Cape Trinity on the Saguenay.
A salient point of Laurentian Gneiss, on an old fiord of Pliocene erosion ([p. 99]).
(From a Photograph by Henderson.)

SOME
SALIENT
POINTS
IN THE
SCIENCE OF
THE EARTH

BY

SIR J. WILLIAM DAWSON

C.M.G., LL.D., F.R.S., F.G.S., &c.

WITH FORTY-SIX ILLUSTRATIONS

NEW YORK
HARPER & BROTHERS PUBLISHERS
1894

[PREFACE.]

The present work contains much that is new, and much in correction and amplification of that which is old; and is intended as a closing deliverance on some of the more important questions of geology, on the part of a veteran worker, conversant in his younger days with those giants of the last generation, who, in the heroic age of geological science, piled up the mountains on which it is now the privilege of their successors to stand.

J. W. D.

Montreal 1893.

[CONTENTS.]

[LIST OF ILLUSTRATIONS.]

TABLE OF GEOLOGICAL HISTORY.

Non-Geological readers will find in the following table a condensed explanation of the more important technical terms used in the following pages. The order is from older to newer.

GREATER PERIODS.	SYSTEMS OF FORMATIONS.	CHARACTERISTIC FOSSILS.
Archæan or Eozoic	Pre-Laurentian Laurentian		Protozoa	Protophyta
Palæozoic	Huronian		Crustaceans	Algæ
	Cambrian		Molluscs	Cryptogamous
	Cambro-Silurian[A]		Worms	and
	Silurian[B]		Corals, etc,	Gymnospermous
	Devonian		Fishes	Plants.
	Carboniferous		Amphibians
	Permian
Mesozoic	Triassic		Reptiles	Pines and
	Jurassic		Birds	Cycads
	Cretaceous		Earliest Mammals.	Trees of modern types.
Kainozoic or Tertiary	Eocene		Higher Mammals
	Miocene		of extinct forms
	Pliocene		Recent Mammals	Modern Plants,
	Pleistocene		and
	Modern		Man.

[A] Ordovician of Lapworth.

[B] Salopian of Lapworth.

[THE STARTING-POINT.]

DEDICATED TO THE MEMORY OF
PROF. ROBERT JAMESON,
Of the University of Edinburgh, my first Teacher in Geology,
whose Lectures I attended, and whose kind Advice and
Guidance I enjoyed, in the Winter of 1840-1841.

Headlands and Spurs—Popular Papers on Leading Topics—Revisiting Old Localities—Dedications—General Scope of the Work

[CHAPTER I.]

THE STARTING-POINT.

A

An explorer trudging along some line of coast, or traversing some mountain region, may now and then reach a projecting headland, or bold mountain spur, which may enable him to command a wide view of shore and sea, or of hill and valley, before and behind. On such a salient point he may sit down, note-book and glass in hand, and endeavour to correlate the observations made on the ground he has traversed, and may strain his eyes forward in order to anticipate the features of the track in advance. Such are the salient points in a scientific pilgrimage of more than half a century, to which I desire to invite the attention of the readers of these papers. In doing so, I do not propose to refer, except incidentally, to subjects which I have already discussed in books accessible to general readers, but rather to those which are imbedded in little accessible transactions, or scientific periodicals, or which have fallen out of print. I cannot therefore pretend to place the reader on all the salient points of geological science, or even on all of those I have myself reached, but merely to lead him to some of the viewing-places which I have found particularly instructive to myself.

For similar reasons it is inevitable that a certain personal element shall enter into these reminiscences, though this autobiographical feature will be kept as much in the background as possible. It is also to be anticipated that the same subject may appear more than once, but from different points of view, since it is often useful to contemplate certain features of the landscape from more than one place of observation.

To drop the figure, the reader will find in these papers, in a plain and popular form, yet it is hoped not in a superficial manner, some of the more important conclusions of a geological worker of the old school, who, while necessarily giving attention to certain specialties, has endeavoured to take a broad and comprehensive view of the making of the world in all its aspects.

