reasons (pages 87 and 88) for be- 
 lieving that the earth is substantially solid. Upon the hypothesis of a 
 substantially solid earth, we explain the great inequalities constituting 
 continental surfaces and ocean-bottoms by unequal radial contraction 
 of the earth. 
 
 According to the nebular hypothesis the earth was at one time an in- 
 candescent liquid globe. It then cooled to a substantial solid, although 
 probably with a sub-ci'ust layer underlying large areas of the solid 
 
 crust, and sepa- 
 rating it from 
 the solid nucleus. 
 When first solidi- 
 fied the earth 
 was doubtless a 
 
 regular ohlate spheroid, and, when sufficiently cool to allow condensa- 
 tion of aqueous vapor, covered with a universal ocean. By continued 
 cooling it gradually contracted, and if the rate of cooling and contrac- 
 tion had been equal in all parts of the surface it would have retained 
 its regular spheroid form. But, without perfect homogeneity of com- 
 position and equality of conductivity and of coefficient of contraction 
 in all parts (which is extremely improbable), such equality of cooling 
 and contraction would be impossible. Some parts, therefore, cooled 
 and contracted toward the center more rapidly than others. These 
 more rapidly contracting areas would form hollows and the less rap- 
 
 * Woodward, Science, 1, 194, 1895. 
 
 f It has been shown by G. H. Darwin that the great inequalities of the earth's surface 
 could not be sustained unless the earth be as rigid as granite fur a depth of 1,000 miles. 
 — ^Proceeding of the Royal Society, June, 1881. 
 13 
 
 Fio. 136. - Diagram illustrating the Conditions of Eqnilibrinm of a Solid 
 Crust on a Liquid Interior. 
 
176 GENERAL FORM AND STRUCTURE OF THE EARTH. 
 
 idly contracting areas protuberances. The waters would be gathered 
 in the hollows and form oceans, while the protuberances would be- 
 come continents. In other words, oceanic basin and land-masses 
 are the result of slight distortion of the regular spheroid by unequal 
 radial contraction. This is evidently a true cause ; and, when we con- 
 sider the smallness of these inequalities in comparison with the size 
 of the earth, it will seem a sufficient cause. The mean inequality of 
 the kind we are now considering is about two and a half miles. This 
 in a globe of two feet in diameter would be less than one one-hun- 
 dredth of an inch — an amount that would be scarcely perceptible. 
 If a globe of clay or of stone of this size were heated to incandescence 
 and in this condition ground to a true sphere and then allowed to 
 cool, it is probable that the inequality would be as great as or greater 
 than the above.* 
 
 It is only the greatest inequalities, viz., land-surfaces and sea-bot- 
 toms, which we account for in this way. Mountain-chains are certainly 
 formed by a diSerent process, which we will discuss under that head 
 (p. 360) ; and it is even possible, though not probable, that the causes 
 which operate to produce mountain-chains may also produce these 
 greatest inequalities. 
 
 The continuance of these causes would tend constantly to increase 
 the extent and height of the land, and to increase the depth, but dimin- 
 ish the extent of the sea. This, on the whole, seems to have been the 
 fact, during the history of the earth, as will be shown in Part III. 
 Nevertheless, local causes, both aqueous and igneous, as already shown 
 in Part I, have greatly modified the general contour, both map and 
 profile, given by secular contraction. 
 
 Suh-ocean Crust is denser. — Or, again : the same result would follow 
 even if there were no difference of conductivity, but only of density over 
 large areas. For in so large a globe as the earth — unless preternatu- 
 rally rigid — such large areas must be in a state of hydrostatic equilibrium 
 (Isostasy). The denser areas must sink and form the ocean-bottoms 
 and the lighter areas rise into continental surfaces. But since denser 
 areas are also probably more conductive, and therefore cool faster, it is 
 evident that the two causes would co-operate. The conclusion, there- 
 fore, is inevitable that ocean-bottoms are lower because, and in pro- 
 portion as, the sub-ocean matter is denser, and continents are higher 
 because, and in proportion as, the sub-continent matter is lighter. 
 
 * Under the planetesimal hypothesis (see pp. 89, 171) the greater inequalities of the 
 earth's surface were initiated by the irregular accretion and unequal density of the grow- 
 ing spheroid ; but subsequent effects of gravitational attraction and unequal contraction 
 tended to preserve and accentuate the primal inequalities. It should be understood that 
 according to this theory the interior heat of the earth is the effect of the contraction and 
 not, as ia the nebular theory, the indirect cause. 
 
BOOKS. 
 
 177 
 
 Most careful recent gravity determinations across the American Conti- 
 nent have confirmed these views.* 
 
 Laws of Contiuental Form— That the general contour of continents 
 and sea-bottoms has been determined by some general cause, such as 
 secular contraction, affecting the whole earth, is further shown by the 
 laws of continental form. The most important of these are as follows : 
 
 1. Continents consist of a great interior basin, bordered by elevated 
 coast-chain rims. This typical form is most conspicuously seen in 
 North and South America, Africa, and Australia. Europe- Asia is 
 more irregular, and therefore the typical form is less distinct. We 
 give in Fig. 137, A and B, an east-and-west section of North America 
 
 h ^ AA ^ ' 
 
 w 
 
 Fio. 137.— ji, section across North America; B, section across Australia (after Guyot). 
 
 and of Australia, as typical examples of continental structure. 
 
 The great rivers of the world, e. g., the Nile, Mississippi, Amazon, 
 La Plata, etc., drain these interior continental basins. 
 
 2. In each continent the greatest range of mountains faces the 
 greatest ocean. Thus in America the greatest range is on the west, 
 facing the Pacific ; while in Africa the greatest range is on the east, 
 facing the Indian Ocean. In Asia the Himalayas face the Indian 
 Ocean, while the Altai face the Polar Sea. In Australia the greatest 
 range is to the east, facing the Pacific. 
 
 3. The greatest ranges have been subjected to the greatest and 
 most complex foldings of the strata, and are the seats of the greatest 
 metamorphism (p. 330) and the greatest volcanic activity. 
 
 4. The outlines of the present continents have been sketched in the 
 earliest geological times, and have been gradually developed and per- 
 fected in the' course of the history of the earth. In the case of the 
 North American Continent this will be shown in Part III. 
 
 The cause of some of these laws will be discussed under the head 
 of Mountain-Chains. 
 
 Bocks. 
 
 In geology the term rock is used to signify any material consti- 
 tuting a portion of the earth, whether hard or soft. Thus, a bed of 
 
 •Putnam and Gilbert, Bull. Phil. Soc, Wash., No. 13, p. 81, 1895. 
 
178 
 
 STRATIFIED OR SEDIMENTARY ROCKS. 
 
 sand or clay is no less a rock than the hardest granite. In fact, it is 
 impossible to draw any scientific distinction founded upon hardness 
 alone, as this is a variable condition, without exact relation to either 
 genesis or composition. Calcareous rock of the same origin may be 
 either coral sand, or hard limestone, or crystallized marble; all sand- 
 stones originate as loose sands and are found in all stages of consoli- 
 dation ; argillaceous beds may be clay, or shale, or slate. The same 
 volcanic materials may be stony, glassy, scoriaceous, or loose sand. 
 
 Classes of Rocks. — All rocks are divided into two great classes, viz., 
 stratified or clastic rocks and unstratified rochs. Stratified rocks ar& 
 more or less consolidated sediments, and are usually, therefore, more 
 or less earthy in structure and of aqueous and eolian origin. Unstrat- 
 ified rocks have been more or less completely fused, and therefore are 
 crystalline in structure and of igneous origin. 
 
 CHAPTER II. 
 STRATIFIED OR SEDIMENTARY ROCKS. 
 
 Section- 1. — Kinds, Steuctuee, and Position. 
 
 Stratification. — Stratified rooks are characterized by the fact that 
 they are separated by parallel division-planes into larger sheet-like 
 masses called strata, and these into smaller layers or ieds, and these 
 
 again into still smaller lamince. 
 These terms are purely relative, 
 and are therefore somewhat 
 loosely used. Usually, however, ' 
 the term stratum refers to the 
 mineralogical character ; the 
 term layer to subdivisions of a 
 stratum distinguishable by dif- 
 ference of color or fineness ; and 
 the term lamina to those small- 
 est subdivisions, evidently pro- 
 
 FiG. 138.— Sections of Horizontal and Inclined strata: /l,,„o^ >,„ J.l,„ z,ny.i^i„„ «„,„,»„ nt 
 e, soil; »«, sandstone; sh, shale; Ls, limestone. UUCea Dy the Sorting poWCr 01 
 
 water. For instance, in the an- 
 nexed figure we have three strata of sandstone, clay, and limestone, each 
 divisible into two layers differing in fineness or compactness of the 
 material, and all finely laminated by the sorting power of water. The 
 lamination, however, is not represented, except in the clay stratum, sh. 
 There is another structure represented in the figure — viz., the cross 
 
STKtTCTURE AND POSITION. IY9 
 
 fractures or joints. These, however, are not peculiar to stratified rocks, 
 and will be discussed at another time. 
 
 Extent and Thickness.— Probably nine-tenths of the surface of the 
 land, and, of course, the whole of the sea-bottom, are covered with 
 stratified rocks. Even where these are wanting it is. because they 
 have been removed by erosion or else covered up and concealed by 
 fused matter outpoured on the surface. This proves that every portion 
 of the surface of the earth has been at some time covered with water. 
 The extreme thickness of stratified rocks is certainly not less than 
 twenty miles ; the average thickness is probably several miles. 
 
 Kijids of Stratified Rocks.— Stratified rocks are of three kinds, and 
 their mixtures, viz., arenaceous or sand rocks, argillaceous or clay 
 rocks, and calcareous or lime rocks. Arenaceous rocks, in their inco- 
 herent state, are sand, gravel, shingle, rubble, etc., and in their com- 
 pacted state and san4stones, gritstones, conglomerates, and breccias. 
 Conglomerates are composed of rounded pebbles, and breccias of angu- 
 lar fragments cemented together. Argillaceous rocks, in their inco- 
 herent states, are muds and clays j partially consolidated and finely 
 laminated they form shales, and thoroughly consolidated they form 
 slates. Calcareous rocks are chalk, limestone, and marble. They are 
 seldom in an incoherent state, except as chalk. 
 
 The'se different kinds of rocks graduate into each other through 
 intermediate shades. Thus we may have argillaceous sandstones, cal- 
 careous sandstones, and calcareous shales or marls. 
 
 The most important points connected with stratified rocks we will 
 now, for the sake of greater clearness, bring out in the form of distinct 
 propositions. On these propositions is based nearly the whole of geo- 
 logical reasoning. 
 
 I. Stratified Rocks are more or less Consolidated Sediments.— The 
 evidence of this fundamental proposition is abundant and conclusive, 
 1. Beds of mud, clay, or sand, as already stated, may often be traced 
 by insensible gradations into shales and sandstones. 2. In many places 
 the process of consolidation is now going on before our eyes. This is 
 most conspicuous in sediments deposited at the mouths of large rivers 
 whose waters contain abundance of carbonate of lime in solution, or on 
 the coasts of seas containing much carbonate of lime. Thus the sedi- 
 ments of the Rhine are now consolidating into hard stone (p. 84), and 
 on the coasts of Florida, Cuba, and on coral coasts generally, com- 
 minuted shells and corals are quickly cemented into solid rock (p. 163). 
 3. All kinds of lamination produced by the sorting power of water 
 which has been observed in sediments, have also been observed in 
 stratified rocks. 4. Stratified rocks contain the remains of animals and 
 plants, precisely as the stratified mud of our present rivers contains 
 river-shells, our present beaches sea-shells, or the mud of pur swamps 
 
1QQ STRATIFIED OR SEDIHENTAKY ROCKS. 
 
 the bones of our higher animals drifted from the high lands. 5. Im- 
 pressions of various kinds, such as ripple-marks, rain-prints, footprints, 
 etc., evidently formed when the rock was in the condition of soft mud, 
 complete the proof. It may be considered as absolutely certain that 
 stratified rocks are sediments. Arenacious and argillaceous rocks arb 
 the debris of eroded land, and are therefore called mecfianical sedi- 
 ments or fragmental rocks. Limestones are either chemical deposits 
 in lakes and seas, or are the comminuted remains of organisms. They 
 are therefore either chemical or organic sediments. Conglomerates, 
 grits, and sandstones, indicate violent action; shales and clays quiet 
 action in sheltered spots. Limestones are sometimes produced by vio- 
 lent action — e. g., coral breccia — sometimes very quiet action, as in 
 deep-sea deposits. 
 
 We have already seen (p. 4) that rocks under atmospheric agen- 
 cies are disintegrated into soils, and these soils are carried by rivers 
 and deposited as sediments in lakes and seas. Now we see that these 
 sediments are again in the course of time consolidated into rocks, to-be 
 again raised by igneous agencies into land, and again disintegrated into 
 soils, and redeposited as sediments. Thus the same material has been 
 in some cases worked over many times in an ever-recurring cycle. 
 This is another illustration of the great law of circulation, so universal 
 in Nature. 
 
 Cause of Consolidation. — The consolidation of sediments into rocks 
 in many cases is due to some cementing material, such as carbonate of 
 lime, silica, or oxide of iron, present in percolating waters. In such 
 cases the consolidation often takes place rapidly. In other cases it is 
 due to long -continued heavy pressure, and in still others to long-con- 
 tinued, though not necessarily very great, elevation of temperature in 
 presence of water. In these cases the process is very slow, and there- 
 fore it has not progressed greatly in the more recent rocks. 
 
 II. Stratified Rocks have been gradually deposited.— The following 
 facts show that in many cases rocks have been deposited with extreme 
 slowness : 1. Shales are often found the lamination of which is beau- 
 tifully distinct and yet each lamina no thicker than cardboard. Now, 
 each lamina was separately forrned by alternating conditions, such as 
 the rise and fall of tide, or the flood and fall of river. 3. Again, on the 
 interior of imbedded shells of mollusca, or on the outer surface of the 
 shells of sea-urchins deprived of their spines, are often found attached 
 other shells, as shown in the following figures. Now, these shells must 
 have been dead, iut not yet covered ivith deposit during the whole time 
 the attached shell was growing. As a general rule, in fragmental rocks 
 the finest materials, such as clay and mud, have been deposited very 
 slowly, while coarse materials, such as sand, gravel, and pebbles, have 
 been deposited rapidly. Limestones, being generally formed by the 
 
STRUCTURE AND POSITION. 
 
 181 
 
 accumulation of the calcareous remains of successive generations of 
 organisms, living and dying on the same spot, must have accumulated 
 with extreme slowness. The same is true of 
 infusorial earths. 
 
 It is necessary, therefore, to hear in mind 
 that all stratified rocks were formed in pre- 
 vious epochs by the regular operation of 
 agents similar to those in operation at pres- 
 ent, and not by irregular or cataclysmic 
 action, as supposed by the older geologists. 
 
 Fio. 139.— Serpula on Shell of an Boliinoderm. 
 
 Fig. 140 — Serpulse on Interior 
 of a Shell. 
 
 Thus, cmteris paribus, the thickness of a rock may be taken as a rude 
 measure of the time consumed in its formation. 
 
 III. Stratified Rocks were originally nearly horizontal.— The hori- 
 zontal position is naturally assumed by all sediments in obedience to 
 the law of gravity. When, therefore, we find strata highly inclined or 
 folded, we conclude that their position has been subsequently changed. 
 It must not be supposed, however, that the planes which separate strata 
 were originally perfectly horizontal, or that the strata themselves were 
 of unvarying thickness, and laid atop of each other like the sheets of a 
 ream of paper. On the contrary, each stratum, when first deposited, 
 must be regarded as a widely-expanded cake, thickest in the middle 
 and thinning out at the edges, and interlapping there with other simi- 
 lar cakes. Fig. 141 is a diagram showing the mode of interlapping. 
 
 Pig. 141. — Diagram showing Thinning out of Beds: a, sandstones and conglomerates; b, limestones. 
 
 The extent of these cakes depends upon the nature of the material. 
 In fine materials strata assume the form of extensive thin sheets, while 
 coarse materials thin out more rapidly, and are therefore more local. 
 
 The most important apparent exception to the law of original hori- 
 zontality is the phenomenon of oblique lamination or cross bedding. 
 
182 
 
 STRATIFIED OR SEDIMENTARY ROCKS. 
 
 This kind of lamination is formed by rapid, shifting currents, bearing 
 
 abundance of coarse materials, or by chafing of waves on an exposed 
 
 beach. Many examples of similar lami- 
 nation are found in rocks of previous 
 epochs. Figs. 142 and 143 represent 
 such examples. In some cases cross 
 bedding may be mistaken for highly- 
 inclined strata; careful examination, 
 however, will show that the strata 
 are not parallel with the laminae. The 
 
 strata were originally (and in the cases represented in the figures are 
 
 still) horizontal, while the laminse are oblique. 
 
 FiQ. 142.— Oblique Lamination or cross 
 bedding. 
 
 Fig. 143,-Section on Mississippi Central Railroad at Oxford (after Hilgard): Oblique lamination. 
 
 Elevated, Inclined, and Folded Strata— We may assume with con- 
 fidence that stratified rooks were deposited as sediments at the bcttom 
 
 Pia. 144. 
 
 Fio. 145.— Contorted Strata. 
 
 Of water and in a horizontal or nearly horizontal position. But we do 
 not now find them usually in this condition, place, or position. Some- 
 
STRDCTCRE AND POSITION. 
 
 183 
 
 times, indeed, they are still soft, but usually stony ; sometimes in the 
 vicinity of water, but oftener far in the interior of continents and high 
 
 Pig. 146.— Crumpled Laminse (after Geikie). 
 
 up the slopes of mountains ; sometimes they are still horizontal though 
 elevated (Fig. 144) ; but often, especially in mountain-regions, we find 
 
 Fig. 147.— Contorted Strata (from Logan). 
 
 them tilted at all angles, folded, contorted (Fig. 145), overturned, 
 broken, and slipped, so that it is difficult sometimes to determine their 
 
 Fig. 148.— Section of Appalachian Cbain. 
 
 original order of superposition. Again, in folded strata, sometimes we 
 have the most intricate crumplings of the finer lamincB, such as may be 
 
 Fig. 149.— Section of the Jura Mountains. 
 
 seen in a hand specimen (Fig. 146). Sometimes whole groups of strata 
 are thus folded, as can be seen at one view on a sea-cliff or caflon wall 
 
184 
 
 STRATIFIED OR SEDIMENTARY ROCKS. 
 
 (Fig. 147). Sometimes the whole crust of the earth, for miles in thick- 
 ness and many miles in extent, is thrown into great crust- waves con- 
 stituting mountain-ranges with their intervening valleys (Figs. 148 and 
 
 Fie. 150.— TJpturneiJ and Eroded Strata, Elk Mountains, Colorado (after Hayden). 
 
 149). In such cases the folded structure is not visible at one view, but 
 only brought out by extended survey. In eases of strong folding the 
 strata are often broken and dislocated (Figs-. 200-307). In all cases 
 of elevated strata, whether level or tilted and folded, large portions 
 of the upper parts are carried away by erosion and the remainder 
 is left in isolated patches and basins, or «lse standing at all angles, 
 with their edges exposed (Figs. 147, 148, and in all the other figures 
 under this head). Such exposure on the surface of the edges of eroded 
 strata is called an outcrop. 
 
 Definition of Terms. — ^There are certain terms in frequent use by 
 geologists which must now be defined. These are dip and strike, anti- 
 cline and syncline and conformity and unconformity. 
 
 Dip and Strike — The dip of strata is their inclination to a hori- 
 zontal plane. There are always two elements to be considered — 
 
 viz., direction and amount. 
 Thus in Fig. 151 the strata 
 dip southward about 30°'. 
 The angle of dip is meas- 
 ured by a clinometer (Fig. 
 152), and the direction of 
 dip by a compass. These 
 two are often convenient- 
 ly united in one instrument. As thus determined the angle of dip 
 varies from 0° to 90°, or from horizontality to verticality. Fig. 153 is 
 an example of vertical strata. In strongly folded rocks the strata may 
 be pushed beyond the perpendicular (Fig 154), or even completely re- 
 versed (Fig. 209 C), so that the change from the original position may 
 be nearly or quite 180°. 
 
 In a series of regularly dipping strata, like that of Pig. 151, it is 
 easy to estimate the thickness of the series. The thickness, 5 c, = 
 distance a 5 X sin. of the angle of dip 30°. We sometimes find an 
 actual section such as that represented in the figure, but more usually 
 
 Fig. 151. 
 
STRUCTURE AND POSITION. 
 
 185 
 
 we observe the successive outcrops on the surface and the angle of dip, 
 and construct an ideal section. This is easy enough if the rocks are 
 
 .Fio. 152.— Clinometer. 
 
 bare, but if covered with soil, we must take advantage of every bare 
 spot, of every ravine, gully, and stream-bed where the rocks may be 
 exposed, of every quarry, railroad-cutting, well, etc., and put these 
 -"together in the attempt to make a map of outcrop and a section. 
 
 The strike of strata is the direction of their trend, or, more ac- 
 curately, is the line of intersection of the strata with a horizontal 
 plane. It is always at 
 right angles to the line 
 of dip. If the dip is nortt 
 or south, the strike is easi 
 and west. If the strata 
 are plane, the strike is a 
 straight line; but if they 
 are bent, the strike may 
 be a curve. For example, 
 if the strata are lifted up 
 in the form of a cone or a 
 dome, the strike will be 
 circular ; if the strata be folded and then tilted in a direction at right 
 angles to the folding force, the strike will be sinuous. Again, if the 
 surface of the ground is level, the outcrop will be the strike and will 
 
 be straight or sinu-" 
 ous, according as the 
 strike is one or the 
 other. But the out- 
 crop is usually far 
 more irregular than 
 the strike, as it is 
 affected also by irregularities of surface produced by erosion ; so that 
 in a broken country the outcrop of folded strata is extremely complex. 
 Anticline and Syncline. — Strata are usually more or less folded, 
 and therefore form alternate saddles and troughs. The saddles are 
 anticlines, the troughs synclines. The line along the top of the saddle 
 
 Fig. 153.— Vertical Strata. 
 
 Fig. 154. 
 
186 
 
 STRATIFIED OR SEDIMENTARY ROCtS. 
 
 is an anticlinal axis, the line along the bottom of the trough a syn- 
 clinal axis. If it were not for erosion, the anticlines would be ridges 
 
 and the synclines val- 
 leys. If erosion cuts 
 down to nearly a 
 plane, as in Fig. 155, 
 then an anticline is 
 known by the strata 
 being repeated on 
 each side of an axis and dipping away from one another ; a syncline 
 by the strata also repeated on each side of an axis but dipping toward 
 one another. In the one case the oldest and lowest strata are on the 
 axis and they become higher 
 
 Fig. 155. 
 
 Fig. 156.— Section of Undulating Strata. 
 
 Fig. 157. 
 
 and newer as we go either 
 way ; in the other the upper- 
 most and newest strata are 
 along the axis, and they be- 
 come lower and older as we 
 go either way. 
 
 But erosion usually forms ridges and valleys. In this case some- 
 times the ridges are anticlines and the valleys synclines, as in Fig. 156, 
 
 but sometimes the reverse 
 is true. It is very common 
 to have synclinal ridges and 
 anticlinal valleys (Fig. 157). 
 In this case the original 
 configuration is completely 
 reversed by erosion. This 
 will-be explained in another chapter (p. 280). 
 
 A mass of rock left isolated by erosion and consisting of strata of 
 higher horizon (superior position or later age) than the rocks imme- 
 diately surrounding it is called 
 an outlier (see Figs. 9, 144, 157). . 
 These may be buttes and mesas (see 
 p. 17). In Fig. 155 the area at a is 
 an inlier, the strata being of lower 
 horizon and earlier age than the 
 surrounding rocks. 
 
 Fig. 158 is a map of the folds 
 which are shown in vertical cross- 
 section in Fig 156, but which are 
 assumed to be tilted or pitching 
 
 The 
 
 Fig. 158.— Plan of Undulating Strata, 
 arrows show the direction of dip. 
 
 toward the north, and now eroded to a horizontal plane. Arrows 
 show the dip of the strata and the pitch of the folds. The sinuosity 
 
STRUCTURE AND POSITION. 
 
 18T 
 
 of the outcrop is the effect of the folding and pitching. The field 
 geologist maps the outcrops, determines dip and pitch, and infers 
 
 Pig. 159.— Anticline and Syncline, producing "parallel outcrops (after Willis). 
 
 the structure. If the strata had been simply folded, without pitching, 
 then the outcrop would have shown parallel lines, like Fig. 159. 
 
 The cases represented by these figures are comparatively simple, 
 as we have represented the hard rock with the mantle removed, so that 
 the outcrop is easily traced. But the mantle of waste and the in- 
 equalities of erosion often conceal the complexities of structure so 
 as to make the mapping of a region a difficult task. 
 
 Conformity and Unconformity. — We have just seen that all land- 
 surfaces are deeply eroded and the strata are left with their edges ex- 
 posed. We have also seen (pp. 140-145) that the crust of the earth is 
 everywhere in a state of slow movement : in some places sea-bottoms 
 are rising and becoming land-surfaces, in others land-surfaces are sink- 
 ing to become sea- 
 bottoms. Now, 
 the same thing has 
 taken place in 
 earlier geological 
 times. Suppose, 
 then, an eroded 
 land - surface with 
 the strata - edges 
 exposed, to sink 
 down and become 
 ocean-bottom, and 
 receive sediments 
 coveringthestrata- 
 edges and filling 
 the erosion - hol- 
 lows, and after- 
 ward to rise again 
 and be submitted 
 to the inspection of the geologist ; Fig. 160 represents in section what 
 he would see. They are interpreted as follows : In A and B the lower 
 
 Z o a o~Oo^ ^ ^ ^ o o O o o o O f> a o ~ 
 
 Fig. 160.— Some Cases of Unconformity. 
 
188 STRATIFIED OR SEDIMENTARY ROCKS. 
 
 series of strata was first deposited ; then the sea-bottom was raised to 
 land-surface and the strata tilled and eroded ; then it went down again 
 and received the upper series ;' and, finally, was raised and inspected 
 by the geologist. In C the process was the same, except that the first 
 series of strata was raised without tilting. In D the second series of 
 strata ivas also tilted in the second raising. Now, the strata of each 
 series are said to be conformable among themselves, but the two series 
 are unconformable with one another. 
 
 Definition — Therefore, strata are said to be conformable when they 
 are parallel, continuous, and therefore formed U7ider the same condi- 
 tions, and are unconformable when they are discontinuous, and formed 
 under different conditions; the discontinuity being always marked by 
 an old eroded land-surface. Unconformable strata are usually non- 
 parallel, and this is often made a part of the definition ; but this is 
 not necessary. In Fig. 160, 0, there is no want of parallelism. The 
 reason we have already explained. 
 
 A section like any one of the foregoing — among the commonest in 
 geology — reveals many interesting events: 1. A long period of quiet, 
 during which sediments of the first series were deposited continuously 
 on a sea-bottom. The length of this period is measured by the thick- 
 ness of the series. 2. A period of elevation, during which the sea- 
 bottom became land-surface. We have no means of estimating the 
 length of this period. . 3. A long period during which the land-surface 
 became deeply eroded. The length of this period is measured by the 
 amount of erosion. 4. A period of subsidence, during which the land- 
 surface became sea-bottom. We can not estimate the length of this. 
 5. A long period of quiet, during which the second series of sediments 
 was continuously deposited. This period is estimated by the thickness 
 of the sediments. 6. Another period of elevation by which the whole 
 was brought into view. Therefore a line of unconformity marks a 
 land-surface period between two sea-bottom periods at that place. It 
 is evident that the first stratum above a line of unconformity is usually 
 a conglomerate, marking an old sea-beach. The process is more fully 
 explained in connection with a concrete example on page 306 of Part III. 
 It is evident, then, that every case of unconformity represents a gap 
 in the geological record at that place; for the geological record is written 
 on strata, and unconformity means a land-surface period, during which 
 there was erosion instead of sedimentation, record-destroying instead of 
 record-making. The gap may be filled and the record recovered by 
 sediments formed at that time in some other place. This is usually 
 the case, but not always. The loss of record may be partly by erosion, 
 but mostly because not written at that place. 
 
 Now, such unconformities and lost records are, as we have seen, the 
 result of crust oscillations. But crust oscillations produce necessarily 
 changes in physical geography, and therefore changes of climate, and 
 
CLEAVAGE STRUCTURE. Xgg 
 
 therefore also changes of faunas and floras. They consequently mark 
 the great divisions and subdivisions of geological history. 
 
 Geological Formations.— A group of strata conformable throughout 
 and containing continuous record, and separated from other con- 
 formable groups by a line of unconformity, is called a geological for- 
 mation. There are, however, other tests of a formation, by which 
 hereafter we will complete the definition. 
 
 Cleavage Structure* 
 
 We have thus far spoken only of the original and universal structure 
 of stratified rocks, together with the tiltings, foldings, and erosion, to 
 which they have been subjected. There is, however, often found in 
 stratified rocks a superinduced structure which simulates, and is often 
 mistaken for stratification. It is called cleavage structure, or (since it 
 is usually found in slates) slaty cleavage. This subject has recently 
 attracted much attention, and is an admirable example of the successful 
 application of physics to the solution of problems in geology. 
 
 Cleavage may be defined as the easy splitting of any substance in 
 planes parallel to each other. Such definite splitting may result, in 
 different cases, from entirely different causes. For example (a), under 
 the influence of the sorting power of water, sedimentary materials may 
 be so arranged as to give rise to easy splitting along the planes of lami- 
 nation. Many rocks may be thus split into large coarse slabs called 
 flag-stones, and are used for paving streets, or even sometimes as roof- 
 ing-slates. This may be culledi flag-stone cleavage, or lamination cleav- 
 age. Again (5), the arrangement of the ultimate molecules of a mineral 
 under the ■ influence of molecular or crystalline forces gives rise to an 
 exquisite splitting along the planes parallel to the fundamental faces 
 of the crystal. This is called crystalline cleavage. Again (c), the ar- 
 rangement of the wood-cells under the influence of vital forces gives 
 rise to easy splitting of wood in the direction of the silver-grain. This 
 may be called organic cleavage. 
 
 N"ow, in certain slates and some other rocks is found a very perfect 
 cleavage on a stupendous scale. Whole mountains of strata may be 
 cleft from top to bottom in thin slabs, along planes parallel to each 
 other. The planes of cleavage seem to have no relation to the strata, 
 but cut through them, maintaining their parallelism, however the strata 
 may vary in dip (Pig. 161). Usually the cleavage-planes are highly 
 inclined, and often nearly perpendicular. It is from the cleaving of 
 such slates that roofing-slates, ciphering-slates, and blackboard-slates 
 
 * This structure might be treated under metamorphism, since it is a change of form and 
 structure resulting from pressure. As a product of the crushing of strata in mountain- 
 malting it might appropriately be studied with mountains (see p. 265). 
 
190 
 
 STRATIFIED OR SEDIMENTARY ROCKS. 
 
 FiQ. 161 — Cleavage-Planee cutting through Strata. 
 
 are made. This remarkable structure has long excited the interest of 
 geologists, and many theories have been proposed to explain it. 
 
 On cursory examination of such rocks, the first impression is, that 
 the cleavage is but a very perfect example of flag-stone or lamination 
 
 cleavage — that the 
 cleavage-planes are 
 in fact stratification- 
 planes, and that we 
 have here an admi- 
 rable example of 
 finely laminated rocks which have been highly tilted and then the 
 edges exposed by erosion. Closer examination, however, will generally 
 show the falseness of this view. Fig. 163 represents a mass of slate in 
 which three kinds of structure are distinctly seen, viz., joint faces. A, 
 B, C, J, J ; stratification-planes, S 8 8, gently dipping to the right ; 
 and cleavage -planes, highly inclined, D D, cutting through both. 
 Cleavage-planes are therefore not stratification-planes. 
 
 Again, it has been compared to crystalline cleavage, on a huge scale. 
 It has bfeen supposed that electricity traversing the earth in certain di- 
 rections, while certain rocks were in a semi-fluid or plastic state through 
 heat, arranged the particles of such rocks in a definite way, giving rise 
 to easy splitting in definite directions. In support of this view it was 
 urged that cleaved slates are most common in metamorphic regions ; 
 and metamorphism, as we shall see hereafter (p. 321 et seq.), indicates 
 the previous plastic state of rocks, which is a necessary condition of the 
 rearrangement of the particles by electricity. The great objections to 
 this theory are — 1. That the cleavage is not like crystalline cleavage, 
 between ultimate 
 molecules, and 
 therefore perfect- 
 ly smooth, but 
 between discreet 
 and quite visible 
 granules; and, 3. 
 That although the 
 phenomenon is 
 indeed most com- 
 mon in metamor- 
 phic- rocks, yet crystallization is by no means a necessary condition ; 
 on the contrary, when the necessary conditions are present, the less 
 the crystallization the more perfect the cleavage. 
 
 It is evident, therefore, that slaty cleavage is not due to any of the 
 causes spoken of above. It is not flag-stone cleavage, nor crystalline 
 cleavage, and of course can not be organic cleavage. 
 
 D 
 
 D J ' 
 
 Pig. 168.— strata, Cleavage-Planes, and Joints. 
 
CLEAVAGE STRUCTURE. 
 
 191 
 
 Sharpe's Mechanical Theory. — The first decided step in, the right 
 direction was made by Sharpe. According to him, slaty cleavage is al- 
 ways due to powerful pressure at right angles to the planes of cleavage, 
 by which the pressed mass has been compressed in the direction of press- 
 ure and extended in the direction of the dip of the cleavage planes. 
 This theory may be now regarded as completely established by the 
 labors of Sharpe, Sorby, Haughton, Tyndall, and others. We will give 
 a few of the most important observations which establish its truth. 
 
 (a) Distorted Shells. — Many cleaved slates are full of fossils. In 
 such cases the fossils are always crushed and distorted as if by powerful 
 pressure, their diame- 
 ter being shortened at "'^m^^^^ "'^^iMM^ .^"V^r^^ 
 
 right angles to the ^~^W^^m- m. ^ffli^ 
 
 cleavage, and greatly ^otSw^ l,MS^ s 
 increased in the direc- ?-. 
 tion of the cleavage- 
 planes. The follow- 
 ing figures (Pig. 163) 
 are examples of dis- 
 tortion by pressure. 
 In Fig. 163, ZZ gives 
 the direction of the 
 planes of cleavage ; Figs. 1, 2, 3, 4, represent one species ; 5, 6, 7, 8, 
 another. In Fig. 164 still another species is represented in the natural 
 and distorted forms. 
 
 (&) Association with Foldings. — Cleavage is always associated with 
 
 strong foldings and contortions of the strata. The folding of the 
 
 strata is produced by horizontal pressure ; the strike of the strata, or 
 
 the direction of the anticlinal and synclinal axes, 
 
 -^ being of course at right angles to the direction of 
 
 Tiressure. Now, if cleavage is produced by the same 
 
 Fio. 163.— Distorted Fossils (after Sharpe). 
 
 B 
 
 C 
 
 Fig. Iftl.— Cardium Hillanum : A, natural form; B and 0, deformed by pressure. 
 
 pressure which folded the strata, then in this case we ought to find the 
 cleavage-planes highly inclined, and their strike parallel with the 
 strike of the strata ; and such we find is usually the fact. In Fig. 165 
 the heavy lines represent the strata and the light lines the cleavage- 
 planes, both outcropping on a nearly level surface, and parallel to each 
 
 other. 
 
 14 
 
192 
 
 STRATIFIED OR SEDIMENTARY ROCKS. 
 
 (c) Jissociation with Contorted LamincB. — The last evidence was 
 taken from foldings on a grand scale of the crust of the earth ; but 
 even fine lines of lamination are often thrown into intricate foldings by 
 squeezing together in the direction of the lamination-planes. In such 
 case, of course, the cleavage ought by theory to be 
 at right angles to the original direction of the 
 lamination, and in such direction we actually find 
 them.. Fig. 166 represents a block of rock in which 
 tjjjree lamination-liues are visible. The lower one, 
 f d, consists of coarse sand which could not mash, 
 
 FiQ. 16^.— Cleavage- Planes intersecting Strata. 
 
 Fio. 166.— Cleavage-Planes 
 (after Tyndfll). 
 
 and therefore has been thrown into folds. As the specimen stands in 
 the figure, the pressure has been horizontal ; the perpendicular lines 
 represent the position of the cleavage-planes. Fig. 167 represents a 
 beautiful specimen of laminated slate, in which the lamination-planes 
 
 have been thrown into folds by 
 pressure. The direction of the 
 pressure is obvious. The planes 
 of cleavage are parallel to the 
 face, c p, and therefore at right 
 angles to the pressure. 
 
 [d) Flattened Nodules. — In 
 some finely-cleaved slates, such 
 as are used for writing-slates, it 
 is common to .find small light- 
 greenish, elliptical-spots of finer 
 hraterial. In clay -deposits of 
 the present day it is also com- 
 mon to find imbe'dded little 
 round nodules of finer mate- 
 rial. It is probable that the 
 greenish nodules' in slate were 
 also rounded nodules of finei 
 clay in the original clay-deposit 
 from which the slate was formed by consolidation. But in cleaved 
 slates these nodules are always very much flattened in the direction'at 
 
 Pio. 167.— A Block of Cleaved Slate (after Jakes). 
 
CLEAVAGE STRUCTDEE. 
 
 193 
 
 right angles to the cleavage-planes, and spread out in the direction of 
 these planes. 
 
 (e) Experimental Proof. — Finally, experiments by Sorby and by 
 Tyndall show that clay (the basis of slates), when subjected to power- 
 ful pressure, exhibits always a cleavage, often a very perfect cleavage, 
 at right angles to the line of pressure. 
 
 Physical Theory. — Cleavage is certainly produced by pressure, but 
 the question still remains : How does pressure produce planes of easy 
 splitting at right angles to its own direction ? What is the physical 
 explanation of cleavage ? 
 
 Sorby's Theory.— Mr. Sorby's view is that all cleaved rocks con- 
 sisted, at the time when this structure was impressed upon it, of a plastic 
 mass, with unequiaxed incompressible foreign particles disseminated 
 through it ; and that by pressure the unexquiaxed particles were turned 
 so as to bring their long diameters in a direction more or less nearly at 
 right angles to the line of pressure, and thus determined planes of easy 
 fracture in that direction. Usually, as in slates, the plastic material is 
 clay, and the unequiaxed particles are mica-scales. 
 
 In proof of this view, Mr. Sorby mixed clay with mica-scales or 
 with oxide-of-iron scales, and, upon subjecting the mass to powerful 
 
 Fig. 168.— Cleavage in Slate between two Dolomite Beds which do not show Cleavage 
 (after Van Hiee). 
 
 compression and drying, he always found a perfect cleavage at right 
 angles to the line of pressure. Furthermore, by microscopic examina- 
 tion he found that both in the pressed clay and in the cleaved slates 
 the ipica-scales lay in the direction of the cleavage-planes. 
 
 Although cleavage is most perfect in slates, yet other rocks are 
 sometimes affected with this structure. In a specimen of cleaved lime- 
 stone, Sorby found under the microscope unequiaxed fragments of 
 
194 
 
 STRATIFIED OB SEDIMENTARY ROCKS. 
 
 - 
 
 B 
 
 A 
 
 
 60%" 0^ 
 
 
 Pig. 169.— Illustrating Sorby's Theory 
 of Slaty Cleavage (after Sorby). 
 
 broken shells, corals, crinoid stems, etc. (organic particles), in a homo- 
 geneous limestone-paste, lying with their long diameters in the direc- 
 tion of cleavage. Originally the limestone was a lime-mud with (he 
 supposes) unequiaxed organic particles disseminated. In some cases, 
 however, Sorby recognized the very important fact that the organic 
 fragments which were encrinal joints, had heen flattened by pressure — 
 had changed their form instead of their position. A, Fig. 169, gives a 
 
 section of the mass in the supposed origi- 
 nal condition, and B the condition after 
 pressure. This observation contained the 
 germ of the theory proposed by Tyndall. 
 Tyndall's Theory. — Tyndall was led 
 to reject Sorby's theory by the observation 
 that cleavage structure was not confined 
 to masses containing unequiaxed particles 
 of any kind, but, on the contrary, the 
 cleavage' is more perfect in proportion as 
 the mass is free from all such particles. 
 Clay, deprived of the last trace of foreign 
 particles by the sorting power of water, 
 when pressed, cleaved in the most perfect 
 manner. Common beeswax, flattened by 
 powerful pressure between two plates of glass and then hardened by 
 cold, exhibits a most beautiful cleavage structure. Almost any sub- 
 stance — curds, white-lead powder, plumbago — subjected to powerful 
 pressure, exhibits to some extent a similar structure. Tyndall explains 
 these facts thus : Nearly all substances, except vitreous, have a gran- 
 ular or a crystalline structure, i. e., consist entirely of discrete gran- 
 ules or crystals, with surfaces of easy fracture between them. When 
 such substances are broken, the fracture takes place between the crys- 
 tals or granules, producing a rough crystalline or granular surface, 
 entirely different from the smooth surface of vitreous fracture. Marble, 
 cast iron, earthenware, and clay, are good examples of crystalline and 
 granular structure. Now, if a mass thus composed yield to pressure, 
 every constituent granule is flattened into a scale, and the structure be- 
 comes scaly ; and as the surfaces of easy fracture will still be between 
 the constituent scales, we have cleavage at right angles to the line of 
 pressure. A mass of iron, just taken from the puddling-furnace and 
 cooled, exhibits a granular structure ; but if drawn out into a bar, each 
 granule is extended into a thread, and the structure becomes fibrous; 
 or if rolled into a sheet, each granule is flattened into a scale, and we 
 have a cleavage structure. 
 
 There can be little doubt that this is the true explanation of slaty 
 cleavage. ' The change of form which, as we have seen, has taken place 
 
CLEAVAGE STRUCTURE. 195 
 
 in the fossil-shells, encrinal Joints, and rounded nodules, has affected 
 every constituent granule of the original earthy mass, so that the 
 structure becomes essentially scaly instead of granular. 
 
 Recent study leads Van Hise to the following conclusion : " Eock- 
 cleayage is due to the arrangement of the mineral particles with their 
 longer diameters or readiest cleavage, or both, in a common direction, 
 and that this arrangement is caused, first and most important, by 
 parallel development of new minerals ; second, by the flattening and 
 parallel rotation of old and new mineral particles; and third, and 
 of least importance, by the rotation into approximately parallel posi- 
 tions of random original particles." (See references, page 233.) 
 
 Geological Application.— It may be considered, therefore, as certain 
 that cleaved slates have assumed their peculiar structure under the in- 
 fluence of powerful pressure at right angles to the cleavage-planes, by 
 which the whole squeezed mass is mashed together in one direction and 
 extended in another. Taking any ideal sphere in the original unsqueezed 
 mass : after mashing the diameter in the line of pressure has been short- 
 ened, the diameter in the line of cleava,ge-dip has been correspondingly 
 extended, and the diameter in the line of cleavage-strike unaffected (since 
 extension of this'diameter in any place must be compensated by short- 
 ening in a contiguous place right or left) ; so that the original sphere 
 has been converted into a greatly-flattened ellipsoid of three unequal 
 diameters. The amount of compression and extension may be estimated 
 in the case a by the amount of distortion of shells of known form (Figs. 
 163 and 164) ; in the case c by a comparison of the transverse diame- 
 ter of the block with the length of the folded line / d (Fig. 166) ; in 
 the case d by the relation between the diameters of the elliptic spots. 
 By these means, but principally by the first, Haughton has estimated 
 that an original ideal sphere has been changed into an ellipsoid, whose 
 greatest and shortest diameters are to each other, in some cases, as 3 : 1, 
 in others as 3 : 1, 4 : 1, 6 or 7 : 1, 9 : 1, and in some even 11 : 1. The 
 average in well-cleaved slates, according to Sorby, is about 6 : 1. Now, 
 since this ratio is the result partly of compression and partly of exten- 
 sion, it is evident that either the compression alone or the extension 
 alone would be the square roots of these ratios. Therefore, we may 
 assume the average compression as 3^ : 1, and the average extension 
 as 1 : 2|. 
 
 It is impossible to overestimata the geological importance of these 
 facts. Whole mountains of strata, whole regions of the earth's crust, 
 are cleaved to great and unknown depths, showing that the crust has 
 been subjected to an almost inconceivable force, squeezing it together 
 in an horizontal direction and swelling it upward. This upward swell- 
 ing, or thickening of the strata by lateral squeezing, is a probable cause 
 of gradual elevation of the earth's crust, which has not been sufficiently 
 
196 
 
 STRATIFIED OR SEDIMENTARY ROCKS. 
 
 noticed by geologists. We will speak again of this important subject 
 in our discussion of mountain-formation. 
 
 There are reasons for believing that the squeezing did not take 
 place, and the structure was not formed, while the strata were in their 
 original condition of plastic sediment, but after they had been consoli- 
 dated into rock and the contained fossils had been completely petrified, 
 otherwise the shells must have been broken by the pressure. Yet, on 
 the other hand, some degree of plasticity seems absolutely necessary to 
 account for so great a compression in one direction and extension in 
 another without disintegration of the mass. It seems most probable 
 that at the time the structure was produced these rocks were deeply 
 buried beneath other rocks and in a somewhat plastic state, through 
 the influence of heat in the presence of water. Afterward, they were 
 exposed by erosion. 
 
 Nodular or Concretionary Structure. 
 In many stratified rocks are found nodules of various forms scattered 
 through the mass or in layers parallel to the planes of stratification. 
 Like slaty cleavage, this structure is the result of internal changes sub- 
 sequent to the sedimentation ; for the planes of stratification often pass 
 directly through the nodules (Figs. 170 and 171). The flint nodules of 
 
 Fig. 170. 
 
 Fie. 171. 
 
 the chalk, and the clay iron-stone nodules of the coal strata and hy- 
 draulic lime-balls, common in many clays, are familiar illustrations of 
 this structure. 
 
 Cause. — Nodular concretions seem to occur whenever a more solu- 
 ble or more suspensible substance is diffused in small quantities 
 through a mass of entirely different and more flxed material. Thus, 
 if strata of sandstone or clay have small quantities of carbonate of lime 
 or carbonate of iron diffused through them, the diffused particles of 
 lime or iron will gradually, by a process little understood, segregate 
 themselves into more or less spherical or nodular masses, in some cases 
 almost pure, but generally inclosing a considerable quantity of the 
 material of the strata. In this manner lime-balls and iron-ore balls 
 and nodules, so common in sandstones and clays, are formed. In like 
 manner, the flint nodules of the chalk were formed by the segregation 
 of silica, originally diffused in small quantities through the chalk-sedi- 
 ment. Very often some foreign substance forms the nucleus about 
 
NODULAR OR CONCRETIONARY STRUCTURE. 
 
 19Y 
 
 which the segregation commeiices. On breaking a nodule open, a 
 shell or some other organisili is often found beautifully preserved. 
 These nodules, therefore, are a fruitful source of beautiful fossils. In 
 most cases, probably in all eases, 
 the segregating substance must have 
 been to some extent soluble in water 
 
 Fia. 172.— Septariiim, from Hamilton shale, Pig. 173. — Section through Septarium, from 
 
 Conesus Lake, N. T. ^scaZe in inches.) Weymouth, England. 
 
 pervading, or suspensible in water percolating the stratum ; and the 
 reason why fhey are so frequently associated with fossils is that 
 decomposing organic matter renders many substances such as lime 
 carbonate, iron oxide, and silica more soluble. Sometimes the nod- 
 ules run together, forming a more or less continuous stratum. In 
 such cases, the segregating material is more impure. 
 
 Forms of Nodules. — The typical and most common form is 
 globular. This is well seen in lime-balls- and iroq-balls. Sometimes 
 these balls are solid, sometimes they have irregular cracks in the cen- 
 
 Fio. 174.— Curious Forms of Clay Concretions, a, from Schoharie Court House, N. Y. ; 6, South 
 Hadley, Mass. ; c. Button Bay, Lake Champlain. 
 
 ter (Fig. 173), sometimes they have a radiated structure, and 
 sometimes they are hollow like a shell (this is common in iron-balls). 
 They vary in size from that of a pea to six and eight feet in diameter. 
 
198 
 
 STRATIFIED OR SEDIMENTARY ROCKS. 
 
 Often, however, instead of the spherical form, they take on various and 
 strange and fantastic shapes (Fig. 174), sometimes like a dumb-bell, 
 sometimes a flattened disk, sometimes a ring, sometimes a flattened 
 ellipsoid, regularly seamed on the surface like the shell of a turtle 
 (turtle-stones, see Fig. 173). Concretions assume a great variety of 
 imitative forms, and are often mistaken by unscientific observers tor 
 
 fossils. The frequent accounts 
 of the finding of "petrified 
 bodies" and other marvelous 
 things are usually based on con- 
 cretionary forms, if they have 
 any basis in fact. 
 
 Kinds of Concretions.— In 
 sandstone strata the concretions 
 are usually either lime or oxide 
 of iron. In clay strata they are 
 lime or carbonate of iron (clay 
 iron-stone of the coal strata), or 
 a mixture of these. In pure 
 limestone the concretions are al- 
 ways silica (see p. 169). The 
 flint nodules of the chalk are 
 arranged in parallel planes. 
 
 Shalloiv-Water and Beach 
 Structures. 
 
 Li LiIiliIj_LLLi:al^- 
 
 Fio. 175.— Wave-riijpleB, from Jura-Trias, 
 Connecticat Valley. 
 
 Current-bedding or cross- 
 bedding is illustrated in Fig. 142 
 (p. 182), and the curving lami- 
 nae of flow-and-plunge structure are shown in Fig. 143. Ripple- 
 marlcs ("washboards" of the quarrymen) are very common features 
 in s*hallow- water deposits (Fig. 175). 
 
 Several structures are characteristic of beach deposits. Ridges, 
 either sharp-crested or rounded (see Fig. 176), with intervening hol- 
 lows from 10 to 80 feet wide, are found in sandstones accumulated on 
 beaches by wave-work. Wave-marhs are the graceful, curving lines, 
 concave toward the water, which mark the reach of the broken waves 
 that slide up the beach slopes. Mud-cracks and rain-prints are other 
 evidences of exposure of muddy shore to sun and storm. 
 
 Fossils: their Oeigin and Distribution. 
 
 Stratified rocks, as we have already seen, are sediments accumulated 
 in ancient seas, lakes, deltas, etc., and consolidated by time. As now, 
 
FOSSILS: THEIR ORIGIN AND DISTRIBUTION. 
 
 199 
 
 SO then, dead shells were imbedded in shore-deposits ; leaves and logs 
 of high land-plants, and bones of land-animals, were drifted into 
 swamps and deltas and buried in mud; and tracks were formed on 
 flat, muddy shores by animals walking on them. These have been 
 
 raf^fWBJT^WMf ffv-iHrvfrffifrrof/a 
 
 Fig. 176.— Wave- work on Shore of Lake Ontario. 
 
 preserved with more or less change, and are even now found in great 
 numbers inclosed in stratified rocks. They are called fossils. A 
 fossil, therefore, is any evidence of the former existence of a living 
 being. Fossils are the remains of the faunas and floras of previous 
 geological epochs. Their presence is the most constant characteristic 
 of stratified rocks. 
 
 Degrees of Preservation. — Sometimes only the tracks of animals, 
 or impressions of leaves of plants, are preserved. More commonly 
 the bones or shells, or other hard parts of animals, are preserved 
 with various degrees of change. Sometimes even the soft and more 
 perishable tissues are preserved. We will treat of these degrees under 
 three principal heads. 
 
 1. Decomposition prevented and the Organic Matter more or less 
 completely preserved. — Cases of this kind are usually found in com- 
 paratively- recent strata, and imbedded either in frozen soils, or in 
 peat, or in stiff clays; although some cases of partial preservation of 
 the organic matter are found even in old rocks. Extinct elephants 
 have been found frozen in the river-bluffs of Siberia so perfectly pre- 
 served that dogs and wolves ate their flesh. Skeletons of men and 
 animals are found in peat-bogs and stiff clays of a comparatively re- 
 cent formation, the organic matter of which is still preserved. In 
 clays of the Tertiary period the imbedded shells still retain the epi- 
 dermis, and even in the Lias (Mesozoic) shells are found retaining the 
 nacreous luster. Coal is vegetable matter changed but not destroyed. 
 
200 STRATIFIED OR SEDIMENTARY ROCKS. 
 
 2. Petrifaction: Organic Form and Structure preserved. — In the 
 last case the organic matter is more or less preserved. In the ease 
 now to be described the organic matter is entirely gone; but the or- 
 ganic form and the organic structure are preserved in mineral mat- 
 ter. This is what is usually called petrifaction or mineralization. 
 The best example of this is petrified wood. In a good specimen of 
 petrified wood, not only the external form of the trunk, not only th'C 
 general structure of the stem, are discernible, but even the micro- 
 scopic cellular structure of the wood, and the exquisite sculpturings 
 of the cell-walls themselves, are perfectly preserved, so that the kind 
 of wood may often be determined by the microscope with the utmost 
 certainty. Yet not one particle of the organic matter of the wood 
 remains. It has been entirely replaced by mineral matter; usually 
 by some form of silica. 
 
 Theory of Petrifaction. — It is well known that the smallest fis- 
 sures and cavities in rocks are speedily filled by infiltrating waters 
 with mineral matters. Now, wood buried in soil soaked with some 
 petrifying material becomes highly charged with the same, and the 
 cells filled with infiltrated matter, and when the wood decays the 
 petrifying material is left, retaining the structure of the wood. But 
 this is not all, for in Kature there is an addi- 
 " * tional process. As each particle of organic mat- 
 
 ter passes away by decay, a particle of mineral 
 matter takes its place, until finally the whole of 
 the organic matter is replaced. Petrifaction, 
 p^g j^^ therefore, is a process of substitution, as well as 
 
 interstitial filling. Now, it so happens, probably 
 from the different nature of the process in the two cases, that the in- 
 terstitial filling always differs, either in chemical coinposition or in 
 color, from the substituted material. As shown in Fig. 177, the mat- 
 ter filling the cells (&) is always different from the matter forming 
 the cell-wall (a). 
 
 The most common petrifying materials are silica, carbonate of 
 lime, and sulphide of iron (pyrites). In the case of petrifaction by 
 pyrites the process is quite intelligible, but the structure is usually 
 very imperfectly preserved. In contact with decaying organic matter, 
 sulphate of iron is deoxidized by the organic matter, the latter pass- 
 ing off as carbonic acid and water, and the former becomes insoluble 
 sulphide (FeSj), and is deposited. 
 
 The process of replacement by silica (silicification) is less clear, 
 but it is probably as follows: Silica is found in solution in many 
 waters, being held in this condition by small quantities of alkali pres- 
 ent in the waters. In contact with decomposing wood the alkali is 
 neutralized by the humic, ulmic, and other acids of decomposition, 
 and the silica therefore deposited. 
 
FOSSILS: THEIK ORIGIN AND DISTRIBUTION. 
 
 201 
 
 Fio. 178. 
 
 3. Organic Form only preserved. — In the third case organic mat- 
 ter and organic structure are both lost, and only organic form is pre- 
 served.' This kind of fossilization is most commonly seen in shells. It 
 may be subdivided into four subordinate cases, represented in section 
 by a, b, c, and d of -Fig. 178. In this figure the horizontal lines repre- 
 sent the original sedi- 
 ment which may or may 
 not have consolidated 
 into rock; the vertical 
 lines represent a subse- 
 quent filling of differ- 
 ent and usually finer 
 material. In a we have a mold of the external form of the shell pre- 
 served in sediment. The shell with the undecayed animal was im- 
 bedded, and afterward entirely dissolved away, leaving only the hol- 
 low mold. In b the same process has taken place, only the mold has 
 been subsequently filled by infiltration of slightly soluble matters. 
 In this case, we have both the mold and the cast of the external form ; 
 the mold being formed of sediment, and the cast of infiltrated matter. 
 These are always of different materials, i. e., different either in chem- 
 ical composition or in state of aggregation. In c we have a mold of 
 the external form in sediment, and a cast of the internal form in the 
 same material with an empty space between, having the exact form 
 and thickness of the shell. In this case, the already dead and empty 
 shell was imbedded in sediment, which also filled its interior ; after- 
 ward the shell was removed, leaving an empty space. In d this empty 
 space was subsequently filled by infiltration. In shore and river de- 
 posits of the present day it is very common to find shells imbedded in, 
 and filled with, sand or mud. In the more recent tertiary rocks shells 
 
 Fig. 179.— ffi, Cast of interior; 
 b, natural form. 
 
 Fio 180.— o, Natural form; 
 b, cast of interior and 
 mold of exterior. 
 
 Fig. 181. — Trigonia Longa, showing 
 cast (o) of the exterior and {.b) of 
 the interior of the shell. 
 
 are commonly found in the same condition precisely ; but in the older 
 rocks more commonly the original shell is removed, and the space either 
 left empty or filled by infiltration. Cases c and d are well represented 
 
202 STRATIFIED OR SEDIMENTARY ROCKS. 
 
 by Figs. 179, 180, and 181. Cases like a and c are most commonly 
 found in porous rocks like sandstone ; h and d, especially the latter, are 
 found in all kinds of rocks. By far the most common infiltration fill- 
 ings are carbonate of lime and silica. 
 
 Often we find impressions of the forms of small portions only of the 
 original organism, as of the leaves of trees, or the feet of animals walk- 
 ing on the soft mud of the fiat shores of ancient bays. Such tracks 
 were afterward covered up with river or tidal deposit, and thus pre- 
 served. On cleaving the rock along the lamination-planes we have on 
 one side a mold and on the other the cast of the foot. 
 
 Between cases 1 and 3 every stage of gradation may be traced. 
 The amount of change, as a general fact, varies with the age of the 
 rock ; but is still more dependent on the kind of rock and the degree 
 of metamorphism. In an impermeable rock, like clay, the changes are 
 much more slow than in a porous rock, like sandstone. 
 
 Distribution of Fossils in the Strata. 
 
 The nature of the fossil species found in rocks is determined partly 
 by the Mnd of rock, partly by the country where the rock is found, and 
 partly by the age of the rock. 
 
 1. Kind of Rock. — It is well known that the species of lower marine 
 animals vary with the depth. They also vary with the kind of bottom. 
 Thus, along shore-lines and on sand-bottom the species differ from 
 those in deep water and on mud-bottom. Shells are found mostly 
 along shore-lines, corals in opener seas, and foraminifera in deep seas. 
 The same was true in every previous epoch. We might expect, there- 
 fore, and do find, that the lotver marine fossils of sandstones, shales, 
 and limestones, differ even when these strata belong to the same coun- 
 try and. geological epoch. The higher marine animals, such as fishes, 
 cuttle-fish, etc., swimming freely in the sea, are more independent of 
 bottoms, and we find their skeletons and shells equally in all kinds of 
 strata. Land animals perish on land, and their skeletons are drifted 
 into bays, river-deltas, and lakes, and buried there mostly in fresh- 
 water or brackish-water deposits of sand and clay. It is, therefore, in 
 such strata that their remains are commonly found. 
 
 2. The Country where found.— It is also well known that the 
 faunas and fioras of different countries at the present time differ as 
 to species, and often as to genera and families ; the difference being 
 generally in proportion to the difference in climate, the physical bar- 
 riers intervening, and the length of time during which the barriers 
 have existed. The same was true of the faunas and fioras of previous 
 epochs, and therefore of the fossils of the same age in different coun- 
 tries. The fossil species of the same epoch in America, in Europe, 
 and in Asia are not usually identical, although there may be a general 
 
DISTEIBUTION OF FOSSILS IN THE STRATA. 203 
 
 resemblance. The geographical diversity, however, is small in the 
 lowest and oldest rocks, and becomes on the whole greater and greater 
 as we pass upward into newer and newer rocks, and is greatest in the 
 fauna and flora of the present day. 
 
 3. The Age. — This introduces the subject of the laws of distribution 
 of organisms in time, or of fossils vertically in the series of stratified 
 rocks. The subject will be more fully treated in Part III, of which it 
 constitutes the principal portion. We now bring out only so much as 
 is necessary as a basis of classification of stratified rocks. 
 
 (a) Geological Fauna and Flora and Corresponding Geological 
 Period and Geological Formation. — As we pass from the oldest and 
 lowest rocks upward to the newest and highest, we find that all the 
 species, most of the genera, and many of the families, change many 
 times. Now, all the species of animals and plants inhabiting the earth 
 at one time constitute the fauna and flora of that geological time. 
 G-eologioal faunas, therefore, have changed many times. In a con- 
 formable series of rocks the change from one fossil fauna or flora to 
 another succeeding is always gradual, the species of the later fauna or 
 flora gradually replacing those of the earlier. But between two series 
 of unconformable strata the change is sudden and complete — as if one 
 fauna and flora had been suddenly destroyed and another introduced. 
 It must be remembered, however, that unconformity always indicates 
 a great lapse of time unrepresented at the place of observation by 
 strata or fossils. It is therefore probable that the apparent suddenness 
 of the change is only the result of our ignorance of the fauna and flora 
 of the period unrepresented, and this is confirmed whenever we find 
 the intermediate strata. Nevertheless, as unconformity always in- 
 dicates chajiges of physical geography, and therefore of climate, it is 
 probable that in the history of the earth there were periods of great 
 changes, marked by unconformity of strata, during which changes of 
 species were more rapid, separated by periods of comparative quiet, 
 marhed by conformity, during which the species were either un- 
 changed, or changed slowly.- Such a period is called a geological 
 period or geological epoch, and the rocks formed during a geological 
 period or epoch are called & formation. 
 
 There are, therefore, two tests of a formation and a corresponding 
 geological period, viz., 1. Conformity of the strata or rock-system, and, 
 3. General similarity of fossils, or life-system. There are also two 
 modes of separating formations and corresponding periods, viz., un- 
 conformity of the rock-system, and great and sudden change of the 
 life-system. A geological formation, therefore, may be defined as a 
 group of conformable rocks containing similar fossils, usually 
 separated from other similar groups containing different fossils by un- 
 conformity. A geological period may be defined as a period of com- 
 
204 STRATIFIED OR SEDIMENTARY ROCKS. 
 
 parative quiet, during which the physical geography, climate, and 
 fauna and flora were substantially the same, usually separated from 
 other similar periods by changes of physical geography and climate, 
 which resulted in changes of fauna and flora. Of these two tests, how- 
 ever, the life-system is usually considered the most important, and in 
 case of disagreement must control classification. 
 
 (b) Geological Faunas and Floras differ more than Geographical 
 Faunas and Floras. — If there were no geographical diversity, species 
 of the same age would be identical all over the earth, and therefore it 
 would be easy to determine strata of the same age (geological horizon). 
 On the other hand, if geographical diversity in any age were as great 
 as the diversity between two successive ages, then it would seem im- 
 possible to establish a geological horizon. But this law states that the 
 difference between two successive faunas is greater than between two 
 contiguous faunas. In other words, the species of successive periods, 
 or fossils of successive formations, differ from each other more than 
 species of the same period or fossils of the same formation in different 
 parts of the earth. There is a general similarity in the species of the 
 same period all over the surface of the earth. Hence by comparison 
 of fossils it is possible to determine what strata, in different portions of 
 the earth, belong to the same period (to synchronize strata). The 
 strata all over the earth, which were formed at the same time, are said 
 to belong ta the same geological horizon. Strata of the same horizon 
 are determinable by similarity of fossils with considerable certainty, 
 until we come up to the tertiary rocks. In all the newer rocks, how- 
 ever, the geographical diversity is so great as to interfere seriously with 
 the ability to synchronize by means of comparison of fossils. Another 
 method, therefore, is used for these higher rooks. 
 
 (c) Increasing Likeness to Existing Forms. — By examining and 
 comparing fossils from the lowest to the highest rocks, it has been ob- 
 served that there is a steady approach of the fossil faunas and floras to 
 the present faunas and floras, first in the families, then in the genera, 
 and finally in the species. The species of fossil molluscous shells begin 
 to be identical with molluscous species of the present day only in the 
 Terfwrt/ rocks, and the proportion of identical species steadily increases 
 as we pass upward. Thus in the newer rocks, just where the other 
 method (comparison of fossil faunas with one another) begins to fail, 
 \ve may synchronize strata of different localities, by comparing their 
 shell fauna with the shell fauna of the present day, in the same locali- 
 ties. Those are said to be of the same age which contain the same per- 
 centage of shells identical with those of the present day. To this w,e 
 may add that, if not species, at least many genera and families, espe- 
 cially among vertebrates, are characteristic of each horizon even of the 
 newest rocks. 
 
classification of stratified rocks. 205 
 
 Section 2. — Classification of Stratified Eocks. 
 
 Geology is essentially a history. Stratified rocks are the leaves on 
 which this history is recorded. The fundamental idea of every clas- 
 sification is therefore relative age. The object to be attained in classi- 
 fication is, j^rs^, to arrange all rocks in chronological order, so that the 
 history may be read as it was written ; and then, second, to collect them 
 into larger and smaller groups, called systems, series, formations, cor- 
 responding to the great eras, periods, epochs, of the earth's history. 
 There are several different methods of determining the relative age of 
 rocks : 
 
 1. Order of Superposition.— It is evident, from the manner in which 
 stratified rocks are formed — viz., by sedimentation — that their original 
 position indicates, with absolute certainty, their relative age, the lower 
 being older than the higher. If, therefore, the original position of any 
 series of strata be retained or not very greatly disturbed, and we have 
 a good section, the relative age of the strata which compose the series 
 may be easily determined. But the strata, as we have already seen, 
 have in many cases been crushed and contorted and folded in the most 
 intricate manner, sometimes even turned over; they have also been 
 broken and slipped, and large masses carried away by erosion, and often 
 so changed by heat and other agents, that their stratification is nearly 
 or quite obliterated. For these reasons it is often very diflBcult to 
 determine the relative position, and thus to construct an ideal sec- 
 tion of the strata of a series of rocks, even in a single locality. Nev- 
 ertheless, the method of superposition is conclusive, and takes prece- 
 dence of all others whenever it can be applied. In spite of all these 
 diflBculties, if the whole geological series were present in any one lo- 
 cality, it would be comparatively easy to construct the geological chro- 
 nology. 
 
 But a series of rocks in any one locality can not give us the whole 
 history of the earth. Since sedimentation only takes place at the bot- 
 tom of water, those places which were land- surfaces during any geo- 
 logical epoch received no deposit, and therefore the strata representing 
 that epoch must be wanting there. Now, as there have been frequent 
 oscillations of land-surfaces and sea-bottoms in past times, similar to 
 those taking place at the present time, we find that in every known 
 local series of strata there exist many and great gaps ; so many and so 
 great that the record may be regarded as only fragmentary. Such gaps 
 are usually indicated by unconformity. It is the task of the geologist, 
 by extensive comparison of rocks in all countries, to fill up these gaps, 
 and make a continuous series. The leaves of the look of Time are 
 scattered hither and thither over the surface of the earth, and it is the 
 duty of the geologist to gather and arrange them according to their 
 
206 STRATIFIED OR SEDIMENTARY ROCKS. 
 
 paging. This is done by comparison of rocks of different localities, 
 partly by their lithological character, but principally by the fossils 
 which they contain. 
 
 2. Lithological Character. — At the present time, in our seas and 
 lakes, deposits are forming composed of sand, clay, mud, and lime, of 
 every kind, in different localities. The same has taken place in previ- 
 ous epochs. Sandstones, limestones, and slates, not differing greatly 
 from those forming at the present time, except in degree of consolida- 
 tion, have been formed in every geological period. Lithological char- 
 acter, therefore, is no test of age. In comparing rocks of widely-sepa- 
 rated localities, as, for example, the rocks of different continents, dif- 
 ference of lithological character is no evidence of difference of age, nor 
 similarity of lithological character of any value in determining a geo- 
 logical horizon. But, as deposits are now being formed of a similar 
 character over considerable areas, so also we find strata (the deposits of 
 previous epochs), continuous and unchanged in lithological character, 
 over large tracts of country. Therefore, in contiguous localities, simi- 
 larity of lithological character becomes a very valuable means of iden- 
 tifying strata. Especially is this true if we find similar groups of 
 strata. If, in two localities not too widely separated, we find a similar 
 rock, e. g., a sandstone of similar grain and color, we conclude that 
 they probably belong to the same age, or are, in fact, the same stratum. 
 
 3. Comparison of Fossils.— This is by far the best, and in widely- 
 separated localities the only, method of determining the age of rocks. 
 The principle of this method is that every geological epoch has its own 
 fauna and flora with many characteristic forms, by which it may be 
 identified everywhere in spite of those slight differences which result 
 from geographical diversity; and, therefore, similarity of fossils shows 
 similarity of age: There are, however, certain limitations to the appli- 
 cation of this method which must be borne in mind : 
 
 (a) The lower marine species are much affected by depths and bot- 
 toms, and therefore we' should expect that sandstone fossils, limestone 
 fossils, and slate fossils, would differ in species even in the same epoch. 
 Again, in lake and delta deposits, the entombed species would probably 
 be entirely different from those of marine deposits. We must be care- 
 ful, therefore, to compare fossils of rocks formed under similar con- 
 ditions. 
 
 {b) We must also make due allowance for geographical diversity- 
 This, as we have already stated, becomes greater and greater as we 
 pass up the series of rocks. In the lower or older rocks the geographi- 
 cal diversity is small: in- strata of the same age in different countries 
 the fossils are quite similar, most of the genera and many of the species 
 being undistinguishable. It is therefore comparatively easy, by com- 
 parison of fossils, to synchronize the strata and determine the geologi- 
 
CLASSIFICATION OF STRATIFIED KOCKS. 
 
 20Y 
 
 cal horizon. In the middle rocks the geographical diversity is greater, 
 but the general similarity is still considerable — the difference between 
 organisms of consecutive epochs (geological faunas and floras) is still 
 much greater than the difference between organisms of the same epoch 
 in different countries (geographical faunas and floras) ; and, therefore, 
 it is still quite possible, by comparison of fossils, to synchronize the 
 strata. In the higher or newer rocks the geographical diversity has 
 become so great that we are compelled to determine age and synchronize 
 strata, no longer entirely by comparison of fossils of the different locali- 
 ties with each other, but also by the comparison of the fossils of each 
 locality with the living species in the same locality. In these rocks we 
 may determine relative age by relative percentage of living species, and 
 similarity of age (geological horizon) by similarity of this percentage. 
 In many cases, however, the age may be determined directly by means 
 of characteristic fossils. 
 
 Manner of constructing a Geological Chronology.— The manner in 
 which a geological chronology has actually grown up, under the com- 
 bined labors of the geologists of all countries, may be briefly stated as 
 follows : First, the order of superposition, and therefore the relative 
 ages of the strata composing the rock-series of many different countries, 
 were determined independently'; next, by comparison of these, partly 
 by lithological character, it the localities are contiguous, and partly iy 
 fossils, the geologist determines those which are synchronous and those 
 which are wanting in each locality. Thus, out of several locpl series, 
 by intercalation, he constructs a more complete ideal series. In case 
 of doubt, he strives to find places where the doubtful strata come to- 
 gether, and observes their relative position. In Fig. 182, A and B rep- 
 
 A B C D 
 
 Fig. 182.— Diagram illnstrating the Mode of determming the Chronological Order of Strata. 
 
 resent two contiguous localities in which by independent study the 
 relative positions and ages of 8 and 9 strata respectively have been 
 determined. By comparison, the rocks of the two series are found to 
 consist of fourteen strata of different ages, some being wanting in the 
 one and some in the other locality. 
 
 In this figure A and B represent conformable strata of contigu- 
 ous localities and traceable throughout. In C and D we represent the 
 15 
 
208 STRATIFIED OR SEDIMENTARY ROCKS. 
 
 more complex case of different countries and where unconformities 
 occur. In i? a series of 8 strata are provisionally made out, although 
 it is known by the unconformity between 4 and 5 that there are some 
 missing. In country C a series of 10 strata are first made out, although 
 an unconformity is noted between 7 and 8. Now the comparison be- 
 gins. First it is noted that 2 in the C series is identical with 1 of the 
 D series. The D series is therefore corrected by making this II instead 
 of l,and all above are advanced accordingly as far as the unconformity. 
 Then it is noted that what had been called 5 in the D series corresponds 
 to 7 of the series. Evidently 6 is wanting. The correction is made 
 and the D series is completed to X. Lastly, it is observed that what we 
 had made 8 of the C series corresponds with X in the corrected D 
 series, and that therefore VIII and IX are wanting at C. The correc- 
 tion is made and the series completed to XII. Thus we make a com- 
 plete series of XII, supplying numbers I and VI from one locality, and 
 numbers VIII and IX from the other. Thus as the examination of the 
 earth's surface progresses, with every new country examined some- gaps 
 are filled up, and the series becomes more perfect. Many gaps still re- 
 main unfilled. The series will continue to be made more perfect, and 
 the chronology more complete, until the geological examination of the 
 earth-surface is finished. As knowledge becomes more complete the 
 process becomes easier and more rapid!' Characteristic forms often de- 
 cide the question at once and elaborate comparison is resorted to only 
 in case of doubt. 
 
 The second object to be attained by classification is the division and 
 subdivision of the whole series into larger and smaller groups, corre- 
 sponding to the eras, periods, and epochs of time. The principle on 
 which this is done is as follows : 
 
 As we have already stated, the gaps in the series are usually indi- 
 cated by unconformity. Now, since unconformity always indicates 
 movements of the crust, changes of the outlines of sea and land, 
 changes of climate, and consequent changes in the fauna and flora, 
 these gaps mark the times of great revolutions in the earth's history, 
 and are therefore the natural boundaries of the, eras, periods, etc. The 
 whole rock-series, therefore, is divided, by means of unconformity and 
 the character of the fossils, into larger groups called systems, and these 
 again into smaller groups called series and formations. The largest 
 groups are founded upon universal, or almost universal, unconformity, 
 and a consequent very great diflerence in character of organisms ; the 
 smaller groups are founded upon a less general unconformity and less 
 difference in character of the organisms. Corresponding with the great 
 divisions and subdivisions of the rock-system are the eras, ages, periods, 
 and epochs of the history. The several terms expressing the divisions 
 and subdivisions, both of the rocks and of the history, are unfortu- 
 
CLASSIFICATION OF STRATIFIED ROCKS. 
 
 309 
 
 nately used in a loose manner. We will try to use them in the manner 
 indicated. It will be observed that the divisions are founded upon (a) 
 unconformity, and (6) change in fossils. These generally accompany 
 each other, since they are produced by the same cause, viz., change of 
 physical geography. In some localities, however, they may be in dis- 
 cordance. In this case, the change .of fossils is considered the more 
 important, and controls classification. 
 
 The following is an outline of the classification used in this work : 
 
 ERAS. 
 
 AGES. 
 
 PERIODS. 
 
 Psychozoic. 
 
 Age of Man. (Quaternai-y.) 
 
 Pleistocene. 
 
 Cenozoic. 
 
 Age of Mammals. 
 Mammalian (Tertiary). 
 
 Pliocene. 
 Miocene. 
 Oligoeene. 
 Eocene. 
 
 Mesozoic. 
 
 Age of Reptiles. 
 Reptilian (Secondary). 
 
 Cretaceous. 
 
 Jurassic. 
 
 Triassic. 
 
 
 Age of Amphibians. 
 Carboniferous. 
 
 Permian. 
 
 Coal-Measures. 
 Subcarboniferous. 
 
 PalBBGZoic. 
 
 Age of Fishes. 
 Doyonian. 
 
 Chemung. 
 
 Portage. 
 
 Hamilton. 
 
 Onondaga. 
 
 Oriskany. 
 
 Helderberg. 
 
 
 Age of 
 Invertebrates. 
 
 Upper 
 Silurian 
 
 Salina. 
 Niagara. 
 
 
 Lower 
 Silurian 
 
 Trenton. 
 Canadian. 
 
 
 Cambrian 
 
 Potsdam. 
 Acadian. 
 Georgian. 
 
 ArchaBozoio. 
 
 Life existed. Algonkian. 
 
 Huronian. 
 
 No proof of life. Archaean. 
 
 Laurentian. 
 
 The geologic time-divisions in the above table are placed in 
 ascending order, to correspond with the succession or superposition 
 of the rock strata. The table therefore applies to the rocks as well 
 as to time. 
 
 It will be seen that up to the Jop of ^he Devonian the names 
 of periods are geographical and American. The names of minor 
 divisions (not given in the table), since they designate rocks of 
 limited areal distribution, are almost entirely geographical, using 
 the names of type localities. 
 
210 
 
 UNSTRATIFIED OR IGNEOUS BOOKS. 
 
 CHAPTER III. 
 
 UNSTRATIFIED OR IGNEOUS ROCKS. 
 
 Characteristics.— The unstratified are distinguished from the strati- 
 fied rocks, a, by the" absence of true stratification— i. e., lamination of 
 sorted materials ; h, by absence of fossils ; c, by a more or less crystal- 
 line or else a glassy structure ; and, d, by their mode of occurrence ex- 
 plained below. 
 
 General Origin. — They have consolidated from a fused or semi-fused 
 condition, and are, therefore, called igneous rocks. This origin is 
 shown by their structure ; by their occurrence in dikes and tortuous 
 veins ; by their effects on stratified rocks with which they come in 
 contact; and by their resemblance in many cases to modern lavas. 
 The question of their proljable mode of origin will be more specifically 
 treated after the description of their kinds. 
 
 Mode of Occurrence. — Igneous rocks occur, a, underlying the strata, 
 and forming the great mass of the earth's interior ; a', forming the 
 
 a 
 
 ^{'~'~)-r^^ [i^Bniptives. 
 '^ '^ - l^iiij GraniticB. 
 
 I~^l Metamorphic. 
 f^^i Falseozoic. 
 t-ft-d Mesozoic. 
 |i^g| Cenozoic. 
 
 Fig. 183. — Diagram showing Mode of Occurrence of Igneous Hocks. 
 
 axes and peaks of nearly all great mountain-ranges ;. W, in vertical or 
 nearly vertical sheets, filling great fissures in stratified or in other 
 igneous rocks ; c, in extensive horizontal sheets overlying the stratified 
 country rock, as if outpoured on the surface ; c', lying conformably 
 between strata, as if forced in a melted condition between them, or else 
 outpoured on the bed of the sea and afterward covered with sediment; 
 and, d, in tortuous veins connected with the great underlying masses. 
 All these positions are illustrated in Fig. .183. In all these modes of 
 occurrence the observed rock is connected with an underlying mass, of 
 which it is but an extension. 
 
 Extent on the Surface. — The appearance of these rocks on the sur- 
 face is far less extensive than that of the stratified rocks. Certainly 
 not more than one tenth of the land-surface is composed of them. 
 
PLUTONIC OR MASSIVE ROCKS. 
 
 211 
 
 But, beneath, they are supposed to constitute the great mass of the 
 earth. 
 
 Classification of Igneous Rocks. — Igneous rocks are best classified, 
 not by means of their relative ages, but partly by their mineralogical 
 character and partly by their mode of occurrence. By this method 
 they most naturally fall into two primary groups — viz., the Plutonic 
 or massive, and the volcanic, or true eruptive rocks. The rocks of the 
 first group occur in great masses ; those of the second group injected 
 into fissures or outpoured on the surface. The former are entirely 
 crystalline (holo-crystalline), and usually very coarse-grained (macro- 
 crystalline) ; the latter are usually ^^ne?" grained (micro-crystalline), or 
 imperfectly crystalline (crypto-crystalline), or partly or even wholly 
 glassy. The former seem to have solidified tVt situ (indigenous) ; the 
 latter have been evidently displaced from their original position 
 (exotic). The two groups, however, pass by insensible gradations into 
 each other, so that the distinction is more or less artificial, and the 
 same rock may sometimes be found in both groups. 
 
 I. — Plutonic or Massive Rocks. 
 
 General Appearance. — The rocks of this group are characterized by 
 a coarse-grained, mottled, or speckled appearance, arising from the 
 fact that they are composed of an aggregation of distinct crystals of 
 different colors and of considerable size (macro-crystalline) ; and, what 
 is much more important, the rock is usually wholly made up of an ag- 
 gregation of such crystals, without any paste or ground-mass, either 
 amorphous or glassy, between them. 
 
 The constituent minerals of this group are mainly quartz, feldspar, 
 mica, and hornblende. In the speckled mass the opaque, white, or 
 reddish or greenish crystals with glistening surface are feldspar, the 
 transparent bluish glassy spots are quartz, and the black specks are 
 usually hornblende. The mica can be easily detected as glistening 
 scales of various shades. a s 
 
 Principal Kinds— Gran- 
 ite. — This rock, which may 
 be regarded as the type 
 of the group, consists of 
 quartz, feldspar, and mica, 
 or else of these, together 
 with hornblende. Some- 
 times the mica and horn- 
 blende are wanting, and 
 
 the quartz exists in the form of bent plates imbedded in feldspar, so 
 that on cross - section they look like Hebrew or Arabic characters 
 (Fig. 184, A and S). The rock is then called graphic granite, or^e^r- 
 
 FiG. 184.— Graphic Granite: A. cross-section; JS, longitu- 
 dinal section. 
 
212 UNSTKATIFIED OR IGNEOUS ROCKS. 
 
 matite. Sometimes the feldspar is ia large, well-formed crystals in a 
 finer but still crystalline ground-mass : then it is called porphyritic 
 granite. Sometimes all the crystals are small, and the mass is evenly 
 granular ; then it is called eurite, or granulite. 
 
 Syenite. — English and many American writers use this term to 
 designate a granitic rock in which mica is replaced by hornblende ; 
 and, when both hornblende and mica are present, they use the term 
 syenitic granite. But on the Continent of Europe the terra syenite is 
 applied to a rock consisting essentially of feldspar and hornblende, 
 and when, in addition, quartz is present (English syenite), they call 
 the rock quartz-syenite. The general aspect of the rock is similar to 
 granite. 
 
 In the rocks thus far mentioned the feldspar is an orthic, or pot- 
 ash-feldspar {orthoclase)—i. e., is a double silicate of alumina and 
 potash. 
 
 Diorite.— This is a dark, speckled, greenish-gray rock, consisting of 
 a crystalline aggregate of clinic or soda-lime feldspar (plagioclase), 
 and hortiblende; and, therefore, differs from syenite of German 
 writers only in the form of the feldspar— viz., plagioclase instead of 
 orthoclase. When quartz is present it is called quartz-diorite. 
 
 Diabase. — This is a dark, greenish crystalline rock, usually fine- 
 grained, but sometimes granitoid, somewhat similar in appearance to 
 diorite, but differing in the fact that augite replaces hornblende. It 
 also often contains olivin. Gabbro is a granitoid variety of diabase, in 
 which the augite takes the form of diallage. 
 
 We have selected these as good types of the groups; but they 
 merge insensibly into each other, giving rise to many varieties, for the 
 description of which we must refer the reader to special treatises on 
 lithology. 
 
 Diorite and diabase are so frequently intrusive and fine-grained 
 that they are often treated in an intermediate or even in the second 
 group ; but they also often occur massive. 
 
 Two Sub-Groups— Acidic and Basic. — Quartz is pure silicic acid. 
 • Feldspar is a silicate of alumina and alkali, with excess of silica — i. e., 
 an acid silicate of these bases. In orthoclase the alkali is potash ; in 
 plagioclase, soda and lime. Moreover, the former is more acid than 
 the latter. Hornblende and augite are basic silicates of somewhat 
 similar composition. Augite is essentially a silicate of magnesia and 
 iron ; while, in hornblende, alumina and lime replace a portion of the 
 magnesia. Kemembering further, that quartz and feldspar are light- 
 colored minerals, with specific gravity of about 3-6, while augite and 
 hornblende are usually black minerals, with specific gravity of 3 to 3"5, 
 it is plain that this group of rocks may be divided into two sub-groups, 
 acidic and basic, often recognizable to the eye. In the one there is a 
 
PLUTONIC OR MASSIVE ROCKS. 
 
 213 
 
 predominance of quartz and feldspar, in the other of hornblende or 
 augite. Also, in the one the feldspar is orthoclase, in the other 
 plagioclase. The one is light colored, of less specific gravity, and 
 more diflBcultly fusible ; the other darker colored, heavier, and more 
 easily fusible. Granite is the best type of the one; diorite, and 
 especially diabase or gabbro, of the other. Syenite is intermediate. 
 The percentage of silica, both free and combined, in granite is 63 to 
 81, and the specific gravity 2-6 to 3'7. The silica percentage in dia-. 
 base is 45 to 56, and the specific gravity 3-7 to 2-9 (Von Gotta). 
 
 Mode of Occurrence. — True Plutonics, especially of the granitic 
 type, such as granite and syenite, occur : 1. In large masses, forming 
 the axes of great mountain- 
 ranges, such as the Sierra and " 
 Colorado ranges (Fig. 185, A); 
 or, 3. In rounded masses, ap- ^ 
 pearing in the midst of strati- 
 fied rocks like islands in the 
 midst of the sea (Pig. 185, B) ; 
 or, 3. Sometimes in tortuous, 
 irregularly branching veins, 
 extending only a little way 
 from the great masses into the overlying stratified rocks, as if forced 
 by pressure of superincumbent weight into small cracks of the latter 
 (Fig. 183, d, Fig. 185, A, and Fig. 186, A and B). But rocks of more 
 basic type, such as diorite and diabase, probably on account of greater 
 fusibility, occur not only as Plutonics in massive form, but also as 
 intrusives in dikes and intercalary beds, like true volcanics. 
 
 Fiw. 185. — Diagram illuBtrating Mode of Occurrence of 
 Granite. 
 
 
 Fig. 186.— Granite Veins. 
 
 The rocks of the Plutonic group are never found in connection 
 with scoriae, glass, ashes, or other evidences of rapid cooling in contact 
 With air. They have never been erujpted on the surface. They were 
 
214: UNSTRATIFIED OR IGNEOUS ROCKS. 
 
 cooled, and have solidified slowly under pressure in great masses and 
 at great depths. Hence, when we find them at the surface, they have 
 been exposed by extensive erosion. They are either fused masses solidi- 
 fied without eruption {a), or they are the solidified reservoirs {g. Fig. 
 183) from which eruptions have come. In either case, they have them- 
 selves been cooled at great depths. 
 
 Intermediate Series. 
 Between the undoubted Plutonics, already described, and the un- 
 doubted volcanics, to be taken up hereafter, there is an intermediate 
 series of rocks, which are sometimes placed in one group, sometimes in 
 the other, and sometimes in a separate group, co-ordinate with the other 
 two, and called trappean or intrusive rocks. They occur mostly in the 
 older and middle rocks in the form of dikes, filling great fissures inter- 
 secting, or as intercalary beds between, the strata. If Plutonics are 
 in great masses beneath the strata, and volcanics are outpoured masses 
 upon the strata, these exist mostly as masses intruded among the 
 strata. Again, if Plutonics are the great reservoirs and volcanics the 
 outpoured liquid, the intrusives are the fillings of the conduits between. 
 Erosion has subsequently carried away the overflowed portions, and 
 exposed the conduits as dikes. 
 
 Kinds. — In the acidic groups, perhaps the most typical is felsite. 
 This rock is a very compact, fine-grained aggregate of quartz and 
 orthoclase, and therefore light-colored. Chemically it has the same 
 composition as granite, and mineralogically it differs only in the fine- 
 ness of texture and in the absence of mica. When the felsitic rock 
 contains, imbedded in the fine-grained mass, large, well-formed crystals 
 of feldspar, then it is called porphyrite. If quartz-crystals are also 
 distinctly visible, then it is called quartz-porphyry, or elvanite, a 
 mottled rock often mistaken for granite. The word porphyritic is 
 often applied to any rock in which distinct crystals are visible in a 
 finer ground-mass. Thus, we have porphyritic granite, porphyritic 
 diorite, etc. The porphyritic structure is probably formed thus : The 
 fused magma first cooled slowly until the large crystals separated ; and 
 then was injected into the fissure and the solidification completed. 
 
 Intrusive rocks of the basic sub-group are usually called green- 
 stones or traps. This term, therefore, includes intrusive diorites, dia- 
 bases, aphanites, melaphyrs, etc. These differ from the massive rocks 
 of the same composition only by being finer grained : but the same is 
 true also of felsites as compared with granites. The difference is prob- 
 ably wholly due to rate of cooling. The same fused mass which, if 
 cooled slowly, forms granite, if injected into fissures and cooled more 
 rapidly, would form felsite or quartz-porphyrite. The difference be- 
 tween massive and intrusive diorites is doubtless due to the same cause. 
 
VOLCANIC OR ERUPTIVE ROCKS. 
 
 215 
 
 II. — Volcanic ok Eruptive Rocks. 
 
 Texture and Appearance. — The rocks of this group are usually 
 micro-crystalline, or even crypto-crystalline, and therefore in appear- 
 ance are either minutely speckled or evenly grayish, of various shades. 
 But the most important characteristic is, that they are not wholly crys- 
 talline, but consist either of crystals imbedded in an amorphous or 
 glassy paste, or else are wholly amorphous or glassy. This texture shows 
 that, as compared with the rocks of the other groups, they ha,Ye cooled 
 qtiicMy, for, on account of the extreme viscosity of fused silicates (glass), 
 complete crystallization can take place only by very slow cooling. 
 
 Physical Conditions. — All the physical conditions already described 
 (p. 93) as characteristic of recent lavas, viz., the stony, the glassy, the 
 scoriaceous, and the tufaceous conditions, are found abundantly in the 
 more typical representations of this group. 
 
 Mineral Composition and Sub-Groups. — The most striking differences 
 between the rocks of this and the other groups are found in their text- 
 ure and mode of occurrence. Mineralogically the rocks of this group 
 consist essentially of some form of feldspar, with hornblende or augite. 
 Free quartz and mica, though sometimes present, especially the former, 
 are neither necessary nor common. These also, like those of the other 
 group, may be divided into two sub-groups, acidic and basic. In the 
 one there is a predominance of orthic feldspar (sanidin) ; in the other, 
 of either hornblende or augite and clinic feldspar (plagioclase). In 
 true volcanics, as seen above, sanidin takes the place of orthoclase of 
 the Plutonics. These, however, belong to the same group (orthoclase 
 group), are equally acidic, and therefore have the same significance in 
 lithology. The two sub-groups are, therefore, characterized by color, 
 specific gravity, and fusibility, as already explained (p. 212), and, with 
 some practice, can usually be distinguished in the field ; though in 
 many cases microscopic or chemical examination is necessary. The 
 silica percentage of the extreme acidic type (rhyolite) is 70 to 82, and 
 specific gravity 2-3 
 to 2-6 ; of the ex- 
 treme basic (basalt) 
 the silica percent- 
 age is 40 to 56, and 
 specific gravity 2-9 
 to 3-1. The follow- 
 ing schedule gives 
 the most common 
 and characteristic 
 kinds under the two 
 sub-groups : - 
 
 VOLCANIC E0CK8. 
 
 ACIDIC. 
 
 BASIC. 
 
 rRhyoIite. 
 Stony J Liparite. 
 condition. ) Trachyte, 
 l^ Phonolite. 
 
 „, ( Light-colored scoriae. 
 ^^???y \ Pumice, 
 condition. 1 Obsidian. 
 
 Basalt. 
 
 Uolerite. 
 
 Andesite. 
 
 Black scoriae. 
 Tachylite. 
 
216 
 
 UNSTRATiriED OR IGNEOUS KOCKS. 
 
 IGNEOUS KOCKS. 
 
 ACIDIC. 
 
 BASIC. 
 
 k 
 
 tl 
 
 I® 
 
 BhyolUe. TraahyU. PhonoUU. 
 
 Vitreous Vitreous Vitreous 
 
 ground-mass. grouud-mass. grouBd-mass. 
 
 ( Quartz- I Orthoolase ^ „ J Sauidiii, 
 ""1 (stSnl ""' (6a"M*°) 1 NepheliB. 
 
 Andesite. Basalt. 
 
 Vitreous Vitreous 
 
 ground-mass, ground-mass. 
 
 Plagioclase, j Plagioclase, 
 X X ■< Augite, or x x ■< Augite, 
 Hornblende. | Olivin. 
 
 1 ■ 
 
 s 
 
 bug 
 
 JI 
 
 Qaa/iie-porphyry. 
 Micro X > ground-mass. FfJaite. 
 
 ( Orthoclase, Micro J Orthodase, 
 " " -\ Quartz, X X 1 Quartz. 
 
 JHorite. Mdbaae. 
 
 Same as Same as 
 
 below, below, 
 
 but micro but micro 
 
 XX XX 
 
 d- 1. 
 
 be . 
 
 a o 
 
 II 
 ©a 
 
 ■ QramiU. Syenite. 
 ( Q"?'"'; ( Orthoclase. 
 " " 1 Mka" '^ '^ I Ho™blende. 
 
 Diorite. Gabbro. 
 
 ^ (Plagioclase.^ \ P^g^'«»«' 
 ""1 Hornblende xx-j^Si;^ 
 
 Principal Kinds. — la the acidic group the commonest and best type 
 is trachyte. This is usually a light-colored rock, with a peculiar and 
 very characteristic rough feel, due to microscopic vesicularity. It con- 
 sists essentially of a ground-mass of orthic feldspar (sanidin) and augite, 
 containing crystals of the former. 
 
 Rhyolite is similar in composition to trachyte, but contains a larger 
 percentage of silica, and is very different in general appearance. It 
 consists of a fluent, vitreous ground-mass or paste, usually containing 
 crystals of sanidin, or even of quartz. When these crystals are con- 
 spicuous, so that the rock has a porphyritic appearance, it is called 
 liparite. In some cases it may have even a granitoid appearance, and 
 is then called nevadite. Such granitoid rhyolite may be easily distin- 
 guished from true granite by the presence of the glassy paste. 
 
 PhonoUte is a light-grayish crypto-crystalline feldspathic rock, 
 breaking or jointing in very characteristic thin tile-like slabs, which 
 ring under the hanimer (hence the name). It consists mainly of orthic 
 feldspar (sanidin and nephelin). 
 
 In the basic sub-group the most common and typical is basalt. 
 This is a very dark, almost black, crypto-crystalline rock, breaking 
 with a dull, conchoidal fracture, and consisting essentially of micro- 
 scopic crystals of plagioclase, augite, and olivin, in a glassy ground-mass 
 of the same. Magnetite is also usually an abundant constituent. Bol- 
 erite has a somewhat similar composition, but lacks the olivin, and is 
 more crystalline in structure, and therefore dark-grayish in appearance. 
 Andesite is a dark-grayish rock, consisting essentially of plagioclase, 
 with hornblende or augite. It is somewhat similar in color to 
 dolerite, but is crypto-crystalline, like basalt, and often, roughish to 
 
VOLCANIC OR ERUPTIVE ROCKS. 217 
 
 the feel, like trachyte. It has, therefore, been sometimes called trachy- 
 
 dolerite. 
 
 - All the rocks of both these sub-groups, but especially the more 
 
 typical, have their scoriaceous and glassy varieties. These are the 
 
 pumices and light-colored scoriae and obsidians on the one hand, and 
 
 the black scoriae and tachylite on the other. 
 
 The table on preceding page is a condensed statement of the com- 
 position of the principal kinds in both primary groups, including also 
 intrusives. The sign x x indicates crystals. 
 
 Modes of Eruption. — There have been in geological times tviro gen- 
 eral modes of eruption. In the one the lavas have come up through 
 great fissures formed by crust-movements and spread out as extensive 
 sheets ; in the other they have come up through chimneys and run off 
 as streams. The one may be called fissure-eruption, the other crater- 
 eruption or volcanoes proper. The one gives rise to extensive lava- 
 fields, the other to lava-cones. The force of eruption in the one case 
 is probably either the same as that which makes mountains — i. e., the 
 lava is squeezed out by interior contraction of the earth, or else in 
 some cases it may be hydrostatic — i. e., a welling out of a lighter liquid 
 by the sinking of a heavier crust within it ; the force, in the other case, 
 is evidently the pressure of elastic gases, especially steam, as already 
 explained (p. 97). We owe this distinction mainly to Richthofen, but 
 it is now universally adopted in this country and quite generally in 
 Europe. According to Richthofen, primary eruptions come always 
 through great fissures and only at great intervals of time ; afterward, 
 surface-waters percolating through these fissure-erupted masses, still 
 liquid within, give rise to secondary eruptions through craters. We 
 have no examples of fissure-eruptions taking place at the present time, 
 and therefore, in treating of igneous agencies in Part I, we spoke only 
 of crater-eruptions. But it is impossible to explain the mode of occur- 
 rence of eruptives in the older rocks unless we admit eruptions in early 
 geological times of a different kind from those occurring now in vol- 
 canoes. 
 
 Modes of Occurrence. — What we say under this head refers mainly 
 to fissure-eruptions. True eruptive rocks occur : 1. As extensive verti- 
 cal sheets filling great fissures which by subsequent erosion outcrop as 
 great dihes, or else filling smaller radiating volcanic fissures as radi- 
 ating volcanic dikes; 3. As sheets between the strata (intercalary 
 beds) as if forced between the separated strata, or else outpoured on 
 the bed of sea or lake, and again covered with sediments; 3. Out- 
 poured on -the land-surface as sheets or streams ; 4. In the form of 
 great dome-like masses on the surface or between the strata ; and, 5. 
 In the form of volcanic necks or plugs standing above the general level 
 of the country. 
 
2^g UNSTRATIFIED OR IGNEOUS ROCKS. 
 
 Dikes.— The fillings of great fissures outcropping on land -surfaces 
 are called dikes. They are very abundant in all the older stratified 
 rocks, especially in mountain-regions. They vary in thickness from a 
 few inches to fifty or one hundred feet ; they may be traced over the 
 country sometimes for many miles, even fifty or one hundred, and 
 extend downward to great but unknown depths. Such dikes, outcrop- 
 ping over the face of the country, may be the exposed roots of ancient 
 overflows which have been removed by subsequent erosion (Fig. 183, 
 I) ; or they may be fillings of fissures which never reached the sur- 
 face (Fig. 183, b'). In either case they are the evidence of extensive 
 
 erosion. Sometimes the outcrop- 
 
 j—^_^^^^ ^ / _ ■ .^ ~— -„^^ ^a ping dike has resisted erosion 
 
 more than the inclosing country 
 rock, and the dike is left stand- 
 ing like a low, ruined wall run- 
 ning over the face of the country 
 (Fig. 18?, a) ; at other times the 
 country rock has resisted more 
 
 Fig. 187.— Dikes. 
 
 than the dike, and the place of the dike is marked by a slight depres- 
 sion, like a shallow ditch, or moat (Fig. 187, h). 
 
 Effect of Dikes on the Intersected Strata.— The strata forming the 
 bounding walls of a dike, or with which igneous rocks come in contact 
 in any way, are almost always greatly changed by the intense heat of 
 the fused matter. Limestones and chalk are changed into crystalline 
 marble; clay is baked into porcelain-jasper, or even changed into 
 schists; impure sandstones are changed into a speckled rock resem- 
 bling gneiss; seams of bituminous coal are changed into anthracite, 
 or sometimes into coke. In all cases the original stratification and the 
 contained fossils are more or less completely destroyed. These effects ex- 
 tend sometimes only a few feet, sometimes many yards, from the dike. 
 
 Lava-Sheets. — Dikes outcropping on the face of the country, as 
 already described, are doubtless in many cases the exposed roots of 
 ancient overflows which have been removed by subsequent erosion, 
 leaving only the intruded portion. But in more recent eruptions the 
 overflow or erupted portions still remain. The fused matter has evi- 
 dently come up through fissures and spread out as sheets, and often 
 sheet after sheet has been successively outpoured forming layer upon 
 layer (Fig. 188), until the whole surface of the country is deeply buried 
 beneath the flood. The extent and thickness of the lava-fields thus 
 formed are almost incredible. The great lava-flood of the Northwest 
 covers Northern California, Northwestern Nevada, the greater part of 
 Oregon, Washington, and Idaho, and extends far into British Columbia 
 and Montana. Its extent is not less than 150,000 square miles, and its 
 extreme thickness where cut through by the Columbia Kiver is 3,000 to 
 
VOLCANIC OB ERUPTIVE ROCKS. 
 
 219 
 
 Fig. 188.— Lava-Sheets. 
 
 4,000 feet. In another place seventy miles distant the Deschutes 
 Eiver cuts into the same lava-field, making a caflon 140 miles long and 
 1,000 to 2,500 feet deep, and 
 has not yet reached bottom. At 
 least thirty successive layers may 
 be counted, one above the other, 
 on the sides of this caflon. 
 About a dozen volcanoes over- 
 dot this great surface. It is 
 simply inconceivable that all 
 this material came from these 
 volcanoes. It evidently came 
 up through great fissures in the Cascade, Blue Mountains, and Coast 
 Range, and poured out on the surface, fiooding the whole intervening 
 country. The Decean lava-field, described by the Indian geologists, is 
 200,000 square miles in extent, 2,000 to 6,000 feet thick, and entirely 
 without detectable volcanic cones from which the lava could have come. 
 These extensive fields are mostly of basalt. In Utah and Colorado, 
 according to King and Endlich, rhyolitic and trachytic lavas reach a 
 'thickness of 7,000 feet. As a general rule, outpourings of basalt reach 
 the greatest extent, but each sheet is thin, as if the basalt had been 
 superfu^edj while acidic lavas like trachyte and rhyolite are ■ outpoured 
 in very thick, sometimes dome-like masses, as if they had been only 
 semifused. 
 
 Intercalary Beds and Laccolites. — Holmes, in Hayden's Eeport for 
 1875, describes- Mount Hesperus, Colorado, as wholly composed of 
 stratified rocks (cretaceous), with intercalated beds of eruptives, as if 
 the lava had forced itself between the strata. Such intercalary sheets, 
 
 
 
 ■Ml mammmsBimmi mammmnmt^ ^ 
 
 
 
 Fio. 188a.— Dike and Sills. 
 
 or sills, which have been often observed by others, probably pass by in- 
 sensible gradations into laccolites — a new form of occurrence to which 
 attention was first drawn by Holmes, but which has been elaborately 
 described by Gilbert as characteristic of the Henry Mountains, and 
 
220 
 
 tJNSTRATIFIED OR IGNEOUS ROCKS. 
 
 .Fie. 189.— Laccolite (after (riibert). 
 
 other groups in the Plateau region. In this case the' liquid matter 
 seems to have come up through fissures as usual, but, instead of break- 
 ing through to the surface, 
 has lifted the upper strata 
 and accumulated beneath 
 in great dome-like masses 
 which, in fact, constitute 
 the bulk of the mountains 
 (Fig. 189). The strata- 
 covered dome thus formed 
 is afterward eroded, and 
 the igneous core or lacco- 
 lite is exposed. 
 
 According to Gilbert, whether lava accumulates between the strata 
 or outpours on the surface is merely a question of relative specific 
 gravity. If the lava is lighter than the strata, then the latter will sink 
 and the lava be outpoured. If, on the other hand, the surface strata 
 be lighter than the lava, then the lava floats it up and accumulates be- 
 neath. It seems more probable, however, that it is rather a question 
 of liquidity than of specific gravity. If the liquidity is perfect as in 
 basalts, then it comes to the surface and outpours, and may extend to 
 very great distances ; but if, on the contrary, the lava is only a stiffly 
 viscous, semi-fused mass, like trachyte and rhyolite, it may lift up the 
 strata on its back in a dome. The quantity of lava accumulated is 
 sometimes enormous. The Hiller laccolite, Henry Mountains, is equiv- 
 alent to ten cubic miles. 
 
 Pig. 190.— Ideal Cross-section of La Plata Mountain (after Cross). The irregular line, o, o, is the 
 
 present surface. 
 
 The passage from idtercalary beds to laccolites is well shown in 
 Fig. 190, taken from Cross. 
 
 Volcanic Necks. — In the general erosion of a country the plugs 
 which filled the interior of ancient volcanoes are often left, as more 
 
CERTAIN STRUCTUKES FOUND IN MANY ERUPTIVE ROCKS. 221 
 
 resistant remnants, standing above the general level of the country. 
 These are called volcanic necks. Some examples are mentioned on 
 p. 5^5. On account of the former frequent and long-continued fusion 
 of these masses during repeated eruptions, their metamorphic effect on 
 surrounding stratified rocks is far more profound and extensive than 
 in the case of dikes. 
 
 Age — how determined. — When two dikes intersect each other, then, 
 of course, the intersecting must be younger than the intersected dike. 
 In this manner the relative age of dikes intersecting the same region 
 may often be determined. The absolute age of igneous rocks can only 
 be determined by means of the strata with which they are associated. 
 If a dike is found intersecting strata of known age {i. Pig. 183), the 
 dike must be younger than the strata. If a dike (b'), intersecting 
 strata and outcropping on the surface, is found overlaid by other strata 
 through which it does not break, then the igneous injection is younger 
 than the former and older than the latter. The series of events indi- 
 cated is briefly as follows : first, the older series of sediments has been 
 formed ; then fissures formed and filled by igneous injection ; then 
 erosion has carried away the upper portion of the strata and its in- 
 cluded dike, so that the dike outcrops along the eroded surface ; and, 
 lastly, the whole has been submerged and again covered with sediment. 
 
 In the case of intercalary beds of igneous rocks, if the strata above 
 and below are both metamorphosed by heat, then the fused matter has 
 been forced between and is younger than the strata ; if, however, the 
 underlying stratum is changed but the overlying is not, then the igne- 
 ous matter has been outpoured on the sea-bed and covered with sedi- 
 ment, and is, therefore, of the same age as the strata. The same prin- 
 ciples determine the age of sheets and streams. If sheets are successively 
 outpoured, one atop the other, then, of course, the order of superposi- 
 tion determines their relative age. So, also, if two streams run across 
 each other, the overlying is the younger. In this way Kichthofen and 
 others have determined the order of succession of different kinds of 
 tertiary eruptives. Absolute age, or the geological time of eruption, 
 can only be determined by the age of the associated strata. 
 
 Of Certain Structures found in many Eruptive Rocks. 
 
 Columnar Structure. — Many kinds of eruptive rock exhibit some- 
 times a remarkable columnar structure. This is most conspicuous in 
 basalt, probably because this rock has been superfused, and is therefore 
 sometimes called basaltic structure. Sheets and dikes of this rock are 
 often found composed wholly of regular prismatic jointed columns, 
 closely fitting together, varying in size from a few inches to a foot 
 or more, and in length from several- feet to fifty or one hundred feet. 
 When these columns have been well exposed on cliffs by the action of 
 
22'2 
 
 TJNSTRATIFIED OR IGNEOUS ROCKS. 
 
 waves, or on river-banks by the erosive action of currents, or even by 
 atmospheric disintegration, they produce a very striking scenic effect 
 (Figs. 191, 193). In Europe the Giant's Causeway, on the coast of 
 
 Fig. 191.— Columnar Basalt, New South Wales (Dana). 
 
 Ireland, and Fingal's Cave, in the island of Staffa on the west coast of 
 Scotland, are conspicuous examples. In the United States we have ex- 
 amples in Mount Holyoke, on the Connecticut River; in the Palisades 
 of the Hudson River ; in the traps on the shores of Lake Superior ; 
 and especially in splendid cliffs of the Columbia and Deschutes Rivers, 
 in Oregon. 
 
 Direction of tie Columns.— The direction of the columns is usually 
 at right angles to the cooling surface. In horizontal sheets, therefore, 
 the columns are vertical, but in dikes they are horizontal (Fig. 193). 
 A dike left standing above the general surface of country sometimes 
 presents the appearance of a long pile of cord-wood. In some cases 
 the columns are curved and twisted in a manner not easy to explain ; 
 sometimes, instead of columnar, a 6ffZ^structure is observed. 
 
 Fig. 192. — Basaltic Columns on St'diiniiUtary Rock, Lake Superior (after Owen). 
 
 Cause of Columnar Structure. — There is little doubt that this 
 structure is produced by contraction in the act of cooling. Many sub- 
 stances break in a prismatic way in contracting. Masses of wet starch, 
 
CERTAIN STRUCTURES FOUND IN MANY ERUPTIVE ROCKS. 223 
 
 or very fine mud exposed to the sun, crack in this way. In basalt the 
 structure is more regular than in any other known substance. The 
 subject of the cause of Jointed columnar structure has been very ably 
 discussed by Mr. Mallet. 
 
 Volcanic Conglomerate and Breccia. — If a stream of fused rock, 
 whether from a crater or a fissure, run down a stream-bed, it gathers 
 up the pebbles in its course, and after solidification forms a conglom- 
 erate which differs from a true conglomerate (p. 179) in the fact that 
 the uniting paste is igneous instead of sedimentary. In a similar 
 manner volcanic breccias are formed by the flowing of a lava-stream 
 over a surface covered with angular fragments or rubble. Breccias 
 
 Fia. 193. — Columnar Bike, Lake Superior (atlai Oweuj. 
 
 and tufas are also formed by cementation of cinders and dust accu- 
 mulated about volcanic vents. 
 
 Pyroelastic Rocks. — These are deposits which are intermediate in 
 character between the volcanic and the true clastic or sedimentary 
 rocks, being composed of volcanic products, but worked over by aque- 
 ous or atmospheric agencies. Beds of volcanic dust on the land are 
 consolidated into tuffs. The fragmehtal materials falling into sea 
 or lake are assorted and made to resemble ordinary land-derived sedi- 
 ments. Under the microscope the volcanic materials are glassy or 
 crystalline. 
 
 Amygdaloid. — Outpoured traps, and especially lava-streams, are 
 very often vesicular — ^i. e., filled with vapor-blebs, usually of a flat- 
 tened, ellipsoidal form. In the course of time these cavities are filled 
 with silica, carbonate of lime, or some other material, by infiltrated 
 water holding these matters in solution. Sometimes the filling has 
 16 
 
224 UNSl RATIFIED OR IGNEOUS ROCKS. 
 
 taken place very slowly by successive additions of different-colored 
 material. Thus are formed the beautiful agate pebbles, or more prop- 
 erly amygdales, so common in trap. The most common filling is 
 
 Fig. 194.— Palisades of the Hudson, View from Hastings. (Photograph from New York State 
 
 Museum.) 
 
 silica, because water percolating through igneous rocks is always alka- 
 line, and holds silica in solution. 
 
 Classification of Igneous Eocks. 
 
 There is no subject connected with geology which is in a state of 
 greater confusion than the classification and nomenclature of igneous 
 rocks. It seems proper, therefore, to mention some of the theories. 
 
 Many geologists think that igneous rocks may be thrown into three 
 groups, characteristic of different periods of the earth's history, and 
 which, therefore, are now found associated with the stratified rocks of 
 different ages. These are : 1. The granitic group, including granites 
 and syenites, associated with Archaean and Palaeozoic rocks; 3. The 
 trappean group, including diorites, porphyry, dolerite, etc., associated 
 with the later Palaeozoic and the Mesozoic rocks ; and, 3. The volcanic 
 rocks, including basalts, trachytes, etc., associated with the Tertiary 
 rocks. They think, therefore, that the earliest eruptions were granitic, 
 then trappean, and lastly volcanic. Furthermore, they think that the 
 first have come up mostly in great, dome-like masses ; the second, 
 mostly intrusive, in dikes and fissures ; and the third through craters 
 forming volcanoes. 
 
 Again, many think that erupted matters, of different times, have 
 become progressively more basic. They think that, although each 
 group may be divided into a more acidic and a more basic sub-group, 
 yet, as a whole, the granitic group is the most acidic and the vol- 
 canic the most basic, the trappean being intermediate, as shown in the 
 accompanying diagram. 
 
OTHER MODES OF CLASSIFICATION. 
 
 225 
 
 Basic. 
 
 Acidic. 
 
 Basic. 
 
 Volcanic, 
 
 Rliyolite. 
 
 Basalt. 
 
 Quartz- 
 Porphyry. 
 
 Granitic. 
 
 Diabase. 
 
 Granite. 
 
 (iabbro. 
 
 Acid. 
 
 Again, these two views, which are usually 
 held by the same persons, are by them con- 
 nected with a third view, in regard to the 
 original constitution of the earth's crust. On 
 first cooling, the outer layer is supposed to 
 have been highly oxidized, highly siliceous, 
 and therefore comparatively light — in other 
 words, granitic ; beneath this was a less oxi- 
 dized, less acid layer, and so on progressively, 
 the deeper layers becoming heavier and 
 heavier, and more and more basic. The 
 first eruptions were from the outer layer, 
 and therefore granitic. Afterward, as the 
 crust grew thicker and thicker, the erup- 
 tions were from deeper and deeper layers, 
 and therefore denser and denser, and more and more basic. 
 
 But, in answer to these views, it may be said that, as to a^e, there 
 can be no doubt that granite, though most commonly associated with 
 the older rocks, is found in strata of all ages up to the middle Tertiary, 
 ' and fissure eruptions have occurred in all ages up to the latest Tertiary. 
 The granite of Mont Blanc was pushed up at the end of the Eocene 
 (Lyell), and the great fissure-eruptions of the Northwest took place 
 at the end of the Miocene and during the Pliocene. On the other 
 hand, basalts are found in pre-Cambrian rocks (Walcott).* Also, as to 
 composition, rhyolite and liparite have much the same chemical com- 
 position as granite, except that more of the silica is in combination and 
 less of it free in the former than in the latter. Some early diorites 
 and gabbros have much the same chemical (if not mineralogical) com- 
 position as basalt. 
 
 Again, others, with much reason, think that all the differences be- 
 tween the three groups in mineralogical character and crystalline 
 structure are due wholly to the different depths at which and the slow- 
 ness with which solidification took place. They think, therefore, that 
 if trachyte or rhyolite (Fig. 183, c) could be traced downward deep 
 enough it would pass into porphyry (b), and finally into granite (g), 
 and similarly basalt would pass into dolerite and diorite, and finally into 
 olivin-diabase or gabbro.f On this view, what we can not do, has been 
 done for us by erosion j and granite is most commonly associated with 
 older rocks only because these have been most eroded, and therefore 
 
 * American Journal of Science, vol. vii, p. 167, 18Y4. 
 
 t This gradual change has very recently been distinctly observed in Southeastern 
 Europe by Judd (Geological Magazine, 1876, vol. xxxii, p. 292), and also in Colorado by, 
 Peale (Hayden's Report for 1873, p. 261), and also by Hague and Iddings in Nevada 
 (United States Geological Survey Bulletin, No. 17, 1885). 
 
226 DNSTRATIFIED OR IGNEOUS ROCKS. 
 
 their deeper parts, or even the fountain-reservoirs from which eruptions 
 have come, have been exposed. Similarly, a less extreme erosion of the 
 Mesozoic rocks has exposed the porphyritic and dioritic dikes through 
 which eruptions came up ; while, of the modern lavas, only the upper 
 or overflowed parts are exposed. This view explains completely all the 
 phenomena of igneous rocks, and the gradations between them, in 
 chemical and mineralogical composition and in crystalline structure 
 and is therefore very probably true. We have substantially assumed 
 it in the preceding descriptions. 
 
 The confusion in the classification and nomenclature of igneous 
 rocks is still further increased by the undoubted fact that many of the 
 kinds of rocks mentioned above as igneous are found also among meta- 
 morphic rocks which have never been erupted at all. This subject is 
 further treated under the head of Metamorphism (p. 330 et seq.). 
 
 RichtJiofen's Classification of Tertiary Eruptives. 
 
 By far the most noted attempt to classify by age, or to corre- 
 late the kinds of igneous rocks with their ages, is found in Richt- 
 hofen's classification of Tertiary eruptives. According to Richthofen, 
 there is a regular and invariable order of succession among the erupt- 
 ive rocks of Tertiary times ; the order being — 1. Propylite.* 2. Ande- 
 site. 3. Trachyte. 4. Rhyolite. 5. Basalt. This order, however, ap- 
 plies only to primary or fissure eruptions ; for, since primary erupted 
 masses may become the seats of subsequent secondary or crater erup- 
 tions, it is evident that secondary eruptions of a lower .group may be 
 synchronous with primary eruptions of a higher group, f 
 
 These views of Richthofen's have attracted wide attention, but have 
 not been generally confirmed. All that is as yet generally accepted 
 in regard to the order of Tertiary eruptives is that the trachytes (in- 
 cluding in this term with the trachytes proper also the andesites and 
 the rhyolites) precede the basalts. 
 
 Button and Iddings find in successive eruptions in the same place 
 a law of differentiation from a generalized type like andesite into more 
 and more specialized acid on the one hand and basic on the other. 
 Judd also, in his work on Volcanoes, admits that an intermediate type 
 like andesite (propylite is usually regarded as a variety) is first erupted, 
 then an acid type like trachyte and rhyolite, and last basalt. He 
 accounts for this by supposing a homogeneous fused mass (such as 
 would be formed by fusion of many different kinds of strata) to be 
 first erupted as soon as formed. This would make an intermediate 
 
 * Propylite is regarded by many as an altered andesite. 
 
 f Richthofen's Natural History of Volcanic Rocks, Memoirs of California Academy of 
 Science, vol. i, Part II. 
 
ORIGIN OF THE VARIOUS KINDS OF ERUPTIVE ROCKS. 227 
 
 type. The remainder of the fused mass after long standing would 
 separate into a lighter acid portion above and a heavier basic portion 
 below. These would, therefore, be successively erupted as rhyolite and 
 basalt. On the other hand Geikie and Teall find a law of increasing 
 acidity, and Brogger confirms this law, but only for plutonics. 
 
 General Origin of Igneous Rocks. 
 In later years the prevailing belief is that the molten rock out- 
 poured on the surface of the earth is mostly derived from original 
 earth-substance, expanded and fused through relief of p'ressure. This 
 idea is in harmony with either the nebular or the planetesimal hypoth- 
 esis. It is thought possible that some eruptive material may consist 
 of fused sedimentary strata.* 
 
 Origin of the Various Kinds of Eruptive Rochs ly Differentiation 
 
 of Bock Magmas. 
 
 Until very recently it was taken for granted that a fused mass 
 would have the same composition throughout and would retain such 
 composition until solidified, and therefore that all eruptions in the 
 same place and from the same magma must have the same composi- 
 tion, chemical if not mineral. When, therefore, diverse species from 
 extreme acid to extreme basic were found in the same locality it was 
 supposed that they came from eruptions at different times and from 
 different magmas, and many ingenious attempts have been made to 
 classify these according to their supposed relative ages. The most 
 celebrated of these attempts is that of Eichthofen in the classification 
 of Tertiary eruptives, given above. But now it has been definitely 
 proved, especially by the observations of Iddings on the eruptives of 
 Electric Peak and Sepulchre Mountains, Montana, that the same molten 
 mass in the act of cooling differentiates into basic kinds on the one 
 hand and acid kinds on the other. Speaking in a general way, it may 
 be said that in the gradual cooling of such a mass the first to crystallize 
 are the more basic minerals. These crystallize first in the oidlying 
 parts when the cooling is most rapid, and then similar materials con- 
 tinue to accumulate and crystallize there by migration of the more 
 basic materials to the solidifying parts, leaving a more acid remnant in 
 the center to solidify last. It is true that this is contrary to what we 
 would expect if we regard only the relative fusibilities of the several 
 minerals, for the basics are the more fusible and therefore ought to be the 
 
 * The latest eoutribution to the subject of rock-classification is found in a book pub- 
 lished by the University of Chicago Press, 1903, entitled Quantitative Classification of 
 Igneous Rocks, under the joint authorship of .Whitman Cross, J. P. Iddings, L. V. Pirs- 
 son, and H. S. Washington. The writers propose a new classification and a new nomen- 
 clature based on chemical composition. 
 
228 METAMORPHIC ROCKS. 
 
 last to solidify. But we must regard all the minerals as in solution in 
 a fused magma of alkaline silicates, and the basic minerals as the more 
 insoluble and therefore as crystallizing first. Thus the phenomena of 
 the origin of different species from a single fused mass may be ex- 
 plained by (1) the tendency to differentiate on cooling; (3) the greater 
 insolubility of the more basic minerals, and therefore their earlier crys- 
 tallization in the outer parts ; and (3) the migration of materials to 
 the point of crystallization. Add to this the fact that different 
 original magmas differ in composition, and all the different kinds of 
 eruptives receive a ready explanation. 
 
 CHAPTEE IV. 
 METAMORPHIC ROCKS. 
 
 There is another class of rocks, derived from both the sedimentary 
 (or clastic) and the igneous rocks by processes of alteration. The 
 rocks of this class often retain some of their original structure and 
 texture, but are usually schistose. They are commonly destitute of 
 fossils. Some of them show every possible gradation into unaltered 
 sediments, and others into the igneous rocks. 
 
 Origin. — These rocks are alteration products of all kinds of origi- 
 nal rocks. They are always changed in texture and structure, and 
 may be changed in composition from the originals. Many of them 
 are certainly clastic rocks which have been subjected to pressure, heat, 
 and other forces that have changed their structure and appearance, 
 sometimes entirely destroying their fossils and even their original 
 lamination or bedding, and inducing instead a schistose structure. 
 The evidence of their sedimentary origin is found in their gradation 
 into unaltered f ossilif erous strata; in the occasional presence of fossils 
 even in greatly changed rocks; and in the interbedding of marbles 
 and quartzites or quartz-schists, as these rocks in large masses are 
 confidently regarded as of clastic origin. It was formerly supposed 
 that all the metamorphic rocks were altered clastic rocks, but it is 
 now known that a large part of them are altered igneous rocks. The 
 reader should now appreciate the fact that rocks of any kind when 
 subjected to heat, pressure, and chemical action, either by deep burial 
 under strata or by crushing as in mountain-making, may be meta- 
 morphosed. 
 
 Position. — All the oldest rocks, those lowest in the geologic column, 
 are probably metamorphic. When appearing at the surface it is 
 because great thicknesses of overlying strata have been removed. The 
 
METAMOEPHIC ROOKS. 229 
 
 converse, however, that metamorphie rocks are always among the 
 oldest, is by no means true. Metamorphism is not a test of age, 
 for metamorphie rocks are found of all geologic periods up to the 
 Tertiary. The Coast Eange of California is much of it metamor- 
 phie, although the strata belong to the Cretaceous and Tertiary peri- 
 ods. Metamorphism seems to be quite universal in the ancient Lau- 
 rentian, and becomes less and less common as we pass up the strata 
 series of the geologic column. 
 
 The date of metamorphism of any rock is to be clearly discrimi- 
 nated from the time of the rock formation, just as the date of moun- 
 tain-making is not the age of the contained strata. Metamorphism 
 has occurred in all geologic periods, and is doubtless now progressing 
 in the deeply-buried strata. 
 
 Metamorphism is generally associated with the crushing, folding, 
 and tiltiQg of thick strata in great mountain-ranges, and often also 
 with vulcanism. 
 
 Extent on the Earth-Surface. — Metamorphie rocks exist, outcrop- 
 ping on the surface, over wide areas. Kearly the whole of eastern 
 Canada and Labrador, and a belt along the east slope of the Ap- 
 palachians, are composed of them; also a large portion of the moun- 
 tainous regions of the western border of this continent. Other areas 
 in eastern North America are the districts west and south of Lake 
 Superior; the Adirondack area; a large part of eastern New York, 
 including Manhattan Island; much of New England; with other 
 smaller areas wherever Archaean strata appear (see p. 296). Vast 
 areas are found in other continents. Beneath the surface they prob- 
 ably underlie all other stratified rocks, and are therefore the most 
 widespread of all rocks except the primitive ones. Their thickness 
 is often immense. The Archeean series of Canada is of vast but un- 
 known thickness, and wholly metamorphie. 
 
 Principal Kinds of Metamorphie Rocks. — It is not practicable to 
 name, much less to describe, the host of metamorphie rock-products. 
 The principal kinds derived from sediments, which form thick and 
 extensive masses, are marble, slate, quartzite, and graywacke of the 
 non-foliated kinds, and gneisses and schists in many varieties of the 
 foliated class. The metamorphie igneous rocks are mainly schists 
 and gneisses. 
 
 Gneisses and Schists. — These are the most typical and important 
 of the metamorphie rocks, since they are the product of the most 
 extreme alteration of both sedimentary and igneous rocks. They also 
 have the greatest thickness and horizontal extent, and show the great- 
 est variation in texture and mineral content. 
 
 Oneiss is a rock showing more or less of a banded structure. How- 
 ever, the banding can sometimes be seen only in larger masses, not in 
 
230 METAMORPHIC ROCKS. 
 
 mere hand specimens. It was formerly supposed that the banding 
 was a relic of original bedding or lamination, and that the gneisses 
 represented an intermediate stage of alteration between siliceous sedi- 
 ments and granite ; but it is now known that gneiss is the product of 
 the extreme change of either sedimentary or igneous rocks, the band- 
 
 FiG. 195. — Gneiss. (Photograph by G. H. Williams, from Brigham's Geology.) 
 
 ing being due to the development of different minerals in planes, by 
 the effect of pressure, movement (mashing), and injection (see p. 
 233). The varieties of gneiss, like those of schist, are named from 
 the chief basic mineral. The most common are mica-gneiss, horn- 
 blende-gneiss, augite-gneiss, etc. 
 
 Schist is a thinly foliated rock in which the foliation is due to 
 the abundance of parallel and scale-like crystals of some highly cleav- 
 able mineral, as mica, chlorite, talc, etc. The foliation structure is 
 the product of extreme metamorphism, mashing under great pressure 
 in the zone of flowage (see p. 334). Petrographers recognize many 
 varieties, according to the basic mineral, as mica-schist, amphibole- 
 schist, augite-schist, chlorite-schist, etc. These may grade into a' 
 quartz-schist and schistose quartzite. 
 
 The mica-schists and the more acid or mica-gneisses, when of 
 igneous origin, have been derived from the more acidic rocks, while 
 the more basic gneisses and schists have been produced from the basic 
 igneous rocks. 
 
 Quartzite. — This term is properly applied to a thoroughly com- 
 pact or crystalline quartz, usually produced by deposition of silica 
 between the quartz-grains of a sandstone. Eoeks are found repre- 
 senting every stage of the cementation process, and quartzitic masses 
 are found of all thicknesses up to 12,000 feet. Quartzite represents 
 less dynamic action than gneisses and schists, and does not require 
 very high temperatures, 
 
THEORY OF METAMORPHISM. 23^ 
 
 Graywacke. — This is a gray, banded rock derived from grits and 
 mudstones — that is, from granular sediments which are not chiefly 
 quartz, but of varied mineral composition. 
 
 Slate. — The origin of slate has been discussed under slaty cleavage 
 on pages 189-195. Slates represent original clays and shales. Earely 
 they may be derived from fine arkose, and from volcanic tuffs. They 
 have various colors, as brown, red, purple, green, dark blue, and drab. 
 
 Phyllite is a name applied to a micaceous slate, and represents an 
 intermediate stage between slate and mica-schist. 
 
 Serpentine. — This is a mineral and rock of varied origin. It 
 forms the green streaks and blotches in marble (ver de-antique). As 
 a rock it is soft and usually of green color. It is produced by altera- 
 tion of some igneous rock rich in magnesian mineral. It is often 
 derived by true metamorphism of buried peridotite, through meta- 
 somatic change of the minerals pyroxene, amphibole, and olivine. 
 
 Marble. — Quarrymen and dealers in constructional materials call 
 any limestone a " marble " which is sufficiently compact or fine- 
 grained to take a good polish. In geology the term is properly 
 restricted to a calcareous rock which has lost its original fragmental 
 character and become crystalline by metamorphism. Marble differs 
 from other metamorphic rocks in the fact that it rarely shows any 
 cleavage or fissility, even when it has been subjected to dynamic action 
 or mashing. The explanation of this lies in the readiness with which 
 calcite crystallizes when deforming influences are withdrawn. The 
 grain of marble varies from the finest statuary marble to large coarse 
 crystals. The colors of variegated marbles are due to iron and other 
 inorganic impurities, the dark colors of organic origin being dis- 
 charged. A black limestone may produce snow-white marble. The 
 earthy impurities of the original sediment form a variety of included 
 silicate minerp.ls, as woUastonite, garnet, micas, amphibole, serpen- 
 tine, etc. 
 
 Besides the rocks briefly described above there are many others 
 of less extent, or less common occurrence. Some of these are steatite 
 or soapstone; magnetite and hematite ores; Griinerite-schist ; ferru- 
 ginous chert; and jaspilite. Anthracite is an example of moderate 
 change, in consolidation and carbonization, from coal interbedded 
 in strata subjected to folding and crushing. It is also produced by 
 the heat from igneous eruptions. 
 
 Theory of Metamorphism. 
 
 Metamorphism is one of the most difficult subjects of geology, 
 since the process is mostly beyond the range of observation and ade- 
 quate experimentation, The study requires the application of the 
 
232 METAMORPHIC ROCKS. 
 
 most advanced knowledge of mechanics, physics, chemistry, and min- 
 eralogy. In recent years the subject has been ably treated by several 
 authors. The present discussion will follow chiefly the writings of 
 Van Hise.* 
 
 In all forms of metamorphism water is the chief agent, and three 
 forces are always present, though in varying intensity, namely, mo- 
 tion or dynamic action, heat, and chemical affinity. 
 
 Water. — At ordinary temperatures water is a potent agent in solu- 
 tion and deposition of mineral material, but at high temperatures 
 its power is greatly increased. The development of the schists and 
 gneisses is largely due to continuous solution and deposition by the 
 included water. At all times during the change the rocks are solid; 
 but they slowly adapt themselves to the forms demanded by the earth- 
 stresses by continuous solution and redeposition. The amount of 
 motion at any one time is almost inappreciable, but is sufficient to 
 slowly transform the rocks from massive to schistose forms. 
 
 While during the dominant process of metamorphism the rocks 
 continuously remain in the solid state, exceptionally and locally, 
 where the temperature is very high, aqueo-igneous fusion may occur. 
 In the dry state rocks may require a heat of some 2,500° F. to melt 
 them; but where water is present this excessive temperature is not 
 required. By cooling and crystallization such aqueo-fused masses 
 form crystallized rocks, containing crystals of quartz, mica, feldspar, 
 etc. It has been shown that there are all gradations between solution 
 and true igneous fusion, through the grades of hydrothermal fusion. 
 " It is thought highly probable that under sufficient pressure and at 
 a high temperature there are all gradations between heated waters 
 containing mineral material in solution and a magma containing 
 water in solution. In other words, under proper conditions water 
 and liquid rock are miscible in all proportions. From the water 
 solutions true impregnation or cementation would take place; from 
 the rock solutions, true injection." 
 
 Dynamic Action.^ — When the rocks are subjected to simple pressure 
 and the movement is chiefly between molecules, the process is called 
 " static metamorphism." Where masses of rock are subject to move- 
 ment and deformation the process is "dynamic metamorphism." 
 There are all gradations between the two processes, and neither one 
 acts entirely alone. 
 
 In discussion of dynamics the earth's crust is theoretically divided 
 into three zones : a superficial zone, where rock movement is mainly 
 
 * C. R. Tan Hise, Principles of North American Pre-Cambrian Geology, Sixteenth 
 Ann. Rep. TJ. S. Geol. Surv., Part I, pp. 581-874, 1896 ; Metamorpbism of Rocks and 
 Rock Flowage, Bull. Geol. Soc. Amer., vol. ix, pp. 269-328, 1898 ; Amer. Jour. Sci., 
 July, 1898, vol. vi, pp. 75-91. 
 
THEORY OF METAMORPHISM. 233 
 
 by fracture ; a lower intermediate zone of fracture and plasticity ; and 
 the underlying zone, where the pressure is so great that movement 
 is mainly by plasticity or flowage. In the zone of fracture the meta- 
 morphic process is mainly static, and the textures and structures of 
 the rocks may not be obliterated. In the zone of flowage the struc- 
 tures and textures disappear by " plastic deformation through con- 
 tinuous solution and deposition, or, in other words, recrystallization." 
 This is the zone in which are produced the schistose rocks, the most 
 intense expression of the metamorphic process. * 
 
 Heat. — The heat of metamorphism may be derived (1) from 
 normal increase of temperature with depth; (3) from crushing, or 
 dynamic action; (3) from intrusions of liquid rock; and (4) from 
 chemical action. The chemical activity is increased, at least within 
 wide limits, by heat and pressure. 
 
 Regional or General Metamorphism. — A practical distinction is 
 usually drawn between localized or contact metamorphism and the 
 deep-seated, general, or regional metamorphism. Like most compari- 
 sons in geology, no clear line can be drawn. Contact metamorphism, 
 being less important, will be described later. 
 
 The metamorphic process, as a whole, includes several effects. 
 The following are described by Van Hise : 
 
 Consolidation. — This is mainly the result of pressure, and is more 
 effective in the case of fine-grained and clayey rocks. 
 
 Cementation.— 'E^ infiltration of mineral matter in solution and 
 its deposition in the interstices of a rock, the mineral grains are bound 
 together. The more important cements are quartz, calcite, and fer- 
 rite (iron oxides) ; but there are several others. The cementation 
 process is more important in the coarser sediments, and occurs mainly 
 in the two upper zones, that of fracture and fracture and flowage. 
 Quartzite is a good example of its effect. 
 
 Injection. — This is the penetration of the molten magma into 
 spaces in the rock. It grades into cementation (see quotation, p. 
 232). The acid magmas are more penetrative as injecting material. 
 With penetration between the grains of a rock the mineral character 
 of the latter m3,y be changed. Schists, for example, may thus become 
 gneisses by injection of a large proportion of feldspar and quartz. 
 
 Metasomatism. — This is the change in the mineral composition of 
 a rock by the alteration of the original minerals, or by their replace- 
 ment, or by recrystallization. These changes may occur separately 
 or together. The minerals most commonly involved' in metasoma- 
 tism are the forms of silica, feldspar, micas, amphibole, augite, calcite 
 and dolomite, serpentine, and the several oxides of iron. 
 
 The rocks which -are most commonly modified by metasomatism 
 and the other processes named above, with or without mashing, are 
 
234 
 
 METAMORPHIC KOCKS. 
 
 the following: Graywacke and graywacke slate, ferruginous chert 
 and jaspilite, Griinerite-schist (iron silicates), actinolite and horn- 
 blende-schists, and marble. 
 
 Mashing. — This term includes the deep-seated movements which 
 produce diminished volume, along with the crushing and sliding 
 movements commonly called shearing. In the zone of fracture this 
 produces fissility. In the zone of flowage it produces schistose and 
 gneissoid structure. Following are the rocks which are characteristic 
 
 Fig. 196.— Metamorpliic Eock ; Contorted Gneiss, Ottawa Hiver, opposite Montebello, Ont. 
 (Photograpli by E. W. Ells.) 
 
 of greater relative effects of mashing : Schistose quartzite and quartz- 
 schist; slate and mica-slate (phyllite), passing into mica-schist; mica- 
 gneiss; chlorite -schist; hornblende - schist and hornblende - gneiss. 
 The schists and cherts named above as characteristic of metasomatism 
 and other processes become more schistose and finer-grained as mash- 
 ing is more effective. The igneous rocks in which mashing has been 
 most effective are likely to have great uniformity of character and to 
 be finely foliated. And the converse conclusion is " that the finely, 
 regularly laminated, homogeneous crystalline schists are usually of 
 igneous origin." The metamorphosed rocks of sedimentary origin 
 can usually be determined by variations in structure, at least when 
 examined in great thickness. 
 
