REESE LIBRARY >F rrtr UNIVERSITY OF CALIFORNIA. ^ c cessions No. <3^- ^ Shelf No. APPLETONS' SCIENCE TEXT-BOOKS APPLIED GEOLOGY. APPLETONS' SCIENCE TEXT-BOOKS. The following works of this new series will be im- mediately issued ; others are to follow : The Elements of Chemistry. BY PROF. F. W. CLARKE, Chemist of the United States Geological Survey. The Essentials of Anatomy, Physiology, and Hygiene. BY ROGER S. TRACY, M. D., Author of " Handbook of Sanitary Information for Householders," Sanitary Inspector of the New York City Health Department. A Compend of Geology. BY JOSEPH LE CONTE, Professor of Geology and Natural History in the University of California ; author of " Elements of Geology," etc. Elements of Zoology. BY C. F. HOLDER, Fellow of the New York Academy of Sciences, Corresponding Member of the Linnaean Society, etc. ; AND J. B. HOLDER, M. D., Curator of Zoology of American Museum of Natural History, Central Park, New York. Descriptive Botany. BY ELIZA A. YOUMANS. Applied Geology. BY SAMUEL G. WILLIAMS, Professor of General and Economic Geology in Cornell University. jftcinite fat-0oks. APPLIED GEOLOGY. A TREA TISE ON THE INDUSTRIAL RELATIONS OF GEOLOGICAL STRUCTURE; AND ON THE NATURE, OCCURRENCE, AND USES OF SUBSTANCES DERIVED FROM GEOLOGICAL SOURCES. BY SAMUEL G. WILLIAMS, PROFESSOR OF GENERAL AND ECONOMIC GEOLOGY IN CORNELL UNIVERSITY. NEW YORK: D. APPLETON AND COMPANY. I, 3, AND 5 BOND STREET. 1886. 'N/ COPYRIGHT, 1885, Bv D. APPLETON AND COMPANY. PREFACE. So far as the author of this book has observed, no work has yet been published in this country which aims to give a connected and systematic view of the applications of geology to the various uses of mankind. A number of European and American treatises have appeared which limit themselves to special departments of applied geolo- gy, some of them discussing the modes of occur- rence and distribution of metallic ores or mineral fuels ; others treating of agriculture in its geologi- cal aspects, or dealing with the geological materials of chemical industries, or devoting themselves to building and ornamental stones, to mortars, or to gems. The work of D'Orbigny and Gente on ge- ology applied to the arts and to agriculture, pub- lished more than a quarter of a century ago, is not only in a foreign language, but is now obviously in- complete ; and the excellent treatise of Dr. Page, which reviews the entire field of applied geology, is naturally too much devoted to English and Euro- vi PREFACE. pean materials and sources of supply to be wholly satisfactory to the American student. Meanwhile an immense amount of work has been done in revealing the geological structure of the American Continent, and in making known its rich and varied resources a work in which many independent investigators and explorers have added much of value to the information gained by the various State and national surveys. The knowledge thus acquired of the existence, the nature, the abundance, and the distribution of substances of practical utility, as well as of the important relations which are sustained by geological structure to hu- man well-being and to the successful pursuit of many important callings, is scattered so widely in geological reports, in scientific and technical jour- nals, and in the transactions of learned associations, as to be in a great measure inaccessible to the stu- dent and the practical man, unless a large library is at hand and abundant leisure to consult it. It seems evident, therefore, that there is need of a treatise such as this aims to be, which, avoiding minute detail, shall give a systematic and compre- hensive account of the most important relations which geology sustains to human interests. This book is written most largely from an American stand-point, yet care has been taken, in the case of all important substances, to give the chief foreign as well as the domestic sources PREFACE. vii whence they may be obtained, since those who may, it is hoped, consult its pages for business pur- poses, will naturally desire to know both where to look for their supplies and whence their sharpest competition is likely to come. With this view, also, tables of the annual production of many lead- ing minerals have been carefully compiled from the most recent attainable data, and for these the excel- lent tables published by the " Engineering and Mining Journal " have furnished the largest part of the materials. A work of this kind is in its very nature a dis- cussion and arrangement of materials derived from various sources, and verified, so far as is practicable, by personal observation and inquiry. The author has endeavored to use the rich materials afforded to him with proper discrimination. If somewhat more space has been given to the chapters on " Agri- culture," on " Materials of Construction,'' on " Min- eral Fuels," and on "Ore Deposits" than to other topics, it will probably be conceded that the wide- reaching and important interests to which they relate will fully warrant this greater fullness of treatment. Where the works from which information has been most largely obtained were likely to be within the reach of those persons for whom this book is chiefly intended, they have been mentioned in the lists of works of reference appended to many of the chap- ters. This has necessarily precluded any specific viii PREFACE. mention of many valuable papers published in scien- tific journals and in the " Transactions of the Ameri- can Institute of Mining Engineers," to which this book is indebted for many items of interest. For the arrangement of the seemingly heterogeneous materials of some of the later chapters, useful hints were derived from the " Geology of Canada," 1863, and from some features in the classification of the economic collection of the Ecole des Mines in Paris. The author wishes also to acknowledge his indebtedness to the kindred works of D'Orbigny and Gente, and of Dr. Page, for many important suggestions, and to the first-named work especially for valuable aid in the preparation of the chapter on agriculture. CORNELL UNIVERSITY, October i, 1885. ANALYSIS OF CONTENTS. CHAPTER I. PAGE INTRODUCTION ROCK-FORMING MINERALS CLASSIFICATION . i Quartz, feldspars, micas, hornblende, pyroxene, calcite, dolo- mite, talc, chlorite, serpentine, clay Classification of rocks- Sedimentary rocks and consolidation Crystalline rocks and their structure Tables of classification and means of consolidation. Structure and texture of rocks. CHAPTER II. DESCRIPTION OF ROCKS 15 Mechanical sediments Chemical sediments Organic sedi- ments Metamorphic rocks Igneous rocks Key for proximate determination of rocks. CHAPTER III. ARRANGEMENT OF ROCK-MASSES . . . . . .27 Stratified and definitions Unstratified Included or vein-like Relative age of rocks Table of ages and periods. CHAPTER IV. ECONOMIC RELATIONS OF GEOLOGICAL STRUCTURE ... 44 Economic geology defined and illustrated Accessibility de- pendent on dip, faults, uplifts Facility of extraction Expense of excavation and tunneling Foundations of structures Water supply Springs Wells Artesian wells Drainage. CHAPTER V. MATERIALS OF CONSTRUCTION ....... 66 Building-stonesProperties of Strength Table of strength Durability Beauty Ease of working Selection of building- x ANALYSIS OF CONTENTS. PAGE stones North American building-stones Geological positions and distribution Granitic Marble and slate Sandstones Lime- stones Brick, terra-cotta, and drain-pipes Materials for mortar and cement. CHAPTER VI. RELATIONS OF GEOLOGY TO AGRICULTURE . . . . 101 Soils, origin of Ingredients Nature and amelioration Table of ash analyses Composition of soils Fertilization Geological fertilizers Drainage and subsoils. CHAPTER VII. RELATIONS OF GEOLOGY TO HEALTH 129 Water supply of households and communities Drainage of dwellings, cities, and districts. CHAPTER VIII. MINERAL FUELS 135 Coals, classification Analyses of twenty-two Geological as- sociations Geological horizons American coal-fields Foreign coal-fields Impurities in coals Fuel-value of coals Adaptation to special uses Peat Coal product of 1881. CHAPTER IX. GEOLOGICAL MATERIALS FOR ILLUMINATION . . . .165 Petroleum Mode of occurrence Geological horizons Re- gions Mode of exploitation Bituminous shales Natural gas Ozocerite. CHAPTER X. MODE OF OCCURRENCE OF METALLIFEROUS DEPOSITS . . 183 Metallic ores Ore associations and gangues Structure of ore deposits Beds and placers Impregnations Mass deposits Veins of segregation Fissure veins Origin of fissures and con- tents Arrangement of contents Positions relative to country rock Disturbances of deposits Surface changes General distri- butionProspectingValue, on what dependent Erroneous ideas regarding ore deposits. CHAPTER XI. 224 O res Mode of occurrence Geological horizons and localities Production Uses. ANALYSIS OF CONTENTS. x i CHAPTER XII. PAGE COPPER 231 Ores Mode of occurrence Distribution, geological and topo- graphic Chief foreign localities Production in 1882 Uses. CHAPTER XIII. LEAD AND ZINC 241 Ores of lead Nature of deposits and geological horizons American centers of production Foreign regions Production Uses Zinc ores Mode of occurrence American localities For- eign centers ProductionUses. CHAPTER XIV. TIN AND MERCURY . 254 Tin ore Mode of occurrence Localities Production and use Ore of mercury Form of deposits Three regions of Produc- tion of 1882 Uses. CHAPTER XV. SILVER 262 Ores Forms of deposit American silver regions Table of production Foreign silver regions Table of world's product Uses. CHAPTER XVI. GOLD . .- . . . . ' 273 Associations Mode of occurrence Regions of gold produc- tion Tables of United States product, and of that of the world Uses of gold Table of gold values Table of uses of gold and silver Extraction of gold. CHAPTER XVII. PLATINUM AND OTHER METALS 284 Platinum Nickel Cobalt Antimony Bismuth Magnesium Aluminium Chromium Manganese Arsenic Iridium Tungsten. CHAPTER XVIII. SUBSTANCES ADAPTED TO CHEMICAL MANUFACTURES OR USE . 296 Pyrites Sulphur Salt Potash and soda Borax Alum- Magnesia Strontia Titanium. xii ANALYSIS OF CONTENTS. CHAPTER XIX. PAGE FICTILE MATERIALS 319 Potter's clay Table of analyses Properties Origin Locali- ties Pottery mixtures and glazes Composition of glass Glass- sand Granulite Coloring materials. CHAPTER XX. REFRACTORY SUBSTANCES . 334 Fire-clays Analyses Geological occurrence Dinas bricks Canister Fire-stones Floating brick Graphite Lime and Magnesia Soapstone Mica Asbestus. CHAPTER XXI. MATERIALS OF PHYSICAL APPLICATION 347 For roads and walks Abrasives: Grindstones, whetstones, millstones, bort, corundum and emery, sand, pumice and tripoli Graphic materials: Graphite, chalk, etc., lithographic lime- stone Pigments : Whiting, ochre, umber, barytes Lubricators : ' Graphite, petroleum, talc, felsite Molding-sand. CHAPTER XXII. ORNAMENTAL STONES AND GEMS 365 Quartz Amethyst Agates Moss-agate Onyx Jasper- Feldspar Nephrite Lapis lazuli Malachite Fluorite Jet- Amber Marbles Onyx marble Alabaster Verd-antique mar- ble Porphyry. Gems : Diamond, corundum, spinel, topaz, beryl, zircon, garnet, tourmaline, hiddenite, turquoise, opal. APPLIED GEOLOGY. CHAPTER I. INTRODUCTION ROCK-FORMING MINERALS CLASSIFICA- TION. THE science of geology has both a theoretical and a practical side. Theoretically, it aims at an exhaustive study of the phenomena presented by the earth's crust, together with the order in time in which they originated, and the forces to whose combined or successive action they are due. It investigates the composition, the struct- ure, the origin, and the arrangement of the earth's rocky masses. It strives to refer the present phenomena of the earth's crust to their appropriate causes. It reconstructs the history of the earth and of its successive inhabitants, using structure as its guide, and the present action of the unchanging forces of nature as its interpreter. On the practical side, geology uses the knowledge of the earth's structure, and of the mode of occurrence and properties of its various products, to subserve human needs and promote human enjoyment. It guides the architect and the builder in the selection of fitting mate- rials for construction good building-stones, mortars, ce- ments, and sands. It reveals to the agriculturist the ori- gin of his soils, and points him to the cheapest and most 2 APPLIED GEOLOGY. effective means for correcting their defects. It teaches the civil engineer that the feasibility and expense of most of his important undertakings, the obstacles that he must overcome, and the aids of which he may avail himself, will depend in large measure on the geological structure of the region in which he must operate ; and that he needs to take this into careful consideration, if he would guard against ruinous disasters, or almost equally ruinous miscalculations as to expense. It furnishes to the mining engineer the only available guide in his arduous calling, teaching him the nature and the modes of occurrence of those valuable substances for which he must seek, the laws to which they are subjected, and the irregularities and dislocations to which they are liable ; and supplying him with those general principles, by applying which, he may make the technical experience gained in any one lo- cality available under other and widely different circum- stances. It aids the sanitarian in securing the two most subtile yet essential conditions of public health pure air and wholesome water both of which depend largely on circumstances purely geological. Not only does practical geology hold such intimate relations with these very important interests, but, more- over, when we consider how large a proportion of the sub- stances which civilized man utilizes for the supply of his multifarious wants is drawn from the bosom of the earth, we shall see how wide-reaching and vital are its connec- tions with the very sources of human progress. Among these substances are the fuels that we burn ; the materials that we use for illumination ; the salt with which we pre- serve or season our food, and which becomes the basis of vast manufactures, some of whose products reach every family ; the clays and sands that we fabricate into myriads of useful and ornamental forms, a number of which are found in every household, even the humblest ; the ores that we smelt to provide ourselves with those implements / ROCK-FORMING MINERALS. by whose ever-widening use we are daily exten< mastery over the blind forces of nature ; and, finally, but' by no means least, those substances by which a cultured taste seeks for itself a refined pleasure brilliant pigments, sparkling gems for jewelry, and handsome stones for do- mestic and architectural adornment. The withdrawal of any one of these classes of materials would seriously crip- ple human resources, and the lack of some of them would have made human advancement very difficult, if not im- possible ; for the stages of man's progress are well marked by the character of his pottery, and, better, by the nature and material of his implements. It is but natural that a science which touches so vitally the interests of nearly all classes should attract the atten- tion of enlightened governments ; and we accordingly find that most civilized states have carried on to some extent geological surveys, which, while primarily revealing the geological structure of their domains, have also care- fully sought out their various mineral resources. The pub- lications of these surveys, giving an authoritative statement of the localities where valuable substances might be found, have naturally attracted capital to the development of such means of wealth, and have, doubtless, repaid mani- fold their cost by the increase in the taxable property of the communities that have carried them on. The two States of Ohio and Illinois published reports of their re- sources, beginning the one in 1870 and the other in 1866. The coal-trade alone of these two States increased from two and a half million tons each in 1870 to more than nine million tons each in 1882 ; and this industry in Illi- nois gave employment to 19,400 men and $8,230,000 capi- tal. There is no good reason to doubt that this great increase in the coal-trade of those States was due in large measure to the reliable information furnished by their surveys. Incidentally, also, such surveys have been of great 4 APPLIED GEOLOGY. service in discouraging misdirected and expensive explo- rations after substances not likely to be found in certain localities ; for, second only in importance to the knowl- edge of what we may fairly expect to find in a given place is the certainty of what we ought not to expect to find. Large sums have been expended in New York by men unacquainted with its geological structure, in a futile search for coal in certain black, slaty rocks, holding geo- logical positions such as have never yet furnished coal, nor are ever likely to do so. Any man would show him- self ignorant indeed who should now undertake a search for coal in New York. From what has already been said, it will be evident that at least an elementary knowledge of the earth's geo- logical structure is essential as a guide in the intelligent prosecution of many great branches of industry. It will be necessary for our purpose, therefore, first to examine the most essential points of geological structure, and after- ward to show their application to the various arts, draw- ing our materials as largely as possible from American sources. Rocks : their Composition and Classification. Geology deals with the rocks which form the earth's framework ; and what is most essential to be known about rocks for our present purpose is (i) their composition, i.e., the mineral substances which enter into them and impart to them most of their properties; (2) their texture and structure, or the characteristics which distinguish them both as rock-individuals and as rock-masses ; (3) their ori- gin, or the agencies through which they assumed their present form ; (4) their mode of arrangement ; and (5) the order in which they occur. Rock-Forming Minerals. Some careful examina- tion of the rocks most commonly met with will prepare the observer to admit that all rocks, whatever their origin, ROCK-FORMING MINERALS. 5 are composed of mineral species ; and, furthermore, that the minerals which play the chief part in their composi- tion, and which most largely condition their use and dura- bility, are comparatively few in number. These minerals, in particles varying greatly in size and regularity of form, aggregated in the most variable proportions, and consoli- dated by many different agencies to the most widely differ- ing degrees of firmness, from mere incoherent masses of sand, to the hardest quartzite and the toughest trap, make up the chief bulk of the most important rocks of the globe. Ready acquaintance with them in their smallest discernible particles, and by their most obvious and easily- tested properties, is highly essential to the practical geolo- gist. Chief among such minerals is quartz, with its most widely-disseminated compounds, viz. : the varieties of feldspar, mica, hornblende, and pyroxene, to which may be added talc, chlorite, and serpentine. Calcite and dolo- mite are the essential components of the various kinds of limestone and marble ; while pyrite, though not largely present in rocks, should be known because of the injuri- ous manner in which it affects their characters. The im- portant ores and other minerals of economic use will be considered in other connections. For a complete knowledge of these minerals, and others that will be mentioned in this treatise, the student should study the minerals themselves all easy to be obtained with the aid of some good treatise on mineralogy, Dana's " Manual of Mineralogy " being the best. The properties to which especial attention should be directed are, color and luster, hardness, cleavage and fracture, behavior with acids, and sometimes fusibility. Quartz is readily distinguished by its glassy luster, its hardness, so great as not to be scratched by a knife, and by the fact that its fracture gives never flat but always curved surfaces (conch oidal fracture). It will scratch all the other minerals named above, being 7 on a scale of 6 APPLIED GEOLOGY. hardness beginning with talc, i, easily impressed with the finger-nail, and ending with diamond, 10. The hardest of the remaining minerals named as chief components of rocks, the feldspars, can be scratched with considerable difficulty by a knife, and their hardness is counted 6. Besides this, the feldspars can be split with flat, shining surfaces cleavage in two directions, making a right angle with each other in orthoclase, the most com- mon kind, and in the other two important varieties, oligo- clase and labradorite, varying but a few degrees from a right angle. The last two, in a good light, usually show on the face of easiest cleavage fine parallel lines, while orthoclase does not. The color of orthoclase and oligo- clase varies from white to light red, while labradorite is usually gray or brown, with a beautiful internal reflection from smooth surfaces. Their luster differs somewhat from that of quartz, inclining to pearly. Their slightly inferior hardness and their flat cleavage surfaces usually make them easily distinguishable from quartz ; but if any doubt still remains, a thin, pointed splinter should be strongly heated with the blow-pipe. Any of the feldspars can be fused with more or less difficulty, while quartz can not. The micas are readily distinguished by their very easy cleavage into thin, elastic, shining leaves. Muscovite mica is usually of light to brownish silvery colors, biotite black, and phlogopite of bronze-color. All are easily scratched with a knife. Pyroxene, of which augite is the most abundant variety, and hornblende, as they are commonly found in rocks, are black, brown, or dark-green minerals, though some varieties are lighter green and white, a little more easily scratched than feldspar their hardness being about 5.5 and more easily fused. Both cleave in two directions, making in pyroxene a little less than a right angle, and in hornblende a very obtuse angle of 124 30'. Hence, when the angle of cleavage can be seen, the two minerals can be ROCK-FORMING MINERALS. 7 easily distinguished, otherwise not. It is helpful, however, to note that the cleavage of hornblende is easier than that of pyroxene, hence gives usually more complete surfaces and brighter luster ; also that hornblende is frequently found associated in rocks with quartz and orthoclase, while augite, the most common form of pyroxene, is rarely so associated. Both are heavy minerals, and give more than usual weight to rocks in which they occur abun- dantly. Calcite and dolomite are easily known by their ready cleavage in three directions, when crystallized, giving rise to a six - sided oblique - angled figure ; by being easily cut with a knife hardness 3 to 4 ; and by effervescing rapidly, from the escape of carbonic acid, with dilute hy- drochloric acid. Their usual color is white. Dolomite is a little harder and a little heavier than calcite, and while calcite effervesces freely in cold acid, dolomite effervesces but slightly, if at all, until the acid is heated. Both are very important minerals, being, as has already been said, the essential constituents of all limestones and marbles. Pyrite, or iron pyrites, is a mineral of metallic luster and light-yellow or golden color, whence it is often mis- taken for gold hence called " fool's gold " but is readily distinguished from it by its great hardness, nearly equal to that of quartz, and by its giving when heated the odor of sulphur. It is little likely to be mistaken for any other mineral save copper pyrites, from which it may be distin- guished by the fact that copper pyrites is much softer and its color is a deeper yellow. Talc is a green, gray, or white mineral of pearly luster, so soft as readily to be scratched by the finger-nail, greasy to the touch, and usually of a scaly, foliated, or fibrous texture. Its softness and its soapy feel render it easy to be distinguished. Chlorite, as it occurs forming a characteristic constit- 8 APPLIED GEOLOGY. uent of rocks, is usually a dark-green earthy mineral, but little harder than talc, and of a pearly luster when cleav- able. Serpentine is usually a massive though sometimes fibrous mineral, of an oily green color, sometimes red or nearly black, of greasy luster and slightly greasy feel, easily scratched with a knife, its hardness being about 3, and with a conchoid or splintery fracture. To these materials of rocks should be added clay, an indefinite mixture of kaolin, which is a soft, unctuous substance resulting from the decomposition of feldspar, with varying amounts of quartz -sand often exceedingly fine, powdered feldspar, iron oxide, and occasionally other substances. It is plastic when wet, shrinks on drying or when strongly heated, and emits an earthy odor when breathed on. The rocks into which it enters are often described as argillaceous rocks, from the Latin name for clay : e. g., slate is an argillaceous rock, and a limestone containing a considerable amount of clay would be termed an argillaceous limestone. Also the following adjective terms are of frequent occurrence, viz. : Quartzose or sili- cious, applied to rocks containing quartz ; calcareous, to those containing calcite ; ferruginous, to those colored by iron oxide usually red, yellow, or brown ; and arenaceous, to those containing sand. Rocks. The minerals here described, with occasion- ally quite subordinate amounts of some other minerals, make up the rocks of chief economic importance. As constituents of rocks they are found, sometimes as crys- tals of usually imperfect outline, sometimes in the form of broken and worn grains, of sizes varying from those so minute as not to be perceptible to the unaided eye, to masses of considerable size. Hence, according to the con- dition of the composing substances, we may distinguish crystalline rocks and fragmental, or, as they may with equal propriety be termed, sedimentary rocks, because de- ROCK-FORMING MINERALS. g posited from suspension or solution in water. The rocks of the latter class are found always arranged in layers or beds, and hence called stratified ; while the crystalline rocks may occur either in beds more or less apparent, or without any signs of a bedded structure, when they may be termed massive. Stratified rocks, i. e., those having a layered structure, are much the most common, and exam- ples of them may be studied in most localities where the rocks appear above the covering soil. Sedimentary Rocks. The sedimentary rocks are of three general kinds : (i) those formed from the worn frag- ments of pre-existing rocks, which may be called mechani- cal sediments, e. g., sandstones and shales ; (2) those de- posited from solution in water, or chemical sediments, as some limestones, many quartz rocks, and probably most beds of iron-ore ; and (3) organic sediments, those formed from the worn and subsequently consolidated results of vegetable and animal growth, as most limestones and coal- beds. Beds of the second class are formed of welded and interlocked crystals, and have a degree of solidity equal to that of the composing mineral. Beds of the two remain- ing classes, though sometimes found as mere incoherent or slightly cohering masses like sand, gravel, and chalk, have more generally been consolidated by various means to a greater or less degree of hardness. The following are the chief means of consolidation : Some rocks seem to be consolidated solely by the great and long-continued pressure of the overlying beds, caus- ing the particles to adhere to each other, as is the case with many shales. When, as is often the case in sand- stones, some finely-disseminated clay is present, making the contact among the sand-particles more complete, pressure gives the rock a greater degree of firmness. The presence of this clay can be detected by subsiding the finely-pow- dered rock in water, when the clay will remain long sus- pended, making the water turbid. A common means of I0 APPLIED GEOLOGY. consolidation is calcite, which has been introduced in solu- tion, as in all sedimentary limestones and some sandstones. Its presence as a consolidating ingredient in rocks other than limestones can be readily detected by its efferves- cence with dilute acids. Silica consolidates mjfciy sand- stones and conglomerates to a very high degree of hard- ness ; and iron oxide is also a frequent means of consoli- dation, giving to rocks a red or yellow color. When red or yellow sandstones are pulverized and heated for a little time in strong hydrochloric acid, the cementing iron is dissolved, giving a deep yellow solution, and colorless grains of quartz remain. Crystalline Rocks. The crystalline rocks, other than the relatively small amounts of chemical sediments, are made up usually of imperfect crystals, sometimes of one mineral, but more commonly of two or more, welded, interlocked, or felted together to a mass as firm at least as the softest abundant constituent, unless a prevailing direc- tion of some readily cleavable mineral like mica, talc, or hornblende, may dispose the rock to split more easily in certain directions. Some of these crystalline rocks have a more or less observable bedded character, often with foliation or schistose structure, and are generally believed to have once been ordinary sedimentary rocks, which, hav- ing been rendered somewhat plastic by heated water under enormous pressure, have crystallized in their present form. Hence they are termed metamorphic rocks, i. e., rocks which have been changed from their original condition. Other crystalline rocks show no signs of bedding what- ever, their condition being probably due to a softening or fusion so complete as to have obliterated all traces of bed- ding, if they ever existed. In this condition they have often been thrust in among or through other rocks, emerg- ing frequently at the surface. Where the subsequent cool- ing has proceeded at a very slow rate, and usually at very considerable depths, the resulting texture is coarsely and ROCK-FORMING MINERALS. II obviously crystalline ; where the rate of cooling has been relatively rapid, the crystalline texture may be so fine and close as not to be apparent to the unaided eye, or the text- ure may in some cases be partly or entirely glass-like, i. e., vitreous. Rocks of this kind are termed igneous or erup- tive, and those obviously crystalline are also frequently called Plutonic rocks, a term which implies the opinion that they were consolidated at great depths, and that our present opportunities for becoming acquainted with them are due to very great subsequent changes in the earth, in consequence of which they have become surface-rocks. To give a connected view of what has just been said, a tabulated summary of rocks in general is here presented, classified according to origin, with their structure as rock- masses and the usual condition of their materials : Classification on Origin. Structure. Condition of Materials. C Mechanical, Sedimentary \ Chemical, I Organic. Metamorphic. Igneous. Stratified. Stratified. Massive. Fragmentary, sometimes crystalline. Crystalline. Crystalline or vitreous. Means of Consolidation : 1. Pressure. 2. Clay and pressure. 3. Silica. 4. Calcite. 5. Iron oxides. 6. Welding, interlocking, or felting of crystals. Structure and Texture of Rocks. By the struct- ure of rocks is meant those characters which distinguish them as rock-masses, and which are usually best displayed on the large scale. Most important of structural characters is stratifica- tion, which is the arrangement of rock-masses in tolerably 12 APPLIED GEOLOGY. parallel sheets or layers, varying in thickness from the fraction of an inch to several feet, and separating readily from each other. Layers of the same kind of rock lying together form a stratum, and alternations of different kinds of rock produce strata (plural of stratum). A stratum of some valuable material, e. g., coal, is frequently termed a seam or bed. Stratified rocks were undoubtedly formed in all usual cases by deposition of their materials from water, in precisely the same way that successive layers of mud and sand are being deposited now in seas, lakes, and rivers ; and it is altogether probable that the division into layers is due to some considerable pause in the act of depo- sition, whereby the lower layer became somewhat com- pacted before the succeeding one was deposited ; while the succession of strata marks changes in the conditions of deposit by which materials of different kinds came to be laid down. The massive structure is contradistinguished from the stratified, and belongs to igneous rocks, or to those which have been so greatly changed from their original condi- tion as to have lost all signs of bedding. The term mass- ive is also used sometimes in contradistinction from lami- nation. Lamination is where rocks reveal the thin succes- sive layers of which they are made up, either by some slight differences of color or texture in the several layers, or by splitting more readily on certain planes, usually par- allel to the bedding. This structural character is a com- mon one in sandstones, especially where they are argilla- ceous, and is occasionally seen in limestones. An excess of lamination in highly argillaceous rocks, causing them to split into thin, irregular, fragile slabs, constitutes the shaly structure. Foliation, or the schistose structure, is a character of metamorphic crystalline rocks, analogous to lamination in the sedimentary series, and is due to the arrangement of the crystalline constituents in more or less definite planes, ROCK-FORMING MINERALS. which often, no doubt, if not always, correspond nal planes of lamination, since these are likely to be the planes of easiest penetration and circulation for fluids. The slaty structure is one which belongs to argillaceous rocks that have been doubled up into folds, and so changed by intense pressure as to develop a tendency to cleave into hard, even slabs, in a direction at right angles to the pressure, and corresponding with the direction of the folds. The planes of cleavage rarely correspond with the original planes of lamination, though they may occasion- ally do so. Joints are divisional planes in rocks, usually but not always nearly vertical, which divide the rocks of many regions into blocks that separate somewhat readily at these planes. These blocks, in regions of jointed structure, vary in width from an inch, or even less, to many feet, the main joints forming the faces of the cliffs and the back walls of the quarries ; and where, as is frequently the case, there are two series of joints, cutting each other at nearly right angles, the weathered faces of the cliffs pre- sent a singular resemblance to regular piles of masonry. This structure is not confined to any one of the great classes of rocks that have been named, but may be found in all of them, occasionally even giving to massive rocks a false appearance of bedding. Practically considered, while the jointed structure greatly facilitates the operation of the quarryman, it also strictly limits the dimensions of the blocks that can be obtained. The columnar structure often seen in volcanic rocks, especially the basalts, seems to be a variety of the jointed structure, in which, by the intersection of several jointing planes, the rock is divided into a series of rude pillars which are at right angles to the original cooling surfaces of the rock. The concretionary structure is one which is displayed in some rocks by the collection of some mineral, notably I 4 APPLIED GEOLOGY. silica, calcite, pyrite, or iron carbonate, into spherical, spheroidal, or irregular forms, e. g., the flinty nodules in chalk and limestone, the silicious balls in some sandstones, the calcareous and pyritous masses in some clay rocks, and the kidney-shaped masses of clay iron-stone. By the texture of rocks is meant the internal arrange- ment of their constituents. The granular texture is dis- played by rocks which are composed of worn grains or irregular crystals. These grains or crystals may vary from those of considerable size, giving a coarse-grained texture, to very minute ones, giving rise to the compact texture, as in many sedimentary limestones, and to the aphanitic or crypto-crystallim texture, as in some igneous rocks in which the really crystalline texture is revealed only by the microscope. The term granitoid is applied to thoroughly crystalline rocks whose crystals are of approximately equal size, as in granite ; while the term porphyritic describes those which contain distinct crystals, notably of feldspar, im- bedded usually in a very fine-grained base or ground-mass. The vitreous or glassy texture resembles artificial glass, and is found only in some eruptive rocks. The terms porous, fibrous, earthy, and vesicular, as applied to text- ure, hardly need explanation. Some eruptive rocks, origi- nally vesicular, have had their rounded cavities subse- quently filled by various minerals, giving rise to a vari- ety of texture called the amygdaloidal, from the resem- blance of many of the filled spaces to the almond, Latin amygdala. CHAPTER II. DESCRIPTION OF ROCKS. Mechanical Sediments. Sand is an unconsoli- dated mass of fine, worn grains of the harder minerals and crystalline rocks, in which quartz usually plays by far the largest and often the almost exclusive part, since it is the hardest and most enduring of the ordinary rock-forming minerals. Where the worn fragments range from the size of a pea to that of an egg, it is called gravel, still coarser gravel being sometimes termed shingle. Most sand con- tains particles of magnetic iron- ore, which can be de- tected by their clinging to a magnet. Sand, consolidated in any way, forms sandstone. In some sandstones pressure seems to be the sole consolidating agent, though doubtless a minute amount of silica cements the points of contact of the granules, producing a porous and often friable rock. The presence of a small amount of clay, forming a film which coats the grains of sand, or of a larger amount partially imbedding them, makes a firmer rock, often highly laminated an argillaceous sand- stone. Iron oxide, usually mingled more or less with clay, is a somewhat common cement, forming a red or yellow sandstone. When silica is the cementing material filling the spaces among the grains, it makes an exceedingly hard rock called a silicious sandstone ; or where it oc- curs, as it usually does, among metamorphic rocks, it is called quartzite. Calcite is not often found as the chief l6 APPLIED GEOLOGY. cementing material of sandstones ; but when it is present, it is readily recognized by its effervescence with acids. A sandstone which works equally well in all directions, without a tendency to split, is often called freestone a name which is also sometimes applied to other rocks of like character. A thin-bedded laminated sandstone is a flag-stone. Coarse, rough-textured sandstones are often called grits a term, however, not very definitely used. A conglomerate, sometimes called pudding-stone, is formed of rounded pebbles, from the size of a pea to a foot or more in diameter, consolidated in any way, and with the spaces filled usually with cemented sand. Where the pebbles, instead of being rounded, are angular, the rock is called a breccia. A shale is a highly laminated argillaceous rock, con- solidated often by mere pressure, and so returning to mud when exposed for some time to the weather. Where it contains a considerable proportion of sand, it becomes an arenaceous shale, and so may graduate into an argillaceous sandstone. Chemical Sediments. These rocks deposited from solution in water by evaporation or cooling of the water, or by dissipation of the chemical agent that held them dissolved, although forming no great proportional amount of the rocks of the earth, still furnish several substances of great economical importance. Calcareous deposits from water in which lime is held in solution by carbonic acid, when porous and friable, often incrusting twigs and leaves, are called calcareous tufa ; when forming pendants from the roofs of caverns, and incrustations on their floors, are called stalactites and stalagmites ; when forming compact beds, are named trav- ertine, which, when banded with various colors, becomes onyx marble ; and when composed largely of rounded concretionary grains, little larger than a mustard-seed, are termed oolites. DESCRIPTION OF ROCKS. ij Gypsum is a sulphate of lime, which, when crystalline, is much softer than calcite, being easily scratched by the fin- ger-nail, and cleaves easily in one direction, forming trans- parent, inelastic plates which quickly whiten when held in a flame. It forms considerable beds, or lenticular masses, which in some cases have been deposited by evaporation of the water that held the gypsum dissolved, and in others have been formed by a change of ordinary lime- stones through infiltration of sulphuric acid from sulphu- retted springs. In the latter case, the gypsum forms a soft, earthy rock, usually of a gray color. When ground fine and heated, gypsum gives off much water, and leaves a powder that will set with water. Salt occurs in beds or masses, sometimes of enormous thickness, which have doubtless been formed by the evapo- ration of inclosed bodies of sea-water. It is usually asso- ciated with beds of gypsum and of anhydrite a mineral like gypsum, but containing no water. The waters of some springs, especially in regions of volcanic disturbance, deposit silica, sometimes on the sur- face as hard, porous incrustations, called silicious sinter, as about hot springs and geysers; sometimes filling fissures in other rocks, forming common vein-stones that are con- nected with many valuable ore-deposits. Iron-ores, which occur usually as beds associated with various other rocks, doubtless owe their origin to chemical deposition. Siderite, i. e., iron carbonate or spathic iron, occurs crystallized in the same form and with the same cleavage as calcite, but is somewhat harder and of con- siderably greater comparative weight specific gravity besides being of a brownish color ; also, when heated in a test-tube, it turns black and becomes magnetic. When it occurs in kidney-shaped concretions, it is termed kid- ney-ore or spherosiderite j when mixed with clay, it is clay iron-stone ; and when forming a black, bituminous, shaly mass, it is called black-band. 1 8 APPLIED GEOLOGY. Limonite is an iron oxide containing some water, and forms masses of a fibrous or earthy texture, and of a color varying from brown to black; but its powder and the streak which it makes on an unglazed porcelain surface are of a dull yellow color. When heated in a test-tube, it yields steam which condenses in the upper part of the tube, and becomes magnetic, though not so before heating. Hematite has the composition of limonite, but without water, and forms beds of a red, steel-gray, or black color, and of a texture varying from earthy or compact, to those mica-like, or to thin, tabular, very brilliant crystals. The streak and powder are of a dark cherry-red. Magnetite is black, has a black streak and powder, and attracts the magnet strongly. It forms a crystalline, granular, or sometimes compact rock, of great weight, and is easily known by its magnetism and its black powder. The last three iron-ores form very heavy rocks, and, when crystalline or compact, are of about the hardness of feld- spar, being scratched with some difficulty by a knife. Organic Sediments. These rocks, formed of the hard parts of very minute organisms, or of the remains of any organic growth ground up or macerated, and after- ward consolidated either by pressure or by partial solu- tion of their own substance, embrace all the coal-beds of the world, and all extensive deposits of limestone, besides those peculiar silicious deposits called tripoli. The limestones, usually composed mainly of calcite, form beds of a drab, gray or blue color, sometimes red or black, and of a texture varying from earthy to sub- crystalline or compact, which last are the most common. These rocks almost always contain a greater or less quan- tity of some impurity iron, giving them a red color ; car- bonaceous matter, making them dark ; or clay and silica, which are often found in such amounts that when the rock is burned for lime it will not slack with water, but when ground and mixed into mortar will set under water to a DESCRIPTION OF ROCKS. ig mass of great hardness, and is hence called hydraulic lime. Many limestones, besides calcite, contain also a consider- able proportion of dolomite, or are made up almost wholly of dolomite. Such are called magnesian limestones or dolomites. Chalk is a very soft, earthy limestone, usually white, made up of the calcareous skeletons of very minute organisms. The limestones, when burned properly, lose their carbonic acid and become quicklime, which, on ap- plication of water, falls into a powder, i. e., slakes, with the evolution of considerable heat, which is greater in the case of the calcitic than in that of the dolomitic limes. Hence the former are called " hot limes," while the mag- nesian are termed " cool limes." The limestones that are found associated with crystal- line rocks have been metamorphosed by the action of heat, are of prevailing white or light colors, though often clouded or tinted by impurities, and are of a crystalline granular texture ; sometimes of very fine grain, as in the best stat- uary and architectural marbles, sometimes coarse-grained. Any limestone which is susceptible of a fine polish is usu- ally called a marble^ the crystalline limestones furnishing probably the largest proportion of these. The crystalline limestones frequently contain certain disseminated miner- als, forming mixtures, some of which are prized for orna- mental purposes, like the verd-antique marble or ophiolite formed by the intermingling of calcite and serpentine. Mineral coals are formed of former vegetable growths which have been more or less macerated, subjected to a peculiar, partially smothered decomposition, and consoli- dated by the pressure of the superincumbent rocks. A rude but convenient commercial classification of them is made according to the amount of volatile combustible mat- ter that they contain. Those that contain little volatile matter, and hence are hard and lustrous, kindling with dif- ficulty, and burning with but slight blue flame, no smoke, and intense heat, are called anthracites. Semi-bituminous 20 APPLIED GEOLOGY. coals are those that contain from ten to about eighteen or twenty per cent of volatile matter, and bituminous coals have a still higher percentage than this. Both these latter kinds kindle easily, and burn with a yellow flame and much smoke. Some of these coals soften while burning, and the pieces fuse together into a mass, which needs to be broken up to admit of ready burning these are called caking coals ; others do not soften while burning such are the non-caking coals, named, from various qualities, splint or block coal, cherry coal, and cannel. The coals will be more fully considered in another place, and are mentioned here merely in their place as organic sedi- ments. Metamorphic or Stratified Crystalline Rocks. A brief description only can here be given of the most widely disseminated and important species of metamor- phic as also of massive crystalline rocks. Many of the varieties to which distinctive names are given by litholo- gists are not frequently met with, and are of little practical importance ; it will not be expedient, therefore, to burden the attention of the student with them in a treatise like this. As has already been said, the metamorphic rocks are those which are thought once to have been ordinary sedi- mentary rocks, and to owe their present crystalline con- dition to a more or less profound change caused by the agency of heat and moisture. They still show their origi- nal bedded structure with more or less distinctness, but the beds are invariably much disturbed, thrown out of their original nearly horizontal position, bent and folded, testifying to the action of enormous mechanical forces. The most widely-diffused and most profoundly changed of these is gneiss, a foliated, crystalline compound of quartz, feldspar usually orthoclase and mica, the foliated ar- rangement of the minerals, sometimes very perfect, giving the rock a highly schistose structure, sometimes so indis- DESCRIPTION OF ROCKS. 2 I tinct as to make the mass difficult to distinguish from gran- ite, which has the same composition, and which differs from gneiss only in the absence of all traces of bedding. Indeed, some masses of gneiss are believed by careful observers to be of eiuptive origin, while it can hardly be doubted that some granite is only the extreme stage of metamorphism of rocks which once were stratified. Where hornblende replaces the mica of gneiss in whole or in part, we have hornblendic or syenitic gneiss. Mica schist is a highly foliated rock composed of quartz and mica, the mica often highly prominent and enveloping the quartz, which is in irregular plates, knots, and seams ; while in other cases the quartz predominates, the mica being present in only sufficient amount to give the mass a schistose structure. Where the mica almost wholly disap- pears, the rock still retaining the schistose structure, it is sometimes called quartz schist, which is therefore a rock consisting almost wholly of quartz, and showing a tendency to split into parallel layers. A rock composed of grains of quartz, sometimes of considerable size, bound together by a silicious cement into a mass of flinty hardness, is called quartzite. It is a sandstone, metamorphosed by the infiltration of a silicious solution, or by the softening of the outlines of its grains, into a rock breaking with the characteristic glassy fracture of quartz, while its granular texture and bedded structure testify to its original condition. A variety of mica schist, in which the quartz is usually in small amount, and the mica is a hydrous variety, i. e., containing water, is called by Dana hydro - mica schist. These schists have usually a grayish or greenish color, a pearly luster, and a greasy feel like talc, whence they are commonly called talcose schist. A true talcose schist is not a common rock. It is a foliated aggregate of scaly talc, with small amounts of quartz or feldspar, of whitish to greenish colors, and unctuous to the touch. 22 APPLIED GEOLOGY. Chlorite schist is a foliated rock composed of chlorite and some quartz, with occasionally small amounts of other minerals. Its usual color is a dark green. It is commonly a soft rock, but sometimes the quartz, which usually occurs in scattered leaves or bunches, so interpenetrates and inter- locks the entire mass as to give it a considerable degree of hardness. Hornblende schist is a black or dark-green foliated rock, composed of dominant granular or fibrous horn- blende, having a foliated arrangement, with minor quan- tities of quartz or feldspar. When the foliated structure is wanting, a rock of similar composition would be called amphibolite or hornblende rock. Serpentine is a dark-green or reddish-brown rock, of compact texture and greasy feel. It is so soft as easily to be scratched by a knife. The mineral serpentine of which it is composed is probably, in all cases, a product of the metamorphism of other minerals or rocks. It usually occurs in irregular beds among metamorphic "schists. The Igneous or Massive Crystalline Rocks. Most important of these is granite, already alluded to un- der gneiss. It is a compound of quartz, feldspar (mostly orthoclase), and mica ; feldspar is usually the predominant ingredient, of an impure white or reddish color, while mica is the least prominent. The quartz varies from white to smoky-brown in color, and may readily be distinguished by its fracture, hardness, and luster. The texture of gran- ite varies from very fine-grained to one made up of crys- tals of considerable size, the crystals being interlocked, or welded together at their surfaces, so as to form a mass of great firmness. The mica in granite may be partially or entirely replaced by hornblende, giving rise to a usually darker-colored granite, called syenitic granite. Where the quartz disappears from a granitic rock it is called minette or mica trap ; where feldspar dies out we have greisen a rock interesting only from its association with tin-ores ; DESCRIPTION OF ROCKS. 23 while the disappearance of mica gives rise to a rock called aplite and pegmatite ; or, if of foliated structure, granulite. Felsite is an intimate mixture of feldspar with some quartz, of an exceedingly fine-grained i. e., aphanitic or flinty texture, and of a variety of colors, from yellowish to nearly black. It greatly resembles some quartz rocks, from which it may be distinguished by its slightly inferior hardness, its hardness being that of feldspar, and by the fact that in thin splinters it can be fused like feldspar be- fore the blow-pipe, while quartz can not. Syenite is a granular crystalline rock, composed of orthoclase and hornblende, the orthoclase predominating, and, from its usually being of a reddish color, giving the rock a prevailing red tint. Sometimes, however, feldspar of a lighter color occurs, yielding grayish syenites. Trachyte is a grayish, or sometimes reddish or brown- ish, rough-textured compound, in which feldspar predomi- nates, often showing glassy crystals, united with some hornblende or augite and dark mica, while magnetite is rarely absent. A trachytic rock of highly silicious charac- ter, and often displaying quartz-granules, but rarely con- taining hornblende, with a matrix usually very compact, or even enamel-like, is called rhyolite or liparite. Diorite is a granular, dark-green, tough rock, composed of oligoclase feldspar and hornblende, with usually some magnetite. It differs from syenite in its kind of feldspar, in its usual range of color, and in being usually of finer texture. Dolerite is a granular rock of gray to black colors, composed of labradorite feldspar and augite, with usually some magnetite. When it is exceedingly fine-grained and compact, it is called basalt. Basalt often contains grains of a bottle-green mineral called chrysolite. When dolerite contains chlorite, giving it a greenish color, it is often called diabase. The rocks described above are by far the most widely 24 APPLIED GEOLOGY. distributed, and therefore most commonly met with ; and with them have been named a few of less frequent oc- currence, as exhibiting interesting variations of composi- tion or structure. Key for Approximate Determination of Rocks.* The following brief key for rock determination, based on (i) texture, (2) hardness, and (3) structure and compo- sition, may prove useful to the beginner : 1. Examine freshly broken, angular fragments with a lens. A. Components not perceptible. See 2. B. Components perceptible. See 4. 2. Test hardness of i A with a knife : a. H i to 3^, easily scratched with a knife sedi- mentary or decomposed : a' Very soft, earthy aspect, plastic when wet, Clay, b' Harder, in thin, irregular, fragile laminae, Shale. c' Cleaving to thin firm plates, Slate. d' H 3, effervescing strongly with cold acid, Limestone. e' H 3 to 4, effervescing sluggishly with cold acid, rapidly with hot, Magnesian Limestone. f H 2.5 to 3.5, usually green, somewhat soapy to the touch, not effervescing, Serpentine. b. H 5 to 6, heavy, becomes black and magnetic by heat: g' Streak and powder yellowish brown, luster earthy to silky, Limonite. h' Streak and powder red, luster earthy to me- tallic, may be perceptibly crystalline, Hematite. c. i' Not scratched by knife, glassy luster, con- choid fracture, Quartz Rock. j' H 5 to 6, black or gray, often holds green grains of olivine, Basalt. k' H 6, fusible in thin splinters. See 3, or pos- sibly, Felsite. * The idea of this key was suggested by Geikie's excellent " Text- Book of Geology." DESCRIPTION OF ROCKS. 2 $ 3. 2 k' may be glassy, when if T Of uniform texture, dark color, translucent on edges, of glassy aspect, Obsidian, m' Of pitchy aspect, various colors, slighty trans- lucent, Pitchstone. n' Of rounded grains, of frequent concentric structure, in enamel matrix, Perlite. n" Of enamel-like matrix, often holding grains of mineral, especially quartz, Rhyolite. NOTE. The exact determination of hard, very fine-grained rocks usually requires microscopic and chemical examination. 4. Test hardness of I B. o' Soft, gray to white, crystalline to earthy, heated yields vapor and whitens, Gypsum. p' Easily scratched, effervesces readily with acid, Limestone. q' Slightly harder than p', effervesces sluggishly with acid unless hot, Dolomite. r' H about 4, brown, effervesces with hot HC1, giving yellow solution, Siderite, etc. s' Of hard, rounded grains, chiefly quartz, ce- ment various, Sandstone. t' Of hard, rounded, or angular pebbles, Conglomerate or Breccia. u' Of quartz-grains cemented by silica, fracture usually glassy, Quartzite. v' H 6, color and streak black, heavy, magnetic, Magnetite. w' H variable, schistose, with glistening surface, of mica and quartz, Mica Schist. x' Soft, color white to light green, soapy feel, schistose or massive, Talc. y' Easily scratched, dark green, slightly soapy, schistose, Chlorite Schist or Hydro-Mica Schist. z' Hard, greenish black, rather heavy, schistose, chiefly hornblende, Hornblende Schist. a" Hard, chiefly quartz, but schistose from a lit- tle mica, Quartz Schist. b" Scratched with difficulty, of interlocked or welded crystals. See 5. 26 APPLIED GEOLOGY. 5. Rocks of 4 b" alternate with other crystalline rocks or show some foliated arrangement of their crystalline constituents metamorphic. See 6. Rocks of 4 b" do not alternate, are massive, send branches into other rocks igneous. See 7. 6. Composed of the following minerals, more or less distinctly foliated : c" Quartz, feldspar, and some mica, Gneiss, d" Quartz, feldspar, and hornblende (mica), Syenitic or Hornblenclic Gneiss. e" Quartz, feldspar, and chlorite or talc, Protogine Gneiss, f" Quartz and orthoclase, often garnets, Granulite. 7. Rocks eruptive or intrusive, composed of g" Quartz, feldspar, and mica, Granite, h" Quartz, feldspar, and hornblende (mica), Syenitic Granite. i" Orthoclase and hornblende, often red, Syenite, j" Oligoclase and hornblende, dark green or black, Diorite. k" Labradorite and augite, gray to black, Dolerite. 