The papers are of various dates; but in revising them for publication I have endeavoured, without materially changing their original form, to bring them up to the present time, and to state any corrections or changes of view that have commended themselves to me in the meantime. Such changes or modifications of view must of necessity occur to every geological worker. Sometimes, after long digging and hammering in some bed rich in fossils, and carrying home a bag laden with treasures, one has returned to the spot, and turned over the débris of previous excavation, with the result of finding something rare and valuable, before overlooked. Or, in carefully trimming and chiselling out the matrix of a new fossil, so as to uncover all its parts, unexpected and novel features may develop themselves. Thus, if we were right or partially right before, our new experience may still enable us to enlarge our views or to correct some misapprehensions. In that spirit I have endeavoured to revise these papers, and while I have been able to add confirmations of views long ago expressed, have been willing to accept corrections and modifications based on later discoveries.

In the somewhat extended span of work which has been allotted to me, I have made it my object to discover new facts, and to this end have spared no expenditure of time and labour; but I have felt that the results of discoveries in the works of God should not be confined to a coterie, but should be made public for the benefit of all. Hence I have gladly embraced any opportunities to popularise my results, whether in lectures, articles, popular books, or in the instruction of students, and this in a manner to give accurate knowledge, and perhaps to attract the attention of fellow-workers to points which they might overlook if presented merely in dry and technical papers. These objects I have in view in connection with the present collection of papers, and also the fact that my own pilgrimage is approaching its close, and that I desire to aid others who may chance to traverse the ground I have passed over, or who may be preparing to pass beyond the point I have reached.

To a naturalist of seventy years the greater part of life lies in the past, and in revising these papers I have necessarily had my thoughts directed to the memory of friends, teachers, guides, and companions in labour, who have passed away. I have therefore, as a slight token of loving and grateful remembrance dedicated these papers to the memory of men I have known and loved, and who, I feel, would sympathise with me in spirit, in the attempt, however feeble, to direct attention to the variety and majesty of those great works of the Creator which they themselves delighted to study.

Since the design of these papers excludes special details as to Canadian geology, or that of those old eastern countries to which I have given some attention, I must refer for them to other works, and shall append such reference of this kind as may be necessary. At the same time it will be observed that as my geological work has been concerned most largely with the oldest and newest rocks of the earth, and with the history of life rather than with rocks and minerals, there must necessarily be some preponderance in these directions, which might however, independently of personal considerations, be justified by the actual value of these lines of investigation, and by the special interest attaching to them in the present state of scientific discovery.

Having thus defined my starting-point, I would now with all respect and deference ask the reader to accompany me from point to point, and to examine for himself the objects which may appear either near, or in the dim uncertain distance, in illustration of what the world is, and how it became what it is. Perhaps, in doing so, he may be able to perceive much more than I have been able to discover; and if so, I shall rejoice, even if such further insight should correct or counteract some of my own impressions. It is not given to any one age or set of men to comprehend all the mysteries of nature, or to arrive at a point where it can be said, there is no need of farther exploration. Even in the longest journey of the most adventurous traveller there is an end of discovery, and, in the study of nature, cape rises beyond cape and mountain behind mountain interminably. The finite cannot comprehend the infinite, the temporal the eternal. We need not, however, on that account be agnostics, for it is still true that, within the scope of our narrow powers and opportunities, the Supreme Intelligence reveals to us in nature His power and divinity; and it is this, and this alone, that gives attraction and dignity to natural science.

[WORLD-MAKING.]

DEDICATED TO THE MEMORY OF
ADAM SEDGWICK AND SIR RODERICK IMPEY MURCHISON,
Whose joint Labours carried
our Knowledge of the History of the Earth
two Stages farther back,
and whose Differences of Opinion served to render
more glorious their Victories.

Fig. 1. Diagram illustrating Folding of the Crust of the Earth.—(a) Undisturbed crust. (b) Primary depression and deposition. (c) Mountain-making folds with their relations to an upper and lower magma.
Fig. 2. Result of folding, faulting, and denudation, as seen at Cascade Mountain, Western Canada
(after McConnell, p. 33).

