Qforttell Hittaeraitg SItbrarg Dtljara. Jfem gnrk BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND THE GrPT OF HENRY W. SAGE 1891 Cornell University Library Q 171.J75 1915 The birth-time of the world and other sc 3 1924 012 237 909 Cornell University Library The original of tliis bool< is in tlie Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924012237909 THE BIRTH-TIME OF THE WORLD AND OTHER SCIENTIFIC ESSAYS THE BIRTH -TIME OF THE WORLD AND OTHER SCIENTIFIC ESSAYS J. JOLY, M.A., Sc.D., F.R.S., FROFSSSOR OF GEOLOGY AND MINERALOGY IN THE UNIVERSITY OF DUBLIN E. P. DUTTON AND COMPANY 68i FIFTH AVENUE NEW YORK L -^ [All right* reserved] CONTENTS PAGE I. The Birth-time of the World - - i II. Denudation ------ 30 III. The Abundance of Life - - - - 60 IV. The Bright Colours of Alpine Flowers 102 V. Mountain Genesis 116 VI. Alpine Structure 146 VII. Other Minds than Ours ? - - - 162 VIII. The Latent Image ----- 202 IX. Pleochroic Haloes ----- 214 X. The Use of Radium in Medicine - - 244 XI. Skating ------- 260 XII. A Speculation as to a Pre-material Universe ------ 288 LIST OF ILLUSTRATIONS Plate I. — ^Lake of Lucerne, looking West FROM Beunnen - - - - Frontispiece „ II. — " Uplifted from the Seas." Cliffs OF THE Titus, Switzerland - to face p. 4 ,, III. — An Alpine Torrent at Work — Val D'H^rens, Switzerland - „ 31 IV. — Earth Pillars— Val D'H^rens, - „ 34 „ V. — " Scenes of Desolation." The Weisshorn seen from Bella Tola, Switzerland - - - ,,40 „ VI. — ^Alluvial Cone — Nicolai Thal, Switzerland - - - - ,, 50 Moraine on Aletsch Glacier Switzerland. VII. — ^In the Region of Tre Croci ; Dolomites. The Rothwand seen from Monte Piano - - ,, 60 „ VIII. — Firs Assailing the Heights of the Madera ner Thal, Swit- zerland ----- ..73 ,, IX. — ^LiFE near the Snow Line ; the Bog-Cotton in Possession. Near THE TsCHINGEL PaSS, SWITZER- LAND ------ „ 80 „ X. — ^The Joy of Life. The Ampezzo Thal ; Dolomites - - - ,,93 „ XI. — " Pines Solemnly Quiet." DOs- sisTocK ; Maderaner Thal - ,, 100 ,, XII. — ^Alpine Flowers in the Valleys „ 105 „ XIII. — Alpine Flowers on the Heights ,, 106 „ XIV. — Mountain Solitudes ; Val de Zinal. From Left to Right : Rothhorn ; Besso ; Ober- Gabelhorn ; Matterhorn ; Pic DE Zinal (through Cloud) ; Dent Blanche - - - - „ 116 LIST OF ILLUSTRATIONS Plate XV. — Sector of the Earth - - - to face p. ii8 Rise of Isogeotherms into a Deposit evolving Radioactive Heat. J, XVI. — " The Mountains Come and Go." The Dent Blanche seen from THE SaSSENEIRE - - - ,, I33 „ XVII. — Diagrammatic Sections of the Himalaya ----- „ 140 „ XVIII. — Residues of Denudation. The Matterhorn seen from the Summit of the Zinal Rothhorn ,, 148 „ XIX. — The Folded Rocks of the Matter- horn, seen from near HShbalm. Sketch MADE in 1906 - - ,, 156 tl XX. — Schiaparelli's Map of Mars of 1882, AND Additions (in Red) of 1892 ----- ,, 166 „ XXI. — Globe of Mars showing Path of In-falling Satellite - - „ 188 „ XXII. — Canals Mapped by Lowell com- pared with Canals formed by In-falling Satellites - - ,, 192 „ XXIII. — Haloes in Mica ; Co. Carlow - ,, 224 Halo in Biotite Contained in Granite. „ XXIV. — Radium Halo, much Enlarged - ,, 228 Thorium Halo and Radium Halo IN Mica. „ XXV. — Halo Round Capillary in Glass Tube ------ „ 230 Haloes round Tubular Passages IN Mica. „ XXVI. — Aletsch Glacier, Switzerland - „ 282 ), XXVII. — ^The Middle Aletsch Glacier JOINING the Great Aletsch Glacier ----- ,, 285 Glaciers of the Lauterbrunnen Thal. „ XXVIII. — Perched Block on the Aletsch Glacier ----- ,, 286 Granite Erratic near Round- wood, Co. Wicklow ; now broken up and removed. And Fifteen Illustrations in the Text, PREFACE This volume contains twelve essays written at various times during recent years. Many of them are studies contributed to Scientific Reviews or delivered as popular lectures. Some are expositions of views the scientific basis of which may be regarded as estabHshed. Others — the greater number — may be described as attempting the solution of problems which cannot be approached by direct observation. The essay on The Birth-time of the World is based on a lecture delivered before the Royal Dublin Society. The subject has attracted much attention within recent years. The age of the Earth is, indeed, of primary importance in our conception of the longevity of planetary systems. The essay deals with the evidence, derived from the investigation of purely terrestrial phenomena, as to the period which has elapsed since the ocean condensed upon the Earth's surface. Dr. Becker's recent addition to the subject appeared too late for inclusion in it. He finds that the movements (termed isostatic) which geologists recognise as taking place deep in the Earth's crust, indicate an age of the same order of magnitude PREFACE as that which is inferred from the statistics of denudative history. 1 The subject of Denudation naturally arises from the first essay. In thinking over the method of finding the age of the ocean by the accumulation of sodium therein, I perceived so long ago as 1899, when my first paper was published, that this method afforded a means of ascer- taining the grand total of denudative work effected on the Earth's surface since the beginning of geological time ; the resulting knowledge in no way involving any assumption as to the duration of the period comprising the denudative actions. This idea has been elaborated in various publications since then, both by myself and by others. " Denudation," while including a survey of the subject generally, is mainly a popular account of this method and its results. It closes with a reference to the fascinating problems presented by the inner nature of sedimentation : a branch of science to which I endeavoured to contribute some years ago. Mountain Genesis first brings in the subject of the geological intervention of radioactivity. There can, I believe, be no doubt as to the influence of transforming elements upon the developments of the surface features of the Earth ; and, if I am right, this source of thermal energy is mainly responsible for that local accumulation of wrinkling which we term mountain chains. The ^ Bull. Geol. Soc. America, vol. xxvi, March 191 5. xii PREFACE paper on Alpine Structure is a reprint from " Radio- activity and Geology," which for the sake of complete- ness is here included. It is directed to the elucidation of a detail of mountain genesis : a detail which enters into recent theories of Alpine development. The weak- ness of the theory of the " horst " is manifest, however, in many of its other applications ; if not, indeed, in all. The foregoing essays on the physical influences affecting the surface features of the Earth are accompanied by one entitled The Abundance of Life. This originated amidst the overwhelming presentation of life which confronts us in the Swiss Alps. The subject is sufficiently inspiring. Can no fundamental reason be given for the urgency and aggressiveness of life ? Vitality is an ever-extending phenomenon. It is plain that the great principles which have been enunciated in explanation of the origin of species do not really touch the problem. In the essay — which is an early one (1890) — ^the explanation of the whole great matter is sought — and as I believe found — in the attitude of the organism towards energy external to it ; an attitude which results in its evasion of the retardative and dissipatory effects which prevail in life- less dynamic systems of all kinds. Other Minds than Ours ? attempts a solution of the vexed question of the origin of the Martian " canals." The essay is an abridgment of two popular lectures on the subject. I had previously written an account of my views which carried the enquiry as far as it was in xiii PREFACE my power to go. This paper appeared in the " Trans- actions of the Royal Dubhn Society, 1897." The theory put forward is a purely physical one, and, if justified, the view that intelligent beings exist in Mars derives no support from his visible surface features ; but is, in fact, confronted with fresh difficulties. Pleochroic Haloes is a popular exposition of an incon- spicuous but very beautiful phenomenon of the rocks. Minute darkened spheres — a microscopic detail — appear everywhere in certain of the rock minerals. What are they ? The discoveries of recent radioactive research — chiefly due to Rutherford — give the answer. The mea- surements applied to the little objects render the ex- planation beyond question. They turn out to be a quite extraordinary record of radioactive energy ; a record accumulated since remote geological times, and assur- ing us, indirectly, of the stability of the chemical elements in general since the beginning of the world. This assurance is, without proof, often assumed in our views on the geological history of the Globe. Skating is a discourse, with a recent addition supporting the original thesis. It is an illustration of a common experience — the explanation of an unimportant action involving principles the most influential considered as a part of Nature's resources. The address on The Latent Image deals with a subject which had been approached by various writers before the time of my essay ; but, so far as I know, an explanation xiv PREFACE based on the facts of photo-electricity had not been attempted. Students of this subject will notice that the views expressed are similar to those subsequently- put forward by Lenard and Saeland in explanation of phosphorescence. The whole matter is of more practical importance than appears at first sight, for the photo- electric nature of the effects involved in the radiative treatment of many cruel diseases seems to be beyond doubt. It was in connection with photo-electric science that I was led to take an interest in the application of radio- activity in medicine. The lecture on The Use of Radium in Medicine deals with this subject. Towards the con- clusion of this essay reference will be found to a practical outcome of such studies which, by improving on the methods, and facilitating the application, of radioactive treatment, has, in the hands of skilled medical men, already resulted in the alleviation of suffering. Leaving out much which might well appear in a pre- fatory notice, a word should yet be added respecting the iUustrations of scenery. They are a small selection from a considerable number of photographs taken during my summer wanderings in the Alps in company with Henry H. Dixon. An exception is Plate X, which is by the late Dr. Edward Stapleton. From what has been said above, it will be gathered that these illustrations are fitly included among pages which owe so much to Alpine inspiration. They illustrate the XV PREFACE subjects dealt with, and, it is to be hoped, they vdll in some cases recall to the reader scenes which have in past times influenced his thoughts in the same manner ; scenes which in their endless perspective seem to reduce to their proper insignificance the lesser things of life. My thanks are due to Mr. John Murray for kindly consenting to the re-issue of the essay on The Birth-time of the World from the pages of Science Progress ; to Messrs. Constable & Co. for leave to reprint Pleochroic Haloes from Bedrock, and also to make some extracts from Radioactivity and Geology ; and to the Council of the Royal Dublin Society for permission to republish certain papers from the Proceedings of the Society. Iveagh Geological Laboratory, Trinity College, Dublin. July, 1915. THE BIRTH-TIME OF THE WORLD ^ Long ago Lucretius wrote : " For lack of power to solve the question troubles the mind with doubts, whether there was ever a birth-time of the world and whether likewise there is to be any end." " And if " (he says in answer) " there was no birth-time of earth and heaven and they have been from everlasting, why before the Theban war and the destruction of Troy have not other poets as well sung other themes ? Whither have so many deeds of men so often passed away, why live they no- where embodied in lasting records of fame ? The truth methinks is that the sum has but a recent date, and the natiire of the world is new and has but lately had its commencement ."* Thus spake Lucretius nearly 2,000 years ago. Since then we have attained another standpoint and found very different limitations. To Lucretius the world com- menced with man, and the answer he would give to his questions was in accord with his philosophy : he would date the birth-time of the world from the time when 1 A lecture delivered before the Royal Dublin Society, Febru- ary eth, 1914. Science Progress, vol. ix., p. 37. ' De Rerum Natura, translated by H. A. J. Munro (Cambridge, 1886). THE BIRTH-TIME OF THE WORLD poets first sang upon the earth. Modern Science has along with the theory that the Earth dated its beginning with the advent of man, swept utterly away this beauti- ful imagining. We can, indeed, find no beginning of the world. We trace back events and come to barriers which close our vista — barriers which, for all we know, may for ever close it. They stand like the gates of ivory and of horn ; portals from which only dreams proceed ; and Science cannot as yet say of this or that dream if it proceeds from the gate of horn or from that of ivory. In short, of the Earth's origin we have no certain knowledge ; nor can we assign any date to it. Possibly its formation was an event so gradual that the beginning was spread over immense periods. We can only trace the history back to certain events which may with consider- able certainty be regarded as ushering in our geological era. Notwithstanding our limitations, the date of the birth- time of our geological era is the most important date in Science. For in taking into our minds the spacious history of the universe, the world's age must play the part of time-unit upon which all our conceptions depend. If we date the geological history of the Earth by thousands of years, as did our forerunners, we must shape our ideas of planetary time accordingly ; and the duration of our solar system, and of the heavens, becomes comparable with that of the dynasties of ancient nations. If by millions of years, the sun and stars are proportionately venerable. If by hundreds or thousands of millions of 3 THE BIRTH-TIME OF THE WORLD years the human mind must consent to correspondingly vast epochs for the duration of material changes. The geological age plays the same part in our views of the duration of the universe as the Earth's orbital radius does in our views of the immensity of space. Lucretius knew nothing of our time-unit : his unit was the life of a man. So also he knew nothing of our space-unit, and he marvels that so small a body as the sun can shed so much heat and light upon the Earth. A study of the rocks shows us that the world was not always what it now is and long has been. We live in an epoch of denudation. The rains and frosts disintegrate the hills ; and the rivers roll to the sea the finely divided particles into which they have been resolved ; as well as the salts which have been leached from them. The sedi- ments collect near the coasts of the continents ; the dissolved matter mingles with the general ocean. The geologist has measured and mapped these deposits and traced them back into the past, layer by layer. He finds them ever the same ; sandstones, slates, limestones, etc. But one thing is not the same. Life grows ever less diversified in character as the sediments are traced downwards. Mammals and birds, reptiles, amphibians, fishes, die out successively in the past ; and barren sediments ultimately succeed, leaving the first beginnings of life undecipherable. Beneath these barren sediments lie rocks collectively differing in character from those above : mainly volcanic or poured out from fissures in 3 THE BIRTH-TIME OF THE WORLD the early crust of the Earth. Sediments are scarce among these materials.^ There can be little doubt that in this underlying floor of igneous and metamorphic rocks we have reached those surface materials of the earth which existed before the long epoch of sedimentation began, and before the seas came into being. They formed the floor of a vaporised ocean upon which the waters condensed here and there from the hot and heavy atmosphere. Such were the probable conditions which preceded the birth-time of the ocean and of our era of life and its evolution. It is from this epoch we date our geological age. Our next purpose is to consider how long ago, measured in years, that birth-time was. That the geological age of the Earth is very great appears from what we have already reviewed. The sediments of the past are many miles in collective thick- ness : yet the feeble silt of the rivers built them all from base to summit. They have been uplifted from the seas and piled into mountains by movements so slow that during all the time man has been upon the Earth but little change would have been visible. The mountains have again been worn down into the ocean by denudation and again younger mountains built out of their redeposited materials. The contemplation of such vast events 1 For a description of these early rocks, see especially the monograph of Van Hise and Leith on the pre-Cambrian Geology of North America (Bulletin 360, U.S. Geol. Survey). Plate II. UPLIFTED FROM THE SEAS. CLIFFS OF THE TIILIS. Facing p. 4. THE BIRTH-TIME OF THE WORLD prepares our minds to accept many scores of millions of years or hundreds of millions of years, if such be yielded by our calculations. The Age as Inferred from the Thickness of the Sediments The earliest recognised method of arriving at an estimate of the Earth's geological age is based upon the measure- ment of the collective sediments of geological periods. The method has undergone much revision from time to time. Let us briefly review it on the latest data. The method consists in measuring the depths of all the successive sedimentary deposits where these are best developed. We go all over the explored world, recognising the successive deposits by their fossils and by their stratigraphical relations, measuring their thick- ness and selecting as part of the data required those beds which we believe to most completely represent each formation. The total of these measurements would tell us the age of the Earth if their tale was indeed complete, and if we knew the average rate at which they have been deposited. We soon, however, find difficulties in arriving at the quantities we require. Thus it is not easy to measure the real thickness of a deposit. It may be folded back upon itself, and so we may measure it twice over. We may exaggerate its thickness by measuring it not quite straight across the bedding or by unwittingly in- cluding volcanic materials. On the other hand, there 5 THE BIRTH-TIME OF THE WORLD may be deposits which are inaccessible to us ; or, again, an entire absence of deposits ; either because not laid down in the areas we examine, or, if laid down, again washed into the sea. These sources of error in part neutralise one another. Some make our resulting age too long, others make it out too short. But we do not know if a balance of error does not still remain. Here, however, is a table of deposits which summarises a great deal of our knowledge of the thickness of the strati- graphical accumulations. It is due to SoUas.^ Feet. Recent and Pleistocene - - - 4,000 Pliocene - . . . . 13,000 Miocene _ - . - . 14,000 Oligocene ----- 12,000 Eocene - - . - - 20,000 Upper Cretaceous - - - - 24,000 Lower ,, _ _ - - 20,000 Jurassic ----- 8,000 Trias - - - - - - iy,ooo Permian ----- 12,000 Carboniferous - . - - 29,000 Devonian ----- 22,000 Silurian - ... - 1^,000 Ordovician ----- 17,000 Cambrian 26,000 Keeweenawan Animikian Huronian - 50,000 Algonkian - - 14,000 - - - 18,000 63,000 69,000 63,000 58,000 82,000 Archaean -----? Total - . - - 335,000 feet. ^ Address to the Geol. Soc. of London, 1909. 6 THE BIRTH-TIME OF THE WORLD In the next place we require to know the average rate at which these rocks were laid down. This is really the weakest link in the chain. The most diverse results have been arrived at, which space does not permit us to consider. The value required is most difficult to deter- mine, for it is different for the different classes of material, and varies from river to river according to the conditions of discharge to the sea. We may probably take it as between two and six inches in a century. Now the total depth of the sediments as we see is about 335,000 feet (or 64 miles), and if we take the rate of collect- ing as three inches in a hundred years we get the time for all to collect as i34millions of years. If the rate be four inches, the time is 100 millions of years, which is the figure Geikie favoured, although his result was based on somewhat different data. Sollas most recently finds 80 millions of years.^ The Age as Inferred from the Mass of the Sediments In the above method we obtain our result by the measurement of the linear dimensions of the sediments. These measurements, as we have seen, are dif&cult to arrive at. We may, however, proceed by measurements of the mass of the sediments, and then the method becomes more definite. The new method is pursued as follows : 1 Geikie, Text Book of Geology (Macmillan, 1903), vol. i., p. 73, et seq. Sollas, loc. cit. Joly, Radioactivity and Geology (Constable, 1909), and Phil. Mag., Sept. 1911. THE BIRTH-TIME OF THE WORLD The total mass of the sediments formed since denuda- tion began may be ascertained with comparative accuracy by a study of the chemical composition of the waters of the ocean. The salts in the ocean are undoubtedly derived from the rocks ; increasing age by age as the latter are degraded from their original character under the action of the weather, etc., and converted to the sedimentary form. By comparing the average chemical composition of these two classes of material — the primary or igneous rocks and the sedimentary — it is easy to arrive at a knowledge of how much of this or that con- stituent was given to the ocean by each ton of primary rock which was denuded to the sedimentary form. This, however, will not assist us to our object unless the ocean has retained the salts shed into it. It has not generally done so. In the case of every substance but one the ocean continually gives up again more or less of the salts supplied to it by the rivers. The one exception is the element sodium. The great solubUity of its salts has protected it from abstraction, and it has gone on collecting during geological time, practically in its entirety. This gives us the clue to the denudative history of the Earth.i The process is now simple. We estimate by chemical examination of igneous and sedimentary rocks the amount of sodium which has been supplied to the ocean per ton of sediment produced by denudation. We also calculate 1 Trans. R.D.S., May, 1899^ 8 THE BIRTH-TIME OF THE WORLD the amount of sodium contained in the ocean. We divide the one into the other (stated, of course, in the same units of mass), and the quotient gives us the number of tons of sediment. The most recent estimate of the sediments made in this manner affords 56 x 10" tonnes.^ Now we are assured that all this sediment was trans- ported by the rivers to the sea during geological time. Thus it follows that, if we can estimate the average annual rate of the river supply of sedunents to the ocean over the past, we can calculate the required age. The larid surface is at present largely covered with the sedimentary rocks themselves. Sediment derived from these rocks must be regarded as, for the most part, purely cyclical ; that is, circulating from the sea to the land and back again. It does not go to increase the great body of detrital deposits. We cannot, therefore, take the present river supply of sediment as representing that obtaining over the long past. If the land was all covered still with primary rocks we might do so. It has been estimated that about 25 per cent, of the existing continental area is covered with archaean and igneous rocks, the remainder being sediments.' On this estimate we may find valuable ^ Clarke, A Preliminary Study of Chemical Denudation (Wash- ington, 1910). My own estimate in 1899 (loc. cit.) made as a test of yet another method of finding the age, showed that the sediments may be taken as sufficient to form a layer i-i mile deep if spread uniformly over the continents ; and would amount to 64 X lo*' tons. " Van Tillo, Compies Rendues (Paris), vol. cxiv., 1892. THE BIRTH-TIME OF THE WORLD major and minor limits to the geological age. If we take 25 per cent, only of the present river supply of sediment, we evidently fix a major limit to the age, for it is certain that over the past there must have been on the average a faster supply. If we take the entire river supply, on similar reasoning we have what is undoubtedly a minor limit to the age. The river supply of detrital sediment has not been very extensively investigated, although the quantities involved may be found with comparative ease and accuracy. The following table embodies the results obtained for some of the leading rivers.