THEORY OF METAMOEPHISM. 235 
 
 Contact MetamorpMsm. — This covers the more localized altera- 
 tions in rocks produced by igneous intrusions and lava-flows. Some 
 authors include here such baking and hardening effects as are pro- 
 duced by the burning of coal-beds. The making of red brick from 
 blue clay, and the various .ceramic processes, are imitations of con- 
 tact metamorphism by dry heat. 
 
 The changes produced on the walls of dikes or igneous intrusions 
 are sometimes surprisingly small, but in the neighborhood of great 
 igneous masses the surrounding rocks may be affected for miles. In 
 the local changes, heat has relatively greater effect and pressure less, 
 according as the work is near the surface. The walls of dikes, or 
 other contact planes, are found to be differently affected, according 
 to the character of the invaded rocks and the temperature and com- 
 position of the intrusive magma. If the latter holds considerable 
 quantity of acid vapors, or " mineralizers," the invaded strata may 
 be greatly changed by cementation, injection, and metasomatism. 
 The effects naturally fade away with distance from the source of heat. 
 Near the contact limestone or chalk becomes marble ; coal-beds change 
 to anthracite or coke; disseminated carbonaceous matter bfecomes 
 graphite; limonite and siderite ores change to hematite; sandstone 
 may become a quartzite; clay rocks are variously altered. Close to 
 the contact the latter are sometimes a dense, dark rock called horn- 
 fels, which grades off into schists, and then to mica-slates. 
 
 In the ease of the great igneous masses called bathyliths, lacco- 
 liths, and bosses (see. p. 330), we have metamorphism on a great 
 scale, between true contact and regional, and showing the essential 
 unity of the two classes. 
 
 CHAPTER V. 
 STRUCTURE COMMON TO ALL ROCKS. 
 
 We have thus far given a brief description of the three classes of 
 rocks, their structure and mode of occurrence. There are still, how- 
 ever, several important kinds of structure which are common to all 
 these classes of rocks, and require description. These are joints, fis- 
 sures, and veins. Mountain-chains, as involving all kinds of rocks 
 and all kinds of structure, and as summing up in their discussion all 
 the principles of structural and dynamical geology, must be taken up 
 last. 
 
 Section 1. — Joints and Fissures. 
 
 Joints. 
 Joints are the cracks or division-planes produced subsequent to 
 the formation of the rocks, and not due to sedimentation. The planes 
 
236 
 
 STRUCTURE COMMON TO ALL ROCKS. 
 
 of bedding or lamination in the stratified rocks are not joints. In 
 igneous rocks all joints, even the horizontal and ball-and-socket joints, 
 
 Fig. 197. — Parallel Maeter-Jointain Medina Sandstone, Albion, N Y 
 
 are produced by shrinkage in cooling, the most perfect result being 
 found in the hexagonal prisms of columnar structure (see p. 333, 
 and Pigs. 191, 193). 
 
 Fig. 198. Joints in Hamilton Shales, King's Perry, Cayuga Lake. (Photograph by D. P. Lincoln, 
 from New York State Museum.) 
 
FISSURES, OR FRACTURES. 
 
 237 
 
 In the sedimentary rocks the joints are due either to shrinkage 
 of the strata in consolidation or to strains by bending and torsion. 
 Joints tend to form at right angles to the bedding, and in two series 
 perpendicular to each other. The direction of the large, or master- 
 joints (see Figs. 197, 198), should be noted in iield-work, as they 
 will usually be found approximately parallel over considerable coun- 
 try and have reference to the direction of strain. • The smaller Joints, 
 which may be limited even to single beds, are called minor joints. 
 They facilitate the work of quarrying. 
 
 In disturbed strata, joints may be classiiied according to direction, 
 as strilce joints when parallel to the strike, and dip joints when in 
 line with the dip. They may also be divided into tension joints and 
 compression joints. The former occur naturally in anticlines and 
 are associated with normal faults; the latter occur in regions of 
 thrust and shearing and grade into fissility. • 
 
 Jointing can not occur in the deeper layers of the earth's crust, 
 the zone«of fiowage, but are characteristic of the superficial layers, 
 the zone of fracture. In the intermediate zone of fracture and 
 flowage only the more brittle rock are broken. 
 
 Fissures, or Fractures. 
 
 No sharp distinction can be drawn between joints and fissures, 
 but the term fissures is applied to the larger fractures which pass 
 through great thickness of rocks. Fissures are sometimes fifty or 
 more miles in length, and pass downward to unknown but certainly 
 very great depths. They often reach down through the rigid strata 
 and permit the outfiow of molten rock from the plastic zone. (See 
 page 218.) 
 
 Cause. — The cause of great fissures is evidently always movements, 
 either by foldings or by liftings of the earth's crust. In either case 
 
 Fig. 1!I9.— Moiioclinal Fold. 
 Section of Nutria- Fold, New Mexico (after Gilbert). 
 
 there would be formed a parallel system of fissures in the direction of 
 the folds, and therefore at right angles to the direction of the folding 
 
238 
 
 STRUCTCllE COMMON TO ALL KOCKS. 
 
 or lifting force. Fissures are usually thus found in systems parallel 
 among themselves, and to^the axes of mountain-chains. 
 
 Nearly always the walls on the two sides of a fissure do not cor- 
 respond with each other, but one side has been pushed up higher or 
 dropped down lower than the other. Such a displacement is called a 
 fault, a slip, or dislocation. This may occur in fissures in any kind of 
 rock, but is most marked and most easily distinguished in stratified 
 rocks. When the strata are sufficiently flexible to admit it, they are 
 bent instead of broken, and a monoclinal fold is formed instead of 
 a fault (Fig. 199). 
 
 Faults.* — In 'faults the extent of vertical displacement varies 
 from a few Inches to hundreds or even thousands of feet. In the 
 Appalachian chain there occur faults in which the vertical dislocation 
 
 Fia. 200.— Fault in Southwest Virginia : a, Silurian ; d, carboniferous (after Lesley). 
 
 is 5,000 to 20,000 feet. In southwest Virginia, according to Kogers, 
 there is a line of fracture extending parallel to the Appalachian chain 
 for eighty miles, in which there 'is a vertical slip of 8,000 feet, the 
 Lower Silurian being brought up on one side until it comes in con- 
 junction with the Lower Carboniferous on the other (Fig. 200). In 
 eastern Pennsylvania, according to Leslie, there is another fault ex- 
 tending for twenty miles, in which the lowermost of the Lower Silu- 
 rian is brought up on a level with the uppermost of the Upper Silu- 
 
 FiQ. 201 Faults and Monoclinal Folds of Plateau Kegion ; section 90 miles long (after Powell). 
 
 rian, the whole Silurian strata being at this place 20,000 feet thick, 
 so that one may stand astride, with one foot on the Trenton limestone 
 (Lower Silurian) and the other on the Hamilton shales (Devonian). 
 On the north side of the Uintah Mountains there is a slip, accord- 
 ing to Powell, of nearly 20,000 feet. The Sevier Valley fault, Utah, 
 
 * In California and in Europe series of fissures are filled with sand from below, called 
 " sandstone dikes." 
 
FISSURES, OR FRACTURES. 
 
 239 
 
 Fie. S02. 
 
 may be traced partly as a slip, partly as a monoclinal fold, for 325 
 miles (GilBiert). On the west side of the Wahsatch range there is a 
 fault of 40,000 feet (King),* and on the east side of the Sierra one of 
 at least 15,000 feet.f 
 
 But nowhere on this continent, or perhaps in the world, are 
 fissures and faults developed on so grand a scale as in the high 
 Plateau region, i. e., the 
 region bounded by the ^ 
 
 Wahsatch, the Uintah, ° 
 and the Colorado Moun- 
 tains. The whole of this 
 elevated region is tra- 
 versed by a system of 
 north and south fissures, 
 extending for hundreds of 
 miles, by which the al- 
 most horizontal strata are 
 
 broken into huge oblong prismatic blocks many miles wide. . The slip- 
 ping of these blocks, some to a higher and some to a lower level, with 
 a difference of 1,000 to 5,000 feet, or even in some cases 13,000 feet, 
 has given rise to the remarkable series of north and south cliffs, which, 
 together with the equally remarkable east and west cliffs, due to ero- 
 sion, to be described here- 
 after (p. 383), form so 
 striking a feature of the 
 scenery of this region. 
 The accompanying sec- 
 tion and perspective view 
 (Fig. 201), taken from 
 Powell, shows several of 
 these occurring in a dis- 
 tance of 90 miles. I 
 
 These fissures were 
 formed by the elevation 
 of the Plateau region, and 
 are parallel to the axis of elevation ; on each side of which they are 
 arranged with wonderful regularity. They were formed in very recent 
 geological times, probably late Pliocene and Quaternary,* and possibly 
 
 ''.--"\'.--"c 
 c..--- •, 
 
 Pig. 203.— Strata repeated by Faults. 
 
 * Survey of the Fortieth Parallel, vol. i, pp. '728-'746. 
 
 t Le Conte, American Journal of Science, vol. xvi, p. 101, 1878. 
 
 X The Kaibab fold and fault is 300 miles long with a slip of 7,000 feet. The Jordan- 
 Araba fault, which gave origin to the Dead Sea, may be traced 350 miles (Nat., 44, p. 
 100, 1891). 
 
 * Dutton, Geology of the High Plateaus, p. 36. 
 
 17 
 
240 
 
 STRUCTDKE COMMON TO ALL BOOKS. 
 
 reaching even into the present epoch, and are therefore little affected 
 by erosion. Add to this the nakedness of the rocks and the horizon- 
 
 fio. SOS.— fault with Cbange of Dip: d, dike. 
 
 Pig. 204.— Section through Portion of Plateau Region of Utah, showing a Succession of Faults 
 
 (after Howell). 
 
 tality of the strata, and it is easy to see what an admirable field is here 
 afforded for the study of faults. 
 
 If such slips were suddenly produced by violent convulsion, then, 
 at the time of formation, there must have been a steep (Fig. 203) or 
 sometimes even an overhanging escarpment (Fig. 300), equal to the 
 displacement. In some cases there is such an escarpment or line of 
 steep mountain-slope corresponding to the line of slip. In the 
 
 Colorado Plateau re- 
 gion the north and 
 south cliffs are pro- 
 duced by faults 
 (Powell). TheZan- 
 dia Mountains, New 
 Mexico, are pro- 
 duced by a drop of 11,000 feet on the western side, leaving an escarp- 
 ment still 7,000 feet high (Gilbert). The precipitous eastern slope of 
 the Sierra and western slope of the Wahsatch are the result of faults. 
 In the Basin Eange region also many of the ridges are formed by faults. 
 But in many cases there is no such escarpment, the two sides of the 
 fault having been cut down to one level by subsequent erosion, so that 
 the unpractised eye detects nothing vinusual along the line of fracture 
 and slip. In Fig. 303 the strong line 
 a a shows the present surface, while 
 the dotted line bbb shows the surface 
 after the displacement as it would be 
 if unaffected by erosion. In many 
 cases, however, it seems more probable 
 that there never existed any such es- 
 carpment as represented in Fig. 303, 
 but that the displacement was pro- 
 duced by a slow, creeping motion, or 
 else by a succession of smaller sudden slips probably accompanied with 
 earthquakes (p. 116), and thus that the slipping and the denudation 
 have gone on together pari passu. In Fig. 356, on page 387, the 
 upper part shows the great Uintah fault restored, while the lower part 
 shows the actual condition of things produced by erosion. 
 
 When faults occur in inclined outcropping strata, the same series 
 
 Pio. 806.- TJnconf onnity on Faulted Strata. 
 
FISSURES, OR FRACTURES. 
 
 241 
 
 of strata may be repeated several times, as in Fig. 203. In such a case, 
 the observei' walking over the surface of the country from A to B 
 might suppose here a series of nine strata, whereas there are but three 
 strata, a, i, c, three times repeated. Fig. 204 is a natural section 
 showing this. Sometimes the dip of the strata on the two sides of a 
 fault are not parallel, the change of inclination being efEected at the 
 time of the displacement, as shown in Fig. 305. Upon the eroded, 
 surface of such dislocated strata, by subsequent subsidence, other strata 
 may be unconformably deposited (Fig. 206). 
 
 Law of Slip. — In faults the plane of fracture is sometimes vertical, 
 but much more generally it is more or less inclined. The inclination is 
 called the Tiade. In such cases, in by far the larger number of great 
 
 Fig. 207.— Section across Tarrow Colliery, showing the Law of Faults (after De la Beche). 
 
 faults, the strata on the upper side (hanging wall) of the fracture have 
 dropped down, while the strata on the lower side (foot-wall) have gone 
 up, as in Figs. 207 and 308 and nearly all the previous figures. The 
 fissure hades to the down throw. These are called normal faults. In 
 some cases of strongly-folded strata, however, the hanging wall seems 
 to have been pushed and made to slide upward over the foot-wall as if 
 by powerful horizontal squeezing. This is the case with the great slip 
 in Southwestern Virginia, represented in Fig. 300. These are called 
 reverse faults. In several hundred cases of great fissures, examined 
 by Phillips, in England, nearly all followed" the law of normal 
 faults.* Fig. 307 is a section across Yarrow Colliery, in which all 
 
 East 
 
 Fig. 208.-Section of Pahranagat Hange, Nevada, showing the Law of Faults (after Gilbert). 
 
 the slips follow this law. Of the numerous slips figured by Powell, 
 Gilbert, and Howell, as occurring in the Plateau and Basin Kange 
 region, nearly all follow this law. Fig. 308 is a section illustratmg 
 this fact. 
 
 * Normal faults are also called gravily faults, and reverse faults are called thrmt 
 faults, or overthrusts. 
 
24:2 
 
 STEUCTURE COMMON TO ALL ROCKS. 
 
 Explanation of the Direction of Slipping.— Eeverse faults are nearly 
 always found in strongly-folded strata such as characterize the struct- 
 ure of most mountain ranges, and are evidently formed by powerful 
 
 lateral pressure in 
 the act of mountain 
 formation. The 
 
 manner in which 
 folds are pushed 
 orer until they be- 
 come reverse faults 
 is shown in the ac- 
 companying figures 
 (Fig. 309, A, B, and 
 O). In extreme cases 
 the fault-plane be- 
 comes nearly hori- 
 zontal, G. These 
 are called thrust- 
 planes* 
 
 The explanation 
 of normal faults is 
 not so obvious. In 
 the case of great 
 faults of this kind the explanation is probably a!s follows : Suppose a 
 portion of crust lifted by intumescence of sub-crust layer, produced 
 either by access of water from above or by hydrostatic pressure trans- 
 
 FiG. S09.— Diagrams showing how Eeverse Faults are formed (after 
 De Margerie and Heim). 
 
 X. 
 
 Fio. 210.— Diagrams showing how Nonual Faults are probably formed. 
 
 ferred from a subsiding area in some other perhaps distant place. 
 The crust would be broken by more or less parallel fissures into great 
 
 * Extreme examples of thrust-planes, such as those in the Scottish Highlands, seem to 
 be formed in a rigid crust by fracture and overriding without folding. 
 
MINERAL VEINS. 
 
 ?43 
 
 oblong blocks. Since the fissures are usually more or less inclined, 
 these crust-blocks would be either rhomboidal or wedge-shaped (Fig! 
 210, A). As soon as the tension is relieved, the blocks would read- 
 just themselves by gravity into new positions. In doing so the rhom- 
 boidal blocks abfg would tilt over on the overhanging side and 
 
 0° 0„ o 0„0 ojo olo;o„9= 
 
 = =■.£ 
 
 •;%■*.•.."■.■.; ■ • . "Z^" 
 
 — T 
 
 ^ir^'-.-'-'i^^'^/a 
 
 ±r 
 
 i---^ - 
 
 — _: 
 
 p, ll T^ ■ 1 ■ 
 
 — - 
 
 
 ' l\ ' >i 4 c[ 
 
 — 
 
 [^^- 
 
 -^ 
 
 Fig. 211.— Illustrating Terms applied to Faulting. Normal or gravity faults. In each diagram the 
 downthrow side and the hanging-waU are on the left ; the upthro^o and foot-wall on the right. 
 Or-c IS throw, b-c is heave ; the angle at a shows the amount of hade ; the angle at b shows the 
 amount ot/aaW-dip. In I the etratigraphic throw is the same as the throw (a-c) : in // it is 
 Or-d; m III It is Or-b. 
 
 heave up on the obtuse-angle side, producing in every case normal 
 faults, and the wedge-shaped blocks c de would sink bodily lower or 
 float bodily higher according as the base of the wedge was upward or 
 downward, producing again in every case normal faults, as shown in 
 Fig. 310, G. 
 
 Thus where fissures are formed by lateral pressure or crushing, 
 thrust faults are formed; but where they are formed by lateral ten-- 
 sion or stretching, gravity or tension faults are produced.* 
 
 Slickensides is the name applied to the striated or polished sur- 
 faces often produced by the friction along a fault plane. 
 
 Section" 2. — Mineral Veins. 
 
 All rocks, but especially metamorphic rocks in mountain-regions, 
 are seamed and scarred in every direction, as if broken and again 
 mended, as if wounded and again healed. All such seams and scars, of 
 whatever nature and by whatever process formed, are often called by 
 the general name of veins. It is better, however, that dikes and so- 
 called granite-veins, or all cases of fissures filled at the moment of for- 
 mation by igneous injection, should be separated from the category of 
 veins. True veins, then, are accumulations, mostly in fissures, of cer- 
 tain mineral matters usually in a purer and more sparry form than they 
 
 * Eeade has shown (Origin of Mountains, chap, yiii) that crust-blocks formed by ten- 
 sion and resting on any kind of yieldinff foundation, -whether solid or liquid, would settle 
 BO as to form normal faults. 
 
244 STRUCTUKE COMMON TO ALL ROCKS. 
 
 exist in the rocks. The accumulation has in all cases taken place sub- 
 sequently to the formation of the fissures, and by a slow process. 
 
 Kinds.^Thus limited, veins are of three kinds : Veins of segrega- 
 tions, veins of infiltration, and great fissure-veins. These three, how- 
 ever, graduate into each other in such wise that it is often difficult to 
 determine to which we must refer any particular case. Some writers 
 make many other kinds, but these may be regarded as intermediate 
 varieties. 
 
 1. Veins of Segregation. — In these the vein-matter does not differ 
 greatly from the inclosing rock. Such are the irregular lines of 
 granite in granite, the lines differing from the inclosing rock only in 
 color or texture; also irregular veins of feldspar in granite or in 
 gneiss. Under the same head belong also the irregular streaks, clouds, 
 and blotches, so common in marble. In these cases there seems to be 
 no distinct line of separation between the vein and the inclosing rock 
 — no distinct wall to the vein. The reason is, these veins are not 
 formed by the filling of a previously-existing fissure, but by the segre- 
 gation of certain materials, in certain spots and along certain lines, 
 from the general mass of the rock, either when the latter was in plastic 
 condition from heat and water, or else by means of percolating water, 
 somewhat as concretions of lime, clay, iron-ore, and flint, are formed in 
 the strata (p. 196). 
 
 3. Veins of Infiltration. — Metamorphic rocks have, probably in all 
 cases, been subjected to powerful horizontal pressure. Besides the 
 wide folds into which such rocks are thus thrown and the great 
 fissures thus produced, the strata are often broken into small pieces by 
 means of the squeezing and crushing. The small fissures thus pro- 
 duced are often filled by lateral secretion from the walls, or else by 
 slowly-percolating waters holding in solution the more soluble matters 
 contained in the rocks. The process is similar to the filling of cavities 
 left by imbedded organisms (p. 201), and still more to the filling of 
 vapor-blebs in traps and lavas, and the formation of agates and car- 
 nelian amygdules (p. 324). In veins of this kind, therefore, a beautiful 
 ribbon- structure is often produced by the successive deposition of 
 different-colored materials on the walls of the fissure. Veins of this 
 kind also, since they are the filling of a previously-existing fissure, 
 have distinct walls. The filling consists most commonly of silica or 
 of carbonate of lime. Gash-veins of authors are probably larger veins 
 of this kind. 
 
 3. Fissure -Veins. — These are fillings of the great fissures produced 
 by movements of the earth's crust. "When these fissures are filled at 
 the time of formation by igneous injection, they are called dikes ; but 
 if subsequently with mineral matter, by a different process, to be dis- 
 cussed hereafter, they are fissure-veins. These veins, therefore, like 
 
MINERAL VEINS. 245 
 
 dikes, outcrop over the surface of the country often for many miles 
 fifty or more. Like dikes, also, they are often many yards in width 
 and extend to unknown, but certainly very great, depths. Like dikes 
 and fissures, also, they occur in parallel systems and are often faulted. 
 
 Characteristics.— The most obvious characteristics of the veins of 
 this class are their size, their continuity for great distances and to 
 great depths, their faulted condition, and their occurrence in parallel 
 systems. As the vein is a filling of a previously-existing fissure, the 
 distinction between the vein and the wall-rock is usually quite 
 marked. In many cases, in fact, the vein-filling is separated from the 
 wall-rock by a layer of tenacious, clayey matter called a selvage or 
 gouge. The selvage is probably formed by decomposition of the wall- 
 rock in immediate contact with the vein, by circulating water assisted 
 doubtless by crushing of the rocks by repeated movements of the 
 walls. These movements also often produce a striation and polishing 
 of the walls called " slicken- sides." The contents of fissure-veins are 
 also far more varied than those of other classes. 
 
 Metalliferous Veins. — Some metals, particularly iron, occur prin- 
 cipally in great beds, being accumulated by a process already described 
 (p. 150). Others, especially lead, often accumulate in flat cavities be- 
 tween the strata, especially of limestone. But most metals occur in 
 veins. All the kinds of veins mentioned above may contain metals, 
 but the segregative veins are usually too irregular and uncertain, and 
 the infiltrative veins too small, to be profitable. True, profitable 
 metalliferous veins are almost always great fissure-veins. We will 
 speak, therefore, principally of these, and the further description of 
 fissure- veins is best undertaken under this head. 
 
 Contents. — The contents of metalliferous veins are of two general 
 kinds, viz., vein-stuffs and ores. The principal vein-stuffs are quartz, 
 carbonate of lime (calc-spar), carbonate of baryta, carbonate of iron, 
 sulphate of baryta (heavy spar), and fiuoride of calcium (fluor-spar). 
 By far the most common of these is quartz, and next is calc-spar. 
 Often, however, the vein-stuff is an aggregate of minerals forming a 
 true rock. Nearly the whole of a vein consists usually of vein-stuff. 
 The ore exists in comparatively small quantities, sometimes forming a 
 central rib or sheet, as if deposited last (Fig. 213, a b) ; sometimes in 
 irregular isolated masses called bunches or pockets, or in small strings, 
 or grains, irregularly scattered through the vein-stuff and extending 
 often a little way into the wall-rock. 
 
 The chemical forms in which metals occur are very various; some- 
 times they occur as pure metal (especially in the case of. gold and 
 platinum, and sometimes in the case of silver and copper), but more 
 commonly in the form of metallic sulphides, metallic oxides, and 
 metallic carbonates. Of these the metallic sulphides are by far the 
 
246 
 
 STBUCTURE COMMON TO ALL BOOKS. 
 
 most common. It is worthy of remark that all these forms are com- 
 paratively very insoluble. The same is true of the vein-stufEs. 
 
 Ribboned Structure. — The ribboned or banded structure, already 
 spoken of under Veins of Infiltration, is very commonly found in 
 great fissure- veins. This structure is as characteristic of veins as the 
 columnar structure is of dikes. The layers on the two sides usually 
 correspond to each other (Fig. 212) ;^ sometimes the successive layers 
 
 Fig. 213. 
 
 Fid. 214. 
 
 are of different color, giving rise to a beautiful, striped appearance. 
 Sometimes the successive layers on both sides are of difEerent materials, 
 as in Fig. 213, in which the central rib, d, is galena, and aa,ib,cc, 
 are successive layers of quartz, fiuor, and baryta. Sometimes, in cases 
 of quartz-filling, the layers are agate, except the center, which is filled 
 up with a comb of interlocking crystals, as in Fig. 214. The same 
 occurs often in amygdules, the last filling being crystalline. Some- 
 times there is evidence of successive openings and fillings, as in Fig. 
 215, where a represents quartz-crystals, interlocking in the center and 
 based on agate layers, i i, while c represents quartz with disseminated 
 copper pyrites. In this case it seems probable that 1 and 2 were the 
 walls when the agate and quartz-filling took place, and that afterward 
 
 the fissure was reopened along 2, so that the walls became 2 and 3, and 
 the new fissure thus formed was filled with cupriferous quartz. The 
 same is well shown in Pig. 216, where a, i, c, d, e,f, are successive 
 quartz-combs, separated by 2, 3, 4, 5, 6, which are clay selvages, and 
 therefore old walls. 
 
MINERAL VEINS. 
 
 24Y 
 
 Irregularities.— Although more regular than other kinds, yet fis- 
 sure-veins are also often quite irregular— sometimes branching, some- 
 times narrowing or pinching out in some parts and widening in others 
 (Fig. 217), sometimes dividing and again coming together, and thus 
 inclosing a portion of the wall-rock (Fig. 318). Such an inclosed mass 
 of country rock in the midst of a vein is called a " horse." Many of 
 these irregularities are probably the result of movements after the fis- 
 sure was formed, or even after it was filled. Thus, it ah c d (Fig. 217) 
 be one wall of an irregular vein, then it is probable that a' V d d' was 
 the original position of this wall ; but, before it was filled, it slipped 
 up to its present position! Or, an open fissure may pinch together in 
 places by what is called creeping of the strata of the wall, i. e., a mash- 
 ing and filling in by pressure of superincumbent weight. Again, 
 movements may reopen a fissure after it is filled. In such cases, if the 
 adhesion of the filling to the wall is strong, portions of the wall-rock 
 
 Fio. 217.— Irregalaritiee in Veins. 
 
 Fio. 218.— Irregularities in Veins. 
 
 are torn away ; and, if a second filling takes place, a " horse " is formed. 
 Thus a a a-and hii (Fig. 218) represent the two original walls of an 
 irregular vein ; but subsequent movement reopened the fissure to b' b' b' 
 and tore away the horse H, after which the vein was again filled. Also 
 crust-movements may form not only a single clean fissure, but some- 
 times many small, irregular fractures, with wall-rock between. The 
 filling of these form irregular veins in which vein-stuff is often inex- 
 tricably mingled with country rock. The vein may thus be filled with 
 a troop of horses. Sometimes there is no distinct fissure but only a 
 loosening of the rock along a certain plane, and the incipient fissure 
 thus formed is filled with vein-matter. Sometimes repeated movements 
 break up the rock into a rubble-filled fissure, which by filling form a 
 hrecciated vein. Finally, in some rocks, especially limestone, percolat- 
 ing waters will hollow out passages in the most irregular way. These 
 also may become filled with vein-stuff and give rise to irregular veins. 
 
Fl8. 819. 
 
 ^48 STRUCTURE COMMON TO ALL ROCKS. 
 
 Veins, of course, usually intersect the strata ; but in some cases 
 where strata-planes are highly inclined the opening is between these 
 planes, and the veins are, therefore, conformable with them. 
 
 Age. — The relative age of veins in the same region is determined 
 in the same way as that of dikes, viz., by the manner in which they 
 intersect each other; the intersecting vein being, of course, younger 
 than the intersected vein. Thus in Fig. 319, which is a section of a 
 
 hill-side in Cornwall, it is evi- 
 dent that the tin vein, a, is the 
 oldest, since it is intersected 
 and slipped by all the others. 
 The copper vein, &, is older than 
 the clay-filled fissure, c. There 
 is a fourth fissure, d, newer than 
 a, but its relation to b and c is 
 not 'shown in this section. 
 
 The absolute age of fissure- 
 veins, or the .geological period 
 in which the fissure was formed, 
 can only be determined by the stratified rocks through which it breaks. 
 The lesd- veins of Cornwall (b b, Fig. 221) break through the Creta- 
 ceous. Their fissures were probably formed by the changes or oscilla- 
 tions which closed the Cretaceous and inaugurated the Tertiary period. 
 The auriferous veins of California break through the Jurassic ; and, as 
 there are good reasons for believing that the Sierras were formed at the 
 end of the Jurassic, it is probable, that these fissures were formed at 
 that time by the foldings of the strata consequent upon the pushing 
 up of this range. The filling, of course, was a slow, subsequent opera- 
 tion, but commenced then. 
 
 Surface-Changes. — Mineral veins seldom or never outcrop on the 
 surface in the condition we havq described them. On the contrary, 
 there are certain changes which they undergo .through the influence of 
 atmospheric agencies, which render their appearance along their out- 
 crop quite different from that of the same vein at some depth below. 
 A knowledge of these changes is, of course, of the greatest practical 
 importance. They are, however, extremely various, differing not only 
 according to the metallic contents, but also according to the nature of 
 the vein-stuffs, and therefore must be learned by observation in each 
 country. We will give three of the most constant as illustrations. 
 
 Cupriferous Veins. — The original form in which copper seems to 
 exist in veins is copper pyrites, a double sulphide of copper and iron 
 (OuFeSg). Now, along the back or outcrop of copper- veins, to a depth 
 of thirty to sixty feet, the vein usually contains no copper at all, but 
 consists of vein-stuff (more or less changed, according to its nature), 
 
MINERAL VEINS. 
 
 249 
 
 among which are scattered masses of a dark reddish or hrownish hy- 
 drated peroxide of iron, in a light, spongy condition. This peculiar 
 form of peroxide of iron, so characteristic of the crop of copper- veins, 
 is called by the Cornish miners gossan, and by the German and French 
 miners iron hat {eiserner hut ; chapeau defer).* Below the influence 
 of atmospheric agencies the yein is in its original condition, i. e., con- 
 sists of vein-stone containing disseminated masses of copper pyrites. 
 Just at the junction of the changed with the unchanged vein — i. e., 
 running along the back of the vein at a depth varying from thirty to 
 sixty feet — occur rich accumulations of copper, as native copper, red 
 and black oxides of copper, green and blue carbonates of copper, etc. 
 These facts are illustrated by Fig. 320, which is a section of the 
 Ducktown mines of Tennessee. The irregular line, s s, is the out- 
 line of a hill, along the crest of which the vein outcrops; the part 
 b consists almost wholly of gossan, with only small masses of quartz- 
 vein stuff ; a is the rich accumulation of copper ore, here about two 
 or three feet thick ; and c is the unchanged vein, consisting of vein- 
 stuff, inclosing arsenical pyrites, and copper pyrites in very large 
 quantities. 
 
 These phenomena may be explained as follows : There can be no 
 doubt that the gossan represents copper pyrites, from which the copper 
 has been entirely washed out, leaving the iron in an oxidized condition. 
 Thus the whole of the copper 
 from b (and probably from 
 much more than b, for the pro- 
 cess of denudation has gone on 
 pari passu with the process of 
 leaching) has been leached out 
 and accumulated at a. Fur- 
 ther, it is probable that the 
 process was as follows : When 
 copper pyrites is exposed to 
 moist air it slowly oxidizes 
 into sulphates of iron and cop- 
 per (CuFeSg + 80 = FeS04 + 
 CuSOi). The iron sulphate 
 (probably assisted by reaction with alkaline or earthy carbonates) quickly 
 passes into ferric oxide and is left in a spongy condition, while the 
 copper sulphate is carried downward. This much seems certain, but, 
 by what subsequent process the copper takes all the forms actually 
 found at a, is little understood, although it is probable that the car- 
 
 Fio. 220. — Dncktown (Tennessee) Copper Vein, show- 
 ing Surface-Changes (after SaiEord). 
 
 * These terms _are applied to many alteration-products containing iron, but they are 
 especially conspicuous in copper veins. 
 
250 STRUCTURE COMMON TO ALL ROCKS. 
 
 bonate is produced by the reaction, on the sulphate, of waters contain- 
 ing alkaline carbonate or bicarbonate of lime.* 
 
 Plumbiferous Veins. — The natural or original form in which lead 
 occurs in veins is sulphide of lead, or galena. But along the backs or 
 outcrops of lead-veins it is found more commonly as carbonate. The 
 explanation seems to be as follows : Lead occurs mostly in veins inter- 
 secting, or in sheets between, strata of limestones. It is probable that 
 the galena (PbS) is oxidized by meteoric agencies and becomes sulphate 
 (PbSOi), and then the sulphate, by reaction with the carbonate of lime 
 derived from the wall-rock or from the calc-spar of the vein-stuff, be- 
 comes carbonate, thus: PbS04-fCa003=PbC03-|-CaS04. In proof 
 of this process it is stated f that galena, thrown out of the old mines of 
 Derbyshire among rubbish of limestone, has all, in the course of ages, 
 been changed into carbonate. Moreover, it is not uncommon to find 
 in lead veins masses of sulphide changed on the outside into carbonate. 
 
 Auriferous Quartz -Veins. — Gold is found either in quartz-veins, in- 
 tersecting metamorphic slates (quartz-mines) or in gravel-drifts in the 
 vicinity of these (placer-mines). Originally it existed in the quartz- 
 veins usually associated with metallic sulphides, particularly the sul- 
 phide of iron (pyrites). If the pyrites be dissolved in nitric acid, the 
 gold is left as minute threads and crystals. Evidently, therefore, it ex- 
 ists in minute threads and crystals scattered through the pyrites. Now, 
 when such a vein is exposed to meteoric agencies, the pyrites is oxi- 
 dized, partly as soluble sulphate, and carried away, and partly as in- 
 Soluble reddish peroxide, which remains.J The quartz-vein stone is, 
 therefore, left in a honey-comb condition by the removal of the pyrites, 
 and more commonly stained of a rusty color by the peroxide. Among 
 the cells of this rusty cellular quartz the gold is found in- minute, 
 sharp grains, evidently left by the removal of the pyrites. Hence, in 
 an auriferous quartz-vein, along the outcrop to a depth of thirty to 
 sixty feet (i. e., as far as meteoric agencies extend) gold is found /ree 
 in small grains among the cellular quartz ; but below the reach of 
 these agencies it is inclosed in the undecomposed pyrites. 
 
 Placer Mines. — If a mountain-slope, along which outcrop auriferous 
 quartz-veins, be subjected to powerful erosion by water-currents, then 
 in the stream-beds will be found gravel-drifts, composed partly of the 
 country rock and partly of the quartz vein-stone. Among the gravel 
 will be found particles of gold, washed out from the upper parts of 
 
 * Bischof, Chemical and Physical Geography, vol. iii, p. 509. 
 
 f De la Beche, Geological Observer, p. 794. 
 
 \ Probably the iron sulphide is oxidized to the condition of sulphate, then reduced to 
 carbonate by water containing alkaline carbonate or bicarbonate of lime, and lastly per- 
 osidized by exchanging carbonic acid for oxygen (Bischof). 
 
LAWS AFFECTING METALLIFEROUS VEINS. 261 
 
 the veins. By the sorting power of water the heavy gold particles are 
 apt to accumulate mostly near the bed of the gravel-deposit (bed-rock). 
 These gravel-deposits are the placers. In these, the gold-particles, like 
 the stone-fragments, are always rounded and worn by attrition. 
 
 Some Important Laws affecting the Occurrence and the Richness of 
 Metalliferous Veins. 
 
 1. Metalliferous veins occur mostly in disturbed and highly-meta- 
 morphic regions, where the strata are tilted, and folded, and metamor- 
 phosed. The tilting and folding are necessary to the formation of 
 fissures; and the conditions under which metamorphism takes place 
 seem necessary for the suhseqaeni filling with mineral matter. Mineral 
 veins, therefore, occur mostly in moun'tain regions, and in the vicinity 
 of more or less obvious evidences of igneous agency. Lead-veins seem 
 to be an exception to this rule. They are often found in undisturbed 
 regions where the rocks are entirely unchanged. The rich lead-mines 
 of Illinois, Iowa, and Missouri, are notable examples, the country rock 
 being horizontal, fossiliferous limestones of the Palaeozoic era. 
 
 2. Metalliferous veins occur mostly in the older rocks. In Great 
 Britain, for example, no profitable veins occur above the Trias. This 
 rule, which was regarded as of great importance by the older geologists, 
 is not so regarded now. There seems to be no close connection be- 
 tween the occurrence of metalliferous veins and simple age alone ; the 
 connection is rather with metamorphista. Metamorphism, as we have 
 seen (p. 328), is most common in the older rocks, and becomes more 
 and more exceptional as we pass upward. The occurrence of metal- 
 liferous veins follows the same law. But when the newer rocks are 
 metamorphic, they are as likely to contain veins as are rocks of the 
 older series. The metalliferous veins of California occur in Jurassic, 
 Cretaceous, and. even Tertiary strata; but these strata are there highly 
 metamorphic, and strongly folded. In Bohemia, also, and elsewhere, 
 metalliferous veins occur in the higher series (Phillips's Geology, 
 p. 549). 
 
 3. Parallel veins are apt to have similar metallic contents, while 
 veins running in different directions (unless sometimes at right angles) 
 are apt to contain different metallic contents. Thus, the nearly east- 
 and-west lodes of Cornwall, a a a and c c (Fig. 331), contain tin and 
 copper, while the north-and-south courses, b b, contain lead and iron. 
 The auriferous veins of California are parallel to each other and to the 
 Sierras, except a few smaller ones, which are at right angles to these. 
 The reason of this rule is, that parallel fissures belong to the same 
 system, and were therefore formed at the same time, broke through 
 the same strata, and were filled under similar conditions, and therefore 
 with the same material; while fissures running in different directions 
 
252 
 
 STRUCTURE COMMON TO ALL ROCKS. 
 
 (unless in some eases at right angles, p. 237) were probably formed at 
 different times, broke through different strata, and were filled under 
 different conditions. Thus, the east-and-west veins of Cornwall, a a, 
 are pre-Triassic ; the north-east and south-west veins, cc, break through 
 the Trias, and are therefore post-Triassic,* while the north-and-south 
 veins break through the Cretaceous. The auriferous veins of California 
 
 Pig. 221.— Map of Cornwall: a and c, tin and copper; J, lead and iron. 
 
 all break through the Jurassic ; they, or their fissures, were probably 
 produced at the same time, viz., at the time of pushing up of the Sierras. 
 
 4. A change of country rock of an outcropping vein is apt to 
 determine some change, either in the contents or in the richness of 
 the vein. Nevertheless, there is not that close connection between the 
 nature of the country rock and the vein-contents which obtains in in- 
 filtrative veins. The reason is, that infiltrative veins derive their con- 
 tents entirely from the wall-rock on either side, while fissure-veins 
 derive their contents from all the strata through which they break, 
 even to great depths, and especially from the deeper strata. The 
 nature of the surface or country rock is, therefore, only one factor, 
 determining the vein-contents. 
 
 5. Metallic veins are usually richer near their point of intersection 
 with granite or with an igneous dike, especially if the strata have 
 suffered metamorphism. This shows the influence of such heat as is 
 present in metamorphism, in determining the metallic contents. 
 
 6. If two veins cross each other, especially if at small angle, one or 
 both are apt to be richer at the point of crossing. No sufiicient 
 reason has been given for this law. It is probably due to the reaction 
 of waters bearing different materials circulating in the two fissures. 
 
 * De la Beche, Geological Observer, p. 757. 
 
THEOKY OF THE ORIGIN OF METALLIFEROUS VEINS. 253 
 
 7. Since veins are the fillings of fissures, they are often slipped hy 
 each other or by dikes or by simple unfilled fissures. If a metalliferous 
 vein is thus slipped, according to the law of slips already given (p. 241) 
 the foot- wall of the vein -has usually gone upward, and the hanging 
 wall dropped downward. The great importance of this law in practical 
 mining is suflBciently obvious. All the slips of Fig. 319, except that 
 made by the fissure c, follow this law. 
 
 8. The surface-indications are to be learned by attentive observa- 
 tion in each case. We have already given these in the case of copper, 
 lead, and gold. 
 
 Theory of the Origin of Metalliferous Veins. 
 
 Our knowledge of the conditions under which, and the chemical 
 process by which, fissures have been filled with mineral matter, is yet, 
 unfortunately, very imperfect. Many vague and crude theories have 
 been proposed. Some have supposed that they have been filled in the 
 manner of dikes and granite veins, by igneous injection ; others, that 
 these fissures, opening below into the regions of incandescent heat, 
 have been filled by sublimation, i. e., by vaporization of certain 
 materials and their condensation in the fissures above. Some suppose 
 that electric currents, such as are known by observation to traverse 
 certain veins, have been the chief agents in the transference and ac- 
 cumulation of the mineral matter. .These three theories may be dis- 
 missed as being untenable or else as too hypothetical. Still others 
 have thought that great fissures have filled in the same manner as the 
 smaller fissures, and cavities of every kind found in the rocks, viz., by 
 infiltration of soluble matters from the fissured rocks. There is cer- 
 tainly considerable analogy between small infiltrative veins and great 
 fissure-veins in their mode of formation ; yet there is a decided differ- 
 ence. The fillings of infiltrative veins are derived, in each part, 
 entirely from the bounding rock on either side. The fissure is filled 
 by a lateral secretion from its walls ; the broken rocks heal themselves 
 "by first intention" by means of a plasma oozing from the sides. 
 But great fissure-veins derive their contents in each part from all the 
 strata to great depths, and especially from the deeper strata. Hence 
 the contents of these veins are far more varied. 
 
 Outline of the Most Probable Theory.— The contents of mineral 
 veins seem to have been deposited from hot alkaline solutions^ coming 
 up through fissures ; in other words, from hot alkaline springs. We 
 will attempt to show this first for the vein-stuffs, especially quartz, and 
 then for the metallic ores, especially the metallic sulphides. 
 
 Vein-Stuflfs.— 1. They were deposited from solutions, (a) The 
 ribbon-structure and the interlocked crystals (Figs. 212-216) suggest 
 at once successive deposition from solution, especially as a similar 
 
254 STRUCTURE COMMON TO ALL ROCKS. 
 
 structure occurs ia the fillings of cavities of all kinds, which could 
 not have been filled in any other way. (S) Quartz is by far the most 
 common of all vein-stufEs. Now, as already explained (p. 233), there 
 are two varieties of silica — one having a specific gravity of 2-2, the 
 other 2-6. The dry way produces only silica-glass, which has a 
 specific gravity of 2-2, while the variety of specific gravity 2-6, or true 
 quartz, can not be formed except by the humid way.* In fact, this 
 variety, as far as we know, is always produced by slow deposition from 
 solution. Now, the quartz of veins is always the variety 2-6, and there- 
 fore was produced by slow deposit from solution. The beautiful crys- 
 tals so often found in veins could be produced in no other way. (c) 
 We have already seen (p. 233) that Jluid cavities are a proof of forma- 
 tion by humid process. Now, such fluid cavities are especially abun- 
 dant in vein-stuffs generally. They are best seen in quartz-vein stuffs, 
 because of their transparency, (d) Not only quartz but many other 
 minerals found among vein-stuffs are of such nature that it is difficult 
 or impossible to understand how they could have been formed except 
 by the humid way, as they will not stand fusing temperature. 
 
 2. The solutions were hot. (a) Fissures running deep into the 
 interior of the earth could hardly remain empty of water. But from 
 their great depth the contained waters must be hot. The solvent 
 power of water, when heated to high temperature under pressure, is 
 well known. Scarcely any substance wholly resists it. (5) The fluid 
 cavities found in quartz and other vein-stuffs are not usually entirely 
 filled, but contain a small vacuous space. Such a vacuous space indi- 
 cates (p. 234) that the inclosed liquid was at high temperature at the 
 time of being inclosed, and has since contracted on cooling. By heat- 
 ing the mineral until the cavity fills and the vacuous space disappears, 
 we ascertain the temperature of deposit. Now, by this process the 
 temperature of deposit of vein-minerals has been ascertained to vary 
 from ordinary temperatures even up 300° and 350°. f (c) The in- 
 variable association of metalliferous veins with metamorphism demon- 
 strates the agency of heat. 
 
 3. The solutions ivere alkaline. Alkaline carbonates and alkaline 
 sulphides are the only natural solvents of quartz, the commonest of 
 vein-stuffs. Moreover, when these waters contain excess of carbonic 
 acid, as is almost always the case, they dissolve also the carbonates of 
 lime, baryta, iron, etc., the next most common forms of vein-stuffs. 
 In California and Nevada such hot alkaline carbonate and alkaline 
 sulphide springs abound, and are daily depositing silica (quartz) 
 
 * Recently under peculiar conditiona crystallized quartz of specific gravity 2'6 has 
 been formed by dry fusion. — American Journal of Science, vol. xvi, p. 155, 1878. 
 f Sorby, Quarterly Journal of tbe Geological Socipty, vol, ,xiv, p. 453 et seq. 
 
THEORY OF THE ORIGIN OF METALLIFEROUS VEINS. ^5^ 
 
 and carbonates of lime and of iron, and even in some cases filling 
 fissures. 
 
 Metallic Ores. — There seems no reason to doubt, then, that, in most 
 cases at least, vein-stufEs have been deposited from hot alkaline solu- 
 tions. Now, it is evident, from their intimate association with the vein- 
 stufEs, that the metallic ores must have b^en deposited from the same 
 solution. The exact nature of the solvent and the chemical reaction 
 is still very doubtful. We may imagine many, by either of which the 
 deposit might take place : 1. Metallic sulphides are by far the most 
 common form of ore, and even when other forms exist we may in many 
 cases trace them to sulphide as their original form (p. 248 et seq.). But 
 metallic sulphides are slightly soluble in alkaline sulphides, and these 
 » latter are often found associated with alkaline carbonates in hot springs 
 (solfataras), as in California and elsewhere. Such waters would hold 
 in solution silica, carbonates of lime, etc., and metallic sulphides, and, 
 coming up through fissures, would deposit them both hy cooling and by 
 relief of pressure. Or, 2. Alkaline carbonate waters holding in solu- 
 tion silica and lime carbonate for vein-stone, and also containing alka- 
 line sulphide, meeting and mingling in the same fissure with other waters 
 containing metallic sulphates, by reaction would precipitate metallic 
 sulphides (NajS-f MS04=]Sra2S044-MS). This seems to be the re- 
 action by which the inky waters of some of the hot springs of the Cali- 
 fornia geysers are formed. Or, 3. The alkaline carbonates still remain- 
 ing for vein-stone, metallic sulphates, in solution in the same waters 
 with organic matter, would be reduced to the form of metallic sulphide, 
 which, being insoluble, would be deposited.* Or, 4. Alkaline sulphide 
 waters holding metallic sulphides and organic matters in solution — the 
 acids of organic decomposition (humus acids) would neutralize the 
 alkalinity and deposit the metallic sulphide. For greater clearness we 
 annex a table expressing these processes : 
 
 ' 1. Alk.S-|-M8 in sol" deposit MS by cooling. 
 3. Alk.S-)-M:S04meeting " MS " reaction. 
 
 3. MS04-f-org° mat' . " MS " reduction.i 
 
 4. Alk. S -i- MS -I- org'=mat'insol° deposit MS by neutralization. 
 
 There are many difficulties in the way of every attempt to place 
 these reactions in a clear and distinct form, but in spite of these diffl- 
 
 * It might at first seem that there is a chemical difficulty iu this case— that metallic 
 sulphate can not coexist in solution with alkaline carbonate, but would be precipitated as 
 metallic carbonate. But it is evident that this reaction would not take place in a weak 
 metallic solution, in the presence of excess of carbonic acid, since in this case the metallic 
 carbonate is soluble. 
 
 t Francis 0. Phillips has shown that powdered AgS reduced by H at high tempera- 
 ture takes the form of interlaced threads. Now, it is a curious fact that both gold and 
 silver are often found in the form of threads. 
 18 
 
 Alk-COa + HCOa-l- 
 
256 STRUCTURE COMMON TO ALL ROCKS. 
 
 culties there seems little reason to doubt that great fissures have been 
 filled by deposit from hot alkaline waters holding various mineral sub- 
 tances in solution. The more insoluble substances are deposited in the 
 vein, while the more soluble reach the surface as mineral springs. 
 
 This view is powerfully supported by the phenomena of hot alka- 
 line springs in California and Nevada. The Steamboat Springs, near 
 Virginia City, Nevada (so called from the periodic eruption of hot 
 water and steam), come up through fissures in comparatively recent 
 volcanic rock. The waters are strongly alkaline, and deposit silica in 
 abundance. By this deposit the fissures are gradually filling up and 
 forming veins. Some fissures are now partially and some entirely filled. 
 The ribbon-structure in some cases is perfect. Moreover, sulphides of 
 several of the metals, viz., iron, lead, mercury, copper, and zinc, have 
 been found in the quartz-vein stuff. Here, then, we have true metallif- 
 erous veins forming under our very eyes.* So also at Sulphur Bank, 
 Lake County, California, hot alkaline sulphide waters,f coming up from 
 beneath, deposit both silica and cinnabar in small, irregular fissures 
 and cavities, forming quartz-veins containing cinnabar. The deposit 
 is so recent that the silica is sometimes still in a soft, hydrated con- 
 dition, which cuts like cheese.J 
 
 After this general discussion of the theory of metalliferous veins, 
 we are now in position to state more clearly their mode of formation. 
 Meteoric waters, circulating in the interior of the earth in any direc- 
 tion — downward, upward, or laterally — deposit slightly soluble matters 
 in their course, in cracks, cavities, or great fissures, forming fossil casts, 
 geodes, amygdules, infiltration- veins, and fissure- veins. As to dir-ection, 
 the up-coming waters, especially in metamorphic and volcanic regions, 
 deposit most freely, and are most metalliferous, because they are hot and 
 often alkaline, and therefore most powerful solvents, and, of course, cool 
 gradually on approaching the surface. But that downward percolating 
 waters may also deposit metallic ores is proved by the fact that these 
 are sometimes found depending, like stalactites, from the roofs of cavi- 
 ties.* As to the different kinds of veins, those of great fissures are 
 most prolific, because these fissures are the highways of water from 
 the heated depths. But every kind of water-way will receive deposits; 
 and, as the kinds of these are infinitely various and pass by insensible 
 gradations into each other, so also will be the veins which fill them. 
 The open fissure is the easiest and therefore the most traveled high- 
 
 * Arthur Phillips, American Journal of Science, vol. xlvii, p. 194 ; and Philosophical 
 Magazine, 1872, vol. xlii, p. 401. 
 
 f The water in this mine is 176° Fahr. — Becker. 
 
 J Le Conte, American Journal of Science, vol. xxiv, p. 23, 1882. 
 
 * Schmidt, American Journal of Science, vol. xxi, p. 502, 1881. Chamberlain's 
 Geology of Wisconsin, vol. iii, p. 495. 
 
THEORY OF THE ORIGIN OF METALLIFEROUS VEINS. 257 
 
 way. In these, therefore, we have the most typical veins, with their 
 banded structure and their selvages, their great size and continuity. 
 But in many cases crust-movements produce only incipient fissures, 
 i. e., a loosening of the rock-cohesion, along planes affected with a 
 multitude of small cracks, with country rock between. These loosened 
 planes become also water-ways, and, by deposit, form those irregular 
 veins so common everywhere, but especially in the cinnabar-veins of 
 California; Or, again, crust-movements may produce not clean open 
 fissures, but rather planes of shattered rock or rubble-filled fissures. 
 Deposit in such a water-way forms a breccia of country rock cemented 
 with vein-stuff, or 5r-ecaafe<? veins. Or, again, in certain country rocks 
 soluble in water, especially limestones, the rock is dissolved along the 
 water-way, and the, vein-stuff deposited pari passu, giving rise to what 
 are called sulstitution-veins. In short, once conceive clearly that 
 mineral veins are filled water-ways, and all these complex phenomena 
 solve themselves. Even porous rocks like sandstones, because of their 
 porosity, become the depositaries of vein-stuff, though not in paying 
 quantities, except along lines or planes where water-transit is more 
 easy and abundant. Examples of such deposits are found in the silver- 
 bearing and copper-bearing sandstones of Utah and New Mexico.* 
 
 Thus there seems no longer any room for doubt that metalliferous 
 veins are deposits from solutions in water-ways of any kind, but mostly 
 from hot alkaline solutions coming up through great fissures. It'is 
 only the exact chemical reaction which is yet obscure. The work of 
 the geologist is all but complete ; the problem must now be turned 
 over to the chemist. It may be interesting, however, before leaving 
 this subject, to consider separately the auriferous veins of California, 
 and apply to them the principles set forth above. 
 
 Auriferous Veins of California. — Gold is one of the most insoluble 
 of substances, and the occurrence of this metal in veins has always 
 been regarded as a difficulty in the way of the solution theory. The 
 laboratory solvents of gold are cyanogen and free chlorine, but these 
 do not exist in Nature, Nevertheless, gold is known to be slightly 
 soluble in the salts, especially the persalts of iron. It is also quite 
 soluble as gold sulphide in alkaline sulphides. It is probable, there- 
 fore, that the usual solvents of gold are iron sulphates, and especially 
 alkaline sulphides. There is also a silicate of gold, which, according 
 to Bischof, is slightly soluble under certain conditions. 
 
 There is abundant evidence that the auriferous quartz- veins of Cali- 
 fornia have been deposited from hot solutions. These veins exhibit in 
 many eases the characteristic ribbon-structure. They exhibit also the 
 water-cavities characteristic of deposits from solutions, and the vacuous 
 
 * Cazin, Newberry, etc., Report on Nacimiento Copper-Mines of New Mexico. 
 
258 
 
 STRUG VD RE COMMON TO ALL ROCKS. 
 
 spaces, indicating that the solutions were hot. By actual experiment,* 
 the temperatures at which the vacuous spaces disappear, and therefore 
 at which the deposit took place, have been ascertained — being 180°, 
 212°, 350° P., and even more. Again, there can be no doubt that 
 the associated metallic sulphides were deposited from the same solu- 
 tions as the vein-stuffs, for they are completely inclosed in the latter. 
 But the gold, as already stated (p. 250), exists as minute crystals and 
 threads of metal inclosed in the sulphide of iron, and must therefore 
 have been deposited from the same solution as the iron. It seems 
 possible that the gold was dissolved in a solution of sulphate of iron, 
 and that the sulphate was deoxidized, and became insoluble sulphide 
 and precipitated ; and that the gold thus set free from solution was 
 entangled in the sulphide at the moment of the precipitation of the 
 latter. Or else, and more probably, the gold was dissolved as sulphide 
 along with iron sulphide in an alkaline sulphide solution and deposited 
 by reactions 1 or 4 given on page 255, the gold, on account of its feeble 
 affinities, giving up its sulphur at the moment of its deposit.f 
 
 There are some phenomena connected with the occurrence of gold 
 in the iron sulphides of the deep placers which seem to prove the truth 
 of this view.| The deep placers of California are gravel-drifts in an- 
 
 N S 
 
 Fio. 222.— Section across Table Mountain, Tuolumne Connty, California: i, lava; G, gravel; 8 S, 
 elate; i?, old river-bed ; J?', present river-bed. 
 
 cient river-beds, covered up by lava- flows 100 to 200 feet thick. These 
 placers are worked by running tunnels beneath the basaltic lava until 
 the river-gravel is reached. Now, the waters percolating through these' 
 lava-flows and reaching the subjacent gravels are charged with alkali 
 from the lava. These alkaline waters are also charged with silica 
 from the same source. Hence, the drift-toood of these ancient rivers 
 has all been silicified by these siliceous waters. The gravels are also in 
 many places cemented by the same material. These percolating waters 
 have evidently also contained iron ; for in contact with the silicified 
 wood is often found iron sulphide. There are two ways, in either of 
 which we may imagine the gold to have been deposited. It may have 
 been in solution in the iron sulphate ; or else, along with the iron in 
 
 * Arthur Phillips, ibid. 
 
 f Gold is soluble in sodium sulphide, probably as gold sulphide. — Seeker. 
 
 X Arthur Phillips, ibid. 
 
THEORY OF THE ORIGIN OV METALLIFEROUS VEINS. 259 
 
 alkaline sulphide. Following out the process on the^rs^ supposition, 
 while the wood decayed it was partly replaced by silica and partly by 
 iron sulphide produced by deoxidation of the sulphate by organic mat- 
 ter (p. 300). The gravel has also in some places been cemented by 
 iron sulphide reduced from solution in a similar way. Now, both in 
 this petrifying and in this cementing sulphide of iron is found (by so- 
 lution in nitric acid) gold : sometimes in rounded grains, and there- 
 fore simply inclosed drift-gold; but also sometimes in minute crystals 
 and threads, exactly as in the sulphide of the undecomposed quartz- 
 vein. Evidently, this gold has been deposited from a solution of sul- 
 phate of iron at the moment of the reduction of the latter to a sul- 
 phide. The process was probably as follows : Percolating water oxi- 
 dized iron sulphide and took it into solution as sulphate. This solu- 
 tipn coming in contact with drift-gQ\A dissolved it, but, subsequently, 
 coming in contact with decaying organic matter, was again deoxidized 
 and deposited as sulphide ; and the gold crystallizing at the same mo- 
 ment is inclosed.* Or following out the process on the second suppo- 
 sition, gold sulphide in solution in alkaline sulphide, coming in contact 
 with decaying wood, would be deposited by neutralization of the alkali 
 along with other metallic sulphides present and be entangled with them. 
 But, on account of its feeble afHnities, the gold would give up its sul- 
 phur either to the alkaline sulphide or to the sulphide of iron and be 
 deposited in a metallic form. Now, a similar reaction would take place 
 in a fissure, and form a gold-bearing vein. In fact, the sub-lava gravels 
 may be regarded as a horizontal water-way or fissui-e with its walls 
 through which water circulates and deposits. 
 
 Suppose, then, we have hot water containing alkaline carbonate and 
 alkaline sulphide, holding in solution silica and metallic sulphides, 
 among them gold sulphide, and coming upward through a fissure. By 
 any of the reactions on page 355, e. g., by cooling, silica would deposit 
 as quartz vein-stnfl and the gold would deposit with other metallic 
 sulphides, giving up, however, its sulphur in the act of deposition, as 
 before explained. If the alkaline waters contained no other metallic 
 sulphide but gold sulphide, then the gold, giving up its sulphur to the 
 alkaline sulphide, would be found in form of metallic gold inclosed in 
 the quartz vein-stuff. 
 
 Illustrations of the Law of Circulation —We have said that the 
 iron sulphate comes from oxidation of sulphide, but also the sulphide 
 from the deoxidation of the sulphate. This is only another example 
 of a perpetual cycle of changes. Again, the gold in the veins is leached 
 from the strata ; the strata doubtless received it from the sea, for small 
 quantities of gold have been detected in sea-water ; but, again, doubt- 
 
 * Arttur Phillips, ibid. 
 
260 ' STRUCTUKE COMMON TO ALL ROCKS. 
 
 less the sea received it from the rocks, and this brings us to another 
 perpetual cycle of changes. 
 
 But in the midst of all these changes there has evidently been an 
 increasing concentration and availability of gold and other minerals. 
 In the strata the quantity is so small as to be undetectable ; it is thence 
 carried and concentrated in veins in a more available form ; it is next 
 set free along the backs of these veins in a still more available form ; 
 it is last carried down by currents along v?ith other materials, neatly 
 sorted, and deposited in placers in a form the most available of all. 
 
 Section 3. — Mountains: theie Oeigin and Stkdctuee. 
 
 Mountains are often regarded as types of permanence. We speak 
 of the everlasting hills. The first lesson taught by geology is that all 
 things, even the most stable, are slowly changing. In this section we 
 treat of the origin, growth, maturity, decay, and death — in a word, 
 the whole life-history of mountains. 
 
 Mountains are the glory of our earth, the culminating points of its 
 scenic grandeur and beauty. But few recognize the fact that they 
 are so, only because they are also the culminating points, the theatres 
 of greatest activity, of all geological agencies. The study of mountains 
 is therefore of absorbing interest not only to the poet and painter, but 
 also and especially to the geologist, because it furnishes the key to 
 many of the obscurest problems of dynamical geology. 
 
 Definitions of Terms. — But we are met at the very threshold of 
 the subject by a difficulty arising from the loose use of the term moun- 
 tain. This term is used for every conspicuous elevation above the 
 geneiral level of the surrounding country, whatever may be its dimen- 
 sions or its mode of origin. No accepted distinction has been made 
 between "hill" and "mountain." The use of the larger term de- 
 pends on the experience of the observer. Doubtless there are a million 
 people in the United States> including some of the readers of this 
 chapter, who have never seen a hill of 500 feet altitude, perhaps not 
 300 feet. To such person a rock mass 1,000 feet high would be a most 
 imposing mountain, while to those who live in the shadow of the great 
 mountains this height is quite indifEerent. Mere ordinary hiUs are 
 locally named mountains. 
 
 Classiflcation of Mountains. — Without fixing any limit of height 
 or size we can make a classification of mountains based on physio- 
 graphic character, or form. There would be: (1) Solitary masses — 
 as peaks, domes, buttes, mesas, and monadnocks. Excepting volca- 
 noes, these are mostly of low altitude, or merely hills. (2) Clustered 
 peahs of irregular grouping. This will include some mountains of 
 respectable size, like the Catskills. (3) Subdued mountains, like the 
 
MOUNTAINS: THEIK ORIGIN AND STEUCTUBE. 261 
 
 Adirondacks and highlands of eastern United States, which through 
 great age in a moist climate have been weathered to low, rounded 
 forms. (4) Ridges. All the great mountain-systems of the world 
 belong in this group. This physiographic classification is, however, 
 too artificial to be of great value. The reader can extend the analysis 
 of forms. 
 
 Another classification might be made, based on structure, or the 
 character, relation, and position of mountain strata. But the most 
 valuable and scientific classification is that based on origin or' man- 
 ner of formation. In a genetic division we may readily distinguish 
 three classes according to the dominant geologic factor, although 
 sharp distinctions can not always be made. The classes are as 
 follows : 
 
 (a) Mountains by Igneous Action. — This includes (1) volcanic 
 cones — the highest su,mmits of terrestrial mountains; (2) laccolithic 
 domes, as the Henry Mountains and the Black Hills, where strata 
 have been lifted into dome shape by the upthrust of fluid or plastic 
 rock (p. 220) ; and combined with erosion (3) trap ridges, as Orange 
 Mountain, New Jersey, the ridges of igneous rock in the Connecticut 
 Valley, and many still better examples in the western country. 
 
 (&) Mountains by Circumerosion. — Here belong the varied forms 
 cut by erosion out of practically horizontal strata, as mesas, or tabu- 
 lar forms, due to resistant capping beds; buttes, the more pointed 
 masses with precipitous sides and horizontal ledges; and the many 
 peculiar erosion carvings which give the singular and often grotesque 
 effect to western scenery, particularly the Bad Lands (see Figs. 222, 
 339, 240, 851). In the eastern United States the best example of 
 mountains of this class is probably the Catskills, rising to 4,000 feet 
 and over, and which are the remnants of a dissected plateau of nearly 
 horizontal strata. Some epeirogenic movement is involved in these 
 cases, the lifting of broad areas to heights permitting deep erosion; 
 but erosion is the immediate, active factor. In reality the valleys are 
 the positive element, the hills and mountains being the negative ele- 
 ment. Land destruction is the great fact. Mount Monad nock. Few 
 Hampshire, is taken as the type of isolated remnants of old, worn- 
 down heights of hard and usually crystalline rocks. 
 
 (c) Mountains by Disturbance of Strata (crushing, folding, tilt- 
 ing, faulting) . — These are the mountains par excellence of the geolo- 
 gist. All great mountain-ranges of the world belong in this class, 
 which is relatively so much more important that other classes are 
 usually ignored, or not considered as mountains. Our further discus- 
 sion will wholly relate to this class. 
 
 Formal faulting produces high escarpments in the arid West, but 
 does not usually give rise to mountain-forms. In the Great Basin, 
 
262 STRUCTURE COMMON TO ALL ROCKS. 
 
 however, the mountain-ridges show so much faulting that the moun- 
 tains have been described as tilted blocks, and a type of orographic 
 structure has been based on them, called " Block Mountains," or 
 " Basin Eange structure," to distinguish it from the type of folded 
 strata, called " Appalachian structure." The great predominance of 
 faulting over folding in the case of the Great Basin and its bordering 
 
 Pia. 2220.— Folded Strata South of Heaven's Peak, Livingston Eange, Montana. (Photograph by 
 R. H. Chapman.) From the snow-banlj to summit is about 2,000 feet. 
 
 mountains has been questioned. We will now pass to the great moun- 
 tains of the world, those produced by horizontal compression of the 
 strata. - 
 
 A Mountain-System is a great complex of more or less parallel 
 ranges in the same general region, but born at different times (poly- 
 genetic). It is a family of mountains. In the Eocky-Mountain 
 system we have the Colorado range (Front range), the Wahsatch 
 range, the Uintahs, and several others. Similarly the Andes and 
 Himalayas consist of several ranges. 
 
 A Mountain-Bang e is a single mountain-individuul produced by 
 one birth-throe (monogenetic), although both the origin and the sub- 
 sequent growth is a slow process. The Sierra, the "Wahsatch, the 
 Uintahs and the Colorado Mountains are good examples. 
 
 A Mountain-Ridge is a subordinate part of a range, produced 
 either by separate folds made at the same time, or by faulting, or by 
 erosion. The Blue Eidge, the Alleghany, and the Cumberland Moun- 
 tains are examples in the Appalachian range. The parallel folds of 
 
MOUNTAIN ORIGIN. 263 
 
 the Jura range — seen in cross-section in Fig. 227 — are probably the 
 best examples. 
 
 On mountain-ridges there are always prominent points which are 
 called Peaks, whether formed by volcanic ejections like Mount Shasta 
 or Mount Rainier, or by erosion like Mount Dana or Mount Lyell. 
 
 Mountain-systems are separated by great interior Continental 
 lasins like the Mississippi-river basin. Eanges are separated by great 
 interior valleys, like Sacramento and San Joaquin Valley, separating 
 the Sierra from the Coast range. Ridges are separated by longitudi- 
 nal mountain-valleys, while the transverse valleys which trench the 
 flanks of ranges or ridges head in the passes which separate the peaJcs. 
 
 Some authors employ the term " mountain-system " for a series 
 of ranges of approximately similar date, and the term " mountain- 
 chain " in the larger sense for which mountain-system is here used. 
 
 The term Cordillera is in general use to designate the main moun- 
 tain axis or anticlinorium of a continent. Thus the several systems 
 or chains, Eocky Mountains, Sierra Nevada, Coast range, etc., to- 
 gether constitute the North American Cordillera. 
 
 A scientific discussion of mountains is really a discussion of ranges 
 or mountain individuals. For, on the one hand, a mountain-system 
 is only a multiplication of such individuals belonging to the same 
 family, and therefore adds no new element to the discussion ; and, on 
 the other, mountain-ridges and peaks belong, mainly at least, to the 
 category of mountain sculpture, not of mountain formation, and there- 
 fore are discussed later. 
 
 Greater Inequalities of the Earth-Surface. — The inequalities of 
 the earth-surface, as already explained (page 174), are of two general 
 kinds, the greater and the lesser. The latter belong to sculpture, and 
 will be taken up later. Of the former there are two orders of great- 
 ness, viz., those constituting land-masses and oceanic basins, and those 
 constituting mountain-ranges and intervening valleys. We have 
 already discussed the former ; we now take up the latter. 
 
 Mountain Origin. 
 
 Leaving aside for the present all disputed points, it is now univers- 
 ally admitted that mountains are not usually pushed up by a vertical 
 force from beneath, as once supposed, but are formed wholly by lateral 
 pressure. The earth's crust along certain lines is crushed together by 
 lateral or horizontal pressure and rises into a mountain-range along the 
 line of yielding, and to a height proportionate to the amount of mash- 
 ing. But the yielding is not by rising into a hollow arch, nor into such 
 an arch filled beneath with liquid (for in neither case could the arch 
 support itself), but by a mashing together and in thickening and 
 
Mi 
 
 STRUCTURE COMMON, TO ALL ROCKS. 
 
 crumpling of the strata and an upswelling of the whole mass along the 
 line of greatest yielding. That this is the immediate or proximate 
 cause of the origin or elevation of mountains is plainly shown by their 
 structure. As to the ultimate cause — i. e., the cause of the enormous 
 lateral pressure — this lies still in the field of discussion. We shall dis- 
 cuss it briefly in its proper place. 
 
 Mountain Structure. 
 
 A mountain-range, then, may be regarded as a mass of enormously 
 thick strata crushed together laterally and swelled up along the line of 
 
 crushing. We have 
 
 A said that this mode of 
 
 origin is revealed in 
 its structure. We can^ 
 best make this plain 
 by an experiment. 
 Suppose, then, we 
 place, one atop anoth- 
 er, several layers of 
 any plastic substance, 
 such as wax, so as to 
 make together a pris- 
 matic mass, as represented in section in Pig. 233, A, and the whoFe 
 resting on a smooth oiled slab of glass or steel, so that there shall be 
 no friction or adhesion. Suppose, further, that very gentle heat be 
 applied beneath along the middle line, so as to soften slightly this part. 
 Of course, such softening would be greatest at the bottom, and become 
 less and less upward ; also greatest along the middle line, and become 
 
 Fig. 233. 
 
 Fio. 284.— Ideal Section across the Uintah Mountains (after Powell). 
 
 less and less outward. This is represented in the figure by the shad- 
 ing and in nature by the metamorphic softening, of which we will 
 
MOUNTAIN STRUCTURE. 
 
 265 
 
 speak later. Suppose, now, we place a board on each side of the pris- 
 matic mass, and press gradually together. All the layers will be 
 
 Fia. 225,— Section ot Uintati Eange, showing Fault. 
 
 thickened and folded, and the whole mass swelled up along the central 
 line into something like Fig. 233, B. We have in miniature both the 
 structure and the mode 
 
 of formation of a moun- a ^/S^"~ 
 
 tain-range. In a simi- JraBJIIIIlk-^ ./ iJR-\ 
 lar way, but on a larger 
 scale, all great moun- 
 tain-ranges seem to have 
 been formed. 
 
 There would be in 
 the experiment, and 
 much more would we 
 expect in Nature, some variety in the result depending upon the soft- 
 ness or stiffness of the strata. This it is that gives rise to diflferjpnt 
 types of mountains. Sometimes the whole mass rises as one great fold 
 (Pig. 234), We have an example of this in the TJintah range, only 
 
 Fig. 326.— Ideal Section of Jura if unaffected by Erosion. 
 
 Fig. 227.— Section of Jura as modified by Erosion. 
 
 that the fold has broken down on one side, forming a great fault 
 (Fig. 335). Sometimes and oftener there are produced several open 
 folds like great earth-waves (Fig. 226). This is the case in the Jura 
 
 Fig. 228.- Section of Coast Eange, showing Plication by Horizontal Pressure. 
 
 (Fig. 227). Sometimes, and oftenest of all, there are produced many 
 closely appressed folds, as in the experiment (Fig. 323, B). This is the 
 
 So 1 c a i f 1 /^ 
 
 Fis. 229.— Generalized and Simplified Section of the Appalachian Chain, 
 
266 
 
 STRUCTURE COMMON TO ALL ROCKS. 
 
 case in the Coast Range of California (Fig. 238), or in the Appa- 
 lachian (Fig. 229). Sometimes the mashing is so extreme that the 
 sides are driven in under the swollen central parts, so that the strata 
 are often reversed. This gives rise to the fan-structures found in 
 many mountains, but conspicuously in the Alps (Fig. 230) and in the 
 Pyrenees. 
 
 Proof of Elevation by Lateral Pressure alone: 1. Folding. — It is 
 evident that foldings such as those represented in all the above figures, 
 and which occur in nearly all mountains, can not be produced except 
 by lateral pressure, and are therefore proof of such pressure. But, 
 moreover, it can be shown that, when we take into consideration the 
 immense thickness of mountain strata and the degree of folding, lateral 
 pressure is siifficient to account for the whole elevation, without calling 
 in the aid of any upward pushing from beneath. For example, the 
 Coast Eange of California (Fig. 228) is composed of at least five anti- 
 clines and corresponding synclines.* If its folded strata were spread 
 
 Section of a portion of the Alps. 
 
 out horizontally in the position of the original sediments, they would 
 undoubtedly cover double the space. Now, supposing the strata here 
 are only 10,000 feet thick — a very moderate estimate — in mashing to 
 one half the extent, they would be thickened to 20,000 feet, which 
 would be a clear elevation of 10,000 feet if they had not been subse- 
 quently eroded. According to Renevier,f a section ^f the Alps reveals 
 seven anticlines and corresponding synclines, and some of these are 
 complete over-folds (Fig. 230). We are safe in saying that Alpine 
 strata have been mashed horizontally into one half their original ex- 
 tent.J Supposing these were originally 30,000 feet thick (they were 
 really much thicker), this would make a clear elevation of 30,000 feet. 
 Of course, most of this has been cut aw^y by erosion. In the Appa- 
 
 * American Journal of Science, vol. ii, p. 297, ISYS. 
 f Archives dea Sciences, vol. lix, p. 5, 18'7'7. 
 i Heim., Arch., vol. Ixiv, p. 122, 1878. 
 
MOUNTAIN STRUCTURE. 267 
 
 lachian range, according to Claypole, the foldings are so extreme that 
 in one place 95 miles of original extent have been mashed into 16 
 miles, or six into one, and yet the Appalachian strata are estimated as 
 40,000 feet thick. Cases of still greater doubling of strata upon them- 
 selves occur. In the Highlands of Scotland the strata by lateral thrust 
 were broken and slidden one over another for ten miles. In the Cana- 
 dian Eocky Mountains there is an overthrust of seven miles, by which 
 the Cambrian is made to override the Cretaceous, and 50 miles of strata 
 are mashed into 25 miles (McConnell). In the Appalachians of 
 Georgia the Rome fault is an overthrust which brings the Cambrian in 
 contact with the Carboniferous, and the fault under difEerent names 
 may be traced northward for 275 miles ; and in the Cartersville thrust- 
 fault there is an overriding of 11 miles (Hayes). The manner in 
 which this was done is illustrated on a previous page (Fig. 309). Evi- 
 dently, then, the whole height of the mountains mentioned above is 
 due to lateral crushing alone. 
 
 2. Slaty Cleavage. — But there is another phenomenon associated 
 with mountains which furnishes additional proof, if any be necessary, 
 viz., slaty cleavage. This is not so universal a phenomenon as folding, 
 because the materials of strata are not always suitable for developing 
 this structure ; but where it occurs its evidence is equally convincing. 
 We have already^ seen (p. 191) that this structure is always produced 
 by mashing together horizontally and extension vertically. We have 
 also seen that in every case of well-developed cleavage the whole rock- 
 mass has been mashed horizontally three parts into one, and swelled up 
 vertically one part into three. Now, again, considering the thickness 
 of mountain strata, this is sufficient to account for the highest moun- 
 tains in the world. It is true we often find slaty cleavage where there 
 are now no mountains. In such cases the elevation produced by the 
 mashing has been swept away by erosion. We find only the bones of 
 the extinct mountains. 
 
 It was once supposed that mountains were pushed up from below 
 by a vertically acting force. Hence came the word upheaval as applied 
 to mountains. The word is still used; and there is no objection to its 
 use, if it be borne in mind that, in mountains of the structure given 
 above, the force of upheaval is > not vertical but lateral. 
 
 Modifications of the Simple Ideal given above.— Thus far, in order 
 to get a clear idea of the process and the result, we have described 
 mountains in their simplest form, and as similar in process of forma- 
 tion and result to the experiment shown in Fig. 223. But in fact the 
 final result in Nature is complicated in many ways. Some of these 
 complications are shown in the foregoing figures of actual mountains, 
 and have been anticipated in their descriptions ; and some have been 
 closely imitated in experiments (see Figs. 231, 232). 
 
268 
 
 STRUCTURE COMMON TO ALL ROCKS. 
 
 1. By Fracture and Slipping. — It is obviously impossible that such 
 violent foldings of the strata should take place in the upper zone, of 
 fracture, without frequent fracturing and slipping of the broken 
 parts. These fractures and faults were produced at the time of 
 
 Fig. 231.— Experimental Imitation of Mountain Folds (after Willis).* 
 
 origin, or else during the growth of the range. If the mountains are 
 very old, erosion has long since cut down the ineqlialities thus pro- 
 duced ; but if the mountains are recent, they may still form conspicu- 
 ous orographic features. In Fig. 256 the lower part shows the Uintah 
 Mountains as they are, and the upper part shows the same as they 
 would be if the eroded strata were restored. The structure here is 
 comparatively simple. 
 
 3. By Metamorphism. — We have said that mountain strata are 
 often of enormous thickness. We shall give abundant proof of this 
 
 hereafter. Butwe 
 have also seen (p. 
 231 et seq.) that 
 the accumula- 
 tions of sediments 
 to great thickness 
 will produce a 
 rise of the isogeo- 
 therms — an invasion of the sediments with their included water by the 
 interior heat, and a consequent hydrothermal softening or incomplete 
 hydrothermal fusion of the lower parts of such accumulations. Now 
 we find that mountain strata are nearly aljvays more or less meta- 
 
 FiG. 232.— Layers of Clay folded by Lateral Pressure (after Favre). 
 
 * Bailey Willis, The Mechanics of Appalachian Structui?e. 
 Geol. Surv., Part 11, 211-282, 1893. 
 
 Thirteenth An. Eep. V. S. 
 
MOUNTAIN STRUCTITEE. 
 
 269 
 
 morphic in their lower parts. Thus every great mountain-range has 
 a metamorphic core. This is represented in the- experimental figure 
 (Fig. 223) by the shading. 
 
 Fig. 233.— Ideal Section of a Mountain-Eange. 
 
 3. By Subsequent Erosion. — The modifications thus far spoken of 
 were produced at the time of preparation or else in the origin and 
 growth of the mountain, and therefore belong to the category of moun- 
 tain formation. But so soon as the .mountain begins to rise, it begins 
 to be sculptured by erosion ; and when we remember that, on account 
 of their great elevation and steep slopes, mountains must be the thea- 
 tres of the greatest activity of erosion, it is evident that the meta- 
 morphic core, will often be exposed by erosion along the cl-ests. Thus 
 the typical structure of a great mountain-range is that of a metamor- 
 phic or granitic axis emerging along the crest and flanked on each side 
 by strata corresponding to one another. It was formerly supposed 
 that the granitic axis was pushed up from below, breaking through the 
 strata and appearing above them. But it is far more probable that the 
 so-called granitic axis is only the metamorphic core formed as already 
 explained, and exposed by subse- 
 quent erosion. Fig. 233 is an ideal 
 of a mountain-range on this view. 
 In this case the core is only meta- 
 morphic ; and remnants of un- 
 changed strata, caught up and left 
 
 among the folds of the crests, show that these strata once extended 
 over the top, and that the metamorphic axis is exposed only by 
 erosion. Only carry the metamorphism a step further and the 
 erosion a little deeper, and we have the granitic axis complete 
 (Pig. 234). 
 
 Mountains are made out of Lines of Thick Sediments.— But the 
 question occurs, What determines the place of a mountain-i^nge ? 
 The answer is, A mountain-range while in preparation — before it be- 
 came a range — was a line of very thick sediments. This is a very im- 
 portant point in the theory of mountain origin, and therefore must be 
 proved. The strata of all mountains, where it is possible to measure 
 them, are found to be of enormous thickness. The strata involved in 
 the folded structure of the Appalachian, according to Hall, are 40,000 
 feet thick ; the strata exposed in the. structure of the Wahsatch, ac- 
 
270 STRUCTURE COMMON TO ALL ROCKS. 
 
 cording to King,* are more than 50,000 feet thick; the Cretaceous 
 strata of the Coast Range, near the Bay of San Francisco, according to 
 Whitney,! are 20,000 feet thick ; and if we add to this 10,000 feet for 
 the Eocene and Miocene strata, the whole thickness is probably not 
 less than 30,000 feet, while the Cretaceous alone in Northern Califor- 
 nia, according to Diller, is 30,000 feeij The Alpine geologists esti- 
 mate the thickness of the strata involved in the intricate structure of 
 the Alps as 50,000 feet* The sti'ata of Uintah, according to Powell, 
 are 33,000 feet thick. 
 
 Now, it must not be imagined that these numbers merely represent' 
 the general thickness of the stratified crust ; only, that in these places 
 the strata are turned up and their edges exposed by erosion, and thus 
 their thickness revealed. On the contrary, it may be shown that the 
 same strata are much thinner elsewhere. The same strata which along 
 the Appalachian range are 40,000 feet thick, when traced westward 
 thin out to 4,000 feet at the Mississippi River. The same strata which 
 along the line of the Wahsatch are 30,000 feet thick, when traced east- 
 ward thin out to 3,000 feet in the region of the Plains. || It is evident, 
 therefore, that mountain-ranges are lines of exceptionally thick strata. 
 
 Mountain-Ranges were once Marginal Sea-Bottoms.— Where, then, 
 do sediments now accumulate in greatest thickness? Evidently on 
 marginal sea-bottoms, off the coasts of continents. The greater part 
 of the washings of continents are deposited within 30 miles of shore, 
 and the whole usually within 100 miles. From this line of thickest 
 and coarsest deposit the sediments grow thinner and finer as we go sea- 
 ward. J3ut evidently such enormous thicknesses as 40,000 feet can not 
 accumulate in the same place without pari passu subsidence such as we 
 know takes place now whenever exceptionally abundant sedimentation 
 is going on (p. 145). Therefore, mountain-ra?iges before they were yet 
 born — while still in preparation as embryos in the womb of the ocean 
 — were lines of thick off-shore deposits gradually subsiding, and thus 
 ever renewing the conditions of continuous deposit. 
 
 As this is a very important point, it is necessary to stop here awhile 
 in order to show that such was actually the fact in the case of all the 
 principal ranges of the American Continent — i. e., that for a long time 
 before they were actually formed, the places which they now occupy 
 were marginal sea-bottoms receiving abundant sediments from an ad- 
 jacent continent. We shall be compelled here to anticipate some things 
 
 * Fortieth Parallel Survey, vol. iii, p. 461. 
 
 f Whitney, on Mountain-Building. 
 
 \ American Journal of Science, vol. xl, p. 476, 1890. 
 
 9 Judd, Volcanoes, p. 295. 
 
 II King, Fortieth Parallel Survey, vol. i, p. 122. 
 
MOUNTAIN STRUCTURE. 
 
 271 
 
 that belong to Part III, but we hope to make statements so general 
 that there will be no difficulty in understanding them, 
 
 1. Appalachian.— The history of this range is briefly as follows : 
 At the beginning of the Palaeozoic era there was a great V-shaped 
 land-mass, occupying the region now covered by Labrador and Canada, 
 then turning northwestward from Lake Superior and extending perhaps 
 to polar regions about the mouth of Mackenzie Kiver. This is shown 
 on map. Fig. 269, on page 303. There was another great land-mass 
 occupying the present place of the eastern slope of the Blue Ridge and 
 extending eastward probably far beyond the present limits of the con- 
 tinent—as shown in the same figure by dotted line in the Atlantic 
 Ocean. The western coast-line of this land-mass was the present place 
 of the Blue Ridge. Westward of this line extended a great ocean— 
 "the interior Paleozoic Sea." The Appalachian range west of the 
 Blue Ridge was then the marginal hoitom of that sea. During the 
 whole of the Cambrian, Silurian, and Devonian, this shore-line re- 
 mained nearly in the same place, although there was probably a slow 
 transference westward. Meanwhile, throughout this immense period of 
 time, the washings from the land-mass eastward accumulated along 
 the shore-line, until 30,000 feet of thickness was attained. At the end 
 of the Devonian some considerable changes of physical geography of 
 this region took place, which we will explain when we come to treat of 
 the history of this period. Suffice it to say now that during the Carbon- 
 iferous the region of the Appalachian was sometimes above the sea as a 
 coal-swamp, and sometimes below, but all the time receiving sediment 
 until 9,000 or 10,000 feet more of thickness was added, and the aggre- 
 gate thickness became 40,000 feet. Of course, it is impossible that 
 such thickness could accumulate on the same spot •without pari passu 
 subsidence of the sea-floor. In fact, we have abundant evidence of 
 comparatively shallow water at every step of the process — evidence 
 sometimes in the character of the fossils, sometimes in the form of 
 shore-marks of all kinds, sometimes in the form of seams of coal, show- 
 ing even swamp-land conditions. Again, of course, the sediments were 
 thickest and coarsest near the shore-line, and thinned out and became 
 finer toward the open sea, i. e., westward. Finally, after 40,000 feet of 
 sediments had accumulated along this line the earth-crust in this re- 
 gion gave way to the lateral pressure, and the sediments were mashed 
 together and folded and swollen up into the Appalachian range. Sub- 
 sequent erosion has sculptured it into the forms of scenic beauty which 
 we find there to-day. 
 
 2. Sierra.— This was apparently the first-born of the Cordilleran 
 
 family. Its history is as follows: During the whole Palseozoic and 
 
 earlier part of the Mesozoic, there was in the Basin region a land-mass, 
 
 whose form and dimensions we yet imperfectly know, but whose Pacific 
 
 19 
 
272 STRUCTURE COMMON TO ALL ROCKS. 
 
 shore-line was east of the Sierra. The Sierra region was therefore at 
 that time the marginal bottom of the Pacific Ocean. Probably the 
 position of this shore line changed considerably at the end of the 
 Palaeozoic. The extent of this change we will discuss hereafter. Suf- 
 fice it to say now that, during the whole of this time, the Sierra region 
 received sediments from this land-mass until an enormous thickness 
 (how much we do not know, because the foldings are too complex to 
 allow of estimate) was accumulated. At last at the end of the Jurassic, 
 the sea-floor gave way to the increasing lateral pressure along the line 
 of thickest sediments, and these latter were crushed together with 
 complex foldings and swollen up into the Sierra. An almost incon- 
 ceivable subsequent erosion has sculptured it into the forms of beauty 
 and .grandeur which characterize its magnificent scenery. 
 
 3. Coast Range. — The birth of the Sierra transferred the Pacific 
 shore-line westward, and the waves now washed against the western 
 foot of that range, or possibly even farther westward in the region of 
 the Sacramento and San Joaquin plains. At this time, therefore, the 
 region of the .Coast Eange was the marginal bottom of the Pacific Ocean. 
 During the whole Cretaceous, Eocene, and Miocene, this region re- 
 ceived abundant sediments from the now greatly enlarged continental 
 mass to the eastward ; until finally, at the end of the Miocene, when 
 30,000 feet of sediments had accumulated along this line, the sea-floor 
 yielded to the lateral pressure, and the Coast Kange was born ; and the 
 coast-line transferred to near its present position. 
 
 4. Wahsatch. — The physical geography of the region to the east of 
 the Wahsatch (Plateau region) during Jura-Trias time is little known. 
 But during the Cretaceous the region of the Wahsatch was the western 
 marginal bottom of the great interior Cretaceous Sea (see map. Fig. 
 760, p. 486), receiving abundant sediments from the great land-mass of 
 the Basin and Sierra region. This greatly increased the enormous 
 thickness of sediments already accumulated along this line in earlier 
 times. At the end of the Cretaceous the sediments yielded, and the 
 Wahsatch was born. It is necessary, however, to say that both the 
 Sierra and Wahsatch underwent very great changes of form produced 
 by a different process and at a much later period. We shall speak of 
 this later. 
 
 5. Alps. — Mr. Judd has recently shown that the region of the Alps, 
 during the whole Mesozoic and Early Tertiary, was a marginal sea- 
 bottom, receiving sediments until a thickness was attained not less 
 than that of the Appalachian strata. At the end of the Eocene these 
 enormously thick sediments were crushed together with complicated 
 foldings and swollen upward to form these mountains and afterward 
 sculptured to their present forms. 
 
 The same may be said of the Himalayas and nearly all other mount- 
 
MOUNTAIN STRUCTURE. 273 
 
 ains. We may, therefore, confidently generalize, and say that the 
 places now occupied by mountain-ranges have been, previous to their 
 formation, places of great sedimentation, and therefore usually mar- 
 ginal ocean-Sotionis. In some cases, however, the deposits in interior 
 seas or mediterraneans have yielded in a similar way, giving rise to 
 more irregular ranges or groups of mountains. 
 
 It is easy to see now why mountain-ranges so often form the bor- 
 ders of continents, and that continents consist essentially of interior 
 basins with coast-chain rims. The view of formation of mountains, 
 above presented, necessitates this as a general form, while it prepares 
 us for exceptions in case of mountains formed from mediterranean 
 sediments. We see also why in the case of parallel marginal ranges of 
 the same system, such as the Sierra and Coast Eanges, these should be 
 formed successively seaward. 
 
 In the above account of mountain-building, for the sake of clear- 
 ness and brevity, we have made the process too simple. It is really 
 much more complex. Mountains are lines of crust-weakness, and 
 therefdre have been subject to repeated movements. In the case of 
 the Sierra, its birth was indeed at the end of the Jurassic ; but it suf- 
 fered another great movement at the end of the Tertiary, of which we 
 shall have much to say hereafter. In the Coast Eange the greatest 
 movement was indeed at the end of the Miocene, but it suffered a pre- 
 vious movement at the end of the Jurassic and a subsequent one at the 
 end of the Tertiary — both of them coincident with the Sierra move- 
 ments. So also the Appalachians have suffered several movements. 
 In each case we have spoken only of the greatest. 
 
 Why Thick Sediments should be Lines of Yielding.— Admitting, 
 tfien, that mountains are formed by the squeezing together of lines of 
 very thick sediments, the question still occurs. Why does the yielding 
 take place along these lines in preference to any others ? This is a capi- 
 tal point in the theory of mountain formation. The answer is as fol- 
 lows : We have already seen (p. 231) that accumulation of sediments 
 causes the isogeotherm to rise and the interior heat of the earth to 
 invade the lower portion of the sediments with their included waters. 
 Now this invasion of heat in its turn causes hydrothermal softening or 
 even fusion, not only of the sediments, but also of the sea-floor on 
 which they rest. Thus a line of thick sediments becomes a line of 
 softening and therefore a line of weakness, and a line of yielding to 
 the lateral pressure, and therefore also a line of mashing together and 
 folding and up-swelling— in other words, a mountain-range. As soon 
 as the yielding commences we have an additional source of heat in the 
 crushing itself. In addition to this, upheaval by lateral crush by the 
 tendency to arch the strata would produce relief of gravitative press- 
 ure, and therefore fusion (p. 103). It follows from this that there is or 
 
274 STRUCTUKE COMMON TO ALL ROCKS. 
 
 was beneath every mountain in the zone of flowage a mass of plastic 
 or semi-fused matter. This we will call the sub-mountain liquid. 
 By cooling and solidification this becomes a metamorphic or granitic 
 core, which by erosion forms the metamorphic or igneous axis and 
 crest of many great mountains. 
 
 Brief History of a Mountain-Range. — The preparation for a future 
 mountain commences by the accumulation of enormous thickness of 
 sediment off a coast-line. This is the embryonic condition of the 
 range ; it is still within the womb of ocean. Next, the line of sedi- 
 ments yields to the ever-increasing lateral thrust, and the mountain is 
 born. As soon as it appears, there begin to act upon it two opposite 
 forces — one upheaving, the other cutting away ; the one interior, the 
 other exterior — which may be compared to the opposite processes of 
 supply and waste in the animal body. So long as the supply exceeds 
 the waste, the mountain grows. When these opposite processes are in 
 equilibriutn, the mountain is mature. When the waste by erosion ex- 
 ceeds the supply by upheaval, the mountain has entered upon its period 
 of decay. Finally, the destructive forces triumph, and the mountain 
 is swept clean away by erosion. This is mountain-death. We find 
 mountains in all these stages. The Sierra, the Wahsatch, and the Coast 
 Eange are probably still growing. The Appalachian is already mature 
 or probably entered on its period of deciy. In the folded structures 
 of the enormously thick rocks of the Archaean region of Canada we un- 
 .doubtedly find the bones of extinct mountains. 
 
 Slowness of Mountain Origin and Growth— Although, as we shall 
 see in Part III, the formation of mountains often marks the boundaries 
 of geological periods, and therefore, in a geological sense, the process 
 is comparatively rapid, yet in a human sense it is always extremely 
 slow — so slow that it may be, and probably is, going on now under our 
 eyes, without attracting our attention. 
 
 Age of Mountains. — The date of mountain-birth is determined by 
 the age of the strata. It must be later than the youngest strata which 
 enter into the folded structure of the mountain or are tilted on its 
 flanks. Thus we say that the Appalachian was born at the end of 
 the Coal period, because all the Palaeozoic strata, including the coal, 
 enter into the composition of its folded structure, but later strata do 
 not. We say that the Sierra was formed at the end of the Jurassic, be- 
 cause these are the youngest strata which are folded and tilted on its 
 flanks. Similarly, the Cretaceous, the Eocene, and the Miocene, are all 
 crumpled up in the Coast Eange, but the Pliocene are not. Therefore 
 we judge that this range was formed at the end of the Miocene. To 
 illustrate : in Pig. 234 (p. 369) it is evident that the strata a were first 
 deposited in a horizontal position, then tilted and eroded, and b were 
 deposited unconformably on their eroded edges. The age of this 
 
MOUNTAIN STKUCTURE. 
 
 275 
 
 mountain, therefore, is younger than a and older than h. Sometimes 
 several movements of lifting are revealed. Thus in Pig. 335 the strata 
 a were deposited horizontally, then tilted by mountain formation and 
 eroded, and I deposited horizontally and unconformably on their edges ; 
 then by a second movement b was lifted (and of course a also at a 
 higher angle than before), and c was deposited unconformably on i. 
 
 Now, by examination of mountains in all parts of the world, it is 
 found, as might have been expected, that all the highest mountains are 
 comparatively young, and that the oldest mountains are of moderate 
 altitude. The reason is 
 obvious : young mountains 
 are in the vigor of youth, 
 and perhaps still growing, 
 while the oldest mountains 
 are in the last stages of decay. The oldest of our American mountains 
 are the low Laurentides ; they are almost gone ; they are pre-Oambrian. 
 Then follow the higher Appalachian ; they are pre-Triassic. Then 
 the still higher Sierra ; they are pre-Cretaceous. To mention some 
 foreign examples : the Alps has certainly risen 10,000 and the Hima- 
 laya 19,000 feet * since Eocene times ; for so high Eocene marine strata 
 have been found on their slopes. 
 
 Other Phenomena associated with Mountains.— The essential phe- 
 nomena demonstrating the process of mountain formation are the 
 folded structure, the slaty cleavage, the thickness of the strata, and the 
 position along the borders of continents. But there are other phe- 
 nomena associated with mountains, which are well explained by the lat- 
 eral-pressure theory, and therefore confirm the theory. 
 
 1. Fissures, Fissure-Eruptions, and Dikes. — The strong foldings 
 of mountain strata inevitably produce fractures. Often these fractures 
 extend down to the sub-mountain liquid, and this latter is squeezed 
 out by the enormous lateral pressure, through the fissures and out- 
 poured on the surface as great lava-floods — such as the great lava-flood 
 of the N"orthwest, and the Deccan lava-flood, already described on pages 
 218 and 219. The outpourings on the surface may be entirely carried 
 away by erosion, and the filled fissures through which they came may 
 be exposed as (?j^es ; or else the sub-mountain liquid may have been 
 forced into fissures which did not reach the surface, and these also 
 may be exposed by erosion as dikes. Thus lava-floods are associated 
 with newer strata, and dikes with all, but especially the older. 
 
 2. Volcanoes. — Great lava-floods come up through fissures and flow 
 off as sheets. By repeated eruptions successive sheets accumulate until 
 the whole mass is several thousand feet thick. The lower parts of such 
 
 * American Journal of Science, vol. xxxvii, p. 413, 1889, 
 
276 STRUCTURE COMMON TO ALL ROCKS. 
 
 lava-masses remain incandescently hot almost indefinitely. Percolat- 
 ing water reaching these hot interior portions develops force sufficient 
 "to eject fused matter and form volcanoes parasitic on the lava-floods; 
 or else water may reach the sub-mountain liquid through the fissures 
 produced by foldings and thus also produce volcanoes. Thus volcanoes 
 also are associated with mountain-ranges. 
 
 3. Mineral Veins. — If the fractures do not penetrate deep enough 
 to reach the sub-mountain liquid, then they are not filled at the time 
 of their formation with liquid lava, but slowly afterward by deposit of 
 mineral matter from percolating waters, and form veins. Thus min- 
 eral veins are especially abundant in mountain-regions. 
 
 4. Faults and Eartliqualces. — The walls of great fissures, as we 
 have already seen, never remain in their original position, but always 
 slip one on the other and thus form faults, which, in case of foldings 
 by lateral pressure, will usually be reverse. Hence faults are associated 
 with mountains. The slipping, however, will not take place all at once' 
 but very slowly, and yet not uniformly, but more or less paroxysmally. 
 Each paroxysm will produce an earthquake. The original fracturing 
 will also produce an earthquake. Thus earthquakes are associated with 
 mountains, especially if the mountains are still growing. 
 
 We see thus the truth of the proposition with which we set out, 
 that mountains are the theatres of the greatest activity of all geological 
 agencies. They are first the places of greatest activity of aqueous 
 agencies in the form of sedimentation in preparation for the future 
 mountains ; then of igneous agencies in the birth and growth of the 
 actual mountain ; and, finally, again of aqueous erosive agencies in 
 sculpturing them into forms of- beauty, but also in the decay and at 
 last in the complete destruction of former mountains. 
 
 Cause of Lateral Pressure.— We have thus proved that the imme- 
 diate cause of the origin and the growth of mountains is lateral press- 
 ure acting on thick sediments, crushing them together and swelliug 
 them up along the line of greatest thickness. But still the question 
 remains, What is the ultimate cause, i. e., the cause of the lateral press- 
 ure ? This, as we have already said, lies still in the domain of doubt 
 and discussion, but the view which seems most probable may be briefly 
 stated as follows : 
 
 Under the nebular hypothesis of earth-genesis it is assumed that in 
 the secular cooling of the earth there would be not only unequal radial 
 contraction, giving rise, as shown on page 17 5, to continents and ocean- 
 basins, hut also unequal contraction of the exterior as compared with 
 the interior. At first, and for a long time, the exterior would cool 
 fastest; but there would inevitably, sooner or later, come a time when 
 the exterior would assume an almost constant temperature, while the 
 interior would still continue to cool and contract. Thus, therefore, 
 
MOUNTAIN SCULPTURE. 
 
 277 
 
 after a while the interior nucleus would contract faster than the ex- 
 terior shell. It would do so partly because it would cool faster, and 
 partly because the co-efficient of contraction of a hot body is greater 
 than that of a cooler body. Now, as soon as this condition was 
 reached, the exterior shell, following down the shrinking nucleus, 
 would be thrust upon itself by a lateral or horizontal pressure which 
 would be simply irresistible. If the earth's crust were a hundred 
 times more rigid than it is (30 times as rigid as steel), it must yield. 
 Mountain-ranges are the lines along which the yielding takes place, 
 and this yielding takes place along lines of thick sediments because 
 these are lines of weakness. 
 
 There are several serious objections which may be brought against 
 this view: Calculations seem to show that the amount of crumpling 
 and folding actually found in mountains is many times greater than 
 could be produced by the contraction of the earth by cooling. But it 
 may be said (1) that the calculations may not take sufficient account 
 of the greater coefficient of contraction at high temperatures, and 
 therefore at great depths, (2) and that there may be other causes of 
 contraction besides cooling. For example, loss of constituent gases 
 . and vapors from the interior of the earth, through volcanic vents and 
 fissures, has been suggested by 0. Fisher (p. 102). However, the 
 above objection remains practically unanswered. But the Planetesi- 
 mal hypothesis of earth origin (see pp. 88, 171, 176) is more favorable 
 to a large amount of contraction and horizontal compression, as 
 earth-accretion by cold particles resulted in considerable porosity 
 and heterogeneity. The elimination of porosity and the rearrange- 
 ment of the heterogeneous materials into denser forms has produced 
 not only interior heat and the atmosphere and ocean (from squeezed- 
 out gases), but the large amount of lateral compression and crustal 
 folding. The origin of mountains by lateral pressure is a fact 
 beyond dispute.* 
 
 Mountain Sculpiure 
 
 As soon as a mountain-range lifts its head above the general level 
 of sea or land, it is im^mediately attacked by erosion. All the grand 
 and beautiful forms of mountain scenery are due to erosive sculpturr 
 ing. The amount carried away is always enormously great, usually 
 many times greater than what remains. In Fig. 256 (p. 287) we have 
 in the upper part the Uintah Mountains with its strata restored, i. e., 
 as it would be if never ravaged by erosion ; in the lower part we have 
 it as it now exists. The extreme thickness removed is about 25,000 
 
 * For a completer discussion of this subject, see Theories of Mountain Origin, Jour. 
 Geol., vol. i, p. 642, 1893. 
 
278 
 
 STRUCTURE COMMON TO ALL liOCKS. 
 
 feet, while only about 8,000 feet remain, for the highest peaks are 
 now only 10,000 to 12,000 feet high. In the Appalachian — an older 
 mountain — probably a much larger proportion has been carried away. 
 The amount in all eases is so great as to obscure the origin of moun- 
 tains and to confuse the use of the term mountain. Hence some have 
 divided mountains into two kinds, viz., mountains of upheaval and 
 mountains of erosion, and some have even gone so far as to say that 
 mountains are mere remnants of denuded continents — the prominent 
 points of a difEerential erosion. But it is best to keep distinct in the 
 mind mountain formation and mountain sculpture. They are both 
 equally important in the final result. If igneous forces do the rough 
 hewing, aqueous forces do the shaping into forms of beauty. When 
 we view mountains from a distance, the blue, cloud-like bank which 
 we see on the horizon is the result of igneous agencies; but when we 
 are among mountains all that we see — every ridge and peak and val- 
 ley — all that constitutes scenery — is the result of aqueous agencies; 
 
 Sculptural Forms. — The mode of mountain formation is more or 
 less concealed in internal structure; but the forms developed by 
 sculpture lie on the surface, and are easily understood, and yet they 
 often reveal structure to the careful observer. A knowledge of these 
 sculptural forms gives additional charm to mountain travel. They 
 are almost infinitely diversified ; yet a Jew of the most common and 
 conspicuous may be given as examples. These forms are not all con- 
 fined to mountains; some of them are the general forms of highland 
 erosion; but they are most conspicuous in mountain-regions. 
 
 1. Horizontal Strata. — (a) These, if sufficiently firm, give rise to 
 table-forms, the top of the table being determined by a slab of hard 
 
 Fig. 2.97. 
 
 stratum, such as sandstone or grit, or by a lava-flow. In the latter 
 case, the horizontal lava-blanket gives rise to tables, whatever be the 
 
 Via. 238.— Section across Oamberiand Plateau and Lookout Mountain, Tennessee. 
 
 position of the underlying strata. Good examples of this form are 
 found in Illinois (Fig. 237), in Tennessee (Fig. 238), and in the 
 mesas of the Plateau region. 
 
MOUNTAIN SCULPTURE. 
 
 21% 
 
 (6) But if the horizontal strata are soft, interstratified sands and 
 >clays, their erosion gives rise to fantastic castellated forms of peaks, 
 
 Fig. 330.—" Little Bad Lands," Sioux County, Nebraska. (Photograph by E. H. Barbour.) 
 
 turrets, etc., such as are found in the Bad Lands of the Plains, which 
 are the almost unlithifie'd ' deposits of the Tertiary lakes (Figs 
 339, 240). 
 
 Fig. 240.— Mauvaises Terres, " Big Bad Lands," South Dakota. (Photograph by E. H. Barbour.) 
 
 3. Gently-undulating Strata. — These give rise to synclinal ridges 
 and anticlinal valleys. This is well shown in diagram (Fig. 241) and 
 in the subjoined section of the Appalachian coal-field in Pennsylvania 
 (Fig. 242). This is usually explained by supposing that the backs of 
 the anticlinals have been broken or loosened by tension in bending; 
 
280 
 
 STRUCTURE COMMON TO ALL ROCKS. 
 
 while the synclinals have been hardened by lateral pressure — and 
 therefore the antielinals have yielded more easily to erosion. But 
 
 Pig. 841.— Diagram showing Synclinal Eidges and Anticlinal Valleys (after NOe and De Margerie). 
 
 Prof.- Davis has shown that such a supposition is at least not neces- 
 sary. For if we have a series of undulating strata, some hard and 
 some soft, and well raised above base-level, the erosion will be most 
 
 Fig. 242.— Section of Coal-Field of Pennsylvania (after Lesley). 
 
 rapid on the antielinals, and the hard stratum will there be reached 
 and cut through first. As soon as the soft stratum beneath is reached 
 the erosion will be still more rapid, and valleys will be formed. 
 
 3. Strongly-folded or Highly-inclined Outcropping Strata. — These 
 give rise to sharp ridges and valleys, the ridges being determined by 
 the outcrop of a hard stratum. Fig. 344 is an ideal diagram, showing 
 
 Fig. 243.— a " Hog-Back," West Escarpment of the Freezeout Anticline, Wyomine. (Photograph 
 
 by B. H. Barbour.) 
 
 how such ridges are formed by erosion. In the Kocky Mountains, where 
 they are finely shown on the flanks of mountains, they are called "hog- 
 backs." Figs. 243-345 represent this fornl of sculpture as it often 
 appears. It is seen that every ridge is formed by outcrop of a hard 
 
MOUNTAIN SCULPTURE. 
 
 281 
 
 sandstone, which has resisted erosion more than the intervening strata 
 Beautiful examples of this form are seen in parts of the Appalachian.' 
 
 F». ^.-Meal Section across '^-^^^fj^^oo^^^^f Alternating Soft and Hard Strata 
 
 Standing on the top of Warm Springs Mountain? Virginia, ten or 
 twelve parallel ridges may be counted, each with long slopes on one side 
 and steep slopes on the other, like billows ready to break.. The crest of 
 each ridge is determined by the outcrop of a hard sandstone. Such 
 ridges may be formed either by the outcrop of successive sandstones 
 
 Fig. 245.— Parallel Kidges. 
 
 **. 
 
 as in Fig. 245, or else by the successive outcrop of the same sandstone, 
 as in Fig. 246. 
 
 In ridges formed in this way the relative angle of slope on the two 
 sides of the ridges will depend on the dip of the strata. If the strata 
 be vertical, the two slopes will be equal. If the strata are inclined, the 
 
 / 
 
 Fig. 246.— Parallel Eidges in Folded, Strata. 
 
 longer slope will be on the side toward which the strata dip ; and the 
 difEerence of the two slopes will increase as the angle of dip becomes 
 less. This is shown in Fig. 247 (a, b, and c). Finally, one slope may 
 
 Fig. 247. 
 
 coincide with the face of the hard stratum, as in Fig. 244. This case, 
 therefore, passes by insensible gradations into the next, viz. : 
 
282 
 
 STRUCTURE COMMON TO ALL ROCKS. 
 
 4. Gently -inclined, almost Level Strata. — These, by erosion, per- 
 haps under peculiar climatic conditions, give rise to a succession of 
 
 Flo. 248.— Bird's-eye View of the Terrace Oafion (after Powell). 
 
 broad, nearly level tables, coincident with the face of a hard stratum, 
 terminated each by a Tertical or nearly vertical clifE. This form of 
 
MOUNTAIN SCULPTURE. 
 
 283 
 
 Fig. 249.— Dotted lines show material carried away by erosion. 
 
 sculpture is developed on a magnificent scale in the Colorado Plateau 
 region. Fig. 248 is a bird's-eye view of three such tables, each 20 to 
 60 miles wide, and terminated by cliffs 1,500 to 2,000 feet high. Pig. 
 
 249 is an ideal sec- 
 
 tion of such ta- 
 bles and cliffs^the 
 dotted lines show- 
 ing the portion car- 
 ried away by ero- 
 sion. It is evident 
 that the drainage of each table is against the cliff ; and every cliff, 
 therefore, recedes partly by under-cutting by a river and partly by 
 rain-wash on its face. In some cases, where the lifting of the strata 
 was dome-lijje, the receding cliffs are circular, producing thus titanic 
 amphitheatres, 100 or more miles across, with cliff-benches 1,000 to 
 2,000 feet high.* How slow the lifting of the strata in this region 
 must have been is shown by the fact that the Green River runs 
 against the slope of the strata, cutting its caflon deeper to the edge 
 of the cliffs, as shown in Fig. 248. Evidently the strata were lifted 
 athwart the course of the river, but so slowly that the river cut as 
 fast as the strata lifted. 
 
 Migration of Divides. — If the slopes on the two sides of a divide 
 are equal, the position of the divide remains stationary; but if one 
 slope be steeper than the other, then by the greater erosion on the 
 steeper slope the divide will move steadily toward the gentler slope. 
 Thus, the rivers on the steeper slope continually increase their drainage 
 areas by appropriating froui the other side, Examples of this may be 
 found in nearly all mountains, but especially in those of the monoclinal 
 type, and in all ridges, but especially in the case of hog-backs (Figs. 
 244, 245). The recession of plateau cliffs is only an extreme case under 
 this law. 
 
 5. Metamorphic and Granitic Rocks. — Sculptural forms in these 
 are usually irregular, and can not be reduced to a simple law. But, in 
 
 some cases, peculiar forms are 
 traceable to peculiar structure. 
 Thus, for example : in and about 
 the Yosemite Valley two kinds 
 of forms are found, viz., (a) per- 
 pendicular cliffs and towers and 
 spires of the valley itself; and 
 (b) rounded domes abundant in the high region about the valley. 
 The one is the result of a rough, imperfect vertical cleavage of the 
 
 Pio. S50.— Ideal Section showing Dome-stractare. 
 Dotted line above shows original surface. 
 
 * Dutton, High Plateaus of Utah, p. 19. 
 
284 DENUDATION, OR GENERAL EROSION. 
 
 rock; the other of a concentric structure on a huge scale, usually 
 undetectable in the sound rock, but brought out by weathering. This 
 is shown in the diagram (Pig. 350). 
 
 6. TJie Kind of Agent. — It is probable that the nature of the erosive 
 agent, whether as rain and rivers or as snow and glaciers, also deter- 
 mines peculiar scenic forms. It is probable that the former tend more 
 to rounded summits and ridges and V-shaped gorges, the latter to 
 sharp summits {aiguilles) and comb-like divides and broad U-shaped 
 valleys. 
 
 CHAPTER VI. 
 DENUDATION, OR GENERAL EROSION. 
 
 As a fit ending of Part II, and preparation for Part III, in which 
 the idea of time is the underlying element, it seems appropriate to 
 make some rough estimate of the amount of general erosion which has 
 taken place in the history of the earth, and of geological time based 
 thereon. 
 
 The term dentidation is used by geologists to express the general 
 erosion which the earth-surface has suffered in geological times. The 
 correlative of denudation is sedimentation, and the amount of denuda- 
 tion is measured by the amount of stratified rocks. 
 
 Agents of Denudation. — The agents of erosion, as we have already 
 seen in Part I, are : 1. Rivers, including under this head the whole 
 course of rainfall on its way back to the ocean whence it came ; 2. 
 Glaciers, including under this head not only glaciers proper, but mov- 
 ing ice-sheets, such as now exist in polar regions, and in the Glacial 
 epoch extended far into now temperate regions, and also moving snow- 
 fields, for it is probable that all extensive snow-fields and snow-caps are 
 in motion ; 3. Waves and tides j and, possibly, 4. Oceanic currents. 
 
 Oceanic currents usually run on a led and between lanks of still 
 water, and therefore produce no erosion. It is possible,- however, that 
 a rising sea-bottom may be eroded by this agent ; but as we have no 
 knowledge of such effects, we are compelled to omit this from our esti- 
 mate of the probable rate of denudation. The action of waves and 
 tides is violent and conspicuous ; yet these agents are so entirely con- 
 fined to the shore-line that their aggregate effect is but a small frac- 
 tion of the whole erosion. Prof. Phillips has shown * that, taking the 
 coast-lines of the world as 100,000 miles, and making the extravagant 
 estimate that the average erosion along this whole line is equal to that 
 
 * Life, its Origin and Sviccession, p. 130. 
 
DENUDATION, OR GENERAL EROSION. 285 
 
 of the English coast, or one foot per annum of a elifE one hundred feet 
 high, still the aggregate wave-erosion is far less than river-erosion, be- 
 ing equivalent to a general land-surface erosion of only ^-^^^ of an inch 
 per annum, or ^ of that which is now going on over the hydrographi- 
 cal basin of the Ganges, and \ of that going on in the basin of the 
 Mississippi. Elvers are the chief agents of land-erosion. But in ele- 
 vated districts glaciers may take the place of streams, removing loose 
 material, abrading the rocks and carrjdng loads of rock-rubbish to lower 
 levels. Their work is mainly transportational, their iield of action 
 limited, and they commonly change into running water. As agents of 
 land denudation streams and glaciers may displace each other, accord- 
 ing as falling water takes the form of rain or snow; both come under 
 the general head of circulating meteoric water. In a general estimate 
 of the rate of denudation we may, therefore, without sensible error, 
 regard erosion as the work of rivers. 
 
 Amount of Denudation. — A mere glance at the figures below will 
 show in a general way the manner in which geologists estimate the 
 amount of denudation in certain regions. In almost all countries, es- 
 pecially in mountain-regions, we find slips varying from a few feet 
 (Fig. 251) to many thousands of feet perpendicular (Fig. 356). There 
 
 are slips in the Appalachian chain which I , 
 
 are estimated to be 8,000 and even one 20,- / 
 
 000 feet, in the Uintah 20,000, in the Wah- ;/ 
 
 satch 40,000 feet, perpendicular. And yet | s4---- -- ------^ 
 
 in most cases the escarpment, which would | s ^^^^ M 
 
 otherwise exist, is completely cut away,, so ^^mmmm ^^^^^^ ^. 
 
 that DO surface indication of the slip ex- fio. 251. 
 
 ists. Evidently in such cases there must 
 
 h9,ve been erosion on the elevated side, at least equal to the amount of 
 
 slip, and probably much greater. The dotted line represents the 
 
 amount of erosion. 
 
 Sometimes the horizontal strata of isolated mountain-peaks corre- 
 sponding to each other (mountains of erosion) show that these are but 
 scattered fragments of a once high plateau, which has been removed by 
 erosion, as shown in the annexed figure (Fig. 252) and in many of the 
 
 Fio 
 
 252.— Denudation of Eed Sandstone, Northwest Coast of Koss-shire, Scotland. 
 
 figures on pages 279 and 281. In such cases the erosion must have 
 been at least equal to the height of the peaks, and may have been to 
 any extent greater. The accompanying section across Middle Tennes- 
 
286 
 
 DENUDATION, OR GENERAL EROSION. 
 
 see shows a vertical erosion of 1,200 to 2,400 feet, over the whole valley 
 of Middle Tennessee, which is sixty miles across and one hundred 
 
 1 la. 233!— Section across Middle Tennessee. The dotted lines show the amount of matter removed. 
 
 miles long. In most cases the removed matter is not so easily esti- 
 mated as in those mentioned. The strata in mountain chains are usu- 
 
 FiG. 254.— Section through Portions of England. 
 
 ally folded in a very complex way, and then denuded. But the ideal 
 restoration of these may be effected, and the amount of erosion approxi- 
 
 ^^^^7^^^^/y//.^^>^^^^'7^^^kx^ 
 
 Fio. 255.— Section through Portions of England. 
 
 mately estimated. Figs. 254 and 355 are sections across the mount- 
 ainous parts of England, as restored by Prof. Ramsay. 
 
 Average Erosion. — By these methods Prof. Ramsay estimates the 
 denudations over many portions of England to be not less than 10,000 
 to 11,000 feet in thickness.* Over the whole Appalachian region the 
 denudation has probably been enormous, in some places 8,000 to 30,000 
 feet. Over the whole region of the high Sierra Range, as we have 
 shown, f erosion has removed the whole of the Jurassic and Triassic 
 slates, and bitten deep into the underlying granite. The thickness of 
 these slates is not known, but it must be many thousand feet. In the 
 Uintah Mountain region, according to Powell, over an area of 3,000 
 square miles, an average thickness of three and a half miles has been 
 taken away (Fig. 256), the extreme thickness removed being nearly 
 
 * Geological Obserrer, p. 819. 
 
 \ American Journal of Science and Arts, vol. v, p. 325. 
 
DENUDATION, OR GENERAL EROSION. 287 
 
 five miles. From the "Walisatch have been removed 33,000 feet, or 
 six miles thickness of strata (King). Over the whole Colorado Plateau 
 
 — -^DWil.. iiiiiiiiiMiiiHiniiiiiiv 
 
 Fia. 856.— Umtah Mountains— Upper Part restored showing Fault, Lower Part showing the 
 Present Condition as produced by Erosion (after Powell) 
 
 region the succession of cliffs, separated by broad tables (Fig. 249), 
 shows enormous erosion. The average erosion over the whole region 
 has been estimated by Powell and Button as 6,500 feet ; and the ex- 
 treme general erosion, not including the caflon-cutting, as 11,000 feet. 
 The whole of this immense mass has been removed, too, since the 
 middle Tertiary. 
 
 It seems impossible to avoid the conclusion, therefore, that the 
 average erosion over all present land-surfaces has been at least several 
 thousand feet. 
 
 There is another mode of estimating the average erosion, viz., by 
 the average thickness of stratified rocks. The debris of erosion is 
 carried down into seas and lakes, and forms strata, and the amount of 
 stratified rocks becomes thus the measure of the erosion ; the average 
 thickness of sediments, if they had been spread over an equal area, 
 would be an accurate measure of the average thickness removed by 
 erosion. Now, the stratified rocks are in some localities 10,000 feet, 
 20,000 feet, and sometimes 40,000 and 50,000 feet thick. They are 
 scarcely ever found less than 2,000 or 3,000 feet. It is certain, there- 
 fore, that the average thickness of strata over the whole known surface 
 of the earth is not less than several thousand feet. Let us take it at 
 only 3,000 feet. But the area of sedimentation, the sea-bottom, is now, 
 and has probably always been, at least three times the area of erosion, 
 the land-surface. Thus an average of 3,000 feet of strata would require 
 an average erosion of 6,000 feet. 
 
 Estimate of Geological Times. — There are many facts connected 
 with geology, especially the facts-of evolution, which can not be under- 
 stood without the admission of inconceivable lapse of time. For this 
 reason it is important that the mind should become familiarized with 
 this idea. It will not be out of place, therefore, to make a rough esti- 
 mate of time based upon the amount of erosion. 
 30 
 
288 DENUDATION, OR GENERAL EROSION. 
 
 We have already seen (p. 11) that, taking the Mississippi as an 
 average river in erosive power (it is probably much more than an 
 average), the rate of continental erosion is now about one foot in 5,000 
 years. At this rate, to remove an average thickness of 6,000 feet 
 would require 30,000,000 years. 
 
 The above estimate takes the average thickness of strata, and sup- 
 poses it spread evenly over the whole sea-bottom. This is strictly 
 admissible only if we suppose, with Lyell, that land and ocean have 
 often changed places, so that every portion of earth-surface has 
 received sediments. But if, as is now most generally believed, the 
 ocean-basins have remained substantially unchanged, and sediments 
 have accumulated almost wholly on their margins, then we must, it is 
 true, make our measuring rod, i. e., the rate of sedimentation, much 
 greater, but we must also take the sum- of the extreme thickness of 
 strata in different localities, as the thing to be measured. We there- 
 fore make another estimate, on this basis, following Mr. Wallace. 
 Taking the whole land-surface (erosion area) at 57,000,000 square 
 miles, and the sedimentation area as thirty miles wide along a coast- 
 line of 100,000 miles {^= 3,000,000 square miles), then with an ero- 
 sion-rate of one foot in 3,000 years, instead of 5,000 years, the sedi- 
 mentation rate would be nineteen feet in the same time, or one foot 
 in 157 years. But the extreme thickness of strata is at least 177,000 
 feet. This would take 28,000,000 years.— (Wallace, Island Life, 
 p. 210.) The reader will understand that these are only suggestive 
 estimates, based on limited knowledge, and are not to be regarded as 
 accurate. 
 
 Some may object to this estimate, on the ground that geological 
 agencies were once much more active than now. But there is good 
 reason to believe that the mechanical agencies of water, i. e., its erosive 
 power, have been constantly increasing with the course of time, and 
 are perhaps greater now than at any previous epoch. 
 
 For observe : The erosive power of water is determined entirely by 
 the rapidity of circulation of air and water, and this is determined by 
 the diversity of temperature in difEerent portions, and this in its turn 
 by the size of continents and the height of mountains. Continents and 
 seas are two poles of a circulating apparatus — at one pole is condensa- 
 tion, at the other evaporation. In proportion to condensation are also 
 evaporation and circulation. Kow, there is good reason to believe that 
 amid many oscillations, there has been throughout all geological time 
 a constant increase in the size of continents and the height of mount- 
 ains. If so, then the circulation of air and water has been becoming 
 swifter and swifter ; the life-pulse of our earth has beaten quicker and 
 quicker, and therefore the waste and supply (erosion and sedimenta- 
 tion) have been greater and greater. 
 
DENUDATION, OR GENERAL EROSION. 
 
 289 
 
 We therefore return to our estimate of 30,000^000 years with 
 greater confidence that it is even far within limits of probability. 
 For, 1. We have taken the average thickness of strata at 3,000 feet, 
 while it is probably much more. 2. We have taken the Mississippi as 
 an average river, and therefore the present rate of general erosion as 
 one foot in 5,000 years : it is probably much less. 3. We have taken 
 the rate of erosion in previous epochs as the same as now, while it was 
 probably much less, for two reasons : 1. The land-surface to be eroded 
 was smaller; and 2. The erosive power of water was less. Taking all 
 these things into consideration, the time necessary to produce the 
 sedimentary rocks is greatly increased. ■ 
 
 But even thisgives us no adequate conception of the time involved 
 in the geological history of the earth. For rocks disintegrated into 
 soils, and deposited as sediments, are again recousolidated into rocks, 
 lifted ifito land-surfaces, to be again disintegrated into soils, trans- 
 ported and deposited as sediments. And thus, the same materials have 
 been worked over and over again, perhaps many times. Thus the his- 
 tory of the earth, recorded in stratified rocks, stretches out in appar- 
 ently endless vista. And still beyond this, beyond the recorded his- 
 tory, is the infinite unknown abyss of the unrecorded. The domain of 
 Geology is nothing less than (to us) inconceivable or infinite time.* 
 
 * Some physicists have indeed set a much lower limit to the ape of the, earth, but 
 George Darwin has recently admitted that the data on which the calculations are based 
 are wholly unreliable (Nature, vol. xlviii, p. 480, 1893). Geologists are therefore left 
 free to make their own calculations on their own data. 
 
 Fig. 256a.-Mt. SuefEel's, San Juan Mountains, Colorado ;14,000|M»: showing waste slopes. 
 (United States Geological Survey. Photograph by Whitman Cross.) 
 
PAET III. 
 HISTORICAL GEOLOGY; 
 
 OB, THE HISTORY OF THE EVOLUTION OF EABTH-STSUCTURE 
 AND OF THE ORGANIC KINGDOM. 
 
 CHAPTER I. 
 aSNEBAL PRmCIPLES. 
 
 Geology is the history of the evolution of earth-forms, earth-struct- 
 ure, and earth-inhabitants. There are certain laws underlying all 
 development — certain general principles common to all history, whether 
 of the individual, the race, or the earth. We wish to illustrate these 
 general principles in'the more unfamiliar field of geology by running 
 a parallel between the history of the earth and other more familiar 
 forms of history. 
 
 1. All history is divided into eras, ages, periods, epochs, separated 
 from each other more or less trenchantly by great events producing 
 great changes. In written history these are treated, according to their 
 importance, in separate volumes, or separate chapters, sections, etc. 
 So earth-history is similarly divided into geological eras, ages, periods, 
 etc. ; and these have been recorded by Nature in separate roch-sy stems, 
 roch-series, rock-groups, and rocTc-formations. In geology these terms, 
 both those referring to divisions of time and those referring to divisions 
 of record, are unfortunately loosely and interchangeably used. We 
 shall strive to use them as definitely as possible, the eras and the cor- 
 responding roch-systems being the primary divisions, and the others 
 subdivisions in the order mentioned. 
 
 3. In all history successive eras, ages, periods, etc., usually graduate 
 insensibly into each other, though sometimes the change is more rapid 
 and revolutionary. In individual history childhood usually graduates 
 into youth, and youth into manhood; yet sometimes a remarkable 
 event determines a more rapid change. In social and political life, too, 
 successive phases of civilization embodying successive dominant prin- 
 ciples usually graduate into each other ; yet great events have some- 
 
 290 
 
GENERAL PRINCIPLES. 291 
 
 times determined exceptionally rapid changes in the direction or the 
 rate of movement. So also is it in geological history. The eras, pe- 
 riods, etc., usually shade more or less insensibly into each other ; yet 
 there have been times of comparatively rapid or revolutionary change. 
 In all history there are periods of comparative quiet, during which 
 forces of change are gathering strength, separated by periods of more 
 rapid change, during which the accumulated forces produce conspicu- 
 ous effects. 
 
 3. Ages, periods, etc., in all history, whether individual, political, or 
 geological, are determined by the rise, culmination* and decline of suc- 
 cessively higher dominant forces, principles, ideas, functions. Thus, 
 in individual development, we have the culmination, first, of the nutri- 
 tive functions ; then of the reproductive and muscular functions ; and, 
 last, of the cerebral functions. And in mental development, also, we 
 have the culmination, first, of the perceptive faculties, and memory ; 
 then, the imaginative and aesthetic faculties ; and, last, the reflective 
 faculties ; the first gathering and storing material, the second vivifying 
 it, the third using it in productive mason-work of science. In social 
 history, too, the successive culminations of different phases of civiliza- 
 tion have been the result of the introduction and culmination of suc- 
 cessive dominant principles or ideas— of successive social forces or 
 functions. So has it been in geological history. The great divisions 
 of time, especially what are called ages, are characterized by the intro- 
 duction and culmination of successive dominant classes of organisms, 
 as these were the highest expression of earth-life. Thus, in geology, 
 we have an age of invertebrates, an age of fishes, an age of reptiles, in 
 which these were successively the dominant class. 
 
 But since (Law 2) successive ages graduate more or less into and 
 overlap each other, we might expect, and do indeed find, that the 
 characteristics of each age commence in the preceding age. Each 
 age is foreshadowed in the previous age. The same is true of all 
 history. We may call this the Law of Anticipation. 
 
 4. In all history, at the close of an age, the characteristic dominant 
 principle or class declines, but does not perish. It only becomes sub- 
 ordinate to the succeeding dominant class or principle. Thus, to illus- 
 trate from individual history : in youth, the characteristic faculties of 
 childhood, viz., perception and memory, decline, and become subordi- 
 nate to the higher faculty of imagination, and this in turn becomes 
 subordinate to the still higher faculty of productive thought ; and thus 
 the whole organism becomes higher and more complex, each stage of 
 development including not only its own characteristicj but also, in a 
 subordinate degree, those of all preceding stages. The same is true of 
 social history. Each stage of social development absorbs and includes 
 the social principles and forces characteristic of previous stages, but 
 
292 
 
 GENERAL PKINCIPLES. 
 
 subordinates them to the higher principles which form its own char- 
 acteristic, and thus the social organism becomes ever higher, more 
 complex, and varied. 
 
 So it is also in geologic history. When the dominance of any class 
 declines at the end of an age, the class does not disappear, but remains 
 subordinate to the next succeeding and higher dominant class, and the 
 organic kingdom, as a whole, becomes successively more and more 
 complex and varied. This is graphically represented by the accom- 
 panying diagram, in which we have five successive ages determined by 
 the culmination of as many successive dominant classes. 
 
 Fig 257.— Diagram illuBtrating the Rising, Culmination, and Decline of Succeesive Dominant 
 Classes, and the Increasing Complexity of the whole. 
 
 5. There are two modes of determining and limiting eras, ages, 
 periods, etc., in geology, viz., unconformity of the rock-system and 
 change in the life-system. In written human history, the divisions of 
 time are recorded in separate volumes, chapters, sectibns, with boards 
 or blank spaces between. These divisions in the record ought to cor- 
 respond to conspicuous changes in the character of the most important 
 contents. So, in the history of the earth, the rock-iSystems, rock-series, 
 rock-formations, are volumes, chapters, sections, respectively, more or 
 less completely separated from each other by unconformity, indicating 
 blanks in the known record ; and the most important changes in the 
 contents, i. e., in the life-system, ought to, and usually do, correspond 
 with the unconformity of the rock-system. But if there should be (as 
 there is in some limited localities) a discordance between these two, 
 we should follow the life-system rather than the rock-system, the con- 
 tents rather than the artificial divisions of the record. 
 
 6. As in human history there is a general onward movement of the 
 race, and yet special modifications in character and rate in each coun- 
 try ; so in geology there has been a general march of evolution of the 
 whole earth and the organic kingdom, and yet special modifications in 
 character and rate in each continent, and to a less extent in different 
 portions of the same continent. The great eras, ages, and periods, be- 
 long to the whole earth alike, and are the same in all countries, but the 
 epochs and the smaller divisions of time, though similar, are probably 
 not contemporaneous in different countries. This fact has probably 
 been too much overlooked by geologists. The term homotaocy is used 
 to express identity in the stage of evolution, as synchronism is used 
 for identity of time. 
 
GENERAL PRINCIPLES. 293 
 
 Great Divisions and Subdivisions of Time.— Eras.— It is upon these 
 principles that geologists have established the divisions of time and 
 the corresponding divisions of strata. 
 
 The whole history of the earth is divided into five eras, with corre- 
 sponding rock-systems. These are : 1. Archmzoic * era, embodied in 
 the Archaean system ; 2. Palmzoic\ era, embodied in the Paleozoic 
 system ; 3. Mesozoic J era, recorded in the Mesozoic system ; 4. Geno- 
 zoic* recorded in the Tertiary and Quaternary systems ; and, 5. The 
 Psychozoic era, or era of Mind, recorded in the recent system. 
 
 These grand divisions, with the exception of the last, are founded 
 on an almost universal unconformity of the rock-system, and a very 
 great and apparently sudden change in the life-system, a change affect- 
 ing not only species but also genera, families, and even orders. Be- 
 tween the Ust. and the preceding, it ia true, neither the unconformity 
 of the rock-system nor the change in the life-system is so great as in 
 the others ; but the introduction of man upon the scene and the sweep- 
 ing changes which are now going on through his agency are deemed 
 sufficient to make this one of the grand divisions of time.|| 
 
 We have already seen (p. 187) that unconformity is the result of 
 deposit of strata on old eroded land-surfaces, and that it therefore 
 always indicates an oscillation of the crust,, and an emergence and sub- 
 mergence of land. In every such case, as already explained, a portion 
 of the record is lost, which may or may not be recovered elsewhere. 
 It is certain that if the lost leaves could be all recovered, and the 
 record made complete, the suddenness of the break in the life-system 
 would disappear. Nevertheless, it is also certain that these general 
 unconformities indicate times of great change in physical geography, 
 and therefore of climate, and therefore of rapid changes of organic 
 forms ; and therefore, also, they mark the natural boundaries of the 
 great divisions of time. 
 
 Ages. — Again, the whole history of the earth is otherwise divided 
 into seven ages, founded, with perhaps the exception of the first, on the 
 culmination of certain great classes of organisms. These are : 1. The 
 ArcTicBan or Archmozoic Age, represented by the Archaean system of 
 rocks; 2. The Age of Invertebrates, represented by the Cambrian, 
 Lower Silurian, and Upper Silurian rocks; 3. The Age of Fishes, 
 represented by the Devonian rocks; 4. The Age of Acrogens, or the 
 Age of Amphibians, represented by the Carboniferous rocks; 5. The 
 Age of Reptiles, represented by the Mesozoic rocks; 6. The Age of 
 Mammals, by the Cenozoie; and, 7. The Age of Man, by the recent 
 rocks. 
 
 * Ancient animal life. f Old life. 1;. Middle life. * Recent life. 
 
 I For a full discussion of the subject see Bull. Geol. Dopt. of Univ. of Cal., No. 11. 
 
294 
 
 GENERAL PRINCIPLES. 
 
 In the accompanying diagram (Pig. 358), vertical height represents 
 the whole course of time, the strong horizontal lines divide this into 
 eras, while the lighter lines, where necessary, separate the ages. The 
 shaded spaces represent the origin, the increase and decrease, in the 
 course of time, of the great dominant classes of animals and plants. 
 To illustrate : The class of reptiles commenced in the uppermost Car- 
 boniferous, increased to a maximum in the Secondary, or Mesozoic, and 
 again decreased to the present time. It will be seen that the ages 
 correspond with the eras, except in the case of the Palseozoic era. 
 This long and diversified era is clearly divisible into three ages. 
 
 Animates. PlAWt^' 
 
 Age of Man, 
 
 Age of 
 Mammals. 
 
 Age of 
 Reptiles. 
 
 Age of 
 Acrogens. 
 
 Age of 
 
 Fishes. 
 
 Age of In- 
 vertebrates. 
 
 Archgean 
 
 Age. 
 
 /iiwiiy 11.11 III 
 
 - I II I'M 11 1^1 J 
 
 Psychozoic. 
 
 Mesozoic. 
 
 PaliEozoic, 
 
 ArchEcozoic. 
 
 Fig. 258. 
 
 Subdivisions. — The subdivisions of eras and ages into periods and 
 epochs are founded, as already explained (p. 308), on less general un- 
 conformity in the rock-system, and less conspicuous changes in the 
 life-system. The names of periods are often, and of epochs are nearly 
 always, local, and therefore different in different countries. We will, 
 of course, use those appropriate to American geology. The table on 
 page 209 represents, as far as periods, the classification used in this 
 country. We have added epochs only in the uppermost part, viz., in 
 the Tertiary and Quaternary. 
 
 We give, also (Fig. 259), an ideal diagram of the principal groups 
 of strata which we shall notice, in the order of 
 their superposition, with some examples of char- 
 acteristic fossils, indicating also the principal places 
 of general unconformity. 
 
 The terms used for the divisions of time, and 
 corresponding divisions of rocks, are shown in the 
 accompanying schedule : 
 
 Time. 
 
 Rocks. 
 
 Eras ) 
 Ages ) • • 
 Periods . . 
 Epochs . . 
 
 Systems. 
 
 Series. 
 Groups. 
 