[CHAPTER II.]

WORLD-MAKING.

G

Geological reading, especially when of a strictly uniformitarian character and in warm weather, sometimes becomes monotonous; and I confess to a feeling of drowsiness creeping over me when preparing material for a presidential address to the American Association for the Advancement of Science in August, 1883. In these circumstances I became aware of the presence of an unearthly visitor, who announced himself as of celestial birth, and intimated to me that being himself free from those restrictions of space and time which are so embarrassing to earthly students, he was prepared for the moment to share these advantages with me, and to introduce me to certain outlying parts of the universe, where I might learn something of its origin and early history. He took my hand, and instantly we were in the voids of space. Turning after a moment, he pointed to a small star and said, "That is the star you call the sun; here, you see, it is only about the third magnitude, and in a few seconds it will disappear." These few seconds, indeed, reduced the whole visible firmament to a mere nebulous haze like the Milky Way, and we seemed to be in blank space. But pausing for a moment I became aware that around us were multitudes of dark bodies, so black that they were, so to speak, negatively visible, even in the almost total darkness around. Some seemed large and massive, some a mere drift of minute particles, formless and without distinct limits. Some were swiftly moving, others stationary, or merely revolving on their own axes. It was a "horror of great darkness," and I trembled with fear. "This," said my guide, "is what the old Hebrew seer called tohu ve bohu, 'formless and void,' the 'Tiamat' or abyss of the old Chaldeans, the 'chaos and old night' of the Greeks. Your mundane physicists have not seen it, but they speculate regarding it, and occupy themselves with questions as to whether it can be lightened and vivified by mere attractive force, or by collision of dark bodies impinging on each other with vast momentum. Their speculations are vain, and lead to nothing, because they have no data wherefrom to calculate the infinite and eternal Power who determined either the attraction or the motion, or who willed which portion of this chaos was to become cosmos, and which was to remain for ever dead and dark. Let us turn, however, to a more hopeful prospect." We sped away to another scene. Here were vast luminous bodies, such as we call nebulæ. Some were globular, others disc-like, others annular or like spiral wisps, and some were composed of several concentric shells or rings. All were in rapid rotation, and presented a glorious and brilliant spectacle. "This," said my guide, "is matter of the same kind with that we have just been considering; but it has been set in active motion. The fiat 'Let there be light!' has been issued to it. Nor is its motion in vain. Each of these nebulous masses is the material of a system of worlds, and they will produce systems of different forms in accordance with the various shapes and motions which you observe. Such bodies are well known to earthly astronomers. One of them, the great nebula of Andromeda, has been photographed, and is a vast system of luminous rings of vapour placed nearly edgewise to the earth, and hundreds of times greater than the whole solar system. But now let us annihilate time, and consider these gigantic bodies as they will be in the course of many millions of years." Instantaneously these vast nebulæ had concentrated themselves into systems of suns and planets, but with this difference from ours, that the suns were very large and surrounded with a wide luminous haze, and each of the planets was self-luminous, like a little sun. In some the planets were dancing up and down in spiral lines. In others they were moving in one plane. In still others, in every variety of direction. Some had vast numbers of little planets and satellites. Others had a few of larger size. There were even some of these systems that had a pair of central suns of contrasting colours. The whole scene was so magnificent and beautiful that I thought I could never weary of gazing on it. "Here," said he, "we have the most beautiful condition of systems of worlds, when considered from a merely physical point of view: the perfection of solar and planetary luminousness, but which is destined to pass away in the interest of things more important, if less showy. This is the condition of the great star Sirius, which the old priest astronomers of the Nile Valley made so much of in their science and religion, and which they called Sothis. It is now known by your star-gazers to be vastly larger than your sun, and fifty times more brilliant.[1] Let us select one of these systems somewhat similar to the solar system, and suppose that the luminous atmospheres of its nearer planets are beginning to wane in brilliancy. Here is one of them, through whose halo of light we can see the body of the planet. What do you now perceive?" The planet referred to was somewhat larger in appearance than our earth, and, approaching near to it, I could see that it had a cloud-bearing firmament, and that it seemed to have continents and oceans, though disposed in more regular forms than on our own planet, and with a smaller proportion of land. Looking at it more closely, I searched in vain for any sign of animal life, but I saw a vast profusion of what might be plants, but not like those of this world.[2] These were trees of monstrous stature, and their leaves, which were of great size and shaped like fronds of seaweeds, were not usually green, but variegated with red, crimson and orange. The surface of the land looked like beds of gigantic specimens of Colias and similar variegated-leaved plants, the whole presenting a most gorgeous yet grotesque spectacle. "This," said my guide, "is the primitive vegetation which clothes each of the planets in its youthful state. The earth was once so clothed, in the time when vegetable life alone existed, and there were no animals to prey upon it, and when the earth was, like the world you now look upon, a paradise of plants; for all things in nature are at first in their best estate. This vegetation is known to you on the earth only by the Carbon and Graphite buried in your oldest rocks. It still lingers on your neighbour Mars,[3] which has, however, almost passed beyond this stage, and we are looking forward before long to see a still more gigantic though paler development of it in altogether novel shapes on the great continents that are being formed on the surface of Jupiter. But look again." And time being again annihilated, I saw the same world, now destitute of any luminous envelope, with a few dark clouds in its atmosphere, and presenting just the same appearance which I would suppose our earth to present to an astronomer viewing it with a powerful telescope from the moon. "Here we are at home again," said my guide; "good-bye." I found myself nodding over my table, and that my pen had just dropped from my hand, making a large blot on my paper. My dream, however, gave me a hint as to a subject, and I determined to devote my address to a consideration of questions which geology has not solved, or has only imperfectly and hypothetically discussed.