^ Mean annual Total annual Ratio of discharge in sediment in sediment cubic feet thousands to water per second. of tons. by weight. Potomac 20,160 5.557 3.575 Mississippi - 610,000 406,250 1,500 Rio Grande - 1,700 3.830 291 Uruguay- 150,000 14,782 10,000 Rhone - - - 65,850 36,000 1.775 Po - - - 62,200 67,000 900 Danube 315,200 108,000 2,880 Nile - 113,000 54,000 2,050 Irrawaddy - 475,000 291,430 1,610 Mean - 201,468 109,650 I : 2,731 We see that the ratio of the weight of water to the ^ Russell, River Development (John Murray, 1898). 10 THE BIRTH-TIME OF THE WORLD weight of transported sediment in six out of the nine rivers does not vary widely. The mean is 2,730 to i. But this is not the required average. The water-dis- charge of each river has to be taken into account. If we ascribe to the ratio given for each river the weight proper to the amount of water it discharges, the proportion of weight of water to weight of sediment, for the whole quantity of water involved, comes out as 2,520 to i. Now if this proportion holds for all the rivers of the world — ^which collectively discharge about 27 x lo^' tonnes of water per annum — ^the river-bom detritus is 1-07 X 10*° tonnes. To this an addition of 11 per cent, has to be made for silt pushed along the river-bed.^ On these figures the minor limit to the age comes out as 47 mUhons of years, and the major Umit as 188 milhons. We are here going on rather deficient estimates, the rivers involved representing only some 6 per cent, of the total river supply of water to the ocean. But the result is probably not very far out. We may arrive at a probable age l5nng between the major and minor limits. If, first, we take the arithmetic mean of these limits, we get 117 millions of years. Now this is almost certainly excessive, for we here assume that the rate of covering of the primary rocks by sediments was uniform. It would not be so, however, for the rate of supply of original sediment must have been continually diminishing ^ According to observations made on the Mississippi (Russell, loc. eit.). II THE BIRTH-TIME OF THE WORLD during geological time, and hence we may assume that the rate of advance of the sediments on the primary rocks has also been diminishing. Now we may probably take, as a fair assumption, that the sediment-covered area was at any instant increasing at a rate proportionate to the rate of supply of sediment ; that is, to the area of primary rocks then exposed. On this assumption the age is found to be 87 millions of years. The Age by the Sodium of the Ocean I have next to lay before you a quite different method. I have already touched upon the chemistry of the ocean, and on the remarkable fact that the sodium contained in it has been preserved, practically, in its entirety from the beginning of geological time. That the sea is one of the most beautiful and magnificent sights in Nature, all admit. But, I think, to those who know its story its beauty and magnificence are ten-fold increased. Its saltness it due to no magic mill. It is the dissolved rocks of the Earth which give it at once its brine, its strength, and its buoyancy. The rivers which we say flow with " fresh " water to the sea never- theless contain those traces of salt which, collected over the long ages, occasion the saltness of the ocean. Each gallon of river water contributes to the final result ; and this has been going on since the beginning of our era. The mighty total of the rivers is 6,500 cubic miles of water in the year ! 12 THE BIRTH-TIME OF THE WORLD There is little doubt that the primeval ocean was in the condition of a fresh-water lake. It can be shown that a primitive and more rapid solution of the original crust of the Earth by the slowly cooling ocean would have given rise to relatively small salinity. The fact is, the quantity of salts in the ocean is enormous. We are only now concerned with the sodium ; but if we could extract all the rock-salt (the chloride of sodium) from the ocean we should have enough to cover the entire dry land of the Earth to a depth of 400 feet. It is this gigantic quantity which is going to enter into our estimate of the Earth's age. The calculated mass of sodium con- tained in this rock-salt is 14,130 million million tonnes. If now we can determine the rate at which the rivers supply sodium to the ocean, we can determine the age.^ As the result of many thousands of river analyses, the total amount of sodium annually discharged to the ocean 1 Trans. R.D.S., 1899. A paper by Edmund Halley, the astronomer, in the Philosophical Transactions of the Royal Society for 1 71 5, contains a suggestion for finding the age of the world by the following procedure. He proposes to make observations on the saltness of the seas and ocean at intervals of one or more centuries, and from the increment of saltness arrive at their age. The measurements, as a matter of fact, are impracticable. The salinity would only gain (if all remained in solution) one millionth part in 100 years ; and, of course, the continuous rejection of salts by the ocean would invaUdate the method. The last objection also invalidates the calculation by T. Mellard Reade (Proc. Liverpool Geol. Soc, 1876) of a minor limit to the age by the calcium sulphate in the ocean. Both papers were quite unknown to me when working out my method. Halley's paper was, I think, only brought to light in 1908. 13 THE BIRTH-TIME OF THE WORLD by all the rivers of the world is found to be probably not far from 175 million tonnes.^ Dividing this into the mass of oceanic sodium we get the age as 807 milUons of years. Certain corrections have to be applied to this figure which result in raising it to a little over go millions of years. Sollas, as the result of a careful review of the data, gets the age as between 80 and 150 millions of years. My own result" was between 80 and 90 millions of years ; but I subsequently found that upon certain extreme assumptions a maximum age might be arrived at of 105 millions of years.^ Clarke regards the 807 millions of years as certainly a maximum in the light of certain calculations by Becker.* The order of magnitude of these results cannot be shaken unless on the assumption that there is something entirely misleading in the existing rate of solvent denu- dation. On the strength of the results of another and 1 F. W. Clarke, A Preliminary Study of Chemical Denudation (Smithsonian Miscellaneous Collections, 1910). ' Loc. cit. ' " The Circulation of Salt and Geological Time " Ifieol. Mag., 1901, p. 350). * Becker (loc. cit.), assuming that the exposed igneous and archaean rocks alone are responsible for the supply of sodium to the ocean, arrives at 74 millions of years as the geological age. This matter was discussed by me formerly [Trans. R.D.S., 1899, pp. 54 et seq.). The assumption made is, I believe, inadmissible. It is not supported by river analyses, or by the chemical character of residual soils from sedimentary rocks. There may be some convergence in the rate of solvent denudation, but — as I think on the evidence — in our time unimportant. 14 THE BIRTH-TIME OF THE WORLD entirely different method of approaching the question of the Earth's age (which shall be presently referred to), it has been contended that it is too low. It is even asserted that it is from nine to fourteen times too low. We have then to consider whether such an enormous error can enter into the method. The measurements involved cannot be seriously impugned. Corrections for possible errors applied to the quantities entering into this method have been considered by various writers. My own original corrections have been generally con- firmed. I think the only point left open for discussion is the principle of uniformitarianism involved in this method and in the methods previously discussed. In order to appreciate the force of the evidence for uniformity in the geological history of the Earth, it is, of course, necessary to possess some acquaintance with geo- logical science. Some of the most eminent geologists, among whom Lyell and Geikie^ may be mentioned, have upheld the doctrine of uniformity. It must here suffice to dwell upon a few points having special reference to the matter tmder discussion. The mere extent of the land surface does not, within limits, afEect the question of the rate of denudation. This arises from the fact that the rain supply is quite insufficient to denude the whole existing land surface. About 30 per cent, of it does, not, in fact, drain to the ^ See especially Geikie's Address to Sect. C, Brit. Assoc. Rep., 1899. 15 THE BIRTH-TIME OF THE WORLD ocean. If the continents become invaded by a great transgression of the ocean, this " rainless " area dimin- ishes : and the denuded area advances inwards without diminution. If the ocean recedes from the present strand Unes, the " rainless " area advances outwards, but, the rain supply being sensibly constant, no change in the river supply of salts is to be expected. Age-long submergence of the entire land, or of any very large proportion of what now exists, is negatived by the continuous sequence of vast areas of sediment in every geologic age from the earliest times. Now sediment-receiving areas always are but a small fraction of those exposed areas whence the sediments are supplied.^ Hence in the continuous records of the sediments we have assurance of the continuous exposure of the con- tinents above the ocean surface. The doctrine of the permanency of the continents has in its main features been accepted by the most eminent authorities. As to the actual amount of land which was exposed during past times to denudative effects, no data exist to show it was very different from what is now exposed. It has been estimated that the average area of the North Ameri- can continent over geologic time was about eight-tenths of its existing area.' Restorations of other continents, so far as they have been attempted, would not ^ On the strength of the Mississippi measurements about i to i8 (Magee, Am. Jour, of Sc, 1892, p. 188). * C. Schuchert, Bull. Geol. Soc. Am., vol. xx., 1910. 16 THE BIRTH-TIME OF THE WORLD suggest any more serious divergency one way or the other. That climate in the oceans and upon the land was throughout much as it is now, the continuous chain of teeming life and the sensitive temperature limits of pro- toplasmic existence are sufficient evidence.^ The in- fluence at once of climate and of elevation of the land may be appraised at their true value by the ascertained facts of solvent denudation, as the following table shows. Mean elevation. Metres. 700 650 300 950 650 In this table the estimated number of tonnes of matter in solution, which for every square mile of area the rivers convey to the ocean in one year, is given in the first column. These results are compiled by Clarke from a very large number of analyses of river waters. The second column of the table gives the mean heights in metres above sea level of the several continents, as cited by Arrhenius.^ Of all the denudation results given in the table, those relating to North America and to Europe are far the ^ See also Poulton, Address to Sect. D., Brit. Assoc. Rep., 1896. 2 Lehriuch der Kosmischen Physik, vol. i., p. 347. 17 C Tonnes removed in solution per square mile per annum. North America - - 79 South America - - 50 Europe - 100 Asia - - - - 84 Africa - 44 THE BIRTH-TIME OF THE WORLD most reliable. Indeed these may be described as highly reliable, being founded on some thousands of analyses, many of which have been systematically pursued through every season of the year. These show that Europe with a mean altitude of less than half that of North America sheds to the ocean 25 per cent, more salts. A result which is to be expected when the more important factors of solvent denudation are given intelligent consideration and we discriminate between conditions favouring solvent and detrital denudation respectively : conditions in many cases antagonistic* Hence if it is true, as has been stated, that we now live in a period of exceptionally high continental elevation, we must infer that the average supply of salts to the ocean by the rivers of the world is less than over the long past, and that, therefore, our estimate of the age of the Earth as already given is ex- cessive. There is, however, one condition which will operate to unduly diminish our estimate of geologic time, and it is a condition which may possibly obtain at the present time. If the land is, on the whole, now sinking relatively to the ocean level, the denudation area tends, as we have seen, to move inwards. It will thus encroach upon regions which have not for long periods drained to the ocean. On such areas there is an accumulation of soluble salts which the deficient rivers have not been able to carry to the ocean. Thus the salt content of certain of 1 See the essay on Denudation. 18 THE BIRTH-TIME OF THE WORLD the rivers draining to the ocean will be influenced not only by present denudative effects, but also by the stored results of past effects. Certain rivers appear to reveal this unduly increased salt supply : those which flow through comparatively arid areas. However, the flow- off of such tributaries is relatively small and the final effects on the great rivers apparently unimportant — a result which might have been anticipated when the extremely slow rate of the land movements is taken into account. The difficulty of effecting any reconciliation of the methods already described and that now to be given increases the interest both of the former and the latter. The Age by Radioactive Transformations Rutherford suggested in 1905 that as helium was con- tinually being evolved at a uniform rate by radioactive substances (in the form of the alpha rays) a determina- tion of the age of minerals containing the radioactive elements might be made by measurements of the amount of the stored heUum and of the radioactive elements giving rise to it. The parent radioactive substances are — according to present knowledge — uranium and thorium. An estimate of the amounts of these elements present enables the rate of production of the helium to be calcu- lated. Rutherford shortly afterwards found by this method an age of 240 millions of years for a radioactive mineral of presumably remote age. Strutt, who carried 19 THE BIRTH-TIME OF THE WORLD his measurements to a wonderful degree of refinement, found the following ages for mineral substances originating in different geological ages : Oligocene 8-4 millions of years. Eocene ----- 31 ,,,,., Lower Carboniferous - - 150 „ „ ,, Archaean ----- 710 ,, „ ,, Periods of time much less than, and very inconsistent with, these were also found. The lower results are, however, easily explained if we assume that the helium — which is a gas under prevailing conditions — escapes in many cases slowly from the mineral. Another product of radioactive origin is lead. The suggestion that this substance might be made available to determine the age of the Earth also originated with Rutherford. We are at least assured that this element cannot escape by gaseous diffusion from the minerals. Boltwood's results on the amount of lead contained in minerals of various ages, taken in conjunction with the amount of uranium or parent substance present, afforded ages rising to 1,640 milhons of years for Archaean and 1,200 millions for Algonkian time. Becker, applying the same method, obtained results rising to quite in- credible periods : from 1,671 to 11,470 mUUons of years. Becker maintained that original lead rendered the deter- minations indefinite. The more recent results of Mr. A. Holmes support the conclusion that " original " lead may be present and may completely falsify results derived 20 THE BIRTH-TIME OF THE WORLD from minerals of low radioactivity in which the derived lead would be small in amount. By rejecting such results as appeared to be of this character, he arrives at 370 millions of years as the age of the Devonian. I must now describe a very recent method of estimating the age of the Earth. There are, in certain rock-forming minerals, colour-changes set up by radioactive causes. The minute and curious marks so produced are known as haloes ; for they surround, in ring-hke forms, minute particles of included substances which contain radioactive elements. It is now well known how these haloes are formed. The particle in the centre of the halo contains uranium or thorium, and, necessarily, along with the parent substance, the various elements derived from it. In the process of transformation giving rise to these several derived substances, atoms of helium — the alpha rays — projected with great velocity into the surround- ing mineral, occasion the colour changes referred to. These changes are limited to the distance to which the alpha rays penetrate ; hence the halo is a spherical volume surrounding the central substance.^ The time required to form a halo could be found if on the one hand we could ascertain the number of alpha rays ejected from the nucleus of the halo in, say, one year, and, on the other, if we determined by experiment just how many alpha rays were required to produce the same 1 Phil. Mag., March, 1907 and February, 1910 ; also Bedrock, January, 1913. See Pleochroic Haloes in this volume. 21 THE BIRTH-TIME OF THE WORLD amount of colour alteration as we perceive to extend around the nucleus. The latter estimate is fairly easily and surely made. But to know the number of rays leaving the central particle in unit time we require to know the quantity of radioactive material in the nucleus. This cannot be directly determined. We can only, from known results obtained with larger specimens of just such a mineral substance as composes the nucleus, guess at the amount of uranium, or it may be thorium, which may be present. This method has been applied to the uranium haloes of the mica of County Carlow.^ Results for the age of the halo of from 20 to 400 millions of years have been obtained. This mica was probably formed in the granite of Leinster in late Silurian or in Devonian times. The higher results are probably the least in error, upon the data involved ; for the assumption made as to the amoimt of uranium in the nuclei of the haloes was such as to render the higher results the more reliable. This method is, of course, a radioactive method, and similar to the method by helium storage, save that it is free of the risk of error by escape of the helium, the effects of which are, as it were, registered at the moment of its production, so that its subsequent escape is of no moment. 1 Joly and Rutherford, Phil. Mag., April, 1913. 22 THE BIRTH-TIME OF THE WORLD Review of the Results We shall now briefly review the results on the geo- logical age of the Earth. By methods based on the approximate uniformity of denudative effects in the past, a period of the order of 100 millions of years has been obtained as the duration of our geological age ; and consistently whether we accept for measurement the sediments or the dissolved sodium. We can give reasons why these measure- ments might afford too great an age, but we can find absolutely no good reason why they should give one much too low. By measining radioactive products ages have been found which, while they vary widely among themselves, yet claim to possess accuracy in their superior limits, and exceed those derived from denudation from nine to fourteen times. In this difficulty let us consider the claims of the radioactive method in any of its forms. In order to be trustworthy it must be true ; (i) that the rate of transfor- mation now shown by the parent substance has obtained throughout the entire past, and (2) that there were no other radioactive substances, either now or formerly existing, except uranium, which gave rise to lead. As regards methods based on the production of helium, what we have to say will largely apply to it also. If some unknown source of these elements exists we, of course, on our assumption over-estimate the age, 23 THE BIRTH-TIME OF THE WORLD As regards the first point : In ascribing a constant rate of change to the parent substance — which Becker (loc. cit.) describes as " a simple though tremendous extrapolation " — ^we reason upon analogy with the constant rate of decay observed in the derived radioactive bodies. If uranium and thorium are really primary elements, how- ever, the analogy relied on may be misleading ; at least, it is obviously incomplete. It is incomplete in a par- ticular which may be very important : the mode of origin of these parent bodies — ^whatever it may have been — is different to that of the secondary elements with which we compare them. A convergence in their rate of transformation is not impossible, or even improbable, so far as we known. As regards the second point ; It is assumed that uranium alone of the elements in radioactive minerals is ultimately transformed to lead by radioactive changes. We must consider this assumption. Recent advances in the chemistry of the radioactive elements has brought out evidence that all three lines of radioactive descent known to us — i.e. those beginning with uranium, with thorium, and with actinium — alike converge to lead.^ There are difficulties in the way of believing that all the lead-like atoms so produced (" isotopes " of lead, as Soddy proposes to call them) actually remain as stable lead in the minerals. For one 1 See Soddy 's Chemistry of the Radioactive Elements (Longmans, Green & Co.). 24 THE BIRTH-TIME OF THE WORLD thing there is sometimes, along with very large amounts of thorium, an almost entire absence of lead in thorianites and thorites. And in some urano-thorites the lead may be noticed to follow the uranium in approximate pro- portionality, notwithstanding the presence of large amounts of thorium.^ This is in favour of the assump- tion that all the lead present is derived from the uranium. The actinium is present in negligibly small amounts. On the other hand, there is evidence arising from the atomic weight of lead which seems to involve some other parent than uranium. Soddy, in the work referred to, points this out. The atomic weight of radium is well known, and uranium in its descent has to change to this element. The loss of mass between radium and uranium- derived lead can be accurately estimated by the number of alpha rays given off. From this we get the atomic weight of uranium-derived lead as closely 206. Now the best determinations of the atomic weight of normal lead assign to this element an atomic weight of closely * It seems very difficult at present to suggest aa end product for thorium, unless we assume that, by loss of electrons, thorium E, or thorium-lead, reverts to a substance chemically identical with thorium itself. Such a change — ^whether considered from the point of view of the periodic law or of the radioactive theory — • would involve many interesting consequences. It is, of course, quite possible that the nature of the conditions attending the deposition of the uranium ores, many of which are comparatively recent, are responsible for the difi&culties observed. The thorium and uranium ores are, again, specially prone to alteration. 