1" Feldspar base and clear crystals of orthoclase, rough to the feel, Trachyte. m" Aphanitic base holding crystals of feldspar or quartz, Porphyry or Quartz Porphyry. This key is intended only as a convenient aid to the student in finding the probable variety of rock with which he has to deal. His specimens should with this aid be carefully compared with descriptions in works on geology or lithology, and much critical study and comparison will be necessary to avoid the probability of error. It is well to be slow and painstaking at first, that one may be rapid later. For a wider study of rocks, the student is referred to the following works : Von Cotta, " Rocks Classified and Described," translated by Lawrence ; Geikie, " Text-Book of Geology," Book II ; Dana, " Manual of Mineralogy and Lithology." CHAPTER III. ARRANGEMENT OF ROCK-MASSES. ROCK-MASSES may be built up into the structure of the earth's crust in any one of three ways : First, and far the most widely diffused, as stratified rocks, or those occurring in nearly parallel beds of various thickness ; second, as great unstratified masses like granite, exhibiting no signs of true bedded structure ; and, third, as included or vein-form sheets, or masses of rock-material, differing from the inclos- ing rocks in composition or in structure, or in both respects, and occupying what were once apparently open fissures or cavities in these rocks. Stratified Rocks. The most striking character that marks the stratified rocks, and that from which they de- rive their name, is their occurrence in parallel sheets or strata piled one upon another to form masses often of vast thickness. These beds, when not metamorphic, usually contain indubitable evidences that they have been gradu- ally and successively deposited in water, and mostly in the waters of the sea, in a manner exactly analogous to that in which beds of mud, sand, gravel, peat, and limestone are being accumulated at the present day. Most convincing of these evidences of formation in water is the frequent occurrence in the bedded rocks, at the most various depths, of the remains of animals, most commonly marine, and occasionally of plants, which often retain their struct- ural characters in a high degree of perfection. Such 28 APPLIED GEOLOGY. traces of the former plants and animals of the globe are called fossils ; and they not only give us some glimpses of the life-history of the usually remote periods during which the rock-materials were accumulated, but they also furnish valuable evidence of the conditions under which they were formed, whether in marshes, or in water, marine, brackish or fresh, clear or turbid, and at greater or less depths. It is obvious that of the beds thus superimposed on each other the lower will have been the earlier formed, while the overlying beds will be successively younger. Thus in stratified rocks whose normal position is obvious, or can by any means be made out, superposition is re- garded as a reliable evidence of relative age. The sev- eral beds in any series of stratified rocks are usually sep- arable from each other with little difficulty at their plane of junction, probably indicating that the lower bed had been somewhat consolidated before the materials of the succeeding one were deposited. A character peculiar to stratified rocks, because it results from successive depo- sition, is lamination, as already defined. It belongs more especially to the finer-grained sediments, like shales, fine- grained and somewhat argillaceous sandstones, and to some argillaceous limestones. Commonly the planes of lamination are parallel, or nearly so, tc> those of bedding ; but in some rocks, especially sandstones, they may be di- agonal to the bedding, giving rise to what is called false bedding or current bedding. Usually, but not invariably, rocks split more easily on the lamination than in other di- rections ; and such rocks, when used in structures, should always be laid with their edges to the weather, as they will be more durable in that position. When a stratified rock becomes metamorphic, lamina- tion gives place to foliation, the planes of mineral ar- rangement, in most cases, probably following the original planes of deposition ; or slaty cleavage takes the place of the original tendency to split on lamination planes, while ARRANGEMENT OF ROCK-MASSES. 29 the laminae may still frequently be displayed in bands of different shades of color. Position of Strata and Definition of Terms. The original position of the beds of stratified rocks must have been nearly horizontal ; but, as the result of the action of forces, for a discussion of which the student should refer to general treatises on geology, the strata in all metamorphic regions, and in many localities where the rocks have undergone no noteworthy transformation, are no longer horizontal, but are bent, doubled, and crumpled on the large scale, and often broken, with the fractured ends slipped past each other. The disturbances of strata, and the changes to which they have been subjected, give rise to the use of several terms, the meaning of which it is important to understand. The dip of strata is the amount of their departure from a horizontal plane. Where the dip is considerable, it is conveniently meas- ured by means of an instrument called a clinometer, a convenient form of which is that of a foot-rule, two inches wide, folding to six inches, in one face of which is hung a delicate pendulum, swinging on the center of a graduated semicircle. (Fig. i.) This instrument held before the eye, and its lower FIG. i. edge made to agree in direction with the slope of the in- clined rocks or, better, set on its edge on a slip of board laid upon the rocks and shifted carefully about until the pendulum shows the greatest possible inclination will give the dip of the strata with a good degree of accuracy. 30 APPLIED GEOLOGY. Where, however, the dip of the rocks is slight, as in much of New York, in western Pennsylvania, and in several Western States, it is found by ascertaining the height of some persistent stratum above a fixed plane like the sea- level, at several points where it appears in natural ex- posures, or is revealed in borings or excavations. The mutual distances of these points being found, the dip per mile and the direction of the dip can be ascertained. The amount and direction of dip are points of great practical as well as scientific importance, and should be carefully observed. The strike of rocks is a direction at right angles with their dip, so that when the second is given the first may be known. For example : the dip of the rocks in a large part of New York is south, inclining a little west. Hence, the strike or the direction in which the rocks range across the State is nearly west ; and it would be the same if the dip were in an exactly opposite direction, or to the north. A monoclinal fold is one in which the strata dip in but a single direction. A common case in our Western Territories is that which is sketched in the following dia- gram, where horizontal strata are sharply folded up into a somewhat steep ridge, and then resume their original nearly horizontal position : An anticlinal fold is one in which the strata dip away from an axis, forming an arch, as in Fig. 3, where a repre- sents the axis of the fold from which the strata dip each way. A common occurrence with such folds is that the strata are broken at the axis, when the agencies of wear either plane down the fold to a level, its presence being ARRANGEMENT OF ROCK-MASSES. 31 indicated only by the opposite dip of the strata ; or, where hard beds occupied the surface, the strata may be cut out FIG. 3. Anticlinal. along the axis, as indicated by the dotted line in Fig. 3, leaving two more or less marked ridges. A synclinal fold is where the strata dip from opposite directions toward an axis, forming a trough, as in Fig. 4. FIG. 4. Synclinal. In greatly disturbed regions, these folds are often so thickly set as to give the strata a crumpled appearance, visible even in hand specimens. Frequently, also, not only in folded regions, but also in those in which the strata retain a nearly horizontal po- sition, the strata are found to have been broken across, and the beds on one side of the break to have been dropped below those on the other, so that the two halves of the same bed no longer occupy the same plane. Such an occurrence is called a fault, and the faulted beds are said to be thrown. Thus we speak of the downthrow and the upthrow. The plane of fracture, though sometimes 32 APPLIED GEOLOGY. vertical, is usually inclined more or less from the vertical. The amount of this inclination from the vertical is called the hade of the fault. Vertical faults, therefore, have no hade. In the great majority of cases, " faults hade in the direction of the downthrow," so that the upper surface of the beds that have slid down makes an acute angle with the plane of fault. (See Fig. 5, in which a and b are planes of fault, of which b has no hade, while a h hades at FIG. 5. Faults. an angle of 50 with the vertical.) The beds c d e f have it may be seen, slid downward along the planes of fault so that the upper surface of the downthrown beds g makes an acute angle with the plane a h. Such a fault is called a normal fault, while the much less frequent case in which the downthrow side makes an obtuse angle with the plane of fault is called a reverse fault. Hence, in mining faulted beds, like those of coal or iron, in the absence of other indications, the continuation of the bed is to be sought down the fault-plane when it slopes from the workings, and up it when it slopes toward the workings, as may be seen from the left side of Fig. 5. The walls of fault-fis- sures, when they consist of firm rocks, are often smoothed or glazed, and striated in the direction of movement. Such glazed surfaces are called slickensides. Where strata are laid open to observation by the re- moval of loose materials, the point of appearance is called their outcrop or basset. Frequent places of outcrop are along the shores of bodies of water, or in the banks of deep-cut streams, or on the eroded sides and summits of hills and mountains. ARRANGEMENT OF ROCK-MASSES. 33 Conformable strata are those which succeed each other in the regular and parallel order of superposition. Unconformable strata are those in which (i) the overlying beds rest against the upturned and eroded sur- face of the lower beds, not agreeing with them in dip, as FIG. 6. Unconformity by Upthrow. in Fig. 6 ; and (2) the overlying beds rest upon the much- eroded surface of the underlying ones, agreeing with them in dip, as in Fig. 7. In either case, " the base of the one set of beds rests in FIG. 7. Unconformity by Erosion. different places on different parts of the other set of beds." The first kind of unconformability is the more commonly observed, and doubtless always includes what is essential in the second, viz., the erosion or denudation of the lower beds, before the deposition of the upper ones. Uncon- formability testifies unmistakably to a considerable lapse of time, during which important physical changes occurred, including notable changes of level, as intervening between the periods of deposition of the two sets of beds. The term denudation is applied to the waste and 34 APPLIED GEOLOGY. wear df/#cks by weathering and by the agencies of water atmosphere. (See Fig. 3 for illustration.) Denu- dation is a phenomenon which is going on constantly be- fore our eyes, not more obviously in the tremendous rend- ing and grinding action of the waves than in the silent activity of rivers, brooks, and rills, whose turbidity testifies that they are tearing down and carrying away to valley or ocean the materials of the uplands. The amount of denu- dation in all elevated parts of the earth is enormous, and to it is due almost wholly the present aspect of the land- surface of the globe. Unstratified Rocks. The structure of these rocks is massive, and, as their name implies, they show no signs of bedding or of successive accumulation, their only divisional planes, where they occur, being of a jointed character. Though it can hardly be doubted that unstrati- fied rocks form the foundation on which all stratified rocks rest, yet they are of far less frequent occurrence as surface appearances than those of the stratified series ; and it is probable that our opportunities for knowing them are due in many cases to great uplifts and enormous denu- dations. They owe their origin in all cases, perhaps, to igneous agencies or to a metamorphism pushed to such an extreme as to become essentially igneous. They occur, sometimes as great bosses, like granite, surrounded by other rocks into which they frequently send out arms ; sometimes as the central portions of great mountain-chains, as in parts of the Sierra Nevadas and the Alps ; some- times as vast sheets of enormous thickness, as in portions of our Western plains ; sometimes as great cake - like masses, called laccolites, thrust into the midst of stratified rocks and bulging them up into dome-like eminences, as in the Henry Mountains of Utah ; and sometimes as great interbedded sheets overlaid by beds deposited apparently since they were poured out as lavas, as in the so-called melaphyre rocks of northern Michigan, whose amygda- ARRANGEMENT OF ROCK-MASS, loidal portions furnish in some cases rich native copper. Included or Vein-like Rocks. The masses here called included fill what, in the great majority of cases if not in all, appear once to have been open fissures or cavi- ties in the inclosing rocks. In some cases the filling mate- rials have evidently been introduced in a state of igneous fusion, such included masses being called dikes. In other cases the fissure or cavity has apparently been filled from solution in water or by sublimation, such inclusions, where they fill fissures of greater or less extent, being called veins, and, where they fill irregular cavities, being called by the German name Stbcke, or stocks. Dikes are usually nearly vertical in position, and have a more regular and wall-like form than veins, whence the name dike, signifying a wall. Indeed, irregular and branching fissures filled with material apparently injected in a plastic state are usually called veins rather than dikes, as in the case of granite veins. The fissures filled by dikes not unfrequently follow pretty closely for consider- able distances the bedding planes of stratified rocks, giv- ing to such dikes the appearance of beds. The rocks which form the walls of dikes have usually been metamor- phosed to varying distances by the heat, common changes being consolidation, baking, and crystallization. The ma- terial of dikes is frequently fissured by joints, which pass often into a columnar structure, the columns being per- pendicular to the walls. Dolerite with its varieties, ba- salt and diabase, is a common dike-forming rock, though some other varieties of igneous rocks are occasionally found forming dikes. Some veins, usually in granite, gneiss, or the crystal- line schists, are filled with material similar to that of the surrounding rock, though in a somewhat different crystal- line state, often coarser ; and their composing minerals were apparently separated from the inclosing rock to fill 36 APPLIED GEOLOGY. rents of small extent during the process of consolidation. Such are called veins of segregation. True veins, called frequently mineral veins, fill what have once been open fissures of variable extent, both ver- tically and horizontally, some veins cutting the rocks to unknown depths, while others are quite shallow ; some be- ing traceable for miles, while others die out in a few rods. The materials with which they are filled usually differ notably from the inclosing or country rock. iThey are usually of a crystalline granular texture, though often earthy from decomposition or other causes, and have often a banded structure of different minerals arranged parallel to the walls. They are frequently the repositories of valu- able metallic ores, and hence they, as also stocks, will be more fully discussed in a subsequent chapter under the head of ore deposits. Relative Age of Rocks. Probably the most fre- quent question asked about rocks by persons little versed in geological science is with regard to the approximate age of certain strata, the marks of whose great antiquity have been so obvious as to impress even the casual observer. To this question it is not probable that any very satisfac- tory answer can ever be given. It can only be said, in a vague and general way, that the time embraced in the events to which geology testifies is very long even to those computations which would make it briefest. The relative age, however, of the stratified rocks can be made out with a good degree of certainty, not only for limited districts, but for all that portion of the globe which has been geologically explored ; and the various strata have been arranged in a series which expresses ap- proximately the order of their appearance in time. This series has also been separated into larger and smaller subdivisions or groups, which, while based on certain interesting facts in their life-history or lithological con- stitution, are of vital importance as affording a means ARRANGEMENT OF ROCK-MASSES. 37 of ready reference for both scientific and economic pur- poses. These groups of strata, which, if piled upon one an- other successively, would make a stupendous mountain- mass more than a hundred thousand feet in height, are nowhere found forming a complete and connected series ; but rather, certain portions are found in one region, while other parts of the series must be studied in other and per- haps distant localities. The reasons for this fragmentary distribution may be briefly stated. They are (i) that during the vast periods of time embraced in geological history, the regions where rock - materials might be de- posited have been slowly but constantly changing, by rea- son of fluctuations of level which have caused great and often repeated changes in the distribution of land and water. Thus, the areas where rocks were laid down have been repeatedly shifted from age to age, regions which had taken no part in rock-making, because they were dry land while certain series of rocks were deposited, subsequently changing places with former water areas, and becoming themselves the theatres of deposition. To this may be added (2) the probability that many strata, once deposited in certain regions, have been en- tirely or partially removed by denudation in the course of subsequent changes. The means by which an orderly arrangement of the members of a series so essentially fragmentary into a con- nected system has been effected are chiefly the following : i. Superposition. From what has already been said about the mode of formation of stratified rocks, it is ob- vious that the lowermost strata will have been first formed, while the overlying ones must be successively more recent. Hence, in any region where the natural succession of the strata has not been too much confused by uplifts and faults with subsequent denudation, the observed order of superposition of the strata, as studied in tolerably con- 8 38 APPLIED GEOLOGY. tinuous outcrops, will give their relative age ; and, if then some well-marked bed or stratum of this region can be positively recognized in some other locality where addi- tional strata occur, the two series may be connected in the order of time, and ultimately the same mode of obser- vation may be extended to include other and far more remote areas. Thus the observed order of superposition is not only a very valuable but wholly indispensable means of studying the relative age of strata. But it fre- quently happens that over wide spaces the succession of the strata can not be directly observed because they are covered by surface accumulations, or separated by bodies of water : how, then, shall we recognize strata already well studied in certain localities, when we come upon them in regions somewhat remote ? Or, again, from what is ap- parently a completely continuous series of strata, whole groups of beds may be wanting from the causes men- tioned above, without leaving anything to mark their ab- sence : how, then, shall we be able to detect this absence, and to assign the strata that would make the series really complete ? This recognition at distant localities of kin- dred strata, that is, those having like positions in similar series, this detection of groups missing from a seemingly consistent series is accomplished by a second and highly important means : 2. The Use of Fossils. Throughout a very large portion of the time during which the stratified rocks have been accumulating, it is certain that forms of life have ex- isted on our globe ; and the fossil evidences of their exist- ence have been preserved, to a very useful degree, in nearly all stratified rocks which are not metamorphic. Now, the various distinguishable stages in the great series of rocks, arranged in the order of their relative age, are character- ized by the prevalence of certain forms of life, species or genera not found in other members of the series ; or by certain groupings of forms which do not exist elsewhere ARRANGEMENT OF ROCK-MASSES. 39 in like relations ; so that by the careful comparative study of the fossils of localities separated from each other more or less widely, the rocks which contained them may be placed in their proper relative place in the chronological series. For figures and lists of the fossils which character- ize the several members of the geological system, the stu- dent will do well to refer to some one of the excellent treatises on geology, like Dana's " Manual of Geology," Geikie's " Text-Book of Geology," Lyell's " Elementary Geology," or Le Conte's " Elements of Geology." Some examples of their use may be profitable. A large and peculiar family of crustaceans called Trilobites, because the body is divided lengthwise by de- pressions into three lobes (see Fig. 8), while found somewhat abundantly in the rocks below the coal-measures, has not yet been seen in any higher rock ; and some of its genera, and nearly all its species, are limited in their range to certain sets of rocks : hence the family of Trilobites is characteristic of the rocks from the coal-measures down- ward ; and its species, and in some cases genera, become distinguishing marks for the groups of rocks to which they are confined. So the Spirifer (see Fig. 9), an easily recognized genus of shells, which is confined to the strata from the Upper Silurian to the Lower Jurassic (rock groups presently to be mentioned), has well-marked species which are confined to the several groups of strata, and hence are used as landmarks for these groups, while the genus as a whole distinguishes all the rocks within the limits named. 3. The lithological characters of strata, though in FIG. 8. 4 APPLIED GEOLOGY. many cases they furnish very unreliable marks for recog- nizing rocks, save within quite limited spaces, from the fact that they do not remain constant, but frequently change, so that within a comparatively short distance a conglomerate may be seen to pass >into a sandstone and then to shade off even into a shale, yet in some cases, and especially among the older rocks, show such persist- ency as to make them very convenient guides for the rocks of certain districts. Thus, in central New York, a band of limestone called the Tully, usually not more than ten to fifteen feet thick, though occasionally rising to as much as twenty-five or thirty, is persistent in character over more than eighty miles from east to west, and fur- nishes a most valuable guide to the relative age of the rocks throughout its extent. So, likewise, in tracing coal- beds from one valley to another, use is made of certain somewhat persistent beds, usually of sandstone or lime- stone, as &ry-rocks, within tolerably regular distances above or below which the coal-beds are likely to be found. The availability of these key-rocks is greatly increased if, in ad- dition to pretty uniform lithological characters, they also contain some well-marked distinguishing fossils ; but, in any case, lithological characters, if carefully used within limited areas, are of great use in giving guesses at truth, to be afterward confirmed by other and more reliable evidence. By the careful use of the three means just described, the relative ages of the stratified rocks are made out. By the use of characters derived from the last two sources, but chiefly from the second, the entire series of strata is also separated into greater and smaller groups, for con- venience of reference, the larger divisions holding the same relative position and bearing the same names over the entire earth; while the smaller subdivisions, which usually differ widely in details in regions very remote from each other, are apt to receive in every country special names of local significance, and are afterward ARRANGEMENT OF ROCK-MASSES. 41 paralleled with each other, as far as possible, by a careful comparison of fossils. Thus the crystalline schists, which underlie all the fossiliferous stratified rocks, are generally termed Archaean ; the fossiliferous rocks which succeed these, and which are characterized throughout by a pro- fusion of invertebrate fossils, a few remains of fishes being found only in the upper beds, are called Silurian, and admit of a generally used division into Lower and Upper Silurian ; the succeeding groups of strata, in which fishes of strange aspect are the dominant though by no means the most abundant forms of life, are called Devonian ; to which succeeds the Carboniferous formation, characterized by the abundance of its coal-beds, and by the prevalence of land-plants belonging mostly to the highest cryptogams. Overlying the Carboniferous are found in many places great series of strata, which, with an abundance of other fossils, are characterized by the remains of reptiles, often of great size and uncouth forms. These rocks, termed usually Mesozoic, are susceptible of a threefold divi- sion, universally used, into Triassic, Jurassic, and Creta- ceous periods. To the Mesozoic succeed the rocks called Tertiary or Cainozoic, which are characterized by the prevalence of mammals, forms of life which up to these rocks are represented only by a few very rare fragments, and in which the invertebrate remains have usually a strong resemblance to, and often identity with, creatures now living. Its widely recognized divisions are called Eocene, Miocene, and Pliocene, Lying upon the Terti- ary deposits, where these occur, are found the more recent and usually unconsolidated surface materials, including drift-clays and bowlders, beach and terrace deposits, and other accumulations of kindred -character, containing in some parts the remains of man or his works, and called Post-Tertiary or Quaternary. The whole series of formations, from the top of the Archaean to the top of the Carboniferous, is usually called APPLIED GEOLOGY. collectively the Palaeozoic i. e., the age of ancient life because all the forms of life found in it resemble so re- motely those now prevalent on the globe ; the term Meso- zoic, applied to the succeeding rocks, signifying their approximation in forms of life to the existing state of things ; while the name Cainozoic (recent life), given to the Tertiary strata, is significant of the resemblance of its fossils to living species. Subjoined is given, in tabulated form, the more com- prehensive divisions just described, with the larger sub- divisions, as recognized by American geologists : Quaternary or Post-Tertiary, Tertiary or Cainozoic, Secondary or Mesozoic, f Carboniferous, Primary or Palaeozoic, Devonian, Upper Silurian, Lower Silurian, including Cambrian or Primordial, Archaean, Recent or terrace, Champlain, Glacial. Pliocene, Miocene, Eocene. Cretaceous, Jurassic, Triassic. Permian or Permo-car- boniferous, Coal-measures, Sub - carboniferous or Lower Carboniferous. Catskill, Chemung, Hamilton, Corniferous, I Oriskany. (Lower Helderberg, Salina, Niagara. Hudson, Trenton, Canadian, Primordial, Potsdam most important. Huron ian, Lauren tian. ARRANGEMENT OF ROCK-MASSES. 43 Of a number of the divisions given, there are sub- divisions of much local interest, for which, as well as for the European subdivisions, the student can, if he desires, consult the treatises mentioned on page 39. By the stu- dent familiar with German, the elaborate tables of Euro- pean strata given in Credner's " Elemente der Geologic " can be consulted with advantage. CHAPTER IV. ECONOMIC RELATIONS OF GEOLOGICAL STRUCTURE. HAVING now briefly considered those portions of structural geology which seem essential to the ready com- prehension of what is to follow, let us consider how geo- logical science may make men's practical endeavors more effective. Economic geology may be defined to be that de- partment of science which treats of the earth's structure and mineral products as they are related to the supply of human wants. The economic geologist considers structure as it con- cerns the adaptability of rocks and strata for certain pur- poses, or as it is related to the occurrence and accessibility of valuable deposits. He regards rocks as in themselves fitted for certain uses, or as the probable repositories of use- ful materials. He is interested in the relative age of strata, and the means by which it may be determined, because it furnishes him an available guide to their possible desirable contents. He aims at an accurate and extended knowl- edge of those geological deposits which have practical utility. Nay, more : these deposits bear to each other practical and often very essential relations. Of these he takes careful note for example, the proximity of metallic ores to the fuels and fluxes necessary for their beneficia- tion, or to the kindred ores with which they may profitably be mixed. Moreover, useful materials are valuable or value- ECONOMIC ASPECTS OF STRUCTURE. 45 less, according to their relations to the currents of human industry and to the means of profitable utilization. What value has an excellent quarry-stone, remote from transpor- tation and from the great centers of construction ? Of what present worth is an ore of moderate richness, at a long dis- tance from the means of smelting or of easy concentration ? What avails a rich placer deposit, without an abundant water-supply for its cheap separation ? To such consid- erations, and others like these, little noted by the ordinary geological observer, the economic geologist must be keenly alive, for they are what constitute the relations of structure and products to the supply of human wants. Nor are these wants, as signified by demand, by any means con- stant. The progress of discovery or invention may change very greatly the economical estimate of a substance once little regarded. The naphtha and Seneca oil of thirty years ago are the petroleum of to-day. Iron pyrites has become a substance of great commercial importance, since its recent use as a source of sulphur in the manufacture of sulphuric acid. The ores of molybdenum and tung- sten, till lately regarded only as interesting minerals, are now called to the attention of the United States geolo- gists by their use as pigments ; while all deposits of nickel have recently become of greatly increased interest since the wide use of this metal in electro-plating. Hence it is desirable that the economic geologist should always bear in mind " that, much as may already have been utilized, there are still many substances in the earth's crust which can be turned to account in the increasing requirements of modern civilization." (Page.) Economic Relations of Geological Structure. The economic bearings of geological structure are numer- ous, and of the most obvious importance. Structure, for example, conditions the relative accessibility of desirable substances ; the facility with which they may be worked ; the ease and consequent expense with which excavations 46 APPLIED GEOLOGY. and tunnels may be made, and their durability when fin- ished ; the reliability of the foundations of important en- gineering and architectural structures ; the accessibility, the abundance, and the continued purity of deep-seated water-supplies ; and not unfrequently the possibility of effective drainage. Accessibility. Among stratified rocks, it is obvious that their dip must exert a paramount influence on the accessibility of any particular bed from the surface. If the dip is slight, the depth below the surface of a bed will increase but slowly as we recede from the outcrop in the direction of dip ; while, if the dip is considerable, the depth, and consequently the difficulty of access, increases rapidly. A dip of one degree carries the strata down ninety-two feet in a mile. The following table shows the descent for a surface-distance of one hundred rods for dips of from one to twenty degrees, and for every five de- grees thereafter up to forty. It will be obvious that when we pass beyond the outcrop of a bed in the line of its as- cent, this bed will disappear and give place to underlying beds : Dip i descent for 100 rods, 28.8 feet. 3 >> 86.5 4 II5-4 5 J 44-3 6 173 7 202.6 8 2 3 2 9 ,, 261.3 10 291 XI 3 2I -5 I2 35-7 13 38 1 14 44 2 ECONOMIC ASPECTS OF STRUCTURE. 47 Dip 1 6 descent for 100 rods, 473 feet. J 7 >, 54-5 18 536 J 9 ,, 568 20 600.5 2 5 769-4 >, 30 ,i 95 2 -7 35 ii55-4 40 ,, J 334-5 It may be seen from this table that even small dips make an important difference in accessibility at some dis- tance from the outcrop, while dips of 5 and upward make necessary, before mining operations are begun, a careful es- timate of the cost of sinking shafts, and the after perpetual expense of hoisting to the surface the water and the min- eral which is the object of search. In all cases, therefore, where the dip of the rocks is known or can be ascertained, it needs to be taken into careful consideration in judging of the depth at which valuable deposits may be reached. In making this estimate also it should be remembered that the rate of deepening below a given plane is greatest di- rectly down the dip, and diminishes each way from this line. Faults also affect the accessibility of deposits relatively to our workings. They may bring the continuation of a bed nearer to the surface or remove it farther from the surface, or, bringing it within reach of denuding agencies, they may have caused it to be entirely removed. In even the most favorable cases, since they interrupt the continu- ity *of beds, faults derange the underground approaches and means of transportation and increase the expenses of working. Great uplifts with subsequent denudation have likewise in many regions brought within easy reach deposits which must otherwise have remained utterly inaccessible. In- deed, it is reasonably certain that the great class of crys- 48 APPLIED GEOLOGY. talline rocks with their valuable stores of building and ornamental stones, and the still more valuable veins of metallic ores which many of them inclose, have by this means alone been made accessible to man. In other cases the agencies of denudation, by excavating deep valleys in undisturbed and nearly horizontal strata, have, while sweep- ing utterly away great masses of valuable deposits, made the outcropping edges of the remainder easy of access and of drainage by tunnels driven into the hill-sides where they are found. Numerous examples of this kind may be found in mining for coal and iron-ores. Relations of Structure to Facility of Extrac- tion. Useful substances, whether building-stones, min- eral fuels, or ores, are extracted from their repositories either by open workings called quarries or by underground mining operations ; and the ease with which these pro- cesses can be carried on, and the resulting materials re- duced to merchantable dimensions, depends in an impor- tant measure on structural characters. In many cases the workings may be so arranged with reference to the dip of the strata as to clear themselves of water or to collect it where it can be most conveniently removed, while the handling of the materials is facilitated by a descending grade. The bedded and jointed structure of many rocks greatly aids the operations of the quarryman, enabling him, where there are two sets of joints at nearly right an- gles, to extract, with little waste of material, tolerably regu- lar blocks of a size limited by the distance apart of the joints and the thickness of the beds. Where the bedding or the jointed structure, one or both, is wanting, recourse must be had to the laborious operations of channeling or drilling, with subsequent wedging or blasting, in the last case often with great waste of material. The jointed struct- ure of coal, called the cleat or face, and the end, is of such importance that the workings must agree with it in direc- tion. Where the beds are very thin, or the joints very ECONOMIC ASPECTS OF STRUCTURE. 49 closely set, the rock may be unfitted for any useful pur- pose, while the presence of a single system of joints at suitable distances may adapt a thick-bedded or massive rock for being extracted for large columns or for mono- liths. The laminated or schistose structure of many rocks is an important aid in reducing them to proper dimen- sions. Availing himself of this, the workman, by repeated blows along the edges, causes thick masses to split parallel with the bedding, and thus with no great difficulty brings them to the thickness desired. The presence of concre- tions or of a concretionary tendency, as also of cross or current bedding, should be carefully noted, as they meas- urably or entirely unfit a rock for use. Relations of Structure to Expense of Exca- vation, Tunneling, etc. The ease and consequent ex- pense with which excavations, tunnels, shafts, and other engineering works of like character can be accomplished, and their permanence when finished, will depend very largely on the nature and structure of the rock formations through which the works must be pushed ; and all esti- mates of expense should be based on the best attainable knowledge in these respects. The hardness of the rocks that must probably be penetrated ; their firmness or ability when cut through to sustain the pressure of the masses above and around them without artificial support ; their durability in sides and roof when exposed to the atmos- phere and weather ; the position of beds, whether hori- zontal or highly inclined ; and their succession* whether tolerably uniform or in alternations of firm beds with others that are friable or of ready disintegration; their permeability^ whether close-grained and solid, or porous and seamed with fissures and joints, so as to make them ready water-ways these and other considerations of like import are of vital interest in all undertakings of this character, and they present questions which can be satis- factorily answered only by a careful geological examina- 50 APPLIED GEOLOGY. tion. Beds of hard, firm rocks with few or no joints will be difficult and expensive to penetrate ; but they will be self-supporting throughout and durable when finished, and in cuttings only a minimum of material needs to be removed. The first cost, therefore, is likely to be the only cost ; while incoherent strata of gravel and sand, though easy of excavation, require support at every step by expensive curbing or by arches of masonry, or, in cut- tings, materials must be removed until the angle of rest is attained, so that the cost in the two cases may eventually prove not very unequal. Friable sandstones, fissile and easily decomposed shales, and not unfrequently the cut edges of highly inclined strata, will need proper support in both sides and roof, while fissured and porous water- bearing beds must have due provision made for carrying away the superfluous water, or must be masked by imper- vious walls. The cutting of one of the most extensive tunnels in this country passed through many vicissitudes, and was ultimately completed only after years of delay, presum- ably through insufficient knowledge on the part of its projectors of the obstacles likely to be presented by the region through which it had to be driven, and consequent insufficient estimates of probable expense ; and the con- tractors for driving a tunnel to supply one of our great lake cities with water, meeting with an unsuspected water- way in the tough clay through which they were cutting, were forced to close the end of their workings by a strong bulkhead, and make an expensive dttour to avoid the obstacle thus unexpectedly presented, yet which careful previous trials would probably have revealed. The his- tory of many similar works would doubtless furnish addi- tional illustrations of the importance of a knowledge of geological structure to those engaged in engineering enter- prises of the kind here considered. Foundations of Engineering and Architectural ECONOMIC ASPECTS OF STRUCTURE. ^ Works. It is evident that the stability of the founda- tions of engineering and architectural structures must de- pend entirely on their adaptation to the geological char- acter of the underlying formations. If firm rock can be reached at reasonable depths, the best possible foundation is gained. Thick beds of tough and homogeneous clay also afford good foundations. But, where a great depth of loose, uncompacted materials is encountered, expensive preparations must be made to insure the stability of heavy structures. The great viaduct in Cleveland, constructed at a cost of more than two million dollars, was built across an alluvial flat, where immense sums had to be expended in deep excavations, driving close-set piles, and building up a substructure of grouting, before the piers of the bridge could be commenced. Every considerable town can furnish numerous examples, in the cracked and dis- torted walls of buildings, not always large nor heavy, of the need of using precautions proportioned to the native instability of the substratum on which the structure must rest. So, too, one occasionally sees important retaining walls yielding to the easily foreseen thrust of alternating beds of clay and quicksand, partly from insufficient at- tention to the character of the beds to be sustained, and partly from the lack of due provision for draining off the water which, in heavy rains, heightens manifold the natu- ral instability of such deposits. In structures intended to hold or convey water, such as dams, reservoirs, and canals, minute attention is needed to the character and structure of the underlying beds. For such constructions, no sub- stratum can be better than tough and compact clay, or close-textured and massive rocks, nor could anything well be worse than loose sands and gravel, or porous, fissured, and jointed rocks. In the first case, little care is needed, save to secure the requisite strength and thoroughness of work ; while in the second no precaution can be too great to remedy the innate defects of the foundation. Espe- 52 APPLIED GEOLOGY. cially is this true when high dams are to be built, in which the pressure of a great column of water will heighten the permeability of the substratum and exaggerate its every defect, and where any defect unremedied is sure to lead to terrible disasters. Structure and Water-Supply. An abundant sup- ply of wholesome water, free from risk of organic contami- nation, is of vital importance to individuals and communi- ties ; and it is a provision which the growth of population and its concentration on limited areas render every day more needful and more difficult. The usual sources of supply for families and small communities, aside from cis- terns filled from roofs, are wholly geological in their nature, and depend for their character, their permanence, and their safety, on the structure of the region in which they are found. They are springs, wells dug or driven in drift or other sur- face accumulations, and artesians bored through drift or rock, often to very considerable depths, in which the water either overflows at the surface, or rises within easy reach of pumping apparatus. The term artesian is often con- fined to wells of this class that overflow, though with no very good reason ; for it will presently be seen that what is really characteristic about wells of this kind is that they derive their water from sources deeper seated than usual, and that the origin of their supplies is not local, but more or less remote. Springs. These are sources of water arising from the underground circulation of the water that penetrates the earth from rain and snow. This water descends through the loose and porous materials until it meets with an im- pervious bed, usually of clay, along which it flows, until it gushes forth in a valley, or on the eroded edge of some hill. Such springs are liable to contamination from im- purities on or near the surface into which their waters first sink ; but, if the point of issuance is at a consider- able distance, the impurities are likely to be removed, ECONOMIC ASPECTS OF STRUCTURE. 53 largely through the chemical agen- cy of the air circulating in the per- meable beds. In Fig. 10, a and b are springs, represented as issuing on the side and at the base of the hill, at the junction of the sand and gravel beds i and 2 with the impenetra- ble clay-beds 4 and 5. The por- ous bed 3 is also a water-way, but does not produce a spring because the valley c is not eroded deep enough to intersect it. The water issuing at a is liable to contami- nation from any sources of impur- ities found between a and 4, and that at b from the area between 4 and 5 ; but the latter, having a greater distance to flow, would be surer to be freed from organic con- taminations by the action of the air circulating in its bed. Both will be likely to take into solution portions of any soluble minerals, like lime or gypsum, which they may meet with in the beds through which they percolate ; and, if such minerals occur in any considerable amount, the water of the springs will be hard ; but, if little or no soluble minerals are met with, it will be soft the terms hard and soft, applied to water, being used to describe the extent to which they are charged with or are free from dissolved minerals, with certain 54 APPLIED GEOLOGY. other properties dependent on this. The abundance and permanence of the flow of such springs will depend on (i) the thickness of their porous beds, (2) the freedom of percolation through these beds, dependent on their texture, (3) the extent of the gathering ground from which their supplies are derived, and (4) the amount of rainfall of the district. Springs are occasionally met with, like those at Union Springs, New York, and the " Big Springs," so abundant in northern Alabama, one of which supplies Huntsville with water, which issue apparently from the mouths of caverns in the solid rock. Such springs, because of the great depth of their source and the extent of their gathering ground, are apt to be of very considerable volume and of great permanence. Also fissured rocks, such as jointed limestones, resting on impermeable strata, cause lines of springs or of wet ground on the sides of hills where they outcrop in the direction of their dip. Another class of springs is found in many regions, ris- ing in strata of moderate dip, along lines of fault or on open joints cutting down to porous, water-bearing strata. They are often very copious, and are usually both durable and of reliable purity. They are indeed a kind of natural artesians. In Fig. n, D represents a spring rising along the plane of fault, D C, and deriving its waters from the porous sand- stones 2 and 4, which are inclosed above and below by the impervious strata i, 3, 5, while B represents a spring rising along a jointing plane which penetrates to the porous bed 2. The broken ends of the water-bearing beds, by reason of the downthrow on the right of the faulting plane, have been brought opposite to strata not easily penetrated on the left, and hence the water with which they are satu- rated rises along the fault or joint from hydrostatic press- ure. The water at B having but little head would merely well out of the ground, while that at D would be likely to ECONOMIC ASPECTS OF STRUCTURE. 55 gush out with considerable force, since its sources at 2 and 4 are elevated above the point of out- flow. The force and abundance of outflow and the quality of the water will depend on the same circumstances as in the case of artesians presently to be de- scribed. Wells. The chief source of water-supply for domestic uses, for isolated dwellings, and small towns, where springs are not at hand, is found in wells, open ex- cavations of varying depths, reaching either to some water- bearing stratum confined by im- pervious beds of clay, or to a common water-level of the dis- trict, below which all the beds are saturated with water. The depth of the well in either case will naturally depend on the depth below the surface of the general water-level, or of the special water-bearing stratum. In many localities the unconsoli- dated materials are of little depth, and do not carry water, so that the well-excavation, if it succeed at all, must be pushed through rock to some porous or open-jointed water-bearing stra- tum, the probability of reaching which within reasonable depth through means so expensive 5 6 APPLIED GEOLOGY. should be carefully considered beforehand, in the light of the geological structure of the district as revealed in ravines and quarries. Otherwise, a costly excavation may end in complete failure, or be forced to depend on the scanty and uncertain supplies oozing from the joints and bedding-planes of close-grained rocks. In still other locali- ties the loose surface materials rest immediately on fissured or even cavernous rocks, through which their water, de- scending unchecked by any impervious bed, are drained away beyond the reach of wells. Such are the so-called dry lots found especially in some limestone regions. In any case, this widely used and convenient, if not essential, source of water-supply is liable to become a source of extreme danger to health, and even life, unless more than usual care is used as regards its location, its surroundings, and its construction, and unless the nature and extent of the precautions that are used are based upon the structure of the locality in which the excavation is made. Where the excavation has passed through a con- siderable thickness of impervious clay before reaching the water-bearing beds, this is highly favorable to security; but even here there is danger that the water may be con- taminated by organic impurities leaching into it through porous beds nearer the surface. This should be guarded against by laying the retaining wall in hydraulic cement, at least from the middle of the clay-seam to a sufficient height above the mouth of the well to be secure from any possible surface inflow; special care being taken where the cemented wall begins in the clay to fill the entire space around the wall with puddled clay or cement. If such precautions are needed to insure safety from vitiation, even in situations favored by the underground structure, what shall be said of those wells excavated wholly through sand and gravel down to the water-level, located, as they too often are, in close proximity to house-drains, cess- pools, and yards where animals are kept ? In such cases ECONOMIC ASPECTS OF STRUCTURE. 57 an outbreak of certain too well-known types of disease, is usually only a question of time and of the power of hu- man beings to resist poisonous influences. In all such localities it would be safer to obtain water for household purposes from well-constructed cisterns, into which the water should be admitted through a filter easily construct- ed with washed gravel, sand, and coarsely powdered char- coal ; but, if a well is to be dug, it should be carefully located as remote as possible from every probable source of contamination ; and, because of the extra hazard, spe- cial precautions should be used in the way of water-tight walls to secure filtration through as wide a space as possi- ble. In a situation like that here described, and such are frequently to be found, even the degree of care here recom- mended may not secure perfect immunity ; less than this is sure to expose health and life to needless hazard. Nor should it be forgotten that the apparent purity and clear- ness of water afford no reliable criterion to its freedom from dangerous contamination. The germs of disease lurk unsuspected in many a bright and sparkling draught ; and it is to use very moderate language to say that a very considerable proportion of the ailments with which human beings are afflicted arise from the tainted waters which they drink. Indeed, in most long-settled, highly culti- vated, and densely peopled districts, the soil becomes so saturated with organic substances that no comparatively shallow and open surface-wells can be considered safe. Driven Wells. These wells, made by driving down to a water-bearing bed an iron pipe shod with an iron point, and pierced with holes around the bottom to admit the water when it is reached, are practicable in unconsoli- dated beds of sand, gravel, and clay, where there are no bowlders to obstruct the driving ; and present some great advantages over the usual open excavations, not only in the ease and rapidity with which they may be made, but in their freedom from risk of contamination from above, 5 8 APPLIED GEOLOGY. by the access of those surface-supplies of water which are liable to be loaded with organic impurities. If they reach to considerable depths, and in their descent pierce through beds of tough clay, the water that they furnish is likely to be excellent and reliable. In some of the southward- reaching valleys of the lakes of central New York, deeply filled as they are with stratified beds of unconsolidated ma- terials, wells of this kind are often sunk to depths of from sixty to more than a hundred feet ; and, in many cases, the structure of the containing beds causes them to over- flow at the surface, sometimes with considerable force, constituting them veritable artesians. The water of these wells, though sometimes very slightly sulphurous, is ex- cellent. Driven wells are feasible only under the conditions mentioned in the first sentence of this paragraph ; but there are large areas in the United States where such con- ditions are presented, and where the driven well would doubtless yield more wholesome water-supplies than those furnished by the common surface excavations. The chances that the water will overflow in any given case will depend on the conditions presently to be mentioned as conditioning the outflow from artesian borings. Artesian Wells. These wells are essentially borings, often of very great depth, which penetrate porous water- bearing strata of moderate dip, confined both above and below by other strata that are practically water-tight, the entire series of water-bearing and impervious beds out- cropping at its elevated edge, often many miles distant from, and at a considerable elevation above, the points where borings are made. In some cases the series of water-bearing beds with their impervious cover form great basin -shaped depressions, around which their elevated edges outcrop on all sides, covered only by loose surface accumulations ; but this kind of structure is by no means essential to success, provided only that the confined waters ECONOMIC ASPECTS OF STRUCK do not find easy egress at some point down the dip of the strata, or provided that the porous strata gradually change their character below the boring, as is frequently the case, and become prac- tically water-tight. In Fig. 1 2, which represents an ideal section across a basin-formed depres- sion, i, 2 is a water-bearing sandstone confined between impervious strata of shale, 4, 5, and 6, 7 ; and 3 is also a stra- tum of porous sandstone, which, near the center of the basin, thins out and becomes merged in the shale ; while the dotted line C, D, marks the level of the opposite edges of the strata. It is evident that water entering at the outcropping edges i, 2, and 3 of the porous beds, and filling them to satu- ration, will, at any points, as A and B, be subjected to a pressure equal to that of a column of water reaching from the dotted line to the top of the bed at that point ; and that, if borings be ex- tended to the water-bearing strata at these points, the water will overflow through them with a force proportioned to the height of the head above the mouth of the well. Should a boring be made at D through both water-bear- ing beds, the water in it would barely reach the surface, because its mouth would be on a level with the upper edges of the beds, while at A the water would be under a great head, and would issue with much force. At 60 APPLIED GEOLOGY. point's between A and D, water would issue with a force varying from that at A to a mere quiet outflow. From this it may be seen that the possibility of obtaining water-sup- plies by artesian borings is entirely dependent on the larger geological structure of the region ; and that this needs to be studied by the aid of the best attainable means, to make success in such necessarily expensive undertakings anything but a mere lucky chance. A brief review of the conditions which insure success will render this more obvi- ous. These are : 1. The existence of porous strata to serve as collectors, conductors, and reservoirs of the water supplied by the rainfall of the region. The most reliable water-bearing beds are usually porous sandstones and conglomerates; or, where the water is derived from deep accumulations of uncemented materials, the same substances as sand and gravel, the materials of ancient beaches. Artesians may occasionally derive their supplies from fissured and cav- ernous limestones ; but the chances of striking such water- pockets are usually too slight to encourage explorations. The thicker such beds are known to be in the region, and the more open their texture, the better will be the chances of success so far as this condition is concerned. 