GENERAL PRINCIPLES. 
 
 295 
 
 Order of Discussion. — 
 
 As in human history, so 
 in the geological history, 
 the recorded events of the 
 earliest times ^re very few 
 and meager, but become 
 more and more numerous 
 and interesting as we ap- 
 proach the present time. 
 Our account of the Ar- 
 chaean era will therefore 
 be quite general, and will 
 not enter into details, al- 
 though this era was very 
 long. In the next era we 
 will go into the descrip- 
 tion of the several ages, 
 in the next into the peri- 
 ods, and in the next even 
 into the epochs. 
 
 Pregeologic Eras.— 
 Previous to even the dim- 
 mest and most imperfect 
 records of the history of 
 the earth there is, as al- 
 ready said (p. 289), an 
 infinite abyss of the unre- 
 corded. This, however, 
 hardly belongs strictly to 
 geology, but rather to 
 cosmic philosophy. We 
 approach it not by written 
 records, but by means of 
 more or less probable gen- 
 eral scientific reasoning. 
 
 It would be appropri- 
 ate in this place to dis- 
 cuss the earth's origin 
 and evolution before the 
 reign of the present geo- 
 logic agencies. Professor 
 Chamberlin has shown 
 that the nebular hypothe- 
 sis breaks down under the 
 
 Ebas. 
 
 Payolio- 
 
 Quater 
 nary. 
 
 YMii'ii'^xh 
 
 Ages. 
 
 Periods. 
 
 Pleistocene. 
 
 Pliocene. 
 
 Cretaceous. 
 
 Jurassic. 
 
 Triassic. 
 
 Life. 
 
 Man. 
 
 Mammals the 
 dominant 
 
 0.5 § 
 
 i!.ip 
 
 l§ 
 
 Permian. 
 Coal-Measures. 
 
 Subcarbonit- 
 erous. 
 
 Salina. 
 Niagara. 
 
 Trenton. 
 Canadian. 
 
 Potsdam. 
 Acadian. 
 Georgian. 
 
 Huronian. 
 
 Laiirentian. 
 
 Reptiles the 
 
 dominant 
 
 class. 
 
 Bh'ds and 
 
 mammals 
 
 appear. 
 
 Cycads culmi- 
 nate. 
 
 Amphibians 
 
 the dominant 
 
 class. 
 
 Acrogens 
 - culminate. 
 
 Fishes the 
 
 dominant 
 
 class. 
 
 Invertebrates 
 still dominant. 
 
 Vertebrates 
 (Fishes) ap- 
 peared. 
 
 All classes of 
 Invertebrates. 
 
 Evidences of 
 life. 
 
 No evidences 
 of life. 
 
 FiQ. 259.— Section of the Earth's Crust, to illustrate 
 Geologic Time and the Progress of Life. 
 
296 ARCH.EAN SYSTEM OF ROCKS. 
 
 test of established laws of dynamics; and he has formulated the 
 " Planetesimal Hypothesis," * which is the direct opposite of the 
 former hypothesis in essential principles. This postulates a super- 
 ficially cold globe, formed by the slow ingathering of the small, cold 
 particles (planetesimals) which had constituted the earth-moon ring. 
 The atmosphere and the ocean have slowly formed from gases expelled 
 from the earth's interior by earth-contraction, but were not initiated 
 until the earth's gravitational attraction was competent to retain the 
 ejected gases upon its surface. The oceanic stage was reached, how- 
 ever, long before the earth attained its present size. Space does not 
 permit discussion of this interesting subject. But our views concern-, 
 ing a number of geologic problems depend on our conception of earth- 
 genesis, and already it has been necessary to refer to certain principles 
 of the two hypotheses (see pp. 88, 173, 176, 277). 
 
 CHAPTER II. 
 ARCH^AN SYSTEM OF ROCKS AND AUCHjEAN ERA. 
 
 • It is one of the chief glories of American geology to have estab- 
 lished this as a distinct system of rocks and a distinct era. 
 
 It had long been known that beneath the lowest Paleozoic rocks 
 there still existed strata of unknown thickness, highly metamorphic 
 and apparently destitute of fossils. These had been usually regarded 
 as lowermost Palseozoic — as the earliest defaced leaves of the Palaeo- 
 zoic volume. But the study of the Canadian rocks, by Sir William 
 Logan, revealed the existence of an enormous thickness of highly-con- 
 torted, metamorphic strata, everywhere unconformable with the over- 
 lying Primordial or Cambrian. More recent observations show this 
 relation not only in Canada, but also in New York, on Lake Superior, 
 in Nebraska, Dakota, Montana, Idaho, Wyoming, Colorado, TJtah, 
 Nevada, Texas, New Mexico, and Arizona. Nor is it confined to our 
 own country, for the same unconformable relation has been found by 
 Murchison on the west coast of Scotland, between the lowest Cam- 
 brian and an underlying gneiss, evidently corresponding to the Lau- 
 rentian of Canada. Similar rocks, and in similar unconformable rela- 
 tion, have been found underlying the primordial in Bohemia, and also 
 in Sweden and Bavaria, and many other places. Such general uncon- 
 formity shows, great and wide-spread changes of physical geography 
 at this time, and therefore marks a primary division of time. 
 
 * See articles of T. C. Chamberlin in Journal of Geology, vols, y-viii, 1897-1900, and 
 in Tear Book No. 3, Carnegie Institution of Washington, 1905, pp. 195-258. 
 
AND ARCHiEAN EUA. 
 
 297 
 
 The following figures (260, 261, 262) give the relation between 
 the Palffiozoic and the Archaean in New Mexico, in Canada, and in 
 Scotland. 
 
 Fig. 260.— Section across Santarita Moiiutain, New Mexico ; c, Carbuniferous ; S, Silurian ; A, 
 Archsean ; m, metalliferous vein (after Gilbert). 
 
 Archaean and Algonkian Rocks. — The name Archaean is generally 
 used throughout this book for all geologic time before the Cambrian, 
 and for all Pre-Gambrian rocks. But there is a philosophic divi- 
 sion of Pre-Cambrian time partly based on distinctions in the rocks. 
 As long ago as 1852 the Canadian geologists recognized two series 
 of rocks, the lower being called Laurentian and the upper Huronian. 
 
 Fig. 261.— Section showing Cambrian unconformable on the Archa-an : 1, Archsean or Laurentian ; 
 
 2. Cambrian (after Logan). 
 
 According to the usage of the United States Geological Survey, the 
 name Archajan is restricted to a lower series of rocks which yield no 
 evidence of life nor even of sedimentary origin, the upper series being 
 called Algonkian. 
 
 The lower, or Archaean, series is a remarkable complexity of ex- 
 tremely foliated, metamorphic rocks intermingled with injected, mas- 
 
 FiG. 262.— Diagram Section, showing the Structure of the North Highlands, Scotland , a, Archsean 
 Gneiss ; b, Pre-Oambrian ; c, Cambrian ; d, Silurian (Jukes). 
 
 sive igneous rocks. They are often referred to as the " basement com- 
 plex," the name being non-committal as to the origin or date of the 
 rocks. They are certainly the oldest and lowest visible rocks of our 
 globe, and opinion favors the belief that they represent primitive 
 earth-material. But they have been subjected to great mashing or 
 extreme dynamic metamorphism (see pp. 228-235) at great depths 
 within the earth, producing foliation structure, and now appear at 
 the surface in consequence of deep erosion and removal of the over- 
 lying rocks. 
 
298 
 
 ARCHAEAN SYSTEM OF EOCKS 
 
 The Algonhian (corresponding partially to the Hnronian) in- 
 cludes the thick series of more or less metamorphosed sediments, often 
 intricately intermingled with intrusive or igneous rocks, which rest 
 between the fundainental complex (ArchEean) and the overlying Cam- 
 brian. The series is usually unconformable with the rocks both above 
 
 Fig. 263.— Contortion of Laurentian Strata (after Logan). 
 
 and below, but in Canada and ISTew Ei}glan(^ they grade into the un- 
 derlying complex without break. Possibly an original unconformity 
 has been obliterated by metamorphism. 
 
 In some cases the thick Algonkian show very little metamorphism ; 
 and even when altered the beds of quartzite, marble, and iron are 
 believed to prove their sedimentary origin. 
 
 The vast sheets of magnetite and hematite ores in Canada, Lake 
 Superior region. New York, New Jersey, Missouri, and other States 
 
 lie interbedded in metamorphosed Algonkian. These iron-ore beds 
 are sometimes 100 to 400 feet in thickness, and make the Algonkian 
 the " iron period." Figs. 264 and 265 show the mode of occurrence 
 of the iron. The copper of Lake Superior occurs in dikes which cut 
 Algonkian rocks. The thickness of the Algonkian is very great. In 
 the Grand Canon they are 13,000 feet; in the Lake Superior region 
 they are said to have a maximum thickness of 65,000 feet. 
 
 Area in North America. — 1- Archsean and Algonkian strata cover 
 the greater portion of Labrador and Canada, and then, turning north- 
 westward, extend to an unknown distance, but probably to the Arctic 
 Ocean. The area forms a broad V, within the arms of which is in- 
 closed Hudson's Bay. It may be seen on maps, pp. 303 and 303. 
 This is the most extensive area known on the continent. 2. On the 
 eastern slopes of the Appalachian chain undoubted patches are found 
 as far south as Virginia, and a larger area in this region extends to 
 Georgia. This is shown on map, p. 302. 3. In the Rocky Mountain 
 and Pacific Coast ranges extensive lines and areas of outcrop are 
 known, trending in the general direction of the chain, and forming 
 the axis of the great ranges. 4. Several small patches are also found 
 
AND ARCU^AN ERA. 299 
 
 scattered about in the basin of the Mississippi, apparently exposed 
 by erosion. 
 
 Doubtless the Archisan rocks are far more extended, but covered 
 and concealed by other and later rocks. The area mentioned is the 
 area of surface-exposure. 
 
 Physical Geography of Archaean Time. — The fact that all exposed 
 Archaean rocks, and most of the Algonkian, are highly metamorphosed 
 proves that they were once deep-seated or far below the surface. This 
 compels the admission that the visible Archaean rocks, under any 
 theory of their origin, are only remnants of deeply eroded masses.* 
 We do not know to what extent the Archaean areas hdve been cov- 
 ered with post-Archsean sediments, subsequently removed. Many of 
 the minor areas have certainly been brought to view by mountain 
 uplift and erosion in later geologic time. Attempts to outline Ar- 
 chaean geography have not usually given sufficient weight to the fact 
 of vast erosion. The present Archaean exposures give no sufficient 
 basis for any map of that time, and we may believe that the geogra- 
 phy of Archaean time was not at all like the map of the present areas. 
 
 Time represented. — The enormous thickness of these rocks (50,000 
 feet in Canada, and still greater in Bohemia and Bavaria) certainly 
 indicates a very great lapse of time. It is probable that the Archaean 
 era is longer than all the rest of the recorded history of the earth put 
 together; and yet, precisely as in the beginnings of human history, 
 the record is imperfect. 
 
 * According to the nebular hypothesis of earth-origin our globe was fully formed 
 before the surface (epigene) agencies began their work, and all the vast deposits of sedi- 
 mentary origin (clastic rocks), even the most ancient, have been primarily derived by ero- 
 sion from the Archiean land areas. It seems, however, difficult to entirely reconcile this 
 view with all the facts of areal distribution of later strata and the accepted theory of 
 permanence of the continental areas. 
 
 The planetesimal hypothesis (see p. 296) allows a modified view. According to this 
 the ocean began its work long before the earth and moon had attained full size by gath- 
 ering to themselves all the particles of the earth-moon ring. Consequently there were 
 oceanic sediments which were not wholly detrital but were primitive world-stufE. The 
 earlier ocean sediments must have been deeply buried under the later, and now may con- 
 stitute part of the interior mass of the globe. It may be that the globe had attained full 
 size before any of the visible clastic rocks were made. With the water on the earth's 
 surface increasing by supplies from the interior and with matter still being gathered in 
 from the exterior, the depressions of the primitive continents were more or less filled 
 by a mixed class of sediments partly formed from clastic material, partly fromvoleanic 
 and partly from the fragments of incoming planetesimals. There were probably also 
 encroachments of the ocean on the continents as in later times, followed by withdrawals 
 as the ocean basins sank and increased their capacity. >As the decomposition of the 
 elastic material was probably less complete than in later times, froiri lack of vegetal 
 covering and other causes, the mixed sediments when metamorphosed resembled original 
 igneous rock, and it is difScult now to distinguish the metamorphosed elastics from true 
 igneous rock. 
 
300 
 
 ARCHiEAN SYSTEM OF ROCKS AND ARCH^AN ERA. 
 
 Evidences of Life. — We have already explained (p. 150) how iron- 
 ore is at present accumulated by the agency of organic matter. It is 
 almost certain that the same is true for all times, and therefore that 
 iron-ore accumulations are the sign of the existence of organic mat- 
 ter, and the quantity of the ore accumulated is a measure of the 
 amount of organic matter consumed in doing the work. The im- 
 mense beds of iron-ore found in the Algonkian rocks are, therefore, 
 evidence of the existence of organisms in great abundance. The mar- 
 bles and limestones are assumed to be of organic derivation, like all 
 calcareous rocks of the present time; while the abundant, diffused 
 graphite is thought to represent the carbonization of organic tissue. 
 There have been found abundantly in the limestones of Canada 
 and elsewhere, large, irregular, cellular masses, which have been re- 
 garded as the remains of 
 a gigantic foraminiferous 
 rhizopod. The supposed 
 species has been called 
 Eozobn Canadense. In 
 Fig. 266 the white is cal- 
 careous matter, supposed 
 to have been secreted by 
 the rhizopod, and the 
 dark occupies the space 
 of the supposed animal 
 matter. 
 
 The organic origin is 
 not now generally ad- 
 mitted. 
 
 Crustacean remains, 
 resembling Eurypterus 
 (see p. 338), have been 
 found in pre-Cambrian beds of Montana. Some obscure tracings, 
 suggesting the existence of marine worms, have been found in Mon- 
 tana, Canada, and Bohemia; and other bodies believed to be organic 
 have been obtained in the Grand Canon and in Newfoundland below 
 the lowest Cambrian. Eadiolarians, foraminifera, and sponges have 
 been reported from Brittany in rocks of supposed pre-Cambrian age, 
 but these bodies are not now regarded as organic. It is impossible 
 to say that other animals of low form did not exist; yet the prevailing- 
 absence of reliable traces in rocks not more metamorphic than some 
 rock of the next era which are crowded with fossils of many kinds 
 seems to indicate a paucity of skeleton-forming organisms. But the, 
 principles of evolution suggest that all the chief groups of inverte- 
 brate animals must have existed long prior to Cambrian time. 
 
 Fio. 266.— Section of the Base of Specinien of EozoSn, 
 X i. From a photograph. (After Prestwich.) 
 
GENERAL DESCRIPTION. 
 
 301 
 
 CHAPTER III. 
 PALMOZOIG SYSTEM OF ROCKS AND PALEOZOIC ERA. 
 
 General Description. 
 
 This is a distinct system of rqcks, revealing a distinct time-world — 
 a distinct rock-system, containing tlie record of a distinct life-system. 
 The rock-system is distinct, being everywhere tmconformed to the 
 Archman below and the Mesozoic above — a bound volume — volume 
 second of the Book of Time. The life-system is also equally distinct, 
 being conspicuously different from that which precedes and that which 
 follows. Whatever of life existed before, its record is too imperfect to 
 give us a clear conception of its character. But in the Palaeozoic the 
 evidences of abundant and very varied life are clear ; more than 20,000 
 species having been described. It stands out the most distinct era in 
 the whole history of the earth. The Archman must be regarded as the 
 mythical period. Here, with the Palaaozoic, commences the true dawn 
 of history. 
 
 Rocks — Thickness, etc. — The rocks of this system, although less 
 powerful than the preceding, are also of enormous thickness compared 
 with those of later geological times, being in the Appalachian region 
 about 40,000 feet ; in N"evada, about 40,000 feet ; in the Wahsatch 
 Mountains, 33,000 feet (King). But these extreme thicknesses are 
 more local than in the case of the Archaean. It is believed that we are 
 safe in saying that the time represented by them is equal to all subse- 
 quent time to the present. 
 
 There is nothing very characteristic in the rocks composing Palaeo- 
 zoic strata, though the practiced eye may often distinguish them by 
 tbeir lithological character. Though strongly folded and highly meta- 
 morphic in some regions, these characters are not so universal as in 
 the Archeean. 
 
 N 
 
 C ' 1) 'US ' L.S Ca\ A ' 
 
 Fig. 267.— Ideal Section north and eonth from Canada to Pennsylvania: A. Archaean; Ca, Cambrian; 
 Z5.and ZJ 5, Silurian; i), Devonian; (7, Carboniferous. 
 
 In the United States the rocks of the whole system are often con- 
 formable — for example, in New York and in Utah. In Europe, on the 
 contrary, the principal divisions are usually tunconformable. In this 
 country, therefore, the subdivisions are i.fajmded > almost -wholly, on 
 
302 
 
 PALEOZOIC SYSTEM OP EOCES. 
 
 change in the life-system ; while in Europe the same subdivisions are 
 founded on unconformity of the rock-system, as well as change in the 
 life-system. Further, in this country, in passing from Pennsylvania, 
 
 
 through New York, into Canada, we pass over the outcropping edges 
 of the whole system, from the highest to the lowest, and filially on to 
 
GENERAL DESCRIPTION. 303 
 
 the Archaean (Fig. 267). This, taken in connection with the con- 
 formity of the rocks, shows that during the Palaeozoic the continent in 
 this part was successively developed, from the north toward the south, 
 by bodily upheaval of the Archaean area and successive exposure of 
 contiguous sea-bottom. In Europe the oscillations seem to have been 
 more frequent and violent. 
 
 Fig. 367 is a section from Pennsylvania to Canada, showing the 
 relation of the subdivisions to each other, and the manner in which 
 they lie on the Archaean. This will be better understood if the map 
 (Fig. 371) on page 309 be at the same time carefully examined. 
 
 Area in the United States. — The area in the Eastern United States 
 in which the country rock belongs to this system is seen in the map 
 above (Fig. 368). It may be stated roughly to embrace all that part 
 included between the Great Lakes on the north, the Blue Eidge of the 
 Appalachian chain on the east, the Plains on the west, and Middle 
 Alabama and Southern Arkansas on the south. It includes the 
 richest portion of our country. Besides this great continuous area 
 there are also areas of imperfectly known size and shape in the Eocky 
 Mountain region, and on either side of the Sierra Nevada. 
 
 Physical Geography of the American Continent. — At the beginning 
 of the Palaeozoic era (Cambrian) the land was substantially the Archce- 
 
 FiG 269.— Map' of Cambrian Times: Black, existing seas and lakes; light shade, portions of the 
 continent then covered by sea; white areas, then land; when limits doubtful, surrounded by 
 dotted line. In case of area 2 the land extended beyond the present shore-line to an unknown 
 distance, represented by the white dotted line. 
 
 an area, already described, joZms certain areas of Archaean rocks which 
 were then land, but have been subsequently covered by later deposits 
 21 
 
304 PALAEOZOIC SYSTEM OF ROCKS. 
 
 — minus certain Archsean areas which have been subsequently exposed 
 by erosion. The map (Pig. 269) * is an attempt to represent approxi- 
 mately the continent of that time. It consisted (1) of a great Northern 
 land-mass corresponding roughly to the Canadian V- shaped Archaeail 
 area. (2) An Eastern land-mass, including the Appalachian Archaean 
 area, but extending far beyond it to the eastward (for the coast strata 
 here are Cretaceous and Tertiary, resting directly on Archaean, without 
 any Palaeozoic between), and probably beyond the present limits of the 
 continent. This is shown by the white dotted line. It possibly con- 
 nected in North Atlantic region with mass No. 1. (3) A large Western 
 land-mass of unknown shape and size in the Basin region. (4) A 
 large land-mass in the region of the Colorado and Park ranges. There 
 are still other small Archaean areas, but these were probably not land 
 at that time, but have been exposed by erosion. Between these land- 
 masses on the north, the east, and the west, there was an immense sea 
 — the great interior Palceozoic or Mississippian Sea. 
 
 The reason for thinking that the Eastern land- mass was an exten- 
 sive one is the immense thickness of Palaeozoic sediments which ac- 
 cumulated in the sea along its western border. The reason for think- 
 ing that there was a large strip of land in the Basin region is, because 
 in a large part of that region the Mesozoic rocks rest directly and un- 
 conformably on Archaean, the whole Palmozoic being vjanting. 
 
 This was the continent at the beginning of the Palaeozoic era. 
 Prom this as a nucleus the continent somewhat steadily developed 
 until the whole of the Palaeozoic area was added to it, and the con- 
 tinent became perhaps somewhat like that represented on page 486, as 
 the continent of Cretaceous times. In this development the Canadian 
 shore-line advanced steadily southward, but the shore-line of the eastern 
 land mass was almost stationary. This accounts for the great thickness 
 of sediments along that line. 
 
 If we compare the Palaeozoic rocks of the Appalachian region with 
 the same in the central portion of the Mississippi basin, we observe the 
 following changes as we go westward : {a) The rocks in the Appalachian 
 region are highly metamorphic ; as we go westward, they become less 
 and less so, until in the region about the Mississippi Eiver they are 
 wholly unchanged. (5) In the Appalachian region they are strongly 
 folded and faulted; as we go west, the folds pass into gentle un- 
 dulations, which die away into horizontality (see section. Pig. 239, 
 on p. 363). (c) In the Appalachian region they are about 40,000 feet 
 thick; as we go west, they thin out until the whole series is only 
 
 * A map similar to the above, but containing also small scattered patches of Archsean 
 exposures, is sometimes spoken of as an Archcean map of North America, or map of 
 Archaean land. It must be borne in mind, however, that it represents indeed land of 
 Archaean strata, but, for that very reason, not of Archaean time, but of Cambrian time. 
 
THE INTERVAL. 305 
 
 4,000 feet at the Mississippi, (d) In the Appalachian region grits and 
 sandstones and shales predominate greatly over limestones; as we go 
 west, the proportion of limestones increases, until these are i\i% predomi- 
 nating rocks. These four changes are closely connected with each 
 other, and all with the formation of the Appalachian chain, as we have 
 already explained in the chapter on Mountain-Formation (p. 369). 
 
 Subdivisions. — The Palaeozoic era is divided into three ages, which 
 are embodied in three subordinate rock-systems. These ages are each 
 characterized by the dominance of a great class of organisms. They 
 are : 1. The Age of Invertebrates, or sometimes called Age of Mol- 
 lusks, in the Lower Palaeozoic system, including the Cambrian and 
 Silurian ; 3. The Age of Fishes, in the Devonian system ; and, 3. The 
 Age of Acrogens and Amphihians, in the Carboniferous system. These 
 are three chapters in the Paleeozoic volume. 
 
 These three systems are generally conformable with each other in 
 the Palaeozoics of the United States, as we have already shown, but 
 elsewhere they are often unconformable. Before taking up the first in 
 the order of time, viz., the Age of Invertebrates, it is necessary to say 
 something of the interval which in our record separates the Archaean 
 from the Palaeozoic era. 
 
 The Interval. 
 
 We have already seen that the lowest Cambrian lies nnconformably 
 on the upturned and eroded edges of the crumpled strata of the 
 Archaean. We have also shown (page 187) that unconformability 
 indicates always an oscillation of the earth's crust at the observed 
 place. More definitely it indicates an upheaval, by which the lower 
 series of rocks became land-surface, and were at the same time, per- 
 haps, crumpled; then a long period unrecorded at that place, during 
 which the land was eroded and the edges of the crumpled rocks were 
 exposed ; then a subsidence, and the deposit of the upper series of 
 rocks on these exposed edges. Now, oscillation necessitates increase 
 and decrease of land-surface. Evidently; therefore, such increase and 
 decrease of land-surface took place in the unrecorded interval between 
 the Archaean and Palaeozoic eras ; and the length of this unrecorded 
 interval is measured by the amount of erosion which the Archaean un- 
 derlying the lowest Palaeozoic has suffered. We have stated that the land 
 at the beginning of the Palaeozoic era was approximately the Archaean 
 area. The shore-line of the earliest Palaeozoic sea was the line of junc- 
 tion between the Cambrian and Archman (see maps. Figs. 368 and 371). 
 But this was not the shore-line at the end of the Archman time. Evi- 
 dently this shore-line was much farther south ; evidently the land-area 
 was much greater at the end of the Archaean than at the beginning of 
 the Palaeozoic. The Archaean era was closed by the upheaval into 
 
306 
 
 PALEOZOIC SYSTEM OP ROCKS. 
 
 land-surface and the crumpling of the strata of the whole Archaean 
 area, and much more. Then followed an interval of which we know 
 nothing, except that it was of long duration, during which the 
 crumpled Archsan strata forming the then land-surface were deeply 
 eroded. Then, at the end of this interval came a subsidence down to 
 the shore-line already indicated as the Cambrian shore-line, and the 
 Palaeozoic era commenced, its first sediments being of course deposited 
 on the exposed edges of the submerged Archaean rocks. 
 
 I have attempted to illustrate these facts by the following diagrams 
 (Fig. 370), in which the last, e, represents a north and south section of 
 
 Land of Archgean time. 
 
 ■/Trchcearv 
 
 Sea 
 
 Land during Interval. 
 
 — ^^4^;\. 
 
 ■• ^ —J — ^ ■^ ' 
 
 s 
 
 Fig. 270.— Ideal Section, showing liow Unconformity was produced on the Canadian Border: 
 S L, sea-level; sh, shore-line. 
 
 the Archaean and Palsozoics of the Canadian border, and southward to 
 Pennsylvania. The crumpled and eroded strata of the Archtean are 
 seen to underlie unconformably the primordial rocks for some distance 
 south — how far we know not. This is the present condition of things. 
 How it came about is shown in a, b, c, and d. In a, we have the sup- 
 posed condition of things in Archaean times. The position of the land 
 was somewhere northward — we know not where. In i, a large portion 
 of Archaean marginal sea-bottom was raised into land, and at the same 
 time crumpled. In c, the same was eroded, so that the edges of strata 
 were exposed. This was during the interval. ' In d, the land sank 
 again to the Cambrian shore-line, and the Palaeozoic era commenced. 
 During the Palaeozoic the land gradually rose so as to expose sucees- 
 
LOWER PALEOZOIC SYSTEM: AGE OF INVERTEBRATES. 307 
 
 sive sea-bottoms of Cambrian, Silurian, Devonian, and Carboniferous 
 ages. It has remained substantially in this condition ever since. 
 
 We have spoken thus far only of the unconformity of the New 
 York rocks on the Canadian rocks. This phenomenon may be ex- 
 plained, as we have seen, by local oscillations, with increase and de- 
 crease of land-area during the lost interval. But, when we remember 
 that the same unconformity is found in the most widely-separated 
 localities, over the whole area of the United States ; that the Grand 
 Caflon of the Colorado cuts through the Cambrian into the Archaean 
 and we find the same unconformity ; that artesian wells in all parts of 
 the PalsBozoic basin reach the Archaean and find there a sudden change 
 to crystalline rocks and therefore an unconformity — we are forced to the 
 conclusion that the lost interval, as compared with the Cambrian, was 
 probably a continental period — a period of widely-extended land com- 
 posed of Archaean rocks. The whole of this land disappeared by sub- 
 mergence at the beginning of the Cambrian, except the Canadian area, 
 a large area east of the Appalachian, probably a considerable area in 
 the Basin region, another in the Colorado mountain region, and per- 
 haps a few isl-ands or larger areas in the Cambrian seas between, as~ 
 shown in map. Fig. 269. In a word, the Interval was a Continental 
 period between two Oceanic periods. 
 
 In all speculations on the origin of the animal kingdom by evolu- 
 tion, it is very necessary to bear in mind this lost interval, for it was 
 evidently of great duration. 
 
 We have spoken of the Interval as one. But there may have been 
 several. Our knowledge of the pre-Oambrian rocks is too imperfect to 
 allow us to speak confidently. 
 
 Section 1. — Lowek Paljeozoio System (iijoludin'G Cambrian 
 AND Silukian) : Age of Invbetebrates. 
 
 The Rock-System. — The rocks of this age have been carefully 
 studied in England, by Sedgwick and Murchison; in Eussia and 
 Sweden, by Murchison ; in Bohemia, by Barrande ; and in New York, 
 by Hall. The divisions and subdivisions established by these geologists 
 have become the standard of comparison elsewhere. The system was 
 first clearly defined by Murchison in Wales. The name Silurian was 
 given by Murchison to the rocks of the whole age. The name Gam- 
 irian was given by Sedgwick to the lower part. The great thickness 
 and exceptional importance of this lower part have iaduced most 
 geologists to erect this into a distinct system equivalent to the 
 Silurian, and to call it Cambrian, or Primordial. From the point 
 of view of the progress of life, however, they may be united as one 
 Age. 
 
Lower Paloeozoio Age or 
 Age of Invertebrates . . 
 
 308 PALEOZOIC SYSTEM OF ROCKS. 
 
 Subdivisions. — The following table gives the divisions and subdi- 
 visions of the rocks and the corresponding periods of the age in this 
 country : 
 
 ( Manlius Period. 
 
 Upper Silurian •< Salina 
 
 ( Niagara 
 
 T ci-1 • i Trenton 
 
 - Lower Silurian j Canadian 
 
 i Potsdam 
 
 Cambrian or Primordial < Acadian 
 
 ( Georgian 
 
 The larger divisions, viz., Cambrian, Lower Silurian (or Ordovician), 
 and Upper Silurian, are generally recognized. The subdivisions are 
 largely local, each country having its own ; but they are synchronized, 
 as far as possible, by comparison of fossils. 
 
 Character of the Rocks. — The rocks of this age, like nearly all 
 rocks, are greatly disturbed and metamorphosed in mountain-regions, 
 though less so than the Archaean ; but in Sweden and Eussia, and in 
 the valley of the Mississippi, they are found in their original hori- 
 zontal position, and not greatly changed from their, original sedi- 
 mentary condition. 
 
 Area in America. — By turning to the map (Pig. 268) it will be 
 seen : 1. That the Lower Palaeozoic is attached to the Canadian 
 Archaean nucleus as an irregular border on the outer side of the 
 V-shaped area; 2. Again, the Appalachian Archaean region, is also 
 bordered on the west side by a narrow strip of the same ; 3. Also we 
 observe large patches in the interior — one about Cincinnati, another 
 occupying the southern portion of Missouri and northeastern portion of 
 Arkansas, and one in Middle Tennessee;, 4. Also narrow bands on the 
 flanks of nearly all the Eocky Mountain ranges ; 5. Also consider- 
 able areas in the Basin region, the outlines of which are little known ; 
 6. Eecently areas have also been found in Northern California (Diller). 
 
 Physical Geography. — At the beginning of this age, as already said, 
 the land was approximately the Archaean area (Fig. 369). The Lower 
 Palaeozoic, which embraces the great V- shaped Archeean' area on the 
 southeast, south, and southwest, was then the sea-bottom border of the 
 coast of the Cambrian continent. The same rocks bordering the 
 Appalachian Archaean was also then a sea-bottom bordering the Cam- 
 brian continent in that region. It is probable, also, that these rocks 
 in the Eocky Mountain region also border Archaean areas, and these 
 areas represent Cambrian continents, and the Cambrian border the 
 marginal sea-bottom of that time. The other patches mentioned in 
 the interior were probably bottoms of open seas. 
 
 Now, the Cambrian and Silurian areas represent so much of sea- 
 bottoms as were raised into land-surfaces during or at the end of that 
 
LOWER PALEOZOIC SYSTEM; AGE OF INVERTEBRATES. 309 
 
 time, and not subsequently covered by sea.* Therefore, at the begin- 
 ning of that time the land was the Archaean area ; while at the end the 
 land was increased by the addition of the Lower Paleozoic area. This 
 addition was not all made at once, but very gradually. The steps of 
 this increase have been carefully studied in New York. The map 
 (Fig. 371) shows the principal successive steps, as does also the section 
 
 c S sc 
 
 Fig. 271.— Geological Map of New York: a, Archaean; PS, Cambrian; LS, Lower Silurian; US, 
 Upper Silurian; a, Devonian; SC, Sub-Carboniferoue; C, Coal-measares; 2fS, line of section, 
 shown in Fig. 367. 
 
 (Fig. 367) with which it should be compared. Inspection of these 
 figures shows not only the Cambrian and Silurian bordering the Ar- 
 chsean, but the rocks of the several periods bordering each other suc- 
 cessively; so that in walking from Pennsylvania to Canada, or to the 
 Adirondack Mountains of New York, along the line S W, we succes- 
 sively walk over the Carboniferous, the Devonian, the Silurian, Cam- 
 brian, and the Archaean ; and in the Silurian and Cambrian over rocks 
 of the successive periods, from the highest to the lowest. This plainly 
 shows that during this age the continent (Archaean area) was slowly up- 
 heaved, and contiguous sea-bottoms successively added to the land, and 
 .the shore-line gradually pushed southward from the Canadian region, 
 and probably westward from the land-mass along the Appalachian. 
 Of course, therefore, the oldest Cambrian shore-line was the most 
 northern and eastern. This is the primordial ieach. 
 
 * This is true as a broad, general fact ; but patches o| Silurian may also be exposed 
 by removal of later deposits by erosion, 
 
310 PALAEOZOIC SYSTEM OF ROOKS. 
 
 1 
 
 Cambrian System. 
 
 Cambrian Fauna. 
 
 As already stated, the elementary character of this treatise renders 
 it impossible to take up separately the several periods of this age. We 
 must confine ourselves to a general description of the age only. But 
 there is so peculiar and special an interest connected with the dawn of 
 life on the earth, that, before taking up the life-system of the whole 
 age, it seems necessary to say something of the earliest fauna. 
 
 We have seen that at the beginning of Cambrian times a large V- 
 shaped mass of land occupied the region now embraced by Canada and 
 Labrador, and stretched northwestward to an unknown distance, the 
 two arms of the V being nearly parallel to the two present shores of 
 the American Continent ; further, that a land-mass of extent unknown 
 occupied the position of the eastern slope of the Appalachian chain ; 
 also, that land of unknown extent occupied the position of the Eocky 
 Mountains and Basin region ; and the continent was thus early sketched 
 out. Now, southward of the first-mentioned land-area and between the 
 other two there was a great interior sea, which we have called the In- 
 terior Palaeozoic Sea. The waves of that sea beat upon the continental 
 masses north, east, and west, and accumulated, on exposed places, a 
 beach. Patches of that earliest beach still remain. They are found, 
 of course, closely bordering the Archaean rocks, Canadian and Ap- 
 palachian, and lying unconformably upon them. They are the primor- 
 dial sandstones and slates of Canada, N"ew York, Pennsylvania, Vir- 
 ginia, and probably Tennessee and Georgia. The fact that these are 
 indeed remnants of a beach is proved by the existence, in almost every 
 part, of shore-marks of all kinds — such as ripple-marks, sun-cracks, 
 worm-tracks, worm-borings, broken shells, etc. 
 
 This, then, is the old primordial beach. It is of the extremest 
 interest to the geologist because it marks the outline of the earliest 
 Cambrian sea. The deposits of finer materials, shales and limestones, 
 which accumulated off-shore in the more quiet waters contain the 
 fuller representation of the earliest known fauna. It is true that ani- 
 mals probably existed in Archsean times, but these can not be said to 
 constitute a fauna. With the very commencement of Cambrian times, 
 however, we find at once a considerable variety of animal life. 
 
 What, then, was the character of this earliest fauna and flora ? If 
 we could have walked along that beach when it was washed by pri- 
 mordial seas, what would we have found cast ashore ? We would have 
 found the representatives of all the great types of animals except the 
 vertebrata. The Protozoa and lowest Metazoa were then represented 
 by Bhizopods and sponges; the Coelenterates by corals and Hydrozoa 
 
CAMBRIAN SYSTEM: AGE OP INVERTEBRATES. 
 
 3U 
 
 Fig. 281. 
 
 Fig. 283. 
 
 Fig. 278. 
 
 Tioe. 272-282.— Ahukioah Cahbbian FoBBua (after Walcott and White): 272. ProtypoB Hitcbcocki, x 2 
 273. Zacanthoidee typicalis, X 2. 274. Agnostns interstrictus. 275. Fordilla Troyensia. 276. Billings- 
 ella transversa. 277. Kntorgina pannula— o, front view ; o', aide view. 278. Oienellue asaphoioes 
 (after Walcott). 280. Hyolithue primordialis. 281, Lingnlella C8elata. 282. Obolella crasaa. 
 
312 
 
 PALAEOZOIC SYSTEM OF ROCKS. 
 
 (graptolites) ; the Bchinoderms by Cystidean Vrinoids ; the Mollusks by 
 Brachiopods (Figs. 376, 377, 381, 283, 385, 388, 389), Lamellihranchs 
 (Figs. 375, 387), Gasteropods (Pleurotoniaria), Pteropods (380, 386), 
 and even Oephalopods (orthoceratites) ; the Arthropods by Crustacea 
 (trilobites and phyllocarids, 373, 373, 374, 378, 390, 391); and ihe Worms 
 by tracks and tv,bes (Fig. 384). Plants were represented by Fucoids 
 (Pig. 383). These widely-distinct classes are already clearly differ- 
 entiated and somewhat highly organized. Nor is the fauna a meager 
 
 Fio 283. 
 
 Fig. 286. 
 
 Fig. 289. 
 
 Fig. 291. 
 
 Fios. 283-291.— Foreign Cambkian Fossils: 283. Oldhamia antiqna, probably a plant. 284. 
 Arenicolites didymus, worm-tubes. 285. Lingnlella- ferniginea. 286. Theca Davidii. 287. 
 Mpdiolopsis Bolvenais. 288. Obolella Hicksii. 289. Orthis sagittalis. 290. Hymenocaris venni- 
 cauda. 291. Olenns macruras. 
 
 <)ne in number of species. In the United States and Canada alone 
 about 400 species are already known in the Cambrian, of which nearly 
 100 are trilobites j and in the lowest zone of the Cambrian, viz., 
 Olenellus beds, there are 141 species, of which 51 are trilobites (Wal- 
 cott). About a dozen species of plants are also known. When we 
 recollect the great age of these rocks and their usual metamorphism, 
 and the fragmentary character of all fossil faunas, it seems certain that 
 great abundance and variety of life existed already in these early 
 seas. Of this life the trilobites, by their size, their abundance, their 
 variety, and their high organization, must be regarded as the dominant 
 type. Among the largest trilobites known at all are some from this 
 period. The Paradoxides, represented in Figs. 393 and 393, attained 
 a length of twenty inches. English beds of the same age furnish 
 specimens of the same genus nearly two feet long. 
 
 We give in the above figures a few of the more remarkable pri- 
 mordial forms taken from the rocks of this country, and of foreign 
 
CAMBRIAN SYSTEM: AGE OF INVERTEBRATES. 
 
 313 
 
 Fig. 292.— Paradoxides Bo- 
 hemicus, Foreign. 
 
 Fio. 293.— Paradoxides Har- 
 lani, X i (after Kogers), 
 American. 
 
 countries. They are intended only to give a general idea of the full- 
 ness and variety of the primordial life; the affinities of these fossils 
 will be discussed hereafter. 
 
 General Remarks on 
 First Distinct Fauna.— 
 There are several points 
 of great philosophic in- 
 terest suggested by the 
 nature of these first or- 
 ganisms : 
 
 1. Plants in this, and 
 most other geological 
 periods, are far less nu- 
 merously represented in 
 a fossil state than ani- 
 mals. This can not be 
 because animals were 
 more abundant than 
 plants, for since the 
 animal kingdom subsists on the vegetable kingdom, and since every 
 animal consumes many times its own weight of food, plants must have 
 been always more abundant than animals. The true reason of the 
 greater abundance of animal remains is to be found in the fact that 
 the hard parts of animals are far more indestructible than any por- 
 tion of vegetable tissue. 
 
 2. At the end of the Archaean times — when the Archaean volume 
 closed — ^we have only obscure traces of a few types of lowly life. But 
 with the opening of the next era, apparently with the first pages of 
 the next volume, we find already all the great types of structure except 
 the vertebrata. And these are not the lowest of each type, as might 
 have been expected, but already trilobites among Arthropods, and 
 Cephalopods among MoUusca — complicated animals which evince 
 great progress from the primitive condition. 
 
 We must not hastily conclude, however, that these widely-divergent 
 and highly-organized types originated together at once. We must re- 
 member that between the Archaean and Palaeozoic there is a lost inter- 
 val of enormous duration. Evidently, therefore, the Cambrian fauna 
 is not the actual first fauna. Evidently we have not yet recovered the 
 leaves in which is recorded the gradual differentiation of these widely- 
 distinct types. All this must have taken place during the lost interval. 
 
 But if, on the Other hand, we suppose, as many do, that evolution 
 proceeds always " with equal steps," then we are forced to the very im- 
 probable conclusion thai the lost interval is equal to all geological times 
 which followed to the present; for the differentiation of types which 
 
314 PALAEOZOIC SYSTEM OF KOOKS. 
 
 occurred during that interval is equal in value to all that has taken 
 place since. 
 
 Therefore, vre are compelled to admit that there have been in the 
 history of the earth periods of rapid change in physical geography, 
 and periods of comparative quiet in this respect; that, corresponding 
 with these, there have been also periods of rapid evolution of the 
 organic kingdom, developing new forms, and periods in which forms 
 ar£ more stationary. The periods of rapid change are marked by 
 unconformity, and are therefore unfortunately often lost.* 
 
 As we proceed, we will probably find many examples of rapid 
 change which must be accounted for in a similar manner. 
 
 Silurian System. 
 Life of Silurian Times. 
 
 There were evidently extraordinary abundance and variety of life 
 in the Silurian. These early seas literally swarmed with living beings. 
 The quantity of life— the number of individuals — was probably not 
 less than at the present time; though orders, classes, and departments 
 were less diversified. Over 10,000 species have been described from 
 the Silurian alone (Barrande) ; and these must be regarded as only 
 a part of the actual fauna of the age. In certain favored localities, 
 the number of species found in a given area of a single stratum will 
 compare favorably with the number now existing in an equal area 
 of our present sea-bottoms. Yet, in all this teeming life there are 
 very few species identical with any found in any other geological 
 time. And not only are the species peculiar, but even the genera, 
 families, and orders are largely different from those now existing. 
 
 We can give only a very brief sketch of this early life, touching 
 only the most salient points, especially such as throw light on the 
 great question of evolution. 
 
 Plants. 
 
 With the exception of a few fragments, doubtfully regarded land- 
 plants, ferns, and club-mosses, found in the Silurian of both this coun- 
 try and Europe, and of which we shall speak again, the only plants 
 
 * In spite of every allowance the suddenness of the appearance of the first fauna is 
 extraordinary. In this connection, Brooks (Jour. Geo)., vol. ii, p. 465, 1894) has thrown 
 out a very suggestive thought. He gives reasons for thinking that the first forms of life 
 were pelagic, floating freely in the open sea, of gelatinous ponsistence, and therefore not 
 preserved. Food was abundant (microscopic plants), struggle for life not severe, and 
 therefore there was little differentiation of forms. About <;he beginning of the Cambrian 
 there was a discovery of the bottom, especially near shore. Now support was necessary, 
 and therefore hard parts were formed and thus they were presei-ved. Now also they 
 became crowded, struggle and competition became severe, and differentiation into main 
 types commenced. 
 
GENERAL LIFE-SYSTEM OF THE SILURIAN. 
 
 315 
 
 yet found are low forms of cryptogams, viz., marine algm or sea- 
 weeds. It is difficult, from the impressions left by these, to determine 
 
 Fig. 2'J4. 
 
 Fig. 296. 
 
 Fig. 895. 
 
 Fio. 297. 
 
 Fig. 298. 
 
 Figs 294-298.-Sii.ubian Plants (after Hall): 249. Biithotrephis succulens. 395 and 296. Butho 
 trephis^acilis. 297. ArthrophycuB Harlani. 298. Buthograptus laxus (after Whitfield). 
 
316 
 
 PALAEOZOIC SYSTEM OF ROCKS. 
 
 genera, much more species, with any degree of certainty. We shall, 
 therefore, call them by the general somewhat indefinite name of Fiv- 
 coids {Fiicus, tangle or Kelp), or Pucus-like plants. As already stated, 
 plants are far less abundantly and perfectly preserved than animals, on 
 account of their want of a skeleton. A few characteristic forms are 
 given in Figs. 394-298. 
 
 Animals. 
 Sponges and Hydrocorallines.— The irregular masses called Eozoon 
 seem entirely characteristic of Archaean times. If they are indeed of 
 
 animal origin, they 
 are replaced in the 
 Lower Palasozoic by 
 more regular forms 
 which were usually 
 called sponges. Of 
 these, the most char- 
 acteristic Silurian 
 genera are Stroma- 
 topora and Recepta- 
 culites (Pigs. 299- 
 305). They seemed 
 to have formed large 
 coralline masses, 
 which are now re- 
 garded either as hy- 
 drocorals (Stroma- 
 topora) or as sponges 
 (Receptaculites). 
 
 Corals. — Corals were very abundant, forming often whole rock- 
 masses, as if they, while livings formed reefs. These, if they indicate 
 warm seas, show a great uniformity of temperature, since they are 
 found in all portions of the earth alike. 
 
 The corals of this age belong principally to three families, viz., Cy- 
 athophylloids, or cup-corals ; Favositidm, or honey-combed corals j and 
 HalysitidcB, or chain-corals. They are remarkable in not usually being 
 profusely and widely branched like most modern corals, but consist- 
 ing mostly of masses of parallel or nearly parallel columns. In Cyatho- 
 phylloids (Figs. 306-308) the corals are sometimes separate and of a 
 horn-like form, and sometimes aggregated in large, rough, columnar 
 masses (Rugosa). Their upper portions are cup-shaped, and the radi- 
 ating lamince are very distinct. In Favositids (Pig. 309) the hexagonal 
 parallel columns are divided somewhat minutely by horizontal plates 
 (Tabulata) (Fig. 309, a), giving a cellular structure which may be fine< 
 
 Fig. 299.— Stromatopora rugosa. 
 
SILUEIAX ANIMALS. 
 
 31Y 
 
 or coarser. The Halysitids (Fig. 311) seem to be made up of small, 
 hollow, flattened columns with imperfect septa, united to form reticu- 
 lating fluted plates, which on section have the appearance of chains 
 
 1 
 
 'i 
 
 
 Fio. 304. 
 
 Fig. 303. 
 
 Fig. 305. 
 
 Figs 30O-305.— Silubian Htdrocokallines and Spongtss : 800. Stromatcpora concentrlca. 301. 
 Section of same. 303. View from above (after Hall). 303. Kcceptaculites fnrmosns (after 
 Worthen). 304. Diagrairi showiug structure of Eeceptaculites (after Nicholson). 305. Brachic 
 spongia digitata, x } (after Marsh). 
 
318 
 
 PALEOZOIC SYSTEM OF EOCKS 
 
 crossing in all directions. These are also minutely tabulated. The 
 
 Syringoporoids (Fig. 310) are 
 
 similar to the Halysitids, except S.'^ltl ///'*''**' 
 
 that the hollow columns are S ^^%Mbrf 
 
 cylindrical and connect with ^ '7^ 
 
 each other only in places. . . , . 
 
 FiQ. 306. 
 
 Fig. 308. 
 
 Pigs. 396-308.— Ctathophtlloid Cobam : 306. Lonsdaleia florif ormis (after Nicholson). 307. o 
 and ft. Zaphrentis bilateralis (after Hall). 308. Strombodes pentagonus (after Hall). 
 
 Fio. 310. 
 
 ->■;'. 
 
 
 Tin. 309. 
 
 Figs. 309-311.— Favositid akdHaltsitid CoBALs: 309. Columnaria alveolata: a, vertical; 6, cross- 
 section (after Hall). 310. Syringopora vertlcillata. 311. Halysites catenulata (after Hall). 
 
SILURIAN ANIMALS. 
 
 319 
 
 Pis. 312. 
 
 Some of the more characteristic species of these families are given 
 above (Figs. 306-311). 
 
 There are many other forms than those mentioned above, but their 
 affinities are little understood, and many are not true corals, but Bryo- 
 zoa and sponges. 
 Nearly all the cor- 
 als of Silurian, in 
 fact, of Palseozoic 
 times, fall under 
 two orders — Rugo- 
 sa and Tabulata. 
 The Cyathophyl- 
 loids are Rugosa, 
 the other families 
 mentioned are Tab- 
 ulata. The Eugo- 
 sa are characteris- 
 tic of the Palaeo- 
 zoic; the Tabulata 
 are also nearly ex- 
 tinct: they have 
 only one family liv- 
 ing, viz., the milli- 
 pores. The Eugosa 
 differ from modem 
 star-corals in hav- 
 ing their radiating 
 septa in multiples 
 of four, while 
 modern star-corals pieg. 3i2_3]4. 
 have theirs in mul- 
 tiples of five or six. 
 Hence star-corals have been divided into two types — a Paleozoic and 
 a Neozoic — the one four-parted (quadripartita), the other six-parted 
 (sexpartita). The latter, however, are known to be quadripartite 
 in early growth stages. Halysitids are characteristic of Silurian; 
 Pavositids, of Silurian and Devonian; and Cyathophylloids, of the 
 PalcBOzoic. 
 
 Hydrozoa. — The perfect forms of this class, viz., Medusae, or jelly- 
 fishes, are so soft and perishable that they could hardly be expected to 
 be preserved as fossils. Nevertheless they occur in Mesozoic rocks, 
 and supposed impressions have' been found even in the lowest Cam- 
 brian (Olenellus zone).* But the incomplete generation of many-Me- 
 
 * Walcott, Tenth An. Rep., V. S. Geol. Surv., p. 587 ; Monograph 30, tj. S. G. S. 
 22 
 
 Fig. 313. 
 
 Living Htdrozoi ; 313. a, Sertularia pinnata; a', 
 same, enlarged ; b, Campanularia. 313. a and b, Different Forms 
 of Sertularia> 314. Flumularia. 
 
320 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 
 dusas is a compound polypoid animal, forming a minutely-branching, 
 horny, or coralline axis. These minutely-branching axes are strung on 
 
 one or both sides with 
 cells, in which are in- 
 closed little polypoid 
 animals. They grow 
 in 'still, quiet waters, 
 and are often mistaken 
 by the unscientific for 
 sea -weed. These, by 
 their composition, are 
 well adapted for pres- 
 ervation, and it is this 
 larval form, therefore, 
 only that we might ex- 
 pect to find. Kgs. 312- 
 314 are examples of liv- 
 ing forms. 
 
 Now, in very fine 
 shales of Silurian and 
 Cambrian age are found 
 abundantly beautiful 
 impressions of an or- 
 ganism which is most 
 probably a compound 
 Hydrozoan allied to 
 Sertularia of the pres- 
 ent day. They are called 
 graptolites. Sometimes 
 the cells are arranged 
 on one side of the axis, 
 sometimes on both sides, 
 sometimes the axis is 
 divided. Whatever be 
 their affinities, they are 
 of great importance, in- 
 asmuch as they are en- 
 tirely characteristic of 
 this age, and those with 
 cells on loth sides, of 
 the upper half of the 
 The 
 twin graptolites (Fig. 
 317) are also wholly 
 
 Fia. 315. 
 
 Fig. 336. 
 
 ''^^^^^ f^^^^^^^^l 
 
 Fig. 317. 
 
 Fig. 319. 
 315. Diplograptus pristis (after Lower Silurian 
 
 Fio. 318. 
 
 FiGB. 315-319.— Gbaptolites : 315. Diplograptus pi 
 
 Nicholson). 316. Phyllograptnatypus (after Hall). 317. Did- 
 
 - ymograptus quinquefractus (after Nicholson). 318. Dicho- 
 graptus Logani, basal part (after Hall). 319. Monograptus 
 priodon: a, side view; b, back view; c, front view. 
 
SILUKIAN ANIMALS. 
 
 321 
 
 characteristic of Lower Silurian. In Figs. 315 to 321 we give some 
 examples of these characteristic Silurian forms. 
 
 Fig. 320. Fio. 321. 
 
 Figs. .320, 321.— Graptolitbs: 320. Diplograptus, Utica Shale, New York (after Kuedemann). 321. 
 Monograptns ClintonenBis (after Hall). 
 
 Bryozoa. — There are many kinds of compound coralline animals, 
 allied to the Bryozoa (sea-mats) (Fig. 332) of our present seas, found 
 in the Silurian. The difficulty to the 
 student of separating them sharply from 
 certain forms of true corals on the one 
 hand, and from certain forms of grapto- 
 lites on the other, seems to require their 
 notice in this connection, although their 
 aiRnities are moUuscoid (see page 325). 
 Two of the Silurian forms are represent- 
 ed in Figs. 323 and 324. 
 
 EcMnoderms. — During Silurian times 
 the class of Echinoderms was represent- 
 ed principally hy Crinoids. A Crinoid 
 is a stemmed Echinoderm, usually with 
 branching arms. The animal consists 
 of a long jointed stalk, rooted to the sea-bottom, and bearing atop a 
 rounded or pear-shaped body, covered with calcareous plates (calyx), 
 from the margin of which spring the arms, which may be long and 
 profusely branched, or short and simple, or absent altogether. In the 
 middle of the calyx, between the bases of the arms, is placed the 
 mouth. Their general structure and appearance will be better under- 
 stood by examination of the following figures (325-327) of living 
 Crinoids. 
 
 At present, leaving out the Holothurians, or sea-cucumbers, which, 
 having no shell, are little apt to be preserved as fossils, the class of 
 Echinoderms may be conveniently divided into three orders, viz. : the 
 Echinoids, or sea-urchins; the Asteroids, or star-fishes; and the Cri- 
 
 FiG. 322.— Living Bryozoa. Flnstratrnn- 
 cata: a, natural size; by enlarged to 
 show the cells. 
 
322 
 
 PALJSOZOIC SYSTEM OF ROCKS. 
 
 noids. The members of the first and second orders are free moving, 
 while those of the third are stemmed. Of these orders the Crinoids 
 
 3 
 
 \ . 
 «■",■ 
 
 FiQ. 334. 
 
 Pio. 323. 
 
 Figs. 323 and 324.— Silurian Brtozoa: 323. Feneetella elegans {after Hall). 324. Stomatopora 
 
 auloporoides (alter Hall). 
 
 are the lowest, as proved not only by their simpler organization, bnt 
 also by the fact that a living Crinoid, the Oomatula or Antedbn (Fig. 
 337), is attached when young, but free when mature. 
 
 Now, during this age the 
 stemmed Echinoderms are 
 very abundant, while the free 
 are very rare : at the present 
 time, on the contrary, the re- 
 verse is the case. Thus, in 
 the course of time, the for- 
 mer decreased until they are 
 now almost extinct, while the 
 latter increased until they are 
 now very abundant. If we 
 take the abundance of Echino- 
 derms during geological times 
 as constant, and represent the 
 course of time by the absciss 
 A B (Fig. 338), and the abun- 
 Pentacrinus dance by distance from A B 
 to CD, then the parallelogram 
 would represent this fact. If, now, we draw the diagonal, C B, then 
 the shaded triangle would represent the stemmed, and the unshaded 
 the free, and the diagonal the line of decrease of the one and increase 
 of the other; and the whole figure the general relations of the two 
 
 Fig. 325. 
 
 Figs. 325 and 3315.— Living Ckinoids 
 Lofotensis (after Thompeon). 
 Caput-Medusae. 
 
 Fig. 326. 
 
 325. Rhizocrinus 
 
SILURIAN ANIMALS. 
 
 323 
 
 sub-classes throughout time. In the Paleeozoic the stemmed predomi- 
 nate; in the Mesozoic the two are equally represented; in modern 
 times the free predominate. 
 
 Fio. 327. — A Living Free Crinoid -Comatiila (Antedon) Tosacea, tlie Featlier-Star: a, free adult; J, 
 
 fixed young (after Forbes). 
 
 Stemmed Echinoderms, or Crinoids, may be divided into three fami- 
 lies, viz. : 1. Crinids ; 2. Cysiids j 3. Blasioids. Crtw«?s are the typic- 
 al Crinoids, with branching arms (brachiate), already illustrated from 
 living examples (Pigs. 325-327). Cystids (Figs. 329-332) are of a 
 iladder-like form (hence the name), and are either without arms, or 
 else haYe few, short, simple arms springing from near the center of the 
 upper part of the body, the mouth being probably on one side 
 (abrachiate). The radiated structure in these is imperfect. Blastoids 
 (Gr. pxluTTo';, a lud) had a bud-shaped body, with five petaloid spaces 
 
 ^____ PALAEOZOIC 
 
 '^'Silurian DeuonS Carionif^ 
 
 CYST OS 
 
 TO as 
 
 NEOZOIC 
 
 D S 
 
 KCH INOIDS 
 
 O ^ 
 
 STEM M ED 
 
 Fio. 328.— Diagram allowing the Distribution in Time of the Class of Echinoderms. 
 
 (ambulacra) radiating from the top and reaching half-way down the 
 body (see Pigs. 530 and 531, page 407). If Crinids are comparable to in- 
 verted Star-fishes with many arms and set upon a stalk, the Cystids and 
 
324 
 
 PALAEOZOIC SYSTEM OF KOCKS. 
 
 Blastoids' may be compared to Sea-urchins similarly set. All these 
 families are found in the Cambrian and Silurian. The Cystids pass 
 away almost entirely with the Silurian, and may be regarded therefore as 
 characteristic of this age. The Blastoids pass away before the end of 
 the Carboniferous^age, and are therefore characteristic of the Palaeozoic 
 
 Fig. 333. 
 
 Fio. 334. 
 
 Figs. 329-334.— Silckian Cbinoids: 329. Caryocrinus ornatus. 330. Plearocystites squamoens 
 331. Paeudocrinus— a cystia restored (after Liltken). 332. Lepadocrinus Gebhardi. 333. Glyp- 
 tocnnuB dccadactylus (after Hall) : a, specimen with arms ; 6, larger specimen without the 
 arms. 334. Ichthyocrinus subtevis (after Hall). Figs. 329-338 are cystids. 
 
 era, but especially of the Devonian and Carboniferous ages. The dis- 
 tribution of the three orders in time is shown'in diagram (Pig. 338). 
 The Crinids continue, thongh in diminished numbers, to the present 
 day; but of course in very different families. Figures of Blastoids 
 are given under the Carboniferous, where they were far more abun- 
 dant. 
 
SILURIAN ANIMALS. 
 
 325 
 
 Fio. 337. 
 
 Pig. 339. 
 
 Fis. 338. 
 
 Figs. 335-339.— Siltihian Crinoids and Astkroids: 335. MariacriDus nobiliesimus (after Hall). 
 336. Homocrinus scopariue (after Hall). 337. Heterocrinus simplex (after Meek). 338. Protas- 
 ter Sedgwickii. 339. Palseaster SlisefEeri (after Hall). 
 
 Molluscoidea. — Bryozoa. — These are compound, coralline animals 
 represented by the sea-mats of our present seas (Fig. 333). They 
 grow in colonies, scores and hundreds of individuals on one frond, and 
 in general appearance are like some of the hydrozoans. The Bryozoan 
 animals are minute, protruding from the cells a horseshoe-shaped pair 
 of arms crowned with cilia, by the movement of which food currents 
 are set in motion toward the mouth. Because of this structure and 
 some other anatomical features the Bryozoa are regarded as primitive 
 or degenerative Mollusks. Figs. 323, 334 show two Silurian forms. 
 
 Brachiopods. — These are bivalved shells, but are unlike the La- 
 mellibranchs (clams, oysters) in having these valves unequal, while in 
 
326 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 the latter they are equal. The valves of the Brachi- 
 opod are upper and lower; in the Lamellibranchs 
 they are right and left. Some naturalists have re- 
 garded the Brachiopods as a distinct departure from 
 the molluscan type and ally them with the Worms. 
 
 
 
 Pio. 340. — Lingala 
 anatina, showing 
 the muscular pedi- 
 cle by which the 
 shell is attached. 
 
 Fio. 341.— Ehynchonella sulcata: side view, dorsal view, and end view, 
 showing suture. 
 
 Brachiopods are abundant in the Cambrian^ and still 
 more so in the Silurian. About 3,000 species are 
 known from the Silurian alone. 
 
 General Description of a BracMopod. — A Brachi- 
 opod shell consists of two valves, a dorsal and a ven- 
 tral. The ventral 
 
 is the larger, and 
 usually projects 
 beyond the dorsal, at the hinge, 
 as a prominent beak. This pro- 
 
 FiG. 343. Pia. 344 
 
 Figs. 342-344.— Showing the Struotuhe of Brachiopods; 842. Spirifer striatns (Oarhoniferons): 
 o, dorsal surface; b, mtenor showing the shelly sjiirals. 343. Magellania flavescens (living 
 species): a. exterior surface ; 6, showing calcareous "loop " for attachment of spiral arms. 343. 
 Spinfer hystericus (Devonian) : a, exterior; A, showing bony spires. 
 
SILURIAN ANIMALS. 
 
 327 
 
 jeeting portion is often open to give passage to a muscular pedicle, 
 by which the shell is attached in the living animal. The following 
 figures (Figs. 340-348) of Brachiopods, living and extinct, will make 
 these points clear. 
 
 The viscera of a Brachiopod fill but a small space in the shell, this 
 cavity being occupied principally by two long spiral arms (hence the 
 name), which probably subserve the functions of respiration and ali- 
 mentation. These arms are attached to a curious shelly apparatus, 
 sometimes in loops (Fig. 343) and sometimes itself spiral in form (343 
 and 344). Figs. 342-344 show the internal structure described above. 
 
 In the present seas the Lamellibranchs are extremely abundant 
 while the Brachiopods are nearly extinct, being represented by com- 
 paratively few species. In Silurian times, on the contrary, the very 
 reverse is the case, bivalve shells being represented mostly by Brachi- 
 opods. 
 
 The abundance of individuals and the number of species of this 
 class in Silurian times are almost incredible. The accompanying fig- 
 ures represent some of the common and characteristic forms. 
 
 It is very difficult to give any general distinctive mark of Silurian 
 Brachiopods, although, of course, the species and even the genera are 
 peculiar, and may be recognized by the palae- 
 ontologist. It may be said, however, that the 
 straight-hinged or square-shouldered Brachi- 
 
 Fio. 345. Pig. 346. Fig. 347. 
 
 Figs. 345-347.— Silurian Brachiopods: 345. Orthis Davidsoui. 346. Orthis Porcata. 347. Pen- 
 
 tameruB Enighti. 
 
 opods, including the Spirifer family, the Orthis, Strophomena, Lep- 
 tsena, and Productus families are characteristic of the PalsBOzoic, 
 though not of the Silurian. 
 
 Lamellibranchs.^We have said that Lamellibranchs are also found 
 in the Silurian and even the Cambrian, but not so abundantly as 
 the Brachiopods. Lamellibranchs are divided into Monomyarians, 
 having one muscle to draw the valves together, and Dimyarians, hav- 
 ing two such muscles. At present the Monomyarians are common 
 (oyster), but they are less ancient than the other tjrpe. The accom- 
 panying figures (349-353) are examples of Silurian Lamellibranchs. 
 
328 
 
 PALAEOZOIC SYSTEM OP ROCKS. 
 
 Gasteropods — Univalves. — Land and fresh-water Gasteropods have 
 not been found in the Silurian. If we divide marine Gasteropods 
 or univalves into those having beaked shells and those having 
 
 smooth-mouthed or beakless shells, the 
 former being carnivorous and the lat- 
 ter herbivorous, then only the smooth- 
 mouthed or beakless shells have been 
 found in the Silurian. The beak-shelled 
 are usually regarded as the more highly 
 organized class. 
 
 FiQ. 348. 
 
 Fio. 349. Fig. 350. Fia. 351. Fio. 352. 
 
 Pias. 348-352.— SilubiastLambllibrakchs: 348. Orthodeema parallelum. 349. Actinopteria com- 
 munis (after Hall). 350. Prolobella Trentonensis (after Hall). 351. AmboDychia bellistnata 
 (after Hall). 352. Tellinomya curta (after Hall). 
 
 Pteropods. — These are small bodies, whose shell is often a long, 
 tube-like cone. The " foot " is developed into a kind of sail, and they 
 are adapted to a life at the surface of the open ocean. In the Palseo- 
 
 FiG. 354. 
 
 Fia. 356. 
 
 FiGB, 353-356. — Silurian Gasteropods; 353. Pleurotomaria dryope. 354. Pleurotomaria agave. 
 355. Polenmita scamnata, Hall (after Clarke). 356. Murchisonia gracilis. 
 
 zoic they were at times extraordinarily abundant, composing entire 
 rock layers (Styliola). They were present in the Cambriaji (Hyoli- 
 thus). Conularia (Fig. 360), commonly referred to the Pteropods, is 
 thought to be allied to the Cephalopods. 
 
SILURIAN ANIMALS. 
 
 329 
 
 Cephalopods— C/iam&ere^ Cells.— These are by far the most 
 highly organized of MoUusks, and the most powerful among Inver- 
 tebrates. They are represented in the present 
 seas by the Nautilus, the Squids, and the Cuttle- 
 fishes. If we divide all known Cephalopods, liv- 
 ing and fossil, into Dibranchs (two-gilled) and 
 Tetrdbranchs (four-gilled), the former being 
 naked and the latter shelled, then, at the present 
 
 Fig. 357. 
 
 Fig. 358. 
 
 Fig. 359. 
 
 Fig. 360. 
 
 Figs. 357-360.— Silurian Gastbkopods: 357. Cyrtolites compressns (after Hall). 358. Trematono- 
 tus algheus, Hall (after Clarke). 359. Conradella Dyeri (after Meek). 360. Conularia Tren- 
 tonensiB (after Hall), a Pteropod. 
 
 time, the Dibranchs, or naked, vastly predominate, there being only 
 a single genus of shelled or Tetrabranchs known, viz., the Nautilus, 
 and of this genus only three or four species. In the Silurian age, 
 and for many ages afterward, only the shelled existed. The naked 
 or Dibranchs are more specialized in organization. 
 
 Again, if we divide chambered shells into those having simple 
 septa and central or subcentral tube or siphuncle (Nautiloid), and 
 those having septa plaited at their junc- 
 tion with the shell '(plaited suture) and 
 ventral * tube (ammonoid), then in this 
 age the former only were represented. 
 
 Again, if we divide the Nautiloids 
 into siratgi^ it-shelled and cotZeif -shelled, 
 then the straight chambered shells 
 greatly predominated. Straight cham- 
 bered shells are called Orthoceratites 
 (op^ds, straight; xepas, horn). The 
 Orthoceratites, therefore, are a very 
 striking feature of the Silurian age. 
 They may be defined as straight chambered shells, with simple su- 
 tures and a central or subcentral siphon-tube (siphuncle). The 
 siphuncle of the family was large in proportion to the shell, and 
 had often a beaded structure (Fig. 363, a, b, c, d). 
 
 They existed in great numbers, and attained very great size. Speci- 
 mens have been found fifteen feet long, and eight to ten inches in 
 
 Fig. 361.— Pearly Kautilus (Nautilus 
 pompiliue): a, mantle; b, its dorsal 
 fold; c, hood; o, eye; t, tentacles; 
 /, funnel. 
 
 * The outside of the whorl is usually called dbrsal, but it is now known to be ventral. 
 
330 
 
 PALJSOZOIC SYSTEM OF ROCKS. 
 
 diameter. They were, without doubt, the most powerful animals of 
 that time, the tyrants and scavengers of these early seas. We give in 
 
 Fig. 363. 
 
 Fig. 363.— Showing Structure of Orthoceratite: a, Honnoceras; ft, Actiiloceras; c, Huronia; d, Sec- 
 tion of Sipliuncle of Huronia. 
 
 Fig. 303.— Eestoration of Orthoceraa, the shell being supposed to be divided vertically, and only its 
 upper part being shown : a, arms; /, mnscular tube ("funnel") by which water is expelled from 
 the mantle-chamber; c, air-chambers; g, siphuncle (after Nicholson). 
 
 Fig. 363 a restoration of the creature. They are entirely character- 
 istic of the Palaeozoic; commencing in the Cambrian, extending 
 through into the Carboniferous, and rare afterward. They attained 
 their maximum of development in size and number in the Silurian. 
 
 I^SjE^-gt-it-^';-- '-■^•' ~-~ T-- 
 
 Fia. 364.— SiLUBiAif Cephalopod : Orthoceras mednllare (after Meek). 
 
 Although straight chambered shells (Orthoceratites) are mostabun- 
 dant and characteristic, and also the earliest, coiled shells of the same 
 tribe (Nautiloids) are also found, and some of them of considerable 
 
SILUBIAN ANIMALS. 
 
 331 
 
 size, but not until the upper Silui'ian. Some of these are close-coiled 
 shells, true Nautilus family ; others open- coiled, and more nearly allied 
 
 Fig. 365. 
 
 Fig. 366. 
 
 Fig. 368. 
 
 Figs. 365-368.— Silurian Cephalopods: 365. Honnoceras tenuifllum, showing chambers and si- 
 phuncle (after Hall). 368. Orthoceras vertebrale (after Hall). 367. Orthoceras multicameratum 
 (after Hall). 368. Orthoceras Uuseri (after Hall). 
 
 to the straight. The gradual change from the straight through the 
 open-coiled to the close-coiled may be traced. It is a most significant 
 fact that the Nautilus in its embryonic development passes through 
 all these stages — i. e., it is first straight, then bent, then open-coiled, 
 and finally close-coiled (Hyatt). Barrande gave 1,623 species of 
 Cephalopods in the Silurian, and the number has been increased. 
 
332 
 
 PALAEOZOIC SYSTEM OF ROCKS. 
 
 Pig. 371. 
 
 Fig. 370. 
 
 Flos. 369-371.— SiLUBiAN Cbphalopods: 369. Trocholites ammoniuB (after Hall): a, exterior; J, 
 cast, showing septa. 370. Lituites graf tonensis (Meek and Worthen). 371. Lituites cornu-arietis. 
 
 Worms. — These are fleshy animals without skeletons, and are there- 
 fore not preserved. They are known only by their trades, their hor- 
 ings, their tubes, and, more rarely, their jaws. Nevertheless, some 
 185 species, according to Barrande, have been described from the 
 Silurian of different countries. Fig. 372 represents worm-tubes. Fig. 
 373 worm-tracks, and Fig. 374 worm-jaws from the Silurian. 
 
 Crustacea — Trilobites.-, — The principal representatives of the Ar- 
 thropods in Cambrian and Silurian times were Crustaceans, but 
 mostly of a very characteristic order of that class, now long extinct, 
 viz., Trilobites (Figs. 375-385). 
 
 General Description. — The carapace or shell of these curious creat- 
 ures was convex, and divided transversely, like most Crustacea, into a 
 number of movable joints. Several of the front joints are consoli- 
 dated to form a head-shield or Ceplialon, and usually a number of 
 the posterior joints are similarly consolidated to form a tail-shield 
 or Pygidium. The whole carapace is divided more or less distinct- 
 
SILURIAN ANIMALS. 
 
 333 
 
 ly into three lobes (hence the name) — a middle, a right, and a left. 
 Some characteristic forms of silurian trilobites are shown in Pigs. 376- 
 
 PiG. 372. 
 
 Fie. 373. 
 
 FiGB. 372, 373.— SiLUBiAN Annelids : 372. ConmliteB serpentarius (Worm-Tabe). 
 
 Annelid (after Hall). 
 
 373. Trail of an 
 
 381. The viscera were contained in the middle lobe, the two side lobes 
 being extensions of the shell, as seen in the section. Fig. 384, A and B. 
 Well-organized compound eyes are distinctly seen in well-preserved 
 
 £x5 ex 10 
 
 Fio. 374.— WormJ^awe from Cincinnati gronp, enlarged (after Hinde). 
 
 specimens on the lateral lobes of the Cephalon (cheeks) (Fig. 375). 
 The under side of the animal has never been distinctly seen. It 
 
 /* 
 
 :?!■- 
 
 /^-P, 
 
 
 Fio. 375.— structure of the Eye of TriJobites : a, Duliniiiiili- pli'uroptyx; S eye slightly maenifled • 
 c, eye more highly magnified ; a, small poitiuu stili uiuiu highly magnified (after Hall;. ' 
 
334 
 
 PALEOZOIC SYSTEM OF KOCKS. 
 
 was formerly supposed, however, that like many lower crustaceans 
 of the present day (Phyllopods) their limbs were mostly or wholly 
 
 
 
 ^ 
 
 "v, 
 
 ^) 
 
 f«,V 
 
 
 ma. 376. 
 
 Fig. 378. 
 
 Figs. 376-378.— Silurian Trilobitbs: 376. Calymene Blamenbachii; a, Same in folded condition. 
 377. Trinucleus Pongerardi, 378. Liclias Boltoni (after Hall). 
 
 leaf-like swimmers. In 1876 Walcott proved the existence of articu- 
 lated legs. In 1893 beautifully preserved specimens of Triarthrus were 
 found in the Utica slate, near Kome, E". Y., and described by Matthew, 
 in which not only legs were more perfectly displayed, but what was not 
 before suspected, a pair of slender many-jointed antennce. Each loco- 
 motive appendage was double, one branch for crawling and one for 
 swimming and probably breathing. The antennae were attached on the 
 under surface of the head. These facts are shown in the restorations, 
 Fig. 382, A and B, in which A shows the dorsal and B the ventral aspect 
 of the animal. Fig. 383, a and I, show the limbs enlarged, and Fig. 384, 
 A and B, are diagrammatic sections — A through the thorax, B through 
 
SILURIAN ANIMALS. 
 
 335 
 
 Pygidium, showing the structure and position of the limbs. We are 
 indebted to Prof. Beecher for remarkable restorations of Triarthrus, 
 shown in Fig. 382. 
 
 Fig. 379. 
 
 
 Fig. 380 a. 
 
 Fio. 381. 
 
 Pios. 379-381.— Silurian Trilobites : 379. Acidaspie crosotus (after Meek). 380. Isotelus gigas, 
 reduced (after Hall). 380 a. Same, side-view. 381. Dalmanites limulurus. 
 
 It is easy to see why the under side is never exposed ; for the mud, 
 in which they were entombed, would become entangled among these 
 leaf-like swimmers and numerous slender legs, and in breaking the 
 rock this would determine the line of fracture over the smooth back, 
 and leave the creature firmly attached by its ventral surface to the 
 lower piece. Not uncommonly Trilobites are found folded up on 
 their ventral surface, so as to bring head and tail together and form a 
 kind of ball. In such cases the Trilobite may be got out of the rocky 
 matrix complete; biit none the less are the legs completely hidden 
 (Pig. 376, a). 
 
 The great number of genera into which this large order is divided 
 is founded principally on the form and sculpturing of the Cephalon, 
 the size and form of the Pygidium, the number of the movable seg- 
 ments, etc. The figures will give an idea of some of these forms. 
 
 It is very interesting to observe that a complex mechanism, the 
 compound eye like that of crustaceans and insects of the present day, 
 was already developed even in the early Cambrian times. 
 
 Trilobites commenced, as already stated, in the earliest Cambrian, 
 continued through the whole Palaeozoic, and then became extinct for- 
 33 
 
336 
 
 PALEOZOIC SYSTEM OF KOCKS. 
 
 ever. They are therefore entirely characteristic of the Palaeozoic. 
 They reached their maximum of development, in size, number, and 
 variety, in the Silurian. Barrande gives the number of species de- 
 scribed in the Silurian alone as 1,579. They reached in some cases a 
 
 Pig. 882.— Triarthrus Becki, restored Tjy Beecher, showing limbs and antennee; 
 a. Dorsal; 6, ventral surface, 
 
 size approaching that of the largest crustaceans now living. The 
 Asaphus (Isotelus) gigas, from the Lower Silurian (Pig. 380), was 
 sometimes twenty inches in length and thirteen wide. Parodoxides 
 (Figs. 292 and 293, p. 313), of the earliest Cambrian, attained a 
 length of twenty-two inches. On account of their great abundance 
 and fine preservation, their embryonic development has been care- 
 fully studied by Barrande (who described and figured twenty steps 
 in the growth of some species) and Beecher (Fig. 385). It is prob- 
 ably true that we know nearly as much of the development of some 
 Trilobites as of any living crustacean. 
 
SILURIAN ANIMALS. 
 
 337 
 
 Affinities of Trilobites.— The affinities of tliis very distinct order 
 are imperfectly understood. Crustaceans are divided into two sub- 
 classes, a higher, Eucrusiacea, and a lower, the Trilobita. Now, 
 Trilobites, though constituting the 
 lower division, are related to some 
 of the higher forms of living crus- 
 taceans. They show certain struc- 
 tural resemblances with the Isopods 
 (sow bugs) on the one hand, and 
 with the Phyllopods, and specially 
 with Limulus (horseshoe-crab)., on 
 the other. To the last of these they 
 present a striking similitude in ex- 
 terior form and construction. They 
 are not to be regarded as the low- 
 est type of crustaceans, but rather 
 as expressing the ancestral form of the higher crustaceans of to-day. 
 The larvae of Limuloids greatly resemble some forms of Trilobites, 
 
 Fig. 383.— Limbs of Triarthrus Becki en- 
 larged. In b the setse are removed to 
 show structure ; ex, exopodite ; en, en- 
 dopodite (after Beecher). 
 
 Fig. 384.— Transverse section of Triarthrus: A, through thorax; B, through pygidium; showing 
 structure and position of the iimhs (after Beecher). 
 
 and especially the larvae of Trilobites. From early generalized forms 
 somewhat like the larvae represented by Fig. 385 there have been prob- 
 
 FiG. 385.— Sao hirsuta: a, b, c, larval stages, x 30; d, adult, x 1 (after Barrande). 
 
 ably differentiated, in one direction the more perfect Trilobites, and 
 in the other the higher forms of crustaceans. 
 
338 
 
 PALEOZOIC SYSTEM OP ROCKS. 
 
 Eurypterids. — In the Upper Silurian was introduced and con- 
 tinued to exist along with Trilobites, during the rest of the Palaeozoic, 
 another group of jointed animals or Arthropods probably in advance 
 
 of Trilobites in organization, viz., Eu- 
 rypter'ida. This order includes the gen- 
 era Eurypterus (broad wing) and Pter- 
 ygotus (winged ear), and some others. 
 Some of the latter are the largest crus- 
 taceans known. The huge Japan crab 
 
 Fig. 387. 
 
 FiQ. 388. 
 
 Fioa. 386-388. — Upper Silurian Eurypterids: 386. Pterygotus osiliensis (after Schmidt), viewed 
 from the under side, reduced in size, and restored: c c, the feelers (antennae), terminating in 
 nipping claws ; o o, eyes ; m m, four pairs of jointed limbs, with pointed extreinities ; n n, 
 swimming-paddles, the bases of which are spiny and act as jaws — Upper Silurian, Island of 
 Oescl, Baltic Sea. 387. Eurypterus Fischeri, greatly reduced, ventral view. 388. Dorsal view. 
 
 {Inachus Koempferi) , with carapace sixteen inches in diameter and 
 legs four feet long, and the Moluccas king-crab {Limulus molucca- 
 nus), three feet long and eighteen inches across the carapace, are the 
 largest crustaceans now living. But the Eurypterids were some of 
 them far greater. The Pterygotus anglicus (Fig. 386) was six feet 
 long and one foot wide, and the Pterygotus gigas seven feet long 
 and proportionately wide. The above figiires (386-388) represent 
 some species of these two genera from the American and English 
 rocks. 
 
 Anticipations of the Next Age. — There are some plants and animals 
 still higher than those mentioned above, but they are so rare that it is 
 best to treat them as anticipations of the next age. The most impor- 
 tant of these may be briefly noted : 1. A few very small land-plants 
 (Ferns and Club-Mosses) have been found in the upper part of the 
 Lower Silurian of this country and of Europe. 2. A few small air- 
 breathers (insects. Cockroaches, Scorpions) have been found in the 
 
SILURIAN ANIMALS. 
 
 339 
 
 Upper Silurian— also of both countries, and recently one (Protoci- 
 mex) in the upper part of the Lower Silurian. We give a figure of 
 one of these very important discoveries (Fig. 389). That they were 
 really air-breathers is shown by 
 the spiracles or breathing-pores, 
 a. 3. A few, small, curiously- 
 formed fishes, of very low organ- 
 ization, somewhat similar to 
 some of the fishes (Pteraspis) 
 in the Lower Devonian, have re- 
 cently been found in the Salina 
 beds (Upper Silurian). We give 
 in Fig. 390 a restoration by 
 Claypole of one of these Upperi 
 Silurian fishes.* Such anticipa-^ 
 tions are in accordance with the 
 law already mentioned (p. 291), 
 that the characteristics of an age 
 often commence in the preceding 
 age. It is better, however, to 
 treat of these classes in connec- 
 tion with the age in which they 
 culminate, or at least become a 
 striking feature. 
 
 The Silurian was, therefore, 
 essentially an age of Inverte- 
 brates. In number, size, and 
 variety these have scarcely been surpassed in any subsequent period. 
 The most characteristic orders were : Among plants, Fucoids ; among 
 animals, Cyathophylloid and Tabulate Corals, Graptolites, Cystideans, 
 
 Fig. 389.— Palaeopternue — a Fossil Scorpion from 
 Upper Silurian of Scotland (after Peach). 
 
 Palseaspis Americana, x J (after Claypole). 
 
 Crinids, Square-shouldered Brachiopods, Beakless Gasteropods, Or- 
 thoceratites^ and Trilobites. Orthoceratites and Trilobites were the 
 highest animals of the age, and the former were the rulers and scav- 
 
 * Still lower findings are reported, e. g., that of Walcott from rocks of supposed Tren- 
 ton age (Lower Silurian). But there is some doubt whether the rocks are really Silurian ; 
 for the fishes are not even of Lowest Devonian, but of full Devonian type. 
 
340 PALAEOZOIC SYSTEM OF ROCKS. 
 
 engers of these early seas. We give below a table showing, ac- 
 cording to Barrande, the number of Silurian species described up 
 to 1872: 
 
 Sponges and other Protozoans ... 1 53 
 
 Corals 718 
 
 Echinoderms 688 
 
 Worms 185 
 
 Trilobites Ifi19 
 
 Other Crustaceans 348 
 
 Brjozoans 478 
 
 Brachiopods 1,667 
 
 Lamellibranchs 1,086 
 
 Heteropods ) ggQ 
 Ptcropods S 
 
 Gastcropods 1,306 
 
 Cephalopods 1,622 
 
 Fishes 40 
 
 Which, with four of uncertain relations, make 10,074 species. The 
 number has been greatly increased since that time. 
 
 Section 2. — Devonian System and Age of Fishes. 
 The name Devonian was given to these rocks by Murehison and 
 Sedgwick, because in Devonshire the system occurs well developed, 
 and abounds in fossils. In England the system is usually unconform- 
 able with the underlying Silurian, and sometimes with the overlying 
 Carboniferous, as in Fig. 391. But in the eastern United States the 
 Palasozoics are essentially conformable throughout (Fig. 367). 
 
 s d ^ 
 
 FiQ. 391 s, Silurian; d, Devonian; c, CarboniferouB (after Phillips). 
 
 Area in United States. — The area over which the Devonian ap- 
 pears as a country rock in the eastern United States is shown in map, 
 page 303. It borders generally the Silurian on the south and south- 
 west, extending with it far southward in the middle region, viz., in 
 Indiana, western Ohio, and Kentucky. It borders also the Silurian 
 strip in the Appalachian region. In the Basin Ean'ge region, espe- 
 cially about White Pine, Nevada, Devonian exists, but the limits of 
 these areas are too imperfectly known to be described. Eecently it 
 hag been found also in Siskiyou County and the Klamath Mountains, 
 California. 
 
 Physical Geogxapliy. — In the eastern portion of the United States 
 the land of the Devonian age was approximately that of the Silurian 
 age already described, increased by the addition of the Silurian area, 
 which Silurian was of course so much marginal sea-bottom exposed 
 by upheaval during and at the end of Silurian times. There was also 
 a large island in the Devonian seas in the region about Cincinnati, 
 viz., the Silurian area, situated there (see map, p. 303). In the Pla- 
 teau region there was a large extent of land in later Silurian and 
 
DEVONIAN SYSTEM AND AGE OF FISHES. 
 
 341 
 
 Devonian times, as shown by the absence of strata of these times in 
 the Grand Canon section. At the end of Devonian times the Devo- 
 nian area was added to the existing land, and the continental mass 
 was further increased. 
 
 Subdivision into Periods.— In the United States the following five 
 periods are usually recognized: 
 
 6. Chemung period. 
 
 4. Hamilton period. 
 
 3. Onondaga (Corniferous) period. 
 
 2. Oriskanj period. 
 
 1. Helderberg period. 
 
 We shall, however, neglect these subdivisions in our general de- 
 scription of the life of the age. 
 
 Life-System of Devonian Age — Plants. 
 
 It will be remembered that during the Silurian age, except doubt- 
 ful vascular cryptogams, the only plants found were Fucoids. These 
 continued, though under different species, in Devonian times. But, 
 in addition to these, were now introduced land-plants in consider- 
 able numbers and variety, and decided complexity of organization. 
 
 Fie. 392.— Microscopic Section of the Silicifled 
 Wood of a Conifer (Sequoia), cut in the 
 long direction of theTibers. Post- tertiary? 
 Colorado (after Kicholson). 
 
 Fio. 393.— Microscopic Section of the Wood of 
 the Common Larch (Abies larix), cat in the 
 long direction of the fibers. In both the 
 fresh and the fossil wood (Fig. 392) are seen 
 the disks characteristic of coniferous wood 
 (after Nicholson). 
 
 They included all the orders of vascular cryptogams, viz.. Ferns, 
 LycopodSj and Equisetce; and also forerunners of the gymnosper- 
 mous Phsenogams; and which by their size and numbers probably 
 formed for the first time in the history of the earth a true forest 
 vegetation. 
 
 The Ferns were represented by several genera, such as Archsop- 
 teris and Ehachiopteris, to which should perhaps be added Psilophy- 
 
342 PALEOZOIC SYSTEM OF ROCKS. 
 
 ton, which had already been introduced in the uppermost Silurian: 
 the Lycopods (club-mosses) by great Lepidodendrids and Sigillarids; 
 and the Bquisetales by Calamarian types. The Gymnosperms were 
 represented by the genus Dadoxylon, distantly allied to the yew 
 (Taxus). They are known to be allied to the conifers by the char- 
 acters of their wonderfully preserved gymnospermous tissue — i. e., 
 the circular disk-like markings on the walls of the wood-cells on 
 longitudinal section (Figs. 392, 393), and the 
 entire absence on cross-section of the visible 
 pores so characteristic of dicotyledonous Exo- 
 gens (Fig. 394). Some of these conifers have 
 been found by Dawson eighteen inches in diam- 
 FiG. 394.— Pine-Wood, Cross- etcr. Ovcr tifty species of laud-plants were re- 
 ectionmagni e . ported by Dawson in the Devonian of Canada. 
 Figs. 395-405 represent land-plants described by Dawson as charac- 
 teristic of the Devonian. 
 
 General Remarks on Devonian Land-Plants. — We will not at pres- 
 ent discuss the affinities of these plants, and their relations to evolu- 
 tion, because they are similar to those found in the coal, where they 
 exist in far greater variety and abundance, and the subject will be 
 discussed under that head. There are, however, some thoughts sug- 
 gested by the first appearance of highly-organized plants which ought 
 not to be omitted. 
 
 1. The ringed structure described in some Devonian conifers 
 shows that, at that time, there was a growing season and a season of 
 rest, and therefore possibly a warm and a cold season. 
 
 3. What were the precursors of this highly-organized forest vege- 
 tation? That there were precursors, from which these were derived, 
 there can be no doubt, for we have already found them in the Upper 
 Silurian ; but that the steps of evolution were Just at this point some- 
 what rapid, seems also certain. It is impossible to account for this 
 comparatively sudden appearance of so highly-organized a vegetation 
 by evolution, unless we admit that there have been periods of rapid 
 evolution, as explained on page 314. When all the conditions are 
 favorable for a great advance, the advance takes place at once, i. e., 
 with great comparative rapidity. 
 
 3. We have seen that the coal vegetation is to some extent an- 
 ticipated in the Devonian. So, also, to some extent, were the. condi- 
 tions necessary to the preservation of this vegetation and the forma- 
 tion of coal. In the Devonian, for the first time, we find dark bands 
 between the strata, impregnated with carbonaceous matter. We find, 
 also, thin seams of coal, with under-clays filled with ramifying rootlets, 
 such as we shall find in the coal ; in other words, we find ancient dirt- 
 beds, fossil forest-grounds, and fossil peat-bogs. All the phenomena of 
 
LIFE SYSTEM OF DEVONIAN AGE— PLANTS. 
 
 343 
 
 b Fio. 401. e 
 
 Hi 
 
 Fig. 400. 
 
 Fia. 
 
 Figs. 395-403. — Detonian Plants (after Dawson) : 395. Psilophyton princeps, restored. 396. a, 
 LepidodendronGaepianiim; i, same with leaves. 397. a, Annnlarialatifolia; 6, fniitof samef?). 
 398. Aneimites obtusa. a Fern. 399. Nenroi^teris polymorpha, a Fern. 400. Archseopteris Jack- 
 eoni, a Fern. 401. Dadoxylon Ouang^ondianum, a gymnosperm : ■ a, Pith ; 6, Pith-sheath ; 
 c. Wood. 402. Sections of same ; x, Longitudinal ; y, Transverse, enlarged— «, greatly magni- 
 fied, showing disk-like markings. v 
 
344: 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 Pig. 403. 
 
 Fig. 404. 
 
 Fig. 405. 
 
 Figs. 403-405.— Dbvonian Plants (after DawsonJ: 403. Cardiocarpon Baileyi, a Fruit. 404. An- 
 tholithus devonicns. 405. Cordaites Eobbii, a Group of Leaves. 
 
 the coal-measures, therefore, are here found, though imperfectly de- 
 veloped, and the coal not workable. The Carboniferous day is already 
 dawning. 
 
 Fia. 408. 
 
 Fio. 409. 
 
 Fios. 406-409.— Dbtonian Cobals: 406. Acervularia Davidsoni (after Hall). 407. Diphyphyllum 
 Archiaci. 408. Zaphrentis Wortheni (after Meek). 409, Favosites hemiBpherica. 
 
DEVONIAN ANIMALS. 
 
 345 
 
 Animals. 
 
 In accordance with our prescribed plan, all we can do in describ- 
 ing Devonian animals is to touch prominent points — to notice what is 
 going out, what is coming in, some few characteristic forms, and to 
 dwell only on what bears on evolution. 
 
 Coelenterates. — Among corals, the chain-corals (Halysitids) have 
 disappeared; the other orders continue under different species (Figs. 
 406-409). Among Hj-drozoa, the Oraptolites of Silurian type are 
 gone. 
 
 Echinoderms. — Among Crinoids, the Cystids are almost gone, but 
 in their place the Blastoids, those curious crinoids, with petaloid 
 markings already spoken of as rare in the Silurian, become more 
 abundant. The Crinids, or plumose-armed crinoids, continue undi- 
 minished. The Blastoids, however, are still more characteristic of the 
 Carboniferous. We therefore defer their illustration to that period. 
 
 Brachlopods. — Brachiopods are still very abundant, and still many 
 of them of the characteristic Palaeozoic, square-shouldered type. 
 Among spirifers, the long-winged species (Fig. 412) are very abundant 
 
 Fig. 413. 
 
 Fig. 413. 
 
 Figs. 410-413.-Dbvonian Braohiopobb: 410. Spirifer fomacula (after Meek and Worthen): o, 
 Ventral valve; 6, Front view. 411. OrtWs Livia: a, Dorsal; J, Side view. 412. Spinfer per- 
 extensus (after Meek). 413. Leptsena rhomboldalis. 
 
 and characteristic. We give a few figures of Devonian bivalves, both 
 brachiopods and lamellibranchs, and a few univalves. 
 
346 
 
 PALAEOZOIC SYSTEM OF ROCKS. 
 
 Cephalopods. — The characteristic Palaeozoic Cephalopods, or Or- 
 tUoceratites, continue, but in greatly-diminished numbers and size; 
 
 Fig. 421. 
 
 Fig. 420. 
 
 Pig. 418. 
 
 FiGB. 414-421. — Devonian Lambllibranchs, GASTEBOPons, and Annelidb : 414. Oonocardium 
 trigonale (after Logan). 415. Avicnlopecten parilis (after Meek). 416. Ctenopietha antiqua 
 (after Meek). 417. Lucina Ohioeiisis (after Meek). 418. Spirorbis omphalodes, enlarged, a 
 shelled annelid. 419. Spirorbis Arkoneneie. 420. Orthonema Newberry! (after Meek). 421. 
 Bellerophon Newberryi (after Meek). 
 
 but the Goniatites, coiled-chambered shells, which seem to be the 
 beginning of the Ammonite order, are introduced first here. This 
 
 order, as already explained, is distin- 
 guished by the complexity of the junc- 
 tion of the septa and the shell (su- 
 ture), and by the ventral position of 
 the siphuncle. In the Ooniatites the 
 sutures are not yet very complex. The 
 group is abundantly developed and the 
 variations of its genera and species 
 constitute the basis of classification of 
 many Devonian beds. Allied to the 
 goniatites is Clymenia, which appears 
 late in Devonian time. 
 
 Omstacea. — The very characteristic 
 Palaeozoic order Triloiites is still 
 abundantly represented, aH hough it has already passed its prime, and 
 is diminishing in number; however, its species here attain their 
 
 Fio. 422.— Goniatites lamellosns 
 (after Pictet). 
 
DEVONIAN ANIMALS. 
 
 347 
 
 greatest size and most extravagant form. The Eurypterids introduced 
 in the Upper Silurian become fewer in number in the Devonian, but 
 Stylonurus and Pterygotus attain great size. 
 
 Insects. — We have already seen (p. 339) 
 that a very few insects (cockroaches and scor- 
 pions) have been found in the Upper Silurian. 
 We treated these as anticipations. In the De- 
 vonian, for the first time, they become somewhat 
 abundant; and, as was to be expected, are found 
 in connection with the abundant -land vegetation 
 of that time (Figs. 425 and 426). 
 
 The Devonian, and, indeed, all the Palaeozoic 
 hexapod- insects, according to Scudder, belong 
 to one order, Palse- 
 odictyoptera (old 
 netted- winged ) , a 
 generalized type 
 connecting the 
 Neuropters and the 
 Orthopters. A 
 chirping organ is 
 believed to have 
 been found in some. 
 If so, it implies also an organ of hearing in these early insects, 
 supposed chirping organ is shown in Fig. 426. 
 
 Fishes. — The Devonian is characterized by the signal development 
 of vertebrates, as represented by the class of fishes and fish-like forms. 
 The earliest indications of vertebrate remains, those of Lower Silu- 
 rian age, are scanty in number and exceedingly primitive in organ- 
 
 FiQ. 424. 
 
 FiQS. 423 and 424. — Devo- 
 nian Thilobites : 423. 
 Phacopsrana (common in 
 Hamilton rocks, Genesee 
 County, New York). 424. 
 Eye of Phacops rana, 
 showing lenses. 
 
 Fio. 425. — Wing of Platephemera 
 antiqua, Devonian, America (after 
 Dawson). 
 
 The 
 
 Fio. 426. — Xenoneura antiqnorum (after Scudder). 
 
 ization (Fig. 390), but with the opening of the Devonian all four 
 principal subclasses into which fishes are divided are represented by 
 well-characterized examples. Under these four main divisions are 
 comprised the Elasmohranchs, including sharks and rays, the Eolo- 
 cephali or Chimaeroids, the Dipnoans or Lung-fishes, and the Tele- 
 
348 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 Fio. 427.— Jaws of Dinichthys terrelli, x ^ (after 
 Newberry). 
 
 ostomes or ganoids and typical bony fishes. The primitive verte- 
 brates known as Ostracophores and Arthrodires, sometimes classed 
 as one group under the name of " Placoderms," differ so radically 
 
 from fishes proper as to prevent 
 their being included in the 
 same class. 
 
 The Elasmobranchs are 
 looked upon as the ancestral 
 stem from which all other 
 groups of fishes have been de- 
 rived. From the evidence af- 
 forded by CladoselacJie (Fig. 439) and other primitive forms, it 
 may be regarded as fairly demonstrated that the fins of fishes 
 have developed from a continuous median fold and a pair of con- 
 tinuous lateral folds of the skin, with subsequent modifications. It 
 is unfortunate that, inasmuch as the skeleton of Elasmobranchs and 
 Chimseroids are entirely cartilaginous, their complete forms are rare- 
 ly met with in the fossil state, their presence, for the most part, being 
 indicated merely by teeth and dermal defenses. These are often 
 of large size and preserved in considerable abundance. On the other 
 haiid, the possession of hard parts among Ostracophores, Arthro- 
 dires, Dipnoans, and Teleostomes renders them much better adapted 
 for preservation, and in consequence their structure is tolerably well 
 
 Fig. 428. 
 
 Pis. 429. 
 
 Fig. 430. 
 
 PiQB. 428-430.— Onychodns sigmoides (after Newberry); 428. Scale, natural size, 
 natural size. 480. A Eow of Presymphysial Teeth, reduced. 
 
 429. A Tooth, 
 
 known. The mimetic resemblances between Ostracophores and a 
 number of contemporary invertebrates adapted for a precisely similar 
 environment is a striking feature of both the Silurian and Devonian 
 faunas. 
 
 Characteristic Examples of Devonian Pishes.— The Cephalaspis 
 (Fig. 431) and Pteraspis (Fig. 433) are among the earliest and most 
 curious forms. The former was a small fish, seven or eight inches 
 
DEVONIAN ANIMALS. 
 
 349 
 
 long, with a broad head, shaped somewhat like the head-shield of a 
 Trilobite, and covered with bony, enameled plates ; and body covered 
 with rhomboidal ganoid scales. In the Coccosteus and Pteriehthys 
 (Figs. 433 and 434) the large, close-fitting, immovable plates covered 
 not only the head but the anterior portion of the body. The huge 
 Dinichthys (Fig. 427) and Titanichthys were similarly plated on head 
 
 Fig. 432. 
 
 Fig. 434. 
 
 Flos. 431-434.— Devonian Fishes : 431. Cephalaspis mnrchisoni (after Woodward). 432. Pteraspis 
 rostrata (after Woodward). 433. Pteriehthys restored (after Traqtiair). 434. Coccosteus deci- 
 plens (after Traquair). 
 
 and body. Others, however, such as the Osteolepis (Fig. 436), the 
 Holoptychius (Fig. 435), Acanthodes (Fig. 438), etc., had more fish- 
 like forms, and were covered with movable ganoid scales, either rhom- 
 boidal or imbricated. 
 
 Perhaps the most extraordinary and certainly the largest of all 
 Devonian fishes belong to the family of Coccosteans. The peculiar 
 structure of the jaws of Dinichthys is shown in Fig. 437, taken from 
 
.350 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 ISTewberry. Almost equally remarkable is another Ohio fish described 
 by Dr. Newberry, the singular teeth and scales of which are shown 
 in Figs. 439 and 430. This form, Onychodus, was a very large and 
 
 Fig. 435. 
 
 Fig. 430. 
 
 Fin. 4.37 
 
 -^ 
 
 Fio. 438. 
 
 Pi09. 435-438. ^Devonian Fishes ; 435. Holoptychiiis flemingi (after Traquaii). 435rt. Holopty- 
 chlns andersoni (af fer Dean). 436. Osteolepis (after Pander). 437. Glyptolepis Kinairdii (after 
 Pander). 438. Acanthodee wardi (after Woodward). 
 
DEVONIAN ANIMALS. 
 
 351 
 
 predaceous fish, and belongs to a group which is very characteristic of 
 the Devonian — viz., Crossopterygians (f ringed-limb), so called be- 
 cause the limbs seem to come out from the body into the fin like a 
 true limb. All the strangest and largest forms — such as the Cephalas- 
 pis, the Coccosteus, the Pterichthys, the Diniehthys, and the Titan- 
 ichthys, are " Placoderms." They were heavy, sluggish, uncouth ani- 
 
 Fm. 439. 
 
 Fig. 440. 
 
 Fig. 440a. 
 
 Fig. 440ft. 
 
 Figs. 439-440*.— Devonian Fibhbs; 439. Cladoselache fyleri (from Dean). Elasmobranchs : Ma- 
 chseracanthiis major, Fin-spine reduced, Comiferous Limestone (after Newberry). 440a. Pha- 
 neropleuron (after Dean). 440ft. Dipterus valenciennesi (after Dean). 
 
 mals, relying for safety upon protective armor rather than upon 
 swiftness. 
 
 Nearest Allies among Existing Fishes. — The Placoderms are with- 
 out any allies among living fishes. They were ofEshoots from an early 
 primitive stem, and became extinct at the close of the Devonian with- 
 out leaving descendants. The Dipnoans and Crossopterygians, how- 
 24 
 
352 
 
 PALEOZOIC SYSTEM OP ROCKS. 
 
 Fio. 443. 
 
 Fig. 444. 
 
 Fio. 446. 
 
 Figs. 441-446.— Nearest Liting Allies of Devonian Fibbes: 441. Lcpidosiren paradoxa. 442, 
 Ceratodus Fosterii. x A (after Gnnther). 443. Polypterns bichir. 444. Lepidosteus osseus (gar- 
 
 Sike). 445. Amia calva (American Mud-fish). 446. Cestracion phillippi (a Living Ceetraciont 
 :om Australia). 
 
DEVONIAN ANIMALS. 
 
 353 
 
 ever, still have living congeners, which throw light upon their struct- 
 ure (Figs. 441-445). Among the nearest allies are the Geratodus 
 of Australian rivers, the Lepidosiren and Protopterus of South Amer- 
 ican and African rivers, and the Polypterus of the Nile. It will be 
 noted that some of these have almost veritable legs instead of paired 
 fins. It is well to note also that the Lepidosiren is the most reptilian 
 or rather amphibian of all fishes, and next in this respect comes 
 Ceratodus. These two have a 
 three-chambered heart and a 
 tolerably good lung and nos- 
 trils, and breathe air as well as 
 water, like many amphibians. 
 They also have cartilaginous 
 skeletons, like Devonian fishes. 
 Less near allies are found in 
 the gar-pike (Lepidosteus) 
 and the mud-fish (Amia) of 
 our Atlantic and Gulf rivers. 
 These also supplement their 
 gill-breathing with a little air 
 gulped down into their vascu- 
 lar air-bladder from time to 
 time. 
 
 The nearest congener of Devonian Elasmobranchs is found in the 
 Cestracion, OT Port Jackson shark of Australia (Fig. 446). This is 
 characterized not only by the strong bony spine supporting the me- 
 dian fins, but also by the cobblestone-pavement teeth (Fig. 447) com- 
 mon among Palasozoic sharks. The family is called Cestracionts, and 
 enjoys with the Ceratodonts a continuous geological history from the 
 Devonian onward. The Cladodonts (Fig. 439) had piercing teeth 
 closely approaching those of modern sharks. 
 
 General Characteristics of Devonian Fishes. — ^Leaving out some low 
 aberrant forms, which are so soft and perishable that they are unlike- 
 ly to be preserved, and therefore are of little geological prominence, 
 fishes may be conveniently divided into four subclasses, as already 
 observed on page 347. 1. Now, of these four subclasses, the Tele- 
 ostomes, comprising both Ganoids and osseous fishes, are by far the 
 most numerous at priesent ; so much so, that the word fish calls up at 
 once this kind. Under this group are placed all ordinary or typical 
 fishes, such as the perch, the salmon, the cod, etc. In' Devonian 
 times, on the contrary, Teleostomes were decidedly inferior in point 
 of numbers and variety, being limited almost wholly to the order 
 of Crossopterygians. 
 
 3. Some of the Ganoids of the present day have bony skeletons 
 
 Fio. 447.— Lower dentition of Cestracion phillippi. 
 
354 
 
 PALAEOZOIC SYSTEM OF ROCKS. 
 
 (Lepidosteus), but most of them cartilaginous skeletons. Most 
 Devonian Telepstomes had cartilaginous skeletons. Elasmobranchs, 
 both now and in all times, had cartilaginous skeletons. Therefore, 
 the majority of Devonian fishes had cartilaginous skeletons. It 
 is well to note that among Teleost fishes this is an embryonic char- 
 acter. 
 
 3. The position of the mouth of Teleosts is usually at the end of 
 the snout, or even directed a little upward. Most existing ganoids 
 have the mouth like Teleosts, at the end of the snout; but some 
 (sturgeon) have it beneath on the ventral surface. The same was 
 true in Devonian times. The earliest Teleostomes had the mouth at 
 end of the snout ; but the Plaeoderms usually on the ventral surface. 
 Elasmobranchs in all times have the mouth beneath. Therefore, all 
 the Devonian fishes, except the Crossopterygian Ganoids and some 
 Plaeoderms, have the mouth in the ventral position. This also may 
 be regarded as an embryonic character. 
 
 4. The tail-fins of fishes are mainly of two types, the homocercal, 
 or even-lobed (Fig. 448), and the heterocercal or uneven-lobed (Fig. 
 449). The one is characteristic of Teleosts, the other of sharks and 
 some other fishes. These differ not only in shape, but still more in 
 structure. In the former, the back-bone stops abruptly in a few large 
 
 Fio. 448.— Homocercal Tail-fln : 
 A, form : B, etracture. 
 
 Pig. 449.— Heterocercal or Vertebrated Tail-fin: 
 A, form ; B, stracture. 
 
 joints, which send off the rays to the fin (Fig. 448, B), in the latter 
 the backbone runs through the Jin and gives off rays in pairs above 
 and below (Fig. 449, B). The former is a, non-vertebrated, the latter a 
 
DEVONIAN ANIMALS. 
 
 355 
 
 ■^-:^^^^-^^^^^^^:^^ ^^^^ 
 
 vertebrated, tail-fin. There is still a third style in which the tail-fin is 
 verteirated but yet symmetric as in Fig. 450, A and B. This style has 
 been called diphycercal by Huxley. It is the most primitive type. It 
 is well to note that in the embryonic development of Teleosts, the tail 
 passes through these stages successively. Now, in living Ganoids, 
 the tail-fin is vertebrated, 
 though in some cases only 
 slightly so ; in Devonian 
 Ganoids the tail-fins are al- 
 ways distinctly vertebrated. 
 All Elasmobranchs, both 
 living and extinct, have 
 vertebrated tail-fins. There- 
 fore, all Devonian fishes, 
 without exception, had ver- 
 tebrated tail -fins — some- 
 times heterocercal (Figs. 432, 435, 438), and sometimes diphycercal 
 (Figs. 433, 436, and 437). 
 
 5. In all Teleosts, and in nearly all living fishes, the paired fins 
 (corresponding to limbs) are simply fins. The bones of the limbs are 
 buried. in the body. But there is one very characteristic Devonian 
 family (Orossopterygians) in which the limb is a lobe of the body run- 
 
 FiQ. 450.— Vertebrated but Symmetrical Fin: A, formi 
 B, structure. 
 
 Fig. 451. — Head and fore limb of a Ceratodus. 
 
 Fie. 453.— Hind-limb of same (after Gunther). 
 
 ning through the fin and supported by a jointed skeleton. It is more 
 like a paddle or flipper than a true fin. The relation between the two 
 styles of paired fins is similar to that of the two styles of tail-fins. If, 
 
 in the other case, we had a vertebrated 
 
 o yZ m. m, ^ilN-. tail-fin, in this we have legged paired 
 
 fins. This style of paired fins is still 
 found in some fishes, as the Ceratodus, 
 Fig. 442, and the structure resembling 
 
 Fig. 453. — structure of a Ganoid Tooth a leg is shoWn in FigS. 451 and 452. 
 
 (after Agassiz): a, External form, nat- „, , ,, j! ' ^ „ "n„„„„;„„ 
 
 nrai size; 6, eniorgfed section, Bbowing 6. The teeth 01 manv Devonian 
 
 structure. 
 
 6. The teeth ol many 
 Ganoids are fluted or channeled on the 
 outer surface "near the base (Fig. 453, a). On section it is found 
 that the inner surface next the pulp is deeply folded (Fig. 453, b). 
 This is called labyrinthine structure. It is still more marked in early 
 Amphibians, and may be regarded as an amphibian character. 
 
356 PALEOZOIC SYSTEM OF ROOKS. 
 
 7. Devonian Blasmobranchs were nearly all Cestracionts, i. e., they 
 all had cobblestone-pavement teeth, instead of the lancet-shaped teeth 
 characteristic of modern sharks. 
 
 Devonian Fishes were Generalized Types.— Teleosts are typical 
 fishes ; Ganoids and Elasmobranchs, especially Devonian Ganoids and 
 Elasmobranchs, were both connecting and embryonic types— i. e., along 
 with their distinctive fish-characters they combined others which con- 
 nect them with higher vertebrates, especially amphibians, and still 
 others which are found in the embryos of Teleosts. The most im- 
 portant connecting characters of Ganoids, especially Devonian Ganoids, 
 are : 1. An external protective armor of thick, bony plates or scales, 
 such as were possessed by early amphibians, and by many reptiles of 
 the present time. 2. Large conical teeth channeled at the base, and of 
 labyrinthine structure on section. This structure was very marked in 
 early amphibians. 3. A cellular air-bladder, freely supplied with blood, 
 opening into the throat, and capable of being used to some extent as a 
 lung. We do not know that this was true of Devonian Ganoids, but 
 it probably was, since it is true of all their nearest living allies, viz., 
 Lepidosteus, Polypterus, Amia, and especially Ceratodus and Lepi- 
 dosiren. 4. In many cases paired fins which had something like 
 jointed legs running through them. 5. The tail-fin vertebrated as in 
 reptiles. 
 
 Combined with these connecting characters are others which are 
 distinctly embryonic — i. e., are found now in the embryos of Teleosts. 
 The most conspicuous of these are : 1. Cartilaginous condition of the 
 skeleton, and even the retention of the fibrous notochord, which pre- 
 cedes in the embryo the segmentation of the vertebral column. 3. In 
 the Placoderms, the ventral position of the mouth, as in the embryo of 
 Teleosts. 3. The vertebrated tail-fin may be regarded as a connecting 
 character, since it is possessed by nearly all amphibians and reptiles. 
 But it may be regarded also as an embryonic character, since the tail 
 of a Teleost passes successively through the stages represented by Figs. 
 448-450, being first diphycercal, then heterocercal, and finally homocer- 
 cal. It is doubtless both connecting and embryonic. 
 
 In Blasmobranchs, both living and extinct, there is a similar com- 
 bination of connecting and embryonic characters, but in this case the 
 embryonic seem to predominate. We have here, as before : 1. The 
 cartilaginous skeleton. 3. The ventral position of the mouth. But 
 in addition to these, also, 3. The absence of an opercle or gill-cover, 
 growing backward and covering the gill-slits. 4. Perhaps the leathery 
 or imperfectly-rayed condition of the fins; and, 5. The ligamentous 
 instead of bony attachment of the teeth. 
 
 On the other hand, the Blasmobranchs, at least those of the present 
 day, have some very high connecting characters in their reproduction. 
 
DEVONIAN ANIMALS. 
 
 35Y 
 
 In all Elasmobranchs the impregnation is internal and not external, as 
 is usual in Teleosts ; and therefore, instead of spawning a great num- 
 ber of small, unimpregnated ovules, they lay either few large, well- 
 covered, impregnated eggs, like birds and reptiles (skates and some 
 sharks), or else incubate their eggs within the oviduct, and bring forth 
 their young alive (ovo-viviparous) like some reptiles. In some cases 
 there is even an attachment between the yolk-sac of the internally- 
 hatched young and the oviduct of the mother, somewhat similar (but 
 not homologous) to that of the placenta to the uterus in the mammal. 
 The young of Placoids also have, at first, a kind of external branchiaB, 
 like those of amphibians. 
 
 The following schedule briefly embodies these facts. It is seen that 
 in the Ganoids the connecting, in the Elasmobranchs emiryonic, char- 
 acters predominate ; but that in the Placoids the connecting characters 
 are very high. The Lepido-ganoids of Devonian and Carboniferous 
 times were far more connecting or reptilian than the Ganoids of the 
 present day. Hence these have been called Sauroids by Agassiz and 
 Herpetichthyes by Huxley : 
 
 Ganoidb. 
 
 Connecting - 
 
 Embryonic 
 
 Bony armor. 
 Teeth labyrinthine. 
 Swim-bladder = lungs. 
 Paired fins = legged. 
 Tail-fin = vertebrated. 
 Skeleton = cartilaginous. 
 Mouth = Tentral. 
 
 ELASHOBBANCnS. 
 
 Beproduction: 
 Tail-fin = vertebrated. 
 Skeleton = cartilaginous, 
 Mouth = ventral. 
 Gill-slits uncoTered. 
 Fins imperfectly rayed. 
 Teeth imperfectly attached. ^ 
 
 Connecting. 
 -Embryonic. 
 
 Bearing of these Pacts on the Question of Evolution. — It is seen 
 above that the Devonian fishes combined certain high characters with 
 certain low characters. Prom one point of view they seem lower, from 
 another higher, than ordinary fishes. There has been some dispute, 
 therefore, whether in the history of fishes we find a law of progress or 
 a law of regress ; in other words, whether or not it sustains a law of 
 evolution. The dispute is a result of a misconception of the nature of 
 evolution. The most fundamental law of evolution is the law of 
 differentiation and specialization, and the Devonian fishes are an ad- 
 mirable illustration of that law. The law may be stated thus : The 
 first introduced of any class, order, or family, are not typical examples 
 of their class, order, etc., but connecting types — i. e., forms which, 
 along with their distinctive class, order, or family, characters, com- 
 bine others which connect them with other classes, orders, etc. In the 
 process of evolution such connecting or generalized forms as a common 
 stem are separated into several specialized branches. Thus the Devo- 
 nian fishes were not typical fishes as we now know them, but Sauroids 
 
358 PALEOZOIC SYSTEM OF ROCKS. 
 
 — i. e., along with their distinctive fish characters they combined others 
 which closely allied them with amphibians. They were the repre- 
 sentatives and progenitors of hoih classes j from this common stem 
 diverged two branches, viz., typical fishes on the one hand, and 
 amphibians on the other. Such connecting links with other classes 
 or orders are variously called connecting types, synthetic types, com- 
 bining types, comprehensive types, generalized types. We shall usually 
 call them generalized types, and their differentiated outcomes specialized 
 types. We shall find many such in the course of the history of the or- 
 ganic kingdom. 
 
 Suddenness of Appearance. — But it is impossible to overlook the 
 apparent suddenness of the appearance of a new class — Fishes — and a 
 new department — Vertebrates — of the animal kingdom. At a certain 
 horizon, and that without break by unconformity, and therefore with- 
 out notable loss of record, fishes appear in great numbers and variety. 
 It looks at first as if they came without progenitors. This apparent 
 suddenness, however, is greatly diminished by recent discoveries. 
 Fishes, few in number, small in size, and low in organization, have 
 now been found far down in the Upper Silurian. The gap is still 
 great, but will be made less and less by continued discovery. Never- 
 theless, in spite of all this it is difficult to account for the enormous 
 increase in the number, size, and variety of fishes at the opening of the 
 Devonian unless we admit paroxysms of more rapid movement in evo- 
 lution — unless we admit that, when the conditions are favorable, and 
 the time is ripe for a certain change, it takes place with exceptional 
 rapidity, perhaps in a few generations. 
 
 Amphibians and reptiles have not yet been found in the Devonian. 
 Fishes, therefore, were the highest and most powerful animals then 
 living. They were the rulers of the Devonian seas. The previous 
 rulers, therefore — viz., Orthoceratites and Trilobites, according to a 
 necessary law in the struggle for life — diminish in number and size, 
 and seek safety in a subordinate position. 
 
 SECTiojr 3. — Caebokifeeous System. — Age of Aceogens and 
 
 Amphibians. 
 
 Retrospect. — Before taking up in detail this important and inter- 
 esting age, it will be instructive to glance back over the ground trav- 
 ersed, and draw some conclusions. 
 
 If we compare, in physical geography, the American with the Eu- 
 ropean Continent, we find the one marked by simplicity and the other 
 by complexity of structure. This is true not only of the map-outline, 
 but also of the profile-outline, or orographic structure. Now, as history 
 furnishes the key to social and political structure, so geology furnishes 
 fh.e kej to physical struc^uj-e. The Amprjcan Continent — ^at least in its 
 
CARBONIFEROUS SYSTEM. 
 
 359 
 
 eastern part — ^has developed comparatively steadily from the Lauren- 
 tian nucleus southward and westward, and probably northward. We 
 have already seen how the Silurian area was added to the Cambrian, 
 and the Devonian to the Silurian. We will show the continuance of 
 this development throughout the whole geological history. 
 
 In the case of America, the continent sketched in outline in the 
 earliest times has been in a general way increasing throughout all 
 subsequent time; with some very considerable oscillations, it is true, 
 determining unconformlity of strata, rapid changes of physical geog- 
 raphy and climate, and therefore of species, thus marking the great 
 divisions of time. In the case of Europe, on the contrary, geological 
 history consists of a series of oscillations so great that it amounts to 
 a successive making and unmaking of the continent. Dana has called 
 North America the type continent. 
 
 Hence, nearly -all geological problems are expressed in simpler 
 terms, and are more easily solved, here than there. Hence, also, while 
 in Europe the ages and periods are separated by unconformity of the 
 rock-system, as well as change in the life-system, in America they 
 are separated mainly by change in the life-system only. 
 
 Suladivisions of the Carboniferous System and Age. — The follow- 
 ing table gives the subdivisions: 
 
 Subdivisions of the American Carboniferous. 
 
 
 In Pennsylvania. 
 
 In the Mississippi 
 VaUey. 
 
 Permian 
 
 Upper barren measures. 
 Upper productive measures. 
 Lower barren measures. 
 Lower productive measures. 
 Pottsville conglomerate. 
 
 Mauch Chunk (red shales). 
 
 Pocono (gray sandstone and conglomerate). 
 
 Permian 
 
 Carboniferous .... 
 Subcarboniferous . 
 
 
 Coal measures. 
 
 Millstone grit. 
 Chester. 
 St. Louis. 
 Osage. 
 Kinderhook. 
 
 The whole thickness of the Carboniferous strata in ISTova Scotia 
 is 16,000 feet; in South Wales it is 14,000 feet; in Pennsylvania 
 9,000 feet, and in Lancashire 16,336 feet. 
 
 The sub-Carboniferous consists mainly of marine formations; the 
 Coal measures largely of fresh- or brackish-water formation — the 
 former mainly of limestone, sandstone, and conglomerates, the latter 
 mainly of sands and clays; the fossils of the former are, therefore, 
 mainly marine animals, of the latter mainly fresh- water and land 
 animals and plants, though marine animals are also found. In both 
 Europe and America the coal-basins are underlaid by the former, 
 which, moreover, outcrop all around^ forming a penumbral margin 
 
360 PAL-ffiOZOIC SYSTEM OF KOCKS. 
 
 to the dark areas representing coal-basins on geological maps (see 
 map, page 303). In the Mississippi Valley the sub-Carboniferous 
 rocks are chiefly limestones, abounding in fossils; In Pennsylvania 
 the hard Pocono and Pottsville form broad plateaus. The latter is 
 the " Olean Conglomerate " at " Eock City," south of Clean, K. Y. 
 The two hard strata form also the double mountain rims about the 
 anthracite basins. 
 
 Carboniferous Proper — Rock-System or Coal-Measures. 
 
 The Name. — The Carboniferous period is but one of the three 
 periods of this age. The Carboniferous age is, again, but one of the 
 three ages of the Paleozoic era, while the Palaeozoic era is itself but 
 one of the four great eras, exclusive of the present, of the whole 
 recorded history of the earth. The Carboniferous period, therefore, 
 is probably not more than a very small part of that recorded history. 
 Yet, during that period were accumulated, and in the strata of that 
 period (Coal-measures) are still inclosed, the larger portion of all 
 the woriced coal, and prolably the larger part of all the worTcable coal 
 'in the world. It is essentially the coal-hearing period. When we 
 remember that every geological period has its characteristic fossils, 
 by means of which the formation may be at once recognized by the 
 experienced eye, it is easy to see the importance of this simple fact as 
 a guide to the prospector. It has been estimated that the money, time, 
 and energy uselessly expended in the State of New York in explora- 
 tions for coal, where any geologist might be sure there was no coal, 
 would suffice to make a geological survey of the State ! The same 
 may be true of Great Britain and other countries. 
 
 Thickness of Strata. — Although constituting so small a portion of 
 the whole stratified crust of the earth, the coal-measures are in some 
 places of enormous thickness. In Nova Scotia they are 13,000 feet; 
 in South Wales, 12,000 feet; in Pennsylvania, 4,000 feet; in West 
 Virginia, over 4,500 feet; in Indian Territory, 8,000 to 10,000 feet. 
 
 Mode of Occurrence of Coal. — Such being the thickness of the coal- 
 measures, it is evident that but a small proportion consists of coal. 
 The coal-measures consist, in fact, of thick strata of sandstone, shales, 
 and limestone, like other formations ; but in addition to these are in- 
 terstratified thin seams of coal and beds of iron-ore. Even in the 
 richest coal-measures, the proportion of coal to rock is not more than 
 as 1 to 50, and the proportion of iron is still much smaller. In some 
 coal-fields, as, for example, in the Appalachian, mechanical sediments, 
 shales, and sandstones predominate; in others, as in the Western 
 coal-fields, organic sediments or limestone predominate. 
 
 The five kinds of strata mentioned are repeated in the same coal- 
 basin very many times — perhaps 100 or more, as in the accompanying 
 
EOCK-SYSTEM OR COAL-MEASURES. 
 
 361 
 
 section ; but, in comparing one coal-field with another, or in the same 
 coal-field, in comparing one portion of the series with another, there is 
 no regular order of succession discoverable. Except that 
 immediately in contact with the seam, and beneath it, 
 
 Sh 
 
 1 1.1/ ! I 
 
 there is nearly always a thin stratum of fine fire-clay, sa 
 This constant attendant of a coal-seam is called the un- 
 der-day. Again, immediately above, and therefore form- 
 ing the roof of the opened seam, there is frequently, 
 though not so constantly, a shale which, being impreg- 
 nated with carbonaceous matter, is called the llach shale 
 or Hack slate. These accompaniments are, however, 
 usually too thin to appear on sections. 
 
 In different portions, however, of the same coal-field 
 at the same geological horizon, we are apt to find the 
 same order. This is the necessary result of the con- 
 tinuity of the strata over the whole basin. If we repre- 
 sent coal-basins, with their five different kinds of strata, 
 by reams of variously - colored paper, then, while the 
 order of succession may be different in the different 
 reams, and in the upper or lower portion of the same 
 ream, yet at the same level we find the same order in 
 every portion of the same ream. This is a test of a pio. 
 coal-field even when separated by denudation into sev- 
 eral basins. It is also a mode of identifying individual 
 coal-seams; for, if the strata be continuous, then the 
 seam will have the same accompanying strata above and 
 below. The Pittsburg seam has been thus identified, 
 with great probability, over an area of 14,000 square miles, and, allow- 
 ing for removal by denudation, over an orignal area of 34,000 square 
 miles. Eogers thinks the original area may have been 90,000 square 
 miles. This rule for the identification of coal-seams of known value 
 is often of practical importance ; but it must be remembered that the 
 strata of coal-measures, both the seams and the accompanying shale 
 and sandstones, like all other strata, were originally overlapping 
 beds with edges thinning out (page 181). Kevertheless, there is fair 
 continuity in the strata of the coal-measures, especially when we 
 take into consideration all the erosion and faulting which they have 
 suffered (Figs. 455-459). 
 
 Plication and Denudation. — Coal-bearing strata, like all other strata, 
 were, of course, originally horizontal (page 181) and continuous, but, 
 like other strata, they are now found sometimes horizontal and some- 
 times dipping at all angles, and folded in the most complex manner. 
 In the Appalachian region, especially in the anthracite region of 
 Northern Pennsylvania, the strata are very much disturbed and the 
 
 454. — Ideal 
 Section, showing 
 Alternation of 
 Different Kinds 
 of Strata : Ss, 
 Sandstone ; Sh, 
 Shale ; I, Limes- 
 tone ; i. Iron; 
 and c. Coal. 
 
362 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 coal-seams interstratified with them are often nearly perpendicular 
 (Fig. 455), while in Illinois and Iowa the coal-strata are nearly or quite 
 
 FiQ. 455.— Section of Panther Creek Coal-Basin (after Ashbumer). 
 
 horizontal (Fig. 456). But, whether horizontal, or gently folded, or 
 strongly plicated, in all cases denudation has carried away much of the 
 
 Fig. 456.— Illinois Coal-Field (after Daddow). 
 
 Upper portions, leaving them in isolated patches as mountains or basins, 
 as shown in the map of Northern Pennsylvania (Fig. 458) and in the 
 section (Fig. 457). 
 
 Fig. 457.— Section of Appalachian Coal-Field, Pennsylvania, showing Effects of Erosion on Gently 
 Undulating Strata (after Lesley). 
 
 Fig. 458. — Map of Anthracite Region of Pennsylvania (after L- 
 
COAL-MEASURES. 363 
 
 By means of the rule for identifying seams given above, it is often 
 easy to trace the same seam from one basin to another, or from one 
 mountain-side to another, with great certainty. 
 
 Faults. — It is plain, from what has been said above, that there is 
 an essential difference between a coal-seam and a metalliferous vein. 
 Coal-seams are conformable with the strata, and are therefore worhed 
 wholly between the strata. This would be a comparatively easy matter 
 if it were not for slips or faults which often occur, and sometimes make 
 the working unprofitable. In case of a fault, it is important to remem- 
 ber the rule already given on page 341, viz., that most commonly the 
 
 Fig. 459.— Section across Yarrow Colliery, showing the Law of Faults (after De la Beche). 
 
 strata on the foot-wall side of the fissure goes upward. In the accom- 
 panying section of Yarrow colliery (Pig. 459) it will be seen that all 
 the slips follow this law. 
 
 Thicksess of Seams. — Coal-seams vary in thickness from a fraction 
 of an inch to forty or fifty feet, or even more. A workable seam must 
 be at least two feet thick. A pure, simple seam is seldom more than 
 eight or ten feet. Mammoth seams, such as occur in the anthracite 
 region of Pennsylvania and in Southern France, are produced by the 
 running together of several seams by the thinning out of the inter- 
 stratified shales and sandstones. They are, therefore, almost always 
 compound seams, i. e., separated by thin partings of clay — too thin to 
 form -a good roof or floor, and therefore all worked together. 
 
 Number and Aggregate Thickness. — In a single coal-field, we have 
 said, the strata, including the coal-seams, are repeated many times. In 
 the South Joggin's section, Nova Scotia, there are eighty-one coal- 
 seams, though most of these are not workable. In North England there 
 are twenty to thirty seams. In South Wales there are more than 100 
 seams, seventy of which are worked. In South Lancashire there are 
 seventy-five seams over one foot thick ; in Belgium 100 seams, and in 
 Westphalia 117 seams. The aggregate thickness of all the seams in 
 Lancashire is 150 feet ; in Pottsville, Pennsylvania, 113 feet ; in West- 
 ern coal-fields, 70 feet ; in Westphalia, 274 feet ; in Mons, 250 feet.* 
 
 The thickest and purest are usually near the middle of the series. 
 Evidently the conditions favorable for the formation and preservation 
 of coal commenced gradually, even back in the Devonian, reached 
 their culmination in the middle Coal-measures, and gradually declined. 
 
 * Nature, vol. xlii, p. 322, 1890. 
 
364 PALAEOZOIC SYSTEM OF ROCKS. 
 
 However, coal has been formed in all geologic ages since the Car- 
 boniferous, and is still forming. 
 
 Coal Areas of the United States. — In no other country are the coal- 
 fields so extensive as in the United States. The principal coal-fields 
 are shown on map of Eastern United States, on page 302. 
 
 1. Appalachian Coal-Field. — This, the greatest coal-field in the 
 world, commences in Northern Pennsylvania, covers the whole of West- 
 ern Pennsylvania and Eastern Ohio, a large portion of West Virginia 
 and Eastern Kentucky, then passes southward through East Tennessee, 
 touches the northwest corner of Georgia, and ends in Middle Alabama. 
 In general terms, it occupied the western slope of the Appalachian 
 from the confines of New York to Middle Alabama. Its area is at 
 least 60,000 square miles. 
 
 2. Central Goal-Field. — This covers the larger portion of Illinois, 
 the southwest portion of Indiana, and the western portion of Ken- 
 tucky. Its area is about 47,000 square miles. 
 
 3. Western Goal-Field. — This covers the southern portion of Iowa, 
 the northern and western portion of Missouri, the eastern portion of 
 Kansas, and then passes southward through Arkansas, Indian Terri- 
 tory, and into Texas. Its area is estimated at 78,000 square miles. 
 These two coal-fields are seen to be connected by sub- Carboniferous. 
 They are probably one immense field separated by erosion. 
 
 4. Michigan Goal-Field. — In the very center of the State of Michi- 
 gan there is another coal-field occupying an area of 6,700 square miles. 
 
 5. Rhode Island Goal-Field. — A small patch of 500 square miles' 
 area is found in Ehode Island, extending a little into Massachusetts. 
 
 6. Nova Scotia and New Brunswick. — This is a large area on both 
 sides of the Bay of Pundy. It is estimated at 18,000 square miles. 
 
 The following table gives approximately the areas of American 
 coal-fields of the Carboniferous age : 
 
 Appalachian 60,000 
 
 Central 47,000 
 
 Western 78,000 
 
 Michigan 6,700 
 
 Ehode Island 500 
 
 192,200 
 Nova Scotia 18,000 
 
 210,000 
 
 Of the 190,000 square miles' coal-area of this age in the United 
 States, 130,000 square miles is estimated as workable. 
 
 Extra-Carboniferous Coal. — All the fields mentioned above belong 
 to the Carboniferous age. But, besides these, the United States is very 
 rich in coal of other periods. Probably 50,000 square miles might be 
 
COAL-MEASDKES. 
 
 365 
 
 added from strata of later times, making in all 170,000 square miles 
 of workable coal. But oi these latter fields we will speak in their 
 proper places. 
 
 Coal-Areas of Different Countries compared. — The following table 
 exhibits the comparative coal-areas of the principal coal-producing 
 countries of the world : 
 
 China and Japan 200,000 square miles. 
 
 United States 194,000 
 
 India 35,000 
 
 Russia 27,000 
 
 Great Britain 9,000 
 
 Germany 3,600 
 
 France 1,800 
 
 Belgium, Spain, and other countries 1,400 
 
 Total 471,800 " 
 
 Relative Production of Coal. — But if the extent of cosl-area repre- 
 sents approximately the amount of wealth of this kind present in the 
 strata, the production of coal represents how much of this wealth is 
 active capital; it represents the development of those industries de- 
 pendent on coal. The following table is compiled from the best 
 sources at hand: 
 
 ANNUAL COAL PRODUCTION IN 
 MILLIONS OF TONS. 
 
 1845. 
 
 1864. 
 
 1874. 
 
 1884. 
 
 1804. 
 
 1899.* 
 
 1901.* 
 
 United States 
 
 4-5 
 31-5 
 
 22 
 90 
 
 io 
 
 10 
 
 50 
 
 128 
 
 46 
 
 a 
 
 15 
 
 106 
 
 160 
 
 70 
 
 20 
 18 
 
 152 
 
 164 
 
 94 
 
 26 
 19 
 
 243 
 295 
 109 
 39 
 33 
 22 
 13 
 28 
 
 266 
 
 
 
 Germany 
 
 
 Austria-Hungary 
 
 
 
 France 
 
 4-1 
 4-9 
 
 
 Belgium 
 
 
 
 
 
 
 
 
 
 
 * Metric tons (2,204-6 pounds). 
 
 Inspection of the table shows that in the principal coal-producing 
 countries there is a rapid increase of production. At the present rate 
 of consumption the world's supply of coal would probably last several 
 centuries, but the rapidly increasing rate is ominous. The statements 
 of former years that the supply of coal was inexhaustible were not 
 only false and foolish, but pernicious. Unfortunately, the mining 
 processes in America are wasteful and conducted with too little 
 regard for the future. As the most valuable product of Nature, 
 essential to modern civilization and impossible of reproduction, the 
 stores of fuel should be carefully guarded for the benefit of all the 
 people. 
 
366 
 
 PALAEOZOIC SYSTEM OF EOCKS. 
 
 Origin of Goal, and of its Varieties. 
 
 That coal is of vegetable origin is now no longer doubtful. We 
 will only briefly enumerate the evidences on which is based the present 
 scientific unanimity on this subject : 
 
 1. The remains of an extinct vegetation are found in abundance in 
 immediate connection with coal-seams ; stumps and roots in the under- 
 clay, and leaves and stems in the roof shale in. contact with the seam 
 and even imbedded in the seam itself. 3. These vegetable remains are 
 not only associated with the coal-seam, but have often themselves be- 
 come coal, though still retaining their original form and structure. 
 3. Not only these easily-recognizable imbedded vegetable fragments, 
 but the imbedding substance also, the whole coal-seam, even the most 
 structureless portions, and the hardest varieties, such as anthracite, 
 when carefully prepared in a suitable manner and examined with the 
 microscope, show vegetable structure. Even the ashes of coal, carefully 
 examined, show vegetable cells with characteristic markings. The fol- 
 lowing figures show the results of such examination. 4. A perfect gra- 
 
 FiG. 460.— Section of Anthracite; a, natural size; 
 6 and c, magnified (after Bailey). 
 
 Fig. 461.— Vegetable Structure in Coal 
 (after Dawson). 
 
 dation may be traced from wood or peat, on the one hand, through 
 brown coal, lignite, bituminous coal, to the most structureless anthra- 
 cite and graphite, on the other, showing that these are all different 
 terms of the same series. In chemical composition, too, the same un- 
 broken series may be traced. 5. Lastly, the best and most structure- 
 less peat, by hydraulic pressure, may be made into a substance having 
 many of the qualities and uses of coal. 
 
 We may, with confidence, say that all the hydrocarbon known to 
 us in the form of peat and coal are certainly of plant origin. The 
 carbon previously existed as carbonic acid in the atmosphere, and 
 has been reduced from that condition only- by organic agency. 
 
ORIGIN OF COAL AND ITS VARIETIES. 357 
 
 Varieties of Coal. — The varieties of coal depend upon the purity, 
 upon the degree of carionization, and upon the proportion of fixed 
 and volatile matter. 
 