25 THE BIRTH-TIME OF THE WORLD 207. By a somewhat similar calculation it is deduced that thorium-derived lead would possess the atomic weight of 208. Thus normal lead might be an admixture of uranium- and thorium-derived lead. However, as we have seen, the view that thorium gives rise to stable lead is beset with some difficulties. If we are going upon reUable facts and figures, we must, then, assume : {a) That some other element than uranium, and genetically connected with it (probably as parent substance), gives rise, or formerly gave rise, to lead of heavier atomic weight than normal lead. It may be observed respecting this theory that there is some support for the view that a parent substance both to uranium and thorium has existed or possibly exists. The evidence is found in the proportionality frequently observed between the amounts of thorium and uranium in the primary rocks.* Or : (6) We may meet the difficulties in a simpler way, which may be stated as follows : If we assume that all stable lead is derived from uranium, and at the same time recognise that lead is not perfectly homogeneous in atomic weight, we must, of necessity, ascribe to uranium a similar want of homo- geneity ; heavy atoms of uranium giving rise to heavy * Compare results for the thorium content of such rocks (appearing in a paper by the author Cong. Int. de Radiologie et d'ElectriciU, vol. i., 1910, p. 373), and those for the radium content, as collected in Phil. Mag., October, 1912, p. 697. Also A. L. Fletcher, Phil. Mag., July, 1910; January, 1911, and June, 1911. J. H. J. Poole, Phil, Mag., April, 1915. 36 THE BIRTH-TIME OF THE WORLD atoms of lead and light atoms of uranium generating light atoms of lead. This assumption seems to be in- volved in the figures upon which we are going. Still relying on these figures, we find, however, that existing uranium cannot give rise to lead of normal atomic weight. We can only conclude that the heavier atoms of uranium have decayed more rapidly than the lighter ones. In this connection it is of interest to note the complexity of tu-anium as recently established by Geiger, although in this case it is assumed that the shorter-lived iso- tope bears the relation of offspring to the longer-lived and largely preponderating constituent. However, there does not seem to be any direct proof of this as yet. From these considerations it would seem that unless the atomic weight of lead in uraninites, etc., is 206, the former complexity and more accelerated decay of uranium are indicated in the data respecting the atomic weights of radium and lead^ As an alternative view, we may assume, as in our first hypothesis, that some elementally different but genetically connected substance, decaying along branching lines of descent at a rate sufficient to practically remove the whole of it during geological time, formerly existed. Whichever hypothesis we adopt 1 Later investigation has shown that the atomic weight of lead in uranium-bearing ores is about 206-6 (see Richards and Lembert, Journ. of Am. Chem. Soc, July, 1914). This result gives support to the view expressed above. 27 THE BIRTH-TIME OF THE WORLD we are confronted by probabilities which invaHdate time-measurements based on the lead and helium ratio in minerals. We have, in short, grave reason to question the measure of uniformitarianism postulated in finding the age by any of the known radioactive methods. That we have much to learn respecting our assump- tions, whether we pursue the geological or the radio- active methods of approaching the age of our era, is, indeed, probable. Whatever the issue it is certain that the reconciling facts will leave us with much more light than we at present possess either as respects the Earth's history or the history of the radioactive elements. With this necessary admission we leave our study of the Birth- Time of the World. It has led us a long way from Lucretius. We do not ask if other Iliads have perished ; or if poets before Homer have vainly sung, becoming a prey to all-con- suming time. We move in a greater history, the land- marks of which are not the birth and death of kings and poets, but of species, genera, orders. And we set out these organic events not according to the passing generations of man, but over scores or hundreds of millions of years. How much Lucretius has lost, and how much we have gained, is bound up with the question of the intrinsic value of knowledge and great ideas. Let us appraise knowledge as we would the Homeric poems, as some- 28 THE BIRTH-TIME OF THE WORLD thing which ennobles Hfe and makes it happier. Well, then, we are, as I think, in possession to-day of some of those lost Iliads and Odysseys for which Lucretius looked in vain.'^ ^ The duration in the past of Solar heat is necessarily bound up with the geological age. There is no known means (outside speculative science) of accounting for more than about 30 million years of the existing solar temperature in the past. In this direc- tion the age seems certainly limited to 100 million years. See a review of the question by Dr. Lindemann in Nature, April 5th, 1915- 29 DENUDATION The subject of denudation is at once one of the most interesting and one of the most complicated with which the geologist has to deal. While its great results are apparent even to the most casual observer, the factors which have led to these results are in many cases so indeterminate, and in some cases apparently so variable in influence, that thoughtful writers have even claimed precisely opposite effects as originating from the same cause. Indeed, it is almost impossible to deal with the subject without entering upon controversial matters. In the following pages I shall endeavour to keep to broad issues which are, at the present day, either conceded by the greater number of authorities on the subject, or are, from their strictly quantitative character, not open to controversy. It is evident, in the first place, that denudation — or the wearing away of the land surfaces of the earth — is mainly a result of the circulation of water from the ocean to the land, and back again to the ocean. An action entirely conditioned by solar heat, and without which it would completely cease and further change upon the land come to an end. To what actions, then, is so great a potency of the 30 Plate III. AN ALPINE TOKKENT AT WORK. YAL d'HIiRENS. Fating p. 31. DENUDATION circulating water to be traced ? Broadly speaking, we may classify them as mechanical and chemical. The first involves the separation of rock masses into smaller fragments of all sizes, down to the finest dust. The second involves the actual solution in the water of the rock constituents, which may be regarded as the final act of disintegration. The rivers bear the burden both of the comminuted and the dissolved materials to the sea. The mud and sand carried by their currents, or gradually pushed along their beds, represent the former ; the invisible dissolved matter, only to be demonstrated to the eye by evaporation of the water or by chemical precipitation, represents the latter. The results of these actions, integrated over geological time, are enormous. The entire bulk of the sedimentary rocks, such as sandstones, slates, shales, conglomerates, Umestones, etc., and the salt content of the ocean, are due to the combined activity of mechanical and solvent denudation. We shall, later on, make an estimate of the magnitude of the quantities actually involved. In the Swiss valleys we see torrents of muddy water hurrying along, and if we follow them up, we trace them to glaciers high among the mountains. From beneath the foot of the glacier, we find, the torrent has birth. The first debris given to the river is derived from the wearing of the rocky bed along which the glacier moves. The river of ice bequeaths to the river of water — of which it is the parent — the spoils which it has won from the rocks 31 THE BIRTH-TIME OF THE WORLD The work of mechanical disintegration is, however, not restricted to the glacier's bed. It proceeds every- where over the surface of the rocks. It is aided by the most diverse actions. For instance, the freezing and expansion of water in the chinks and cracks in those alpine heights where between sunrise and sunset the heat of summer reigns, and between sunset and sunrise the cold of winter. Again, under these conditions the mere change of surface temperature from night to day severely stresses the surface layers of the rocks, and, on the same principles as we explain the fracture of an unequally heated glass vessel, the rocks cleave off in slabs which slip down the steeps of the mountain and collect as screes in the valley. At lower levels the expansive force of vegetable growth is not unimportant, as all will admit who have seen the strong roots of the pines penetrating the crannies of the rocks. Nor does the river which flows in the bed of the valley act as a carrier only. Listening carefuUy we may detect beneath the roar of the alpine torrent the crunching and knock- ing of descending boulders. And in the pot-holes scooped by its whirling waters we recognise the abrasive action of the suspended sand upon the river bed. A view from an Alpine summit reveals a scene of re- markable desolation (PI. V, p. 40) . Screes lie piled against the steep slopes. Cliffs stand shattered and ready to fall in ruins. And here the forces at work readily reveal themselves. An occasional wreath of white smoke among 32 DENUDATION the far-off peaks, followed by a rumbling reverberation, marks the fall of an avalanche. Water everywhere trickles through the shaly ddbris scattered around. In the full sunshine the rocks are almost too hot to bear touching. A few hours later the cold is deadly, and all becomes a frozen silence. In such scenes of desolation and destruction, detrital sediments are actively being generated. As we descend into the valley we hear the deep voice of the torrents which are continually hurry- ing the disintegrated rocks to the ocean. A remarkable demonstration of the activity of mechanical denudation is shown by the phenomenon of " earth pillars." The photograph (PI. IV.) of the earth pillars of the Val d'H6rens (Switzerland) shows the peculiar appearance these objects present. They arise under conditions where large stones or boulders are scattered in a deep deposit of clay, and where much of the denudation is due to water scour. The large boulders not only act as shelter against rain, but they bind and con- solidate by their mere weight the clay upon which they rest. Hence the materials underlying the boulders become more resistant, and as the surrounding clays are gradually washed away and carried to the streams, these compacted parts persist, and, finally, stand like walls or pillars above the general level. After a time the great boulders fall off and the underl3dng clay be- comes worn by the rainwash to fantastic spikes and ridges. In the Val d'H^rens the earth pillars are formed 33 D THE BIRTH-TIME OF THE WORLD of the deep moraine stuff which thickly overlies the slopes of the valley. The wall of pillars runs across the axis of the valley, down the slope of the hill, and crosses the road, so that it has to be tunnelled to permit the passage of traffic. It is not improbable that some additional influence — possibly the presence of lime-^ has hardened the material forming the pillars, and tended to their preservation. Denudation has, however, other methods of work than purely mechanical; methods more noiseless and gentle, but not less effective, as the victories of peace are no less than those of war. Over the immense tracts of the continents chemical work proceeds relentlessly. The rock in general, more especially the primary igneous rock, is not stable in presence of the atmosphere and of water. Some of the minerals, such as certain silicates and carbonates, dissolve relatively fast, others with extreme slowness. In the process of solution chemical actions are involved ; oxida- tion in presence of the free oxygen of the atmosphere ; attack by the feeble acid arising from the solution of carbon dioxide in water ; or, again, by the activity of certain acids — ^humous acids — ^which originate in the decomposition of vegetable remains. These chemical agents may in some instances, e.g. in the case of car- bonates such as limestone or dolomite — bring practically the whole rock into solution. In other instances — e.g. granites, basalts, etc. — they may remove some of the 34 DENUDATION constituent minerals completely or partially, such as felspar, olivine, augite, and leave more resistant sub- stances to be ultimately washed down as fine sand or mud into the river. It is often difficult or impossible to appraise the rela^ tive efficiency of mechanical and chemical denudation in removing the materials from a certain area. There can be, indeed, httle doubt that in mountainous regions the mechanical effects are largely predominant. The silts of glacial rivers are little different from freshly- powdered rock. The water which carries them but httle different from the pure rain or snow which falls from the sky. There has not been time for the chemical or solvent actions to take place. Now while gravitational forces favour sudden shock and violent motions in the hills, the effect of these on solvent and chemical denuda- tion is but small. Nor is good drainage favourable to chemical actions, for water is the primary factor in every case. Water takes up and removes soluble combinations of molecules, and penetrates beneath residual insoluble substances. It carries the oxygen and acids downwards through the soils, and finally conveys the results of its own work to the rivers and streams. The lower mean temperature of the mountains as well as the perfect drainage diminishes chemical activities. Hence we conclude that the heights are not generally favourable to the purely solvent and chemical actions. It is on the lower-lsdng land that soils tend to accumulate, 35 THE BIRTH-TIME OF THE WORLD and in these the chief solvent and the chief chemical denudation of the Earth are effected. The solvent and chemical effects which go on in the finely-divided materials of the soils may be observed in the laboratory. They proceed faster than would be anticipated. The observation is made by passing a measured quantity of water backwards and forwards for some months through a tube containing a few grammes of powdered rock. Finally the water is analysed, and in this manner the amount of dissolved matter it has taken up is estimated. The rock powder is examined under the microscope in order to determine the size of the grains, and so to calculate the total surface exposed to the action of the water. We must be careful in such experiments to permit free oxidation by the atmosphere. Results obtained in this way of course take no account of the chemical effects of organic acids such as exist in the soils. The quantities obtained in the laboratory will, therefore, be deficient as compared with the natural results. In this manner it has been found that fresh basalt exposed to continually moving water will lose about 0-20 gramme per square metre of surface per year. The mineral orthoclase, which enters largely into the constitu- tion of many granites, was found to lose under the same conditions 0-025 gramme. A glassy lava (obsidian) rich in silica and in the chemical constituents of an average granite, was more resistant still ; losing but 0-013 gramme per square metre per year. Hornblende, a minersJ 36 DENUDATION abundant in many rocks, lost 0-075 gramme. The mean of the results showed that o-o8 gramme was washed in a year from each square metre. Such results give us some indication of the rate at which the work of solution goes on in the finely divided soils.* It might be urged that, as the mechanical break up of rocks, and the production in this way of large surfaces, must be at the basis of solvent and chemical denuda- tion, these latter activities should be predominant in the mountains. The answer to this is that the soils rarely owe their existence to mechanical actions. The alluvium of the valleys constitutes only narrow margins to the rivers ; the finer debris from the mountains is rapidly brought into the ocean. The soils which cover the greater part of continental areas have had a very different origin. In any quarry where a section of the soil and of the underlying rock is visible, we may study the mode of formation of soils. Our observations are, we will suppose, pursued in a granite quarry. We first note that the material of the soil nearest the surface is intermixed with the roots of grasses, trees, or shrubs. Examining a handful of this soil, we see glistening flakes of mica which plainly are derived from the original granite. Washing off the finer particles, we find the largest remaining grains are composed of the all but indestructible quartz. 1 Proc. Roy. Irish Acad., VIII., S«r. A, p. 21. 37 THE BIRTH-TIME OF THE WORLD This also is from the granite. Some few of the grains are of chalky-looking felspar ; again a granitic mineral. What is the finer silt we have washed off ? It, too, is composed of mineral particles to a great extent ; rock dust stained with iron oxide and intermixed with organic remains, both animal and vegetable. But if we make a chemical analysis of the finer silt we find that the composition is by no means that of the granite beneath. The chemist is able to say, from a study of his results, that there has been, in the first place, a large loss of material attending the conversion of the granite to the soil. He finds a concentration of certain of the more resistant substances of the granite arising from the loss of the less resistant. Thus the percentage amount of alumina is increased. The percentage of iron is also increased. But silica and most other substances show a diminished percentage. Notably lime has nearly dis- appeared. Soda is much reduced ; so is magnesia. Potash is not so completely abstracted. Finally, owing to hydration, there is much more combined water in the soil than in the rock. This is a typical result for rocks of this kind. Deeper in the soil we often observe a change of tiexture. It has become finer, and at the same time the clay is paler in colour. This subsoil represents the finer particles carried by rain from above. The change of colour is due to the state of the iron which is less oxidised low down in the soil. Beneath the subsoil the soil grows 38 DENUDATION again coarser. Finally, we recognise in it fragments of granite which ever grow larger as we descend, till the soil has become replaced by the loose and shattered rock. Beneath this the only sign of weathering apparent in the rock is the rusty hue imparted by the oxidised iron which the percolating rain has leached from iron-bearing minerals. The soil we have examined has plainly been derived in situ from the underljnng rock. It represents the more insoluble residue after water and acids have done their work. Each year there must be a very slow sinking of the surface, but the ablation is infinitesimal. The depth of such a soil may be considerable. The total surface exposed by the countless grains of which it is composed is enormous. In a cubic foot of average soil the surface area of the grains may be 50,000 square feet or more. Hence a soil only two feet deep may expose 100,000 square feet for each square foot of surface area. It is true that soils formed in this manner by atmo- spheric and organic actions take a very long time to grow. It must be remembered, however, that the process is throughout attended by the removal in solution of diemically altered materials. Considerations such as the foregoing must convince us that while the accumulation of the detrital sediments around the continents is largely the result of activities progressing on the steeper slopes of the land, that is, 39 THE BIRTH-TIME OF THE WORLD among the mountainous regions, the feeding of the salts to the ocean arises from the slower work of meteorological and organic agencies attacking the molecular constitution of the rocks ; processes which best proceed where the drainage is sluggish and the quiescent conditions permit of the development of abundant organic growth and decay. Statistics of the solvent denudation of the continents support this view. Within recent years a very large amount of work has been expended on the chemical investigation of river waters of America and of Europe. F. W. Clarke has, at the expense of much labour, collected and compared these results. They are expressed as so many tonnes removed in solution per square mile per annum. For North America the result shows 79 tonnes so removed ; for Europe 100 tonnes. Now there is a notable difference between the mean elevations of these two continents. North America has a mean elevation of 700 metres over sea level, whereas the mean elevation of Europe is but 300 metres. We see in these figures that the more mountainous land supplies less dissolved matter to the ocean than the land of lower elevation, as our study has led us to expect. We have now considered the source of the detrital sediments, as well as of the dissolved matter which has given to the ocean, in the course of geological time, its present gigantic load of salts. It is true there are further solvent and chemical effects exerted by the sea water 40 DENUDATION upon the sediments discharged into it ; but we are justified in concluding that, relatively to the similar actions taking place in the soils, the solvent and chemical work of the ocean is small. The fact is, the deposited detrital sediments around the continents occupy an area small when contrasted with the vast stretches of the land. The area of deposition is much less than that of denudation ; probably hardly as much as one twentieth. And, again, the conditions of aeration and circulation which largely promote chemical and solvent denudation in the soils are relatively Umited and ineffective in the detrital oceanic deposits. The summation of the amounts of dissolved and detrital materials which denudation has brought into the ocean during the long denudative history of the Earth, as we might anticipate, reveals quantities of almost unrealisable greatness. The facts are among the most impressive which geological science has brought to light. Elsewhere in this volume they have been mentioned when discussing the age of the Earth. In the present connection, however, they are deserving of separate consideration. The basis of our reasoning is that the ocean owes its saltness mainly if not entirely to the denudative activities we have been considering. We must establish this. We may, in the first place, say that any other view at once raises the greatest difficulties. The chemical com- position of the detrital sediments which are spread over 41 THE BIRTH-TIME OF THE WORLD the continents and which build up the mountains, differs on the average very considerably from that of the igneous rocks. We know the former have been derived from the latter, and we know that the difference in the composi- tion of the two classes of materials is due to the removal in solution of certain of the constituents of the igneous rocks. But the ocean alone can have received this dissolved matter. We know of no other place in which to look for it. It is true that some part of this dissolved matter has been again rejected by the ocean ; thus the formation of limestone is largely due to the abstraction of lime from sea water by organic and other agencies. This, however, in no way relieves us of the necessity of tracing to the ocean the substances dissolved from the igneous rocks. It follows that we have here a vera causa ior the saltness of the ocean. The view that the ocean " was salt from the first " is without one known fact to support it, and leaves us with the burden of the entire dissolved salts of geological time to dispose of — Where and how ? The argument we have outlined above becomes con- vincingly strong when examined more closely. For this purpose we first compare the average chemical com- position of the sedimentary and the igneous rocks. The following table gives the percentages of the chief chemicial constituents : * ^ F. W. Clarke : A Preliminary Study of Chemical Denudation, P-I3- 42 DENUDATION Igneous. Sedimentary. Silica (St Oa) - - - - 59-99 58-51 Alumina (Al^Of) 15-04 13-07 Ferric oxide (FjO,) . . - 2-59 3-40 Ferrous oxide (Fe 0) - 3-34 2'O0 Magnesia {Mg 0) - - - 3-89 2-S3 Lime {CaO) 4-8i 5-42 Soda (NfljO) - - . . 