2. An equally essential condition of success is that the water-bearing strata should be covered and underlaid by continuous, impervious strata, confining the waters, and pre- venting their dissipation by percolation either above or below. The most reliable strata for this purpose are thick masses of clay or shale ; though compact rocks of other kinds, when free from fissures, like some limestones, may, in certain regions, prove useful auxiliaries. The continuity of impervious cover throughout the entire extent of the beds, while they retain their character as water-ways, is a point of great importance. 3. A third essential condition is, that the series of strata should have a moderate dip from their outcrop to- ECONOMIC ASPECTS OF STRUCTURE. 6l ward the point where the boring is proposed. A dip of one degree, as has been said on a former page, will carry the strata down about ninety-two feet in a mile, and one of two degrees one hundred and eighty-five feet per mile. Hence, any very considerable dip would, in no great dis- tance from the outcrop, carry the strata beyond the reach of practical exploration. The table given on pages 46 and 47 will, where the dip is known, aid in estimating approxi- mately the depth to which the boring must be carried. The inclination of the beds, as it may carry the outcrop of the water-bearing strata above the level of the well-mouth, will cause the water to overflow, or bring it within the reach of pumps. A deduction, however, of several feet for a distance of a number of miles, needs always to be made from the height to which the water might theoretically be expected to rise, on account of friction, and the resistance which even the most porous beds oppose to the free flow of water. 4. A consideration of much importance as regards the abundance of the water-supply that may be looked for from any porous beds, and one also which depends on the amount of dip, is the breadth of absorbing surface which these beds expose at their outcrop. The breadth of ex- posure on a level surface of beds one hundred feet thick, with a dip of one degree, would be a trifle more than a mile, and for two degrees dip, about half a mile, the breadth of surface exposure varying inversely as the dip. Hence a moderate degree of dip will give a greater extent of gathering-ground, or area of catchment, as it is often termed. 5. A fifth essential condition is, that there shall be no obstructions to a free flow between the site of the boring and the outcrop of the water-bearing beds. Such obstruc- tions may be presented either by faults interrupting the continuity of the strata and rendering possible springs of the kind described in a preceding paragraph, or by dikes of volcanic origin cutting across the strata, and rendering 4 62 APPLIED GEOLOGY. hopeless any flow below the obstruction, although success may be achieved above. Fig. 13, in which A represents a volcanic dike intersecting the water-bearing stratum B, FIG. 13. Illustrating effect of an Obstruction. (After Page.) will illustrate the effect of this kind of obstruction. In this case, a boring between A and B, as at the point i, would be likely to succeed, while one below A, as at 2, would be hopeless. Such obstructions, in regions where they are likely to occur, are usually not difficult to dis- cover, and should be sufficient to deter men from under- takings that are sure to be futile. 6. The last consideration to be mentioned, which is meteorological rather than geological, has reference to the usual amount of rainfall which may be depended on to supply with water the gathering-ground of the porous strata. In large areas west of the Mississippi, the average rainfall is but small, yet it may be sufficient, under condi- tions otherwise favorable, to make artesian borings fairly successful ; but in all the region east of the Mississippi the usual annual amount of rainfall is so abundant as to make the question of sufficient supply, under proper con- ditions, a reasonable certainty. A rainfall of thirty inches per annum, which is well within the average rainfall of the Eastern United States, would supply to the gathering-area of a hundred-foot stratum, dipping at an angle of one de- gree, 3,400 barrels of water a year for every foot in width across the outcrop ; of which, if but one third is taken up by the stratum, upward of 1,100 barrels per year will be stored in every foot of its width. Hence the enormous ECONOMIC ASPECTS OF STRUCTURE. 63 flow from some noted artesians need excite no surprise. An artesian well in the city of Louisville is said to yield 330,000 gallons every twenty-four hours from a depth of 2,086 feet ; one in the city of Paris, the Crenelle well, dis- charges over half a million gallons per day, from a depth of i, 806 feet ; while one, bored by a French engineer in the Sahara Desert, is said to have yielded at the outset 1,000 gallons per minute, or about 1,500,000 gallons per day. The quality of the water yielded by such borings will naturally depend on the character of the strata which form the water-ways. In many cases it is very good ; but in oth- ers the water derived from certain strata is found to be too heavily charged with mineral substances to be adapted for domestic use. It is usually difficult to predict the quality of the water that is likely to be obtained from a given set of beds ; but a single test is commonly sufficient for a large district, for these deep-seated water-ways are apt to underlie extensive regions with strata of a tolerably uni- form composition. From what has been said of the structural characters which are essential conditions of the success of artesian wells, it may easily be understood that they should not be undertaken without a careful consideration of the geologi- cal character of the region. Much indispensable informa- tion may be gained with regard to the nature, thickness, order of succession, and dip of the strata, and the direc- tion of their inclination, by consulting the geological re- ports and maps published by many of the States, and now being issued by the United States for the Western States and Territories. This, supplemented by such local obser- vations as may be possible, will enable a careful person to form a judgment as to the probabilities of success in any given case. To enter upon such undertakings without such care would be to incur a great and needless hazard. The student desiring larger information on the impor- 64 APPLIED GEOLOGY. tant subject of water-supply and artesian wells is referred to the " Reports of the Geological Survey of New Jersey" for 1876, 1882, and 1884, the last two of which are espe- cially valuable ; and to the first volume of the " Geologi- cal Survey of Wisconsin" (i873~'79), P- 689, from which Fig. 12 was copied: the second volume of the same re- port, pp. 149-171, has several interesting sections, show- ing the conditions under which artesian borings have suc- ceeded in that State. Also the second "Report of the Geological Survey of Arkansas," pp. 52-67, has much of interest on this same topic ; and notices of wells and bor- ings may be found in many places in the " Final Reports of the Ohio Geological Survey." Structure and Drainage. The matter of effective drainage, so important for both sanitary and agricultural purposes, has also its geological aspects, though these may not in the majority of cases be the chief ones. The neces- sity for drainage, in not a few cases, arises from causes purely geological, and in many of these the evil may be remedied by means suggested by a knowledge of the geo- logical structure. Fields rendered wet and cold by an impervious hard-pan may be found capable of ameliora- tion by the mere use of the subsoil-plow, breaking through a thin crust to porous beds below. House-drainage on clay sites may be found practicable by sinking cess-pools to beds of sand and gravel beneath, in which case it is well to remember that the water-supply derived from neighboring wells will naturally be endangered. Districts may be rendered swampy and malarious by impervious strata at no great depth below the surface, where the to- pography of the region is not such as to offer outlets for drains. In some instances of this kind effectual relief has been found in the existence of deeper-seated porous or fis- sured strata, wells sunk to which have furnished the requi- site outlets for drains. Still other districts have been made pestilent marshes by the presence of outcrops of rock or ECONOMIC ASPECTS OF STRUCTURE. 65 tough clay obstructing the natural drainage by streams, where the removal of such obstacles might reclaim to fer- tility large tracts of land, with immediate improvement of the health of the surrounding region. A work of this kind has recently been completed in New Jersey, while others are suggested all justly regarded as legitimately belong- ing to the geological survey of the State. (See " Geologi- cal Reports of New Jersey " for 1869, 1870, 1877, and 1884.) From what has been said in the preceding pages, it will be apparent that questions of geological structure are of deep concern to many prominent branches of human industry ; and that in some matters of paramount im- portance they touch the interests of nearly every family. Other highly interesting relations of geological structure will be more appropriately treated of hereafter, when we come to consider the mode of occurrence of ore deposits. CHAPTER V. MATERIALS OF CONSTRUCTION. AMONG the many useful substances which the earth's crust yields for the supply of human wants, the materials of construction may justly claim a leading place, both on account of their wide diffusion and their very general and highly important uses in both architectural and engineer- ing structures. These, leaving out of view for the present iron, so largely used in modern structures, as rather an in- direct than a direct geological contribution to the arts of construction, are the various kinds of building and or- namental stones, the brick clays, the mortars, and the cements. Building-Stones. The qualities which fit a building- stone for its various uses may be conveniently considered as belonging to two classes : (i) the necessary qualities, which are obviously strength and durability ; and (2) the desirable ones, which are facility of working and beauty, whether of color, texture, or susceptibility of finish. Un- less a rock has strength sufficient to endure any strains to which it may probably be subjected, and such powers of resistance to the usual agencies of decay as to enable it to withstand them for long periods under the conditions in which it is to be placed, it is wholly unfit for use in any important structure. When these essential qualities are assured, any properties which it may possess that will fa- cilitate the work of reducing it to desirable forms will MATERIALS OF CONSTRUCTION. 67 diminish largely the expenses of construction, while what- ever may make it pleasing to the eye will greatly enhance its value for architectural purposes and for many orna- mental uses. I. Strength. Let us first consider those properties on which the strength of stones depends. These are (i) Closeness and compactness of texture, in virtue of which all the grains of the stone being closely approximated touch each other at many points, and thus mutually sustain each other. Where such grains are large and loosely arranged, the tendency of strain is to press them more closely to- gether, and so to tear them loose from their consolidating means, and when this is done the stone crumbles. (2) Degree and means of consolidation. The more completely the consolidating medium enwraps the particles of the stone and fills all the spaces among them, the stronger it will be. Some of the porous sandstones and earthy lime- stones have evidently but a small proportion of cementing material ; a thin film of clay or of clay and iron oxide, a minute amount of silica or calcite at the points where the grains touch each other, seems to be all that holds them together ; and, in the case of some friable rocks, it would seem that the particles are consolidated merely by the ad- hesion of their faces. Such rocks are not likely to have any great amount of strength, though some of them may be used for purposes where no considerable strength is required. Again, among the several consolidating mate- rials, some like silica have greater inherent firmness than others, and this they are likely to impart to the stones which they cement. (3) Hardness and deavability of grains. It is natural to expect, especially in the case of crystalline rocks whose grains are held in place by the interlocking or felting of the crystals, or by the welding together of their faces, that the intrinsic hardness of the grains and their susceptibility to cleavage will determine in a great degree the strength of the rocks. Moreover, 68 APPLIED GEOLOGY. where cleavable minerals are largely present, the smaller the size of the grains the more varied will be the direction which the planes of cleavage will be likely to have within a given compass, and the less the liability to yield to crushing from this cause. (4) Direction of strain. The great majority of bedded rocks offer a decidedly greater resistance to crushing when the strain is exerted in a di- rection at right angles to their planes of bedding ; and the difference in the power of resistance to transverse or par- allel strains is the greater the more distinctly laminated or foliated the rock is. This fact affords a good reason why such stones should always be laid on their natural bed. (5) Elasticity. The results of experiments recently pub- lished in the Geological Report of Indiana for 1881, indi- cate that where weight is to be sustained by stones with only the ends supported, as in the case of lintels and beams, elasticity is an important consideration, and that the elasticity of limestones is probably greater than that of sandstones or even of granite. The strength of building-stones is determined by crush- ing cubes of a given size, usually of two inches edge, in a press which indicates the amount of force applied, and then reducing the result to terms of the force exerted on a square inch of surface. A table of the strength of sev- eral well-known building-stones, derived chiefly from the determinations of General Gillmore, is given below, with the percentage of water absorbed by each. Where the absorption is given as " very little," as in the marbles and granites, it is far below one per cent. The extremes of strength in the stones tested by General Gillmore are : for granites, from 9,500 pounds to 24,040 pounds ; for mar- bles, from 7,612 pounds to 20,025 pounds ; for limestones, from 3,450 pounds in a Caen freestone to 25,000 pounds ; and for sandstones, from 4,250 pounds in a stone which absorbed nearly seven per cent of water to 17,250 pounds in No. ii of the following table. It will be seen from MATERIALS OF CONSTRUCTION. S > pq i S 69 * $ $ c s a O O O O 3 I j mtnoooOM 3 8 S q S ?q ?7, 3 -' C^ O^ >^ CJ QO i-T cf / n m vO CM %s 3 m O M CO &$ 8 O M CO vO m O CO s, CO vO t-x CM in in CM en o *"* H O CO H in ONO n* CO o CO O m fx m 8 R 5 OO vO g O t^ o r^ M s J^ 3 M CM c* M O 01 O CM * ^- w M r> CM f i. co M O CO CO 0* O rf OO O^ 8N2 3- c, 3; gco O m co CO vO M f "*" m t^ M n- ON M CO M M 5 & O M CO CO H M N ON s CO co in m M CO CM in co O t^ M Q t O O CO CO & O m O M M o <* in co O m M m O ON O Tj- CO M M M O M M 6 CM' O CO CM i t"x ON M CO co m M ^ O co O in RvB 8 M CO %-i CO 00 O co t^ * co 1 2 N O M M CO Tfr I s ** sO M ?1 M O^ M Tj- M M in M t>> I O in ON CO M CO CM O^ w> ci cl c? CM t> CO od H CO O CO O in M CO 2 9 j M o 5- ON O i^ co O S ? 2" s s O f^ in w O O m M in cs rf * * rf CO CM o in H O -l C< N M .8 M o co s 5 CO CO Tj- t^ CO oo CO M O CM r^. $ in rf " ^ CM CM O **"> vO 1 00 hH CO O CM M N CO CO CO CM M CM M " t^ CO en M m co CO CO CO ?> M" CM" .. e g 8 < S M in s$ CO N S ? CO M M m JJ M O N w ON I" M O O 1 M CO CO CM vO ^8 S- Tt N ON O w O & *? * : : .; j s rt 1 1 gram . . re straw gram rley straw.. . (S I to i gram aize stalk . . . V c }_l X 2 rt w bJO "rt o> ^5 as vines G 'S 2 to tft ets root irnips root . . tatoes tuben )bacco leave- ops entire pi ^ & PQ O " S PQ X, ' PQ =q H fi H ffi 114 APPLIED GEOLOGY. of nourishment, to favor a proper circulation of air, and to retain the moisture needed for plant-growth while yield- ing ready outflow to all excess, every fertile soil must pos- sess also sufficient amounts of the inorganic substances and nitrogen which enter into the tissues of plants. What are the inorganic substances appropriated from the soil by the various cultivated plants can be learned from the analyses of their ashes, and a table of such analyses for a number of common plants, derived from French authori- ties, is given on the preceding page. Tables of the mineral components of the above plants, derived from the ash analyses of Emil Wolff, may also be found in the Geological Report of Ohio for 1870, pages 366 and 367, which, while differing somewhat from the above in the relative proportions of some constituents, present no material differences in the substances them- selves, and these, as they are present in some proportion, doubtless subject to considerable variations, in the tissues of all cultivated plants, are obviously essential to their growth and health. These substances must, with slight exceptions, be supplied by the soil ; and a very impor- tant part of scientific agriculture consists in knowing by what means to keep up in the soil a due amount of these important constituents, which would otherwise tend to ex- haustion by successive cropping. Some of these, like silica and iron, need little attention, being present in sufficient amounts in nearly every soil, and being rendered readily available for plant- growth by natural causes. In many soils, lime and magnesia also are found in proportions sufficient to supply the needs of a long series of crops, while in others there is a deficiency of these substances. An average soil will give about two million pounds per acre, for a depth of eight inches. If, then, it contains one per cent of lime, this will make available with ordinary cultivation at least 20,000 pounds per acre. It will be seen, by reference to the table, that tobacco is the most RELATIONS OF GEOLOGY TO AGRICULTURE. 115 exhaustive of lime among the common crops, containing about 9^ pounds per hundred of dried leaves, or 190 pounds per ton. It would require, therefore, one hun- dred crops of a ton per acre much more than the usual crop to exhaust this element from a soil containing one per cent. It is obvious that this is an extreme case for any soil ingredient. For an ordinary rotation of crops, one per cent of lime or magnesia in a soil would suffice for a long succession of crops. It may be observed that, among the cereals, lime predominates in the straw and magnesia in the grain. Hence the latter is likely to tend to more rapid exhaustion than the former, since, in good farming, the straw is mostly returned to the soil in the form of manure. Of the mineral ingredients of soils, those that need most attention are phosphoric acid and the alkalies potash and soda, especially potash, which, as may be seen by the table, enters largely into most cultivated plants. It is justly thought, therefore, that phosphates, potash, and ni- trogen are vital points in the art of fertilization ; and a high authority says, " A fertilizer may be considered com- plete when it contains lime, potash, lime phosphate, and a nitrogenous substance." Before considering the geo- logical means which may be made available for keeping up the fertility of the soil, it will be well to examine a few analyses of soils of various kinds ; for, although questions are often raised as to their practical value, based on the local variability of soils, yet there can be no reasonable doubt that, when properly made after careful sampling, they may be of the greatest service to the agriculturist in revealing to him the capabilities of his soils and their needs. The soil No. 3 of the Barrens is striking, from its de- ficiency in phosphoric acid, the alkalies, and organic mat- ter ; and its very small proportion of alumina, the basis of clay, shows it to be excessively leachy, whence, doubtless, u6 APPLIED GEOLOGY. ,Sn S en co *>. o o q q en g M en in q m CO M pp ouoqdsoqj en ON M en I ,PO S ? a * m JU3D jad 'qsBjoj vq juao jad ^t* d W XO M . M in vq vq M M 5 ,U3D in O en in g jad 'aunq M M w in juao jad O Tf Q CO CO M r^ o co O & en in ON 'apixo UGJJ co m M ex en rf rf N M r^ O ^" in M tA O I ON CO jad 'Buiuiniy ^ * M ^ M M JU3D in rj- O in ON t^ ^ en en jad 'BOIJICJ t> vO ON CO CO CO 5 S rf in juao jad 'jaj Tf- Q O ON en W Tt co in en o CO ct en -JBUI OIUBSjQ ^t" M ci C4 M ON CO ^ M N 8 : I * 1 T3 O i o? O >; a & 3 T^ JJ rt rt C TJ 'S ^ O 8 g 2 ft >; s U C bfl ^ r$ *"U ^ & O 1 "i 1 1 1 2 u s ft 1> fc t > o b/J o o !> .S2 ei 2i s 8 _r ^ W ^i d J" r^ ^ a, 1 -- = x9 7 ^8 a s-; * 'S -^ n3 e rt OS > j- (^ Pu c/3 O c/2 1 1 j 1 1 Black swam i H es en rf in o tA CO* ON RELATIONS OF GEOLOGY TO AGRICULTURE. 117 its deficiencies originate. Soil No. 5 probably owes its exhaustion to its low proportion of organic matter and of lime. Nos. 7, 8, and 9 abound in fertilizing elements, but would be likely to need attention to their physical condi- tion. No. 4, which is considered still good after a cent- ury of culture, though evidently not abounding in organic matter, has in eight inches of depth, on the moderate estimate of two million pounds to the acre Phosphoric acid, 3,000 pounds per acre. Potash, 14,800 Lime, 19,400 Magnesia, 15,000 Using now the table of ash analyses and per cent of ash given on a preceding page, it may be seen that a crop of twenty-five bushels of wheat = 1,500 pounds, if the straw, etc., equals fifty-six per cent of the crop, will take from the soil Phosphoric acid, 11.175 pounds in grain and 4.1 pounds in straw. Potash, 5^ 18.1 Lime, -j% 4j Magnesia, 2j Several other crops draw much more of these ingredi- ents from the soil. An estimate made in the " Geological Report of New Jersey," 1879, at page 116, of the amounts of important minerals withdrawn from the soil by a five years' rotation, of clover two years, and Indian corn, pota- toes, and wheat, each one year, gives 581 pounds potash, 259 pounds lime, and 179 pounds phosphoric acid, of which, however, nearly all the lime, and considerably more than one half of the potash and phosphoric acid found in the clover, straw, corn-stalks, and potato-tops would, in care- ful farming, be retained on the estate and returned to the soil in the form of manure. The tables that have been given, and the specimen of computations that may be based on them, will serve to indicate the proportions of Il8 APPLIED GEOLOGY. essential mineral elements that are found in various fertile soils, the approximate amounts that are certain to be with- drawn from them by various crops, and the importance of restoring to them in some form the fertilizing principles that have been withdrawn, to prevent a progressive ex- haustion. An examination of Table I will show that, while lime preponderates over magnesia in the straw of the various cereals, the reverse is true for the grain ; and when to this is added the fact that magnesia, from its great power of absorbing and retaining moisture, tends to give freshness to soils, it will suggest the expediency of testing magnesian quicklime on soils in which lime is deficient, despite the prejudice against it. Geological Fertilizers. Recalling now to mind the native composition of fertile soils, and that the constant tendency of the most judicious cultivation is to withdraw from them certain substances of capital importance, espe- cially nitrogenous compounds, the phosphates, the alkalies potash and soda, as also lime and magnesia, it becomes a question of much importance what materials the earth's crust can supply to enhance the fertility of the soil without undue expense. Among these substances, one of the most widely distributed and cheaply available is peat, or swamp- muck. There are few localities in the Northern United States or Canada where it does not occur, and often in de- posits of very considerable extent, in marshy spots, or at small depths beneath the surface, occupying the sites of for- mer swamps and ponds. It not only improves the color of soils, making them more readily warmed, and their texture, rendering them more pulverulent and more retentive of moisture, but it also adds to them small but important amounts of alkalies, and often phosphoric acid, while by its decomposition it furnishes to growing plants supplies of nitrogen and carbonic acid ; and it is claimed that it also absorbs ammonia from the air. It should be weathered in heaps for some months before being used ; or, better, it RELATIONS OF GEOLOGY TO AGRICULTURE. 119 may be composted in various ways. It may be composted with barn-yard manures, to which it not only adds its own fertilizing principles, but aids very materially in retaining the nitrogenous substances which might otherwise be dis- sipated in the process of fermentation. It is also com- posted with quicklime, or with lime and a small amount of salt, a good mixture being, it is said, a bushel of freshly slaked quicklime, or of lime slaked by brine, to twenty bushels of peat. " Experience has fully sustained its claims as a useful fertilizer, and chemical analysis shows that it contains the elements needed to stimulate the growth of farm-crops." (" Geology of New Jersey," 1868, p. 486.) Another widely diffused mineral fertilizer, previously mentioned in another connection, is lime, which is already much used in agriculture, and is destined, doubtless, to a much wider application, with the spread of better methods of tillage. Not only those wide-reaching formations of cal- citic and magnesian limestones, mentioned in the section on building materials, but also thinner and more locally developed seams, little regarded as building-stones, and somewhat too largely charged with impurities to be favor- ites for mortars, may furnish cheap local supplies for agri- cultural uses, benefiting the soil as well by the silicates and sulphates of lime developed in the burning, as by the caustic lime and magnesia which they furnish in their most finely divided and active form. These, as has already been remarked, make clay soils lighter and silicious ones more firm, lighten and sweeten damp and turfy soils, and contribute to the destruction of weeds and insects, while furnishing elements which analysis shows to be essential to the growth of most cultivated plants. Their efficiency in promoting the solution of other constituents of the soil is also, doubtless, very considerable. To derive the fullest benefits from their use, their application should usually be followed by that of organic manures. Besides the use of quicklime as a fertilizer, a stimulant, 120 APPLIED GEOLOGY. and a solvent, benefit would doubtless be derived by many soils from the application of calcareous marls, where they may be obtained in the immediate neighborhood. Such marls may be found, usually in small ponds, in some por- tions of the Northern and Eastern States, where they are occasionally burned for lime ; but their original pulveru- lent condition permits their application to the soil in their raw or unburned state, where their action as a source of lime is more gradual and prolonged than that of caustic lime. Also, under many peat-beds is found a calcareous marl, formed of fresh-water shells, which may be advan- tageously used for the same purpose. Beds of calcareous marls of marine origin are extensively developed in the Cretaceous and Tertiary formations of the States bordering the Atlantic and the Gulf of Mexico, from New Jersey southward, which, besides their carbonate of lime, contain often important amounts of potash and phosphoric acid, and which are destined to be largely used in the regions where they occur. Of greater importance, however, than these last-named marls are the greensand or glauconitic marls, which are found in similar geological formations and in the same re- gions, and which derive their chief value from the very im- portant proportions of potash and phosphoric acid with which they are charged. These marls have been very largely used in New Jersey, where they abound in three beds of somewhat different properties ; and the effects that have followed from their use are thus strongly stated by Prof. Cook, "Geology of New Jersey," 1868, page 442 : " The marl which has been described in the preceding pages has been of incalculable value to the country in which it is found. It has raised it from the lowest stage of agricult- ural exhaustion to a high state of improvement. . . . Lands which in the old style of cultivation had to lie fallow, by the use of marl produce heavy crops of clover and grow rich while resting. Thousands of acres of land which had RELATIONS OF GEOLOGY TO AGRICULTURE. 121 ppe ounqdjng apixo uojj Bununjy DOB ouoqasoifjj M d Tt CO N O RcoO w TtOcOvO O 9 *? *"1 ^ H ^ *"1 *9 cococoinTtTtTtinin 8 u "rt (3 ^si! o en Tt CO Tt Tt O M N M O CO H H M H cj 'S .& s fi -s a 1 J 1 s ffi S S 122 APPLIED GEOLOGY. been worn out and left in commons are now, by the use of this fertilizer, yielding crops of the finest quality. In- stances are pointed out everywhere in the marl district, of farms which in former times would not support a family, but are now making their owners rich from their produc- tiveness. Bare sands, by the application of marl, are made to grow clover, and then crops of corn, potatoes, and wheat." The work from which this is quoted gives, in the succeeding pages, an account of the mode of using this fertilizer and its results, which the student can profitably consult ; as also Prof. Kerr's " Report on North Carolina Geology," 1875, in which will be found an account of the Tertiary calcareous marls of that State and their great value in agriculture. On page 121 are given a few analyses of greensand marls from New Jersey which may be found use- ful, those being selected which have been approved in use. It will be observed that in all these marls phosphoric acid is present in considerable proportion, and to this sub- stance much of their efficiency is ascribed. In many of them, -also, potash is found in very considerable amounts, and there is no good reason to doubt that its liberation in the soluble form, in the course of the decompositions that go on in the soil, gradually furnishes to plants this impor- tant element in their nutrition. Of the silicic acid, a very considerable proportion exists in an easily soluble condi- tion ; and when it is considered how large a proportion of this substance is found in the stems of plants, the prob- able significance of this fact will be apparent. Doubt- less, some other elements in these fertilizers, especially lime, aid in enhancing their value. The use of these marls in New Jersey is fully 100,000 tons per year, 1,080,000 tons having been dug in that State in 1882 for use and ex- port ; and it is certain that with the advancement of agri- culture in the Southern seaboard and Gulf States, in which these and other marls are known to occur, they will be sought out and used with great benefit to agricultural in- RELATIONS OF GEOLOGY TO AGRICULTURE. 123 terests ; though, from the few analyses at present attain- able, it would seem that the greensand marls are not there so rich in phosphoric acid and potash as those of the more northern localities. A rich supply of the phosphates needed in agriculture is obtained from the region in the vicinity of Charles- ton, S. C, where it is estimated that nearly eight hundred square miles are underlaid more or less abundantly with phosphatic masses, of which twenty thousand acres are counted worth working with the present appliances for obtaining it. In this region, the phosphatic nodules are found along the courses and in the beds of streams, from which they are dredged, or underlying the surface at vary- ing depths in a stratum which, according to Prof. Holmes, averages about fifteen inches in thickness. It is reported that, in 1883, 332,079 gross tons were produced, the rock being sold on a guarantee of containing not less than 55 per cent of lime phosphate, or about 25 per cent of phosphoric acid ; and in the same year the shipments of manufactured fertilizers from Charleston are reported as amounting to 130,000 tons. These figures will give an idea of the vast extent to which the supply of this valu- able fertilizer has already attained, from a source whose importance had not come to be understood so recently as 1868. Another source of phosphoric acid which is rapidly attaining importance in this country is found in the mineral apatite, which occurs as beds and veins in rocks, chiefly of Archaean age. Deposits which may prove of economic importance occur at Bolton, Mass., and at Crown Point, N. Y., the latter of which is said to be extensive and has been mined to a limited extent. The deposits of greatest present importance are those found in Canada, in a region extending northeastwardly from near Kingston in Ontario, into Ottawa County, Province of Quebec. The deposits here occur in both beds and veins, of which the former 124 APPLIED GEOLOGY. afford the largest and purest supplies. The amount mined in 1883 reached, it is said, 23,000 tons of rock, containing from 75 to 85 per cent of lime phosphate. A small por- tion of this comes to the United States, but most of it is sent to England, where it is made available for agriculture by treatment with sulphuric acid. Guano, also, which attains to the rank of a kind of geological deposit on certain islands off the coast of Peru, and to some extent of Africa, may pioperly be mentioned here. These deposits, formed from the droppings and remains of sea-fowls, during countless generations, in re- gions nearly rainless, are very rich in compounds of am- monia and phosphorus, and have for forty years been largely imported into Europe, and to some extent into this country, for use in agriculture. According to estimates made in 1873 of the amounts then remaining available, the supply is destined to speedy exhaustion, as at that time less than twenty years' supply could apparently be count- ed on. A geological source of the nitrogen so needful for plant- growth may be found in the waste from the distillation of bituminous coal in gas-making and coking. Nearly all the bituminous coals of Ohio and Indiana which have been fully analyzed show a content of nitrogen amounting to an average of about one and a half per cent, and the same is doubtless true of other coals of this class. In the process of distillation this nitrogen is driven off in the form of ammonia, which may be converted into the sul- phate or used to increase the ammonia in the compost- heap. A mineral fertilizer very largely used as a top-dressing for various crops, especially clover and Indian corn, is ground gypsum, commonly known as land-plaster. This substance is a sulphate of lime, and there is a wide diversity of opinion as to the cause of the surprising results attending its use in many cases. The Atlantic seaboard States are RELATIONS OF GEOLOGY TO AGRICULTURE. 12$ supplied with it from Nova Scotia, where it is found in enormous beds in rocks of Lower Carboniferous age. New York has large deposits in rocks of the Salina period, ranging from Oneida County westward, near the line of the Erie Canal ; and it is quarried at many places and shipped to considerable distances, both ground and un- ground. Near Sandusky, O., it is obtained from rocks of the same age, and prepared both for agricultural use and for plaster of Paris. The great deposits in Michigan, along Saginaw Bay and near Grand Rapids, are found in rocks of the Lower Carboniferous ; and those at Fort Dodge, Io., are associated with rocks of the same age, these last deposits being of especial interest, because fur- nishing this fertilizer to an extensive region otherwise nearly destitute of it. Important beds of gypsum occur in two sections of Kansas, in the western part of Virginia on a branch of the Holston River, and in Pike County, Ark., while vast supplies of it are known to exist in the Triassic rocks of Texas. Great beds and lenticular masses of this substance, often of wonderful purity, are known to exist in nearly all the States and Territories of the far West, partly, as in Arizona, in rocks of the Carboniferous period, but chiefly in beds of the Triassic or of still later geological age. It will thus be seen that most sections of the United States and of the British Provinces are abun- dantly supplied with this mineral fertilizer, and that it occurs chiefly in rocks of the Salina, the Lower and Upper Carboniferous, and Triassic periods. The European de- posits are found chiefly in the Permian and Triassic, some also occurring in the Eocene Tertiary. Besides their use as fertilizers, many of these gypsum deposits are of suffi- cient purity to be available for use in the arts as plaster of Paris, more particular mention of which will be made in another connection. Common salt, also largely used as a fertilizer to supply to plants soda and chlorine, is very widely distributed 126 APPLIED GEOLOGY. over the United States and Canada, being obtained chiefly from brine-wells sunk in rocks of the Salina period, in western New York, largely at Syracuse and Warsaw, and at Goderich in the Province of Ontario ; and in rocks of the Lower Carboniferous and Carboniferous periods in eastern Michigan, West Virginia, and the adjacent part of Ohio. Great deposits of rock-salt are found at Petit Anse in Louisiana, in materials of somewhat recent geological formation, and throughout the far Western and Pacific States and Territories abundant supplies await the devel- opment of those regions. In these latter regions are also found at several points mixtures of salt with sulphates and nitrates of potash and soda, affording substances which must ultimately become of great importance in agriculture as sources of nitrogen and potash. Similar crude salts are obtained for use in agriculture and for other purposes from South America in the rainless western regions ; and crude salts of potash used in European and American ag- riculture are obtained from beds occurring in the Permian salt deposits of Stassfurt in Germany. What have here been briefly enumerated and described are the chief fertilizers supplied to agriculture from geo- logical sources, and the judicious use of which may be ex- pected to increase largely the productive capacity of the soil. The beneficial effects of some of these are produced at once, and are quite limited in their duration, while others, acting more gradually, constitute a permanent im- provement of the soil. Both of these classes of fertilizers may be used with advantage; but questions of expense incurred, as compared with benefits received and returns obtained, depend on many circumstances which belong rather to the science and art of agriculture than to applied geology. Drainage and Subsoils. The geological considera- tions which influence drainage, whether undertaken in the interests of agriculture, or for the promotion of healthful RELATIONS OF GEOLOGY TO surroundings, or for the reclamation of waste lan< already been suggested on page 64. They consist in the presence of a sufficient declivity to insure the easy passage of water through under-drains, and ultimately the free outflow of the collected waters of drainage, or, in the case of flat-lying districts, in the possible existence in the sub- soil or underlying rocks of porous beds or fissured and jointed strata, which may serve as water-ways and afford an underground outlet to drains and cess-pools ; or, on a larger scale, in the removal of geological barriers and ob- structions caused by geological agencies, such as have con- verted tens of thousands of acres in central New York into the pestilent fen called the Montezuma Marsh. An example of the reclamation of a similar district by the re- moval of a barrier has recently been presented by the suc- cessful draining of the " Great Meadows " in Warren County, N. J., where an area of five thousand five hun- dred acres has been opened to cultivation, while the sur- rounding region has been freed from a fruitful breeding- place of malarial diseases. In all cases of difficult drainage examination should be made of the structure of what lies beneath the soil. Not unfrequently it may be found that the need of drainage arises from the presence of a com- paratively thin crust of hard-pan, and that if this be broken up the difficulty will disappear. In a much greater pro- portion of cases than would be supposed, also, porous or fissured strata at no very considerable depths will furnish an easy outlet for both farm and house drains, promoting at the same time agricultural fertility and personal health and comfort. Prof. Emmons, in his report on New York agriculture, vol. i, calls marked attention to this too often neglected means of drainage. Such an examination can be easily and cheaply made, and, though it may not be needed for the purpose of facilitating drainage, it will re- veal to the agriculturist the nature and resources of his subsoils, giving him information which is second in im- 128 APPLIED GEOLOGY. portance only to a knowledge of the capabilities and needs of the soil ; for the subsoil may aggravate the defects of the arable surface by its tenacity or its permeability, or, on the other hand, it may furnish a ready means of reme- dying these defects by beneficial mixtures. Very fre- quently it will be found capable of restoring to the soil elements of fertility of which it may be measurably ex- hausted, or it may even be found to contain at no great depth unsuspected deposits of valuable fertilizers, as has been found true already in many sections of our country. Expedient as such careful examinations clearly are in all ordinary cases, their importance becomes especially great in regions where valuable fertilizers are known sometimes to occur, as well as in those where it may reasonably be suspected that deposits of valuable minerals like iron and coal may exist. It has frequently happened that estates have been sold merely for their value as farming-lands, from the mineral resources of which well-instructed in- vestors have derived great wealth wealth, too, which the former owners might have shared had they taken the pains to make or procure a proper examination of their lands. Scientific surveys made by governments can afford little benefit to those who permit themselves to be ignorant of their results, or who neglect to apply their teachings by such careful local examinations as they ought obviously to suggest. Works which may profitably be consulted. In general, the Geological and Agricultural Reports of one's own State. " Natural History of New York, Agriculture," vol i ; " New Jersey Geological Report," 1868, pp. 378-500; and 1879, pp. 103- 120; "Ohio Geological Report," 1870, pp 320-381 and pp. 452- 459; "Second Geological Report of Arkansas," p. 42-54 and pp. 171-179, etc. ; " Geological Report of North Carolina," 1875, pp. 162-217. The " Annual Report of New Jersey for 1870 " also con- tains an account of the drainage of marshes. I have also been greatly indebted in the preparation of this chapter to the following French works : Meugy, " Geologic Applique"e a 1'Agriculture," and D'Orbigny et Gente, " Geologic Applique"e aux Arts et a 1'Agriculture." CHAPTER VII. RELATIONS OF GEOLOGY TO HEALTH. Two highly essential conditions of health for both in- dividuals and communities are supplied by wholesome water and pure air. Indeed, it can not be doubted that a large part of the diseases to which human beings are liable is due to the lack of one or both of these essentials. Both are very largely dependent on geological agencies, or on geological structure ; and hence it is proper that the im- portant subject of sanitation should be considered here in its geological aspects. The purely geological sources of water-supply have al- ready been discussed in the chapter on springs, wells, and artesians, in which also were pointed out the dangers of contamination, and the precautions needed in some cases to secure a tolerable degree of purity. The importance of the subject is so great, however, that there is little dan- ger of its being pressed too strongly upon public attention ; since, even with the wide diffusion of information with regard to it, large numbers of people thoughtlessly persist in exposing both health and life to imminent risk by the use of readily obtainable water-supplies from sources pe- culiarly liable to contamination, while quite generally also showing a disposition to attribute the disorders resulting from this carelessness to some other than the real cause. Doubtless, a considerable portion of diseases incident to the settlement of some of our new territories could be 130 APPLIED GEOLOGY. avoided by the use of filtered rain-water ; while in thick- ly settled villages and cities, the water of all wells, save those most favored by the underground structure, and most carefully guarded, can be used only at great risk to health. Even in the case of deep driven wells passing through thick beds of clay, a source of danger has re- 'cently been revealed, in the occasional corrosion of the iron tubing by foul superficial waters, which may thus gain unsuspected access to the domestic supply, suggest- ing the expediency of a frequent examination of these tubes, possibly by drawing up to view the portion that is exposed to risk of corrosion. In any use of the water from wells and from springs, save those from exception- ally deep-seated and remote sources, safety can be assured only by the exercise of intelligent care at the outset, and of constant vigilance afterward. So limited, however, is the supply from most of the geological sources, and so great is the risk of dangerous contamination in those most widely used, that nearly all large cities seek their water from other sources. Many, like Philadelphia and St. Louis, draw their supplies from the higher reaches of riv- ers on which they are situated, trusting to the purifying effects of atmospheric exposure to so far free the waters from the organic impurities with which they are more or less largely charged as to bring them within reasonable limits of safety ; this source of supply being open to the obvious objection that, whatever may be the present con- dition of the water, it is sure to undergo a progressive de- terioration from the growth of cities, villages, and manu- factories on the upper course of the river, all of which will discharge their waste into it ; not to speak of the impor- tant increase in amount of organic matter that must find its way into it from fields coming more widely into a high state of cultivation. Other cities, like Chicago and Cleve- land, drive expensive tunnels far out beneath great bodies of fresh water, where the geological nature of the bottom RELATIONS OF GEOLOGY TO HEALTH. 131 makes this feasible, deriving thereby abundant and unob- jectionable supplies. Still others, like New York, construct costly dams and reservoirs and aqueducts, to gather and bring water from distant, sparsely settled, and elevated dis- tricts ; in which case many important circumstances need to be carefully weighed, some of which, and those of no minor importance, involve questions of geological structure. For not only is it necessary to consider the average amount of rainfall and the extent of gathering-ground, but also the geological character of the entire area becomes a matter of serious importance, since it is sure to influence the character of the water derived from it, and to condition both the feasibility and the expense of the dams that are to be constructed, and the ability of reservoirs to retain the water that may be collected into them. The water derived from a granitic area of catchment will differ greatly from that drawn from a limestone region, or from one underlaid with ferruginous sandstones and shales, and containing, it may be, considerable tracts of swampy ground. It is worthy of observation, also, that those dis- tricts which are likely to yield the most unobjectionable supplies of water are those least likely in the course of time to attract a numerous population, and thus to furnish an ultimate source of defilement. So, too, " the rocks of one glen may be retentive and eminently suited for a reservoir, while those of another may be so porous as to cause perpetual leakage ; the rocks and springs of one tunneled aqueduct might be innocuous to the supply, while those of another might contaminate it with sa- line and metallic impurities." (Page's "Economic Geolo- gy.") It is evident, then, that the problem of wholesome water-supply is by no means a very simple one, requiring, in the case of small communities, the intelligent applica- tion of geological principles and precautions ; while, where great numbers are to be provided for within small areas, it may tax the resources of the highest engineer- 132 APPLIED GEOLOGY. ing ability, aided by no slight knowledge of structural geology. The securing of pure and healthful atmospheric condi- tions is, in a very large degree, a matter of proper drain- age. Malarious localities are usually wet or at least damp ones, those in which certain forms of vegetation flourish and decay, giving rise to unhealthful exhalations, to which any organic waste from neighboring dwellings adds a deep- er taint. When the damp spot is dried, the wet or marshy tract drained of its superfluous water, the peculiar prod- ucts of organic decomposition which cause disease cease after a time to be supplied, and the region becomes more salubrious. Drainage for sanitary purposes, as well as for agricultural improvement, depends in numerous cases on expedients suggested by facts of geological structure. Ac- cording to the testimony of the Geological Survey of New Jersey ("Report" of 1880), the drainage of the Great Meadows in that State by the removal of a geological ob- struction has been quite as marked a success for sanita- tion as for agriculture, as is shown in the striking decrease of malarial diseases in the surrounding region. This is but one of many instances that could be given, where the sanitary improvement of considerable tracts of *' drowned lands " could be effected by the removal of geologically formed barriers to drainage. The reports of engineers show that the vast malarial region previously mentioned as the Montezuma Marshes, in central New York, owes its existence to such a barrier, and that its restoration to healthfulness can be effected only by the removal of this barrier. Of similar import is the necessity for sanitation, in grading portions of cities where great hollows occur surrounded by impervious barriers, of making sufficient provision for the under-drainage of these hollows before filling them up for building. Otherwise, even if unobjec- tionable materials are used in the filling, they are destined, through percolation from the streets and leakage from im- RELATIONS OF GEOLOGY TO HEALTH. 133 perfect sewers, to become ultimately subterranean reser- voirs of filth, the emanations from which can not but affect unfavorably the health of such localities. The sewerage systems of cities will always present some questions of geological significance. The course of the main sewers is naturally dictated by the slope of the ground, the oppor- tunities for safe outlet, and, not unfrequently also, by the relative expense of excavation. Besides this, in some lo- calities, the only desirable object may be the safe convey- ance of sewage, while in others it may be highly desirable to provide also for the drainage of wet tracts ; such con- siderations, in either case, controlling the choice of the materials with which the sewer should be constructed. In villages and small cities, where no general sewerage sys- tem is provided, the needful sanitary arrangements for dwellings must depend mainly upon supplying subterra- nean outlets through porous beds for superfluous or con- taminated fluids. Where, from the nature of the under- ground structure, such drainage is not practicable, careful provision should be made for the frequent disinfection and proper discharge of impervious receptacles. When porous beds are made the outlets for house-drainage, it should always be borne in mind that any water-supplies derived from them will inevitably be contaminated. Sewage, how- ever filtered and diluted, is not a fit beverage for human use. Numerous cases of severe and often fatal illness can, with a little care, be traced to this cause. Should any one think that such careful provision for pure water and untainted air as has here been suggested is unnecessary, or too troublesome, it will be well to reflect that it accords with the uniform experience of civilized mankind ; and that matters of such vital consequence as the health and happiness of human beings are too serious to be trusted to chance. All experience has shown that regions well drained and supplied with wholesome water are healthful ones ; that cities kept properly clean and 134 APPLIED GEOLOGY. abundantly supplied with pure water show a diminished death-rate ; that great epidemics, like cholera and yellow fever, either leave such cities and regions unscathed, or visit them with greatly mitigated violence, having their breeding-places in regions of filth, and confining their ravages chiefly to uncleanly and badly watered localities ; and that diseases like diphtheria and typhoid fever can usually be traced to defective drainage and impure water. CHAPTER VIII. MINERAL FUELS. AMONG all the mineral substances procured from the earth, the mineral fuels doubtless hold a foremost rank in importance, contesting even with iron for the supremacy in supplying the wants of civilized man. Indeed, the in- dustrial rank of nations may be very accurately judged from the extent to which they utilize their fuel supplies. Great Britain, the United States, and Germany, the three foremost manufacturing nations, produce four fifths of the mineral fuels of the entire globe. These highly important substances, whether anthra- cites, bituminous coals, lignites, or peat, are generally con- ceded to have resulted from a peculiar decomposition of vegetable tissues. There are a number of questions as to the particular mode in which these deposits originated, and the special forms and portions of vegetation that fur- nished their chief materials, which, although they are of much theoretical interest, are yet not of such practical im- portance to the student of economical geology as to claim our consideration here. It is sufficient for our present purpose to observe that the chief constituents of all vege- table tissue are carbon, oxygen, and hydrogen, with small proportions of nitrogen and some earthy substances. When these tissues decay or are burned with free access of air, their elements are dissipated in the form of carbonic acid and watery vapor, and ultimately nothing remains 136 APPLIED GEOLOGY. but an inorganic residue constituting the ash of the plants. When, however, vegetable substances undergo decay out of contact with the air, whether covered with earth or heaped together in wet places, and partly or wholly covered with water, the changes that take place in them are due mainly to chemical rearrangements that occur among their own elements. Of these, the oxygen unites with somewhat more than one third its own weight of carbon and with one eighth its weight of hydrogen to form carbonic acid and water. A portion of the hydrogen also unites with one third its weight of carbon to form marsh-gas, the fire-damp of coal-mines. The result of these several changes is that the relative amount of oxygen in the mass is diminished, while that of carbon, originally about one half of the whole, is increased ; the color be- comes darker, first brown, then nearly or quite black, from the increasing preponderance of coaly carbon, while the relative proportion of hydrogen is but slightly changed. The resulting substance, in the slow process of ages of this kind of change, passes through the condition of peat or brown coal, to become what is known as bituminous coal, or ultimately to be converted into anthracite, in some much-disturbed regions where probably heat accelerated the dissipation of most of the oxygen and hydrogen still remaining in the coal. That this process of chemical change is a gradual and protracted one, continuing even to the present day, is shown by the fact that marsh-gas and carbonic acid, or " choke-damp," are still eliminated from most coal-beds, and present some of the most dreaded dangers of coal-mining, against which careful provisions for ventilation, and the use of safety-lamps, do not always avail to prevent frightful casualties. Thus oxygen, useless as a fuel, is progressively eliminated, while the combustible elements, carbon and hydrogen, become ever more dominant, during the process by which coal is formed. By reference to the table of analyses given on a MINERAL FUELS. 