 Varieties depending upon Purity. — Coal consists partly of organic 
 or combustible and partly of inorganic or incombustible matter. On 
 burning coal, the organic, combustible matter is consumed, and passes 
 away in the form of gas, while the inorganic, incombustible, is left as 
 ash. Now, the relative proportion of these may 'vary to any extent. 
 We may have a coal of only one or two per cent asl^. We may have a 
 coal of five, ten, fifteen, twenty per cent ash ; the coal is now becoming 
 poor. We may have a coal of thirty or forty per cent ash; this is 
 called bony coal, or shaly coal; it is the valueless refuse of the mines. 
 We may have a " coal " of fifty or sixty per cent ash ; but it now loses 
 the name as well as the ready combustibility of coal, and is called 
 coaly shale. Finally, we may have a deposit of seventy, eighty, ninety, 
 ninety-five per cent ash; and thus it passes, by insensible degrees, 
 through black shale into perfect shale. This passage is often observed 
 in the roof of a coal-seam. 
 
 ISTow, all vegetable tissue contains incombustible matter, which, on 
 burning, is left as ash. The amount of ash in vegetable matter is on 
 an average about one to two per cent. But, as in the process of 
 change from wood to coal, much of the organic matter is lost (p. 369 
 et seq.), and the relative amount of ash is thereby increased, we may 
 say that, if a coal contains five per cent or less of ash, it is absolutely 
 pure — i. e., its ash comes wholly from the plants of which it is com- 
 posed; but if a coal contains more than ten per cent ash, it is prob- 
 ably impure — i. e., mixed with mud at the time of its accumulation. 
 
 Varieties of Coal depending on the Degree of Carbonization.— The 
 previously-mentioned varieties consist of pure and impure coals; 
 these consist of perfect and imperfect coals. We find the vegetable 
 matter, accumulated in different geological periods, in different 
 stages of that peculiar change called carbonization. Brown coal and 
 lignite are examples of such imperfect coal. They are always com- 
 paratively modern. 
 
 Varieties depending upon the Proportion of Fixed and Volatile 
 Matter. — Coal, even when pure and thoroughly carbonized, consists 
 still of many varieties, having different uses, depending upon the pro- 
 portion of fixed and volatile matters. These are the true varieties of 
 coal. 
 
 In pure and perfect coal, then, the combustible matter is part fixed 
 and part volatile. These may be easily separated by heating to red- 
 ness in a retort. By this means the volatile matter is all driven off 
 and may be collected as tar, oil, etc., in condensers, and as permanent 
 gases in gasometers ; and the fixed matter is left in the retort as coke. 
 25 
 
368 PALEOZOIC SYSTEM OF ROCKS. 
 
 'Now, the proportion of these may vary greatly in different coals, and 
 affect the uses to which the coal is applied. For example, when the 
 coal consists wholly of fixed carbon, it is called graphite. This is not 
 usually considered a variety of coal, because it is not readily combusti- 
 ble ; but it is evidently only the last term of the coal series. Its soft, 
 greasy feel, its metallic luster and incombustibility, and its uses for 
 pencils, as a friction-powder, and as a material for crucibles, are well 
 known. 
 
 When the conj,bustible matter of the coal contains ninety to ninety- 
 five per cent fixed carbon, it is .called anthracite. This is a hard, brill- 
 iant variety, with conchoidal fracture and high specific gravity. It 
 burns with almost no flame and produces much heat. It is an admira- 
 ble coal for all household purposes, and, witli liot blast, may be used in 
 iron-smelting furnaces. 
 
 If the combustible matter contains eighty to eighty-five per cent 
 fixed carbon, and fifteen to twenty per cent volatile matter, it becomes 
 semi-anthracite, or semi-bituminous coal, of various grades. These are 
 free-burning, rapid-burning coals, producing long flame and high tem- 
 perature, because they do not cake and clog. They are admirably 
 adapted for many purposes, but especially for the rapid production of 
 steam, and therefore for locomotive-engines, and hence are often called 
 steam-coals. 
 
 If the volatile combustible matter rises to the proportion of thirty 
 to forty per cent, it becomes full bituminous coals,- which always burn 
 with a strong bright flame, and often cake and form clinkers. This is 
 perhaps the commonest form of coal, and may be regarded as typical 
 coal. 
 
 If the volatile matter approaches or exceeds fifty per cent, then it 
 forms highly bituminous or fat or fusing coals. This variety is espe- 
 cially adapted to the manufacture of gas and of coke. 
 
 Besides these there are several varieties depending on physical 
 character. Thus cannel or parrot coal is a dense, dry, structureless, 
 lusterless, highly-bituminous variety, which breaks with a conchoidal 
 fracture. There may be also some varieties depending upon the kind 
 of plants of which coal was made, but of this we have no certain evi- 
 dence. 
 
 Origin of these Varieties.— There can be little doubt that these, 
 the true varieties, are produced by slight differences in the nature and 
 degree of chemical change in the process of carbonization. 
 
 It will be seen by the following table, giving approximate formulas, 
 that vegetable matter and coal of various grades have the same general 
 composition, except that in the latter case some of the carbon and 
 much of the hydrogen and oxygen have passed away in the process of 
 change : 
 
ORIGIN OF COAL AND ITS VARIETIES. 
 
 369 
 
 Vegetable matter, cellulose CjuHcoOso 
 
 Bituminous coal CjeHjoOa 
 
 Anthracite " C40H8O 
 
 Graphite " pure 
 
 The gradual loss of the hydrogen and oxygen is still better shown 
 in the following table, in which the constituents are given in propor- 
 tionate weights instead of equivalents, and the carbon reduced to a con- 
 stant quantity : 
 
 KINDS OF VEGETABLE MATPEE AND COALS. 
 
 • 
 
 Carbon. 
 
 Hydrogen. 
 
 Oxygen. 
 
 Cellulose 
 
 100 
 100 
 100 
 100 
 100 
 100 
 100 
 
 13-88 
 6-88 
 6-58 
 4-63 
 3-20 
 1-66 
 0-00 
 
 111-11 
 86-42 
 63-33 
 34-60 
 10-26 
 3-33 
 0-00 
 
 • 
 
 Wood 
 
 Peat 
 
 Lignite 
 
 Cannel coal 
 
 Anthracite coal 
 
 Graphite coal 
 
 
 Now, there are two modes of decomposition to which vegetable 
 matter may be subjected, viz. : 1. In contact with air ; and, 2. Out of 
 contact with air. The first is partly decomposition, and partly oxida- 
 tion by the air (eremacausis) ; the second is wholly decomposition. 
 
 In Contact with Air.- — Under these conditions the carbon of the 
 vegetable matter unites with the oxygen of the vegetable matter, form- 
 ing carbonic acid (COg) ; and the hydrogen of the vegetable matter 
 unites with the oxygen of the air, forming water iJiiO). Further, it 
 is evident that, for every equivalent of carbon thus lost, there are two 
 equivalents of oxygen and four equivalents of hydrogen lost, so as 
 always to maintain the same relative propor- 
 tion of H, and viz., the proportion forming 
 water (HgO). The final result of this process 
 is pure carbon. It is very improbable, how- 
 ever, that anthracite or graphite is formed in 
 . this way ; for vegetable matter, by aerial de- 
 cay, falls to powder. It is very probable, however — nay, almost cer- 
 tain — that a peculiar substance, pulverulent and retaining vegetable 
 structure in a remarkable degree, called mineral charcoal, found very 
 commonly in some stratified coals has been formed by partial aerial 
 decay, somewhat as represented in the table. Mineral charcoal has 
 a high percentage of carbon, with very little hydrogen and oxygen. 
 
 Out of Contact with Air.— When vegetable matter is buried in 
 mud or submerged in water, its elements react on each other. Some of 
 the carbon unites with some of the oxygen, forming carbonic acid 
 (COg) ; some of the carbon unites with some of the hydrogen, forming 
 
 Cellulose CseHeoOso 
 
 Decayed CssUssOjs 
 
 More decayed. . C84llBa026 
 Final result. . .C21 
 
370 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 carbureted hydrogen or marsh-gas (OH4) ; and some of the hydrogen 
 unites with some of the oxygen, forming water (HgO). These products 
 are probably formed in all cases of vegetable decomposition under these 
 conditions : If, for example, we stir up the mud at the bottom of stag- 
 nant pools where weeds are growing, the bubbles which. rise always 
 consist of a mixture of COg and CH4. In every coal-mine these same 
 gases are constantly given off ; the one being the deadly chohe-damp 
 and the other the terrible fire-damp of the miners. Now, by varying 
 the relative amounts of these products, it is ^asy to see how all the 
 principal varieties of bituminous coal may be formed. I have given 
 below the approximate composition of typical varieties of bituminous 
 coal, and of graphite, and constructed formulae expressing the chemical 
 change by which they are formed : 
 
 Vegetable matter — cellulose CaaHeoOjo* 
 
 . ( 9C0, ) 
 
 Subtract \ 3CH4 \ CuHsiOa, 
 
 ( llHjO ) 
 
 And there remain CatHaeO = eannel. 
 
 Again, vegetable matter CsoHjoOso 
 
 Subtract \ SCHi )■ CioH^oOjs 
 
 ( 14HaO ) 
 
 .... . n TT r> i bituminous coal from 
 
 And there remam, OjeHjoOs = -j 
 
 Again, vegetable matter CsbHouOso 
 
 f 1000, ) 
 Subtract \ IOCH4 \ CjoHaoOso 
 
 ( lOHsO ) 
 
 And there remains Cu = graphite. 
 
 Staffordshire. 
 
 The composition of vegetable matter varies considerably. The 
 composition of the varieties of coal is differently given by different 
 authorities. Different reactions from those above given might be con- 
 trived which would give as good results. These reactions, therefore, 
 are not given as certainly the actual reactions which take place. They 
 are only intended to show the general character of the changes which 
 take place in the formation of coal. 
 
 MetamorpMc Coal. — It is probable that bituminous coal is the nor- 
 mal coal formed by the above process, and that the extreme forms, an- 
 thracite and graphite, are the result of an after-change produced by 
 
 * The composition of wood — timber — is usually given as about CuHisOa. I have 
 taken the formula of cellulose instead, viz., CaHioOa; or, taking six equivalents for con- 
 venience of calculation, CaaHeoOso. I believe this to be much nearer the composition of 
 vegetable matter of the Coal period than is the formula of hard wood like oak or beech. 
 All the results may be worked out, however, with equal ease by the use of either formula 
 for vegetable matter. 
 
ORIGIN OF COAL AND ITS VARIETIES. 371 
 
 effects resulting from the disturbances and folding of the enclosing 
 strata. These effects are partly pressure, partly a moderate degree of 
 heat due to the pressure, and partly volatilization permitted hy the 
 fracturing and erosion of the strata. 
 
 The variation in chemical and physical characters of the coals is 
 due to several factors: conditions of deposition, length of exposure 
 before burial, porosity of the rock-cover, and, finally, the disturb- 
 ances of the enclosing strata. It has been shown that there is no 
 close relation in Pennsylvania between the folding of the rocks and 
 the anthracitism of the coal.* It should be noted that the name 
 "bituminous" is a misnomer, since even the coals rich in volatile 
 matter do not contain bitumen, although it is produced from the coal 
 by distillation. No large store of oil or gas has been traced to the 
 coal-beds. It is true that gases are passing off from the coals (see 
 page 370), but they do not seem to have been reservoired (see page 
 401 and following). 
 
 There can be no doubt that the graphitic and anthracitic varieties 
 of coal are usually associated with folding and metamorphism of the 
 strata : 1. In the universally-folded and metamorphic Archasan rocks 
 only graphite is found. 2. In Pennsylvania, in the strongly-folded 
 eastern portion of the field, the coal is anthracite; while, as we go 
 westward^ and the rocks are less and less disturbed, the coal is gen- 
 erally more bituminous, until, when the rocks are horizontal and 
 unchanged, the coal is usually highly bituminous. The same has been 
 observed in Wales: anthracite is always found in metamorphic re- 
 gions, and the coal is more and more bituminous as the rocks are less 
 and less metamorphic. 3. Again, the anthracite condition of coal may 
 be sometimes traced to the local effect of trap or volcanic overflows. 
 
 Anthracite may, indeed, be regarded as metamorphic coal, but it is 
 not probable that bitumen is its necessary correlative; it is not prob- 
 able that the heat of metamorphism is sufficient to produce destructive 
 distillation. We have already shown (page 230) that a moderate heat 
 of 300° to 400° Fahr. in the presence of water is sufficient to produce 
 metamorphism. Such a degree of heat would, doubtless, hasten the 
 process explained on page 370. The folding and erosion of the rocks, 
 and the consequent exposure of the edges of the seams,- would still 
 further hasten the process, and bring about anthracitism by facili- 
 tating the escape of the products of decomposition. In all coal-mines 
 CO2, CH4, and HjO, are eliminated now; only continue this process 
 long enough, and anthracite and, finally, graphite is the result. We 
 must conclude, then, that high heat is not necessary to produce an- 
 
 * J. J. Stevenson, Origin of the Pennsylvania Anthracite, Bull. Geol. Amer., vol. v, 
 pp. 39-70, 
 
372 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 thracitism ; for, if it is unnecessary for metamorphism of rocks, much 
 less is it necessary for metamorphism of coal. . 
 
 Plants of the Coal — Their Structure and Affinities. 
 
 The flora of the coal-measures is one of the most abundant and 
 perfect of all extinct floras. Although no enumeration has been pub- 
 lished in many years and the literature on the subject is widely scat- 
 tered, it is estimated that there are about 13,500 known fossil species 
 of plants, and of these about 2,500, or nearly one-fourth, are from 
 the coal-measures. This florar is peculiarly interesting to the geolo- 
 gist, not only on account of its relative abundance, but also and 
 chiefly because, being the first diversified and somewhat highly-organ- 
 ized flora, it is natural to suppose that the great classes and orders 
 of the vegetable Mngdom commenced to diverge here; and therefore 
 it furnishes a key to the evolution of land-plants. "We will therefore 
 discuss the affinities of these plants somewhat fully. 
 
 Where found.' — The plants of the Coal are found principally : 1. In 
 the form of stools and roots in their original position in the under 
 clay. 2. Of leaves, and branches, and flattened trunks, on the upper 
 surface of the coal-seam, and in the overlying shale; 3. And, finally, 
 in the form of logs, apparently drift-timber, in the sandstones above 
 the coal-seam. The " roof " shale overlying the seam is often full of 
 leaves and fronds of ferns, and of the flattened trunks of ofher fami- 
 lies, in the most beautiful state of preservation, so that even the flnest 
 venation of the leaves is perfectly distinct. In some cases where the 
 shale is light-colored, so as to contrast strongly 
 with the jet-black leaves, the effect on first opening 
 a seam is very striking, and has been compared to 
 the frescoes on the ceilings of Italian palaces. 
 
 Principal Groups. — Leaving out some plants of 
 doubtful affinity, the plants of the Coal may be re- 
 ferred to five groups or divisions, viz.: Oymno- 
 spermSj Ferns, Lepidodendrids, Sigillarids, and 
 CalamaricB. It is usual to refer these last three to 
 the two orders, Lycopods and Equisetse; but they 
 are so peculiar, and their affinities still so doubt- 
 ful, that we prefer to treat them as distinct groups. 
 All these, as already seen, commenced in the 
 D.evonian, as did also the preservation of their tis- 
 sues as coal ; but both the vegetation and the condi- 
 tion necessary for their preservation culminated in the Coal period, 
 and therefore we have put off their discussion until now. Contrary 
 to our usual custom, we will commence with the highest, viz. : 
 
 1. Gymnosperms, — A considerable number of genera of these are 
 
 a Gymnoeperm : a, 
 bart ; b, wood ; c, 
 medallary Bheath ; 
 d, pith. 
 
PLANTS OF THE COAL. 
 
 373 
 
 known, but all qtiite different from living Conifers. They are mostly 
 found: 1. In the form of trunks or logs in the sandstones above the 
 coal-seams (Fig."462) ; 2. In the form of leaves, 
 l^li^.^^^ twigs, and leafy branches in the roof-shale 
 
 (Fig. 463) ; 3. In the form of nut-like fruits 
 of many kinds, also in the roof-shale. But 
 they are not found as stumps and roots in situ 
 in the under-clay. From this we conclude that 
 they did not grow in the coal-swamps, but on 
 
 Fig. 463.— Araucarites gracilis, 
 reduced (after Daweon). 
 
 Fig. 464.— Section of same : b, woody i 
 and pith-rays. 
 
 ; c, pith 
 
 the high ground about them; that their leaves, small branches, and 
 fruits were washed down into the swamps, and their trunks were some- 
 , times drifted down by floods which overwhelmed and buried the coal. 
 
 Fig. 465. 
 Figs. 465-468. 
 
 Fig. 466. 
 
 Fig. 408. 
 
 Fig. 467. 
 ■Broad-Leaved Gtmnosperms. Living Kepresbntatives of some Coal-Plant 
 TVPES. 465. Ginlcgo biloba, a brancli. 466. Section of fruit. 467. A leaf, natural size. 
 468. Phyllocladus, a brancli. 
 
 The trunks and woody branches are known to be those of Gym- 
 nosperms by the characteristic Gymnospermous structure of the wood 
 (Figs. 392, 393, and 394, page 341), especially the disk-like markings 
 
3Y4 
 
 PALAEOZOIC SYSTEM OF BOCKS. 
 
 on longitudinal section; and their relationship to Conifers is shown 
 by a distinct bark, rings of growth, and pith (Fig. 463). But the 
 large size of the pith of some seems to ally them with the Cycads. 
 
 Fig. 471. 
 
 Figs. 469-471. — Fruits ov Gtmnospebms, pboeablt including those of Cordaites: 469. Trig- 
 nocarpum (after Newberry). 470. Cardiocarpon (after Newberry and Dawson). 471. Khabdo- 
 carpos. 
 
 But the leaves, leafy branches, and fruits are still more interesting 
 and significant. By the study of these, Carboniferous Gymnosperms 
 
PLANTS OF THE COAL. 
 
 375 
 
 seem to fall naturally into two groups, viz., those with small, spine- 
 like leaves (Fig. 463), reminding us of the yew or the Araucaria, and 
 those with broad, strap-shaped, or tongue-like leaves, with parallel or 
 radiated venation, like that strange, broad-leaved living Gymnosperm, 
 the Ginkgo (Pig. 467). One of the common- 
 est and most characteristic of this group is the 
 Gordaites. Ail parts of this plant are known ; 
 so that we may restore it with some confidence 
 (Fig. 472). We may imagine a cjdindrical, 
 branching trunk, sometimes sixty to seventy 
 ifeet high, clothed atop with long, strap-shaped 
 leaves like a Dracaena, and bearing clusters of 
 nut-like fruits. Many of the fruits repre- 
 sented in Figs. 469-471 are from this tree. 
 
 Affinities of Carboniferous Gymnosperms.— 
 Most of the Gymnosperms of this time were 
 not typical Conifers, and it is only in "the 
 uppermost Coal-Measures and the Permian 
 that real Conifers are found. There are few 
 signs of true cones in the coal. All the Cor- 
 
 daites bore nut-like or winged fruits. Cycads 
 
 and the broad-leaved Ginkgo are the chief i'ig. 472.-CordaiteB (restored 
 types that now bear fruits which might be ^ 
 
 compared with thgse. These Gymnosperms bear similar plum-like 
 fruits,' with large, nut-like seeds (Figs. 465, 466). The fruit of the 
 California nutmeg (Tumion, yew family) is also comparable. It is 
 about the size of a large plum, with a nut-like seed as large as a 
 pecan-nut. It is therefore in the Cycads, the Ginkgos, and the yew 
 
 FiQ. 473 —Evolution of the Ginkgos : o, J, and c, Cordaites, Carboniferous ; d, Ginljgopliyllum, 
 Permian ; e, Ginkgo digitata, OOlite ; /, Ginkgo biloba, living. 
 
 family that we must seek for allies of the coal Gymnosperms. In 
 fact, all gradations in shape of the leaf may be traced between the 
 Cordaites (Fig. 473, a, I, c) of the Carboniferous and Ginkgophyl- 
 lum of the Permian {d) to Ginkgo {e, f) of the Jurassic and the 
 
376 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 present time. The Cordaites family may be regarded as the most 
 generalized of the true Gymnosperms, connecting Ginkgos and Cycads 
 on the one hand with Taxaceous Conifers on the other. 
 
 2. Ferns. — Ferns are the most abundant plants of the Coal period, 
 both as to individuals and as to variety of species. About one third to 
 one half of all the known species -of coal-plants, both in this country 
 and in Europe, belong to this order. They represent both ordinary 
 forms, i. e., those with creeping stems, and Tree-fernSj like those now 
 growing only in warm latitudes (Fig. 474). They are known to be 
 ferns by their large complex fronds (Fig. 475), sometimes ten to 
 twenty feet long; by the dichotomous venation of their leaves (Fig. 
 479) ; and by the position of their org'ans of fructification (spore- 
 cases) on the under-surfaces of the leaves (Figs. 480 and 481). In 
 some localities these spore-cases are so abundant that the coal seems 
 
 to be almost wholly made up 
 of them. The trunks of Tree- 
 ferns are known by the large, 
 ragged, ovoid marks left by 
 the falling of the fronds (leaf- 
 
 PiQ. 474.— Living Tree-Fern. 
 
 Fig. 475.— Megaphytum. a Coal-Fern 
 restored (alter Dawson). 
 
 scars — Figs. 489-491). Some coal Tree-ferns had their large fronds 
 in two vertical ranks (Megaphytum — Fig. 475). 
 
 , The Ferns of the coal are in general most nearly related to the 
 small, tropical order Marattiacese, among living plants, though spe- 
 cies have rarely been met which appear to show a connection with 
 several modern families, including the Gleicheniaceae and the Hy- 
 menophyllaceas. However, besides the types whose fern, nature is 
 
 _ clearly shown there is also a large class of stems, petioles, and fronds, 
 such as Alethopteris, whose forms^are precisely similar to those of 
 Ferns, but whose internal structure combines so many of the charac- 
 ters of Cycads with those of Ferns as to lead to the recognition of a 
 
 - group, Cycadofilices, intermediate between the two. 
 
PLANTS OF THE COAL. 
 
 377 
 
 The next three groups we will discuss more fully for two reasons : 
 First, the Gymnosperms were probably mostly upland plants, and 
 only found their way into the coal-swamps by accident, being in fact 
 brought down by freshets. The Ferns formed the thick underbrush 
 of the coal-swamps. Neither of these contributed a very large share 
 to the material of the coal-seams. The great trees of the coal- 
 swamps, and which formed the larger part of the material preserved 
 as coal, were Lepidodendrids, Sigillarids, and Calamarim. 
 
 Again, the Cordaites and Ferns were unmistakably Gymnosperms 
 and Ferns, though certainly with characters connecting with other 
 orders and classes; but the three orders now about to be discussed 
 
 Fig. 479. 
 
 Fio. 476. 
 
 Fig. 477. 
 
 Fig. 478. 
 
 Fig. 480. 
 
 Figs. 476-480. — Coal-Ferns : 476. Callipteridium Sullivantii (after Lesquerenx). ^77. Pecopteris 
 StroBSii (after Lesquereux). 478. Alethopteris masBilunis (after Lesquereux). 479. Same en- 
 larged to show dichotomous venation. 480. Neuropteris llexuosa (after Brongniart). ^ 
 
 combine so completely the characters of widely-separated classes that 
 for a long time there was doubt as to their real place. For that very 
 reason, however, they are peculiarly interesting to the evolutionist. 
 
378 
 
 PALAEOZOIC SYSTEM OF ROCKS. 
 
 FiQ. 484. 
 
 Fig. 485. 
 
 Fig. 487. 
 
 Figs. 481-488.— Coai-Fkbits (after Lesquerenx): 481. Pecopteris Strongii, ehowing fructification; 
 6, a leaflet enlarged. 483. Odontopteris Wortheui. 483. Sphenqpterie alatns. 484. Neuropteris 
 ovata. 485. Nenropteria Schauchzeri. 486. Alethopteris lonchitica. 487. OdontopteriB gracil- 
 lima (after Newberry). 488 Sphenopteris splendens (after Xeequereux), 
 
PLANTS OF THE COAL. 
 
 8Y9 
 
 Fig. 489. 
 
 Fio. 490. Fig. 491. 
 
 Pies. 489-491.— Coal-Febns: 489. Leaf -Scars of Palaeopteris, x i (after Dawson). 490. Leaf-Scar 
 , of Megaphytum, x i (alter Dawson). 491. Caulopteris primaeva, showing Leaf-Scars. 
 
 3. Lepidodendrids. — These are so called from the typical genus 
 Lepidodendron. We will (describe only this genus. 
 
 Lepidodendrons are found most commonly in flattened masses rep- 
 resenting portions of the trunk or branches, very regularly marked in 
 rhomboidal pattern, and much resembling the 
 impression of the scaly surface of a Ganoid 
 fish. The name Lepidodendron (scale-tree) 
 is derived from this fact (Figs. 493 to 495). 
 These marks are the scars of the regularly-ar- 
 ranged and crowded leaves. All portions of 
 the plant, however, viz., the roots, the trunk, 
 the branches, the leaves, and the fruit, have 
 been found in abundance. From these the 
 general appearance of the tree has been ap- 
 proximately reconstructed. Imagine, then, a 
 tree two to four feet in diameter at base, forty 
 to sixty feet high, with wide-spreading roots, 
 well adapted for support on a swampy soil ; 
 the surface of the trunk and branches regu- 
 larly marked in rhomboidal pattern, repre- 
 senting the phyllotaxis ; the irunh dividing 
 and subdividing, but not profusely, into 
 branches which are thickly clothed with scale- 
 like, or spine-like, or needle-like leaves (Figs. 
 496 and 498), and terminated by a club-shaped extremity (Figs. 497, 
 499, and 500) like the terminal cones of some conifers, or still more 
 like the club-shaped extremities of club-moss branches — and we will 
 have a tolerably correct idea of the Lepidodendron. 
 
 Fio. 492. — Eeetoration of a Lepi- 
 dodendron, by Dawson. 
 
380 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 The geaeral appearance of the tree is that of an Araucarian conifer, 
 or of a gigantic cliib-rnoss. The fruit, however, turns the scale of afiBn- 
 ity in favor of the club-moss ; for the examination of these, which are 
 
 Fia. 498. 
 
 Pig. 497. 
 
 Fio. 500. 
 
 Figs. 493-500.— Lepidodbndbids: 493. Lepidodendron modulatum (mold of leaf scare) 494 Leoi- 
 dodendron diplotegioides (after Lesquereux). 495. Lepidodendron politnm (after LesQuereux) 
 496. Lepidodendron corrugatum, branch and leaves (after Dawson). 497. Lepidodendron cor- 
 mgatum, branch and fruit (after Dawson). 498. Lepidodendron rigens (after Lesquereux) 
 499. Lepidophloios Acadianus, fruit (alter Dawson). SOO. Lepidostrobua (after Lesquereux) 
 
PLA.NTS OF THE COAL. 
 
 381 
 
 found in great abundance, 
 and known under the 
 name of Lepidostrobus 
 (scale-cone), has shown 
 that they bear on the 
 bases of their scales 
 spores like club-mosses, 
 and not seeds like coni- 
 fers. Also, like club- 
 mosses, there are in some 
 of these plants two kinds 
 of spores *^microspores 
 and macrospores. This 
 would again suggest the 
 conifers, for these organs 
 may be said to represent 
 the stamens and pistils - 
 of higher plants (Fig. 
 501). The external ap- 
 pearance and inflores- 
 cence, therefore, indicate 
 that they are Lycopods, 
 with certain coniferous 
 characters. ' 
 
 This conclusion is en- 
 tirely borne out by the 
 internal structure. -Fig. 
 503 represents an ideal 
 cross and longitudinal 
 section of the stem of a 
 Lepidodendron. It is seen that the stem consists of a dense outer 
 bark or rind, inclosing a great mass of loose cellular tissue or inner 
 
 bark, through the center of which 
 runs a comparatively small fibro-vas- 
 cular cylinder, often with distinct 
 pith. Bundles go from the cylinder 
 •outward to form the nerves of the 
 leaves. Now, the structure of a club- 
 moss is almost the same, except for 
 the occasional development in Lepi- 
 
 Fio, 502.— Ideal Section of a L"pidoden- j j j j> -u j i.i. 
 
 dron: o, pith; s, vascular cyimder; c, dodendron 01 a pith, and the presence 
 /?™sc'"fihfera'^ofngmhfietT' nearly always, in the larger stems, of 
 
 Fig. 501.— Lepidodendron compared with Club-Moes: a, club- 
 moss; ft, fii', scales enlal-ged: ft, lower scales with macro- 
 spores ; ft', upper scales with sporanjre containing' micro- 
 spores; c, microspores; (^, macroppores; .r, lepidostrobus; 
 y and 2;, the scales containing spores; m, microspores; 
 ft, raacrosporcs (after Balfour). 
 
 * Williamson, Nature, vol. viii, p. 498. 
 
382 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 a distinct growth of secondary (exogenous) wood, which places the 
 genns far above living Lycopods, and constitutes a character in com- 
 mon with the living Exogens. 
 
 4. Sigillarids. — The .typical genus of this family is Sigillaria. 
 These plants are found, like Lepidodendrids, mostly as flattened 
 
 
 i pj ^ '' I jp I '"' LI' w 
 
 Pig. 505. 
 
 Fig. 506. 
 
 Fig. 507. 
 
 Figs. 503-507.— Sigillarids : 503. Sigillaria recticnlata (after Leaqnereux). 504. Sigillaria Grseserl 
 505. Sigillaria obovata (after Lesquereux). 506, 507. Sigillaria Brardii (506 ia reduced i) (after 
 Fairchnd). 
 
 masses, which are portions of trunks, but also as roots and leaves. 
 The trunk-impressions are distinguished from those of Lepidoden- 
 drids by longitudinal ribbings or fiutings, ornamented with seal-like 
 impressions {sigillaj a seal), in vertical rows (Figs. 503-506). Their 
 leaves were similar to those of Lepidodendron (Fig. 507), though 
 generally much longer and grass-like. The slender leaves of these 
 two genera are exceedingly common impressions in the shales. 
 
PLANTS OP THE COAL. 
 
 383 
 
 The best general conception which we can form of the Sigillaria 
 would represent it as a tall, gently-tapering trunk, longitudinally 
 fluted like a Corinthian column, and ornamented with seal-like im- 
 pressions in vertical ranks, representing the phyllotaxis ; unbraiiched 
 or else dividing only into a few large 
 branches, clothed thickly with long, stiffish, 
 tapering leaves. From the base of the trunk 
 extended large, radiating roots, branching 
 dichotomously and sparsely, with many 
 long, cord-like rootlets penetrating the soil 
 below. The stumps of Sigillaria and Lepi- 
 dodendrons, with these large, horizontally- 
 spreading roots and cord-like appendages, 
 are very common in the under-clay, and 
 were long supposed to be a peculiar plant, 
 and called Stigmaria on account of the fiq. bos.— stigmaria ficoides 
 round spots (Stigma) on their surface (Fig. ^"'^"^ esquereux). 
 
 508). They are now known to belong to Sigillarids and Lepido- 
 dendrids, and are either roots or spreading rhizomes, some of which 
 may have floated in the water. 
 
 In the following figure (509), taken from Dawson, we have at- 
 tempted to realize the general appearance of a Sigillaria. Their 
 trunks were sometimes of prodigious length and' diameter. They 
 were probably the largest trees of the time. In a coal-seam in Dau- 
 phin County, Pennsylvania, flattened stems were found four feet and 
 even five feet in width. Some of these were exposed for fifty feet, 
 with but little apparent diminution. One was exposed sixty-five feet, 
 and was estimated to have extended at least thirty feet more. An- 
 other was exposed seventy feet, and was estimated to have been eighty 
 to one hundred feet when growing. 
 
 The Sigillarids are regarded as closely allied to the Lepidoden- 
 drids. Indeed, the two groups shade into each other in such wise that 
 there are some species the position of which, whether in the one 
 group or in the other, is doubtful. The typical Sigillaria, however, 
 differs in general port from the typical Lepidodendron, chiefly in pos- 
 sessing a more Palm-like, or Cycas-like, or Dracena-like stem. They 
 are evidently, like the Lepidodendrids, to be included in the Lycopo- 
 diales,'but their affinity with higher classes is even closer than that 
 of the Lepidodendrids. 
 
 The internal structure of the stem indicates this affinity. A cross- 
 section (Fig. 510) of a Sigillaria-stem shows a hard external rind, d, 
 inclosing a great mass of loose, cellular tissue (inner and middle 
 bark), c c, through the center of which runs a comparatively sniall, 
 double woody cylinder, b i, and in the center of this again a large 
 26 
 
384 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 pith, a a. From the inner zone of the woody cylinder go bun- 
 dles of fibro-vascTilar tissue, / /, through the outer zone and the 
 
 cellular tissue of the inner bark, 
 to the leaves, e e. Anatomically 
 the stems of Sigillaria are, if de- 
 corticated, hardly distinguishable 
 from those of Lepidodendron. 
 The principal differences, usually 
 present, in Sigillaria are the 
 larger pith and the more or less 
 distinct separation of the primary 
 (endogenous) wood in strands at 
 the bases of the corresponding 
 wedges of the secondary (exoge- 
 nous) wood. The presence of ex- 
 ogenous (outer zone) wood with 
 medullary rays, g g, and punc- 
 tate traeheids led Brongniart and 
 Dawson to associate Sigillaria 
 with the Gymnosperms, the closer 
 analogy being with the Cyeads 
 (Cycas, Zamia, etc.). For the 
 sake of a comparison we have given (Fig. 511) a cross-section of a 
 Cycas; the letters represent the same as in the previous figure. 
 
 The development of a secondary (exogenous) tissue, with charac- 
 ters such as were formerly supposed to be confined to Phanogams, is 
 now known to have existed in some of the Calamarian types as well 
 as in Lepidodendron and Sigillaria. In spite of the structural fea- 
 
 Fia. 509.— Restoration of Sigillaria, by Dawson. 
 
 Pis. 510.— Ideal Section of a Sigillaria-Stem: a, pith; 
 b, woody cylinder; c, inner oark; d, rind; e, bases 
 of leaves ;/, vascular thread running to the leaves ; 
 g, medullary rays. 
 
 Fig. 511.— Cross-Section of 
 stem of Cycas. 
 
 tures in common with the Cyeads, the Sigillarise are shown to be Cryp- 
 togams hardly more than generically distinct from Lepidodendron. 
 Recent investigations substantiate this position; for, in connection 
 with Sigillaria, inflorescence similar to that of Lepidodendron, and 
 containing both microspores and macrospores, has also been found. 
 
PLANTS OF THE COAL. 
 
 385 
 
 The occurrence of both exogenous and endogenous wood in the 
 same trunk is one of the most striking features of the great Coal 
 Measures types, though traces of such growth are still rarely met 
 among certain of the living Cryptogams. 
 
 5. Calamarise.— We include under this name, Calamites, Calamo- 
 dendron, Asterophyllites, Annularia, etc. These are plants having 
 long, slender, tapering, reed-like stems, jointed and hollow, or else 
 with large pith. The exterior surface of the stem is finely striated, or 
 fluted, but the strise are not continuous nor marked with leaf-scars 
 
 likel the flutings of the 
 Sigillaria, but are inter- 
 rupted at the joints in the 
 manner shown in Figs. 
 512 and 513. At the joints 
 are attached in whorls the 
 leaves, which are either 
 scale-like, or strap-like, or 
 thread ' like. Sometimes 
 at the joints of the main 
 stem come out in whorls 
 
 Fio. 515. 
 
 Pig. 516. 
 
 Figs. 512-516.— Cat-amites and their Allies : 512. Lower End of Stem of Calamites from Nova 
 Scotia. 513. Lower End of stem of Calamites cannieformiB. .514. Sphenophyllum emarginatnm 
 (after Daweon). 515. Asterophyllites equisetiformis, England (after Nicholson). 516. Annula- 
 ria inflata (after Lesqnerenx). 
 
 thread-like, jointed branches bearing scale-like or thread-like leaves. 
 At the lower end of the stem the joints grow rapidly smaller and 
 shorter, so that this end is conical. From these short, rapidly-taper- 
 ing joints issue the thread-liJce roots. The cone-like fruit (Fig. 517) 
 was terminal on stem or branches, sometimes axillary. 
 
386 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 Pig. 518.— Eestora- 
 tion of a Catamite 
 (after Dawson). 
 
 What has been said thus far applies well to Equisetum; but the 
 Bquisetae of the present day are small, rush-like plants, never much 
 
 thicker than the finger, and seldom more 
 than three or four feet high, although 
 in South America (Caracas) they grow 
 thirty feet high, but are very slender; 
 while CalamariEe were certainly two feet 
 or more in diameter, and thirty feet 
 high. Fig. 518 is an attempt to recon- 
 struct the general appearance of a Cala- 
 mite by Dawson. 
 
 The internal structure of Calamariaj 
 still further removes them from Equise- 
 tse; for they seem to have had (some of 
 them, at least) a thick, woody cylinder of 
 exogenous structure, i. e., growing by 
 Cambium layers. And if, as is generally 
 accepted, many of the striated jointed 
 stems called Calamites are only casts of 
 the pith, the stems must have even been 
 much larger than stated above. 
 
 Thus, in the Lepidodendrids, the 
 Sigillarids, and the Calamarige we find 
 an organization higher than the living Lyeopods and Equisetse, 
 and foreshadowing the structures typical of the living flowering 
 plants. 
 
 General Conclusion. — The conclusion which we draw from this ex- 
 amination of Coal plants is: 1. That they belong to the highest Cryp- 
 togams, viz.. Vascular Cryptogams, and the lowest Phsenogams, viz., 
 Gymnosperms ; 2. That they included types intermediate between those 
 now widely-separated classes, and connected them closely. These facts 
 are strictly in accordance with the law already announced (page 357), 
 viz., that the earliest representatives of any class or order are not typ- 
 ical representatives of that class or order, but connecting or compre- 
 hensive types — that is, types which, along with their distinctive classic 
 or ordinal characters, united others which connected them with other 
 classes or orders. Thus the now widely-separated classes and orders of 
 organisms, when traced backward, in time approach each other more 
 and more, and probably unite in one common stem, although we are 
 seldom able to find the point of actual union. Thus, in this case, the 
 now widely-separated Cryptogams and Phtenogams, when traced back- 
 ward, approach until in the Coal they are nearly, if not completelj, 
 united. The organic kingdom may be compared to a tree whose trunk 
 is probably to be found, if found at all, in the lowest strata ; its main 
 
 Fig. 517.— Fruit 
 of Calamite 
 (after Lea- 
 quereux). 
 
THEORY OF THE ACCUMULATION OF COAL. 387 
 
 branches begin to separate in the Palaeozoic, the secondary branches in 
 the Mesozoic, and so the branching continues until the extreme ramifi- 
 cation, and also the flower and fruit, are found in the fauna and flora of 
 the present day. The duty of the evolutionist is to trace each bough 
 to its fellow-bough, and each branch to its fellow-br'anch, and thus 
 gradually to reconstruct this tree of life, and determine the law and 
 the cause of its growth. 
 
 Theory of the Accumulation of Coal. 
 
 There is no question connected with the Carboniferous period con- 
 cerning which there has been more discussion than the mode in which 
 coal has been accumulated. There are some things, however, about 
 which there is little difference of opinion. These we will state first, 
 and thus narrow the field of discussion. 
 
 Presence of Water. — ^That coal has been accumulated in the pres- 
 ence of water, or at least of abundant moisture, is evident : a. From 
 the preservation of the organic matter. By aerial decay vegetable 
 matter is either entirely consumed, or else crumbles into dust. Only in 
 the presence of water is it preserved and accumulated in larger quanti- 
 ties, b. The interstratified sand and clays and limestones have, of 
 course, been deposited like all strata in watei'. c. The coal itself is not 
 unfrequently distinctly and finely stratified, d. The plants found in 
 connection with the coal-seams are mostly such as grow in moist 
 ground. 
 
 Thus far, then, theorists agree, but from this point opinions diverge, 
 and until recently have very widely diverged. Some have thought 
 that coal has accumulated by the growth of plants " in situ" as in 
 peat-bogs and peat-swamps of the present day. Others have supposed 
 that it has accumulated by driftage of vegetable matter by rivers, like 
 the rafts now found at the mouths of great rivers of the present day. 
 According to the one view, a coal-seam is an ancient peat-swamp ; 
 according to the other, it is an immense buried raft. The one is called 
 the " Peat-bog theory," the other, the Estuary or raft theory. 
 
 Eecently, however, scientific opinions have converged toward a 
 common belief. We will not, therefore, discuss these two rival theo- 
 ries, but simply bring out what is most certain in the present views on 
 this subject : 
 
 1. Coal has been accumulated by growth of vegetation in situ, as in 
 peat-swamps of the present day. This fact is now demonstrable. 
 The reasons for believing it are the following : a. The purity of coal. 
 The coals of the American coal-fields are, with few exceptions, abso- 
 lutely pure, i. e., the amount of ash is not greater than would result 
 from the ash of the plants of which it is composed. The same is true 
 of coals of most extensive coal-fields everywhere. Kow, it has already 
 
388 
 
 PALAEOZOIC SYSTEM OJ? ROCKS. 
 
 been shown (p. 149) that in extensive peat-swamps, like the Great Dis- 
 mal Swamp, absolutely pure vegetable accumulations unmixed with 
 sediment occur ; but in buried rafts or drifted vegetable matter of any 
 kind there must be a large admixture of mud. b. The preservation oj 
 the most complex and delicate jjarts of the plant in their natural rela- 
 tions to each other. Large fronds are spread out and pressed as in a 
 botanist's herbarium. Delicate leaves are preserved with all their 
 finest venation perfectly visible. This is exactly what we would expect 
 if they lay where they fell, but it is incompatible with driftage by 
 rapid currents to long distances, c. The position of these perfect speci- 
 mens only on the upper part of the seam, as would be the case with 
 the last fallen leaves, instead of mixed throughout the seam, as would 
 be the case with drifted matter, d. The presence of stumps with their 
 spreading roots penetrating the under-day exactly as they grew. This 
 is not an occasional phenomenon, but is found in the under-clay of 
 very many coal-seams. In South Wales there are 100 seams of coal, 
 every one of which is underlaid by clay crowded with roots and some- 
 times with stumps. In Nova Scotia there are seventy-six seams, 
 twenty of which have erect stumps standing in their original position 
 with spreading roots still penetrating the under-clay. The other seams 
 have each its under-clay filled with stigmaria-roots. Besides these 
 
 seams there are many dark 
 bands (dirt-beds) indicat- 
 ing old forest-grounds. 
 
 The following section 
 
 (Fig. 519) shows some of 
 
 ^ ^ these seams and dirt-beds 
 
 ^ ■■■■'■ '^'^''*" 
 
 or forest -grounds, with 
 penetrating roots and erect 
 trunks. Pig. 520 shows 
 an area of about one quar- 
 ter acre of surface of the 
 under-clay of an English 
 coal-seam in which there are seventy-three stumps in situ. This last 
 evidence (d) is demonstrative. Beneath nearly every coal-seam there 
 is a fossil soil — an ancient forest-ground. 
 
 Recapitulation. — We may sura up the evidence, and at the same 
 time make it clearer, by describing a section of a peat-bog, and com- 
 paring with a coal-seam. In such a section we have always an under- 
 clay, on which accumulated the moisture, and on which grew the 
 original trees of the locality. This under-clay is often full of roots 
 and stumps of the original growth. Above this is a fine, structureless, 
 carbonaceous mass, corresponding to the coal-seam. On this are the 
 last-fallen leaves, not yet disorganized, and the still-growing vegeta- 
 
 *^'C 
 
 Fio. 
 
 ■Erect Fossil Trees, Ooal-Measures, Nova Scotia. 
 
THEORY OF THE ACCUMULATION OF COAL. 359 
 
 tion. Fow, imagine this overwhelmed and buried by mud or sand, the 
 whole subjected to powerful pressure^ and a slow subsequent process of 
 carbonization; and we have 
 a complete reproduction of 
 the phenomena of a coal- 
 seam with its accompanying 
 under-clay filled with roots, 
 and its black shale filled with 
 leaf and branch impressions. 
 There are, however, many 
 cases of coal-seams in which 
 no evidences are found of 
 forest ground. It seems 
 probable, therefore, that coal 
 
 ■^as indeed accumulated USU- f,g. 530.-Ground-PIan of a. FosbII Forest, Parkfleld 
 
 ally in situ in extensive peat- coiuery. 
 
 swamps as already described; but that often in the center and lowest 
 parts of these swamps there were shallow lagoons in which fine, partly 
 decomposed material was accumulated by gentle driftage; and such 
 drifted material formed often the finest and most structureless kinds 
 of coal, like cannel and the like.* 
 
 3. Coal has teen accumulated in delta regions, broad lowland areas ; 
 in localities subject to floods by the river and incursions by the sea. 
 It is otherwise impossible to account for the clays and sands (often 
 inclosing drift-timber), and limestones, interstratified with the coal. 
 The phenomena of an individual seam prove the accumulation by 
 growth in situ; the general phenomena of a coal-basin, with its suc- 
 cession of strata, prove that this took place in wide, flooded tracts. 
 Thus, the field of discussion is narrowed to very small limits. 
 
 We conclude, therefore, that coal has been accumulated in extensive 
 peat-swamps at the mouths of great rivers, and therefore subject to oc- 
 casional floodings by the river and inundations by the sea. That pure 
 peat may accumulate under these circumstances is sufficiently proved 
 by the fact mentioned by Lyell, that over large tracts of ground in the 
 river-swamp and delta of the Mississippi pure peat is now forining, in 
 spite of the annual floods; the sediments being all stopped by the 
 thick jungle-growth surrounding these spots, and deposited on the 
 margins, while only pure water reaches the interior portions, f 
 
 But if coal has indeed been formed at the mouths of great rivers, we 
 ought to find at least something analogous to a coal-field in sections of 
 great river-deltas. And so, indeed, we do. We have seen (p. 143) that 
 a great river-delta, like that of the Mississippi or the Ganges, consists 
 
 * Grand Eury, M^moire sur la formation de la Houille. 
 t Lyell, Elements of Geology, p. 488. 
 
390 PALEOZOIC SYSTEM OF ROCKS. 
 
 of alternate layers of river-sediments (sands and clays) and marine sedi- 
 ments (limestones) with thin layers of peaty matter, and old forest- 
 grounds with stamps and roots. It is, in other words, a coal-field, 
 though an imperfect one, in the process of formation. It will be re- 
 membered, also, that we accounted for this alternation, not by oscilla- 
 tions, but by the operation of two opposing forces, one depressing (sub- 
 sidence), the other up-building (river-deposit), with varying success. 
 When the up-building by river-deposit prevailed, the area was re- 
 claimed, and became covered with thick jungle vegetation ; when the 
 subsidence prevailed, it was again covered with water, and buried in 
 river-sediments, etc. Now and then, when the subsidence was unusu- 
 ally great, the sear invaded the same area, and limestone was formed. 
 It is substantially in this way that coal-fields were probably formed. 
 
 Application of the Theory to the American Coal-Fields : a. Appala- 
 chian Coal-Field. — A glance at the map (p. 302) will show that, during 
 Carboniferous times, there was high land to the north, east, and west of 
 this field, and the black area, representing the Coal-measures, was then a 
 trough, into which, therefore, drained rivers from every side except the 
 south. This trough was sometimes a peat-swamp, sometimes a lake 
 emptying southward, sometimes an arm of the sea connecting with the 
 ocean southward. When it was a peat-marsh, a coal-seam was formed ; 
 when a lake, sands and clays were deposited by the rivers ; when an 
 arm of the sea, marine deposits^ — limestones — were formed. 
 
 This alternation of conditions we explain as follows : There were 
 three forces at work on this area : 1. A general continental upheaval, 
 affecting this along with all other parts of the continent ; 3. An up- 
 building by sedimentary deposit ; 3. A local subsidence. The evidence 
 of all these is complete. The continental upheaval, as we have already 
 seen, was unceasing throughout the previous periods, and, as we shall 
 see, continued throughout the s,ubsequent periods. The up-building by 
 sediments and- the ^aW joassM subsidence are as clearly marked as in 
 deltas of the present day, by shore-marks, by shallow-water fossils, and 
 especially hy forest-grounds repeated through several thousand feet of 
 vertical thickness. The existence of these three forces, therefore, is 
 not a doubtful hypothesis. Now, the first two would tend to reclaim, 
 the third to submerge, the area. When the reclaiming forces pre- 
 dominated, the area became swamp-land, and covered with coal vegeta- 
 tion, and the river- water, strained through the thick growth, slowly went 
 southward by a kind of seepage. When the submerging forces pre- 
 dominated, the area became a lake, and sediments in great quantities 
 were brought down by the rivers. It is possible, perhaps probable, that 
 correlative with the more rapid local subsidence which formed the lake 
 there was also a more rapid elevation of the high lands on all sides, pro- 
 ducing more torrential river-currents and greater sedimentary deposits. 
 
ESTIMATE OF TIME. 391 
 
 Now aad then, at long intervals, the subsidence would bring the area 
 below sea-level, and would thus form an interior sea, or mediterranean. 
 During such times, limestones would be formed, and marine animals 
 would be imbedded as fossils. 
 
 b. Western Coal-Fields. — The Central' and Western coal-fields may 
 be regarded as one, having been subsequently separated by denudation. 
 This immensely extensive field may have been, like the Appalachian, a 
 hollow surrounded on all sides by higher land. If so, the western land 
 has since been submerged, and covered by more recent deposits. Or it 
 may have been an extensive jungly flat, bordering a western sea, the 
 many small rivers with inosculating deltas, flowing westward and seep- 
 ing through the thick, marshy vegetation. There were here far less 
 mechanical sediments, because less high land, and far more marine 
 deposits, because there was a larger and opener sea ; but, in other re- 
 spects, the process may be regarded as similar. 
 
 Appalachian Revolution. — This state of oscillation and incertitude 
 was terminated by the Appalachian revolution. At the end of the 
 Coal period, the sediments which had been so long accumulating in 
 the Appalachian region, until their aggregate thickness had now 
 reached 40,000 feet, at last yielded to the horizontal p^ressure pro- 
 duced by interior contraction of the earth (p. 374), and were crum- 
 pled and mashed, and thickened up into the Appalachian chain. At 
 the same time the Western coal-swamps were upheaved sufficiently to 
 become permanent dry land. This revolution closed the Carbonifer- 
 ous age and the Palseozoic era. 
 
 Estimate of Tim,e. 
 
 We have said (p. 387) that it is important that the mind become 
 familiarized with the idea of the immense time necessary to explain 
 geological phenomena. We therefore embrace this opportunity to 
 make a rough estimate of the Coal period. The estimate may be made 
 either by taking the whole amount of coal in a coal-field as the thing 
 to be measured, and the rate at which vigorous vegetation now makes 
 organic matter as the measuring-rod; or else by taking the whole 
 amount of sediments in a coal-basin as the thing to be measured, and 
 the rate of accumulation of sediments by large rivers as the measur- 
 ing-rod. We will give both, though the latter is probably the more 
 reliable : 
 
 1. From Aggregate Amount of Coal.— The only comparison which 
 we can make bearing on the rate of accumulation of the coal deposits 
 is with the peat accumulations of the present time. As would be ex- 
 pected, the rate of growth of the present peat beds is very variable. 
 The deposition has been reported as rapid as one foot in ten years, 
 and even in five years. On the estimate of one foot of anthracite 
 
392 PALEOZOIC SYSTEM OF KOCKS. 
 
 requiring eight feet of peat this would mean something like 1,000 
 or 3,000 years for the 30-foot " mammoth seam " at Summit Hill to 
 accumulate. But the conditions of peat formation in the Carbonif- 
 erous may possibly have been so unlike those of the present time 
 that the comparison is of no value except as a suggestion. The " coal 
 plants " were cryptogams, with most likely a luxuriant growth, and 
 they probably yielded as much carbonaceous matter proportionately 
 to bulk as the peat-making Sphagnum of the present day. If we 
 allow ten years for the formation of one foot of the Carboniferous 
 peat, or 3,500 years for the Mammoth seam, then the 113 feet of coal 
 in the Pottsville section indicate about 10,000 years. This is a much 
 more moderate estimate than the 1,000,000 years of some writers. 
 
 2. From -Amount of Sediment. — We are indebted to Sir Charles 
 Lyell for the following estimate of the time necessary to accumulate 
 the Fova Scotia Coal-measures. This coal-field is selected because the 
 evidences of river-sediments are very clear throughout. The area of 
 this coal-basin is given on page 364 as 18,000 square miles; but the 
 identity in character of portions now widely separated by seas — e. g., 
 on Prince Edward's Island, Cape Breton, Magdalen Island, etc. — 
 plainly shows that all these are parts of one original field, which could 
 not have been less than 36,000 square miles. The thickness at South 
 Joggins is 13,000 feet. At Pictou, 100 miles distant, it i& nearly as 
 great. We shall certainly not err on the side of excess, therefore, if 
 we take the average thickness over the whole area as 7,500 feet. This 
 would give the cubic contents of the original delta deposit as about 
 51,000 cubic miles. Now, the Mississippi Eiver, according to Hum- 
 phrey and Abbot, carries to its delta annually sediment enough to 
 cover a square mile 368 feet deep, or nearly exactly one twentieth of 
 a cubic mile. Therefore, to accumulate the mass of sediment men- 
 tioned above would take the Mississippi about 1,000,000 years. 
 
 It may be objected to this estimate that it is founded on a particu- 
 lar theory of the accumulation of the Coal-measures. The answer to 
 this is plain. Any other mode would only extend the time, for this 
 mode is more rapid than any other. Again, it may be objected that 
 we have evidence of a very rapid accumulation in stumps and logs and 
 erect trunks, either bituminized or petrified, and which, therefore, 
 must have been completely buried before they could decay. The an- 
 swer is, that these are only examples of local rapid deposit, and do not 
 at all afEect the general result. Precisely the same happens now in 
 river-deltas. Again, it may be objected that the agencies of Nature 
 were far more energetic then than now (see p. 388). A forceful 
 objection is that the strata of the Joggins section are much coarser 
 materials than the Mississippi delta silts, and imply much more rapid 
 deposition, and the estimate of 1,000,000 years may be far too large. 
 
PHYSICAL GEOGRAPHY AND CLIMATE OF THE COAL PERIOD. 393 
 
 Physical Geography and Climate of the Goal Period 
 
 Physical Geography. — In the eastern part of the American Conti- 
 nent the area of land during this period is approximately shown in the 
 map (p. 302). It included the Archsean, the Cambrian, the Silurian, 
 and Devonian areas, during the whole age. In the sub-Carboniferous 
 period the sub-Carboniferous and Carboniferous areas were covered 
 by the sea, but in the Carboniferous period proper the sub-Carbon- 
 iferous area was land, and the Carboniferous area, as already seen, 
 was in an uncertain state, sometimes above and sometimes below the 
 sea-level. It is probable, also, that the Eastern border-land extended 
 then much beyond the line of th'e Tertiary deposits (see map, p. 303), 
 and even beyond the present coast-line (see map. Fig. 269, p. 303), 
 and was partly submerged in the elevation of the Appalachian chain, 
 at the end of the Coal period. 
 
 In the Eocky Mountain jegion there were considerable bodies of 
 land, mainly in the Basin region, but their limits are not accurately 
 known. 
 
 Again, it is almost certain that all the lands were comparatively 
 low. None of the great mountain-chains of the continent were yet 
 formed. It is also probable that the same was true of the other conti- 
 nents. Nearly all the high mountain-chains are either more recent in 
 their origin^ or else in their principal growth. In general terms, 
 then, the lands were smaller and lower, and the conditions more 
 oceanic, than at present. 
 
 Climate. — The climate of the Coal period was probably charac- 
 terized by greater warmth, humidity, and uniformity than now pre- 
 vails over the greater part of the earth's surface. Most of these char- 
 acteristics, if not all, are indicated by the nature of the vegetation. 
 
 1. The warmth is shown by the existence of a tropical or sub- 
 tropical vegetation. Of the present flora of Great Britain about one 
 thirty-fifth are Perns, and none of these Tree-ferns. Of the Coal flora 
 of Great Britain about one half were Ferns, and many of these Tree- 
 ferns. At present in all Europe there are not more than sixty known 
 species of Ferns: in European Coal-measures there are nearly 550 
 species, and these are certainly but a fraction of the actual number 
 then existing. That this indicates a tropical climate is shown by the 
 fact that out of 1,500 species of living Ferns known forty years ago, 
 1,200, or four fifths, were tropical species. The number of known liv- 
 ing Ferns is now about 3,500,* but the proportion of tropical species is 
 still probably the same. Even in the tropics, however, the proportion 
 of Ferns is far less than in Great Britain during the Coal period. 
 
 * Underwood, Our Native Ferns, p. 60. 
 
394 PALEOZOIC SYSTEM OF ROCKS. 
 
 Again, Tree-ferns, arborescent Lyeopods, Cycads, and Araucarian 
 Conifers, are now wholly confined to tropical or sub-tropical regions. 
 The prevalence of these tropical families and their immense size, com- 
 pared with their congeners of the present day, would seem to indicate 
 at least sub-tropical if not tropical conditions. And these conditions 
 prevailed not only in the United States and Europe, but northward 
 into polar regions ; for in Melville Island, 75° north latitude, Grinnell 
 Land, 81° 43', and Spitzbergen, 77° 33' north latitude, have been 
 found coal-strata containing Tree-ferns, gigantic Lyeopods, Cala- 
 mites, etc. 
 
 2. The humidity is indicated by the fact that Tree-ferns and arbo- 
 rescent Lyeopods are most abundant now on islands in the midst of 
 the ocean; and further by the great extent of the Coal swamps, and 
 perhaps iilso by the general succulence of, or the predominance of 
 cellular tissue in, the plants of that period. 
 
 3. The uniformity is proved by the great resemblance and often 
 identity of the species in the most widely-separated regions. Accord- 
 ing to Lesquereux, out of 434 American and 440 European species, 
 176 are common, and the remainder far less diverse ^n character 
 than the species of the two floras at present. Again, in all latitudes, 
 from the tropics to 75° north latitude. Coal species are extremely 
 similar. Such uniformity of vegetation shows a remarkablfr uni- 
 formity of climate. Prom the earliest times until the present there 
 has been probably a gradual evolution of continents — a gradual differ- 
 entiation of land and water, a consequent differentiation of climates, 
 and a corresponding differentiation of faunas and floras. 
 
 4. It is almost certain that the amount of carbonic acid in the 
 atmosphere has fluctuated within unknown but moderate limits.* 
 The period of the Coal-measures was apparently a time of atmos- 
 pheric enrichment in COj, and in consequence of warm, uniform 
 climate. The proportion of carbonic acid in the atmosphere is now 
 about -^ per cent (-j^Vir)- N'ow, since carbonic acid is the necessary 
 food of plants, it is natural to expect that up to a certain limit the 
 increase of atmospheric carbonic acid would increase the luxuriance 
 of vegetation. Experiments by Daubeny f prove that this is true 
 especially for vascular Cryptogams. 
 
 We may therefore picture to ourselves the climate of this period 
 as warm, moist, uniform, stagnant (for currents of air are deter- 
 mined by difference of temperature). Such physical conditions are 
 extremely favorable to vegetation, but unfavorable to the ' highei" 
 forms of animal life. 
 
 * See writings of T. C. Chamberlin, Jour. Geol., vol. yi, p. 609 ; vol. vii, p. 646. 
 f Beport of British Association for 1849, p. 62, and 1860, p. 159. 
 
PHYSICAL GEOGRAPHT AND CLIMATE OF THE COAL PERIOD. 395 
 
 Cause of this Climate. — The moisture and uniformity were the 
 necessary result of the physical geography already given. They were 
 due to the wide extent of ocean and the absence of large continents and 
 high mountains. High mountains are the precipitating points for the 
 atmosphere — points through which it discharges its superabundant 
 moisture. As these did not exist, the atmosphere was always highly 
 charged. The prevalence of the ocean also, as is well known, produces 
 uniformity. 
 
 The greater warmth of high latitudes is partly explained by the 
 uniformity. But there is good reason to believe that there was then 
 a higher mean temperature than now exists. This was probably due 
 not to the greater interior temperature of the earth, as usually sup- 
 posed, but to the constitution of the atmosphere. This may be shown 
 as follows : 
 
 The surface-temperature of the earth is now almost wholly due to 
 external., not to internal causes. It has been calculated that only one 
 twentieth of a degree Tahr. is now due to the latter cause. In going 
 downward the heat increases about 1° Fahr. for every 50 to 60 feet, 
 i. e., the internal heat for every 50 feet of depth increases twenty times 
 the surface-temperature, so far as this is due to internal causes. Now, 
 - it has been shown by Fourier and Hopkins that the same would be 
 true whatever be the surface-temperature from internal causes. For 
 example, if the surface-temperature from internal causes be 1°, then 
 for every 50 feet of depth the interior heat would increase 30°. If the 
 surface-temperature from internal causes be 10°, then for every 50 feet 
 of depth the interior heat would increase 200° — a condition of things 
 entirely inconsistent with the growth of plants, since all the springs 
 would be boiling. We can not, therefore, attribute, as many have 
 done, even a few degrees' increase of mean temperature to causes in- 
 terior to the earth. In fact, it seems almost certain that during the 
 whole recorded history of the earth, i. e., during the time it has been 
 inhabited by organisms, the surface-temperature of the earth has 
 been almost wholly due to external causes. Now, the composition 
 of the atmosphere is an external cause, which greatly affects the sur- 
 face-temperature, but which has hitherto been almost wholly neg- 
 lected. The thorough explanation of this point will require some dis- 
 cussion of the properties of transparent media in relation to light and 
 heat. 
 
 Many bodies which are transparent to light are opaque to heat. 
 Such bodie?, however, will freely transmit heat, if the heat be accom- 
 panied with intense light. It is as if the light carried the heat through 
 with it Heat thus associated with light is sometimes called light-heat, 
 while that which is not thus associated is called dark heat. Now, the 
 bodies spoken of are transparent to light-heat, but opaque to dark heat. 
 
396 PAliEOZOIC SYSTEM OF ROCKS. 
 
 Glass is such a body. If a pane of glass be held between the face and 
 the sun, the heat passes freely and burns the face, but the same pane 
 would act as a partial screen before ajire, and as a perfect screen be- 
 fore a hot, but not incandescent, cannon-ball. 
 
 It is in this way we explain the fact that a glass greenhouse, even 
 in the coldest sunshiny winter's day, becomes insupportably warm if 
 shut up. The sun-light and heat pass freely through the glass, and 
 heat the ground, the benches, the flower-pots ; but the light-heat 
 thereby becomes converted into dark heat, and thus is imprisoned 
 within.* Now, the earth and its atmosphere are such a greenhouse. 
 The light-heat passes readily through, warms the ground, changes 
 into dark heat, and is in a measure imprisoned by the partial opacity 
 of the atmosphere to this kind of heat. The atmosphere is a kind of 
 blanket put about the earth to keep it warm. So much has long been 
 recognized. But Tyndall has shown that the property of opacity to 
 dark heat in the ease of the atmosphere is due wholly to the small 
 quantity of carbonic acid and aqueous vapor present; that oxygen and 
 nitrogen are transparent to dark heat, and, therefore, if the atmos- 
 phere consisted only of these two gases, it would not be heated by 
 radiation from the earth, and the ground would lose all its heat by 
 radiation during the night, and become intensely cold like space. In x 
 other words, the blanket put about the earth to keep it warm is woven 
 of carbonic acid and aqueous vapor. 
 
 It is almost certain that the Coal period was a time of comparative 
 enrichment of the atmosphere in carbonic acid and aqueous vapor. f 
 The atmosphere was then a double llanhet, and therefore kept the 
 young earth much warmer. We believe that Prof. T. S. Hunt was 
 the first to apply this discovery of Tyndall to the explanation of the 
 climate of the Coal period. E. B. Hunt had previously attributed 
 it to greater density of the air; but this is a wholly different principle. 
 
 Thus the physical geography explains the humidity and uniform- 
 itj', and the greater humidity and the carbonic acid explain the greater 
 mean temperature. But there is still the carbonic acid to be ac- 
 counted for. 
 
 The reader will appreciate the fact that all the carbon stored in 
 the earth temporarily, as peat, coal, and other organic matter, and 
 that permanently stored as carbonates (limestone, CaCOg, for exam- 
 ple) has been derived from the atmosphere. The total amount of the 
 carbonic acid withdrawn from the air by carbonation of the crystalline 
 rocks and by organic agency has been " estimated from 30,000 to 
 
 * On Mount Whitney, in the sunshine, Langley got, in a box covered with glass, a 
 temperature of 236° Fahr. or 113-3° C, while in the shade of the open air the temper- 
 ature was only 58'6° Fahr. or 14'8° C. 
 
 ■)■ This does not mean clouds or fogs, but transparent invisible vapors. 
 
IRON-ORE OF THE COAL-MEASURES. 39Y 
 
 200,000 times the present content." * Such amount of carbon in the 
 air does not seem consistent with the fact of ordinary conditions of 
 climate and life in the earliest geologic times. Certainly the amount 
 of CO2 in the air has never exceeded in geologic time an amount 
 possible with animal life. The old idea that all the carbon of the 
 world was held in the primitive atmosphere must be abandoned. We 
 are forced to the conclusion that there has been through geologic 
 time a constant supply of carbonic acid to fairly balance the with- 
 drawal. Such supply is found in the crystalline rocks and in the 
 emanations from the earth's -interior, observed especially in volca- 
 noes and carbonic-acid springs. The two processes of supply and 
 withdrawal have not been precisely balanced and the COj content 
 of the ^atmosphere has varied within narrow limits. Depletion would 
 cause a season of cold and aridity, like the Salina or the Glacial 
 periods, while enrichment would produce a warm and humid cli- 
 mate like that of the Carboniferous period. The discussion of this 
 subject involves the origin of the atmosphere. The Planetesimal 
 hypothesis best explains the facts (see pp. 396, 299). 
 
 Iron- Ore of the Goal- Measures. 
 
 We have already stated that the Coal-measures consist of alternat- 
 ing layers of sandstones, shales, and limestones, containing seams of 
 coal and bands of iron-ore. We have already discussed the mode of 
 occurrence, the varieties, and the theory of accumulation of the coal. 
 We come now to discuss the same points in regard to the iron-ore. 
 
 Mode of Occurrence. — The mode of occurrence of iron-ore is, in 
 many respects, like that of coal. Like coal, it is found in seams, which 
 vary in thickness from a fraction of an inch to forty or fifty feet. 
 Like coal, these very thick seams are apt to be impure, being largely 
 mixed with clay. Seams pure enough to work profitably are seldom 
 more than three or four feet thick. Like coal, the seams are repeated 
 many times in the same section (Pig. 454, p. 361), but without any dis- 
 coverable order of succession. Like coal, the seam is usually underlaid 
 by clay. 
 
 Kinds of Ore. — The form of iron-ore found in all strata, except 
 those containing coal, is usually ferric oxide, either hydrated (brown 
 hematite — limonite), or anhydrous (red hematite), or else magnetic ox- 
 ide ; but in the Coal-measures of this period, and in the Coal-measures 
 of every other period — i. e., in all strata containing coal — the iron is in 
 the form of ferrous carbonate. This is usually mixed with clay, and 
 therefore called clay iron-stone. It is often nodular and mammillated, 
 and called kidney iron-ore. Sometimes it is mixed intimately with 
 
 * Professor T. C. Chamberlin has discussed this subject in the Journal of Geology, 
 Tol. vii, pp. 645-684. 
 
398 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 carbonaceous matter, and is called black-band ore. This last very valu- 
 able ore is found in Pennsylvania, Ohio, and in Scotland. 
 
 The importance of the association of coal and iron in the same 
 strata can not be overestimated. For this reason, the raising of coal 
 and the manufacture of iron are conducted in connection with each 
 other, and the smelting furnaces are often situated at the mouths of 
 the coal-mines. It is easy to understand, therefore, why Great Britain, 
 the greatest coal-producing country in the world, should be also the 
 greatest iron-producing country. Most of the iron-ore worked in 
 Great Britain is taken from her coal-measures. In this country, much 
 iron was formerly made from the iron carbonates of the Coal-meas- 
 ures, but now chiefly from the peroxide and magnetic ores found 
 elsewhere, especially in Algonkian (p. 298). 
 
 The following table gives a comparative view of the annual iron- 
 production, in tons, of the principal iron-producing countries of the 
 world. It will be seen that Great Britain once made most of the 
 iron of the world, but that the United States is now the leading 
 country, having produced in 1901 nearly 30,000,000 tons. The rapid 
 increase in the production of this great agent of civilization in other 
 countries is also seen. 
 
 IRON AND STEEL. 
 
 1845. 
 
 1850. 
 
 1873. 
 
 1884. 
 
 189T.* 
 
 1901.* 
 
 Great Britain 
 
 United States 
 
 2,200,000 
 602,000 
 460,000 
 
 3,600,000 
 1,000,000 
 
 6,566,000 
 2,560,000 
 1,381,000 
 
 10,600,000 
 6,200,000 
 2,600,000 
 4,600,000 
 
 27,300,000 
 
 13,489,822 
 17,096,423 
 3,479,082 
 11,955,699 
 54,116,271 
 
 12,966,019 
 29,741,581 
 3,865,311 
 14,229,426 
 71,830,667 
 
 
 World 
 
 
 7,000,000 
 
 14,485,000 
 
 
 
 * Metric tons. 
 
 Theory of the Accumulation of the Iron-Ore of the Coal-Measures. — 
 
 We have already explained (p. 150) how iron-ore is now accumulated 
 by the agency of decaying organic matter. We have also shown that 
 if the organic matter is consumed in doing the work of accumulation, 
 the iron-ore is left in the form of iron pei'oxide ; but if it is accumu- 
 lated in the presence of excess of organic matter, it retains the form 
 of ferrous carbonate. We will now give additional evidence, taken 
 from the occurrence of iron-ore in the strata of the earth, that the 
 same agency has accomplished the same results in all geological times : 
 1. Immense beds of iron-ore are found in the strata of all geological 
 ages ; but, wherever we find them, we find also associated a correspond- 
 ing amount of strata, decolorized or leached of their iron coloring-mat- 
 ter. Contrarily, wherever we find thn rocks extensively red, we usually 
 find also an absence of valuable beds of iron-ore. We are thus led to 
 conclude that the iron-ore of iron-beds has been washed out of the 
 strata, which are thereby left in a decolorized condition. 
 
IRON-OEE OF THE COAL-MEASUEES. 
 
 399 
 
 2. That this has been done by the agency of organic matter is shown 
 by the fact that, wherever we find evidences of organic matter, whether 
 in the form of fossils or of coal, we find the sandstones and shales are 
 white or gray— i. e., leached of coloring-matter. Conversely, red rocks 
 are usually barren of fossils or of coal. For example, all the sand- 
 stones of the coal-measures, or of all other strata containing coal, are 
 gray, while the Old Bed sandstone below the coal, and the New Bed 
 sandstone above the coal, and, in fact, all red sandstones, are very 
 poor in fossils or evidences of organic matter of any kind. Thus, 
 evidences of organic matter, and the decoloring of the strata, and 
 the accumulation of iron-ore, are closely associated as cause and 
 effect. 
 
 3. In all the strata, whether older or newer, in which there is no 
 coal, i. e., in which there is no excess of organic matter in a state of 
 change, the iron-ore is peroxide (ferric and magnetic oxide) ; while in 
 coal-measures of all periods, whether Carboniferous, or Jurassic, or Cre- 
 taceous, or Tertiary, or in all cases where there is organic matter in ex- 
 cess in % state of change (not graphite), the iron-ore is in the form of 
 carbonate protoxide, or ferrous carbonate (FeCOg). 
 
 Therefore, we conclude that both now and always iron-ore is, and 
 has been, accumulated by organic agency ; * again, that both now and 
 always there are, and have been, three conditions of iron-ore, each as- 
 sociated with the absence or presence in smaller or larger quantities of 
 changing organic matter : 1. It may be universally diffused as a color- 
 ing-matter of rocks and soils, and unavailable for industries ; in this 
 case there has been no organic matter to leach it out and accumulate it. 
 2. It may be accumulated as ferric oxide ; in this case there has been 
 organic matter only sufficient to do the work of accumulation, and was 
 all consumed in doing that work. 3. It may be accumulated as ferrous 
 carbonate ; in this case there is excess of organic matter, usually in the 
 form of coal. 
 
 This much is certain ; but, as to the exact mode and time of the 
 leaching and accumulation, there is some difference of opinion. There 
 are two ways in which the accumulation may have occurred : It may 
 have accumulated in the coal-marshes during the Coal period, being at 
 that time leached out of the surrounding soils, which were therefore 
 left in a decolorized condition, and in this condition subsequently 
 washed down as sediments into the coal-marshes. Or, it may have 
 been brought down as the coloring-matter of red sands and clays; 
 and afterward, perhaps after the Coal period, leached out by percolat- 
 ing waters containing organic matter from the coal-beds, carried down- 
 
 * Some writers hare 'contested this statement. See Winchcll, Minnesota Geological 
 Survey, Bulletin VI, pp. 246-248, 1891. 
 
 37 
 
400 PALEOZOIC SYSTEM OF ROCKS. 
 
 ward until stopped by an impervious clay-stratum, and accumulated 
 there. The former mode is the more probable.* 
 
 The above view is true as a general statement, but the accumulation 
 is not always direct. On the contrary, it may be (a) by replacement 
 of limestone by ferrous carbonate which becomes oxidized into ferric 
 oxide ; or (S) ferrous sulphate may react with lime carbonate and form 
 lime sulphate and ferrous carbonate (FeSOi + CaCOs = CaSOi + Pe 
 CO3), the latter becoming by oxidation ferric oxide ; or, finally (c), fer- 
 riferous limestone may be leached of its lime and the residual iron ac- 
 cumulated. 
 
 But, in any case, organic matter has been the agent in. some stage 
 of the change ; and, therefore, in this case, as in all other cases, iron- 
 ore is the sign of organic matter, and the measure of the amount of 
 organic matter consumed in its accumulation. There are, therefore, 
 four signs of the previous existence of organisms used by geologists ; 
 they are coal, iron-ore, limestone (or marble), and fossils. 
 
 We can not dismiss this subject without making one passing re- 
 flection suggested by the mention of these four signs of lifq: 
 
 The organic kingdom is so much matter taken from the atmosphere, 
 embodied for a brief space in individual living forms, to be again dis- 
 solved by death, and returned to the atmosphere whence it came. The 
 same material is again taken by the next generation, embodied and 
 again returned at its death. The same small quantity of matter in the 
 atmosphere is embodied and disembodied, again embodied and disem- 
 bodied, and thus worked over and over again by constant circulation 
 thousands, yea, millions of times, in the history of the earth. Now, in 
 this constant circulation of the elements of organic matter, besides the 
 work done in the fact of circulation itself, viz., the wonderful but fleet- 
 ing phenomena of vegetable, animal, yea, of human life, there was an- 
 other work, the results of which accumulated from age to age — a work, 
 too, of the greatest importance to the well-being of the human race. 
 A portion of this circulating matter, in its course downward from the 
 organic to the mineral kingdom, stopped half-way, and was accumulated 
 as great beds of coal — reservoirs of stored force. As circulating water 
 descending seaward is stopped and stored in reservoirs to complete its 
 descent under the control of man, and do his work ; so circulating or- 
 ganic matter descending is stopped and stored, and is now completing 
 its descent under the control of man, and doing his work, and thus 
 becomes the great agent of modern civilization. 
 
 A second portion of circulating organic elements completes its de- 
 scent, but in doing so accumulates iron-ore, the second great civilizer 
 of the human race, and a third portion forms limestone. 
 
 * Bischoff, Chemical Geology, vol. i, p. 315. 
 
BITUMEN, PETROLEUM, AND NATURAL GAS. 40I 
 
 A fourth portion also completes its descent, but accumulates 
 neither coal nor iron-ore; but it accomplishes a work far more sub- 
 tile and beautiful than either of the others. As each particle of 
 organic matter returns to the atmosphere, it compels a particle of 
 mineral matter to take its place, thus completely reproducing its 
 form and structure. Thus fossils are formed, and thus is the history 
 of the organic kingdom self-recorded. Thus, while the other two 
 portions have subserved the material wants of man, this portion has 
 subserved his higher intellectual wants. 
 
 Bitumen, Petroleum, and Natural Gas. 
 
 The nature of bitumen and petroleum is so similar to that of coal, 
 that although not coniined to, nor even found principally in, the 
 Coal-measures, the subject is best taken up in this connection. 
 
 It is well known that coal or any organic matter, by suitable dis- 
 tillation, may be broken up into a great variety of products: some 
 solid, as coal-pitch; some tarry, as coal-tar j some liquid, as coal-oil; 
 some volatile, as coal-naphtha; and some gaseous, as coal-gas. Kow, 
 we find collected, in fissures beneath the earth, or issuing from its sur- 
 face, a very similar series of products: some soli^, as asphalt; some 
 tarry, as bitumen; some liquid, as petroleum; some volatile, as roclc- 
 naphtha; and some gaseous, as marsh-gas of burning springs. There 
 has been little doubt that these also are of organic origin. The util- 
 ization of all these products, especially petroleum and gas, has now 
 become a great industry. 
 
 Geological Relations. — Bitumen and petroleum are found in all fos- 
 siliferous rocks, from the lowest Silurian to the uppermost Tertiary, 
 under certain conditions, among which are the local abundance of or- 
 ganisms from which these substances are formed, and the absence of 
 great metamorphism. The signs of their presence in any locality are 
 iridescent scums on the water of springs (oil-show), and the issuing of 
 combustible gases (burning springs). In regard to the first sign, it 
 must be remembered that iridescent scums are produced by many other 
 substances besides petroleum. The second sign is considered the best, 
 although combustible gases may issue from decomposing organic matter 
 of any kind, or from coal. Some of the burning springs in the oil- 
 region of Kentucky are said to produce a flame twenty to thirty feet 
 long. It is a significant fact that petroleum is often associated with 
 salt. It is so in Pennsylvania, in Virginia, and in many other lo- 
 calities. 
 
 Oil-Formations. — I have said that petroleum and bitumen are found 
 in all fossiliferons formations, but in each country there are certain for- 
 mations where it especially abounds : in Europe it is found principally 
 in the Tertiary ; in Eastern United States it is found almost wholly in 
 
402 PALEOZOIC SYSTEM OF ROCKS. 
 
 the Palaeozoic, below the Coal-measures ; in California it is found in 
 the Tertiary. 
 
 Principal Oil-Horizons of the United States.— In Pennsylvania and 
 Kentucky oil is found in the Upper Devonian ; in Canada, in the 
 Lower Devonian ; in West Virginia, in the sub-Carboniferous ; in Ohio, 
 in the Coal-measures, Upper Devonian (Huron shales), and especially 
 in the Lower Silurian (Trenton limestone) ; in Colorado it is found in 
 the Cretaceous : in California, in the Miocene Tertiary of the Coast 
 Range, all the way from Los Angeles to Cape Mendocino. These have 
 been called oil-horizons. 
 
 Laws of Interior Distribution. — The mode of interior distribution 
 of petroleum is similar to, yet different from, that of water. Like 
 water, it collects in porous strata, especially if these are covered with 
 impervious strata, and in fissui-es and cavities of all kinds ; like water 
 and with water, it collects in ordinary wells, or sometimes spouts in 
 immense quantities from artesian wells. Some of the great spouting- 
 wells in Pennsylvania, when first opened, yielded 3,000 barrels per day, 
 some in Ohio 5,000 barrels, or even more, and some of the great wells of 
 Baku, on the Caspian Sea, even 1,000,000 gallons, or 35,000 barrels per 
 day. But, unlike water, there is no perennial large supply ; the accu- 
 mulations of ages being exhausted sometimes in a few years. Unlike 
 water, the force of ejection is not hydrostatic pressure directly, but 
 hydrostatic pressure transmitted through elastic compression of the 
 gases generated from the petroleum itself. The great spouting- wells, 
 therefore, being the fortunate tappings of the accumulations of ages, in 
 fissures and cavities, are enormously productive when first opened, but 
 are also in the same proportion rapidly exhausted. It is evident that 
 the same is much more true of gas-wells : they must be still more 
 short-lived. In cases where the accumulation occurs in pores and nu- 
 merous small fissures, the supply is less abundant but more perma- 
 nent ; although some very productive wells have been opened in porous 
 sandstones of Pennsylvania and the limestones of Ohio where no de- 
 cided cavities have been demonstrated. Where oil is associated with 
 water and gas, especially in cavities, the three materials arrange them- 
 selves in the order of their specific gravities. It follows, therefore, that 
 gas and oil usually come up first, and water only after these are ex- 
 hausted. 
 
 Kinds of Rocks which bear Petroleum. — As already stated, petro- 
 leum, like water, is found principally in pores, fissures, and cavities of 
 all kinds. The same kinds of rocks, therefore, which are water-bearing 
 are also oil-bearing — viz., sandstones and limestones, especially if these 
 have an impervious shale cover. In Canada and Ohio it is found in 
 limestone, and the peculiar porous character of the Trenton limestone 
 of Ohio which makes it oil-bearing is shown in Pigs. 521 and 522. In 
 
BITUMEN, PETROLEUM, AND NATURAL GAS. 
 
 403 
 
 Pennsylvania it is found in sandstone with intervening barren shales. 
 In Pennsylvania there are three oil-bearing sandstones separated by 
 
 
 
 Fig. 531. 
 
 Fig. 522. 
 
 Pigs. 531 and 522.— Sections of Trenton limestones of Ohio, magnified (from Orton). 
 
 about 200 feet of intervening shales. If a well reaches the first sand- 
 stone without finding oil, the boring is continued to the second, or even 
 to the third. Pig. 523 (taken from Lesley) represents a section through 
 the Pennsylvania oil-regions, showing the three principal oil-horizons 
 of the Eastern United States recognized at that time, viz., the Venango 
 County (Pennsylvania) horizon with its three sandstones ; the Virginia 
 
 BDAOYS BCno 
 
 Fio. 533. 
 
 sub-Carboniferous horizon above ; and the Canada horizon below. To 
 these must now be added the Trenton limestone horizon of Ohio, still 
 lower. It is believed that the oil-generating stratum is usually a shale. 
 Above this is the oil-reservoir stratum of sandstone or limestone. 
 Above this again is the impervious shale-cover. 
 
 Petroleum (especially the lighter oils) is usually found only in hori- 
 zontal or gently-folded strata, because strongly-folded and crumpled 
 strata are always metamorphic, and the heat which produced meta- 
 morphism has also concreted the oil into bitumen or asphalt. Also the 
 outcropping of the edges of highly-inclined strata favors the escape of 
 gas and the concretion of the oil. It is hardly probable, therefore, 
 that a light oil will ever be found in the California oil-region.* 
 
 In gently-folded strata the most productive portions seem to be 
 along a line of anticline ; because there we may expect large, fissures, 
 
 * Some tolerably good oil has been found in California in metamorphic strata. 
 
404 PALEOZOIC SYSTEM OF ROCKS. 
 
 and also, perhaps, because the oil working np on the surface of water 
 is apt to accumulate under the saddles of the strata. 
 
 In California asphalt in very pure condition occurs in the form of 
 dihes, filling great fissures in Miocene sandstone of the Coast Eange. 
 It is possible that its source is a bituminous or petroliferous underly- 
 ing shale. Crust movements produced fissures, and pressure squeezed 
 the liquid matter in a pure form into the open fissures, where it 
 concreted as asphalt. The same phenomenon is observed in West 
 Virginia and in Bulgaria. 
 
 Origin of Petroleum and Bitumen. 
 
 We have seen that the whole petroleum and bitumen series may be 
 made artificially by destructive distillation of coal. There seems also 
 to be little doubt that certain organic matters at ordinary temperature, 
 in presence of abundant moisture, and out of contact of air, will un- 
 dergo a species of decomposition or fermentation by which an oily or 
 tarry substance, similar to bitumen, is formed. In the interior of 
 heaps of vegetable substance such bituminous matter is often found. 
 
 The prevailing theory has been that all the hydrocarbons found 
 in the earth were derived from the atmosphere by organic agency. 
 We are quite sure that this is true of the carbon in coals and lime- 
 stones. It was natural to make the theory cover all the analogous 
 volatile compounds.* 
 
 Many limestones are dark-colored and " foetid " with hydrocar- 
 bons, but make white lime when roasted. Many shales yield, when 
 heated, large percentages of volatile hydrocarbons. Indeed, before 
 the days of oil-wells "rock oil" was obtained commercially by dis- 
 tillation of the black shales. It has seemed plausible that such hydro- 
 carbons might have been deposited in the shales and limestones from 
 the tissues of marine animals and plants under the influence of 
 salt water. From this conception it is but a step to the assumption 
 that the great masses of bituminous substances found in various local- 
 ities, even in the igneous rocks, had been derived from some unknown 
 petroliferous shale or limestone. However, it has been impossible 
 to reasonably account for such immense localizations of these sub- 
 stances, as, for example; the pitch lake of Trinidad and the Baku 
 oil-field. 
 
 The organic theory of hydrocarbons was almost compulsory under 
 the nebular theory of the earth's origin, and the conception of a 
 
 * G. H. Eldridge, in Twenty-second Ann. Rep. U. S. Geol. Surr., classifies the hydro- 
 carbons as follows: Gaseous — marsh gas and rock gas. Bituminous — petroleum, min- 
 eral tar (malthite), asphaltite (many forms). Resinous — succinite (amber), copalite, am- 
 brite. Cereous — ozocerite. Crystalline — ^hartite. 
 
ORIGIN OF PETROLEUM AND BITUMEN. 405 
 
 primitive atmosphere holding all the CO2 of the world. We have 
 already shown (p. 397) that the latter conception is certainly wrong. 
 The interior of the earth has probably been the primal source of all 
 the CO2 and the atmosphere only a secondary medium. Under the 
 Planetesimal hypothesis (p. 296) we may easily concede that the 
 superficial rocks may hold great quantities of hydrocarbons which 
 have been expelled by rising temperatures from the earth's interior 
 and have been condensed in the colder outer layer.* 
 
 Origin of Varieties. — However formed, there can be no doubt that 
 the different varieties of this series are formed from one another by a 
 subsequent process. It is certain that from all varieties CH^ is con- 
 stantly passing off, and that the result of this, together with oxidation, 
 is a slow consolidation. By this process light oil is changed into heavy 
 oil, heavy oil into bitumen, and bitumen into asphalt. Some of the 
 grandest fissure-reservoirs of oil have thus been changed into solid 
 asphalt. In the upper barren Coal-measures of West Virginia there 
 is a vein of asphalt (Grahamite) four feet thick, over 3,000 feet long, 
 and of imknown depth. It fills a great fissure which breaks through 
 the rocks nearly perpendicularly, and outcrops on the surface. 
 
 There are, therefore, two series of substances of carbonaceous 
 matter, viz.," the coal series and the oil series. In each series the pro- 
 portion of carbon increases by subsequent change until, perhaps, pure 
 carbon may be reached. In the coal series we have fat coal, bitunii- 
 nous coal, semi-anthracite, anthracite, and, finally, graphite. In the 
 oil series we have light oil, heavy oil, bitumen, asphalt, probably jet, 
 and possibly, finally, diamond: for Liebig has suggested that diamond 
 is most probably formed by crystallization of carbon from a liquid, 
 hydrocarbon, in which the proportion of carbon is constantly increas- 
 ing by loss of CII4. 
 
 Future of this Industry.— The oil in the United States is rapidly 
 being exhausted. The finding of great reservoirs, producing spout- 
 ing-wells, has always been, and always will be, very uncertain, and the 
 duration of their productiveness limited ; but a moderate return for 
 industry and capital is certain for indefinite but limited time. A 
 large portion of the Palaeozoic basin, including an area of about 
 200,000 square miles, is underlaid by rocks which are more or less 
 oil-bearing. The eastern portion of the United States (unless we 
 except the borders of the Caspian Sea about Baku) is the great oil- 
 bearing, as it is the great coal-bearing, country of the world. The 
 gas supply will probably be much more quickly exhausted. 
 
 * References to the literature bearing on occurrences of hydrocarbons may be found 
 in a discussion of this subject— The Volcanic Origin of Natural Gas and Petroleum, by 
 Eugene Coste, Can. Min. Inst., March, 1903. 
 
406 
 
 PAL^SOZOIC SYSTEM OF BOCKS. 
 
 Fauna of the Carboniferous Age. 
 
 As heretofore, we will disregard the subdivisions, and treat of the 
 fauna of the whole age, or at least the two periods sub-Carboniferous 
 and Carboniferous, together. It must be borne in mind, however, that 
 most of the lower marine animals mentioned are from the sub-Carbon- 
 iferous, while most of the fresh-water and land 
 animals are from the Coal-measures. We can 
 notice only what important families are going out, 
 wha^ important families are coming in, and a few 
 which are very characteristic. We shall dwell only 
 on what bears on the progress of life. 
 
 Among rUzopods Fusulina (Fig. 524) is very 
 FiQ. 524.— PoBuiina cyiin- abundant and characteristic of certain limestones 
 
 diica, magnified. 
 
 Fig. 625. 
 
 Fig. 537. 
 
 FiGB. 525-527. — Cabbonipbbous Hhizopobb, Brtozoa, and Ookals: 525. Lithostrotion Calif or- 
 nienee (after Meek"). 526, Clisiophyllum Gabbi (after Meek). 527. a, Arcbimedcs Wortbeni 
 (after Hall); 6, portion of frond, enlarged to sbow structure. 
 
 and shales of this age in the Mississippi Valley and westward to the 
 Pacific coast. 
 
 Among corals the same general characteristic Palaeozoic type 
 
FAUNA OF THE CARBONIFEROUS AGE. 
 
 407 
 
 (Quadripartita) continues to prevail, though in greatly diminished 
 variety of families; for the Favositid^ and Halysitidae have passed 
 away, and only the Cyathophylloids, or cup-corals, remain. The most 
 
 Fig. 532, 
 
 Fto. 533. 
 
 Fig. 534. 
 
 Figs. 528-534. — Echinoderihs of the Carboniferous AaTi—Blastoids: 528. Pentremitee Burling- 
 tonlensis (after Meek). 529. Pentremites gracilis (after Meek). 530. Pentremitee cervinus (after 
 Hall). 631. Pentremites pyriformis (after Hall). 531a. Pentremite restored (after Llltken). 
 Crinids: 532. Batocrinns Christyi (after Meek). 533. Scaphiocrinas scalaris (after Meek). 534. 
 Porbesiocrinus Wortheni (after Meek). 
 
 beaU|tiful and characteristic are the Columnar Lithostrotion (Fig. 535), 
 a polyp-coral, and the curious corkscrew-like Archimedes (Fig. 527), a 
 Bryozoan. 
 
 Among Grinoids, the Gystids no longer exist, for they passed out 
 in early Devonian, but the Blastoids and Crinids (Fig. 528-535) 
 increase in number and beauty. Also among free Echinoderms the 
 Asteroids (Fig. 538) are more abundant, and Echinoids (Figs. 536 and 
 537), introduced in small numbers in the Devonian, are more nu- 
 
408 
 
 PALAEOZOIC SYSTEM OF ROCKS. 
 
 Fig. 638. 
 
 Fig. 537 a. 
 
 TiGB. 635-538.— BoHiNODERMs OF THE Cabbokipbrous Age— CWreirf; 535. Zeacrinns elegans (after 
 Hall). EehincAAs and Asteroids: 536. Oligoporus nobilis, x i (after Meek). 587. a, Archaeocl- 
 daris Wortheni (after Hall) ; 6, Spine of same, natnral size. 538. Onychaster flexilis (after Meek). 
 
 merous here. Fig. 539 represents the (Jistribution of these orders in 
 time. 
 
 .^__- PALAEOZOIC 
 
 ''silarian DevonS Carboniff 
 
 NEOZOIC 
 
 ^1° Ss 
 
 STEM [VI ED 
 
 Pig. 539.— Diagram showing General Distribution of Ecbinoderms in Time: Shaded portion, 
 stemmed; unshaded, free. 
 
 Among Brachiopods, the straight-hinged or square-shouldered kinds 
 continue, but pass out almost wholly with this age. 
 
FAUNA OF THE CARBONIFEROUS AGE. 
 o 6 
 
 409 
 
 Flu. 541 
 
 Fig. 543. 
 
 Pios. 540-543.— CARBONirEROus Braohiopodb: 540. Spirifer plenus (after Hall) : a, dorsal view; 6 
 Bide view. 541. Chonetee Dalmaniana. 542. Productus punctatuB (after Meek). 543. Productus 
 mesialiB (after Hall); a, ventral. view; 6, side view. 
 
 Land and fresh-water shells (Figs. 544-548) begin to appear first 
 in the Coal-measures. The genus Pupa, a land air-breathing gastero- 
 pod, and the genus Cyclas, a fresh- water bivalve, and the genus Cypris, 
 
 Fig. 545. 
 
 Fig. 547. 
 
 Fig. 546. 
 
 Fig. 548. 
 
 Fios. 544-548.— CARBONirBBOcs Laotj and Fbbbh-wateb Shells: 544. Pupa vetusta (after Daw- 
 son) — a Land-Shell; a. natural size; b. enlarged. 545. Cypris (after Dawson); a, natural size. 
 546. Naiadites (after DawBon). 547. Dawsonella Meekii (after Bradley). 548. Anthracopnpa 
 ohioensis (after Whitfleld). 
 
410 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 a little crustacean bivalve, all of which are still represented by living 
 species, are found. It would seem that evolution-changes, both pro- 
 gressive and differential, are 
 more slow in fresh-water 
 forms (White), 
 
 Of course, marioie spe- 
 cies, both Lamellibranchs 
 and Gasteropods, are abun- 
 dant. Some figures of these 
 are given below. 
 
 Among Cephalopods, Or- 
 thoceratites still continue, 
 
 Fioa. 549-558.— CiRBONiMKons Lameliibranchs (after Meek): 549. Solenomya anodontoides. 
 550. AUtvisma ventricosa. 551. Allorisma pleuropistha. 552. Astartella Newberryi. 
 
 but in diminished number, variety, and size. Goniatites, mtrodvicedL 
 in the Devonian, or even earlier in Europe, also continue, but both 
 
 Fia. 553. 
 
 Fia. 554. 
 
 Fia. 556. 
 
 Fia. 555. 
 
 Pigs. 553-556.— Carbohipeboub Gasteropods (after Meek): 553. Macrocheilua Newberryi. 554. 
 Fleorotomaria ecitula. 565. Eiiomphalus subquadratus. 556. Bellerophon sublffivis (after Hall). 
 
 may be said to pass out with this age, although a few seem to pass into 
 the Lower Triassic. 
 
 Trilobites and Eurypterids also continue ready to disappear at the 
 end, but an advance in the Crustacean class is observed in the Limu- 
 ZoitZs (king-crabs), Fig. 559, and Macrourans — long-tailed Crusta- 
 ceans (lobsters, crawfish, shrimps, etc.), Figs. 562 and 563. Here, 
 then, we have two important steps in the progress of life foreshad- 
 owed in the Devonian. The gradual process of change may be clearly 
 traced in the one, but not yet in the other. Although Limuloids are 
 clearly differentiated in the Devonian, and transition forms may be 
 
FAUNA OF THE CARBONIFEROUS AGE. 
 
 411 
 
 Fir. 557. 
 
 Fig. 558. 
 
 Figs. 557, 558.— Caebonifbroub Goniatites: 557. Goniatites Lyoni (after Meek); o, Bide view; 6, 
 end view. 558. Goniatites crenistria (European); a, side view; ft, end view. 
 
 traced even to the Upper Silurian, yet the type first becomes con- 
 spicuous in the Carboniferous. If, with Packard, we divide Crusta- 
 ceans into two groups — Palsocarida and Neoearida (old style and 
 
 Fig. 561 
 
 Fig. bG2. 
 
 Fig. 563. 
 
 Figs. 559-563. — CABBomrEROus Cbttstacbans : 559. EuproOps Dan% (after Heek and Wortlien). 
 560. Phillipsia Lodieneis (after Meek). 561. Acanthotelson Stimpsoni restored (after Packard). 
 562. FalEeocaris typua (after Meek and Worthen). 563. Anthracopalgemon gracilis (after Meek 
 and Worthen). 
 
412 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 new style Cmstaceans) — -then TrilobiteSi Eurypterids, and Limuloids 
 belong to the Palaeocarida. That these were all derived from the 
 Trilobite is shown by the transition forms 564 a and bj which must 
 be compared with figures of Trilobites and Limulus previously given. 
 As already seen (p. 337), the same view is confirmed by embryology. 
 The genesis of the Neocarida we do not know. They certainly did 
 not come from thd Palaeocarida, but probably from some early and 
 low form of Crustaceans like Hymenocaris (Fig. 390, p. 313). If 
 so, then the earliest pre-Cambrian Crustacea separated into two 
 branches, (1) the Trilobites and (3) the Phyllocarids, both of which 
 
 Fig. 564.- 
 
 Psendoniscus Eoosevelti (after Clarke): a Eurypterid from Upper Silurian, b, Ne- 
 olimulus falcatus (after Woodward): a Limuloid from Upper Silurian. 
 
 are found in the Cambrian. The Trilobites developed into Euryp- 
 terids and Limuloids, while the Phyllocarids barely held their own 
 until the Trilobites were about to disappear, and then they developed 
 into the Keocarida or modern Crustacea (Walcott). 
 
 Insects now, for the first time, appear in considerable numbers and 
 variety. As might be expected, these are associated with the abundant 
 land vegetation of the Coal. Many of the principal orders are here 
 represented, viz.. Dragon-flies (Feuropters), Figs. 568 and 571; grass- 
 hoppers and cockroaches (Orthopters), Fig. 567; spiders and scor- 
 pions (Arachnids), Figs. 565 and 566; and centipeds (Myriapods), 
 Figs. 570 and 570a. It is noteworthy, however, that the three highest 
 orders, viz., the butterflies (Lepidopters), the social insects, such as 
 bees, ants, etc. (Hymenopters), and the flies (Dipters), are still want- 
 ing. These are not only the highest but also the flower-loving, honey- 
 sucking orders. True flowering plants (Angiosperms) did not yet 
 exist. Beauty and fragrance and sweetness were not ye,t character- 
 istic of the reproduction of plants. 
 
 Eecently immense numbers of Carboniferous insects have been 
 found at Commentry and described by Brongniart, among them a 
 
FAUNA OF THE CARBONIFEROUS AGE. 
 
 413 
 
 phasma (Fig. 571), about a foot long and twenty-six or twenty-eight 
 inches across the extended wings. As already said (p. 347), all the 
 Palaeozoic hexapod insects belong to one order — the Palceodictyoptera 
 of Scudder — a generalized type, connecting the three lower orders — 
 Neuropters, Orthopters, and Hemipters — of existing insects. 
 
 Fio. 567. 
 
 Fie. 569. 
 
 Fig. 570. 
 
 Fio. 571. 
 
 Figs 565-571.— Carbohifxhoiis Insects : 565. Eoscorpins carbonarius (after Meek and Worthen) 
 566. Arthrolycoea antiqua (after Beecher). 567. BJatta helvetica, x J, restored (after Heer) 
 568. Miamia Danse (after Scndder). 569. Euphoberia armigera (after Meek and Worthen) 
 570. Zylobius sigillariae (after Dawson) : a, Anterior portion enlarged. 571. Corydaloides Scud- 
 deri, x | (after Brongniart). 
 
414 
 
 PALEOZOIC SYSTEM OF ROCKS. 
 
 In Palseozoie insects, according to Brongniart, we have the follow- 
 ing generalized characters: 1. The three joints of the thorax were 
 not yet consolidated. 3. There were three pairs of wings correspond- 
 ing to the three pairs of legs, the anterior pair being small, almost 
 rudimentary. 3. The pairs of wings were all alike diaphanous, the 
 anterior pair being afterward hardened in many kinds, as in grass- 
 hoppers and beetles. 4. Tracheo-branchiae were present on the side 
 of the abdomen.* 
 
 Vertebrates (Fishes).— During the Carboniferous the great group 
 of Elasmobranchs increased prodigiously in point of numbers, size, 
 and variety, and attained a world-wide distribution, but their rapid 
 culmination which took place at the opening of this era was followed 
 toward its close by an equally notable decline, approaching almost to 
 the verge of extinction during the Permian. The Acanthodian (Pig. 
 438), Cladodont (Pig. 578), and Cestraciont (Pig. 447) types of 
 cartilaginous fishes, all originating in the Devonian, persist through- 
 out the remainder of the Palaeozoic, and the same is true of certain 
 fringe-finned and spiny-finned groups of Teleostomes; but the primi- 
 tive Cladoselache-like sharks (Pig. 439), together with the host of 
 Ostracophores and Arthrodires so characteristic of the Devonian, 
 have all passed away. 
 
 Fig. 574. 
 
 Flos. 572-574.— Carbonipeeous 'Fisuks— Elasmobranchs : 572. Symphysial dentition of Edestns 
 minor. 573. Head-spine of Pleuracanthus (after Nicholson). 574. Pin-spine of Gyracanthus 
 (after Nicholson). 
 
 Some of the Carboniferous sharks were formidably armed, the 
 largest fin-spines and most powerful crushing, cutting, and piercing 
 
 * Bull. Soc. de I'industrie minerale, vol. vii, p. 5V8. 
 
FAUNA OF THE CARBONIFEROUS AGE. 
 
 415 
 
 Fii;. 580. 
 
 Fig. 579. 
 
 FiGB. 575-580.— Cakboniperous Fishbb. 575. Dental plates of Cochliodus contortus. 576. Resto- 
 ration of Pleuracanthus Gaudryi. Brongn., x J (after Brongniart), from the Coal-measures of 
 Prance. 577. Orodusmammilaris (after Newberry). 678. Cladodns spinosus (after Newberry). 
 579. Amblypterus macropterus. 580. Tooth of Ehijsodus Hibberti, nataral size. 
 
 teeth known to the science of ichthyology (Figs. 572-577) having 
 been (ieveloped during this era. Great size and powerful armature 
 are also displayed among the Crossopterygian fishes, Ehizodus (Fig. 
 580), Megalichthys and C(jelacanthus being the principal genera. An- 
 cestral forms of the modern Ceratodus (Fig. 443) are by no means 
 uncommon, and those of modern Sturgeons (PalEeoniscidse) are rep- 
 resented in great abundance and variety. An example of the latter 
 is shown in Fig. 579, and in Fig. 576 is given a restoration of an 
 interesting generalized shark from the French Coal-measures. 
 38 
 
416 
 
 PALEOZOIC SYSTEM OP BOOKS. 
 
 Amphibians. — The first known appearance on the earth of air- 
 hreathing or land vertebrates , was in this age, and, as might have been 
 expected, in the lowest form, viz., Amphibians. 
 
 Amphibians were formerly classed as one of the orders of Eeptiles, 
 then as a sub-class; but now they are recognized as a distinct class in- 
 termediate between Fishes and Eeptiles, and approaching more nearly 
 the former than the latter. True Eeptiles are not certainly known to 
 be represented in the Carboniferous. Amphibians are divided into 
 four orders, viz.: 1. Tailless Amphibians (Anura), such as frogs, 
 toads, etc.; 2. Tailed Amphibians (Urodela), such as tritons, sala- 
 manders, sirens, etc. ; 3. The rare snake-like forms (Ophiomorpha or 
 Gymnophiona) ; and 4. Stegocephalia. Of these, only the Stegocepha- 
 lians were represented in the Carboniferous. The other three orders 
 still exist, but the last has been long extinct. ■ Many of the Stego- 
 cephalians were of large or even gigantic size. They were most of 
 them salamandriform, with long tails, weak limbs, and sluggish move- 
 ments. Some were pisciform, and had paddles instead of feet. 
 
 We can only briefly describe a few representatives of the class, and 
 draw some conclusions. 
 
 1. Amphibian Footprints. — In the sub-Carboniferous of Pennsyl- 
 vania, near Pottsville, have been found tracks of a four-footed, crawl- 
 ing animal {Sauropus primcevus), having thick, fleshy feet about four 
 inches long, ^d making a stride of about thirteen inches. The im- 
 
 FiG. 581.— Fossil Eain-prints of the Coal Periqd. 
 
 pression of a dragging tail is also visible. The surface of the slab 
 on which the tracks are found is marked with distinct ripple-bars and 
 rain-prints. This is the earliest known land-vertebrate. 
 . Similar tracks have also been found in the Coal-measures of Penn- 
 sylvania, on a slab afEected with sun-cracks (Fig. 582). The reptile 
 had evidently walked on the cracked and half -dried mud at low tide. 
 
FAUNA OF THE CARBONIFEROUS AGE. 
 
 417 
 
 Tracks have also been found in the Coal-measures of Illinois, Indiana, 
 Kansas, and Nova Scotia, and in the latter region beautiful specimens 
 
 Pig. 582.— Slab of Sandstone with Amphibian Footprints, from Coal-measures of 
 Pennsylvania, x |. 
 
 of rain-prints (Fig. 581). In Fig. 583 we give also foot-prints found 
 in the coal-measures of Kansas. 
 
 There can be little doubt that the reptiles making the tracks men- 
 tioned above were Stegocephalians. 
 
 Fio 583 —Footprints in Coal-measures of Kansas, x fy: a, Dromopus agilis; b, Allopus littoralis 
 
 (after Marsh). 
 
4.18 PALEOZOIC SYSTEM OF ROCKS. 
 
 3. Dendrerpeton. — In the Coal-measures of Nova Scotia have been 
 found quite a number of small amphibians, belonging, to several genera. 
 Among these one is especially interesting, on account of the conditions 
 under which it seems to have been preserved. It is called the Den- 
 drerpeton — tree-reptile (Fig. 584), because it was found by Dawson and 
 Lyell in sandstone, filling the hollow stump of a Sigillaria (Fig. 585), 
 along with another small species of amphibian, a number of land-shells 
 —pupa, etc. (Fig. 544, p. 409), and a myriapod (Fig. 570, p. 413). The 
 Sigillaria possessed a thick, strong bark, which was more resistant of de- 
 composition than the cellular interior. Stumps of these trees are often 
 found, consisting only of coaly bark filled with sandstone, evidently de- 
 
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^"^" Fig. 585.— Section of Hollow Sigil- 
 Fig. 584. — Jaw of Dendrerpeton acadianiim, and Section of iaria Stump, filled with Sand- 
 
 Tooth, enlarged (after Dawson). stone (after Dawson). 
 
 posited within the hollow. These sands are rich repositories of organic 
 remains. We can easily imagine the circumstances under which the 
 Dendrerpeton was preserved. A dead Sigillaria tree, rotted to the base 
 and only its hollow stump remaining, stood on the margin of a coal- 
 swamp ; river-fioods filled the stump with sand ; in the stump lived and 
 perished a Dendrerpeton ; or else, more probably, the dead body of the 
 reptile, together with shells and other organic remains, was floated into 
 the hollow stump and buried there. This amphibian was probably a 
 Stegocephalian, and closely related to the genus described in the next 
 paragraph. 
 
 3. Archegosaurus {Primordial Saurian). — In the Bavarian Coal- 
 measures has been found the almost perfect skeletons of animals about 
 three and a half feet long, which combine in a remarkable degree the 
 characters of Amphibians with those of Ganoid Fishes. It seems to 
 have been a Stegocephalian Amphibian, with general form and struct- 
 ure adapted for a pufrely aquatic life. It had, certainly in tbe early 
 stages of its life, probably throughout life, both gills and lungs, and 
 therefore, like all the Amphibians of the present day at this stage, or 
 like Perennibranchiate Amphibians throughout life, breathed both air 
 and water. The locomotive organs were paddles, adapted for swim- 
 ming, not for walking. The body was covered with imbricated ganoid 
 scales (Fig. 586,^), and the head with ganoid plates. The structure 
 of the teeth {B) was also ganoid. The bodies of the vertebr33 were 
 not ossified nor even cartilaginous,.but retained the early embryonic, 
 fibrous condition of a notochord. It was apparently a connecting link 
 
FAUNA OF THE CARBONIFEROUS AGE. 
 
 419 
 
 between the lowest Perennibranchiate Amphibians and the Sauroid 
 Fishes (Owen), with, perhaps, some alliances with the marine Saurians 
 
 Fia. 586.— Archegosaurus. 
 
 which afterward appeared. Large numbers of this Amphibian are 
 found, mostly in lower Permian, and chiefly in iron concretions. The 
 skeleton of this animal is given above (Fig. 586) with the limbs (C 
 and D) and jaw {E) of a Proteus — a perennibranchiate amphibian 
 — for comparison. 
 
 4. Eosaurus. — In the Coal-measures of Nova Scotia, in 1861, Prof. 
 Marsh found the vertebra of what he thinks, with some reason, was a 
 marine Saurian ; an order which is largely developed in the Mesozoic. 
 If so, it would be the earliest known reptile. But as only the bodies 
 of a few vertebrse have been found, and as the bi-concavity of these is 
 the chief evidence of marine Saurian affinity and as bi-concavity also 
 exists among Am-i 
 phibians, the later 
 authorities regard 
 it as a Stegocepha- 
 lian, related to An- 
 thracosaurus and 
 Loxomma. The size 
 of some of the ver- 
 tebrse was two and 
 a half inches in di- 
 ameter, indicating 
 an animal of large 
 dimensions. 
 
 Many other gen- 
 era have been de- 
 scribed by authors both in Europe and America. Among these, 
 Archegosaurus and Branchiosaurus, European species, are the most 
 abundant and best known of Palaeozoic Amphibians. Only the Stego- 
 cephalians are found earlier than the cretaceous. 
 
 Very recently a large number (thirty-four species referable to seven- 
 teen genera) of small Amphibians have been brought, to light by the 
 
 Fig. 587. — Two Vertebrse of Eosaurus acadianus (after Marsh). 
 
420 
 
 PALJiJOZOIC SYSTEM OF EOCKS. 
 
 Ohio Survey, and described by Cope. These are all Stegocephalians,of 
 several families, mostly Microsauridae. Some of them have the usual 
 
 broad heads of 
 Amphibians, but 
 a large number 
 are remarkable 
 for their long, 
 limbless, snake- 
 like forms and 
 pointed heads. 
 These are eyi- 
 dently among 
 the lowest forms 
 of Amphibians, 
 and have strong 
 affinities also 
 with Ganoid 
 
 Fig: 588.— Ptyoniiis (after Cope). 
 
 fishes. Pigs. 588 and 589 represent two of the Ohio Amphibians. 
 Some General Observations on the Earliest Land Vertebrates.— With- 
 out any exception, so far as known, all the air-breathing vertebrates of 
 the Carboniferous were Stegocephalians. Some were remarkable on 
 account of the extraordinary labyrinthine structure of their teeth, pro- 
 duced by the intricate infolding 
 of the surface and of the cavity. 
 The same structure is observed 
 in Ganoid teeth, but in a far 
 
 Pig. 589.— TuditanuB radiatuB, x i (after Cope). Fig. 590.— Section of Tooth of a Labyrinthodont. 
 
 less degree. The simple infoldings of Ganoids (Pig. 453, p. 355) be- 
 come intricate in Labyrinthodonts (Fig. 590). 
 
 The Labyrinthodonts were probably the most complete example of 
 a connecting type which has yet been discovered. Pirst, they were 
 true Amphibians in the strictest sense, having all of them in the early 
 stages of' their life — some throughout life — both lungs and gills, and 
 thus connecting water-breathers with .air-breathers. Again, they were 
 
SOME GENERAL OBSERVATIONS ON THE WHOLE PALEOZOIC. 421 
 
 very different from the slimy-skinned Amphibians of the present day, 
 ■in being covered, at least partly, with bony plates or scales over the 
 body, and with closely-fitting bony plates over the head. Again, they 
 differed wholly from the present Amphibians in having jaws thoroughly 
 armed with very large and powerful teeth, the structure of which is 
 labyrinthine. All of these characters connected them with Sauroid 
 fishes which preceded them, and'the great Saurian reptiles which suc- 
 ceeded them. Finally, they seemed to possess also characters connect- 
 ing them with several orders of subsequently-existing reptiles. In the 
 Labyrinthodonts and Sauroid fishes we can almost find the point of 
 separation of the two great branches. Amphibian and Fish, of the ver- 
 tebrate stem ; and in the former the commencing differentiation of the 
 several orders of Reptiles. All the earliest Amphibians had persistent 
 notochord (Cope). 
 
 Some General Observations on the Whole Palmozoic. 
 
 We have defined geology as the history of the evolution of the 
 earth. Evolution, therefore, is the central idea of geology. It is this 
 idea alone which makes geology a distinct science. This is the cohe- 
 sive principle which unites and gives significance to all the scattered 
 facts of geology — which cements what would otherwise be a mere inco- 
 herent pile of rubbish into a solid and symmetrical edifice. It seems 
 appropriate, therefore, that at the end of the long and eventful Palaeo- 
 zoic era we should glance backward and briefiy recapitulate the evi- 
 dences of progressive change (evolution), physical, chemical, and vital. 
 
 Physical Changes. — The Palaeozoic era opened on this continent 
 with a V-shaped mass of land —the Archaean area — to the north ; also, 
 a land-mass of Archaean rocks, of unknown shape and extent, on the 
 eastern border, and probably some islands and masses of larger extent 
 in the Basin and Rocky Mountain regions. This condition of things is 
 represented on the map on page 303. Throughout the Palaeozoic era 
 there was an accretion of land to this nucleus by upheaval of con- 
 tiguous sea-bottoms ; a development of the continent southward (and 
 perhaps northward) from the northern area, and both eastward and 
 westward from the eastern border area, until at the end of the Palaeo- 
 zoic the eastern half of the continent included certainly all the Arch- 
 aean, Silurian, Devonian, and Carboniferous areas shown on the map 
 on page 303, and probably also some on the eastern border of the eastern 
 Archaean area, which was subsequently covered by the sea, and is there- 
 fore now concealed by more recent deposits. The loss of Palaeozoic 
 land on the eastern border probably took place during the Appalachian 
 revolution. In the Rocky Mountain region the development was prob- 
 ably less steady. Unconformity of Carboniferous on Silurian strata 
 shows extensive land areas there during Devonian times. The conti- 
 
4,22 PALEOZOIC SYSTEM OF ROCKS. 
 
 nent was already sketched in the beginning of the Palaeozoic, and 
 the process of development went on during that era, so that at the 
 end the outlines of the continent were already unmistakable. 
 
 Fig. 590a.— Map of North America after the Appalachian Revolution (after Dana). 
 
 Progressive Change in Organisms. — Corresponding with these 
 changes, physical and chemical, it is natural to expect changes in spe- 
 cies, genera, families, etc., of organisms : and such we find. The law 
 of continuance or geological range of species, genera, families, orders, is 
 very similar to that of extent or geographical range of the same groups ; 
 i. e., the laws of distribution in time are similar to those of distribution 
 in space. The period of continuance (range in time) of species is, of 
 course, less than that of genera (because the genus is continued in other 
 species of the same genus), and that of genera less than that of fami- 
 lies, etc. According to Prof. Hall, there have been in the Silurian and 
 Devonian ages alone at least thirty almost complete changes of species. 
 The changes of genera are, of course, much less numerous, and those 
 of families still less than those of genera. These general laws may be 
 illustrated by any Palaeozoic order ; but I select the order of Trilobites, 
 because they are very numerous, very diversified, and well studied, and 
 because they came in with the Palaeozoic, continued throughout the 
 whole era, and then passed away for ever. 
 
 The diagram (Fig. 591) illustrates these laws in the order of Trilo- 
 bites. It is seen that this order continues through the whole era, 
 commencing in small numbers, reaching its highest development in 
 
SOME GENERAL OBSERVATIONS ON THE WHOLE PALEOZOIC. 423 
 
 the Lower Silurian, and declining to the end. But the families are 
 changed several times. Six groups are given, to show how they come 
 and go successively. If we should attempt the distribution of genera, 
 the changes would be much more numerous, and of species still more 
 
 1. Paradosides.. 
 
 2. Bathyurus, Agnos- 
 tus, etc 
 
 3. Asaplius, Eemo- 
 
 pleurides, Tri- 
 iiiicleiis, etc.. . . 
 
 4. Calymene, Acidas- ) 
 
 pis, etc f 
 
 5. Homalonotus, Li- ) 
 
 chas, etc j 
 
 6. Pllillipsia, Griffith- I 
 
 ides f 
 
 7. Disiribution of 
 
 species of Caly- 
 mene, etc 
 
 Fie. 591.— Diagram illustrating Distribution of Families, etc., m Time. 
 
 SO. In the lower portion of the diagram we have attempted to showin 
 a very general way how the distribution of species of Calymene and 
 Acidaspis might be represented. 
 
 General Comparison of the Fauna of Paleozoic with that of Neozoic 
 Times. — The changes above explained were gradual ; but at the end of 
 the Palaeozoic there occurred a more rapid and revolutionary change, 
 and the greatest which has ever occurred in the history of the organic 
 kingdom. As human history is primarily divided into Ancient and 
 Modern, so the whole history of the earth may be properly divided into 
 Palmozoic and Neozoic times. We wish to contrast broadly the fauns 
 of these two great divisions of time. In the diagram on next page, 
 the vertical line represents the dividing line between the old and the 
 neio time-world. In this country it is appropriately called the Appa- 
 lachian revolution. On the left is the Palaeozoic, on the right the 
 Neozoic. When families or orders of animals are placed on one or the 
 other side without mark, it means that they are the only kind of the 
 contrasted families found on that side, or nearly so. If the orders or 
 
424 
 
 PALJ50Z0IC SYSTEM OF ROCKS. 
 
 families so placed are marked with the sign -f-, it means that they are 
 the predominant kinds ; if + +» greatly so. For example, among Ce- 
 
 Falaeozoic times.. 
 
 .Neozoic times. 
 
 + Quadripartita 
 
 + + Stemmed, or CriDoids. 
 + Armless, or simple arms. 
 
 Badiata. 
 
 Corals. 
 
 I . . Sexpartita + . 
 
 Echinoderms. 
 
 I . .Free, or Echinoida and Asteroids + +. 
 
 Crinoids. 
 I . .Plumose arms. 
 
 + Bracbiopods 
 
 + Square-shouldered . . . 
 
 + TJnsiphonated 
 
 Marine , 
 
 Unbeaked — Herbirorous. . 
 Shelled, or Tetrabranchs. . 
 
 + Straight 
 
 Orthoceratites. 
 
 N 
 
 MOLLUSKS. 
 
 Bivalves. 
 
 I . . Lamellibranchs + + . 
 
 Bracbiopods. 
 
 I . .Sloping-shouldered. 
 
 Lamellibranchs. 
 
 I . . Siphonated + . 
 
 Oasteropods. 
 
 I . . Land, fresh-water, and marine. 
 
 Marine. 
 
 I . .Beaked — Camirorous +. ^ 
 
 Ceplialopods. 
 
 I . .Naked, or Dibrauchs + +. 
 
 Shelled. 
 I ..Coiled.* 
 
 Goniatites. 
 
 Ceratites. 
 
 Ammonites. 
 
 Palaeocarida . 
 
 Trilobites. 
 
 Abiheofoda. 
 
 Crustacea. 
 
 .Neoearida +. 
 
 Eurypterids. 
 
 Limuloids. 
 
 Macrourans. 
 
 Brachyourans. 
 
 Vektebkata. 
 
 I 
 Fishes. 
 
 Heterocercals I . . Homocereals +. 
 
 Ganoids and Elasmobranohs . . | Teleosts +. 
 
 • Elasmobranchs. 
 Cestracionts. 
 
 Hybodonts 
 
 Amphibians . 
 
 Squalodonts-I-. 
 j . .True Kcptiles +. 
 
 * Baculites of the Cretaceous are an exception. 
 
GENERAL PICTURE OF PALEOZOIC TIMES. 425 
 
 phalopods, the Tetrabranch, or shelled family, are the only kinds 
 found in the Paleozoic ; in the Neozoic, both families exist, but the 
 Dibranchs or naked ones vastly predominate. 
 
 General Picture of Palceozoic Times. 
 
 Perhaps it is not inappropriate to group some ofthe more impor- 
 tant facts in a very brief outline-picture of Palseozoic times. We must 
 imagine, then, wide seas and submerged continental areas. The phys- 
 ical and climatic conditions probably are not very different from more 
 recent time, with variations of temperature and moisture. If an ob- 
 server had walked along these early beaches he would have found cast 
 up, in great numbers, the shells of Brachiopods ; clinging to the rocks 
 and hiding away among their hollows, instead of sea-urchins and star- 
 fishes and erabs, he would have found crinoids and trilobites. In the 
 open sea he would have found as rulers, instead of whales and sharks 
 and teleosts and cuttle-fish, huge cuirassed Sauroids and the straight- 
 chambered Orthoceras. Turning to the land, he would have seen at 
 first only desolation; for there were almost no land-plants until the 
 Devonian, and almost no land-animals until the Coal. During the 
 Coal there were extensive marshes, overgrown with great trees of 
 Sigillaria, Lepidodendron, and Catamites, with dense underbrush of 
 Ferns, inhabited by insects and amphibians ; no umbrageous trees, no 
 fragrant flowers or luscious fruits, no birds, no mammals. These 
 " dim, watery woodlands " are flowerless, fruitless, songless, voiceless, 
 except the occasional chirp of the grasshopper and the croak of Am- 
 phibians. The observer would notice also the complete absence of 
 modern types of plants and animals — it would be like another world. 
 
 Appalachian Revolution. — This long dynasty was overthrown, this 
 reign of Fishes and Amphibians ended, the physical conditions de- 
 scribed above were changed, and the whole fauna and flora destroyed 
 or transmuted, by the Appalachian revolution. Not a single species 
 is known to have crossed this line. At the end of the Palseozoic, the 
 sediments which had been so long accumulating in the Appalachian 
 region at last yielded to the slowly-increasing horizontal pressure, and 
 were mashed, folded, and lifted into the earliest Appalachian chain, 
 with metamorphism. Perhaps the geographic and biologic changes of 
 this time make the greatest revolution which has taken place in the 
 earth's history. At the same time the Acadian range of East Canada 
 and the Ouachita range of Arkansas seems to have been formed (Dana) . 
 At the same time also great changes took place in the West. The Utah 
 basin region was upheaved to form land, the Nevada basin region sank 
 and became sea-bottom, and the Pacific shore-line was transferred 
 eastward to the 117th meridian about Battle Mountain. In other 
 words, the Basin region Palseozoic continent was transferred eastward 
 
426 PALEOZOIC SYSTEM OF ROCKS. 
 
 its own breadth to form the Basin region Mesozoic continent (King). 
 Similar and very extensive changes in physical geography must have 
 taken place in other portions of the globe, otherwise we can not account 
 for the enormous changes in physical conditions and fauna and flora. 
 Many of these have been traced, but we can not yet trace them as 
 clearly as in America. The greatest of these and one of the greatest 
 in the history of the earth was the formation of a great southern con- 
 tinent (Gondwana Land) connecting with South America, South Africa, 
 and Australia. We shall have occasion to mention this again. 
 
 Transition from the Palmozoic to the Mesozoic — Permian Period. 
 
 The Permian a Transition Period. -^The Palaeozoic era was closed 
 and the Mesozoic inaugurated by the Appalachian revolution. All 
 the great revolutions in the earth's history are periods of oscillations. 
 Such oscillations produce unconformity. They also produce changes 
 of climate, and therefore of fauna and flora. We flnd, therefore, that 
 the Mesozoic rocks are universally, or nearly universally,* uncon- 
 formable on the Carboniferous ; and, corresponding with this uncon- 
 formity, there is a wonderful change in fauna and flora — a change 
 the greatness of which we have attempted to show in the contrast on 
 the previous page. Now, the older geologists regarded this change as 
 one of instantaneous destruction and recreation, because they took no 
 account of a lost interval. But we have already shown (pp. 188, 305) 
 that in all cases of unconformity there is such a lost interval, which 
 in some cases is very large. In order to account for the very great 
 change in the organic world, it is only necessary to suppose that 
 periods represented by general unconformity are critical periods in 
 the earth's history — periods of rapid change in physical geography, 
 climate, and therefore of rapid change in fauna and flora, by the pass- 
 ing out of old types and the differentiation of new types. Unfor- 
 tunately, in the earth's history' as in human history, it is exactly these 
 critical periods — these periods of change and revolution — the record of 
 which is apt to be lost. In both histories, too, this is truer the farther 
 back we go. Of the long interval between the Archaean and Palaeozoic, 
 not a leaf of record has yet been recovered with any certainty ; but of 
 the interval now under discussion many leaves of record have been 
 recovered. These have been bound together in a separate volume or 
 chapter and called the Permian. I shall regard the Permian, there- 
 fore, as essentially a transition period ; its rocks were deposited dur- 
 ing the period of commotion ; its fossil types are in a state of change, 
 though more nearly allied to the Palseozoic. Among the great oscilla- 
 
 * In the Rocky Mountain region there seems to be complete conformity in some 
 places. (King, Fortieth Parallel Survey, vol. i, p. 266.) 
 
TRANSITION FROM THE PALEOZOIC TO THE MESOZOIC. 427 
 
 tions which occurred during this time is that already referred to on 
 the previous page. We have good evidence, especially from Permian 
 plants, that there existed at this time a great continental land-mass 
 connecting South America, South Africa, Australia, and South India 
 with one another and all with Antarctica. This hypothetical continent 
 has been called by Suess Gondivana Land. 
 
 . From what has just been said, it will be anticipated that the uncon- 
 formity of the Mesozoic on the Palseozoic sometimes takes place between 
 the lowest Mesozoic and the Permian, and sometimes between the Per- 
 mian and the Coal. The Permian, therefore, is sometimes conformable 
 with the Coal, as, e. g., in this country, sometimes conformable with the 
 Triassic, as in England. It thus allies itself stratigraphically some- 
 times with the Palaeozoic, sometimes with the Mesozoic. Paleontologi- 
 cally it is always more allied to the Palseozoic. The English section, 
 and the history of opinion concerning it, admirably illustrate this 
 point. Pig. 593 is an ideal section through the Devonian, the Coal 
 and Triassic (Lower Mesozoic) of England. Lying unconformably on 
 the eroded surface 
 of the Coal, 6, there 
 is seen a continuous 
 and perfectly con- 
 formable series of 
 strata, a. This se- 
 ries, moreover, is lithologically characterized throughout, especially the 
 lower part, by frequent alternations of Red sandstones, and therefore has 
 been called New Bed sandstone, to distinguish it from the Devonian, 
 which is often called Old Red sandstone. It is further distinguished 
 throughout especially the upper part, by variegated shales, and therefore 
 called altogether Poecilitic group. It is also distinguished throughout 
 by the presence of salt, and therefore called the Saliferous group. Here, 
 then, there were the strongest reasons for regarding the whole as one 
 group, distinctly separated by unconformity from the underlying Coal. 
 The upper part of this continuous series contained undoubted Mesozoic 
 fossils. The line of unconformity was, therefore, naturally believed 
 to be the line between Palaeozoic and Mesozoic. Unfortunately, the 
 lower portion is very barren of fossils, and this means of correcting 
 the stratigraphic conclusion was at first nearly wanting. When fossils 
 were discovered in sufiScient numbers, however, they showed a greater 
 alliance •V7ith the unconformable Coal below than with the conformable 
 strata above. Thus, if we make the division between Palaeozoic and 
 Mesozoic on stratigraphical grounds, we would find it between the 
 Coal and the overlying strata; while, if we make it on paleontological 
 grounds, we would have to draw the line through the midst of the 
 conformable strata, a, giving one half to .the Palaeozoic and the other 
 
 PiQ. 592.-(AfterLyell.) 
 
4:28 
 
 PALAEOZOIC SYSTEM OF ROCKS. 
 
 half to the Mesozoic. The lower PalaBozoie half is called the 
 Permian* 
 
 As a broad general fact, therefore, the rapid evolution which is 
 called the Appalachian revolution took place, or commenced to take 
 place, at the end of the Coal period. But the fauna and flora were not 
 immediately exterminated, but struggled on, maintaining, as it were, 
 a painful existence, under changed conditions, themselves meanwhile 
 changing, until complete and permanent harmony was re-established 
 with the opening of the Mesozoic. If we may use an illustration, the 
 Appalachian revolution was the death-sentence of Palaeozoic types, but 
 
 the sentence was not in- 
 stantly executed. This 
 transition period, be- 
 tween the sentence and 
 the execution of Palaeo- 
 zoic types, is the Per- 
 mian. 
 
 It is well here to draw 
 attention to the fact of 
 this great change of or- 
 ganisms, the greatest in 
 the whole history of the 
 earth, taking place in 
 the midst of conformable 
 strata (Fig. 593, a), and the change must have been comparatively 
 rapid. 
 
 We have given the history of change of opinion in regard to the 
 English section (Pig. 593), because it is a typeof many discussions and 
 changes which have occurred and will still occur in geological opinion. 
 Area in the United States. — The Permian has been found in the 
 United States, in Kansas, bordering on, and conformable with, the coal 
 of that region (map, p. 303) ; also in New Mexico and Western Texas, 
 and probably also overlying the coal of Illinois (Cope). It gradates so 
 completely into the upper Coal-measures that no attempt has been 
 made to separate them in the map. A considerable number of mol- 
 lusks (Figs. 593-597), fishes, amphibians and reptiles, and plants are 
 known from the American Permian. But the study of the plants and 
 invertebrates is not sufficiently advanced to give complete knowledge. 
 An elementary treatise like this must dwell mainly on culminating 
 periods, and their characteristic forms ; and yet to the philosophic stu- 
 dent it is the transitional forms and periods which are the most inter- 
 
 FiG. 593. 
 
 Fig. 596. 
 
 Pigs. 593-597.— Amebioan Pbbmian Fossils (after MeekV 593 
 Bumicrotis Hawni. 594. Myalina Permiana. 595. Bake 
 wellia parva. 596. Pleurophoras sabcuneatus. 697. A Gas. 
 teropod. 
 
 * In Germany it is closely allied stratigraphieally with the Triassic, and therefore by 
 many put in the Mesozoic, and called Dy<m. 
 
TRANSITION FROM THE PALEOZOIC TO THE MESOZOIC. 4,29 
 
 Pigs. 598-602.— BubopeanPermiast Fossils: Plants: 598. Walchia pinifonnis (Permian of Europe). 
 599. Ginkgophyllum. Fishes: 600. Platysomas gibbosus (Permian of Europe). 601. Pleuracan- 
 thus paralTems, restored (after Pritsch). Sepiile: 602. Limnerpeton laticeps, natural size (after 
 Fritsch). 
 
 esting. The Permian is pre-eminently such a transitional period, and 
 contains many transitional forms. In it we have a passing away of 
 
430 MESOZOIC ERA— AGE OF REPTILES. 
 
 Palaeozoic types, a coming in of Mesozoic types, and a co-existence of 
 the two side by side. The change from tlie one to the other, there- 
 fore, was not sudden and by exterminations and recreations, but grad- 
 ually by extinction of some old forms and modification of others into 
 new forms ; and all the new forms were thus derived. Under the in- 
 fluence of changing conditions, the more specialized and rigid forms 
 became extinct, while the more generalized and plastic forms gave 
 rise to modified descendants perhaps in several directions. 
 
 The main features of the Permian life, therefore, were: 1. A lin- 
 gering of coal types of plants, such as Sigillarids and the Calamarife, 
 and several genera of Ferns, but extinction of Lepidodendron and in- 
 crease and advance of gymnosperms to more varied modern forms, 
 such as Walchia, Ginkgophyllum, etc. (Pigs. 598, 599). 2. A lingering 
 of Orthoceratites, square-shouldered Brachiopods, such as Productus 
 and Spirifer, and perhaps of Groniatites, but complete extinction of 
 Trilobites and Burypterids. 3. A continuance of Ganoids, but under 
 more modern forms (Figs. 600, 601). 4. The Carboniferous amphib- 
 ians continue in the form of Stegocephalians, of which some are 
 very modern in form (Pig. 603), but true reptiles are introduced in 
 considerable numbers. These first reptiles, as might have been ex- 
 pected, are wonderfully generalized in structure. They connect, on 
 the one hand, with Amphibians, from which they were derived, and, 
 on the other, with the lowest Mammals, to which they gave origin. 
 On account of this connection with Mammals, Cope has called them 
 Theromorphs (beast-like). (See page 436.) 
 
 The Permo-Carboniferous of Australia, India, South Africa, and 
 Brazil all contain enormous glacial deposits and other evidences of 
 glaciation. Apparently Permian glaciation was on a vaster scale than 
 that of the Pleistocene in the northern hemisphere. 
 
 The peculiar Permian flora of the southern hemisphere, called the 
 " Glossopteris Flora,'"' is unlike that of the Carboniferous and allied 
 to that of the Mesozoic, and indicates land connection of all the 
 southern continents. 
 
 CHAPTEE IV. 
 MESOZOIC ERA—AGM OF REPTILES. 
 
 The PaliEOzoic era, we have seen, was very long, and very diversi- 
 fied in dominant types, of both animals and plants. It was during this 
 long era that originated nearly all the great branches, and even sub- 
 branches, of the organic kingdom. We have during this era, therefore, 
 three very distinct ages : an age of Invertebrates, an age of Fishes, and 
 an age of Aerogens and Amphibians. The Mesozoic was far less long 
 
TRIASSIC PERIOD. 43I 
 
 and far less diversified in dominant types. It consists of only one age, 
 viz., the ago of Eeptiles. Never in the history of the earth, before or 
 since, did this class reach so high a point in numbers, variety of form, 
 size, or elevation in the scale of organization. 
 
 General Characteristics.— The general characteristics of the Meso- 
 zoic era are the culmination of the class of Reptiles among animals, and 
 of Gycads among plants, and the first appearance of Teleosts (common 
 osseous fishes). Birds, Mammals among animals, and of Palms and 
 Dicotyls among trees. 
 
 Subdivisions. — The Mesozoic era is divided into three periods, viz. : 
 1. Triassic, because of its threefold development where first studied in 
 Germany; 2. Jurassic, because of the splendid development of its 
 strata in the Jura Mountains; 3. CVeteeoMS, because the chalk of Eng- 
 land and France belongs to this period. 
 
 Mesozoic Era. 
 
 3. Cretaceous period. 
 2. Jurassic period. 
 1. Triassic period. 
 
 In this country the Triassic and Jurassic are not so distinctly sepa- 
 rable as they are in Europe, nor as they are from the Cretaceous. They 
 form, in fact, one series, and if the Mesozoic had been studied first in 
 this country, the whole would probably have been divided into only two 
 periods. We shall therefore speak of the Mesozoic of this country as 
 consisting of two periods, viz., the Jura-Trias and the Cretaceous. On 
 account of their fuller development in Europe, it will be best to speak, 
 first, of the Triassic generally, then of the Jurassic generally, taking 
 our illustrations mainly from European sources, and then of the Jura- 
 Trias in America. Also, on account of the comparative poverty of the 
 Trias in organic remains, we will dwell much less on this period than 
 on the subsequent Jurassic ; for in this latter period culminated all the 
 distinctive characters of the- Reptilian age. 
 