3-41 I-I2 Potash {K^O) - - - - 2-95 2 -So Water (HjO) - - - - 1-92 4-28 Carbon dioxide (CO^) - - - — 4-93 Minor constituents - - - 2 -06 1-95 lOO'OO lOO'OO In the derivation of the sediments from the igneous rocks there is a loss by solution of about 33 per cent ; i.e. 100 tons of igneous rock jdelds rather less than 70 tons of sedimentary rock. This involves a concentra- tion in the sediments of the more insoluble constituents. To this rule the lime-content appears to be an exception. It is not so in reality. Its high value in the sedi- ments is due to its restoration from the ocean to the land. The magnesia and potash are, also, largely restored from the ocean ; the former in dolomites and magnesian Umestones; the latter in glauconite sands. The iron of the sediments shows increased oxidation. The most notable difference in the two analyses appears, however, in the soda percentages. This falls from 3-41 in the igneous rock to i*i2 in the average sediment. Indeed, this 43 THE BIRTH-TIME OF THE WORLD deficiency of soda in sedimentary rocks is so characteristic of secondary rocks that it may with some safety be applied to discriminate between the two classes of sub- stances in cases where petrological distinctions of other kinds break down. To what is this so marked deficiency of soda to be ascribed ? It is a result of the extreme solubility of the salts of sodium in water. This has not only rendered its deposition by evaporation a relatively rare and unimportant incident of geological history, but also has protected it from abstraction from the ocean by organic agencies. The element sodium has, in fact, accumulated in the ocean during the whole of geological time. ' We can use the facts associated with the accumulation of sodium salts in the ocean as a means of obtaining additional support to the view, that the processes of solvent denudation are responsible for the saltness of the ocean. The new evidence may be stated as follows : Estimates of the amounts of sedimentary rock on the continents have repeatedly been made. It is true that these estimates are no more than approximations. But they undoubtedly are approximations, and as such may legitimately be used in our argument; more especially as final agreement tends to check and to support the several estimates which enter into them. The most recent and probable estimates of the sediments on the land assign an average thickness of one mile of 44 DENUDATION secondary rocks over the land area of the world. To this some increase must be made to allow for similar materials concealed in the ocean, principally around the continental margins. If we add lo per cent, and assign a specific gravity of 2-5 we get as the mass of the sediments 64 x 10" tonnes. But as this is about 67 per cent, of the parent igneous rock — i.e. the average igneous rock from which the sediments are derived — we conclude that the primary denuded rock amounted to a mass of about 95 x 10" tonnes. Now from the mean chemical composition of the secondary rocks we calculate that the mass of sediments as above determined contains 0-72 x lo" tonnes of the sodiimi oxide, NajO. If to this amount we add the quantity of sodium oxide which must have been given to the ocean in order to account for the sodium salts contained therein, we arrive at a total quantity of oxide of sodium which must be that possessed by the primary rock before denudation began its work upon it. The mass of the ocean being well ascertained, we easily calcu- late that the sodium in the ocean converted to sodium oxide amounts to 2-1 x lo^' tonnes. Hence between the estimated sediments and the waters of the ocean we can account for 2-82 x 10" tonnes of soda. When now we put this quantity back into the estimated mass of primary rock we find that it assigns to the primary rock a soda percentage of 3-0. On the average analysis given above this should be 3 •41 per cent. The agreement, 45 THE BIRTH-TIME OF THE WORLD all things considered, more especially the uncertainty in the estimate of the sediments, is plainly in support of the view that oceanic salts are derived from the rocks ; if, indeed, it does not render it a certainty. A leading and fundamental inference in the denudative history of the Earth thus finds support : indeed, we may say, verification. In the light of this fact the whole work of denudation stands revealed. That the ocean began its history as a vast fresh-water envelope of the Globe is a view which accords with the evidence for the primitive high temperature of the Earth. Geological history opened with the condensation of an atmosphere of immense extent, which, after long fluctuations between the states of steam and water, finally settled upon the surface, almost free of matter in solution : an ocean of distilled water. The epoch of denudation then began. It will, probably, continue till the waters, undergoing further loss of thermal energy, suffer yet another change of state, when their circulation will cease and their attack upon the rocks come to an end. From what has been reviewed above it is evident that the sodium in the ocean is an index of the total activity of denudation integrated over geological time. From this the broad facts of the results of denudation admit of determination with considerable accuracy. We can estimate the amoimt of rock which has been de- graded by solvent and chemical actions, and the amount of sediments which has been derived from it. We are, 4^ DENUDATION thus, able to amend our estimate of the sediments which, as determined by direct observation, served to support the basis of our argument. We now go straight to the ocean for the amovmt of sodium of denudative origin. There may, indeed, have been some primitive sodium dissolved by a more rapid denudation while the Earth's surface was still falling in temperature. It can be shown, however, that this amount was relatively small. Neglecting it we may say with safety that the quantity of sodium carried into the ocean by the rivers must be between 14,000 and 15,000 million million tonnes : i.e. 14,500 x 10^" tonnes, say. Keeping the figures to round numbers we find that this amount of sodium involves the denudation of about 80 X 10^' tonnes of average igneous rock to 53 x 10" tonnes of average sediment. From these vast quantities we know that the parent rock denuded during geological time amounted to some 300 miUion cubic kilometres or about seventy million cubic miles. The sediments, derived therefrom possessed a bulk of 220 million cubic kilometres or fifty million cubic miles. The area of the land surface of the Globe is 144 million square kilometres. The parent rock would have covered this to a uniform depth of rather more than two kilometres, and the derived sediment to more than 1-5 kilometres, or about one mile deep. The slow accomplishment of results so vast conveys some idea of the great duration of geological time. 47 THE BIRTH-TIME OF THE WORLD The foregoing method of investigating the statistics of solvent denudation is capable of affording information not only as to the amount of sediments upon the land, but also as to the quantity which is spread over the floor of the ocean. We see this when we follow the fate of the 33 per cent, of dissolved salts which has been leached from the parent igneous rock, and the mass of which we calculate from the ascertained mass of the latter, to be 27 x lo*' tonnes. This quantity was at one time or another all in the ocean. But, as we saw above, a certain part of it has been again abstracted from solution, chiefly by organic agencies. Now the abstracted soHds have not been altogether retained beneath the ocean. Movements of the land during geological time have resulted in some portion being uplifted along with other sediments. These sub- stances constitute, mainly, the limestones. We see, then, that the 27 x 10" tonnes of substances leached from the parent igneous rocks have had a three- fold destination. One part is still in solution ; a second part has been precipitated to the bottom of the ocean ; a third part exists on the land in the form of calcareous rocks. Observation on the land sediments shows that the calcareous rocks amount to about 5 per cent, of the whole. From this we find that 3 x 10" tonnes, approxi- mately, of such rocks have been taken from the ocean. This accounts for one of the three classes of material 48 DENUDATION into which the original dissolved matter has been divided. Another of the three quantities is easily estimated : the amount of matter still in solution in the ocean. The volume of the ocean is 1,414 million cubic kilometres and its mass is 145 x lo^^ tonnes. The dissolved salts in it constitute 3 4 per cent, of its mass ; or, rather more than 5 x io^» tonnes. The limestones on the land and the salts in the sea water together make up about 8 X 10" tonnes. If we, now, deduct this from the total of 27 x 10" tonnes, we find that about 19 x lo** tonnes must exist as precipitated matter on the floor of the ocean. The area of the ocean is 367 x 10*' square metres, so that if the precipitated sediment possesses an average specific gravity of 2-5, it woiild cover the entire floor to a uniform depth of 218 metres ; that is 715 feet. This assumes that there was uniform deposition of the abstracted matter over the floor of the ocean. Of course, this assumption is not justifiable. It is certain that the rate of deposition on the floor of the sea has varied enormously with various conditions — principally with the depth. Again, it must be remembered that this estimate takes no account of solid materials otherwise brought into the oceanic deposits ; e.g., by wind-trans- ported dust from the land or volcanic ejectamenta in the ocean depths. It is not probable, however, that any considerable addition to the estimated mean depth of deposit from such sources would be allowable. 49 E THE BIRTH-TIME OF THE WORLD The greatness of the quantities involved in these determinations is ahnost awe inspiring. Take the case of the dissolved salts in the ocean. They are but a fraction, as we have seen, of the total results of solvent denudation and represent the integration of the minute traces con- tributed by the river water. Yet the common salt (chloride of sodium) alone, contained in the ocean, would, if abstracted and spread over the dry land as a layer of rock salt having a specific gravity of 2-2, cover the whole to a depth of 107 metres or 354 feet. The total salts in solution in the ocean similarly spread over the land would increase the depth of the layer to 460 feet. After considering what this means we have to remember that this amount of matter now in solution in the seas is, in point of fact, less than a fifth part of the total dissolved from the rocks during geological time. The transport by denudation of detrital and dissolved matter from the land to the ocean has had a most impor- tant influence on the events of geological history. The existing surface features of the earth must have been largely conditioned by the dynamical effects arising there- from. In deaUng with the subject of mountain genesis we will, elsewhere, see that all the great mountain ranges have originated in the accumulation of the detrital sediments near the shore in areas which, in consequence of the load, gradually became depressed and developed into synclines of many thousands of feet in depth. The most impressive surface features of the Globe originated 50 Plate VI. ALLUVIAL LONL : MLiiLAi ILAI '^.T"^ MORAINE ON ALETSCII GLACIER.' Facing p, 50. DENUDATION in this manner. We wUl see too that these events were of a rhythmic character; the upraising of the mountains involving intensified mechanical denudation over the elevated area and in this way an accelerated transport of detritus to the sea ; the formation of fresh deposits ; renewed synclinal sinking of the sea floor, and, finally, the upheaval of a younger mountain range. This extraordinary sequence of events has been determined by the events of detrital denudation acting along with certain general conditions which have all along involved the growth of compressive stresses in the surface crust of the Earth. The effects of purely solvent denudation are less easily traced, but, very probably, they have been of not less importance. I refer here to the transport from the land to the sea of matter in solution. Solvent denudation, as observed above, takes place mainly in the soils and in this way over the more level continental areas. It has resulted in the removal from the land and transfer to the ocean of an amount of matter which represents a uniform layer of one half a kilometre ; that is of more than i,6oo feet of rock. The continents have, during geological time, been lightened to this extent. On the other hand all this matter has for the greater part escaped the geosyncUnes and become uni- formly dilKused throughout the ocean or precipitated over its floor principally on the continental slopes before the great depths are reached. Of this material the ocean 51 THE BIRTH-TIME OF THE WORLD waters contain in solution an amount sufficient to increase their specific gravity by 27 per cent. Taking the last point first, it is interesting to note the effects upon the bulk of the ocean which has resulted from the matter dissolved in it. From the known density of average sea water we find that 100 ccs. of it weigh just 1027 grammes. Of this 3-5 per cent, by weight are solids in solution. That is to say, 3-594 grammes. Hence the weight of water present is 991 grammes, or a volume of 99-1 CCS. From this we see that the salts present have increased the volume by 0-9 ccs. or 0-9 per cent. The average depth of the ocean is 2,000 fathoms or 3,700 metres. The increase of depth due to salts dissolved in the ocean has been, therefore, 108 feet or 33"24 metres. This result assumes that there has been no increased elastic compression due to the increased pressure, and no change of compressional elastic pro- perties. We mky be sure that the rise on the shore line of the land has not been less than 100 feet. We see then that as the result of solvent denudation we have to do with a heavier and a deeper ocean, expanded in volume by nearly one per cent, and the floor of which has become raised, on an average, about 700 feet by precipitated sediment. One of the first conceptions, which the student of geology has to dismiss from his mind, is that of the immobility or rigidity of the Earth's crust. The land we live on sways even to the gentle rise and fall of ocean tides 52 DENUDATION around the coasts. It suffers its own tidal oscillations due to the moon's attractions. Large tracts of semi- liquid matter underlie it. There is every evidence that the raised features of the Globe are sustained by such pressures acting over other and adjacent areas as serve to keep them in equilibrium against the force of gravity. This state of equiUbrium, which was first recognised by Pratt, as part of the d5mamics of the Earth's crust, has been named isostasy. The state of the crust is that of " mobile equilibrium." The transfer of matter from the exposed land surfaces to the sub-oceanic slopes of the continents and the increase in the density of the ocean, must all along have been attended by isostatic readjustment. We cannot take any other view. On the one hand the land was being hghtened ; on the other the sea was increasing in mass and depth and the flanks of the continents were being loaded with the matter removed from the land and borne in solution to the ocean. How important the resulting movements must have been may be gathered from the fact that the existing land of the Globe stands at a mean elevation of no more than 2,000 feet above sea level. We have seen that solvent denudation re- moved over 1,600 feet of rock. But we have no evidence that on the whole the elevation of land in the past was ever very different from what it now is. We have, then, presented to our view the remarkable fact that throughout the past, and acting with extreme 53 THE BIRTH-TIME OF THE WORLD slowness, the land has steadily been melted down into the sea and as steadily been upraised from the waters. It is possible that the increased bulk of the ocean has led to a certain diminution of the exposed land area. The point is a difficult one. One thing we may without much risk assume. The sub-aereal current of dissolved matter from the land to the ocean was accompanied by a sub-crustal flux from the ocean areas to the land areas ; the heated viscous materials creeping from depths far beneath the ocean floor to depths beneath the roots of the moimtains which arose around the oceans. Such movements took ages for their accomplishment. Indeed, they have been, probably, continuous all along and are still proceeding. A low degree of viscosity will suffice to permit of movements so slow. Super-imposed upon these movements the rh3rthmic alternations of depression and elevation of the geosynclines probably resulted in releasing the crust from local accumulation of strains arising in the more rigid surface materials. The whole sequence of movements presents an extraordinary picture of pseudo-vitedity — reminding us of the circulatory and respiratory systems of a vast organism. All great results in our universe are founded in motions and forces the most minute. In contemplating the Cause or the Effect we stand equally impressed with the spectacle presented to us. We shall now turn from the great effects of denudation upon the history and evolution of a world and consider for a moment activities 54 DENUDATION so minute in detail that their operations will probably for ever elude our bodily senses, but which nevertheless have necessarily affected and modified the great results we have been considering. The ocean a little way from the land is generally so free from suspended sediments that it has a blackness as of ink. This blackness is due to its absolute freedom from particles reflecting the sun's light. The beautiful blue of the Swiss and Italian lakes is due to the presence of very fine particles carried into them by the rivers ; the finest flomr of the glaciers, which remain almost indefinitely suspended in the water. But in the ocean it is only in those places where rapid currents running over shallows stir continually the sediments or where the fresh water of a great river is carried far from the land, that the presence of silt is to be observed. The beautiful phenomenon of the coal-black sea is familiar to every yachtsman who has sailed to the west of our Islands.^ There is, in fact, a very remarkable difference in the manner of settlement of fine sediments in salt and in fresh water. We are here brought into contact with one of those subtle yet influential natural actions the explanation of which involves scientific advance along many apparently unconnected lines of investigation. * See Tyndall's Voyage to Algeria in Fragments of Science. The cause of the blue colour of the lakes has been discussed by various observers, not always with agreement. 55 THE BIRTH-TIME OF THE WORLD It is easy to observe in the laboratory the fact of the different behaviour of salt and fresh water towards finely divided substances. The nature of the insoluble sub- stance is not important. We place, in a good light, two glass vessels of equal dimensions ; the one filled with sea water, the other with fresh water. Into each we stir the same weight of very finely powdered slate : just so much as will produce a cloudiness. In a few hours we find the sea water limpid. The fresh water is still cloudy, however ; and, indeed, may be hardly different in appearance from what it was at starting. In itself this is a most extraordinary experi- ment. We would have anticipated quite the opposite result owing to the greater density of the sea water. But a still more interesting experiment remains to be carried out. In the sea water we have many different salts in solution. Let us see if these salts are equally responsible for the result we have obtained. For this purpose we measure out quantities of sodium chloride and magnesium chloride in the proportion in which they exist in sea water : that is about as seven to one. We add such an equal amount of water to each as represents the dilution of these salts in sea water. Then finally we stir a Uttle of the finely powdered slate into each. It will be found that the magnesium chloride, although so much more dilute than the sodium chloride, is con- siderably more active in clearing out the suspension. We may now try such marine salts as magnesium sulphate, 56 DENUDATION or cfilcium sulphate against sodium chloride ; keeping the marine proportions. Again we find that the mag- nesium and calcium salts are the most effective, although so much more dilute than the sodium salt. There is no visible clue to the explanation of these results. But we must conclude as most probable that some action is at work in the sea water and in the salt solutions which clumps or flocculates the sediment. For only by the gathering of the particles together in little aggregates can we explain their rapid fall to the bottom. It is not a question of viscosity (?.e. of resist- ance to the motion of the particles), for the salt solutions are rather more viscous than the fresh water. Still more remarkable is the fact that every dissolved sub- stance will not bring a,bout the result. Thus if we dissolve sugar in water we find that, if anything, the silt settles more slowly in the sugar solution than in fresh water. Now there is one effect produced by the solution of such salts as we have dealt with which is not produced by such bodies as sugar. The water is rendered a con- ductor of electricity. Long ago Faraday explained this as due to the presence of free atoms of the dissolved salt in the solution, carrying electric charges. We now speak of the salt as " ionised." That is it is partly split up into ions or free electrified atoms of chlorine, sodium, magnesium, etc., according to the particular salt in solu- tion. This fact leads us to think that these electrified 57 THE BIRTH-TIME OF THE WORLD atoms moving about in the solution may be the cause of the clumping or flocculation. Such electrified atoms are absent from the sugar solution : sugar does not become " ionised " when it is dissolved. The suspicion that the free electrified atoms play a part in the phenomenon is strengthened when we recall the remarkable difference in the action of sodium chloride and magnesium chloride. In each of the solutions of these substances there are free chlorine atoms each of which carries a single charge of negative electricity. As these atoms are alike in both solutions the different behaviour of the solutions cannot be due to the chlorine. But the metallic atom is very different in the two cases. The ionised sodium atom is known to be monad or carries but one positive charge ; whereas the magnesium atom is diad and carries two positive charges. If, then, we assume that the metalUc, positively electrified atom is in each case responsible, we have something to go on. It may be now stated that it has been found by experi- ment and supported by theory that the clumping power of an ion rises very rapidly with its valency ; that is with the number of unit charges associated with it. Thus diads such as magnesium, calcium, barium, etc., are very much more efficient than monads such as sodium, potassium, etc., and again, triads such as alu- minium are, similarly, very much more powerful than diad atoms. Here, in short, we have arrived at the active cause of the phenomenon. Its inner mechanism 58 DENUDATION is, however, harder to fathom. A plausible explanation can be offered, but a study of it would take us too far. Sufficient has been said to show the very subtile nature of the forces at work. We have here an effect due to the sea salts derived by denudation from the land which has been slowly augmenting during geological time. It is certain that the ocean was practically fresh water in remote ages. During those times the silt from the great rivers would have been carried very far from the land. A Mississippi of those ages would have sent its finer suspensions far abroad on a contemporary Gulf stream : not improbably right across the Atlantic. The earlier sediments of argillaceous t3^e were not collected in the geosj^nclines and the genesis of the motmtains was delayed propor- tionately. But it was, probably, not for very long that such conditions prevailed. For the accumulation of calcium salts must have been rapid, and although the great salinity due to sodium salts was of slow growth the salts of the diad element calcium must have soon introduced the co-operation of the ion in the work of building the mountain. 