[1] In evidence of these and other statements I may refer to Huggins' recent address as President of the British Association, and to the "Story of the Heavens," etc., by Sir Robert Ball.

[2] We shall see farther on that there is reason to believe that the primitive land vegetation was more different from that of the Devonian and Carboniferous than it is from that of the present day.

[3] Mars is probably a stage behind the earth in its development, and the ruddy hue of its continents would seem to b: due to some organic covering.

Such unsolved or partially solved questions must necessarily exist in a science which covers the whole history of the earth in time. At the beginning it allies itself with astronomy and physics and celestial chemistry. At the end it runs into human history, and is mixed up with archæology and anthropology. Throughout its whole course it has to deal with questions of meteorology, geography and biology. In short, there is no department of physical or biological science, with which this many-sided study is not allied, or at least on which the geologist may not presume to trespass. When, therefore, it is proposed to discuss in the present chapter some of the unsolved problems and disputed questions of this universal science, the reader need not be surprised if it should be somewhat discursive.

Perhaps we may begin at the utmost limits of the subject by remarking that in matters of natural and physical science we are met at the outset with the scarcely solved question as to our own place in the nature which we study, and the bearing of this on the difficulties we encounter. The organism of man is decidedly a part of nature. We place ourselves, in this aspect, in the sub-kingdom vertebrata and class mammalia, and recognise the fact that man is the terminal link in a chain of being, extending throughout geological time. But the organism is not all that belongs to man, and when we regard him as a scientific inquirer, we raise a new question. If the human mind is a part of nature, then it is subject to natural law, and nature includes mind as well as matter. Indeed, without being absolute idealists we may hold that mind is more potent than matter, and nearer to the real essence of things. Our science is in any case necessarily dualistic, being the product of the reaction of mind on nature, and must be largely subjective and anthropomorphic. Hence, no doubt, arises much of the controversy of science, and much of the unsolved difficulty. We recognise this when we divide science into that which is experimental, or depends on apparatus, and that which is observational and classificatory—distinctions these which relate not so much to the objects of science as to our methods of pursuing them. This view also opens up to us the thought that the domain of science is practically boundless, for who can set limits to the action of mind on the universe, or of the universe on mind. It follows that science, as it exists at any one time, must be limited on all sides by unsolved mysteries; and it will not serve any good purpose to meet these with clever guesses. If we so treat the enigmas of the sphinx nature, we shall surely be devoured. Nor, on the other hand, must we collapse into absolute despair, and resign ourselves to the confession of inevitable ignorance. It becomes us rather boldly to confront the unsolved questions of nature, and to wrestle with their difficulties till we master such as we can, and cheerfully leave those we cannot overcome to be grappled with by our successors.