 Sectiost 1. — Tkiassic Peeiod. 
 
 As already stated, the Triassic strata are nearly always uncon- 
 formable with the Coal, and the period opens with a fauiTa and flora 
 wholly and strikingly different from the preceding. In many places, 
 however, there is found an intermediate series, the Permian, some- 
 times conformable with the Coal and unconformable with the Trias, 
 sometimes conformable with the Trias and unconformable with the 
 Coal. Its fauna and flora are also to some extent intermediate, though 
 more nearly allied to those of the Coal. The explanation of this has 
 already been given. 
 
432 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 Subdivisions. — The subdivisions of the Triassic rocks and period in 
 several countries are given below. 
 
 OSBMAH. 
 
 Fbbnoh. 
 
 Enolish. 
 
 3. Keuper. 
 
 2. Muschelkalk. 
 
 1. Bunter Sandstein. 
 
 Marne irises. 
 Muschelkalk. 
 Grfes bigarre. 
 
 Variegated marl. 
 
 Wanting. 
 
 Upper New Red sandstone. 
 
 Fig. 603. 
 
 Pro. 605. 
 
 Pisa. 603-605.— Tbiassio OoNrPEBS and Ctoabs (after Nicholson) : 603. Voltzia heterophylla, a 
 conifer. 604. Pterophyllum Jceg^ri, a cycad. 605. Podozamites Emmonai, a cycad. 
 
 Plants. 
 
 The flora of the Trias is very imperfectly known. We find, how- 
 ever, no longer the great coal- making trees of the Carboniferous — Sig- 
 illarids, Lepidodendrids, and Calamariae — though tree-ferns still con- 
 tinue in abundance, but of different types from those of the coal. 
 The forest-trees seem to have been principally Tree-ferns, Cycads, and 
 Conifers, although the last two did not reach their highest develop- 
 ment until the next period. For this reason we will put ofE the fuller 
 discussion of them until we come to that period. 
 
TRIASSIC PEEIOD. 
 
 433 
 
 Animals. 
 
 Among the Echinoderms we find no longer any Cystids and Blas- 
 toids ; but Crinids, beautiful lily Encrinites, with long plumose arms, 
 are very abundant (Fig. 606). 
 
 Among Brachiopods the familiar square-shouldered forms, includ- 
 ing the Spirifer family, the Strophomena family, 
 and the Productus family, are almost if not wholly 
 gone ; only a few Spirifers remain. Among Cephal- 
 opods, we find no longer Orthoceratites * or Oonia- 
 tHes, but Ceratites (Fig. 614), with the Ammonites, 
 take tlieir place. In Ceratites, the suture is more 
 complex than in Goniatites, but not so complex as 
 the subsequent Ammonites. Among Crustaceans, 
 we find no longer Trilobites nor huge Eurypterids ; 
 but Macrourans, which began in the Carbonifer- 
 ous, are now more abundant, and of more modern 
 forms (Fig. 615). 
 
 Insects. — As already seen, all the hexapod in- 
 
 FiG. 606.— Bncrinus liliformie. 
 
 Flo. 607.— Aspidnra loricata, an asteroid: a, Dor- 
 sal ; b. Ventral surface. 
 
 sects of Palaeozoic belong to one family — the Palseodictyoptera — but 
 this was a generalized type connecting the three lower existing orders, 
 viz., Orthopters, Neuropters, and Hemipters. Now, with the opening 
 of the Trias, we have these three orders distinctly differentiated, and 
 Coleopters (beetles) added (Fig. 616). But still the higher sucking 
 insects are wanting. 
 
 Fishes. — Among fishes, still we find no Teleosts, only Granoids, 
 Selachians, and Dipnoi, f The Ganoids are some of them hetero- 
 cereal or vertebrated-tailed like the Pafeozoic Ganoids, some are only 
 slightly vertebrated, and some wholly non-vertebrated-tailed, or homo- 
 cereal. The Ceratodus, a remarkable genus of Dipnoan fishes, one spe- 
 cies of which still lives in Australian rivers (Fig. 443, p. 353), is traced 
 back to this period. Being known in a fossil state only by the curious 
 
 * A very few seem to have croased the line. 
 
 •)■ The classification of the vertebrates in this book will generally follow Zittel's 
 Paloeontology, vol. ii, as revised by Eastman. 
 
434 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 palatal teeth (Fig. 617), it was formerly classed with Elasmobranchs. 
 The Elasmobranchs are partly Cestracionts (Fig. 618) and partly 
 Hybodonts (Fig. 619). 
 
 Amphibians. — Stegocephalians have already been described, in 
 
 Fig. 610. 
 
 Pia, 612. 
 
 Fig. 613. 
 
 Figs. 608-613.— Lamelldbranchb (after Nicholson): 608. Daonella Lommelli. 609. Pccten Valoni- 
 ensis. 610. Myophoria llneata. 611. Cardiam Bhseticum. 612. Avicula contorta. 613. Avicula 
 Bocialis. 
 
 connection with the Carboniferous when they first occur. They cul- 
 minate, however, in size and in complexity of tooth-strncture — if not 
 in number and vaViety — in the Triassic, and then become extinct. In 
 
 Pig 614 — Ceratites nodosas. 
 
 Fig. 616. — Glaphroptera pterophylli (after Heer). 
 
 some cases they reached gigantic proportions. The head of the Mas- 
 todonsaurus (Fig. 630) was three feet long and two feet wide. The 
 tooth of the typical genus Labyrinthodon was three and a half inches 
 long and one and a half in diameter at the base (Pig. 623). The com- 
 
TRIASSIC PERIOD. 
 
 435 
 
 Fig. 6ir. 
 
 plex labyrinthine structure is shown in Fig. 623. Attention was filrst 
 
 drawn to these animals by the discovery in Triassie strata of certain 
 tracks made by a 
 clumsy-footed ani- 
 mal (Fig. 624), 
 which was at first 
 mistaken for a 
 mammal and 
 
 called Cheirother- 
 ium (hand-beast). 
 Its true nature was 
 made known by 
 Prof. Owen, who 
 called it Labyrin- 
 th odon. 
 
 Reptiles.— The 
 
 t'l * 4.1, m • Figs. 617-619.— Trassic Fishes: 617. a, Dental Plate of Ceratodus eer- 
 repClieS OI tne ±ri- mtus; *. Dental Plate of Ceratodus altus. Keuper (after Agassiz). 
 
 oooir, .,..^ ;™^„.. 618. Acrodus minimus. 619. Hybodus apicalis (after Agassiz). 
 
 dooic cire imper- 
 fectly known. They belong mainly to three orders : 1. Rhyncosaurs 
 (beaked Saurians) ; 2. Anomodonts (lawless-toothed); 3. Tkeriodonts 
 (beast-toothed). The last two are sometimes united into one order, 
 
 Fio. 618. 
 
 Fig. 619. 
 
 r/-3 i . \ 
 
 
 ^W"-^ 
 
 c**— 
 
 Fig. 620. 
 
 Fig. 631. 
 
 Figs. 620, 621.— Tbiassio Amphibians— ioSj^nn<Aoiio«<*; 620. Mastodonsaurus Jsegeri. 621. Tre- 
 
 matoBaoras (after Huxley). 
 
436 
 
 MESOZOIC BRA— AGE OF REPTILES. 
 
 called Theromorpha (beast-form). All these orders are very charac- 
 teristic of the Trias, although a few Theromorphs are found in the 
 Permian. 
 
 The Rhyncosaurs had strongly-hooked, horny beaks, like that of a 
 
 parrot (Fig. 638). The curious rep- 
 tile Sphenodon, or Hatteria, of New 
 Zealand (Fig. 639), is the nearest liv- 
 ingtally. 
 
 The Anomodonts (lawless- toothed) 
 had jaws covered with horn, like 
 tortoises and birds, sometimes tooth- 
 less, as in Oudenodon (Fig. 636), 
 and sometimes with two great ca- 
 nines only, as in Dicynodon (Fig. 
 625). These reptiles were of great 
 size. The head of the Dicynodon 
 tigriceps was twenty inches long and 
 eighteen inches wide. 
 
 Fig. 623. Fig. 623. 
 
 Tigs. 633, 623.— Tbiassio Amphibians— iaftynjiiftodorefe .■ 622. Tooth of LabyrinthodoB, natural 
 size. 623. Section of same enlarged, showing structure. 
 
 The Theriodonts (beast-toothed) are so called on account of the 
 resemblance of their teeth to those of the lowest and earliest mammals. 
 The following are the main points of resemblance : 1. The teeth are 
 in three sets, viz., incisors, canines, and molars. 2. The canines are 
 much larger than the others, and separated from them by a wide space 
 (diastema). 3. The molars (jaw-teeth) are in many cases not conical, 
 like reptilian teeth, but have commenced to develop cusps (Fig. B30) 
 like those of mammals, especially of the earliest Mesozoic mammals. 
 (Compare this figure with Fig. 715, p. 466.) The canines of some of 
 these Theriodonts have been found five and six inches long. A large 
 
TRIASSIC PERIOD. 
 
 437 
 
 FiQ. 630. 
 T. _. /»«o,. n«l7PIl^• R24 Tracks of a Cheirotherium (an amphibian). 
 
 Figs 624-B30.-TBiASSro Kbptiles (after Owen). B^.iracKo u Lvcosaxinis. e28. Ehyncosanrs 
 
438 MESOZOIC ERA— AGE OF REPTILES. 
 
 number of these animals — as also of the previous order — have been 
 found in the Karoo beds of South Africa, and described by Prof. 
 Owen. Turtles are found in Upper Trias of Germany. 
 
 Birds. — No birds have yet been found in the strata of the Triassic 
 age, unless we except the so-called bird-tracks of the sandstone of the 
 Connecticut Valley and elsewhere, which we will discuss further on. 
 
 Mammals. — Remains of two or three small insectivorous Marsupials, 
 or perhaps monotremes, have been found in the uppermost Triassic, 
 both of Europe and of the United States. Figures of a tooth of one 
 of these, Microlestes antiquus, are given (Fig. 631). The remains of 
 the mammals of the Triassic are so few and fragmentary that it is 
 difficult to make out their affinities, but it is probable that they were a 
 generalized type connecting marsupials with the still lower monotremes 
 
 and both with Theriodont Rep- 
 tiles. But as these are found in 
 "RS I '111 rf ^^B^ very small numbers and only in 
 "wl HI *^^ uppermost T^riassic beds, and 
 
 ^^ '"' as similar animals are found in 
 
 Fig. 631. — Tooth of the Microlestes antiquus. , , i • ii 
 
 much greater numbers m the 
 Jurassic, it seems best to regard these as anticipations, and to put off 
 the further discussion of the affin ties of the earliest mammals until 
 we take up that period. 
 
 Mammals probably preceded Birds. This is not a little remarkable. 
 But it must be remembered that Birds are very closely allied to Rep- 
 tiles, and may be regarded as a secondary offshoot of the reptilian 
 branch. 
 
 The sudden coming in of new types here and especially of the 
 characterigtic Reptiles is certainly remarkable. They probably origi- 
 nated in the southern hemisphere (Gondwana Land) and migrated 
 thence northward. 
 
 Origin of Roch- Salt. 
 
 Neither rock-salt nor coal is confined to the rocks of any particular 
 age. Both have been formed in every age ; both are forming now. 
 But as the subject of the origin of coal-deposits was discussed in 
 connection with that age during which it was accumulated in the 
 greatest abundance — the Carboniferous — so the origin of rock-salt is 
 best discussed in connection with the so-called Saliferous or Triassic. 
 
 Age of Rock-Salt. — As already stated, rock-salt is found in strata 
 of all ages, and is forming now. Moreover, there is no period which 
 deserves the name Saliferous to the same extent that the Carboniferous 
 deserves its name. The salt of Syracuse, New York, is found in the 
 Upper Silurian ; that of Canada, which exists in immense beds 100 
 feet thick, is found in the Upper Silurian or Lower Devonian ; that of 
 
ORIGIN OF ROCK SALT. 439 
 
 Pennsylvania is Upper Devonian ; of Southwest Virginia is sub-Car- 
 boniferous; that recently discovered in Kansas is in the Trias; * that 
 of Petite Ansa, Louisiana, is uppermost Cretaceous or lowest Tertiary 
 (Hilgard). In Europe, the English salt- beds are Triassic, the German 
 beds Permian, Triassic and Jurassic; the celebrated Polish beds at 
 Cracow are Tertiary. 
 
 Mode of Occurrence. — Salt occurs in immense beds of pure rock-salt, 
 or else impregnating strata. It is obtained by direct mining, or else by 
 boiling down the saline waters either of natural springs or of artesian 
 wells sunk into the salt-bearing strata. The further explanation of its 
 mode of occurrence is best and most concisely given by comparing it 
 with coal. 
 
 1. Like coal, it occurs in isolated basins, but these are far more 
 limited than the great coal-fields. 3. Like coal, it is interstratified 
 with sands and clays, the whole series repeated often many times. In 
 Galioia, for example, there are found seven salt-beds in the same sec- 
 tion. In the Kansas Trias there are seven beds. Like coal, also, each 
 bed is usually underlaid with clay. 3. But it differs from coal in the 
 great thickness of the beds. In Canada the salt-bed is 100 feet thick 
 (Gibson).t In Cheshire, England, there are two beds, one 100 feet, the 
 other 90 feet thick, separated by 30 feet of shale. At Stassfurt, alter- 
 nating beds of salt and gypsum have been penetrated 1,000 feet, and 
 the bottom not yet reached. J The Berlin salt-well is 4,172 feet deep, 
 and, except the upper 293 feet, penetrates solid salt.* 4. Recollecting 
 the somewhat limited extent of basins, it is evident that salt-beds thin 
 out far more rapidly than coal. The English salt-beds thin out fifteen 
 feet per mile. Coal, therefore, lies in extensive sheets, salt in lenticular 
 masses. 5. Goal has its characteristic valuable accompaniment in iron- 
 beds, salt in beds of gypsum. Thus, as coal-measures consist of repeti- 
 tions of sands, clays, occasional limestones, with valuable beds of coal 
 and iron-ore many times repeated, so salt-measures consist of sands, 
 clays, and occasional limestones, with valuable beds of salt and gypsum 
 many times repeated. Gypsum-beds are often entirely separate from 
 salt-beds, but each salt-bed is apt to be underlaid by gypsum. 6. While 
 coal-measures are remarkable for the abundance of organic remains, 
 both vegetable and animal, salt-measures are equally remarkable for 
 extreme poverty in this respect. The presence of these remains in the 
 one case, and their absence in the other, are the cause of the difference 
 in \he color of the sandstones. "Coal-measure sandstones are white or 
 gray, being leached of their oxide of iron by organic matter. Salt- 
 
 * Hay, American Geologist, toI. t, p. 65, 1890. 
 
 f American Journal of Science, vol. v, p. 362, 1873. 
 % Bischof, Chemical Geology, vol. i, p. 383. 
 
 * Nature, vol. xv, p. 240, 1877. 
 
440 MESOZOIC ERA— AGE OF REPTILES. 
 
 measure sandstones are usually red, the iron being diffused as coloring- 
 matter. 
 
 Theory of Accmnulation. — We have already seen (p. 80) that salt- 
 lakes are evaporated residues of river- water or sea-water in dry climates, 
 and are now, most of them, depositing salt ; also, that sea- water evap- 
 orated deposits first gypsum, then salt: also, that these deposits of 
 salts and gypsum alternate annually with sediments of sand and clay — 
 the salt or gypsum deposit representing the dry season, and the me- 
 chanical deposits representing the season of floods. It is, therefore, 
 natural to look in this direction for an explanation of salt and gyp- 
 sum deposits — to think that salt-basins are dried-up salt-lakes. 
 But the immense thickness of the beds plainly shows that there must 
 have been important modifications of this process. It is plain that 
 the alternations of salt and sedimentary deposit were not annual but 
 secular. 
 
 The conditions under which salt-measures were formed are not cer- 
 tainly known, but most probably they are a dry climate, a low coast, 
 with bordering salt lagoons or bays, partly cut off from the sea by 
 bars, subject to intense evaporation, and resupplied with salt-water by 
 tides or by winds, or perhaps at longer intervals by crust-movements. 
 It is easy to imagine how salt-measures with their alternation of gyp- 
 sum, salt, and sediments, may thus have been formed. We have ex- 
 amples of the process now going on, on the east shore of the Caspian 
 Sea, in a bay nearly cut off from the main body, where salt has been 
 depositing for ages,* even though the water of the Caspian is much 
 fresher than that of the ocean. On the other hand, it seems to us that 
 the recent observations of Gilbert and Eussell on the deposits of the 
 great dried-up lakes Lahontan and Bonneville of the Basin region (p. 
 590) throw much light on this subject, and that in the phenomena of 
 these deposits we probably have at least an additional method in which 
 salt-measures may be formed. There is abundant evidence that these 
 lakes have filled and dried up and left beds of salt, more than once, 
 and that at each refilling the lake commenced as afresh lake. The 
 process was briefly as follows : The great lake, at first fresh, gradually 
 became saline and finally dried away, leaving a thick bed of salt. 
 This salt-bed was then covered by the washing in of fine, imper- 
 vious" clay, and thus protected from re-solution when the lake re- 
 formed. This process was repeated in the case of Lake Lahontan 
 three times — that is, there are now beneath the salt-lakes of this 
 region, two beds of salt separated by clay, and the third deposit is now 
 forming. Salt-beds are now reached and worked in many places of 
 
 * Ochsenius, Proceedings of the Academy of Natural Sciences, Philadelphia, 1888, 
 p. 181. 
 
JURASSIC PERIOD. 
 
 441 
 
 this region by penetrating the fine clay which marks the places of the 
 old lakes.* 
 
 In the deposits of salt-lakes or saturated lagoons we would not ex- 
 pect to find many animal remains, but the tracks of animals along their 
 muddy shores, as also sun-cracks and rain-prints, would be found as on 
 other shores. Now, although in the strata associated with salt organic 
 remains are rare, shore-marks of all kinds are common. Thus de- 
 posits of gypsum and salt may be taken as evidence of dry climate. 
 
 Section 2. — Jukassic Period. 
 
 This is the culminating period of the Mesozoic era and Eeptilian 
 age. In it all the characteristics of this age reach their highest de- 
 velopment. We must discuss this somewhat more fully than the last. 
 
 The strata belonging to this period are magnificently developed in 
 the Jura Mountains, and hence the name Jurassic. These mountains 
 are an admirable illustration of the manner in which ridges and valleys 
 are formed by the folding of strata (Fig. 632) ; they also abound in 
 fossils of this period. 
 
 Some English geologists call the period Oolite (egg-stone) on account 
 of the abundant occur- 
 rence in that country 
 of a peculiar limestone 
 composed often wholly 
 of small, rounded 
 grains like the roe of 
 a fish. They divide 
 the whole period into 
 three epochs, viz.: 
 1. Lias : 2. Oolite 
 proper; 3. Wealden.j They also subdivide the Oolite proper into 
 Lower, Middle, and Upper Oolite, separated by 'intervening Oxford 
 
 
 Via. 633.— Section of the^ia Moantams. 
 
 Lower Middle 
 oolite. oolite. 
 
 OOUte. 
 
 Chalk. 
 
 London 
 Clay. 
 
 
 i 
 
 Lias. Oxford Clay. 
 Fig. 633. 
 
 Kimmeridge 
 Clay. 
 
 Gaiilt. 
 
 
 and Kimmeridge clays. All these divisions and subdivisions are well 
 shown in the section (Fig. 633) passing from London westward. This 
 
 * Gilbert, Lake BonneTille, Wheeler's Surrey, vol. iii ; American Journal of Science, 
 vol. xxxi, p. 384, 1886; Russell, Lake Lahontan, Monograph of United States Geological 
 Survey, vol. xi, pp. 2, 261, and 268. 
 
 f The Wealden is now often put in the Cretaceous. 
 
442 MESOZOIC ERA— AGE OF REPTILES. 
 
 section is interesting not only as exhibiting all the divisions and sub- 
 divisions of the Oolitic period, but also as showing their conformity 
 among themselves and with the overlying chalk, and the unconformity 
 of these with the overlying Tertiary. It also shows how parallel ridges 
 and intervening hollows are formed by the outcroppings of a series of 
 strata alternately hard and soft. 
 
 Origin of Oolitic Limestones. — These are composed of rounded 
 grains with concentric structure. We have already seen, page 163, that 
 on coral shores a kind of sand is formed by the action of waves on frag- 
 ments of coral and shells. These fragments are rounded by attrition ; 
 then often enlarged by deposit of concentric layers of lime from the 
 saturated sea-water ; and, finally, cemented by the same into hard rock. 
 In several European countries at least thirty subdivisions of the 
 Jurassic have been determined. The rocks of this period have been 
 studied with greater detail, probably, than any other series, chiefly 
 on account of their remarkable profusion of fossils. In such manner 
 oolitic limestones have been formed in all geological periods. We 
 conclude, therefore, that in Jurassic times great coral reefs existed 
 where England now stands. In the Jura Mountains it is believed 
 that the remains of fossil circular reefs or atolls of this period are 
 still detectable (Heer). 
 
 Jurassic Coal-Measures. — In the Jurassic times we have reproduced 
 on a large scale the conditions favorable to luxuriant growth of plants, 
 and for their accumulation and preservation in the form of coal. 
 Hence in many countries we have Jurassic coal-fields. To this period 
 belong the Yorkshire coal of England and the Brora coal of Scotland. 
 To this or the previous period belong coal-fields of India * and China. 
 The fine coal-measures of New South Wales, Australia, covering an 
 area of 20,000 square miles, are partly, though not mainly, Jurassic 
 or Triassie, as are also those of South Africa. Jurassic coal-measures 
 have a general structure similar to those of the Carboniferous. Like 
 the latter, they consist of alternations of sands and clays, and occa- 
 sional limestones, containing seams of coal and beds of iron-ore. The 
 iron-ore too is of the same kind, viz., clay iron-stone. We find here 
 also under-clays, with stumps and roots, and roof -shales filled with 
 leaf-impressions. It is fair to conclude, therefore, that the mode of 
 accumulation was similar to that already described, viz., in marshes 
 subject to occasional floods. -Jurassic coal, though perhaps inferior 
 as a general. rule to Carboniferous, is often of good quality, occurring 
 in thick and profitable seams. 
 
 * The plant-beds of India (Gondwana series of Indian geologists) are Permian to 
 Jurassic inclusive. (Manual of Indian Geology, p. 102 et seg.) The North Carolina and 
 Virginia fields are now regarded as Triassie. 
 
JURASSIC PERIOD. 
 
 443 
 
 Dirt-Beds— Fossil Forest-Grounds.— Coal-seams with tlieir under- 
 lying clays are fossil swamp-grounds ; dirt- beds are fossil soils ov forest- 
 grounds. The one graduates insensibly into the other, and both are 
 occasionally found in all strata, from the Devonian upward. In the 
 Upper Oolite of England, at the Isle of Portland and elsewhere, there 
 occurs an interesting example of such a fossil forest-ground with the 
 ierect stumps and ramifying roots still in situ, though silicifled, and 
 the logs, also silicified, still lying on the fossil soil (Pigs. 634, 635). It 
 is evident that the sequence of events at this place in Jurassic times 
 was as follows : 1. The place was sea-bottom, and received sediment 
 which consolidated into Portland-stone. 2. After being flooded and 
 covered with river-deposit, it was raised to land and became forest- 
 
 FiG. 634.— Section in ClifE east of Lul- 
 wortliCove: a, Dirt-bed. 
 
 Fie. 635.— Section in the Isle of Portland: 
 a. Dirt-bed. 
 
 ground, covered with trees and other vegetation peculiar to that time, 
 the decaying leaves of which accumulated as a rich and thick vegetable 
 mold. 3. It became flooded with fresh water, and the trees therefore 
 died and rotted to stumps. 4. The whole ground, with its stumps and 
 logs, became covered with mud, which hardened into slates. 5. Fi- 
 nally, the whole was 
 raised into high land, 
 and in the first figure 
 (Fig. 634) tilted at a 
 considerable angle. 
 
 Thus, we have here 
 not only an old forest- 
 ground with its vegeta- 
 ble mold, but also the 
 stumps and logs of the 
 trees which grew there, 
 still in place ; and closer 
 examination easily detects the kinds of trees which grew in the forest. 
 They are Cycads and Conifers (Figs. 636, 637, and 641, 643). Still fur- 
 ther, there is good reason to believe that the remains of some of tho 
 animals which roamed these forests have also been found. Of these 
 we will speak in their proper place. 
 
 Fie. 636.— Zamia spiralis, a Living Cycad of Australia. 
 
Ui 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 Plants. 
 
 Although the conditions under which coal was accumulated were 
 probably similar in all geological periods, yet the kinds of plants out of 
 
 Fig. 637. 
 
 Fig. 639. 
 
 Fig. 640. 
 
 Fig. 641. 
 
 Fig. 642. 
 
 Fios. 637-642.— Jurassic Plants— Cycdde and Ferns : 637. Pterophyllum comptnm (a Cycad). 638. 
 Hemitelites Brownii (a Fern). 639. Coniopteris Miirrayana. 640. Pachypteris lanceolata. Oon> 
 ifere : 641. Cone of a Pine. 642. Cone of an Araacaria. 
 
JURASSIC PLANTS. 
 
 446 
 
 which the coal was made varied. As already seen, the principal coal- 
 plants of the Carboiiiferous period were vascular Cryptogams. On the 
 contrary, the principal coal-plants of the Jurassic period were Ferns, 
 OycadSj and Conifers. The Jurassic may be called the age of Oym- 
 nospermSj as the Carboniferous was of the Pteridophytes. The Gym- 
 nosperms, especially the family of Cycads, reached here their highest 
 development. This is shown in diagram on page 394. The leaves 
 (Fig. 637) and short stems of Cycas and Zamia (Pig. 644) are found 
 very abundantly in connection with the coal-bearing strata. It is prob- 
 able, therefore, that the coal is composed largely of these plants. Some 
 remains of Jurassic plants are given (Pigs. 637-642), and also of living 
 Cycads (Pigs. 636, 643), for comparison. 
 
 The animals of the Jurassic, marine, fresh-water, and land, were 
 very abundant, and have been well preserved. It is impossible, there- 
 fore, in the lower depart- 
 ments, to do more than 
 touch lightly the most sal- 
 lent points. In the higher 
 departments we will dwell a 
 little longer. 
 
 Corals have assumed now 
 the modern type and style 
 
 Fia. 643.— Cycas circinalis, x y^, a Living Cf cad of the 
 Moluccas (after Decaisne), 
 
 Fio. 644.— Stem of Cycadeoidea megalo- 
 ptiylla, X }. 
 
 of partitions (Fig. 645). Among EcMnoderms, the Crinids, or plu- 
 mose-armed Crinoids, are very abundant and very beautiful ; in fact, 
 they seem to have reached their highest point in abundance, diver- 
 sity, and gracefulness of form (Figs. 646, 647). But the free forms, 
 Echinoids and Asteroids, are now equally abundant (Figs. 648-650). 
 
446 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 Fig. 646. 
 
 Fiii. W8. 
 
 Fig. 6S0. 
 
 Figs. 645-6S0.— Jurassic Corals and Echinoderms: 645. Prionastrea oblongata. 646. Apiocrinns 
 BoissianUs. 647. Saccocoma pectinata (a free Grinoid). 648. Asteria lombricalis. 649. Clypeus 
 Flotii. 650. a b, Hemicidaris crenularis. 
 
 Brachiopods are still abundant, though far less so than formerly ; 
 but they now belong almost wholly to the modern or sloping-shouldered 
 
 ffiQ. 651. 
 
 Fig. 653. 
 
 Figs. 6.51-6.'i3.— .Jurassic Lameli.ibranchs anii Brachiopods 
 op England; 651. Direras Arietina, Middle OOlite (after 
 Nicholson). 653. Astarte excavata. 653. Trigonia cla- 
 veilata. 
 
JURASSIC ANIMALS. 
 
 44Y 
 
 types, such as Terebratula and Ehynchonella. Only a very few small 
 specimens of the Palseozoie type linger until the Lias. 
 
 Lamellibranchs, or common bivalves, are extremely abundant. 
 Among the common and characteristic forms are GFryphsea and Exo- 
 gyra, belonging to the oyster family; Trigonia and the strangely- 
 
 FiG. 658. 
 
 Fio. 659. 
 
 PiGt. 656. 
 
 Fio. 657. 
 
 Figs. 654-659.— Jubassic Lahelltbbancbs and Beaohiopods of England: 654. Oetrea Sowerbyi. 
 655. Pecten flbrosue. 656. Ostrea Marshii. 657. Ehynchonella varians. 658. Terebratula sphae- 
 roidalis. 659. Terebratula digona (after Nicholson). 
 
 shaped Diceras (Fig. 651). The genus Ostrea (oyster) had appeared 
 in the Carboniferous, or the Trias. 
 
 Gephalopods. — One of the most striking characteristics of the Juras- 
 sic period is the cul- 
 mination of the class 
 of Gephalopods in 
 number, diversity of 
 forms, and, if we ex- 
 cept some of the Si- 
 lurian Orthoceratites, 
 in size. They were 
 represented by the 
 Ammonites and the 
 Belemnites, the one 
 belonging to the or- 
 der of Tetrabranchs, 
 or shelled, the other 
 to the Dibranchs, or naked Gephalopods. It is important to observe 
 that the highest order of Gephalopods, the Dibranchs, by far the most 
 abundantly represented at the present time, which were introduced 
 in the Trias, were now abundant. 
 30 
 
 Fig. 660.— Ammonites Humplirejbianua. 
 
448 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 Ammonites. — The typical Ammonites, which are distinguished, 
 as already explained (p. 329), hy the outer or ventral position of the 
 siphuncle and the complexity of the suture, are represented in extreme 
 
 Fig. 
 
 Pis. 664. 
 
 Figs. 661-664.— Jubassio Cbphalopods— jlmmonifes.' 661. Hildoceras bifrons. 662. Amaltheua 
 margaritatnm. 663. Cosmoceraa Jason : a, side view; 6, sliowing suture. 664. Cardioceras cor- 
 datum: a, side view; h, showing septum. 
 
 U -s^ \^f li 4f\f i$i% 
 
 f/n^ 
 
 Ceratite. 
 
 Ooniatite. 
 
 
 
 MautUoids, 
 
 OrtTvocerailte. 
 
 Fia. 665.— Diagram showing Form of the Suture. Position of Siphuncle, and Order of First Appear- 
 ance of Families in Oephalopods. 
 
JURASSIC ANIMALS. 
 
 449 
 
 abundance by a great many genera.* Nearly 2,000 species of this 
 group are known, ranging in lime from the Carboniferous through 
 the Cretaceous. They are in general characteristic of the Mesozoic. 
 They varied extremely in shape, and in size from half an inch to a yard 
 or more in diameter. The accompanying figures represent some of the 
 most common species. About 7,500 species of Tetrabranchs are known. 
 In the true Ammonites * the distinguishing character of the group, 
 viz., the complexity of the suture, reached its highest point. In this 
 
 group, the edge of the septum 
 which was only zigzag in Gonia- 
 tite, and lobed in the Ceratite, 
 becomes elaborately frilled. We 
 give in Fig. 665 a diagrammatic 
 representation of the form of su- 
 ture in the different groups of 
 shelled Cephalopods, in the order 
 of their appearance. In each case 
 
 Fio. 666. 
 
 Fre. 667. 
 
 Figs. 666-668.-666. Internal Shell of Belemnite (restored by D'Orbigny). 667. The Animal (restored 
 by Owen). 668. A living Sepia for comparison. 
 
 the suture is supposed to be divided on the inner or dorsal surface, 
 and spread out, so that the central part in the figure represents the 
 outer or ventral portion, and the two extremities the dorsal. The 
 evolution of form and structure was in the following order : First the 
 
 * This genus is now broken up into many, but it is still convenient to retain the name 
 ' f or a very distinct group of Cephalopods. 
 
450 
 
 MESOZOIC EKA— AGE OF REPTILES. 
 
 straight Orthoceras, then the curved Gyroceras, then the coiled Nau- 
 tiloids, then the simple suture heeame angled in Ooniatite, then scal- 
 loped in Ceratite, and finally complexly frilled in 
 Ammonite. It is remarkable, however, that one of 
 the simpler forms, viz., the nautiloids, although 
 also one of the earliest, has outlived them all. The 
 corresponding figures on the left are sections show- 
 ing the position of the siphuncle. 
 
 The order in which the several groups appeared, 
 and their continuance, are shown in the diagram 
 (Fig. 675) on page 451. 
 
 FlQ. 
 
 Pig. 670. 
 
 Fig. 673. 
 
 Fio. 674. 
 
 Fioa. 669-674.— 669. Fossil Ink-Bags of Belemnjtes. 670. Belemnites Owenii. 671. Belemnites hsB- 
 tatus. 673. Belemnites imicanaliculatus. 673. Belemnites clavatns. 674. Acanthoteuthis anti- 
 quus (after Mantell). 
 
 Belemnites. — The Belemnite {^eXtfivov, a dart) was nearly allied to 
 the squid and cuttle-fish of the present day. Like the squid, it had 
 
JURASSIC ANIMALS. 
 
 451 
 
 an internal bone (the pen of the squid), except that the bone is much 
 larger and heavier in the Belemnite. It is this bone, or the lower por- 
 tion of it, which is usually fossilized (Figs. 670-673). When perfect 
 it is expanded and hollow at the upper end, and in the hollow is a 
 small, conical^ chambered, siphuncled shell, the phragmocone. Fig. 666, 
 a and b, shows the perfect bone, and Fig. 670 the upper part broken 
 and the phragmocone in place. Like the squid, too, it had an ink-bag, 
 from which it doubtless squirted the inky fluid to darken the water 
 and escape its enemy. These ink-bags are often well preserved (Fig. 
 669), and the fossil ink has been found to make good pigment (sepia), 
 and drawings of these extinct animals have actually been made with 
 the fossil ink of their own ink-bags (Buckland). Belemnites were some 
 of them of great size, and evidently formidable animals. The bone of 
 the Belemnites giganteus has been found two feet long and three to 
 four inches in diameter at the larger or hollow end. A very per- 
 fect specimen of an allied genus, from the Oolite of England, is shown 
 in Fig. 674. 
 
 The following diagram shows the order of succession of families of 
 the class Cephalopoda : 
 
 
 vkT.A7.nr.mr 
 
 
 NEOZOIC. 
 
 
 MB30Z0IC. 
 
 Cbnozoic. 
 
 Camb'n. 
 
 SiPn. 
 
 Dev'n. 
 
 Carb. 
 
 Trias. 
 
 Juras. 
 
 Cret. 
 
 Tert. 
 
 Pres. 
 
 
 
 
 cepha: 
 
 ^OPODS. 
 
 
 
 
 
 She 
 
 lied or 
 
 Tetrabran 
 
 3hs. 
 
 Slu 
 
 N a k 
 led. 
 
 e d 
 
 r D i b 
 
 rant 
 
 h s . 
 
 r t 
 
 h c e 
 
 r a t i 1 
 
 e s . 
 
 
 
 
 
 
 - 
 
 N 
 
 a 
 6( 
 
 u 
 miatites. 
 
 A m 
 
 t 
 
 Ceratites 
 m I 
 
 ed. 
 B e 1 
 
 1 
 
 I i t ^ 
 B m n i 
 
 1 
 
 ! S . 
 
 t e s . 
 
 i 
 Sep 
 
 d 8. 
 i a . 
 
 Fio. 675.— Diagram showing Distribution of Cephalopoda in Time. 
 
452 
 
 MESOZOIC ERA— AGE OF -REPTILES. 
 
 We have shown how the different shelled forms were derived. Now 
 the phragmocone corresponds to the shell. We may suppose then that m 
 -^ y naked forms the shell first hecame 
 
 small and then was overgrown 
 and inclosed by the soft parts. 
 
 Crustacea. — Crustacea were 
 represented in the Palaeozoic first 
 by the Trilobites ; then Eurypte- 
 rids; then Limuloids; then, in 
 the last period, by a few Mac- 
 rourans. In the Triassic the 
 Macrourans became more abun- 
 
 Fie. 677. 
 Pigs. 676, 677.— JnRASsio Crustaceans: 676. 
 Eryon arctiformis, Solenhofen. 677. 
 Eryon Barrovensis, England. 
 
 dant and of more modern type. In the Jurassic the Macrourans con- 
 tinue, with also many Limuloids, but the former make here a decided 
 approach to the Brachyourans or true crabs, by the shortening of the 
 
 tail in some (Fig. 
 676) ; and the ear- 
 liest true crab, Pa- 
 Iseinachus — a spi- 
 der-crab — has been 
 found in the Ju- 
 rassic of England. 
 The same change — 
 i. e., shortening of 
 the tail — may be 
 seen in the embry- 
 onic development of 
 a crab (Fig. 678). 
 Insects. — As 
 
 Fig. 678. — Development of Carcinus moenaa: A. zooea stage; B, mega- might be CXpectcd 
 lops stage; C, final state (after Couch). ° '^ 
 
 from the abundant 
 forest vegetation, insects have been found in considerable numbers and 
 variety (Figs. 679-684). According to Heer, 143 species of insects are 
 known from the Lias alone. Of these, about three fourths are beetles. 
 
JURASSIC ANIMALS. 
 
 463 
 
 The earliest of the higher group of insects seem to have been intro- 
 duced here, although they do not become abundant until the Tertiary. 
 
 Fig. 684, 
 
 Pigs. 679-6&4. — Jurassic Insects : 679. Blattina f ormosa (after Heer). 680. Glaphyroptera gracilis 
 (after Heer). 681. .Sschna eximia (Eager). 683. Libelliila. 683. Buprestidium. 684, Hemero- 
 bioides gigantens. 
 
 Fishes. — It will be remembered that the Elasmobranchs of the 
 Palaeozoic were nearly all Cestracionts, or crushing-toothed sharks. The 
 Hybodonts, or sharks with teeth pointed, but rounded on the edges, 
 commenced in the Carboniferous and increased in the Triassic. Now, 
 in the Jurassic the Cestracionts continue (Fig. 685), but in diminished 
 numbers. The Hybodonts culminate (Fig. 686), and the Squalodonts, 
 or modern sharks, with lancet-shaped teeth, commence in small numbers. 
 Rays (Fig. 687), which may be regarded as among the most specialized 
 of Elasmobranchs, are found in considerable numbers in the Jurassic. 
 
 Ganoids continue, but take on far more modern forms, and have 
 now in most cases lost the vertrebrated structure of the tail-fin, thus 
 foreshadowing the Teleosts, which appear in the Upper Lias. Among 
 the most characteristic Ganoids of this period, and, in fact, of this 
 age, are the Stylodonts, a family characterized by a broad, flat body, 
 rhomboidal enameled scales, pavement palatal teeth, and persistent 
 notochord (Fig. 688). 
 
454 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 Reptiles. — The huge reptiles which form the distinguishing feat- 
 ure of this age culminate in the Jurassic period. Their number and 
 
 Figs. 685-688. — Jurassic ¥KTfEs—BlasmiObranche: 685. Tooth of Acrodns nobilis. 686. Hybodus 
 reticulatas, Spine and Tooth. 687. Squatina acanthoderma. 688. Ganoid: Tetragonolepis, re- 
 stored, and Scales of the same. 
 
 variety are so great that we can only select a few from each order for 
 description. They were emphatically rulers in every department of 
 Nature — rulers of the sea, of the land, and of the air. We shall treat 
 of them under the three heads thus indicated, viz. : 1. Enaliosaurs 
 (sea-saurians), or rulers of the sea ; 2. Dinosaurs (huge saurians), or 
 rulers of the land ; and, 3. Pterosaurs (winged saurians), or rulers of 
 the air. The first were wholly swimming, the second walking, the 
 third flying, saurians. Intermediate between the first and second was 
 a fourth order, the Crocodilians, which both swam and crawled. 
 
 1. Enaliosaurs. — Prom the immense variety of these we select only 
 two for description as representative genera, viz.. Ichthyosaurus and 
 Plesiosaurus (Figs. 689 and 690). 
 
 The Ichthyosaurus (fish-lizard) was a huge animal, in some cases 
 thirty to forty feet in length, with a stout body, short neck, and enor- 
 mous head, sometimes five feet long, and jaws set with large conical, 
 
JURASSIC ANIMALS. 
 
 455 
 
 striated teeth, sometimes 200 in number. The enormous eyes, some- 
 times fifteen inches in diameter, were provided with radiating, bony 
 
 Fir. 691. Fig. 603. 
 
 Fios. 689-692.— Jurassic Reptiles — Iclithyosaurus and PleHosaurvs : 689. Ichthyosaurus commu- 
 nis, X tJb. 690. Plesiosaurus dolichodeirus, restored, x A. 691. Vertebrse of Ichthyosaurus and 
 Section of same, showing structure. 692. Tooth of Ichtnyoaaurns, natural size. 
 
 plates (sclerotic bones), as are the eyes of birds and some living 
 and many extinct reptiles, apparently for adjusting the eye to dif- 
 ferent distances. The tail was long, and provided terminally with a 
 
 Fis. 
 
 193.— Ichthyosaurus quadriscissus, found in Wflrtemberg, showing Tail-Fin and Dorsal Fin, 
 X i»j (after Fraas). 
 
 vertical, fin-like expansion, unsupported by rays (Owen). This pre- 
 vision of Owen has been entirely verified by recent discoveries in the 
 Lias of Wiirtemberg of specimens which clearly show this vertical ex- 
 pansion, and also the remarkable fact that the vertebral column runs 
 into the lower instead of the upper lobe, as in sharks. Median dorsal 
 fins are also shown (Fig. 693). In addition to the powerful fin-tipped 
 tail, the locomotive organs were four short stout paddles, composed of 
 
456 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 numerous closely-united . bones, but without distinct toes. These 
 paddles were surrounded by an expanded, ray-supported web (Fig. 
 694), which greatly increased their surface, and therefore their effi- 
 ciency as swimming-or- 
 gans (Lyell). The bod- 
 ies of the vertebrae were 
 not united by ball-and- 
 socket joint, as in most 
 living reptiles, but were 
 M-concave (amphicce- 
 lous), like those of fishes 
 (Fig. 691). 
 
 That the habits of 
 the creature were preda- 
 tory and voracious is suf- 
 ficiently attested by the teeth. It is further proved by the contents of 
 the stomach, which are sometimes partly preserved. These consist 
 largely of fish-scales. 
 
 From the description given above it is plain that the Ichthyosaurus 
 combined in a remarkable degree the characters of saurian reptiles 
 with those of fishes. The vertically-expanded tail- 
 tip, the paddles, with surrounding ray-supported 
 web, and the bi-concave vertebral bodies, are all de- 
 cided fish characters. In most other respects it was 
 reptilian. This combination is expressed in the name. 
 
 Fis. 694.— Skull and Paddle of Ichthyosaurus. 
 
 FiQ. 695.— a, Head of a Pliosanrus, greatly reduced; 6, Tooth of the same, natural size. 
 
 The Plesiosaurus (allied to a lizard) was a less heavy and powerful 
 animal than the last. It was remarkable for its short, stout, almost 
 turtle-shaped body ; its long,*snake-like neck, consisting of twenty to 
 forty vertebrae ; its small head ; its short tail, unadapted for powerful 
 propulsion ; its long and powerful paddles, which were its sole swim- 
 ming-organs ; and its bi-concave vertebral bodies. Recent discoveries 
 in Kansas show that sclerotic bones were present in this order also.* 
 Sixteen species have been found in the Jurassic and Cretaceous rocks 
 
 * Williston, Science, yoI. xvi, p. 262, 1890. 
 
JURASSIC ANIMALS. 
 
 457 
 
 of Great Britain alone, and one, P. dolichodeirus, was twenty-five to 
 thirty feet long (Pig. 690), with paddles six to seven feet long. 
 
 The Pliosaurus (more lizard-like) (Fig. 695) had the large head 
 and shorb neck of the Ichthyosaurus, with the powerful paddles of 
 
 Fig. 696.— Paddle of a Pliosaurus, x ^. 
 
 the Plesiosaurus. A perfect paddle of this animal has heen found 
 seven feet long (Fig. 696) ; the animal was probably at least forty 
 feet long. 
 
 Intermediate between this group and the next — inhabiters both of 
 land and water — Orocodilians existed in great numbers, and of great size. 
 
 Pig. 697.— Teleosanrue brevidens: a, skull; 6, side view of snout showing the teeth (after Phillips). 
 
 Some, like the Teleosaurus (Fig. 697), were narrow-snouted like the Ga- 
 vials of the Ganges, but had amphiccelous vertebrae like the Enaliosaurs. 
 
 2. Dinosaurs. — Among these were the largest reptiles — in fact, the 
 largest land-animals that have ever existed. They were also in many 
 respects the highest of all reptiles, since they possessed many characters 
 which connected them closely with mammals, and especially with birds. 
 
 Connecting Characters. — The most important of these were : (1) 
 Large limb-bones and firm sacrum composed of several (four to five) 
 consolidated vertebrae. These characters show that these animals 
 walked with a free step, the body well borne above the ground, like mam- 
 mals and birds, and did not crawl in the manner of reptiles. (2) In 
 many cases the hind-legs were very large and long, and the fore-legs very 
 small in comparison. This, together with the backward elongation of the 
 ischium (Fig. 698, B) — suitable for erecting the body — show that some 
 of them walked habitually on their hind-legs alone, in the manner of 
 birds. (3) Like birds and some mammals, many Dinosaurs tread on 
 their toes (digitigrade) and not like reptiles on the whole foot (planti- 
 grade). (4) Like birds, also, many — but not all — had only three func* 
 
458 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 tional toes, and therefore made tridactyle tracks ; and even the number 
 of toe-joints follows the order of those of birds — i. e., there were three 
 
 Fig. 698.-4, Dromieae; B, DinoBanr; C, Crocodile: As, astragalus; Ca, calcanenm. 
 
 in the inner toe, four in the middle, and five in the outer toe. (5) 
 Still more curious is the resemblance to birds, in the structure of the 
 ankle-joint. In mammals the joint is between the shank-bones and 
 the tarsus. In reptiles the motion takes place in the middle of the 
 tarsus. In birds the upper tarsals (astragalus and calcaneum) are 
 consolidated with the shank and the lower tarsals with the metatarsals, 
 and the joint is of course between these two bones. Now some Dino- 
 saurs are like birds in this regard. Fig. 698, ABC, illustrates this 
 point. We shall very briefly describe only the most remarkable. 
 
 The Iguanodon was one of the best known as well as one of the 
 largest. It was a huge herbivorous Dinosaur, found in the Upper 
 Jurassic and Lower Cretaceous of Europe. It takes its name from 
 the resemblance of its teeth (Fig. 699) to those of an Iguana — a living 
 herbivorous reptile, about four or five feet long, although in other 
 respects there is little affinity. Until recently, only portions of the 
 skeleton were found ; but the enormous size of these indicated an ani- 
 mal nearly thirty feet long, and exceeding the weight of an ele- 
 phant. It was impossible from these to form any idea of its general 
 appearance. In 1880, however, several complete skeletons were found 
 by Dollo in the Wealden* of Belgium, and restored first by Dollo 
 
 * The Wealden is a transition between the Jurassic and Oretaceous, sometimes put in 
 the former and sometimes in the latter. 
 
JUEASSIC ANIMALS. 
 
 459 
 
 and then more perfectly by Marsh. From these it is learned that the 
 animal certainly walked on its hind-legs, using its powerful tail also 
 as a support ; also that the anterior part of its jaws was toothless and 
 covered with horn, so as 
 to form a nipping-beak 
 like a turtle's. Fig. 700 
 is a restoration by Marsh. 
 
 The Megalosaur was a 
 somewhat smaller but a 
 more formidable carniv- 
 orous reptile, which lived 
 through the whole Juras- 
 sic period. Its huge jaws 
 were armed with, large, 
 curved, flattened, saber- 
 like teeth. A femur has 
 been found forty - two 
 inches long (Phillips), and 
 a tibia thirty-six inches. The animal was at least thirty feet long 
 (Owen). The Megalosaurs also were bipedal. 
 
 The Geteosaur (whale-lizard) was the largest reptile yet found in 
 Europe, though much larger have been found in the Jurassic of the 
 United States. It has been classed among the Crocodilians, but Prof. 
 
 Fig. 099.— Tooth of an Iguaiiodo 
 
 FiQ. 700.— Ignanodon Bernissartensis, Boulenger, x ^, Upper Jura, Belgium (after Marsh). 
 
 Huxley has shown that its true position is among the Dinosaurs. A 
 thigh-bone has been found sixty-four inches long, 27"5 inches in cir- 
 cumference at the shaft, forty-six inches and 44'35 inches in circum- 
 ference at the two ends, respectively. According to Phillips, the ani- 
 
460 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 mal was at least fifty feet long, ten feet high when standing, and of 
 bulk proportionate. It was like the Iguanodon a vegetable feeder. 
 
 The Compsognathus was a carnivorous reptile of smaller size, 
 from Bavaria, being, indeed, the smallest known Dinosaur, but of 
 most extraordinary bird-like character, viz., 
 small head, long, flexible neck, large and long 
 hind-leg, and small and short fore-leg. From 
 its structure, it must have walked habitually 
 on its hind-legs alone, and in this position was 
 about two feet high (Fig. 701). 
 
 As an example of a European 
 quadrupedal Dinosaur we give 
 a restoration by Marsh of 
 the Scelidosaurus (Fig. 703), an 
 herbivorous Di- 
 nosaur allied to 
 the Stegosaur (p. 
 480). 
 
 3. Ptero- 
 saurs. — These 
 flying reptiles 
 
 were certainly among the most extraordinary animals that have ever 
 existed. The order includes several genera, but we will describe only 
 the best known, viz., the Pterodactyl (wing-finger), and the Eham- 
 phorhynchus (beak- snout). 
 
 Fis. 701.— CompsognathuB (restoration by Marsh). 
 
 Fig. 702.— Scelidosaurus Harrisonii, Oweu, x ^, Jurassic, England Restored by Marsh). 
 
 The Pterodactyl (Fig. 703) combined the short, compact body; the 
 strong shoulder-girdle, firmly united with the keeled sternum; the 
 short, aborted tail ; the long, flexible neck, and hollow, air- filled limb- 
 bones, characteristic of birds — with the head, and jaws, and teeth, of a 
 reptile, and the membranous wings of a bat. In the bat, however, the 
 membrane is supported by four fingers, enormously elongated for the 
 purpose, and only one finger is free and clawed ; while in the Pterodactyl 
 there is only one finger that is enormously elongated and strengthened 
 for the support of the web, and the others are free and clawed. 
 
JURASSIC ANIMALS. 
 
 461 
 
 The Rhamphorhynchus differed from the Pterodactyl in having a 
 long tail ; and in one species, R. pJiyllurus (Fig. 704) (leaf-tail), this 
 was Tertically expanded at the tip so as to act as a rudder in flying. 
 
 Fig. 704. — Rhamphorhynchus phyllurns (after Marsh). 
 
 Fie. 705.— Bestoration of Bhampliorhynclius phyllnrus (after Marsh). One seventh natural size. 
 
462 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 In a specimen from the celebrated Solenhofen limestone of Bavaria, 
 and now in possession of Prof. Marsh, even the membranes of the 
 
 wings were perfectly 
 preserved (Fig- 704). 
 Fig. 705 is a restoration 
 of this species in flight. 
 The Pterosaurs were 
 of many kinds, which 
 varied in size from two 
 or three feet to eighteen 
 or twenty feet in alar 
 extent. 
 
 Birds. — The class of 
 Birds is now so dis- 
 tinctly separated from 
 all others and the con- 
 necting links obliter- 
 ated, that the earliest 
 birds are of especial in- 
 terest as throwing light 
 on the evolution of this 
 class. Until 1863 birds 
 had been found only in 
 the Tertiary, and these 
 were already distinctly 
 differentiated as typical 
 birds ; but in that year 
 there was found in the 
 Solenhofen limestone, 
 so celebrated for its mar- 
 velous preservations of 
 organisms, a flying 
 feathered biped, and 
 therefore presumably a 
 bird. But how different from our usual conceptions of this class ! 
 Along with its distinctive bird-characters of feet, limb-bones, beak, 
 and especially of feathered wings, it had the long tail (Fig. 706) 
 and toothed jaws (Pig. 708) of a reptile. The structure of the tail is 
 especially significant. In ordinary birds the tail proper is shortened 
 up to a rudiment, and ends in a large bone, from which radiate the 
 feathers of the tail-fan. In this earliest bird, on the contrary, the tail 
 proper is as long as all the rest of the vertebral column put together, 
 consisting, as seen in the figure (Pig. 707), of twenty-one joints from 
 which the fan-feathers come off in pairs on each side. The tailfan 
 
 Tig. 706. — Arclioeopteryx macrou- 
 ra, X \ (after Dames). 
 
JURASSIC ANIMALS. 
 
 463 
 
 of this bird differs from that of typical birds precisely as the tail-fin of 
 earliest fishes differs from that of typical fishes. The tail-fan of this 
 earliest bird, like the tail-fin of earliest fishes, was vertebrated. This 
 wonderful reptilian bird was called Archmpteryx (primordial winged 
 creature), and the species macroura (long-tailed). 
 
 In 1873 another specimen of Archaeopteryx was found in the same 
 locality, and is now in the Berlin Museum. This Berlin specimen has 
 been carefully examined by Vogt, Marsh, and Dames ("Pigs. 706 and 
 708). From examination of these two specimens the following singu- 
 
 FiG. 707. — A, Tail of Archseopteryx macroura; B, VertebrsE enlarged; C, a Feather; B, Tail of a 
 Vulture; B, Bide view of the same, 
 
 lar combination of bird and reptilian characters has been made out. 
 Among bird characters are (1) The strong shoulder-girdle and keeled 
 sternum necessary for flying (but Pterosaurs also have these). (3) A 
 horny beak (but turtles and Ehynchosaui's and some Dinosaurs have 
 this). (3) Tridactyl feet (some Dinosaurs have these). (4) Feathered 
 wings and tail. But, along with these, besides the toothed jaws and 
 long tail of reptiles, already mentioned, there were also the following 
 characters : 1. The metacarpals and possibly the metatarsals (three in 
 number) were separate, as in reptiles and embryo of birds. 3. The three 
 fingers were all free and armed with claws. In fact, except for the feath-. 
 ers, the fore-limbs were more like legs than wings. 3. The pelvic bones 
 were unconsolidated, as in reptiles and embryo of birds. So complete 
 is the mixture of the two kinds of characters that some zoologists (Vogt) 
 believe that the reptilian characters predominate, and that it should be 
 called a bird-like reptile. Most agree, however, that it is a reptilian bird. 
 It is interesting to note the different ways in which the same func- 
 31 
 
464: 
 
 MESOZOIC EEA— AGE OF REPTILES. 
 
 tion — that of flying — is effected in different animals, without violating 
 the law of limb-structure. In the Bat the resisting plane is produced by 
 
 Fio. 708.— Head of Archaeopteryx macroura {after Dames). 
 
 stretching a membrane between the enormously elongated palm-bones 
 and finger-bones ; in the Pterodactyl only one finger is enormously en- 
 larged and elongated for this purpose ; in the Bird the same bones are- 
 
 A BO D 
 
 Fig. 709.— 4, Fore-limb of Bat; B, Bird; C, Archseoptcryx; J), Pterodactyl. The dotted lines pass 
 through corresponding parts. 
 
 shortened and consolidated, and the resisting plane is got by the use 
 of feathers. This was the method also in the Archseopteryx, but the 
 consolidation was not yet complete. Fig. 709 represents wings of these 
 four kinds — the dotted lines run through corresponding parts, and 
 show the identity of structure. 
 
JURASSIC ANIMALS. 
 
 465 
 
 Origin of Birds.— There can be no doubt, then, that Birds came 
 from Reptiles. Further, it is quite possible that they came from 
 Dinosaurs. It is true that Dinosaurs are the largest of reptiles, while 
 birds, with some exceptions, are comparatively small animals; but 
 Marsh has shown that some American Dinosaurs were very small. The 
 time of their origin, or separation from the reptilian stem, is still doubt- 
 ful, but the wonderfully reptilian character of Archaeopteryx shows 
 that it can not be far from the point of origin. It was probably in 
 the Lower Jurassic or Upper Triassic. 
 
 Mammals.— We have already seen (p. 438) that the first appearance 
 of this class was in uppermost Trias ; but as these were few, in nu-m- 
 t)er, and very near the confines of Jurassic, we regarded them as an- 
 ticipations and put off their discussion. In the Jurassic this anticipa- 
 tion was fully realized. In the same formation (Upper Jurassic) in 
 which we found the old forest-ground (p. 443) have been found also 
 fourteen genera of small mammals. To this may be added five genera 
 
 Fio. 712. 
 
 Fie. 713. 
 
 Fig. 714. 
 
 Figs. 710-714.— Jdeassio Mammais: 710. Amphitherinm Prevostii. 711. Phascolotheriam. 712. 
 Amphithermm. 713. Tnconodon. 714. Plagiaulax. 
 
 from a lower horizon (Stonefield states). If we add to these again 
 fourteen genera (twenty-five species), recently described by Marsh, 
 from the American Jurassic, we have at least thirty-three Jurassic gen- 
 era known. Besides these, at least :fiTe genera are found in the Upper 
 Trias of all countries, and sixteen genera (twenty-four species), recently 
 (1889) described by Marsh, from Upper Cretaceous (Laramie). We 
 may say, therefore, that there are now known at least fifty-four genera 
 of Mesozoic mammals. The number of species is, of course, much 
 greater. 
 
 Affinities of Jurassic Mammals. — The Jurassic, and indeed the Meso- 
 zoic mammals, as contrasted with mammals of later times, may be 
 characterized in a general way as small insectivorous ma,rsupials, or, 
 perhaps better, as a type connecting insectivores and marsupials, and 
 therefore lower and more generalized than either. They were, espe- 
 cially the earliest or Triassic, decidedly reptilian in some of their char- 
 acters. Of these we mention only two. 
 
466 IIESOZOIC ERA— AGE OF REPTILES. 
 
 1. Teeth.— A. glance at Fig. 715, a, in comparison with figure of The- 
 riodont (Pig. 630, h), on page 437, shows that the teeth of some of the 
 
 ^ ^ 
 
 a b c d e / ■ 
 
 j'lG T15. aSekies ofMolaksofTriassio AND JubassioMammals: a, Dromatherinm; 6, Micro- 
 
 conodon; c, Amphilestes; d, Phascolotherium; e, Triconodon; /, Splalacotherium (after Osborn). 
 
 earliest mammals differed little from those of Theriodont reptiles ; in 
 which, as already explained, the tuberculation of the molars character- 
 istic of mammals had already commenced. In the subsequent course 
 of evolution the subordinate cusps of Fig. 715, a, b, c, d, e, were 
 shifted outward in the upper jaw and inward in the lower jaw, so that 
 'the cusps interlocked. This forms the tritubercular molar of Cope 
 (Fig. 715,/), so common in Mesozoic animals. From this simple gen- 
 eralized type were afterward developed the more complex molars of the 
 specialized animals of the Tertiary and present time. 
 
 3. Reproduction. — There seems to be no doubt that many of these 
 animals were marsupials, although more generalized than any existing 
 marsupials. Now, marsupials in their reproduction approach reptiles. 
 In typical mammals the embryo is attached to the mother by the pla- 
 centa, so that the whole embryonic development is within the uterus ; 
 in marsupials, on the contrary, there is no placental attachment, and 
 therefore the intra-uterine development is very short and imperfect, 
 and is, in fact, completed outside the uterus in the pouch (marsupium). 
 In true mammals the whole embryonic development is within (gesta- 
 tion), and the young are born in perfect condition. They are young- 
 bearers (viviparous). In birds and reptiles — egg-bearers (oviparous) — 
 the whole of the development takes place without (incubation). In 
 marsupials the development is partly within hut mostly without. 
 These, therefore, may be called semi-oviparous, or reptilian mammals. 
 
 Thus the class of mammals has been divided into two sub-classes — 
 placentals or true mammals, and noti-placentals or reptilian mammals. 
 The latter includes the marsupials, semi-oviparous, and the monotremes 
 (Ornithorhynchus, Echidna, etc.), which are true egg-layers (ovipa- 
 rous), like birds and reptiles. The non-placentals, with the exception 
 of a few opossums in America, are wholly confined now to the Aus- 
 tralian region. In Jurassic times they roamed in great numbers all 
 over Europe and America. 
 
 Origin of Mammals.— In Theromorphs we see reptiles reaching 
 upward and forward toward mammals. In Jurassic and especially 
 Triassic mammals we see this class reaching downward and back- 
 ward toward reptiles. But the point of union has not yet been 
 
JUEASSIO ANIMALS. 467 
 
 found. The lowest and most reptilian of mammals, the egg-laying 
 monotremes, have not yet with certainty been found fossil ; but 
 the calcified teeth recently found in the embryo of the Ornithorhyn- 
 chus so strongly resemble the teeth of one family of Mesozoic mam- 
 mals—viz., the AUotheria (Pig. 848, p. 519)— that it is now believed 
 that these were, indeed, monotremes. It is probable, therefore, that 
 the point of union between the classes reptiles and mammals will 
 be found, not, indeed, in monotremes proper (for these are already 
 specialized), but in a generalized type connecting monotremes and mar- 
 supials. The time of origin was probably the Lower Trias or Upper 
 Permian. The earliest mammals, such as the Microlestes and the Dro- 
 matherium from the American Trias, were not far removed from such 
 a generalized type. The order of evolution has been expressed by 
 Huxley thus : 1. Hypotheria (below mammals) ; 2. Prototheria (first 
 or lowest mammals) ; 3. Metatheria (transition mammals) ; and, 4. 
 Eutheria (perfect or true mammals). The first is represented by the 
 Theromorphs of Permian and Trias, or, better, by a generalized type 
 between these and the monotremes ; the second by a hypothetical gen- 
 eralized type connecting monotremes and marsupials of the Triassic ; 
 the third by insectivorous marsupials of the Jurassifi, and the fourth 
 by the true placentals of the Tertiary. Further, it is probable, as 
 suggested by Osborn,* that the *Prototheria of the Triassic separated 
 very early into two branches of Metatheria — one more like the mar- 
 supial, the other like insectivora. From the latter came the Eutheria, 
 which again differentiated into many specialized orders. 
 
 Mammals, then, existed in considerable numbers in the Jurassic. 
 These, however, were not able to contend with the great Dinosaurs. 
 It was still the age of reptiles. This class not only predominated, but 
 impressed their character on all higher classes. The birds and the 
 mammals were still reptilian. From the reptilian stem the bird and 
 mammal branches were not yet so completely separated that connect- 
 ing links were obliterated. 
 
 Sbction 3. — Jura-Tbias in America. 
 
 We have already explained that these two periods are not well sepa- 
 rated in America. This is partly on account of the poverty of fossils, 
 and partly on account of the continuity^of conditions throughout. It 
 seems best, therefore, in the present state of knowledge to treat them 
 together as one period. Doubtless they will be better separated here- 
 after. 
 
 Distribution of Strata. — 1. Atlantic Border. — Lying in plication- 
 
 * Mesozoic Mammalia, p. 261, Transactions of tlie Academy of Sciences, Philadelphia, 
 vol. ix, No. 2, 1888. 
 
468 MESOZOIC ERA— AGE OF REPTILES. 
 
 hollows, or denudation-hollows, unconformably on the gneiss (meta- 
 morphic Archsean or Cambrian) of the eastern slope of the Appala- 
 chian chain, are found very remarkable isolated patches of sandstones 
 or sandstones and shales, which are referred to this period. These 
 patches are strung along nearly parallel to the chain, and to the coast, 
 from Nova Scotia to the border of South Carolina. They are repre- 
 sented on the map (p. 303) by oblique lines. One of them is found in 
 Prince Edward's Island, another in Nova Scotia ; another is the cele- 
 brated Connecticut River Valley sandstone ; a fourth commences in 
 New Jersey, passes as a narrow strip through Pennsylvania, Maryland, 
 and into Virginia ; a fifth and sixth form the Eiclimond and Piedmont 
 coal-fields of Virginia ; a seventh and eighth, the Dan River and Deep 
 River coal-fields of North Carolina. As they are isolated, and without 
 contact with any other formation unless unconformably, their age can 
 not be even conjectured from their stratigraphical relations ; but the 
 few fossils which they contain seem to refer them either wholly to the 
 Triassic, or else, more probably, partly to the Triassic and partly to 
 the lower Jurassic. 
 
 In connection with nearly all these patches are found columnar 
 trap or dolerite ndges. These are -interstratified with the sandstones, 
 and were partly outpoured on the sediments while these were deposit:- 
 ing, and partly forced subsequently betVeen the strata (Davis). Mounts 
 Tom and Holyoke are examples in the Connecticut Valley, the Pali- 
 sades of the Hudson in the New Jersey patch ; similar trap-ridges are 
 also found in all the other patches. 
 
 2. Plains and Rocky Mountain Region. — The geology of this re- 
 gion is still little known, but there seems no doubt that Jura-Trias is 
 widely distributed though largely concealed by subsequent deposits of 
 Cretaceous and Tertiary. They are exposed, however, in narrow bands 
 on the flanks of the Black Hills, the Colorado, Uintah, and Wahsatch 
 Mountains, and over wider areas in Northwest Texas, New Mexico, 
 Arizona, and Utah, where they are called " Red beds." Their outcrop 
 forms one of the most conspicuous erosion-cliffs (p. 282) of the region 
 north of Grand Caflon. As may be inferred from their almost univer- 
 sal red color, they are very barren of fossils. The same might be in- 
 ferred from the presence of great beds of gypsum in the Plateau region 
 and beds of salt in Kansas. 
 
 3. Basin Region and Pacific Border. — They occur also over all the 
 western part of the Basin region. Covered in the valleys by recent 
 deposits, but exposed on the flanks of all the mountains. On both 
 sides of the Sierra and Cascade Ranges they occur as the auriferous 
 slates of California and northward. 
 
JURA-TRIAS IN AMERICA. 
 
 469 
 
 Life- System. 
 
 The characterization of the life-system of the Jura-Trias period 
 in America is best brought out in connection with a description of 
 some of the more interesting localities and of their remarkable records. 
 
 Connecticut River Valley Sandstone — The Strata. — This locality 
 has been made classic ground for the geologist by the indefatigable 
 labors of the late President Hitchcock, of Amherst. The strata border 
 
 Fig. 716. — General Section across Connecticut Hiver Sandstone (after Davis): The black, trap. 
 
 the Connecticut Eiver, on both sides, through the whole of Massachu- 
 setts and Connecticut, as far as Middletown, where the river trends to 
 the east while the sandstone area passes straight on to the Sound at 
 New Haven. The whole forms an irregular area about 110 miles long 
 and 20 miles wide. They consist of red sandstones and shales, dip- 
 ping somewhat regularly to the east, at an angle of about 30° to 30°, 
 indicating a thickness of at least 5,000 feet (Dana) to 10,000 feet 
 (Hitchcock). The general relations of the strata with the intrusive 
 trap are shown in the accompanying figure (716). The trap is 
 seen to be conformable with the strata, but the whole series has 
 been subsequently' fissured and faulted in such wise that the strata 
 are repeated and the thickness is apt to be overestimated, as already 
 explained on page 241. The trap-ridges -are formed by the out- 
 crop of the tilted and faulted sheets of lava. This regular dipping 
 to the east throughout the whole series can be most easily explained 
 by supposing that at the end of this period the whole area of pre- 
 viously-horizontal strata (Fig. 717, A) was lifted into an incline of 
 20° or more, and afterward cut away by denudation, as shown in the 
 diagram (Fig. 717, B). In the elevation the strata were fissured and 
 faulted, as shown in Fig. 716. 
 
 Fie. 717. 
 
 The whole series of sandstone is very distinctly stratified, and in 
 many parts beautifully fissile. When these parts are broken open 
 
470 MESOZOIC ERA— AGE OF REPTILES. 
 
 along'their lines of lamination, all kinds of shore-marks are found in 
 the greatest perfection, viz., ripple-marks, rain-prints, sun-cracks, 
 leaf -impressions, and tracks of animals. It is evident, therefore, that 
 this was, throughout, a littoral or shoal-water deposit. But it is at 
 least 5,000 feet thick. Therefore, there must have been subsidence to 
 that extent. Here, then, we have evidence of rapid deposit (for the 
 materials are coarse), invasion of interior heat with aqueo-igneous 
 fusion, subsidence, formation of fissures, and ejection of lava. 
 
 These sandstones are poor in fossils, but the few that are known in- 
 dicate the horizon of the Keuper or Upper Triassic of Europe.. As 
 these are found near the middle of the series, it is probable that the 
 series represents the whole of the Trias and part of the Juras of 
 Europe. 
 
 The Eecord. — The general redness of the sandstone is suflBcient evi- 
 dence that organic remains are very scarce ; and so, indeed, we find it. 
 
 
 Fig. T18.— a, Twigs; b, Cone (after Hitchcock). 
 
 Several species of fishes, a few leaves, the most perfect of which is a 
 species of fern — Clathopteris— and a fir-cone (Fig. 718), and a few 
 small fragments of thin, hollow bones, which may have belonged to 
 either birds or reptiles, are all that until recently had been yet found. 
 
 
 
 ■ ^. .*. ^ *«. IMU, .uu. .... VI UU 
 
 ^~:^ -::~ Sv ^ • -^^^^•^■^ — ^^ --v Ephemera (after Hitch- 
 
 Fig. 720.— Larva of 
 Ephem 
 cock). 
 
 Fig. 719.— a, 6, c, Tracks of Insects, Crustacea, or Worms (after 
 Hitchcock). 
 
 But by far the most interesting portion of the record in this locality 
 consists of tracks. These are partly tracks of Insects and Crustaceans, 
 
JURA-TRIAS IN AMERICA. 471 
 
 and partly of Reptiles aud, possibly, of Birds. Some of those which 
 have been referred to Crustaceans and Insects are shown in Fig. 719, 
 a, b, c. There has been found, also, the whole form of one insect ap- 
 parently the larva of an Ephemera (Pig. 730). It is quite probable 
 that many of the tracks were formed by similar larvae inhabiting the 
 water. 
 
 Reptilian Tracks. — By far the larger number of tracks are those of 
 Reptiles. More than fifty species have been described by Hitchcock.* 
 These vary extremely, both in size and in character. In size, they vary 
 from the track of a living Triton, a half-inch long, to that of the Oto- 
 zoum (Fig. 731), twenty inches long, and with a stride of three feet. 
 Some had five toes, some four, and some only three functional toes on 
 the hind-feet. Again, some had hind and fore feet of nearly equal size, 
 and evidently walked or crawled in true quadrupedal style. Others had 
 hind-feet much larger than fore-feet, and were essentially bipedal in 
 locomotion, only putting down their small fore-feet occasionally ; but 
 walking bird-like, not hopping kangaroo-like, on their hind-legs. In 
 connection with the bipedal tracks there have been found what seemed 
 to be the impressions of a dragging tail (Fig. 733) ; but these are so 
 rare and doubtful that it is generally believed the animals were mostly 
 long-legged and short-tailed ; or else they lifted their tails in walking. 
 
 The general conclusion from an attentive study of these tracks, in 
 connection with the findings elsewhere of bones and teeth, is that they 
 are the tracks of Dinosaurs. The hugest among them, the Otozoum 
 Moodii (Fig. 731), was probably a long-legged biped Dinosaur, which 
 stood twelve feet high. The Ano?nwpus (Fig. 733), a common form, 
 was also probably a Dinosaur, which walked often on two legs only, 
 and in resting brought the whole tarsus and heel on the ground, in 
 the manner of a kangaroo. 
 
 The doubts in regard to the character of these reptiles have now 
 been cleared up by the fortunate discovery by Marsh of nearly perfe'ct 
 skeletons. In Fig. 734 we give a restoration of one of these. 
 
 Supposed Bird-Tracks. — Those which have been referred to birds 
 are : 1. Wholly bipedal, i. 6., there is no evidence of fore-feet at all. 3. 
 They are tridactyl. 3. They have a regular progression in the number 
 of joints in the tracks, the inner toe having two, the middle toe three, 
 and the outer toe tour joints. Now, in birds, the inner toe has three, 
 the middle toe four, and the outer toe five joints, but the last two joints 
 in each case make but one division of the track, so that the track is ex- 
 actly what is given above. The discovery, however, that many Dinosaurs 
 have but three functional toes on the hind-foot, and that they also have 
 the same number of joints as birds, has greatly shaken confidence in 
 
 * More than 100 different varieties of footprints have been found in the Connecticut Valley. 
 
4T2 
 
 MESOZOIO EEA— AGE OF REPTILES. 
 
 the ornithic character of these tracks. Only the absence of fore-feet 
 tracks, therefore, remains. But as many of these early reptiles walked 
 
 occasionally on two legs, it is not impos- 
 sible that sofiie of them always walked 
 thus. It is proiable, therefore, that all 
 these tracks are those of Eeptiles. As- 
 
 C3 
 
 Fig. 721. Fig. 722. Fig. 723. 
 
 Figs. 721-723.— Eeptile Tracks (after Hitchcock): 721. Otozonm Moodii; 
 
 fore-foot, X A- 732. Gigantitherium caudatum, x ^. 738. Anomcepas minor, x J 
 foot; b, fore-foot. 
 
 hind-foot, x A; 6, 
 : a, hi 
 
 ind- 
 
 suming them to be those of Birds, they vary in size from those of a 
 snipe to those of the great Brontozoum, eighteen inches long, and with 
 a stride of fohr feet (Pig.. 725). This huge bird, if 
 bird it was, must have been at least fourteen feet high 
 (Dana). Such a huge animal must have been wingless, 
 like the ostrich, etc., for its size is far beyond the limit 
 within which flight is possible. 
 
 We have expressed a doubt as 
 to whether these tracks be those 
 of birds or reptiles. This is not 
 so strange as it may at first appear. 
 These two classes are, 
 indeed, now very wide- 
 ly separated, but then 
 they were very closely 
 allied. There were 
 probably animals then 
 
 Fio. 724.— AncMsaurus colnras. Marsh, X jij, Triassic, Connecticut i-,- „ „,-uj„i, .^„„^ it 
 
 (aftei Marsh). living which, even II 
 
JURA-TRIAS IN AMERICA. 
 
 4Y3 
 
 we saw them, might puzzle us to decide whether to call them reptilian 
 birds or bird-like reptiles. These two classes were perhaps not yet 
 fairly disentangled and separated from each other. 
 
 We may easily imagine the circumstances under which these tracks 
 were formed. During the Jura- Trias 
 period there was in the region of the 
 Connecticut Valley a shallow inland 
 sea, connected by a narrow outlet with 
 the ocean. Into this the tides flowed 
 and again ebbed, leaving extensive flats 
 of mud or sand ribbed with ripple- 
 marks. A passing shower pitted the 
 soft mud, and the sun, coming out 
 again from the breaking clouds, dried 
 and cracked it. Huge bird-like rep- 
 tiles, and possibly reptilian birds, saun- 
 tered near the shore-margin in search 
 of food. The tide came in again with 
 its freight of fine sediments, gently 
 covered the tracks, and preserved them "*' 'toimff°S'^conne?tkufvan"yf ^°'°' 
 forever. This occuri'ed constantly for 
 
 many ages about the end of the Triassic or the beginning of the 
 Jurassic period, for the tracks are found near the middle of the 
 series of strata. 
 
 Richmond and North Carolina Coal-Fields. — The patches occurring 
 in Virginia and North Carolina are co.al-iearing. They constitute the 
 
 Eichmond and 
 
 Piedmont coal-fields 
 of Virginia, and the 
 Deep River and Dan 
 Eiver coal-fields of 
 North Carolina. 
 Fig. 737 gives a 
 ' generalized section 
 of the Richmond 
 coal - fields taken 
 from Daddow. The 
 strata of this field 
 are sandstone and 
 shales, 700 to 800 
 feet thick, lying in 
 irregular erosion- 
 hollows of t^e 
 
 Fia. 786.— Portion of a Slab with Tracks of several Species of Bronto- „_„^„- All +>if> 
 
 zoum (after Hitchcock). gneiSS. All lUB 
 
474 
 
 MESOZOIC ERA— AGE OP REPTILES. 
 
 phenomena of a coal-field are here repeated, viz., interstratified seams 
 of coal and beds of iron-ore, under-clays with roots, and roof-shales with 
 leaf -impressions. There are several seams of coal, the lowest of which 
 is almost in contact with the gneiss. Some of the seams are of great 
 
 Fig. 727. — Section across Richmond Coal-field (after Daddow). 
 
 thickness — thirty to forty feet — and the coal is very pure. It is prob- 
 able that this coal, like that of the Carboniferous times, was formed in 
 a marsh, which was sometimes converted into a lake. The plants 
 found are very decidedly Upper Triassic and Lower Jurassic, viz., 
 Oycads, Conifers, Equisetse, and Ferns. Fontaine makes them Rhcetic, 
 i. e., transitive between Triassic and Jurassic. The animals indicate 
 the same horizon. 
 
 Fig. 7i8.— Dictjopyge macrura, a Ganoid (.after Emmons). 
 
 The Deep Eiver and Dan Eiver coal-fields of North Carolina are 
 very similar to those in Eastern Virginia, except that in the Deep Eiver 
 coal-fields the coal- bearing portion, which seems to correspond with 
 
 the whole of the Eichmond 
 strata, is underlaid by 3,000 
 feet of barren sandstone. 
 If we call the coal-measures 
 Upper Trias or Lower 
 
 1/ 
 
 
 Figs. 729, 730.— Fossils op Nobth Carolina and Richmond Coal-Basins (after Emmons): 
 729. Palissya diffusa. 730. Fodozamites Emmousi. 
 
JURA-TEUS IN AMERICA. 
 
 Fig. 731. 
 
 Fig. 733, 
 
 Fio. 733, 
 
 FiG3. 731-734.— Fossils op North Carolina and Richmond Coal-Basins (after Emmons): 731. 
 Acrostichites linnsesef olia — Kichmond Coal. 732. Asterocarpus f alcatuB. 733. Laccopteris lanceo- 
 lata. 734. Jaw of Dromatherium sylvestre. 
 
 Juras, these barren sandstones are certainly Triassic. In their upper por- 
 tion, and therefore probably in the Upper Triassic, Emmons found jaws 
 of a Marsupial, which he names Dromatherium sylvestre (Fig. 734). As 
 this is one of the earliest, so it is also one of the most reptilian of mam- 
 mals. According to Osborn, it had many reptilian characters of teeth, 
 e. g., conical premolars and imperfectly divided fangs, and imperfect 
 cusps in the molars (Pig. 715, a) as in the Theromorph reptiles. Until 
 the recent discoveries of Marsh, this, and perhaps another genus from 
 the same place, was the only mammal known from the Jura-Trias of 
 America. We give in Figs. 728-734 some of the plants and animals of 
 these two basins. Tridactyl tracks like those in Connecticut have also 
 been found in New Jersey and in Pennsylvania. 
 
 Other Patches. — In other patches, especially in New Jersey, Penn- 
 sylvania, and Nova Scotia, reptilian bones and teeth have been found, 
 representing Dinosaurs and Crocodilians or Lacertians. 
 
 Interior Plains and Pacific Slope. — The Jura- Trias of the interior 
 plains are singularly deficient in fossils. The gypsum in many of them 
 furnishes the explanation. They were probably formed in interior and 
 very salt seas, which are usually deficient in life. The two periods are, 
 
476 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 however, in some places at least, better separated than on the Atlantic 
 slope, probably because of more Tariable conditions. 
 
 Fie. 735. 
 
 IfiG. 736. 
 
 Figs. 735, 736.— Jurassic Fossils op Wyoming (after Meek) : 735. Belemnites densns. 736. Gryphsea 
 
 calceola. 
 
 On the slopes of the Black Hills and on the North Platte undoubt- 
 ed Jurassic fossils occur, indicating an open sea. In New Mexico 
 Newberry found impressions of plants, indicating the same horizon 
 as in North Carolina and Virginia^ — i. e., Upper Triassic. Some of 
 these are given (Figs. 737-744). 
 
 On the Pacific coast marine life no doubt abounded, as this was the 
 margin of an open sea ; but the rocks here are very highly metamor- 
 phic, and the fossils, therefore, mostly destroyed. Wherever this is 
 not the case, the rocks abound in fossils. In Humboldt County, Ne- 
 vada, for example, the strata in some places seem almost wholly made 
 up of Trachyceras Whitneyi (Fig. 747). In the same locality the re- 
 mains of an Enaliosaur (sea-saurian) have been found. On account 
 of the marine conditions prevalent, the two periods are more easily 
 
 Fig. 737. 
 
 Fig. 740. 
 
 Fig. 739. 
 
 Fig. 738. 
 
 Fiss. 737-740.— PiAHTs OF THE Jura-Tbias (after Newberry): 737. Branch of Conifer (Brachyphyl- 
 lum). 738. Branch of Conifer. 739. Conifer, Branch and Fruit. 740. Zamites occidentalis. 
 
JURA-TRIAS IN AMERICA. 
 
 477 
 
 Fio. 743. 
 
 Fio. 744. 
 
 Fig. 741. Pig. 743. 
 
 Pigs 741-744.— Plants of the Jura Tkias (after Newberry) ; 741. Otozamites Macombii. 742. 
 Podozamites crassifolia. 743. Tseniopteris elegans. 744. Alethopteris Whitneyi. 
 
 separable, on the Pacific coast. In fact, perhaps the completest illus- 
 tration of the Jura found at all in the United States is that reported 
 in 1892 by Diller in Northern California.* 
 
 Pig. 745. 
 
 Pig. 746. 
 
 Pig. 747. 
 
 Figs. 745-747.— California Juka-Trias Shells : 745. Gryphaea speciosa (after Gabb). 746. Tri- 
 gonia pandicosta (after Gabb). 747. Trachyceras Whitneyi (after Gabb). 
 
 Upper Jurassic Reptiles. — In Colorado and Wyoming, in beds 
 which are referred to the uppermost Jurassic, a large number of most 
 extraordinary reptiles were found and described by Marsh and Cope. 
 Also, in the Wyoming beds, Marsh discovered some twenty-five species 
 of Marsupial mammals. His reptilian bird (Laopteryx) is more 
 probably a pterodactyl. The beds from which all these have been 
 taken are called the Como beds, named after Como, Wyoming, the 
 
 * Bull. Geol. Soc. Amer., vol. iii, pp. 369-394. 
 
478 MESOZOIC ERA— AGfE OF REPTILES. 
 
 type locality beds. These discoveries are treated separately, not only 
 on aceonnt of their great importance, but also and especially because 
 they belong to an entirely different horizon, viz., the uppermost Juras- 
 sic, passing into the Cretaceous.* 
 
 Dinosaurs. — The most abundaiit and the largest reptiles found here 
 are Dinosaurs. Some ten or twelve species of this order have been de- 
 scribed by Cope, and thirty or forty species by Marsh. Some of these 
 are from the east slope of the Colorado Mountains, but the most impor- 
 tant have been found on the west slope. In the museum of Yale College 
 there are now the remains of several hundred individu- 
 als. These American Jurassic Dinosaurs were proba- 
 bly the largest land animals that have ever lived. 
 Cope describes one (Camarasaurus) with a thigh-bone 
 six feet long, and Marsh describes one Camarasaurus 
 immanis) with a thigh-bone of still greater length. 
 Along with these huge animals lived also the small- 
 est Dinosaurs yet known — one of them, Nanosaurus 
 Fig 748— Dorsal ver- ^■gilis, being about half the size of a common fowl, 
 tebra of Cceiurus The characteristics of these ancient reptiles have 
 
 fragihs, trans- . i -in nr i 
 
 verse section been worked out With great skill by Marsh, according to 
 
 whom the vertebrse of many of them were full of large 
 
 cavities, so as to make these enormous bones as light as possible. This 
 
 character reached its highest expression in Cceluria of Marsh (Fig. 748). 
 
 The American Dinosaurs were not only remarkable for their size and 
 number but also for their great variety of forms. According to Marsh, 
 some of them were reptile-footed {Sauropoda), some beast-footed ( I^e^-o- 
 poda), some bird-footed {Ornithopoda), and some belonged to a most re- 
 markable family, Stegosauria (plate-covered Saurians), not previously 
 recognized. 
 
 The Sauropoda were the hugest of all. They vf ere five-toed, planti- 
 grade, and quadrupedal. Their large limb-bones (Pig. 749) and 
 massive pelvis (Pig. 750) show that they walked with the body well 
 lifted from the ground (Fig. 751). They were all herbivorous. 
 Good examples of these are seen in the Camarasaurus (a thigh of which 
 was found more than six feet long and twenty-five inches thick, the 
 animal itself being probably seventy or eighty feet long) ; the Bronto- 
 saurus, sixty feet long (Fig. 751) ; and the Morosaurus (Pig- 749, 
 750). The restoration of the Brontosaurus (Fig. 751) shows the ex- 
 
 * The Como beds hare been classed with the Jurassic, mainly because their vertebrate 
 fauna is of this period, and partly because of the great gap between it and the Dakota 
 Cretaceous. The question whether they should be called uppermost Jurassic or lower- 
 most Cretaceous has, however, been raised by some geologists. They apparently corre- 
 spond to the Wealden, which many geologists class with the Cretaceous. Marsh, how- 
 ever, regards them as decidedly Jurassic. 
 
JUEA-TRIAS IN AMERICA. 
 
 479 
 
 Pis. 749.— 1. Bones of left fore-leg of Moronaarus grandis (after Marsh). One twentieth natural 
 size. «, scapula; c, coracoid; h, humerus; r, radius: w, ulna; uc, ulnar carpal; 1, first meta- 
 carpal; Vme, fifth metacarpal. 2. Bones of left hind-leg of Moroeaurus grandis. One twentieth 
 natural size. il. ilium; is, ischium; p, pubis; /, femur; t, tibia; /', fibula; a, astragalus; c, cal- 
 caneum; Vmt, fifth metatarsal. 
 
 treme smallness of the animal's head, and the brain-cayity shows a still 
 more remarkable smallness of the brain. 
 
 The Theropoda included, among foreign representatives, the Me- 
 
 galosaur and Compsognathus, already figured (p. 460), and among 
 
 American genera Anchisaurus (p. 473) and Ceratosaurus (Fig. 752). 
 
 They were/owr- to five-toed, digitigrade, and bipedal. This is shown 
 
 S3 
 
480 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 by the disparity in size of hind and fore limbs. They were carni- 
 vorous. 
 
 The Ornithopoda included, among foreign representatives, the Igu- 
 anodon, already figured (p. 459), and Hypsilophodon (Fig. 819, p. 503), 
 
 "^•s 
 
 
 V 
 
 
 \ s\ A / 
 
 Fio. 750. — Pelvic arch of Moroeaurus grandis (after Marsh), seen from in front. One sixteenth 
 natural size: a, first sacral vertebra; b, transverse process of first sacral vertebra; c, trans- 
 verse process of second vertebra; p, fourth or last sacral vertebra; nc, neural canal; il, ilium; 
 is, ischium; pb, pubis. 
 
 together with many American genera, such as Laosaurus (Fig- 753) 
 and Camptosaurus (Fig. 754), Olaosaurus (Fig. 847, p. 518), etc. They 
 were three-toed, digitigrade, bipedal herbivores. 
 
 Fig. 751. — Brontosaurus excelsis, x ^ (restored by Marsh). 
 
 The Stegosaurs were perhaps the most remarkable of all. The 
 restoration of this strange animal (Fig. 755) shows two rows of broad 
 plates rising three feet high along the whole dorsal ridge and four 
 caudal spines at the end of the tail. The use of these extraordinary 
 appendages it is difficult to conceive. In spite of the great disparity 
 in the length of the hind and fore limbs, Marsh regards them as quad- 
 rupedal. The brains of all Jurassic Dinosaurs were very small in com- 
 parison with living reptiles, but this was especially true of Stegosaurs. 
 
JTJRA-TKIAS IN AMERICA. 
 
 481 
 
 Fio. 752.— CeratoBauras naeicornis (after Marsh), x ^, Jurassic, Colorado. 
 
 Fio. 753.— Restoration of Laosaurus by Marsli, A- !• Tootli of Laosaurus altus (after Marsli), 
 front view. 2. Tlie same, side view. Both twice natural size. 
 
 Fig. 764.— Camptosaurus dispar (restored by Marsh), x ^, Jurassic, Wyoming. 
 
482 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 Via. 755.— Stegosaurus angulatuB (after Marsh), x ^, Jurassic, Wyoming. 
 
 To make up for this deficiency they had an enormous enlargement of 
 the spinal cord in the sacral region. This sacral brain — if we may so 
 call it — was ten to twenty times bigger than the 
 cranial brain (Fig. 756). It was necessary in order 
 to work the powerful hind-legs and tail. 
 
 Ichthyosaurs and Plesiosaurs. — Besides the Dino- 
 saurs, Marsh describes from the same formation (Ju- 
 rassic), 'out from a lower horizon, an Ichthyosaurian, 
 but differing entirely from the Ichthyosaurus of the 
 European Jurassic in being toothless. On this ac- 
 count he calls the genus Baptanodon (Pig. 757). 
 This reptile had six digits in both fore and hind feet. 
 Also the fore-arm is not distinctly differentiated from 
 the Carpus. It is therefore a more generalized or else 
 a more degraded form than the Ichthyosaurus. In 
 the same beds also he has recently found remains 
 of a Plesiosaur, the first yet found below the Cretaceous in-America. 
 
 In 1881 Marsh discovered in the same beds, the Como beds of Wy- 
 
 FiG. 756. —Outlines rep- 
 resenting transverse 
 sections throngli 
 brain of Stegosaurae 
 ungulatus, and sa- 
 cral cavity: &, brain; 
 «, sacral cavity. One 
 fourth natural size 
 (after Marsh). 
 
 OOo 
 
 OOOoo 
 Ooo 
 OOooo 
 
 o 
 
 o , 
 
 o 
 
 O o o-v 
 
 Fig. 757.— Left hind-paddle of Baptanodon discus (after Marsh), seen from „- 
 below. One eighth natural size : /, femur ; t, tibia ; i, fibula ; /, first , . 
 digit ; F, fifth digit. '01- 
 
 ommg, remains 
 of what he re- 
 garded as a Ju- 
 rassic bird (La- 
 opteryx). Later 
 students think it 
 is probably a 
 pterodactyl. It 
 had teeth and 
 concave verte- 
 
JUKA-TRIAS IN AMERICA. 
 
 483 
 
 Irce; but the remains are too imperfect to permit distinct charac- 
 terization. 
 
 Manunals. — Lastly, in the same beds, Marsh has discovered some 
 twenty-five species of small mammals. According to him, these early 
 mammals were not typical Marsupials, but a generalized type con- 
 necting that order with Insectivora. He makes of them two sub- 
 orders, Pantotheria and Allotheria. Figs. 758 and 759 are represen- 
 tatives of these two types. According to Zittell, the Allotheria were 
 probably monotremes, and therefore egg-layers. 
 
 Physical Geography of the American Continent during the Jura- 
 Trias Period. — During Palaeozoic times the Atlantic shore-line was 
 certainly farther east 1;han it was subsequently, probably farther east 
 than it is now (p. 303). At the end of the Palaeozoic occurred the Ap- 
 palachian revolution. Coincidently with the up-pushing of the Appa- 
 lachian chain, the sea-border probably vrent downward, and the shore- 
 
 Fio. 758.— Bight lower jaw of Dicrocynodon victor (after Marsh), outside view. 
 a, canine; b, condyle; c, coronoid process; d, angle. 
 
 Twice natural size: 
 
 line advanced westward on the land which previously had extended to 
 the submerged continental border. During the Jura-Trias the shore- 
 line to the north was still beyond what it is now, for no Atlantic 
 border deposit is visible ; and along the Middle and Southern States 
 
 Fio. 759.— Left lower jaw of Ctenacodon serratus (after Marsh), inner view. Four times natural size 
 
 it was certainly beyond the bounding-line of Tertiary and Cretaceous 
 (see map, p. 303), for all the Atlantic deposits of this age have been 
 covered by subsequent strata ; and yet probably not much beyond, for 
 some of these Jura-Trias patches seem to have been in tidal connection 
 
484 MESOZOIC ERA— AGE OF REPTILES. 
 
 with the Atlantic Ocean. It is probable, therefore, that the shore-line 
 was a little beyond the present New England shore-line, and a little 
 within the present shore-line of the Middle and Southern Atlantic 
 States. 
 
 A little back from this shore-line, and at the foot of the then Ap- 
 palachian chain, there was a series of old erosion or plication hollows 
 stretching parallel to the chain. The northern ones had been brought 
 down to the sea-level, and the tides regularly ebbed and flowed there 
 then as in the bay of San Francisco, or Puget Sound, at the present 
 time. In the waters of these bays lived swimming Eeptiles, Croco- 
 dilian and Lacertian, and on their flat, muddy shores walked great 
 bird-like Reptiles, and possibly reptilian Birds. The more southerii 
 hollows seemed to have been above the sea-level, and were alternately 
 coal-marsh and estuarj or lake, emptying into the Atlantic. Since 
 that time the coast has risen 200 or 300 feet, and these patches are 
 therefore elevated so much above the sea-level. 
 
 Meanwhile, somewhat similar changes were going on in the western 
 portion of the continent. During Palaeozoic times, the Pacific shore- 
 line was just east of the Sierra Range, and the place of this range was 
 a marginal sea-bottom. At the end of the Palaeozoic, coincidently with 
 Appalachian revolution already explained (p. 435), the Utah Basin 
 region was elevated and became land, while the Nevada Basin region 
 subsided, and the Pacific shore-line advanced eastward to Battle Mount- 
 ain. But the whole area between this Basin region continent and the 
 Palaeozoic area of eastern North America, including the Plateau region 
 and the Plains region, was covered by one or more shallow inland seas, 
 with imperfect connection, or none at all, with the ocean, and in which, 
 therefore, gypsum and salt deposited by evaporation. At least once 
 during Jurassic times this inland sea became broadly connected wjth 
 the ocean, so that oceanic conditions prevailed. The place npw occu- 
 pied by the Wahsatch Mountains was then a marginal sea-bottom, bor- 
 dering the Basin region continent. On the west the Pacific shore-line 
 was some distance east of the Sierra, and the place of that range was 
 still a sea-bottom, though not so closely marginal as in Palaeozoic 
 times. 
 
 Disturbances which closed the Period. — This long Jura- Trias period 
 was closed, and the Cretaceous period inaugurated, by the Sierra revo- 
 lution, by which the sediments accumulated along the then Pacific 
 shore-bottom, yielding to the lateral pressure, were mashed together 
 and swollen up into the Sierra and Cascade Ranges, and the coast-line 
 transferred westward to the other side of these ranges. Probably at the 
 same time some changes occurred in the region of the Coast Range by 
 which islands were formed off the then coast. Coincidently with these 
 changes probably occurred on the Atlantic slope the elevation of the 
 
CRETACEOUS PERIOD. 485 
 
 Jura-Trias sounds and the outbursts of igneous matter, forming the 
 trap-ridges already spoken of (pp. 468 and 469). Extensive changes also 
 occurred at the same time over the whole region of the inland seas, by 
 subsidence and the inauguration of oceanic conditions, which continued 
 to prevail during the Cretaceous. There is reason to believe also that 
 many of the Basin ranges were formed at this time (King), although 
 their present forms as well as that of the Sierra were given much later 
 (p. 276). It was essentially a period of mountain-making in the west- 
 ern part of the American Continent. 
 
 Section 4. — Cretaceous Period. 
 
 The most general characteristic of this period is its transitional 
 character. In it Mesozoic types are passing out, and Cenozoic or 
 modern types are coming in, and the two types therefore coexist side 
 by side. In most places in America the Cretaceous lie unconformably 
 on the Jurassic or still lower rocks. 
 
 Rock-System — Area in America.—!. On the Atlantic harder going 
 southward, we find no Cretaceous rocks (except a little patch on Mar- 
 tha's Vineyard) until we reach New Jersey. Here we find a narrow 
 strip peeping out from under the edge of the overlying Tertiary, and 
 marked on the map (p. 302) by oblique interrupted lines. This strip 
 passes through New Jersey, Delaware, Maryland, to the borders of 
 Virginia. - Passing south, we find no continuous area until we reach 
 Georgia; yet it underlies the Tertiary in all this region, as is shown 
 by the fact that the rivers in North and South Carolina cut through 
 the Tertiary and expose the Cretaceous in many places. 2. The 
 Gulf-border Cretaceous commences in Western Middle Georgia, 
 covers all the prairie region of Middle Alabama, the northeastern or 
 prairie region of Mississippi, then runs northward as a narrow strip 
 through Tennessee nearly to the mouth of the Ohio. It then dis- 
 appears beneath the Tertiary, to reappear as an area bordering the 
 Gulf Tertiary on the west side. 3. On the interior plains, the Cre- 
 taceous connecting with the Gulf-border area stretches northwestward 
 to arctic regions, occupying nearly the whole of the great, grassy, level 
 Western Plains called Prairies — though much of it is overlaid by the 
 subsequent Tertiary. 4. In the Rocky Mountain region Cretaceous 
 strata occupy all the Plateau region — i. e., the region between the East- 
 ern range and the Wahsatch range, except where overlaid by Tertiary 
 or removed by erosion. Eecent investigations in Mexico * render it 
 probable that this area stretches also westward through Northern 
 Mexico to the Pacific. 5. On the Pacific border. Cretaceous strata 
 form a large part of the Coast Eanges, and also in places the lowest 
 
 * American Journal of Science, vol. x, p. 386, 1875. 
 
486 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 western foot-hills of the Sierra Range. Whitney has estimated the 
 thickness of the Cretaceous rocks in portions of the Coast Range as 
 20,000 feet, and Diller, 30,000 feet. 
 
 Physical Geography in America.— It is not difiBcult from the Creta- 
 ceous area just given to reconstruct approximately the physical geog- 
 raphy. At that time the Atlantic shore-line in all the northern portion 
 of the continent was farther out or east than now, for the Cretaceous 
 of this part is all now covered by sea. From New Jersey southward 
 the shore-line was then farther in or west than now. From Maryland 
 to Georgia the shore-line, though farther in than now, was farther out 
 than during the Tertiary, as the Cretaceous is covered by the later de- 
 posits. The Gulf was much more extended both northward and west- 
 ward than either now or in Tertiary times, its shore-line being along 
 the extreme limit of the Cretaceous of this region. From the Gulf 
 there extended northwestward an immensely wide sea, covering the 
 Plains region and the Rocky Mountain region as far westward as the 
 Wahsatch Range, and dividing the continent into two continents, an 
 eastern or Appalachian, and a western or Basin region continent. The 
 place of the Wahsatch range was then the marginal bottom of this in- 
 terior Cretaceous sea. The Pacific Ocean at that time washed against 
 the foot-hills of the Sierra Range, the place of the Coast Range being 
 thus its marginal bottom. These facts are represented in the accom- 
 panying map. It was" an age of great erosion and peneplanation. 
 
 Fig. 760.— Map of American Continent in later Cretaceous Times, shaded part covered with water. 
 
CRETACEOUS PERIOD. 
 
 487 
 
 Rocks. — The rocks of the Cretaceous period consist of sands, and 
 clays, and limestones, as in other periods, but, as a whole, are less fre- 
 quently metamorphic than in the older rocks. There is, however, one 
 kind of rock found in this age in Europe, and also recently in America, 
 which is so peculiar and so interesting that it must not be passed over 
 in silence. We refer to the white chalk of England and France, from 
 which the formation and the period take their name, " Cretaceous." 
 
 Chalk. — Chalk is a soft, white, pure carbonate of lime. Scattered 
 through the soft mass 
 are found very char- 
 acteristic nodules of 
 pure flint. These 
 nodules are of various 
 sizes and shapes, some- 
 times scattered irreg- 
 ularly, sometimes ar- 
 ranged in layers. 
 Often some fossil, es- 
 pecially a sponge, 
 forms the nucleus 
 around which the ag- 
 gregation of the sili- 
 cious matter takes place, 
 
 Fia. 761.— Chalk-Cliffs with Flint-Nodules. 
 
 On account of Its extreme softness, chalk 
 is often sculptured by erosive agencies 
 
 into fantastic 
 761). 
 
 cliffs and needles (Fig. 
 
 Fig. 764. Fia. 765. Fig. 766. 
 
 Figs. 762-766.— FoKAMiHiFEBA o» Chalk: 762. Chalk as seen under the Microscope (after Nichol- 
 son). 763. Ouneolina pavonia. 764. Flabellina rugosa. 765. Lituola nautiloides. 766. Chrysa- 
 lidina gradata (after D'Orbigny). 
 
488 
 
 MESOZOIC ERA— AGE OF KEPTILES. 
 
 Examined with the microscope, chalk is found to be composed 
 largely of Khizopod shells, and of Coccoliths and Ooccospheres (sup- 
 
 Fio. 767. — ^Viewof Iowa Chalk nnder the microscope (after Calvin). 
 
 posed shells of unicelled plants), some perfect, more broken, most of 
 all completely disintegrated (Pig. 763). The flint-nodules, similarly 
 examined by section, show spicules of sponge and silicious shells of 
 Diatoms. Chalk such as described was supposed to be found nowhere 
 except in Europe, but recently good chalk composed of Poraminiferal 
 shells, and containing flints, has been found in Texas (Hill), and in 
 Kansas and northward to Dakota. We give in Pig. 767 a microscopic 
 view of American chalk. Figs. 763-766 represent some of the more . 
 common Ehizopods found in chalk of Europe, and Pig. 768 of those 
 from the chalk of United States. 
 
 Fio. 788.— Foraminifera from the Chalk of Iowa, x 100 (after Calvin); a, Globigerina cretacea; 6, 
 Textalaria globulosa; c, Bulimina sp?. 
 
CRETACEOUS PERIOD. 
 
 489 
 
 Origill of Chalk.— A material so unique must have been formed 
 under peculiar conditions. Eecent investigations show that deep-sea 
 ooze resembles chalk. In all the deep-sea soundings and dredgings 
 recently undertaken, it is found that the sea-bottom between the 
 depths of 3,000 and 30,000 feet, where not too cold, is a white ooze. 
 
 Fia. 769.— Deep-sea Ooze, magnified 700 diameters, a, BathyUus with Coccoliths ; b. Individual 
 Discoliths and Cyatnoliths ; c, Coccospheres ; d, Olobigerina ; e, Globigerina with bursted 
 test ; /, TextMlaria ; g, g', Eadiolaria ; h, i, Diatoms ; k, I, Sponge spicules ; m, Mineral frag- 
 ment (Zittel). 
 
 consisting mainly of Ehizopod shells (Globigerina, Eadiolaria, etc.) 
 and Coccoliths, Coccospheres, etc., through which are scattered sili- 
 cious shells of Diatoms (p. 169). These shells are in every stage of 
 change : some living or at least still retaining sarcode ; some perfect, 
 though dead and empty; some broken; most of them completely dis- 
 integrated into an impalpable mud. From the great abundance of 
 one genus of Ehizopods, this calcareous mud has been called Olohi- 
 gerina ooze. In deep-sea bottoms, therefore, chalk is now forming. 
 
490 MESOZOIC ERA— AGE OF REPTILES. 
 
 Also, strange to say, many Sponges, and Starfishes, and Echinoids, 
 and Crustaceans, very similar to those found in the chalk of Cre- 
 taceous times, have been brought up from present deep-sea bottoms. 
 
 There seems little doubt, therefore, that chalk is a deep-sea for- 
 mation. The flint-nodules have been formed by a subsequent process 
 similar to that which gives rise to other nodules (p. 196). The silica, 
 which in the ooze was at first scattered, is slowly aggregated into pure 
 flint-nodules, and the matrix is left in-a condition of pure carbonate 
 of lime.* 
 
 Extent of Chalk Seas of Cretaceous Times in Europe.— Chalk of 
 nearly homogeneous aspect prevails from the north of Ireland through 
 Middle Europe to the Crimean and Caucasus,! a distance of 1,140. 
 miles; and, in the other direction, from the south of Sweden to the 
 south of Bordeaux, a distance of 840 miles (Lyell). It is evident, 
 therefore, that at that time a deep sea ocQupied a large portion of 
 Central Europe. The white chalk of England and France is about 
 1,000 feet thick. This thickness indicates a very great lapse of time. 
 
 Cretaceous Coal. — Coal is again found in large quantities in rocks 
 of this period in the United States. The mode of occurrence is 
 similar to that found in rocks of other periods; but as most of this 
 coal is found in the Laramie, and as this is a transition group to 
 the Tertiary, we shall put ofl! the discussion to the end of the Creta- 
 ceoti^s. 
 
 Subdivisions of the Cretaceous. — In the localities where the Amer- 
 ican Cretaceous was first well studied, viz., in ISfew Jersey and in the 
 Western Plains and Plateau region, the lower part of the series was 
 wanting, and hence a great gap was supposed to exist here in the 
 American geological record. But recently the Lower Cretaceous has 
 been found in many widely-separated regions and by different observ- 
 ers, viz., in California, by Whitney (Shasta group) ; in Texas, by Hill 
 (Comanche group) ; J in Canada, by Dawson (Kootanie group) ; and 
 on the Atlantic border, by McGee (Potomac group).* 
 
 The Cretaceous series may be conveniently divided into Upper and 
 Lower. The subdivisions of these are of course local. In Europe the 
 Tertiary is nearly everywhere unconformable on the Cretaceous, show- 
 ing a gap at this horizon ; in America this gap may be wholly filled in 
 the West by a transition group called the Laramie. The relation be- 
 tween the main divisions of the American Cretaceous on the interior 
 
 * Wallace thinks that chalk is a coral mud formed in warm seas full of foraminiferal 
 life (Island Life, p. 84). 
 
 ■|- Favre, ArchiTes des Sciences, vol. xxxTii, p. 118 et seq. 
 
 \ Marcou had long ago (1853) discorered Neocomian in New Mexico, but the discovery 
 was not recognized by American geologists. 
 
 * This is partly a transition to Jurassic. 
 
CEETACEOUS PERIOD. 
 
 plains and Atlantic border, and of both with the European 
 is shown in the following table : 
 
 491 
 
 Cretaceous, 
 
 LOWEK 
 
 Tbktiabt. 
 
 AMERICAN. 
 
 EUROPEAN. 
 
 Wbstben Plains. 
 
 Atlantic Border. 
 
 Pacific Boeder. 
 
 Wahsatch and 
 Pnerco. 
 
 Eo-IigDitic. 
 
 Tejon. 
 
 Thanet sande. 
 Cernay beds. 
 
 Transition. 
 
 Laramie. 
 
 Wanting. 
 
 Wanting. 
 
 Wanting. 
 
 Upper Creta- 
 ceous. 
 
 Lower Creta- 
 ceous. 
 
 J Montana group. 
 
 1 Colorado group 
 
 Dakota group . . 
 
 Upper Cretaceous 
 I of N. J., Penn., 
 and Miss. 
 
 [ Chico. 
 
 Chalk. 
 Greensand. 
 
 Xeocomian. 
 
 ■ Comanche. 
 
 Raritan clays. 
 Potomac upper 
 part. 
 
 Shasta. 
 Mariposa. 
 
 Transition. 
 
 © 
 
 Potomac lowest 
 part. 
 
 Wealdeu. 
 
 Upper Jurassic. 
 
 Baptanodon beds. 
 
 Wanting. 
 
 Purbeck. 
 
 Life-System: Plants. 
 
 Leaf-impressions are very abundant in the American Cretaceous, 
 and the most cursory examination reveals at once a type of plants not 
 seen in any lower rocks, viz., Angiosperms, both Dicotyls and Palms. 
 
 Pig. 770. 
 
 Fio. 771. Fig. 772. 
 
 Fibs. 770-772. — Crbtacboits Plants, Dakota Group fafter Lesqnereux): 770. Llquidambar in- 
 tegrifollnm. 771. Lauras Nebrascensis. 772. Quercus primordialis. All reduced. 
 
492 
 
 MESOZOIO ERA— AGE OF REPTILES. 
 
 Fig. 7T7. 
 
 Figs. 773-777.— Cretaceous Plants, Dakota Group (after Lesquerenx): 773. Sassafras Mudgii. 
 774. Sassafras cretaceum var. 775. Salix proleEefolia. 776. Fagus polyclada. 777. Protophyllum 
 quadratum. All reduced. 
 
 We have said that the Sierra revolu tion at the end of the Jura- Trias 
 produced important changes in America. A great break in the record 
 occurs at this time in the region (the Plains) where these plants were 
 first found. When the record commences again in the Dakota epoch 
 we observe a very great difEerence in the subject-matter. The whole 
 aspect of field and forest must have been different and much more mod- 
 
CKETACEOUS PERIOD. 493 
 
 ern. Nearly all the genera of our modern trees are presentj^e. g., Oahs, 
 Maples, Willows, Sassafras, Dogwood, Hickory, Beech, Poplar, Tulip- 
 tree (Liriodendron), Walnut, Sycamore, Sweet-gum (Liquidambar), 
 Laurel, Myrtle, Mg, etc. Out of 460 species of plants found in the 
 Dakota group, about 400 species are Dicotyls (Ward) and at least half 
 of these belong to living genera (Lesquereux). And if we include 
 the Laramie in the Cretaceous we may add 236 more species to the list, 
 but these latter are quite different and more Tertiary in type. A few 
 Palms have also been found in Vancouver's Island. So fully were these 
 highest plants introduced here that although the Ceno^otc era com- 
 menced with the Tertiary, the Genophytic may be said to commence 
 with the Cretaceous.* 
 
 It is a noteworthy fact that many of the most characteristic Creta- 
 ceous genera, and those most abundant and varied in species at that 
 time, are now represented by only one or two species. For example, 
 there are now only one or two species of Sassafras ; two or three species 
 of Plane-tree ; one of Liriodendron ; and two of Liquidambar. These 
 are evidently the remnants of an extinct flora. 
 
 Origin of Dicotyls. — The appearance of these, the highest order of 
 plants, in fully differentiated forms, seems sudden and without pro- 
 genitors. But the obvious reason is, that where first discovered there 
 was a great loss of record. The gap is now filled by the discovery of 
 the Comanche group ; and in the lowest part of this group on the At- 
 lantic border (Potomac formation) have recently been found and de- 
 scribed by Fontaine over 700 species of plants mostly of Jurassic types 
 (Conifers, Cycads, and Ferns), but among them, and from the upper 
 part of the formation, 96 species of Dicotyls. These earliest known 
 Dicotyls (Figs. 778-783), though of very generalized character so far 
 as genera and families are concerned, are yet well-differentiated, unmis- 
 takable Dicotyls. We must, therefore, look still lower, i. e., in the Jura, 
 for their point of origin and for connecting links with other classes. 
 These important discoveries leave us still in doubt as to the class of pre- 
 viously existing plants from which they may have sprung. It is very 
 noteworthy, however, that certain curious leaves found in the Upper 
 Jura and Lower Cretaceous, and heretofore referred to Ferns, are be- 
 lieved by Saporta to have been those of ancestors of the Dicotyls, and 
 therefore called Pro-Angiosperms (Ward). It seems not impossible, 
 therefore, that the Dicotyls have come from the Ferns. 
 
 But if the highest plants, the Dicotyls, are abundant, so are also the 
 
 * As an explanation of the somewhat sudden appearance of Dicotyls it has been sug- 
 gested by Woodworth that in Jura times the Dicotyls occupied isolated highlands, the 
 richer plains being held by Mesozoic types by pre-emption right. ' Changing conditions 
 gradually gave the advantage to the Dicotyls, which then came down to the plains, where 
 their remains would be more likely to be preserved. 
 
494 
 
 MESOZOiC JiRA— AGE OF BEPTILES. 
 
 Flo. 778. 
 
 FiQ. 781. 
 
 Fig. 782. 
 
 Pigs. 778-782.— Plants or thb Potomac Formation (after Fontaine)— Cfwii/is?'*; 778. Baieropsia 
 foliosa 779. Sequoia ambisna: o, Leafy branch; 6, Cone. Dicotyledons: 780. Aralisepbyllttm 
 obtuBilobum, x \ 781. Hederaephyllum angulatum, x |. 782. Sassafras cretaceum, x j. 
 
CRETACEOUS AiTIMALS. 
 
 495 
 
 lowest Protophyles, or uni- 
 celled plants. Destnids and 
 Coccospheres are abundant in 
 the chalk of Europe. 
 
 Animals. 
 
 Protozoa. — As already 
 stated, chalk is made up al- 
 most wholly of shells of Fo- 
 raminifera (Rhizopods) and of 
 certain uni-celled plants. Ac- 
 cording to Ehrenberg, a cubic 
 inch often contains millions of 
 microscopic organisms. More 
 than 120 species of Foramin- 
 ifers have been found in the 
 English chalk alone. Some of 
 these seem to be species still 
 living in deep seas. These are 
 all extremely minute, but some 
 
 of larger size are found in the Cretaceous limestone of Texas, 
 from the chalk have already been given (pp. 487 and 488). 
 
 Sponges are extremely common in the chalk, as they are also in 
 deep-sea bottoms of the present day. About one hundred have been 
 found in the chalk. 
 
 Echinoderms. — The free Echinoderms are now for the first time in 
 excess of the stemmed. The Echinoids are especially abundant and 
 
 Via. 784. 
 
 Figs. 783, 784. — Cretaceous Sponges: 783. Siphonia 
 flciis. 784. Ventriculites simplex. 
 
 Those 
 
 Fig. 786. Fig- 787. 
 
 Pigs. 785-787.— Echinoidb of the Cretaoeous of Etibope: 785. Galerites albogalerue. 786. Dls- 
 coidea cylindrica. 787. Goniopygas major. 
 33 
 
496 
 
 MESOZOIO BRA— AGE OF REPTILES. 
 
 decidedly modern in type ; and in the chalk some genera are identical 
 with, and some species very similar to, those recently got from deep- 
 sea ooze. The above are from the European Cretaceous. 
 
 Fig. 788. 
 
 Pigs. 788, 789. 
 
 -Lamslubbanchs : 788. Tapes {Baroda) fragilis, d'Ort. sp. 
 Gosau, Austria. 789. Inoceramiis dim'idius (after White). 
 
 Fig. 789. 
 
 Upper Cretaceous, 
 
 MoUusks. — For the first time Lamelliiranchs are fairly in excess of 
 BracMopods. Among the latter the modern family of Terelratulm are 
 especially conspicuous. Among the former the most noteworthy fact 
 is the abundance of the Oyster family — Ostrea, Gryphoea, Exogyra, 
 etc. ; and the Avicula family, Avicula, Inoceratnus, etc., some of which 
 are of great size. We give some characteristic forms from the recently 
 established Comanche group (Figs. 790-795). 
 
 Two very strange and characteristic groups of bivalve-shells occur 
 here, and are very abundant, viz., the Eudistes or Hippuritidm and 
 the GhamidcB. In the former, one valve is small and often flat, while 
 the other is enormously elongated like a cow's horn or even extended 
 into fluted cylinders. In the latter one or both valves are elongated, 
 and often coiled in the manner of a ram's horn. We give some figures 
 
 Fig. 790. Fig. 791. 
 
 Figs. 790, 791,— C0MANCHESHELL3(afterWliite): 790. Grypliffia washitaensis. 791. Exogyra Texana. 
 
CRETACEOUS ANIMALS. 
 
 497 
 
 Fig. 792. 
 
 FiQ. 793. 
 
 PiQ. 794. Fig. 795. 
 
 Figs. 792-795.— Lower Cretaceou8 Shells (after White): 792. Ancella crassicoUis, Knoxville 
 group, Cal. 793. Aucella, side view. 794. Bequienia patagiata. 795. Eequienia Texana. 
 
 of these strange forms (796-799) from foreign localities and some (794 
 and 795) from our own country. 
 
 Among Oasteropods (Figs. 796-799), the beaked or siphonated 
 kinds are now for the first time abundant, as in the present seas. 
 
 Among Cephalopods the Ammonites and Bele?nnifes still continue 
 in great numbers and size, but they die out at the end of this period 
 forever. In the Cretaceous of the Western Plains some Ammonites 
 have been found over three feet in diameter (Dana). This family 
 seemed to have reached its culmination just before its extinction. But 
 what is still more remarkable is the introduction of many new genera 
 of very strange and unexpected forms. These are sometimes partly 
 uncoiled, as in ScapMtes (boat), Crioceras (ram's-horn), Toxoceras 
 (bow-horn), Ancyloceras (hook-horn), Hamites (hook) ; sometimes 
 
49S 
 
 MESOZOIC EBA— AGE OF REPTILES. 
 
 Fig. 796. 
 
 Fig. 797. 
 
 Fig. 
 
 Fia. 799. 
 
 Fias. 796-799.-796. Hippurites Toucaeiana, a large individual with two small ones attached (after 
 B'Orbigny). 797. Section of a Radiolites cylindriasus, showing structure. 798. Upper Valve of 
 Badiolites mammilaris. 799. Caprina adversa (after Woodward). 
 
 Fig. 800. 
 
 Fig. 802 
 
 Fig. 801. 
 
 Fioa. 800-802.— Cketaceous Gastekopods : 800. Lychnus matheroni, Eegnien Upper Cretaceous 
 (Garumnian), Eognac, Provence. 801. Anchura falciformis (after Gabb). 802. Scalaria Siln- 
 mani (after Owen). 
 
CRETACEOUS ANIMALS. 
 
 499 
 
 completely uncoiled, as in Baculites (walking-stick) ; sometimes coiled 
 spirally, like a Gasteropod, as in Turrilites and Helioceras. Belem- 
 nites (Fig. 810) also continue, though in diminishing numbers. 
 
 These strange forms have been likened by Agassiz to death-contor- 
 tions of the Ammonite family ; and such they really seem to be. They 
 
 Fig. 806. 
 
 Fiss. 803-809. — Cektaoeous Cbphalopods : 803. Schloenbachia Cbicoensis (after Gabb). ,804. 
 Scaphites seqaalis (after Pictet). 805. Criocerae, restored (after Pictet). 806. Helioceras 
 Eobertianns (after Pictet). 807. Ancyloceras percostatus, x i (after Gabb). 808. Baculites an- 
 ceps, X i (after Woodward). 809. Turrilites catenatus (after D'Orbigny). 
 
 are degenerate forms of a declining type. Prom the point of view of 
 evolution, it is natural to suppose that under the gradually-changing 
 conditions which evidently prevailed in Cretaceous times, this vigorous 
 MesozcJic type would be compelled to assume a great variety of forms, 
 in the vain attempt to adapt itself to the new environment, and thus 
 
500 
 
 MESOZOIC EEA— AGE OF REPTILES. 
 
 to escape its inevitable destiny. Tlie curve of its rise, culmination, 
 and decline, reached its highest point just before it was destroyed. 
 The wave of its evolution crested and broke into strange forms at the 
 moment of its dissolution. 
 
 Among Crustaceans, the Brachyurans, short-tailed Crustaceans 
 (crabs), which were barely introduced in the Jurassic, are here repre- 
 sented by several genera. 
 
 Vertebrates— Fishes. — In the development of this class some de- 
 cided steps in advance are here recorded. Placoids and Ganoids still 
 continue, but Teleosts, or true typical modern fishes, are here abim- 
 
 FiG. 810.— Belemnites impressus (after Gabb). 
 
 dant for the first time,* having appeared in the Jurassic, and some of 
 gigantic size. These earliest Teleosts were related to salmon, herring, 
 perch, pike, etc. Beryx, a genus still found in open seas, is found in 
 the Chalk of Europe and Upper Cretaceous of America. Among Blas- 
 mobraiichs, too, although the Cestracionts and Hybodonts continue (the 
 latter, however, passing out with the Cretaceous), the modern type, the 
 true sharks or Squalodonts, having lancet-shaped teeth, are for the 
 first time abundant. We give figures of Oestraciont (813) and Squalo- 
 dont (811) teeth, and also a tooth, natural size, of a gigantic pike, eight 
 feet long, from American Cretaceous, and a restoration of the same by 
 Cope ; also, two Teleosts from European Cretaceous. 
 
 Fia. 811. — Cretaceous ¥iBWBi—Masmobranchs: Otodus (after Leidy). 
 
 * Some geologists make Teleosts appear in Jura; most, how ever, regard these sup- 
 posed Teleosts as bomocercal Ganoids. 
 
CRETACEOUS ANIMALS. 
 
 601 
 
 Pio. 816. 
 Fios. 812-816.— Cretaceous ¥i%BES^Elasmobranc/LS ; 812. Ptychodus Mortoni (after Leidy). 
 TeUosts: 813. Portheus molossus— Tooth, natural size (after Cope). 814. Portheus, restored, 
 X 4s (after Cope). 815. Beryx Lewesiensis. 816. Osmeroides Mantelli. 
 
502 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 The Hybodonts were essentially a Mesozoic type ; the Squalodonts 
 are essentially Tertiary and modern. The two types coexist in the Cre- 
 taceous, the former passing out, the latter increasing, and finally dis- 
 placing the former. The accompanying f gure (Fig. 817) represents the 
 succession, rise, culmination, and decline of the three families of sharks. 
 
 Cope gives ninety-seven species of North American Cretaceous 
 fishes known in 1875. Of these, if we include the Chimera family, 
 
 Faleeozoic 
 
 Mesozoic 
 
 Cenozoic 
 
 Fio. 817.— Diagram representing the Distribution in Time of Placoids. 
 
 an aberrant type of sharks very common in the Cretaceous, forty-five 
 were Elasmohranchs. The rest are mostly Teleosts, for the Ganoids 
 are rapidly disappearing. In Europe twenty-five genera of Cycloids 
 and' fifteen of Ctenoids are found in the Cretaceous (Dana). 
 
 Reptiles. — This class seems to have culminated about the end of 
 the Jurassic or the beginning of the Cretaceous period. If their re- 
 mains are more abundant in the Jurassic in Europe, they are far more 
 abundant on the American continent in the various marine and lacus- 
 trine deposits regarded as Cretaceous. In fact, we had here in Amer- 
 ica during the Cretaceous an extraordinary abundance and variety of 
 reptilian life, including all the principal orders already mentioned, 
 viz., Enaliosaurs, Dinosaurs, Pterosaurs, and Crocodilians, and also 
 a new type, introduced in the Cretaceous for the first time, the Mosa- 
 saurs, wholly marine in habits, but of long and lizard-like form, and 
 attaining a length of twenty-five feet. Turtles were also found in 
 large numbers and of great size. We can mention only a very few 
 of the most remarkable of the Cretaceous reptiles. 
 
 PiQ. 818.— Teetli of Tracliodon (after teidy) : a. Pavement of Teetti ; * and c, Tootli separated. 
 
CRETACEOUS ANIMALS. 
 
 503 
 
 Among Enaliosaurs the Ichthyosaurus is not found in America, 
 but the PlesiosauridcB were abundant, and attained much greater size 
 than in Europe. Leidy describes one, the huge Elasmosaurus, of 
 Cope, which was fifty feet long, with a neck of sixty vertebrae and 
 twenty-two feet long. Among Dinosaurs the Trachodon from New 
 Jersey was twenty-eight feet long; and, judging from the huge 
 size of its hind-legs and massiveness of its hips and small size of its 
 fore-legs, it seems to have been able to stand and walk in the man- 
 ner of birds. This animal was a vegetable feeder, with teeth some- 
 what like those of the Iguanodon, but set in several rows, so as to 
 form a kind of tessellated pavement (Fig. 818). We give Fig. 819, 
 a restoration by Marsh, of an allied form from the European Creta- 
 ceous. In the New Jersey Cretaceous have been found also the Lcelaps, 
 which is very similar to the Megalosaur and twenty-four feet long, 
 
 Fig. 819.— Hypsilophodon (A) (restored by Marshj. 
 
 and the Ornithotarsus (bird-shank), thirty-five feet long, which stood 
 twelve to fifteen feet high when walking on their hind-legs. Among 
 Pterosaurs, Marsh has found in the Western Cretaceous the remains 
 of at least seven species, two of which were twenty feet in alar extent, 
 and another eighteen feet. 
 
 The American Pterosaurs differ from all other known Pterosaurs 
 in the fact, recently brought to light by Marsh, that their jaws were 
 entirely toothless, and probably sheathed with horn, as in birds. They 
 belong in three genera, Eteranodon, Nyctodactylus, and Dermodacty- 
 lus. They are closely related to Pterodactylus and are grouped in 
 the same sub-order by Williston, and partly in the same family. One 
 
504 
 
 MESOZOIO ERA— AGE OF REPTILES. 
 
 {Tb 
 
 /* 
 
 'm 
 
 Vs 
 
CRETACEOUS ANIMALS. 
 
 505 
 
 of them, Pteranodon ingens, had toothless jaws four feet long, and 
 an expanse of wing of more than twenty-two feet. 
 
 Among the many Chelonians (turtles) found in the Cretaceous of 
 the Western Plains, of the Rocky Mountain region, and of New Jer- 
 sey, one, the Atlantochelys gigas, had a length of nearly thirteen feet, 
 and a breadth across the extended flippers of fifteen feet (Cope). The 
 structure of this huge turtle was singularly embryonic. The flattened 
 ribs, which by their coalescence make the greater part of a shell of a 
 turtle, were in this species, as in the embryo of modern turtles, not yet 
 coalesced. 
 
 But the most remarkable and characteristic reptiles found in the 
 
 
 \C^ 
 
 ^i>xix- 
 
 FiG. 823.— Head of a Tylosaurus proriger (after Merriam). 
 
 Cretaceous are the Mosasaurs {Pythonomorpha of Cope). The first 
 specimen of the order was found in Europe, on the river Meuse, and 
 
 ._v 
 
 Fig. 834.— X. Scapular arch and fore-limbs of Plattcarpus simus (after Marsh), seen from below, 
 one sixteenth natural size, with outline of sternum from Clidastes. B. Pelvic arch and hind- 
 limbs of Platecarpus simus, seen from below. One twelfth natural size. U, ilium ; pb, pubis; 
 U, ischium; /, femur; t, tibia; f\ fibula; mt, metatarsal. The paddles are represented as hori- 
 zontal, and the bones of the arches are somewhat displaced to bring them into the same plane. 
 
506 MESOZOIC ERA— AGE OF REPTILES. 
 
 hence the name Mosasaurs ; but they seem to have been far more abun- 
 dant in America. At least fifty species (Cope) have been found in 
 the Cretaceous of New Jersey, the Gulf States, and Kansas. Of these, 
 the Mosasaurus.princeps was twenty to thirty feet long, and Tylo- 
 saurus (Liodon) dyspelor probably was about the same length, twen- 
 ty-five feet. These reptiles seemed to have united the long form of 
 the crocodile, and the short, strong, well-fingered paddles of the whale, 
 with the essential characters of a lizard. Another snake-like charac- 
 ter possessed by this order was rows of teeth on the pterygoid bones, 
 in addition to those in the jaws; and a peculiar joint in the lower 
 jaws, by means of which, when aided by the recurved teeth, the jaws 
 could act separately like arms, in dragging down their throats prey 
 which was too large to swallow directly (Fig. 835). 
 
 Fio. 885.— Jaw of a Clidaetes, x J (after Cope). 
 
 The number of species are yearly increasing by new discoveries. 
 The remains of at least fourteen hundred individuals of Mosasauroids 
 alone are in Marsh's collection. 
 
 According to Cope, 117 species of reptiles have been described 
 from the Cretaceous of North America, of which twenty are Mosa- 
 saurs, forty-eight Testudinata (turtles'and tortoises), eighteen Dino- 
 saurs, fourteen Crocodilians, thirteen Sauropterygia (Plesiosaur- 
 like), and four Pterosaurs. At least three more Pterosaurs have 
 been found, making the whole-number seven (Marsh). 
 
 In Europe, Iguanodons, Teleosaurs, Ichthyosaurs, Plesiosaurs, and 
 Pterosaurs still continue in the Cretaceous, some of the last being 
 twenty feet in expanse of wing; Mosasaurs were also introduced. 
 
 Birds. — The history of the discovery of the earlier fossil birds is 
 instructive. Until 1858, with the exception of the doubtful tracks in 
 the Connecticut River sandstone, no birds had been found lower than 
 the Tertiary. In that year the bones of a bird, probably related to the 
 gull, were found in the upper greensand of England. In 1861 the won- 
 derful reptilian hiTiArchceopteryx macroMra^alreadydescribed(p.462), 
 was foimd in the Solenhofen limestone of Germany (Upper Jurassic). 
 In 1870, and subsequently, Marsh discovered in the Cretaceous of New 
 Jersey and Kansas about twenty species of birds. Those from New Jer- 
 sey were from the Uppermost Cretaceous (Foxhill group), and are 
 probably true birds — waders and swimmers — though not of the higher 
 
CRETACEOUS ANIMALS. 
 
 507 
 
 orders. Those from Kansas are from a lower horizon (Colorada 
 group), and are all wonderful, toothed birds, entirely different from 
 any existing order. With the exception of the Archaeopteryx, these 
 are the most extraordinary birds yet discovered. Some of them, be- 
 longing to the two genera Ichthyornis and Apatornis, may have been, 
 partly at least, without the horny beak so characteristic of existing 
 birds, but instead had thin, long, slender jaws, furnished with many 
 sharp, conical teeth, set in sockets, twenty on each side below, and some- 
 
 Fi6. 826.— Kestoration of Ichthyornis victor {after Marsh). One third natural size. 
 
 what fewer above (Fig. 836). The edentulous anterior part was prob- 
 ably covered with horn. Their vertebra? were amphiccelous or bi- 
 concave, as in fishes and many extinct reptiles, but in no modern bird 
 
508 
 
 MESOZOIC EKA— AGE OF REPTILES. 
 
 (Fig. 828). Like modern birds, however, they had a keel on the 
 breast-bone for the attachment of the powerful muscles of flight. The 
 
 Fia. 828. 
 
 Fig. 830. 
 
 Fig. 831. 
 
 Fig. 837. 
 Figs. 837-831.— Odoktobnithus (after Marsh) 
 
 Fig. 829. 
 
 837. Lower Jaw of Tchthyomis dispar. x 2. 828. 
 Cervical Vertebra of same, x 2. 829. Lower Jaw of Hesperornis regalis, x J. 830. Dorsal Ver- 
 tebra, X J. 831. Tooth of same, x 2. 
 
 tail also is worthy of attention, being not like that of the Jurassic 
 Archaeopteryx, but much shorter and not so reptilian (Marsh). These 
 birds were about the size of a pigeon, and were evidently powerful 
 fliersi Pig. 826 is a restoration by Marsh of one of this type. The 
 other toothed birds had similar jaws, but their teeth were set in grooves 
 
CRETACEOUS ANIMALS. 509 
 
 instead of distinct sockets (Fig. 839), and they differed also in having 
 no keel and in having ordinary bird-vertebrfe (Fig. 830). These were 
 evidently divers, and incapable of flight. Two of them — Hesperornis 
 regalis and Hesperornis crassipes — were of gigantic size, being from 
 five to six feet from snout to toe. In the accompanying figure (Fig. 
 832) we give a restoration by Marsh of one of these remarkable birds. 
 
 PiQ. 832.— Hesperornis regalis, x ^ (restored by Mareh). 
 
 The anterior toothless part of the beak was probably horny. In these 
 birds, therefore, we have the most extraordinary combination of bird 
 characters with reptilian and. fish characters. So extraordinary and 
 exceptional is this combination of characters, that Marsh placed them 
 in a new sub-class, Odontornithes {toothed birds). Later authorities * 
 do not consider the presence of teeth as of such over-balancing im- 
 portance in classification, but retain, however, Marsh's orders, Odon- 
 tolca (teeth in grooves), represented by Hesperornis, and Odontor- 
 mce (teeth in sockets), represented by IcMliyornis, as super-orders of 
 
 * See chapter on Aves by F. A. Lucas, in Zittel's Palaeontology, vol. ii. Translation 
 and revision by 0. E. Eastman. 
 
510 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 the sub-class (2) Ornithurce. Archmopteryx now stands alone as 
 representing a sub-class (1) Saururm (reptile-tailed). Exceptional 
 as these characters may seem, they are just what the law of evolution 
 would lead us to expect in the earliest birds. As already stated (p. 
 473), this branch had not yet been fairly separated from the reptilian 
 stem. It is a noteworthy fact that these toothed birds lived at the 
 same time and in the same localities with the toothless Pterosaurs 
 mentioned on page 503. 
 
 It is well to observe. that in the earliest representatives of each 
 class the brain is relatively very small. This is true of reptiles, birds, 
 and mammals, as Marsh has sho.wn. We give below figures taken 
 
 from Marsh, showing the rela- 
 tive size of the brain in living 
 and Cretaceous birds. 
 
 Mammals. — For many years 
 after mammals were known from 
 the Triassic and Jurassic none 
 were knovni from the Cretaceous. 
 It was certain that they existed 
 then, for mammals of the same 
 nature. Marsupials, lived in the 
 Tertiary of both Europe and 
 America, and still exist in Aus- 
 tralia and elsewhere; and it is a 
 well-established law in Palaeon- 
 tology that if a type becomes ex- 
 tinct it never reappears: Evolu- 
 tion never goes backward: Na- 
 ture never repeats herself. Mam- 
 mals are now found in the Cre- 
 taceous in greater numbers and 
 variety than in the Jurassic, but 
 nearly all of small size. They 
 occur in both Europe and Amer- 
 ica, especially at the base of the 
 Cretaceous and in the uppermost 
 or Laramie beds, and only in 
 fresh-water deposits. The lower 
 Cretaceous remains are fragmentary, and similar to those in the 
 Jurassic. 
 
 Continuity of the Chalk. 
 The deep Atlantic bottom, where chalk is now forming, is perhaps 
 continuous with the chalk of England and Europe. In other words, in 
 Cretaceous times a deep sea ran from the mid-Atlantic far into what 
 
 Fig. &33. Fib. 834. 
 
 PiGB. 833, 834.-833. Outline of the skull and brain 
 cavity of Ichtbyomis victor (after Marsh), seen 
 from above. Five sixths natural size. 834. 
 Outline of the skull and brain-cavity of Sterna 
 cantiaca (after Gmelin), same view. Natural 
 size. 0^, olfactory lobes; c, cerebral hemi- 
 spheres ; op, optic lobes ; cd, cerebellum. 
 
CONTINUITY OF THE CHALK. 
 