59 THE ABUNDANCE OF LIFE^ We had reached the Pass of Tre Croci» and from a point a little below the summit, looked eastward over the glorious Val Buona. The pines which clothed the floor and lower slopes of the valley, extended their multitudes into the furthest distance, among the many recesses of the mountains, and into the confluent Val di Misurina. In the sunshine the Alpine butterflies flitted from stone to stone. The ground at our feet and ever3^where through- out the forests teamed with the countless milUons of the small black ants. It was a magnificent display of vitahty ; of the aggres- siveness of vitaUty, assailing the barren heights of the limestone, wringing a subsistence from dead things. And the question suggested itself with new force : why the abxmdance of life and its unending activity ? In trying to answer this question, the present sketch originated. I propose to refer for an answer to d5mamic considera- tions. It is apparent that natural selection can only be concerned in a secondary way. Natural selection defines ^ Proc. Roy. Dublin Soc, vol. vii., 1890. ' In the Dolomites of South-east Tsrrol; during the summet of 1890. Much of what follows was evolved in discussion with my fellow-traveller, Henry H. Dixon. Much of it is bis. 60 THE ABUNDANCE OF LIFE a certain course of development for the organism ; but very evidently some property of inherent progressiveness in the organism must be involved. The mineral is not affected by natural selection to enter on a course of continual variation and multiplication. The d3mamic relations of the organism with the environment are evidently very different from those of inanimate nature. General Dynamic Conditions attending Inanimate Actions It is necessary, in the first place, to refer briefly to the phenomena attending the transfer of energy within and into inanimate material systems. It is not assumed here that these phenomena are restricted in their sphere of action to inanimate nature. It is, in fact, very certain that they are not ; but while they confer on dead nature its own d5m£imic tendencies, it will appear that their effects are by various means evaded in living nature. We, therefore, treat of them as characteristic of inanimate actions. We accept as fundamental to all the con- siderations which follow the truth of the principle of the Conservation of Energy.^ 1 " The principle of the Conservation of Energy has acquired so much scientific weight during the last twenty years that no physiologist would feel any confidence in an experiment which showed a considerable difference between the work done by the animal and the balance of the account of Energy received and spent." — Clerk Maxwell, Nature, vol. xix., p. 142. See also Helmboltz On the Conservation of Force. 61 THE BIRTH-TIME OF THE WORLD Whatever speculations may be made as to the course of events very distant from us in space, it appears certain that dissipation of energy is at present actively progress- ing throughout our sphere of observation in inanimate nature. It follows, in fact, from the second law of thermo- d3mamics, that whenever work is derived from heat, a certain quantity of heat falls in potential without doing work or, in short, is dissipated. On the other hand, work may be entirely converted into heat. The result is the heat-tendency of the universe. Heat, being an undirected form of energy, seeks, as it were, its own level, so that the result of this heat-tendency is continual approach to uniformity of potential. The heat-tendency of the universe is also revealed in the far-reaching " law of maximum work," which defines that chemical change, accomplished without the inter- vention of external energy, tends to the production of the body, or system of bodies, which disengage the greatest quantity of heat.^ And, again, vast numbers of actions going on throughout nature are attended by dissipatory thermal effects, as those arising from the motions of proximate molecules (friction, viscosity), and from the fall of electrical potential. Thus, on all sides, the energy which was once most probably existent in the form of gravitational potential, is being dissipated into unavailable forms. We must 1 Berthelot, Essai de Mecanique Chimique. 62 THE ABUNDANCE OF LIFE recognize dissipation as an inevitable attendant on inanimate transfer of energy. But when we come to consider inanimate actions in relation to time, or time-rate of change, we find a new feature in the phenomena attending transfer of energy ; a feature which is really involved in general statements as to the laws of physical interactions."^ It is seen, that the attitude of inanimate material systems is very generally, if not in all cases, retardative of change — opposing it by effects generated by the primary action, which may be called " secondary " for convenience. Further, it will be seen that these secondary effects are those concerned in bringing about the inevitable dissi- pation. As example, let us endeavour to transfer gravitational potential energy contained in a mass raised above the surface of the Earth into an elastic body, which we can put into compression by resting the weight upon it. In this way work is done against elastic force and stored as elastic potential energy. We may deal with a metal spring, or with a mass of gas contained in a cylinder fitted with a piston upon which the weight may be placed. In either case we find the effect of compression is to raise the temperature of the substance, thus causing its • Helmholtz, Ice and Glaciers. Atkinson's collection of his Popular Lectures. First Series, p. 120. Quoted by Tate, Heat, p. 311. 63 THE BIRTH-TIME OF THE WORLD expansion or increased resistance to the descent of the weight. And this resistance continues, with diminishing intensity, till aJl the heat generated is dissipated into the surrounding medium. The secondary effect thus delays the final transfer of energy. Again, if we suppose the gas in the cylinder replaced by a vapour in a state of saturation, the effect of increased pressure, as of a weight placed upon the piston, is to reduce the vapoiu: to a liquid, thereby bringing about a great diminution of volume and proportional loss of gravitational potential by the weight. But this change will by no means be brought about instantaneously. When a little of the vapour is condensed, this portion parts with latent heat of vaporisation, increasing the tension of the remainder, or raising its point of saturation, so that before the weight descends any further, this heat has to escape from the cylinder. Many more such cases might be cited. The heating of india-rubber when expanded, its cooling when compressed, is a remarkable one ; for at first sight it appears as if this must render it exceptional to the general law, most substances exhibiting the opposite thermal effects when stressed. However, here, too, the action of the stress is opposed by the secondary effects developed in the sub- stance ; for it is found that this substance contracts when heated, expands when cooled. Again, ice being a sub- stance which contracts in melting, the effect of pressure is to facilitate melting, lowering its freezing point. But 64 THE ABUNDANCE OF LIFE so soon as a little melting occurs, the resulting liquid calls on the residual ice for an amount of heat equivalent to the latent heat of Hquefaction, and so by cooling the whole, retards the change. Such particular cases illustrate a principle controlling the interaction of matter and energy which seems uni- versal in application save when evaded, as we shall see, by the ingenuity of life. This principle is not only revealed in the researches of the laboratory ; it is manifest in the history of worlds and solar systems. Thus, consider the effects arising from the aggregation of matter in space under the influence of the mutual attraction of the particles. The tendency here is loss of gravitational potential. The final approach is however retarded by the temperature, or vis viva of the parts attending collision and compression. From this cause the great suns of space radiate for ages before the final loss of potential is attained. Clerk Maxwell^ observes on the general principle that less force is required to produce a change in a body when the change is unopposed by constraints than when it is subjected to such. From this if we assume the external forces acting upon a system not to rise above a certain potential (which is the order of nature), the constraints of secondary actions may, under certain circumstances, lead to final rejection of some of the energy, or, in any 1 Theory of Heat, p. 131. 65 F THE BIRTH-TIME OF THE WORLD case, to retardation of change in the system — dissipation of energy being the result.^ As such constraints seem inherently present in the properties of matter, we may summarise as follows : The transfer of energy into any inanimate material system is attended by effects retardative to the transfer and conducive to dissipation. Was this the only possible djmamic order ruling in material systems it is quite certain the myriads of ants and pines never could have been, except aU generated by creative act at vast primary expenditure of energy. Growth and reproduction would have been impossible in systems which retarded change at every step and never proceeded in any direction but in that of dissipation. Once created, indeed, it is conceivable that, as heat engines, they might have dragged out an existence of alternate life and death ; Ufe in the hours of sunshine, death in hours of darkness : no final death, however, their lot, till their parts were simply worn out by long use, never made good by repair. But the sus- tained and increasing activity of organized nature is a fact; therefore some other order of events must be possible. ^ The law of Least Action, which has been appHed, not alone in optics, but in many mechanical systems, appears physically based upon the restraint and retardation opposing the transfer of energy in material systems. 66 THE ABUNDANCE OF LIFE General Dynamic Conditions attenoing Animate Actions What is the actual dynamic attitude of the primary organic engine — the vegetable organism ? We consider, here, in the first place, not intervening, but resulting phenomena. The young leaf exposed to solar radiation is small at first, and the quantity of radiant energy it receives in unit of time cannot exceed that which falls upon its surface. But what is the effect of this energy ? Not to produce a retardative reaction, but an accelerative response : for, in the enlarging of the leaf by growth, the plant opens for itself new chaimels of supply. If we refer to " the living protoplasm which, with its unknown molecular arrangement, is the only absolute test of the cell and of the organism in general," ' we find a similar attitude towards external sources of available energy. In the act of growth increased rate of assimilation is involved, so that there is an acceleration of change till a bulk of maximum activity is attained. The surface, finally, becomes too small for the absorption of energy adequate to sustain further increase of mass (Spencer^), and the acceleration ceases. The waste going on in the central parts is then just balanced by the renewal at the surface. By division, by spreading of the mass, by 1 Claus, Zoology, p. 13. * Geddes and Thomson, The Evolution of Sex, p. 220. 67 THE BIRTH-TIME OF THE WORLD out-flowing processes, the normal activity of growth may be restored. TUl this moment nothing would be gained by any of these changes. One or other of them is now conducive to progressive absorption of energy by the organism, and one or other occurs, most generally the best of them, subdivision. Two units now exist ; the total mass immediately on division is unaltered, but paths for the more abundant absorption of energy are laid open. The encystment of the protoplasm (occurring under conditions upon which naturalists do not seem agreed^) is to all appearance protective from an unfavourable environment, but it is often a period of internal change as well, resulting in a segregation within the mass of numerous small units, followed by a break-up of the whole into these units. It is thus an extension of the basis of supply, and in an impoverished medium, where unit of surface is less active, is evidently the best means of preserving a condition of progress. Thus, in the organism which forms the basis of all modes of life, a definite law of action is obeyed under various circumstances of reaction with the available energy of its environment. Similarly, in the case of the more complex leaf, we see, not only in the phenomenon of growth, but in its extension in a flattened form, and in the orientation of greatest siirface towards the source of energy, an attitude towards 1 However, " In no way comparable with death," Weismann, Biological Memoirs, p. 158. 68 THE ABUNDANCE OF LIFE available energy causative of accelerated transfer. There is seemingly a principle at work, leading to the increase of organic activity. Many other examples might be adduced. The gastrula stage in the development of embryos, where by invagina- tion such an arrangement of the multiplying cells is secured as to offer the greatest possible surface consistent with a first division of labour ; the provision of cUia for drawing upon the energy supplies of the medium ; and more generally the specialisation of organs in the higher developments of Ufe, may alike be regarded as efforts of the organism directed to the absorption of energy. When any particular organ becomes unavailing in the obtain- ment of supplies, the organ in the course of time becomes aborted or disappears. ^ On the other hand, when a too ready and liberal supply renders exertion and speciahsation unnecessary, a similar abortion of functionless organs takes place. This is seen in the degraded members of certain parasites. During certain epochs of geological history, the vege- table world developed enormously ; in response probably to liberal supplies of carbon dioxide. A structural adaptation to the rich atmosphere occurred, such as was calculated to co-operate in rapidly consuming the supplies, and to this obedience to a law of progressive transfer of energy we owe the vast stores of energy now accumulated 1 Claus, Zoology, p. 157. ^9 THE BIRTH-TIME OF THE WORLD in our coal fields. And when, further, we reflect that this store of energy had long since been dissipated into space but for the intervention of the organism, we see definitely another factor in organic transfer of energy — a factor acting conservatively of energy, or antagonistically to dissipation. The tendency of organized nature in the presence of unlimited supplies is to " run riot." This seems so universal a relation, that we are safe in seeing here cause and effect, and in drawing our conclusions as to the attitude of the organism towards available energy. New species, when they come on the field of geological history, armed with fresh adaptations, irresistible tUl the slow defences of the subjected organisms are completed, attain enormous sizes under the stimulus of abundant supply, till finally, the environment, living and dead, reacts upon them with restraining influence. The exuberance of the organism in presence of energy is often so abundant as to lead by deprivation to its self-destruction. Thus the growth of bacteria is often controlled by their own waste products. A moment's consideration shows that such progressive activity denotes an accelerative attitude on the part of the organism towards the transfer of energy into the organic material system. Finally, we are con- scious in ourselves how, by use, our faculties are developed ; and it is apparent that all such progressive developments must rest on actions which respond to supplies with fresh demands. Possibly in the present and ever- 70 THE ABUNDANCE OF LIFE increasing consumption of inanimate power by civilise^ races, we see revealed the dynamic attitude of the organ- ism working through thought-processes. Whether this be so or not, we find generally in organised nature causes at work which in some way lead to a progressive transfer of energy into the organic system. And we notice, too, that all is not spent, but both im- mediately in the growth of the individual, and ultimately in the multiplication of the species, there are actions associated with vitedity which retard the dissipation of energy. We proceed to state the dynamical principles involved in these manifestations, which appear character- istic of the organism, as follows : — The transfer of energy into any animate material system is attended by effects conducive to the transfer, and retarda- tive of dissipation. This statement is, I think, perfectly general. It has been in part advanced before, but from the organic more than the physical point of view. Thus, "hunger is an essential characteristic of living matter " ; and again, " hunger is a dominant characteristic of living matter,"* are, in part, expressions of the statement. If it be objected against the generality of the statement, that there are periods in the hfe of individuals when stagnation and decay make their appearance, we may answer, that 1 Evolution of Sex. Geddes and Thomson, chap. xvi. See also a reference to Cope's theory of " Growth Force," in Wallace's Darwinism, p. 421. 71 THE BIRTH-TIME OF THE WORLD such phenomena arise in phases of life developed under conditions of external constraint, as will be urged more fuUy further on, and that in fact the special conditions of old age do not and cannot express the true law and tendency of the d3mamic relations of life in the face of its evident advance upon the Earth. The law of the unconstrained cell is growth on an ever increasing scale ; and although we assume the organic configuration, whether somatic or reproductive, to be essentially unstable, so that continual inflow of energy is required merely to keep it in existence, this does not vitiate the fact that, when free of all external constraint, growth gains on waste. Indeed, even in the case of old age, the statement remains essentially true, for the phenomena then displayed point to a breakdown of the functioning power of the cell, an approximation to configurations incapable of assimila- tion. It is not as if life showed in these phenomena that its conditions could obtain in the midst of abundance, and yet its law be suspended ; but as if they represented a degradation of the very conditions of life, a break up, under the laws of the inanimate, of the animate contriv- ance ; so that energy is no longer available to it, or the primary condition, " the transfer of energy into the animate system," is imperfectly obeyed. It is to the perfect contrivance of hfe our statement refers. That the final end of aU will be general non-availability there seems little reason to doubt, and the organism, itsejf dependent upon differences of potential, cannot 73 Plate VIII. FIRS ASSAILING THI^, H1',I(.]ITS. ^LAI H^: l-IA N LK IHAL, I'taing ft. 73. THE ABUNDANCE OF LIFE hope to carry on aggregation of energy beyond the period when differences of potential are not. The organism is hot accountable for this. It is being affected by events external to it, by the actions going on through inanimate agents. And although there be only a part of the received energy preserved, there is a part preserved, and this amount is continually on the increase. To see this it is only necessary to reflect that the sum of animate energy — capability of doing work in any way through animate means — at present upon the Earth, is the result, although a small one, of energy reaching the Earth since a remote period, and which otherwise had been dissipated in space. In inanimate actions throughout nature, as we know it, the availability is continually diminishing. The change is all the one way. As, however, the supply of availabls energy in the universe is (probably) limited in amount, we must look upon the two as simply effecting the final dissipation of potential in very different ways. The animate system is aggressive on the energy available to it, spends with economy, and invests at interest till death finally deprives it of all. It has heirs, indeed, who inherit some of its gains, but they, too, must die, and ultimately there will be no successors, and the greater part must melt away as if it had never been. The inanimate system responds to the forces imposed upon it by sluggish changes ; of that which is thrust upon it, it squanders uselessly. The path of the energy is very different in the two cases. 73 THE BIRTH-TIME OF THE WORLD While it is true generally that both systems ultimately result in the dissipation of energy to uniform potential, the organism can, as we have seen, under particular cir- cumstances evade the final doom altogether. It can lay up a store of potential energy which may be permanent. Thus, so long as there is free oxygen in the universe, our coalfields might, at any time in the remote future, generate light and heat in the universal grave. It is necessary to observe on the fundamental distinction between the growth of the protoplasm and the growth of the crystal. It is common to draw comparison between the two, and to point to metaboUsm as the chief distinction. But while this is the most obvious distinction the more fundamental one remains in the energy relations of the two with the environment. The growth of the crystal is the result of loss of energy ; that of the organism the result of gain of energy. The crystal represents a last position of stable equilibrium assumed by molecules upon a certain loss of kinetic energy, and the formation of the crystal by evaporation and concentration of a liquid does not, in its dynamic aspect, differ much from the precipita- tion of an amorphous sediment. ^ The organism, on the other hand, represents a more or less unstable condition formed and maintained by inflow of energy ; its formation, indeed, often attended with a loss of kinetic energy (fixation of carbon in plants), but, if so, accompanied by 1 It appears exceptional for the crystal line configuration to stand higher in the scale of energy than the amorphous. 