137 subsequent page, it may be seen that, in the course of this series of changes, the carbon, from being originally a little less than 50 per cent of the whole, becomes 60 per cent in well-formed peat, more than 66 per cent in brown coal from 70 to more than 80 per cent in ordinary bituminous coal, and finally 90 per cent or more in anthracite ; that the hydrogen, originally 6^ per cent, remains tolerably uniform in relative amount till the anthracites are reached, when it becomes, together with other volatile ingredients, not more than from 3 to 10 per cent, while oxygen dimin- ishes from 43 per cent to an average of about 10 per cent in bituminous coals (a considerable portion of this being due to the presence of water), and to a much smaller amount in anthracite. Now, these progressive changes in the relative propor- tions of the constituent elements are attended with con- siderable differences in the physical character of the suc- cessive products, and in their behavior when used as fuels. On these differences has been based a convenient prac- tical classification of those variable substances called collectively mineral coals. This classification is primarily into anthracite and bituminous coal, the first of which neither softens nor swells in burning, yielding no smoke and little or no yellow flame, while the second softens and often swells in the fire, emitting much smoke and abun- dant yellow flame. These two great classes admit of a somewhat convenient subdivision, not always observed in practice, into hard and semi-anthracites, semi-bituminous and bituminous coals a subdivision which is based on the relative proportion of volatile combustible substances con- tained in them, together with certain tolerably well-marked differences in their physical characters. The hard anthracites, which usually contain less than 5 per cent of combustible gases, kindle with difficulty, and burn with an intense heat and little blue flame, have a more or less marked conchoidal fracture, a brilliant luster, 138 APPLIED GEOLOGY. and a specific gravity of from 1.5 to 1.8, being the heaviest and hardest of all coals. The semi-anthracites, containing from 5 to 1 1 per cent of volatile combustible materials, kindle and burn more readily than the former class, giving a strong heat, often accompanied at first with a little yellow flame. They have a specific gravity of from 1.4 to 1.5 and sometimes more, are softer and less lustrous than the hard anthra- cites, and have usually an angular fracture with a tend- ency to break up while burning. The semi-bituminous coals have from 12 to 20 per cent of volatile constituents and a specific gravity between 1.3 and 1.45, while the bituminous coals have more than 20 per cent of volatile matter, and their specific gravity is from 1.2 to 1.35, that of some of the Ohio coals being even more than 1.4, though the average gravity of this class of coals is less than 1.3. Both these kinds of coal liberate a part of their volatile matter, when heated, in the state of a dense oily liquid resembling bitumen, whence their name ; they also emit a bituminous odor when burning. A further subdivision of the bituminous coals is made on physical characters of much economical importance, into caking, cherry, splint or block, and cannel coals. The caking coals, when heated, soften greatly, and the fragments fuse together, or agglutinate into an adhesive mass, which is puffed up, by the gases liberated by the heat, into a hard and highly cellular substance called coke, consisting of the fixed carbon and mineral matters originally present in the coal. This property fits them to be used for the manufacture of coke, and for purposes where a " hollow fire " is desirable, as in blacksmithing, while rendering them much less convenient for domestic use. The cherry coals, which owe their name to the beauty of their appearance, are usually highly lustrous but very brittle coals, which do not agglutinate when heated. MINERAL FUELS. 139 Their brittleness gives rise to a great amount of waste in mining and transportation, while their lack of adhesive- ness when heated fits them for use as a domestic fuel. The splint or block coals are hard, highly laminated, and difficult to be broken across, have a dull luster, and do not agglutinate when heated. Their properties adapt them especially for use in iron-smelting, for which they are largely utilized. They are often called dry-burning or open-burning coals, a name equally applicable to any of the non-agglutinating coals. The cannels, of which Prof. H. D. Rogers proposed to make a distinct primary class under the name of hydro- genous coals, are characterized by their large proportion of volatile matter and their small amount of coke-like residue, their dull luster, their conchoidal or slaty fracture, and their tendency to split when burning with a crackling noise, somewhat like the chatter of a parrot, whence they are often called parrot-coals. They derive the name can- nel (i. e., candle) coals from the readiness with which they take fire, and the cheerful flame with which they burn. This makes them favorites for use in open grates ; they are also largely used in making illuminating gas. The lignites or brown coals are of much more recent geological origin, and usually much less completely car- bonized, than those which have just been described. They are called lignites, because they frequently exhibit the woody structure of the plants from which they are de- rived, from the Latin word for wood, and brown coals, from their color or that of their powder. They burn read- ily without fusing, and emit a sooty smoke and a disagree- able smell. The lignites, as a class, contain a much larger proportion of water than other coals a circumstance which greatly diminishes their value as fuel, since so large a portion of their heating power is wasted in converting into steam the water which they contain. The lignitic coals, which occupy vast areas in the western part of this 140 APPLIED GEOLOGY. continent, differ widely in quality. Some are hardly dis- tinguishable in appearance or character from the true bi- tuminous coals, having but a small per cent of water, and being sometimes capable of yielding a good coke ; while others have a high per cent of water, often from 12 to 20 per cent, and crumble to a coarse powder when exposed to the air, being on both accounts very indifferent fuel. It will be convenient, for purposes of reference, to re- sume in tabular form the classification of the mineral fuels, with the characters on which chiefly it is based, omit- ting for the present any consideration of peat : Anthracites do not soft- en ; no smoke ; little flame. Hard anthracite volatile to 5 per cent ; sp. gr. 1.5 to 1.8; hard; lustrous; conchoidal fracture. Semi-anthracite volatile 6 to n per cent ; sp. gr. 1.4 to 1.5 ; less hard ; luster dull ; fracture angular. Semi-bituminous volatile 12 to 20 per cent ; sp. gr. 1.3 to I 45. Bituminous volatile above 20 per cent ; sp. gr. 1.2 to 1.4. Caking agglutinates. Cherry non-agglutinating ; lustrous ; brittle. Splint or block non - agglutinating ; dull ; tough ; laminated. Cannel largely volatile ; dull luster ; I conchoidal or slaty fracture. Lignite brown powder ; usually contains much water ; no fusion ; sooty smoke ; bad smell. Bituminous soften ; yield oily fluid ; much smoke and flame. . . . The following table of analyses, derived from various sources, is given to illustrate the composition of the vari- ous classes and kinds of mineral fuel ; to which is added an average analysis of woody tissue derived from several different kinds of tissue. About one half of these are what are called proximate analyses, i. e., those giving only the per- centages of fixed carbon, volatile constituents, and ash, with sometimes those also of water and sulphur. The re- MINERAL FUELS. 141 -* eoinr^MOcocoONNTt- rt w co in ON m ON t^* co t** co CJ o* d d d d d d IN d w d COO O N co O co incom co t^ O M in co MO M o f^-t^OCO MCOO ON ^1 1 \O CO M t^ ON rt* O vO , r^o^MOcovo rfo ininininininTJ-vd co co O O vO in vO m vO *** mo ONf^coO inw rJ-rJ-ONd O t^OO Tf Mdco'ModcTNd ** t^ r^ co co co t^ i^ CO M Q w co q r^ \o Tt* W o A SWMOMininr^OOcoQ OcoO inOmcorj-ONMMcoON ar^O o CO cotNint^t>ONCOinONMCO ONO MWCOCOCOM ^-inm p;r coomONOi-iinininin *f O OWOcocMONMMinONMco OmQ R CO in &$ '&'8 5c?^ * t^ CNJ in rj- ON O d t>. co' ci d w 8 w 8coOOMONHf^ininininiNvNOOcoOrj-t->.O MOmMvOMt^MCOTj-CONinTj-MvOOCOMO ovd TJ-cdvdvd M d inci M coco>ne4 cot>-coT}-ci ci oyibadg ON m O O c* vO O vO w in w t^ co M co b/> . . -"rt . >^ : j" 8 V j S a ^ . j d 05 !^ 1 : : i i *. g s c^ ^=f 0-^ -a : ; ^1^-rts^^bJD ^^i^y ) e :>. iIi;ilfll!iKii4f S ^ J* S limits 111 | lllll 1 Ititlllll! r ^ s - s ^ S je .-a 6 f 5 , ^ fc I 'J3 -g Tf ig. Wigan, Lancashire.. . 20. Brown coal, Bovey, England. 21. Lignitic coal, Bellemonte, Col.. 22. Woody tissue, average 5 ~ s s 'S 'S 1 ' ~ g = = a g = | = .-a O w c cOTfinvo' t^-cd I 4 2 APPLIED GEOLOGY. mainder are ultimate analyses, giving the percentage of all the elements ; while five of them, taken from the " Geo- logical Report of Ohio," 1870, combine both forms of analysis : Geological Associations of Mineral Fuels. The coals and lignites occur as beds of varying thickness, in- terstratified with other beds of sandstones, shales, fire- clays, and occasionally limestones. The coal-beds, or seams, as they are frequently called, vary in thickness from the fraction of an inch to many feet. The Mammoth bed, in the Pennsylvania anthracite region, measures, at two points mentioned by Ashburner, one hundred and one hundred and fourteen feet, ranging between sixty and ninety feet over a large area in the Black Creek basin ; while at St. Etienne, near Lyons, France, the main coal, according to Geikie, averages forty feet in thickness, and swells out oc- casionally to as much as one hundred and thirty feet. The main seam at Pictou, Nova Scotia, is about forty feet in thickness, and the Xaveri seam in Upper Silesia is, ac- cording to Credner, sixteen metres or over fifty-two feet thick. On the other hand, in every coal-region there are large numbers of very thin seams which are economically worthless, a thickness of three feet being usually consid- ered as small as can be profitably worked by underground operations. Of the eighty or more seams found along the head of the Bay of Fundy, not more than four or five are workable. Southern Wales has twenty-three workable seams out of more than eighty. Southern Russia is said to have, on the river Donetz, as many as two hundred and twenty-five coal-seams, of which but forty-four are consid- ered worth working ; while of the one hundred and thirty- two seams in the Westphalian coal-field, near the Rhine, seventy-four are workable. These few examples, which could be greatly multiplied, will serve to show both the wide variations in thickness which coal-beds, like other strata, may assume, and also the extent to which they may MINERAL FUELS. 143 alternate with other rocks in the series of strata or meas- ures in which they occur. Very thick coal-seams, like some of those mentioned above, are by no means made up entirely of coal. They are nearly always separated, by seams of shaly matter or of very impure coal, into several subordinate layers or benches, which often differ consider- ably in character. Thus the Mammoth seam, where it is one hundred and fourteen feet thick, has eight feet of rock other than coal interlaminated with it ; and the Pictou main seam, where nearly forty feet thick, affords but about twenty-four feet of good coal, being interstratified with six bands of shale and ironstone or coarse impure coals. Besides the seams of coal, the rock series, constituting coal-measures, is made up of various alternations of sand- stones, fire-clays, shales containing not unfrequently valu- able deposits of clay ironstone, and, less frequently, strata of limestone. Occasionally, also, there occur in some re- gions seams of highly bituminous iron carbonate called black-band iron-ore, highly esteemed as a source of iron. The coal-seams are almost invariably found to be under- laid by a bed of fire-clay, or of clayey sandstone, varying from a few inches to several feet in thickness, and contain- ing usually great numbers of fossil roots and curiously pitted stumps, called stigmarice, which are evidently the remnants of a former vegetation that grew on them as soils. These under-days are therefore generally believed to be the ancient dirt-beds from which sprang the vegeta- tion that was transformed into coal. The under-clays are often found to be clays of such purity as to be capable, after being properly disintegrated by weathering, of being wrought into pottery, or molded into highly refractory fire-brick, whence their name of fire-clays. Their refrac- tory character is, in all probability, due to the circumstance that the vegetation of the coal-beds withdrew from them those ingredients, like potash and lime, which cause clays to fuse at very high temperatures. (Newberry.) 144 APPLIED GEOLOGY. Aside from the usual position of the under-clays, there is no fixed order of sequence of the strata which make up coal-measures ; though it is very common to find a layer, sometimes quite thin, of bituminous shale, or very shaly coal filled with leaves and fragments of plants, resting im- mediately on the coal-seam. The nature of the strata which immediately overlie the coal is a matter of great practical importance, since upon it depend very much the ease and safety with which the coal may be mined. A roof of firm, thick-bedded sandstone greatly facilitates mining operations; while one of slippery and shivery shales is sure to cause difficulty and danger. Sandstones? however, sometimes present a curious danger of their own, in the form of what are called coal-pipes, the skeletons of ancient trunks of trees extending in a nearly vertical di- rection through the strata, the place of the bark being occupied by a tender film of coal, while that of the wood is filled with a solid column of sandstone. These, enlarg- ing downward and generally destitute of branches, are easily dislodged, and in their fall crush whatever may be underneath, a peculiar example, as Lyell remarks, of the long-deferred action of gravity. But though the various kinds of rocks which make up coal-measures in general present no settled order of rela- tive arrangement, yet in any particular coal-field the lead- ing strata, though often varying considerably in thickness, commonly show a surprising and very helpful degree of persistency in character and relative position. This is true, within limited areas, of some of the more important sandstone strata, but is more widely true of the leading seams of coal and limestone. For instance, Prof. H. D. Rogers estimates .that the great Pittsburg seam of the Ap- palachian coal-field underlies an area of not less than fourteen thousand square miles, in a continuous sheet of varying thickness, some other coal-seams showing a simi- lar constancy of position, though probably more limited in MINERAL FUELS. 145 extent. In like manner, some of the limestones of the Pennsylvania coal series are recognized in similar posi- tions in Ohio, where they are found persistent over large areas. Thus these persistent strata, whether of coal, of limestone, or sometimes of sandstone, become valuable standards of reference, or key-rocks, for determining the existence and the position of the useful rocks, which have been observed at some points to lie at a certain distance below or above them, due allowance being made for possi- ble local changes in character and thickness of strata. To illustrate what has been said as to the mode of oc- currence and associates of coal-seams, and as to persistent strata, the following general section of the lower coal- measures of Ohio has been taken from the second volume of the Ohio Geological Report : Thickness in feet. 36. Red and gray shales of barren measures 35. Stillwater sandstone, often conglomerate o to 50 34. Gray shale alternating with No. 35 o 50 33. Buff limestone, ferruginous " mountain ore ".... o 10 32. Blackband iron-ore, often replacing No. 33. ... o 14 31. Coal No. 7, " Cambridge," etc., seam 2 7 30. Fire-clay 3 5 29. Limestone in eastern and southern counties. ... o TO 28. Shale and sandstone 40 50 27. Coal No. 6 a, or " Norris" coal, sometimes with limestone over it o 6 26. Fire-clay 3 5 25. Mahoning sandstone, often conglomerate o 50 24. Gray or black shale, alternating with No. 25... . 5 50 23. Coal No. 6, " Straitsville " or "Big Vein" Upper Freeport of Pennsylvania 3 12 22. Fire-clay 3 5 21. Limestone in eastern counties = Freeport of Pennsylvania 2 8 21. Gray or black shale, nodular ii-on-ore at base ... 25 50 20. Coal No. 5, " Mineral Point," " Newberry " = " Lower Freeport " of Pennsylvania 2 5 19. Fire-clay, often non-plastic and excellent 3 6 18. Shale and sandstone 20 ,,4 I4 6 APPLIED GEOLOGY. Thickness in feet. 17. Limestone, " Putnam Hill " or " Gray " 2 to 8 16. Coal No. 4, often double, " Flint Ridge cannel " = " Kittanning " of Pennsylvania i 7 15. Fire-clay 2 12 14. Shale and sandstone, sometimes with coal 3 a. . 20 90 13. Blue limestone with iron-ore = Ferriferous of Pennsylvania 2 6 12. Coal No. 3, " Creek vein " i 3 II. Fire-clay, extensively used for pottery 5 15 10. Shale and sandstone, " Tionesta " sandstone.. . 30 50 9. Coal No. 2, generally thin, " Strawbridge " coal I 5 " 8. Fire-clay I 3 7. Shale 20 50 6. Massillon sandstone 20 80 5. Gray shale 5 ,,40 4. Coal No. i, " Brier Hill," " Massillon " 3 6 3. Fire-clay 3 5 2. Sandstone and shale 10 ,, 50 I. Conglomerate The average thickness of the rocks in this section is about four hundred feet, and a considerable number of the strata included in it are recognized as identical with those holding corresponding positions in the lower coal series of Pennsylvania. In this series of four hundred feet of strata there is a maximum thickness of fifty-one feet of coal, with a probable average of about twenty-five feet or one foot of coal to sixteen feet of the measures. This is doubtless considerably above the average ratio of coal to rock. In the Pictou coal-field there is one foot of good coal to about twenty-six feet of poor coal and rock ; in that of Illinois, one to twenty-five or thirty feet ; in the Saarbriick area, the ratio is one to twenty-six ; in that of Westphalia, one foot of workable coal to thirty- two feet of rock ; and in the Southern Wales coal-basin, if the entire thickness of the Carboniferous rocks be con- sidered, which is said to be twelve thousand feet, the ratio is about one to one hundred. In nearly all cases, areas of coal-measures are basin- MINERAL FUELS. 147 shaped that is, they thin out on all sides as they approach their limits, and are surrounded by older rocks, somewhat like a picture set in a frame. They owe this form occasion- ally, it is probable, to the original form of the area in which they were deposited. This appears to be true of the great Appalachian coal-field as a whole, which seems to have been deposited in a long and shallow trough, inclosed on one side by land which now forms the crests of the Appalachians, and on the other by a low anticlinal ridge, extending through western Ohio and central Kentucky, the bottom of this trough having evidently been lowered by gradual subsidence to permit the deposition of the suc- cessive strata. In a case like this, the chief upper coal- seams would be likely to be more extended than those lower in the series, as is true of the Pittsburg seam. In much the greater number of instances, however, the basin- form is due to disturbances of position that have taken place since the rocks were deposited ; the strata, by move- ments of the earth's crust, having been thrown into folds, sometimes wide and gentle, sometimes very abrupt; and when the crests of these folds have been removed by subse- quent denudation, areas once continuous have been left as isolated, basin-shaped remnants. A striking illustra- tion of this is presented in the sharply folded and denuded anthracite basins of Pennsylvania ; while it is probable that the present separation of the coal areas of Illinois and Missouri is due to the denudation of a wide and gentle fold, cutting away the strata down to the rocks that underlie the coal. In these latter cases, the chief lower coal-beds would be likely to be most extended and contin- uous, the upper ones being largely swept away. Geological Horizons of Mineral Fuels. Al- though thin layers of carbonaceous matter are occasion- ally met with in rocks of Silurian and Devonian age, and even, as stated by Murchison, a small deposit of anthra- cite, from one to twelve feet thick, occurs in the Lower Si- 1 48 APPLIED GEOLOGY. lurian of Ireland, the material for which has apparently been derived from masses of sea-weeds, yet no beds of mineral fuel, of any considerable economic importance or reliability, have yet been found below that series of rocks which is called the Carboniferous, from the great preva- lence in it of land-plants and beds of coal. The strata of the middle portion of this series are frequently called the coal-measures par excellence, because they furnish very much the largest part of the mineral fuel of the world, although coal-measures of great importance occur at sev- eral other geological horizons presently to be mentioned. The carboniferous rocks, omitting the upper or Permian portion, which is not coal-bearing and has little develop- ment on this continent, admit of the following subdivisions, recognizable in a general way in most American localities of these rocks, and nearly all of which, under various names, are found also in the European Carboniferous : 7. Upper barren measures with thin coals ; Washing- ton seam workable in West Virginia. 6. Upper productive measures Pittsburg seam the chief, in Appalachian area. 5. Lower barren measures Mahoning sandstone at base, with thin coals. 4. Lower productive coal-measures. 3. Millstone grit, or conglomerate. 2. Sub-conglomerate measures coals of Arkansas; Sharon coal of Pennsylvania ; lower or " edge coals " of Scotland ; coal horizon of Russia and northern Spain. i. Sub-carboniferous limestone, etc. The uppermost of these subdivisions is thought by Messrs. White and Fontaine to show Permian characters in West Virginia, where it contains a three-foot seam of coal, besides several thin seams. The upper productive coal-measures (6) have their greatest economic importance in the Appalachian coal area, and in western Kentucky. The lower productive MINERAL FUELS. 149 coal series is the most widely reliable of all, in both America and Europe ; while the millstone grit, usually considered the base of the coal-bearing series, and hence sometimes called the Farewell rock, because when it is reached in mining the miners consider that they bid fare- well to further hopes of coal, still has beneath it the coal- bearing rocks of Arkansas and northern Spain, most if not all those of Russia, and the lower or " edge coals " of Scotland. Above the geological horizon of the Carboniferous, val- uable measures of coal of the usual character are found in rocks of probable Triassic age, in central Virginia and North Carolina, and also in the Lower Oolite, a subdivision of the Jurassic, of Great Britain. Next in importance to the Carboniferous, on this continent, as a horizon of min- eral fuel, is the rock series of probable Upper Cretaceous age, whose vast and wide-spread measures of lignitic coal are of so great importance to the development of the re- gion lying west of the Missouri River. Valuable deposits of brown coal are found in Europe in the Middle Tertiary, and are extensively utilized in Germany and Austria, but none of importance have yet been found in the Tertiary of North America. Thus the geological horizons of mineral fuels are : 7. Middle Tertiary brown coals. 6. Upper Cretaceous lignitic coals. 5. Lower Oolite in Great Britain bituminous. 4. Triassic bituminous chiefly. 3. Upper productive measures of Carboniferous. 2. Lower productive measures of Carboniferous. i. Sub-conglomerate coal of Carboniferous. Regions of Mineral Fuel. The easternmost coal area of North America is that of northern Nova Scotia, east New Brunswick, and Cape Breton Island. It covers about eighteen thousand square miles, much of which seems likely to be of little value. There is a small area in 150 APPLIED GEOLOGY. Rhode Island, extending a little way into Massachusetts, and containing about five hundred square miles, the coal of which is a very hard variety of anthracite. It is not largely worked, the product reported in 1882 being only ten thousand tons. In Jhe extent, variety, and excellence of its coal-beds, the Appalachian area surpasses any other on this conti- nent, or indeed in the world. This vast coal-field, covering nearly fifty-nine thousand square miles, occupies a large part of western Pennsylvania and West Virginia, the western extremity of Maryland and Virginia, southeastern Ohio, the eastern part of Kentucky and Tennessee, and northern Alabama, with a corner of Georgia. The northeast ex- tremity of this area furnishes the anthracite of Pennsyl- vania, the best in the world, in several detached basins carved out of the folds of the Alleghanies, and contain- ing in all about four hundred and seventy square miles. In the Appalachian area, workable coal is obtained from all the coal-bearing horizons of the Carboniferous that have been enumerated, stretching from the Sharon sub- conglomerate seam in No. 2 of our section, p. 148, to the Washington seam in the upper barren measures, No. 7. The Pittsburg seam, so celebrated for its vast extent, its considerable thickness, and the superiority of its coal for coking purposes, is at the base of the upper productive measures, No. 6 ; while most of the coal of Ohio is ob- tained from the lower productive measures, No. 4. The Illinois coal-field covers a large part of central and southern Illinois, the southwestern part of Indiana, and the western portion of Kentucky, occupying somewhat more than forty-seven thousand square miles. This area is producing large and rapidly increasing amounts of bitu- minous coals, chiefly from the lower productive measures, with some in Kentucky from the upper productive. The largest in superficial extent of the Carboniferous coal areas is the Western one, occupying, it is estimated, MINERAL FUELS. 151 seventy-nine thousand square miles, in southwestern Iowa, northern and western Missouri, eastern Kansas and In- dian Territory, northern Texas, and western Arkansas. Over much of this area the coal-seams are thin, and the coal not of the best quality. The producing horizons are chiefly the sub-conglomerate measures in Arkansas, some of -whose coals are semi-anthracites, and the lower pro- ductive measures in Missouri and Iowa. The largest pro- duction is from Iowa and Missouri, Kansas also furnish- ing nearly a million tons annually. Besides these there is a rudely circular area in central Michigan, covering about six thousand seven hundred square miles with Carboniferous coal-measure rocks, about three hundred feet in maximum thickness, which contain, at several points, one seam three to four feet thick of bi- tuminous coal, somewhat sulphurous, but considered a good fuel for steam purposes. The area seems not to be very promising for a large coal production. The Triassic coal-fields of Virginia and North Caroli- na occupy four narrow, elongated basins running parallel with the Blue Ridge Mountains in the east central part of those States. These areas, although some of them have been long known, have been as yet but little developed. The one best known and most largely worked is in the near vicinity of Richmond, where one of its seams attains sometimes a thickness of forty feet. The coal is highly bituminous, as is also that of the other basins, save that of the Dan River in North Carolina, stretching into Vir- ginia, which is shown by analyses to be semi-bituminous. The productive area of the several basins does not proba- bly reach five hundred square miles. The lignitic coal-fields of probable Upper Cretaceous age, in the far Western States and Territories, have not yet been sufficiently explored to give more than a vague ap- proximation to their extent ; but they are known to cover vast areas, especially in Colorado, Wyoming, Dakota, and 152 APPLIED GEOLOGY. Montana. Those best known and most largely worked at present are those along the eastern base of the Rocky Mountains, through much of Colorado, and extending some distance into New Mexico ; those along the Union Pacific Railway in southern Wyoming ; those on the Weber River, and at other points, at no great distance from Salt Lake City in Utah ; on Bellingham Bay and Puget Sound, in Washington Territory ; and at Mount Diablo, near San Francisco, California. Several seams of superior anthra- cite and bituminous coal occur twenty-five miles south- west of Santa Fe, New Mexico. Valuable deposits of anthracite and coking bituminous coal are found at Crested Butte, on the upper branches of the Gunnison River in Colorado, and are coming into extensive use ; while near Durango, in the same State, and extending south into New Mexico, are enormous de- posits of lignitic coal of excellent quality, some of the seams being said to range from twelve to near ninety feet in thickness. Valuable deposits occur also at Coos Bay in Oregon, and in Vancouver's Island. Rough estimates assign to the lignitic measures of Colorado about thirty thousand square miles of area, and to those of Wyoming twenty thousand square miles ; but those which claim for Montana sixty thousand square miles, and for Dakota one hundred thousand square miles of coal-bearing territory, appear likely to be great overestimates. As has already been remarked, the lignitic coals pre- sent very wide variations in character and value. Some, like parts of the seams of Crested Butte and Santa Fe, are anthracites, apparently equal in quality to those of Penn- sylvania ; others, like those of southern Colorado and ad- jacent parts of New Mexico, and part of those at Crested Butte, are coking coals which furnish a superior coke. Some, like those of Cafion City, Colorado, and part of those in Wyoming, are firm and open-burning, with a low per cent of water, much resembling " block-coal " ; while MINERAL FUELS. 153 many others have much water, and crumble readily on ex- posure, hence furnishing an inferior fuel. All kinds, with the increase of population and the growth of mining and other industries, are destined to be eagerly sought out, and to furnish supplies of inestimable value to a vast re- gion otherwise scantily supplied with fuel. Six of the Western States and Territories had already, in 1882, a re- ported production of two million three hundred and fifty thousand gross tons, ranging from about one hundred and fifty thousand tons each in California and New Mexico, to nearly a million tons in Colorado, and two thirds as much in Wyoming. Foreign Coal-Fields. The chief coal areas of Eu- rope are those of Great Britain, Belgium and France, Germany and Austria, southern Russia, and Spain. The coal-fields which have long given England its industrial supremacy occupy an area of less than twelve thousand square miles, and extend, in many separate basins, from South Wales, northeasterly through western England to the great Newcastle coal-field on the North Sea, with areas of sub-conglomerate coals in southern Scotland. All these areas of any considerable importance belong to the Carboniferous age, and the coal is mostly bituminous, with some valuable anthracite in South Wales. The Belgian coal-field, of five hundred and eighteen square miles area, extends in a lengthened belt eastward from near Valenciennes, in France, to Aix-la-Chapelle ; and its apparent eastern continuation across the Rhine forms the great Westphalian coal-field northeast of Diis- seldorf. The coal-fields of Germany, with an area of about eighteen hundred square miles, consist of several basins, mostly small in extent, the chief of which are those of West- phalia and Saarbruck, near the Rhine, Upper and Lower Silesia, and some small basins in Saxony. There are also important deposits of lignite in the Tertiary of North 154 APPLIED GEOLOGY. Germany, some of them of great thickness. Austria has coal-fields and deposits of lignite of considerable extent in Bohemia. Russia, which is credited with about thirty thousand square miles of coal territory, has a large portion of this in the more central provinces, supplied with but a few thin seams of inferior coal ; its most valuable coal area being about eleven thousand square miles on the river Donetz, with one hundred and fourteen feet of workable coal, at the geological horizon of the millstone grit. (Credner and Murchison.) The coal-fields of France aggregate two thousand and eighty-six square miles, in many isolated basins, scattered widely over its territory, some of which contain anthracite coal. Some of the more noteworthy are those of Valen- ciennes near the borders of Belgium, of Autun, and of St. Etienne, previously mentioned, in the southern part. In some of these basins the coal series occurs in the sub- conglomerate, but in most, at the usual horizon of the Carboniferous coal-measures. The Spanish Peninsula has three thousand five hun- dred and one square miles of 'coal area, chiefly in the province of the Asturias, in the north part of the king- dom, and on the southern declivity of the Sierra More- na, both in rocks subordinate to the Carboniferous con- glomerate. India is reported to have about two thousand square miles of coal-fields, chiefly of Triassic age, and Japan five thousand square miles in the Tertiary. China is known to be exceptionally rich in coal, of Triassic or Lower Ju- rassic age, with some Carboniferous coal in the province of Hunan ; but our knowledge of that country is too im- perfect to permit any estimate of the area which bears coal-seams. The map published by Prof. Pumpelly, in the " Smithsonian Contributions," indicates the possibility that a very large portion of China proper is covered by MINERAL FUELS. 155 rocks pf the same age with those that bear valuable coal- seams at many known points. Further than this our knowledge does not extend. It is also reported that coal- beds, of Carboniferous, Jurassic, and Tertiary age, occur in Siberia. True Carboniferous rocks with coal-seams are found in the eastern colonies of Australia, and especially in New South Wales, where there are said to be a number of beds of coal ranging from three to thirty feet in thickness. The following table, the materials for which are taken with slight change from the report on mineral resources of the United States, will give in compact form the prob- able areas of fossil fuels in the various countries, with their reported or estimated production in 1881 : AREAS. Square miles. PRODUCTION. Gross tons. Great Britain II,QOO I 4 184 7QO United States . ... .... IQI QQ4 76 67Q 4QI I.77O 6l ^4O 47^ France . 2 086 IQ QOO O^7 Austria .. I 8OO 19 ooo ooo 5 l8 1 7, c OO.OOO India . . 2 OO4 4 ooo ooo Russia 3O,OOO' a 2 at V (3) by faulting the vein, a; while the deposit, d, which is everywhere conformable to the bedding, and is faulted by a, is, so far as these circumstances show, prob- ably a bed contemporaneous in origin with the country rock. Disturbances of Metalliferous Deposits Faults. All the forms of metalliferous deposits are liable to have their continuity interrupted, either in depth or in hori- zontal extension, by faults caused by fissures formed since their deposition by disturbances of the earth's crust. These faulting fissures may themselves have subsequently been filled with minerals from solution, constituting veins ; or they may have remained merely crevices, filled only with materials formed by the attrition or decomposition of their walls. As has already been remarked in a preceding chapter, the displacement has been caused in the great majority of cases by the sliding downward of the hanging wall of the faulting fissure. Such faults are therefore called normal faults, or simply slides. In cases, however, where the fault- ing is an attendant result of powerful disturbances and considerable folding of the strata, examples may occur METALLIFEROUS DEPOSITS. 207 where the hanging- wall side of the faulting fissure has been thrust upward, producing a reverse fault, or heave. In Fig. 19, representing faults of veins produced by fissures whose course is ap- proximately parallel to that of the veins, i, 2, and 3 illus- trate normal faults, or slides, and 4, 5, and 6, heaves ; i and 4 being caused by fis- sures dipping toward the veins, 2 and 5 by fissures dipping in the same direction as the vein at a lower angle, and 3 and 6 by fissures dip- ping with the vein at a steeper angle. A simple inspection of the figures will make it obvious that, in i and 6, the continuation of the vein may be found by a cross-cut from the interrupted end into the hanging wall of the vein in the direction of the arrows ; that in 2 the cross-cut should be into the foot-wall of the vein ; that in 3 and 5 a verti- cal shaft or winze should be sunk, and cross-cuts made in the direction of the hanging wall of the vein ; while in 4 the vein would be found by a winze. The cases i, 2, and 3 will be those most frequent- ly met with. In the absence of any other means of infor- 208 APPLIED GEOLOGY. mation as to the direction of the faults of a new region, it is safest to assume at the outset that the faults, if any occur, are normal, and to act accordingly. When, however, defi- nite information as to the direction of faulting has been ob- tained in some cases by exploration, then it is well to re- member that the faults produced by the same system of fis- sures are likely to agree in direction, i. e., to be all slides or all heaves. The examples given above represent cases where the continuity of the vein is interrupted in depth. But cases may occur where a vein is faulted by a fissure striking across it at a wide angle, in which case, unless the vein be vertical, or even then if the direction of movement be oblique, the continuity of the vein in length will be interrupted. Such cases are not easily represented by diagrams ; but the thoughtful student, by an attentive consideration of the respective dips of the vein and of the faulting fissure, will be able to solve for himself the problem of the relative positions of the parts of the vein with any given direction of movement. For example, suppose a vein, in a line with the observer and dipping to the right, to be cut by a fis- sure at right angles to its course, and dipping toward him ; then it is obvious that a slide would throw the portion nearest to the observer out of line with the rest of the vein to the left, while a heave would displace it to the right. Indications of the direction of movement will be likely to be obtained in practice from striations of the walls of the faulting fissure, or from the relative positions on its oppo- site sides of peculiar zones or beds of rock. Displacements occurring in beds, mass deposits, and impregnations are not likely to present cases more compli- cated in character than those of veins, or differing from them in principle. Surface Appearance of Ore Deposits. The char- acter of those portions of veins and other ore deposits which are near the surface is commonly very different from that which the same deposits present at considerable depths. METALLIFEROUS DEPOSITS. 209 This change of character, which is due to the action of the air, and of water charged with various chemical agents, is usually confined chiefly to the uppermost fifty or sixty feet ; but not unfrequently, in the case of permeable and fissured deposits, it extends to much greater depths. " The general character of these altered outcrops consists in a disintegration and softening of the adjacent country rock, in the lack of sulphur compounds, and the preva- lence of metallic oxides, salts of the metals, hydrates, car- bonates, phosphates, arseniates, chlorides, etc., which often produce very striking colors ; these change-products are also, mayhap, accompanied by the development of metallic copper and silver. In depth, these products of decompo- sition pass often very gradually into everywhere preva- lent sulphides of the metals or into iron carbonate." (Von Cotta.) The superficial materials resulting from this change have received various names in different regions. In this country they are usually called gossan, a name de- rived from the mining districts of Cornwall ; the Germans apply to them the significant name of the iron hat, and have an ancient rhyming rule which signifies that however good a vein may be, it will have an iron hat ; while in Mexico and South America they are called pacos, colorados and negrillos. The nature of the change that occurs, and the special character which the altered outcrop is thus caused to assume, will naturally depend in every case on the original character of the contents of the deposit, both ores and gangues. Probably the most widely diffused and obvious change is the one which is signalized in the Ger- man and French name iron hat^ applied to weathered de- posits, and which originates in the conversion of the wide- ly disseminated compounds of iron, notably pyrites, into the hydrated peroxide, giving to the mass a reddish or yellowish-brown color, and in some cases making it to a certain depth an available source of iron. Thus the out- crops of copper deposits present usually a mass of spongy 210 APPLIED GEOLOGY. iron oxide mingled with the original veinstone, and show- ing few if any traces of copper, which has been changed from the original sulphide to the soluble sulphate (blue vitriol) and washed away. This may be succeeded below by a rich zone of copper oxides and carbonate with metallic copper, and finally by the unchanged sulphides of copper and iron. The copper veins of Ducktown, Tenn., illustrated by Safford in his " Geology of Tennes- see," and also by Le Conte in his " Elements of Geology," will afford a good example of this kind of transformation. Deposits of lead and zinc are in like manner found changed to the carbonates of those metals, cerusite and smithsonite, sometimes inclosing cores of the original galena or blende but partially transformed; and where pyrites was originally mingled with the ores, the carbonates are reddened or intimately mixed with spongy oxide of iron, as is the case with the argentiferous carbonates of Leadville and Eureka. The superficial portions of silver deposits are apt to contain the precious metal in the form of native silver or of the chloride, mingled sometimes with the bromide and iodide, succeeded at greater depths by the usual compounds of silver with sulphur, antimony, and arsenic. Auriferous quartz veins, containing, as they usually do, disseminated iron pyrites or chalcopyrite, present at the surface masses of rusty cellular quartz from which the py- rites has been removed, leaving the rock stained with iron oxide, and containing the threads and grains of gold in a state such that it may easily be obtained by crushing and amalgamation. At no great depth, the unaltered form of the vein is met with, in which the gold is so associated with the metallic sulphides as to be by no means so easily and completely secured. It is obvious that a knowledge of the surface appearances usually presented by the ore deposits of any region is of very great importance to those engaged in searching for METALLIFEROUS DEPOSITS. 211 such deposits in that region j yet it would be a great error to suppose that inferences derived from the examination of the deposits in any one district can be safely treated as unerring guides in the exploration of all others. For example, however true it may usually be that the outcrops of gold-veins are indicated by iron-stained and cellular quartz, and however expedient it may be to follow up and test carefully any such indications in a district that is known to be gold-bearing, yet the converse of the propo- sition is by no means true, that every outcrop of rusty cellular quartz is probable evidence of the existence of gold ; for such appearances occur in many places where no gold has ever been found. To an important extent, every mineral region is likely to present distinctive char- acters of its own ; and general statements as to the effects of atmospheric and aqueous agencies upon ore deposits need to be supplemented by a careful study of the special modifications that are liable to be met with in any particu- lar district, from differences, it may be, in the nature of the minerals with which the ores may be associated, or in that of the substances with which the permeating water may be charged. General Distribution of Ore Deposits. Since, as has already been remarked, ore deposits seem in all cases to be concentrations, under favorable conditions, of sub- stances once widely disseminated in rocks, it is obvious that they are most likely to be found in localities where the conditions for such a concentration have been pre- sented. Such favorable conditions are most likely to be found in regions cut by ancient eruptive rocks, since they bespeak the former activity of forces that would produce fractures and fissures, and would furnish the heat essen- tial for the solution of many substances found in ore de- posits ; in regions of fractured, folded, and altered rocks, mountainous regions, because in them also fissures would be likely to be opened, the circulation of fluids facilitated, 212 APPLIED GEOLOGY. and heat generated by the intense exertions of mechanical force ; in regions of rocks of great geological antiquity, rather than in those of more modern date, because the more ancient rocks, by reason of their age, have been longer exposed to occasions for the action of those slow- working and protracted agencies by which ore deposits have doubtless been most largely produced, and because, to effect the solution and deposition of many highly re- fractory substances frequently found in veins, masses, and impregnations, the action of water at a very elevated tem- perature must be requisite, needing the concurrence of heat with the pressure of a great thickness of covering rock, a circumstance which implies not only relative an- tiquity in the rocks which were the deep-seated theatre of such action and deposition, but also the lapse of vast pe- riods of time during which these deeply placed rocks were elevated and laid open to human search by an enor- mous denudation ; whence also mountain-regions, whose rounded forms and comparatively slight elevation above the general surface show that their very roots have been exposed by wear, are likely to be more favorable than those whose rugged and elevated peaks testify to a briefer exposure to elemental waste. It will thus be seen that conditions favoring the ac- cumulation of ore deposits are presented (i) by great disturbances of the earth's crust by which fissures may be produced, heat generated, and circulation promoted; (2) by heat, such as initiates, accompanies, and succeeds out- bursts of volcanic activity ; (3) by original depth of action and consequent pressure, through which the solvent possi- bilities of heated waters are enormously increased ; and (4) by great lapse of time during which the repeated and protracted action of agencies seemingly feeble may pro- duce important accumulations, which may subsequently be brought within reach of human explorations by great uplifts and denudation. METALLIFEROUS DEPOSITS. 213 The regions, therefore, in which the great majority of valuable ore deposits are found are (i) those which are in close proximity to eruptive rocks, especially those of some- what ancient date ; (2) mountainous regions, more par- ticularly those whose low and rounded outlines show that large portions of their original bulk have been removed by denudation ; and (3) regions of rocks geologically ancient, the more recent formations containing usually little of value besides iron-ore. It has been observed also that regions where rocks of very dissimilar character are found in contact are favorable to the accumulation of ore deposits, hence contact deposits, whether from their lia- bility to separate and form fissures as the result of disturb- ances, or from their presenting planes of easy percolation to metallic solutions, or from some favoring circumstances of the wall-rocks. It should by no means be inferred that regions like those here enumerated are likely in every case to furnish valuable ores in some portion of their extent ; but only that ore deposits occur mainly in such connections and much more rarely elsewhere. It is well also to bear in mind that the conditions which have produced one dis- covered ore deposit in a region are quite likely to have produced others also which are apt to bear to this some definite relation of kind, position, or direction. Prospecting. What has been said as to the general distribution of ore deposits may be useful to the observer at the outset in directing him to the kind of localities which are likely to reward his search. Its proper appli- cation will depend, as may be seen, upon some knowledge of the geological structure of the region, and a prelimi- nary acquaintance with the general character of its rocks. Without these, any first discovery of valuable minerals would be due merely to a lucky accident, as indeed most first discoveries have probably been. In the absence of other sources of information, traces of ancient workings 214 APPLIED GEOLOGY. may prove useful guides to the explorer, indications such as would be given by old pits not yet wholly obliterated, and heaps of debris whose weathered contents may afford some hints of what explorations would be likely to reveal. Such ancient workings of the aboriginal inhabitants of the country have led, it is said, to the discovery of some of the copper-mines of Lake Superior, and of the best mica deposits of North Carolina. Mere local traditions of the occurrence of minerals, however, when unsupported by perceptible traces of former workings, are notoriously unreliable. In districts where there is a strong probability of the existence of ores, useful indications to aid in their search may be gained in several ways : from peculiarities of vege- tation, since many ore deposits exert a special influence on the vegetation along their course ; from the contents or the depositions of springs issuing from the hidden courses of veins, etc. ; or from some marked features of the topog- raphy, such as sharp, narrow ridges marking the outcrop of veins harder than the country rock, or linear hollows suggesting the presence of those made up of materials softer and more easily decomposed than the inclosing walls. The best and most helpful aid is furnished, how- ever, by the debris arising from the disintegration and wear of ore deposits, which is likely to be found strewed along stream-courses and slopes below the outcrop of the parent formation. Such transported materials, called usually shode-stones, or in our Western mining regions more commonly float, will naturally present the surface appear- ances of the deposits from which they were derived, such as cellular iron-stained quartz and the like. These float minerals, indicating the possible proximity of an ore de- posit, are traced carefully upward along stream-beds or slopes, to the point beyond which they are no longer found; and at this point further search is made for the originating deposit by trenches or pits excavated to the METALLIFEROUS DEPOSITS. 215 underlying rock. Should this examination reveal the probable presence of a vein or some other form of mineral deposit, more extended explorations are made by means of pits and shafts, to determine its direction, extent, and character ; and these explorations are accompanied by assays, which, if made upon samples fairly taken, may in- dicate the possible value of the deposit, and whether it is likely to justify extended working. Circumstances which condition the Value of Ore Deposits. Sound business discretion will naturally dictate that the work of exploration should be pushed far enough to reveal the real nature and probable abundance of the valuable mineral, in both depth and extent, and that the conditions on which the present and prospective value of such a deposit must depend should be carefully considered, before the necessarily costly preparations for extensive mining and for the beneficiation of the product should be undertaken. A primary consideration in determining the value of an ore deposit will, of course, be the relative amount of the valuable metallic substance which the ore mass con- tains. Where the ore is intimately mingled with the gangue, the value should be estimated on the basis of the entire mass that must be subjected to the processes of concentration and reduction. When, however, the ore is found concentrated into a somewhat definite pay-streak, or in a narrow vein, while the value of the ore may be esti- mated on this same basis, careful consideration should be given to the fact that with the ore a sufficient amount of barren rock must be taken down to give room for con- venient mining operations, usually three feet or more in width, increasing by so much the cost of getting the really valuable ore. The value of ores of the precious metals is usually stated as so many dollars or so many ounces per ton ; thus, an eighty-dollar ore is one contain- ing that value of gold or silver in a ton. Sometimes the 2i6 APPLIED GEOLOGY. value of low-grade gold-rock is given as so much per cord, the cord being approximately eight tons. In the case of the less valuable metals, like mercury, copper, lead, and iron, the percentage which the metal bears to the ore mass is given. It is obvious that to attain even an ap- proximately reliable estimate of the average value of a deposit, the samples that are subjected to assay should fairly represent what must be treated as ores ; otherwise, all further calculations must be mere wild guess-work, as indeed too many estimates of the prospects of new mines are apt to be. Reasonably fair samples can be obtained only by some systematic operation which will exclude en- tirely the chance for even an unintentional selection, such as by taking shovelfuls indiscriminately from many parts of a well-mixed ore-pile, breaking this material into small fragments, heaping it up, and subjecting it to successive quarterings, until a specimen of convenient bulk is ob- tained for the assayer. Before, however, a final decision is reached, a mill test should be made, by hauling several tons of what is to be considered ore to the most con- venient reduction-works, and finding what it will yield to this practical test. Second only in importance to the relative amount of metal in the ore mass is the state in which it occurs : whether native, and obtainable by a process merely of crushing and washing, like the copper-rock of Lake Su- perior ; or free milling, like some ores of gold and silver, which after crushing yield their metallic contents mostly to amalgamation, with little accessory treatment ; or in some simple form of combination from which the metal may be liberated by a process involving few operations, like galena and iron oxide ; or involved in such complications with other substances as to require an intricate and costly se- ries of operations for its beneficiation ; whether also, in case the ore is intimately mingled with so much gangue as to reduce it below the limits of profit, it is in such physi- METALLIFEROUS DEPOSITS. 217 cal condition, and bears such relations of gravity to the gangue, as to admit of easy concentration, and whether in such case there is a sufficient supply of water for the pur- pose. It is easy to see that, if one ore costs ten dollars per ton more for reduction than another, it needs to be ten dollars richer to pay ; and that if fifty dollars' worth of ore disseminated through ten tons of vein-stone can, with but little loss, be concentrated into one ton worth nearly fifty dollars, it may, if the process of concentration is made cheap enough by abundant water, become valuable when it would otherwise be valueless. The question of ready and cheap transportation is also one of vital importance. Remote regions, difficult of access, can utilize at first only their richest ores, those whose value is so concentrated as to bear heavy transpor- tation charges and still leave a margin for profit. Every improvement in the means of communication, every re- duction in the charges for carriage, will render available ores of lower and still lower grade, and will bring the products of such regions nearer in value to more favored localities. Many districts in our own country of well- known promise have their mining industries still hampered by the difficulties and cost of transportation. For what avail mines capable of producing an abundance of ores of fair nominal value, all of which and even more may be consumed by the charges for mining, reduction, and ex- cessively dear transportation ? The probable expense of working the deposit also needs the most attentive consideration, depending as it does on several circumstances, such as the cost of labor; the hardness of the rock that is to be dealt with; the structure of the deposit, whether likely to need much or little support for roof or walls, and whether the timber for this purpose is at hand ; the cost of food, tools, and mining appliances in general ; and the cost of the power that must be used for hoisting ores, and for handling the water 2l8 APPLIED GEOLOGY. that is likely to be encountered. All these elements of inevitable expense must vary greatly, as may readily be seen, with the circumstances of different localities, and must be carefully estimated in view of such circumstances, if one would avoid the risk of unprofitable undertakings. Finally, the relation which the particular metal that is to be produced is likely to bear to the supply of human wants, as indicated by the state of the market for that metal, needs to be taken into account. For example, a deposit of copper which, in view of all the considerations above enumerated, would seem likely to yield a good profit when the metal is selling at sixteen cents per pound, might be found to promise no margin of profit with copper selling at fourteen cents or less. The practical importance of the considerations given above, and the frequency with which some of them are overlooked, sometimes intentionally, by promoters of mining enterprises, will justify a brief abstract of the chief conditions on which depends the value of ore deposits : 1. On the relative amount of metal in what must be treated as ore, needing a. Fair sampling to secure a reliable estimate of the average value. b. Due consideration of the amount of dead rock to be handled in securing the ore. 2. On the nature of the combination in which the metal occurs ; often also on susceptibility to concentration. 3. On situation with respect to cheap transportation. 4. On the cost of exploitation, which includes a con- sideration of a. The cost of labor. b. The hardness of the rock to be mined. c. The structure of the deposit as regards the need of costly support. d. The cost of food, tools, mining supplies, etc. e. The cost of power for hoisting and pumping. METALLIFEROUS DEPOSITS. 