 611 
 
 is now Central Europe, and in the whole of this deep sea chalk was 
 then formed. At the end of the Cretaceous period the eastern part 
 was raised and formed a portion of Europe, while the rest remained 
 as deep-sea bottom, and continued to make chalk until now. Thus 
 there is no doubt that in the deep Atlantic, o£E the coast of Europe, 
 there has been an unbroken continuity of chalk-making from the 
 Cretaceous times until nozv. But we have seen (p. 495) that many of 
 the living deep-sea species are identical with, and nearly all extremely 
 similar to, those found in the chalk of Cretaceous times. Thus there 
 has been not only a continuity of chalk-formation, but also to some 
 extent of the chalk-fauna, to the present time. 
 
 These facts were certainly unexpected, but, so far from shaking the 
 foundations of geological science, as some have imagined, they are in 
 perfect accordance with the fundamental principles of geological suc- 
 cession properly understood ; as we now proceed to show : 
 
 1. The facts of identity have been exaggerated. Many of the 
 Foraminifera only are identical. Among Echinoderms the identity 
 is generic, not specific. 2. In comparing higher with lower species, 
 we find that the lower species are widely distributed both in space 
 (geographically) and in time (geologically), and that the continuance 
 or range in time becomes less and less in proportion as we rise in the 
 scale. Fig. 835 is constructed to illustrate this point ; we see that liv- 
 
 CKETACEOUS 
 
 T E R T / A B 
 
 rqUATERNARV 
 
 EOCENE |IVIIOCENE. [PL/OCCNC |6LiHC | CHAM. | TER 
 
 RECENT 
 
 Fio. 835.— Diagram illustrating the Belative Duration of Lower and Higher Species. 
 
 ing species of mammals extend back only a little way into the Quater- 
 nary, living species of moUusks back to the beginning of the Tertiary, 
 while living species of Foraminifera, as we might expect, extend back 
 into the Cretaceous. 3. There is a necessary relation between fauna 
 and external conditions. Changes in the latter determine correspond- 
 ing changes in the former. Now, deep-sea conditions are evidently 
 far less subject to change — far more continuous — than shallow-water 
 and land conditions. For this reason, we should expect deep-sea faunas 
 to change very slowly. 4. But this can not affect the geological chro- 
 nology, because this chronology rests almost wholly on the remains of 
 shallow-water and land animals. Chalk is the only profound sea- 
 bottom formation certainly known. It is, therefore, wholly exceptional. 
 S4 
 
512 MESOZOIC ERA— AGE OF REPTILES. 
 
 ' 5. The reason it is exceptional is that, as a broad general fact, the pres- 
 ent continents have been, through all geological times, steadily heaved 
 upward out of the ocean, growing larger and higher ; and, therefore, 
 the successive additions have been nearly always- shallow marginal 
 bottoms and shallow interior seas. That the exception should occur in 
 Europe more than in America, too, is in keeping with the general 
 character of the development of the European as contrasted with the 
 American Continent. Chalk is also found in Texas, Kansas, and north- 
 ward ; but here also was a deep interior sea, an extension of the Mexi- 
 can Grulf. 6. Conversely, the fact that chalk is so exceptional is proof 
 of the development of continents as indicated under the last head — 
 proof that, as a general fact, the great inequalities of the earth's crust, 
 which constitute land-surfaces and sea-bottoms, have remained sub- 
 stantially unchanged in position from the first, while steadily increas- 
 ing in vertical dimensions. 
 
 General Observations on the Mesozoic. 
 
 The Mesozoic, and especially the Jurassic, is characterized by the 
 culmination of two great classes of animals, viz., Gephalopod Molluslcs 
 and Reptiles, and one of plants, the Cycads. This is shown in the dia- 
 gram on page 294. The culmination of reptiles is, of course, its most 
 distinguishing characteristic. That it was pre-eminently an age of 
 Eeptiles, may be shown by a comparison of its reptilian fauna with 
 that of the present day. There are now, on the whole face of the 
 earth, only six or seven large reptiles over fifteen feet long — two or 
 three in India, one in Africa, three in America — and none over twenty- 
 five feet long. In the Wealden and Lower Cretaceous of Great Britain 
 alone there were sixteen great Dinosaurs, several twenty to fifty feet 
 long, ten to twelve Orocodilians and Enaliosaurs ten to fifty feet 
 long, besides Pterodactyls, turtles, etc. (Dana). Again, in the Cre- 
 taceous of the United States alone the fullness of reptilian life was 
 even greater; for 150 species of reptiles have been found, most of 
 them of gigantic size. Among these were twenty species of Mosa- 
 saurs, some twenty to thirty feet long ; many huge Dinosaurs, twenty 
 to fifty feet long; besides Enaliosaurs, Pterosaurs, and gigantic tur- 
 tles (Cope). These are preserved! But the known fossil fauna of 
 any period is but a fragment of the actual fauna of that period. Not 
 only did reptiles greatly predominate, but the age seemed to impress 
 its reptilian character on all other higher animals existing at that 
 time. The birds were reptilian birds, the mammals were reptilian 
 mammals. The mammals were doubtless semi-oviparous (marsu- 
 piajs). The Ichthyosaurs and possibly the Dinosaurs were viviparous. 
 
 That the climate was then warm and uniform is sufficiently attested 
 by the character of the fauna and flora. All great reptiles and all Cy- 
 
LARAMIE, OR TRANSITION EPOCH. 513 
 
 cads and Tree-ferns are found now only in tropical or sub-tropical re- 
 gions. This tropical fauna and flora were substantially similar in all 
 latitudes in which the strata have been found — even as far north as 
 Spitzbergen (Nordenskiold) * and to Exmouth Island, 77° (Dana). 
 During the latter portion of the Cretaceous period, as indicated by the 
 abundance of deciduous Dicotyls, the climate of North America had 
 become cooler, being about 8° or 10° warmer than now. Temperature 
 zones seem to begin to appear first in the Eocene. 
 
 Disturbance which closed the Mesozoic— Rocky Mountain Revolu- 
 tion. — The disturbance which in America closed the Cretaceous period 
 and the Mesozoic era was an arching of the earth's crust over the whole 
 Plains and Plateau region, by which the great interior Cretaceous sea, 
 which previously divided America into two continents, was abolished, 
 ,and the continent became one. At the same time the Wahsatch and 
 Uintah Mountains were principally formed, and the eastern Eocky 
 Mountain range greatly elevated. As the Paleeozoic closed with the 
 Appalachian revolution, so the Mesozoic closed with what may be called 
 the Rocky Mountain revolution. The disturbance, as usual with those 
 which close an era, was probably to some extent oscillatory — i. e., the 
 continent was probably higher and cooler during the latter part of the 
 Cretaceous than during the subsequent Eocene. The change of physi- 
 cal geography was enormous, and the change of climate was doubtless 
 correspondingly great. We ought to be prepared, therefore, to find, 
 with the opening of the next era, a very great change in the organ- 
 isms. 
 
 Laramie, or Transition Epoch. 
 
 In the schedule on page 491, we have indicated a transition epoch 
 called the Laramie. There has been much controversy about the true 
 position of these strata. Some have put them in the Tertiary, some in 
 the Cretaceous, and some have regarded them as completely transitional 
 between the two ; while still others would solve the difficulty by assigning 
 the lower part to the Cretaceous and the upper part to the Tertiary. 
 Stratigraphically the Laramie is continuous with the Cretaceous below, 
 and in some places also with the Tertiary above ; so that the Creta- 
 ceous of the West in some places gradates through the Laramie into the 
 Tertiary without any break in the strata, f The difficulty of drawing 
 the line of separation on palseontological grounds is equally great. 
 The plants are decidedly Tertiary in general aspect, but the animals, 
 especially the land-animals, are as decidedly Cretaceous; the shells 
 meanwhile have changed from marine and 'brackish-water into f resh- 
 
 * Geological Magazine, November, 1875. 
 
 f In California the Tojon group seema to fofm a complete transition, but farther 
 north it is found that there is a break representing the entire Laramie and the lowest 
 Eoceile. 
 
514 
 
 MESOZOIC ERA— AGE OF REPTILEa 
 
 water forms. Cretaceous Dinosaurs still linger, but Tertiary types of 
 Plants have already taken possession. Many palaeobotanists claim it 
 
 for Tertiary. Nearly 
 all palaeozoologists put 
 it in the Cretaceous. 
 There is little doubt 
 that it is really transi- 
 tional, although prob- 
 ably more closely allied 
 with the Cretaceous. 
 
 The explanation of 
 these facts is obvious : 
 We have seen that at 
 the end of the Creta- 
 ceous the great interior 
 Cretaceous sea was 
 abolished by elevation, 
 and its place (as we 
 shall see hereafter) was 
 partly occupied by 
 great fresh-water lakes. 
 Now, this change took 
 
 B'iG. 837. Fia. 
 
 Pigs. 836-838.— 836. Aralia digitata. 837. Leguminositis arachioides. 838. Popnlus cnneata. 
 
 place somewhat gradually, the oceanic condition passing into the lake- 
 condition through an intermediate brackish- water condition of isolated 
 seas, the sedimentation going on all the time. While oceanic condi- 
 
LAEAMIE, OK TRANSITION EPOCH. 
 
 515 
 
 tions prevailed, the deposits are undoubtedly Cretaceous. When lake- 
 conditions are fairly established, they are undoubtedly Tertiary; the 
 intermediate brackish-water deposits are the Laramie. But, as the 
 change was gradual and the sedimentation continuous, of course the 
 strata were in places conformable throughout. Thus, then, the Creta- 
 ceous was before, the Tertiary after, and the Laramie during, the Eocky 
 Mountain revolution. 
 
 In regard, to the Life-system the explanation is similar. The aboli- 
 tion of the interior Cretaceous sea and the unification of the continent 
 was a great event, and produced very great change in physical condi- 
 tions. There was, therefore, a corresponding change in the Life-sys- 
 tem. But this was also gradual. The Cretaceous Dinosaurs still lin- 
 gered, ready to disappear; but as new land appeared it was taken 
 possession of by new types of Plants, probably migrated from the 
 north : and thus Cretaceous land-animals and Tertiary land-plants ex- 
 isted side by side. The beds contain marine vertebrates along with 
 reptiles, birds, and mammals of the land; and there is a commingling 
 of marine and fresh-water invertebrates. Meanwhile the marine shells 
 by changing conditions were destroyed. 
 
 Fig. 839. Fig. 840. 
 
 Figs. 839, 840.— 839. Viburnum Newbeirianum. 840. Alnue Grewiopsis. 
 
 Such transition strata are of especial interest, and deserve separate 
 treatment in order to emphasize their transitional character. 
 
 Area. — Prom what is said above it is evident that the Laramie ex- 
 
516 MESOZOIC ERA— AGE OF REPTILES. 
 
 ists over very wide areas in the region of the interior Cretaceous sea, 
 but it is largely covered by' Tertiary lake deposits. It is, however, 
 exposed along the eastern base of the Colorado mountains, from 
 New Mexico northward into British America; also in the Laramie 
 plains, where it is traversed by ]the Union Pacific Railroad. This is 
 the typical locality from which it takes its name. In the typical 
 locality, on the Laramie plains, the strata are several thousand feet 
 thick. It represents, therefore, a long period of time. On the Pa- 
 cific coast, a part at least of the Tejon group, and also the principal 
 coal-fields of California, Washington, and British Columbia, are now 
 regarded as Tertiary. 
 
 Life-System — Plants. — The vegetation was very abundant, and 
 the plants had already assumed a Tertiary aspect. About 323 species 
 of plants are known, of which 336 species are Dicotyls. We give a 
 few illustrations of these from Ward (Pigs. 836-840). 
 
 Coal. — As the Palaeozoic, so also the Mesozoie closes with a great 
 coal period (Dana). Conditions seem to have been again favorable 
 for the accumulation and preservation of the abundant vegetation. 
 Next to the Carboniferous, by far the largest coal-fields of the United 
 States and of British America belong to the Cretaceous, and especially 
 to this horizon. The most important of these Cretaceous coals are 
 the following : 1. A large field along the eastern base of the Front 
 range of mountains in Colorado. 3. Another valuable field in New 
 Mexico, of almost equal size. 3. Still another of greater size in Dako- 
 ta, and extending northward far into British America. These are, all 
 of them, on the Plains. 4. On the Plateau a valuable field covers 
 nearly the whole of the Laramie plains in Wyoming, and stretch- 
 ing to the border of Utah. The area of these coal-fields of the 
 Plains and Plateau region is not known, but must be enormous. 
 Some of the fields are also of extraordinary richness, the seams being 
 often fifteen to twenty feet thick. They almost rival the great fields 
 of the Carboniferous, already described. On the Pacific harder there 
 are several fields, which belong to the Cretaceous and early Tertiary. 
 1. Monte Diablo and Corral Hollow coal-field in California. 3. 
 Seattle, Carbon Hill, and Bellingham Bay coals of Washington. 3. 
 Nanaimo or Wellington coals of Vancouver's Island, British Colum- 
 bia. This last, however, probably belongs to the Cretaceous proper, 
 not to the Laramie. 
 
 Cretaceous coal occurs also in other countries in large quantities, 
 especially in Northern France and in China. 
 
 It is usual to call all these later coals Lignite's, and to imagine that 
 they are very inferior; but much of the Laramie coal is of good 
 quality, and hardly distinguishable in appearance from coal of the 
 Carboniferous age. 
 
LAEAMIE, OR TRANSITION EPOCH. 
 
 51Y 
 
 Animals. — We give a few characteristic shells, taken from White 
 (Figs. 841-844) ; but the greatest interest centers in the Dinosaurs, 
 
 Fig. 841. 
 
 Fig. 844. 
 
 Fig. 843. 
 
 Figs. 841-844 ^Lakamie Shells (after White): 841. Unio HolmesianuR. 842. Corbicula fracta. 
 
 843. Melania Wyomingensis. 844. Viviparas trochiformis. 
 
 and especially the recently discovered mammals of this epoch. As we 
 have already said, the Dinosaurs still continued to linger, but under 
 rapidly changing conditions, and ready to disappear. And here, again, 
 as in the case of Ammonites (p. 499), we observe that the last survivors 
 take on strange and grotesque forms. In this class, also, as in the case 
 of Ammonites, the wave of evolution crested a,nd broke into strange 
 forms at the moment of its dissolution. The most remarkable of all 
 Dinosaurs were the different species of Triceratops (three-horned face, 
 ,Fig. 845). This genus was characterized by the possession of two 
 
 Fig. 845.— Triceratope prorsus (after Marsh;, x ^, Cretaceous, Wyoming. 
 
 enormous horns, three feet long and six inches in diameter on the 
 frontal bones, and one of smaller size on the nose ; and by a large oc- 
 cipital crest projecting backward and outward and curving downward, 
 
518 
 
 MESOZOIC ERA— AGE OF REPTILES. 
 
 and fringed around with short horns somewhat in the manner of the 
 horned lizard (Phrynosoma) . The end of the snout also was tooth- 
 less, and covered with horn forming a beak. A head of one of these 
 has been found more than six feet long and four feet wide, and an- 
 
 FiG. 846.— Trachodon mirabilis, x ^ (after Cope). 
 
 other Over eight feet long. Of all reptiles this was probably the most 
 beast-like in its tread. 
 
 Another strange Dinosaur of this time was the Trachodon mira- 
 bilis of Leidy, a head of which is given in Fig. 846 and a restoration 
 by Marsh of another similar genus in Fig. 847. This was a huge 
 bipedal herbivore, thirty feet long, and head 
 three and a half feet, with curious spoon-bill-like 
 beak and magazines of numerous teeth (two thou- 
 sand in all), somewhat like those of the Hadro- 
 saur already described (p. 503). 
 
 Mammals. — The gap between the Ju- 
 rassic and Tertiary mammals men- 
 tioned on page 510 was, in 1889, 
 partly filled by the discovery by 
 Marsh of a considerable number 
 of species of 
 mammals from 
 the Laramie. The 
 teeth of two of the 
 most characteristic 
 species are given 
 in Figs. 848 and 849. These very important discoveries of Marsh 
 were supposed to be unique. But in 1890 Lemoine found at Cernay, 
 France, a mammalian fauna iu which Metatheres and monotremes, 
 extremely similar to those of the Laramie, are associated with 
 Eutheres characteristic of the lowest Tertiary (Puerco-beds).* Thus 
 the connection of the Laramie with the Tertiary is made still closer. 
 Nevertheless a gap still remains; we still look in vain for the im- 
 mediate progenitors of the Tertiary mammals. They will doubtless 
 
 Fig. 847.— Claosaurus annectens (after Marsh), x ^, Laramie, Wyoming. 
 
 Bulletin, Geological Society of France, vol. xviii, pp. 219, 321 (1890). 
 
CENOZOrc ERA— AGE OF MAMMALS. 
 
 519 
 
 Fio. 848. 
 
 FiQ. 849. 
 
 Figs. 848 and 849.— Laramie Mammals (after Marsh): 848. Cimolomys gracilis, x 3. 849. Halodon 
 
 Bculptus, X 2, 
 
 yet be found in the Cretaceous and probably in the Laramie of this or 
 possibly some other country, from which they migrated at the begin- 
 ning of the Tertiary. 
 
 CHAPTER V. 
 CENOZOIC ERA—AQM OF MAMMALS. 
 
 This deserves the rank of a distinct era, and the corresponding 
 rocks that of a distinct system, because there is here a great break in 
 the rock-system, and a still greater break in the life-system. Between 
 the rocks of the Cretaceous and Tertiary there is, in Europe, almost 
 universal unconformity. In America the unconformity is not so 
 pronounced, and the Laramie seems to be a transition series. But 
 the Mesozoic ended with great mountain-making and volcanic dis- 
 turbances, on a much vaster scale than the closing of the Palaeozoic. 
 Yet here, no less than in Europe,, there is at a certain horizon a 
 rapid and most extraordinary change in the life-system. " This it 
 seems impossible to explain on the -theory of evolution unless we 
 admit periods of rapid evolution. The reason why there is no gen- 
 eral unconformity in America is, evidently, that the movement here 
 was continental. Such continental movements, however, would pro- 
 duce great changes in climate, and therefore in organic forms. The 
 end of the Jurassic was a period of mountain-making, and therefore 
 of unconformity — the end of the Cretaceous, pre-eminently a time 
 of continent-making, with superposed mountain-making and great 
 change of climate. Therefore, although the interval lost in America 
 seems greater at the end of the Jurassic, the change of fauna and 
 flora was far greater at the end of the Cretaceous. 
 
 General Characteristics of ithe Cenozoic Era.— As indicated by the 
 name, modern history commences here ; modern types were introduced 
 
520 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 or became predominant ; the present aspect of field and forest com- 
 mences, and the present adjustment of the relations of the great classes 
 and orders was established. Then, as now, the rulers of the seas were 
 great sharks and whales ; the rulers of the land, mammalian quadru- 
 peds ; and the rulers of the air, birds and bats. Many of the genera 
 and some of the species of both animals and plants were identical with 
 those still living. The dominant class becomes now Mammals : Eep- 
 tiles, therefore, in accordance with a necessary law, decrease in size and 
 number, and thus find safety in a subordinate position. In some of 
 these characteristics the Cenozoic era was anticipated in the Upper 
 Cretaceous, in accordance with the law that the first beginnings of each 
 age is in the preceding age. 
 
 Divisions. — The Cenozoic era, or age of Mammals, embraces two 
 periods, viz. : 1. The Tertiary, and 3. The Quaternary. In the Ter- 
 tiary all the mammals are now wholly extinct, but the invertebrate 
 species are some of them still living, and an increasing percentage of 
 living species appears as time progresses. In the Quaternary most, 
 though not all, of the mammalian species are extinct, but nearly all 
 (ninety- five or more per cent) of the invertebrate species are living. 
 
 Fig. 850.— Diagram illustrating tlie Relative Duration of Lower and Higher Species. 
 
 These facts are graphically represented in the following diagram, in 
 which the curved ascending lines are the lines of appearance of living 
 species, and of extinction of extinct species of Foraminifera, of mol- 
 luscous shells and of mammals. In each case the lower shaded space 
 represents living species appearing in small numbers, and increasing 
 with the progress of time; and the upper unshaded or less shaded 
 space, previous species gradually dying out and becoming extinct. It 
 is seen that living species of Foraminifera commenced in the Creta- 
 ceous, and very steadily increased in number; those of shells com- 
 menced in the earliest Tertiary, and increased somewhat more rapidly ; 
 while those of mammals commenced only in the Quaternary, and in- 
 creased correspondingly rapidly. Also the relative proportion of living 
 and extinct at any time is shown by comparing the amount of space 
 above and below the line at that time. Also the relative range in time 
 of low and high species, and the amount of overlapping of successive 
 faunae are shown. 
 
TERTIARY PERIOD. 521 
 
 The mammalian class probably culminated near the end of the Ter- 
 tiary or during the Quaternary period. 
 
 Sectiok 1. — Tertiary Period. 
 
 Subdivisions. — We have already stated that the general differential 
 characteristic of this period, as compared with the next, is that all the 
 mammals, and most of the invertebrates, are extinct ; but of the latter 
 a percentage, small at first but increasing with the progress of time, 
 are still living. It is upon this percentage of living shells that Lyell 
 has based his division of the Tertiary period into three epochs — a 
 Lower, Middle, and Upper Tertiary, or Eocene, Miocene, and Pliocene. 
 
 Tertiary period. 
 
 Pliocene epoch, or Upper Tertiary = 60-90 per cent living shells. 
 Miocene epoch, or Middle Tertiary = 30 per cent living shells. 
 Eocene epoch, or Lower Tertiary = 6-10 per cent living shells.* 
 
 These percentages are expressed graphically in the diagram, Fig. 
 850. In these, as in the strata of all periods, however, there are cer- 
 tain characteristic species by which the epoch may be known, without 
 counting the number of species and calculating the percentage of liv- 
 ing. When mammalian species are found, these are especially charac- 
 teristic of the epoch. 
 
 Rock-System— Area in the United States.— On the Atlantic border, 
 going southward, there is no Tertiary, except a small patch on Martha's 
 Vineyard, off the coast of Massachusetts, and another on Long Island, 
 until we reach New Jersey. From this point southward the Tertiary 
 is a broad strip, about one hundred miles wide, bordering the coast, 
 and shown on the map (p. 303) by the space shaded with oblique lines 
 running to the right. It constitutes the low-countries of the Southern 
 Atlantic States. At its junction with the metamorphic region of the 
 up-countries, there are in nearly all the rivers cascades which determine 
 the head of navigation. Here, therefore, are situated many important 
 towns — e. g., Richmond, Virginia ; Raleigh, North Carolina ; Colum- 
 bia, South Carolina; Augusta, Milledgeville, and Macon, Georgia. 
 This has been called the Fall-line. The same strip of flat lands' 
 borders also the Gulf, expands, in the region of the Mississippi River, 
 northward to the mouth of the Ohio, and then continues around the 
 western border of the G-ulf. In the Gulf-border region, however, the 
 Tertiary is in contact below with the Cretaceous, instead of with 
 Archaean, as on the Atlantic border. This whole Atlantic-border and 
 Gulf-border Tertiary is, of course, a marine deposit. 
 
 * A series of marine strata in Europe, called Ohgocene, lie between the Eocene and 
 Miocene. In America no marine beds are yet identified, but the White River and other 
 lake deposits are referred to this epoch. 
 
522 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 In the interior, on the Plains and in the Eocky Mountain region, 
 there are enormous areas of fresh-water deposit of all epochs, Eocene 
 to Pliocene, which are of extreme interest (Fig, 853). 
 
 Among the Eocene basins the most remarkable are : 1. The Green 
 Eiver basin. 2. The Uintah basin. Both of these are on the east 
 side of the Wahsatch Mountains, and separated from each other by the 
 Uintah Mountains, one being north and the other south of that range. 
 They were possibly once united, but now separated by erosion. The 
 strata of the Green Kiver basin are 6,000 to 8,000 feet thick. 
 
 The White River basinj in Nebraska, is Oligocene. 
 
 Among the Miocene basins the most interesting are : 1. The John 
 Day lasin, of Oregon. This latter is 5,000 feet thick, but is largely 
 overlaid by the great lava-flood of the Northwest. 2. Loup Fork beds 
 or Niobrara basin, occupying partly the same locality as the Miocene 
 White River basin, but more extensive, reaching southward in patches 
 almost to the Gulf. 3. Patches of Miocene scattered about in Nevada 
 and California are of somewhat doubtful age. 
 
 Of Pliocene basins : 1. In Oregon also there is a Pliocene basin, 
 occupying partly the same region as the previous Miocene. 2. An- 
 other discovered by Cope in the basin of the Rio Grande. 3. Accord- 
 
 Fio. 851.— Big Bad Lands, South Dakota. View from Wounded Knee battle-fleld, looliing toward 
 Sheep Mountain. (Photograph by Barbour.) 
 
 ing to King, the Oregon and Nevada lake-deposit was in Pliocene 
 time greatly extended, so as to cover the whole Basin region, but has 
 been largely removed by erosion or covered by Quaternary deposits. 
 
 All these deposits are imperfectly lithified sand and clays in nearly 
 horizontal position, and many of them have been worn by erosive agen- 
 
TERTIARY PERIOD. 523 
 
 cies in the most remarkable way, sometimes into knobs and buttes like 
 potato-hills on a large scale, sometimes into castellated and pinnacled 
 forms, which resemble ruined cities. . These are the " Mauvaises 
 Terres " or " Bad Lands " of the West (Figs. 339, 240, 851). 
 
 On the Pacific coast, a large portion of the Coast Ranges from 
 Southern California to Washington is Tertiary, as ate also in many 
 places the lowest foot-hills of the Sierras. 
 
 Physical Geography. — From what has been said of the distribution 
 . of the rocks of this age, it is easy to reconstruct in a general way the 
 physical geography of the American Continent during the early Ter- 
 tiary period. In the northern part the Atlantic shore-line was prob- 
 ably beyond the present line, for there is no Tertiary deposit visible there. 
 The shore-line of that time crossed the present shore-line in New Jersey, 
 theil passed along the line of Junction of the Tertiary, first with the 
 Cretaceous of N"ew Jersey ; then with the Metamorphic, its waves wash- 
 ing shores of Archsean rocks all along the Atlantic coasts, as it does now 
 in the northern portion only ; then along the junction of the same again 
 with the Cretaceous of Georgia, Alabama, and Mississippi. The whole 
 low-countries of the Southern Atlantic States and the whole of Florida 
 were then a sea-bottom. The Oulf of Mexico was far more extensive 
 than now, and especially it sent a wide bay northward to the mouth of 
 the Ohio. The Mississippi River below that point did not then exist. 
 The Ohio, Arkansas, and Red Rivers emptied by separate mouths into 
 th€ embay men t of the Gulf. 
 
 This was at the beginning. During the course of the Tertiary the 
 shore-line was gradually transferred eastward along the Atlantic, and 
 southward along the Gulf, as shown by the dotted lines introduced in 
 the Tertiary areas in the map on page 302. 
 
 In the interior, in the region of the Plains, the Plateau, and the 
 Basin, there were at different times immense fresh-water lahes. The 
 places of some of these are indicated on map, Fig. 852, in dotted out- 
 line. These outlines, however, are not intended to be accurate. These 
 lakes drained some of them into the Mississippi, some into the Colo- 
 rado, and some into the Columbia River. 
 
 The Pacific shore-line at that time was along the foot-hills of the 
 Sierra Range, and therefore the whole region occupied by the Coast 
 Ranges and the Sacramento and San Joaquin Valleys, and also portions 
 of Western Oregon, were then a sea-bottom with possibly a chain of 
 islands off the coast in the position of the present Coast Range. These 
 facts are roughly represented on map. Fig. 852. The positions of the 
 principal mountain-chains, e. g.. Sierra, Wahsatch, Uintah, the eastern 
 border of the Rocky Mountains, and Appalachian, are represented by 
 heavy lines, in order the better to locate the lakes. It will be observed 
 that the continent is nearly finished. 
 
524 
 
 CENOZOIO ERA— AGE OF MAMMALS. 
 
 Europe is now remarkable for its inland seas. It was much more 
 so in Tertiary times. Many great cities, as, for example, London, 
 
 Pie. 852.— Map of Tertiary Times, showing Outline of Coast and Places of Principal Tertiary Lakes. 
 
 Paris, Vienna, are situated on Tertiary strata, partly because these 
 strata are usually found on the borders of continents, and partly be- 
 cause they are often found in the course of great rivers, which once 
 drained lake-basins. 
 
 Character of the Rocks. — ^^The rocks of this period, along the At- 
 lantic border and in the interior Plains and Rocky Mountain region, 
 are mostly imperfectly lithified ; but on the Pacific coast they are not 
 only of stony hardness, but in many cases completely metamorpMc. 
 Much of the rock in the Coast Chain is scarcely distinguishable from the 
 schists of the Palaeozoic or still older periods. The reason is evident — 
 metamorphism is closely connected with mountain-making, and moun- 
 tain-making continued until the end of the Tertiary on the Pacific coast. 
 
 Coal. — Again, in the Tertiary rocks we find coal, although more 
 usually in the imperfect condition called lignite. ' We have already 
 stated that the Rocky Mountain coal-fields are by some referred to the 
 Tertiary. We have referred these to the Laramie. But there are 
 others about which there is as yet no controversy. The Ooos Bay coal, 
 of Oregon, is probably Miocene-Tertiary. The ISTevada coal is prob- 
 ably Oligocene or Miocene. The geologists of the survey of Can- 
 ada have reported large fields of coal on the Qu'Appelle and the 
 
TERTIARY LIFE-SYSTEM. 525 
 
 North' Saskatchewan Eivers, covering an area of 35,000 square miles, a 
 ^part, at least, of which is referred to the Tertiary. Much' of this coal 
 is of good quality. It seems most probable, however, that this also 
 belongs mostly to the Laramie. 
 
 In Europe also an imperfect coal (lignite) is found in the Miocene 
 in considerable quantity. 
 
 Petroleum. — In strata of this age occur the petroleum and asphalt 
 so abundant in the Coast Range of South California. 
 
 Lava-fields. — The great lava-fields of the western part of the con- 
 tinent belong mostly to the Tertiary : (1) The great Lava-flood of the 
 Northwest (already spoken of on p. 318), which covers Northern 
 California, Northwestern Nevada, a large part of Oregon, Washington, 
 and Idaho, and extends far into Montana and British Columbia. 
 This is one of the largest fields in the world. (3) The lava-field of 
 the Coast Range of California, especially in Napa and Lake Counties, 
 and northward into Oregon. (3) Enormous fields in the Plateau and 
 Basin regions. The Tertiary was undoubtedly a period of exceptional 
 volcanic activity, but it must be remembered that earlier outpour- 
 ings have been mostly removed by erosion and only their roots left in 
 the form of dikes. Even Tertiary eruptions have in many cases been 
 largely thus removed. We have a striking illustration of this in the 
 Mt. Taylor group, which, according to Button, consists of mere wrecks 
 of Tertiary volcanoes. During later Tertiary times not only their over- 
 flows, but the strata through which they came up, have been swept 
 clean away, and only the cores of lava filling their craters have been 
 left as " necks " standing above the surrounding country as witnesses 
 of the amount of general erosion. 
 
 Life- System. 
 
 General Remarks. — We have already spoken of the great and rapid 
 change in the life-system between the Cretaceous and the Tertiary, 
 even where the two series of rocks seem continuous and conformable. 
 This indicates, undoubtedly, a more rapid rate of evolution at that 
 time. But it also indicates, as one cause of this rapid evolution, a 
 migration of species brought about by changes in physical geography 
 and climate, and the. imposition of one fauna and flora upon another, 
 and the extermination or else modification of one by the other. It is 
 diflScult to conceive of these sudden changes taking place otherwise. 
 We shall speak more fully of this important point under the Quaternary. 
 
 The general character of the life-system of the Tertiary, as already 
 said, was in the main similar to the present. Nearly all the genera 
 and many of the species of plants and invertebrate animals were the 
 same as now, and the difference in aspect would hardly be recognized 
 by the popular eye; it was certainly not greater than now exists 
 
526 CENOZOIC ERA— AGE OF MAMMALS. 
 
 between difEerent countries. It is only among Mammals that the 
 difference was very conspicuous. 
 
 Plants. 
 
 Among plants, nearly all the genera of Dicotyls, Palms, and 
 Grasses were the same as now, though most of the species are extinct. 
 The cereals, however, were not yet introduced. The genera were the 
 same as now, but not in the same localities. On the contrary, the 
 vegetation indicated a much warmer climate than exists now in the 
 same localities. For example, if we regard the Lignitic as Eocene- 
 Tertiary (instead of Cretaceous), as do paleontological botanists gener- 
 ally, then of more than 300 species of plants found a very large pro- 
 portion were Palms, and many of them of great size ; and among the 
 Dicotyls many, like Magnolias, indicated a warm climate. Lesquereux 
 thinks the climate of Port Union was then similar to that of Florida 
 and Lower Louisiana now: There has been a southward migration 
 of forms since that time. Again, in Eocene times there were fifteen 
 species of Palms in Europe ; and in the Tyrol the flora, according to 
 Von Ettingshausen, indicated a temperature of 74° to 81° Fahr., and 
 many of the plants are Australian in type. In the Pliocene, on the 
 contrary, many European plants were like those in America at the 
 present time. 
 
 During the Miocene, Europe was covered with evergreens such as 
 could grow now only in the southernmost part ; and that even as far 
 as Lapland, and Iceland, and Spitzbergen. It has been estimated that 
 the Miocene flora indicates a mean temperature of 12° to 15° higher 
 than now exists in Middle Europe. In America, during the same 
 epoch. Sequoias almost identical with the Big Tree and Eedwood of 
 California ; and Libocedrus, one of them a near relative of L. decur- 
 rens of California ; and Magnolias similar to the M. grandifiora of the 
 Southern Atlantic States ; and Taxodium distichum, the cypress of the 
 swamps of Carolina and Louisiana, all existed in Greenland, and most 
 of them also in Northern Europe, and Iceland, and Spitzbergen, and 
 even Grinnell Land, 81° north latitude. Heer estimates the tempera- 
 ture of Greenland in the Miocene as 30° higher than now. Evidently 
 there was no polar ice-cap at that time. The testimony of the 
 plants is entirely conflrmed by that of the fossil shells. According 
 to Dall, the mean temperature of the Sea of Okhotsk in Miocene 
 time must have been 60° to 70°, where now it is 28°. There is little 
 doubt that the luxuriance of vegetation everywhere was far greater 
 than now. 
 
 It is interesting to note living remnants of former types of vegeta- 
 tion now almost extinct. According to Ward, there are about fifty 
 species of Sequoias known. They ranged in time from the Lower 
 
TERTIARY PLANTS. 
 
 527 
 
 Cretaceous to the present and in space from Greenland and Spitz- 
 bergen on the north to Chili and New Zealand on the south, but 
 their culmination in number was in the Tertiary. Only two remain, 
 and these only in isolated patches in California. 
 
 These facts show not only a warm but a uniform climate, and prob- 
 ably also a connection in high latitudes between the American and Eu- 
 ropean Continents. A similar connection, shown also by the vegeta- 
 
 Pia. 860. 
 
 Fibs. 853-860.— Ambrican Tertiart Plants Cafter Saflord and Lesqnerenx) ; 853. Cinnainomum 
 affine. 854. Quercns crassinervis. 855. Andromeda vaccinifoliaeamnis. 856. Carpolithes irrega- 
 laris. 857. Pagus f errnginea— Nut. 8.58. Fruit of Sequoia Langsdorfii (after Heer). 859. Branch- 
 let of Sequoia Langsdorfii (after Heer). 860. Quercus Saffordi. 
 
 tion, probably existed between Alaska and the Asiatic Continent at 
 that time. The accompanying figures represent some of the Dicotyls 
 and Monocotyls of American and European Tertiary. 
 
 Another conclusion to be drawn from the foregoing facts is that, in 
 the race of evolution, Europe seems to have distanced most other coun- 
 tries. The Australian flora is now only where the European flora was 
 85 
 
628 
 
 CENOZOIC ERA— AGiS OF MAMMALS. 
 
 Fig. 865. Fig. 866. 
 
 Pias. 861-867.— Plants of European Tertiabt: 861. Chamaerops Helvetica. 868. Sabal major. 
 863. Platannsaceroldes: a, Leaf; 6, Core of aCluster of Fruits; c. Single Fruit. 864. Cinnamo- 
 mum polymorphum; a, Leaf; *, Flower. 865. Acer trilobatum: a, Leaf; 6, Flower; <;, Seed. 
 866. Podogonium Knorrii. 867. Liquidambar Bnropenm, from CEningen: a, heat; b, Fruit {after 
 Heer). 
 
 in Eocene times, and the American flora now where the European was 
 in the Pliocene. The probable reason is that, in Europe, in these later 
 
TERTIARY PLANTS. 
 
 529 
 
 geological times,* changes of physical geography and climate, and con- 
 sequent migrations of species, were more frequent, and the struggle for 
 life more severe. Australia especially, probably on account of its isola- 
 tion, has advanced more slowly than most other countries. Many rem- 
 nants of extinct faunas and floras exist there still. 
 
 Still another conclusion is that the floras of Europe, America, and 
 Australia were far less differentiated from one another then than now. 
 
 It is also very noteworthy that while Sequoias and Cypresses and 
 Taxodiums were so abundant, we find few true Pines until the Mid- 
 Tertiary. These are the latest as they are also the most specialized of 
 Conifers. 
 
 Diatoms. — If the highest of plants — Dicotyls and Monocotyls — 
 were abundant, probably more abundant than now,- so also were the 
 lowest order of uni-celled plants — the Diatoms. Immense deposits, 
 consisting wholly of the silicious shells of these microscopic plants, are 
 
 ^■■■,^.^=s!isHSa\iurnuiriiitnnfi!trK^ li;-. 
 
 Pia. 868.— Microscopic View of Richmond Infusorial Earth (by Ehrenberg). 
 
 found in the Tertiary. In Europe the Bohemian deposit is celebrated. 
 It is fourteen feet thick, and every cubic inch of the material, accord- 
 
 * In Cretaceous times the flora of America seema to have been more advanced than 
 that of Europe. 
 
530 
 
 CENOZOIC ERA— AGE OP MAMMALS. 
 
 axis ; b, without axis (after 
 Barbour). 
 
 ing to Ehrenberg, contains 40,000,000,000 shells. The Eiehmond 
 (Virginia) deposit is equally well known. It is thirty feet thick, and 
 many miles in extent. Similar deposits are especially abundant in 
 California. They are found in at least a dozen localities where the 
 Tertiary rocks prevail, as, for example, at 
 San Pablo, in Shasta County, and near Mon- 
 terey, the last deposit being fifty feet thick. 
 Deposits of this kind are usually called 
 infusorial earths. They may often be recog- 
 nized, • even without microscopic examina- 
 tion, by their soft, chalhy consistence, their 
 insolubility in acids, and their extreme light- 
 ness. 
 
 Daimonelix. — In the sands of the Arika- 
 ree (Loup Fork) formation, Miocene, over 
 an area of more than 100 square miles in 
 Nebraska and Wyoming, there occur in enor- 
 mous numbers some very remarkable fossils 
 Fig. sesa—DuimoneiilTa, With known to the ranchmen as "devil's cork- 
 screws." Barbour has studied and described 
 them as fresh-water plants, because they show 
 plant structure throughout. They vary from those small and sim- 
 ple in outline to those large and complex, the latter being spiral 
 forms, with or without an axis, standing six to eight feet high 
 (Fig. 868a).* 
 
 Animals. 
 
 As already stated, among Invertebrates there was a general simi- 
 larity to the present fauna. Nearly all the genera and many of the 
 species were identi- 
 cal with those still 
 living. The relation 
 between the various 
 orders which pre- 
 vail now commenced 
 then. The present 
 
 basis of adjustment Pio, 869.— Nummnlina lievigata. 
 
 was then established. 
 
 Then, as now,Brachiopods and Crinoids were nearly all gone, Bchino- 
 dermswere nearly all free, and Bivalves were nearly all Lamellibranchs. 
 Then, as now, naked Cephalopods and short-tailed Crustaceans greatly 
 
 * E. H. Bavbour: in Science, Feb. 19, 1892; Bull. Geol. Poe. Amer., vol. viii, pp. SOB- 
 SIB, 1896 ; Nebraska Univ. Studies, vol. xi, No. 2, Jan., 1S91, pp. 81-124. 
 
TEBTIARY ANIMALS. 
 
 531 
 
 predominated. A glance at the following figures of Tertiary shells (Pigs. . 
 870-883) will show the general resemblance to those of the present seas. 
 In regard to the Invertebrates, there are only three or four points 
 of sufflcient importance to arrest our attention in a rapid survey. 
 
 Fig. 875. 
 
 Pig. 876. 
 
 Fig. 877. 
 
 PiGB. 870-877.— Eocene Tertiart Shells : 870. Ostrea sellseformis (after Meek). 871. Ostrea 
 Georgiana (after Meek). 872. Pecten nuperam (after Wailes). 873. Scapharca MiBsissip- 
 piensia (after Conrad). 874. Umbraculum planalata (after Wailes). 875. Turritella alveata 
 (after Wailes). 876. Volutilithes dumosa (after Wailes). 877. Volutilithes symmetrica (after 
 Wailes). 
 
 Among Rhizopods, N"ummulites (a foraminifer,Fig.869) abounded 
 to an extraordinary degree. Eocene strata, many thousand feet thick. 
 
532 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 are formed of these shells. The J^ummulitic limestone of the Alps 
 extends eastward to the Carpathians, westward to the Pyrenees, and 
 southward into Africa. It was largely quarried to build the Pyramids 
 of Egypt. It occurs also extensively in Asia Minor and in the Hima- 
 layas. 
 
 Pie. 878. 
 
 Fio. 879. 
 
 Fig. 881. 
 
 Fig. 882. 
 
 Fig. 883. 
 
 Fig. 884. 
 
 Figs. 878-884.— California Miocene Shells (after Gabb): 878. Ostrea titan, x J. 879. Arcamac- 
 rodonta (Conrad). 880. Venas pertenuis. 881. Toldia impressa (Conrad), fe. CanceUaria ve- 
 tnsta. 883. Ficus pyriformis. 884. fichinaraclinias Brewerianns. 
 
TERTIARY ANIMALS. 
 
 533 
 
 This limestone occurs in the Alps 10,000 feet, in the Pyrenees 
 11,000 feet, and in the Himalayas 15,000 and even 19,000 feet above 
 the sea-level. We see, then, the immense changes which have occurred 
 by mountain-making since the Eocene. 
 
 Among bivalve shells, common forms of the present day, such as 
 the oyster, the clam ( Venus), the scallop-shell (Pecten), etc., were very 
 numerous, and some of very large size. Oysters especially seemed to 
 have reached their maximum development in the Tertiary. The 
 Ostrea Georgiana (Fig. 871) was ten inches long and four wide ; the 
 Osirea Caroliniensis was of equal size, but shorter and broader. A 
 specimen of the Ostrea titan of California and Oregon now lies before 
 us, which by measurement is thirteen inches long, eight wide, and six 
 thick (Fig. 878), and a specimen of Pecten cerrosensis of California, 
 a Pliocene species, nine inches across. Among univalves also nearly 
 all the forms are familiar. The illustrations are taken from the 
 Eocene and Miocene. The Pliocene shells are almost undistinguish- 
 able from living shells, except by the practiced eye. It seems useless 
 to give them in an elementary work. 
 
 Insects. — There are several interesting points connected with this 
 class which must not be omitted. We have usually found insects 
 abundant in connection with luxuriant vegetation. During the Mio- 
 cene, phenogamous vegetation was even more abundant than now ; 
 there was also extreme fullness of insect-life. All orders, even the 
 
 Pia. 885.-INSBCT9 OF European Miooehb (after Heer): a, Apia Adamitica; 6 Ponera veneraria 
 male, 6' female: c, Vespa atavina; li, d. Ammophila infema; e.Imhofta pallida;/,/,/ ..Bor- 
 jnica lignitum—female, male, and worker; a, Myrmica tertiana; A, Iclineumon mfernaliB, i, 
 Xylocopa seniliB; *, Bombus Jurinei; I, Scalea saussureana. 
 
 highest, viz., Lepidoptera (butterflies— Fig. 889) and Hymenoptera 
 (bees, ants, etc. — Fig. 885), were represented. 
 
534 CENOZOIO ARA— AGE OF MAMMALS. 
 
 In the Miocene of Europe, 1,550 species of insects have been found; 
 and of these more than 900 species at (Eningen in a stratum only a few 
 feet thick (Lyell). In places the stratum is black with the remains of 
 insects. The same stratum is also full of leaves of Dicotyls, of which 
 Heer has described 500 species. Mammalian remains and fishes are 
 also found in them. 
 
 It is interesting to inquire into the conditions under which these 
 strata were formed and filled with these remains. On Lake Superior, 
 at Eagle Harbor, in the summer of 1844, we saw the white sands of 
 the beach blackened with the bodies of insects of many species, but 
 mostly beetles cast ashore. As many species were here collected in a 
 few days, by Dr. J. L. Le Oonte, as could have been collected in as 
 many months in any other place. The insects seem to have flown over 
 the surface of the lake; to have been beaten down by winds and 
 drowned, and then slowly carried shoreward and accumulated in this 
 harbor, and finally cast ashore by winds and waves. A small river 
 emptying into the harbor carried also many beetles and ants. Doubt- 
 less, at (Eningen, in Miocene times, there was an extensive lake sur- 
 rounded by dense forests, through which ran a small river emptying into 
 the lake ; and the insects drowned in its waters, and the leaves strewed 
 by winds on its surface, were cast ashore by its waves. Heer believes 
 also that carbonic-acid emissions helped to kill, and deposits of car- 
 bonate of lime to preserve, the insects. Over five hundred of the 
 CEningen insects were beetles. 
 
 Among the insects found at Glningen, Switzerland, and Radoboj, 
 Croatia, are a great many ants (Eig. 885). In all Europe there are 
 now about fifty species of ants. Heer found in the Miocene of CEnin- 
 gen and Radoboj rrcore than 100 species* And, what is very remark- 
 able, nearly all are winged ants. Ants of the present day are male, 
 female, and neuter. The males are winged throughout life, and never 
 live in the nests, but soon perish. The females are also winged until 
 they are fertilized ; then they drop their wings and live in communi- 
 ties in a wingless condition ever afterward. The neuters are always 
 wingless, and therefore always live in nests or in communities. It is 
 probable that ants at first were only winged males and females, living 
 in the open air like other insects. The wingless condition and the 
 neutral condition are both connected with their peculiar social habits 
 and instincts, and have been gradually developed along with the devel- 
 opment of their habits and instincts. It is probable that all these re- 
 markable peculiarities, viz., the wingless condition, the neutral condition, 
 the wonderful instincts, and organized social habits, have been devel- 
 oped together since the introduction of this order in Early Tertiary. 
 
 * Pouchet, Popular Science Monthly, June, 1873. 
 
TERTIARY ANIMALS. 
 
 535 
 
 In the fresh- water Miocene of Auvergne, France, there is a remark- 
 able stratum called indusial limestone, because it is largely composed 
 of the cast-off hollow cases (indusia) of the caddis-worm or larva of 
 the caddis-fly (Phryganea), cemented together by carbonate of lime. 
 The number of these cases is countless. The caddis-worm of the 
 present day forms for itself a hollow cylindrical case, of bits of stick 
 or pieces of shell, or sometimes of whole small shells, binding these 
 together by means of a kind of web. In this hollow cylinder it lives, 
 only putting out the head and two or three first joints of the body, to 
 which the feet are attached, in walking. When they complete their 
 metamorphoses, they leave their cases. Fig. 888 is a recent caddis- 
 worm with its case of small shells stuck together; Fig. 887 are indusia 
 of the Miocene cad- 
 dis-worm ; and Fig. 
 886 is the limestone 
 in place, a being 
 the indusial layer. 
 
 In Auvergne, 
 in Miocene times, 
 there existed a 
 shallow lake, in 
 which carbonate of 
 lime was deposit- 
 ing, as in many 
 lakes of the present 
 day. In this lake 
 lived myriads of 
 caddis-worms, and 
 their indusia ac- 
 cumulated for 
 countless genera- 
 tions. 
 
 In the Tertiary 
 strata, about the 
 shores of the Baltic, 
 and also in Sicily, 
 in Asia Minor, and 
 several other local- 
 ities usually asso- 
 ciated with lignite, 
 are found masses of amber. This substance is a fossil resin of 
 several species of Conifer, especially Pinites succinifer. It is often 
 quite transparent, and inclosed within may be seen perfectly pre- 
 served insects of many kinds. Over 800 species of insects and 
 
 Fig. 887. 
 
 Fio. 888. 
 
 Fiaa. _ 
 
 Water Marls, 
 ganea Cases. 
 
 5. Indusial Limestone interstratified with Fresh- 
 887. A Portion (natural size) showing the Phry- 
 888. Kecent Larra of a Phrygknea, with its Case. 
 
536 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 fragments of many species of plants have been found thus inclosed. 
 
 The degree of preservation is marvelous ; even the most delicate parts, 
 
 the slender legs, the 
 jointed antennae, and 
 the gauzy wings are 
 perfect. The man- 
 ner in which these 
 insects were entan- 
 gled, inclosed, and 
 preserved, may be 
 easily observed even 
 at the present day. 
 The gum issuing 
 from Conifers is at 
 first in the form of 
 semi-liquid, transpar- 
 ent tears. Flies, 
 gnats, etc., alighting 
 
 on these, stick fast, and by the running down of further exudations are 
 
 enveloped and preserved forever. The legs, both in the modern and 
 
 the fossil resin, are often found broken by 
 
 the struggles of the insects to extricate 
 
 themselves. The insects of the Tertiary, 
 
 like the plants, show a decided tropical 
 
 character. 
 
 But probably the richest beds in insects 
 
 yet found are at Florissant, Colorado. 
 
 Here fresh- water shales of Green River age 
 
 are black with remains of insects of all or- 
 ders now existing. According to Scudder,* 
 
 about 1,000 species are recognizable, besides 
 
 FiQ. 889.— Prodryas Pereephone (after Scudder). 
 
 Flo. 890. — Sackenia arcnata, from 
 Tertiary of Utah (after Scudder). 
 
 many plants, several fishes, and a bird with feathers preserved. Of 
 
 Fig. 891.— Apionrefrenatum, x 12 (after 
 Scudder). 
 
 Fie. 893.— Balaninns minnsculus, x 8 (after Scudder) 
 
 * Bulletin of the United States Geological Survey, vol. vi, No 2. 
 
TERTIAEY ANIMALS, 
 
 53Y 
 
 30,000 specimens of insects in all museunis, about one half are from 
 this locality. Here, also., as in Europe, Hymenopters and Coleopters 
 are most abundant, and all the species indicate tropical climate. Of 
 one family alone, the Ehyncophora or Weevils (Figs. 891 and 893), 116 
 species were found, and all entirely peculiar (Scudder). 
 Among the insects found here are seven species of but- 
 terflies (nine are known as fossils from all the rest of 
 the world). A beautifully preserved specimen is shown 
 in Fig. 889. At Florissant, in Oligocene time there was a 
 lake, and insects were cast ashore and accumulated in the 
 
 Pig. 897. 
 
 Figs. 893-897.— Tbbtiabt ViBBEB—Elaemobrancfis : 893. Lamna elegans (after Agassiz). 894. No- 
 tidanue primigeniue (after Agassiz). 895. Carcharodon auriculatuB (after Gibbes). 896. Car- 
 charodon megalodon, x J (after Gibbes). Tdeost: 897. Diplomystus altas (after Leidy). 
 
 manner already described. Other Tertiary lake-deposits in the West 
 are also rich in insects (Fig. 890). 
 
_l 
 
 538 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 Fishes. — The present relation between the three great orders of 
 Fishes — Teleosts, Ganoids, and Selachians — was first fairly established 
 in the Tertiary. Teleosts were first introduced in the Jurassic, but 
 only in the Tertiary did they become very abundant. Ganoids, on the 
 contrary, became fewer in number ; they sank into their present sub- 
 ordinate position. .Among Elasmobranchs, the Hybodonts are gone, 
 the Cestracionts are few in number, but the Squalodonts reach their 
 maximum development, both in number and size. In the marine Ter- 
 tiary of the Atlantic border, both Eocene and Miocene, sharks' teeth 
 are found in immense numbers, and of very great size. Some of the 
 triangular teeth of the Garcharodon megalodon (Pig. 896) are found 
 six and a half inches long and six inches broad at the base. The 
 
 FiQ. 899. 
 
 Pigs. 898, 899.— Tertiary Fishbs— refeosta.- 898. Rhombus minimus, Lower Eocene. 899. Lebias 
 
 cepbalotes, Miocene. 
 
 owners of such teeth must have been fifty to seventy feet long. Some 
 of the more common forms of sharks' teeth of the American Tertiary, 
 
TERTIARY ANIMALS. 
 
 539 
 
 and Teleosts from American and European Tertiary, are given in the 
 preceding figures. 
 
 AmpMbians.— As already said (p. 434), the class of Amphibians in 
 the form of Stegocephalians culminated in the Trias and that order 
 died out. During the Jura and Cretaceous we have said nothing 
 about Amphibians, although they certainly existed in less numbers 
 and in more modern forms. In the Tertiary we again find them 
 somewhat abundant, and now not only the tailed, as before, but 
 also for the first time the highest and most specialized forms, the tail- 
 less or frogs. In the Miocene of Europe at (Eningen, a Salamandroid 
 Amphibian was found and described in 1728 by Scheuchzer, a physician 
 and naturalist, professor in the University of Altorf. He gave it the 
 title " Homo Diluvii Testis,^'' believing it to be the skeleton of a human 
 being destroyed by the deluge. The length was 
 about four feet. It was reserved for Cuvier to show 
 that the fossil was not human, though the name 
 Andrias Scheuchzeri (Fig. 900) had become per- 
 manently attached to it through Scheuchzer's 
 mistake. A living species of the same group is 
 now found in Japan, and is of gigantic size. 
 A representation of it is given in Fig. 901, 
 for comparison with its fossil precursor. 
 
 Reptiles.— The age of 
 Eeptiles is past. The huge 
 Enaliosaurs, Dinosaurs, 
 Mosasaurs, and Pterosaurs, 
 are all extinct. Their 
 class is now represented by 
 Crocodiles, Lizards, Tur- 
 tles, and Snakes, though 
 their place as rulers is sup- 
 plied by Mammals and 
 Birds. Five species of 
 Snakes, some of them eight 
 feet long, and nine Croco- 
 dilians, have been found 
 in the Eocene of Wyo- 
 ming, and several also in piq, 901. 
 
 Europe. The Miocene of Fiqs. 900, 901—900. Andrias scheuchzeri, Miocene of Switz- 
 ,, XT- 1 J! •! erland, X A, (nfter Heer). 901. Sieboldia japonica, a living 
 
 the Himalayas furnishes a salamander from Japan, X A (after Heer). 
 
 gigantic turtle (Testudo 
 
 atlas), the carapace of which was twelve feet long and eight feet wide, 
 and seven feet high in the roof, and the whole animal was probably 
 twenty feet long. Over sixty species of Tertiary turtles, and eighteen 
 
 Fio. 900. 
 
540 
 
 CENOZOIC ERA— AGE OP MAMMALS. 
 
 or twenty species of crocodiles, have been described from foreign 
 countries (Dana). 
 
 The Crocodilians, the highest living order of reptiles, first appeared 
 in the Triassie, but only in generalized forms — Stagonolepis, Belodon, 
 etc. — which closely connected them with the Dinosaurs. From this 
 early form Huxley has traced with consummate skill the gradual 
 difEerentiation of this order, in the position of the posterior nares, the 
 structure of the head and the form of the vertebral bodies, step by 
 step through the Jurassic, Cretaceous, to the Tertiary, where the type 
 reached its perfection. 
 
 Birds. — The class of Birds in the Cretaceous was represented only 
 by the reptilian birds and ordinary water-hixA&. Now, in the Tertiary, 
 
 however, the reptilian birds — verfcebrated- 
 tailed and socket- toothed — have disap- 
 peared. The bird-class is fairly differen- 
 tiated from the reptilian class, and the 
 connecting links destroyed. Birds of all 
 kinds now appear — land-birds as well as 
 water-birds. In America, among land- 
 birds, woodpeckers, owls, eagles, etc., have 
 been discovered and described by Marsh. 
 The number of species found in Europe 
 is much greater than in America. The 
 Miocene beds of Central Prance alone 
 have, according to Milne-Edwards, af- 
 forded seventy species. The Miocene 
 birds, like the plants and insects, show 
 a decided tropical character. " Parrots 
 and Trogons inhabited the woods ; Swal- 
 lows built, in the fissures of the rocks, 
 nests in all probability like those now 
 found in certain parts of Asia and the 
 Indian Archipelago; a Secretary-bird, 
 nearly allied to that of the Cape of Good 
 Hope, sought in the plains the serpents 
 and reptiles which at that time, as now, must have furnished its 
 nourishment. Large Adjutants, Cranes, Flamingoes, Palaeolodi (birds 
 of curious forms intermediate between Flamingoes and ordinary 
 Grallae), and Ibises, frequented the margins of the water where insect- 
 larvse and moUusks abounded. Pelicans floated on the lakes; and, 
 lastly, Sand-grouse and numerous Gallinaceous birds assisted in giving 
 to this ornithological population a strange physiognomy which recalls to 
 mind the descriptions given by Livingstone of certain lakes in South- 
 ern Africa." 
 
 Pio. 902.— Eestoration of Oastornis 
 Edwardsii (after Meunier). 
 
TERTIARY ANIMALS. 
 
 541 
 
 But although the class of birds was already well differentiated, yet 
 some remnants of generalized forms still remained. A toothed bird 
 has been found in the London clay (EoCene), and named by Owen 
 Odontopteryx (Fig. 903). But this is not a true socket-toothed bird. 
 
 Fig. 903.— Skull of Odontopteryx tollapicas, restored (after Owen). 
 
 The so-called teeth are only dentations of the bony edge of the bill. 
 In the Eocene of the Paris basin was found a gigantic bird ( Qastornis) 
 ten feet in height, combining the characters of a wader with those of 
 an ostrich (Pig. 902). 
 
 In 1876 Cope published the discovery of a gigantic bird from the 
 lowest Eocene of the San Juan basin. The Diatryma gigantea, ac- 
 cording to Cope, combines the characters of the Cursores (ostrich 
 family) with those of the extinct Gastornis of the Paris basin. Judg- 
 ing from its foot, it was double the size of an ostrich. Lucas thinks 
 that this huge bird was more closely related to the waders. Marsh 
 also found a gigantic ostrichlike bird {Bar amis r eg ens) in the 
 Eocene of New Jersey which is similar to Gastornis. 
 
 Mammals — General Remarks. — 1. We have already seen that the 
 evolution of this class may be traced back to the borders of the Palaeo- 
 zoic. The probable steps are : First, the 
 Hypotheria, represented by the Thero- 
 morphs, or perhaps a hypothetical gen- 
 eralized type connecting these with the 
 monotfemes of the Permian ; then the 
 Prototheria, represented by the general- 
 ized monotremes of the Trias ; then the 
 Metatheria of Jurassic and Cretaceous ; 
 and, finally, the Eutheria, or typical 
 placentals of the Tertiary. 2. But 
 nothing is more noteworthy than the 
 suddenness of the appearance of this 
 last term of the series. We find only 
 Mesozoic types even to the borders of the Tertiary (Laramie), and 
 then without warning there appears the higher type, Eutheria, of the 
 Tertiary. This might be explained in Europe, where there is un- 
 
 C /? £■ TA\f,CE:OUS 
 
 'f 
 
 FRIMAl. EUTHEBIUM 
 
 Fio. 904. — Diagram showing Differentia- 
 tion of Main Orders of Tertiary Mam- 
 mals. 
 
542 CENOZOIO EEA— AGE OF MAMMALS. 
 
 conformity at this horizon, by the gap in the record ; but here in 
 America the record seems almost complete, and yet at the same horizon 
 a great change occurs. It is impossible to explain this unless we admit 
 times of rapid evolution. But even this is not sufficient. We must 
 suppose, also, that these new types appeared here in America by migra- 
 tion about the end of the Cretaceous from some other country, where 
 we hope yet to find the intermediate links. 3. Their appearance was 
 not only sudden but in great numbers and considerable variety. In 
 the very lowest beds of the Lower Tertiary (Puerco beds) Cope finds 
 ninety-three species, and already all the main divisions, such as Car- 
 nivores, Herbivores, Insectivores, and Primates. 4. But, although 
 these main divisions are distinguishable, they are-wo^ yet widely sepa- 
 rated, as we now know them. At that time there were no typical Car- 
 nivores, Herbivores, etc. ; on the contrary, they were aXl-^Qry generalized 
 types — i. e., they approached each other very closely, as shown in the 
 diagram (Fig. 904) — so closely, indeed, that if they lived to-day we 
 would probably put them all, or nearly all, in the same group or order. 
 As time went on, not only were they separated more and more by 
 adaptive modification, but also divided into subordinate branches (not 
 shown in the diagram). In order to indicate the fact that these orders 
 were not yet distinctly specialized, it has been proposed to call them 
 /iro- Carnivores, ^ro-Herbivores, /^ro-Simise, etc. — i. e., progenitors of 
 these now widely distinct orders. They were all probably five-toed 
 Plantigrades, with tuberculated molars (Bunodont), and therefore 
 Omnivores. By tracing the divergent lines of the diagram downward, 
 they meet in the Cretaceous in a hypothetical ancestor, which was 
 
 Fig. 905. — TapiruB Indicus. 
 
 probably an Insectivore. 5. In the course of the Tertiary the mam- 
 malian faunas change completely many times. 
 
 The Tertiary mammals are of so great interest, from the evolution 
 point of view, that we must dwell upon them somewhat in detail. But 
 
TERTIARY ANIMALS. 
 
 543 
 
 it seems impossible to present selections from the immense mass of 
 material at hand in an interesting manner, except by taking a few clas- 
 sic localities from different epochs and different countries, and briefly 
 describing what has been found in each. We will commence with 
 some foreign localities, because these were first discovered : 
 
 1. Eocene Basin of Paris. — This basin has been made celebrated by 
 the labors of the immortal Ouvier. The discovery in the early portion 
 
 Fio. 906.— Palseotherium magnum, x "^ (after Saudry). 
 
 of the present century of the rich treasures imbedded in the strata of 
 this basin, and the consummate skill with which they were worked up 
 by Cuvier, gave an incredible impulse to geology. Fifty species of 
 mammals, of which forty species were tapir-like ; ten species of birds, 
 among which one, the Gastornis (Fig- 903), was a huge wader as large 
 as an ostrich ; besides reptiles, fishes, and shells in abundance, were 
 discovered. In Eocene times the Paris basin seems to have been an 
 estuary full of shells and fishes, etc., into whjch the bodies of birds and 
 mammals were drifted. Among the many remarkable mammals we 
 will select two as types, viz., the Palmothere and the Anoplothere. 
 
 The Palaeothefe, like the Rhinoceros and like some of the earlier 
 
 86 
 
 Fio. 907. — Anoplotherium commune, restored. 
 
544 CENOZOIC ERA— AGE OP MAMMALS. 
 
 representatives of the horse family, had three hoofed toes on all the 
 feet. It is usually supposed to have had also the general form and the 
 short flexible snout of a tapir (Fig. 905),* and it is with this family 
 that Ouvier supposed it has its nearest alliance, and his restoration was 
 based on this view. But the discovery of more complete skeletons 
 shows that the neck and limbs were much longer than had been sup- 
 posed. In general form (Fig. 906) it seems to have been as much like 
 the horse family as the tapirs. 
 
 The Anoplothere (Fig. 907) was a slender and graceful animal with- 
 out snout, and possessing only two toes, like ruminants. Most of its 
 characters, however, allied it to the tapirs. Among these characters 
 was the possession of a third rudimental or non-functional toe (Cope) 
 and a full set of front teeth. It was, therefore, a remarkable connect- 
 ing link between the tapirs and ruminants. 
 
 2. Siwalik Hills, India — Pliocene. — Near the base of the Himalaya^ 
 occurs a range of hills formerly regarded as fresh-water uppermost 
 Miocene strata. They are extremely rich in vertebrate and especially in 
 mammalian remains, which have been thoroughly studied by Falconer. 
 One hundred and fifty species of mammals are described from this lo- 
 cality. They are of great variety of forms, both Carnivora and Her- 
 
 bivora, but the latter are most abundant. 
 Among these, perhaps the two most remark- 
 able are Dinotherium f and Sivatherium. 
 The Dinothere has been found also in 
 the European Miocene. It was a huge 
 animal, probably one of the largest of land 
 mammals (Gaudry), with a skull three feet 
 long, to which was attached a proboscis. 
 The lower jaw was bent downward, and 
 carried two long, tusk-like teeth, projecting 
 also downward. The whole height of the 
 %%Se-um:freliy r^edS"" l^^ad, froHi the points of thesc lowcr teeth 
 
 to the top' of the cranium, was five feet. 
 Eeeently a perfect pelvis has been found, showing the great 
 massiveness of these bones, and showing also, in these huge animals, 
 something which suggested marsupial bones. This strange animal 
 combined, in the structure of its head, the characters of Elephant, 
 Hippopotamus, Tapir, and Dugong; but it also had affinities with 
 marsupials. The earliest of Proboscidians is Paleomastodon, from 
 the Lower Oligocene of Egypt. 
 
 * The tapir has three toes on the hind-foot and four on the fore-foot, but the outer 
 one is small and not functional. 
 
 f The Dinothere is found in the Miocene of India, though not at Siwalik. 
 
TERTIARY ANIMALS. 
 
 545 
 
 The Sivathere was a four-horned antelope, of elephantine size and 
 some elephantine characters. The four-horned antelope of the present 
 
 Pig. 909.— Head of a Sivatherium gigantetim, greatly reduced. 
 
 day lives in the same locality, but is a comparatively small animal, with 
 two short conical horns from the front part of the frontal bone, and two 
 somewhat longer ones in the usual place on the back part of the same 
 bone. The Sivathere, on the other hand, was of elephantine height, 
 though of slenderer form, with two short conical horns in front, and two 
 large, palmately branching ones behind. The form of the nose-bones 
 suggests the existence of a snout. The feet and legs were clearly those 
 of a ruminant. It seems to have combined the characters of a Rumi- 
 
 Fia. 910.— Elephas Ganesa, x ^ (after Falconer). 
 
 nant and a Pachyderm. The Bramathere was a similar animal, of 
 equally gigantic size, found in strata of the same age. 
 
 In the same locality were found also three species of Mastodons, 
 
546 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 seven species of Elephants, one of them E. ganesa (Fig. 910), remark- 
 able for the prodigious length and size of its tusks ; three species of the 
 
 Fig. 911. — Skeleton of Hipparion gracile, restored (after Gaudry). 
 
 Horse family ; five species of Ehinoceros ; four to seven species of Hip- 
 popotamus, and three species of hog ; also, Anoplotheres, Camels, Ca- 
 
 FiQ. 912.— MesopithecuB Pentelici, restored x J (after Gaudry). 
 
 melopards, Oxen, Sheep, Antelope, Musk-ox, Monkeys, etc. ; also, many 
 Keptiles, among which were narrow-nosed Crocodiles, like the Gavials 
 
TERTIARY ANIMALS. 
 
 547 
 
 now living in the Ganges, and the huge Turtle, Testudo atlas, already 
 mentioned (p. 539). 
 
 The most characteristic representative of the Horse family in the 
 Old World Miocene was a three-toed animal called Hipparion. A 
 restoration of this graceful creature is given in Fig. 911. 
 
 In the Miocene and Pliocene of Europe are first found remains of 
 that most destructive of carnivores, the saher-toothed tiger — Machai- 
 
 
 -^t- 
 
 Fig. 913.—^, Sknll of Kachairodus cultridens, without the lower jaw, reduced in size; JB, Canine 
 Tooth of the same, one half the natural size. Pliocene, France. 
 
 rodus (Fig. 913). In the Miocene of Europe, also, the first irua. 
 Monkeys (Fig. 912) were introduced (Flower), unless Wortman has 
 a true Monkey from the Eocene of North America. 
 
 Perhaps it is well to call attention to the fact that, while the 
 tapir-like Pachyderms predominate in the Eocene, the huge forms, 
 e. g., Ehinoceros and Hippopotamus family, and Proboscidians, were 
 first introduced and immediately became abundant in the Miocene. 
 
 3. Upper Eocene of Patagonia. — The richness of the Tertiary and 
 Quaternary of the southern part of South America almost exceeds be- 
 lief. Ame'ghino has collected 50,000 specimens, among which he finds 
 750 species. The most wonderful of the different horizons there dis- 
 covered is the Pyrotherium teds, which is probably Upper Eocene. In 
 these beds have been found 220 species of.mammals, besides many 
 strange birds, and all entirely peculiar to this region. In the Pyro- 
 therium — an animal of huge dimensions — Ameghino thinks he finds 
 the long-sought ancestor "of the Proboscidians, although it has affini- 
 ties also with many other families. The suggestion of relationship 
 with the Marsupials is very doubtful. Still more wonderful are the 
 
548 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 gigantic flightless birds found in the same beds. One of these — 
 Phororhacos longissimus — was eight feet high, and far more massive 
 than the Dinornis and Epiornis of the Quaternary of New Zealand 
 and Madagascar (p. 631). And still more strange, instead of the 
 small head of Dinornidse, it carried an enormous head, twenty-six 
 inches long and more massive than that of any living mammal except 
 the Elephant, the Rhinoceros, and Hippopotamus. It is probable that 
 these wonderful discoveries will fill many gaps in the history of the 
 development of mammals. The great distinctness of this early fauna 
 plainly points to South America as a distinct center of origin of many 
 mammalian forms. 
 
 North American Localities— 4. Marine Eocene of Alabama.— We 
 select this as an example of American marine Eocene. At Claiborne, 
 Alabama, according to Lyell, there occur no less than 400 species of 
 shells, besides many Ecliinoderms, and abundance of sharks' teeth. 
 But the most remarkable remains found there are those of an extinct 
 whale — Zeuglodon cetoides: — so called from the 
 yoke-like form of the double-fanged molar teeth, 
 which were sis inches in length (Pig. 914). The 
 skull was long and pointed (Fig. 915), and set with 
 the double-fanged teeth behind and conical ones in 
 front. The vertebrae (which were in such abundance 
 that very exaggerated accounts have been published 
 concerning them) are, some of them, eighteen 
 inches long and twelve inches in diameter (Dana), 
 and the vertebral column has been found in place 
 nearly seventy feet long (Lyell). The animal must 
 have been more than seventy feet long, and the re- 
 mains of at least forty individuals have been found 
 (Lyell ) . They have been found in southern Georgia 
 as well as in Alabama, and probably their range was quite extensive. 
 This animal is peculiarly interesting as the first appearance of the 
 very distinct order Cetacea. No intermediate links have yet been 
 
 Fig. 914. — Tooth 
 Basilosanrus cetoides. 
 X i (after Gaudry). 
 
 FiQ. 915.— Head of Basilosaurus cetoides, x ^V (after Gaudry). 
 
 found connecting this with other orders of mammals, or with the 
 great reptiles. And yet, from their large size and marine habits, they 
 are more likely than land mammals to have been found, if they existed 
 
TERTIARY ANIMALS. 549 
 
 in earlier or Cretaceous times. The origin of whales is not known, 
 although they probably came from land mammals iy retrograde changes 
 adapted for aquatic life. 
 
 Lake Basins of the Interior.— The Atlantic and Gulf border strata 
 are of course all marine, and therefore contain very few land-animals. 
 It is to ihQ fresh-water basins of the interior that we must look for a 
 
 ItW^.lii.lHrh-l.fJati^ 
 
 A 
 
 Fia. 916.— Shark's teeth, from Charleston, S. C, phosphate deposits. 
 
 full record of the mammalian fauna of America in Tertiary times. 
 These basins furnish the fullest and most continuous record of the 
 whole Tertiary which has ever yet been found. The Tertiary (espe- 
 cially the Miocene) fauna of America was wholly different in species 
 and in genera, and even largely in families, from that of Europe. This 
 shows that the two continents were then, as now, widely separated, or 
 at least with communication difficult. It will be best to take them in 
 the order of their age, as we can thus best show the evidences, if any, 
 of derivation of the later from the earlier faunae. 
 
 5. San Juan Basin— Puerco Beds— Lowest Eocene. — In these, the very 
 lowest part, of the Lower Eocene — so low that they are regarded by 
 some even as partly Laramie— Cope has found a great number of most 
 extraordinary mammals, more generalized than any before known. 
 These earliest true mammals seem to have been very abundant, for, out 
 of 106 species of vertebrates found, 93 were mammals. They represent 
 already all the main divisions of the Mammalian class. Besides marsu- 
 pials continued from the Mesozoic, there were Creodonts, Herbivores, 
 Insectivortes, and Lemurine Primates ; but in forms so generalized that 
 they scarcely deserve these names, and may well be called Pro- Carni- 
 vores, Pro-Herbivores, etc., or progenitors of these now widely-distinct 
 orders. The remains of these animals are not so perfect as those on 
 higher horizons. We select for illustration an almost perfect hind-limb 
 of the Periptychus of Cope, one of the most generalized of known animals. 
 It is seen that the foot-structure is perfectly generalized and the tread 
 completely plantigrade. It is an admirable example of the primitive foot. 
 
550 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 FiQ. 917.— Periptychus rhabdodon : A, Hind-foot, x J ; S, Hind-limb, x J (after Osbom). 
 
 6. Green River Basin— Wahsatch Beds— Lower Eocene.— Imme- 
 diately above the last, but still in the Lower Eocene, is found another 
 mammalian fauna equally abundant in species and equally remarkable, 
 
 Fig. 918.— An almoat perfect Skeleton of a Phenacodus primsevus (after Cope). 
 
 but almost wholly different. From this fauna we select two, Phena- 
 codus and the Ooryphodon (peak-tooth). The Phenacodus (Fig. 918) 
 is certainly one of the most generalized mammals known. It may be 
 
TERTIARY ANIMALS. 
 
 551 
 
 FiQ. 919.— Coryphodon hamatus restored (after Marsh), k ^i A, Hind-foot ; B, Fore-foot, x J. 
 
 regarded as the ancestor of the Ungulates, or hoofed animals, but with 
 almost equal right may be claimed as the ancestor of other orders. It 
 was plantigrade, five-toed, each toe provided with a flat nail, which 
 was neither claw nor hoof, but between the two. It had bunodont 
 molars, a full complement of unmodified teeth without diastema. It 
 was, therefore, probably omnivorous in habit. Cope has described nine 
 species partly from this horizon and partly from the previous. They 
 were about the size of a sheep, or perhaps a little 
 larger. The Coryphodon was a genus of large 
 animals, of very generalized structure, uniting the 
 characters of the more generalized Ungulates, 
 such as Tapirs, with those of the more generalized 
 Carnivores, such as Bears. They were five-toed 
 Ungulates with full number of unmodified foot- 
 bones, and a tread somewhat like that of an Ele- 
 phant. Eight or ten species of Coryphodontidse 
 have been described, varying in size from that of 
 a Tapir to that of an ox or larger (Pig. 919). 
 
 In the same beds are found the remains of 
 what is believed to be the earliest progenitor of 
 the horse family, viz., the Eohippus (dawn-horse). 
 This was a small animal about the size of the fox, 
 with three hoofed toes and a vestigial fourth (No. 5) on the hind-feet, 
 and four hoofed toes and a vestigial fifth toe (No. 1) on the fore-feet 
 (Fig. 930). 
 
 As already said, generalized Carnivores, Insectivores, and lemurine 
 monkeys, Pro-Simim, are found in this and the previous horizon. 
 
 7. Green River Basin— Bridger Beds— Middle Eocene.— From this 
 wonderfur fresh- water deposit there have been described by Marsh, 
 Cope, and Leidy, 150 species of vertebrates, of which the larger number 
 are mammals. This shows a marvelous abundance of mammalian life 
 
 Fio. 920.— Feet of Eohip- 
 pus : A, Fore-foot ; B, 
 Hind-foot, x J (after 
 Marsh). 
 
652 
 
 CEVOZOIC ERA— AGE OF MAMMALS. 
 
 in this early Tertiary time. The most numerous of these are tapir-like 
 animals, such as Hyracfhyus, Limnohyus {Palcaosyops — Pig. 923), etc. ; 
 but the most formidable are the Dinocerata, an order established by 
 Marsh and including the genera Dinoceras (Marsh), Uintatherium 
 (Leidy), and Tinoceras (Marsh), or Loxolophodon (Cope). The re- 
 mains of thirty species and more than one hundred and fifty distinct 
 individuals of this order hare been obtained from the Middle Eocene 
 of Wyoming and deposited in the Museum of Yale College, where they 
 have been carefully studied. 
 
 The type genus of this order is the Dinoceras. Almost every bone 
 in the skeleton of this animal is now known. Although elephantine 
 in size, there is no evidence in the skull of the existence of a proboscis; 
 the proportions of the neck and fore-limbs, Jurthermore, show that 
 
 Fig. 921.— Dinoceras mirabile, x J (after Marsh) ; A, Skull; B, Hind-foot, x J; 0, Fore-foot, x f 
 
 its presence was unnecessary. Three pairs of horns are indicated by 
 the projecting cores (Fig. 931), one pair of which stood far in front 
 
TERTIARY ANIMALS. 
 
 553 
 
 on the nasal bones, another on the maxillary bones immediately above 
 the canines, and a third and much larger pair farther back on the 
 parietal bones. This last pair were sheathed with a thickened integu- 
 
 Fio. 922.— Restoration of Tinoceras ingens, x jg (after Marsh). 
 
 ment, which may have developed into true horn, as in the Prong- 
 horned Antelope. The three pairs of elevations are present in both 
 sexes, but proportionately smaller in the females. In addition to these 
 
 Fig. 923.— Limnohyus (Palaeosyops) (after Leidy). 
 
 formidable weapons, both sexes were provided with canine tusks, those 
 of the males being very powerful, in some eases seven or eight inches 
 in length. 
 
554 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 The largest, most specialized, and latest of the Dinocerata was the 
 huge monster Tinoceras. The head of this animal was four feet in 
 length, and the horn-cores much longer than in Dinoceras. Pig. 922 
 is a restoration by Marsh of this magnificent animal. 
 
 The animals of this entire order seem to have been quite abundant 
 for a short time during the latter part of the Middle Eocene. They 
 then became extinct, leaving apparently no successors, though possi- 
 bly the Elephant tribe of to-day may be their greatly modified de- 
 scendants. Their feet were provided each with five toes (Fig. 921), 
 and the brain was proportionally smaller than in any other land 
 mammal. 
 
 Another extraordinary group of animals discovered by Marsh in the 
 Eocene beds has been placed by him in a new order called Tillodontia 
 (Eig. 934). These animals combine the head and claws of a bear with 
 the incisors of a Rodent and the general characters of Ungulates. 
 The order must be regarded, therefore, as a remarkable generalized 
 type. 
 
 Pig. 924.— Eocene Mammal: Skull of Tillotherium (after Marsh). 
 
 "We have seen the earliest in the line of descent of the horse family 
 — EoJiippus — in the Lower Eocene Wahsatch beds. In the Middle 
 Eocene Bridger beds we find the next in the series— the OroMppus 
 (mountain-horse). This was of similar size; but already the fifth 
 metacarp and rudimentary toe are gone, and there were now three 
 hoofed toes on the hind-feet and four functional toes on the fore- 
 feet. 
 
 Although the Herbivores predominated, there were many mammals 
 belonging to other orders. For example, there were species allied to 
 
TERTIARY ANIMALS. 
 
 555 
 
 the Cat, Wolf, and Fox ; also Bats, Squirrels, Moles, and Marsupials ; 
 also many Monkeys allied to the Lemurs, Marmosets, etc., but more 
 generalized than any living Lemur. In Pig. 925 we give a restoration 
 
 Fig. 925.— Patriofelia ferox, x ^ (after Woi-tman). 
 
 by Wortman of an Eocene carnivore — Patriofelis — of very generalized 
 structure and plantigrade feet. It may be regarded as the generalized 
 ancestor of the Cats. 
 
 8. Mauvaises Terres of Nebraska— White River Basin— Oligocene. 
 From this, the earliest discovered of the Tertiary basins of the West 
 (see Pig. 851, p. 532), have been collected by Hayden and described by 
 Leidy more than 40 species of mammals, of which 25 are Ungulates, 
 8 Carnivores, and the remainder mostly Rodents. Many other species 
 have been discovered in the same locality since that time. All the 
 species, nearly all the genera, and many even of the families, are entirely 
 different from those found in the preceding epoch, and much more 
 modern. Although the tapir-like animals still prevail, species of the 
 deer, the camel, the horse, and the dog families are added. This is 
 seen in the following schedule : 
 
 Carnivores . 
 
 Ungulates. 
 
 Hyena, allies. I j,„gf^^i,y_ 
 
 Tiger, " ) 
 
 Panther, " f 
 Rhinoceros family. 
 Brontotheridae. 
 Tapir-like animals. 
 Deer family. 
 Camel " 
 Horse " 
 Rodents. 
 Turtles. 
 
 Oat 
 
 The most extraordinary animals of this time were the Brontotheri- 
 dae. This family, according to Marsh, included the Brontotherium, 
 the Menodus (Titanotherium), the Brontops, and several other genera. 
 
556 ZENOZOIC ERA— AGE OP MAMMALS. 
 
 They were of elephantine size, with singular, saddle-shaped head like a 
 Ehinoceros, and with at least one pair of large horns on the maxillaries. 
 
 Fio. 926.— Brontops, restored by Harsh, x A- 
 
 These are sometimes enormously elongated. Pig. 926 is a restoration 
 of Brontops by Marsh. They are a very distinct family, character- 
 
 FiG. 927. — Elotherium crassnm (after Marsh), x A. Miocene. 
 
 istie of Oligoeene, but their nearest living allies are the Ehinoceros 
 and the Tapirs. Like the latter, they had three hoofed toes on the 
 
TERTIAEY ANIMALS. 
 
 557 
 
 hind-feet and four on the fore-feet. In Fig. 937 we give a restoration 
 of another very remarkable animal of this period. 
 
 Fio. 928. — Aceratheriiim tridactylum, x ^ (after Oebom and 'Wortman). 
 
 The Rhinoceros family commenced here, and were abundant in 
 America. A restoration of an early generalized form is given in Fig. 
 928. 
 
 Several of the Horse family are found in Oligocene, especially the 
 Mesohippus and the Miohippus. These had lost the fourth toe on the 
 
 Fio. 929.— Mesohippus bairdii, x A (restored by Scott). 
 
 fore-feet possessed by the Orohippus, and therefore had three foes on 
 all the feet. They may be regarded as the first of the true horse family, 
 
658 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 EquidcB. These three-toed horses were about the size of a sheep. In 
 Fig. 939 we give a restoration of the Mesohippus. 
 
 The Oreodon was another remarliable animal of generalized struct- 
 ure, intermediate between the Hog and the Deer, which at this time 
 inhabited in great numbers the whole continent from Nebraska to 
 Oregon. Thirty-five species of Oreodontidse are known, although not 
 all from this horizon. The head of one is given below (Fig. 930). 
 
 Pio. 930.— Oreodon cnlbertsoni (after Gaudry). 
 
 Another most extraordinary and very generalized Artiodactyl, found 
 in both the White River and the John Day basins, is the AgriochaeruB, 
 a restoration of which is given in Fig. 931. The singular combination 
 
 Fib. 931.— Agriochserus latifrone, x }g (after Wortman). 
 
 of claw and hoof and the plantigrade tread, especially of the hind- 
 feet, will be noted. 
 
 The great abundance of the Dog family in Oligocene of America 
 and their comparative scarcity in the Old World, and also the much 
 greater abundance of Ehinoceroses, Horses, and Camels, indicate that 
 all those families probably originated here. In Fig. 933 we give a res- 
 
TERTIAEY ANIMALS. 
 
 559 
 
 toration of the Poebrothere, an early form of Camel, and in Pig. 933 a 
 most remarkable and very generalized form of the Dog family. 
 
 Fig. 932.— Pcebrotheriuni labiatum x J (after Scott). 
 
 Among Carnivores, besides many species of the Cat family. Cope 
 has described ten species of the Dog family. The saber-toothed Tiger, 
 
 37 
 
 Fia. 933.— Hyaenodon cruentus, x i (restored by Scott). 
 
560 
 
 CENOZOIC ERA— AGE OP MAMMALS. 
 
 Fia. 934.— Hoplophoneus robustue, x % (after Adams). 
 
 a most remarkable family, wliieh culminated later in the Quaternary, 
 seems to have made its first appearance here. In Fig. 934 we give an 
 
 early Oligocene form of 
 this family of Cats. 
 
 It is well to note that 
 in the Oligocene, for the 
 first time, existing fami- 
 lies of mammals began 
 to appear. We have here 
 the families of the dog, 
 the eat, the deer, the 
 camel, the horse, and the 
 rhinoceros. It is well to 
 note also that the Amer- 
 ican Continent, as shown by the uniqueness of its mammalian fauna, 
 was largely, if not completely, isolated. 
 
 9. Mauvaises Terres— Niobrara Basin — Loup Fork Beds— Miocene. 
 — In nearly the same locality overlying the last, but extending farther 
 south, occur lake-deposits of the Miocene times, full of mammalian re- 
 mains, but again wholly different in spe- 
 cies. Among Ungulates there was a Ehi- 
 noceros, as big as the Indian species; an 
 Elephant {E. Columhi), the same which 
 lived in the Quaternary, bigger than any 
 now living ; a Mastodon, but smaller than 
 the great Mastodon of the Quaternary; a 
 large number of the horse family and sev- 
 eral of the camel family, besides many 
 other families of Ungulates, Carnivores, 
 Eodents, etc. Both the horse and the 
 camel family were more numerously rep- 
 resented at that time in America than in the Eastern Continent. In 
 fact, it is not at all improbable that they originated here, and emi- 
 grated to the other continent. From the presence of Elephants, Mas- 
 todons, Ehinoceros, Camels, and Horses on both continents, we con- 
 clude that the two continents were probably connected in Miocene times. 
 Among the horse family found here, the most interesting, as show- 
 ing the gradual approach toward the modern horse, are the Proto- 
 hippus and the Pliohippus. These were larger than Oligocene horses, 
 being about the size of the ass. The former was three-toed, but the 
 two side toes were smaller and shorter and scarcely functional, unless 
 on marshy ground ; the latter had already lost the side-toes, and was 
 almost but not quite a perfect horse. 
 
 We see here for the first time existing genera. Elephas, Ganis, and 
 
 Rhinoceros. 
 
 Elephant. 
 
 Mastodon. 
 
 Several of the Camel family. 
 
 Many of the Horse family. 
 
 Oreodon. 
 
 Doer. 
 
 Fox. 
 
 Wolf. 
 
 Tiger. 
 
 Beaver. 
 
 Porcupine. 
 
TERTIARY ANIMALS. 561 
 
 in the higher beds Equus begin to appear, but not yet existing species^ 
 for these do not appear until the Quaternary. 
 
 Pliocene. — In America the Pliocene is not largely represented. On 
 the Atlantic coast some small areas are thought to be latest Tertiary. 
 In Mexico and Central America it has wide extent. On the Pacific 
 coast marine Pliocene forms a narrow strip from California to Wash- 
 ington, but of great thickness in the San Francisco peninsula, nearly 
 6,000 feet of sandstone, the Merced series. Some lake deposits in the 
 interior are regarded as Pliocene. Mountain-making was continued 
 over the western part of the continent, and volcanic eruptions were on 
 a vast scale. The immense lava floods of Washington, Oregon, Neva- 
 da and California, and the Yellowstone Park are Pliocene or later. 
 The climate was cooler than in earlier Tertiary. The mammalian 
 life is not well known in America, but shows continued evolution 
 toward modern species. The great Edentates of South America found 
 their way into North America. 
 
 Some General Observations on the Tertiary Mammalian Fanna.— 1. 
 Size of Brain. — Lartet has shown that the brain-cavity of some of the 
 Tertiary animals is decidedly smaller relatively than that of their liv- 
 ing congeners. Marsh has, moreover, traced a gradual increase in the 
 relative size of the brain from the earliest Eocene to the present time. 
 The brain of the Corypliodon, Lower Eocene, is not only extremely 
 small in proportion to the size of the animal, but the higher portion of 
 the brain — the cerebral lobes — is very small in proportion to the cere- 
 bellum. The brain of the Middle Eocene Dinoceras is only about one 
 eighth the size of that of a living Ehinoceros of equal bulk. The brain 
 of the Oligocene Brontothere is larger than that of the Eocene Dino- 
 ceras, but much smaller than that of the Pliocene Mastodon of nearly 
 the same size, and proportionally much smaller than that of the horse 
 (Figs. 936, 937, and 938) . Through the whole line of ancestry of the 
 horse the gradually-increasing size of the brain may be traced. 
 
 2. Genesis of Existing Orders. — We have seen that the main 
 branches of the Mammalian class if traced backward, approach one 
 another very cltosely in the Early Tertiary ; and if we could trace them 
 still farther back, they would unite in the Cretaceous in a common 
 stem or primal mammal. This was doubtless a plantigrade, five-toed, 
 bunodont, omnivorous animal. From this common stem the Car- 
 nivores and the Ungulates — to take only the two most widely-con- 
 trasted types — diverged more and more in all their characters — the 
 one becoming more and more adapted to flesh-eating, the other to 
 herb-eating; the one for seizing, the other for escaping — until the 
 present extreme types were attained. 
 
 3. Genesis of Existing Families. — Not only did these two main 
 branches separate more and more, but each of them branched again to 
 
562 CENOZOIC ERA— AGE OF MAMMALS. 
 
 form existing families. To illustrate this we take the order of Ungu- 
 lates as the best known. 
 
 Cuvier divided all Ungulates into two orders, viz., Pachyderms and 
 Ruminants. The Pachyderms are a heterogeneous order, but the Eu- 
 
 FiG. 938. 
 
 FiGB. 936-938. — Brainb op Dinocbrab, Bbontothbrium, and Horse, compared (after Marsh): 
 936. Dinoceras, Skull and Brain, x J. 937. Brontotheriam, Skull and Brain, x^. 938. Horse,' 
 Skull and Brain, x \. 
 
TERTIARY ANIMALS. 
 
 563 
 
 minants have been regarded as one of the most distinct of all mamma- 
 lian orders. Their horns in pairs, their hoofs in pairs, absence of upper 
 front-teeth, complex stomachs, and the habit of rumination, differenti- 
 ated them widely from all other animals. But Prof. Owen showed that 
 this distinction, so clear in zoology, was untenable in paleontology. 
 He found, in studying extinct Ungulates, that another distinction, viz., 
 foot-structure, was more fundamental and persistent. He therefore 
 divided all Ungulates into Perissodactyls (odd-toed) and Artiodactyls 
 (even-toed). A Perissodactyl may have five toes, as in the Oorypho- 
 don ; or three toes, as in the Palseolhere, the Rhinoceros, and the 
 Tapir; or one toe, as in the Horse. The Artiodactyls always have 
 their toes in pairs : there may be only two toes, as in Anoplothere and 
 in Euminants ; or f oui*, as in the Hog and the Hippopotamus. The 
 
 TAPIR 
 
 RHm ELEPH HIPP? HOO 
 I 
 
 *■ Ruminants. 
 
 Primal Ungulate 
 ( Phenacodus.) 
 
 rio. 939.— Diagram illustrating the DifEerentiation of the Different Families of Ungulates. 
 
 Elephant, Mastodon, etc., may be regarded as a distinct order. Probos- 
 cidians. It is probable therefore, that Ungulates very early divided 
 into three branches. 
 
 Now in the Earliest Tertiary the sub-orders Artiodactyls and Peris- 
 sodactyls and Proboscidians were united in a common ancestor or 
 •primal Ungulate., from which they afterward separated. The Phenac- 
 odus of Cope (Fig. 918, p. 550) is perhaps such a primal Ungulate. 
 Each of the primary branches then divided and again divided, until 
 the extreme branch in one direction became the Horse, and the 
 extreme branch in the other direction the Ox. In the tree above we 
 have attempted, in a general way, to represent the differentiation of 
 the several orders of Ungulates. The Cuvierian orders, Pachyderms, 
 
564 CENOZOIC ERA— AGE OF MAMMALS. 
 
 and Ruminants, are indicated by a vinculum. It is seen at a glance 
 why, in studying living animals alone, the Kuminants seem so distinct. 
 
 Genesis of the Horse.— In conclusion, it will be interesting and in- 
 structive to run out one of these branches and show in more detail the 
 genesis of one of the extreme forms. For this purpose we select the 
 Horse, because it has been somewhat accurately traced by Huxley and 
 by Marsh. About thirty-five or forty species of this family, ranging 
 from the earliest Eocene to the Quaternary, are known in the United 
 States. The steps of evolution may therefore be clearly traced. 
 
 In the lower part of the Eocene basin ( Coryphodon beds) of Green 
 Kiver is found the earliest known animal in the direct line of descent 
 of the horse family, viz., the EoMppus of Marsh. This animal had 
 three toes on the hind-foot and four perfect, Serviceable toes on the 
 fore-foot ; but, in addition, on the fore-foot an imperfect fifth meta- 
 carpal (splint), and possibly a corresponding rudimentary fifth toe (the 
 thumb), like a dew-claw. Also, the two bones of the leg and forearm 
 were yet entirely distinct. This animal was no larger than a fox. 
 Next, in the Middle Eocene (Bridger beds), came the OroMppus of 
 Marsh, an animal of similar size, and having similar structure, except 
 that the rudimentary thumb or dew-claw is dropped, leaving only four 
 toes on the fore-foot. Next came, in the Oligocene, the MesoMp- 
 puSj in which the fourth toe has become a rudimentary and useless 
 splint. Next came, but in the Miocene, the Miohippus of the United 
 States and nearly-allied Anchithere of Europe, more horse-like than 
 the preceding. The rudimentary fourth splint is now almost gone, 
 and the middle hoof has become larger; nevertheless, the two side- 
 hoofs are still serviceable. The two bones of the leg have also become 
 united, though still quite distinct. This animal was about the size of 
 a sheep. Next came, in the Upper Miocene and Lower Pliocene, the 
 Protohippus of the United States and allied Hipparion of Europe, an 
 animal still more horse-like than the preceding, both in structure and 
 size. Every remnant of the fourth splint is now gone; the middle 
 hoof has become still larger, and the two side-hoofs smaller and shorter, 
 and no longer serviceable, except in marshy ground. It was about the 
 size of the ass. Next came, in the Pliocene, the Pliohippus, almost a 
 complete horse. The hoofs are reduced to one, but the splints of the 
 two side-toes remain to attest the line of descent. It differs from the 
 true horse in the skull, shape of the hoof, the less length of the molars, 
 and some other less important details. Last comes, in the Quaternary, 
 the modern horse — Equus. The hoof becomes rounder, the splint-bones 
 shorter, the molars longer, the second bone of the leg more rudimentary, 
 and the evolutionary change is complete. 
 
 Similar gradual changes, becoming more and more horse-like, may 
 be traced in the shape of the head and neck, and especially in the 
 
TERTIARY ANIMALS. 5^5 
 
 gradually-increasing length and complexity of structure of the grind- 
 
 Egims: Qoaternaiy and 
 Beoent 
 
 fllohippns: Pliocene. 
 
 Frotohippus: Upper Miocene. 
 
 Miohippus; Miocene. 
 
 Mesohippus : Oligocene. 
 
 Orohippus: Eocene. 
 
 Pio. 940.--Diagram illnstrating Gradual Changes in the Horse Family. Throuighont a ie fore-foot; 
 0, hind-foot; c, fore-arm; d. shank; e, molar on side view; /and a, grindmg surface of upper 
 and lower molars. (After Marsh.) 
 
566 CENOZOIC ERA— AGE OF MAMMALS. 
 
 ing teeth. These changes are shown in Pig. 940, for which we are 
 indebted to the kindness of Prof. Marsh. The Eohippus is not rep- 
 resented, but figures of its feet are given in Pig. 930, p. 551. 
 
 There can be no doubt that if we could trace the line of descent still 
 further back we would find a perfect five-toed ancestor. Prom this 
 normal number of five, the toes have been successively dropped, ac- 
 cording to a regular law. In the Perissodactyl line first the thumb, 
 Fo. 1, was dropped ; then the little finger, No. 5 ; then the first and 
 ring-fingers, Nos. 2 and 4, were shortened up more and more and finally 
 disappeared, and only the middle finger. No. 3, remained in the modern 
 horse. In the Artiodactyl line, after the dropping of No. 1, then Nos. 
 2 and 5 of the four-toed foot were shortened and gradually disappeared, 
 and Nos. 3 and 4 remained in the ruminants. 
 
 In a similar way Cope has traced the line of descent of the camel 
 from the Pantolestes of the Early Eocene, through the Poebrotherium 
 (Pig. 933) of Oligocene, and the Procamelus of the Miocene, to the 
 modern camel.* Similarly also the modern deer, with its branching 
 antlers, may be traced from the Lower Pliocene, where they had antlers 
 of one or two points, through the Upper Pliocene, where the antlers are 
 more complex, to tlie magnificent, many-branched antlers of the Qua- 
 ternary and modern times. 
 
 Prom the earliest and most generalized types, therefore, to the pres- 
 ent specialized types, the principal changes have been, first, from planti- 
 grade to digitigrade ; second, from short-footed digitigrade to long- 
 footed digitigrade, i. e., increasing elevation of the heel; third, from 
 digitigrade to unguligrade, i. e., rising on tips of the toes ; fourth, from 
 five toes to one toe in the Horse, or two toes in Euminants; and, 
 fifth, from simple omnivorous molars to the complex herbivorous 
 millstones of the Horse and the- Ox. 
 
 The change from plantigrade to digitigrade and from digitigrade 
 to unguligrade, with increasing elevation of the heel, when taken in 
 connection with increasing size of the brain, and therefore presumably 
 with increasing brain-power, shows a gradual improvement of struct- 
 ure adapted for speed and activity, and a pari-passu increase of nerv- 
 ous and muscular energy, necessary to work the improved structure. 
 
 4. Not only does the mammalian fauna of the Miocene difEer com- 
 pletely from that of the Eocene, which precedes, and from the Pliocene, 
 which succeeds it, but there seem to have been at least three or four 
 distinct Eocene and seven or eight distinct Miocene faunas. Thus 
 there have been many complete changes in the mammalian fauna in 
 Tertiary times. 
 
 * American Naturalist, vol. xx, p. 611, 1886. 
 
GENERAL OBSEKVATIONS ON THE TERTIARY PERIOD. 5(57 
 
 General Observations on the Tertiary Period. 
 
 We have already seen (p. 486) that during Cretaceous times a wide 
 sea, occupying the position of the Western Plains and Plateau region, 
 divided America into two Continents, an Eastern and a Western. We 
 have also seen (p. 513) that at the end of the Cretaceous this sea was 
 obliterated by continental upheaval, and the continent became one. 
 During the Eocene, the eastern portion of the place formerly occupied 
 by this sea was probably dry land, but in the Plateau region there 
 were great fresh-water lakes, one north of the Uintah Mountains, 
 Green Eiver Basin, and one south of the same, and probably one in 
 Oregon. There were possibly others yet unknown. At the end of 
 the Eocene, there was a rise in the Plateau region, which drained the 
 Eocene lakes, through the Colorado Eiver, and a corresponding depres- 
 sion in the Plains region on the one side, and the Basin region on the 
 other, not sufficient to form a sea again, but sufficient to form great 
 Miocene lakes there. During the Miocene, the bared bottoms of the 
 Eocene lakes were subject to prodigious erosion, and much of the gen- 
 eral erosion of the Plateau region occurred at that time. At the end of 
 the Miocene occurred the greatest event of the Tertiary period, one of 
 the greatest in the history of the American Continent. At that time 
 the sea-bottom off the then Pacific coast was crushed together into the 
 most complicated folds (p. 270), and swollen up into the (joast Chain, 
 and at the same time fissures were formed in the Cascade Range, with 
 the outpouring of the great lava-flood of the Northwest, already spoken 
 of (pp. 218, 375). Coincidently with this there was a further letting 
 dotvn of the region of the Plains and of the Basin, and a consequent 
 extension of the Pliocene lakes in these regions, attended probably with 
 a further rise of the Plateau region. During the Pliocene, the greater 
 part of the caflon-cutting of" the Plateau region, and nearly all the great 
 lava-flows of the West, took place. At the end of the Tertiary, these 
 Pliocene lakes were in their turn obliterated by the further upheaval 
 of the continent, which inaugurated the Quaternary. Coincident with 
 this general uplift, mountain-making by crust-block tilting occurred 
 on a grand scale. The Sierra, the Wahsatch, and the Basin Eanges 
 assumed their present form and height (p. 272), and the great north 
 and south fault-cliffs of the Plateau region were mainly formed. At 
 the same time there occurred another elevation of the Coast Range, 
 and a folding of its Pliocene strata with outpouring of lavas. And last 
 of all the final sculpturing of both Sierra and Coast Eanges began, and 
 all the grand caflons of the Sierra and the inner gorge of the Colorado 
 caflon were formed since that time. 
 
 While this was going on in the western portion of the continent, on 
 the southeastern and southern border the continent gained, by gradual 
 
568 CENOZOIO ERA— AGE OF MAMMALS. 
 
 rise, nearly all the area shaded as Tertiary on map (p. 534). In this 
 direction the continent was finished with the exception of a large por- 
 tion of Florida and the sea-islands and alluvial flats about the shores 
 of the Southern Atlantic and Gulf States. These belong to a still later 
 period. 
 
 Thus we see that from the end of the Cretaceous to the end of the 
 Tertiary there was a gradual upheaval of the whole western half of the 
 continent, by which the axis, or lowest line, of the great interior con- 
 tinental basin was transferred more and more eastward to its present 
 position, the Mississippi Eiver. Probably correlative with this up- 
 heaval of the western half of the continent was the down-sinkiag of 
 the mid-Pacific bottom, indicated by coral-reefs (p. 160). Also as a 
 consequence of the same upheaval the erosive power of the rivers was 
 greatly increased, and thus were formed those deep cations in the 
 regions (New Mexico, Colorado, and Arizona) where the elevation was 
 greatest. Thus the down-sinking of the mid-Pacific bottom, the bodily 
 upheaval of the Pacific side of the continent, and the down-cutting of 
 the river-channels into those wonderful caflons, are closely connected 
 with each other. 
 
 Section 3. — Quaternary Period or Pleistocene. 
 
 Characteristics. — The chief characteristic of the Quaternary is that 
 it is a period of great and widely extended oscillations of the earth's 
 crust in high-latitude regions, attended with great changes of climate. 
 During this period the class of mammals seem to have culminated. 
 During this period also man seems to have appeared on the scene. 
 We do not call it the age of Man, however, because he had not yet 
 established his reign. His appearance here is rather in accordance 
 with the law of anticipation (p. 391). As already stated, the inverte- 
 brate fauna was almost identical with that still living, but the mam- 
 malian fauna was almost wholly peculiar, differing both from the 
 Tertiary -which preceded and from the present which followed it. 
 
 Subdivisions. — The Quaternary has been divided into two epochs, 
 Glacial and Ghamplain, these time divisions being characterized by 
 the attitude of the land surface and the character of the climate. The 
 Glacial epoch is characterized by the elevated position of the land 
 surface in high latitudes, at least in the first part of the epoch, the 
 continents in those regions standing 1,000 to 3,000 feet above their 
 present height. The lifting had taken place, entirely or chiefly, dur- 
 ing the Tertiary. Large portions of these regions seem to have been 
 sheeted with ice, and an arctic rigor of climate extended far into now 
 temperate regions. 
 
 The Champlain epoch, on the contrary, is characterized by a down- 
 
GLACIAL EPOCH. 569 
 
 ward motion of land- surfaces in tlie same region until the sea stood 
 relatively 500 to 1,000 feet above its present level, covering, of course, 
 mucli that is now land-surface. It was, therefore, a period of inland 
 seas. Coincident with this sinking was a moderation of climate, and a 
 melting of the ice. It was, therefore, also a period of great lakes and 
 flooded rivers. Over the inland seas and great lakes, masses of ice, 
 loosened from the ice-sheet on their northern borders, floated. It was, 
 therefore, also a period of icebergs. From. this subsided condition the 
 land rose again gradually to its present condition. This restoration is 
 sometimes called the Terrace epoch. 
 
 Although we call these divisions epochs, yet we must not suppose 
 that they are equal in length to the epochs of earlier times. As we 
 approach the present time, and the number and interest of events in- 
 crease, our divisions of time become shorter and shorter. 
 
 It is so diflBcult to separate these epochs sharply from each other in 
 all countries, and to synchronize them, that it seems best to treat of the 
 whole Quaternary period, taking up the >epochs successively — first in 
 Eastern North America, as the type or term of comparison, then of 
 the same on the Pacific coast, and last of the same in Europe. 
 
 Quaternary Period in Eastern North America. 
 
 I. Glacial Epoch. 
 
 The Materials — Drift. — Strewed all over the northern part of 
 North America, over hill and dale, over mountain and valley, covering 
 alike nearly all the country rock, Archaean, Palaeozoic, Mesozoic, and 
 Tertiary, to a depth of 30 to 300 feet, and thus largely concealing 
 them from view, is found a peculiar surface soil or deposit. It con- 
 sists of a heterogeneous mixture of clay, sand, gravel, pebbles, sub- 
 angular stones of all sizes, unsorted, unstratified, unfossiliferous — of 
 all sorts of materials on all sorts of bed rock, wholly unrelated to the 
 underlying rock and therefore universally shifted. The lowest part, 
 lying in immediate contact with the subjacent country rock, is often 
 a stiff clay inclosing subangular stones— i. e., rock-fragments with the 
 corners and edges rubbed off. This we will call the "Stony clay'' 
 or ''Bowlder clay " or " Till." It is precisely like the ground-moraine 
 of a glacier (p. 55). Over this is often found in places a looser material 
 with angular stones, like the top moraine of glaciers. Lying on the 
 surface of this drift-soil are found many bowlders of all sizes, often of 
 huge dimensions, sometimes even 100 tons or more. The imbedded 
 subangular stones are usually marked with parallel scratches (Fig. 941), 
 and the large surface-bowlders are usually angular and unscratched. 
 The depth of this material is greatest in the valleys and least on hill 
 and mountain tops. 
 
570 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 It is difficult, nay, impossible, to give a description of this peculiar 
 deposit, which will apply in all cases. Sometimes scattered about 
 irregularly through the unstratified mass are portions which are 
 roughly and irregularly stratified, the laminae being often contorted 
 
 Pio. 941.— Glacial Bowlders, LimeBtone, from the Drift, a, from Toledo, Ohio; J, from Rochester, 
 
 New York. 
 
 in the most fantastic way. Sometimes the true stony clay or till is cov- 
 ered with a more regularly stratified material, consisting of sand and 
 gravel, apparently subsequently deposited from water. This is par- 
 ticularly the case in the basin of the Mississippi, as, e. g., in Ohio, 
 Illinois, and Iowa. It is probable, however, that much of this belongs 
 
 Fig. 942.— Drumlin, Wayne County, New York. View looking northeast. The south end is cut 
 away by wave erosion of Lake Iroquois. 
 
 to the next epoch, Champlain. Sometimes irregular mound-like de- 
 posits are left in the retreat of the ice. These are called Jcames, 
 drumlins, and esJcers (see p. 73). Karnes are mound-like deposits 
 of stratified materials (see Fig. 61). When elongated and meander- 
 
GLACIAL EPOCH. 5Y1 
 
 ing they are called eskers (osar) (see Fig. 63). Drumlins are mounds 
 or ridges of till elongated in the direction of glacial motion. The 
 conditions under which these are formed are imperfectly understood, 
 but it is believed that kames and eskers are deposits from super-glacial 
 or subglacial streams, while drumlins are masses of ground-moraine 
 
 Flo. M3.— Till on Crose-bedded Dakota Sandstone, Bennett, Nebraska. {Photograph by E. H. 
 
 ^Barbour.) 
 
 heaped into rounded and dolphin-back forms by the unequal flow and 
 pressure of the ice (see p. 71, and Figs. 60, 942). 
 
 We have said that the deposit is peculiar. In the Southern Atlan- 
 tic States, for instance, the soil is mostly either the insoluble residue 
 of rocks decomposed in situ^ or else consists of neatly stratified sands 
 and clays. 
 
 Drift-material is not usually represented on geological maps, since 
 it covers all kinds of country rock ; or else the colors representing the 
 
 Fio. 944.— Outcropping Eroded Country Eock overlaid by Prift. 
 
 various kinds and ages of country rock are simply dotted to indicate 
 the presence of this surface-material. In sections, of course, it is 
 easily represented, as in Fig. 944. 
 
 The Bowlders.— The most casual examination of the great bowlders 
 is sufficient in many cases to show that they do not belong to the coun- 
 try where they now lie, for they are of entirely different material from 
 
572 CENOZOIC ERA— AGE OF MAMMALS. 
 
 the country rock. For example, blocks of granite are found where 
 there is no granite within many miles, blocks of sandstone on a coun- 
 
 FiG. 945.— Glaciated Limestone, Kingston, Iowa. (Pliotograph by F. M. Fultz, Iowa Geological 
 
 Survey.) 
 
 try rock of limestone, or vice versa. In some cases it is easy to find 
 the parent ledge from which these great fragments were torn, and thus 
 to trace the direction of their transportation. From many observations 
 
 FiQ. 946.— Bed-rock scored with Glacial Marks, near Amherst, Ohio. (From a photograph by 
 
 Chamberlin.) 
 
GLACIAL EPOCH. 
 
 573 
 
 of this kind it has heen determined that in New England the bowlders 
 have come usually from the northwest, in Ohio from the north, and in 
 Iowa from the northeast. In other words, from the highlands of 
 Canada and a ridge running thence northwestward (Archtean area), 
 the general direction of travel has been southeast, south, and south- 
 west. Worth of the Archsean areas the travel was probably in some 
 cases even northward. The distance carried may be only a few miles, 
 or may be ten, fifty, one hundred, or even several hundred miles. In 
 many cases they must have been carried across valleys 1,000 or 3,000 
 feet deep, and lodged high up on the mountain beyond. In many 
 portions of New England and about Lake Superior the number of 
 fragments, small and great, is so large as seriously to encumber the 
 soil. Not only the large bowlders, however, but the whole mass of 
 
 Fio. 947.— Glacial Flutings of Bed-rock, near Burlington, Iowa, x A (after Keyes). 
 
 the material we have been describing, seem to have been shifted to a 
 greater or less extent. It is for this reason that the material has been 
 called Drift. 
 
 Surface-Eock underlying Drift.— On removing the drift-covering 
 the underlying rock is often found to be polished, planed, and scored 
 with parallel lines, strice (Figs. 945, 946), and rarely deeply fluted 
 (Fig. 947), and, if very hard, perhaps moutonneed. Examinations 
 of the scorings show that they often pass straight up inclines for 
 considerable distances, i. e., up one side of a hill, over the top, and 
 down the other side. Their direction is uninfluenced by smaller in- 
 equalities of surface, though they are thus influenced by the great 
 valleys and mountain-ridges. 
 
 The general direction of the scorings corresponds with that of 
 
574 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 transportation of the bowlders, showing that they are due to the same 
 cause. Perfect soil on perfect sound rock alwaj's shows -that the soil 
 has not been formed in situ, but has been shifted: the polishing, plan- 
 ing, scoring, etc., of the rock show that the agent of the shifting has 
 been ice. 
 
 Extent.- — The general extent of these more conspicuous and char- 
 acteristic phenomena, viz., the glaciation, the stony clay, and' the great 
 bowlders, is down to about 38° north latitude in the Mississippi 
 valley. The southern boundary is given on page 579, and in Fig. 
 949. South of this line the characteristic phenomena mentioned 
 above are not found except as produced by local glaciers in high 
 
 Fig 948 —Moraines of Grap3 Creek Sangre del Custo Mountains Colorado (after Stevenson) 
 
 mountains, as in Colorado, where the glaciation and the moraines 
 are very conspicuous (Fig. 948). But the valleys leading southward 
 or away from the glaciated territory contain an enormous amount 
 of detritus, valley-train drift, carried down by the profuse glacial 
 drainage. 
 
 Marine Deposits. — Along the Atlantic coasts we find no marine 
 deposits of this time, for the obvious reason that the continent was 
 then more elevated than now; whatever marine deposits were then 
 formed are now covered by the sea. 
 
 Theory of the Origin of the Drift. 
 
 When the phenomena of the Drift were first observed, they were 
 supposed to indicate the agency of powerful currents. A sudden 
 upheaval of the ocean-bed in northern regions was supposed to have 
 precipitated the sea upon the land, as a huge wave of translation. 
 
THEORY OF THE ORIGIN OF THE DRIFT. 5*75 
 
 which swept from north toward the south. Hence the deposit was 
 often called' Diluvium (deluge-deposit). Now, however, they are 
 universally ascribed to the agency of ice acting slowly through great 
 periods of time. Hence the name Glacial epoch* 
 
 Statement of the most Probable View. — The most probable view 
 for America, and also for other countries, is, that the Drift, or at least 
 the most characteristic phenomena of the Drift, viz., the glaciation, 
 the unsorted bowlder-clay^ and in many cases also the great traveled 
 bowlders, are due to the action of glaciers. They are therefore a land 
 deposit, and not a sub-aqueous deposit. For general proof of this, lei 
 any one study the phenomena of living glaciers, in the Alps and else- 
 where; then let him study the appearances left by the recently dead 
 glaciers of the Sierra ; and then let him study the phenomena of the 
 Drift, especially the stony clay and the underlying glaciated surfaces. 
 It will be impossible for him to come to any other conclusion than 
 that the same agent has been at work in all these. In some cases 
 still more conclusive evidence is found in the existence of distinct 
 terminal moraines. 
 
 Objections answered. — Many objections have been brought against 
 this view, which may be compendiously stated as follows : 1. In glacial 
 regions, like Switzerland, the Himalayas, etc., the glaciers run in all 
 directions; but the Drift was carried over wide areas, in a general 
 direction. Such a general direction is easily accounted for by the 
 iaction of icebergs carried by marine currents. 3. The agent of the 
 Drift seems to have been often uninfluenced by the direction of valleys 
 and ridges even of considerable size ; thus, for instance, bowlders are 
 carried across valleys 500 or 1,000 feet deep, and lodged as high up 
 on the mountain-slope on the other side. This is perfectly consistent 
 with the action of icebergs drifting over an uneven sea-bottom, but 
 inconsistent with our usual notions of glacial action. 3. The great 
 distance carried, sometimes one hundred miles or more, is precisely 
 what we might expect of icebergs, but difficult to reconcile with our 
 usual notions of glaciers. 4. Alpine glaciers will not move on a slope 
 of less than 2° or 3°, but such a slope, carried several hundred miles, 
 would produce an incredible elevation of land. A slope of 2|° for 300 
 miles would produce an elevation of nearly nine miles ! 
 
 These were unanswerable objections so long as our ideas of glaciers 
 were confined to those of temperate climates; but they all find their 
 complete answer in the phenomena of the polar ice-sheet. Greenland 
 is 1,300 miles long and 400 or 500 miles wide. This whole area of 
 over a half-million of square miles is covered 3,000 to 6,000 feet deep 
 
 * For an account of the dilurial hypothes^ and the history of the glacial theory in 
 America, see American Geologist, vol. xxii, pp. 184-189. Proc. Amer. Assoc. Adv. Sci., 
 vol. xlvii, 1898, pp. 257-290. 
 38 
 
576 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 with ice. This ice-mantle moves en masse seaward, molding itself on 
 the surface inequalities of the country, and chiseling that surface be- 
 neath itself, producing universal glaciation, and only separating into 
 distinct glaciers at its margin. In antarctic regions, the general ice- 
 sheet is even still more extensive and thick. Its extent has been esti- 
 mated as 4,000,000 to 8,000,000 square miles, and its thickness 10,000 
 feet. Now, it is to such an ice-mantle that the Drift is to be ascribed, 
 for it moves irrespective of smaller valleys, in one general direction 
 over great areas, to great distances, and over a slope of only 1° or 
 even -|°. 
 
 Condition of the Continent during the Glacial Epoch— Centers 
 of Glaciation. — During Tertiary time the northern part of the con- 
 tinent was probably 2,000 to 3,000 feet above its present level. The 
 
 Fia. 948a.— Glacial Area in North America, and Centers of Ice Dispersion (after Salisbnry). 
 
 shore-line was at least as far out as the submerged continental mar- 
 gin, and all the coast islands of this part were added to the continent. 
 The evidence of this is found in submarine channels off the mouths 
 of all the great rivers, such as the St. Lawrence, the Hudson, the 
 Delaware, etc., trenching the submerged continental plateau and 
 deeply notching its border ; for these were evidently formed by erosion 
 during the Tertiary. The axis of elevation was the Canadian Archae- 
 
THEORY OF THE ORIGIN OF THE DRIFT. 577 
 
 an highlands, and thence it became less both northward and south- 
 ward, but undoubtedly extended to the shores of the Gulf. Either 
 coincidently with this elevation or subsequently (the facts are not 
 yet clear), much of the northern part of the continent was covered 
 with glacial ice : 10,000 feet thick over Canada, 6,000 feet over New 
 England, and thinning to its border. It was formerly supposed that 
 the ice-sheet covered, as a single mass, all the circumpolar lands. It 
 is now known that a large part of Alaska and the low lands of the 
 Arctic archipelago were not glaciated. From study of the drift phe- 
 nomena it is also found that there were three centers of ice disper- 
 sion; that is, of ice accumulation and radial outflow (Fig. 948a). 
 It is believed, furthermore, that these three ice bodies were not en- 
 tirely contemporaneous, but that there was an eastward progress of 
 the maximum glacier development. The westernmost and earliest of 
 the centers was the Cordilleran, which developed in the mountain 
 region of British Columbia (see p. 587) ; the intermediate center 
 was the Keewatin, west of Hudson Bay; while the third and prob- 
 ably somewhat later ice body was the Labradorian, east of Hudson 
 Bay. A fourth center, the Greenlandian, is in full existence to-day. 
 From these glacial centers the ice flowed in all directions, but espe- 
 cially southward, on the side of greater warmth and moisture (see 
 p. 617). The ice moved southeastward, southward, and southwest- 
 ward over Kew England, New York, Ohio, Illinois, Iowa, and Dakota, 
 regardless of all but the greatest inequalities — filling the valleys, 
 sweeping over the mountain-tops, and glaciating the whole surface in 
 its course. Its eastward limit was beyond the present coast-line; its 
 southern limit about 38° to 40° north latitude (Fig. 949). Even 
 farther south, high mountain-ranges, like the Colorado mountains, 
 were ice-covered, and great Alpine glaciers streamed down their 
 flanks and left their moraines (Fig. 948). Along the New England 
 coast possibly the ice-sheet in many places ran into the sea and pro- 
 duced icebergs. 
 
 Glacial and Interglacial Epochs.— The glacial history in America is 
 complicated not only by the fact of several centers of ice-accumulation 
 and dispersion, probably somewhat discordant in time, but also by 
 great oscillations in the positions of the ice-sheet margins. There 
 was not simply one advance of the ice and then a final retreat, as was 
 formerly supposed, but the continental glaciers advanced and receded 
 several times. The proof of temporary removals of the ice (deglacia- 
 tion) is found in old soils or forest-grounds, peat-beds and lake de- 
 posits interbedded with the till, and erosion channels, all requiring 
 open land surface. Indications of mild climate are given by the re- 
 mains of certain species of plants and animals. After much discus- 
 sion, it is now generally believed that the areas and the time involved 
 
378 
 
 CENOZOIC EKA— AGE OF MAMMALS. 
 
 in the deglaciation intervals are quantitatively sufficient to constitute 
 interglacial epochs. This applies to both Europe and America. 
 
 In Europe, six glacial and five interglacial epochs are recognized, 
 the second glacial invasion being the greatest. In Europe and Amer- 
 ica the oscillations of climate seem to be contemporaneous.* 
 
 * See Geikie's The Great Ice Age, particularly the concluding chapter by Chamberlin. 
 Also the Journal of Geology, vol. iii, 210 ; iv, 872. 
 
THEORY OF THE OJJIGIN OF THE DRIFT. 579 
 
 The Glacial time divisions in America have been given geographic 
 names, following Chamberlin. In the following table * these are 
 arranged in stratigraphic order. 
 
 Divisions of American Pleistocene. 
 
 The present time of deglaciation. 
 6. Late Wisconsin drift sheet. 
 
 Unnamed recession interval (short). Fifth. 
 5. Early Wisconsin drift sheet. 
 
 Peorian interglacial beds. Fourth. 
 4. lowan drift sheet, and main loess deposit. 
 
 Sangamon interglacial beds. Third. 
 3. Ulinoian drift sheet. 
 
 Yarmouth interglacial beds. Second. 
 2. Kansan drift sheet. 
 
 Aftonian interglacial beds. First. 
 1. Alberton or sub- Aftonian drift sheet. 
 
 Limits of the Drift— Terminal Moraines.— The extreme limit of 
 glaciation in America is shown in Figs. 948a, 948&, 949. The east- 
 ernmost end emerges from beneath the sea at Cape Cod; thence it 
 passes southwest through Nantucket, Martha's Vineyard, and Long 
 Island. It crosses the ancient Hudson Valley at the "Narrows," 
 where the morainal hills nearly block the valley and support the 
 fortresses which guard the entrance to New York harbor. It then 
 runs north of west through New Jersey and northeastern Pennsyl- 
 vania into New York at Salamanca. It then swings to the south- 
 west, following in general the north side of the Ohio River to the 
 Mississippi; thence it follows the Missouri along the south side; and 
 so northwestward through Montana into British America. This may 
 be called the glacial boundary. It is but little affected by topography, 
 passing over hill and dale quite indifferently. 
 
 From Cape Cod to western Pennsylvania the glacial limit as given 
 above is the terminal moraine of the Wisconsin drift. But there is 
 a correction to be made here. In 1892 Salisbury showed that in New 
 Jersey and Pennsylvania is an area of very ancient and extremely 
 weathered and eroded glacial drift extending beyond the reach of the 
 Wisconsin ice-sheet. This is indicated in the map. Fig. 9486. It may 
 be as old as the Kansan. 
 
 Westward from Pennsylvania the glacial limit is formed of the 
 
 * The table of American diyisiona of the Pleistocene is modified from Leverett'a 
 filacial Formations and Drainage Features of the Ohio and Erie Basins, Monog. xli, 
 U. S. Geol. Surv., 1903. 
 
580 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 attenuated edges of the older drift sheets, which were not entirely 
 overridden by the Wisconsin. In western Pennsylvania this is the 
 Kansan (or pre-Kansan), but from central Ohio westward it is the 
 Illinoian to the Mississippi, and the Kansan west of the Mississippi. 
 
 Fig. 949. — Map showing the Extreme Boundary of the Ice-sheet, the moraines of the Wisconsin 
 epoch, and the south end of Lal^e Agassiz, 
 
 (See Plate I in Monograph XXXVIII, United States Geological 
 Survey.) The lowan is not a border drift, but forms areas on the 
 Kansan, east and west of the "Driftless Area'' (see p. 581). The 
 Kansa:n is the drift sheet which is the most widespread, and marks 
 the greatest southward extension of the ice. The age of the Kansan 
 is estimated as fifteen times that of the Wisconsin. 
 
 West of central Ohio the Wisconsin drift forms the remarkable 
 series of concentric, lobate, retreatal moraines (roughly suggested in 
 Fig. 949), which mark the successive positions held by the oscillating 
 margin of the ice in its general retreat. The lobation of the Wiscon- 
 sin ice front is a striking character.* 
 
 One can not but be struck with the great difEerences between the 
 earlier and later advances of the ice-sheet, both as to the character of 
 the border and the distinctness of the moraine. The limit of the first 
 advance' is comparatively even and its moraine indistinct. The limit 
 
 * The reader should consult the following classics on this subject : T. C. Chamberlin, 
 in 3d An. Kep. U. S. Geol. Surv. ; Frank Leverett, Monographs xxxviii, xli, U. S. Geol. 
 Surv. ; R. D. Salisbury, Geol. N. J. ; Frank Taylor, Jour. Geol., v, 421 ; C. R. Dryer, Studies 
 in Indiana Geo". 
 
CHAMPLAIN EPOCH. 
 
 581 
 
 of the later advance is deeply lohed and its moraine very distinct. 
 It is probable that bgth these peculiarities are due to differences in 
 accumulation and motion of the ice near the border. In the first 
 advance the extreme limit was determined not so much by glacial mo- 
 tion as by southern limit of perpetual snow. The motion near the 
 border was sluggish and the drift border therefore attenuated. In the. 
 later advance the border was reached wholly by onward glacial mo- 
 tion, which, of course, accumulated a distinct moraine. The lobes 
 were in the line of swiftest motion. 
 
 Driftless Areas,— On the map, Fig. 9486, may be seen in the upper 
 part of the dark-shaded region of the older drift a light-tinted tract, 
 chiefly in Wisconsin but reaching into Iowa and Illinois, marked 
 " Drif tleSs Area." Here is a surprising fact in glacial geology. This 
 is a tract of some 10,000 square miles which has not been glaciated, 
 although the ice-sheets overran all the surrounding territory. The 
 proofs of non-glaciation are clear. The mantle is all residuum from 
 rock decay (geest), and not drift. There are no narrow ravines, no 
 lakes, no cataracts, all of which abound in the surrounding glaciated 
 region. On the other hand, the erosion forms are those of atmospheric 
 action, and rock towers and pillars exist, along with open valleys. It 
 will be evident to the reader that no glacier ever swept over the land 
 and left in position such forms as are shown in Figs. 949a. 
 
 The explanation of the driftless area, which is not an elevated 
 tract, is believed to be the diversion of the ice-flow into directions 
 away from the area, along with insufficient quantity or depth of ice 
 
 Fig. 949a.— Rock Towers in Driftless Area, Iowa, a, Oneota limestone, near Waulcon ; b. Galena 
 limestone, near Dubuque. (Photographs by S. Calvin.) 
 
 at this point. The lowan ice-sheet failed to conquer the area, and the 
 Wisconsin halted at the eastern margin. Since the area was described 
 by Chamberlin and Salisbury in 1886 * another small area was dis- 
 
 • In the 6lh An. Rep. tJ. S. Geol. Surv. 
 
582 CENOZOIC ERA— AGE OF MAMMALS. 
 
 covered by Salisbury, 1891, farther south on the Mississippi, chiefly 
 in Illinois, which is also shown in the map. 
 
 Post-Glacial Time — " Champlain Epoch." 
 
 During the early part of the Glacial epoch the whole northern 
 portion of the continent was elevated 1,000 to 3,000 feet above the 
 present condition; the northern ice-sheet had advanced southward lo 
 40° latitude, with still farther southward projections favored by local 
 conditions; and an arctic rigor of climate prevailed over a large part 
 of the United States. During this epoch an opposite or downward 
 movement of land-surface over the same region, possibly increased 
 by the weight of accumiilatihg ice, commenced and continued until 
 a depression of 500 to 1,000 feet below the present level was attained. 
 As a necessary consequence, large portions of the now land were sub- 
 merged ; it was therefore a time of inland seas. Another result, or at 
 least a concomitant, was a moderation of the climate, a melting of 
 the glaciers, and a final retreat of the ice-sheet northward. It was 
 therefore a time of flooded lahes and rivers. Lastly, over these inland 
 seas and great lakes loosened masses of ice floated as icebergs. It was 
 therefore pre-eminently a time of iceberg action. The evidences of 
 the condition of things described above are found in raised sea 
 beaches, old lake shore-lines, elevated river plains, and terraces. 
 
 1. Elevated Sea-Beaches— Marine Deposits.— Old sea-margins, con- 
 taining shells and other remains of living species, are found all along 
 the Northern Atlantic coast, becoming higher as we pass northward 
 and landward. In southern New England the highest beaches are 
 40 to 50 feet; about Boston they are 75 to 100 feet; in Maine they 
 are 300 feet and upward; on the Gulf of St. Lawrence they are 470 
 feet; in Labrador 1,500 feet (Upham). In arctic regions they are in 
 some places 1,000 feet (Dana). 
 
 The limit of continental subsidence was reached, at least in the 
 eastern part of the United States, long before the Wisconsin ice-sheet 
 disappeared, and re-elevation was in progress during the final retreat 
 of the glacier. The altitude of the land, however, was so much lower 
 than now that when the ice melted away from the St. Lawrence Valley 
 the ocean invaded the basins of Champlain and Ontario. The water 
 of Ontario was then a gulf of the sea. The valleys of Champlain and 
 Hudson formed a strait connecting New York and Hudson Bays. 
 The high-level marine deposits in the Champlain Valley were recog- 
 nized long ago by the abundance of marine shells and the skeleton 
 of a whale. It was these deposits, found up to the height of 400 
 feet over the present lake, which gave the name "Champlain" (Ed- 
 ward Hitchcock) to the Postglacial time of low land-level. With the 
 subsequent uplift of the land the Ontario and Champlain waters 
 
CHAMPLAIN EPOCH. 533 
 
 were cut ofE from the sea, and have been rinsed out to be fresh-water 
 bodies. 
 
 The marine terraces in the Hudson "Valley have altitudes at New 
 York 70 feet, near Newburg 180 feet, at Albany 335 feet (Merrill), 
 and in the Champlain Valley 400 feet at the south end to 500 feet at 
 the north end. These proofs of greater recent submergence of the 
 Hudson Valley may be seen by the traveler along the Hudson in the 
 conspicuous leveled stretches of alluvium on the west side of the 
 valley, which are chiefly the deltas built by streams pouring into the 
 sea from the side valleys. 
 
 Extending up the Mohawk Valley from Albany to west of Sche- 
 nectady is a vast plain of sand and gravel, traversed by the Few York 
 Central Eailroad. This is the great delta built in the sea by the 
 powerful river, the Iroquois-Mohawk, which was the functional prede- 
 cessor of the St. Lawrence, since it carried the overflow of the Great 
 Lakes while the ice-sheet blocked the St. Lawrence outlet (see p. 585). 
 The crust-oscillations characteristic of this period are detectable along 
 the South Atlantic and Gulf coast. During the early Quaternary 
 (Glacial epoch) the continental elevation is shown by the erosion of 
 the La Fayette formation, referred by McGee to the latest Pliocene 
 and by Hilgard to the early Quaternary. During the period of subsi- 
 dence j the coastal plains were again covered by the sea, and the shore 
 was again at the fall-line. The deposits of this time form the Colum- 
 bian formation of McGee. Finally, from this subsided condition the 
 land rose to its present level, forming a succession of elevated beaches 
 or terraces. 
 
 2. Glacial Lakes. — The term " glacial lake " signifies a body of 
 water which owes its existence to a glacier as a barrier. The history 
 of the glacial waters is the closing chapter in the dramatic story of 
 the Ice Period. Many larger lakes in the region affected by the Drift 
 show unmistakable evidences of a far more extended and higher con- 
 dition of the waters than now exists. About these lakes is found a 
 succession of terraces or old lake-margins. The highest of these 
 marks the highest water-level, and is the oldest; the lower ones .mark 
 successive steps in the draining away of the waters. For example, 
 about Lake Ontario successive margins are found up to 600 feet 
 above the present lake-level; about Lake Erie up to 250 feet; about 
 Lake Superior, up to 603 feet (Lawson) ; and similar margins are 
 found about Lakes Michigan and Huron. It is now certain that the 
 retreating ice-front acted as a barrier, against which accumulating 
 water formed enormous lakes, over which floated icebergs loosened 
 from the glacier. These lakes drained southward into the Ohio and 
 Mississippi until the barrier was removed by the final retreat of the 
 ice-sheet ; and then northeastward, as now, through the St. Lawrence. 
 
584 
 
 OENOZOIC ERA— AGE OF MAMMALS. 
 
 It will be evident to the reader that no glacial lake could form at 
 the ice front where the latter was south of the divide and the drain- 
 age was free. Here were hooded streams, carrying heavy loads of 
 detritus from the glacier. The south-leading valleys are deeply filled 
 (aggraded) with the products of glacial action, distributed by the 
 glacial drainage (see p. 5866). But as soon as the ice front at any 
 point receded to northward of the divide, standing waters would be 
 held between the glacier and the land slopes facing it. (In many 
 cases, particularly in valleys, the divides were newly established by 
 the moraine drift, the work of the glacier itself. This is the case 
 in all the valleys of the Finger Lakes region of central New York.) 
 
 Fig. 9496.— Shore of Lake Iroquois, three miles south of Adams, N. Y. 
 
 The present Great Lakes of the Laurentian basin had their in- 
 ception in three primitive glacial lakes, all tributary to the Missis- 
 sippi. One was Lake Duluth, held by the glacier in the west end of 
 the Superior basin, having its outlet by the St. Croix River. Another 
 was Lake Chicago, impounded by the glacier in the south end of the 
 Michigan basin, its drainage having made the great channel now 
 utilized by the Chicago drainage canal. Still another was Lake Mau- 
 mee, in the western end of the Erie basin, overflowing at Fort Wayne 
 to the Wabash River. As the broad front of the glacier lobes re- 
 treated the lakes correspondingly expanded. As Lake Chicago had 
 the lowest outlet across the divide, it finally received the overflow 
 of the other lakes mentioned, or made them tributary to itself. After 
 a time a lake held in the Saginaw Valley, with outlet by the Grand 
 River to Lake Chicago, received the overflow of the successor to Lake 
 
CHAMPLAIN EPOCH. 535 
 
 Maumee, called Lake Whittlesey. The highest of the beaches in the 
 Erie basin is of course the shore-line of Lake Maumee, correlating 
 with the Fort Wayne outlet; but the highest along the south side 
 of the basin extending into New York is the Whittlesey shore-line, 
 commonly known as the " Belmore " beach. Finally, all the broad 
 waters in the Erie and Huron basins became confluent with those in 
 the Saginaw Valley, and the expanded waters are called Lake Warren. 
 It was tributary to Lake Chicago through the Grand Eiver Valley, 
 probably with a slight fall. As the Erian-Ontarian lobe of the gla- 
 cier continued its recession. Lake Warren crept eastward past the ice 
 front into central New York, reaching ultimately as far as Syracuse. 
 Here the long persistent Lake Warren came to its extinction through 
 the opening of channels of escape for the water past the ice front to 
 the Mohawk Valley, lower than its old outlet westward across Michi- 
 gan. In the Syracuse region are most remarkable channels cut by 
 the escaping Warren and Hypo-Warren waters. These are great 
 canons lying athwart the high north-and-south ridges, with several 
 huge extinct cataracts. In the amphitheaters of the latter are plunge- 
 basin lakes, such as would exist at the foot of Niagara were the 
 river to cease its flow. These fossil cataracts and canons attest the 
 long-continued work of rivers which were literally the predecessors of 
 Niagara. 
 