74 THE ABUNDANCE OF LIFE a more than compensatory increase of potential mole- cular energy. Thus, between growth in the living world and growth in the dead world, the energy relations with the environ- ment reveal a marked contrast. Again, in the phenomena of combustion, there are certain superficial resemblances which have led to comparison between the two. Here again, however, the attitudes towards the energy of the environment stand very much as + and -. The life absorbs, stores, and spends with economy. The flame only recklessly spends. The property of storage by the organism calls out a further distinction between the course of the two processes. It secures that the chemical activity of the organism can be propagated in a medium in which the supply of energy is discontinuous or locaUsed, The chemical activity of the combustion can, strictly speaking, only be propagated among contiguous particles. I need not dwell on the latter fact ; an example of the former is seen in the action of the roots of plants, which will often traverse a barren place or circumvent an obstacle in their search for energy. In this manner roots will find out spots of rich nutriment. Thus there is a dynamic distinction between the pro- gress of the organism and the progress of the combustion, or of the chemical reaction generally. And although there be imstable chemical systems which absorb energy during reaction, these are (dynamically) no more than the expansion of the compressed gas. There is a certain 75 THE BIRTH-TIME OF THE WORLD initial capacity in the system for a given quantity of energy ; this satisfied, progress ceases. The progress of the organism in time is continual, and goes on from less to greater so long as its development is unconstrained and the supply of energy is unlimited. We must regard the organism as a configuration which is so contrived as to evade the tendency of the universal laws of nature. Except we are prepared to believe that a violation of the second law of thermo-dynamics occurs in the organism, that a " sorting demon " is at work within it, we must, I think, assume that the interactions going on among its molecules are accompanied by retardation and dissipation like the rest of nature. That such conditions are not incompatible with the definition of the djmamic attitude of the organism, can be shown by analogy with our inanimate machines which, by aid of hypotheses in keeping with the second law of thermo-dynamics, may be supposed to fulfil the energy-functions of the plant or animal, and, in fact, in all apparent respects conform to the definition of the organism. We may assume this accomplished by a contrivance of the nature of a steam-engine, driven by solar energy. It has a boiler, which we may suppose fed by the action of the engine. It has piston, cranks, and other movable parts, all subject to resistance from friction, etc. Now there is no reason why this engine should not expend its surplus energy in shaping, fitting, and starting into action other engines : — in fact, in reproductive sacrifice. All 76 THE ABUNDANCE OF LIFE these other engines represent a multiplied absorption of energy as the effects of the energy received by the parent engine, and may in time be supposed to reproduce them- selves. Further, we may suppose the parent engine to be small and capable of developing very little power, but the whole series as increasing in power at each generation. Thus the primary energy relations of the vegetable organism are represented in these engines, and no violation of the second law of thermo-dynamics involved. We might extend the analogy, and assuming these engines to spend a portion of their surplus energy in doing work against chemical forces — as, for example, by decom- posing water through the intervention of a d3mamo — suppose them to lay up in this way a store of potential energy capable of heating the boilers of a second order of engines, representing the graminivorous animal. It is obvious without proceeding to a tertiary or carnivorous order, that the condition of energy in the animal world may be supposed fulfilled in these successive series of engines, and no violation of the principles governing the actions going on in our machines assumed. Organisms evolving on similar principles would experience loss at every transfer. Thus only a portion of the radiant energy absorbed by the leaf would be expended in actual work, chemical and gravitational, etc. It is very certain that this is, in fact, what takes place. It is, perhaps, worth passing observation that, from the nutritive dependence of the animal upon the vegetable, THE BIRTH-TIME OF THE WORLD and the fact that a conversion of the energy of the one to the purposes of the other cannot occur without loss, the mean energy absorbed daily by the vegetable for the purpose of growth must greatly exceed that used in animal growth ; so that the chemical potential energy of vegeta- tion upon the earth is much greater than the energy of aU kinds represented in the animal configurations.* It appears, too, that in the power possessed by the vegetable of remaining comparatively inactive, of surviving hard times by the expenditure and absorption of but little, the vegetable constitutes a veritable reservoir for the imiform supply of the more unstable and active animal. Finally, on the question of the manner of origin of organic systems, it is to be observed that, while the Ufe of the present is very surely the survival of the fittest of the tendencies and chances of the past, yet, in the initiation of the organised world, a single chance may have decided a whole coiurse of events : for, once originated, its own law secures its increase, although within the new order of actions, the law of the fittest must assert itself. That such a progressive material system as an organism was possible, and at some remote period was initiated, is matter of knowledge ; whether or not the initiatory living configuration was rare and fortuitous, or the probable result of the general action of physical laws acting among innumerable chances, must remain matter of 1 I find a similar conclusion arrived at in Semper's Animal Life, p. 32. 78 THE ABUNDANCE OF LIFE speculation. In the event of the former being the truth, it is evidently possible, in spite of a large finite number of habitable worlds, that hfe is non-existent elsewhere. If the latter is the truth, it is almost certain that there is life in all, or many of those worlds. Evolution and Acceleration of Activity The primary factor in evolution is the " struggle for existence." This involves a " natural selection " among the many variations of the organism. If we seek the underljdng causes of the struggle, we find that the necessity of food and (in a lesser degree) the desire for a mate are the principal causes of contention. The former is much the more important factor, and, accordingly, we find the greater degree of speciahsation based upon it. The present view assumes a dynamic necessity for its demands involved in the nature of the organism as such. This assumption is based on observation of the outcome of its unconstrained growth, reproduction, and life-acts. We have the same right to assert this of the organism as we have to assert that retardation and degradation attend the actions of inanimate machines, which assertion, also, is based on observation of results. Thus we pass from the superficial statements that organisms require food in order to live, or that organisms desire food, to the more fundamental one that : The organism is a configuration of matter which absorbs energy acceleratively, without limit, when unconstrained. n THE BIRTH-TIME OF THE WORLD This is the dynamic basis for a " struggle for existence." The organism being a material system responding to accession of energy with fresh demands, and energy being limited in amount, the struggle follows as a necessity. Thus, evolution guiding the steps of the energy-seeking organism, must pre-suppose and find its origin in that inherent property of the organism which determines its attitude in presence of available energy. Turning to the factor, " adaptation," we find that this also must pre-suppose, in order to be explicable, some quality of aggressiveness on the part of the organism. For adaptation in this or that direction is the result of repulse or victory, and, therefore, we must presuppose an attack. The attack is made by the organism in obedience to its law of demand ; we see in the adaptation of the organism but the accumulated wisdom derived from past defeats and victories. Where the environment is active, that is living, adaptation occurs on both sides. Improved means of defence or improved means of attack, both presuppose activity. Thus the reactions to the environment, animate and inanimate, are at once the outcome of the eternal aggressiveness of the organism, and the source of fresh aggressiveness upon the resources of the medium. As concerns the " survival of the fittest " (or " natural selection "), we can, I think, at once conclude that the organism which best fulfils the organic law under the cir- cumstances of supply is the " fittest," ipso facto. In many 80 Plate IX. ,. ■ Si- ^ .,.. T--^. M-i W -*'-^-'ji^ LIFE NEAR THE SXOW-LIXE. THE LOG-COIION IN I'UbbEbilUiV : XSCHINGKL Facing p. So. THE ABUNDANCE OF LIFE cases this is contained in the common-sense consideration, that to be strong, consistent with concealment from enemies which are stronger, is best, as giving the organism mastery over foes which are weaker, and generally renders it better able to secure supplies. Weismann points out that natural selection favours early and abundant repro- duction. But whether the qualifications of the " fittest " be strength, fertility, cunning, fleetness, imitation, or concealment, we are safe in concluding that growth and reproduction must be the primary qualities which at once determine selection and are fostered by it. Inherent in the nature of the organism is accelerated absorption of energy, but the qualifications of the " fittest " are various, for the supply of energy is limited, and there are many competitors for it. To secure that none be wasted is ultimately the object of natural selection, deciding among the eager competitors what is best for each. In short, the facts and generalisations concerning evolution must presuppose an organism endowed with the quality of progressive absorption of energy, and retentive of it. The continuity of organic activity in a world where supplies are intermittent is evidently only possible upon the latter condition. Thus it appears that the dynamic attitude of the organism, considered in these pages, occupies a fundamental position regarding its evolution. We turn to the consideration of old age and death, endeavouring to discover in what relation they stand to the innate progressiveness of the organism. 8i G THE BIRTH-TIME OF THE WORLD The Periodicity of the Organism and the Law of Progressive Activity The organic system is essentially unstable. Its aggres- sive attitude is involved in the phenomenon of growth, and in reproduction which is a form of growth. But the energy absorbed is not only spent in growth. It partly goes, also, to make good the decay which arises from the instability of the organic unit. The cell is molecularly perishable. It possesses its entity much as a top keeps erect, by the continual inflow of energy. MetaboUsm is always taking place within it. Any other condition would, probably, involve the difficulties of perpetual motion. The phenomenon of old age is not evident in the case of the unicellular organism reproducing by fission. At any stage of its history all the individuals are of the same age : all contain a like portion of the original cell, so far as this can be regarded as persisting where there is continual flux of matter and energy. In the higher organisms death is universally evident. Why is this ? The question is one of great complexity. Considered from the more fundamental molecular point of view we should perhaps look to failure of the power of cell division as the condition of mortality. For it is to this phenomenon — that of cell division — that the continued life of the protozoon is to be ascribed, as we have already seen. Reproduction is, in fact, the saving factor here. As we do not know the source or nature of the stimulus 82 THE ABUNDANCE OF LIFE responsible for cell division we cannot give a molecular account of death in the higher organisms. However we shall now see that, philosophically, we are entitled to consider reproduction as a saving factor in this case also ; and to regard the death of the individual much as we regard the fall of the leaf from the tree : i.e. as the cessation of an out-growth from a development extending from the past into the future. The phenomena of old age and natural death are, in short, not at variance with the progressive activity of the organism. We perceive this when we come to consider death from the evolutionary point of view. Professor Weismann, in his two essays, " The Duration of Life," and " Life and Death,"^ adopts and defends the view that " death is not a primary necessity but that it has been secondarily acquired by adaptation." The cell was not inherently limited in its number of cell-generations. The low unicellular organisms are potentially immortal, the higher multicellular forms with well-differentiated organs contain the germs of death within themselves. He finds the necessity of death in its utility to the species. Long life is a useless luxury. Early and abimdant reproduction is best for the species. An immortal individual would gradually become injured and would be valueless or even harmful to the species by taking the place of those that are sound. Hence natural selection will shorten life. 1 See his Biological Memoirs. Oxford, 1889. 83 THE BIRTH-TIME OF THE WORLD Weismann contends against the transmission of ac- quired characters as being unproved.^ He bases the appearance of death on variations in the reproductive cells, encouraged by the ceaseless action of natural selec- tion, which led to a differentiation into perishable somatic cells and immortal reproductive cells. The time-limit of any particular organism ultimately depends upon the number of somatic cell-generations and the duration of each generation. These quantities are " predestined in the germ itself " which gives rise to each individual. " The existence of immortal metazoan organisms is con- ceivable," but their capacity for existence is influenced by conditions of the external world ; this renders necessary the process of adaptation. In fact, in the differentiation of somatic from reproductive cells, material was provided upon which natural selection could operate to shorten or to lengthen the life of the individual in accordance with the needs of the species. The soma is in a sense " a secondary appendage of the real bearer of life — the reproductive cells." The somatic cells probably lost their immortal qualities, on this immortality becoming useless to the species. Their mortality may have been a mere conse- quence of their differentiation [loc. cit., p. 140), itself due to natural selection. " Natural death was not," in fact, " introduced from absolute intrinsic necessity inherent in the nature of living matter, but on grounds of utility, 1 Biological Memoirs, p. 142. 84 THE ABUNDANCE OF LIFE that is from necessities which sprang up, not from the general conditions of Ufe, but from those special con- ditions which dominate tlie life of multicellular organisms." On the inherent immortality of life, Weismann finally states : " Reproduction is, in truth, an essential attribute of hying matter, just as the growth which gives rise to it. , . . Life is continuous, and not periodically inter- rupted : ever since its first appearance upon the Earth in the lowest organism, it has continued without break ; the forms in which it is manifest have alone undergone change. Every individual aUve to-day — even the highest — ^is to be derived in an unbroken line from the first and lowest forms."^ At the present day the view is very prevalent that the soma of higher organisms is, in a sense, but the carrier for a period of the immortal reproductive cells (Ray Lan- kester)* — an appendage due to adaptation, concerned in their supply, protection, and transmission. And whether we regard the time-limit of its functions as due to external constraints, recurrently acting till their effects become hereditary, or to variations more directly of internal origin, encouraged by natural selection, we see in old age and death phenomena ultimately brought about in obedience to the action of an environment. These are not inherent in the properties of Uving matter. But, in spite * Loc. cit., p. 159. » Geddes and Thomson, The Evolution of Sex, chap, xviii. 85 THE BIRTH-TIME OF THE WORLD of its mortality, the body remains a striking manifestation of the progressiveness of the organism, for to this it must be ascribed. To it energy is available which is denied to the protozoon. Ingenious adaptations to environment are more especially its privilege. A higher manifestation, however, was possible, and was found in the development of mind. This, too, is a servant of the cell, as the genii of the lamp. Through it energy is available which is denied to the body. This is the masterpiece of the cell. Its activity dates, as it were, but from yesterday, and to-day it inherits the most diverse energies of the Earth. Taking this view of organic succession, we may liken the individual to a particle vibrating for a moment and then coming to rest, but sweeping out in its motion one wave in the continuous organic vibration travelling from the past into the future. But as this vibration is one spread- ing with increased energy from each vibrating particle, its propagation involves a continual accelerated inflow of energy from the surrounding medium, a dynamic con- dition unknown in periodic effects transmitted by in- animate actions, and, indeed, marking the fundamental difference between the djmamic attitudes of the animate and inanimate. We can trace the periodic succession of individuals on a diagram of activity with some advantage. Considering, first, the case of the unicellular organism reproducing by subdivision and recalling that conditions, definite and inevitable, oppose a limit to the rate of growth, or, for our 86 THE ABUNDANCE OF LIFE present purpose, rate of consumption of energy, we pro- ceed as follows : Fig.i. Lifer Waves ofthcAnueba. Along a horizontal axis units of time are measured ; along a vertical axis units of energy. Then the life-history of the amoeba, for example, appears as a line such as A in Fig. I. During the earlier stages of its growth the rate of absorption of energy is small ; so that in the unit interval of time, t, the small quantity of energy, e^, is absorbed. As life advances, the activity of the organism augments, till finally this rate attains a maximum, when «» units of energy are consumed in the unit of time.^ 1 Reference to p. 76, where the organic system is treated as purely mechanical, may help readers to understand what is involved in this curve. The solar engine may, unquestionably, have its activity defined by such a curve. The organism is, indeed, more complex ; but neither this fact nor our ignorance of its mechanism, affects the principles which justify the diagram. 87 THE BIRTH-TIME OF THE WORLD On this diagram reproduction, on the part of the organism, is represented by a line which repeats the curvature of the parent organism originating at such a point as P in the path of the latter, when the rate of consumption of energy has become constant. The organism A has now ceased to act as a unit. The pro- ducts of fission each carry on the vital development of '^* .'«"'. " Time. Fig. 2. Life- Carves of Frimiiive Organisms. the species along the curve B, which may be numbered (2), to signify that it represents the activity of two indi- viduals, and so on, the numbering advancing in geo- metrical progression. The particular curvature adopted in the diagram is, of course, imaginary ; but it is not of an indeterminate nature. Its course for any species is a characteristic of fundamental physical importance, regard- ing the part played in nature by the particular organism. 88 THE ABUNDANCE OF LIFE In Fig. 2 is represented the path of a primitive multicellular organism before the effects of competi- tion produced or fostered its mortality. The lettering of Fig. I applies ; the successive reproductive acts are marked Pi, Pa ; Qu Qz, etc., in the paths of the succes- sive individuals. Time. Fig.3. Cmnmincing interfemtte cf Primitive OrgaivisvK. The next figure (Fig. 3) diagrammatically illustrates death in organic history. The path ever turns more and more from the axis of energy, till at length the point is reached when no more energy is available ; a tangent to the curve at this point is at right angles to the axis of energy and parallel to the time axis. The death point is reached, and however great a length we measure along the axis of time, no further consumption of energy is 89 THE BIRTH-TIME OF THE WORLD indicated by the path of the organism. Drawing the line beyond the death point is meaningless for our present purpose. It is observable that while the progress of animate nature finds its representation on this diagram by lines sloping upwards from left to right, the course of events in inanimate nature — for example, the history of the ft) fe) ^ y _j» Time. Fig.4. Life- Waves of a Species. organic configuration after death, or the changes pro- gressing — ^let us say, in the solar system, or in the process of a crystallisation, would appear as lines sloping down- wards from left to right. Whatever our views on the origin of death may be, we have to recognise a periodicity of functions in the life- history of the successive individuals of the present day ; and whether or not we trace this directly or indirectly to go THE ABUNDANCE OF LIFE a sort of interference with the rising wave of life, imposed by the activity of a series of derived units, each seeking energy, and in virtue of its adaptation each being more fitted to obtain it than its predecessor, or even leave the idea of interference out of account altogether in the origination or perpetuation of death, the truth of the diagram (Fig. 4) holds in so far as it may be supposed to graphically represent the dynamic history of the individual. The point chosen on the curve for the origination of a derived unit is only appUcable to certain organisms, many reproducing at the very close of Ufe. A chain of units are supposed here represented.* The Length of Life If we lay out waves as above to a common scale of time for different species, the difference of longevity is shown in the greater or less number of vibrations exe- cuted in a given time, i.e. in greater or less " frequency." We cannot indeed draw the curvature correctly, for this would necessitate a knowledge which we have not of the activity of the organism at different periods of its life-history, and so neither can we plot the direction of the organic line of propagation with respect to the 1 Projecting upon the axes of time and energy any one complete vibration, as in fig. 4, the total energy consumed by the organism during life is the length E on the axis of energy, and its period of Ufe is the length T on the time-axis. The mean activity is the quotient -. 91 THE BIRTH-TIME OF THE WORLD axes of reference as this involves a knowledge of the mean activity.^ The group of curves which follow, relating to typical animals possessing very different activities (Fig. 5), are therefore entirely diagrammatic, except in respect to the approximate longevity of the organisms, (i) might represent an animal of the length of life and of the activity of Man ; (2) , on the same scale of longevity, "■ In" the relative food-supply at various periods of life the curvature is approximately determinable. 