219 5. On the relations to the supply of human wants, in- dicated by current price. Erroneous Ideas regarding Ore Deposits. There are prevalent among persons engaged in mining a number of false or only partially justified notions, arising partly from an imperfect knowledge of the true character of ore deposits, partly from a tendency to too wide gener- alization in formulating as general laws applicable to all mining regions the results of an experience gained in some limited district whose conditions were possibly largely peculiar to itself. As these ideas in many cases tend to foster too sanguine expectations, and to encourage too hazardous ventures without proper examination, while in others they may unduly discourage careful investigation, they deserve to be briefly stated and discussed in a work of practical character, as this aims to be. 1. A somewhat prevalent idea of this kind is, that fis- sure-veins are likely to increase in width as they descend. From what has already been said as to the manner in which open fissures are formed, partly by a faulting move- ment of walls of irregular contour, partly by the aid of detached masses of the country rock, it may be seen that this idea is likely to be baseless. Veins may be expected to vary greatly in width, passing from a mere narrow clay seam in one place, to a bulge of considerable width in another. If now at the present surface, resulting always from denudation, the vein happens to be encountered at a narrow point, it will naturally widen for a time, sometimes to a considerable depth, before again contracting ; if, however, it should be struck at a wider portion, the con- trary may be true. The idea has probably sprung from men's disposition to believe easily what they strongly de- sire, coupled with the well-known tendency to permit a single success to blot out the remembrance of many fail- ures. 2. Somewhat closely akin to this error is the notion that 220 APPLIED GEOLOGY. fissure-veins grow richer in depth. This may have arisen from the fact that where the products of the decomposi- tion of the ores are soluble, as in the case of copper and silver, the outcropping portions of the veins are impover- ished, and their true character does not appear until the weathered portions are passed. When, however, the me- tallic substance is itself unchangeable, e. g., gold, the out- cropping portion may be not only relatively richer, but also much more easily reduced than the unweathered part of the vein ; so that it may very well happen that a mine which " pays from the grass-roots " may pay nowhere else, for the reason that the sparsely distributed metal may be so involved with other substances in the unchanged vein as not to yield itself to any cheap method of beneficiation. Veins, where found in their natural condition in depth, are likely, as has been stated on a former page, to have their chief value collected in richer zones alternating with tracts of ground practically barren, the richer zones being met with more commonly in the wider parts of the vein. It will therefore be a mere accident dependent upon de- nudation, whether the vein shall be struck in a richer or poorer portion of its extent. The opinion, once current on high geological authority, that gold has been accumu- lated in paying quantities only in the superficial portions of veins, is probably entertained by very few persons at present, since mining investigations have shown that it was based on incomplete data. 3. Another current opinion, viz., that certain directions of strike in veins are decisive indications of their possible value, and its modification ascribing certain specialties of course and form to veins of certain metals, may furnish good illustrations of too sweeping generalizations. It is undoubtedly true that, within given regions, the courses of veins, and also of other forms of deposit that have been greatly disturbed, are likely to have a tolerably definite direction, conforming themselves, indeed, in a general way, METALLIFEROUS DEPOSITS. 2 2I to the prevailing structural lines of the region due to up- lifts, as if related to them in origin, as they doubtless are. The error, then, is not in expecting certain prevailing di- rections in the courses of deposits in a given region, but in looking to find the same in all regions, without regard to that which conditions their direction, viz., the structural characters produced by upheaval. Still more, it is to be considered that it is merely the existence of the fissure that is due to the causes which control its direction, and not the nature of its contents, whether or not they shall be met- alliferous, or what ores they shall contain. The filling of the fissure is a subsequent process, and is due to a quite different agency. For the forces which produced all the fissures of any region of fissure-veins, and which hence con- trolled their direction, were mechanical, and thus totally different from the chemical agencies which filled them, and so conditioned the nature of their contents. The same kind of mechanical forces, exerted in the same region at a subsequent period and in a somewhat different direction, may produce a second set of fissures varying in direction from the first, and which, if filled by solutions of a different kind, may form veins containing the ores of a different metal. To this cause is due the fact that veins of the same region which course differently are apt to have unlike me- tallic contents. Yet veins of similar ores in distinct min- ing regions which have different structural features may have widely different courses, because their courses, and not their contents, are conditioned by such structural causes. 4. The sentiment in favor of some kinds of country rock, as likely to be favorable to richness in deposits, and against others as likely to be unfavorable, is not without justification so long as it is restricted to districts in which such influences have been observed. There is no reason to doubt that from several causes, some of which have been briefly mentioned on a preceding page, the country 222 , APPLIED GEOLOGY. rock does exert an influence on the deposition of the con- tents of veins. What influence, however, is a matter which needs to be carefully studied in each region for itself, and not to be hastily inferred of any region because of observa- tions made in a different one. For it is to be borne in mind that the nature of the solutions circulating in fissures must have been an influential factor in determining the deposition of ores upon one kind of wall-rock rather than upon another, the interaction between the two varying with the nature of the solution ; also, that the relative com- position of rock species is to a great extent variable and indefinite, so that one is liable, while using the same rock name, to be dealing with rocks that, from the difference in the relative amounts of their constituents, might be likely to exert notably different influences on ore deposition.* 5. Finally, it may be well. to mention in this connection the prejudice, common among men engaged in mining, in favor of fissure-veins, and against some other forms of ore deposits. It is true that a fissure-vein whose average rich- ness gives evidence of being satisfactory, has the great advantage of affording such promise of continuance as to justify large expenditures for its proper development, but coupled with the certainty that the cost of both explora- tion and extraction must increase greatly as depth is at- tained. Other forms of deposit are, however, not without their compensating advantages. Mass deposits, for exam- ple, though of very uncertain extent and duration, are frequently of vast dimensions, and their uncertainty is fortunately counterbalanced, as Rossiter W. Raymond re- marks, not only by this circumstance, but also by " their comparative small depth and the consequent ease and cheapness of extraction and of exploration." As a matter of fact, very large portions of our mineral wealth are de- rived from deposits other than fissure-veins. Not to men- tion the vast stores of iron-ore obtained from beds, it is * Von Cotta, " Erzlagerstatten." METALLIFEROUS DEPOSITS. enough to allude, for a few examples out of many, to the gold derived from placers ; the copper from the deposits of Lake Superior, whether they be called beds or impreg- nations ; and the silver and lead from the mass deposits and quasi veins of Leadville and Eureka. Hence, it is well for men interested in mining enterprises to cherish no prejudices for or against particular forms of deposit, but to endeavor, by the wise adaptation of methods to the special deposits in hand, to extract from them the greatest attainable profit, which is the true purpose of all intelligent mining. The student will do well to consult, for further information with regard to ore deposits, " A Treatise on Ore Deposits," J. A. Phillips ; De La Beche, " Geological Observer " ; R. W. Raymond, chapter on ore deposits in " United States Report on Mineral Resources," 1870 ; Burat, " Geologic Applique " ; and Von Cotta, "Erzlagerstatten," Part I ; also papers on ore deposits by Dr. J. S. Newberry. CHAPTER XI. IRON. IRON may justly claim the foremost place among the metals, from the indispensable relations which it bears to most forms of human industry. The sources from which it is obtained commercially are the oxide ores and the carbonates, viz., magnetite, hematite, limonite, spathic ore or siderite, clay iron-stone, and black-band. Richest among these is magnetite, which when pure contains a little more than 72 per cent of metallic iron. It is highly mag- netic, yields a black powder and a black streak on un- glazed porcelain,and is so hard as to be scratched with diffi- culty by a knife. It is often crystalline granular, the faces of the crystals being triangular when perfect. Hematite when pure contains 70 per cent of iron. It is not usually magnetic, though sometimes it slightly affects the mag- netic needle, and its powder and streak are of a dark red. It varies much in appearance, being sometimes hard and of a steely metallic luster, when it is called specular ore ; often constituting a reddish ochreous mass of an earthy texture ; occasionally composed of black, shining, mica- like scales, and hence called micaceous ore ; and some- times made up of red, oolitic grains. Limonite differs from hematite in being hydrated (combined with water), and so containing a smaller percentage of metallic iron about 60 per cent and in yielding a brown powder and streak. It is often found in stalactitic and semi-concre- IRON. 22$ tionary forms, with a smooth and shining surface, and a fibrous, often radiated, internal structure. The pure iron carbonate called siderite or spathic iron-ore, which con- tains about 48 per cent of metallic iron, is a sparry mineral of brownish color, and of an easy, threefold rhombohedral cleavage, in which it closely resembles calcite and dolo- mite, from which its cleavage angles differ but little. When strongly heated, it decrepitates, turns black, and be- comes magnetic ; and when heated in hydrochloric acid, it dissolves with effervescence, yielding a yellow solution. In its impure forms it occurs abundantly in certain shaly strata of coal-regions, mingled with a considerable propor- tion of earthy matter, forming beds of clay iron-stone, or collected into kidney-shaped concretions disseminated through the beds, when it is called kidney-ore ; or some- times it is found mingled with much bituminous matter forming black, shaly-looking seams called black-band. These impure carbonates, though not so rich in iron as several other ores, by reason of their close proximity to fuels and fluxes, and of the ease with which they are re- duced, are a large and valuable source of iron. Mode of Occurrence. Although iron- ores are some- times found filling fissures and irregular cavities, their usual mode of occurrence in this country is in bedded deposits, whether disseminated in the beds like the kidney- ores, or forming nearly the entire bulk of strata which are not unfrequently of great dimensions. Where the strata with which they are associated have been greatly altered and thrown into highly inclined positions, the ore-beds have much the appearance of veins and are often so called ; but there is little reason to doubt that they are really beds, often of lenticular shape, formed as part of the regular series of events by which the strata in which they are in- closed were accumulated. Many of the limonites seem to have arisen from the transformation or disintegration of other kinds of iron-bearing strata, and occupy somewhat 226 APPLIED GEOLOGY. ill-defined positions, yet related to those of the probable parent deposits. Geological and Topographical Distribution. Though small amounts of iron-ores may be found in near- ly every geological position, still their occurrence in work- able quantities is chiefly confined to a comparatively few geological horizons. Of these horizons in this country, the Archaean is much the most prolific in excellent ores, magnetite and hematite. From this horizon come the ores, so largely worked, and furnishing more than half the iron of the United States, of the Lake Superior region, of northeast New York and adjacent Canada, of northwest New Jersey, and of the celebrated Iron Mountain region of southeast Missouri. Enormous beds of iron-ore occur also in this horizon in southern Utah, and along the Ap- palachian range south of New Jersey, especially in North Carolina. From the horizon of the Lower Silurian Potsdam and Calciferous are derived most of the valuable deposits of limonite which occur along the Appalachain range from New York and Connecticut to Alabama, and which are largely worked for local use at many points along this range, in New York, Pennsylvania, western Virginia, East Tennessee, and Alabama. The horizon of the Clinton Group of the Upper Silu- rian affords a singularly persistent seam of oolitic hema- tite, which extends with some interruptions from central New York through Pennsylvania, etc., into Alabama, and ranges in thickness from one foot to a maximum of twelve or more feet. Above this horizon little of value is found until the Carboniferous is reached, where beds of clay iron-stone, kidney-ore, and black-band, are met with in most coal- regions, furnishing large local supplies of ores which are destined to become of increasing value with the rapid growth of the iron industry on this continent. Ores of this same character are also found associated with the IRON. 227 coal-beds of Triassic and Cretaceous age in the United States, and much of the iron-ore of France, according to Lebour, is derived from the Jurassic and Lower Creta- ceous. A famous iron horizon occurs in the Middle Lias (Jurassic period) of Great Britain, where a clay carbonate in the so-called Cleveland District, Yorkshire, yields near- ly one tenth of the iron of the world from an ore averag- ing 30 to 35 per cent of iron. Besides the iron regions mentioned above, the United States is known to possess rich deposits in the Rocky Mountain region and on the Pacific slope, though they are still undeveloped save to a limited extent in Colorado and Oregon. The magnetite deposits of southern Utah are said to be very extensive. Besides our native supplies of ore, considerable amounts are yearly imported, chiefly from the island of Elba, from Algiers, and from Spain, which last country is reported to mine annually for export about four million tons of iron-ore. Other highly important foreign regions of iron produc- tion, besides those that have been named, are those of the coal districts of Great Britain ; those of Germany, which raise her to the third place as an iron-producer ; those in the ancient crystalline rocks of Sweden and Norway ; and that of Luxembourg, which supplies much of the iron-ore smelted in Belgium. It is also recently reported that southeast Cuba, through American enterprise and capi- tal, is likely soon to become a considerable producer of iron-ores. In the case of a substance so abundant and widely dif- fused as iron-ore, its economic importance must largely depend on (i) its proximity to the fuels and fluxes needed for its reduction to the metallic state, (2) its freedom from injurious ingredients not readily removed in smelting, and (3) the percentage of iron which it is capable of yielding. The fuels used for its reduction are anthracite and dry-burn- ing bituminous coals, coke, and charcoal ; while limestone is 228 APPLIED GEOLOGY. the flux most largely employed for removing in the form of slag the usual silicious and clayey impurities. Near- ness to the prime necessaries may bring into early use comparatively lean ore deposits ; while even richer ones, less favorably located, may wait long for development. Where, therefore, abundant iron-ores of reasonable rich- ness are found in convenient proximity to good fuels and limestone, there prosperous centers of iron production are likely to arise, and transportation facilities to be furnished. To such fortunate concurrences is largely due the suprem- acy in iron production of Great Britain, where the ores most largely utilized are only moderately rich. Many lo- calities in our own country afford examples of a similar character, which are likely to be considerably multiplied in the near future. Where abundant and cheap fuel and limestone are not at hand, an iron-ore needs usually to be both pure and rich to warrant distant transportation. The most troublesome impurities in iron-ores are sulphur and phosphorus, neither of which is easily eliminated from the iron in the process of smelting, and both of which necessitate increased ex- pense for even their partial removal. A small amount of sulphur in iron causes it to be " red-short," i. e., brittle and difficult to work at a red heat ; while more than a tenth of one per cent of phosphorus makes it "cold- short," or brittle when cold, thus unfitting it for many uses where great strength is required, and rendering it wholly unsuitable for the manufacture of steel. Where ores are sufficiently free from these injurious accessories, and are capable of yielding 60 per cent or more of pig-iron, they may be profitably transported to smelting centers at con- siderable distances. Hence the Archaean ores of New York, Missouri, and of the Lake Superior region, are largely car- ried for reduction to Pennsylvania, Ohio, and Illinois ; while the rich and pure ores of Spain and Elba are brought by cheap ocean-carriage to be mixed with other IRON. 229 ores in iron for various steel-making processes. A re- cently devised modification of the Bessemer process, which, by the use of a basic lining for the converter, con- sisting essentially of some mineral rich in magnesia, frees iron from phosphorus, promises to make available for the highest uses ores otherwise unobjectionable, but held in bad repute because of their large amount of phosphorus. According to a somewhat careful estimate of the iron production of 1882 The production of the world was 20,656,184 tons gross or metric ; Great Britain, 8,493,287 gross tons ; United States, 4,623,323 ,, Germany, 2,945,007 metric tons these three leading producers having, therefore, furnished somewhat more than sixteen million tons, or nearly four fifths of the product of the world. The steel product for the same year was given as 6,307,756 tons, of which Great Britain produced 2,259,649 tons and the United States 1,736,692 tons, these two nations together producing nearly two thirds of the steel of the world. These figures will serve to give some idea, not only of the vast proportions of the industries for which iron-ores furnish the basis, but also of the countries which, by a fortunate combination of circumstances, seem to be best adapted to be leaders in those industries. The rapid growth of the iron industry in the United States may be seen when it is considered that in 1854 the entire product was 656,445 gross tons, and that it rose in twenty-six years to 3,835,191 gross tons in 1880. Among the States of the Union, Pennsylvania is foremost in pro- duction, from causes that may easily be inferred, yielding in 1882 more than 47 per cent of the entire product of the United States, with Ohio, New York, and Illinois hold- ing second, third, and fourth rank ; while Michigan, New Jersey, Tennessee, Missouri, and Alabama each produced 100,000 or more gross tons. 11 230 APPLIED GEOLOGY. The uses of iron and steel may justly be said to be coextensive with civilized industry. Some of its leading uses only can here be indicated, viz., in constructing and operating railways, for rails, bridges, and rolling-stock ; in ship-building ; in architecture, for pillars, girders, and mul- tifarious other purposes ; in tools and machinery for both agricultural and manufacturing uses ; in pipes for the con- veyance of water and petroleum, and in tanks for storage ; in stoves, furnaces, and boilers ; and in wire for fencing and for lines of telegraph. The works to which the diligent student might refer for more complete information with regard to the ores of this important metal are very numerous. He will do well to consult the Geological Re- ports of Missouri, Michigan, and Wisconsin, and those of the States along the great Appalachian range, from Canada and New York to Alabama, some or all of which may be within his reach. Many valu- able papers on this subject may also be found in the volumes of " Transactions of the American Institute of Mining Engineers." The " Statistics and History of Iron and Steel," in the "Report of the Tenth Census of the United States," and the article " Iron," in the " Mineral Resources of the United States," published by the Geologi- cal Survey, 1883, should be consulted ; also Wright's " Reports on Mineral Statistics of Michigan," for iSyy-'yS, i88o-'82 ; and Phillips's " Treatise on Ore Deposits." CHAPTER XII. COPPER. THE chief sources whence are derived the supplies of this metal of great and growing importance in the arts, are the native metal, and the sulphides, chalcopyrite, bornite, and chalcocite. These yield more than seven eighths of the world's supply of copper, the sulphides furnishing fully three fourths, while native copper affords somewhat more than a seventh, mostly from the Lake Superior region. The remainder is supplied by the car- bonates, malachite and azurite, and by the red and black oxides formed by the transformation of other ores, with minor amounts from the silicate, chrysocolla, and tetra- hedrite or gray copper. Metallic copper and all its com- mon ores yield with no great difficulty to the knife, having a hardness varying from about three to four ; they are also soluble with more or less ease in nitric acid, giving green or blue solutions, into which, if a clean knife-blade be dipped, it will soon be covered with a red coating of copper. The native metal is easily distinguished by its well- known red color, its bright metallic luster, and the flexi- bility of a thin shaving cut off with a knife. Chalcopyrite, its most common ore, somewhat resembles iron pyrites, with which it is often associated, but is easily distinguished by its greatly inferior hardness, and by its deeper shade of yellow, with a tint verging on green. It 232 APPLIED GEOLOGY, is a double sulphide of copper and iron, and yields, when pure, about 34 per cent of copper. Bornite, called usually variegated copper pyrites and erubescite, is also a sulphide of iron and copper of some- what variable composition, carrying from 55 per cent to more than 60 per cent of copper. Its color varies from red to brown, and it easily tarnishes on exposure, taking the variegated colors from which it derives its common name. Chalcocite, or copper glance, is of a dark, lead-gray color, with usually a blue or green tarnish, and is somewhat softer than the two preceding ores, with which it is often associated. It is a simple sulphide of copper, and con- tains nearly 80 per cent of the metal. These three sul- phides of copper give fumes of sulphur when heated on charcoal, and when dissolved in nitric acid, with heat if necessary, leave a residue of sulphur. Malachite is a light-green carbonate of copper, holding nearly 57 per cent of the metal ; and azurite is a blue car- bonate, with about 55 per cent of copper. Their hardness is about four, and when dissolved in nitric acid they effer- vesce from the escape of carbonic acid. They are easily distinguished by these characters and that of their solu- tion. When malachite occurs in thick, compact incrusta- tions, showing delicate bands of color, as in some of the Siberian mines, it is considerably used as an ornamental material in inlaid work. The black oxide of copper, called tenorite, and the deep red oxide, called cuprite and tile ore, or, when it occurs in crystals, ruby copper, are both minerals of high specific gravity, and contain respectively, when pure, 80 and 88 per cent of the metal. Both dissolve in nitric acid, and, when heated with the blow-pipe on charcoal, yield a malleable globule of copper. These oxides are often found in some abundance in the middle and lower zones of the decomposed parts of copper veins, and are valuable COPPER. 233 sources of the metal. Large, rounded masses of tenorite, streaked with green, were found, at an early day, in con- siderable abundance in the Lake Superior copper regions. Chrysocolla, a bright bluish-green silicate of copper, which contains, when pure, about 36 per cent of copper, is found in sufficient amount in some of our Western cop- per regions to be a valued source of copper. It has nearly the same hardness as malachite, for which it* is often mistaken ; but its shade of color is noticeably differ- ent, and it does not, like malachite, effervesce with nitric acid. Tetrahedrite, called usually gray copper , from its pre- vailing color, is a complex sulphide of copper and anti- mony, with commonly some other metals, notably sil- ver. It occurs somewhat abundantly in some of the mines of the Rocky Mountain region, where it is valued rather as a source of silver than of copper. Mode of Occurrence. Copper or its ores occurs in all the great classes of metalliferous deposits that have been described in a preceding section : (i) It is found in veins intersecting the older rocks, or forming lenticular deposits in certain planes of their highly inclined bedding, as at many points along the Appalachian Mountains, at the Bruce and other mines on the north shore of Lake Huron, at the mines like the Cliff on Keweenaw Point, which have become famous from the enormous masses of native cop- per which they have yielded, and in the very rich district around Butte City in Montana. (2) It occurs in mass deposits, as along the base of the Sierra Nevada in Cali- fornia, in the Harz Mountains at Goslar, and in the enor- mous deposits in southwest Spain on the Rio Tinto, in all of which localities the copper ore is mingled with large proportions of pyrites. The very rich copper deposits of Globe, Arizona, and of the Copper Queen, seem also to be of this character, though the ores are widely different. (3) It occurs disseminated in beds, as in the deposits of 234 APPLIED GEOLOGY. Ste. Genevieve County, Mo., which are in two beds of Lower Silurian limestone, at several points in the Lower Silurian beds of Canada, which have not yet risen to great commercial importance, and in the famous copper slate of the Harz Mountains, which, in the vicinity of Mansfeld, yields so large a portion of the copper of Germany from a seam of but inconsiderable thickness. (4) It is found in impregnations, as in the rich deposits of native copper, disseminated in amygdaloids and conglomerates, on Ke- weenaw Point, in northern Michigan ; in the oxide and carbonate ores which enrich enormous zones in beds of felsitic rock, on the boundaries of Arizona and New Mexico, near the Gila River ; and in the beds of con- glomerate and underlying slate, impregnated with copper sulphides and oxide, in the Oscuras Mountains of central New Mexico. Thus far, in this country, the deposits which have here been classed as veins and impregnations have been much the most largely worked, and with the greatest profit, though important amounts are also pro- duced from the other two classes of deposit. Geological and Topographical Distribution. Although workable deposits of copper are sometimes found in formations as late as the Permian, as at Mansfeld, and in the possibly younger beds of the Oscuras Mountains, yet they are most largely accumulated in the ancient crys- talline or eruptive rocks of the Archaean and in the often much-disturbed and altered beds of the earlier Silurian. The most notable copper region in North America is that of the southern shore of Lake Superior, in the north- ern peninsula of Michigan. The copper here occurs in the native state, in a very thick series of interbedded vol- canic rocks, sandstones, and conglomerates, of probably later Archaean age, though they are thought by some ex- cellent geologists to belong to the Cambrian. The metal is found partly in fissure-veins, in which the copper has been met with largely in masses, sometimes of enormous COPPER. 235 size, several having been discovered which weighed from two hundred to nearly five hundred tons ; partly as one of the minerals filling amygdaloidal cavities in the volcanic rocks, some of the irregularly shaped masses here also at- taining considerable dimensions ; and partly disseminated in conglomerates, in which it constitutes a portion of the cementing material. The fissure-veins are no longer so productive as they once were, the great masses being now unfrequently found, so that the product depends chiefly on the copper disseminated in lumps, strings, and grains in the vein-rock. The largest part of the product is de- rived from the amygdaloids, in which, besides the fine grains and strings of metal with lumps of a few pounds in weight, irregular masses weighing more than a ton are sometimes encountered, filling large scoriaceous cavities in the ancient lava-beds ; and from the cupriferous conglom- erates, in which one great mine, the Calumet and Hecla, produces considerably more than half the copper of the region from a conglomerate impregnated with about five per cent of the metal. The amygdaloids are more easily worked than the conglomerates, and their average of metal varies from about three per cent in the Quincy mine to 0.72 per cent in the Atlantic. The process of extraction consists in freeing the lumps and masses, as far as possible, from the accompanying minerals, by steam-hammers, rock- breakers, and stamps, stamping the finer copper and gangue to a coarse powder, and washing away the waste rock in jigs and buddies, and then smelting the lumps, masses, and washed grains to rid them of the remaining gangue in the form of slag. Second in the list of copper-producers is the region im- mediately around Butte City, Montana, which in 1882 produced over four thousand gross tons of metal from rich sulphide-ores, yielding also usually valuable amounts of silver, and in 1884 reached a production of over eighteen thousand gross tons. 236 APPLIED GEOLOGY. Ranking third in amount of metal produced since 1883 are the copper-producing districts of Arizona, at present three in number. The Clifton district is in the southeast part of the Territory, on the Gila River, near the boundary- line of New Mexico. The ores, mostly carbonates and oxides, are said to occur in enormous zones in vertical beds of felsite rock, and to average fifteen per cent of cop- per in a gangue of manganese and iron oxides. The Cop- per Queen mine at Bisbee is the largest producer in Ari- zona, having a very rich body of carbonates and oxides in limestone with, it is said, some native copper, and copper glance in the deeper workings. A block of this ore, weigh- ing three tons, recently sent to the Museum of Cornell University by Prof. W. P. Blake, is made up chiefly of malachite intermingled with black oxide of manganese and calcite. The Globe District, in Gila County, though situ- ated badly in regard to transportation, is yet producing largely in several mines, the ores of all which are carbon- ates and oxides, containing also small amounts of the pre- cious metals. The Old Dominion mine, in this district, is said to yield annually more than two thousand net tons of copper. Besides these chief producing centers there are some other promising mines in this remote Territory, of which the Peabody, in Cochise County, a little north of the famous Tombstone region, is stated (" Report of the Director of the Mint for 1882 ") to be producing at the rate of eighteen hundred tons per year, from an ore carry- ing a high percentage of gold and some silver. In 1884 the estimated yield of Arizona was 11,920 gross tons of copper. Colorado produces considerable amounts of copper, solely as a secondary product from ores worked chiefly for their gold and silver. Most of this is from the mines of Gilpin County, west of Denver, with smaller amounts from the San Juan region, and from a locality near Canon City. New Mexico, though not yet producing more than COPPER. 237 four or five hundred tons per year, is known to have very rich deposits in not less than six counties, many of the mines carrying also important amounts of the precious metals. Wyoming, in 1883, increased its copper product about twelve-fold, producing nearly six hundred tons from mines on the Platte River, ninety miles north of Cheyenne. The ores are rich carbonates and cuprite. Vermont has long had a steady production from low-grade pyritiferous ores, chiefly in Orange County. Besides these main pro- ducing regions, promising deposits are known to exist and have been considerably worked in many places along the Appalachian range, chiefly in western Virginia, the north- west part of North Carolina at Ore Knob, and at Duck- town in southeast Tennessee ; as well as in California, Nevada, Utah, Ste. Genevieve County, Missouri, and in Maine. Other North American deposits of copper are found in the southeast part of Cuba, near Santiago de Cuba, which formerly yielded annually as high as thirty thousand tons of eighteen-per-cent ore ; and in the British domin- ions, on the north shores of Lakes Superior and Huron, in southern Quebec, and in Newfoundland. Judging from the statistics of production, these are rather regions of promise than of present vigorous working, with the ex- ception of Newfoundland, which in 1883 is credited with a product of ten hundred and fifty-three tons from two localities, and of Capelton, in the southern part of Que- bec, which annually sends to the United States a large amount of cupriferous pyrites to be used in the manufact- ure of sulphuric acid, from which is extracted about four hundred and fifty tons of copper. Under the existing conditions of production, arising from large output and low prices of copper, the chief North American centers of growth for this industry for the im- mediate future seem likely to be those of Lake Superior, Arizona, Butte, with probably Wyoming, New Mexico, and 238 APPLIED GEOLOGY. Newfoundland, and those sections in which, like Colorado, the production of copper is made an accessory to the ex- traction of the precious metals, or to the manufacture of sulphuric acid. Of the foreign producers of copper on a large scale, Chili, with Bolivia, still ranks foremost, although the pro- duction of Chili has greatly diminished in recent years, while Spain and Portugal have risen to almost equal rank. The product of Spain is obtained from enormous mass deposits of copper-bearing pyrites near the Rio Tinto, in the extreme southern part of the peninsula, and extending into adjacent Portugal. These great deposits, called mass deposits (Stocke) by Von Cotta, are pronounced fissure- veins in a recent account by a French engineer (" Engi- neering and Mining Journal," November 17, 1883), and yield an average of about three per cent of copper. Next to Spain, as a producer of copper, is Germany, whose largest product by far is derived from the beds of Mansfeld, before mentioned, the residue coming from cu- priferous pyrites, mainly from great mass deposits in the Harz Mountains. Australia also furnishes large amounts, chiefly from the divisions of South Australia and New South Wales. England, once a large producer of copper-ores, has maintained her supremacy in the copper industry mainly by large importations of ores, cupriferous pyrites, and par- tially reduced copper, from Spain, South America, the Cape of Good Hope, Australia, and some other countries, her own once famous mines in Cornwall, Devon, Anglesea, etc., yielding little more than three thousand tons an- nually. The following table of the product for 1883, recently compiled in London, partly from estimates, will give an idea of the most important sources of supply. In this the German product has been corrected from more recent statistics, as also that of the Cape of Good Hope. France, COPPER. 239 which in 1882 produced 3,627 tons, is for some reason omitted from this table : Tons. United States 52,080 Chili and Bolivia 44,349 Spain and Portugal 43,655 Germany 18,205 * Australia. 12,000 Cape of Good Hope 5,175 Venezuela 4,018 Norway and Sweden 3,43O England 3,000 Russia 3,000 Japan 2,800 Italy 1,600 Newfoundland 1,053 Hungary 1,000 Algiers 600 Austria 500 Mexico 489 Peru 395 Canada 329 Argentine Republic. . . 293 Total 197,971 A table of production of the various parts of the United States in 1882, prepared by the United States Geo- logical Survey, will show the distribution of our own prod- uct. It is reduced to gross tons of 2,240 pounds : Tons. Lake Superior region 25,439 1 Arizona 8,025 Montana, Butte 4,44 Colorado 667 Vermont 564 New Mexico 3^9 California 369 Utah 271 Southern States 180 Nevada 156 * Of which 17,501 was from Mansfeld. f Calumet and Hecla mine, 14,309 tons. 2 4 APPLIED GEOLOGY. Tons. Missouri o ...... 132 Maine 130 Wyoming 45 Pyrites, mostly Canadian 446 From desilverizers 56 Total 40,913 The increase in 1883 was due mostly to the first three regions in the list and to Wyoming, and in 1884 the esti- mated product of the United States was 64,831 gross tons. Uses of Copper. The uses of copper are numerous and important. Among these is its employment for sheathing the hulls of wooden ships ; in wire, in the vari- ous appliances connected with the widely and rapidly de- veloping applications of electricity ; in the fashioning of many articles for domestic uses, and also for manufactur- ing purposes, such as boilers and evaporating-pans for sugar-works and stills for distilleries ; as one of the ele- ments in some forms of galvanic battery ; and as a chief component in several alloys very largely used in the arts, such as brass for many parts of machinery and for numer- ous other uses, and bronze for cannon, bells, and statuary. It has also a considerable use as an essential or subsidiary in- gredient in alloys for coins, and for the manufacture of vari- ous ornaments. Besides this, several of its salts are largely used in the arts, such as the sulphate, called blue vitriol or blue-stone, the acetate, known as verdigris, and the brilliant though dangerous green pigments formed by its combina- tions with arsenic. Works to be consulted. "Mineral Resources of the United States," 1882, article "Cop- per " ; Von Cotta, " Erzlagerstatten," Part II, for Europe ; Geological Reports of Michigan, Missouri, Tennessee, and North Carolina ; Geological Report of Canada, 1863 ; " Third Annual Report of the United States Geological Survey" I rving's Report ; Wright's "Re- ports on Mineral Statistics of Michigan," iSj'j-'jS, 1880, 1882; Phil- lips, u Treatise on Ore Deposits." CHAPTER XIII. LEAD AND ZINC. Lead. Lead was smelted in the United States as early at least as 1825, but during nearly half a century from that date, down to the close of 1872, with wide fluc- tuations in the amount of production, the annual out- put had never exceeded 27,000 gross tons. Since that date, the discovery of rich stores of argentiferous lead- ores in Colorado, Nevada, Utah, and some other Western regions, has swelled our production of lead, mainly as an accessory to the extraction of silver, to five-fold its for- mer amount, and we now rank foremost among producers of this metal. The sources from which lead is derived are the sul- phide (galena) and the carbonate, with minor amounts from the sulphate, which is often associated with galena as a product of its transformation by atmospheric agencies, as is also the carbonate. All these ores yield easily to the knife, their hardness not exceeding 3 ; they are of high specific gravity, and are easily fused by the blow-pipe, being reduced to a mal- leable bead of lead, with the exception of the sulphate, which requires the addition of soda for its reduction. Galena, the fundamental and most common ore, occurs in granular or in cubical crystals, has an easy cubical cleavage, a lead-gray color, and a brilliant metallic luster, and contains 86 per cent of lead. The carbonate, cerus- 242 APPLIED GEOLOGY. site, which contains 77 per cent of lead, is usually white or gray in color, occurs massive or in right rhombic prisms, its crystals have a brilliant luster, and it dissolves with effervescence in nitric acid. Anglesite, the lead sulphate, holding about 68 per cent of lead, occurs massive or gran- ular, and is of white or gray color, and bright, resinous luster. It melts very easily, but yields a bead of lead only by the addition of soda carbonate ; and it does not effer- vesce with acids, by which characters it may be distin- guished from the carbonate. Nature of Deposits and Chief Geological Hori- zons. Ores of lead occur (i) most largely in mass de- posits in limestone formations, filling irregular cavities formed by the enlargement of joints, or extending between beds, or occurring at the plane of contact of limestone with some rock of dissimilar character. Of this kind are the deposits of Eureka district, Nevada, of southeast Missouri, of the Galena district of Illinois and Wiscon- sin, and of Wythe County, Virginia, occurring in limestone of Lower Silurian age ; and those of Leadville, and of southwest Missouri and adjacent Kansas, in limestone of the Carboniferous. (2) They are found disseminated in beds, as, e. g., in beds of Lower Silurian limestone in East Tennessee (Saf- ford) ; and near Commern, in the Rhenish Province of Prussia, where they impregnate abundantly thick beds of loose white sandstone of Triassic age, constituting the richest lead deposits of Germany. (3) They occur in veins cutting strata of different kinds, but productive chiefly in limestone, between whose beds, or at their contact planes, they not unfrequently form also flat deposits connected with the fissures, as in northern England, in Derbyshire, and in the two northern counties of Wales. (4) They are also met with in veins, usually more or less argentiferous, cutting ancient crystalline formations, LEAD AND ZINC. 243 as at Georgetown and in the San Juan region, Colorado, at Freiberg in Saxony, and in Cornwall. The chief lead-bearing geological horizons of this country and of England are the Lower Silurian and the Carboniferous, with some in crystalline formations; the same appears to be true also for Spain ; while in Germany, lead is derived mostly from Triassic rocks. Limestone appears to be a rock which is especially favorable to the deposition of ores of lead. These ores are usually associ- ated with more or less of silver, sometimes in proportions too minute to be separated with profit, but not unfre- quently the silver contents equal or surpass in value the lead with which they are blended. Chief American Centers of Production. Of the lead production of the United States more than 43 per cent is credited to Colorado, in which State its extraction is wholly accessory to that of silver ; and the larger portion of the product is derived from the famous region about Leadville. The ore masses are found here chiefly at the contact of a limestone of Lower Carboniferous age with overlying masses of porphyry, and, according to Emmons, they owe their origin to a replacement of the substance of the magnesian limestones by silver-lead solutions which were derived from the overlying eruptive rocks. The ores are argentiferous lead sulphide and carbonate in a gangue of ferruginous silica and clay. Besides the Leadville re- gion, the silver-lead veins around Georgetown and in the San Juan region, cutting Archaean rocks, afford consider- able amounts of lead. Next in production to Colorado is Utah, 60 per cent of whose product in 1882 was derived from the Horn Sil- ver mine in Beaver County, most of the residue coming from the region around Salt Lake City. Here, also, as in all the Rocky Mountain region, the extraction of lead is an accessory to that of the precious metals, the value of which usually equals or surpasses that of the lead. 244 APPLIED GEOLOGY. The mines of Eureka district, in Eureka County, yield nearly all the lead of Nevada, the reported product varying from about 8,000 to 28,000 gross tons per annum. The ores here, which are chiefly carbonate of lead in a highly ferruginous gangue, carrying 20 to 30 per cent of lead with a high value in gold and silver, occupy great chambers in a magnesian limestone of Lower Silurian age. The inclos- ing limestone is tilted up at a considerable angle, and bears evidence of great compression, in consequence of which it -is much fractured and crushed, so that the ore masses, in their mode of introduction and after -concentration, seem to have a considerable resemblance to fissure-veins. They therefore belong to that variety of mass deposits which in a preceding chapter has been described as " quasi veins," i. e., those which, while mass deposits in mode of occurrence, are allied to true veins in having derived their ores from some deep-seated source rather than from local concentrations. The State of Missouri, which is an important producer of lead, has two geological horizons of lead-bearing strata. A very considerable area in the southeast portion of the State, with some of the central counties, has deposits of lead-ores in Lower Silurian limestones, partly occurring in mass deposits, partly disseminated in certain of the beds, according to Prof. Brodhead. The deposits, how- ever, which are at present most largely worked, are those occurring in crevices and flats, true mass deposits, in the Lower Carboniferous limestones of the southwest part of the State, about Joplin and Granby, and extending into adjacent Kansas. The ores here are associated with im- portant amounts of zinc ores, but contain only insignificant proportions of silver. In the Galena district of Illinois, Wisconsin, and Iowa, lead-ores, associated with zinc but poor in silver, are found in vertical crevices formed by the widening of the joints of the Lower Silurian limestone in which they occur, or LEAD AND ZINC. 245 sometimes in flats between the beds of the limestone. This region does not appear to be a large producer at present. Besides these well-known and most largely productive districts, most of the States and Territories of the Rocky Mountain division are reported to have promising deposits of lead-ores, though little worked as yet, unless where they contain paying amounts of the precious metals. This is especially true of Montana and of the Wood River region in Idaho, from both of which a considerable production of argentiferous lead was reported in 1882. In Wythe Coun- ty, Va., also, large bodies of sulphide and carbonate of lead, associated with ores of zinc, are known to exist and have been somewhat worked, in limestone of Lower Silu- rian age ; and they need only good facilities for transporta- tion to build up a prosperous center of metallic production. The lead product of the United States for 1882, which was considerably increased in 1883, was reported to be 120,832 gross toris, distributed as follows : Tons. Colorado 52,360 Utah 26,786 Missouri, Kansas, Illinois, etc 25,906 * Nevada 7,670 Idaho 4,45O Montana .... 3,660 Total 120,832 The foremost foreign producers of lead are Spain, Ger- many, and England, with minor amounts from Austria, Greece, Italy, and France. Of these, Spain is much the largest producer. The lead-producing regions of this kingdom are in the provinces of Murcia and Almeria on the southeast coast near Cartagena, and about Linares, in the province of Jaen, a little farther inland, on the head-waters of the Guadalquiver. The district about Linares is said to yield * Less than one tenth from Illinois and Wisconsin. 246 APPLIED GEOLOGY. nearly two thirds of the lead, but it is poor in silver ; while the coast deposits about Cartagena, which, according to Von Cotta, are veins of galena and blende, cutting Silurian limestones and slates, contain profitable amounts of the precious metals. The large lead product of Germany is derived from Commern, in the Rhine Province ; from Upper Silesia, where it is subordinate to a very large output of zinc ; from the Harz Mountains, Nassau, and Freiberg. At Com- mern, according to Credner, the galena is found richly im- pregnating a friable white sandstone of Triassic age, which attains sometimes a thickness of eighty metres, or more than two hundred and sixty feet. In Upper Silesia, ac- cording to the same author, the associated ores of lead and zinc occur in mass deposits in a dolomitic limestone of the Muschelkalk (Triassic). England has also a large but somewhat decreasing pro- duction, chiefly from Alston Moor, from Derbyshire, and from Flintshire and Denbighshire in North Wales, with some from other localities. The following table of the lead production of the world, from the latest attainable statistics, will afford a good idea of the most important lead-producing countries. The amounts are given in gross tons for England and the United States ; for the Continental states of Europe they are supposed to be metric tons of 2,204^ pounds : Tons. United States, 1883 129,722 Spain, ,, 123,000 Germany, . 89,767 England, 1882 50,328 Austria, ,, 11,899* Greece, 1881 njoof Italy, 1873 15, 500 J France, 1882 8,067 Total 439,983 * Partly litharge. f Amount exported. \ Sardinia. LEAD AND ZINC. 247 Chief Uses of Lead. The very great increase in the production of lead within the past ten years has doubt- less been attended by a corresponding increase in its use. It is employed in the arts, in the form of metal, in a num- ber of important alloys, and in several chemical combina- tions. As metal, it is used in sheets for covering roofs, for lining sulphuric-acid chambers in chemical works, and for conden sing-pans and cisterns, and for lining tea-chests. It has a large use in pipes for the conveyance of water and gas. Coated with a thin film of tin, as tin-foil, it has a large and increasing use for linings and wrappers of many articles for culinary and other purposes. Its alloys with tin, bismuth, and antimony are used as soft solder and pewter, and for type and stereotype metal. Either alone, or slightly alloyed with arsenic, it is used for bullets and shot. White lead, an artificial carbonate, the chromate, or chrome-yellow, and red lead, are largely used as pig- ments ; both litharge and red lead enter into the composi- tion of the most brilliant kinds of glass ; and the acetate, called also sugar of lead, is largely used in the arts and in medicine. Books of reference. " Geological Reports of Missouri " ; " Geological Reports of Illi- nois," Vol. I ; " Geological Report of Wisconsin," Vols. II and IV ; " First Geological Report of Iowa," Vol. I, Part I ; " Second Geological Report of the United States" Emmons on Leadville ; "Mineral Resources of the United States," 1882 ; Wallace, "Laws which Reg- ulate the Deposition of Lead-Ores in Veins " ; Phillips, " Treatise on Ore Deposits." Zinc. The ores from which zinc is extracted are the sulphide, called blende, smithsonite, the carbonate, and cala- mine, a silicate of zinc ; besides which, in a New Jersey locality, three minerals, which are rare elsewhere, occur abundantly and constitute valuable ores of the metal, viz., the red oxide zincite, ivillemite another silicate, and franklinite. 248 APPLIED GEOLOGY. The most widely diffused ore is that popularly known as blende, or black-jack, but whose scientific name is spha- lerite, and which contains 67 per cent of zinc. It occurs commonly massive, but sometimes in crystals ; has an easy cleavage, is of a variety of colors, the more com- mon ones being yellow, brown, and black, with a resin- ous luster; and its hardness is that of dolomite, yielding with no great difficulty to the knife. It is infusible before the blow-pipe on charcoal ; but, when strongly heated, it yields fumes of zinc oxide which coat the coal with a yellow film that becomes white when cold ; and in nitric acid it dissolves, giving the disagreeable odor of sulphu- retted hydrogen. The carbonate, smithsonite, which results from the weathering of the sulphide, contains about 52 per cent of zinc, and occurs usually in dirty-white or brownish masses, crusts, or stalactites, which when crystalline have a pearly luster. It is harder than blende, being somewhat difficult to scratch ; it dissolves in nitric acid with effer- vescence, and before the blow-pipe behaves like blende. This ore is the " dry bone " of Western miners. Calamine, the common zinc silicate, called Galmei by the Germans, contains about 54 per cent of the metal, and occurs usually in whitish masses or crusts, but sometimes in rhombic prisms with a pearly luster. Its hardness is in- termediate between that of blende and smithsonite ; and it dissolves in hot sulphuric acid, the solution becoming jelly-like when cold. Zincite, the native oxide of zinc, containing 80 per cent of the metal, is of a deep-red color, very easy cleavage, and brilliant luster, and is found usually in cleavable, foli- ated masses. It is infusible before the blow-pipe, but gives a zinc film like blende on coal, and, when heated with borax, yields a yellow glass. It dissolves in nitric acid, and its hardness is a little greater than that of blende. Willemite, a second zinc silicate containing 58 per cent LEAD AND ZINC. 249 of zinc, occurs usually massive, but sometimes in rhom- bohedral crystals. It has various colors, as yellow, green, red, and yellowish brown, and, with soda on charcoal, it gives a zinc film before the blow-pipe. It dissolves in hydrochloric acid, yielding a jelly of silica, like calamine. Franklinite, a complex compound of oxides of iron, manganese, and about 17 per cent of zinc, greatly resembles magnetite in form, color, magnetism, and hardness ; but its streak is reddish brown, and before the blow-pipe on charcoal with soda it yields a film of zinc. Mode of Occurrence. In their mode of occurrence and geological horizons, the ores of zinc present no marked differences from those of lead, with which, in the majority of cases, they are intimately associated. Thus, in the lead regions of Missouri, and of the Galena dis- trict, forming mass deposits occupying flats or irregular fissures discontinuous in depth, in limestones of the Lower Silurian and Lower Carboniferous, the two sets of ores are found associated ; and in the Galena district, as shown by Chamberlin, in tolerably equal amounts, though with a tendency to occupy somewhat different levels ; while in deposits of similar character in Lower Silurian limestone near Bethlehem, Pa., the zinc-ores are remarkably free from lead. In the veins, often following faulting fissures, productive chiefly in Lower Carboniferous limestones, of North Wales, Derbyshire, and northern England, the two ores are also frequently found associated. In the silver- bearing veins cutting Archaean rocks about Georgetown, Col., zinc blende is a frequent large constituent of the ore, making a mixture from which it is difficult to extract the silver without great loss by volatilization ; and the remark- able deposits of franklinite, zincite, and willemite, near Franklin, N. J., in Archaean limestones, form part of the series of highly metamorphosed and greatly disturbed beds of that region. These few examples will serve to show that, although the ores of zinc and lead are not always 250 APPLIED GEOLOGY. found together, their modes of occurrence are yet striking- ly similar, even when they form distinct and separate deposits. American Centers of Production of Zinc Ores. The Lower Carboniferous lead region of southwestern Missouri and adjacent Kansas, mentioned in the previous 'section, is at present the foremost producer of rich zinc- ores in the United States, it being estimated to yield fully two thirds of the zinc which we produce. The ores are blende, with considerable amounts of calamine. The zinc deposits of eastern Missouri, covering, in connection with lead, copper, and nickel, a considerable area in portions of ten counties, and once yielding a considerable supply of ores, are said to be doing little at present. The zinc-ores of the Galena district, blende and smithsonite, according to Chamberlin are proving fully equal in amount to those of lead, and show a marked tendency to accumulation in the limestone crevices at lower levels than the galena with which they mingle in the middle zones of deposit. Here, as in Missouri, in the earlier periods of mining, they were thrown on the waste- heaps as worthless " black-jack " and " dry bone," but have later been collected as the basis of a prosperous industry. The ores of zinc with lead occurring in eastern Ten- nessee, in the Lower Silurian (Knox dolomite), are re- ported to be worked for zinc near Knoxville. Passing northeastward from this point, we meet with the zinc deposits of Wythe County, Va., and of Lehigh County, Pa., both in strata of the same geological age as the Knoxville deposits. According to C. R. Boyd (Institute of Mining Engineers, June, 1883), the ores of Wythe County are carbonate and sulphide of zinc, remarkably free from lead, occurring in great mass deposits in dolo- mite, and yield a zinc of exceptional purity. The deposits in Lehigh County, near Bethlehem, are not worked at present. The ores, blende with the results of its transfer- LEAD AND ZINC. mation, smithsonite and calamine, occur in crevices, some- times parallel, sometimes perpendicular, to the bedding of greatly disturbed and fractured magnesian limestones, and seem to belong to the variety of mass deposits which have been described as " quasi-veins." The unique deposits of franklinite, zincite, and wil- lemite, in Essex County, N. J., in the vicinity of Franklin, are found in Archaean limestone, in beds conformable to the highly inclined and crystalline strata of the region. They are of great dimensions, and furnish important sup- plies of ore for the manufacture of a high grade of metal, and also of white zinc oxide and spiegeleisen. The re- gions above described are at present the only important producers of zinc-ores in North America. Foreign Zinc-producing Regions. Among for- eign producers of zinc, Prussia ranks easily foremost, her mines in Upper Silesia, in the Rhenish Province, and Westphalia, yielding more than two fifths of the zinc of the entire world. The famous zinc district of Upper Silesia, which yields annually about seventy thousand met- ric tons of the metal, obtains its ores, chiefly calamine with minor amounts of blende, from mass deposits in a dolomitic limestone of Triassic age ; while in the Rhenish district and Westphalia the ore is blende with but a small proportion of calamine, in irregular deposits in the De- vonian or Lower Carboniferous limestone, which is chiefly dolomitic. The very large product of Belgium is derived in but small measure from its native ores. According to the latest returns available, less than 12 per cent of the zinc- ores smelted in that country came from Belgian mines, which resemble in character and horizon those of the Rhine Province ; the residue being imported from Greece, Sardinia, Spain, Sweden, Germany, and France, most largely from the two regions first named. England is a considerable producer of zinc from her lead regions in Wales, northern England, Cornwall, and Devonshire. 