 Within the glaciated area many valleys leading northward con- 
 tained local glacial lakes. Many readers of these pages may be able 
 to explain local features by this fact. This is strikingly true of the 
 large valleys in the Finger Lakes region of central New York. The 
 glacial lake in the Seneca Valley, with outlet at Horseheads south- 
 ward to the Chemung River at Eliiiira (see Fig. 950), was the largest. 
 It finally attached to itself the waters of Cayuga and Keuka Valleys 
 on either side, and is called Lake Newberry. This lake and all the 
 local glacial lakes of central New York were eventually blended into 
 Lake Warren. 
 
 The last stage of the glacial waters in this region was Lake Iro- 
 quois, which occupied the Ontario basin, with outlet at Eome to the 
 Mohawk Valley, as long as the glacier blocked the St. Lawrence outlet. 
 The Iroquois beach is a well-known feature encircling the present 
 lake in the Ontario basin, and usually supports a " ridge road." 
 Students of this subject believe that on account of the low altitude 
 of the land during the ice retreat the waters of Superior and Huron 
 basins found lower escape for a time from Georgian Bay through 
 the Trent River to Lake Iroquois than by St. Clair and Detroit 
 Rivers and Lake Erie; and that later the escape was through the 
 Nipissing and the Ottawa River directly to the sea. 
 
 Probably the largest glacial lake in area was Lake Agassiz, in the 
 
586 CENOZOIC ERA— AGE OF MAMMALS. 
 
 Winnipeg basin, with outlet south at Lake Traverse and Big Stone 
 Lake to the Minnesota River (see Fig. 949).* 
 
 The history of the glacial waters, merely outlined above, is de- 
 ciphered by tracing the old shore-lines and the correlating outlet 
 channels; also the moraines which mark the positions of the glacial 
 barriers. The deformation of the beaches, or change from the orig- 
 inal horizontal position, which gives us some idea of the amount of 
 land uplift and warping and of the shifting of lake outlets, will be 
 discussed later. 
 
 Postglacial Land Warping. — The drowned valleys of the northern 
 coasts, as the Chesapeake, Delaware, Hudson, St. Lawrence, and all 
 the bays on the Pacific coast, and. all the deep fiords of' high-latitude 
 coasts, are evidence of the much higher altitude of northern lands 
 during Tertiary time, and consequently of later subsidence; while 
 the occurrence of very recent marine deposits stranded above sea- 
 level is proof of that much rise of the land in more recent time. It 
 will be understood, with mere statement, that the up-and-down move- 
 ment of any limited area of the earth's surface requires a tilting of 
 the land on the borders of such area. It appears that during Pleisto- 
 cene time the northeastern portion of the United States has been 
 such border region of tilting. The fact is implied in the former state- 
 ments that the uplifted marine deposits (p. 582) are progressively 
 higher to the northward. 
 
 The fact of elevated beaches about the Great Lakes does not alone 
 prove land elevation, but only higher waters by ice-damming. But 
 there is positive proof of epeirogenic movement in the interior of 
 the continent in recent time, amounting to hundreds of feet. It is 
 found in the present slope of the glacial lake beaches. They have 
 been more or less continuously traced about all the Great Lake 
 basins, and they invariably show a rise to the northward. It is quite 
 unnecessary to say more than that these beaches could have been 
 formed only in horizontal position, and that therefore any present 
 lack of horizontality is due to land movement. If the great area 
 had lifted bodily without tilting the beaches would still be level and 
 parallel. However, surveys show that the glacial lake beaches are not 
 only sloping, but not even parallel, which indicates that the canting 
 of the land was progressing during the ice retreat. 
 
 It is estimated that the direction of maximum uplift over the 
 Great Lakes area is north, 37° east (Taylor and Gilbert). In the 
 
 * Description of Lake Agassiz will be found in Monograph xxt, IT. S. Geol. Surv., hy 
 Warren TJpham. Maps of the glacial lakes in the Huron and Erie basins are found in 
 Leverett's Monograph xli, TJ. S. Geol. Surv., and in articles by F. B. Taylor. The glacial 
 waters in Ifew York have been described by H. L. Fairehild in articles in Bull. Geol. Soc. 
 Amer., and in Reports of the New York State Geologist for 1900 and later. 
 
CHAMPLAIN EPOCH. 
 
 586a 
 
 Erie and Ontario basins the Warren shore-line has a slope of about 
 two feet to the mile, on the average. At the east end of the Ontario 
 basin the Iroquois beach from Eichland to Watertown has a rise of 
 over five feet to the mile. 
 
 Thus we have not only proofs of continental uplift in very recent 
 time, but equal proof of differential uplift, or warping of the land. 
 The reader will naturally ask if the uplifting has entirely ceased, 
 and the topic will have more life when we answer: No, the tilting 
 is still in progress. 
 
 By remeasuring the engineers' benches, which were established by 
 the United States Lake Survey in 1870-'75, and determining their 
 present relation to the lake levels, Gilbert has found that the basins 
 of the lakes are now tipping, producing a rise of the waters on the 
 
 Pig. 950.— Terraces at Horseheads, N. Y. Ancient flood-plains of the outltt of glacial Lake 
 
 Newberry. 
 
 south sides and a lowering of the waters on the north sides of the 
 basins. He has estimated that the rate of land-tilting during the last 
 thirty years is equal to five inches in 100 miles in one hundred years.* 
 This may seem a small or slow change, but geologically it is rapid 
 and of great importance. At this rate of tilting it will require only 
 about three thousand years for the waters of Lake Erie and the 
 upper lakes to be diverted from Niagara to the former outlet at 
 Chicago to the Mississippi. 
 
 3. River Terraces and Old Flood-Plain Deposits.— Nearly all the 
 rivers in the eastern portion of the continent, over the Drift region, 
 are bordered with high terraces, which have been cut wholly out of 
 an old flood-plain deposit belonging to the Champlain epoch (see 
 Eig. 17, p. 25). 
 
 * 6. E. Gilbert. Recent Earth Movements in the Great Lakes Region, Eighteenth 
 Ann. Rep., U. S. Geol. Surv. 
 
5865 CEKOZOIC ERA— AGE OP MAMMALS. 
 
 An examination of the rivers north of the fortieth parallel shows : 
 1. An old river-valley far deeper and broader than the present; 2. 
 This deep and broad river-valley is filled up, often several hundred 
 feet deep, by old river-deposit j 3. Into this old river-deposit the 
 stream is again cutting, but usually far above the bottom of the old 
 river-bed. This cutting into the old river-deposit produces bluffs and 
 terraces on each side. It is evident that the great river-bed was 
 gouged out during late Tertiary and early Glacial epochs; the filling 
 up took place during the Champlain, and the cutting and terracing 
 during the re-elevation to the present condition. 
 
 The Connecticut Eiver is bordered on each side by a succession 
 of terraces rising one above and beyond the other, composed wholly 
 of old river-deposit. Beyond this, of course, is the country ro(?k of 
 Jura-Trias sandstone, covered more or less with drift. 
 
 The Mississippi River is bordered on each side by its present flood- 
 plain deposit, or river-swamps. This, as already said (p. 35), extends 
 from the mouth of the Ohio Eiver to the head of the delta, a distance 
 of 500 miles, and has an average width of thirty miles. This, its pres- 
 ent flood-plain deposit, is limited on the eastern side by bluffs in some 
 places 200 to 400 feet high, composed of Tertiary strata, capped with 
 an old river-silt, or Loess, fifty to seventy feet thick, and this, again, 
 covered by a yellow loam, which extends beyond the limits of the 
 Loess. A layer of La Fayette sand separates the Loess from the Ter- 
 tiary. Patches of the Loess or Mujf-deposit are found also on the 
 western side, showing that the old flood-plain extended beyond the 
 present flood-plain on both sides; but on the west side it has been 
 mostly removed by subsequent erosion. Also similar deposits, often 
 of great extent, form banks on each side of all the great tributaries 
 of the Mississippi. Beneath the present river swamp-deposit is found, 
 by borings, a deposit belonging, like the Loess, to the Champlain 
 
 \rv_^^w^--^- -;l__^<s^ 
 
 Fie. 951.— Ideal Section across Mbsissippi below Vicksbnrg : OS, Orange sand or La Payette ; P77, 
 Port Hudson, estuary deposit, Champlain ; Is, loess or old flood-plain deposit, Champlain ; 
 /, loam covering the Loess, but more extensive ; rs, river-swamp deposit, modern. 
 
 epoch, but to an earlier period, probably an estuary deposit, and 
 called by Hilgard " Port Hudson," varying in thickness from thirty 
 feet at Memphis to several hundred feet in the delta. Beneath this 
 is flrst the La Fayette sand and then the Tertiary. 
 
 All these facts are represented in the ideal section of the river and 
 
CHAMPLAIN EPOCH. 
 
 586o 
 
 the strata in its vicinity (Fig- 951), constructed from the investiga- 
 tions of Prof. Hilgard. It is evident that a great trough was hollowed 
 out in the Tertiary strata during the late Tertiary and early Glacial 
 epoch, filled with deposit to the level I I during the Champlain, and 
 again partly cut out diiring the subsequent re-elevation. 
 
 The cause of the filling of the river-valleys was partly the de- 
 pression of the land, forming estuaries; partly the smaller angle of 
 slope of the rivers, by reason of which the waters in their lower parts 
 ran off less rapidly, and therefore also deposited more sediment; 
 partly the greater abundance of the water-supply, from the melting 
 of the glaciers ; but chiefly, in many cases, the heavy load of detritus 
 contributed by the glacier. 
 
 Origin of the Loess. — Over large areas bordering the Mississippi 
 and its tributaries, and forming the conspicuous bluffs of these rivers, 
 there is found a peculiar deposit of very fine, even-grained, and usu- 
 
 Fia. 951a.— Loess (10-23 feet) overlying glacial drift (50-60 !eet), Endicott, Nebraska. (Photograph 
 
 by E. H. Barbour.) 
 
 ally unstratified material, remarkable for forming by river-erosion 
 perpendicular walls — although soft enough to be easily spaded. It is 
 usually destitute of organic remains, but when these are found they 
 consist of fresh-water shells, and especially of land-shells. When 
 fresh-water shells are found, the material is usually obscurely strati- 
 fied. Similar bluff -materials are found bordering nearly all the Euro- 
 pean rivers, such as the Ehine and Danube, and are there called 
 Loess, and- referred to the Champlain epoch. 
 
 Origin and History of the Great Lakes.— The origin of these lake- 
 basins is still doubtful. They probably did not exist in the Tertiary 
 period, but in their place was a great depression draining northeast- 
 ward. During the Glacial epoch this depressed area was swept out 
 and possibly deepened by the advancing ice-sheet. The irregular 
 gouging of the ice-sheet, the irregular choMng of the drainage area 
 by debris left by its retreat, and especially the irregular warping of 
 the earth-crust in re-elevation, rising more northeastward, probably 
 gave origin to the lakes. 
 
586(^ CENOZOIC ERA— AGE OF MAMMALS. 
 
 Quaternary Period on the Western Side of the Continent. 
 
 All the most characteristic phenomena of this period, such as old 
 sea-margins, general glaciation, flooded lahes, and old river-beds, are 
 abundant and conspicuous on the western side of the continent. As 
 it is impossible to synchronize perfectly these phenomena with those 
 already described on the eastern side, it will be best to take them in 
 the order named above and trace each kind through the whole period. 
 
 1. Sea. — The phenomena along the sea-coast show both elevation 
 and depression. A more elevated condition than the present is shown 
 by the bold, rocky coast and high islands standing a little way off the 
 coast. The islands ofE the coast of the southern part of California, and 
 separated from the mainland by the Santa Barbara Channel, are evi- 
 dently continental islands. They were undoubtedly a part of the con- 
 tinent during the late Tertiary and early Quaternary times, and were 
 separated subsequently by subsidence. This is clearly shown by their 
 flora, and especially by the remains of the Mammoth on one of them 
 — Santa Eosa. Another very striking proof of continental elevation 
 is found on this, as on the Eastern coast, in the existence of deep sub- 
 marine channels cutting through the submerged continental plateau, 
 and evidently produced by subaerial erosion during late Tertiary 
 times. I am indebted to Prof. Davidson for facts concerning these. 
 There are about twenty of these ofE the California coast, nine or ten of 
 which are very marked. Commencing at Cape Mendocino, and going 
 southward, four very deep ones are found in twenty-five miles — one, 
 very marked, in the Bay of Monterey, one in Carmel Bay, one off the 
 eastern entrance of Santa Barbara Channel, two in the Bay of Santa 
 Monica, and one off the harbor of San Diego. These channels show a 
 previous elevation of 2,500 to 3,000 feet. But there is one peculiarity 
 of these as compared with those on the Eastern coast, viz., that they 
 do not, in any evident way, correspond to the mouths of the present 
 rivers, but, on the contrary, often abut against a bold coast, rising to 
 3,000 feet within three miles of shore. The explanation of this differ- 
 ence is found in the enormous orographic changes which occurred on 
 this coast in early Quaternary tiines. Of this we will speak again. 
 
 Subsequent subsidence and partial re-elevation are still more clear- 
 ly shown by raised sea-margins. Lawson, confirming Davidson, finds 
 12 to 15 terraces at San Pedro and up to 1,200 feet above sea-level. He 
 has also found on the island of San Clemente 20 successive terraces up 
 to 1,500 feet above sea-level. Similar terraces are found also at Santa 
 Cruz up to 1,200 feet, and near Monterey up to 800 feet. It is doubt- 
 ful, however, whether these are Champlain or earlier. Lawson thinks 
 them Pliocene. During this period of subsidence (Champlain), the 
 Bay of San Francisco covered all the fiat lands about the bay, and all 
 
QUATERNARY PERIOD ON THE WESTERN SIDE OF THE CONTINENT. 587 
 
 the Talley continuations of the bay, north and south, such as Sonoma 
 and Napa Valleys on the north and Santa Clara Valley on the south. 
 Also the sea then passed through the Strait of Carquinez and covered 
 the whole San Joaquin and Sacramento plains, forming a great interior 
 sea 300 miles long and fifty miles wide. The margins of this sea are 
 still visible in the upper Sacramento Valley. At the same time the 
 sea entered the Columbia River and spread over the Willamette Val- 
 ley, forming a great sound, and passed up to, and possibly beyond, 
 the Cascades. About Puget Sound similar evidences of former ex- 
 tension are plain, especially at the southern end; while in British 
 Columbia Dawson finds old sea-margins up to 3,000 or even 3,000 
 feet above the present sea-level. Since that time, the coast-line has 
 been re-elevated to its present level, leaving successive lower terraces 
 which are conspicuous in some places. , Lake Tulare is a remnant of 
 the interior San Joaquin Sea, although it was probably first freshened 
 by an outlet into the San Joaquin River, and again salted by loss of 
 its outlet. 
 
 2. Ice. — We have already (p. 276) spoken of a great elevation of the 
 Sierra Range, which occurred, at the beginning of the Quaternary. 
 This mountain-lifting doubtless contributed to the development of gla- 
 cial phenomena at this time, but must not be confounded with the 
 general continental elevation which took place at the same time, as 
 shown by the sea-margin phenomena. 
 
 During the fullness of glacial times — as shown by Dawson * — a 
 continental ice-sheet covered nearly the whole of British Columbia, 
 Northwest Territory, and Alaska, connecting in high latitudes with the 
 Eastern sheet. The center of radial movement was a high area ex- 
 tending from 55° to 59° north latitude. - Prom this area the ice moved 
 southward, south westward, westward, and even northwestward. South- 
 waTd it certainly reached beyond 48°. Westward it flowed over the 
 Coast Ranges, filled the valleys (now submerged) separating the great 
 coast islands from the mainland, flowed over these islands, and ran into 
 the sea beyond (see p. 576). 
 
 At the same time it is certain that the Sierra f was completely 
 mantled with snow ; and great glaciers, some of them forty to fifty 
 miles long filled all the profound cafions which trench its flanks. At 
 the same time also there is some evidence that even the Coast Ranges, 
 favored by proximity to the sea, had their perpetual snow-cap from 
 which issued glaciers filling the principal valleys.| 
 
 * Geological Magazine, vol. v, p. Sil, ] 888. 
 
 f For a fuller account of the glaciers of the Sierra, and the condition of things during 
 the Glacial epoch, see American Journal of Science, vol. iii, p. 325, and vol. i, p. 26. 
 
 J: Undoubted marks of ancient glaciers are found about Berkeley, 300 feet above the 
 bay. 
 
 39 
 
588 CENOZOIC ERA— AGE OF MAMMALS. 
 
 It is impossible to describe all the great ancient glaciers whose 
 tracks have been traced. They filled all the larger caflons, and their 
 tributaries all the higher and smaller valleys and meadows. Their 
 tracks are everywhere marked by glaciation and strewed bowlders, and 
 their terminus at different times by a succession of terminal moraines 
 and lakelets. We will mention three or four as examples : 
 
 a. During the epoch spoken of, a great glacier, receiving tributaries 
 from Mount Hoffman, Cathedral Peaks, Mount Lyell, and Mount Clark 
 groups filled Yosemite Valley, and passed down Merced Caflon. The 
 evidences are clear everywhere, but especially in the upper valleys, 
 where the ice-action lingered longest. 
 
 6. At the same time tributaries from Mount Dana, Mono Pass, and 
 Mount Lyell, met at the Tuolumne meadows to form an immense 
 glacier, which, overflowing its bounds a little below Soda Springs, sent 
 a branch down the Tenaya Caflon to join the Yosemite glacier, while 
 the main current flowed on down the Tuolumne Caflon and through 
 Hetchhetchy Valley. Knobs of granite, 500 to 800 feet high, standing 
 in its pathway, were enveloped and swept over, and are now left round, 
 and polished, and scored, in the most perfect manner. This glacier 
 was at least forty miles long and 1,000 feet thick at Soda Springs, for its 
 stranded lateral moraine may be traced so high along the slopes of the 
 bounding mountain, and 2,500 thick farther down, for it filled Hetch- 
 hetchy Valley to the brim. 
 
 c. The Sierra Eange on its western side slopes gradually for fifty or 
 sixty miles ; but on the eastern side it is very precipitous, so that the 
 plains 5,000 to 7,000 feet below the crest are reached in four or five 
 miles. In glacial times long and complicated glaciers with many tribu- 
 taries occupied the western slope, while on the eastern slope innumer- 
 able short, simple glaciers flowed in parallel streams down the steep in- 
 cline and out for several miles on the level plain, or even into the waters 
 of Lake Mono. One of the largest of these took its rise in the snow- 
 fields about Mono Pass, flowed down Bloody Canon, and six to seven 
 miles out on the plain, and evidently into the waters of Lake Mono, 
 which was then far more extensive and higher than now. Parallel mo- 
 raines, 300 feet high, formed by the dropping of glacial debris on each 
 side of the icy tongue, as it ran out on the plain or on the bottom of 
 the shallow lake, are very conspicuous, as are also the successive ter- 
 minal moraines left in the subsequent retreat. Behind these moraines 
 water has accumulated, forming lakelets. 
 
 d. Many glaciers, whose tracks are still easily traced, at that time 
 ran down the steep mountain-slope into Lake Tahoe. The most con- 
 spicuous of these are three at the southern end, which, issuing from as 
 many caflons, ran out on the level plain three or four miles, and into 
 the swollen waters of the lake to form icebergs. The beautiful lakelets 
 
QUATERNARY PERIOD ON THE WESTERN SIDE OF THE CONTINENT. 589 
 
 and the lake-like bay which form so conspicuous a feature of the 
 scenery of the southern end of the great lake, were partly scooped out 
 by these steeply descending glaciers, and partly dammed by the debris 
 left when they retired; and the long, parallel ridges of earth and 
 bowlders bordering the lakelets and stretching down to the shores of 
 the great lake, are lateral moraines dropped on each side as the glaciers 
 ran out into the lake * (Fig. 953). 
 
 With the decline of glacial conditions all these glaciers of the Sierra 
 retreated, leaving very distinct terminal moraines, where they rested 
 
 Fio. 952.— Diagram of Moraines at the Southern End of Lake Tahoe : a, Fallen-Leaf Lake; b. Cas- 
 cade Lake; c, Emerald Bay. 
 
 awhile, behind which, drainage- waters accumulating, have formed beau- 
 tiful little lakes. Thus they have gone backward and upward, until 
 they have now mostly retired within the snow-fields which gave them 
 birth. The feeble remains of some may still be found hidden away 
 among the coolest and shadiest hollows of the highest summits. 
 
 Lakes. — A period of flooded lakes, marked by successive terraces 
 about the present lakes, is well shown, especially in the Basin region. 
 The period of the flooded lakes in this region seems to have corre- 
 
 * American Journal of Science, vol. x, p. 126, 1876. 
 
590 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 sponded with the Glacial epoch, for the great glaciers ran into some or 
 them. 
 
 About Lake Mono there are five or six very distinct terraces, the 
 highest being about 700 feet above the present water-level. Evidently 
 at that time its waves washed against the steep slope of the Sierra, 
 and many of the glaciers in this region ran into it. About Salt Lahe, 
 several terraces are very conspicuous, the highest being about 1,000 feet 
 above the present lakfe-level. Traced out by this highest level, the out- 
 line of the lake embraced an enormous area. Similarly about all the 
 saline lakes of the Nevada basin terraces have been traced up to more 
 than 600 feet about the present level. In general terms, we may say 
 that the Basin region at that time was occupied by two great lakes : 
 the one filling the Utah basin, the other the Nevada basin, the eastern 
 shore of the one washed against the Wahsatch, the western shore of 
 
 Pio. 953.— Map of the Qnaternary Lakes Bonneville (a) and Lahontan (J) (after Gilbert and Kussell). 
 
 the other against the Sierra. The former has been accurately mapped 
 by Gilbert and called Lake Bonneville (Fig. 95.3 a) — the latter, also 
 accurately mapped by King and Russell, and called Xake Lahontan 
 (Fig. 953 6), in honor of these early explorers. Lake Bonneville when 
 at its 1,000-foot level, emptied northward into the Snake and Colum- 
 bia Rivers. It eroded its outlet down to the 600-foot level ; there lost 
 its outlet and dried away to its present condition. Lake Lahontan 
 when at its 600-foot level had a complicated, deeply-dissected outline, 
 with the numerous motintain-ridges of the Basin region forming high 
 islands and promontories. So far as known, it had no outlet. As the 
 Quaternary period passed away, these great lakes dried away more and 
 
QUATERNARY PERIOD ON THE WESTERN SIDE OF THE CONTINENT. 591 
 
 more. The residues of the one are Great Salt Lake, Utah Lake, and 
 Sevier ^Lake; of the other, Pyramid, Winnemucca, Humboldt, Carson, 
 Walker, and Soda Lakes.* 
 
 In both of these great lakes, according to Gilbert and Eussell, 
 there are abundant evidences of two flooded periods separated by a 
 period of complete desiccation. If the flooded periods correspond 
 with periods of great development of the ice-sheet, as seems probable, 
 we have here also — as in the eastern part of the continent — glacial 
 and interglacial epochs. 
 
 River-BedSi — Old river-beds are found in many countries, and es- 
 pecially in the Drift region of the eastern portion of our continent 
 (p. 586&), but those of California are peculiar. In the East and else- 
 where, the Tertiary river-beds are in the same places, but below the 
 present river-beds; in California they are far above, and in many cases 
 
 Fig. 954.— Map of a portion of the Region of the Deep Placers of the Yuba Eiver : The black, lava- 
 flows ; the dotted spaces, gravel (after Whitney). 
 
 in different places — i. e., the rivers have been displaced from their 
 former beds and cut much deeper. In map (Fig. 954) we give a por- 
 tion of the country about the upper Yuba, and Fig. 955 is an ideal 
 section across the river-beds 'along the line N S, Fig. 954. It is seen 
 
 * G. K. Gilbert: Lake Bonneville, Monograph I, IT. S. Geol. Surv. I. C. Russell: 
 Lake Lahontan, Monograph XI, U. S. Geol. Surv. 
 
592 
 
 CENOZOIC ERA— AGE OP MAMMALS. 
 
 that there are remnants of old lava-flows on the divides between the 
 deep river-channels. Beneath these lavas there are river-gravels, and 
 
 Fio. 955. — Section along the Line, nortli and soutli: r' r', old river-beds; r r, present river-beds* Z 
 
 lava; el, slate. ' ' 
 
 beneath these gravels, trough-shaped river-beds with their smoothly 
 and variously eroded bed-rock. The section shows, moreover, that the 
 present rivers have commenced their beds on the old divides (shown by 
 dotted lines), but have cut much deeper, leaving the old beds high up 
 on the present divides. 
 
 Such are the facts. The history of the process is briefly as follows : 
 At the end of the Tertiary there was an outburst of lava near the crest 
 of the Sierras.* The lava flowed down the river-beds, filled them up, 
 and displaced the rivers. These immediately commenced cutting new 
 beds on the old divides, because the lava was thinner or absent there. 
 Now, coincidently with the lava-flow, there was an elevation of the 
 Sierra crest by faulting or folding, or hath effects combined, and there- 
 fore increase of the Sierra slope. Such tilting was attended possibly 
 with a very great amount of displacement or faulting on the eastern 
 side. On account of the increased slope, the rivers seeking their base- 
 level cut down far below their previous level. This increase of slope 
 is shown, if possible, still more plainly, in some of the rivers of the 
 
 W 
 
 FiG. 956.— Ideal Section across a Kiver-bed in Southern California beyond the Eegion of the 
 
 Lava-flow. 
 
 southern part of the State, beyond the limits of the lava-flow. Here 
 also the tilting and the increased slope took place, but the rivers were 
 not displaced. They therefore retained their - beds, but deepened 
 their channels, leaving the old river-gravels high up on their sides 
 (Fig. 956). The river-beds of California show, therefore, not con- 
 
 * The great lava-flooding of the Tertiary commenced probably at the end of the Mio- 
 cene, and continued through the Pliocene. These flows, in California, seem to have been 
 the last. 
 
THE QUATERNARY PERIOD IN EUROPE. 
 
 593 
 
 tinental crust-oscillations like those of the East, but mountain-mak- 
 ing by faulting and tilting, or local uplift. 
 
 History of the Sierra Range.— This range was bom out of the ocean 
 by horizontal crushing and bulging, as already explained (p. 269), at 
 the end of the Jurassic. During the whole Cretaceous and Tertiary it 
 was subjected to erosion, until by the end of that time the rivers had 
 reached their base-levels, and the range was reduced to very moderate 
 height. The crest was then about the region of the Yosemite, for the 
 erosion into the granite is deepest about that region. Then came, at 
 the end of the Tertiary and beginning of the Quaternary, the further 
 uplift of the Sierra mountains, the formation of the great faults, and 
 
 Fig 956a — Gibbs Cafion of the Sierra Nevada 
 
 the transference of the crest tp the extreme eastern- side ; the outpour- 
 ing of the lava ; the displacement of the rivers ; and the cutting of the 
 new river-beds. By this great movement the already old Sierra was 
 rejuvenated, and entered upon a new cycle of changes by erosion, 
 which is still progressing. The sharply accented, even savage char- 
 acter of the scenery of the Sierra is the result of the comparative 
 recency of its latest movement. 
 
 The Quaternary Period in Europe. 
 In Europe the phenomena were more irregular, the oscillations 
 more numerous, and perhaps more local, than in America. This is m 
 accordance with the general difference in the geological history o± the 
 
694 
 
 CENOZOIC ERA— AGE OF MAMMALS, 
 
 two continents. Nevertheless, the general character of the phenomena 
 was similar in the two countries. 
 
 1. Epoch of Elevation — Glacial Epocll. — During the Early Qua- 
 ternary the whole of Nojthern Europe seems to have been elevated 
 1,000 to 1,500 feet and sheeted with ice. The continental mai'gin was 
 considerably farther west than now. The British Isles were then a 
 part of the continent, there being then no Baltic and North Sea. 
 The area of highest elevation, and of thickest ice, and therefore of 
 radial movement, was the Scandinavian Peninsula. From this area 
 the ice moved westward into the Atlantic, as far at least as the line 
 of 100 fathoms' (shown by the dotted line. Fig. 957); southwestwai-d 
 over the British Isles, southward over the beds of the Baltic and North 
 Seas and into Northern Germany as far as the frontiers of Bohemia ; 
 
 Pig. 957.— Map of Europe, showing the limit of the Ice-sheet and also subordinate Ice-sheets in 
 
 mountain regions. 
 
 and southeastward and eastward over Eussia, far beyond Moscow, gla- 
 ciating the whole surface in its course. The southern boundary of the 
 ice-sheet has been traced. It passed through Cornwall, across Dover 
 Strait, through Mjddle Germany and Southern Eussia to the Ural 
 Mountains, following nearly the 53d parallel of latitude. The gen- 
 eral outline and extent of the ice-sheet in Europe during the period 
 of its maximum is shown in the map, Fig. 957. 
 
 At the same time, the whole Alpine region of Middle Europe, al- 
 
THE QUATERNARY PERIOD IN EUROPE. 
 
 595 
 
 though heyond the limits of the ice-sheet, was mantled with snow to a 
 degree much greater than at present, and developed glaciers on a pro- 
 digious scale. Some of these have been traced out with great care and 
 skill. Especially has this been done for the great Rhdne glacier by 
 Guyot, and more recently by Favre. At that time a great glacier came 
 down the valley of the Rh6ne, emerged on the plains, and filled the 
 whole valley of Switzerland, fifty miles wide, between the Alps and the 
 Jura, forming a great mer de glace 50 miles wide, 150 miles long, and 
 4,000 to 5,000 feet deep. A figure is given below of this great glacier. 
 The dotted lines show the direction of motion as determined by 
 bowlders left in the valley or stranded high up on the slopes of the 
 Jura. 
 
 Fior958 —Map showing the Oatline and Course 
 of Flow of the Great EhOne Glacier (after 
 Lyell). 
 
 Fig. 959. — Map showine the Lines of iJeWs. ex- 
 tending from the Alps into the Plains of the 
 Po (after Lyell). 
 
 Lakes Geneva and Nenfchdtel were filled and their bottoms scoured 
 by this great glacier. 
 
 At the same time, also, on the southern slopes of the Alps, long 
 glaciers stretched out on the plains of Lombardy, as shown by the pro- 
 digious piles of debris (moraines) still left. Some of these moraines 
 are 1,500 feet high. Pig. 959 is a map of these lines of debris. 
 
 Evidences of glaciers of this time are also found in the Vosges, in 
 the Pyrenees, and other high mountains of Central Europe. 
 
 During this time also Europe was probably connected with Africa 
 by one or more highways, through the Mediterranean Sea. 
 
 In Europe, as in America, there are evidences of several retreats 
 and readvances of the ice. Geikie * recognizes six glacial and five in- 
 
 * James Geikie: The Great Ice Age. 
 
596 CENOZOIC ERA— AGE OF MAMMALS. 
 
 terglacial epochs. The second advance of the glacier was the most 
 extensive. 
 
 2. Epoch of Subsidence— Champlain.— Following the epoch of ele- 
 vation was an epoch of subsidence, during which the same regions which 
 were before most elevated became now most depressed. It is believed 
 by some that in Scotland the land was 3,000 feet below the present 
 level. By this depression a great part of Northern Europe was sub- 
 merged, and Great Britain was reduced to an archipelago of small 
 islets. Over the area thus submerged icebergs loosened from the 
 Scandinavian ice-fields drifted. 
 
 At the same time, partly by subsidence, and therefore slackened 
 water-currents, and partly by moderated climate and melting of glaciers, 
 there was a flooded condition of rivers and lakes in Middle Europe, 
 France, Germany, and Switzerland. At the same time, also, the north- 
 ern portion of Asia and the lake-region of that continent were sub- 
 merged. The Caspian Sea, Lake Aral, and other lakes in that region, 
 were probably then united into one great inland sea, connected either 
 with the Black Sea or the then greatly- extended Arctic Ocean, or with 
 both.* 
 
 Evidences of this condition of things are found in old sea-margins, 
 lake-margins, river-terraces, and flood-plain deposits. 
 
 The subsidence was followed, as in America, by a re-elevatiou, 
 shown by successive beaches and terraces on sea-shores, about lakes, 
 and along rivers. In some places, the re-elevation seems to have gone 
 beyond the present level, and the British Isles for a brief time were 
 again united to the continent. Then the land went down again to its 
 present condition. 
 
 Southern Hemisphere. 
 
 Similar phenomena to those described have been observed also in 
 high latitude regions of the Southern Hemisphere, i. e., in the south- 
 ern parts of South America, Australia, Africa, and New Zealand. In- 
 deed, the facts of distribution of organisms strongly suggest that in 
 glacial times (as also in Permian) Antarctica was greatly elevated, and 
 so extended that it connected with South America, South Africa, and 
 Australia. This condition was attended with glaciation as severe and 
 possibly as extensive as that in the Northern Hemisphere, but the 
 subsequent subsidence was greater and more permanent, and therefore 
 much of the glaciated region is now covered by the sea. 
 
 * Nature, vol. xiii, p. 74 ; Natural History Magazine, vol. xvii, p. 176 ; Archives des 
 Sciences, vol. liv, p. 427. 
 
SOME GENERAL RESULTS OF GLACIAL EROSION. 
 
 697 
 
 Some General Results of Glaciation. 
 
 1. Fiords. — We have seen that the phenomena of rivers, in the 
 region affected by the Drift, show elevation, then subsidence, and then 
 re-elevation to a less height than the first. The first elevation is shown 
 in their deep, ancient beds ; the subsidence, in the filling up of these 
 with deposit ; the re-elevation, in the cutting down into the deposit, 
 and forming terraces. Now, all these changes are also shown in the 
 phenomena ot fiords (Dana). 
 
 It will be remembered (p. 38) that the Norway coast is wonderfully 
 bold and deeply dissected, consisting of high, rocky headland?, sepa- 
 rated by deep inlets running 50 to 100 miles into the country ; and off 
 shore there is a line of high, rocky isles, evidently the remnants of an 
 old shore-line. These deep inlets are called in Norway Fiords j and 
 the name is now used for all such deep inlets separating high head- 
 lands. The coast of Greenland has a precisely similar structure. It, 
 also, consists of bold, rocky headlands, separated by fiords running far 
 into the country; and off 
 
 shore a line of rocky isles 
 2,000 feet high. In Green- 
 land these fiords are now oc- 
 cupied by glacial extensions of 
 the general ice-mantle. The 
 same coast-structure is found 
 on the western side of the 
 continent in high latitudes. 
 The coast of British America 
 and Alaska is also bold and 
 deeply dissected by fiords; 
 and in Alaska these fiords are 
 now occupied by great gla- 
 ciers running down to the sea. 
 The fiords of Norway 
 have been attributed (p. 38) 
 partly to the erosive agency 
 of waves and tides, but it is 
 certain that they are mainly 
 due to a partial subsidence of 
 a bold coast deeply trenched 
 with gorges. In a word, 
 fiords are deeply eroded and half-drowned valleys. These valleys 
 can in most cases be traced as submarine troughs, far out to sea. In 
 Greenland, for instance, the extension of these troughs, deep below 
 the present sea-level and far out beyond the reach of the present gla- 
 
 FiG. 960.— Fiords in the coast of Maine. 
 
598 CENOZOIC ERA— AGE OF MAMMALS. 
 
 eiers, shows a former more elevated condition; and terraces and re- 
 cent deposits up to 500 feet show a subsidence below, and a re-eleva- 
 tion to, the present level. 
 
 All shores in northern regions are bold and rocky and deeply dis- 
 sected, and have rocky islets off shore ; in other words, are more or less 
 affected with fiord-structure. They have been elevated, eroded, and 
 subsided. It is probable, that during the epoch of greatest elevation a 
 iroad continental connection existed between America and Asia, in- 
 cluding the whole area between the Aleutian Isles and Bering Strait. 
 
 3. Lakes due to Glaciers. — Lakes occur in all countries, and are 
 doubtless due to many different agencies, but the small lakes, so abun- 
 dant in the region covered hy the ice-sheet and by ancient glaciers, are 
 undoubtedly due to glacial agency. It is only necessary to look at a 
 good map of the United States to see at once the great contrast in this 
 regard between the Northern and Southern parts. In the single State 
 of Minnesota there are several thousand lakes. South of the line of 
 the ice-sheet there is not one except in Florida, and there due to en- 
 tirely different causes. 
 
 These lakes are formed in several ways: (a) They may be rock- 
 basins scooped out by glaciers where the rocks are softer or else where 
 there is a sudden change in the slope of the bed from a higher to a 
 lesser angle; or (&) they may be formed by the damming of drainage 
 waters behind terminal moraines of a retreating glacier; or (c) by the 
 disappearance of snow from old cirques^ the fountains of ancient 
 glaciers. These three kinds are very abundant in all the highest 
 mountains, such as the Sierra or the Colorado; the last among the 
 highest summits, the first high up the valleys, and the second a little 
 way down. Again, (d) along northern coasts elongated lakes are 
 often formed by the elevation of fiords. Many lakes in ^orway and 
 Scotland are formed in this way; (e) lastly, the thousands of small 
 lakes which over-sprinkle the surface left by the ice-sheet, especially 
 after its latest advancoj are due to irregular dumping of glacial 
 debris. Such are either kettle lakes or morainal lakes. 
 
 It is necessary to remember that lakes are ephemeral features 
 of topography. They are inevitably in time either drained away by 
 down-cutting of their outlets, or else filled up by sediments or vege- 
 tal growth. This process is especially rapid in mountain-regions. 
 The little glacial lakes are rapidly being -filled and converted into 
 marshes and meadows, called "vlies" in the Adirondacks. Every- 
 where in the Sierra the region of meadows is the region of the old 
 glaciers. Lakes, then — especially small lakes — are a feature of new 
 topography. The topography of all the Southern States is extremely 
 old, while that of the drift area is new. 
 
LIFE OF THE QUATEENARY PERIOD. 599 
 
 Life of the Quaternary Period. 
 
 Plants and Invertebrates.— Eemains of the life of the Quaternary, 
 both animal and vegetable, are very numerous, and often very well pre- 
 served. Both the plants and the invertebrate animals are almost 
 wholly identical with those now living on the earth. We will there- 
 fore dismiss these with one important remark : The plants and the 
 marine shells show an arctic climate in now temperate regions. The 
 species found are still living, but living farther north. There has 
 been a migration of species northward since Glacial times. In Ter- 
 tiary times (p; 526), we noted a migration of forms southward, indicat- 
 ing a contrary change of climate at that time. 
 
 Mammals. — But the mammalian fauna of the Quaternary is almost 
 wholly peculiar. It differs greatly from the Tertiary fauna preceding, 
 and the present fauna succeeding. The species are, moreover, very 
 numerous, and many of them of extraordinary size ; for it is the culmi- 
 nation of the mammalian age. It is necessary, therefore, to describe 
 some of them, and the conditions under which they were preserved, 
 and thus to realize in some degree the conditions under which they 
 lived. We will take our first illustrations from Europe, because the re- 
 mains are more numerous and have been more thoroughly studied there. 
 
 Mammalian remains of this time are found in Europe-^1. In cav- 
 erns, where in great numbers they have become entombed; 2. On 
 beaches and terraces, where their floating carcasses have become strand- 
 ed; 3. In marshes and peat-bogs, where, venturing in search of food, 
 they have mired and perished ; 4. In ice-cliffs and frozen soils, where 
 they have been hermetically sealed and preserved to the present time. 
 
 1. Bone-Cavems. — The richest sources of Quaternary -mammalian 
 remains are undoubtedly bone-caverns. These occur in nearly all 
 countries, often along the course of streams, but high above the pres- 
 ent stream-level. Their formation and their filling are in some way 
 connected with the floods of the Interglacial and Champlain epochs. 
 They are rich in organic remains to a degree which is almost incredi- 
 ble. One of the most striking peculiarities of these remains is, that 
 they often consist of a heterogeneous mixture of all kinds, carnivorous 
 and herbivorous, and all sizes, from the Elephant and Cave-bear on the 
 one hand down to Eats and Weasels on the other ; sometimes perfect, 
 more often broken, mingled with earth and gravel, forming unstratified 
 bone-rubbish. Another peculiarity of these deposits is that they are 
 often covered and, as it were, sealed by a stalagmitic crust formed by 
 subsequent drippings from the roof, and thus preserved against even 
 the suspicion of disturbance to the present time. We give (Pig. 961) 
 a section of the cave of Gailenreuth, with its bone-rubbish and stalag- 
 mitic crust. 
 
600 
 
 CENOZOIC EKA-AGE OF MAMMALS. 
 
 Among the remains of Herbivores found in bone-caverns, the most 
 remarkable are those of the Elephant, Ehinoeeros, Hippopotamus, the 
 
 '^.. 
 
 -•^Tn, 
 
 
 V 
 
 
 ^ ' 
 
 / 
 
 V 
 
 'T 
 
 
 -< 
 
 "i:- 
 
 4 
 
 A 
 
 --< 
 
 
 ^1 
 
 -< V 
 
 -'••' 
 
 Fig. 961. — ^Vertical Section through Gailenreuth Cave, Fraiiconia. 
 
 great Irish Elk, besides Horses and Oxen. Some large and remark- 
 ably perfect skeletons of the Irish Elk have been found in peat-bogs 
 in which the animal had sunk. The antlers of one specimen dis- 
 covered had a spread of twelve feet. Among Carnivores are the 
 
 Fig. 961ffl.— Teeth and Leg-bones of the Cave-bear, from Gailenreuth Cave. 
 
 Cave-bear (Ursus spelceus), larger than the Grizzly, the Cave-hyena,* 
 the Cave-lion,* the Saber-toothed Tiger {Machairodus latidens), with 
 
 * These are supposed to be the same species as the African lion and hyena of the 
 present day, but much larger. 
 
LIFE OP THE QUATERNARY PERIOD. 
 
 601 
 
 its saber-like tusks, ten inches long, besides smaller animals of the same 
 order. The remains of the larger Carnivora, espeeiallj the Cave-bear 
 
 
 "^5^3^ 
 
 ^l 
 
 Fig. 963.— Skull of Ursus spelseus, k J. 
 
 and the Cave-hyena, are the most abundant. The hones of tie smaller 
 HerMvores bear the marks of teeth, as if they had been gnawed. The 
 skeletons of the large Pachyderms are usually more perfect. In the Kirk- 
 dale Cave, England, the teeth and other parts of 300 individuals of the 
 Cave-hyena were found. In the Gailenreuth, Cave, Pranconia (Fig. 961), 
 the remains of 800 Cave-bears were obtained. In a Polish cave Romer 
 recently found the remains of at least 1,000 Cave-bears,* and from one - 
 in Sicily, twenty tons of hippopotamus-bones have been taken.f In 
 
 Skall of Hyena Bpelsea, x J. 
 
 many bone-caves are found also the bones and rude implements of 
 primeval man. Of these we will speak more fully hereafter. 
 
 Origin of Cave Bone-Rubbish. — When it was supposed that the Drift 
 was caused by a great wave of translation sweeping across the conti- 
 nent and carrying ruin in its course, the phenomena of bone-caves were 
 supposed to give countenance to this view. Apimals of all sizes and 
 
 * Science, vol. iii, p. 490, 1884. 
 
 ■)■ Prestwioh, Geology, vol. ii, p. BOS. 
 
602 CENOZOIC ERA— AGE OF MAMMALS. 
 
 kinds were supposed to have huddled together in these caves, forget- 
 ting their mutual hostility in the sense of a common danger, and per- 
 ished miserably together there. 
 
 But at present it is usually believed : 1. That these caves vfere the 
 dens of the larger Carnivores, especially the Cave-bear and Cave-hyena, 
 which dragged their prey there to devour them, and also later the 
 abodes of men ; 2. That also the floating bodies of large Herbivores, 
 such as the Elephant, Ehinoceros, etc., were carried into them by the 
 flooded rivers which then ran at that level ; and 3. That during the 
 Champlain epoch, when water ran through these caves in large quanti- 
 ties, bones and earth were drifted in from above, through fissures and 
 subterranean passages, and thus found their lodgment in the caves. 
 This last was probably the principal source of the bone-rubbish in 
 most cases, and it explains also ossiferous fissures, which are com- 
 mon. 
 
 Origin of Bone-Caverns.— In limestone regions caverns are very 
 abundant everywhere. Many do not seem to be enlarging now, but 
 on the contrary to be in some cases filling up eithpr with rubbish or 
 with stalactitic and stalagmitic deposit. In some cases streams still 
 run through them. It seems probable that they are due to the action 
 of subterranean waters in pre-Champlain times. At that time full 
 streams ran through and excavated them, partly by erosion, partly by 
 solution. Gradually, as the re-elevation came on, the great streams 
 into which these cavern tributaries ran cut down their beds to lower 
 levels, the subterranean waters sought lower levels, and the part run- 
 ning through the caverns was reduced to drippings; and stalagmitic 
 crusts covered the Champlain rubbish and preserved them. Thus, 
 then, the date of the caves is pre-Champlain ; of the bone-rubbish is 
 Champlain ; of the stalagmitic crust is later. 
 
 3. Beaches and Terraces. — On these are found the remains of bodies 
 which have floated and become stranded. The most abundant of these 
 are remains of Elephas primigenius or Mammoth. It is believed that 
 the bones of 500 individuals have been found on the coast of Norfolk 
 . and Suffolk, and over 3,000 grinders have been dredged up by the fish- 
 ermen of the little village of Happesburgh (Woodward). On river- 
 terraces associated with bones of Quaternary animals have been found 
 also the rude implements of primeval man already referred to. 
 
 3. Marshes and Bogs. — As might have been anticipated, the re- 
 mains found in these are mainly those of the larger Herbivores — ele- 
 phants, oxen, stags, etc. It is in these that were found most of 
 the fine skeletons of the gigantic Irish elk (Cervus megaceros). 
 This magnificent elk was eight to ten feet in height to the top of 
 its palmate antlers, and eight to ten feet between the antler-tips 
 (Fig. 964). 
 
LIFE OF THE QUATERNARY PERIOD. 
 
 603 
 
 Pig. 964 — Skeleton of the Irish Elk (Cervus megaceros), Post-Pliocene, Britain. 
 
 4. Frozen Soils and Ice-Cliffs. — As in these have been found the most 
 perfect specimens of the Mammoth {Elephas primigeniics), this seems 
 to be the proper place to describe the animal. 
 
 The genus Elephas ranges in time from the early part of the Plio- 
 cene to the present. There are about fifteen fossil species known. 
 The genus seems to have reached its maximum development in the 
 Quaternary. During that period three species inhabited Europe, viz. : 
 E. antiquus, E. nieridionalis, E. primigenius (Lyell), besides two 
 dwarf species, E. Meliiensis, four and a half feet high, and E. Fal- 
 coneri, three feet high, found in the Quaternary of Malta. Of these, 
 not largest, but most numerous and the latest, was the primigenius or 
 Mammoth. This species roamed in immense herds all over Europe, 
 from the shores of the Mediterranean to Siberia, and extended also 
 over the northern portions of North America. In Siberia the tusks 
 are so abundant and so vrell preserved that much of the ivory of 
 commerce is got from this source. 
 
 The Mammoth (Fig. 965) equalled in bulk and weight the lar- 
 40 
 
604 
 
 CENOZOIO ERA— AGE OP MAMMALS. 
 
 gest modern species, and was perhaps somewhat taller. It was thick- 
 ly covered with a brownish wool^ and in parts with long hair; and 
 
 Pig. 966.-i^keletoii of the Mammoth (Blephas primigenius). Portions of theintemiment still adhere 
 to the head, and the thick skin of the soles is still attached to the leet. 
 
 was therefore well adapted to endure cold. It may seem strange that 
 we should speak of the hair and wool and the color of an extinct 
 animal ; but perfectly-preserved specimens have been found sealed in 
 the ice in Siberia^so perfectly preserved that, when first exposed, 
 wolves and dogs of the present epoch fed on the flesh of this animal 
 helonging to an extinct fauna. The whole skeleton, with portions 
 of the skin, hair, wool, hoofs, and eyes of this animal, is now to be 
 found in the museum at St. Petersburg. The existence of elephants 
 so far north does not indicate a warm climate, although the Cham- 
 plain epoch was doubtless far less rigorous than the Glacial. These 
 elephants were covered with thick wool, as was also the European 
 rhinoceros of that time. 
 
 Quaternary Mammalian Fauna of England. — In England alone there 
 were, in Quaternary times, of Carnivora, the great Cave-bear, the Cave- 
 hyena, a tiger larger than the Bengal, the saber-toothed tiger, as large, 
 with its flat, curved tusks, eight inches beyond the gums, besides wolves 
 and lesser Carnivores. Of Herbivores, there were the Mammoth in 
 herds, two species of rhinoceros, one hippopotamus, the great Irish elk, 
 
MAMMALIAN FAUNA IN NORTH AMERICA. g05 
 
 three species of oxen, two of them of gigantic size, besides. horses, deer, 
 and other smaller species. Surely this was the culmination of the 
 Mammalian age in England. 
 
 Mammalian Fauna in North America. 
 
 The animals of North America, in Quaternary times, were equally 
 abundant ; but the country has been less perfectly explored, and the 
 collections, therefore, less complete. Bone-caverns, the richest sources 
 of European collections, are also far more rai-e. 
 
 Among Herbivores, the most remarkable were the great Mastodon 
 {M. Americanus) ; two species of elephants, the E. Americanus and the 
 R primigenius ; at least two gigantic bisons, one of which was prob- 
 ably ten feet between the horn-tips ; * horses of present size ; huge 
 rodents allied to the beaver {Castor aides) ; a gigantic stag {Cervus 
 americanus), fully as large as the Irish elk; tapirs, peccaries, and 
 a large number of Edentates, an order now mostly confined to South 
 America, to which belong the sloths and armadillos. Many of these 
 were also of gigantic size. Carnivores were not so abundant as in 
 Europe. The most remarkable were a lion {Felis atrox), as large 
 as the European, and two species of bear ( Ursus pristinus and am- 
 pUdens). 
 
 We have already seen (page 560) that the Equidse originated on this 
 continent and migrated to Eurasia. They continued in great numbers 
 throughout the Tertiary, and apparently culminated in the early 
 Quaternary (Equus beds). They soon after became extinct in America 
 and have been reintroduced only in historic times by man. 
 
 Bone-Caves. — Caves are found in limestone regions in America as 
 elsewhere, but they do not seem to have been to the same extent the 
 dens of Carnivores. In a vertical opening in limestone strata in Penn- 
 sylvania, a kind of cave, mammalian remains have been found belong- 
 ing to thirty-four species, among which wei'e six Edentates, eight Un- 
 gulates, and twelve Eodents. A number have also been found in the 
 caves of Virginia, and a few in those of Illinois (Cope). 
 
 Marshes and Bogs. — Most of the remains of large Herbivores have 
 been found in marshes and bogs. In the Big Bone Lick, Kentucky, 
 the remains of one hundred mastodons and twenty elephants are said 
 to have been dug up. Many very perfect skeletons of the great masto- 
 don have been obtained from marshes in New York, New Jersey, In- 
 diana, and Missouri. One magnificent specimen was found in a marsh 
 near Newburg, New York, with its legs bent under the body and the 
 
 * A specimen of Bos latifrons has been found in Ohio, the horn-cores of which were 
 twenty inches around the base and six feet six inches between the points. Between the 
 horn-tips must have been much more, possibly as much as ten feet. 
 
606 
 
 CENOZOIC ERA— AGE OP MAMMALS. 
 
 head thrown up, evidently in the very position in which it mired. The 
 teeth were still filled with the half-chewed remnants of its food, which 
 consisted of twigs of spruce, fir, and other trees ; and within the ribs, 
 
 Fig. 966.— Mastodon americanus, x A (after Martili). 
 
 in the place where the stomach had been, a large quantity of simi- 
 lar material was found. In 1866 a very perfect skeleton was found 
 in a pot hole at Cohoes, New York. Many others have been found. 
 
 The Mastodon americanus (Fig. 
 966) was more heavily built than 
 the ordinary elephant, but was not 
 as large as E. imperator or E. co- 
 lumbi. It differed from the ele- 
 
 FiQ. 967.— Tooth of Mastodon americanus from 
 Big Bone Lick, Kentuclcy. 
 
 Fig. 968.— Perfect Tootli of the Mammoth, 
 Elephas primigenius. 
 
 phant chiefly in the character of its teeth. The difference is seen 
 in Figs. 967, 968, 969. The elephant's tooth, given in Fig. 968, 
 is sixteen inches long, and the grinding surface eight inches by four 
 inches. 
 
 The two genera of Proboscidians, Mastodon and ElepMs, appeared 
 successively, the one in the later Miocene, the other in early Pliocene, 
 and ranged together through the rest of the Tertiary, the species, of 
 
MAMMALIAN FAUNA IN NORTH AMERICA. 
 
 601 
 
 course, changing several times. At the end of the Tertiary, the mas- 
 todon became extinct on the Eastern Continent, but continued through 
 the Quaternary, with its companion, the elephant, in America. At the 
 end of the Quaternary, the mastodon became extinct wholly, and the 
 elephant in America 
 and Europe, though 
 it still continues in 
 Asia and Africa. 
 During the Quater- 
 nary, therefore, one 
 species of mastodon 
 and two species of 
 elephant roamed in 
 herds over North 
 America from the 
 Gulf to arctic re- 
 gions. Of the two 
 species of elephant, 
 however, the primi- 
 genius was mostly 
 confined to the higher 
 latitudes, and the Columhi to the southern portions. The latter is 
 distinguished from the former by less crowded enamel plates in the 
 grinders and less curved tusks. According to Cope, about fifty species 
 of Proboscidians are known. Of these five are Dinotheres, twenty- 
 five Mastodons, six Elephants, and five of uncertain place. 
 
 Genesis of Proboscidians. — The origin of this remarkable order is 
 obscure. It probably branched ofE in early Tertiary from some gener- 
 alized form, like Coryphodon or perhaps Pyrothere, but was not well 
 declared until the Miocene. It is well to observe, however, that of 
 the three known genera the order of introduction was: 1. Dinothere; 
 2. Mastodon; 3. Elephas. Now this is also the order of increasing 
 specialization, especially in complexity of the structure of the molars. 
 
 Fig. 969. — Teeth of Mammoth (Elephas prim,igeniiis) : a, grinding 
 surface ; b, side view, showing'the roots (after Lyeli). 
 
 T e: F=p -riA^ F=? 
 
 
 :.^-'es ^.•?'A.*-,x-„,„ 
 
 '■=■*/£;'>.> 
 
 MIOCENE PUIOCENE QUATERNARY- PRESENT 
 
 Pio. 970.— Diagram showing Distribution in Time of Proboscidians. 
 
 and in the size and complexity of the brain. The order of appearance 
 and of extinction of these three forms are shown in diagram (Pig. 
 970). 
 
 Among Edentates, a Megatherium, a Megalonyx, . and several 
 Mylodons have been found in North America; but, as their prin- 
 
608 
 
 CENOZOIO ERA— AGE OF MAMMALS. 
 
MAMMALIAN FAUNA IN NORTH AMERICA. 609 
 
 cipal home was in South America, we will describe them under that 
 head. 
 
 River-Gravels. — In many portions of the United States, but espe- 
 cially in California, remains of mastodon and elephant, and bison, etc., 
 are found in great numbers in river-gravels. The river-gravels of Cali- 
 fornia are spoken of again further on. 
 
 Quaternary in South America. — A large number (335) of species of 
 mammals have been found in the soil of the pampas and in the caves 
 of Brazil, far more than live there at present (Zittell). They are mas- 
 todons (different species from the North American), llamas, horses, 
 . tapirs, rodents, many species of panther-like carnivores, large saber- 
 toothed tigers {Machairodus neogceus and necator), with curved, saber- 
 like tusks twelve inches long and eight inches beyond the gums (Fig. 
 971), and especially a large number of Edentates allied to the sloths 
 and armadillos, but of gigantic size. 
 
 Of the Edentates, the most remarkable, in fact, one of the most 
 remarkable animals which have ever existed, is the Megatherium (great 
 beast) americanum. The genus Megatherium ranged in Quaternary 
 times through South American, and into North America as far as the 
 shores of Georgia and South Carolina. At the mouth of the Savan- 
 nah Eiver the remains of several individuals of a species of this genus 
 (M. mirabile) have been found. But the largest species and the most 
 perfect specimens have been found in South America. 
 
 The Megatherium americanum, of which we give a figure (Fig. 
 973), was larger than a rhinoceros, but was still more remarkable for 
 
 Pig. 972.— Megatherium americanum. 
 
 the clumsy raassiveness of its skeleton than for its size. This is espe- 
 cially true of its hind-legs, hip-bones, and tail. For this reason it is 
 supposed to have been able to stand on its hind-legs and tail, while it 
 used its long free-moving arms, with hands a yard long, to tear down 
 
610 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 branches on which it fed. The great siieleton represented above is 
 eighteen feet long, and its thigh-bones are three times as thick as those 
 of an elephant. The grinding surface of its molar teeth (it had no 
 
 Fig. 973.— Lower Jaw of a Megatherium, showing the Gradual Surface of the Teeth (after Owen). 
 
 others) is traversed by triangular ridges admirably adapted to triturate 
 its coarse food. 
 
 Megalonyz (big claw) (Pig. 974) is the name of another genus of 
 these gigantic sloths, and Mylodon of a third. Both of these genera 
 extended into North America. In fact, the Megalonyx was first dis- 
 
 Fio. 974.— Claw-Core of a Megalonyx, x J {drawn from a cast of the original). 
 
 Fia. 975.— Sceledotheriam leptocephalus, x ^ (after Boule). 
 
MAMMALIAN FAUNA IN NORTH AMERICA. 
 
 611 
 
 covered in Greenbrier County, Virginia, and named Megalonyx by 
 Thomas Jefferson. The larger species of Mylodon and Megalonyx 
 
 
 
 Vie. 976.— Skeleton of Glyptodon clavipes, x ^„, Quaternary, South America. 
 
 were about the size of a buffalo,-or larger, and Scelidothere (Pig. 975) 
 still larger. These gigantic animals, though allied to sloths, were of 
 course not tree-climbers like modern 
 sloths. They have been well called 
 Ground Sloths. 
 
 Of the Armadillos or mailed Eden- 
 tates, there were several of gigantic size 
 belonging to the genera Glyptodon^ 
 Chlamydotherium, and Fachytherium. 
 The accompanying cut represents one ^"'^ ''^'i'|'o°|.'.^fio^*™'^'^„°^^^^^^ 
 of these eight feet long, with an invul- 
 
 nerable coat of mail. Some species of the genus CMamydotheritim 
 were much larger — one as big as a rhinoceros, and of Pachytherium as 
 big as an ox (Dana). 
 
 Fie. 978.— Thylacoleo, Skull reduced (after Flower). 
 
612 CENOZOIC ERA— AGE OF MAMMALS. 
 
 Australia. — In Australian caves, also, great abundance of remains 
 has been found, and th^y show the same prevalence of gigantic spe- 
 cies. As itow^ so then, the mammals of Australia were almost all 
 Marsupials, but the present species are dwarfs in comparison. The 
 largest of these was the Diprofodon (two front .teeth), a pachyder- 
 moid wombat as big as a rhinoceros. A reduced figure of the skull, 
 which was three feet long, is given herewith. 
 
 Among other remarlcable species of marsupials were Macro pus 
 (kangaroo) titan and M. atlas, of great size; Nototherium miichelli, 
 as large as a bullock, and a very remarkable species, supposed by Owen 
 to have been carnivorous, and therefore called Thylacoleo (pouched 
 lion) carnifex, as large as a lion. The striking peculiarity of this 
 animal was the existence of a broad trenchant premolar, as shown 
 in Fig. 978. 
 
 GeograpMcal Faunas of Quaternary Times. — We observe, t&en, that 
 already the geographical distribution of families was similar to that 
 which we find at present. Then, as now. Herbivores greatly predomi- 
 nated in America, while Carnivores were very abundant, and of great 
 size, in the Eastern Continent. Then, as now, sloths and armadillos 
 and llamas characterized the fauna of South America, while Marsu- 
 pials characterized that of Australia. But in each locality the animal 
 life seems to have been then more abundant, and the species gigantic. 
 According to Zittel, there were three great centers of origin and dis- 
 persion of the present mammalian species — viz., Australia, South 
 America, and Arctogcea or Holarctica — i. e., North America and Eu- 
 rasia north of Sahara and the Himalayas. 
 
 Some General Observations on the Whole Quaternary. 
 
 1. Cause of the Climate. — This h-as been one of the difiicult ques- 
 tions in geology. There seems to be no doubt that during the Quater- 
 nary there were wide-spread oscillations of the earth's crust in high- 
 latitude regions, and a general coincidence of climatic changes with 
 these oscillations. Furthermore, there is little doubt that the cold 
 and the ice-accumulation were attended with northern elevation, and 
 the moderation of temperature and melting of the ice, with subsidence 
 in the same region. But the coincidence of the climatic changes 'with 
 the crust-oscillations was not exact; that in many places, at least, the 
 maximum of ice-accumulation was associated with subsidence. The 
 differences may be reconciled and the facts well explained by suppos- 
 ing that northern elevation produced ice-accumulation ; ice-accumula- 
 tion by weight produced subsidence ; subsidence produced moderation 
 of temperature and melting of ice, and this last by lightening of load 
 produced re-elevation. But (and this is the important point) the 
 
SOME GENERAL OBSERVATIONS ON THE WHOLE QUATERNARY. 613 
 
 effects in each case lagged greatly behind the cause. This is well 
 known to be true in all cases of accumulated effects^ biit in this ease 
 the lagging is great. On this view the accompanying diagram (Fig. 
 
 PUOCENE Q U AT E R N ~-i<VR_JV^____J-PKrs E N T 
 
 Fig. 979.— Diagram showing tlie Eelation of Land Elevation and Ice- Accumulation. Tlio line a b, 
 course of time, and also the present condition as to elevation and ice. 
 
 979) graphically represents the assumed case. It is seen that, at the 
 time of maximum ice, the subsidence had already commenced. 
 
 As to the cause of the cold, it is supposed that northern elevation 
 would produce cold, and depression a moderation of temperature in 
 the regions thus affected, all other conditions remaining the same. 
 The facts, however, do not seem consistent with the topographic 
 hypothesis. The lifting of the continents did not occur near the 
 beginning of the cold climate. The long Tertiary age had been an 
 era of broad extension and high elevation of northern lands, with 
 contemporaneous mild climate even within the arctic circle. 
 
 But admitting that increase in the area and height of polar lands 
 would increase the rigor of- the climate, and decrease of area and 
 height of polar lands would moderate the climate of northern regions, 
 and that the amount of this effect it is difficult to estimate — yet the 
 effect was so enormous and so wide-spread that the cause, even when 
 supplemented by changes in the course of oceanic currents such as the 
 Gulf Stream, has seemed to most physicists and geologists to be in- 
 sufficient. They have cast about, therefore, for some other possible 
 cause, external to the earth itself — i. e., cosmical ■cause — to explain it. 
 
 Croll's Hypothesis. — This attributes the cold of the Glacial period 
 to the combined influence of precession of the equinoxes and secular 
 changes in the eccentricity of the earth's orbit. By the former — viz., 
 precession — winter, which in the northern hemisphere occurs now 
 when the earth is nearest the sun (perihelion), is gradually in 10,500 
 years brought round so as to occur when the earth is farthest off from 
 the sun (aphelion). The effect of this, it is claimed, would be to 
 make longer and colder winters, and shorter but hotter summers in 
 the northern hemisphere, such as occur now in antarctic regions. By 
 the latter — viz., increasing eccentricity (which forms a much longer 
 cycle)— these effects, which are now small on account of the nearly 
 circular form of the earth's orbit, would become very great. At the 
 time of greatest eccentricity, the earth would be 14,000,000 miles 
 farther off from the sun in winter than in summer, the winters would 
 
614 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 be twenty-two days longer and 30° colder, and the summers twenty- 
 two days shorter, but much hotter than now. 
 
 Fig. 980 is a diagram representing the effect of precession. In A 
 we have the, condition as it now exists — i. e., the north pole, n p, is 
 turned away from the sun, B (winter), at perihelion, and toward the 
 sun (summer) at aphelion. But the earth, rotating on its axis like 
 a spinning-top, does not maintain the same position of its axis — does 
 not sleep in its spinning — but wabbles on its center, the ends of the 
 axis describing a small circle (as shown by the dotted line) in 31,000 
 years.* In 10,500 years, therefore, the axis will be tilted the other 
 way, so that B represents the condition of things at that time. It is 
 seen that winter (north pole turned away from the sun) will be in 
 aphelion, and summer (north pole turned toward the sun) in peri- 
 helion. Now, according to Croll, the coincidence of aphelion winter, 
 
 Fig. 980.— Diagram showing e'ffcct of Precession : A, condition of things now; B, as it will be 10,500 
 years hence. The eccentricity is of conrso greatly exaggerated. 
 
 with a period of greatest eccentricity, produces a glacjal climate. 
 The cycle of aphelion winter, as already said, is 31,000 years, that 
 of greatest eccentricity is much longer and far less regular. 
 
 Again, these effects, CioU thinks, would be still further increased 
 by changes in the direction of oceanic currents. During aphelion 
 winter in the northern hemisphere the equator of heat would be soutli 
 of the geographical equator instead of north of it, as at present. The 
 equatorial current of the Atlantic (p. 40), instead of turning north- 
 ward to form the Gulf Stream, would be turned southward by the 
 wedge-shaped eastern point of South America, and the northern 
 
 * The cycle of precession is 26,000 years, but the advance movement of the major 
 axis of the orbit makes the cycle of aphelion winter 21,000 years. 
 
SOME GENERAL OBSERVATIONS ON THE WHOLE QUATERNARY. 615 
 
 hemisphere would be still further chilled by the withdrawal of this 
 great moderator of northern climates. Finally, to all these effects 
 must now be added the important effect of the extreme range of tem- 
 perature- during an aphelion-winter, period, especially at a time of 
 maximum eccentricity. McGee * has shown that the effect of in- 
 creased range is to diminish the mean temperature ; while Hill f has 
 shown that it increases the mean evaporation, and therefore the mean 
 precipitation, as snow. 
 
 If this theory be true, one corollary is the recurrence of Glacial 
 epochs many times in the history of the earth. Another, according 
 to Croll, is the alternation of colder and warmer periods many times 
 during every period of greatest eccentricity, and a similar alternation 
 of each between the two poles, so that the cold period at one pole corre- 
 sponds with the warm period at the other. Of alternations of colder 
 and warmer periods during the Glacial epoch there are evidences 
 both in Europe and America. Of the recurrence of Glacial epochs 
 in the history of the earth there is as yet no conclusive evidence ex- 
 cept for the Permian (p. 426). What seem to be Glacial drifts with 
 scored bowlders, etc., have been found at several geological horizons. 
 Mr. Wallace substantially accepts Croll's view, but thinks that 
 astronomical changes alone will not produce a Glacial epoch, but 
 must be coincident with geographical changes favoring the same re- 
 sult. He maintains that, until the Quaternary, geographical condi- 
 tions favored warm, uniform climates, especially by several open cur- 
 rent-ways from tropical to polar seas, notably one from the Indian 
 Ocean through Western Asia; and that at the beginning of the Qua- 
 ternary these warm currents were cut off by northern elevation, while 
 the elevation itself would tend still further to increase the cold. The 
 Glacial epoch was therefore the result of several causes, astronomical 
 and geographical, viz., aphelion winter, maximum eccentricit]^, and 
 northern elevation. On this view it is easy to see why there should 
 have been few Glacial epochs. 
 
 Mr. Wallace has certainly put the astronomic theory in its best 
 form, yet physicists are by no means agreed as to what particular 
 conditions would produce this effect. 
 
 3. Time involved in the Quaternary Period.— If we accept Croll's 
 and Wallace's view, then it is possible to estimate with accuracy the 
 length di the Glacial epoch and the time elapsed since its close, for it 
 is needless to say that astronomical cycles are calculable with great 
 certainty. According to Croll and Wallace, the Glacial period com- 
 menced 240,000 years ago, lasted 160,000 years, and 80,000 years 
 have elapsed since its decline. 
 
 * American Journal, vol. xxii, p. 437, 1881. 
 f Geological Magazine, vol. viii, p. 481, 1881. 
 
616 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 Other and more direct methods of estimation, however, such as the 
 recession of waterfalls (p. 15) and of lake-shores (p. 35) and the ex- 
 treme ireshness of glacial scorings and polishings, seem to indicate a 
 much shorter time since the disappearance of the ice-sheet. This is 
 again a strong reason for believing that astronomical changes were 
 not the main cause of the colder climate. 
 
 Meteorological Theory.— The discussion of glacial climate, up to 
 recent years, has invoked the remote and abstruse — continent-lifting 
 forces and astronomic changes. Let us turn to near-by and more 
 familiar agencies — the atmospheric phenomena. 
 
 Primarily, the problem of glacial climate is not geologic, but me- 
 teorologic. The phenomena are wholly atmospheric, affected, doubt- 
 less, by geography and topography, but the geologic influence is in- 
 direct. There are two elements in this meteorological problem : first, 
 the cause of the lower temperature; second, the localization of the 
 precipitation (snowfall) in limited areas. The discovery that there 
 
 Fi». 981.— Paths of Cyclonic Storms. 
 
 had been no universal polar ice-cap, but only limited areas of glaeia- 
 tion, and those in middle latitudes (see p. 577), is a fact of prime 
 importance. The explanation is found in the migration of revolving 
 storms. We might call it a matter of " fossil cyclones." The cyclonic, 
 storms of Pleistocene time probably followed in general the paths 
 which they pursue to-day (Fig. 981).* The centers of glacial accu- 
 
 * If the reader is not already familiar with the phenomena and laws of cyclonic 
 storms he should consult a textbook in meteorology, as Waldo or Pavis. Practically all 
 the storms which occur ia the United States are cyclonic, and have an eastward or north- 
 eastward progression. > 
 
SOME GENEEAL OBSERVATIONS ON THE WHOLE QUATERNARY. 617 
 
 mulation were the localities along the cyclonic paths of heaviest snow- 
 fall. The region of greatest concentration of migrant storms to-day 
 is over the lower Great Ijakes and the St. Lawrence. The center of 
 the latest or Wisconsin ice body was the northern or northwestern 
 quadrant of this storm area, where the precipitation was chiefly snow 
 instead of rain. If the average annual temperature should be low- 
 ered only a few degrees, centers of snow and glaciation would prob- 
 ably form again in British Columbia, Quebec, and Scandinavia, the 
 chief centers of the Pleistocene ice bodies. It is quite certain that 
 the general atmospheric circulation in the northern hemisphere 
 was not essentially different in the Glacial period from that of 
 to-day, and consequently the areas of high and- low barometric 
 pressures and the cyclonic movements must have been similar to 
 the present.* 
 
 The more important element in the glacial problem is the cause 
 of the lower temperature. The fact of Permian glaciation in low 
 latitudes, either side of the equator, rules out the astronomic hypothe- 
 sis, and continental elevation alone is insufficient. But a sufficient 
 cause of secular changes of temperature, affecting the whole earth 
 alike, is found in the variation in amount of the carbon dioxide of the 
 atmosphere. Some facts bearing on this subject were given on pages 
 893-397, and the origin of the atmosphere, which becomes an essen- 
 tial part of the theory, is there discussed. 
 
 The "COj is the minimum and critical constituent of the atmos- 
 phere. It is the least in amount of the constituent gases because of 
 its chemical properties and its consumption in geologic processes — 
 rock decay. Nitrogen is the largest constituent because it is inert 
 and not consumed. It is certain that the present composition of the 
 atmosphere is the resultant of interaction of atmosphere, land and 
 ocean, throughout geologic time. 
 
 On account of its heat-absorbing properties the COj is vastly the 
 most important element affecting climate. It now forms only about 
 j^ part of the atmosphere. With its thermal potency it will be seen 
 that comparatively slight variation in amount would produce great 
 climatic effects. Physicists have long recognized the fact. It is be- 
 lieved that doubling the present small amount of 00^ would produce 
 mild climate to the poles, and that halving the present amount would 
 bring on another glacial period. It was long ago suggested by Tyn- 
 dall that variations in the amount of carbon dioxide might have been 
 the cause of the Glacial cold. But it remained for Dr. Arrhenius 
 
 * F. W. Harmer, lufluence of Winds upon Climate during the Pleistocene Epoch, 
 Quart. Jour. Geol. Soc. (London), vol. Mi, 190i, pp. 405-476. T. C. Chamberlin, Jour. 
 Geol., vol. vii, pp. 752-7V1. 
 
618 CENOZOIC ERA— AGE OF MAMMALS. 
 
 and Prof. Chamberlin to show the mode of such variation by normal, 
 ordinary geologic processes.* The scientific world is indebted to 
 Chamberlin for placing the matter in shape as a working theory. 
 
 The amount of COj withdrawn from the air and stored as coal 
 and carbonates is 20,000 or 100,000 times the present content. The 
 former idea that this was all in the air at one time and has been 
 gradually withdrawn is no longer reasonable. The air receives acces- 
 sions to-day from volcanoes, solfataras, and mofettes, from acid 
 springs, from erosion of crystalline rocks, all from the earth's in- 
 terior. The conclusion from all the facts and probabilities is that 
 through geologic time there has been a fair balance held between 
 supply and withdrawal, though not an exact adjustment. If the 
 supply has been fairly uniform, the consumption has not. Broad 
 and high land areas mean rapid depletion by carbonation of the 
 rocks. Small land areas and wide seas allow enrichment of the at- 
 mosphere on account of lack of withdrawal by land erosion. (The 
 ocean is a reservoir of carbonic acid, containing about eighteen times 
 as much as the air, and it acts as an equalizer, by diffusion, to check 
 extreme depletion of the air.) Considerable increase in the propor- 
 tion of CO2 means warm climate over the whole earth, as in Tertiary 
 time, in spite of elevated northern lands. Depletion below the aver- 
 age means cold and dryness, like the climates of the Salina, Permo- 
 Triassic, and Pleistocene, and perhaps other periods. 
 
 The several factors in our present climate — atmospheric, astro- 
 nomic, geographic, and geologic — are so delicately balanced that any 
 slight change might produce great effects. Of these factors, the 
 amount of carbon dioxide (and depending on it the amount of water 
 vapor) is doubtless the most influential. We may believe that the * 
 Pleistocene ice-fields were produced by an average temperature only 
 a few degrees lower than we have to-day; that this was the effect of 
 reduction in 'the amount of CO2 in the atmosphere; and that the 
 depletion had been brought about by the excessive demands for car- 
 bonation of the rocks over the extensive and elevated land areas of 
 the Tertiary. It is possible that the attitude of the earth in relation 
 to the sun had some effect ; and it may be possible that the alternation 
 of the glacial and interglacial epochs had some relationship to the 
 precession of the equinoxes, according to Croll's hypothesis. The 
 geography of the land masses probably had some influence, the same 
 as to-day, in determining the location of the great barometric areas, 
 and through them the paths of the cyclonic storms. It is evident 
 that glaciation is not a simple effect, but the product of the inter- 
 
 * Svante Arrhenius, Phil. Mag., April, 1896, pp. 2S1-216. T. C. Chamberlin, Jour. 
 Geol., vol. vii, pp. 545-684, 667-683, '752-738, 
 
SOME GENERAL OBSERVATIONS ON THE WHOLE QUATERNARY. 619 
 
 action of several forces and agencies, like most other broad effects 
 in -nature. 
 
 The very remarkable and extensive glaciation at the close of the 
 Palasozoic in low latitudes in India, Africa, and Australia, and pos- 
 sibly in South America, is a fact which any theory must explain. It 
 seems most probable that it was produced by the great exposure of 
 new land areas following the Appalachian revolution. The southern 
 continents were then connected and possibly united to the Antarctic 
 land. Chamberlin suggests an atmospheric circulation in the south- 
 ern hemisphere, due to the land configuration, which drove the cold 
 of antarctic currents into the Indian Ocean, somewhat as the oblique 
 circulation of the northern hemisphere in the Pleistocene and the 
 present time concentrates glaciation about the north Atlantic. 
 
 Some indications of glaciation have been reported from other 
 horizons than the Permo-Triassic, especially the close of the Creta- 
 ceous and in the Tertiary. With attention directed to ancient glacial 
 phenomena, and with a receptive mental attitude, it may be found 
 that glaciation was not such a rare phenomenon as was formerly sup- 
 posed — that the " Final Winter " has had so many premonitions in 
 frosty seasons or arid climates of the past that we may not anticipate 
 its near arrival. 
 
 3. The Quaternary a Period of Revolution — a Transition between 
 the Cenozoic and the Psychozoic Eras.— We have already seen (pp. 393 
 and 305) that between the great eras, and perhaps also at other times, 
 there have been periods of oscillation of the earth's crust, and therefore 
 of changes of physical geography, marked by unconformity of strata ; 
 and of changes of climate, marked by apparently abrupt changes of 
 species. These have been the critical periods of the earth's history- 
 periods of revolution and rapid change. But for that very reason they 
 are also periods of lost records. We have already also spoken of the lost 
 .interval at the end of the Archaean, evidently the greatest of all ; again, 
 of a lost interval at the end of the Palffiozcic, partly recovered in the 
 Permian, evidently the next greatest ; again, of a lost interval at the end 
 of the Cretaceous, in a large measure recovered in the Laramie beds. 
 There are doubtless many others of less extent. These periods are 
 always marked by unconformity of the strata and change in the life- 
 system. The old geologists regarded these changes as sudden and 
 cataclysmic. All geologists now regard the suddenness as largely ap- 
 parent, and the result of lost record. 
 
 Now, the Quaternary is also a critical period. It corresponds with 
 one of the lost intervals ; only in this case, on account of its nearness 
 to us, the record has been recovered. By the study of this period, 
 therefore, we may hope to solve many problems which have heretofore 
 puzzled us. Here, for example, we have oscillations of the crust on a 
 41 
 
620 CENOZOIC EEA— AGE OF MAMMALS. 
 
 grand scale, producing great changes of physical geography and cli- 
 mate, and therefore of fauna and flora. Here we have wide-spread un- 
 conformity of present sediments on eroded surfaces of^all previous 
 strata, over the whole sea-bottom as far as the submerged continental 
 margin, and, if the antarctic continent was connected with South 
 America, South Africa, and Australia, also 'over the whole antarctic 
 ocean bottom. If we add to this the universal unconformity of the 
 drift on the eroded rock of all other ages, we have an unconformity as 
 extensive as any known. But we observe that in this case these effects 
 have been produced slowly, and that the fauna and flora have not been 
 suddenly destroyed and suddenly recreated, but have continued to live 
 throughout, the species gradually changing. But, what is still more 
 interesting, much light is thrown also on the hitherto insoluble prob- 
 lem of the mode and the cause of the comparatively rapid change of 
 species in these critical periods. The attentive study of the Quater- 
 nary shows that, in addition to the direct effect of change of climate, 
 one great cause of change of species has been migration : migration 
 north and south, enforced by change of temperature ; migration in any 
 direction, permitted by change of physical geography. This point is 
 so important, that we must explain it somewhat fully. 
 
 It will be remembered (p. 526) that in Miocene times Greenland, 
 Iceland, and Spitzbergen were covered with a luxuriant, temperate 
 vegetation. The congeners of the vegetation of that time are found 
 now in California, along the shores of the Southern Atlantic States, and 
 in Southern Europe. Evidently at that time there was no polar ice- 
 cap, and therefore no arctic plants. At the end of the Pliocene, the 
 vegetation shows a climate not greatly differing from the present. It 
 is probable, therefore, that the cold had increased until an ice-cap had 
 formed, such as now exists in polar regions, with its accompaniment 
 of arctic species. As the Glacial epoch came on and culminated, the 
 polar ice slowly extended — its margin crept slowly southward, until 
 it reached 40° in America and 53° in Europe, with local extensions 
 stretching still farther southward, in mountain regions. The southern 
 polar regions were probably similarly affected, either simultaneously or 
 alternately. 
 
 We must not confound this movement southward of the southern 
 limit of the ice with the current motion of the ice-sheet itself. The 
 limit of the ice-cap is like the lower limit of a glacier (p. 48). It may 
 be stationary, or advancing or retreating, but the glacial stream flows 
 ever onward. Again, the motion of a glacial current is slow — perhaps 
 one to three feet^er day — but the extension or recession of the glacial 
 limit may be far slower, perhaps a few feet per annum. We may thus 
 easily appreciate the immense time necessary to advance this limit of 
 the ice-cap to 40° latitude. 
 
SOME GENEEAL OBSERVATIONS ON THE WBOLE QUATERNARY. 621 
 
 At the end of the Glacial and the commencement of the Champlain 
 epoch a movement of the ice-limit in a contrary direction— a retreat 
 northward— commenced and continued, with perhaps some alternate 
 progressions and regressions, to its present position. 
 
 Now, the efFect of this advance and retreat of polar ice upon plants 
 and animals must have been very marked. Temperate plants, inhabit- 
 ing Greenland in the Miocene, were pushed to the shores of the Gulf. 
 Arctic plants — i. e.,*those which haunt the margin of perpetual ice — 
 were pushed to Middle United States and to Middle Europe ; and arc- 
 tic shells were similarly driven southward, slowly, generation after gen- 
 eration. We say slowly, for otherwise they must have been destroyed. 
 With the return of temperate conditions, and the retreat of the ice- 
 cap, these species, both shells and plants, again went northward to their 
 appropriate place. But the plant species, and some land invertebrate 
 species, such as insects, had an alternative which the shells had not, 
 viz., to seek arctic conditions also^upward on mountains. Many did 
 so and were left stranded there. Thus is explained the remarkable fact 
 that Alpine plant-species in Europe are similar to and largely identical 
 with those in America ; and both with the present arctic species. This 
 indicates a former wide distribution of identical arctic species all over 
 Europe and America, and their subsequent retreat northward into 
 polar regions and upivard into Alpine isolation. Grote has observed 
 a similar isolation of Labrador insect-species on Mount Washington, 
 and on the Colorado mountains.* 
 
 There was probably a similar movement, to a less extent, of temper- 
 ate species. In the Taxodium of the Southern Atlantic and Gulf 
 swamps, and the Sequoias of California, we doubtless have examples of 
 species wide-spread in Miocene times, which have been destroyed by 
 these climatic changes, except in certain limited areas. 
 
 But plants and lower species of animals are far less affected by 
 changes in physical conditions than are the higher species of animals. 
 This is shown by the wide range both in space and time of the former 
 as compared with the latter. Under these great changes and enforced 
 migrations, therefore, plants and invertebrate animal species maintained 
 their specific characters mostly unchanged, or but slightly changed. 
 But in the case of mammals destruction or change was inevitable. 
 Both took place^destruction of some and change of the remainder. 
 
 In America some time during Quaternary, perhaps during the 
 period of northern subsidence, there was prohaily a broad land-con- 
 nection of North America with South America by the Caribbean Sea 
 region ; and certainly, as shown by the similarity of plants, with North- 
 ern Asia by the region between the Aleutian Isles and Bering Strait. 
 
 * American Journal of Science, 1875, vol. x, p. 335. 
 
622 CENOZOIC ERA— AGE OF MAMMALS. 
 
 Thus migrations were not only enforced by climatic changes, but per- 
 mitted by geographical connections with adjacent continents. Also 
 the great Pliocene lake, 1,000 miles long (p. 533), which separated West- 
 ern from Eastern North America was abolished, and migrations became 
 freer between the East and West. It is evident that from all these 
 causes mammalian faunas from widely-different regions were precipi- 
 tated upon each other, and struggled together for mastery. Large 
 numbers of species were destroyed, and the fittest only survived, 
 and these only under changed forms. It is quite possible that man 
 came to America with the Asiatic mammalian invasion. If so, his 
 earliest remains in America may be looked for on the Pacific coast. 
 
 Of course we use the word Migrations in its widest sense, as change 
 of habitat of species as well as of individuals.* In the case of plants 
 and many lower animals, the place of species only moved slowly from 
 generation to generation. In the case of mammals there was more de- 
 cided movement of individuals. ^ 
 
 This very important subject has been more closely studied in Europe 
 than here, although we believe that America is the simplest and best 
 field for its elucidation. During the Quaternary probably at least four 
 distinct mammalian faunas struggled together for mastery on European 
 soil : 1. The Pliocene autochthones. 2. Invasions from Africa, per- 
 mitted by geographical connection opening a gateway through the 
 Mediterranean, since closed. 3. Invasions from Asia, by opening of a 
 gateway which has remained open ever since ; with this invasion prob- 
 ably came man. 4. Invasions from arctic regions. Probably more than 
 one such invasion took place ; certainly one occurred during the second 
 Glacial epoch, called on that account the Keindeer period. 
 
 The final result of all this struggle was, that the Pliocene autoch- 
 thones were destroyed or driven southward into Africa; the southern 
 species were mostly destroyed or driven back with changed forms and 
 diminished size ; the northern species, reindeer, glutton, etc., retreated 
 again northward, and the Asiatics remained in possession of the field, 
 but greatly changed by the struggle. Man was among these, and cer- 
 tainly one of the principal agents in the change. Speaking more ac- 
 curately, the present fauna of Europe may be said to be a product of 
 all these factors ; but the Asiatic invasion seems to be the largest factor. 
 
 Thus, then, the gradual progress of evolution through" all geological 
 time, and the causes of the phenomenon of rapid change of species at 
 critical periods of the earth's history, may be briefly summarized as 
 follows : 
 
 1. A gradual, extrem.ely slow evolution of organic forms under the 
 operation of all the forces and factors of evolution known and un- 
 
 * The term dispersal is often used. 
 
SOME GKNERAL OBSERVATIONS ON THE WHOLE QUATERNARY. 623 
 
 known, whatever we may conceive these to be. This cause acting 
 alone would produce gradual changes in time (geological faunas), but 
 without geographical diversity. It would be easy to synchronize strata 
 in different countries, because fossils of the same period would be iden- 
 tical everywhere. But we know this is not true. 
 
 2. This slow evolution takes different directions in different places 
 and under different physical conditions, and thus gives rise to geo- 
 graphical faunas and floras. Such geographical faunas and floras, 
 if isolated by physical barriers, become more and more diverse so long 
 as the barriers are maintained. This cause acting alone would produce 
 extreme geographical diversity, greater than any now known, and ren- 
 der determination of synchronism impossible. This also is not true. 
 
 3. During critical periods physical changes and consequent migra- 
 tions, partly enforced by changes of climate, partly permitted by re- 
 moval of barriers, and the precipitation of adjacent faunas and floras 
 upon each other, and the consequent severe struggle for life, give rise 
 to far more rapid changes of species, but at the same time to greater 
 geographical uniformity. This more rapid change of organic forms 
 is produced partly by severer pressure of external conditio?is, certainly 
 one factor of change ; partly by severer struggle for life, certainly an- 
 other factor of change ; and partly due to the effect of new dominant 
 types, another factor of change ; and doubtless .partly also to the more 
 active operation of other factors of change, which we do not yet under- 
 stand. These critical periods tend to produce not only more rapid gen- 
 eral evolution, but also to destroy extreme geographical diversity ; and 
 since it operates on animals rather more than plants, plant species 
 are more apt to be local, and are less certainly carried along with the 
 stream of general evolution, and are therefore less reliable in deter- 
 mining geological age than animals. 
 
 4. Ee-isolations in new positions. This would again produce diver- 
 gence of geographical faunas and floras increasing with time, as long 
 as the isolation continued. Thus it is seen that geographical diversity 
 is a product of three factors — viz., difference of environment, isolation. 
 
 The last of these critical periods was the Quaternary. Therefore in 
 the changes of physical geography and climate of this period we find 
 the main cause of the present distrilution of species ; and, conversely, 
 this distribution furnishes the key to the geographical changes and the 
 direction of migrations during the Quaternary. 
 
 The principles enumerated above are so important, that some ex- 
 amples illustrating seem necessary. 
 
 1. Australia. — This one is less dependent on the Glacial period, but 
 is an excellent illustration of the principle. The fauna and flora of 
 Australia are the most peculiar known anywhere. Confining our at- 
 
624 CENOZOIC ERA— AGE OF MAMMALS. 
 
 tention to mammals ; of about one hundred and thirty species known 
 in Australia, all except two or three bats and rats* (of all animals the 
 most likely to be accidentally introduced) are non-placentals, i. e., mar- 
 supials and monotremes. And, moreover, with the exception of sev- 
 eral opossums in America, North and South, non-placentals are not 
 found anywhere except 'in Australia and neighboring islands. The 
 explanation is as follows : Of all countries, Australia has been the 
 longest isolated from all other continents. The wide migrations of 
 the Quaternary which mingled the faunas and floras of other conti- 
 nents did not reach this one. It will be remembered that, in Jurassic 
 times, marsupials in great numbers inhabited Europe and America, 
 and doubtless all other great continents, Australia among the number. 
 It will be remembered also that true placental mammals were not in- 
 troduced until the Tertiary. It is evident, then, that Australia was 
 separated before the Tertiary, and has been isolated ever since. The 
 severe struggle which determined the evolution of placentals elsewhere 
 did not affect that continent. Placentals were not evolved there, nor 
 could they get there from abroad. 
 
 ,2. Africa. — The mammalian fauna of Africa, south of Sahara, as 
 shown by Wallace (Island Xiife), consists of two very distinct groups — 
 viz., a group of small animals of very generalized type — insectivores and 
 lemurs ; and a group of large, powerful, and highly-specialized animals 
 — carnivores and herbivores. The animals of the former group are 
 peculiar to Africa, and Madagascar, and are probably indigenous ; the 
 animals of the latter group are similar to the Pliocene animals of Eu- 
 rasia, and are probably invaders. The explanation is as follows : Diir- 
 ' ' ing late Tertiary times, Africa was separated from Eurasia probably 
 by a sea, and inhabited only by the group which we called indigenes. 
 Then came the Glacial oscillations, which opened a gateway into Africa, 
 and the concomitant climatic changes which drove the Eurasian Plio- 
 cene animals southward. These invaders soon dominated the weaker 
 indigenes and were subsequently isolated in their new home. The 
 struggle which followed has produced considerable change in both 
 groups, but especially in the indigenes. 
 
 3. Madagascar. — The mammalian fauna of Madagascar is very re- 
 markable ; nearly all the species bein^ peculiar to that island. There 
 is, however, a general resemblance to the indigenes of Africa. The 
 explanation is as follows: During Tertiary times, Madagascar was a 
 part of the African Continent, and both inhabited by the same animals, 
 viz., the indigenes. But in Pliocene times, before the northern inva- 
 sion, it was separated, and therefore the invasion did not reach it. 
 
 * The dingo or native dog is no exception, because, according to Wallace, it was in- 
 troduced by man. — Island Life, p. 45. 
 
SOME GENERAL OBSERVATIONS ON THE WHOLE QUATERNARY. 625 
 
 Meanwhile by long isolation, the Malagasian fauna changdd slowly to 
 its present state, but the change was not so great as in their African 
 congeners, who had to bear the brunt of the struggle with invaders. 
 Therefore, we have in the Malagasian fauna a somewhat nearer ap- 
 proach to the Tertiary fauna of both. 
 
 4. British Isles.— The fauna and flora of the British Isles are al- 
 most but not quite identical with those of Europe. Between the two 
 there are strong varietal but not specific diilerencfes. They are also 
 somewhat less rich, some species being wanting which are found on 
 the continent. This is especially true of Ireland. The explanation is 
 as follows : The climatic changes of the Glacial epoch, but especially 
 the ice-sheet and subsequent submergence of the Champlain completely 
 destroyed the indigenous species of these islands. But, during the 
 elevation of later Pleistocene time, they were again broadly con- 
 nected with the continent, and therefore colonized by continental spe- 
 cies. They have been again separated by subsidence, and divergence 
 of organic forms has again commenced ; but the period of connection 
 was so brief that the colonization, especially in the extreme parts, was 
 not completed before re-isolation ; and the time since re-isolation has 
 been too short for the divergence to go very far ; it has reached only 
 varietal differences. 
 
 5. Coast Islands of California.— MoTig the coast of the southern 
 part of California there is a string of bold, rocky islands, nearly two 
 thousand feet high, and about fifty miles off shore. The flora of these 
 islands, as shown by Prof. Greene,* is very remarkable. Of nearly 
 three hundred species found there, about fifty are entirely peculiar — 
 being found nowhere else in the world. Of the others, all are charac- 
 teristic California species. Now for the explanation : During late Ter- 
 tiary and early Quaternary times the continent was higher than now, 
 and these islands were a part of California. We have already given 
 proof of this fact on page 586. During that time California, includ- 
 ing these islands, was occupied by a flora not greatly different from 
 that of the islands now. By the oscillations of the Quaternary the is- 
 lands were separated. Then came the northern invasion of species, 
 changing some of the native species and destroying others, and form- 
 ing the California flora of to-day. The islands were spared this inva- 
 sion by isolation. It is probable, therefore, that in the island flora we 
 have a somewhat near approach to the flora of California before the 
 invasion, f 
 
 * Bulletin of the California Academy of Sciences, No. T. 
 
 f American Journal of Science, vol. ixxiv, p. 457, 1887. This deduction has recently 
 been confirmed by the marine fauna of Santa Catalina. A large percentage of the living 
 species there are extinct on the main coast, being fossils of the Pliocene, and the rest are 
 arctic species. — Jour. Geol., vol. iii, pp. 453 and 487, 1895. 
 
626 CENOZOIC EKA— AGE OF MAMMALS. 
 
 Thus, then, regarding the , Cenozoic and the Modern as coDsecutive 
 eras, and the Quaternary as the transitional, revolutionary, or critical 
 period between, we see a great, and, if we had lost the Quaternary, an 
 apparently sudden, change of species. Yet this change, as great as it 
 is, is not to be compared in magnitude with that which, separates the 
 great eras or even ages from each other. Evidently, therefore, we must 
 regard the lost interval between the Archaean and Palseozoic, and that 
 between the Palaeozoic and Mesozoic, yes, even that between the Meso- 
 zoio and Cenozoic (as small as this latter is in comparison with the 
 others), as all of them far greater than the whole Quaternary period ; 
 or else the forces of evolution must have been far more active in those 
 earlier times than more recently. But, on the other hand, we must re- 
 member that the change is not yet completed ; that the introduction of 
 man has continued and increased the changes commenced by physical 
 and organic causes. When completed — i. e., when civilized man shall 
 have occupied the whole earth — the change will then be as great as 
 any that has ever occurred in the history of the earth. 
 
 4. Drift in Relation to Gold.— As already stated (p. 250), gold oc- 
 curs in two positions, viz., in quartz veins intersecting metamorphic 
 slates (quartz-mines) or in Tiyer-gravels (placer-mines). The auriferous 
 slates may be of various ages. In the Appalachian, the Ural, and in 
 Australia they are metamorphic, Silurian, or Cambrian.* In California 
 they are mainly Jura-Trias. The placer-mines are nearly always late 
 Tertiary or early Quaternary gravels. There has been throughout all 
 geological time a progressive concentration of gold and other metals in 
 more and more available form. 1. It was disseminated in excessively 
 small quantities in the slates — too small to be easily detected — probably 
 derived from the sea, in the waters of which small quantities are de- 
 tectable. 3. After upheaval, crumpling, metamorphism, and fissuring, 
 it was leached out and accumulated along with silica and .metallic 
 sulphides in the fissures, as auriferous veins. 3. Atmospheric agencies 
 acting on the outcropping veins dissolved away the sulphides, leaving the 
 gold free and therefore in more available form along the backs of the 
 veins.v 4. In the meantime the weathering of the slates on a low angle 
 of slope, preceding the Post-Tertiary elevation (page 276), resulted in 
 deep residual soil, abundantly mixed with imperishable quartz frag- 
 ments containing gold. 5. Then came last the rushing waters of latest 
 Tertiary and earliest Quaternary — i. e., after the upheaval commenced 
 — carrying to the sea the finer soil, but accumulating the quartz frag, 
 ments in the form of pebbles in the river-beds, where they are sorted 
 and panned, leaving the coarser gold high up the slopes and at the 
 bottom of gravels, forming the placers, the richest of all. 
 
 * Pre-Cambrian in Appalachian (Becker). 
 
SOME GENERAL OBSEUVATIONS ON THE WHOLE QUATERNARY. 627 
 
 The placers of California, however, are of two kinds, viz., the ordi- 
 nary or superficial placers, and the deep placers. The superficial placers 
 are gravel-drifts in the present river-beds. The deep placers are gravel- 
 drifts in old river-leds. These old river-beds, as already stated (pp. 
 258, 591), are in many cases covered up with lava. Usually the general 
 direction of the old bed coincides with that of the present river-system, 
 but sometimes the present river-system cuts across the old river-system. 
 In all cases, however, it is evident that the old river-gravels were 
 formed before the lava flow, and the newer gravels after the lava-fiow. 
 In all cases also the present river-system has cut down far below the 
 old beds, in this respect entirely different from the old river-beds of the 
 eastern portion of the continent. The reason of this has already been 
 explained (p. 591). 
 
 The following figures are ideal sections altered a little from Whit- 
 ney's : Fig. 983, of a case in which the old and the present river-beds 
 are parallel to each other, and Fig. 984, where the later cut through 
 the earlier. In the former case the section is across the lava-flow, as 
 well as across the river-beds ; in the latter case it is in the direction of 
 the lava-flow, and therefore of the old river-bed, but across the present 
 river-beds. 
 
 In Fig. 983, which is a section across Table Mountain, in Tuolumne 
 County, California, L is the lava-cap, 140 feet thick, beneath which is 
 
 IV 
 
 Fig 983 —Section across Table Mountain, Tuolumne County, California: L, lava; G, gravel; S, 
 slate; iJ, old river-bed; 5', present river-bed. 
 
 the old river-bed, R, with its gravel, G, now worked by a tunnel, driven 
 through the rim-slate S. More recent gravels, G', are seen in the pres- 
 ent river-beds, R': In this locality G represents the deep placers, and 
 G' the superficial placers. 
 
 The history of changes shown in these sections is sufficiently obvi- 
 ous. In the time of the old river-system, R was a river-bed, doubtless 
 with a ridge on either side represented by the dotted lines. In this 
 ted accumulated gravel, containing gold. Then came the lava-flow, 
 which of course ran down the valley, displacing the river and covering 
 up the gravels. The displaced rivers now ran on either side of the 
 resistant laxa, and cut out new valleys, 2,000 feet deep, in the solid 
 slate, leaving the old lava-covered river-beds and their auriferous gravels 
 high up on a ridge. The deeper cutting was the result of the higher 
 
628 
 
 CENOZOIC ERA— AGE OF MAMMALS. 
 
 slope. In other cases the convulsion which ejected the lava also 
 changed greatly the direction of the slope of the country, and there- 
 fore the direction of the streams. In such cases of course the present 
 river-system cuts across the old river-beds and gravels, and their cover- 
 ing lavas, as shown in Fig. 984. 
 
 Fis. 984.— Lava-Stream cut through by Rivers: a a, basalt; b b, volcanic asliea; c c. Tertiary; 
 d d. Cretaceous rocks; H B, direction of the old river-bed; It' B', sections of the present 
 river-beds (from Whitney). 
 
 Age of the River-Gravels. — The age of the old river-gravels is still 
 doubtful ; that of the newer river-gravels is undoubtedly Champlain. 
 Below we give a list, taken from Whitney, of the remains found in 
 these gravels : 
 
 Newer placers. 
 
 Deep placers. 
 
 Great mastodon. 
 
 Mammoth. 
 
 Bison. 
 
 Tapir, modem. 
 
 Horse, modern. 
 
 Man's works. 
 
 Great mastodon.* 
 
 Mammoth. 
 
 Mylodon. 
 
 Tapir, modem. 
 
 Rhinoceros (ally). 
 
 Hippopotamus (ally). 
 
 Camel (ally). 
 
 Horse, extinct species. 
 
 It will be seen that the fauna of the deep placers unite Pliocene 
 and Quaternary characters. The great mastodon, the mammoth, the 
 tapir, and mylodon, are distinctively Quaternary, while the others are 
 Pliocene. The plants, according to Lesquereux, are decidedly Pliocene, 
 or even late Miocene. Therefore Whitney has not only put the deep 
 placers in the Pliocene, but made them the representative of the whole 
 Pliocene, and probably Miocene, and the lava-flow as the dividing-line 
 between the Tertiary and Quaternary. But, all the facts considered, it 
 seems most probable that -both the filling of the old river-beds, and 
 their protection by lava, took place comparatively rapidly, and were 
 together the closing scene of the Tertiary drama. The deep gravels, 
 therefore, may be placed indifferently in the late Pliocene or earliest 
 
 * Whitney states (Geological Survey of California, vol. i, p. 262) that neither the 
 mastodon nor the mammoth is found in deep placers ; but both have since been found 
 there. 
 
PSYCHOZOIC ERA— AGE OF MAN— RECENT EPOCH. 629 
 
 Quaternary. The newer gravels are undoubtedly Quaternary and re- 
 cent. 
 
 In any case, we have here an admirable illustration of the immen- 
 sity of geological times. The whole work of cutting the hard slate- 
 rock 2,000 feet or more has been done since the lava-flow, and therefore 
 certainly since the beginning of the Quaternary. But it is necessary 
 to remember that, on account of the high slope of the new river-beds, 
 the work was exceptionally rapid. 
 
 CHAPTER VI. 
 PSYCHOZOIC ERA— AGE OF MAN— RECENT EPOCH. 
 
 Characteristics. — The Quaternary, and, indeed, all previous ages, 
 were reigns of brute force and animal ferocity. A condition of things 
 prevailed which was inconsistent with the supremacy of man. The age 
 of man, on the contrary, is characterized by the reign of mind. There- 
 fore, as was necessary, the dangerous animals decreased -in size and 
 number, and the useful animals and plants were introduced, or else 
 preserved by man. 
 
 Distinctness of this Era. — In regard to the distinctness and impor- 
 tance of this era, there are two views which will probably ever divide 
 geologists, depending on the two views regarding the relation of man 
 to Nature. From the purely structural and animal point of view, man 
 is very closely united with the animal kingdom. He has no depart- 
 ment of his own, but belongs to the vertebrate department, along with 
 quadrupeds, birds, reptiles, and fishes. He has no class of his own, 
 but belongs to the class Mammalia, along with quadrupeds. Neither 
 has he an order of his own, but belongs to the order of Primates, along 
 with monkeys, lemurs, etc. Even a family of his own, the Hominidce, 
 is grudgingly admitted by some. But from the psychical point of 
 view it is simply impossible to overestimate the space which separates 
 man from all lower things. Man must" be set off not only against the 
 animal kingdom, but against the whole of Nature besides, as an 
 equivalent: Nature the book— the revelation— and man the inter- 
 preter. 
 
 So in the history of the earth : from one point of view the era of 
 man is not equivalent to an era, nor to an age, nor to a period, nor 
 even to an epoch. But from another point of view it is the equivalent 
 of the whole geological history of the earth besides. For the history 
 ,of the earth finds its consummation, and its interpreter, and its signifi- 
 cance, in man. 
 
630 
 
 rSYCHOZOIC ERA— AGE Of MAN— EECENT EPOCH. 
 
 But there is still another and perhaps a better reason for making 
 this, a primary division. There is now going on under our eyes, and 
 by the agency of man, a change of fauna and flora as sweeping, and far 
 more rapid, than any which has ever taken place in 
 the history of the earth. We do not sufficiently ap- 
 preciate this, only because we are in the midst of it. 
 The change will be completed when civilized man 
 dominates the whole earth. 
 
 FiQ. 985 Dinomis giganteuB, x ^ (from a pho- 
 tograph of a skeleton in Christchurch Mu- 
 Beum, New Zealand). 
 
 Fio. 986.— Aptomis didiformis, x -f; (from a ' 
 photograph cf a skeleton in Christchurch 
 Museum, New Zealand). 
 
 The rocks of this epoch are the present river-deposits, lake-deposits, 
 sea-deposits, volcanic ejections, etc., already treated of in Part I. The 
 fauna and flora of this epoch are the species still living on the earth. 
 These are different from those of the Tertiary, and largely from those 
 of the Quaternary, times ; but the change, as we have already shown, 
 has been gradual, not sudden; man himself being one of the chief 
 agents of change. 
 
 The Change still in Progress— Examples of Recently-Extinct Species. 
 — The gradual change of fauna has been, going on through many ages, 
 and is still going on under our eyes. Many remarkable Quaternary 
 species have lingered, and become extinct by the agency of man, even 
 in historic times. Among the most remarkable of these are the' huge . 
 wingless birds, the remains of which have been discovered in New 
 
PSTCHOZOIC ERA— AGE OF MAN— RECENT EPOCH. 
 
 631 
 
 Zealand, Madagascar, and Mauritius, viz., the Dinornis (huge bird), 
 JEpyornis (tall bird), Palapteryx (old wingless bird), the Solitaire,' 
 and the Dodo. Through the kindness of Mr. C. D. Voy, I am able 
 to give good figures of the skeletons of several of these extraordinary 
 extinct birds, taken from photographs (Pigs. 985-987). 
 
 The Dinornis giganteus of New Zealand, and the JSpyornis of 
 Madagascar, were eight to ten feet high. The tibia of the former has 
 been fonnd nearly a yard long, and as thick as the tibia of a horse, 
 and the egg of the latter, well preserved, thirteen inches 
 long and ,nine inches in diameter, with a capacity of two 
 gallons. The toe-bones of the D. elepliantopus (Fig. 987) 
 rivaled in size those of the elephant (Owen). These huge 
 birds must have been capable of making tracks nearly as 
 large as those of the supposed birds of the Connecticut 
 Valley sandstone (p. 471). Such tracks have indeed been 
 recently fonnd in New Zealand, in a very soft sandstone. 
 
 The Dodo, of Mauritius, a 
 heavy, clumsy bird, of fifty 
 pounds' weight, with loose, 
 downy feathers, and imper- 
 fect wings, like a new-born 
 chicken, became extinct 
 only about a hundred and 
 fifty or two hundred years 
 ago. The Apteryx, to 
 which of all living birds 
 the Dinornis, Aptornis, 
 etc., are most nearly allied, 
 still survives, ready to dis- 
 appear (Pig. 988). 
 
 The Bos primigetiius, 
 the gigantic ox of Quater- 
 nary times, is supposed to 
 be the same as the Urus 
 of Caesar, and therefore 
 became extinct since Roman times. The Quaternary bison of Europe 
 would have been now entirely extinct but for the imperial -edict which 
 preserves a few in the forests of Lithuania. The Great Auk and the 
 Rhytina have disappeared within a century. The American Buffalo 
 will probably be gone in a short time. All the fiercer and larger ani- 
 mals are disappearing before the advance of civilized man. 
 
 Thus, in passing from geological to present times we trace rocks 
 into sediments and soils ; geological agencies into chemical and physi- 
 cal agencies, now in operation ; extinct faunas and floras into the liv- 
 
 Fia. 987. — ^Dinornis elephantopus, x -fg fafter Owen). 
 
632 
 
 PSYCHOZOIC ERA— AGE OF MAN— RECENT EPOCH. 
 
 ing fauna and flora ; in a word, geology into chemistry and physics, 
 and paleontology into zoology and botany. 
 
 
 Pig. 988.— Apteryx australis. 
 
 Now, in this gradual change of fauna, when did man first appear 
 upon the scene, and whai was the character of primeval man? This 
 introduces us to two very important but very difficult and obscure sub- 
 jects. 
 
 I. — Antiquity oe Man. 
 
 On this interesting subject the three sciences — History, Archaeology, 
 and Geology — meet and co-operate ; and the recent rapid advance has 
 been the result of this union, and especially of the application of geo- 
 logical methods of research. 
 
 Archaeologists have long ago divided the history of human civiliza- 
 tion into three epochs or ages, named, from the materials of which 
 weapons and tools are made, respectively the Stone age, the Bronze 
 
ANTIQUITY OF MAN. 633 
 
 age, and the Iron age. We are here concerned only with the Stone 
 age; the others belong to history. 
 
 Closer study has again divided the Store age into two, viz., the 
 Palwolithic (old Stone age) and the Neolithic (newer Stone age). 
 During the former, only chipped stone implements were used; while 
 in the latter polished stone implements were also used. It is princi- 
 pally with the PalcBolithic that we are here concerned. But these ages 
 of stone, bronze, and iron are of no value as measures of time, 
 and do not necessarily have any geological significance. They only 
 designate phases of culture or evolution of handicraft. The South- 
 Sea Islanders, for example, are still in the Stone age. The American 
 Indians were in the Stone age only three centuries ago. 
 
 Undoubted human remains carry man back to the Champlain 
 or even an interglacial epoch. There are some geologists who think 
 they find evidence of a much earlier existence of man. We will, there- 
 fore, very rapidly review the evidences of his antiquity, and will take 
 up European localities first, because the subject has been more care- 
 fully studied there. 
 
 Primeval Man in Europe. 
 
 Supposed Miocene Man — Evidence unreliable. — The earliest period 
 in the strata of which any supposed evidences of the existence of man 
 have been found is the Miocene. These evidences, however, are con- 
 fessedly meager, and by all careful investigators considered unreliable. 
 Some irregular flint-flakes, so rough that they may be the result of 
 physical instead of intelligent agencies; some bones of animals 
 marked with parallel scratches, as if scraped, but the scratches may 
 have been produced by- currents, or, as Lyell thinks, by the teeth of 
 Eodents ; some more positive evidences of man's agency, but in strata 
 of doubfful age, or else the result of accidental mixture not contem- 
 poraneous with the deposit itself — such is, in brief, the evidence. The 
 Miocene man is not acknowledged by a single careful geologist. Mor- 
 tillet thinks that there may have existed in Miocene times a tool- 
 making animal, but not true man. 
 
 Supposed Pliocene Man.— The evidence of the existence of man 
 in Europe during the Pliocene period is, if possible, still more meager 
 and unreliable. M. Hamy thinks he has found undoubted evidence of 
 human agency in flint implements in Pliocene strata at Savone ; but 
 the contemporaneousness of the flints and the deposit is regarded as 
 doubtful. Again, Palaeolithic implements have been found in Madras 
 in strata supposed by Falconer to be Pliocene ; but more recent inves- 
 tigations make the strata Quaternary.* Of the supposed Pliocene 
 
 * American Journal of Science, 1816, vol. x, p. 232. 
 
634 PSYCHOZOIC ERA— AGE OF MAN— RECENT EPOCH. 
 
 man in California we will speak farther on. Suffice it to say that 
 
 Dawkins, summing up the evidence in 1882,* Boule in 1888,f and 
 
 Evans in 1890,1 decide that the existence of Tertiary man is yet 
 
 unproved. 
 
 Quaternary Man. — But of the existence of man in Europe and 
 
 America as early as the middle of the Quaternary period there seems 
 
 to he abundant evidence. In Europe still closer study, in connection 
 
 with geology, has again divided the Palaeolithic into an earlier and a 
 
 later. The earlier, being contemporaneous with the mammoth, is 
 
 called the Mammoth age; and the later, for similar reasons, the 
 
 Reindeer age. The mammoth, however, existed also in this later 
 
 age. The former seems to correspond with the Champlain, or a time 
 
 of mild climate, and the latter with the return of cooler climates, 
 
 passing into the recent epoch. The following table expresses the 
 
 time relations : 
 
 „ . , f 4. Iron. ) 
 In recent or superficial 3 o rj ( Historic. 
 
 P ■ ' 2. Neolithic — Domestic animals. ) 
 
 ( Reindeer stage. pto"e age. Prehistoric 
 In geologiC3,l deposits. 1. Palseolithic | jia^^otj, gtage. 1 " Europe. 
 
 These divisions and their relation to geological epochs have been 
 established in Europe. They would probably apply also to some 
 parts of Asia and Africa, for in portions of these old countries 
 man has doubtless passed, successively and slowly, through all these 
 stages. 
 
 The greatest break in time and in physical conditions between 
 these cultural stages occurs in Europe, not between the Stone and 
 Bronze ages, but between the, two divisions of the Stone age, the 
 Palaeolithic and the Keolithic. The Palaeolithic remains are found 
 in deposits which are distinctly geologic — that is, the_ deposits or the 
 caverns were formed under conditions of land altitude, drainage, 
 climate, and life very different from those of the present time. The 
 Neolithic remains, on the contrary, are in mounds or tumuli or super- 
 ficial deposits which have been accumulated under the present geo- 
 logic conditions. In Western Europe an unbridged gulf lies be- 
 tween the Palaeolithic and the Neolithic. These relations are "sug- 
 gested in the table given above. 
 
 The relics of Pateolithic man are varied and abundant. They in- 
 clude unpolished flints, as lance and arrowheads, hatchets, etc.; 
 arrow and harpoon heads, fishing-hooks, awls, needles, etc., made of 
 bone and horn; teeth, shells, etc., notched and perforated as if for 
 
 * Nature, vol. xxvi, p. 434. -j- Revue d'Anthropologie, vol. iii, p. 679. 
 
 X Nature, vol. xlii, p. 508, 1890. 
 
PRIMEVAL MAN IN EUROPE. 
 
 635 
 
 ornament; engravings, especially of animals, on ivory, bone, and 
 antler; engravings and pietographs of animals on the walls of caves; 
 and human skeletons. These are divided, somewhat arbitrarily, ac- 
 cording to location, as river-drift implements and cave relics. 
 
 The unpolished, worked flints, representing the Paljeolithic stage 
 of human evolution are widespread in the Old World. They have 
 been found, sometimes in large numbers, throughout southern and 
 western Europe, northern and central Africa, Asia Minor, and India. 
 
 River-drift Flints. — The implements found in the ancient gravel 
 deposits of flooded river valleys of western Europe are regarded as 
 
 Fie. 989.— 
 
 Flint implements from the Somme river gravels. 
 . St,. Aclienl. 
 
 <i, from Abbeville ; the others ttom 
 
 the oldest undoubted relics of man yet discovered. Naturally, they 
 are mainly the imperishable flint tools. The river-drift remains are 
 associated with a warm-climate fauna in which the Mammoth is con- 
 spicuous, and is thought to represent in time the Champlain sub- 
 mergence. The Somme Valley, in northern Prance, is the type local- 
 ity (Figs. 989, 990). 
 
 Fig. 990.— Section across Valley of the Somme ; 1. peat, twenty to thirty feet thicli, resting on 
 gravel, a ; 2, lower level gravels, with elephant bones and flint implements, covered with river- 
 roam, twenty to forty feet thiclc ; 3, upper level gravels, with similar fossils covered with loam, 
 in all, thirty feet thick ; 4, upland-loam, five to six feet thick ; 5, Eocene-Tertiary. 
 
 In the terraces of the river Somme, near Abbeville, were found 
 in 1841, and later years, by M. Boucher de Perthes, chipped flint im- 
 42 
 
636 PSYCHOZOIC ERA— AGE OF MAN— RECENT EPOCH. 
 
 plements, associated with bones of the mammoth, rhinoceros, hippo- 
 potamus, hyena, horse, etc. In 1850 they were found at St. Acheul, 
 a suburb of Amiens. The doubts with which the first announcement 
 of these facts were received have been entirely removed by careful 
 examination of the locality by many scientists both of France and 
 England. 
 
 The findings were in undisturbed gravels, both lower (2) and 
 upper (3), beneath river-loam twenty to thirty feet thick. Suppos- 
 ing that the upper loam (4) represents the full Champlain flood- 
 deposit, then 3 and 2 represent the later Champlain epoch. 
 
 In England, also, at Hoxne, similar flint implements, associated 
 with bones .of extinct animals, were found in strata underlying- the 
 higher-level river-gravels, but overlying the lowlder-drift or true gla- 
 cial deposit. This fixes the age as Champlain. 
 
 Gave Deposits. — The more instructive and abundant Palaeolithic 
 remains. are found in the eaves of Prance, Belgium, Germany^ and 
 England. One of these caverns was described on page 600. The 
 great variety of Palaeolithic objects mentioned above are mostly from 
 the caves. They are associated with a fauna which held a number of 
 northern animals, as the Musk- Ox and Keindeer, whence the time 
 was named by Lartet the Reindeer epoch. The fauna indicates a re- 
 turn of cold climate, following the Champlain and ushering in the 
 present period, or perhaps representing the last ice invasion of north- 
 ern Europe. 
 
 , The west-European cave men were artistic, being proficient in 
 the delineation of contemporaneous animals, as the mammoth, bison, 
 reindeer, etc. One of the earliest (but not the best) etchings discov- 
 ered is shown in Fig. 994. Since 1895 many caves in southwestern 
 France have been found to bear on the walls the etchings and picto- 
 .graphs of extinct and living mammals. In some caves they are 
 mainly incised outlines or etchings, sometimes with a suggestion of 
 color; rarely there was an attempt at relief by scraping away the 
 rock around the figure. In the cave of Comborelles in the Dordogne 
 109 figures were found, representing many animals, 14 figures being 
 of the Mammoth. These cave engravings are similar to the etchings 
 on bone and- antler, and were certainly made by men who drew from 
 the life. 
 
 Still more noteworthy are the earliest known frescoes; represen- 
 tations of extinct and recent mammals on cavern walls in colors. 
 The pigment used were ochres or oxides of iron and manganese. 
 Some drawings of the human figure have also been found. 
 
 Some authorities think that the Palaeolithic men were a " small, 
 swarthy race of mound-dwellers, possibly of Lappish affinities" 
 (John Ehys). 
 
PRIMEVAL MAN IN EUROPE. 
 
 637 
 
 We will notice below a few of the older or better known examples 
 of the Palseolithie. 
 
 Engis SklQl. — In the caYes of France, Belgium, and Germany 
 have been found human bones associated with extinct animals. A 
 good example is that of the skull found in a cave at Engis, on the 
 banks of the Meuse, near'Liege. Of the great antiquity of this skull 
 there seems to be no doubt. It was found in bone breccia, associated 
 with bones of Quaternary extinct species ajid living species, beneath 
 a stalagmitic crust. This association unmistakably indicates the mid- 
 dle or latter part of the Quaternary period. 
 
 Neanderthal Skull. — In a cave at Neanderthal, near Diisseldorf,was 
 found a very remarkable human skeleton, which has greatly excited the 
 interest of scientific men. The limb-bones are large, and the protuber- 
 ances for muscular attachments very prominent ; the skull very thick, 
 very low in the arch, and very prominent in the brows. It has been 
 supposed by some to be an intermediate form between man and the 
 ape; but, according to the best authority, it is in no respect inter- 
 mediate, but truly human. It is 
 probably the skeleton of a 
 man exceptionally muscular in 
 body and low in intelligence. 
 The evidences of antiquity are 
 of the same kind, but less 
 complete than in the case of 
 the Engis skull, though it prob- 
 ably belongs to the same or, 
 perhaps, even an earlier epoch. 
 The Engis skull, on the other 
 hand, is a well-shaped average 
 human shull. A figure of the 
 Engis skull is given herewith 
 (Fig. 991), and a comparison 
 in outline of the Neanderthal 
 with the ape and European 
 (Fig. 992). 
 
 Men of Spy.— There have 
 been found in a cave at Spy, Bel- 
 gium, two nearly complete skele- 
 tons, which seem to be of the 
 same type as the Neanderthal 
 man, and with the latter are sup- 
 posed to belong to a distinct and very early race. They are believed 
 to have been men of short stature, broad-shouldered, bowed thighs, 
 slightly-bent knees, and semi-erect posture, but nevertheless distinctly 
 
 Fia. 991.— Engis Skull, reduced (after Lyell). 
 
 Fig. 998.— Comparison of Forms of Skulls : 
 European ; b, the Neanderthal man ; c, 
 chimpanzee (after Lyell). 
 
638 PSYCHOZOIC ERA— AGE OF MAN— RECENT EPOCH. 
 
 human. The skeletons were found associated with the remains of 
 all the characteristic Quaternary animals and implements of the 
 rudest kind. Their age was either Champlain or interglacial.* 
 
 Mentone Skeleton. — Several years ago an almost perfect skeleton 
 of a Palffiolithic man was found in a cave at Mentone, near Nice. It 
 is that of a tall, well-formed man, with average or more than average- 
 sized skull, and a facial angle of 85°. The antiquity of this man is 
 undoubted, for his bones. are associated with those of the cave-lion, 
 cave-bear, rhinoceros, reindeer, together with living species. The 
 bones of the skeleton are all in place, surrounded with the implements 
 of the chase (flint implements), and the spoils of the chase, viz., the 
 bones of reindeer, perforatad teeth of stag, etc. Of the latter, twenty- 
 two lay about his head. These are supposed to have been worn as a 
 chaplet. This Quaternary man seems to have laid himself down 
 quietly in his cave-home and died, and Nature covered his grave with 
 a tablet of stalagmite. Other skeletons have since been found in the 
 region of Mentone. 
 
 All these, and many more which might be mentioned, belong to 
 the early Palceolithic, although the last is probably a transition to the 
 next or Eeindeer age. They were contemporaneous with the mam- 
 moth, the rhinoceros, the hippopotamus, the cave-bear, the cave-lion, 
 the cave-hyena, and other extinct animals; but the reindeer had not 
 yet, to any extent, invaded Middle Europe from the north. • They 
 seem to have been savages of the lowest type, living by hunting and 
 dwelling in caves, and their implements were of the rudest kind. 
 There is no evidence of agriculture or of domestic animals. In many 
 cases there have been found some anatomical characters of a low or 
 animal type, such as flattened shin-bones, very prominent occipital 
 protuberance, less than usual separation between the temporal ridges, 
 large size of the wisdom teeth, and, in the case of the Neanderthal 
 race, a very low arch of the skull, and bent knees, etc. But all these 
 characters, unless we except the last two, are found now in some sav- 
 age races, either as racial or as individual peculiarities. The earliest 
 men yet found are in no sense connecting links between man and ape. 
 They are distinctively human. 
 
 Reindeer Age or Later Palfflolitliic. — During this age man was 
 still associated in Middle Europe with Quaternary animals, but also 
 now with arctic animals, especially the reindeer. It probably corre- 
 sponds with the Terrace or perhaps the latest ice epoch in Europe. 
 The implements were still chipped, but much more neatly. 
 
 The abundant remains in the many caves of south and southwest 
 France belong mostly to this time. The following is a type. 
 
 * Nature, vol. xxxv, p. 564, 1887. 
 
PRIMEVAL MAN IN EUROPE. 
 
 639 
 
 Aurignac Cave. — This sepulchral cave and its rich contents were 
 accidentally discovered by a French peasant. Fig. 993 is a diagram 
 section of the cave, taken from Lyell. 
 
 On removing the talus, e, a slab of rock, / g, was exposed, covering 
 the mouth of the cave, a. In this cave were found seventeen human 
 skeletons of both sexes and of all sizes, to- 
 gether with entire bones of extinct animals 
 and works of art. Outside of the cave was 
 found a deposit, c and d, consisting of 
 ashes and cinders, mingled with 
 burnt and split and gnawed bones 
 of recent and extinct 
 animals, and works 
 ' //■i'-rfril^a^ilSfe;;:^:^:^^ ^^rx of art. The 
 
 conclusion 
 reached by 
 M. Lartet is, 
 that this was 
 a family or 
 tribal burial- 
 place ; that 
 in the cave 
 along with 
 the bodies were placed funereal gifts in the form of trinkets and 
 food ; and that the funereal feast was cooked and eaten on the level 
 space in front of the cave; and, finally, that carnivorous . beasts 
 gnawed the bones left on the spot. It is evident that the Aurignac 
 men practiced religious rites which indicated a belief in future life. 
 The following is a list of the animals the remains of which were 
 found in and about the cave ; those marked f are either wholly extinct 
 or extinct in this locality : 
 
 Fig. 993.— a Section of the Aurignac Cave: a, vault in which remains of seven- 
 teen human skeletons were found ; b, made ground, two feet thick, in 
 which human bones and entire bones of extinct and Uviny mammals, and 
 works of ait, were imbedded ; c, layer of ashes and charcoal, eight inches 
 thick, with broken, burnt, and gnawed bones of extinct and living mam- 
 mals, also hearth-stones and works of art; d, deposit with similar contents; 
 e, talus washed down from hill above ; /' (/. slab of stone which closed the 
 vault ;/i, rabbit-burrow, which led to "discovery. 
 
 FAUNA OF AUEIGNAC CAVE. 
 
 OABWirOEES. 
 
 HKEBIVOBEB. 
 
 f Cave-bear 8 or 6 
 
 Brown bear 1 
 
 • Badger 1 or 2 
 
 Polecat 1 
 
 fCave-lion 1 
 
 Wild-cat 1 
 
 f Cave-hyena 5-6 
 
 Wolf 3 
 
 Fox 18-20 
 
 f Mammoth 2 molars. 
 
 f Rhinoceros 1 
 
 tHorse 12-16 
 
 f Ass 1 
 
 Hog 1 
 
 Stag 1. 
 
 firish elk 1 
 
 Roebuck.. 3-4 
 
 fReindeer 10-12 
 
 f Aurochs 12-16 
 
L 
 
 640 PSYCHOZOIC ERA— AGE OF MAN— RECENT EPOCH. 
 
 Perigord Caves. — In southwestern rrance, along the course of the 
 river Vezere, are found many caves in which are preserved interesting 
 relics of man ranging from early to late Palaeolithic. The Palaeolithic 
 Aquitanians seem to have heen somewhat more advanced^ and of a 
 
 Fig. 994.— Drawing of a Mammoth by a Contemporaneous Man. 
 
 more peaceful temper, than the early Palaeolithic men. Although 
 there is no evidence of agriculture, they lived by fishing as well as 
 by hunting, shown by the number of fishing-hooks of bone found 
 there. Their artistic taste and skill in drawing contemporaneous but 
 now extinct animals has been already described. Fig. 994 is a piece 
 of reindeer horn on which is a rude etching of the mammoth. 
 
 Conclusions. — It seems evident that in Europe the earliest men 
 were contemporaneous with a large number of now extinct animals, 
 and were a principal agent in their extinction; that they saw the 
 flooded rivers of the Champlain epoch, and possibly the glaciers of 
 the latest Glacial epoch ; but there is no reliable evidence of their 
 existence before the Pleistocene. 
 
 Neolithic Man. 
 
 The Neolithic represents the beginning of Western civilization. 
 The remains are found over all of Europe except the extreme north, 
 and belong to a people occupied in husbandry and skilled in many 
 crafts, as gardening, spinning, weaving, boat-building, pottery, car- 
 pentry, etc. The race were taller and probably more warlike than the 
 Paleolithic, and were perhaps Libyan' or Iberian. They were over- 
 whelmed by the wave of Celtic immigration, which was possibly as 
 early as 700 b. c. (Rhys). They were probably enslaved by and par- 
 tially amalgamated with the early Celts. 
 
 The Neolithic remains are too varied to be enumerated here. 
 The old kitchen-middens, shell-mounds, and refuse-heaps are at- 
 tributed to Neolithic men; also the oldest of the lake-dwellings. A 
 Crannog on the Clyde is thought to be Neolithic or oldest Bronze, 
 although these structures are usually of the Bronze age. Stone- 
 
NEOLITHIC MAN. 
 
 641 
 
 henge, on Salisbury Plain, England, is found by excavation to be at 
 least earlier than the common use of bronze. It is believed to have 
 had an astronomical purpose, and to date from 1680 b. c. Boyd 
 Dawkins thinks that the Cro-Magnon men were Neolithic. In 
 Western Europe the age of polished stone utensils shaded into that of 
 metals without any break. 
 
 In Northern Europe, especially in Denmark, are found shell- 
 mounds of great size, 1,000 feet long, 200 feet wide, and ten feet high. 
 They are probably the accumulated refuse of annual tribal feasts. The 
 early races of men in all countries seem to have had the custom of 
 gathering in large numbers at stated intervals and feasting on sihell- 
 fish and other animals, and leaving their remains in large heaps to 
 mark the spot of assembly. The evidences of a very marked advance 
 are found in these heaps. The implements are many of them care- 
 fully shaped or else polished by rubbing. There are no longer any re- 
 mains of extinct animals, but only of living animals; and there are 
 now found remains of at least one domestic animal, viz., the dog, 
 though not yet any evidence of agriculture. We have evidence also at 
 this time of organized communities. 
 
 Transition to the Bronze Age— Lake-Dwellings. — In the Swiss, 
 Austrian, and Hungarian lakes are found abundant evidences of a 
 more advanced race than any yet mentioned, which had the singular 
 custom of dwelling in houses constructed on piles in the lakes, and 
 
 Fig. 995.— Lake-Dwellings, restored (after Mortillet). 
 
 connected with the land by means of piers or bridges. Similar lake- 
 dwellings are found now in New Guinea, Africa, and in South Amer- 
 ica. For generations objects were lost overboard, and by means of 
 dredging, a great number and variety of implements of polished stone 
 and of bronze have been obtained. Some of these were evidently 
 
642 
 
 PSYCHOZOIC ERA— AGE OF MAN— RECENT EPOCH. 
 
 used for ornament, some for domestic purposes, some for agriculture ; 
 some were weapons of war, some fishing-tackle. Many of these are 
 wrought with great skill and taste. Domestic animals — ox, sheep, 
 goat, and dog ; cereal grains — wheat and barley ; fruits — ^wild apples, 
 blackberry, etc.; coarse cloth, not woven but plaited — have also been 
 found. In a word, we have here all the evidences of communities far 
 above the state of savagism. 
 
 From this time the history of man may be traced, by means of his 
 remains, through the time of Megalithic structures, through the Ro- 
 man age, step by step, to the present time. But this belongs to the 
 archffiologist, not the geologist. The Neolithic may be regarded as 
 the beginning of the Psychozoic era — the connecting link between 
 geology and archeology. The Bronze age and all that follows it 
 belong clearly to archaeology. 
 
 Supposed Pliocene Man. — Several cases were long ago reported of 
 human bones and works of art having been found in the sub-lava drift 
 
 Fig. 996.— A yonng man's skull (prehistoric) discovered at Mentone. 
 
 described on page 637. The most famous cases were the Calaveras 
 skull and the Table Mountain skull. Besides these there are sev- 
 eral cases reported of mortars and pestles found in the sub-lava de- 
 posit. These were regarded by some persons as evidence of the 
 existence of man in a somewhat advanced stage of progress (at least 
 as much so as the Neolithic man of Europe), on the Pacific coast, 
 during the Pliocene period. The history of the Calaveras skull has 
 been carefully investigated by eminent experts and is pronounced to 
 be an imposition. The best that can be said of other sub-lava finds is 
 that they are extremely doubtful. 
 
 The doubts in regard to this extreme antiquity of man are of four 
 kinds, viz. : 1. Doubts as to the Pliocene age of the gravels — ^they 
 may be early Quaternary. 2. Doubts as to the authenticity of the 
 finds, no scientist having seen any of them in situ. 3. Doubts as to 
 the undisturbed condition of the gravels, for 'auriferous gravels are 
 
MAN IN AMEEICA. 
 
 643 
 
 4 
 
 Wa"\ 
 
 i 
 
 i 
 
 I 
 
 i 
 
 I 
 
 especially liable to disturbance, and therefore may have been dis- 
 turbed by natiye races before the arrival of the white man. 4. The 
 character of the implements said to have been found gives peculiar 
 emphasis to this last doubt, for they are not Palmolithic, but Neo- 
 lithic, and are practically identical with the work of modern Indians. 
 
 Theoretically it is very improbable that 
 we should find Neolithic remains in Ameri- 
 can Tertiary when even Palaeolithic im- 
 plements are not found in Old World Ter- 
 tiary. 
 
 Carson Footprints.— In 1883 scientific at- 
 tention was first drawn to certain remarkable 
 tracks, resembling those of gigantic men, in 
 the sandstone-quarry near Carson, Nevada. 
 The floor of the quarry (which constitutes 
 the yard of the State Prison) is a level area 
 of about two acr^s. The whole surface of 
 this area is covered with the tracks of many 
 kinds of animals. The depth of the tracks 
 shows that the material was soft mud at the 
 time the tracks were made. The most re- 
 markable are undoubted tracks of elephants 
 (mammoth) and especially certain strangely 
 man - like tracks . of enormous size. These 
 were eighteen to twenty inches long and eight inches wide. The stride 
 was about a yard, and the distance between right and left series was 
 nineteen inches. 
 
 There has been much discussion as to the nature of these tracks. 
 
 Some think that they 
 ^^^ are human, and ac- 
 
 count for their great 
 size by supposing that 
 the men wore large 
 sandals. Others think 
 that they are the 
 tracks of a large 
 ground-sloth such as 
 the mylodon, which is 
 known to have lived 
 on the Pacific coast 
 in -Quaternary times.* 
 Both in size and shape they are certainly much like the hind-foot of the 
 
 FiQ. 997.— Two Scries of Tracks 
 in Carson Prison-yard. 
 
 Via. 998.— Left hind-foot of Mylodon robustne, x 4 (after Owen). 
 
 *Am. Journ. Sci., vol. xxvi, p. 139, Aug., 1883. 
 
644 PSYCHOZOIC ERA— AGE OP MAN— RECENT EPOCH. 
 
 mylodon (Fig. 998). But if made by a quadruped, the larger hind- 
 foot must have obliterated the impression of the fore-foot, for 
 there are apparently but two series of tracks; and the feet must 
 have been clogged with mud, for no impression of toes is seen. It 
 is significant, however, that the elephant-tracks, also, formed but 
 two series. 
 
 The weight of evidence is probably in favor of the mylodon, but in 
 any case there seems no reason to believe the age of the strata to be 
 earlier than the Quaternary. The only reason for assigning them to 
 an earlier period (Pliocene) is their lithified condition. But the 
 presence in the quarry of hot springs, containing abundance of lime- 
 carbonate, sufficiently accounts for this. 
 
 Pleistocene Man. — The existence of Glacial man in America is 
 not yet proved to the satisfaction of all cautious archaeologists and 
 geologists. " Finds " have been reported from many localities, scat- 
 tered over the continent, and much has been written about them. 
 Most of the discoveries are isolated and single, and none of them, 
 unless we may possibly except those, at Trenton, have been verified 
 by a succession of discoveries in the same locality. 
 
 In Ehgland and France the doubting geologists were able to per- 
 sonally verify the discoveries, but such attempts in America have not 
 been satisfactory. The stone implements of the recent Indian race 
 are scattered over the surface of all the country, and in various ways 
 might be inserted into Pleistocene beds, or involved in deposits which 
 could be mistaken for Pleistocene. 
 