92 Plate X. THE JOY OF LIFE. THE AlIPEZZO THAL. DOLOMITE ALPS. Faliiig p. 93. THE ABUNDANCE OF LIFE one of the smaller manunals ; and (3), the life history of a cold blooded animal living to a great age ; e.g. certain of the reptilia. It is probable, that to conditions of structural develop- ment, under the influence of natural selection, the question of longer or shorter life is in a great degree referable. Thus, development along lines of large growth will tend to a slow rate of reproduction from the simple fact that unlittiited energy to supply abundant reproduction is not procurable, whatever we may assume as to the strength or cunning exerted by the individual in its efforts to obtain its supplies. On the other hand, de- velopment along Unes of small growth, in that repro- duction is less costly, will probably lead to increased rate of reproduction. It is, in fact, matter of general observation that in the case of larger animals the rate of reproduction is generally slower than in the case of smaller animals. But the rate of reproduction might be expected to have an important influence in determining the particular periodicity of the organism. Were we to depict in the last diagram, on the same time-scale as Man, the vibrations of the smaller and shorter-lived Uving things, we would see but a straight line, save for secular variations in activity, representing the progress of the species in time : the tiny thrills of its units lost in comparison with the yet brief period of Man. The interdependence of the rate of reproduction and 93 THE BIRTH-TIME OF THE WORLD the duration of the individual is, indeed, very probably revealed in the fact that short-lived animals most gener- ally reproduce themselves rapidly and in great abundance, and vice versa. In many cases where this appears contra- dicted, it will be found that the young are exposed to such dangers that but few survive {e.g. many of the reptilia, etc.), and so the rate of reproduction is actually slow. Death through the periodic rigour of the inanimate environment calls forth phenomena very different from death introduced or favoured by competition. A multi- plicity of effects simulative of death occur. Organisms will, for example, learn to meet very rigorous conditions if slowly introduced, and not permanent. A transitory period of want can be tided over by contrivance. The lily withdrawing its vital forces into the bulb, protected from the greatest extremity of rigour by seclusion in the Earth ; the trance of the hibernating animal ; are instances of such contrivances. But there are organisms whose hfe-wave truly takes up the periodicity of the Earth in its orbit. Thus the smaller animals and plants, possessing less resources in themselves, die at the approach of winter, propagating themselves by units which, whether egg or seed, undergo a period of quiescence during the season of want. In these quiescent units the energy of the organism is potential, and the time-energy function is in abeyance. This condition is, perhaps, foreshadowed in the encyst- 94 THE ABUNDANCE OF LIFE ment of the amoeba in resistance to drought. In most cases of hibernation the time-energy function seems main- tained at a loss of potential by the organism, a diminished vital consumption of energy being carried on at the expense of the stored energy of the tissues. So, too, even among the largest organisms there will be a diminu- tion of activity periodically inspired by cUmatological conditions. Thus, wholly or in part, the activity of Time. J'ig.t. Life-WavtsofaCtrial. organisms is recurrently affected by the great energy- tides set up by the Earth's orbital motion. Similarly in the phenomenon of sleep the organism responds to the Earth's axial periodicity, for in the in- terval of night a period of impoverishment has to be endured. Thus the diurnal waves of energy also meet a response in the organism. These tides and waves of activity would appear as larger and smaller ripples 95 THE BIRTH-TIME OF THE WORLD on the life-curve of the organism. But in some, in which Hfe and death are encompassed in a day, this would not be so ; and for the annual among plants, the seed rest divides the waves with lines of no activity (Fig. 6). Thus, finally, we regard the organism as a dynamic phenomenon passing through periodic variations of intensity. The material systems concerned in the trans- fer of the energy rise, flourish, and fall in endless suc- cession, hke cities of ancient dynasties. At points of similar phase upon the waves the rate of consumption of energy is approximately the same ; the functions, too, which demand and expend the energy are of similar nature. That the rhythm of these events is ultimately based on harmony in the configuration and motion of the molecules within the germ seems an unavoidable con- clusion. In the Ufe of the individual rhjrthmic dynamic phenomena reappear which in some cases have no longer a parallel in the external world, or under conditions when the individual is no longer influenced by these external conditions.^ In many cases the periodic pheno- mena ultimately die out under new influences, like the oscillations of a body in a viscous medium ; in others when they seem to be more deeply rooted in physiological conditions they persist. The " length of life is dependent upon the number 1 The Descent of Man. 96 THE ABUNDANCE OF LIFE of generations of somatic cells which can succeed one another in the course of a single life, and furthermore the number as well as the duration of each single cell- generation is predestined in the germ itself."^ Only in the vague conception of a harmonising or formative structural influence derived from the germ, perishing in each ceU from internal causes, but handed from cell to cell till the formative influence itself degrades into molecular discords, does it seem possible to form any physical representation of the successive events of life. The degradation of the molecular formative influence might be supposed involved in its frequent transference according to some such dynamic actions as occur in inanimate nature. Thus, ultimately, to the waste within the ceU, to the presence of a force retardative of its perpetual harmonic motions, the death of the individual is to be ascribed. Perhaps in protoplasmic waste the existence of a universal death should be recognised. It is here we seem to touch inanimate nature ; and we are led back to a former conclusion that the organism in its unconstrained state is to be regarded as a contriv- ance for evading the d5mamic tendencies of actions in which lifeless matter participates.^ ^ Weismann, Life and Death ; Biological Memoirs, p. 146. * In connection with the predestinating power and possible complexity of the germ, it is instructive to reflect on the very great molecular population of even the smallest spores — ^giving rise to very simple forms. Thus, the spores of the unicellular 97 H THE BIRTH-TIME OF THE WORLD The Numerical Abundance of Life We began by seeking in various manifestations of life a dynamic principle sufficiently comprehensive to embrace its very various phenomena. This, to all appearance, found, we have been led to regard life, to a great extent, as a periodic dynamic phenomenon. Fundamentally, in that characteristic of the contrivance, which leads it to respond favourably to transfer of energy, its enormous extension is due. It is probable that to its instability its numerical abundance is to be traced — for this, necessitating the continual supply of all the parts already formed, renders large, undifferentiated growth, incompatible with the hmited supplies of the environment. These are fundamental conditions of abundant life upon the Earth. Although we recognise in the instability of living systems the underlying reason for their numerical abund- ance, secondary evolutionary causes are at work. The most important of these is the self-favouring nature of the phenomenon of reproduction. Thus there is a tendency not only to favour reproductiveness, but early reproductiveness, in the form of one prolific reproductive Schizomycetes are estimated to dimensions as low as i/io,ooo of a millimetre in diameter (Cornil et Babes, Les Bacteries, i. 37). From Lord Kelvin's estimate of the number of molecules in water, comprised within the length of a wave-length of yellow light (The Size of Atoms, Proc. R. I., vol. x., p. 185) it is probable that such spores contain some 500,000 molecules, while one hundred molecules range along a diameter. 98 THE ABUNDANCE OF LIFE act, after which the individual dies.* Hence the wave- length of the species diminishes, reproduction is more frequent, and correspondingly greater numbers come and go in an interval of time. Another cause of the numerical abundance of life exists, as already stated, in the conditions of nourish- ment. Energy is more readily conveyed to the various parts of the smaller mass, and hence the lesser organisms will more actively functionate ; and this, as being the urging d3mamic attitude, as well as that most generally favoTirable in the struggle, will multiply and favour such forms of hfe. On the other hand, however, these forms will have less resource within themselves, and less power of endurance, so that they are only suitable to fairly uniform conditions of supply ; they cannot survive the long continued want of winter, and so we have the seasonal abundance of summer. Only the larger and more resistant organisms, whether animal or vegetable, will, in general, populate the Earth from year to year. From this we may conclude that, but for the seasonal energy-tides, the development of life upon the globe had gone along very different Unes from those actually followed. It is, indeed, possible that the evolution of the larger organisms would not have occurred ; there would have been no vacant place for their develop- ment, and a being so endowed as Man could hardly * Weismann, The Duration of Life. 99 THE BIRTH-TIME OF THE WORLD have been evolved. We may, too, apply this reasoning elsewhere, and regard as highly probable, that in worlds which are without seasonal influences, the higher developments of Ufe have not appeared ; except they have been evolved under other conditions, when they might for a period persist. We have, indeed, only to picture to ourselves what the consequence of a continu- ance of summer would be on insect life to arrive at an idea of the antagonistic influences obtaining in such worlds to the survival of larger organisms. It appears that to the dynamic attitude of life in the first place, and secondarily to the environmental con- ditions limiting undifferentiated growth, as well as to the action of heredity in transmitting the reproductive quahties of the parent to the offspring, the multitudes of the pines, and the hosts of ants, are to be ascribed. Other causes are very certainly at work, but these, I think, must remain primary causes. We well know that the abundance of the ants and pines is not a tithe of the abundance around us visible and invisible. It is a vain endeavour to reaUse the countless numbers of our fellow-citizens upon the Earth ; but, for our purpose, the restless ants, and the pines solemnly quiet in the sunshine, have served as types of animate things. In the pine the gates of the orgsmic have been thrown open that the vivif5nng river of energy may flow in. The ants and the butterflies sip for a brief moment of its waters, and again vanish into the 100 Plate XL PINES SOLEMNLY rjUILI. JIADERANELJ THAL. Facing p. 100. THE ABUNDANCE OF LIFE inorganic : life, love and death encompassed in a day. Whether the organism stands at rest and life comes to it on the material currents of the winds and waters, or in the vibratory energy of the aether ; or, again, whether with restless craving it hurries hither and thithet in search of it, matters nothing. The one principle — the accelerative law which is the law of the organic — ■ urges all ahke onward to development, reproduction and death. But although the individual dies death is not the end ; for hfe is a rhythmic phenomenon. Through the passing ages the waves of life persist : waves which change in their form and in the frequency to which they are attuned from one geologic period to the next, but which still ever persist and still ever increase. And in the end the organism outlasts the generations of the hills. lOI THE BRIGHT COLOURS OF ALPINE FLOWERS^ It is admitted by all observers that many species of flower- ing plants growing on the higher alps of mountainous regions display a more vivid and richer colour in their bloom than is displayed in the same species growing in the valleys. That this is actually the case, and not merely an effect produced upon the observer by the scant foliage rendering the bloom more conspicuous, has been shown by comparative microscopic examination of the petals of species growing on the heights and in the valleys. Such examination has revealed that in many cases pigment granules are more numerous in the in- dividuals growing at the higher altitudes. The difference is specially marked in Myosotis sylvatica. Campanula rotundifoUa, Ranunculus sylvaticus, Galium cruciatum, and others. It is less marked in the case of Thymus serpyllum and Geranium sylvaticum ; while in Rosa alpina and Erigeron alpinus no difference is observable.' In the following cases a difference of intensity of colour is, according to Kerner (" Pflanzenleben," ii, 504), specially noticeable : — Agrostemma githago, Campanula 1 Proc. Royal Dublin Society, 1893. 2 G. Bonnier, quoted by De Varigny, Experimental Evolution, P- 55- 102 BRIGHT COLOURS OF ALPINE FLOWERS pusilla, Dianthus inodorus {silvestns), Gypsophila repens, Lotus corniculatus, Saponaria ocymoides, Satureja hortensis. Taraxacum officinale, Vicia cracca, and Vicia septum. To my own observation this beautiful phenomenon has always appeared most obvious and impressive. It appears to have struck many improfessional observers. Helmholtz offers the explanation that the vivid colours are the result of the brighter sunlight of the heights. It has been said, too, that they are the direct' chemical effects of a more highly ozonized atmosphere. The latter explanation I am unable to refer to its author. The following pages contain a suggestion on the matter, which occurred to me while touring, along with Henry H. Dixon, in the Linthal district of Switzerland last summer.^ If the bloom of these higher alpine flowers is especially pleasing to our own aesthetic instincts, and markedly con- spicuous to us as observers, why not also especially attractive and conspicuous to the insect whose mission it is to wander from flower to flower over the pastures ? The answer to this question involves the hypothesis I would advance as accounting for the bright colours of high-growing individuals. In short, I believe a satis- factory explanation is to be found in the conditions of insect life in the higher alps. In the higher pastures the summer begins late and * The summer of 1892. 103 I THE BIRTH-TIME OF THE WORLD closes early, and even in the middle of summer the day closes in with extreme cold, and the cold of night is only dispelled when the sun is well up. Again, clouds cover the heights when all is clear below, and cold winds sweep over them when there is warmth and shelter in the valleys. With these rigorous conditions the pollinating insects have to contend in their search for food, and that when the rival attractions of the valleys below are so many. I believe it is these rigorous conditions which are indirectly responsible for the bright colours of alpine flowers. For such conditions will bring about a comparative scarcity of insect activity on the heights ; and a scarcity or uncer- tainty in the action of insect agency in effecting fertiliza- tion will intensify the competition to attract attention, and only the brightest blooms will be fertilized.^ This will be a natural selection of the brightest, or the 1 Grant Allen, I have recently learned, advances in Science in Arcady the theory that there is a natural selective cause fostering the bright blooms of alpines. The selective cause is, however, by him referred to the greater abundance of butterfly relatively to bee fertUizers. The former, he says, display more aesthetic instinct than bees. In the valley the bees secure the fertiUzation of all. I may observe that upon the Fridolins Alp all the fertilizers we observed were bees. I have always found butterflies very scarce at altitudes of 7,000 to 8,000 feet. The alpine bees are very light in body, like our hive bee, and I do not think rarefaction of the atmosphere can operate to hinder its ascent to the heights, as Grant Allen suggests. The observations on the death-rate of bees and butterflies on the glacier, to be referred to presently, seem to negative such a hypothesis, and to show that a large preponderance of bees over butterflies make their way to the heights. 104 Plate XII. ^m0m '■^: ,^ '^- v^.v6 ';/»i}'^'^ ■ ^ ,„-*, /;.'■: ; ,, ; *-v 'f* '.^ ^ * , ■ .7 ALPINE FLOWERS IN THE VALLEYS. I-'acing p. \Q$. BRIGHT COLOURS OF ALPINE FLOWERS brightest will be the fittest, and this condition, along with the influence of heredity, will encourage a race of vivid flowers. On the other hand, the more scant and uncertain root supply, and the severe atmospheric conditions, wUl not encourage the grosser struggle for existence which in the valleys is carried on so eagerly between leaves and branches — ^the normal offensive and defensive weapons of the plant — and so the struggle becomes refined into the more aesthetic one of colour and brightness between flower and flower. Hence the scant foliage and vivid bloom would be at once the result of a necessary economy, and a resort to the best method of securing reproduction under the circumstances of insect fertilizing agency. Or, in other words, while the luxuriant growth is forbidden by the conditions, and thus methods of offence and defence, based upon vigorous development, reduced in importance, it would appear that the struggle is mainly referred to rivalry for insect preference. It is probable that this is the more economical manner of carrying on the contest. In the valleys we see on every side the struggle between the vegetative organs of the plant ; the soundless battle among the leaves and branches. The blossom here is carried aloft on a slender stem, or else, taking but a secondary part in the contest, it is relegated to obscurity (PI. XII.). Further up on the mountains, where the con- ditions are more severe and the supplies less abundant, the leaf and branch assume lesser dimensions, for they are costly weapons to provide and the elements are unfriendly 105 THE BIRTH-TIME OF THE WORLD to their existence (PI. XIII .) . Still higher, approaching the cUmatic limit of vegetable Hfe, the struggle for existence is mainly carried on by the aesthetic rivalry of lowly but conspictious blossoms. As regards the conditions of insect life in the higher alps, it came to my notice in a very striking manner that vast numbers of such bees and butterflies as venture up perish in the cold of night time. It appears as if at the approach of dusk these are attracted by the gleam of the snow, and quitting the pastures, lose themselves upon the glaciers and firns, there to die in hundreds. Thus in an ascent of the Todi from the Fridolinshiitte we counted in the early dawn sixty-seven frozen bees, twenty-nine dead butterflies, and some half-dozen moths on the Biferten Glacier and Fim. These numbers, it is to be remembered, only included those lying to either side of our way over the snow, so that the number must have mounted up to thousands when integrated over the entire glacier and firn. Approaching the summit none were found. The bees resembled our hive bee in appearance, the butterflies resembled the small white variety common in our gardens, which has yellow and black upon its wings. One large moth, striped across the abdomen, and measur- ing nearly two inches in length of body, was found. Upon our return, long after the sun's rays had grown strong, we observed some of the butterflies showed signs of reanimation. We descended so quickly to avoid the inconvenience of the soft snow that we had time for no io6 Plate XIII. ALPINE FLOWERS ON THE HEIGHTS. Fuin^ p. io6. BRIGHT COLOURS OF ALPINE FLOWERS close observation on the frozen bees. But dead bees are common objects upon the snows of the alps. These remarks I noted down roughly while at Linthal last summer, but quite recently I read in Natural Science^ the following note : " Late Flowering Plants. — ^While we write, the ivy is in flower, and bees, wasps, and flies are jostling each other and struggling to find standing-room on the sweet- smeUing plant. How great must be the advantage obtained by this plant through its exceptional habit of flowering in the late autumn, and ripening its fruit in the spring. To anyone who has watched the struggle to approach the ivy-blossom at a time when nearly all other plants are bare, it is evident that, as far as transport of pollen and cross-fertiUzation go, the plant could not flower at a more suitable time. The season is so late that most other plants are out of flower, but yet it is not too late for many insects to be brought out by each sunny day, and each insect, judging by its behaviour, must be exceptionally hungry. " Not only has the ivy the world to itself during its flowering season, but it delays to ripen its seed till the spring, a time when most other plants have shed their seed, and most edible fruits have been picked by the birds. Thus birds wanting fruit in the spring can obtain little but ivy, and how they appreciate the ivy berry is evident ' For December, 1892, voL i., p. 730. 107 THE BIRTH-TIME OF THE WORLD by the purple stains everywhere visible within a short distance of the bush." These remarks suggest that the ivy adopts the con- verse attitude towards its visitors to that forced upon the alpine flower. The ivy bloom is small and incon- spicuous, but then it has the season to itself, and its in- conspicuousness is no disadvantage, i.e. if one plant was more conspicuous than its neighbours, it would not have any decided advantage where the pollinating insect is abundant and otherwise unprovided for. Its dark-green berries in spring, which I would describe as very inconspicuous, have a similar advantage in relation to the necessities of bird life. The experiments of M. C. Flahault must be noticed. This naturalist grew seeds of coloufed flowers which had ripened in Paris, part in Upsala, and part in Paris ; and seed which had ripened in Upsala, part at Paris, and part at Upsala. The flowers opening in the more northern city were in most cases the brighter.