252 APPLIED GEOLOGY. Besides these countries, France, Spain, Austria and Poland, Greece and Italy, yield important amounts; France, as appears from Von Cotta's description, chiefly from veins in crystalline and eruptive rocks ; and Spain partly from the lead district near Cartagena, mentioned in the preceding section, and partly from the province of Santander, on the northern coast, where large mass de- posits and impregnations (?) occur in Cretaceous strata between dolomite and clay slate, which yield nearly two thirds of the zinc of Spain. The zinc product of the world, according to the latest available data, approximates 290,000 gross or metric tons, distributed as follows : Tons. Prussia, 1883 116,644 Belgium, ,, 78,220 United States, ,, 29,747* England, ,, 27,661 f France, 1882 18,325 Spain, 1881 7>O32 Austria, 1882 4>79* Poland, 1883 3,783 Total 286,203 Zinc is used in sheets as a covering for roofs, as a lin- ing for various receptacles, and as a protection for floors and walls against the heat of stoves. It has a very im- portant use in most forms of galvanic battery. It is very largely used for coating sheet-iron and wire for fencing to protect them from rust, a process which is called galvaniz- ing. A single manufactory in this country is said to use more than three thousand tons annually for galvanizing fence-wire. Several of its alloys, like brass, Mosaic gold, German silver, hard solder, and Babbitt's metal, are largely used in the arts. Among its compounds, zinc-white is a highly valued paint, zinc sulphate is used in medicine and * And 9,000 gross tons zinc oxide. f Estimated. LEAD AND ZINC. 253 in the arts, and zinc chloride is employed in the process called Burnettizing, for the preservation of timber, as also for a disinfectant. As works of reference, most of those mentioned under lead may be consulted with profit, to which should be added " Geology of New Jersey," published in 1868. 12 CHAPTER XIV. TIN AND MERCURY. Tin. Although a sulphide of tin is occasionally met with, the only ore that seems to be relied upon as a source of the metal is cassiterite^ an oxide which contains y8f per cent of tin. It is a brown or black mineral of brilliant luster when in crystals, and is of nearly the hardness of quartz. It is infusible by the blow-pipe on charcoal, but, if soda be added, it yields a white, malleable bead of tin. It is found sometimes crystallized in modified square prisms and octahedrons, but more commonly massive, in grains, lumps, and kidney-shaped masses, which, when they have a concentric and radiated structure, are called wood tin, or toad's-eye tin. Mode of Occurrence and American Localities. Tin-ore occurs (a) disseminated in bunches and grains in veins cutting ancient crystalline rocks like granite, gneiss, micaceous and hydro-micaceous schists, and is often as- sociated with a peculiar kind of granitic rock called greisen, composed of quartz and mica without feldspar. It is accompanied by a great number of minerals, like pyrite, chalcopyrite, albite feldspar, tourmaline, and wol- fram. (<) From its hardness and unalterability by atmos- pheric agencies, cassiterite is one of the ores which is found largely accumulated \nplacer deposits, in the neigh- borhood of tin-veins, from whose denudation it has been accumulated in favorable localities ; and it is said that a TIN AND MERCURY. 255 large proportion of the tin product is still obtained from this source. Hence the name stream-tin, since these tin placers are often called streams. Tin-ore has not been found hitherto in quantities of economic importance in North America, although a num- ber of localities, apparently of great promise, have been discovered within the last few years which seem likely soon to give both the United States and Mexico a rank among producers of tin. Quite recently, Prof. W. P. Blake has reported the occurrence of tin-stone in the Black Hills of Dakota. It is there found both in placers and in irregular bunches and seams in veins of coarse granite, associated in some places with greisen, and in others in a greisen-like rock of albite and mica. Tin is reported as occurring in very promising deposits in two of the southern counties of California, ores from San Bernardino County giving an analysis of about 60 per cent of the metal. In Clay County, Ala., deposits of tin- stone have been opened and worked to some extent since 1 88 1. The ore here occurs disseminated in grains in vertical beds of gneiss, interstratified with micaceous and chloritic schists. Six beds of the tin-bearing gneiss are said to occur, some of them yielding an average of i\ per cent of the oxide. Tin-ores are said also to have been discovered at King's Mountain in North Carolina, and at several other points in the United States, but whether in quantities sufficient to justify mining, is still to be shown. Mexico is reported to have deposits of cassiterite of great extent and high promise in the States of Durango and Chihuahua, but they are as yet very little worked, and have not apparently added anything to the supply of the world. From South America, Bolivia yields annually about one thousand metric tons, and the States of Colom- bia are said also to produce small amounts. Foreign Producers. The chief supplies of tin are from three regions, viz., from Cornwall, England ; from 256 APPLIED GEOLOGY. Banca and Billiton, in the Straits of Malacca, hence called Banca tin and Straits tin ; and from the eastern part of Aus- tralia, chiefly from New South Wales, with some from adja- cent Queensland and Victoria. The tin deposits of Corn- wall have been worked for many ages, the earliest workings extending back, it is supposed, some centuries before the Christian era. The ore is still obtained to some extent from placers, but chiefly from veins in ancient crystalline rocks. The Australian deposits, which in New South Wales are found over an area of 8,500 square miles, oc- cur in narrow veins, irregularly disseminated in bunches, grains, and seams, and associated with quartz, feldspar, greisen, and chlorite, the country rock being, like that of Cornwall, granite and crystalline schists. The largest supplies are obtained, however, from extensive placer deposits derived from the disintegration and wash of the veins. The latest government report gives the product of New South Wales for 1883 as 9,125 gross tons of tin and its equivalent in ore, and the chief hindrance to making the output much greater evidently arises from the fre- quent defective supply of water to wash the ore-bearing gravels. Some of these placer deposits are of very con- siderable depth, occupying the sites of ancient water- courses, and are covered with masses of basalt, presenting a striking resemblance to the deep gold placers of Califor- nia. The large supplies of Banca and Billiton are said to be derived chiefly from placers, which yield annually about eight thousand tons. Besides these, small amounts of tin are produced in Germany and Bohemia, from de- posits similar to those of Cornwall, the product of the two regions amounting together to one hundred and thirty-six tons in 1882. The entire product of the world for 1881 is said to have been 38,123 gross tons. The statistics of production, so far as they could be obtained, are as follow : TIN AND MERCURY. 257 Tons. England, 1882 9,158 New South Wales, 1883 9,125^ Banca and Billiton about 8,000 Bolivia, 1881 1,000 Germany, 1882 (from Saxony) IO2 Austria (from Bohemia) 34 Tin, used somewhat in castings, is much more exten- sively employed as a coating for other metals, as, for ex- ample, iron in the widely used tin-plate, copper in many vessels for culinary purposes, and lead in the so-called tin-foil. Its alloys, chiefly with copper, but somewhat with lead and bismuth, are numerous and important. Among them are bronze, bell-metal, gun-metal, britannia, pewter, soft solder, Babbitt's metal, and the amalgam with mercury for coating mirrors, besides several others. Several of its compounds also have important uses in the arts. Tin oxide is used for enamels, as a coating for razor-strops, and for giving a fine polish to some orna- mental stones ; the chlorides have valuable applications in dyeing and calico-printing ; and the bisulphide, under the name of bronze-powder, is considerably used for ornamental purposes. Mercury. Although mercury or quicksilver is not unfrequently found native in small quantities, the only source of it which is of economic importance is cinnabar, the sulphide, which contains when pure about 87 per cent of the metal. This ore is of a bright red or brownish red color and scarlet streak ; is of high gravity, about 9, and is easily scratched, its hardness being less than that of calcite. Before the blow-pipe it is easily dissipated in vapor, leaving no residue save the substances with which it may be mingled. Mode of Occurrence and Localities. Its mode of occurrence in all the great producing regions, three in number, is the same, viz., as an impregnation, either from solution or from vapor, in certain porous or fissured 258 APPLIED GEOLOGY. beds of tilted and sometimes metamorphosed stratified rocks. The three regions, however, while agreeing in the character of the deposits, contain them in rocks of widely different geological age ; the Spanish deposits being in- closed in Silurian strata, the Austrian in rocks of the Lower Triassic, and the Californian in strata not older than the Cretaceous. The production of mercury in the United States, which is now nearly one half the entire product of the world, is confined wholly to the vicinity of the Coast Range in California. In this region, at least eight coun- ties, ranging from Fresno on the south to Trinity County on the north, are known to contain workable deposits of cin- nabar. The richest deposits that have been opened hith- erto are those of New Almaden, in Santa Clara County, while important supplies are also derived from Napa, Lake, Sonoma, and Fresno Counties, the mines in other sections seeming to depend for their working upon favor- able prices for quicksilver. The inclosing strata in the entire region are usually serpentine, and sandstones and shales, the last-named rocks being sometimes much metamorphosed, in other cases wholly unchanged, and in some localities containing fossils of probable Tertiary age. The cinnabar occurs in irregular deposits, impregnating in some cases talcose, argillaceous, and jaspery slates ; in others, sandstone ; while in others, quartzites and opaline quartz form the gangue. The average contents of metal in the New Almaden mine are said to be about 3^ per cent, and the average cost of production in well-conducted mines is said by Wagoner to be 27 -J- cents per pound. Throughout the region, irregular deposits of chromic iron are said to be as constant as cinnabar. As an indication of the location of the mines whose product is at present the most important, the following table is given for the fis- cal year ending June 30, 1883 5 it is stated in flasks of 76 \ pounds : TIN AND MERCURY. 259 Flasks. New Almaden (Santa Clara County) 28,753 Napa Consolidated (Napa County) 6,351 Great Western (Lake County) 4,514 Sulphur Bank ,, 4,053 Reddington 2,555 Great Eastern (Sonoma County) 2,673 New Idria (Fresno County) 1,720 Other mines 671 Total 5 1,290 The famous Spanish quicksilver mines of Almaden, northeast of the city of Cordova, have been wrought for many centuries, having been known, it is said, to the an- cient inhabitants of the peninsula before the time of the Roman occupation. The ore deposits here occur in ver- tical Silurian strata of sandstone, quartzite, and bitumin- ous schist, with hard sandstone and limestone which do not contain ores. The cinnabar, in a compact or earthy condition, is found, in the largest mine, impregnating a gray sandstone to such a degree that the mass may yield as much as 25 per cent of mercury, and leave as a residue when distilled only loose sand. In other cases the impreg- nated beds are of quartzite, creviced with fissures running in all directions, into which the cinnabar has penetrated, forming sometimes also great masses, with occasional cavi- ties containing metallic mercury. That these deposits are really impregnations, and not bedded veins, as they have sometimes been considered from the presence of a selvage, seems to be conclusively shown by the fact that the origi- nal planes of stratification of the beds are often percep- tible in the midst of the deposits. The chief mine in 1851 was already 1,050 feet in depth, and the width which had been mined out at the 8oo-foot level was said to be 67 feet. No ores are treated here which carry less than two per cent of mercury, and the cost of production is not more than twenty cents per pound. The quicksilver-mines of Idria are in Carniola, in the 260 APPLIED GEOLOGY. southern part of Austria, not far from the Adriatic Sea, and have been worked since the latter part of the fifteenth century. They occur in greatly inclined strata of Triassic age, impregnating black bituminous schists, or forming contact deposits between dolomites and slates, or filling transverse fissures in dolomite and limestone. The work- ings have now reached the depth of 950 feet, and the ore- bearing rock is found to grow richer as greater depth is gained, confirming the opinion that the cinnabar has been derived from a deep-lying source by infiltration or subli- mation. The ores of the Idrian mines are reported to average about 1.6 per cent of mercury, and the annual production is much smaller than in the other two regions. Besides these three chief sources of supply, compara- tively insignificant amounts of mercury are obtained from Italy and other parts of Europe ; but the total supply es- timated to be received from these scattered localities is of little importance, as may be seen from the following statis- tics of the world's production in the year 1882. In this table the product is given in flasks, of which those of the United States, as has already been said, contain 76.5 pounds of mercury, while those of Spain and Austria hold 76.07 pounds. The amounts are also given in a sec- ond column in metric tons of 2,204.6 pounds : PRODUCTION OF MERCURY IN 1882. Flasks. Metric tons. United States 52,372 1, 8^O Spain . . AC Q2I I 6lO Austria . ii, 8^ 4OQ Italy etc., estimated 2,000 <*^y 60 Total 112,506 7 q-;8 California, therefore, furnished about 46^ per cent of the mercury of the world, and the New Almaden mine alone fully 25 per cent. TIN AND MERCURY. 2 6l Uses of Mercury. The largest uses to which mer- cury is applied are in the extraction of gold and silver, and in the preparation of the brilliant pigment vermilion. From the valuable property which this fluid metal possesses, of readily forming alloys, called amalgams, with the precious metals at ordinary temperatures, it has become indispensa- ble in the processes by which these metals are cheaply extracted from ores of too low grade to be smelted with profit ; and about 45 per cent of all mercury is used for amalgamation. A still larger proportion of the product is employed in the manufacture of vermilion, the artificial sulphide of mercury, used as a pigment. Other important applications of mercury are found in the making of mirrors and philosophical and meteorologi- cal instruments, such as barometers and thermometers, in the manufacture of fulminates for percussion caps, and of various preparations for medical use, as well as in a pro- cess for preserving timber from decay, called kyanizing. Works of reference. "Geological Report of California," Whitney, Vol. I; J. Ross Browne, " Report on Mineral Resources of the United States," 1867, p. 170 ; R. W. Raymond, " Report on Mineral Resources of the United States," 1873, p. 18 ; Williams, " Report on Mineral Resources of the United States," 1883 ; " Engineering and Mining Journal," Nos. for December 24, 1881, and October 7 and December 23, 1882 ; Von Cotta, " Ore Deposits," Part II, pp. 248 and 455 of German edition ; Phillips, " Treatise on Ore Deposits." CHAPTER XV. SILVER. THIS, which is counted one of the two precious metals, and which in all ages of the world has been held in high estimation and largely used for coinage and for articles of luxury and ornamentation, is found native in small amounts in most great regions where it is mined, when it is easily distinguished by its pure white color, often with a dark superficial tarnish, by the ease with which it may be cut and its brilliant luster on a cut surface, and by its solution in nitric acid, from which it may readily be pre- cipitated by a clean slip of copper, yielding a coating of silver, or by a solution of common salt, yielding a white chloride of silver which soon becomes discolored on ex- posure to light. More commonly it is found in various combinations with other substances, forming ores of silver. Those most largely met with are its combination with sul- phur, called argentite j with sulphur and antimony, forming stephanite and pyrargyrite ; with sulphur and arsenic, called proustite ; with chlorine, called cerargyrite, or horn-silver; and with sulphur, antimony, and lead, called freieslebenite, a mineral found as an ore in the mines of Guadalajara in Spain. It also frequently replaces a part of the copper in tetrahcdrite, or gray copper, thus making it a valuable ore of silver, as has been mentioned in the chapter on copper. In many of our Western mines, also, it is largely obtained from its associations with ores of lead and with zinc blende. SILVER. 263 All these ores of silver are so soft as to be easily cut with a knife, and have a specific gravity varying from 5^ to 7^ ; all melt with little difficulty before the blow-pipe, emitting fumes of sulphur, antimony, arsenic, or chlorine, and yield- ing a bead of silver, either alone or by addition of soda carbonate ; and all, save cerargyrite, dissolve in nitric acid with precipitation of any sulphur, antimony, and arsenic that may be present, and the silver may be deposited from this solution on a clean slip of copper, or may be precipi- tated as chloride by salt water. These ores may be dis- tinguished from each other argentite, or silver glance, by its dark lead-color and lustrous streak, its malleability and sectility, and its yielding a silver bead by heat on charcoal without soda ; stephanite, or brittle silver, by its black color and streak ; pyrargyrite, by its usual dark-red though some- times black color, and its red streak, from which it takes its common name of ruby silver ; proustite, also called ruby, or light-red silver-ore, by its light-red color and the odor of garlic which it emits when heated ; freieslebenite, by its steel-like color, and its yielding when heated on coal a globule of silver-lead, from which the lead may be burned off by heating with the blow-pipe on a little cup of boae- ash, leaving a bead of silver, an operation which is termed cupellation ; and cerargyrite, called usually horn-silver, by its looking and cutting somewhat like horn, and by its emitting peculiar pungent fumes when heated on charcoal, and yielding a bead of silver without soda. When pure, argentite contains 87 per cent of silver, stephanite 69 per cent, pyrargyrite 59 per cent, proustite 65 per cent, frei- eslebenite about 24 per cent, and cerargyrite 75 per cent. Argentiferous galena requires no special description. Its silver contents may be ascertained by cupelling the silver- lead globules obtained by heating on charcoal. When it is considered that an ore-mass containing one thousand dollars' worth of silver per ton would hold no more than a thousand ounces avoirdupois per gross ton 264 APPLIED GEOLOGY. of rock, or about three per cent of silver, and that such an ore-mass would be counted very rich, while one yielding one half of one per cent, if abundant, would be worked with enormous profit, it will be obvious to the student that the ores of silver, described above, can not usually be ex- pected to occur in pure and easily determinable masses of considerable size, but rather as strings, thin seams, and stains disseminated in a comparatively large bulk of gangue rock, most commonly quartz or calcite, where its determin- ation as a silver-ore, and as to the amount which it may yield per ton, will often be easier and of greater economic impor- tance than any exact answer to the question of precisely what silver-ores are present in the mass. For this reason the description of the most common silver-ores has here been made chiefly as general as possible, embracing those characters which are common to them all, as in this form it will be more likely to be generally useful to the practical man. For more complete descriptions, and for desirable additions to the few specific characters here given, the stu- dent can refer to any good manual of mineralogy like Dana's. Mode of Occurrence of Silver Deposits. The forms of deposit in which workable silver-ores are found are various, including most, if not all, the chief classes of deposit described in a preceding chapter. They occur in veins, cutting granitoid rocks, and crystalline schists of the Archaean, as in the Reese River region of Nevada, in the Atlanta and associated lodes of Salmon River, Idaho, in the mines about Georgetown, Col., and in those of Kongs- berg, Norway, and Freiberg, Saxony. Some of the great- est silver-veins of the world are incased in or associated with volcanic rocks of Tertiary age, called variously an- desite, propylite, and sometimes diorite, e. g., the celebrated Comstock vein of Nevada, the Veta Grande of Zacatecas, and some others in Mexico, and those of Felsobanya and Schemnitz in Hungary. It occurs in impregnations, as in the Triassic sand- SIL VER. 265 stones of Silver Reef, in southwestern Utah, and in the joints and bedding planes of Devonian limestones of the White Pine region, Nevada. Associated with ores of lead, it is found in mass deposits and ^zfcWf-veins, as at Lead- ville, in many mining districts of New Mexico, and at Eureka, Nev. It forms flat deposits, connected in origin with mineralized dikes of eruptive nature, of which char- acter, according to W. P. Blake, are the silver deposits of Tombstone in southern Arizona. Finally, as an example of silver in beds, may be cited the copper schists of Mans- feld, which, besides affording much of the copper of Ger- many, yield also important amounts of silver. An inter- esting occurrence of silver may also be noted here, viz., that in the regions of native copper on Lake Superior, where the two native metals are not unfrequently found forming parts of the same lump, and thoroughly welded together without being alloyed. Regions producing Silver. Of the vast silver pro- duction of North America, derived almost entirely from the United States and Mexico, it may be said in a general way that, with comparatively trivial exceptions, it is ob- tained from the great mountainous region of the western part of the continent, comprised between the Front range of the Rocky Mountains on the east, and the Cascade and Sierra Nevada ranges on the west, with their southern ex- tension into Mexico. The only exceptions worthy of note are the product of Dakota, which might without great vio- lence be included in the first, and that of the Appalachian range mostly from North Carolina, and of Canada, the three together amounting to little more than three hundred thou- sand dollars in value in a product of more than seventy- five million dollars. A similar statement may also be made with regard to the silver production of South Amer- ica, second only to that of the United States and Mexico, which is derived from the Andes and their western slope. Within the great mountain-region indicated above, the 266 APPLIED GEOLOGY. United States has much the largest silver production of any country in the world. Of the eleven States and Territo- ries included within its limits, all save Wyoming, Oregon, and Washington, in 1882 yielded amounts of silver valued at eight hundred thousand dollars or more. The State ranking highest in silver production in that year was Colo- rado, whose sixteen and a half million dollars' worth of sil- ver was derived most largely from three chief districts : that of which Leadville may be considered the center, in- cluding Lake County and small portions of Summit, Gun- nison, Eagle, and Chaffee ; Clear Creek County, of which Georgetown is the center ; and the San Juan region, in- cluding portions of about six very rugged and mountain- ous counties, whose chief centers seem to be Silverton and Ouray. Besides these chief regions, Boulder, Custer, Gilpin, and Park Counties yield important amounts. The mines of these four counties are chiefly in veins, and the vein system in all of them yields' gold as well as silver; that of Gilpin County, in particular, affording six times as much gold as silver. The two great mines of Custer County, the Bassick and the Bull Domingo, present features worthy of mention, since their gangue is a kind of breccia of the country rock, carrying the ores of gold and silver of the first, and of silver of the second named mine, as a cementing incrustation of the blocks of stone ; while the ore-bearing fissure of the Bassick has the character of a chimney of unknown depth but limited extent, giving rise to the theory that it is the pipe of an ancient hot spring. Next in value of silver output to Colorado is Arizona, in which the noted Tombstone region, in the southernmost county of the Territory, yields fully two thirds of its sil- ver ; while Final County, chiefly through the Silver King mine ; Gila County, so rich in copper ; Yavapai, Yuma, and Final Counties are also important producers. The large silver product of Utah may conveniently be said to be de- rived from three chief districts, of which what may be SILVER. \ V J 267 called the Salt Lake district, since its mines use City as a center or are in convenient proximity to it, in- cludes Salt Lake and Tooele Counties and the Tintic dis- trict of Juab County, the ores of which are mostly treated near Salt Lake ; as also Summit County, in which the very rich Ontario mine produces yearly about two million four hundred thousand dollars in silver. In the Frisco dis- trict of Beaver County, the Horn Silver mine is much the largest producer ; and the Harrisburg or Silver Reef dis- trict, in the very southernmost part of the territory, yields about nine hundred thousand dollars a year from its unique reefs of sandstone permeated with ores of silver. Nevada, so short a time ago the foremost State in sil- ver production, mainly from the Comstock mines, the Eu- reka and Reese River districts, and from Esmeralda and White Pine Counties, has during the past few years sunk to the fourth place, the great diminution in the yield of the Comstock mines not having been compensated by a corre- sponding increase elsewhere. Besides the regions named above, Elko, Lincoln, and Nye Counties are important producers of silver. Of the silver produced in Montana, about five sixths are reported to come from the near vicinity of Butte City, the remaining sixth being made up mostly by three coun- ties, Beaver Head, Deer Lodge, and Jefferson, which sur- round it, in the western portion of the Territory. The silver of Idaho, amounting to about two million dollars per year, is derived almost wholly from the three counties of Custer, Alturas, and Owyhee: in the first, from the region on the head-waters of the Salmon River ; in Alturas, from the Atlanta vein and the Wood River re- gion, these districts being in near proximity to each other ; while the mining districts of Owyhee County are in the southwest corner of the Territory, in the vicinity of Silver City. Most of the silver of New Mexico so far has been derived from mines along the Mimbres, or Black range, 268 APPLIED GEOLOGY. and the Socorro Mountains, in portions of Grant, Dona Ana, and Socorro Counties, in the southwest part of the Territory ; and that of California from the Sierra Nevada Mountains, chiefly on their eastern declivity. The an- nexed table of the silver product of the United States in 1882 will aid the student to gain a clearer idea of its rela- tive distribution from the preceding brief description. The values are reckoned on the coinage estimate of silver, viz., $i.29 1 2 o 9 o- P er ounce, troy. As the selling price of un- coined silver during that year was not more on the aver- age than $1.11 per ounce, troy, the real value of the total is given also at that rate. Colorado $16,500,000 Arizona 7,500,000 Utah 6,800,000 Nevada 6,750,000 Montana 4,370,000 Idaho 2,000,000 New Mexico 1,800,000 California 845,000 Oregon 35,ooo Dakota 175,000 North Carolina 25,000 Total $46,800,000, or $40,179,440 value at $i.n per ounce troy. Foreign Silver Regions. In amount of silver pro- duced, Mexico is second only to her neighboring republic, the United States. Some of the mines, like those of Gua- najuato and Zacatecas, have been long known, having been opened even before the time of the Spanish conquest, and, though worked fitfully and without system, have yielded enormous quantities of the precious metal. In more recent times many of them have fallen into the hands of English and American capitalists, and with im- proved methods are yielding regularly and largely. These silver deposits, chiefly veins, or, as at Fresnillo, stockworks accompanied by impregnations, follow the line SIL VER. 269 of the Cordilleras from Tasco, south of the city of Mexi- co, as far northward at least as Batopilas in the southwest corner of Chihuahua. The foremost silver-producing States are Guanajuato and Zacatecas, both of which have famous mines, as the Valencian in Guanajuato and those of Zacatecas, Sombrerete, Fresnillo, Pachuco, and Real del Monte in Zacatecas. Besides these States, silver in im- portant amounts is obtained from Queretaro, and from parts of Jalisco, Durango, and Chihuahua. The Mexi- can yield of silver in 1883 is reported to have been more than twenty-nine million five hundred thousand dollars. The deposit of Silver Islet, on the north shore of Lake Su- perior, which has yielded three million dollars' worth of the metal, mostly from native silver in a vein cutting Ar- chaean schists and dikes, is no longer a considerable pro- ducer; and its companion veins, if any exist, have not yet been discovered on the mainland. The silver of South America is derived mainly from Bolivia and Chili, with much smaller amounts from Colom- bia and the Argentine Republic, Peru not being named in a recent list of silver-producing countries published by the Director of the United States Mint, although in 1880 its average annual product was given as 79,365 kilogrammes =$3,298,410, mostly from Cerro de Pasco. These silver deposits, as has already been said, are in the Andes Mountains, and on their Pacific slope. The mines of Po- tosi in Bolivia have been long celebrated, but are now greatly surpassed by those of Huanchaca and Colque- chacq, west and north from it. The most important mines of Chili are in the regions near Copiapo and Iquique, a port belonging until recently to Peru. The large silver product of Germany is derived mostly, it is said, from the vicinity of Freiberg, from the Harz, and from Mansfeld where it is an accessory to the production of copper. The silver mines of the Austrian Empire are in the Tyrol, and on the slopes of the Carpa- 2/0 APPLIED GEOLOGY. thians at Schemnitz, Kremnitz, and Felsobanya in Hun- gary, and in Transylvania. Spain produces a consider- able amount of silver from the mines of Hiendelencia in the province of Guadalajara, northeast of Madrid, as also from the argentiferous lead deposits on the southeast coast in the vicinity of Cartagena and in the northeast part of the province of Almeria. The product of Norway from Kongsberg, of Russia from its Siberian provinces, and of Japan, are none of them so much as four hundred thou- sand dollars per annum. The silver of Japan, according to Prof. Lyman, of the University of Tokio, is derived from argentite, antimonial sulphides, and native silver, which occur mostly in veins, though sometimes in irregular mass deposits in volcanic rocks. The production of Japan was formerly much more considerable than at present. A table of the production of the precious metals throughout the world for the year 1883, prepared by the Director of the United States Mint, has recently been pub- lished, and the table below is a copy of that portion of this which relates to silver : Weight in kilogrammes. Mint value. United States I III 4^7 Mexico. . . 711 "347 2o 568 ^76 Colombia 18 28^ Bolivia 284 021 16 ooo ooo Chili 128 106 Argentine Republic IO IOO ,j^5,uoo Canada AQ one Russia 7 78l Austro- Hungary. . 48 708 J^J4^7 Germany 27O 6oA Norway e f\A >D 9)3 I ^82 ^J4. from Thibet, where it was found in the borders of a saline lake, and the process of refining was long kept secret by the Dutch and Venetians. Sup- plies of tincal were also obtained from Nepaul, in India, and from Ceylon. Later, it was made largely from the boracic acid which issues with steam from the hot springs of the lagoons of Tuscany. To these sources are now added the rainless region of Chili, in the vicinity of Iquique, where boronatrocalcite is found in large quanti- ties, and the borax lakes and marshes of Nevada and Cali- fornia. Large deposits of berates have also recently been discovered near the Sea of Marmora in Asiatic Turkey. The first locality in the United States where borax was discovered was in a small saline lakelet,, very near Clear Lake, in Lake County, Cal., where it occurred in crystals enveloped in the gelatinous mud and underlying clay of the bottom. Hot springs in the vicinity were also found to contain boracic acid. For a number of years, a con- siderable amount of borax was derived from this lake, but it seems now to be superseded by richer or more acces- sible localities. The largest amount of borax produced in this country at present is derived from the borax marshes near Columbus, in the southeast part of Esmeralda County, Nev. It occurs here in extensive salines or marshes, called Teel's Marsh, and Fish Lake, Columbus, and Rhodes Marshes. These are all in oval alkaline flats, occupying closed basins, which are dry during a portion of the year, but in the wet season have shallow pools in their lowest parts. The borax occurs forming incrusta- tions mingled with salt, soda, and earthy substances, from which it is freed by dissolving it with the aid of steam, and then crystallizing it. A considerable amount of the double borate of lime and soda is also found in these marshes in the usual white fibrous balls. In 1882 nearly half the borax produced in the United States was derived APPLIED GEOLOGY. from Teel's Marsh, a considerable quantity being also ob- tained from Fish Lake Marsh. Similar borax deposits occur in Slate Range Marsh, San Bernardino County, Cal., from which a large amount of borax is obtained ; and very promising deposits are reported also to occur in Inyo County, about one hundred miles northward from the last. The output of borax in the United States for 1884 was 3,500 tons of 2,000 pounds. The result of the late discoveries of borax has been to reduce the wholesale price to about thirteen cents per pound, which is not more than two fifths of the price that formerly prevailed. The largest uses of borax are based upon its property of dissolving the oxides of many of the metals at a high temperature, and forming with them a kind of glass, which, in a number of cases, has characteristic colors. Hence it is used as a flux in refining metals ; by iron and steel workers in welding, to preserve the surfaces of the metal clean from oxide during the operation ; by braziers and jewelers in soldering ; by enamelers ; and by chem- ists, as a most valuable reagent in blow-pipe operations. It is an essential ingredient in all artificial gems ; is a component of some varnishes and fine toilet soaps ; and is said to enter into some kinds of glass. Considerable amounts are also used as a detergent for household pur- poses, by packers in preserving meats, and in some me- dicinal applications. The student will gain some additional information about borax from " Mineral Resources of the United States " for 1867, p. 178, which contains an account of the first discovery of borax in the Unit- ed States, by the discoverer ; " Mineral Resources of the United States," 1883 ; Ure's " Dictionary of Arts," etc. ; and Watt's " Dic- tionary of Chemistry." Alum. This well-known substance is a hydrous dou- ble sulphate of potash, soda, or ammonia, with alumina, the base of clay. It is sparingly found native as an efflo- rescence on rocks, where it originates from the weathering SUBSTANCES FOR CHEMICAL PURPOSES. 315 of pyritous clays containing potash, but is more commonly manufactured from pyritous shales, called alum-shales, or from alunife, an insoluble sulphate of potash and alumina, called commonly alum-stone. The latter occurs in rocks of volcanic regions, where it probably originates from the action of sulphurous vapors on feldspars containing pot- ash. It is a somewhat rare substance, but is found in quantities of commercial importance at Tolfa near Rome, and at two or three localities in Hungary, where it forms considerable beds. The mineral is carefully calcined to avoid fusion and loss of sulphur, then kept moist in heaps, and left to the action of the weather, by which it is disintegrated, with the development of soluble alum. This is leached out and crystallized, forming opaque cubes ; and, under the name of Roman alum, derived from the chief locality whence it is obtained, it is pre- ferred to other alums for some uses. By far the most abundant material for the manufacture of alum is afforded by the alum-shales. Those best adapted to the purpose of alum-making are pyritous clay rocks, in which coaly mat- ter is disseminated, thus affording readier access to the air, by which the decomposition of the pyrites is effected. The decomposition of the pyrites, accelerated usually by the long-continued application of a low degree of heat in extensive piles, converts the alumina of the clay into sul- phate of alumina, which is leached out, concentrated, and converted into alum by the addition of a proper amount of sulphate or chloride of potash or ammonia. The sul- phate of alumina for this purpose is also largely made by treating with sulphuric acid calcined clays which are as free as possible from lime and iron oxide. For this use, the excellent clays which abound in the Cretaceous beds of New Jersey are admirably adapted ; and there can be no doubt that pyritous shales, adapted to alum-making, can be found in many portions of our own country, es- pecially in the coal and lignite regions, from which they 3 i6 APPLIED GEOLOGY. are mostly extracted in Europe, though it has recently been stated that most of the clays used in the United States for alum-making are imported. It has also been proposed to manufacture alum from the greensand which abounds in the Cretaceous of New Jersey, by treating the gently ignited greensand with sulphuric acid, the green- sand furnishing the requisite potash and alumina. On account of the strong affinity of its aluminous base for organic coloring-matters, alum is largely used as a mordant in dyeing, and by manufacturers of what are called lakes, which are compounds of organic coloring principles with alumina, of which madder lake, and the brilliant cochineal lake called carmine, are familiar ex- amples. It is also used in clarifying liquors, in some pro- cesses of tanning skins, in medicine as an astringent, in pastes for paper, and in small amounts by bakers for whitening and raising bread. Besides the substances applicable to chemical manu- facture or use that have already been described, some mention should also be made in this connection of mag- nesia, strontia, and titanium. Magnesia will require some mention in the chapter on refractory materials ; but, be- sides the use based on its resistance to heat, are others of a chemical nature. The sulphate, which is much used in medicine under the name of Epsom salt, is found native at Stassfurt as the mineral kieserite, and is also ob- tained from the residues after extraction of potash from some other Stassfurt salts. It is said to be used as a cheap substitute for sulphuric acid in the preparation of blanc fixe, a white pigment obtained by the precipitation of chloride of barium, and also in the manufacture of pearl-white, to be used in paper-making. Epsom salt and magnesia alba can also be manufactured from magnesite, a carbonate of magnesia, much resembling calcite and dolo- mite in color and cleavage, but containing no lime, be- sides being somewhat harder and more sluggish in its SUBSTANCES FOR CHEMICAL PURPOSES. 317 effervescence with acids. It occurs in considerable beds in the Lower Silurian rocks of Bolton and Sutton in Que- bec, near the boundary-line of Vermont, where it is as- sociated with beds of dolomite, steatite, and serpentine, and in one locality with argillite ; and it will doubtless be discovered in similar associations elsewhere, whenever an active demand for it shall arise. Strontia, the almost sole use of which has been here- tofore in pyrotechny in the form of the nitrate for making red fire, is recently coming into a greatly increased de- mand, since it has been found that it can be utilized in recovering sugar from the " melasse" which has hitherto occasioned great loss in making beet-sugar. The two minerals in which it occurs in economically important amounts are strontianite, the carbonate, and a sulphate called celestite (Latin ccdum), from its frequent sky-blue tint. They are both heavy minerals, their specific gravity being from 3.6 to 4 ; both are quite brittle, and both give a bright-red colored flame when heated before the blow- pipe. Like other carbonates, strontianite effervesces with acids, and by this it may readily be distinguished from celestite. These two minerals are sparingly distributed, being found in nests and crevices, most commonly in lime- stones, in the United States and Canada, but sometimes also in sandstone and clay, or associated with gypsum. They have been foun4 in the Lower Silurian limestones of Manitoulin Islands, somewhat abundantly at Kingston, and on the Ottawa River in Canada, as also in Jefferson County, N. Y. ; and in Upper Silurian limestone near Scho- harie and Lockport, N. Y., in Blair and Mifflin Counties, Pa., and on Strontian and Put-in Bay Islands, Ohio, where celestite is more than usually abundant. Strontianite is obtained from Argyleshire in Scotland, where it was first discovered, and somewhat abundantly in Westphalia, where it occurs in veins or shrinkage cracks in Cretaceous clays; while Sicily is much the most considerable producer of 3 i8 APPLIED GEOLOGY. celestite, exporting, it is said, about four thousand tons annually. For its new use, in the manufacture of beet- sugar, caustic strontia is obtained from strontianite by heating it to redness to expel the carbonic acid. This, when boiled with " melasse," forms a compound with the sugar from which the strontia is separated by carbonic acid, leaving the sugar to be dissolved and crystallized. On account of its infusibility, caustic strontia is also utilized in making tuyeres for blast-furnaces. The nitrate of strontia, for use in pyrotechny, is obtained by treating strontianite with nitric acid, or by heating celestite, mixed with charcoal, to a high temperature, and then treating with nitric acid the sulphide of strontia thus formed. The compounds of titanium, which are now consider- ably used in the manufacture of artificial teeth and in porcelain-painting, are probably destined to a greatly in- creased use in the manufacture by various chemical means of a number of brilliant and permanent pigments. It is found abundantly, in the form of ilmenite, or titanic iron, in the Archaean rocks of Canada and Norway, where it bears a great resemblance to magnetite, being, however, very little magnetic It occurs also in crystalline rocks as titanic acid, forming the minerals rutile and brookite. CHAPTER XIX. FICTILE MATERIALS. THE arts of the potter and the glass-maker afford a striking exemplification of what human skill can accom- plish by a dexterous use of the properties of substances which in their original condition are among the most com- mon and least valued objects. What could be more dis- similar to the magnificent creations of porcelain and of glass which, in varied forms, deck the tables and adorn the mansions of the rich, and which are objects of eager desire to princes, or even to the humbler wares which spread the board and minister to the modest wants of the poor laborer, than heaps of clay and sand, of lime and feldspar, with bins of soda, potash, salt, and borax, and a few metallic oxides ? Yet the former are but the latter, mingled by knowledge bought by generations of experi- ence, fashioned by skill and taste, and subjected to a treat- ment adapted to develop to the utmost their latent capa- bilities. The art of shaping rude vessels from clay and hardening them by fire is one which has been practiced in the infancy of civilization ; but the highest and most refined developments of this art tax to the utmost the sci- entific resources and the cultivated taste of the most en- lightened nations. A number of the substances used as materials for the manufacture of porcelain, earthenwares, and glass, have already been described, as regards their geological occur- 3 20 APPLIED GEOLOGY. rence, in the preceding pages. Such are potash, soda, and lime, used as fluxes in glass-making and in glazes for pot- tery ; such is oxide of lead, used as a flux for flint-glass and in many glazes ; such are the oxides and a few other compounds of the metals employed in glass- staining and porcelain-painting ; such is salt, used as a glaze for stone- ware, and borax, used also in some glazes, and as a partial substitute for silica in some fine sorts of glass and artifi- cial gems. Of the remaining substances, including clay, silica, feldspar, granulite, steatite, and baryta, all of which are used more or less largely in one or both of these arts, clay is of the greatest interest, since it forms the basis of all pottery- wares, and has also some other highly important applications. This substance is a highly variable mixture of kaolin, the mineral on which its valuable properties depend, with silica, iron, lime, magnesia, the alkalies pot- ash and soda, and often a small amount of mica and par- tially decomposed feldspar. In blue and black clays, or- ganic matter is also present, and disappears on burning, leaving the clay white. Kaolin is a usually white and unctuous 'hydrous silicate of alumina, which contains in round numbers 46 per cent of silica, 40 per cent of alu- mina, and 14 per cent of water. From this it will be seen that two and a half times the alumina given in the analysis of a clay will show the amount of kaolin that enters into its composition. In some of the best clays this mineral is much the largest ingredient, but small proportions of other substances being mingled with it ; while in others it may constitute considerably less than half of the aggregate, to which, nevertheless, it gives its essential characters. Kao- lin, then, is the essential ingredient of every true clay, and by itself constitutes a clay of the finest quality ; all other ingredients are non-essential accessories, and in some cases injurious ones, rendering the clay unfit for its highest uses. The most invariable accompaniment of kaolin in clay is free silica, occurring in the form of sand intimately min- FICTILE MATERIALS. 321 gled with the mass, and varying in amount from a mere fraction of one per cent to more than fifty per cent of the whole. This silica, though sometimes in grains of moder- ate size, frequently exists in the state of an almost im- palpable powder or dust, yet showing itself under the microscope as minute angular particles of white, transpar- ent quartz. The quartz in clay to be used for pottery can hardly be considered as anything but a diluent of the clay. Indeed, for the purposes of the potter, rich or fat clays need to be mingled with finely comminuted silica, in preparation for their use. By itself in a clay, it is inert, acting, however, physically to counteract the tendency to shrinkage and the production of checks and cracks which kaolin alone exhibits when subjected to great heat. When, however, verifiable bases, like potash, soda, and lime, are present in the clay, the readiness of finely divided silica to form with them fusible compounds at a high tempera- ture causes that slight incipient fusion which gives rise to the hardness and strength of the productions of the pot- ter. Some one or all of the three bases that have just been named, but potash much the most generally, are found in nearly all clays, but usually in small quantities in the best. It seems quite probable that these alkaline substances which analysis reveals, and which produce their effect on the fusibility of the clayey mass, are due, in some cases at least, to partially decomposed feldspar, and sometimes to mica present in the clay. Both of these minerals contain potash, and feldspar usually contains some soda and lime also. Feldspar in clays occurs in small, sandy particles. Mica, from the ready flotation of its minute laminae, is little likely to be found in clays which are somewhat remote from their place of origin, and which have possibly been worked over more than once by transporting agencies before resting in their present beds. The most undesirable contamination of clays for potter's use is iron, which in some of its forms, as oxide, carbon- 322 APPLIED GEOLOGY. ate, or sulphide, seems never to be wholly absent from any clay. Sometimes its proportions sink to not more than a fifth of one per cent ; more frequently, however, it is pres- ent to the extent of two or three per cent or even more, unfitting the clay for any save the coarsest and most com- mon wares, since it imparts to them yellow, red, or brown colors, according to its amount and the degree of heat to which the articles are subjected. The following table of analyses of a few approved pottery clays will give a fair idea of their composition, and of the extent to which the various ingredients other than kaolin may be present without proving seriously detrimental. The titanic acid, which will be observed to be present in several of the clays, especially those from New Jersey, seems to be wholly inert, producing no appreciable effect on their properties. Following the excellent arrangement of analy- ses given in the New Jersey Report on Clay Deposits, and in the Ohio Report on Economic Geology, the kaolin- forming compounds, the inert substances, and the com- pounds which promote fusibility, with their respective amounts, are placed in separate groups. It may here be said that, for their finest uses, clays are washed by mixing them thoroughly with water, and then allowing the creamy liquid in which the clay will remain long suspended to flow off into settling-vats where the clay is deposited. By this means the coarser and heavier impurities are easily separated. The properties of clays which are of chief interest to the potter are plasticity, and a tendency to shrink at a high temperature. Most clays which are used by potters when properly moistened are tenacious and pasty, and are sus- ceptible of being easily shaped into any desirable form in molds or on the potter's wheel. The forms thus made harden considerably on drying, and when heated to a high temperature assume the stony consistency which is famil- iar to every one in earthenware and porcelain. This FICTILE MATERIALS. 323 sjuanjt^s CO t R in o CO CM 5 n CO CO m u . I>1 M o M CO O M in l-l CO M apixo uoaj m H H d CO CO M in d ^0 M d w d" H I BisauSe M M CM CO M o M CO vO M * ' O d O in CO O ** d CO *0 *P<>S d 6 1^ in CM M ~T CM *o w M \JCV-\Q r M CM l^ CO ^ rr QN ^~ vO d d O M o CM d d sjuan CO o c> CO i- N 8 in O -5IJSU03 JJ3UJ d M H CO CO d rj M co- co ptDB OIUBJI X CO o 8 O M M M M M M O CO o O in rS.a d pUBC CO N m Q\ CO O CO Q\ o o n ^ o co cS !^ 3 '35 CO M M CO JjL sjuanjijs g- in CO J? % J^ -UOO UIJOB^ CO o J-^ 00 ^j. O^ ri O O^ in o *> m CO O* M m vn R ^ CO in o * 3 ^M. co -f Tf CM (A. tC. 6 M M m CO vO f,. in Tf CM w CO M M CO CO M ' CO CO $ in CO M CO ct s CO BOIJIS rj- O CO H o M R CO o ^ M p 3 uiquio D 5 5 V - | * * 3- CO in | 1 > 4 - o d I * ^ a * C/2 W) 1 d X 6 hH 6 4) bJO G H s g Ware clay, Woodbrid Select paper clay, S. , White clay, Middlese Stoneware clay, China clay, Lawrence U & o PH jf "u t/5 -Si "o I I China clay, Cornwall, cJ 3 .2 M "3 O 73 N CM CO 4 >n + CO c> 2 324 APPLIED GEOLOGY. valuable property of plasticity belongs solely to the kaolin of the clay ; and plastic clays, rich in alumina, admit the addition of a considerable amount of fine sand without any material diminution of their plasticity. The plas- ticity of clays is doubtless dependent in part on the water held in chemical combination by the kaolin, since, when this water is driven off by a red heat, plasticity is perma- nently lost, and can not be restored by any treatment of the stony product with water. That it is by no means due wholly to the combined water, however, is shown by the fact that some highly valued porcelain clays or kaolins are but slightly plastic. An example of this is presented by the clay of which the beautiful Sevres porcelain is made, which, when prepared for use, is so little tenacious as to require a quite special and expensive mode of hand- ling in shaping the articles which are fashioned from it, a fact to which the high price of this porcelain is in a great measure due. Prof. George H. Cook, in his report on the clay deposits of New Jersey, has shown that very probably the plasticity of kaolin is largely due to a minute sub- division of the crystalline plates and bundles of which the mineral is originally composed, since recognizable crystals of kaolin are found, by microscopic examination, to abound in clays which are deficient in this property, while they are absent, or nearly so, from highly plastic clays. The shrinkage of clays, when subjected to great heat, is a character quite as remarkable as their plasticity. This arises partly, no doubt, from the expulsion of water ; but that this is not the only cause, is shown by the fact that the clay continues to contract with an increase of temperature, even after the water has been entirely ex- pelled. On this fact was based the pyrometer of Wedg- wood, which attempted to measure very elevated tempera- tures by the degree of contraction which they produced in rods of clay ; an attempt which was not entirely suc- cessful, on account of irregularities in the contraction FICTILE MATERIALS. 325 of clays when exposed to long-continued heat. Highly aluminous or fat clays shrink the most by heat, while very sandy or lean clays shrink less or not at all. Hence, to counteract the excessive shrinkage of fat clays, which is apt to cause irregularities and cracks in the wares when burned, they are tempered by mixing them intimately, be- fore molding, with a proper amount of finely divided silica, or with thoroughly burned and pulverized clay. Clays originate doubtless from the decomposition of feldspathic rocks, such as granites, gneisses, and porphy- ries. The feldspars, from whose decomposition kaolin is derived, are orthoclase, albite, and oligoclase, albite being the most readily attacked by the agencies of decay, but orthoclase, from its greater abundance, being the most important source. These minerals, which are silicates of alumina, with potash, soda, and lime, when exposed to the action of carbonic acid and water, slowly lose their alka- line constituents and some of their silica, take in water, and so are ultimately converted to kaolin. When kaolin is found on the place of its origin, it is naturally associ- ated with the quartz and mica, which are the remaining constituents of granite and gneiss ; or, with quartz alone, when it is derived from the variety of granite called aplite or graphic granite, which contains little or no mica. Such clays are usually deficient in plasticity, probably from the undisturbed crystalline condition of their kaolin. Of this kind are apparently the porcelain clays of China, from which the names kaolin and china clay have been de- rived ; that of Saint Yrieix-la-Perche, not far from Li- moges, which is the basis of the French manufacture of porcelain ; that of Saxony, from which Dresden porcelain is made ; and the china clay cf the granite district of Cornwall. The Chinese kaolin and that of Cornwall, ac- cording to Ure, have more plasticity than that of France and Germany. On account of the slowness with which kaolin subsides in water, with which it readily forms a 15 326 APPLIED GEOLOGY. milky mixture, and of the consequent ease with which it may be transported to long distances from the place of its origin, much the largest portion which is formed is washed away from its parent rock, and deposited in low grounds or in bodies of water, forming often considerable beds, like those found so abundantly in parts of New Jersey, and those which constitute the under-clays of many coal- beds. These translocated clays, as a result of their trans- portation by moving water, have usually been freed from most of their mica, and from their free silica, save that which existed in a state of fine subdivision. They are also commonly highly plastic, although those which have been much solidified by pressure need to be softened by weathering before they exhibit this character. These clays are occasionally of such purity as to be adapted to the finest uses in the manufacture of porcelain ; such, however, are found in but few localities. Clays, adapted to the manufacture of the more common articles of white and ornamented stoneware, are more abundantly dis- tributed, while others, which are too much contaminated with iron for this purpose, are used for making jars, jugs, and many other articles of a coarser kind. Pottery clays are known to occur at many points in the Archaean districts along the Appalachian range, from New England to Georgia, and they are dug to a limited extent in several localities. These are all surface deposits of geologically recent origin, and some of them may be found suitable for porcelain-making. Clay deposits, suit- able for common wares, are reported at a number of points in the far West, and are said to be utilized to some extent ; but none of the very best quality, apparently, have yet been found, unless the clay of Golden, Col., given in analysis No. 10, on a preceding page, should prove to be one. The clay deposits most largely wrought in this country hitherto are of Cretaceous and Carbonifer- ous age. The Cretaceous clays of New Jersey, chiefly in FICTILE MATERIALS. 