 Another uncertainty arises from the doubt as to the true age 
 of the enclosing deposits. This is illustrated by the skeleton found at 
 Lansing, Kansas, in March, 1902. This was twenty feet below 
 the surface in a deposit of uncertain nature. There is no question 
 here of the conditions of the "find," but disagreement as to the 
 origin and antiquity of the deposit. The other difficulty is illus- 
 trated by the Trenton (New Jersey) material. Many thousands of 
 worked flints are in the museums, collected from the gravel terraces 
 of the Delaware. There is little doubt that the older Trenton gravels 
 are of Glacial time, and similar in origin to those of the Thames and 
 Somme Valleys in Europe. But many experts have sought in vain 
 to find, for themselves, the artifacts in the ancient gravels, and their 
 conclusion has naturally been that the flints were Indian and essen- 
 tially superficial. However, some human crania and other objects 
 have been found at Trenton under conditions which argue very 
 strongly for Glacial age. As the supposed Pleistocene remains found 
 over the country are not distinguishable from those of the Indian 
 race, which has left such abundance of relics over the surface, the 
 greatest circumspection and scientific skill are necessary to properly 
 
MAN IN AMERICA. 
 
 645 
 
 determine the geological relations of buried h^iman remains. The 
 prevailing opinion among American men of science has been that 
 positive and sufficient proof of Glacial man in America had not 
 been presented. The Delaware Valley material may be convincing, but 
 for the present we may regard the question as unsettled, and wait for 
 unanimity of opinion among those men who are qualified to have 
 opinions. 
 
 The history of the American man can be traced clearly in refuse- 
 heaps and shell-mounds ; in the great mounds of the so-called mound- 
 builders, scattered over the whole Eastern part of the continent, but 
 especially abundant in the valley of the Mississippi^ and, finally, in the 
 wonderful cliff-dwellings and buried cities of New Mexico and Arizona. 
 But all this, though of extreme interest, belongs to archeology rather 
 than geology. 
 
 Quaternary Man in Other Countries. — In India* Palaeolithic imple- 
 ments, precisely like those found in Europe and elsewhere, were found, 
 in 1873, associated with extinct- species of elephant, hippopotamus, 
 rhinoceros, and bear, in Quaternary deposits. In the South American 
 bone-caverns human remains have been found associdTted with Quater- 
 nary animals. 
 
 ' Very recently (1895) there comes the news of the finding in Java, 
 in deposits of earliest Quaternary or late Pliocene age, of a supposed 
 
 Fio. 999.— Eestoration of the Skull of Pithecanthropus erectus, x % (after Du Bois). 
 
 veritable missing link — i. e., of an anthropoid, more man-like than any 
 yet known. It has been made by its finder — Du Bois — into a new genus 
 
 * American Journal of Science, 1875, vol. x, p. 232. 
 
646 PSYCHOZOIC ERA— AGE OF MAN— RECENT EPOCH. 
 
 and called Pithecanthropus (man-ape) erecfus. The skull and the 
 teeth of this creature are far lower and more ape-like than those of 
 any supposed man yet found, but the thigh-bone shows undoubted 
 
 Fia. 1000.— Profile outlines of the Skull of Pithecanthropus (PcS) compared with those of a Papuan 
 man, the man of Spy, Neanderthal man {N't), Hylobatee (HI), Semnopithecus {dm), and An- 
 thropopithecuB (At) (from a figure by Bu Bois, modified by Marsh). 
 
 erect attitude. Judging from the skull and teeth it is certainly inter- 
 mediate between ape and man, but on which side of the dividing line 
 it should be assigned is still doubtful. In Pig. 999 we give a restora- 
 tion of the. skull of this animal, and in Fig. 1000 outlines of the vault 
 of the skulls of modern man, Palaeolithic man. Pithecanthropus, and 
 several apes. 
 
 Man, therefore, has been traced back with certainty, at least in 
 the Old World, to the Champlain epoch. It is possible that he may be 
 hereafter traced farther to the Glacial or pre-Glacial period. Some 
 confidently expect that he will be traced to the Miocene, but this 
 seems extremely improbable, for the following reasons: 
 
 a. He has been diligently searched for, without success, iffow 
 while negative evidence is rightly regarded as of little value in geol- 
 ogy, yet, in this instance, it is undoubtedly of far more than usual 
 value, because man's works are far more numerous and far more 
 imperishable than his bones. 
 
 b. Man probably came in with the present mammalian fauna. We 
 repeat here the diagram illustrating the law of extinction and appear- 
 ance of species. It is seen that lower species are far less rapidly 
 
MAN IN AMERICA. 
 
 647 
 
 changed than higher. Living foraminifers may be traced back into 
 the Cretaceous ; living shells and other invertebrates to the beginning 
 of the Tertiary ; but living mammals pass out rapidly and disappear 
 in the Middle Quaternary. Hardly a single species of mammal now 
 
 Fia. 1001. 
 
 living is found in the Tertiary. Shall man, the highest of all, be a 
 rare exception? Man is one of the present mammalian fauna, and 
 came in with it. 
 
 c. But, again, many distinct mammalian faunas have appeared and 
 disappeared since the beginning of the Miocene. The Miocene mam- 
 malian fauna is totally different from the Eocene ; the Pliocene totally 
 different from the Miocene ; the Quaternary from the Pliocene ; and 
 the present from the Quaternary. This is graphically represented in 
 the diagram, Fig. 1002, in which the alternate shaded and white spaces 
 represent five consecutive mammalian faunas (there are really many 
 more than five) overlapping each other, but substantially distinct. It 
 seems in the highest degree improbable that man, a mammal, should 
 survive the appearance and disappearance of several mammalian faunas. 
 
 Or, again, to put it still another way: We have seen (pp. 561- 
 566) that, speaking generally, existing mammalian species commenced 
 to be introduced in the Quaternary ; existing genera in the Pliocene ; 
 and existing families in the Miocene. If, therefore, a tool-making 
 animal should be found in the Miocene, as some believe, it might be of 
 the family of Homi- 
 nidce, but not the ge- 
 nus homo. If such 
 should be found in 
 the Pliocene, it might 
 be of the genus homo, 
 but not the species fiq. 1002. 
 sapiens. Even the 
 earliest Quaternary mail— the so-called Neanderthal race — is supposed 
 by Mortillet to have been a different species from existing man. 
 
 Time since Man appeared.— Geology reckons her time in periods, 
 epochs, etc. ; History, hers in years. It is impossible to express the 
 
 -Diagram ilhiBtrating the Appearance and Extinction 
 of Successive Mammalian Paunse. 
 
PSYCHOZOIC ERA— AGE OF MAN— KBCENT EPOCH. 
 
 one chronology in terms of the other except in a very rough approxi- 
 mative way, for want of a reliable common measure. If Mr. Croll's 
 theory of glacial cold should indeed prove true, then we might hope to 
 measure man's time on the earth with some degree of accuracy. But 
 in the absence of confidence in this theory, our only resource is to use 
 the measure which we have already used on several occasions, viz., the 
 effects of causes now in operation. This measure, however, can give 
 but very rough approximate results. 
 
 There is no doubt that very great changes, both in physical geog- 
 raphy and in the mammalian fauna, have taken place since man ap- 
 peared. Judging by the rate of changes still in progress, we are natu- 
 rally led to a conviction of a lapse of time very great in comparison 
 with that recorded iu history. On the other hand, some attempts to 
 estimate more accurately by means of the growth of deltas in which 
 have been found implements of the Eoman age, the Bronze age, and 
 the Stone age ; and by the progressive erosion of lake-shores and the 
 recession of waterfalls, which is supposed to have commenced after the 
 Champlain epoch, have led to very moderate results, viz., 7,000 to 10,- 
 000 years. While these results can not be received with any confidence, 
 yet it is hoped that many such will continue to be made. 
 
 In conclusion, we may say that we have as yet no certain knowledge 
 of man's time on the earth, unless we adopt Croll's theory of the Gla- 
 cial climate. It may be 100,000 years, or it may be only 10,000 years. 
 
 II. — Character of Primeval Mait. 
 
 In regard to the second question, viz., the character of primeval 
 man, we will make but one remark. We have seen that the earliest 
 men yet discovered in Europe or America, though low in the scale of 
 civilization, were distinctively human, and not in any sense an inter- 
 mediate link between man and the ape. Nevertheless, we must not 
 forget that the cradle of mankind was probably in Asia. Man came to 
 Europe and America by migration. The intermediate link, if there 
 be any such, must be looked for in Asia, and more probably in southern 
 Asia; and there, indeed, such a link is supposed to have been found in 
 Pithecanthropus. This question can only be settled by a complete 
 knowledge of the Quaternary of that country. 
 
 In any case, man is the ruler only of the Psychozoic era. The 
 presence of man in Quaternary times must be regarded as an example 
 under the law of anticipation (p. 391). He only fairly established his 
 supremacy in the Recent epoch, and therefore the age of man and the 
 Psychozoic era ought to date from that time. 
 
APPENDIX, 
 
 Law of Variation.— If the surface of the obstacle is constant, the 
 force of running water varies as the velocity squared : f ccv' (1). This 
 may be easily proved. Suppose we have an obstacle like the pier of a 
 bridge, standing in water running with any given velocity. Now, 
 if from any cause the velocity of the current be doubled, since mo- 
 mentum or force is equal to quantity of matter multiplied by velocity 
 (M= Qx V), the force of the current will be quadrupled, for there 
 will be double the quantity of water striking the pier in a given time 
 with double the velocity. If the velocity of the current be trebled, 
 there will be three times the quantity of matter striking with three 
 times the velocity, and the force will be increased nine times. If the 
 velocity be quadrupled, the force is increaised sixteen times, and so on. 
 
 Next, if the velocity of the current remains constant, while ithe size 
 of the opposing obstacle varies, then evidently the force of the current 
 will vary as the opposing surface: if the opposing surface is doubled, 
 the force is doubled ; if trebled, the force is trebled, etc. But in similar 
 figures, surfaces vary as the square of the diameter. Therefore, in this 
 case, force varies as diameter squared : f^ cud^ (2). Therefore, when 
 both the velocity of the current and the size of the stone or other 
 obstacle vary, then the force varies as the square of the velocity of 
 the current multiplied by the square of the diameter of the stone : 
 F<xv^Xd^ (3). 
 
 This last equation gives the law of variation of the moving force. 
 
 But the resistance to be overcome, or the tveigkt of the stone, varies 
 
 as the cube of the diameters : W a d^. We have, therefore, both the 
 
 { F oc v^ "X d^ 
 law of the moving force and the law of the resistance : •< t,t^ « 
 
 Now the case we wish to consider is that in which the current is just 
 able to move the stone, or when F a. W. In this case d^ o: v^ X d^, 
 or d <x v^. Substituting, in the third equation, for d its value, 
 F ocv^Xi:^ = «". We place these equations together, so that they 
 may be better understood : ' 
 
 When surface = constant 
 
 When velocity = constant 
 
 When both vary 
 
 But. 
 
 And when W cc F, then 
 
 Dividing by cP 
 
 Substituting in 3 
 
 Or . 
 
 /a«'(l) 
 
 /' a ^' (3) 
 Focv' X cP (3) 
 Woid' (4) 
 d'cx.v'x d? 
 d ccv' 
 Foci)' XI)* 
 Fkv' 
 
 649 
 
INDEX. 
 
 A 
 
 PA6B 
 
 Abbot 11, 120 
 
 Ablation 61, 54 
 
 Acanthodes wardi 350 
 
 Acanthotelson Stimpsoni 411 
 
 Acanthoteuthis antiguus 450 
 
 Acer trilobatum 528 
 
 Aceratherium tridaotylum :f. 567 
 
 Acervularia Davidsoai 344 
 
 Acid, humus 4 
 
 Acidaspis creosotus 335 
 
 Acrodus minimus 435 
 
 nobilis 464 
 
 Acrogens, age of 293,358 
 
 Actinoceras 335 
 
 Actinopteria communis 328 
 
 Adjustment of rivers 23,31 
 
 ^piornis 631 
 
 ^scbna eximia 453 
 
 Agassiz, A 55, 59, 140, 164, 167,357 
 
 Lake 580 
 
 Louis 164, 449 
 
 Age of acrogens and amphibians 358 
 
 lishes 340 
 
 invertebrates 307 
 
 mammals 519 
 
 man 629 
 
 • reptiles 430 
 
 rock-salt 438 
 
 Agencies 3 
 
 aqueous . .- 9 
 
 atmospheric 3 
 
 igneous 84 
 
 organic 146 
 
 Ages 293 
 
 Agnostus interstrictus 211 
 
 Agrioohaerus latifrons 558 
 
 Aiguilles 284 
 
 Aitkin 63 
 
 Alethopteris lonchitica 378 
 
 massilonis 377 
 
 Whitneyi 477 
 
 Algae in hot waters 115 
 
 Algoukian rock 297 
 
 Alkaline lakes 80 
 
 Allopus littoralis 417 
 
 Allorisma pleuropistha 410 
 
 ventricosa 410 
 
 Alluvial fans 27 
 
 Alluvium 4 
 
 Alnus grewiopsis 515 
 
 Alps 264 
 
 Amazon River 32a 
 
 Amblypterus raacropterus 415 
 
 Ambonychia bellistriata 328 
 
 American mud-9sh 352 
 
 American River 15,32(7, 
 
 Amia colva 352 
 
 Ammonia 4 
 
 Ammonites bifrons 448 
 
 Chicoensis -499 
 
 cordatus 448 
 
 Humphreysianus 447 
 
 Jason 448 
 
 43 
 
 TAGD 
 
 Ammonites, Jurassic 448 
 
 margaritanus 448 
 
 Ammophila interna 633 
 
 Amphibians, age of 223,368 
 
 carboniferous 416 
 
 tertiary 639 
 
 Amphilestes 466 
 
 Amphitherium 465 
 
 Prevostii 465 
 
 Amygdaloid 223 
 
 Amygdules 224 
 
 Anchisaurus colurus 472 
 
 Anohithere 664 
 
 Anchura (alcif ormis 498 
 
 Ancyloceras percostatus 499 
 
 Andesite 216 
 
 Andrews 35 
 
 Andrias Japonica 639 
 
 Scheuchzeri 639 
 
 Andromeda vaccinifoliae afflnis 527 
 
 Aneimites obtusa 343 
 
 Angiosperms 491 
 
 Animals, Carboniferous 406 
 
 Cretaceous 495 
 
 Devonian 345 
 
 Jurassic 445 
 
 Jura-Trias 470 
 
 Permian 428 
 
 Quaternary 599 
 
 Silurian 316 
 
 Tertiary 530 
 
 ■ Triassic 433 
 
 Annelids, Silurian 333 
 
 Annularia infl£.ta 385 
 
 latifolia 343 
 
 Anomalocardia Mississippiensis 531 
 
 Anomodonts .435, 436 
 
 Anomcepus minor 472 
 
 Anoplotherium commune, restored.... 543 
 
 Anoura 416 
 
 Antecedent rivers 32 
 
 Antedon rosacea 323 
 
 Antholithus devonicus 344 
 
 Anthophyllitis devonicus 344 
 
 Anthracite 368 
 
 region of Pennsylvania, map 362 
 
 , section, magnified 366 
 
 Anthracopupa Ohioensis 409 
 
 Anthracosaurus 419 
 
 Anthrapalaemon gracilis 411 
 
 Anthroiycosa antiqua 413 
 
 Anticline 185 
 
 Antiquity of man 632, 645 
 
 Apateon ; 419 
 
 Apatornis 507 
 
 Apiocrinus Rolssianus 446 
 
 Apion refrenatum 536 
 
 Apis Adamitica 333 
 
 Appalachian chain 264 
 
 coal-field 361 
 
 revolution 391, 425 
 
 Apteryx Australis 632 
 
 Aptornis didiformis 630 
 
 Aqueo-igneou^ fusion 93 
 
 651 
 
653 
 
 INDEX. 
 
 PAQB 
 
 Aqueous agencies 9 
 
 Aralia digitata 514 
 
 Aralisephyllum obtusilobum 494 
 
 Araucaria, cone 444 
 
 Arauoarites gracilis 373 
 
 Area macrodonta 532 
 
 Archaean age 293 
 
 ■ and Palaeozoic eras, interval be- 
 tween 305 
 
 ■ '■ area in North America 298 
 
 era, time represented 299 
 
 evidences of life 299 
 
 - — -rocks, evidences of lite 299 
 
 system of rocks 296 
 
 times, physical geography 299 
 
 Archgeocidaris Wortheni 408 
 
 Archaeopteris 341 
 
 Jacksoni 343 
 
 Archaeopteryx macroura 462 
 
 Berlin specimen 463 
 
 Archaeozoic age 293 
 
 era 293 
 
 Archegosaurus 418 
 
 Archimedes Wortheni 406 
 
 Arenicolites didymus 312 
 
 Armadillos 611 
 
 Armstrong 365 
 
 Artesian wells 76 
 
 Arthrophycus Harlani 315 
 
 Artiodactyls 563 
 
 Asaphus gigas 336 
 
 Asphalt 404, 406 
 
 Aspidura loricata 433 
 
 Astarte excavata 446 
 
 Astartella Newberryi 410 
 
 Asteria lombricalis 446 
 
 Asteroids, Silurian 321 
 
 Asterophyllites 385 
 
 equisetif ormis 385 
 
 Atlantochelys gigas 505 
 
 Atlantosaur beds 478 
 
 Atlantosaurus immauis 478 
 
 Atmosphere, mechanical agencies of.. 8 
 
 Atmospheric agencies 3 
 
 Atolls , 155 
 
 ■ small 156 
 
 Aucella Erringtonii 497 
 
 Augite 212 
 
 Auriferous quartz veins 250 
 
 Aurignac Cave 639 
 
 Avicula contorta 434 
 
 socialis 434 
 
 Aviculopecten parilis 346 
 
 Axes, anticlinal 186 
 
 synclinal 186 
 
 Babbage's theory 145 
 
 Bache 39 
 
 Baculltes anceps 499 
 
 Bad Lands 279, 522 
 
 Lands, Miocene mammals 555 
 
 Baieropsis foliosa 494 
 
 Bakewellia parva 428 
 
 Baku oil-field 404 
 
 Balanced stones 58 
 
 Balanius minusculus 536 
 
 Ball structure of rocks 222 
 
 Banks, submarine 42, 43 
 
 Baphetes 419 
 
 Baptanodon discus -. 482 
 
 Barornis regens 541 
 
 Barrande 331 
 
 Barren Island, section 98 
 
 Bars 326 
 
 Basalt 216 
 
 columnar structure 221 
 
 Base-level of rivers 23, 31 
 
 Basilosaurus -. 548 
 
 Basin, hydrographical 10 
 
 PAGE 
 
 Bat, fore-limb 464 
 
 Batocrinus Chrystii 407 
 
 Bay of Fundy 32a 
 
 Beach structures ; 198 
 
 Beaches and terraces 602 
 
 Becker 266, 258" 
 
 Beecher , 335 
 
 Bee-Hive geyser 107 
 
 Belemnites 450 
 
 • clavatus 450 
 
 densus 476 
 
 fossil ink-bags 450 
 
 ■ hastatus 450 
 
 impressus 500 
 
 Owenil 450 
 
 unicanaliculatus 460 
 
 Bellerophon Newberryi 346 
 
 sublaevis 410 
 
 Belodon 540 
 
 Beryx Lewesiensis 501 
 
 Big Bone Lick 605 
 
 Billingsella transversa 311 
 
 Bird, fore-limb 464 
 
 Birds, Cretaceous 506 
 
 Jurassic 462 
 
 origin 465 
 
 Tertiary 540 
 
 gigantic extinct, of New Zealand. 631 
 
 toothed 460 
 
 Bird-tracks, supposed 471 
 
 Bischof 80, 83, 260, 267, 400, 439 
 
 Bitumen, geological relations 401 
 
 origin 404 
 
 Bituminous coal 368 
 
 Blandford 98 
 
 Blastoids 323, 346 
 
 Carboniferous 407 
 
 Blatta Helvetica 413 
 
 Blattina formosa 453 
 
 Bog-iron ore 150 
 
 Bombus Jurinei 533 
 
 Bone-caverns 599, 605, 637 
 
 origin 602 
 
 Bone-rubbish, cave, origin 601 
 
 Bores 32o 
 
 Bos primigenius 631 
 
 Bowlders 571 
 
 of disintegration 6 
 
 Brachiopods, general description 326 
 
 Carboniferous 409 
 
 Cretaceous 496 
 
 Devonian .-. . . 345 
 
 Jurassic 446 
 
 Silurian 326 
 
 Brachiospongia digitata 317 
 
 Brachyphyllum 476 
 
 Brahmapootra delta 27 
 
 Brains of coryphodon, dinoceras, etc.. 562 
 
 Bramathere 545 
 
 Branner 32, 146 
 
 Brazil, decay of rock 5 
 
 Breccia 223 
 
 Bridger beds 551 
 
 Brogger 227 
 
 Brogniart 412 
 
 Brontops restored 656 
 
 Brontosaurus 478 
 
 excelsis 480 
 
 Brontotheridae 655 
 
 Brontotherium, skull and brain 562 
 
 Brontozoum giganteum 473 
 
 Bronze age 632 
 
 transition to 641 
 
 Brooks 314 
 
 Bryozoa 319, 321, 325 
 
 Bryozoan coral 167 
 
 Buff ....: 396 
 
 Bunsen 109,111,112 
 
 Buprestidium 463 
 
 Buthograptus laxus 315 
 
 Buthotrephis suooulens 31B 
 
 gracilis 315 
 
INDEX. 
 
 653 
 
 PAGE 
 
 Buttes 17 
 
 Buttes of the Cross 16 
 
 Calamarise 377, 385 
 
 Calamite, restoration 386 
 
 Calamites and their allies 385 
 
 cannaeformis 385 
 
 Calaveras skull 640 
 
 Calcareous deposits 151, 167 
 
 Calc-spar 345 
 
 Calderas 98 
 
 California Miocene shells 532 
 
 Callipteridium SuUivanti 377 
 
 Calymene Blumenbachii 334 
 
 Camarasaurus 478 
 
 Cambrian fossils 312 
 
 — — system 303, 307, 310 
 
 Camptosaurus dispar 481 
 
 Canary islands 84 
 
 Cancellaria vetusta 532 
 
 Cailon, Grand 17 
 
 Caiions, how formed 15 
 
 Cape May 36 
 
 Caprina adversa 498 
 
 Carbonic acid springs 78 
 
 Carboniferous age 367 
 
 animals 406 
 
 braohiopods 409 
 
 conifers, affinities 375 
 
 corals 406 
 
 crustaceans 411 
 
 echinoderms 407, 408 
 
 fishes 414 
 
 Gasteropods 416 
 
 goniatites 411 
 
 insects 412 
 
 • Lamellibranchs 410 
 
 land and fresh-water shells 409 
 
 period proper, estimate of time... 391 
 
 period proper, rock system 360 
 
 . plants, structure and affinities 372 
 
 .system and age, subdivisions 359 
 
 vertebrates 414 
 
 Carcharodon augustidens 637 
 
 • megalodon 537 
 
 Carcinas moenas, development 452 
 
 Cardiocarpon 374 
 
 Baileyi 344 
 
 Cardium Hillanum 191 
 
 . Rhsetlcum 434 
 
 Carpolithes irregularis 527 
 
 Carrying power of water 18,20 
 
 Carson footprints 643 
 
 Caruthers 376 
 
 Caryocrinus ornatus 324 
 
 Caspian Sea 83 
 
 Castle geyser 104 
 
 Casts of organic remains 201 
 
 Catpkill period 341 
 
 Caulopteris primeva 379 
 
 Cave bear 601 
 
 deposits 636 
 
 Gailenreuth 600 
 
 ^ teeth and leg-bones 600 
 
 hyena 601 
 
 Caves, limestone 77 
 
 Cazin 257 
 
 Celenterates 345 
 
 Cenozoie era 519 
 
 divisions 520 
 
 general characteristics 619 
 
 Cephalaspis murchisonia 349 
 
 Cephalopods, Carboniferous 410 
 
 Cretaceous 499 
 
 Devonian 346 
 
 . — • diagram showing distribution in 
 
 time 451 
 
 Jurassic 447 
 
 Silurian 329 
 
 _ . , PAGE 
 
 Cephalopods, suture and siphon 448 
 
 Ceratites, nodosus 434 
 
 Ceratodus 353 
 
 altus, dental plate 435 
 
 Fosterii 351 
 
 serratus, dental plate 435 
 
 structure of limbs 355 
 
 Ceratosaurus nasicornis 481 
 
 Cervus Americanus 605 
 
 megaceros, skeleton 603 
 
 Cestraolon PhlUippi 352 
 
 Ceteosaur 459 
 
 Chalk 42, 168, 487 
 
 cliffs 487 
 
 continuity 510 
 
 ■ f oramiuif era of 487 
 
 origin 489 
 
 seas of cretaceous times 490 
 
 seen under the microscope 488 
 
 Chalybeate waters 79 
 
 Chamaerops Helvetica 528 
 
 Chamberlain 256 
 
 Champlain in Europe 596 
 
 epoch 568, 679 
 
 Charleston earthquake 116, 122 
 
 Cheirotherium 437 
 
 Chemical effects of waters 74, 77 
 
 deposits 42, 80, 83 
 
 Chemung period 341 
 
 Chert 169 
 
 Chlamydotherium 611 
 
 Chlorite-sohlst 229 
 
 Choke-damp 370 
 
 Chonetes Dalmaniana 409 
 
 Chronology, manner of constructing.. 207 
 
 Chrysalidina gradata 487 
 
 Church of Reoulvers 37 
 
 Cimolomys gracilis 519 
 
 Cinder-cone, section 96 
 
 Cinnamomum Mississippiense 527 
 
 polymorphum 528 
 
 Circulation, illustrations of law 259 
 
 Cirque 51 
 
 Cladodus 350 
 
 spinosua 415 
 
 Cladoselaohe fyleri 350, 414 
 
 Claosaurus annectens 518 
 
 Clay formation 7 
 
 . slate 229 
 
 Claypole 265 
 
 Cleavage, association with contor- 
 tions 192 
 
 association with foldings of strata, 191 
 
 crystalline 189 
 
 flag-stone 189 
 
 organic 189 
 
 physical theory of 193 
 
 planes 192 
 
 slaty, Sharpe's theory 191 
 
 Sorby's theory 193 
 
 structure 189 
 
 theory, geological application 195 
 
 Tyndall's theory 194 
 
 Cliff 36 
 
 Clinometer 184 
 
 Clinton coral reefs 167 
 
 Clisiophyllum Gabbi 406 
 
 Club-moss compared with lepidoden- 
 
 dron 367 
 
 Clupea alta 537 
 
 Clymenia 346 
 
 Clypeus Plotii 446 
 
 Coal areas of different countries com- 
 pared 365 
 
 . -areas of the United States 364 
 
 conifers 372 
 
 Cretaceous 490, 516 
 
 estuary or raft theory 387 
 
 extra-carboniferous 364 
 
 fat or fusing 368 
 
 ferns 376 
 
 field, Appalachian 275, 390, 391 
 
654 
 
 INDEX. 
 
 FAGX 
 
 Coal field, central 3S1 
 
 field, Richiuond and North Caro- 
 lina 473 
 
 field. Western 391 
 
 forests 152 
 
 formation, estimate of time 391 
 
 formation of 363 
 
 growth, conditions of 153 
 
 islands 153 
 
 islands, amount of vertical sub- 
 sidence 160 
 
 islands, area of land lost 160 
 
 islands, crater theory...'. 157 
 
 islands, Murray's theory 159 
 
 - — -islands, rate of subsidence...;... 161 
 
 ■ islands, subsidence 162 
 
 • islands, subsidence, theory of 157 
 
 islands, subsidence, time involved 162 
 
 . Jura-Trias 473 
 
 Jura-Trias, fossils 474 
 
 lepidodendrids 379 
 
 measures, iron-ore 397 
 
 ■ measures, Jurassic 442 
 
 measures, plication and denuda- 
 tion 361 
 
 measures, thickness of strata 360 
 
 ■ metamorphic 370 
 
 modes of occurrence 360 
 
 origin 366 
 
 peat-bog theory 387 
 
 period, climate 393 
 
 period, physical geography 393 
 
 plants, fruits 365 
 
 plants, general conclusions 386 
 
 plants, principal orders 372 
 
 plants, where found 372 
 
 polyp 152 
 
 reefs 151, 152 
 
 reefs, ancient 166 
 
 • reefs, barrier 155 
 
 reefs, barrier and circular, the- 
 ories 156 
 
 reefs, circular 155 
 
 reel^, Darwin's theory 157 
 
 reefs, Florida 145, 163 
 
 reefs, fringing 154 
 
 reefs, Murray's theory 159 
 
 reefs. Pacific ., 154 
 
 relative production . .'. 365 
 
 • seams, faults 363 
 
 seams, number and thickness 363 
 
 sigill'arids 382 
 
 steam 368 
 
 theory of accumulation 387 
 
 • varieties 367 
 
 ■ varieties, origin 368 
 
 vegetable structure in 366 
 
 water present during accumula- 
 tion 387 
 
 Coast of North Carolina 44 
 
 Coast Range of California 263,270 
 
 Bange, time of formation 567 
 
 Coasts, erosion of 37 
 
 of Florida 39 
 
 Cocooliths 488 
 
 Coocospheres 488 
 
 Coccosteus 361 
 
 declpiens 349 
 
 Cochliodus contortus 415 
 
 Cockroaches 339 
 
 Ccelurus fragllis 478 
 
 Colorado Canon 17, 19 
 
 River 22 
 
 Colossochelys Atlas 539 
 
 Columbia River falls 14 
 
 Columnar structure of rocks 221 
 
 Columnaria alveolata 318 
 
 Columns, granitic 236 
 
 Comanche group 490 
 
 Comatula rosacea 323 
 
 Compsognathus 460 
 
 Concretions 196 
 
 PAGB 
 
 Conductivity of heat 87 
 
 Cones, volcanic 95 
 
 Conformable strata 188 
 
 Conformity 187 
 
 Conglomerate 84, 179 
 
 - — - volcanic 223 
 
 Coniferous wood, fossil and recent 341 
 
 Conifers of Jura-Trias 476 
 
 Triassic 432 
 
 Coniopteris Murrayana 444 
 
 Connecticut River sandstone 469 
 
 Conocardium trigonale 346 
 
 Conradella Dyeri 329 
 
 Consequent rivers 32 
 
 Consolidation 179 
 
 Continental areas 42, 144, 174 
 
 ■ ■ form, laws ,' 177 
 
 ice sheet 50, 68 
 
 Conularia Trentonensis 329 
 
 Cook 144 
 
 Coon Butte 99 
 
 Cope ..420, 428, 466, 477, 478, 505, 506, 507, 612 
 
 Copper-veins 248 
 
 Coral, compound, or eorallum 152 
 
 Corals 316 
 
 Carboniferous 406 
 
 chain ziS 
 
 cup 316 
 
 Devonian 344 
 
 Favositid ". 3I6 
 
 Halysitid 316 
 
 honeycombed 316 
 
 Jurassic 445 
 
 Silurian 316 
 
 Corbicula fracta 517 
 
 Cordaites 375 
 
 Robbii ■. 344 
 
 Cordillera 260 
 
 Corniferous period 341 
 
 Cornulites serpentarius 333 
 
 Cornwall, map 252 
 
 Corydaloides Scudderi 413 
 
 Coryphodon beds 550 
 
 hamatus 551 
 
 skull and brain 662 
 
 Coseismal lines 123, 135 
 
 Crane 326 
 
 Crater Lake 99 
 
 Cretaceous 485 
 
 animals 495 
 
 birds 606 
 
 coal 490, 616 
 
 echinoderms 495 
 
 fishes 500 
 
 mammals 510 
 
 mollusks 496 
 
 period 485 
 
 physical geography in America 486 
 
 -plants 491 
 
 reptiles 502 
 
 rocks 487 
 
 rocks, area in America 486 
 
 sponges 495 
 
 1 subdivisions 490 
 
 Crevasses 51 
 
 Crinids 323 
 
 Crinoids, Carboniferous 407 
 
 distribution in time 408 
 
 — Jurassic 445 
 
 living 321 
 
 Silurian 321 
 
 Triassic 433 
 
 Crioceras 499 
 
 Cristellaria subarcuatula 169 
 
 Critical periods 426, 619 
 
 Crocodilians 467 
 
 CroU 41, 65 
 
 Croll's hypothesis of glacial climate.. 613 
 
 Cross 220 
 
 Cross-bedding 198 
 
 Crossopterygians 350 
 
 Crust of the earth „... 173 
 
INDEX. 
 
 655 
 
 PAQQ 
 
 Crust movements 23, 88, 140 
 
 Crustaceans, Carboniferous 410 
 
 ■ Devonian 346 
 
 Jurassic 452 
 
 Silurian ' 332 
 
 Ctenacbdon serratus 483 
 
 Ctenopistha antiqua 346 
 
 Cumberland Plateau and Lookout Mt.. 279 
 
 Cuneolina pavouia 487 
 
 Cupriferous veins 248 
 
 Cyathophylloids 316 
 
 Cycadeoidea megalophy Ua 445 
 
 Cycads, Triassic 432 
 
 Cycas circinalis 445 
 
 cross-section of stem 384 
 
 Cyclonic storms, paths of 616 
 
 Cyprea Matthewsonii 498 
 
 Cypris 409 
 
 Cyrtolites compressus 329 
 
 Cystlds 323,345 
 
 Dadoxylon Ouangondianum 343 
 
 Dalmoncllx 530 
 
 Dalmanites pleuroptryx 333 
 
 ■ limulurus 335 
 
 Dames 462 
 
 Dana .... 34, 40, 42, 46, 49, 50, 51, 91, 92, 
 147, 158, 159, 233, 235, 238, 359, 382, 416, 469 
 
 Daonella Lommelli 434 
 
 D' Archiac 50 
 
 Darwin, C 159,161,162,167 
 
 Darwin, G. W 175,289 
 
 Daubeny 394 
 
 Daubree 93, 106, 231 
 
 Davis 280 
 
 Davy 101 
 
 Dawkins 359 
 
 Dawson, J. W 342, 384, 418 
 
 Dawson, G. M 490 
 
 Dawsonella Meekii 409 
 
 Dead Sea 83 
 
 Decay of rocks 5, 6, 7 
 
 Deformation of levels 144 
 
 De Geer 142 
 
 De la Beche 250, 252 
 
 Delaware River 32 
 
 Delesse 233 
 
 Deltas 27 
 
 formation , 28 
 
 rate of growth 30,143 
 
 structure 29, 30 
 
 Dendrerpeton 418 
 
 Acadeanum, jaw and tooth 418 
 
 Density of earth 172 
 
 Denudation 284 
 
 agents - . • ^^^ 
 
 amount 285 
 
 geological time estimated by 287 
 
 Deposits, chemical, in seas 42,83 
 
 deep-sea 41, 169 
 
 fresh- water 168 
 
 from carbonated springs 79 
 
 from icebergs 73 
 
 from wave-action 39 
 
 in lakes 80,81,82 
 
 in springs 78 
 
 river 25 
 
 shell 168 
 
 Depression of coast of South Atlantic 
 
 States 143 
 
 of deltas of rivers 143 
 
 of earth-crust in Pacific Ocean 144 
 
 Derby 405 
 
 Detrital cones 27 
 
 Detritus 4 
 
 Devonian ag^, anticipations 338 
 
 age, division into periods 341 
 
 age, life-system 341 
 
 age, physical geography.; 340 
 
 FAGB 
 
 Devonian animals 345 
 
 brachlopods 345 
 
 cephalopods 346 
 
 corals 345 
 
 Crustacea 346 
 
 fishes 347 
 
 — fishes, general characteristics 353 
 
 fishes, nearest living allies 3.)2 
 
 fishes, rank 356 
 
 insects 347 
 
 land-plants 342 
 
 • — - plants 341 
 
 system 340 
 
 system, area in United States 340 
 
 Diabase 312 
 
 Diastrophism 31, 140, 145 
 
 Diatems of Tertiary 529 
 
 ooze 42 
 
 Diatryma gigantea 541 
 
 Dibranchs 329 
 
 Diceras arietina 446 
 
 Dichograptus Logani 320 
 
 Diclouius mirabilis 518 
 
 Dicotyls, first appearance 493 
 
 Dictyopyge macrura 474 
 
 Dicynodon lacerticeps 437 
 
 DidymograptuB V-fractus 320 
 
 Dikes, definition 218 
 
 age, how determined 221 
 
 ■ — ■ at the base of the Serra del Sol- 
 
 fizio 96 
 
 effect on intersected strata 218 
 
 radiating, of volcanoes 97 
 
 Diller 268 
 
 Dinichthys Terrelli 348 
 
 Dinoceras mirabile 552 
 
 skull and brain 562 
 
 Dinocerata 652 
 
 Dinornis elephantopus 631 
 
 giganteus 630 
 
 Dinosaurs 457, 471 
 
 Dinotherium giganteum, head 544 
 
 Diorite 212 
 
 Dip, definition 184 
 
 Diphyphyllum Archiaci 344 
 
 Diplooynodon victor 483 
 
 Diplograptus 321 
 
 pristls S20 
 
 simplex 311 
 
 Dipnoans 348 
 
 Diprotodon Australis, skull 611 
 
 Dirt-beds, Jurassic 443 
 
 Discoidea cylindrica 495 
 
 Disintegration of rocks 5 
 
 Dismal Swamp ' 149 
 
 Dismembered rivers 32 
 
 Distributaries 27 
 
 Divides, migration 32, 283 
 
 Dodo 631 
 
 Dolerite 216 
 
 Dollo 458 
 
 Dolomite containing concretions 197 
 
 Drainage, evolution of 31 
 
 Drift 4, 69, 569 
 
 in relation to gold 626 
 
 theory of origin 574 
 
 timber 150 
 
 Dromatherium 466 
 
 sylvestre, jaw 475 
 
 Dromopus agilis 417 
 
 Drowned rivers 32 
 
 Drumlins 71, 570 
 
 Dryptosaurus 503 
 
 Dunes 8 
 
 Dust, volcanic 92 
 
 Dutton ... 123, 136, 138, 226, 239, 275, 283, 287 
 
 Eads 34 
 
 Eagres 32a 
 
656 
 
 INDEX. 
 
 PAOB 
 
 Earth, crust of, definition 173 
 
 crust of, thickness 174 
 
 crust of, gradual oscillations 140 
 
 crust of, means of observation... 173 
 
 crust, section of 295 
 
 density 172 
 
 diameter 170 
 
 - — -form 170,174 
 
 interior SB, 172 
 
 surface configuration 174 
 
 temperature of 84 
 
 Earthquake bridges 128 
 
 epicentrum 118, 135 
 
 effect of moon on 138 
 
 fissures 129 
 
 focus 126, 133, 135 
 
 great sea- wave 129, 130 
 
 phenomena, explanation 124 
 
 relation to seasons 139 
 
 rotation 171 
 
 ■ 'Shocks in mines 127,128 
 
 Earthquake vfave, spherical 121 
 
 character 122 
 
 • velocity 122 
 
 ■ waves, their kinds and properties, 
 
 118, 126 
 
 Earthquakes 115 
 
 ■ cause 118 
 
 connection with igneous agency.. 116 
 
 -circle of principal destruction 127 
 
 distribution 116 
 
 elevation or depression during. 116, 110 
 
 ■ examples 117 
 
 explosive 124 
 
 irequency 115 
 
 horizontally progressive 125 
 
 ■ minor phenomena 126 
 
 ■ — - motion 126 
 
 originating beneath ocean 129 
 
 sounds 126 
 
 vorticose 125 
 
 Earth-surface, greater inequalities 261 
 
 Echinoderms 345 
 
 Carboniferous 495 
 
 ■ ■ Cretaceous 495 
 
 . Jurassic 445 
 
 . Silurian 321 
 
 Triassic 433 
 
 Echinoids 321 
 
 Echinarachnius Brewerianus 532 
 
 Edestosaurus of velox 504 
 
 Edestes minor 414 
 
 Elasmobranchs 348, 350, 415 
 
 Elephas Americanus 605 
 
 antiquus 603 
 
 Falconeri 603 
 
 Ganesa 545 
 
 Melitensis 603 
 
 meridionalis 603 
 
 primigenius 603 
 
 Elevation and depression of earth's 
 
 crust 140 
 
 theories 145 
 
 Babbage's theory 145 
 
 general theory 146 
 
 Herschel's theory 146 
 
 in deltas 143 
 
 in Greenland 142 
 
 in Italy 141 
 
 in Pacific Ocean 144 
 
 in Scandinavia 142 
 
 in South America 140 
 
 in South Atlantic 143 
 
 interior of continents 144 
 
 of Northern Europe in Glacial 
 
 epoch 594 
 
 Elk, Irish 603 
 
 Elvanite 214 
 
 Emmons 474 
 
 Enaliosaurs 454 
 
 Enorinus liliformls 433 
 
 Endlich 219 
 
 FAGB 
 
 Engls skull 637 
 
 Engrafted rivers 32 
 
 Entelodon crassus 556 
 
 Entomostraca 337 
 
 Eocene basin of Paris 543 
 
 epoch 521 
 
 lowest mammals 549 
 
 marine, of Alabama 548 
 
 middle, mammals 551 
 
 Tertiary shells 531 
 
 upper, of Patagonia 547 
 
 Eohippus 551 
 
 Eosaurus Acadianus 419 
 
 Eoscorpius carbonarius 413 
 
 Eozoon Canadense 300 
 
 Epeirogenic movement 261 
 
 Ephemera, larva 470 
 
 Epicentrum 118,135 
 
 Epochs 294 
 
 Equatorial currents 40 
 
 Equisetae 341 
 
 Equus 563 
 
 Eras 293 
 
 prehistoric 296 
 
 Erosion, average 10, 236 
 
 by glaciers 56 
 
 by rain and rivers 10, 11, 12 
 
 by waves 32b, 34, 36 
 
 general 284 
 
 glacial, some general results 597 
 
 examples of great 12 
 
 of coasts 37, 38 
 
 of continents, rate 10 
 
 Erosive power of water, law of varia- 
 tion 11 
 
 Eruption, modes of 217 
 
 Eruption of volcanoes 91 
 
 Eruptive rocks 215 
 
 Eryon arctif ormis 452 
 
 Barroveusis 452 
 
 Eskers 72 
 
 Estuaries 32 
 
 deposits in 32 
 
 mode of formation 32 
 
 Etna, volcano 92, 99 
 
 Eumicrotis Hawaii 428 
 
 Euomphalus subquadratus 410 
 
 Euphoberia armigera 413 
 
 Euproops Danae 411 
 
 Eurite 212 
 
 Eurypterids, Devonian 347 
 
 pre-Cambrian 300 
 
 Silurian 338 
 
 Burypterus Fischeri 338 
 
 remipes 338 
 
 Evolution, general process 290 
 
 fundamental law of 357 
 
 in geologic history 292 
 
 of coal plants 386 
 
 of drainage 31 
 
 of early birds 462 
 
 of early land vertebrates 420 
 
 of early mammals 465,561 
 
 of organic kingdom, Devonian 
 
 fishes 357 
 
 the central idea In geology 421 
 
 Ewing ■••• |f2 
 
 Excelsior geyser Ho, ii| 
 
 Exogyra Texana 49b 
 
 Experiments, power of currents 18 
 
 F 
 Fagus f erruginea ^^7 
 
 i^Sf^!!^'l:-::::::::::::::-237;s,.| 
 
 cause fjf 
 
 Pall line °i\ 
 
 in coal-measures JJJ 
 
 law of slip jS 
 
 two kinds *** 
 
INDEX. 
 
 657 
 
 PAGE 
 
 Fauna and flora, geological 203 
 
 first distinct 313 
 
 Quaternary mammalian, in North 
 
 America 605 
 
 Quaternary mammalian, of Eng- 
 land 604 
 
 still changing 605 
 
 Fauna ot the Carboniferous age 406 
 
 Favosites hemispherica 344 
 
 Favositidae 316 
 
 Favre 256,490 
 
 Faye 176 
 
 Feldspar 7,211 
 
 Felis atrox 605 
 
 Fenestella elegans 322 
 
 Ferns 341 
 
 coal 376 
 
 Ficus pyriformis 532 
 
 Fingal's Cave 222 
 
 Fiords 32a, 38, 597 
 
 Fire-clay 361 
 
 Fire-damp 370 
 
 Firehole River 106 
 
 Fisher 102,275 
 
 Fishes, age of 340 
 
 Cretaceous 500 
 
 Carboniferous 414 
 
 Devonian 347, 358 
 
 Jurassic 453 
 
 sudden appearance 358 
 
 — Tertiary 5S8 
 
 -Triassio 433 
 
 Fissures 237 
 
 cause 238 
 
 earthquake 129 
 
 Flabellina rugosa 487 
 
 Flint 169 
 
 implements 635 
 
 Flint- veins in gneiss 5 
 
 Flood-plain deposits ?5, 6S1 
 
 Florida reefs 163 
 
 compared with other reefs 165 
 
 formation 164 
 
 history of changes 16o 
 
 - — -keys 84 
 
 Fluor-spar jjj 
 
 Flustra truncata 321 
 
 Folding 264 
 
 Fontaine *J2 
 
 Footprints, amphibian 416 
 
 Foraminifers ^^' tS5 
 
 of chalk 488 
 
 shells of living ■• 489 
 
 Forbes's theory of glaciers °\„, 
 
 Porbesiocrinus WorthenI 407 
 
 Fordilla Troyensis 311 
 
 Forel v^,--- *^ 
 
 Forest, fossil, ground plan of Car- 
 
 bonif erous 585 
 
 fossil, Jurassic ■ • ■ • 443 
 
 Formation, geological, definition.. 189,^03 
 
 Formica lignitum °gj 
 
 Forms of drift ^J 
 
 Fossils, definition J^°° 
 
 degrees of preservation laa 
 
 distorted jai 
 
 distribution in strata ,.•• 'S"^ 
 
 increasing likeness to existing 
 
 forms ^"4 
 
 nature determined by age ^"is 
 
 nature determined by country 
 
 where found ■.-.■■y ■ V'-,- ,„, 
 
 nature determined by kind of rock ^0^ 
 
 origin and distribution U' 
 
 primordial, American |ii 
 
 primordial, foreign oj^ 
 
 • rain-prints • • • ■ ■ 41" 
 
 stratified rocks classified by 
 
 means of 206 
 
 Fouqufi 1^^ 
 
 Fractures Jj ' 
 
 Free crinoid, living ^^g 
 
 French Broad, gorge of l» 
 
 FAQE 
 
 Frost, geological action g 
 
 Fucus 316 
 
 Fumaroles 103 
 
 Fusing-point 87, 93 
 
 Fusculina cylindrlca 406 
 
 G 
 
 Gabbro 212 
 
 Gaileureuth Cave 600 
 
 Galerites albogalerus 495 
 
 Galesaurus planiceps 437 
 
 Ganges, average erosion 11 
 
 delta 27 
 
 Ganocephala 419 
 
 Ganoids, Devonian 348 
 
 Jurassic 453 
 
 Gar-fish 352 
 
 Gas, smoke, and flame from volcanoes 95 
 
 natural 401 
 
 Gasteropods, Carboniferous 410 
 
 Devonian 346 
 
 Cretaceous 498 
 
 Silurian 328, 329 
 
 Tertiary 533 
 
 Gastornis Edwardsii 540 
 
 Gault 441 
 
 Geest 4, 8 
 
 Geikie 227, 265 
 
 Genesis of existing orders, families, 
 
 etc 561 
 
 Geographical Fauna ot Quaternary 
 
 times 612 
 
 Geological chronology 207, 295 
 
 fauna and flora 204 
 
 formations 189 
 
 horizon, definition 204 
 
 ■ observation, means 173 
 
 period, tested by life-system 203 
 
 period, tested by rock-system 203 
 
 Geology, definition 1, 2 
 
 departments 1 
 
 ■' dynamical 3 
 
 historical 290 
 
 structural 170 
 
 German Ocean, tides 43 
 
 Geyserite 80 
 
 craters 108 
 
 Geysers, Bunsen's artificial 112 
 
 Bunsen's investigations of 109 
 
 definition 103 
 
 deposits 80 
 
 description 105 
 
 Jaggar's experiments 114 
 
 Mackenzie's theory 109 
 
 of the Yellowstone 106 
 
 phenomena of eruption 105 
 
 theories ot eruption 109 
 
 types 114 
 
 Giant's Causeway • 222 
 
 Gibbs Canon of the Sierra Nevada 593 
 
 Gibson 439 
 
 Gigantitherium caudatum iij 
 
 Gilbert.9, 14, 17, 81, 115, 177, 219, 239, 297, 441 
 
 Ginkgo biloba 373 
 
 • evolution ■■•■ »i5 
 
 Ginkgophyllum 375, 429 
 
 Glacial deposit •■•• =8 
 
 epoch 569, 670 
 
 climate, Croll's hypothesis 613 
 
 climate, meteorological theory — 616 
 
 climate, Wallace's views 615 
 
 drift 69 
 
 drumlins 71 
 
 epoch, first BSB 
 
 epoch, drift-materials 669 
 
 epoch, in Europe 594 
 
 erosion °6 
 
 erosion, general results 587 
 
 field ™ 
 
 flutings of bed-rock 573 
 
 lakes 59,144,698 
 
658 
 
 INDEX. 
 
 PAGE 
 
 Glacial Scorings 57,572 
 
 times in America, probable condi- 
 tion during 576 
 
 valley, section across 58 
 
 Glaciation 57, 572 
 
 Glacier, great Rh6ne 535 
 
 Zermatt 54 
 
 Glaciers, advance and retreat 47 
 
 as a geological agent 56 
 
 cirques ol 
 
 classes 67 
 
 conditions necessary for.....". 45 
 
 definition 45 
 
 description 57 
 
 ditEerential motion 59 
 
 earth and stones on surface...... 54 
 
 erratics 57, 58 
 
 evidences of former extension 58 
 
 evidences o£ motion 59 
 
 fissures 51, 53, 66, 68 
 
 general description 50 
 
 in Western North America 585 
 
 irregularities of surface 53 
 
 line of lower limit 49 
 
 moraines 54,58 
 
 motion 47 
 
 motion and its laws 59 
 
 motion, theories of 61 
 
 ■ CroU's theory of 65 
 
 Forbes's theory of 62 
 
 Thompson's theory of 65 
 
 Tyndall's theory of 63 
 
 moulins 53 
 
 needles 53 
 
 physical theory of veins 70 
 
 ramifications 47 
 
 structure 65 
 
 surface 51, 53 
 
 transporting power 57 
 
 veined structure 66 
 
 Glaphyroptera' gracilis 453 
 
 ■ pterophylli 434 
 
 Globigerina bulloides 169 
 
 cretacea 488 
 
 ooze 169 
 
 Glyptocrinus decadactylus 324 
 
 Glyptodon clavipes 611 
 
 Glyptolepis Kinairdli 350 
 
 Gneiss 229 
 
 decay 7 
 
 Gold, auriferous veins 250, 257 
 
 drift in relation to 626 
 
 Goniatites, crenistria 411 
 
 lamellosus 346 
 
 Lyoni 411 
 
 Goniopygus major 495 
 
 Gorges, how formed 15 
 
 Gossan 249 
 
 Gradation of streams..-. 23,31 
 
 Grand Canon of the Colorado 17 
 
 Grand Plateau 17 
 
 Granite, decay 7 
 
 graphic 211 
 
 origin 233 
 
 porphyrltic 212 
 
 syenitic 212 
 
 veins 213 
 
 Granite rocks, chemical composition 
 
 and kinds 211 
 
 rocks, mode of occurrence 213 
 
 Granulite 212 
 
 Graphite 368 
 
 Graptolites 320 
 
 Great Geyser 104, 112 
 
 Great Salt Lake 29, 81, 82, 83 
 
 Greenland coasts 142 
 
 glaciers 60 
 
 Green River Basin, Wahsatch beds 560 
 
 River Basin, Bridger beds 551 
 
 Green-stones 214 
 
 Grotto geyser -. 112 
 
 Ground-water, perpetual 75 
 
 Growth of deltas 30 
 
 FAGB 
 
 Gryphsea calceola 476 
 
 Pitcher! 496 
 
 speciosa 477 
 
 Guano 169 
 
 Gulf Stream 40 
 
 probable agency in forming reefs. 165 
 
 Guppy 168 
 
 Gymnophiona 416 
 
 Gymnosperms 342, 372, 373, 374 
 
 affinities . . . : 375 
 
 Gypsum deposited from springs SO 
 
 Gyracanthus 414 
 
 H 
 
 Hade 241 
 
 Hadrosaurus 502 
 
 Hague 225 
 
 Hall 267,422 
 
 Halodon sculptus 519 
 
 Halysites catenulata 318 
 
 Halysitidae 316 
 
 Hamilton period 341 
 
 Hamites 497 
 
 Haughton 191, 195 
 
 Hawaii 89, 90, 91, 96, 98, 99, 162 
 
 Hay 439 
 
 Hayden 108, 219, 279 
 
 Hayes 265 
 
 Heat, interior of the earth 84 
 
 of volcanoes 101 
 
 Heavy spar 245 
 
 Hebrides islands 38 
 
 Hedercephyllum angulatum 494 
 
 Heer 442 
 
 Helioceras Robertianus 499 
 
 Helland 61 
 
 Hemerobioides giganteus 453 
 
 Hemicidaris crenularls 446 
 
 Hemitelites Brownii 444 
 
 , Henessey ; 171 
 
 Hercuianeum 89,92 
 
 Herpetichthyes 357 
 
 Herschel ...34, 36, 40, 74,' 90, 92, 102, 145, 171 
 
 theory of movements of earth's 
 
 crust 145 
 
 Hesperornis regalis 508 
 
 Heterocrinus simplex 325 
 
 Hilgard 25, 31, 34 
 
 Hill 490 
 
 Hipparion 664 
 
 gracile, restored 546 
 
 Hippurites Toucasiana 498 
 
 Hitchcock 471 
 
 Holmes 219 
 
 Holoptychius Hibberti, flemingi 349 
 
 tooth 415 
 
 Homoceras 330 
 
 tenuifilum 331 
 
 Homocrinus scoparius 325 
 
 Hopkins 68, 88, 237 
 
 Hopkins's law 118, 136 
 
 Hoplophoneus robustus 560 
 
 Horizon, geological 204 
 
 Hornblende 211 
 
 Hornblende-schist 229 
 
 Hornstone 169 
 
 Horse 247 
 
 skull and brain 562 
 
 Horse family, diagram of changes 565 
 
 genesis 564 
 
 Hot Springs 103,169 
 
 Howell 241 
 
 Hudson River 32 
 
 Hugi 59 
 
 Humboldt 42, 85, 87, 90, 121, 174 
 
 Humphreys 11 
 
 Humus acid 4 
 
 Hunt 422 
 
 B. B 396 
 
 T. S 233,396 
 
 Huronia ■ 330 
 
INDEX. 
 
 659 
 
 PAGB 
 
 Hutton 2 
 
 Huxley 357,419, 467 
 
 Hyatt 331 
 
 Hy^nodon cruentus 559 
 
 Hybodus apicalis 435 
 
 retioulatus, spine and tooth 454 
 
 Hydrocarbons 404 
 
 Hydrocorallines 316 
 
 Hydrograpbical basin 10 
 
 Hydrothermal fusion 93, 231 
 
 Hydrozoa 319 
 
 Silurian 320 
 
 Hyena spelsea, skull 601 
 
 Hy lerpeton 419 
 
 Hylonomus 419 
 
 Hymenocaris vermicauda 312 
 
 Hyolithus prlmordlalis 311 
 
 Hyperodapedon Trias 437 
 
 Hypsilopbodon 603 
 
 Hyracbyus 552 
 
 Ice, agency of 45 
 
 during the Quaternary period 587 
 
 floating 70 
 
 pillars 51 
 
 shearing force of 66 
 
 Icebergs as a geological agent 72a 
 
 deposits from 73 
 
 formation 72a 
 
 Ice-blades 52 
 
 Ice-caves 53 
 
 Ice-clifiCs containing remains of mam> 
 
 moth 603 
 
 Ice-pillars, formation 51 
 
 Ice-sheet, Continental 50, 68 
 
 ■ work of 68 
 
 limit moraine 578 
 
 Iceland 104 
 
 Ichneumon inf emails 533 
 
 Ichthyocrinus sublaevis 324 
 
 Ichthyornis 507 
 
 dispar 508 
 
 victor 507 
 
 Iclithyosaurs of Jura-Trias 482 
 
 Ichthyosaurus communis 464, 455 
 
 paddle-v7eb 466 
 
 ■ — - quadriscissus 465 
 
 Iddings 225 
 
 Igneous agencies , 84 
 
 Igneous rocks, classiflcation 211 
 
 Iguanodon 458 
 
 Bernessartensis 459 
 
 Illinois coal-fleld 362 
 
 Imhoffla pallida 533 
 
 Inachus Ksempferi 338 
 
 Infusorial earth, Richmond 530 
 
 Index-circle 123 
 
 Inoceramus dimidius 496 
 
 Insects, Carboniferous 412 
 
 Devonian 347 
 
 Jurassic 462 
 
 ■ Tertiary 633 
 
 Intercalary beds 219 
 
 Interior heat of the earth 84 
 
 of earth, increasing temperature. . 85 
 
 condition of earth 88 
 
 Interval between Archaaan and Pa- 
 
 lEeozoic 305 
 
 Intrusive rocks 214 
 
 Invariable temperature, stratum of 84 
 
 Invertebrates, age of 293 
 
 Irish elk, skeleton .-■• 603 
 
 Iron age ^'"^ J" 
 
 hat of copper vein 249 
 
 ore in bogs 160 
 
 ore of the coal-measures 397 
 
 springs, deposits in 79 
 
 Irving 232 
 
 Islands, coral ^2j 
 
 bordering *' 
 
 FAOO 
 
 Islands, mangrove 165 
 
 Isogeotherms 86 
 
 Isopods 337 
 
 Isoseismal lines 123 
 
 Isotelus gigas 335, 336 
 
 Italy, change of level 141 
 
 Jointing, regular, of limestone 236 
 
 Joints 190, 236, 270 
 
 Judd 91,225,226,268,270 
 
 Jukes ..-. 92,121,142,297 
 
 Julieu 4 
 
 Jupiter Serapis, temple of 141 
 
 Jura Mountains, section 263 
 
 Jurassic animals 445 
 
 ammonites 448 
 
 belemnites 450 
 
 birds 462 
 
 cephalopods 447 
 
 coal-measures 442 
 
 Crustacea 452 
 
 fishes 463 
 
 insects 452 
 
 mammals 465 
 
 ■ period 441 
 
 plants 444 
 
 reptiles 464 
 
 Jura-Trias, bird-tracks 471 
 
 distribution of strata 467 
 
 disturbances which closed it 484 
 
 ichthyosaurs 482 
 
 in America 467 
 
 life-system 469 
 
 mammals 483 
 
 of Connecticut Valley 469 
 
 of interior plains and Pacific slope 475 
 
 of Richmond and North Carolina 
 
 coal-flelds 473 
 
 physical geography of America 
 
 during 483 
 
 plants 476 
 
 record 470 
 
 tracks, reptilian 471 
 
 K 
 
 Kames 72,570 
 
 Kane 71 
 
 Kaolin, formation 7 
 
 Kelvin ^ ■ . . 88 
 
 Kettles, glacial 70 
 
 Keys of Florida 84 
 
 Kilauea, volcano 89, 99 
 
 Kimmeridge clay 441 
 
 King 219, 239, 268, 287, 301, 485 
 
 Kitchen-middens 639 
 
 Knott 139 
 
 Krakatoa 90, 91 
 
 Kriimmell 174 
 
 Kutorgina pannula 311 
 
 Labyrinthodonts 434, 435, 436 
 
 teeth 420,436 
 
 Laccolites 219 
 
 La Fayette formation, Mississippi 673 
 
 Lagoons 24 
 
 Lagoonless islands 156 
 
 Lake-basins of the interior 549 
 
 Lake-dwellings 641 
 
 Lakes ■• 33,80 
 
 alkaline 80 
 
 Champlain 82 
 
 chemical deposits in 80 
 
 during the Quaternary period ... 589 
 
 Elton 83 
 
 flooded 680 
 
660 
 
 INDEX. 
 
 PAGE 
 
 Lakes, glacial 59, 598 
 
 ■ • glacial, origin 598 
 
 • -history o£ the great 684 
 
 morainal 59 
 
 salt SO 
 
 Lake Agassiz 580 
 
 Bonneville 83, 590 
 
 Geneva 29, 30 
 
 ^ Lahontan 590 
 
 Mono 79, 81, 590 
 
 ^ Owen .- 81 
 
 Superior, effect of waves on shore, 37 
 
 Tahoe 82, 589 
 
 Warren 35 
 
 Lamellibranchs 325, 328, 434 
 
 Carboniferous 410 
 
 Cretaceous 496 
 
 ■ Devonian 346 
 
 ■ Jurassic 447 
 
 Silurian 328 
 
 Triassic 434 
 
 Laminae crumpled 183 
 
 Lamination 21 
 
 oblique 29, 181 
 
 Lamna elegans 537 
 
 Land formed by ocean agencies 44 
 
 Land-surfaces and sea-bottoms 174 
 
 Land vertebrates 420 
 
 Langley 396 
 
 Laosaurus altus 481 
 
 La Plata rivers 32o 
 
 Laramie animals 517 
 
 ■ epoch 513 
 
 group, area 515 
 
 mammals 518 
 
 plants 516 
 
 Laurentian lakes 29, 34, 144 
 
 Laurus Nebrascensis 491 
 
 Lava 93 
 
 ■ classification 94 
 
 composition 93, 94 
 
 consistence 93 
 
 fields 525 
 
 hardened 94 
 
 minerals 94 
 
 sheets 218 
 
 stony 93 
 
 streams 16, 103 
 
 Law of anticipation 291 
 
 ■ differentiation and specialization.. 357 
 
 stream transportation 20 
 
 Lead veins 250 
 
 Lebias cephalotes 538 
 
 Leidy 602 
 
 Leguminosites arachioides 514 
 
 Lepadocrinus Gebhardi 324 
 
 Lepidodendrids 342, 377, 379 
 
 Lepidodendron 379 
 
 ■ compared with club-moss 381 
 
 corrugatum 380 
 
 diplotegioides 380 
 
 Gaspianum 343 
 
 ideal section 381 
 
 modulatum 380 
 
 politum 380 
 
 rigens 380 
 
 Lepido-ganoids, Devonian 351 
 
 Lepidophloios Acadianus 380 
 
 Lepidosiren paradoxa 351 
 
 Lepidosteus osseus 351 
 
 Lepidostrobus 380 
 
 Leptffina 327 
 
 rhomboidalis 345 
 
 Lesley 237 
 
 Lesquereux 314, 393, 491 
 
 Lestornis crasslpes 509 
 
 Lestosaurus simus 505 
 
 Levies, natural 26 
 
 artificial 26 
 
 Lewis, C. A. W 405 
 
 Lias 441 
 
 Libellula 453 
 
 Llchas Boltoni 334 
 
 PAGE 
 
 Life- system a test of formation 203 
 
 Lime-accumulations 79, 151, 163 
 
 Limestone caves 77 
 
 concretions 196 
 
 crinoidal 167 
 
 decay 7 
 
 mollusoan 167 
 
 nummulitio 167, 532 
 
 phosphatic 169 
 
 pillars 77 
 
 with hydrocarbons 404 
 
 Limnerpeton laticeps 429 
 
 Limnohyus (PalEeosyops) 563 
 
 Limuloids 337 
 
 Limulus Moluccanus 338 
 
 Lingula anatina 326 
 
 Lingulella celata 311 
 
 ferruginea 312 
 
 Liparite 216 
 
 Liquidambar integrifollum 491 
 
 Europeum 528 
 
 Lisbon earthquake 130 
 
 Lithodomus 141, 146 
 
 Lithostrotion Californiense 406 
 
 Lltuites cornu-arietis 332 
 
 graftonensis 332 
 
 Lituola nautiloides 487 
 
 Loess 4, 9, 583 
 
 Logan 296 
 
 Lonsdaleia floriformis 318 
 
 Lookout Mountain 279 
 
 Loup Fork beds 560 
 
 Lower Helderberg period 308 
 
 Lower Palaeozoic system 307 
 
 rocks 307 
 
 area in America 308 
 
 physical geography 308 
 
 Loxolophodon .7 652 
 
 Lucina Ohioensis 346 
 
 Lycopods 341 
 
 Lycosaurus 437 
 
 Lyell 2, 13, 15, 
 
 25, 31, 91, 124, 142, 149, 150, 225, 288, 456 
 Lymnohyus 552 
 
 M 
 
 Machseracanthus major 351 
 
 Machaerodus cultridens ^47 
 
 latidens 600 
 
 necator 608 
 
 McKenzie 109 
 
 Macrocheilus Newberryi 410 
 
 Macrourans 433 
 
 Maelstrom 37 
 
 Magellania flavescens 326 
 
 Malacostraca 337 
 
 Malaspina glacier 50, 68 
 
 Mallet, 102, 115, 116, 119, 124, 126, 127, 137, 232 
 
 Mammals, age of 519 
 
 Cretaceous 510 
 
 Eocene 543 
 
 ■ Genesis of orders 561 
 
 Jurassic 465 
 
 Laramie 518 
 
 origin 466 
 
 Tertiary 641 
 
 Triassic ' 438 
 
 first, affinities 465 
 
 of Tertiary, general remarks on.. 561 
 
 Mammoth 603 
 
 drawing of, by contemporaneous 
 
 man 638 
 
 Mammoth Hot Springs 79 
 
 Man, age of 293,629 
 
 antiquity 632, 645 
 
 Miocene, supposed 633 
 
 Neolithic 640 
 
 Pleistocene 644 
 
 Pliocene, supposed 633,642 
 
 primeval 648 
 
 primeval, character 646 
 
INDEX. 
 
 661 
 
 PAGm 
 
 Man in Europe 633 
 
 Quaternary 634, 645 
 
 Mangrove Islands in land-formation... 165 
 
 Mantle-rook 4 
 
 Marble 229 
 
 Marcou 490 
 
 Marengo cove 77 
 
 Mariacrinus nobilissimus 325 
 
 Marly soil, formation 7 
 
 Marsh 295, 419, 462, 465 
 
 Marshes and bogs. Quaternary mam- 
 mals in 602, 605 
 
 Marsupials 466 
 
 Martinique 92 
 
 Mastodon Americanus 606 
 
 Mastodonsaurus Jsegeri 435 
 
 Matthew 334 
 
 Mauna Loa, volcano 92 
 
 Mauvaises Terres 279, 522 
 
 of Nebraska 655 
 
 McConnell 265 
 
 McGee , 490, 615 
 
 Meanders of streams 24 
 
 Mechanical agencies of the atmosphere 8 
 
 agencies of water 9, 73 
 
 theory of slaty cleavage, Sharpe's, 191 
 
 Medlicot ;. 98 
 
 Medusae 319 
 
 Megalonyx, claw-core 610 
 
 Megalosaur 459 
 
 Megaphytum 376, 379 
 
 leaf-scar of 379 
 
 Megatherium Americanum 609 
 
 mirabilis 609 
 
 Melania Wyomingensis 517 
 
 Men of Spy 637 
 
 Mentone skeleton 638 
 
 Mer de Glace 55,61,63,67 
 
 Mesas ^^' ^1 
 
 Mesohippus 557 
 
 Mesopithecus Pentelici 546 
 
 Mesozoic animals 433 
 
 era 293,430 
 
 era, disturbance which closed 513 
 
 era, subdivisions 431 
 
 general observations 512 
 
 system '■ • - 293 
 
 Metadiorite 235 
 
 Metamorphism 230 
 
 contact 235 
 
 crushing 232 
 
 dynamic 232 
 
 general 230 
 
 heat as agent ^;J 
 
 local 235 
 
 pressure as agent 231 
 
 regional ^- 233 
 
 rocks 228, 283 
 
 theory 231 
 
 water as agent 232 
 
 Metasyenite 235 
 
 Meteorological theory 616 
 
 Miamia IJanEB *13 
 
 Mica-schist 229 
 
 Microconodons 466 
 
 Microlestes antiquus 438 
 
 Migration of divides 32, 283 
 
 Millstone grit ■ • • ■ ?a9 
 
 Milne 114,123,126,138 
 
 Minnehaha Palls ]i 
 
 Mineral veins 243 
 
 Minerals, in lava 94 
 
 Mines, placer 260 
 
 Miocene epoch 521 
 
 basins °22 
 
 •— *^ ITlRPPtS ■••■■••»■•■• ■••*• ■■■-•• vOO 
 
 mammals ' of' Siwalik Hills 544 
 
 man, supposed o33 
 
 shells, California B3d 
 
 Miohippus Vo on 
 
 Mississippi, delta 'iS. ^" 
 
 average erosion .•■ -Ji 
 
 Mississippi, flood plain 24,149 
 
 FAGB 
 
 Mississippi River, history 685 
 
 Misslssippian Sea 304 
 
 Modiolopsis solvensis 312 
 
 Molluscoidea 325 
 
 Mollusks, age of 293 
 
 ■ Cretaceous 496 
 
 ■ Silurian 325 
 
 Monkeys 547 
 
 Monograptus Clintonensis .'. 321 
 
 priodou 320 
 
 Mono, Lake 81 
 
 Monotremes 466 
 
 Mont Blanc glacier region 46 
 
 Monticules 92 
 
 Moon, effect on earthquakes 139 
 
 Moraines 54 
 
 • ground 55, 58, 70 
 
 ■ in Colorado 589 
 
 lateral ; 54 
 
 medial 55 
 
 of ice-sheet 70, 577 
 
 terminal 66, 68, 70 
 
 Morosaurus grandis 480 
 
 Mosasaurs 605 
 
 Mosasaurus princeps 506 
 
 Motion of glaciers 59 
 
 Moulins 53 
 
 Mount Mazama 99 
 
 Shasta 99 
 
 Mountain-ranges, age 274 
 
 -cause of pressure producing 276 
 
 ■ classiflcation 260 
 
 ■ elevation by lateral pressure 266 
 
 • faults and earthquakes in 276 
 
 ■ fissure-eruptions in 275 
 
 general form, how produced 264 
 
 history of 274 
 
 ^ made of thick sediments 269 
 
 • metamorphism 268 
 
 mineral veins in 276 
 
 ■ ■ monoclinal 275 
 
 • once marginal sea-bottoms 270 
 
 origin and structure 270 
 
 — - volcanoes in 276 
 
 Mountain-formation, rate 274 
 
 Mouutain-forms resulting from erosion 279 
 
 Mountain-origin 260, 263 
 
 Mountain-range 262 
 
 Mountain-ridge 261 
 
 Mountain-sediments, thickness 269 
 
 Mountain-sculpture 278 
 
 Mountain-structure 260, 264 
 
 Mountain-system 262 
 
 Muds, deep sea 42 
 
 MUgge 67 
 
 Muir glacier 50, 61, 726 
 
 Murchison 83, 296, 340 
 
 Murchisonia gracilis 328 
 
 Murray 159 
 
 Myalina Permiana 428 
 
 Mylodon 610 
 
 ■ -left hind-foot 641 
 
 Myophoria lineata 434 
 
 Myrmica tertiaria 533 
 
 N 
 
 Naiadites 409 
 
 Nanosaurus agilis 478 
 
 Nathorst 319 
 
 Nautiloids 329 
 
 Nautilus pompilius 329 
 
 Neanderthal skull 637 
 
 Nebular hypothesis 172, 175, 299 
 
 Needles 61 
 
 Neolimulus falcatus 412 
 
 Neolithic age 633 
 
 man 640 
 
 Neuropteris 475 
 
 flexuosa 377, 378 
 
 - — -linasfolia 475 
 
 ovata 378 
 
662 
 
 INUEX. 
 
 PAGE 
 
 Neuropteris polymorpba 343 
 
 Scheuchzeri 378 
 
 Nevadite 216 
 
 N6ve 51 
 
 Newberry 257,298,351,352 
 
 Newfoundland, Banks of 43 
 
 Niagara Falls, description 12 
 
 gorge, time necessary to form.... 15 
 
 period 308 
 
 Nile, flood-plain 26,27 
 
 delta 27,31 
 
 Niobrara basin 661) 
 
 Nodular or concretionary structure... 196 
 
 Nodules, flattened by pressure ■. 192 
 
 flint, in chalk-clitEs 198 
 
 form 197 
 
 Noggerathia 373 
 
 Norfolk cliJEs, effect of waves on 37 
 
 Nordenskiold 513 
 
 North Carolina coast 41 
 
 Norway, effect of waves on the coast. ■ 38 
 
 Notidamus primigenius 537 
 
 Nototherium Mitchelli 612 
 
 Nummulina laevigata 530 
 
 Nummulitic formation 531 
 
 Obolella crassa 311 
 
 Hioksii 312 
 
 Obsidian 93,215 
 
 Ocean 34 
 
 currents 40 
 
 saltness of 82 
 
 Oceanic agencies, land formed by.... 44 
 
 circulation 40 
 
 deposits 41, 83 
 
 depth 174 
 
 Ocean-waves, effect of 34 
 
 Ochsenius 440 
 
 Odontolcae 509 
 
 Odontopteris gracillima -. 378 
 
 Wortheni 378 
 
 Odontopteryx / 541 
 
 toliapicus, skull 541 
 
 Odontornithes 609 
 
 Odontotormse 509 
 
 Oil-bearing strata of the Eastern U. S. 402 
 
 Oil-formations 401 
 
 Old Faithful geyser 108, 111 
 
 Oldhamia antiqua 312 
 
 Olenus macrurus 312 
 
 Olenellus asaphophoides 311 
 
 Oligocene of Nebraska 522, 555 
 
 mammals 560 
 
 Oligoporus nobilis 408 
 
 Onychaster flexilis 408 
 
 Onychodus sigmoides 348 
 
 Oolite 441 
 
 Oolitic limestones, origin 442 
 
 Ooze, deep-sea 42, 489 
 
 globigerina 42, 169 
 
 Ophiderpeton >. 419 
 
 Ophiomorpha 416 
 
 Orange sand, Mississippi, section of, 
 
 570, 571 
 
 Orbulina universa 169 
 
 Orders, genesis of existing 561 
 
 Oreodon 558 
 
 Ores 245,298 
 
 metallic, formation 255 
 
 Organic agencies 146 
 
 remains, decomposition prevented, 199 
 
 sediments 42 
 
 Organisms, progressive change in.... 422 
 
 Oriskany period 341 
 
 Orkney islands 38 
 
 Ornithes 509 
 
 Ornithopoda 478, 480 
 
 Ornithotarsus 503 
 
 Orodus mammilare 415 
 
 Orohippus 567 
 
 Orthls Davidsonil 327 
 
 Livia 346 
 
 porcata 347 
 
 sagittalis 312 
 
 Orthoceras Duseri 331 
 
 multicameratum 331 
 
 vertebrale 331 
 
 Orthoolase 212 
 
 Orthoceratite 329, 330 
 
 Orthodesma parallelum 328 
 
 Orthonema Newberryi 345 
 
 Osborn 467,475 
 
 Osmeroides Mantelli 501 
 
 Osteolepis 350 
 
 Ostrea Caroliniensis 533 
 
 Georgiana 531 
 
 Idriaensis 49^ 
 
 Marshil 447 
 
 sellsef ormls 531 
 
 Sowerbyi 447 
 
 -—Titan b32 
 
 Otodus 500 
 
 Otozamites Macombii ; 477 
 
 Otozoum Moodii 471 
 
 Ottawa River 15 
 
 Oudenodon Bainli 437 
 
 Outcrop 4S4 
 
 Owen 435, 437, 438, 455 
 
 Oxford clay 441 
 
 Oyster, first appearance 447 
 
 P 
 
 Pachyderms 552 
 
 Pachypteris lanceolata 444 
 
 Pachytherium 611 
 
 Pacific Ocean 144 
 
 Palaeaspis Americana 339 
 
 Palaeaster Shaeff eri 326 
 
 Palaeocarus typus 411 
 
 Palaeolith 642 
 
 Palaeolithic age 637 
 
 Falaeoniscus aculeatus 412, 415 
 
 Palaeopteris, leaf-scars 379 
 
 PalEBopternus 339 
 
 Palseosyops 552 
 
 Fateotherium magnum 543 
 
 Palaeozoic era 293, 301 
 
 era, chemical changes during 422 
 
 era, general observations 421 
 
 era, physical changes during 421 
 
 era, physical geography 303 
 
 era, subdivisions 305, 308 
 
 fauna, compared with Neozoic... . 423 
 
 progressive changes in organisms. 422 
 
 rocks, area in the United States... 303 
 
 rocks, thickness 301 
 
 system 293 
 
 times, general picture 425 
 
 transition from, to Mesozoic 426 
 
 Palapteryx 631 
 
 Palisades 224 
 
 Palmier! 133 
 
 Panther Creek Coal-basin 362 
 
 Paradoxides Bohemicus ' 313 
 
 Harlani 313 
 
 Paris, Eocene basin 543 
 
 Paths of cyclonic storms 616 
 
 Patriofelis ferox 655 
 
 Peaks of mountains 261 
 
 Peale 225 
 
 Peat, alternation with sediments 149 
 
 bogs and swamps 147, 390 
 
 composition and properties 147 
 
 conditions of growth 149 
 
 mode of growth 148 
 
 rate of growth 148 
 
 Pecopterls falcatus 475 
 
 Strongii 377, 378 
 
 Pecten cerrocensis 533 
 
 fibrosus 447 
 
 nuperum 531 
 
INDEX. 
 
 663 
 
 Pecten Valonlensls 434 
 
 Pegmatite '" 2U 
 
 Pel§e, volcano .'.'." 09 
 
 PeiS's Hair .";."""' 93 
 
 Pemphyx Sueurii i " 434 
 
 Peneplain V.V 22, 31 
 
 Peneroplis planatus 169 
 
 Pentacrinus Caput-MedusEe 322 
 
 Pentamerus Knightii 327 
 
 Pentremites Burlingtoniensis 407 
 
 cervinus 407 
 
 gracilis " 407 
 
 pyritormis . 407 
 
 Periods 294 
 
 Pfirigord caves ] " .' 640 
 
 Periptychus rhabdodon 550 
 
 Perissodactyls 563 
 
 Permian period 359, 426 
 
 • reptiles, affinities 430 
 
 rocks, area in United States 428 
 
 shells 428 
 
 Perry II4 
 
 Petrifaction 199 
 
 theory of 200 
 
 Petroleum, geological relations 401 
 
 kinds of rocks which bear 402 
 
 laws of interioi^ distribution 402 
 
 origin, theories of 404 
 
 ■ origin of varieties •. 405 
 
 Phacops latif rons 347 
 
 ■ — ■ rana 347 
 
 Phascolotherium „ 465,466 
 
 Phaneropleuron 351 
 
 Phenacodus primsevus 550 
 
 Philips, A 256, 258, 259 
 
 . J 74, 241, 261, 255, 284, 361 
 
 Phillipsia Lodiensis 411 
 
 Pholas 146 
 
 Phonolite 216 
 
 Phororachus longissimus 548 
 
 Phosphate deposits 169 
 
 Phryganea cases 535 
 
 Phyllocladus 373 
 
 Phyllograptus typus 320 
 
 Phyllopods 333,337 
 
 Physical geography of America and 
 
 Europe compared 358 
 
 Pine-cone, Jurassic 444 
 
 Pithecanthropus erectus, restoration 
 
 of the skull 645 
 
 Placer-mines 250, 627 
 
 Placoderms 352 
 
 Placo-ganoids 35 
 
 Placoids 500 
 
 Cretaceous 600 
 
 distribution in time 500 
 
 Jurassic 453 
 
 Tertiary 638 
 
 Plagioclase 212 
 
 Plagiaulax 466 
 
 Plana 173 
 
 Planetesimal hypothesis 88, 171, 
 
 176, 227, 277, 296, 299, 397, 405 
 
 Plants, Carboniferous 372 
 
 Cretaceous 491 
 
 ■ Devonian 341, 342, 343, 344 
 
 effects on rocks 146 
 
 Jurassic 444, 445 
 
 of Jura-Trias 476, 477 
 
 Silurian 314 
 
 Tertiary 526 
 
 Plasticity 64 
 
 Platanus aceroides . . . ; 528 
 
 Plateaus 17,31 
 
 Platephemera antigua 347 
 
 Platysomus gibbosus 429 
 
 Playfair 173 
 
 Pleistocene man 644 
 
 Plesiosaurus 456 
 
 dolichodeirus 455 
 
 Pleuracanthus 414 
 
 parellelus 429 
 
 Pleurocystites squamosus 324 
 
 Pleurophorus subcuneatus 42S 
 
 Pleurotomaria agave 328 
 
 dryope "; 328 
 
 scitula 410 
 
 Pliocene epoch sVi 551 
 
 ——man, supposed .'.....'634 
 
 Pliohipipus 664 
 
 Pliosaurus io7 
 
 Plumbif erous veins 260 
 
 Plumularla .' 319 
 
 Plutonic rocks .'. 211 
 
 Po, River '.'.'.'.'.26, 30 
 
 Pocket .... 245 
 
 Pocono sandstone 359 
 
 Podogonium Knorrii 528 
 
 Podozamites crassifolia 477 
 
 Emmonsi 432, 474 
 
 Poebrotherium labiatum 659 
 
 Polar currents 40 
 
 Poleumita scamnata '..'..'. 328 
 
 Polypterus bichir 361, 353 
 
 Pompeii 89, 92 
 
 Ponera veneraria 633 
 
 Populus cuneata 514 
 
 Porphyrite 214 
 
 Portheus molossus, tooth 501 
 
 restored 501 
 
 Potomac formation 490 
 
 Pouohet 534 
 
 Powell 239, 240, 268, 287 
 
 Precession, diagram showing effects of 614 
 
 Prestwich 54, 102 
 
 Primary rocks 296 
 
 Primeval man, character 646 
 
 in America 640 
 
 in Europe 633 
 
 Prionastrea oblongata 446 
 
 Proboscidians 544, 563 
 
 genesis 607 
 
 Prodryas persephone 636 
 
 Productus mesialis 409 
 
 punctatus 409 
 
 Prolabella Trentonensis 328 
 
 Protaster Sedgwickii 325 
 
 Protaxites 342 
 
 Proterozoic 297 
 
 Protohippus 564 
 
 Protophyllum guadratum 492 
 
 Protopterus 353 
 
 Protozoa, Cretaceous 495 
 
 Protypus, Hitchcocki 311 
 
 Pseudocrinus 324 
 
 Psilophyton princeps 343 
 
 Psychozoic era 293, 629 
 
 Pteranodon 503 
 
 Pteraspis rostrata 349 
 
 Pterichthys 349 
 
 Pterodactyl 460 
 
 Pterodactylus crassirostris 461 
 
 Pterophyllum comptum 444 
 
 Jeegeri 432 
 
 Pteropods, Silurian 312, 328 
 
 Pterosaurs 460, 602 
 
 Pterygotus osiliences 338 
 
 gigas 338 
 
 Ptychodus Mortoni 601 
 
 Ptyonius 420 
 
 Puerco beds 549 
 
 Puget Sound 32a 
 
 Pumice 95 
 
 Pupa vetusta 409 
 
 Pyramid lake 82,83 
 
 Pyrenees 264 
 
 Pyrites, copper 248 
 
 iron 248 
 
 Pyroclastic rocks 223 
 
 Pyrotherium 547 
 
 Pythonomorpha 505 
 
 Q 
 
 Quartzite 229 
 
 Quartz-syenite 212 
 
664 
 
 INDEX. 
 
 PAGE 
 
 Quartz veins, auriferous 250 
 
 ■ in gneiss 5, 7 
 
 Quaternary, a period of revolution.... 619 
 
 climate, Croll's theory ^.... 614 
 
 mammalian fauna of England.... 604 
 
 mammalian fauna in North Amer- 
 ica 605 
 
 man 634, 642 
 
 period 668 
 
 period, cause of climate 612 
 
 ■ period, characteristics 568 
 
 period in Australia 612 
 
 period in Eastern North America. 569 
 
 period in Europe 593 
 
 period in South America 609 
 
 -period in the Southern Hemi- 
 sphere 596 
 
 period, mammals 599 
 
 period, migration of species dur- 
 ing 620 
 
 period on the western side of 
 
 America 585 
 
 ' period, plants and invertebrates. . 599 
 
 ■ period, subdivisions 668 
 
 period, time involved in 616 
 
 period, general observations 612 
 
 system 293 
 
 times, geographical fauna 612 
 
 Quercus crassinervis 527 
 
 primordialis 491 
 
 Satfordl 527 
 
 R 
 
 Rachiopteris 341 
 
 Radiolaria 300, 489 
 
 Radiolites cyllndriasus 498 
 
 mammellaris 498 
 
 Rain-prints, fossil 416 
 
 • sculpture 12 
 
 Ramsay, Prof 286 
 
 Raniceps 419 
 
 Rankine 18 
 
 Ravines, how formed '.. 15 
 
 Reade 243 
 
 Recent epoch ',. 629 
 
 Recently extinct species, examples.... 630 
 
 Receptaculites f ormosus 317 
 
 Reefs, coral, of Florida 163 
 
 coral, of the Pacific 154 
 
 Refuse-heaps 639 
 
 Regelation t 64 
 
 theory of glaciers, of Tyndall 63 
 
 Reindeer age 634, 638 
 
 Rejuvenated streams 23 
 
 Renevier 264 
 
 Reptiles, age of „ 293 
 
 Reptiles, Carboniferous 415 
 
 Cretaceous 502 
 
 ganoids allied to 357 
 
 Jurassic 455,477 
 
 Tertiary 539 
 
 Triassic 435 
 
 Reptilian tracks of Jura-Trias 471 
 
 Requlenia patagiata 497 
 
 Texana 497 
 
 Revived rivers 32 
 
 Rhabdocarpos 374 
 
 Rhamphorhynchus phyllurus 461 
 
 Rhine delta 84 
 
 Rhizoorinus Lofotensis 322 
 
 Rhizodus 415 
 
 Rhombus minimus 538 
 
 Rh6ne, delta 29,30 
 
 Rhotomahana 115 
 
 Rhynchonella sulcata 326 
 
 varians 447 
 
 Rhynchosaurs 435, 436, 437 
 
 Rhyolite 216 
 
 Rib 246 
 
 Ribboned structure 246 
 
 Rice 80 
 
 Richthofen 9, 217 
 
 PAGE 
 
 Rich thof en's classification -. 226 
 
 Ried 6 
 
 Rink 51,71 
 
 Ripple-marks, how formed 39 
 
 River, age of the 628 
 
 River-beds of California, old and n6w. 691 
 
 River-deposits, age of 30,31 
 
 River-gravels 609 
 
 River-swamp 25 
 
 River-terraces 23, 24, 681 
 
 Rivers, agency 9 
 
 classes of 32 
 
 Rivers during the Quaternary period.. 591 
 
 erosion of 10, 22, 23 
 
 evolution of 31 
 
 flood-plains 25 
 
 graded 23 
 
 transporting, law of deposit 20,22 
 
 Rivers as indicators of crust move- 
 ments 23 
 
 -winding course of, meanders 24 
 
 Roches moutonn^es 56 
 
 Rock-basins 59 
 
 Rock-froth 93 
 
 Rock-disintegration 5 
 
 Rock-salt, age 438 
 
 mode of occurrence 439 
 
 origin 438 
 
 theory of accumulation 440 
 
 ■Rock-spray 93 
 
 Rock-system, as a test of a formation. 203 
 
 Rocking stones 6, 58 
 
 Rocks, classes 177 
 
 — definition 179 
 
 eruptive or volcanic 215 
 
 igneous 210 
 
 igneous, classification 210 
 
 igneous, different modes of classi- 
 fying 224 
 
 igneous, origin 227 
 
 intrusive 214 
 
 ■ — - metamorphiq 227 
 
 • metamorphic, principal kinds .... 229 
 
 Plutonic 211 
 
 -Plutonic, mode of occurrence 213 
 
 pyroclastic 223 
 
 schists 229 
 
 stratified 180 
 
 stratified or sedimentary 178 
 
 stratified, cause of consolidation.. 180 
 
 stratified, classification 205 
 
 stratified, comparison of fossils... 206 
 
 stratified, kinds 179 
 
 stratified, llthological characters. 206 
 
 stratified, are consolidated sedi- 
 ments 179 
 
 stratified, originally nearly hori- 
 zontal 181 
 
 stratified, order of superposition,. 205 
 
 structure and position 173 
 
 structure common to all 235. 
 
 trappean, general characteristics. 214 
 
 trappean, varieties 214 
 
 unstratified or Igneous 210 
 
 volcanic 216 
 
 - — -volcanic, modes of eruption 217 
 
 -volcanic, modes of occurrence... 217 
 
 Rose 233 
 
 Ross 72,73 
 
 Rotalia concamerata 169 
 
 Rotation of earth 171 
 
 Rubble 223 
 
 Rugosa 319 
 
 Ruminants 562 
 
 Rush Creek, section on 670 
 
 Russell 441 
 
 S 
 
 Sabal major 528 
 
 Saccocoma pectinata 446 
 
 Sackenia arcuata 536 
 
INDEX. 
 
 665 
 
 „ ~ PAGE 
 
 Safford 249 
 
 Saliferous group 438 
 
 Sallna period 308 
 
 Salisburia 373 
 
 Salix proteaefolia 492 
 
 Salt-laJ(es, formation 80, 81 
 
 deposits in 82 
 
 Sand-spits 44 
 
 Sandstone, Connecticut River 469 
 
 Sandstone dikes 238 
 
 Sandstones, decay 7 
 
 Sanidin 216 
 
 San Juan basin 549 
 
 Sao Hirsuta 337 
 
 Sassafras araliopsis 492 
 
 cretaceum 494 
 
 Mudgei 492 
 
 Sauroids 357 
 
 Sauropoda 478 
 
 Sauropus prim^vus 416 
 
 Saururse 509 
 
 Scalaria Sillimani 498 
 
 Scalea saussureana 523 
 
 Scandinavian sea-beaciies 142 
 
 Scaphiocrinus scalaris 407 
 
 Scaphltes aequalis 499 
 
 Sceledotherium leptoceplialus 610 
 
 Scelidosaurus Harrisonii 460 
 
 Schists 229 
 
 Schmidt 118, 256 
 
 Schmidt's law 119,138 
 
 Scoresby 71 
 
 Scoriae, volcanic 92 
 
 Scorpion, Silurian 339 
 
 Scotland, effect of waves on coast 38 
 
 Scott 376 
 
 Scrope 98 
 
 Scudder 413 
 
 Sea-bottom 174 
 
 Sea-cliff 35 
 
 Sea-deposits 32 
 
 Sea-islands 44 
 
 Sea-margins, old 579 
 
 Sea- waves produced by earthquakes.. 129 
 
 Seas, chemical deposits in 83 
 
 during the Quaternary period 586 
 
 Sedimentation 22, 205, 284 
 
 Sediments, transportation and distri- 
 bution 18, 41 
 
 thick, material for mountain- 
 ranges 267 
 
 thick, why lines of yielding 271 
 
 Seebach 136 
 
 Seiches 36 
 
 Seismographs 133 
 
 Sekiya 122,123,134 
 
 Selvage 245 
 
 Senarmont 231 
 
 Sepia, living 449 
 
 Septaria ]^ 
 
 Sequoia ambigua 494 
 
 Langsdorfii o27 
 
 Serapis, temple of 141 
 
 Serpentine 229 
 
 Sertularia pinnata 319 
 
 Severn River 32o 
 
 Shale, black, of coal-measures 361 
 
 Sharpe ■ • i°J; 
 
 Shasta, volcano 90 
 
 Shell-deposits 167 
 
 Shell-mounds o^9 
 
 Shells, as a rock-forming agent • • ^°° 
 
 bivalve and univalve 409,419 
 
 distorted IW 
 
 microscopic 16| 
 
 Permian 428 
 
 Shetland islands 38 
 
 Shinarump mesa ij 
 
 Shore-ice AAA'V,V» eno 
 
 Sierra Nevada 269,276,593 
 
 Sigillarla elegans, leaf fsl 
 
 Brardil 382 
 
 Grseserl **" 
 
 PAGE 
 
 Sigillarla obovata 382 
 
 ■ restoration 384 
 
 reticulata 382 
 
 section of stump 384 
 
 Slgillarids 342, 377, 382 
 
 Silica deposited from geysers 105, 169 
 
 -deposited from springs 80, 169 
 
 Silt 
 
 Silurian age, general lite-system 
 
 age, physical geography 
 
 • • animals 
 
 plants 
 
 scorpions 
 
 system, area in America 
 
 system, rocks 
 
 system, subdivisions 
 
 Siphonia flcus 
 
 Sivatherium giganteum 
 
 Siwalik Hills, India, Miocene of 
 
 Skapter Jokull 
 
 Slate-rock, decay 
 
 Slaty cleavage 
 
 Slickensides 
 
 Slip, law in faults 
 
 Smilodon necator 
 
 Soils, depth 
 
 -how formed 
 
 Solenomya anodontoides 
 
 Solfatara Lake 
 
 Solfataras 
 
 Solidity of earth 
 
 Sollas 
 
 Sorby 191, 193, 234, 
 
 Sorting power of water 18 
 
 Southern coast of U. S., wave-action.. 
 
 change of level 
 
 Spencer 
 
 Sphalacotherium 
 
 Sphenodon, living 
 
 Sphenophyllum emarginatum 
 
 Sphenopteris alatus 
 
 - — • splendens 
 
 Spirifer 327, 
 
 fornacula 
 
 hysterica 
 
 perextensus 
 
 plenus 
 
 striatus 
 
 Spirorbis, Arkonensis 
 
 omphalodes 
 
 Silurian 
 
 Sponges, Cretaceous 
 
 Springs 
 
 alkaline 
 
 carbonated 
 
 chalybeate 
 
 chemical deposits in 78, 
 
 * fissure 
 
 kinds 
 
 origin 
 
 Spy, cave near 
 
 Sgualodonts 
 
 Squatina acanthoderma 
 
 Stagonolepis ; 
 
 Stalactites 
 
 Stalagmites 
 
 St. Anthony, Falls of 
 
 St. Pierre, W. I , 
 
 Stegocephali 416, 417, 
 
 Stegosauria 
 
 Stegosaurus ungulatus 
 
 Sterna cantiaca 
 
 Stevenson 
 
 Stigmaria ficoides • 
 
 Stone age 
 
 Stones, balanced 
 
 rocking 
 
 erupted from volcanoes 
 
 Strata, elevated, inclined, and folded. . 
 
 gently inclined 
 
 highly inclined 
 
 horizontal 
 
 outcrop, definition 
 
 314 
 308 
 316 
 314 
 339 
 308 
 308 
 308 
 495 
 545 
 544 
 
 92 
 
 7 
 
 193 
 
 243 
 
 241 
 
 608 
 
 5 
 
 4 
 
 410 
 
 83 
 103 
 
 88 
 155 
 254 
 , 20 
 
 36 
 143 
 
 15 
 466 
 437 
 385 
 378 
 378 
 433 
 345 
 326 
 345 
 409 
 326 
 346 
 346 
 316 
 495 
 
 75 
 
 79 
 
 i, 83 
 
 75 
 
 75 
 
 74 
 
 636 
 
 453 
 
 454 
 
 540 
 
 77 
 
 77 
 
 13 
 
 92 
 
 420 
 
 478 
 
 482 
 
 510 
 
 34 
 
 383 
 
 633 
 
 58 
 
 58 
 
 92 
 
 182 
 
 282 
 
 280 
 
 278 
 
 185 
 
666 
 
 INDEX. 
 
 PAGE 
 
 Strata, strongly folded 280 
 
 — —upturned and eroded 184 
 
 vertical 185 
 
 Stratification 21, 178 
 
 Streams — see Rivers. 
 
 Strike, definition 184 
 
 Etromotopora auloporoides 322 
 
 concentrica 317 
 
 rugosa 316 
 
 Strombodes pentagonus 318 
 
 Stromboli 89 
 
 Strophomena 327,433 
 
 Structural geology 170 
 
 Structure of deltas 29 
 
 Subangular stones 570 
 
 Sub-Carboniferous period 359 
 
 Sublimation 253 
 
 Submarine banks 40, 42, 44 
 
 Subsequent rivers 32 
 
 Subsidence during the Quaternary 579 
 
 of Northern Europe 594 
 
 ■ ■ of Pacific floor 144 
 
 of Southern Atlantic States 143 
 
 amount of vertical 160 
 
 area of land lost 160 
 
 rate 161 
 
 Sulphur deposited from springs 80 
 
 Sunk Country 115 
 
 Superimposed rivers 32 
 
 Superior, Lake, erosion of shores 36 
 
 Surface-rock underlying drift 572 
 
 Susquehanna River ....'. 32 
 
 Syenite 212 
 
 Syncline 185 
 
 Syringoporoids 318 
 
 Syringopora verticillata 318 
 
 Table of geologic time 295 
 
 Table mountain of California 279 
 
 Table-rocks 13 
 
 Tabulata 319 
 
 Tachylite 215 
 
 Taeniopteris elegans 477 
 
 Tail-fin, heterocercal 354 
 
 homocercal 354 
 
 Talcose schist 229 
 
 Tallulah River Gorge 18 
 
 Talus , 8 
 
 Tapirus Indicus 542 
 
 Taylor 383 
 
 Teall 227 
 
 Teleosaurus brevidens 457 
 
 Teleostomes 353, 414 
 
 Teleosts, Cretaceous 600 
 
 Tellenomya curta 328* 
 
 Temperature of earth 85 
 
 — of lava 93 
 
 Terebratula digona 447 
 
 sphaeroidalis 447 
 
 Terraces, river 23, 26, 581 
 
 shore 35, 36 
 
 Tertiary amphibians 539 
 
 animals 530 
 
 birds 540 
 
 coal 524 
 
 diatoms 529 
 
 fishes 538 
 
 insects 533 
 
 lava-fields 525 
 
 life-system 525 
 
 mammals 541 
 
 mammalian fauna 561 
 
 • — - North American localities 548 
 
 • period 421 
 
 . — -period, general observations 567 
 
 period, physical geography 523 
 
 petroleum 525 
 
 plants 526 
 
 reptiles 539 
 
 rocks, area in the United States.. 521 
 
 FAOB 
 
 Tertiary rocks, character 624 
 
 subdivisions 521 
 
 system 293 
 
 times, map of United States in. . . 524 
 
 Tetrabranchs 329 
 
 Tetragonolepis 454 
 
 Textularia globulosa 488 
 
 variabilis 169 
 
 Theca Davidii 312 
 
 Theriodonts 435, 436 
 
 Theromorpha 436, 466 
 
 Theropoda 478, 479 
 
 Thin-crust theory of earth 86 
 
 Thomassy 30 
 
 Thompson, J 66 
 
 - — ; W 88 
 
 Thylacoleo carnifex 612 
 
 Tides, effect 32o, 34, 35, 42, 171 
 
 currents 38, 42 
 
 in lakes 36 
 
 of the German Ocean 43 
 
 Tiger, saber-toothed 600 
 
 Till 69 
 
 Tillodontia 554 
 
 Time, divisions and subdivisions.. 209, 293 
 
 involved in the Quaternary period 617 
 
 since man appeared 645 
 
 geological, estimate 287 
 
 Tinoceras ingens 553 
 
 Titanichthys 348 
 
 Titanotherium 665 
 
 Tomboro 91, 92 
 
 Tooth, ganoid, structure 355 
 
 Topography 31 
 
 Torreya 375 
 
 Trachyte 216 
 
 Trachyceras Whitneyi 476 
 
 Trade winds 40 
 
 Transition period 426 
 
 Transportation of sediments 18, 22 
 
 — — by glaciers 57 
 
 Transporting power of waves 39 
 
 Traps 214 
 
 Travertine 79 
 
 Tree-fern, living 376 
 
 Tree-ferns of Coal Period 376 
 
 Trees, erect fossil, in coal-measures.. 388 
 
 Trematonotus alpheus 329 
 
 Trematosaurus 435 
 
 Trent Valley 15 
 
 Trenton period 308 
 
 Triarthrus 334, 335, 337 
 
 Becki 336 
 
 Triassic amphibians 434, 435 
 
 animals 433 
 
 ■ birds 438 
 
 ■ fishes 433, 435 
 
 ■ ■ insects 433 
 
 ■ mammals 438 
 
 period 431 
 
 ■ period, subdivisions 432 
 
 ■ plants 432 
 
 reptiles 435, 437 
 
 Trieeratops prorsus 517 
 
 Triconodon 465, 466 
 
 Trigonia clavellata 446 
 
 longa, shell and cast 201 
 
 pandicosta 477 
 
 Trigonocarpum 374 
 
 Trilobites, affinities of 337 
 
 Devonian 346 
 
 Silurian 332 
 
 Trinidad, pitch lake of 404 
 
 Trinucleus Pongerardl 334 
 
 Trocholites ammonius 332 
 
 Tsieng-Tang River , . . . 32o 
 
 Tuditanus radiatus 420 
 
 Tufa 93 
 
 Tumion 3(5 
 
 Tuolumne River _15 
 
 Turritella alveata 531 
 
 Turrulites catenatus 499 
 
INDEX. 
 
 667 
 
 Tyloaaurus dyspelor 606 
 
 proriger 505 
 
 Ty ndall .... 60, 61, 6», 64, 65, 69, 191, 193, 194 
 
 V 
 
 Uintah basin 522 
 
 —-range V.V.V ¥63, 287 
 
 Ulntatlierium .552 
 
 Umbrella planulata !.!.!!!."!." 531 
 
 Unconformity 187 
 
 — — between Cambrian and ArciiEean.. 305 
 
 Underclay of coal-Seam 361 
 
 Ungulates, differentiation of families. 563 
 
 Unio Holmesianus 517 
 
 Univalves, Silurian 328 
 
 Urodela 416 
 
 Ursus amplidens '.V. 605 
 
 pristinus 605 
 
 spelaeus 601 
 
 V 
 
 Valleys 31,32,47 
 
 Van Hise 194, 195, 296 
 
 Vapors, volcanic 95 
 
 Variation, laws of 649 
 
 Vegetable accumulations 147 
 
 structure in coal 3B6 
 
 Vein-stuffs 245, 253 
 
 Veins, age, how determined 241 
 
 auriferous quartz 250 
 
 auriferous, of California 257 
 
 cupriferous 248 
 
 fissure 244 
 
 metalliferous 245 
 
 metalliferous, contents 245 
 
 metalliferous, laws affecting 251 
 
 metalliferous, ribboned structure. 246 
 
 metalliferous, theory 253 
 
 metalliferous, vein-stuffs 253 
 
 mineral 243 
 
 mineral, characteristics 245 
 
 — fissure, irregularities 247 
 
 of infiltration 244 
 
 of segregation 244 
 
 plumbiferous 250 
 
 pockets in 245 
 
 surface-changes 248 
 
 Ventriculites simplex » 495 
 
 Venus pertenuis 532 
 
 Vertebrates 358 
 
 Vespa avatina 533 
 
 Vesuvius 89,92,97 
 
 Viburnum Newberrlanum 515 
 
 Virgin River, section 18 
 
 Viscosity 64 
 
 theory of glaciers, Porbes's 62 
 
 Viviparus troehiformis 517 
 
 Volcanic cone, formation 96 
 
 cones, kinds 95 
 
 conglomerate 223 
 
 necks 220 
 
 phenomena, subordinate 103 
 
 rocks, decay 7 
 
 rocks, mineral composition 215 
 
 Volcanoes 89 
 
 aqueo-igneous theory 101 
 
 chemical theory 101 
 
 cones 95 
 
 craters 98 
 
 definition 89 
 
 estimate of age 99 
 
 internal fluidity theory 100 
 
 issuing of superheated gases 102 
 
 materi9,ls erupted 92 
 
 mechanical theory 102 
 
 phenomena of an eruption 91 
 
 Prestwich's theory • 102 
 
 size, number, and distribution 90 
 
 -^-superheated gas theory 102 
 
 44 
 
 Volcanoes, theory °1 
 
 types °» 
 
 vapors gt 
 
 water-supply ',',', in? 
 
 Volutalithes dumosa .... to 
 
 symmetrica cot 
 
 Voltzia heterophylla . . JqJ 
 
 Von Cotta 5?S 
 
 voy ::::::::::::::::: 586 
 
 w 
 
 Wagner ,74 
 
 Wahsatch beds '.'.'.'.'.'.'.'.'.'.'. 550 
 
 • range " ' 'oVn 977 
 
 Walchia difl-usus .■.■.".■.■.■.■.■.■. . . . .' 474 
 
 piniformis 429 
 
 S*}?"" 225,'3i9.'334, 339 
 
 Wallace 288, 490,616 
 
 ——modification of Croli's theory 616 
 
 Ward .. 372,493,516 
 
 Water, chemical agencies 74 
 
 comparison of different forms 73 
 
 mechanical agencies 9, 73 
 
 volcanic 74 
 
 Waterfalls 12 
 
 Water planes 144 
 
 Water-shed 10 
 
 Waters, underground 74 
 
 chemical effects of underground. . 77 
 
 Waves, erosion by 326, 34 
 
 and tides, examples of action 36 
 
 deposits 39 
 
 marks 198 
 
 ripples 198 
 
 transporting power of 39 
 
 Wealden 458 
 
 Weed 108,169 
 
 Wells, artesian 76 
 
 West Indies 84 
 
 White ; 311, 497 
 
 White River Basin 555 
 
 Whitney 268, 490, 628 
 
 Wilkes 71 
 
 Williamson 381,383 
 
 Williston 456 
 
 Winehell, A 15, 399 
 
 Winding course of rivers 24 
 
 Winds, action 8 
 
 Wood, petrified 199 
 
 Woodward '. 175, 275 
 
 Worm, marine trail 333 
 
 Worm-teeth 333 
 
 Worms, tracks and borings, Silurian.. 332 
 Wright 61 
 
 Xenacanthus Dechenii 415 
 
 Xenoneura antiquarum 347 
 
 Xilocopa senilis 533 
 
 Yellowstone Park, springs in 79 
 
 deposits 169 
 
 geysers of 80, 103, 106 
 
 Yoldia impressa 537 
 
 Yosemite, falls of 15 
 
 Zacantholdes typicalis 311 
 
 Zamia spiralis 443 
 
 Zamites occidentalis 476 
 
 Zaphrentis bllateralls 318 
 
 Worthenl 344 
 
 Zeacrinus elegans 408 
 
 Zermatt glacier > 54 
 
 Zeuglodon cetoides 548 
 
 Zylobius sigillarlse 413 
 
INTERNATIONAL EDUCATION SERIES. 
 
 Bibliography of Education. 
 
 By Will S. Monroe, A.B., Department of 
 Pedagogy and Psychology, State Normal School, 
 Westfield, Mass. Vol. 42. ismo. Cloth, $2.00. 
 
 This book will prove of great use to normal schools, training 
 schools for teachers, and to educational lecturers and all special 
 students seeking to acquaint themselves with the literature of any 
 particular department. It will be of especial value to librarians 
 in the way of assisting them to answer two questions : (a) What 
 books has this library on any special educational theme ? (i) What 
 books ought it to obtain to complete its collection in that theme ? 
 
 In America no less than in Europe there has been marked 
 development in the collection of books on education. The library 
 connected with the Bureau of Education at Washington has over 
 50,000 books and 150,000 pamphlets on education and subjects 
 more or less directly allied to education. Movements have 
 recently been organized to establish state educational libraries in 
 Massachusetts and New Jersey, and county libraries in New 
 Jersey and California. Colleges and universities are segregating 
 the books in their collections bearing on education, and giving 
 special attention to the acquisition of pedagogical books. These 
 activities make possible and desirable the publication of a 
 systematic Bibliography of Education. This work contains in 
 all the titles of 3,200 books and pamphlets. The selection has 
 been limited to publications in the English language supposed to 
 be obtainable in the ordinary course of trade. For convenience 
 and economy of space the titles have been grouped into classes 
 and these broken into sections and subsections. Much care has 
 been taken to secure the titles of British books as Well as 
 American in the belief that it is helpful to the teachers in all 
 English-speaking countries to know the best books on education 
 in the mother tongue without regard to political boundaries. 
 
 D. APPLETON AND COMPANY, NEW YORK. 
 
♦'A BUTTERFLY BOOK OF BEAUTY." 
 
 How to Know the Butterflies. 
 
 By John Henry Cqmstock, Professor of Ento- 
 mology in Cornell University, and Anna Botsford 
 Cqmstock, Lecturer in Nature Study in Cornell 
 University. With 45 full-page colored plates, and 
 many illustrations in the text. 8vo. Cloth, $2.25 
 net ; postage additional. 
 
 This book is designed as a general treatise on butter- 
 flies and a manual of the species of the United States east 
 of the Rocky Mountains. It is intended especially for 
 beginners and for students of nature ; but it will also serve 
 as an introduction to a serious study of this group of in- 
 sects. This book is richly illustrated, without a confusing 
 array of figures of species from remote parts of our coun- 
 try ; it contains brief descriptions of species, but suffix 
 ciently full that the reader can definitely determine the 
 species studied ; and it gives the more important facts of 
 the lives of our butterflies. 
 
 " This book gives the unscientific reader a direct acquaintance with a 
 large number of species, in such simple terms that classification is not 
 difficult, and with. the aid of profuse colored illustrations tha,t excite the 
 admiration of those who have contented themselves heretofore with view-' 
 ing these beautiful creatures on the "Wing, Butterfly catching is regarded; 
 by many as a cruel pastime, but there are ways of capturing these ephem- 
 erals which may rightly be regarded as humane and decent, and the 
 authors, filled with an abounding love of nature, recommend nothing that 
 is not compatible with their beliefs. Notes of the habitat of each species 
 and the facts of butterfly life are given abundantly, and, with, the pigtures, 
 form an unusually important book, which is certain to widen the circle of 
 those who know the joys of butterfly collecting." — The Washi'ngfon Star. 
 
 " Such blending of tints would seem to be a task fit for the painter 
 only instead of the printer. Investigation reveals the fact that the- work 
 is a veritable treasure-house of information — perhaps the most carefully 
 prepared volume yet placed before the public dealing with the subject in 
 hand." — St. Lotiis Gtobe-Democrcit. 
 
 " One of the most interesting, valuable, and beautiful of all the nature 
 books published this spring.'-' — Brooklyn Standard- Union. 
 
 D. APPLETON AND COMPANY, NEW YORK. 
 
BOOKS ON ASTRONOMY. 
 
 The Earth's Beginning. 
 
 By Sir Robert Stawell Ball, LL.D., F. R. S., Author of "Thp Story 
 of the Sun," "An Atlas of Astronomy," ''Star-Land," etc.; Lowndean Pro- 
 fessor of Astronomy and Geometry in the University of Cambridge ; Director 
 of the University Observatory, etc. With four colored Plates and numerous 
 Illustrations. i2mo. Cloth, |i.8onet; postage i8 cents additional. 
 
 This book will make admirable reading for persons of any age. It provides a clear and popu- 
 lar explanation of the great problem of the earth's beginning. It is believed that no exposition 
 of the nebular theory, and its infinitely wide ramifications, has been made that is at once so 
 simple, so original, and so comprehensive. Dr. Eall's recent success as a lecturer in this country 
 indicates his gift of {popular exposition, and this book will rank as one of the most attractive 
 presentations of scientific fact and theory for general readers. 
 
 Popular Astronomy. 
 
 A General Description of the Heavens. By Camille Flammarion. 
 
 Translated from the French by J. Ellard Gore. With 3 Plates and 288 
 
 Illustrations. 8vo. Cloth, $4.50. 
 
 " Flammarion talks, and his conversation is free from those technical expressions which make 
 the obscure style more obscure. He treats the most abstruse problems in such a fashion that yoii 
 see through them more clearly than you ever thought it possible to do without years of study."— 
 New York Herald. 
 
 Studies in Spectrum Analysis. 
 
 By J Norman Lockyer, F. R. S., Correspondent of the Institute of France, 
 
 etc. Wjth 60 Illustrations. i2mo. Cloth, $2.50. 
 
 ** The study of spectrum analysis is one fraught with a pecidiar fascination, and some of the 
 author's experiments are exceedingly picturesque in their result. They are so lucidly described, 
 too, that the reader keeps on, from page to page, never flagging in interest in the matter before 
 him, nor putting down the book until the last page is reached."— iWiu York Evening Express. 
 
 The Story of the Stars. 
 
 By G. F. Chambers, F. R. A. S., Author of " Handbook of Descriptive and 
 
 Practical Astronomy,'' etc. With 24 Illustrations. . ( Library of Useful Stories.) 
 
 i6mo. Cloth, 35 cents net ; postage 4 cents additional. 
 
 " One can here get a clear conception of the relative condition of the stars and constellations. 
 Mid of the existent universe so far as it is disclosed to view. The author, presents his wonderful 
 and at times bewildering facts in a bright and cheery spirit that makes the book doubly attract- 
 ive." — Boston Home Journal. 
 
 D. APPLETON AND COMPANY, NEW YORK. 
 
BOOKS BY GARRETT P. SERVISS. 
 Other Worlds. 
 
 Their Nature, Possibilities, and Habitability in the Light of the 
 Latest Discoveries. Illustrated. i2mo. Cloth, $1.20 net; post- 
 age, li cents additional. 
 
 This book presents the very latest conclusions in regard to 
 the nature and the habitability of the other planets. It is 
 written in popular style, and, at the same time, is scientifically 
 accurate in its statements. It is a convenient handbook of 
 information concerning the solar system, but by no means a dry, 
 scientific treatise on the subject. It might be said to resemble 
 Proctor's celebrated " Other Worlds than Ours " brought up to 
 date. The last chapter, on " How to Find the Planets," is unique 
 and should prove very useful. 
 
 Pleasures of the Telescope. 
 
 A Descriptive Guide for Amateur Astronomers and all Lovers of 
 the Stars. Illustrated with charts of the heavens and with draw- 
 ings of the planets and charts of the moon. 8vo. Cloth, $1.50. 
 
 " This is a book which will give intense pleasure to everyone who 
 uses it and follows its clear instructions." — Louisville Courier- Journal. 
 
 " Every person of culture should possess at least a pissing acquaint- 
 ance with the planets, stars, and constellations. With a little patience 
 and comparatively small effort Mr. Serviss's new book will enable anyone' 
 to obtain this knowledge." — Los Angeles Herald. 
 
 Astronomy with an Opera-Glass. 
 
 A Popular Introduction to the Study of the Starry Heavens with 
 the Simplest of Optical Instruments. 8vo. Cloth, $1.50. 
 
 " We are glad to welcome this popular introduction to the study of 
 the heavens. . . . There could hardly be a more pleasant road to 
 astronomical knowledge than it affords. . . . A child may under- 
 stand the text, which reads more like a collection of anecdotes than any- 
 thing else, but this does not mar its scientific value." — Nature. 
 
 D. APPLETON AND COMPANY, NEW YORK. 
 
POPULAR SCIENCE. 
 
 Popular Astronomy. 
 
 A General Description of the Heavens. By Gamille Flam- 
 MARiON Translated from the French by J. Ellard Gore, F.R A S 
 With 3 Plates and 288 Illustrations. 8vo. Cloth, $4 50 
 
 The Story of the Earth's Atmosphere. 
 
 By Douglas Archibald, M.A., Fellow of the Royal Meteor- 
 ological Society, London. With 44 Illustrations. Cloth, 35 
 cents net. 
 
 An exceedingly interesting and valuable discussion of a topic which inter- 
 ests everyone. Scientific and authentic in its facts, yet free from technicalities, 
 and designed for the general reader. 
 
 Ice-Work, Past and Present. 
 
 By T. G. BoNNEY, D.Sc, LL.D., F.R.S., etc., Professor of 
 Geology at University College, London, Fellow of St. John's 
 College, Cambridge, etc. i2mo. Cloth, $1.50. 
 
 The author has outlined in this treatise the facts upon which are based the 
 many theories of glacial action. A book of ripe thought and deep learning. 
 
 Popular Lectures on Scientific Subjects. 
 
 By H. Helmholtz, Professor of Physics in the University of 
 Berlin. First Series. Translated by E. Atkinson, Ph.D., F.C.S. 
 With an Introduction by Professor Tyndall. With 51 Illustra- 
 tions. i2mo. Cloth, $3.50. 
 
 Contents. — On the Relation of Natural Science to Science in General. 
 On Goethe's Scientific Researches. On the Physiological Causes of Harmony 
 in Music. Ice and Glaciers. Interaction of the Natural Forces. The Recent 
 Progress of the Theory of Vision. The Conservation of Force. Aim and 
 Progress of Physical Science. 
 
 D. APPLE TON AND COMPANY, NEW YORK, 
 
ELECTRICITY AND MAGNETISM. 
 
 Elementary Treatise on Natural Philosophy. 
 
 By A. Privat Deschanel, formerly Professor of Physics in the 
 
 Lyc^e Louis-Ie-Grand, Inspector of the Academy of Paris. Translated 
 
 and edited, with extensive modifications, by J. D. Everett, Professor of 
 
 Natural Philosophy in the Queen's College, Belfast. Complete in Four 
 
 Parts. Illustrated by 783 Engravings on Wood and 3 Colored Plates. 
 
 I. Mechanics, Hydrostatics, and Pneumatics. 8vo, cloth, $1.50. II. Heat. 
 
 8vo, cloth, $1.50. III. Electricity and Magnetism. 8vo, cloth, $1.50. 
 
 IV. Sound and Light. 8vo, cloth, $1.50. Complete in i vol., 8vo. With 
 
 Problems and Index. Cloth, $5.75. Latest revised edition. 
 
 Electricity — Part III of Everett's Deschanel — has been expanded on the lines of 
 modem electrical theory. Hence I'art III forms a new and thoroughly modem text- 
 book of electricity — the need for which, in view of the great advance in electrical 
 science, has been long apparent to every teacher. 
 
 Electricity. 
 
 The Science of the Century. A Sketch for General Readers. By 
 E. M. Caillard, author of "The Invisible Powers of Nature." Illus- 
 trated. i2mo. Cloth, $1.25. 
 
 An admirable treatise, giving such an outline of modern electrical science as may 
 be readily understood by readers who have no previous acquaintance with the subject. 
 
 The Story of Electricity. 
 
 By John Munro, C.E. (Library of Useful Stories.) i6mo. Cloth, 
 35 cents net ; postage, 4 cents additional. 
 
 A Popular Exposition of Electricity. 
 
 With Sketches of Some of its Discoverers. By Martin S. Brennan. 
 i6mo. Cloth, 75 cents. 
 
 Lessons in Electricity, at the Royal Institution, 
 . i875-'76. 
 
 By Prof. John Tyndall. i2mo. Cloth, $1.00. 
 
 A series of experimental lessons involving the use of apparatus so simple and 
 Inexpensive as to be within everybody's reach ; the author's aim being to make his 
 readers acquainted with the history, facts, and principles of the science of electricity 
 and to teach them how to work at it. 
 
 D. APPLETON AND COMPANY, NEW YORK. 
 
TWENTIETH CENTURY TEXT-BOOKS. 
 
 The Life of the Ancient Greeks, with Special 
 Reference to Athens. 
 By Charles Burton Gulick, Ph. D., As- 
 sistant Professor of Greek in Harvard Uni- 
 versity. ^1.40. 
 
 This book gives clearly and simply those essential 
 facts about the daily life of the Greeks which expe- 
 rience has shown that the high-school pupil may learn 
 profitably while reading Greek authors or studying 
 Greek history. It will lessen the teacher's task, and 
 help his pupils to external acquaintance with the facts 
 that bristle on every page of ancient history. 
 
 For readers of the " Anabasis " the correlation be- 
 tween that work and this is complete ; all passages that 
 bear on antiquities have been gathered, and have been 
 made the basis of final appeal when new facts are given. 
 Thus, by the use of this history a pupil may read Xen- 
 ophon with a new knowledge and a new purpose ; in- 
 deed, many passages may now be studied solely with 
 reference to antiquities. The scope of the book is lim- 
 ited to Athens in the fifth and fourth centuries b. c, 
 thus making it primarily a companion to the drama- 
 tists, the historians, and the orators ; but Homeric life 
 is touched on by way of contrast or to show historical 
 continuity. 
 
 The work has been illustrated with the utmost care 
 and fulness. The pictures, which are beautifully exe- 
 cuted, have been chosen not merely for their pictorial 
 effect, but chiefly for their illustrative value. By means 
 of a unique index, the teacher will find it possible to 
 assign topics for composition or class-room discussion, 
 material for which is given in several illustrations. 
 
 D. APPLETON AND COMPANY, NEW YORK. 
 
POPULAR SCIENCE. 
 
 Stellar Evolution and Its Relation to Geological Time. 
 
 By James Croll, F.R.S., author of " Climate and Time," 
 " Climate and Cosmology." i2mo. Cloth, $i.oo. 
 
 A treatise upon the probable origin of meteorites, comets, and nebulae, upon 
 the age of the sun's heat, and upon the prenebular condition of the universe. 
 
 Discussions on Climate and Cosmology. 
 
 By James Croll, LL.D., F.R.S. With Chart. i2mo. Cloth, 
 
 $2.00. 
 
 Climate and Time in Their Geological Relations. 
 
 A Theory of Secular Changes of the Earth's Climate. By 
 James Croll, of H. M. Geological Survey of Scotland. With 
 • Maps and Illustrations. i2mo. Cloth, $2.50. 
 
 Creation or Evolution ? 
 
 A Philosophical Inquiry. By George Ticknor Curtis. 
 i2mo. Cloth, $2.00. 
 
 The Origin of the Fittest. 
 
 Essays on Evolution. By Prof. E. D. Cope. With numerous 
 Illustrations. 8vo. Cloth, $3.00. 
 
 Contents. — Part I. General Evolution. II. Structural Evidence of Evo- 
 lution. III. Mechanical Evolution. IV. Metaphysical Evolution. 
 
 The Comparative Anatomy of the Domesticated Ani- 
 mals. 
 
 By A Chauveau, Professor at the Lyons Veterinary School. 
 New Edition, Revised and Enlarged, with the Co-operation of 
 S. Arloing, late Principal of Anatomy at the Lyons Veterinary 
 School. Translated and edited by James Fleming. With 585 
 Illustrations. Bvo. Cloth, $7.00. 
 
 D. APPLETON AND COMPANY, NEW YORK. 
 
BY R SCHUYLER MATHEWS. 
 
 Familiar Flowers of Field and Garden. 
 
 New edition. With 12 orthochromatic photographs of character- 
 istic flowers by L. W. Browneil, and over 200 drawings by the 
 Author, izmo. Cloth, $1.40 net ; postage, 18 cents additional. 
 
 The new photography's revelations of nature have found perfect expression in Mr. 
 Brownell's remarkable pictures. The beautiful series included in this new edition 
 will be appreciated by every one, and prized by students and nature-lovers. 
 
 Familiar Trees and their Leaves. 
 
 New edition. With pictures of representative trees in colors, 
 and over 200 drawings from nature by the Author. With the 
 botanical name and habitat of each tree and a record of the pre- 
 cise character and color of its leafage. 8vo. Cloth, $1.75 net ; 
 postage, 1 8 cents additional. 
 
 Mr. Mathews has executed careful and truthful paintings of characteristic trees, 
 which have been admirably reproduced in colors. The great popularity of his finely 
 illustrated and useful book is familiar to nature-lovers. The new edition in colors 
 forms a beautiful and indispensable guide to a knowledge of foliage and of trees. 
 
 Familiar Life in Field and Forest. 
 
 With many Illustrations. i2mo. Cloth, $1.75. 
 
 "Avery attractive book, which contains a mass of useful information and curious 
 anecdote." — San Francisco Chronicle. 
 
 " The book is one that is apt to please the young naturalist, as it is not over- 
 crowded with scientific words of such dimensions as are usually a bugbear to the 
 young student. The information is given in a pleasant way that is attractive as well 
 as instructive." — Minneapolis Tribune. ^ 
 
 Familiar Features of the Roadside. 
 
 With 130 Illustrations by the Author. i2mo. Cloth, I1.75. 
 
 " A faithful guide-book for our roadsides. . . . Can be unhesitatingly com- 
 mended for summer strolls. " — New York Evening Post. 
 
 " Which one of us, whether afoot, awheel, on horseback, or in comfortable 
 carriage, has not whiled away the time by glancing about ? How many of us, how- 
 ever, have taken in the details of what charms us ? We see the flowering fields and 
 budding woods, listen to the notes of birds and frogs, the hum of some big bumble- 
 bee, but how much do we know of what we sense ? These questions, these c oubts 
 have occurred to all of us, and it is to answer them that Mr. Mathews sets forth. It 
 is to his credit that he succeeds so well. He puts before us in chronological order the 
 flowers, birds, and beasts we meet on our highway and byway travels, tells us how to 
 recognize them, what they are really like, and gives us at once charming drawings in 
 words and lines, for Mr. Mathews is his own illustrator." — Boston Journal. 
 
 D. APPLETON AND COMPANY, NEW YORK. 
 
TWENTIETH CENTURY TEXT=BOOKS OF SCIENCE. 
 TEXT-BOOKS OF ZOOLOGY, 
 
 By David Starr Jordan, Ph. D., LL. D., President of Leland 
 Stanford Junior University ; Vernon L. Kellogg, M. S., 
 and Harold Heath, Ph. D., Professors in Leland Stanford 
 Junior University. 
 
 Animal Studies. 
 
 An Elementary Zoology. $1.25. 
 
 Animal Life. 
 
 A First Book of Zoology. $1.20. 
 
 Animal Forms. 
 
 A Text-Book of Zoology. $1.10. 
 
 Animals. 
 
 Animal Life and Animal Forms in one volume. $1.80. 
 
 Animal Structures. 
 
 A Laboratory Manual of Zoology. By D. S. Jordan and 
 George C. Price. 75 cents. 
 
 An Introduction to Physical Geography. 
 
 By Grove K. Gilbert, LL. D., United States Geological Sur- 
 vey, and Albert P. Brigham, Professor of Geology, Colgate 
 University. $1.25. 
 
 A Text-Book of Geology. 
 
 By Albert Perry Brigham, A. M. $1.40. 
 
 An Elementary Chemistry. 
 
 With Experiments. By Robert Hart Bradbury, A. M., 
 Ph. D., Teacher of Chemistry, Central Manual Training School, 
 Philadelphia. $1.25. Experiments separately, 45 cents. 
 
 The Elementary Principles of Chemistry. 
 
 By Abram Van Eps Young, Ph. B., Northwestern University, 
 Evanston, 111. 95 cents. With Experiments, $1.10. Laboratory 
 Experiments separately, 45 cents. 
 
 D. APPLETON AND COMPANY, NEW YORK. 
 
HERBERT SPENCER'S WORKS. 
 Essays : Scientific, Political, and Specula±ive. 
 
 A New Edition, uniform with Mr. Spencer's other 
 Works, including Seven New Essays. Three volumes. 
 i2mo. 1,460 pages, with full Subject Index of 24 pages. 
 Cloth, $6.00. 
 
 These Essays are devoted to the entire range of subjects cov- 
 ered in Mr. Spencer's numerous works, and embrace the social 
 and poHtical sciences, education, and many other pertinent topics 
 of general interest. 
 
 Descriptive Sociology. 
 
 A Cyclopaedia of Social Facts. Representing the Con- 
 stitution of Every Type and Grade of Human Society, 
 Past and Present, Stationary and Progressive. Eight 
 numbers, royal folio. 
 
 No. I. ENGLISH $4 00 
 
 II. MEXICANS, CENTRAL AMERICANS, CHIB- 
 
 CHAS, AND PERUVIANS 4 00 
 
 III LOWEST RACES, NEGRITO RACES, and 
 
 " MALAYO-POLYNESIAN RACES 4 00 
 
 IV. AFRICAN RACES 4 00 
 
 V. ASIATIC RACES 4 00 
 
 VL AMERICAN RACES 4 0° 
 
 . VII. HEBREWS AND PHCENICIANS 400 
 
 VIII. FRENCH (Double Number) 7 00 
 
 The Indiiction of Ethics. 
 
 The Ethics of Individual Life, Parts II and III of The 
 Principles of Ethics. One volume. i2mo. Cloth, $1.25. 
 
 Philosophy of Style. 
 
 i2mo. Flexible cloth, 50 cents. 
 
 D. APPLETON AND COMPANY, NEW YORK. 
 
SPENCER'S MISCELLANEOUS WORKS. 
 
 Social Statics. 
 
 New and revised edition, including *' The Man versus The State," a series 
 
 of essays on political tendencies, heretofore published separately. i2mo, 420 
 
 pages. Cloth, $2.00. 
 
 CoNTENTb. — Happiness as an Immediate Aim. Unguided Expediency. The Moral- 
 Sense Doctrine. What is Morality ? The Evanescence [i Diminution] of Evil. Greatest 
 Happiness must be sought indirectly. Derivation of a First Principle. Secondary Deriva- 
 tion of a First Principle. First Principle. Application of the First Principle. The Right of 
 Property. Socialism. The Right of Property in Ideas. The Rights of Women. The 
 Rights of Children. Political Rights. The Constitution of the State. The Duty of the 
 State. The Limit of State Duty. The Regulation of Commerce. Religious Establishments, 
 Poor-Laws. National Education. Government Colonization. Sanitary Supervision. Cur- 
 rency, Postal Arrangements, etc. General Considerations. The New Toryism. The Com- 
 ing Slavery, The Sins of Legislators. The Great Political Superstition. 
 
 Facts and Comments. 
 
 Uniform edition. i2nio. Cloth, $1.20 net ; postage, 12 cents additional. 
 
 From the analytical brain of a philosopher of the greatness of Herbert Spencer— a great- 
 ness that has extended over more than two generations — the subjects treated in this, his last 
 volume, assume a commanding importance. Such topics as "Americanisms," "Presence of 
 Mind," "The Corruption of Music," "The Origin and Development of Music," "Estimates 
 of Men," "State Education," etc., are invested with a life and actuality only possible under 
 his stimulating treatment. 
 
 Education : Intellectual, Moral, and Physical. 
 
 i2mo. Cloth, $1.25 ; paper, 50 cents. 
 
 Contents. — What Knowledge is of most Worth ? Intellectual Education. Moral Educa- 
 tion. Physical Education. 
 
 The Study of Sociology. 
 
 The fifth volume in the International Scientific Series. i2mo. Cloth, $1.50. 
 
 Contents. — Our Need of it. Is there a Social Science? Nature of the Social Science. 
 Difficulties of the Social Science. Objective Difficulties, Subjective Difficulties, Intellectual. 
 Subjective Difficulties, Emotional. The Educational Bias. The Bias of Patriotism. The 
 Class Bias. The Political Bias. The Theological Bias. Discipline. Preparation in Biology. 
 Preparation in Psychology. Conclusion. 
 
 The Inadequacy of " Natural Selection." 
 
 i2mo. Paper, 30 cents. 
 
 This essay, in which Professor Weismann's theories are criticized, is reprinted from the 
 Contemporary Review, and comprises a forcible presentation of Mr. Spencer s views upon the 
 general subject indicated in the title. 
 
 D. APPLETON AND COMPANY, NEW YORK. 
 
TWENTIETH CENTURY TEXT-BOOKS. 
 
 Elementary Chemistry. 
 
 By Robert Hart Bradbury, A.M., Ph.D., 
 Teacher of Chemistry in the Philadelphia Central 
 Manual Training School; formerly Lecturer on 
 Physical Chemistry in the Department of Philosophy, 
 University of Pennsylvania. i2mo. Cloth, |i.oo. 
 With Laboratory Manual, $1.25. 
 
 There is no dearth of text-books of Chemistry, but all seem 
 to have fallen short in some essential particulars, and fail to meet 
 the actual requirements of class work. This book attempts to 
 remedy such faults. It is, therefore, thoroughly fresh in material 
 and treatment. It is not a compilation from existing manuals, 
 but the result of a survey of the recent literature of the science ; 
 yet nothing has been introduced that has not been tested practi- 
 cally in the class-room and found to be available. Special effort 
 has been made to attain precision and clearness of statement. 
 The theoretical and general portions of the subject are not hurled 
 at the student in an overwhelming and unintelligible mass. The 
 introduction of each generalization is deferred until a particular 
 case of it has been encountered. Formulae and equations are not 
 introduced until the student is able to receive them, and the atomic 
 theory is reserved until the student is able to understand it. 
 
 Note. — This text-book was scarcely off the press'when it was adopted in 
 Boys' High School, New York (the largest high school in the world). 
 High School of Commerce, New York. 
 Erasmus Hall High School, Brooklyn. 
 Manual Training High School, Brooklyn. 
 Central Manual Training-School, Philadelphia. 
 High School, Hartford, Conn. 
 
 A Laboratory Manual of Chemistry. 
 
 By Robert Hart Bradbury, A.M., Ph.D., 
 
 Cloth, 45 cents. 
 
 The laboratory guide aims to supply an outline of work which 
 can be completed by the average student in one school year. 
 Constant questions, problems, and exercises serve to prevent the 
 student's work from becoming thoughtless or mechanical. 
 
 D. APPLETON AND COMPANY, 
 
 NEW YORK. BOSTON. CHICAGO. LONDON. 
 
WORKS OF THOMAS H. HUXLEY. 
 
 Physiography. 
 
 An Introduction to the Study of Nature. With Illustrations 
 and Colored Plates. i2mo. Cloth, $2.50. 
 
 Essays upon Some Controverted Questions. 
 
 i2mo. Cloth, $2.00. 
 
 In this volume Professor Huxley has brought together a number of his more 
 important recent essays, and has added certain new matter. Among the topics dis- 
 cussed are "Mr. Gladstone and Genesis," "The Evolution of Theology," "Science 
 and Pseudo-Science," " Agnosticism," and " The Rise and Progress of Paleontology." 
 
 The Crayfish. An Introduction to the Study of 
 Zoology. 
 
 With 82 Illustrations. i2rao. Cloth, $1.75. 
 
 The object of Professor Huxley's new book is to afford an opportunity to students 
 to commence the study of zoology by means of a careful verification of nearly all that 
 is known concerning a single animal, the common crayfish. The book is properly 
 termed an " Introduction to Zoology." 
 
 On the Origin of Species; or, The Causes of the 
 Phenomena of Organic Nature. 
 
 izmo. Cloth, $1.00. 
 
 American Addresses; with a Lecture on the Study of 
 Biology. 
 
 i2mo. Cloth, $1.25. 
 
 A Manual of the Anatomy of Vertebrated Animals. 
 
 Illustrated. i2mo. Cloth, $2.50. 
 
 A Manual of the Anatomy of Invertebrated Animals. 
 
 Illustrated. lamo. Cloth, $2.50. 
 
 " My object in writing the book has been to make it useful to those who wish to 
 become acquainted with the broad outlines of what is known of the morphology of 
 the Invertebrata." — The Author, 
 
 Lay Sermons. 
 
 lamo. Cloth, $1.75. 
 
 D. APPLETON AND COMPANY, NEW YORK. 
 
■r4W, 
 
 0^