^ If this observation may be considered indisputable, as appears to be the case, the question arises. Are we to regard this as a direct effect of the more rigorous climate upon the development of colouring matter on the blooms opening at Upsala ? If we suppose an affirmative answer, the theory of direct effect by sun brightness must I think be abandoned. But I venture to think that the explanation of the UpsaJa 1 Quoted by De Varigny, Experimental ^volution, p. 56- 108 BRIGHT COLOURS OF ALPINE FLOWERS experiment is not to be found in direct climatic influence upon the colour, but in causes which lie deeper, and involve some factors deducible from biological theory. The organism, as a result of the great facts of heredity and of the survival of the fittest, is necessarily a system which gathers experience with successive genera- tions ; and the principal lesson ever being impressed upon it by external events is economy. Its success depends upon the use it makes of its opportunities for the recep- tion of energy and the economy attained in disposing of what is gained. With regard to using the passing opportunity the entire seasonal development of life is a manifestation of this attitude, and the fleetness, agihty, etc., of higher organisms are developments in this direction. The higher vegetable organism is not locomotory, save in the transferences of pollen and seed, for its food comes to it, and the necessary relative motion between food and organism is preserved in the qmck motion of radiated energy from the sun and the slower motion of the winds on the surface of the earth. But, even so, the vegetable organism must stand ever ready and waiting for its supplies. Its molecular parts must be ready to seize the prey offered to it, somewhat as the waiting spider the fly. Hence, the plant stands ready ; and every cloud with moving shadow crossing the fields handicaps the shaded to the benefit of the unshaded plant in the adjoining field. The open bloom 109 THE BIRTH-TIME OF THE WORLD is a manifestation of the generally expectant attitude of the plant, but in relation to reproduction. As regards economy, any principle of maximum economy, where many functions have to be fulfilled, will, we may very safely predict, involve as far as possible mutual helpfulness in the processes going on. Thus the process of the development towards meeting any particular external conditions. A, suppose, will, if possible, tend to forward the development towards meeting conditions B ; so that, in short, where circumstances of morphology and physiology are favourable, the ideally economical system will be attained when in place of two separate processes, a, /3, the one process y, cheaper than a + /8, suffices to advance development simultaneously in both the direc- tions A and B. The economy is as obvious as that involved in " killing two birds with the one stone " — ^if so crude a simile is permissible — and it is to be expected that to foster such economy will be the tendency of evolution in all organic systems subjected to restraints as those we are acquainted with invariably are. Such economy might be simply illustrated by con- sidering the case of a reservoir of water elevated above two hydraulic motors, so that the elevated mass of water possessed gravitational potential. The available energy here represents the stored-up energy in the organism. How best may the water be conveyed to the two motors [the organic systems reacting towards conditions A and B] so no BRIGHT COLOURS OF ALPINE FLOWERS that as little energy as possible is lost in transit ? If the motors are near together it is most economical to use the one conduit, which will distribute the requisite supply of water to both. If the motors are located far asunder it will be most economical to lay separate conduits. There is greatest economy in meeting a plurality of functions by the same train of physiological processes where this is consistent with meeting other demands necessitated by external or internal conditions. But an important and obvious consequence arises in the supply of the two motors from the one conduit. We cannot work one motor without working the other. If we open a valve in the conduit both motors start into motion and begin consuming the energy stored in the tank. And although they may both under one set of conditions be doing useful and necessary work, in some other set of conditions it may be needless for both to be driven. This last fact is an illustration of a consideration which must enter into the phenomenon which an eminent biologist speaks of as physiological or unconscious " memory,"' For the development of the organism from the ovum is but the starting of a train of interde- pendent events of a complexity depending upon the experience of the past. * Ewald Hering, quoted by Ray Lankaster, The Advancement of Science, p. 283. Ill THE BIRTH-TIME OF THE WORLD In short, we may suppose the entire development of the plant, towards meeting certain groups of external conditions, physiologically knit together according as Nature tends to associate certain groups of conditions. Thus, in the case in point, climatic rigour and scarcity of pollinating agency will ever be associated ; and in the long experience of the past the most economical physiological attitude towards both is, we may suppose, adopted; so that the presence of one condition excites the apparent imconscious memory of the other. In reahty the process of meeting the one condition involves the process and development for meeting the other. And this consideration may be extended very generally to such organisms as can survive under the same associated natural conditions, for the history of evolution is so long, and the power of locomotion so essential to the organism at some period in its life history, that we cannot philoso- phically assume a local history for members of a species even if widely severed geographically at the present day. At some period in the past then, it is very possible that the individuals to-day thriving at Paris, acquired the experi- ence called out at Upsala. The perfection of physiological memory inspires no Umit to the date at which this may have occurred — possibly the result of a succession of severe seasons at Paris ; possibly the result of migrations — and the seed of many flowering plants possess means of migration only inferior to those possessed by the flpng and swimming animals. But, again, possibly the experi- II3 BRIGHT COLOURS OF ALPINE FLOWERS ence was acquired far back in the evolutionary history of the flower.* But a further consideration arises. Not only at each moment in the life of the individual must maximum income and most judicious expenditure be considered, but in its whole life history, and even over the history of its race, the efficiency must tend to be a maximum. This principle is even carried so far that when necessary it leads to the death of the individual, as in the case of those organisms which, having accomplished the reproductive act, almost immediately expire. This view of nature may be repellent, but it is, nevertheless, evident that we are parts of a system which ruthlessly sacrifices the individual on general grounds of economy. Thus, if the curve which defines the mean rate of reception of energy of all kinds at different periods in the Ufe of the organism be opposed by a second curve, drawn below the axis along which time is measured, representing the mean rate of expenditure of energy on development, reproduc- tion, etc. (Fig. 7), this latter curve, which is, of course, "■ The blooms of self-fertilising, and especially of cleistogamic plants (e.g. Viola), are examples of unconscious memory, or unconscious " association of ideas " leading to the development of organs now functionless. The Pontederia crassipes of the Amazon, which develops its floating bladders when grown in water, but aborts them rapidly when grown on land, and seems to retain this power of adaptation to the environment for an indefinite period of time, must act in each case upon an un- conscious memory based upon past experience. Many other cases might be cited. 113 I THE BIRTH-TIME OF THE WORLD physiologically dependent on the former, must be of such a nature from its origin to its completion in death, that the condition is realized of the most economical rate of expenditure at each period of life.^ The rate of expendi- ture of energy at any period of life is, of course, in such a curve defined by the slope of the curve towards the axis of time at the period in question ; but this particular slope must be led to by a -previous part of the curve, and Fig 7- involves its past and future course to a very great extent. There wUl, therefore, be impressed upon the organism by the factors of evolution a unified course of economical expenditure completed only by its death, and which will give to the developmental progress of the individual its prophetic character. In this way we look to the unified career of each organic unit, from its commencement in the ovum to the day 1 See The Abundance of Life. 114 BRIGHT COLOURS OF ALPINE FLOWERS when it is done with vitaUty, for that preparation for momentous organic events which is in progress through- out the entire course of development ; and to the economy involved in the welding of physiological processes for the phenomenon of physiological memory, wherein we see reflected, as it were, in the development of the organism, the association of inorganic restraints occurring in nature which at some previous period impressed itself upon the plastic organism. We may picture the seedling at Upsala, swayed by organic memory and the inherited tendency to an economical preparation for future events, gradually developing towards the aesthetic climax of its career. In some such manner only does it appear possible to account for the prophetic development of organisms, not alone to be observed in the alpine flowers, but through- out nature. And thus, finally, to the effects of natural selection and to actions defined by general principles involved in biology, I would refer for explanation of the manner in which flowers on the Alps develop their peculiar beauty. "5 MOUNTAIN GENESIS Our ancestors regarded mountainous regions with feelings of horror, mingled with commiseration for those whom an unkindly destiny had condemned to dwell therein. We, on the other hand, find in the contemplation of the great alps of the Earth such peaceful and elevated thoughts, and such rest to our souls, that it is to those very solitudes we turn to heal the wounds of life. It is diificult to explain the cause of this very different point of view. It is probably, in part, to be referred to that cloud of superstitious horror which, throughout the Middle Ages, peopled the solitudes with unknown terrors ; and, in part, to the asceticism which led the pious to regard the beauty and joy of life as snares to the soul's well-being. In those eternal sohtudes where the overwhelming forces of Nature are most in evidence, an evil principle must dwell or a dragon's dreadful brood must find a home. But while in our time the aesthetic aspect of the hills appeals to all, there remains in the physical history of the mountains much that is lost to those who have not shared in the scientific stydies of alpine structure and genesis. They lose a past history which for interest com- Ii6 MOUNTAIN GENESIS petes with anything science has to tell of the changes of the Earth. Great as are the physical features of the mountains compared with the works of Man, and great as are the forces involved compared with those we can originate or control, the loftiest ranges are small contrasted with the dimensions of the Earth. It is well to bear this in mind. I give here (PI. XV.) a measured drawing showing a sector cut from a sphere of 50 cms. radius ; so much of it as to exhibit the convergence of its radial boundaries which if prolonged will meet at the centre. On the same scale as the radius the diagram shows the highest mountains and the deepest ocean. The average height of the land and the average depth of the ocean are also exhibited. We see how small a movement of the crust the loftiest elevation of the Himalaya represents and what a little depression holds the ocean. Nevertheless, it is not by any means easy to explain the genesis of those small elevations and depressions. It would lead us far from our inxmediate subject to discuss the various theoretical views which have been advanced to account for the facts. The idea that mountain folds, and the lesser rugosities of the Earth's surface, arose in a wrinkling of the crust under the influence of cooling and skrinkage of the sub-crustal materials, is held by many eminent geologists, but not without dissent from others. The most striking observational fact connected with mountain structure is that, without exception, the ranges 117 THE BIRTH-TIME OF THE WORLD of the Earth are built essentially of sedimentary rocks : that is of rocks which have been accumulated at some remote past time beneath the surface of the ocean. A volcanic core there may sometimes be — probably an attendant or consequence of the uplifting — or a core of plutonic igneous rocks which has arisen under the same compressive forces which have bowed and arched the strata from their original horizontal position. It is not uncommon to meet among unobservant people those who regard all mountain ranges as volcanic in origin. Volcanoes, however, do not build mountain ranges. They break out as more or less isolated cones or hills. Compare the map of the Auvergne with that of Switzer- land ; the volcanoes of South Italy with the Apennines. Such great ranges as those which border with triple walls the west coast of North America are in no sense volcanic : nor are the Pyrenees, the Caucasus, or the Himalaya. Volcanic materials are poured out from the summits of the Andes, but the range itself is built up of folded sedi- ments on the same architecture as the other great ranges of the Earth. Before attempting an explanation of the origin of the mountains we must first become more closely acquainted with the phenomena attending mountain elevation. At the present day great accumulations of sediment are taking place along the margins of the continents where the rivers reach the ocean. Thus, the Gulf of Mexico re- ceiving the sediment of the Mississippi and Rio Grande ; li8 Plate XV. SECTOR OF THE EARTH. RISE OF ISOGEOTHEEMS INTO A DEPOSIT EVOLVING KADIOACTUE HEAT. Fctang p. 1 iS. MOUNTAIN GENESIS the north-east coast of South America receiving the sedi- ments of the Amazons ; the east coast of Asia receivihg the detritus of the Chinese rivers ; are instances of such areas of deposition. Year by year, century by centuty, the accumulation progresses, and as it grows the floor of the sea sinks under the load. Of the 3delding of the crust under the burthen of the sediments we are assured ; for otherwise the many miles of vertically piled strata which are uplifted to our view in the mountains, never could have been deposited in the coastal seas of the past. The flexure and sinking of the crust are undeniable reaUties. Such vast subsiding areas are known as geosynclines. From the acciunulated sediments of the geosynclines the mountain ranges of the past have in every case originated ; and the mountains of the future will assuredly arise and lofty ranges will stand where now the ocean waters close over the collecting sediments. Every mountain range upon the Earth enforces the certainty of this prediction. The mountain-forming movement takes place after a certain great depth of sediment is collected. It is most intense where the thickness of deposit is greatest. We see this when we examine the structure of our existing mountain ranges. At either side where the sediments thin out, the disturbance dies away, tm we find the com- paratively shallow and undisturbed level sediments which clothe the continental surface. Whatever be the connection between the deposition and iig THE BIRTH-TIME OF THE WORLD the subsequent upheaval, the element of great depth of accumulation seems a necessary condition and must evidently enter as a factor into the physical processes involved. The mountain range can only arise where the geosyncline is deeply filled by long ages of sedimentation. Dana's description of the events attending mountain building is impressive : " A mountain range of the common type, like that to which the Appalachians belong, is made out of the sedi- mentary formations of a long preceding era ; beds that were laid down conformably, and in succession, imtil they had reached the needed thickness ; beds spreading over a region tens of thousands of square miles in area. The region over which sedimentary formations were in progress in order to make, finally, the Appalachian range, reached from New York to Alabama, and had a breadth of 100 to 200 miles, and the pile of horizontal beds along the middle was 40,000 feet in depth. The pile for the Wahsatch Mountains was 60,000 feet thick, according to King. The beds for the Appalachians were not laid down in a deep ocean, but in shallow waters, where a gradual subsidence was in progress ; and they at last, when ready for the genesis, lay in a trough 40,000 feet deep, filling the trough to the brim. It thus appears that epochs of mountain-making have occurred only after long intervals of quiet in the history of a continent. "^ ^ Dana, Manual of Geology, third edition, p. 794. 120 MOUNTAIN GENESIS On the western side of North America the work of mountain-building was, indeed, on the grandest scale. For long ages and through a succession of geological epochs, sedimentation had proceeded so that the accumu- lations of Palaeozoic and Mesozoic times had collected in the geos3Ticline formed by their own ever increasing weight. The site of the future Laramide range was in late Cretaceous times occupied by some 50,000 feet of sedimentary deposits ; but the limit had apparently been attained, and at this time the Laramide range, as well as its southerly continuation into the United States, the Rockies, had their beginning. Chamberlin and SaUsburyi estimate that the height of the mountains developed in the Laramide range at this time was 20,000 feet, and that, owing to the further elevation which has since taken place, from 32,000 to 35,000 feet would be their present height if erosion had not reduced them. Thus on either side of the American continent we have the same forces at work, throwing up mountain ridges where the sediments had formerly been shed into the ocean. These great events are of a rhythmic character ; the crust, as it were, pulsating under the combined influences of sedimentation and denudation. The first involves downward movements under a gathering load, and ultimately a reversal of the movement to one of up- heaval ; the second factor, which throughout has been in 1 Chamberlin and Salisbury, Geology, 1906, iii., 163. 121 THE BIRTH-TIME OF THE WORLD operation as creator of the sediments, then intervenes as an assailant of the newly-raised mountains, transporting their materials again to the ocean, when the rhythmic action is restored to its first phase, and the age-long sequence of events must begin all over again. It has long been inferred that compressive stress in the crust must be a primary condition of these move- ments. The work required to efEect the upheavals must be derived from some pre-existing source of energy. The phenomenon — intrinsically one of folding of the crust — suggests the adjustment of the earth-crust to a lessening radius ; the fact that great mountain-building movements have simultaneously affected the entire earth is certainly in favour of the view that a generally prevailing cause is at the basis of the phenomenon. The compressive stresses must be confined to the upper few miles of the crust, for, in fact, the downward increase of temperature and pressure soon confers fluid properties on the medium, and slow tangential compression results in hydrostatic pressure rather than directed stresses. Thus the folding visible in the mountain range, and the lateral compression arising therefrom, are effects confined to the upper parts of the crust. The energy which uplifts the mountain is probably a surviving part of the original gravitational poten- tial energy of the crust itself. It must be assumed that the Crust in following downwards the shrinking sub- crustal magma, develops immense compressive stresses in 123 MOUNTAIN GENESIS its materials, vast geographical areas being involved. When folding at length takes place along the axis of the elongated sjmcline of deposition, the stresses find relief probably for some hundreds of miles, and the region of folding now becomes compressed in a transverse direction. As an illustration, the Laramide range, according to Dawson, represents the reduction of a surface-belt 50 miles wide to one of 25 miles. The marvellous trans- latory movements of crustal folds from south to north arising in the genesis of the Swiss Alps, which recent research has brought to hght, is another example of these movements of rehef , which continue to take place perhaps for many millions of years after they are initiated. The result of this 3delding of the crust is a buckling of the surface which on the whole is directed upwards ; but depression also is an attendant, in many cases at least, on mountain upheaval. Thus we find that the ocean floor is depressed into a syncline along the western coast of South America ; a trough always parallel to the ranges of the Andes. The downward deflection of the crust is of course an outcome of the same compressive stresses which elevate the mountain. The fact that the yielding of the crust is always situated where the sediments have accumulated to the greatest depth, has led to attempts from time to time of establish- ing a physical connexion between the one and the other. The best-known of these theories is that of Babbage and Herschel. This seeks the connexion in the rise of the 123 THE BIRTH-TIME OF THE WORLD geotherms into the sinking mass of sediment and the consequent increase of temperature of the earth-crust beneath. It will be understood that as these isogeo- therms, or levels at which the temperature is the same, lie at a uniform distance from the surface all over the Earth, unless where special variations of conductivity may disturb them, the introduction of material pressed down- wards from above must result in these materials partaking of the temperature proper to the depth to which they are depressed. In other words the geotherms rise into the sinking sediments, always, however, preserving their former average distance from the surface. The argument is that as this process undoubtedly involves the heating up of that portion of the crust which the sediments have displaced downwards, the result must be a local enfeeblement of the crust, and hence these areas become those of least resistance to the stresses in the crust. When this theory is examined closely, we see that it only amounts to saying that the bedded rocks, which have taken the place of the igneous materials beneath, as a part of the rigid crust of the Earth, must be less able to withstand compressive stress than the average crust. For there has been no absolute rise of the geotherms, the thermal conductivities of both classes of materials differ- ing but little. Sedimentary rock has merely taken the place of average crust-rock, and is subjected to the same average temperature and pressure prevailing in the sur- rounding crust. But are there any grounds for the 124 MOUNTAIN GENESIS assumption that the compressive resistance of a complex of sedimentary rocks is inferior to one of igneous materials ? The metamorphosed siliceous sediments are among the strongest rocks known as regards resistance to compres- sive stress ; and if hmestones have indeed plastic qualities, it must be remembered that their average amount is only some 5 per cent, of the whole. Again, so far as rise of temperature in the upper crust may affect the question, a temperature which will soften an average igneous rock will not soften a sedimentary rock, for the reason that the effect of solvent denudation has been to remove those alkaline sihcates which confer fusibihty. When, however, we take into account the radioactive con- tent of the sediments the matter assumes a different aspect. The facts as to the general distribution of radioactive substances at the surface, and in rocks which have come from considerable depths in the crust, lead us to regard as certain the widespread existence of heat-producing radioactive elements in the exterior crust of the Earth. We find, indeed, in this fact an explanation — at least in part — of the outflow of heat continually taking place at the surface as revealed by the rising temperature inwards. And we conclude that there must be a thickness of crust amounting to some miles, containing the radioactive elements. Some of the most recent measurements of the quantities of radium and thorium in the rocks of igneous origin — e.g. granites, syenites, diorites, basalts, etc., show that the 125 THE BIRTH-TIME OF THE WORLD radioactive heat continually given out by such rocks amounts to about one millionth part of 0-6 calories per second per cubic metre of average igneous rock. As we have to account for the escape of about 0-0114 calorie* per square metre of the Earth's surface per second (assuming the rise of temperature downwards, i.e. the " gradient " of temperature, to be one degree centigrade in 35 metres) the downward extension of such rocks might, prima facie, be as much as 19 kilometres. About this calculation we have to observe that we assume the average radioactivity of the materials with which we have dealt at the surface to extend uniformly all the way down, i.e. that our experiments reveal the average radioactivity of a radioactive crust. There is much to be said for this assumption. The rocks which enter into the measurements come from all depths of the crust. It is highly probable that the less silicious, i.e. the more basic, rocks, mainly come from considerable depths ; the more acid or silica-rich rocks, from higher levels in the crust. The radio-activity determined as the mean of the values for these two classes of rock closely agrees with that found for intermediate rocks, or rocks containing an intermediate amount of silica. Clarke contends that this last class of material probably represents the average composition of the Earth's crust so far as it has been explored by us. 1 The calorie referred to is the quantity of heat required to heat one gram of water, i.e. one cubic centimetre