327 Middlesex County, are abundant, and of qualities fitting them for various uses. The excellent pottery clays are not only largely sent to other States, but are the basis of a very important manufacture of wares of various kinds at Trenton, Jersey City, and Elizabeth, New Jersey produc- ing nearly three fifths of the pottery wares that are made in the United States. It can hardly be doubted that some of the New Jersey clays may be used for the manu- facture of the best porcelain. Some of the under-clays of the lower coal-measures, in several of the coal-producing States, are suited to the manufacture of pottery. They have been most largely utilized for this purpose at Liver- pool, O., on the Ohio River, and at two or three other localities in the same State, where they are mixed with clays from other regions, Ohio ranking next to New Jersey in the amount of wares produced. At Huron, Ind., and at other points in Lawrence County and also in Owen County, noted deposits of kaolin called indianaite occur, an analysis of which, showing an unusual propor- tion of water, has been given on a preceding page. This clay is used at Indianapolis for making encaustic tiles of the highest grade of excellence, and at various points in the United States in the manufacture of fine qualities of white ware ; and it seems to be suitable for the very high- est uses of the potter. No attempt has here been made to enumerate the many promising localities of pottery clays which are known to exist in the United States, but which have not as yet been much developed. It is certain, however, that clays adapted to the more common uses are widely distributed, while it is probable that here, as in all other countries, kaolins suitable for the manu- facture of fine porcelain will be found to be rare. Any mention of fire-clays has been purposely deferred to a succeeding chapter ; and those coarser clays, which are so widely used for brick-making and similar purposes, have already been described in treating of building materials. 328 APPLIED GEOLOGY. The materials on which is based the vast English manufacture of pottery and porcelain in Staffordshire are derived from the southwest counties of Cornwall, Devon, and Dorset, in which are found extensive deposits of ex- cellent clays and kaolin. Although clay is the basis of pottery, several other minerals are mingled with it to form the pastes that are employed for the various kinds of ware. Of these, silica has the most universal use, being mingled with the clays in proper proportions to correct their tendency to too great and irregular shrinkage in burning. This may be obtained in the state of clean silicious sand, or of flint, found disseminated in chalk and other limestone rocks ; or of massive quartz, from veins of this mineral occurring in regions of granitic rocks and silicious schists, such as the Archaean areas described in treating of building- stones. From whatever source derived, the silica is ground to a very fine powder before it is used, and the massive forms are frequently calcined before grinding, to render them more brittle. This finely divided silex is not only mingled intimately with the clay which forms the body of the ware, but also enters into most of those vitri- fiable mixtures which are used as glazes. Both silex and pure clay or kaolin, however, are wholly infusible at the temperature attained in porcelain-kilns. Hence, to im- part to the clay mixture a tendency to that incipient vitri- faction which increases the strength of the more common wares, and gives to fine porcelain the translucency which is so much admired, minerals like feldspar, lime, and crys- tallized gypsum, are added, which at high temperatures form with silica fusible compounds. The Chinese use for their porcelain a mixture of kaolin with a silicious feld- spar called petuntse, which mixture requires an exceed- ingly high temperature for its vitrifaction. The standard mixture for Sevres porcelain is, according to Ure, 59 per cent of silica, 35.2 per cent of alumina, 2.2 per cent of FICTILE MATERIALS. 329 potash, and 3.3 per cent of lime, which may be formed by mingling kaolin with proper proportions of feldspar, flint, and chalk. The English " tender porcelain" is composed of clay and flint, with bone-dust, and sometimes potash, as a vitrifying agent ; and in Wedgwood-ware, baryta is used as a flux for the clay. The feldspar which is used in these mixtures, to add the needful alkalies, is to be sought, as might be expected, in regions of coarsely crys- talline granitic rocks. That which is used in this country seems to be obtained mostly from near Middletown and Portland, Conn., and from middle Virginia; but numer- ous other localities are known in the New England and Atlantic seaboard States, where it can be found abun- dantly. The glazes which give to wares their impermeability, and their smooth and often brilliant finish, are various mixtures of flint, feldspar, ground glass, lead oxide, borax, potash, soda, and lime. From among these substances, various manufacturers compound for their wares glazes which experience teaches them to be most suitable for their purposes, the glazes being artificial glasses, some- times transparent, sometimes opaque, which coat the wares to heighten their beauty, or sometimes to conceal their defects. Some porcelain has a glaze of feldspar only. Many coarser articles of pottery are glazed by merely throwing salt into the kiln among them at the proper stage of the baking ; the salt is decomposed by the heat, and its soda forms a fusible glaze with the silica and alumina of the surface of the wares. The colors which are used for the ornamentation of pottery are mostly oxides of the metals, with a few chlo- rides and chromates. These are mingled or fused with proper fluxes, ground fine, and applied to the wares before their final burning in a medium of gum-water, or of some volatile oil. The colors are in some cases fused into the glaze of the wares, and in others they are laid on under the 330 APPLIED GEOLOGY. glaze and show through its transparent substance. The oxides, which are chiefly used for painting porcelain and other wares, are those of cobalt, iron, copper, antimony, uranium, nickel, manganese, chromium, tin, and titanium, with chlorides of gold, silver, and platinum, and a few chro- mates. By a proper treatment of these substances and their fluxes, the skillful porcelain-painter attains as com- plete a mastery over the effects that he desires to produce with these coloring materials that must pass through the fire before showing their real nature, as the artist who paints on canvas with ordinary pigments. Glass. It may be stated in a general way that this beautiful, transparent, and impervious substance, which plays so large a part in the comforts, conveniences, and elegancies of civilized life, is a double silicate of potash or soda and lime or lead. Its foremost materials are there- fore silica, the alkaline substances, and lead oxide. In some of the finer kinds of glass, boracic acid takes the place of a portion of the silica. To correct the effects of impurities in these materials, a little niter is commonly used, as also small amounts of arsenic, and of black oxide of manganese, which, from its purifying effects, is often called glass soap. The geological occurrence of most of these substances has already been described elsewhere. The silica, which constitutes the largest ingredient in all varieties of glass, was formerly prepared for the finer kinds by calcining and grinding flint, from which is derived the name of flint or crystal glass, applied to the very dense, lustrous, and highly refracting double silicate of potash and lead. It has, however, been found that, in somewhat nu- merous localities, sand may be obtained of sufficient pu- rity to be used for all the purposes of glass-making. For all except the coarser varieties of glass a tolerably fine, angular, white sand is needed, free from earthy impurities, and especially from iron, which gives to glass a green tint. In some localities, sea-sands are found of sufficient purity FICTILE MATERIALS. 331 for any purpose. Thus the English manufacturers obtain much of their sand from the Isle of Wight, and from points on the coast of Norfolk and of Holland. In south- ern New Jersey a large number of glass-houses obtain an inexhaustible supply from a bed of Tertiary sand more than ninety feet thick, and of very considerable extent, much of which is so pure as to require no washing before being made into window-glass. The glass-works in cen- tral New York obtain a good sand for window-glass from the modified drift around Oneida Lake.- In four counties of central and southern Indiana great deposits of pure white sand and slightly indurated sandstone occur, from which an approved quality of plate-glass is manufactured. Besides such deposits of incoherent sands of Tertiary age and of recent origin, which are pure enough for glass- making, white silicious sandstones are occasionally met with in much more ancient rocks, which are so friable as to be readily reduced to sand, and are then used for the manufacture of glass. Notable among these is the St. Peter's sandstone of the Lower Silurian, which occupies considerable areas in Missouri, Minnesota, and Wisconsin, and in La Salle County, 111. At many of its exposures, it occurs as a clean white sandstone, remarkably free from impurities, and so friable as to be readily extracted from its beds by pick and shovel. A considerable manufacture of glass is already based upon this sand, and its use seems destined to be greatly increased. The Potsdam sand- stone, which occupies the lowest horizon of the Lower Silurian, also occurs of sufficient purity to afford a good material for glass, in portions of northern New York, Canada, and Wisconsin. A few only of the more note- worthy exposures of sands which have been proved by use to be sufficiently pure for the manufacture of the bet- ter grades of glass have here been mentioned. Many others will doubtless be eventually brought into use with- in our broad domains ; but it will easily be conceived 332 APPLIED GEOLOGY. that, though sand is a very widely and abundantly dis- tributed substance, yet that which is of the high degree of purity needed for the manufacture of fine white glass is by no means common. For the making of bottle-glass, in which purity of color is not required, inferior sands are largely utilized. For this last purpose a rock called granulite has recently come into quite extensive use in Saxony and in southern England. Granulite, though sometimes granular, is usually a schistose rock composed of alternating layers of quartz and feldspar, with little or no mica, and is usually of a white color, so that it is called by the Germans weiss-stein, or white stone. The Saxon granulite contains from 70 to 80 per cent of silica, with a considerable per cent of potash in its feldspar, and less than one per cent of iron; and, when melted with the addition of sufficient lime to secure perfect fusion, makes a pale- green bottle-glass, at about two fifths of the usual cost for this article. Rock of this character, or that which will serve the same purpose, viz., granite free from mica and containing but a minimum amount of iron, may doubt- less be found in the Archaean areas of Canada and New England, as well as elsewhere, and where met with it will afford excellent opportunities for the profitable invest- ment of capital. The Saxon production from this source is said to have reached twenty-two million bottles in 1880, and to have increased rapidly since that time. It has recently been proposed to use this glass for gas and water pipes and other large castings, and, should this idea be carried out successfully, deposits of granulite and graphic granite, favorably located with respect to transportation, will naturally assume great economic importance. The substances which are used for coloring glass, like those employed in porcelain-painting, are metallic oxides and a few other compounds of the metals, all of which, it need hardly be said, are obtained from geological sources. Thus the white opaque glass called enamel derives its FICTILE MATERIALS. 333 color and opacity from the oxide of tin ; a blue color is given by the oxide of cobalt, green by oxide of copper, yellow by chromate of lead and by silver chloride, and other colors by similar means. Without at all entering into the technicalities of glass-making, it may appropri- ately be said here, in illustration of the geological origin of its materials, that the chief varieties of glass are com- pounded of the following ingredients : Common bottle-glass, of silica, alumina, soda, and lime ; Bohemian glass, of silica, potash, and lime ; crown- glass, of silica, potash or soda, and lime ; window-glass and mirror-plate, of silica, soda, and lime ; crystal and flint glass, of silica, potash, and lead oxide ; strass for arti- ficial gems, of silica and boracic acid, potash, and lead oxide. The differences of quality are due to the relative purity of the ingredients, the proportions in which they are compounded, and the skill and care with which they are treated. For additional information with regard to materials for the manu- facture of pottery and glass, the student is referred to the following works : Ure's " Dictionary of Arts," etc., articles on clays, glass, and pottery ; " Geology of New Jersey," 1868 ; the " New Jersey Report on Clay Deposits," 1878 ; and " Ohio Geological Report," Vol. V, chap. ix. CHAPTER XX. . REFRACTORY SUBSTANCES. FOR numerous and highly important purposes among civilized nations, materials are required which will endure very high degrees of heat without injury; and every im- provement whereby more elevated temperatures are se- cured by the skillful use of fuel, renders the need of such refractory substances more imperative. It is necessary only to direct attention to the furnaces used for various metallurgical operations, and especially those in which iron and steel are to be treated ; the kilns in which pottery is baked and the materials of glass are fused ; the seggars, or fire-proof boxes, in which earthenware and porcelain are exposed to the heat of the kiln ; the large pots or crucibles in which the ingredients of glass, and metals like copper, silver, and steel, are melted ; and the linings of Bessemer converters, in which molten iron is to be subjected to ebullition by the action of a current of air to burn out its impurities to indicate the variety and im- portance of the uses for which refractory substances are required, and the fierce heats which they are called upon to endure without softening. All these substances are minerals which enter into the composition of rocks, and are therefore derived from geological sources. Foremost in importance among these is fire-clay, both from its great infusibility, and from the readiness with which it may be fashioned into convenient forms. This REFRACTORY SUBSTANCES. 335 clay does not differ from the pottery clays described in the preceding chapter in any respect save in its greater necessary freedom from the fluxing ingredients, potash, soda, lime, magnesia, and iron oxide. The presence of any considerable proportion of these fluxes in a clay, to the extent, for example, of two or three per cent, in- juriously affects its heat-resisting properties ; and the combination of two or more of them proves more detri- mental than a like amount of any one, because the com- pound silicates are more fusible than the simple ones. The more completely a clay is composed of kaolin, or of kaolin and silicious sand, the more refractory it is likely to show itself, since both these substances are wholly in- fusible at the temperatures attained in industrial opera- tions. This may be seen by examining the following analyses of several of the most celebrated fire-clays of this country and of Europe. They are arranged in the order of their resistance to an extreme fire-test, made by exposing small triangular prisms of each with sharp edges, for a half-hour, to a heat in which platinum was melted. Exposed to this heat, some of the clays retained their sharp edges ; others, while retaining the sharpness of their edges, were more or less blistered or distorted ; in others, the edges were rounded and fused, and a number melted. This series of tests was undertaken by the Geological Sur- vey of New Jersey, and its results and methods are pub- lished in the annual report of that State for 1880. On this was founded a tentative division of the clays into seven classes, according to their relative refractoriness ; and to this classification the numbers in the first column refer. The analyses of the same clays have been selected from those given in the New Jersey report on clay de- posits, to which reference has been made before. Neither soda nor lime appears in any of these analyses. As all these clays are well esteemed for their resistance to heat, it may be assumed that the amount of the flux- 336 APPLIED GEOLOGY. sjuanjps -uoo Suixni j M M q M M CO m CO in CO M ? ? in CO o M ci M ^ CO vn in Q M (^ CO j^ spixo UDJJ O O 6 CO a q oi M d vO M M S H M M CO CO BIS3UST5H 6 d d d USBJOJ f 8 d M in S" in CO d o d o in d o H CO d sjuamps CO s 3 o M O M in M in CO in m 3 CO -uoo }jaui 04 vO VO M CO CS M CO CO rj- in CO O in in in in O 8 8, o M M M M M H o M putJS M H R in I in s m" M d q M in CO R q CO M CO CO * in sjuanjns CO a CO ^ CO in CO r? CO CO CO in m CO -uoo uno'B"\r S & O ^ in CO CO i vO M vO % 2> in O o s> 8 to co aa^M. rf w CO d O CO ti CO vd CO CO o o o Q Tt CO N CO O Q CO Q M in CO o in Q vO t?uiuin IV ^ in CO o CO M CO CO in CO CO CO * M a m M BOIJIS s c> o R in CO in O O m m in CO p 3 uiquiO D $ 3- 5 CO CO M 3 ^ gi 9, 0? CO M w-D M M 0, CO * * m a * * i i c | | 1 ' ^ 1 1 S 1/5 xJ c rt "So c J> C g s? T5 1* * ^ I M rt o .s I (A 5* u 1 o 1 I J5' 1 M i ta J2 i O s PH c 2 M REFRACTORY SUBSTANCES. 337 ing ingredients in a fire-clay can not safely exceed what is found in these, especially as one of the clays which occu- pies the lowest class contains the most of the fluxes. When it is considered, also, that in these tests pure rock- crystal was melted, a reason will be found why the four clays that contained the most free silica rank lowest in this list. It would be difficult to assign reasons for some other differences in refractoriness shown by the clays in the table, as, for example, why clay No. 7 should not have been as refractory as Nos. 2 and 3, unless it is to be found in the texture and density of the clays. Aside from the very superior fire-clays obtained from the Cretaceous clay deposits of New Jersey, the great bulk of the refractory clays of Europe and the United States are derived from the under-clays of coal-beds not only those of the coal-measures proper, but also, as in several of our Western Territories, those bearing similar relations to the lignitic coals of the Upper Cretaceous. These under-clays doubtless owe their freedom from alka- line constituents to the fact that, having once been soils which sustained a luxuriant vegetation, these substances have largely been withdrawn from them by the processes of plant-growth. When first dug, they are hard and stony, but can be softened and rendered somewhat plastic by sufficient weathering. Frequently, however, they are merely ground fine with water, mixed with a proper amount of previously burned and pulverized fire-clay called calcine, and sufficient sandy, plastic clay to serve as a bond, and then molded and burned for fire-brick, glass-pots, retorts for gas and zinc works, terra-cotta wares, chimney-tops, and many other articles which are either to be exposed to high temperatures, or which need to be fired strongly to secure the characters desired. Dinas or silicious bricks, which are employed where an excessive temperature is attained, as in the melting-cham- ber of regenerative furnaces, in which ordinary fire-brick 338 APPLIED GEOLOGY. does not endure well, were originally made from a sili- cious rock locally called clay, though containing about 97 per cent of silica, occurring in the Carboniferous strata of South Wales. This rock was disaggregated and mixed with a small portion of lime to serve as a cement, then molded and burned at a high heat for several days. At the high temperature employed, the lime combines with an equivalent amount of silica to form a refractory silicate which binds the whole together. Similar bricks are now made from any pure silicious rock, which is ground and mixed with about one per cent of milk of lime to form a bond for the mass when burned. The silicious rock em- ployed for this purpose should be free from iron and mica. Silicious bricks expand somewhat when heated, and so keep the parts of the furnace tight. The substance called ganister, used as a refractory lin- ing for Bessemer converters, is a very fine-grained and tough sandstone, or quartzite, containing a certain amount of finely disseminated aluminous matter. When this is ground fine and mixed with water, the contained alumina acts as a sufficient bond. Rock for this purpose is ob- tained in England from a silicious under-clay of the coal- measures at several points, the best being found in the vicinity of Sheffield. A rock of a similar character is found in the Archaean strata in the immediate vicinity of Marquette, Mich., where a thin-bedded and ripple-marked quartzite is quarried to a considerable extent for this use. Any pure silicious rock, ground to a fine powder and mixed with a proper amount of good fire-clay, is said to answer well in place of ganister. What are called fire-stones are usually silicious sand- stones, which should be free especially from iron, and from mica the potash in which renders it a fluxing in- gredient. Fire-stones may be found by careful exam- ination and trial in many localities, where their cheap- ness makes them a reasonably good material for many REFRACTORY SUBSTANCES. 339 purposes, as for the hearths of furnaces and fireplaces, and for the construction of kilns, though their use is now largely superseded by that of fire-brick. Where used, it is hardly necessary to say that they should be thoroughly dried before being subjected to heat. For a number of purposes bricks are very desirable which shall combine with the ability to endure unchanged all ordinary degrees of temperature, very feeble conduc- tivity for heat, and much less specific weight than common fire-brick. Such materials, called floating bricks, because they are lighter than water, are made from an infusorial earth called "fossil meal," composed of the microscopic skeletons of silicious organisms, and forming a whitish earthy mass, very light, and resembling chalk in appear- ance, but yielding no effervescence with acids. This sub- stance, mingled with a small amount of clay, may be made into bricks which weigh less than one fifth as much as or- dinary bricks, which resist heat well, and which when red- hot at one end are not perceptibly warm at the other. An earth of this kind is abundant in Tuscany ; and it is prob- able that the Tertiary infusorial earth which occurs in a bed thirty feet thick near Richmond, Va., and in a still thicker deposit at Monterey, Cal., is adapted to this use. Graphite or plumbago, under the name of black-lead, is familiar to every one from its wide use in lead-pencils. It is a soft, black mineral, of a greasy feel and metallic luster, and easily gives a lead-gray mark on paper, on which ac- count it is used in the manufacture of pencil-leads. Aside from the impurities with which it is often contaminated, it is pure carbon, having the same composition as the dia- mond, to which in other respects it is so unlike ; and it is in all probability the ultimate stage in the series of changes which vegetable matter undergoes, passing through the conditions of peat, lignite, and mineral coal, to end in graphite, which is not only infusible, but also incombusti- ble under the conditions which are presented in the in- 340 APPLIED GEOLOGY. dustrial use of heat. It is usually found in quantities of economic importance only in the most ancient crystalline rocks, associated frequently with limestones, and also with gneiss and schistose rocks. In these it occurs, either dis- seminated more or less abundantly in certain horizons of the rock, or forming pockets and nests, or filling vein-like fissures with mineral of a high degree of purity. It is met with at many points in the Archaean region, extending from the Province of Quebec, in Canada, through New York, New Jersey, etc., to North Carolina and Alabama ; but in most of the localities it is either too sparingly dissemi- nated to pay for its extraction, or is of such physical char- acter as not to admit of cheap separation from its impuri- ties. It has been mined to some extent at Bloomingdale, N. J., Bucks County, Pa., and Sturbridge, Mass., being found in graphitic gneiss ; but the chief place in the United States where it is mined at present is near Ticon- deroga, N. Y., where it is obtained from a graphitic schist, about fifteen feet thick, and containing from 8 to 15 per cent of disseminated graphite. This locality yielded two hundred net tons of graphite in 1882, the remainder of the United States producing only twelve tons. In Ottawa County, Quebec, extensive deposits occur in the Laurentian limestones, containing in some localities 20 to 30 per cent of disseminated graphite. Fis- sure-veins are also found here, which yield a very pure mineral, but it is said to be usually in quite limited amounts. Graphite deposits have also been worked at intervals in the Archaean rocks near St. John, New Bruns- wick, and it is reported to occur in graphitic schists in the Archaean area of northern Michigan, as also in some of the Western Territories. The Island of Ceylon furnishes it in immense vein deposits of singular purity at Travancore, and from these the largest supplies of the world are de- rived, although Austria and Bavaria produce annually from 15,000 to 18,000 metric tons. The rocks in which REFRACTORY SUBSTANCES. 341 available graphite is most likely to be found are, there- fore, those of Archaean age, though small amounts occur in strata as late as the coal-measures. The famous de- posit of Borrowdale in England, which is now no longer worked, occurs in veins in interbedded trap ; and its product was once sold at from $8 to $12 per pound, for the manufacture of pencils, extraordinary precautions be- ing taken to prevent theft. The present price of graphite is from $25 to $200 per ton, according to its purity and fineness. The properties on which depend the important uses of graphite in the arts are its infusibility, its unchangeable- ness in the air, even when exposed to high heat, its soft, unctuous texture, its ready conduction of electricity, and its graphic quality, from which is derived its name graph- ite, from the Greek grapho, I write. Of these, its in- fusibility properly concerns us in this place ; but, for the sake of completeness, its leading uses may be briefly enumerated here, although some of them belong properly in the succeeding chapter, where they will be referred to. Fully one third of all the graphite that is produced is used for refractory articles, such as small furnaces, nozzles and stoppers for the Bessemer process, and crucibles for melting steel, silver, copper, and brass. For these pur- poses it should be free from lime and iron oxide, with which it is liable to be contaminated ; since, for such uses, it must be intimately mingled with a proper propor- tion of fire-clay to give it strength, and the silica of the clay would form fusible compounds with iron and lime. Other large uses of graphite are for stove-polish, to pro- tect iron articles from rust, and for foundry-facings, two fifths of the product being employed for these purposes, an additional amount being also used for glazing powder and shot. A fourth highly important and increasing use is for the lubrication of heavy machinery, in which it is employed in the state of a fine powder, and in various 342 APPLIED GEOLOGY. patent greases. Its use in pencil-leads is familiar to every one, besides which it is considerably employed in electro- typing and for several minor purposes. Although caustic lime is one of the most infusible as well as most easily obtained of known substances, it is not capable of being used in the large way as a refractory material, because of the readiness with which it absorbs water from the air and then crumbles to powder. It is, however, used for constructing the small furnaces and crucibles in which platinum is melted and refined by the heat of the oxyhydrogen blow-pipe flame, a small but quite important use. Caustic magnesia is also highly in- fusible, and in Germany is converted into a very refrac- tory brick, being cheaply obtained from the waste liquors of the Stassfurt salts described in a preceding chapter, by precipitation from its chloride by milk of lime, or by sub- jecting the chloride to the action of an oxidizing flame and superheated steam. A cheap and effective mode of utilizing in the large way the refractory properties of a combination of these two alkaline earths has recently been devised, whereby the lime produced by calcining strongly a somewhat silicious dolomite is made into a paste with pitch, and then molded into bricks, or used directly as a refractory lining for Bessemer converters. By gradual heating, the pitch is burned out, and the re- fractory earths are left in the shape required. This is the so-called " basic lining," by the agency of which a consid- erable percentage of phosphorus may be eliminated from iron, rendering available, for steel-making purposes, iron hitherto wholly unfit for this use. Magnesian limestones, suitable for this purpose, are widely distributed among the geological formations, and need no special mention in this connection. It is said by Bloxam, on the authority of Gilchrist, that the best composition of a magnesian lime for the basic process is, lime, 52 per cent ; magnesia, 36 per cent ; silica, 8 per cent ; alumina and iron, 4 per cent. REFRACTORY SUBSTANCES. 343 Steatite, called commonly soapstone or potstone, is a soft, compact, gray or greenish form of talc, and derives its name soapstone from its soapy feel. In composition, it is a hydrous silicate of magnesia, and is highly infusible, on which account it is considerably used as a fire-stone in hearths, stoves, and furnaces, and for register borders and pipe-holes, as also in gas-jets and in several articles for household purposes. It is found in the ancient crystal- line rocks of the Atlantic border States, and is quarried chiefly in Vermont and New Hampshire, though similar deposits are known to occur in several other States. Mica and Asbestus. The leading uses of these two minerals are based upon their infusibility, coupled in the one case with toughness and great transparency, and in the other with a highly fibrous texture and a very slight conductivity for heat. The only desirable variety of mica is muscovite, in large transparent crystals, free from irreg- ularities and accessory minerals. Such crystals occur chiefly in veins of exceedingly coarse-grained granite, and, as might naturally be expected, they are to be sought for chiefly in regions of Archaean rocks, as along the Appala- chian range, and in the vicinity of the Rocky Mountains and the Sierra Nevadas. The chief production of mica has hitherto been from western North Carolina, and from the Black Hills, near Deadwood. In North Carolina, ac- cording to the Geological Report of that State in 1875, the mica occurs in veins of coarse granite with walls of gneiss, in which are found rude crystals of mica weighing from thirty to fifty pounds, and in a few instances even as much as a thousand pounds, affording, occasionally, sheets three feet across. The most profitable workings here are on the sites of pits and galleries of some ancient race of men. Similar ancient workings are reported by Prof. Smith to exist at various points of eastern Alabama, giving promise of merchantable mica in that State. The mica from the Black Hills is reported to be of very fine quality, 344 APPLIED GEOLOGY. and plates of large size are sometimes produced. " The main ledge is said to be fourteen feet wide, and to consist of a central mass of feldspar and 'porphyry,' with a casing of mica which varies in width from three to four feet on each side. The country rock is granite." Mica is pro- duced also in Maine and New Hampshire ; and a com- pany with large capital is reported to have been lately formed in Marquette to develop a promising mica prop- erty in northern Michigan, and another in Chaffee County, Col., for a like purpose. It is well to bear in mind that it has been observed in North Carolina that, wherever horn- blendic rocks or chloritic schists form the walls of the mica-bearing veins, the mica is apt to be badly specked with magnetite. The chief use of mica is for the trans- parent plates of stoves and furnaces, and for lanterns, some of the larger plates being also occasionally utilized in surveyors' instruments in the place of glass. Finely pulverized mica is also used as an absorbent of nitro- glycerine in one variety of high explosives, and likewise as a finish for wall-papers, and for some other ornamental purposes. The price of sheet-mica varies at present from twenty-five cents to five dollars per pound, according to size and quality, exceptionally large and fine sheets bring- ing even a higher price. Asbestus affords a curious example of a mineral whose leading properties have been known for many centuries, and have caused it to be somewhat used by the ancients for incombustible fabrics, which were objects of curiosity rather than of practical utility ; yet whose important in- dustrial capabilities have been neglected until very recent years. It is a fibrous form of several minerals, like horn- blende, pyroxene, and serpentine, is of a white, light green, or brownish color, and is practically infusible by the heat of ordinary fires. The most valuable kinds occur in long, silky, parallel fibers, which are strong and flexible, and capable of being spun like flax by proper REFRACTORY SUBSTANCES. 345 machinery, and woven into fabrics that are incombustible. Hence its name, which is a Greek word applied to the mineral with reference to this property. Other varieties, in which the fibers interlace so as to form a kind of natural felt, are called mountain leather and mountain cork, while the fine, silky, fibrous variety is sometimes called amianthus, from a Greek word meaning unpolluted, because the fabrics woven from it, when soiled, may be readily cleansed by passing them through fire. To be of any considerable economic importance, asbestus needs to have length and fineness of fiber, combined with tough- ness and flexibility. These qualities are often lacking in mineral which has a promising appearance, the fiber being short, or brittle and harsh to the touch, making a sub- stance of little or no value. Hence the expediency, when a new deposit is discovered, of having the mineral care- fully tested in respect to these qualities, before incurring any considerable expense in working it. Asbestus is found in regions of crystalline rocks, most commonly associated with serpentine, occupying vein-like crevices which are of uncertain and usually quite limited extent, causing great difficulty in mining it with profit. The finest is produced in the Italian Alps and in Corsica ; but a considerable amount of asbestus of good quality is ob- tained from the Province of Quebec, from several of our Atlantic seaboard States, ranging from New York to Georgia, and from some of the far Western States, es- pecially California. Doubtless more diligent search with- in our great areas of crystalline rocks, stimulated by the rapidly growing demand for this mineral, will result in many new discoveries, some of which may yield an article equal in quality to the best Italian. The uses of asbestus are based upon its fibrous text- ure, its resistance to fire, and its very feeble conduction of heat and electricity. It is most largely used for packing the joints and working parts of steam-machinery ; for 346 APPLIED GEOLOGY. covering boilers and steam-pipes to prevent loss of heat by radiation ; and as a fire-proof lining for floors and ceilings, and for the walls of wooden buildings. For some of these purposes it is spun into yarn by the aid of special machinery, or woven into sheets and tape, with the addition, for some uses, of India-rubber ; for others, it is felted and pressed into sheets of a kind of paper called mill-board, of any required thickness. In this latter form it is used also as an insulator in dynamos. It is woven into fire-proof cloth for the drop-curtains of theatres, for furnace-men's aprons and leggings, and for other similar purposes ; and it has been proposed to construct from such cloth light fire-proof shields to protect firemen from the heat of conflagrations. Twisted into cord and rope it may be used for fire-escapes, since it has great tensile strength. It has long had a limited use in incombustible wicks for lamps, for which it is admirably adapted. It is also used for making fire-proof cements and paints. There is no reason to doubt that, with the probable in- crease in the production and diminution in cost of this useful mineral, there will be a large increase in its indus- trial applications in the immediate future. The United States production of asbestus in 1882 was reported to be twelve hundred tons, and its average value at the mines about thirty dollars per ton, varying from fifteen to sixty dollars, according to quality, exceptionally fine mineral commanding much higher prices than these. With reference to the substances treated of in this chapter, the stu- dent can profitably consult the following works, to which many others might easily be added : Bloxam on Metals the chapter on " Refrac- tory Materials " ; " New Jersey Report on Clay Deposits," 1878, and Annual Report for 1880 ; " Ohio Geological Report," Vol. V ; " Geo- logical Report of North Carolina," 1875 ; " Geology of Canada," 1863, section vi of chapter xxi ; " Mineral Resources of the United States," 1883 ; also any good encyclopaedia ; and the files of the " Engineering and Mining Journal," by the aid of its excellent indexes. CHAPTER XXI. MATERIALS OF PHYSICAL APPLICATION. A VERY considerable number of purposes, some of which are sufficiently common and consequently of a high degree of importance, are subserved by substances of geo- logical origin by reason of their possession of certain physical properties, as texture, hardness, and color ; little previous preparation, and that of a purely mechanical nature, being necessary to adapt them for their uses. Such are the substances which are used for mending roads and improving streets and walks ; for grinding vari- ous kinds of grain as well as many minerals ; for giving a keen edge to cutting instruments, and for imparting a fine polish to wood, stone, and metals ; for drawing purposes, and for the cheap and rapid reproduction of pictures ; for diminishing friction ; for making molds for castings in metal ; and for some other uses of analogous character. The mere enumeration of these utilities is sufficient to show how nearly some of them touch the comforts and conveniences of civilized man ; how much others affect the efficiency of his efforts ; and how intimately still others concern his opportunities for refinement. Materials for Roads and Walks. The commer- cial rank and the industrial advancement of any commu- nity are pretty fairly expressed in the excellence of its means of communication, not merely by lines of railway, but also by those more numerous and highly important 348 APPLIED GEOLOGY. avenues of travel and intercommunication which afford ready access to every hamlet and every home. The im- provement of country roads is usually effected by the judicious use of those materials which are most easily accessible in any given locality. In very many regions, deposits of gravel, the accumulations of streams, and sometimes of the ocean, or the relics of the glacial age, afford a convenient means of improvement, which, from the usual hard and silicious nature of the pebbles, is both cheap and durable, making, with due preparation of the foundations, and by proper arrangement of the coarser and finer portions, excellent and enduring roadways. In some few localities where gravel is not found, ledges of conglomerate, not too closely cemented, may be acces- sible, which, at some slight cost for crushing, may afford excellent material for roads. In other cases, silicious limestones of the vicinity, crushed by rock-breakers, or broken to proper sizes with hammers, are used for road purposes, needing occasional renewal on account of the comparative softness of the stone. Harder and more en- during material is afforded by the hornstone and chert which occur at most of the exposures of the largely quarried Corniferous limestone across the State of New York and westward, and which are found accompanying some of the limestones of the Lower Carboniferous age in the Western States. In regions of crystalline formations, rocks of the granite class quartzites, felstones, tough porphyries, and still tougher traps may be made avail- able for road-metal. All these rocks, of hard and tough character, can be most cheaply reduced to sizes proper for macadamizing roads by means of rock-crushers driven by steam or water power ; and though the first cost of the roads constructed from such materials may be somewhat large, yet their convenience and durability, when once properly made, will more than compensate for the original outlay. In European countries, permanent roadways are MATERIALS OF PHYSICAL APPLICATION. 349 constructed from all the substances that have here been enumerated ; their use is increasing in the more thickly settled portions of our own country ; and there can be no doubt that, ere long, a people so progressive and so prac- tical as ours will become impatient at the too often wretched condition of our roads, and will seek, in durable rock materials, for a permanent means of improvement. The need of previous careful drainage, and the prepara- tion of a suitable foundation for a road, before using any of these materials, has not been insisted on here, because it is a matter which belongs rather to the road-engineer than to the geologist. For those streets of cities and large towns which are devoted chiefly to residences, and which are little used for transportation, macadamized roadways, properly con- structed of materials such as have already been mentioned, present the advantage of being comparatively noiseless an advantage which may compensate in a good degree for their liability to dust in dry weather. .But for streets which are much used as thoroughfares for heavy traffic, the road materials need to be employed in larger and more solid forms, to secure stability under stress. For this purpose, rectangular blocks of hard and tough varie- ties of stone are used, arranged in courses, such width of the blocks being best as affords the most convenient hold for the feet of horses. A number of kinds of rock are well adapted to this use, such as granites, hard sandstones, quartz schist, felstone, trap, and porphyry. The granites most suitable for pavements are those of medium fineness of grain, in which quartz rather than feldspar is a domi- nant ingredient, or those into which hornblende enters in a considerable amount, those being naturally selected in which a somewhat easy rift in certain directions facilitates their reduction to proper shapes. Quartz schists, or those highly silicious mica schists in which the mica is barely in sufficient amount to impart a schistose structure, may 16 350 APPLIED GEOLOGY. be wrought with ease into good paving-blocks. Felstone is also sometimes used for pavements where its structure admits of easy working. These three kinds of paving ma- terials may be obtained in those regions of Archaean rocks which were described in the chapter on building-stones, and which have since been several times mentioned. In a number of our Northern cities, of which Rochester, Buffalo, and Cleveland are examples, a silicious sandstone obtained from the lower member of the Niagara period in western New York, and called the Medina sandstone, from one of the villages where it is largely quarried, is extensively used for pavements, and is found excellent for this purpose. In the region about Medina and Albion it is a hard, well- cemented sandstone of extraordinary strength, susceptible of being wrought without much difficulty into convenient blocks, and of sharp grit, so that it shows little tendency to become smooth by wear. In the northeast part of New York, also, very hard silicious sandstones occur in strata of the Potsdam period, which are admirably suited for use in paving. In the immediate neighborhood of New York city, at many points in Connecticut and New Jersey, and in elongated belts of strata which stretch parallel to the Atlantic border even to the boundary of South Carolina, occur dikes of basaltic trap-rock which has a very exten- sive use for paving-blocks. It is a hard, heavy, and very tough rock, and makes pavements of unsurpassed dura- bility ; but its tendency to become smooth and slippery by wear renders it expedient to shape it into narrower blocks than those which are commonly used. It is per- haps needless to say that only those portions of the trap- rock are fitted for this use whose structure admits of their being easily split into the required forms. It will be seen, therefore, that for all purposes of road construction, a rock needs to be hard, that it may endure wear ; tough, that it may not easily yield to blows ; of such structure as to admit of being wrought without too great MATERIALS OF PHYSICAL APPLICATION. 351 expense ; and, if possible, of such texture as to remain some- what rough in use. The qualities which are desired in a material for the construction of sidewalks, and for some other kindred uses, are evenness of surface, closeness of texture to resist the penetration of moisture, and a sufficient degree of hardness to withstand the kind of wear to which it is to be subjected. The ability to secure slabs of different di- mensions and thickness, to adapt them to use under a variety of circumstances, is also very desirable. These qualities are well combined in what are called flag-stones, which are even-bedded and somewhat argillaceous sand- stones, occurring in sheets of from two to eight inches in thickness, associated with shales and thicker bedded sand- stones. Such flagging is largely quarried in beds of the upper part of the Hamilton period and of the Lower Che- mung (Portage group), near the Hudson River, in Ulster and Greene Counties ; at the south end of Cayuga Lake near Ithaca, in strata of the Chemung period ; in the northern part of Wyoming County, Pa., in strata which are referred by the Pennsylvania geologists to the lower part of the Catskill period ; and near Warren, Ohio, in beds of the Lower Carboniferous (Waverly group). Where such flag- stones can not be obtained without too great expense, re- sort is often had to thin-bedded or easily divided rocks of other kinds. Thus, thin-bedded limestones are sometimes applied to this purpose, though the surface is liable to be somewhat uneven, and to become dangerously smooth by use. In northern Ohio, soft sandstones, of Lower Car- boniferous age, are split or sawed into slabs of proper thickness, which, although somewhat porous and liable to wear, make very handsome walks. In many localities, sidewalks and sometimes roadways are constructed from a concrete of fine gravel, pulverized limestone, and asphal- tum, or of sand and hydraulic cement, which, when prop- erly made, are very good. 352 APPLIED GEOLOGY. Asphaltum, for this purpose, is obtained chiefly from the Island of Trinidad, and some also from Santa Barbara County, Cal., which is used on the Pacific coast. The tar from gas-works serves as a fair substitute for asphaltum for this use. Many of the streets of Paris are paved with a calcareous asphalt, obtained from Val de Travers and elsewhere in Switzerland ; and this substance is also im- ported into the United States to a considerable extent, to be used in sidewalks and for coating roofs. The Geo- logical Report of Canada for i88o-'82 announces the dis- covery, on the Athabasca River, of a bituminous sand-rock, which is probably suitable for walks and water-proofing. It is worthy of consideration whether a valuable applica- tion of such water-proof concretes could not be made in the pavements of cities, especially on streets devoted to residences, by using them as an impervious cement be- tween the paving-blocks, thus preventing, at least in a measure, the unhealthful emanations which arise in warm weather from the putrefaction of organic matters, while at the same time guarding against displacements by the action of frost. This enumeration of some of the leading geological substances which are utilized for roads and walks may serve as an indication of those physical properties of rocks and minerals which best adapt them to such uses, and may guide the inquirer to still other substances in his own neighborhood that may be employed for a like pur- pose. Abrasives. What are here classed as abrasives are those rocks and minerals which, by reason of their in- trinsic hardness, or of certain grades of hardness and texture, are used for sharpening all kinds of edge-tools, for triturating grain and minerals, for polishing wood, stone, and metals, and for rock-drills. These are, with a single exception, wide-reaching as well as important uses, affecting the convenience and efficiency of many arts and MATERIALS OF PHYSICAL APPLICATION. 353 trades, and some of them concerning every household. And foremost among these in treatment as in importance may justly be placed those substances used to give a keen edge to cutting instruments, the grindstones and whet- stones; for, not to speak of the many occupations which owe much of their efficiency to the excellence and variety of their edge-tools, there are few individuals who do not find daily occasion to use such articles as knives and scissors. A better description could not well be given of the conditions which must combine to make a good grind- stone-rock than that of Dr. Dawson, in his "Acadian Geology," p. 154: " These grindstones have been formed from beds of sand, deposited in such a manner that the grains are of nearly uniform fineness, and they have been cemented together with just sufficient firmness to give 'cohesion to the stone, and yet to permit its particles to be gradually rubbed off by the contact of steel. A piece of grindstone may appear to be a very simple matter, but it is very rarely that rocks are so constituted as perfectly to fulfill these conditions." The infrequency of occur- rence here spoken of is well exemplified in this country and Canada, which, in all their vast area, have as yet de- veloped but three or possibly four regions in which occur strata of the proper quality to yield first-rate grindstones : one, near the head of the Bay of Fundy in Nova Scotia ; a second, in northern Ohio, near and west of Cleveland ; and a third, at Point au Barques in Michigan. These are all in strata of the Carboniferous age, and mostly in its lower portion ; though one of the two geological horizons which yield grindstones in Nova Scotia lies above the productive coal-seams. Besides these localities, what is called the "Gray Band," in the lower portion of strata of the Niagara period (Medina group), in the Province of Ontario, Canada, is said at some points to present the characters requisite to make grindstones of good quality. 354 APPLIED GEOLOGY. It is interesting to observe that in England, also, most of the rock which is used for grindstones is derived from the grits of the Carboniferous age. Of this age are the grind- stones quarried near Newcastle and Sheffield, as also in Yorkshire and Staffordshire, and at a few other localities. It would seem that in this age, more frequently than in the others,' conditions were presented favorable for the formation of an even-grained, homogeneous sand-rock, not too closely cemented. Rock suitable for the manufacture of whetstones and hone3 is composed of some very hard mineral, like quartz, and occasionally garnet, in the condition of fine, even grains, cemented to a firm mass. If the grains are some- what coarse, the stone cuts down instruments rapidly, but gives a coarse edge. In the best honestones for delicate instruments, the grain is almost imperceptibly fine. The finer-grained and stronger portions of grindstone-rock are wrought into a coarser kind of whetstones for sharpening farm implements and other tools, in which a fine, smooth edge is not required. Stones of similar character but tougher fiber are made from mica schists or slates which contain, thoroughly disseminated, a large proportion of fine-grained silica. Such is the rock which is manu- factured into whetstones in the southern part of Quebec on Lake Memphremagog, at Bridgewater, Vt., and doubt- less at other points in regions of mica slates. Whetstones for finer uses are made from varieties of very fine-grained silicious slates called nov acuities, some of the most valued among which are nearly pure quartz in an excessively minute state of division, and cemented by silica. Such is the Arkansas or Ouachita oilstone obtained at the Hot Springs of Arkansas, which, according to two different analyses, contains from 98 to 99^- per cent of silica. This rock is of the age of the Lower Carboniferous, and, ac- cording to Dr. Owen, it owes its snowy whiteness and its impalpably fine grain to the long-continued action of hot MATERIALS OF PHYSICAL APPLICATION. 355 silicious waters. The finest of these stones are known to the trade as Arkansas oilstones, while those of somewhat coarser grain are sold at much cheaper rates as Ouachita stones. The Turkish oilstones are also highly esteemed, their grain being slightly less fine than that of the best Arkansas stone. The very superior yellow Belgian hone- stones owe their fine quality to microscopic garnets set in a garnet paste. For the grinding of grain, almost any hard, tough, sharp-grained rock will serve fairly well, and several kinds of rock of this character have been and still are employed locally for this purpose, some of which have even more than a local use. Thus, tough, coarse-grained gneisses, and some firmly cemented conglomerates, are so em- ployed. A white, hard, sharp-grained sandstone, of sub- Carboniferous age, found at Peninsula, O., is used near where it is found, and also sent elsewhere, for preparing oatmeal and for pearling barley, for which purposes it ap- pears to be specially fitted. A basaltic lava, found in Germany, is used for millstones, especially for grinding minerals, because of its peculiarities of texture. The rock, however, which is most suitable for millstones of any yet known, is a highly cellular quartz-rock called buhrstone. That which has the highest reputation, and is most largely used, is obtained from the vicinity of Paris, France, from rocks of earlier Tertiary age. It is of fresh- water origin indeed, often contains great numbers of si- licified fresh-water shells, and in the best portions the cellular spaces occupy more than one third the bulk of the stone. Its superiority is due to its cellular structure and its hardness. The stone is cut into blocks of proper form, which are fitted together and held to their place by iron bands to form millstones. Rock of similar charac- ter, and in strata of about the same geological age, is found also in South Carolina, Georgia, and Alabama. The use of millstones in making flour has been, to a con- 356 APPLIED GEOLOGY. siderable extent, superseded in large flouring establish- ments by that of iron rollers ; but for other purposes, and in most small mills, there is likely to be always a wide de- mand for stones to be used in grinding. There will be needed here no more than an allusion to the use of stone in heavy wheels for pulverizing clays, quartz, and other minerals as well as ores, and for some pulping purposes ; and the much ruder use of heavy stone blocks, dragged round and round on a pavement of stone, for grinding ores in the arrastra. For the rapid grinding, cutting, drilling, and polishing of the harder rocks and minerals and of steel, resort is had to the hardest of known minerals, the diamond and corundum, or to the impure and somewhat less hard but tougher variety of the latter mineral called emery. The diamond, because of its rarity and great cost, is confined to special uses. Small crystals and angular fragments are firmly cemented into handles to be used in cutting and ruling glass, in drilling and cutting rubies, sapphires, and some other gems, and for the fine dressing of millstones. Diamond drills, used for prospecting mineral deposits and veins at considerable depths, are made by cementing small diamonds around the edge of a hollow cylinder of steel. This, being swiftly revolved by machinery, not only cuts rapidly through rocks, but also enables the miner to bring up from various depths a solid cylindrical core of rock for examination. For this purpose, black diamonds, not suited for jewelry, are used, called borts, carbons, or carbonados. They are procured, it is said, chiefly from the Brazilian diamond regions. Other dia- monds of inferior quality are used for the other purposes that have been named, or crushed to fine powder to be used for cutting and polishing the harder gems and the diamond itself. The mineral corundum, which is inferior only to the diamond in hardness, in the condition of transparent crys- MATERIALS OF PHYSICAL APPLICATION. 357 tals of various colors furnishes the gems sapphire, ruby, emerald, etc. That which is used as an abrasive is most commonly gray and imperfectly transparent, and is of no value as a gem. It has been found in the Appalachian region of the United States at many localities, the most important of which are in Clay and Macon Counties, N. C., and Chester County, Pa. Masses of corundum are said to have been found in Clay County, N. C., weighing from three to six hundred pounds, associated with the olivine rock of that region. It is estimated that about five hun- dred tons are produced annually by the United States. Emery, which is an impure form of corundum contaminated with varying amounts of iron oxide, whence it derives its dark color, is obtained chiefly from near Smyrna, in Asia Minor, where it occurs in considerable masses, and from the island of Naxos. It has also been mined at Chester, Mass. Both corundum and emery are pulverized to a powder of different degrees of fineness for different pur- poses, and sold, under the name of emery, for polishing glass and the harder kinds of stone and metals, a large part of the price at which it is sold being due to the labor of reducing to fine powder minerals of such hardness. The powder of emery, though not so hard as that of pure corundum, and hence not abrading so rapidly, is said to be less brittle and so more durable. What are called em- ery-wheels, so largely used in machine-shops for grinding and polishing iron and steel, are made by mixing powdered emery into a paste with water-glass, fire-clay, or some other cementing material, then molding into the proper shape and baking. Emery-paper is made by cementing emery- powder to stout paper with glue. Sand-paper, to be used for polishing wood, is made in like manner from sharp* quartz sand. Sand is also largely used -as an abrasive in sawing and rubbing to a smooth surface marble and sandstone. Other mineral substances, which are utilized for polishing wood 358 APPLIED GEOLOGY. and stone, bone and ivory, as also metallic articles, are pumice and tripoli. Pumice is a light, porous, felspathic lava which is brought chiefly from the neighborhood of Mount Vesuvius and the Lipari Islands, but is said to occur abundantly also in San Francisco County, Cal. Tripoli is a silicious, infusorial earth of very fine grain which is found near Richmond, Va., and Monterey, Cal., as also in Nevada and at a number of foreign localities. Tripoli has also been somewhat used as an absorbent of nitro-glycerine in making dynamite. Graphic Materials. What have been thus grouped in this place are those geological substances which, by reason of their texture, softness, color, and some other properties, are used with no other than a mechanical prepa- ration for making, or for receiving and transferring, draw- ings and writings. As is well known, great improvements have been made within the present century in the adapta- tion of means for these purposes, whereby the multiplica- tion of writings and of works of art has been greatly facili- tated and cheapened, to the great advantage of business, while bringing within the reach of all classes of people better means for cultivating a refined taste, and for the illustration of subjects otherwise difficult of comprehen- sion. Some portion of this improvement has been due to the discovery, or adaptation and preparation, of geological substances, such as graphite, chalk, steatite, and litho- graphic limestone. Graphite, the mode of occurrence and localities of which have been given in the preceding chap- ter, has long been used in pencils for drawing and writing, being sawed into slender prisms from blocks of granular graphite ; and for this use that of Borrowdale, England, had a special value, being pure and of granular texture. Now, however, purified graphite, in a fine state of divis- ion, is either compressed intp solid masses by hydrostatic pressure, to be afterward sawed into pencil " leads," or else mingled into a paste with certain proportions of the finest MATERIALS OF PHYSICAL APPLICATION. 359 clay, run into molds, dried, and heated to such tempera- tures as are needful to secure the degrees of hardness which are requisite for different purposes. Chalk, so largely used in crayons for school and other purposes, is a soft, white, earthy limestone, composed of the calcareous skeletons of microscopic organisms. This forms nearly the uppermost deposit of rocks of the Cretaceous period in southern England and northern France, where it covers considerable areas. Because of its peculiar soft and fria- ble condition it is easily pulverized and molded into proper shapes, either alone or mingled with various coloring in- gredients. Its physical condition fits it also to be used in some porcelain mixtures, and to be mingled with a proper proportion of clay for burning into hydraulic cements. The so-called red chalk, used for graphic purposes, is an argillaceous ochre, i. e., a soft, earthy form of red iron oxide mingled intimately with clay, which occurs in re- gions of iron-ores. The massive granular form of talc, called steatite and soapstone (see preceding chapter), is used, under the name of French chalk, for marking on cloth, and in crayons for drawing in fine white lines on a dark ground ; and pyrophyllite, a soft, aluminous silicate, closely resembling talc in its light colors, its softness, and its greasy feel, is much used for slate-pencils. The latter occurs in the Archaean slates of Georgia and both Caro- linas, and near Little Rock, Ark. The very important graphic material known as litho- graphic limestone is a very fine-grained, compact, and per- fectly homogeneous limestone, of conchoid fracture, and usually of a pale-gray or yellowish tint, and having a suf- ficient degree of porosity to slightly absorb water and oil. On the smoothed or finely granulated surface of such a stone, drawings are executed with a properly prepared greasy pigment, called lithographic chalk and lithographic ink, or such drawings may be transferred to it from spe- cially prepared paper. The stone absorbs the greasy draw- 360 APPLIED GEOLOGY. ing material sufficiently to retain it firmly, and, if it now be moistened with water, all except the greasy portions absorb the water and become wet. A roller charged with the oily printer's ink, passed over the moistened stone, will now wet only the greasy lines of the drawing, which may then be printed from as from an engraving. Limestones possessed of this peculiar combination of characters are very rarely met with. Hitherto they have been obtained wholly from certain thin-bedded limestones of the upper part of the Jurassic period at Solenhofen, Bavaria, a local- ity famous also for the remarkably preserved fossils which it affords. Limestone of the required quality is, however, reported to occur in strata of the Trenton period in Mar- mora, Hastings County, Ontario, and in a yellowish dolo- mite of the Salina period on the Saugeen River in Bruce County, of the same province. It is said, also, that litho- graphic limestones in small slabs may be obtained at some localities in the Lower Carboniferous limestone of Mis- souri, portions of which, however, are apt to show spots of different texture, and so to be worthless. Pigments. A great majority of the pigments that are in common use are derived from the metals by chemi- cal processes, and hence have already been mentioned in their proper places among the useful applications of the metals from which they are derived. Such, for example, are the various pigments manufactured from lead, zinc, chromium, mercury, arsenic, antimony, copper, and cobalt. Besides these, however, there are some other substances which, with no other than a mechanical preparation, are used as cheap pigments. Thus, graphite, so largely utilized for other purposes that have been mentioned before, is also somewhat used as a black paint. Finely pulverized chalk, under the name of whiting and Spanish white, is used as a white or tinted wash for walls ; and caustic lime is also widely employed for the same purpose. Besides these substances, which have already been described in other MATERIALS OF PHYSICAL .APPLICATION. 361 connections, ochre, umber, and barytes have a large use as pigments. Ochre is a soft, pulverulent form of hydrated peroxide of iron, mingled usually with more or less con- siderable proportions of clay, silica, and organic matter, and affording various shades of yellow, red, and brown. It occurs in deposits of various geological ages, and often as superficial accumulations of recent periods. Thus, the softer earthy portions of some hematite beds are ground and used as pigments, called iron paints. The ochre de- posits of Great Britain are found chiefly at the base of the Cretaceous system, while the extensive beds of ochre along the St. Lawrence in Canada are superficial deposits which, in some cases, are interstratified with peat, and have been accumulated by the solvent action on iron compounds of organic acids resulting from vegetable decomposition, and the subsequent deposition of the iron oxide by atmospheric oxidation. Ochre is procured also from the muddy fer- ruginous waters pumped from mines. Its color may be greatly modified by calcination, thus driving off its water of hydration. Beds of red and reddish-brown clay-rocks, colored by iron oxide, are also ground and used as a cheap paint. Umber is a soft, earthy variety of ochre, which is colored brown by oxide of manganese, and becomes red- dish brown by calcination. It occurs usually in crystalline rocks, and is brought mostly from the island of Cyprus. It is found, also, at a few localities in Great Britain, and is said to be produced to some extent in this country. The mineral barytes, called also heavy spar, because of its great specific gravity, is a white crystalline or massive sulphate of baryta, of about the same hardness as calcite, and is fusible by the blow-pipe, giving a green color to the flame. On account of its great weight, it is little liable to be mistaken for any other white mineral save celestite, which has nearly the same weight and hardness ; and from this, the color imparted to the blow-pipe flame readily dis- tinguishes it, that of celestite being a bright red. It oc- 362 APPLIED GEOLOGY. curs commonly as a vein-stone, especially in veins of lead and copper. It is found in workable quantities at quite a number of localities in North America ; as in the copper veins on the north shore of Lake Superior ; in the central Missouri lead region, especially in Miller and Morgan Counties; in several counties of East Tennessee, being worked in some; and in Wythe, Smyth, and Campbell Counties, Va., a single mine in the county last named be- ing reported to be able to produce a hundred tons per day. Considerable amounts are produced also in Penn- sylvania and Maine. The largest production is from Missouri and Virginia ; Connecticut grinds also a large amount of barytes imported from Germany. About twenty-five thousand tons a year are mined in the United States, of which much the largest part is used for mixing with white lead and zinc white, in the preparation of white paint. This employment of barytes is commonly considered an adulteration, and manufacturers do not seem eager to publish the fact of its use ; yet, when properly prepared, it produces a good opaque white color, which is not, like lead, liable to discoloration from sul- phuretted hydrogen. Lubricators. The mineral substances which are most largely employed for diminishing friction in ma- chinery, viz., graphite and the heavy varieties of petroleum, have already been mentioned in other connections as fitted for this use. The foliated varieties of talc, when free from needles and grains of the harder minerals, are also used to a considerable extent in lubricating compositions. This last-named mineral, which, like soapstone, its massive form from which it is distinguished commercially, occurs in crystalline schists, is found in several of the States of the Atlantic border most largely in Georgia, Pennsylvania, New York, and Vermont. The fibrous form of this miner- al, which is found in considerable quantities near Gouver- neur, N. Y., is quite largely mined and ground for pulp to tSE- -^ MATERIALS OF PHYSICAL APPLICA%$^ \^' ' be used in paper-making. It may readily be judged that only the fibrous variety could be used for this purpose, since only this has any staple to form a felt ; and the St. Lawrence mineral may, it is said, enter into printing paper to the extent of twenty per cent, or even more. Talc has also a quite extensive use in soap-making, and in dressing skins and leather, these various applications rendering it a mineral of considerable economic importance. In the " Geological Report on the Midland Counties of North Carolina," 1856, Prof. Emmons speaks of a valuable anti- friction hornstone as abounding in several counties of that State. This rock, probably a felstone, since it gradu- ated into porphyry, was of flinty aspect and very fine and compact texture, and was highly valued locally as a bear- ing for the axles of heavy wheels. From its fine texture and great hardness, this distinguished geologist pro- nounced it to be fitted to take the same part in diminish- ing the friction of heavy machinery that rubies play in the works of watches. Molding-Sand. This substance, which is of so much importance for foundry use, is an intimate mixture of quartz sand with just sufficient proportions of clay and ochre to enable it to retain the form given by the pattern, and to withstand in founding the current of molten metal without displacement. If the proportions of the cohesive substance are too small, even if the mold retains its form before it is used, it is apt to wash, i. e., to be swept away in places by the flowing metal, and so to cause irregulari- ties in the casting, or to ruin it wholly. If, on the other hand, there is more clay than is needed, it is burned in the founding, and forms a crust on the casting which is some- what troublesome to remove. A good sand for molder's use should contain about 92 per cent of fine quartz sand, 6 per cent of clay, and 2 per cent of iron oxide. The fineness and delicacy of the impression that can be given will depend on the fineness of the sand that is present in 364 APPLIED GEOLOGY. the molding mixture. For some very fine castings, an artificial mixture is prepared by calcining loamy sand, grinding it very fine, and adding some substance to impart the necessary adhesiveness. Good molding-sand is of a yellow color, soils the fingers when dry, and when damp, if grasped in the hand, it retains a delicate impression of the fingers. It occurs in superficial deposits, usually of no great thickness, and is liable to great variations in quality at points little removed from each other. Mold- ing-sand is by no means of common occurrence, and the foundries of very considerable sections of country are often obliged to depend for their supplies on material brought from a distance. Saratoga County, N. Y., fur- nishes a molding-sand of fine reputation and of various qualities fitted for special purposes, which is transported to long distances. Good sand for this purpose is found at some localities in New Jersey, from which supplies are sent to the Southern seaboard States. Tompkins County, N. Y., has a fair quality of sand which supplies the local demand for ordinary foundry uses. For some purposes, as for large castings in bronze, molding-sand is even im- ported from Europe. For the facing of molds, called foundry facings, graphite is largely used, as has already been said. A cheaper facing, and one which, for some purposes at least, is less liable to wash, is afforded by hydraulic lime. CHAPTER XXII. ORNAMENTAL STONES AND GEMS. A TREATISE which is intended to present any just view of the contributions which geology makes to the supply of the multifarious wants of mankind, can not omit some ac- count of those substances which, while not ministering to man's necessities, nor promoting his comfort, nor increas- ing the efficiency of his efforts, are nevertheless strongly desired by him as a gratification to his tastes, as the ex- pression of his wealth and social consequence, or as fitted to be fashioned into the most permanent monuments of his culture and refinement ; objects which, though not necessary, are yet essential, because without them some- thing would be lacking for the complete satisfaction of his many-sided nature. Man loves beauty and craves orna- ment, and all that ministers to this sentiment and craving is more elevating in its tendency than what satisfies merely his bodily wants. Many of the substances which are drawn from geological sources lend themselves to these higher wants of mankind by their durability, combined with their beauty, their brilliancy of color or of luster, and often their rarity. Several of them are found in consider- able abundance, and a great part of the estimation in which they are held is due to their adaptation to the pur- poses of refined and artistic workmanship. Such are the ornamental stones, the objects wrought from which usually far surpass the raw material in value. Others add to 366 APPLIED GEOLOGY. beauty of color and brilliancy of luster a greater or less degree of hardness and of rarity, and, while gratifying the taste of their possessor, become in a certain degree badges of his wealth and importance. Such are the gems, a large part of whose value is usually intrinsic, i. e., dependent in but a minor degree on excellence of workmanship. Ornamental Stones. On account of the hardness and unalterability of the mineral, the various forms of quartz have, for many centuries, been used for ornamental purposes. The transparent varieties were fashioned by the ancients into crystal cups and vases, and set in jewelry. Its use for most such purposes is now largely superseded by that of the finer kinds of glass, which are more brilliant and cheaply formed, but more liable to be marred in use because of their inferior hardness. Clear white quartz has a considerable use in lenses and for spectacles ; and un- der such names as Rhine-stone and California diamond, quartz is still quite largely cut and polished for cheap jewelry, that which is of a clear yellow color figuring as false topaz, and that of a smoky tint as Cairngorm-stone. The purple variety of quartz called amethyst, when trans- parent crystals of sufficient size and proper depth of color are met with, is cut for valuable jewelry. Much, however, that is sold under these various names is artificial, being made from strass. Handsome crystals and clusters of crystals of quartz are held in some estimation as house- hold ornaments. Fine specimens for this purpose are found at the Hot Springs of Arkansas, and in Herkimer County, N. Y. ; as also frequently in regions of Archaean rocks. The most valued amethysts are brought from India, Ceylon, Siberia, and Brazil ; and they are found also on Keweenaw Point, and in some of the Eastern States, but seldom good enough for jewelry. The massive translucent varieties of quartz with waxy luster, and es- pecially those which present alternating bands and spots of different colors and shades of color, due to impurities ORNAMENTAL STONES AND GEMS. 367 introduced during the successive deposition of the layers from silicated waters, make very handsome ornamental stones, and are wrought into a variety of beautiful objects, such as vases, cups, boxes, necklaces, seals, buttons, knife- handles, and small columns for cabinets ; or they are merely cut and polished to display their spots and bands of color, and used for mantel and cabinet ornaments. Varieties of milky and bluish tints are called chalcedony, abundant in geodes in Iowa and Illinois ; of bright, rich red, carnelian, brought from the East Indies ; of concen- tric and often zigzag bands of color, agates, found on Lake Superior ; of smoky tints, containing moss-like figures in metallic oxides, moss-agates, occurring in the Rocky Mountain region ; and of flat, parallel layers of white and black or brownish shades, onyx and sardonyx. These last are the materials in which are cut miniature articles of sculpture called cameos, in which the alternation of layers of different colors is dexterously made to heighten the effect, and in the art of cutting which the ancients had attained as great skill as is displayed by modern artists. The opaque red, yellow, and green variety of quartz, called jasper, when it occurs in bands of different colors, is val- ued for ornaments like vases, handles, boxes, and small cabinets, and especially for mosaics and inlaid work. Handsome varieties are found in Calaveras County, Cal. ; Graham County, Kan. ; near Troy, N. Y. ; and at Chester, Mass. Some of the varieties of feldspar also afford orna- mental material. Thus sunstone, a yellowish or grayish feldspar, containing minute scales of mica, and moonstone, a milky opalescent feldspar with pearly reflections, are cut for jewelry ; and labradorite, a dark-gray or brown feld- spar, which when polished often presents a beautiful play of bright bluish and greenish colors from internal reflec- tions, is a handsome material for ornamental uses. The last-named mineral is obtained of good quality from Lab- 368 APPLIED GEOLOGY. rador, whence its name, being also found in northern New York ; while the first two occur in Amelia County, Va., and Delaware County, Pa. Moonstone is brought also from Ceylon, and sunstone from Norway. The feld- spars used for ornament occur in regions of .crystalline rocks. The tough, heavy, compact, and translucent stone, called nephrite and jade, of green and blue colors, obtained from China, India, Siberia, Alaska, and New Zealand, is used for making carved ornaments, for which purpose it has long been held in high estimation by the Chinese. Lapis lazuli, a mineral usually compact and of rich blue color, occurring in the ancient crystalline rocks of Persia, China, Siberia, and Thibet, furnishes a valued material for objects of luxury, like vases, rich mosaics, and the inlaid work of costly furniture, besides being used in jewelry. When powdered, it becomes the costly blue pigment, ultramarine, which is now, however, prepared artificially at much smaller expense than that from the native min- eral. The use of malachite, the green banded carbonate of copper, in magnificent inlaid furniture, has already been mentioned in the chapter on copper. It is a common ore of copper in our Southwest Territories ; but large concre- tionary masses, fit to be cut for ornamental uses, are not often met with, the Ural Mountains being still the chief source of supply for such purposes. The fluoride of calcium, called fluor-spar and Derby- shire spar, which occurs both massive and crystalline as a vein-stone in many veins, especially those of lead, when transparent, and of fine colors, such as green, purple, and red, is sometimes wrought into ornamental articles, like vases, snuff-boxes, and candlesticks. Derbyshire, England, affords a handsome blue fluorite, whence the mineral has derived one of its common names. Fluorite fit for orna- mental uses is said to be found in Hardin County, 111., and in Colorado. The chief use of the mineral, however, ORNAMENTAL STONES AND GEMS. 369 is for a flux in metallurgical operations, and as a glaze for pottery. A hard, compact, and lustrous variety of brown coal, which admits of a high polish, is used on this ac- count, and because of its black color, for personal orna- ments, especially mourning jewelry, under the name oijet. It occurs abundantly in El Paso County, Col., and at some localities in Texas ; also in England (Whitby be- ing a celebrated locality), in France, and in Spain. Like the lignites and brown coals, jet occurs in the later geo- logical deposits, the Tertiary and Upper Cretaceous ; and like these, also, it is very light when compared with other minerals, by which character it may easily be distinguished from its imitations made of glass. Another very light mineral substance, largely used for small ornamental objects, is amber, a transparent fossil resin of yellow and orange colors, frequently inclosing in- sects. It occurs in irregular lumps in the Tertiary beds of several European and Asiatic localities, and on the Atlantic borders of Massachusetts and New Jersey ; but much the most important source of supply is the Baltic coast, chiefly of Prussia, where it is washed out of its con- .taining strata and thrown on the shore by the action of the waves. It is manufactured into ornaments for the person, such as ear-pendants, bracelets, necklaces, and brooches, and into boxes, mouth-pieces for pipes, and han- dles for canes and paper-knives. As its weight is less than half that of an equal bulk of glass, this character, as well as its softness, affords an easy means of distinguishing it from imitations. The ornamental employment of marbles in the interior decoration of houses has already been mentioned under building-stones ; but, aside from this, a large use of mar- bles of fine texture and pleasing and varied colors is made in the ornamentation of articles of furniture and in sculpt- ure, one of the noblest of the fine arts. For the latter purpose marble is required which is of fine and even text- 370 APPLIED GEOLOGY. lire, free from any foreign minerals, and of a pure and uniform white color. Such marble is of rare occurrence, and hence the celebrity of some of the marbles of Italy and Greece, those of Carrara and Paros. What is called onyx marble is a translucent stalagmite, prettily banded with different light shades, and obtainable in masses of considerable size. It is a beautiful material for ornamental purposes, and may be wrought into many pleasing objects. Attention has recently been called to it by large specimens from Algiers and Mexico, exhibited at some of the World's Expositions. Alabaster, a compact, translucent variety of gypsum, and verd-antique marble, a rock composed of green serpentine and white calcite, are also used in ornamental work. Mention should also be made here of the porphyries, hard and tough varieties of rock, made up of a very fine- textured felspathic base inclosing well-defined crystals* usually of feldspar. Where the base and inclosed crystals are of pleasing and finely contrasted colors, as dark red, green, and white, this rock, from its susceptibility to high polish, has in all ages been an admired material for orna- mental objects, such as vases, caskets, columns, parts of furniture, and handles of knives. The antique red and green porphyries have an ancient celebrity. As porphyry is of volcanic origin, its geological position is naturally in dikes ; and material suitable for ornamental uses is more likely to occur in those which cut rocks of great geological antiquity. Gems. The minerals which, from their transparent brilliancy, their beauty of color, and their hardness, coup- led with their rarity, are held in esteem as gems are but few in number, not more than a dozen in all. They are the diamond, corundum, spinel, topaz, beryl, zircon, gar- net, tourmaline, spodumene, turquoise, and opal, some even of these holding but a doubtful place in a list of gems, although occasional examples of uncommon size and beau- ORNAMENTAL STONES AND GEMS. 371 ty sell at a considerable price. Of these, only the trans- parent varieties, and those of pleasing and uniform colors, have any considerable value as gems, some others being utilized on account of their hardness, like the black dia- mond and bort, and the gray and black corundum, or being valued merely as mineralogical specimens. With the exception of the opal, which occurs in nests and veins in volcanic rocks like the rhyolites, all the gems have their birthplace in the ancient crystalline rocks, although several are most commonly met with in alluvial deposits formed from the ground-up and assorted debris of such rocks. Where used as gems, all are transparent save turquoise, which is opaque, and opal, which is usually merely trans- lucent. They range in hardness from the diamond and corundum, which scratch all other minerals, to opal and turquoise, which may be scratched by quartz ; all but the last two can therefore be easily distinguished from their glass imitations by their superior hardness, since that of the brilliant variety of glass called strass or paste, from which imitation gems are made, is not more than 5 on the scale of hardness, while that of the softest gems is 6, and of quartz 7. Hardness is essential in gems, since, though entailing greater expense in cutting, it preserves their colors and polish undimmed for ages. A few of the gems are colorless, like the diamond, and occasionally the topaz and zircon ; but most of them present various clear shades of red, green, blue, and yellow ; and some of them, like corundum and beryl, afford gems of several different colors which bear different names. The carat, in which the weight of many precious stones is reckoned, is a con- ventional weight, equal, according to Ure, to about 3.88 grains troy, although sometimes used as no more than 3.1 grains. Gems are cut, according to their nature and shape, in four different styles, of which the brilliant consists of a truncated double pyramid, the truncated ends being octa- gons, and the sides made up of a combination of triangular 372 APPLIED GEOLOGY. and rhomboid or pentagonal facets ; the rose cut has a flat base surmounted by a pyramidal dome, made up usu- ally of twenty-four triangular facets ; the table has a rect- angular face and beveled edges ; and the en cabochon cut has a flat base and smooth, rounded dome. As is well known, the diamond is the most highly val- ued of the gems. This mineral, which is pure crystallized carbon, the same element which in other conditions con- stitutes charcoal and graphite, is the hardest of all known substances, readily scratching every other mineral and being scratched by none. The peculiar charm of the dia- mond lies in its singular brilliancy of luster, in which it as far surpasses all other gems as it does in hardness, and which depends on the great refractive and dispersive power that it exerts on the rays of light. The diamond is usually colorless, but has not unfrequently a slight tinge of color, of which yellow is the most common and least esteemed. A diamond of the first water is perfectly trans- parent and colorless, and free from spots or flaws, those of clear green and rose tints being also very highly prized. Diamonds are occasionally found of considerable size : the largest from South Africa weighed 308 carats, the largest from Brazil 254!- carats, and one is mentioned from India which is said to have weighed originally 900 carats. Those weighing more than twenty carats are rarely met with, the vast majority of those found being much smaller than this ; and they lose, on the average, about one half their weight in cutting and polishing operations which can be performed only by the aid of the powder of the diamond itself. The diamond has very rarely been found in any other than alluvial deposits made up probably of the debris of its original rocky matrix ; so that there has been much conjecture as to the nature of the formations in which it originated. In Brazil it is found in a peculiar rounded gravel of milky quartz, associated with coarse ferruginous sand, called by the miners cascalho. This may ORNAMENTAL STONES AND GEMS. 373 have been derived from a ferruginous conglomerate, or, more probably, it is thought, from a laminated and some- times slightly flexible quartzite called itacolumite, which belongs to the ancient crystalline series of that country. In India, where its mode of occurrence is said to be simi- lar to that in Brazil, a French geologist, M. Chaper, has recently found the diamond in situ, associated with corun- dum, in a matrix of rose-colored pegmatite, a variety of granite, the granitic rocks in the vicinity of the gems being traversed by veins of feldspar and epidotiferous quartz ; thus we have reliable information of one mode of original occurrence of this gem, if not the only one. The great diamond-producing regions of the world are three in num- ber, viz., the southern part of Hindostan, Brazil, and South Africa. The diamond region of the Indian Peninsula has been known from a remote antiquity, and from it have been derived most of the famous diamonds which are among the crown jewels of European sovereigns. The Brazilian diamond-fields are chiefly in the provinces of Minas-Geraes and Bahia, north of Rio Janeiro, though gems are found also in Parana, Goyaz, and Matto-Grosso. The black diamonds, or carbonados, mentioned in the pre- ceding chapter, are found in Bahia. The Brazilian prod- uct is said to amount to from forty to fifty pounds troy per annum. The latest discovered and most prolific re- gion is that of Griqualand and the Orange Free State in South Africa, of which Kimberley is the center, and which has been known only since 1867. The workings here ex- tend to the depth of some hundreds of feet, and the value of the product for 1881 is said to have been about $22,- 000,000. Besides these chief regions, diamonds are found in the Ural Mountains and in Borneo, and a few isolated occurrences have been noted in the United States in Georgia, North Carolina, Virginia, and California. Corundum, which ranks next to the diamond in hard- ness, is pure crystallized alumina, and, when occurring in IT 374 APPLIED GEOLOGY. transparent crystals of pure colors, yields gems which rank next to the diamond in value, and which receive different names in jewelry according to the colors that they present. Thus, the transparent blue corundum is called sapphire j the red, oriental ruby ; the green, oriental emerald; the violet, oriental amethyst j and the yellow, oriental topaz white stones also occurring which have passed for dia- monds. While the original matrix of these gems, like that of ordinary corundum, is in crystalline rocks, they are most frequently found in alluvial deposits. The finest stones are obtained mostly from the East Indies, some be- ing found also in Saxony, Bohemia, and France. Gems of the corundum species are found occasionally in North Carolina ;' also in southern Colorado, New Mexico, and Arizona, in sand with garnets. The spinel is a mineral composed of alumina and mag- nesia, with usually a little iron, is in hardness next below corundum, by which it may be scratched, and when used as a gem is of a fine rosy red color, though green and violet tints also occur. This gem, which is called by jewelers spinel ruby and balas ruby, is obtained chiefly from Siam and Ceylon, where it occurs in crystalline rocks, but most- ly in alluvial deposits derived from their wear. Spinel is also found in Sussex County, N. J., and Orange County, N. Y., sometimes in crystals of large size, but rarely if ever fit for jewelry. The topaz, which is a silicate of alumina containing a considerable proportion of fluorine, occurs in rhombic prisms with perfect cleavage across the prism, has a hard- ness about equal to that of spinel, and its color is most commonly yellow, but sometimes green, blue, and white. Like the other gems, it occurs in crystalline rocks, or in their cttbris. Those used in jewelry are mostly brought from Siberia, Kamchatka, and Brazil ; it is found also in Saxony and Bohemia, in Arizona and New Mexico, and on Pike's Peak ; the last-named locality, which has recent- ORNAMENTAL STONES AND GEMS. 375 ly been discovered, gives promise, it is said, of yielding a light-blue topaz which will be valuable for gems color- less and pellucid crystals being also found. Beryl, a silicate of alumina and glucina, which occurs in six-sided prisms, sometimes of great size, in the crystal- line rocks of some of the Eastern States, when transparent and of fine colors affords the valuable green gem, emerald, the sea-green or bluish aqua marine, and the yellow or light-green beryl. Its hardness is somewhat less than that of the spinel and topaz, by which it may be scratched. Crystals fit for jewelry are sometimes found in New England and in Alexander County, N. C., but the emerald and aqua marine are mostly obtained from New Granada, Brazil, Hindostan, and Siberia. Zircon, the silicate of zirconia, transparent red crystals of which constitute the gem called hyacinth, and colorless or smoky ones, the jargoon, although found in crystalline rocks at several localities in North Carolina, New York, and New England, has not yet afforded any valuable gems in the United States. These are derived from Ceylon, which furnishes so many other gems, from Siberia, Green- land, and some European localities. The hardness of zir- con is about the same as that of beryl, and exceeds that of quartz. The garnet, which is a silicate of quite variable com- position, is of about the same hardness as quartz ; and though of quite common occurrence in mica schist, horn- blende schist, and some other crystalline rocks, still, clear red crystals of proper size are held in some estimation as gems. Stones of the finest quality are found in south- ern Colorado, New Mexico, and Arizona, excellent ones being also obtained from Greenland and Ceylon. It is usually cut in thin tables, or low, rounded forms. The tourmaline is a variable compound of silica, alumi- na, and boracic acid, with several other substances. It oc- curs in prisms, usually black, of three, six, nine, or twelve 376 APPLIED GEOLOGY. sides, with a low, three-sided pyramidal end, has about the same hardness as quartz, and is found as a common acces- sory of various ancient crystalline rocks. It is occasion- ally met with in transparent crystals of clear yellow, green, blue, and pink colors, when it becomes a gem of consider- able value. Fine yellow gems of this mineral are obtained from Ceylon, and sold often as topaz. Paris, in Oxford County, Me., is a celebrated locality for tourmaline gems of various colors, yielding, it is said, more than two thou- sand dollars' worth per year ; and two or three other lo- calities in the vicinity of Paris give promise of yielding similar gem-stones. Hiddenite, or lithia emerald, a variety of spodumene, and composed of silica, alumina, and lithia, is a gem re- cently discovered at Stony Point, Alexander County, N. C., where it occurs in small open pockets in gneiss-rock, asso- ciated with emeralds and several other crystallized min- erals. The most valued gems are of a brilliant grass-green color, those of light-green and yellow colors as well as colorless being also found, but held in less esteem. Ac- cording to its discoverer, the gem has a brilliant cleav- age, and is somewhat harder than the emerald. The lo- cality is being diligently explored for the mineral, which is in good demand for cabinet specimens as well as for gems. Turquoise is a hydrous phosphate of alumina, opaque, of a delicate blue or bluish-green color, due to copper, and of a hardness inferior to that of quartz. Despite its in- ferior hardness and opacity, it has long been held in esteem as a gem, because of its pleasing color and the beautiful combinations that it makes when cut with a smooth, rounded surface and set with diamonds or pearls. It occurs in small, rounded masses, or in thin veinlets trav- ersing eruptive or crystalline rocks. The best has for ages been obtained from Khorassan, a province of Persia. Attention has recently been called to two localities of this ORNAMENTAL STONES AND GEMS. 377 mineral that were largely worked by the ancient Mexicans, among whom, at the time of the Spanish conquest, it was highly prized as a gem under the name of chalchihuitl, or chalchuite. One of these localities, showing old workings of vast extent, is in the Los Cerillos Mountains, twenty miles southeast of Santa Fe, and the other in Cochise County, Arizona. The mineral at both these localities is bluish green. It has also been found at a locality in south- ern Nevada of a rich blue color, disseminated in grains in a hard sandstone, which is polished and makes a beautiful mottled stone for jewelry. Opal is a peculiar, massive, uncrystalline form of quartz, containing a variable proportion of water, somewhat softer than crystalline quartz, by which it may be scratched, and also of a lower specific gravity, its weight rarely exceeding 2.2 that of water, while that of quartz is about 2.65. When used as a gem it is translucent, and usually of a milky color, and presents a vivid, iridescent play of colors, due to internal reflections with decomposition of the luminous rays, by microscopic laminae. (Zirkel, " Die mikrosko- pische Beschaffenheit der Mineralien," etc., p. 116.) To this charming opalescence, which is best displayed when the gem is cut with a smooth convex surface, it owes the high estimation in which it was held by the ancients not less than by modern nations. It occurs in small nests and thin veins traversing certain volcanic rocks. The precious opal, and the girasol, or fire opal, have not yet been found fit for jewelry in the United States. They are obtained from Hungary, Honduras, and Mexico, and to some ex- tent from the Faroe Islands. Besides the minerals here briefly described as precious stones, some others are occasionally used in jewelry, for example, chrysoberyl, kyanite, idocrase, and chrysolite ; of which it will be sufficient to say that the first named, which nearly equals corundum in hardness, is a valuable gem in the rare cases when it is transparent and free from 378 APPLIED GEOLOGY. flaws ; and that chrysolite is in some demand because of its olive-green tint. Although most of the gems are by nature singularly indestructible, still, from the comparative unfrequency of the occurrence of stones suitable for gems of the first qual- ity, it may be doubted whether the increase in the supply more than keeps pace with the increase in wealth and lux- ury, and with the consequent disposition to acquire precious stones. Even the recent large increase in the supply of diamonds, resulting from the discoveries in South Africa, does not appear yet to have produced any perceptible effect in diminishing their price as gems. The demand for several of the precious stones is indeed subject to the ca- prices of fashion, like that for most things which are objects of taste and preference rather than of necessity. Hence occur temporary fluctuations in their price, which bear little or no relation to variations of supply. Yet, on the whole, these minor fluctuations serve but to accentuate more sharply the fixedness and constancy of the passion for the more indestructible gems, showing how unchange- able is the principle of human nature in which it has its roots. INDEX. Abrasive substances, 352. Accessibility of deposits, 46. Agate, 367. Age of rocks, 36, 40, 42. Agordo, pyrites, 299. Agriculture, geologic relations, 101. Alabaster, 370. Alkalies, geological sources, 309. Almaden, mercury, 259. Alston Moor, 246. Aluminium, 290. Alum shales, 315. sources, 315. uses, 316. Alunite, 315. Amber, 369. Amethyst, 366. Oriental, 374. Amphibolite, 22. Amygdaloidal texture, 14. Analyses of soils, 116. Ancient workings of deposits, 214. Anglesite, 242. Anthracite coal, 19, 137. Anticlinal, 30. Anti-friction hornstone, 363. Antimony, 288. Aphanitic, 14. Aplite, 23, 325. Aqua marine, 375. Archaean rocks, where found, 81. Arenaceous, 8. Argillaceous, 8. sandstone, 15. Arrangement of rocks, 27. vein contents, 201. Arsenic, 292. Arsenical ores, 185. Artesian wells, 58, 60. Asbestus, needful qualities, 344, 345. uses, 346. Ash in coals, 156. Ashes of plants, analyses, 113. Asphalt, 352. Associations of ores, 186. Atlanta vein, Idaho, 267. Augite, 6. Australia, 238, 256, 276, 280. Banca, tin, 256. Banded structure of veins, 202. Barytes, 361. Basalt, 23, 350. Basic lining of converters, 229. Basins of coal, 147. Bassick mine, Col, 202, 266, 274. Bauxite, 290. Beauty of building-stones, 75. Bedded deposits of ores, 189, 191. structure, 48. Belgium, zinc, 251. Beryl, 375. Billiton, tin, 256. Bismuth, 289. Bituminous coal, 21, 138, 140. Black-band ore, 17, 143, 225. Black Hills, 255, 279. Blanket lodes, 195. Blende, 248. Block coal, 139. Bonanzas, 203. Borax, occurrence and uses, 312, 314. Bornite, 232. INDEX. Bort, 356. Breccia, 16. Brecciated vein structure, 202. Brick clays, 92, 93. kiln, perpetual, 95. Brown coal, 139. Bruce mine, 233. Building -stones, desirable quali- ties, 66. choice of, 78. distribution of, 80. essential qualities, 66, 67. of America, 80. Bull Domingo mine, 266. Butte City, 233, 235. Calamine, 248. Calaverite, 274. Calcareous, 8. tuff, 16. Calciferous period, hydraulic lime, 99. Calcite, 5, 7. California, 258, 278, 313. Caking coal, 138, 140. Cameos, 367. Canadian period, limestone, 89. Cannel coal, 20, 139, 140. Capelton, Quebec, 237. Carat, 371. Carbonate ores, 185. Carbons, 356, 373. Carboniferous, subdivisions, 148. Carnallite, 289. Carnelian, 367. Cassiterite, 254. Cement, hydraulic, 19, 97, 359. Cerussite, 242. Chalcedony, 367. Chalchuite, 377. Chalcocite, 232. Chalcopyrite, 231. Chalk, 19, 359. Chamber deposits, 189, 195. Characteristics of fissure veins, 203. Chemical manufacture, geological materials of, 296. Chemical sediments, 16. Chemung period, sandstone, 88. Cherry coal, 20, 138, 140. Chili, copper, 238. Chimneys of ore, 203. Chloride ore, 185. Chlorite, 7. schist, 22. Chromium, 290. Chrysocolla, 233. Classes of rocks, table, II. Clay, 8, 92, 320. ironstone, 17, 225. Clay County, Ala., tin, 255. Clays, origin, 325. pottery, 321, 326. properties, 322. Cliff mine, 233. Clifton District, Arizona, 236. Clinometer, 29. Coal, adaptation to uses, i5i. analyses, 141. American regions, 149, 156. foreign regions, 153. fuel value, 159. geologic associations, 142. geologic horizons, 148, 149. impurities, 156. kinds, 19, 137. origin, 19, 135. pipes, 144. product of 1881, 155. relative thickness, 146. Cobalt, 288. Coke, 162. Cold-shortness of iron, 158, 228. Colorados, 209. Coloring for glass and pottery, 329, 332. Columbus Marsh, borax, 313. Columnar structure, 13. Commern, 193, 242, 246. Compact texture, 14. Complications of ores, 186. Comstock vein, 200, 203, 205, 267. Concentration of ores, 188. Concrete for paths, 351. Concretionary structure, 13. Conditions of ore deposits, 211, 212. Conformability of strata, 33. Conglomerate, 16, 348. Consolidation, means of, n, 67, 70. Contact deposits, 195. veins, 205. Cool limes, 19, 96. INDEX. 381 Copper, forms of deposit, 233. glance, 232. ores, 231. production, 239. uses, 240. Copper Queen mine, 233, 236. Corniferous period, limestone, 90. Cornwall, tin, 255, 256. Corundum, 356, 373. Country rock, 36, 196, 199. Cretaceous coals, 149, 151. Cryolite, 290. Cuba, copper, 237. Cuprite, 232. Denudation, 33. Derbyshire, lead, 246. Derbyshire spar. See Fluorite, 368. Diamond, 356, 372. Diabase, 23. Dikes, 35. Dip of rocks, 29. effect on accessibility, 46. on ease of extraction, 48. Diorite, 23. Dinas brick (silicious brick), 337. Distribution of ore deposits, 211. of ores in deposits, 203. Dolerite, 23. Dolomite, 7, 19. Drainage, agricultural, 127. dependence on structure, 64. sanitary, 132. Dressing of stone, effects, 77. Driven wells, 57. Druses, 202. Ducktown copper, 237. Durability of building-stones, 70. Earth-worms, agency in soils, 108. Economic geology defined, 44. Elasticity in building-stones, 68. Emerald, beryl, 375. Oriental, 374. Emery, 356, 357. wheels, 357. England, 153, 238, 246, 251, 255- Erroneous ideas regarding ore de- posits, 219. Eureka District, Nev., 210, 244. Excavations, 49. Facility of dressing building- stones, 76. Fahlun, Sweden, pyrites, 299. False or current bedding, 28. Faults, 31, 206, 297. effect on accessibility, 47. Feldspar, 6, 328, 367. Felsite, 23. Ferruginous, 8. Fertilizers, geological, 118. Fertilizing ingredients of soils, 114, 116. Fictile materials, 319. Filling of veins, etc., 200. Fire-clay under coal-seams, 143. Fire-clays, composition, 335, 336. tests of, 335. uses, 337. Fire opal, 377. Fire-stones, 338. Fissures, how formed, 197, 199. Fissure-veins, 189, 197. Flagging-stones, 16, 351. Flats, 195. Floating brick, 339. Flucan, 204. Fluor-spar, fluorite, 368. Foliation, 12. Foot-wall, 199. Forms of ore deposits, 189. Fossils, 28. use of, 38. Foundations, dependence on structure, 51. Foundry facings, 364. Franklin, N. J., 249, 251. Franklinite, 249. Freestone, 16. French chalk, 359. Fuels, mineral, 135. Galena, 241. Galena District, 242, 244, 250. Gangues, 183, 187. Canister, 338. Garnet, 375. Gas, natural, 166, 180. Gems, 365, 366, 370. forms in which cut, 371. Genesee and Huron shale, 180. Geology, practical purposes, I. theoretic objects, I. Georgetown, Col., 243, 249, 266. 382 INDEX. Germany, Commern, lead, 246. Gilpin County, Col., gold, 274, 279. Girasol, 377. Glacial agencies in soils, 105. materials, nature, etc., 107. Glass, 330, 333. Glazes of pottery, 329. Globe, Arizona, 233, 236. Gneiss, 20. Gold Hill, Col., tellurides, 274. Gold, extraction of, 282. modes of occurrence, 274. production, tables, 277, 278. regions, 277. surface appearance of deposits, 210. . uses of, table, 281, 282. value, table, 282. Goslar, pyrites, 233, 299. Gossan, 209. Gouge, 204. Granite, 22, 26, 82. Granitic building-stones, distribu- tion, 8 1. Granitoid texture, 14. Granular texture, 14. Granulite, 23, 332. Graphic materials, 358. Graphite, plumbago, 339, 358, 360, 362. Gravel, 15, 348. Gray-band, sandstone, 88, 353. Gray copper, tetrahedrite, 186, 233. Great Meadows, N. J., drained, 127, 132. Greisen, 22. Grindstones, 353, Grit, 16. Guano, 124. Gypsum, 17, 124. Hade of veins, 32. Hanging-wall, 199. Health, geological conditions of, 129. Heavy spar, 361. Hematite, 18, 224. Hiddenite, 376. Honestone, 354. Hornblende, 6. Hornblendic gneiss, 21. Hornblende schist, 22. Horn Silver mine, 243, 267. Hornstone, anti-friction, 363. Horses or riders of veins, 200, 204, 206. Hot limes, 19, 96. Huron shale, 180. Hyacinth, 375. Hydraulic lime, 19, 97. geologic occurrence, 98. Hydro-mica schist, 21. Idria, mercury, 259. Igneous rocks, II, 22. Illuminating substances, 165. Impregnations, 189, 192, 257, 275. Iridium, 293. Iron ores, 17, 224. chief geologic horizons, 226. forms of deposit, 225. paints, 361. production, 1882, 229. Irregularities in width of veins, 199, 219. Itacolumite, 373. Jade, 368. Japan, 270, 280. Jargoon, 375. Jasper, 367. Jet, 369. Johnstown cement, 99. Jointed structure, 48. Joints, 13. Joplin and Granby lead and zinc, 244, 250. Kainite, 310. Kaluscz, 309. Keweenaw Point, 233, 234. Key for determining rocks, 24. Key rocks, 145. Kidney ore, 17, 225. Kieserite, 310, 316. Kimberley, S. Africa, 373. Labradorite, 367. Laccolites, 34. Lake Superior copper, 234. Lamination, 12, 49. Lancaster Gap mine, 286. Lapis lazuli, 368. Lead, chief uses, 247. forms of deposit, 242. ores, 241. product, 1882, 245, 246. INDEX. 383 Leaders or stringers of veins, 203. Leadville, 195, 210, 243, 266. Lignite, 139, 140. Lime, 96, 119, 342. Limestone, 18, 19, 89, 92. Limonite, 18, 224, 225. Liparite, 23. Lithographic limestone, 359. Lode, 196, 197. Los Cerillos Mountains, 377. Louisville cement, 99. Lower Helderberg limestone, 90, 99. Lubricators, mineral, 362. Magnesia, 316, 342. Magnesian limestone, 19. Magnesite, 289, 316. Magnesium, 289. Magnetite, 18, 224. Malachite, 232, 368. Manganese, 291. Mansfeld, copper, 234, 238. Marble, 19, 84, 369. Marls, calcareous, 120. greensand and analyses, 120, 121. Mass deposits, stocks, 189, 194. Massive rocks, 9. structure, 12. Materials of physical application, 347- Medina sandstone, 87, 350. Mercury, three regions of, 257. Mesozoic sandstone, 88. Metamorphic ore deposits, 195. rocks, 10, 20. Mexico, 255, 268. Mica, 6, 343. schist, 21. Millstones, 355. Milwaukee cement, 99. Mine la Motte, 286. Mineral lubricators, 362. Minette, 22. Mispickel, 293. Missouri, 244, 250, 360. Molding sand, 363. Molybdenite, 293. Monoclinal, 30. Montezuma Marsh, N. Y., 127, 132. Moonstone, 367. Mortar, 95. Moss agate, 367. Muck, 118. Nagyagite, 274. Nephrite or jade, 368. New Almaden, 258. New Mexico, 234, 236, 267. Niagara limestone, 90, 92. Nickel, 286. Nitre, 309. Nitrogen from coal and shale, 124, 181. Normal faults, 206. Nuggets of gold and platinum, 277, 284. Ochre, iron paint, 361. Ohio lower coal measures, 145. Oil sands of Bradford, 166, 170. Oil Creek, Pa., 168. Warren, etc., Counties, Pa., 170. West Va. and Ohio, 171. Oil territory of Baku, 171. Burmah, 172. California, 171. Oil wells, how bored, 173. how operated, 176. Oil shales, 180. Old Dominion mine, 236. Ontario mine, 267. Onyx, 367. marble, 16, 370. Oolite, 16. Opal, 371, 377. Ophiolite, 19. Ores, defined, 183. agents of mineralization, 184. Ore chimneys, 203. deposits, 184. Ore Knob, N. C., 237. Organic sediments, 18. Origin of ore deposits, 188. Ornamental stones, 365, 366. Oscuras Mountains, 234. Outcrop, 32. Oxide ores, 184. Parker's cement, 99. Paving-stones, 349. Pay streaks, 202. Peabody mine, Arizona, 236. INDEX. Pegmatite, 23. Periods of rocks, table, 42. Petroleum, nature, etc., 165. refining and use, 177. Petzite, 274. Phosphates, mineral, 123. Phosphorus in coal, 158. Pigments, mineral, 360. Pike's Peak, topaz, 374. Pittsburg coal seam, 144. Placers, 190, 275. Platinum, 284. Plumbago. See Graphite. Plutonic rocks, n. Porphyries, ornamental, 370. Porphyritic texture, 14. Portland cement, 99. Positions of strata, 29. Potash, 126, 309. Potsdam sandstone, 87, 331, 350. Pottery clays, 320, 323. Proportions of precious metals in ores, 187. Prospecting, 213. Pumice, 358. Pyrite, 7, 296. qualities needed, 300. uses, 299. Pyrolusite, 292. Pyrophyllite, 359. Pyroschists, 180. Pyroxene, 6. Quartz, 5, 21, 328, 366. Quartzite, 15, 21. Quasi-veins, chambers, 189, 195, 251, 275. Red chalk, 359. Red-shortness of iron, 158, 228. Regions of vein-fissures, 198. of ore deposits, 211, 213. Reopening of veins, 204. Reverse faults, 207. Rhyolite, 23, 25. Rift of granites, 83, 349. Rio Tinto, Spain, 233, 238, 298. Road materials, 347. Rocks, condition of components, 8. crystalline, 8, 10. mineral components, 4. sedimentary, 9, 15. Rocks, stratified, 9. Rock masses, arrangement, 27. Rosendale cement, 99. Ruby, balas, and spinel, 374. Ruby, Oriental, 374. Salometer, 305. Salt and uses, 17, 125, 304, 308. Salt, forms of deposit, 304. geological horizons, 306. Sampling ores, 216. Sand, 15, 95, 330, 357. Sand-paper, 357. Sandstone, 15, 86, 357. Sanitation, geologic considerations, 129. San Juan region, 236, 243, 266. Sapphire, 374. Sardonyx, 367. Schistose structure, 12. Seam, 12. Sedimentary rocks, 9, 15. Segregated veins, 36, 196. Selvage, 204. Semi-anthracite coal, 138, 140. Semi-bituminous coal, 138, 140. Serpentine, 8, 22. Shale, 13, 16. Shingle, 15. Sicily, 303. Siderite, 17, 225. Silesia, 246, 251. Silicate ores, 185. Silicious, 8. Silver, American regions, 265. foreign regions, 268. forms of deposit, 264. ores, 260. production, 268, 270. uses, 271, 282. Silver Islet, 269. Silver King mine, 266. Silver Reef, 265, 267. Sinter, silicious, 17. Slate, 85. Slate Range Marsh, borax, 314. Slaty structure, 13. Slickensides, 32, 204. Smithsonite, 248. Soapstone, 343, 359. Socorro Mountains, N. M., 268. Soda, 310. Soils, amendments, in. INDEX. 385 Soils, composition, 101. from various rocks, 103. of disintegration, 103. of transport, 104, 109. origin, 102. physical characters, no. Solenhofen, 360. Spain, 238, 245, 259, 270. Spathic iron, 17, 225. Sperenberg, 306, 307. Sphalerite, 248. Spinel, 374. Spirifer, 39. Splint coal, 138, 140. Springs, 52. Stalactite and stalagmite, 16. Stassfurt, 126, 306, 310. Steatite, 359. Ste. Genevieve County, Mo., 234, 237- Stocke, 35, 194. Stockworks, 189, "95. St. Peter's sandstone, 331. Strass, 371. Stratification, n. Stratified rocks, 27. Stream tin, 255. Strength of building-stones, 67. of stones, table, 69. Strike of rocks, 30. Strontium, 317. Structure, economic relations, 45, 48, 49. of rocks, n. Sub-carboniferous limestones, 91. sandstones, 88. Subsoils, 107, 127. Sulphide ores, 184. Sulphur in coal, 158. Sulphur, origin and uses, 302, 303. Sunstone, 367. Superposition, test of relative age, 37- Surface appearance of ores, 208. Syenite, 23, 26. Syenitic granite, 22, 26. Synclinal, 31. Sylvanite, 274. Sylvite, 310. Talc, 7, 362. Talcose schist, 21. I Tell's Marsh, borax, 313. 1 Telluride ores, 185. Temperature changes, effects on building-stones, 73, 74. Tenorite, 232. Tetrahedrite, 186, 233. Texture of rocks, 14. Tin, 254. Titanium, 318. Tombstone District, 266. Topaz, 374. Torpedoes in oil-wells, 177. Tourmaline, 375' Trachyte, 23, 26. Transportation, importance of, 217. Travertine, 16. Trenton limestone, 89. Triassic, coal-fields, 149. Trilobites, 39. Tripoli, 358. Tungsten, 294. Turquoise, 371, 376. Ultramarine, 368. Umber, 361. Unconformability of rocks, 33. Under-clays of coals, 143. Unstratified rocks, 34. Uplifts, effect on accessibility, 47- Uranium, 294. Utica slate, oil shale, 180. Value of ore deposits, 215, 218. Veins, 35, 196. Vein-stone, 183, 187. Verd - antique marble, 19, 84, 370. Vermont, 237, 354. Vitreous texture, 14. Vugs, i.e., druses, 202. Water in coals, 157. Water-lime group, 99. Water supply, 52, 129. Wells, 55. Whetstones, 354. Whiting, 360. Wieliczka, 306, 307. Willemite, 248. Wolfram, 254, 294. 386 INDEX. Wood's Mine, Pa., 291. Wood River region, 245. Working ore deposits, costs, 217. Wyoming, 237, 311. Wythe County, Va., 245, 250. Zinc, American localities, 250. foreign centers, 251. ores, 247. product and uses, 252. Zincite, 248. Zircon, 375. THE END. APPLETONS' SCIENCE TEXT-BOOKS. D. 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