Fortunately, as a geologist, I do not need to invite attention to those transcendental questions which relate to the ultimate constitution of matter, the nature of the ethereal medium filling space, the absolute difference or identity of chemical elements, the cause of gravitation, the conservation and dissipation of energy, the nature of life, or the primary origin of bioplasmic matter. I may take the much more humble rôle of an inquirer into the unsolved or partially solved problems which meet us in considering that short and imperfect record which geology studies in the rocky layers of the earth's crust, and which leads no farther back than to the time when a solid rind had already formed on the earth, and was already covered with an ocean. This record of geology covers but a small part of the history of the earth and of the system to which it belongs, nor does it enter at all into the more recondite problems involved; still it forms, I believe, some necessary preparation at least to the comprehension of these. If we are to go farther back, we must accept the guidance of physicists rather than of geologists, and I must say that in this physical cosmology both geologists and general readers are likely to find themselves perplexed with the vagaries in which the most sober mathematicians may indulge. We are told that the original condition of the solar system was that of a vaporous and nebulous cloud intensely heated and whirling rapidly round, that it probably came into this condition by the impact of two dark solid bodies striking each other so violently, that they became intensely heated and resolved into the smallest possible fragments. Lord Kelvin attributes this impact to their being attracted together by gravitative force. Croll[4] argues that in addition to gravitation these bodies must have had a proper motion of great velocity, which Lord Kelvin thinks "enormously" improbable, as it would require the solid bodies to be shot against each other with a marvellously true aim, and this not in the case of the sun only, but of all the stars. It is rather more improbable than it would be to affirm that in the artillery practice of two opposing armies, cannon balls have thousands of times struck and shattered each other midway between the hostile batteries. The question, we are told, is one of great moment to geologists, since on the one hypothesis the duration of our system has amounted to only about twenty millions of years; on the other, it may have lasted ten times that number.[5] In any case it seems a strange way of making systems of worlds, that they should result from the chance collision of multitudes of solid bodies rushing hither and thither in space, and it is almost equally strange to imagine an intelligent Creator banging these bodies about like billiard balls in order to make worlds. Still, in that case we might imagine them not to be altogether aimless. The question only becomes more complicated when with Grove and Lockyer we try to reach back to an antecedent condition, when there are neither solid masses nor nebulæ, but only an inconceivably tenuous and universally diffused medium made up of an embryonic matter, which has not yet even resolved itself into chemical elements. How this could establish any motion within itself tending to aggregation in masses, is quite inconceivable. To plodding geologists laboriously collecting facts and framing conclusions therefrom, such flights of the mathematical mind seem like the wildest fantasies of dreams. We are glad to turn from them to examine those oldest rocks, which are to us the foundation stones of the earth's crust.

[4] "Stellar Evolution."

[5] Other facts favour the shorter time (Clarence King, Am. Jl. of Science, vol. xlv., 3rd series).

What do we know of the oldest and most primitive rocks? At this moment the question may be answered in many and discordant ways; yet the leading elements of the answer may be given very simply. The oldest rock formation known to geologists is the Lower Laurentian, the Fundamental Gneiss, the Lewisian formation of Scotland, the Ottawa gneiss of Canada, the lowest Archæan crystalline rocks. This formation, of enormous thickness, corresponds to what the older geologists called the fundamental granite, a name not to be scouted, for gneiss is only a stratified or laminated granite. Perhaps the main fact in relation to this old rock is that it is a gneiss; that is, a rock at once bedded and crystalline, and having for its dominant ingredient the mineral orthoclase, a compound of silica, alumina and potash, in which are imbedded, as in a paste, grains and crystals of quartz and hornblende. We know very well from its texture and composition that it cannot be a product of mere heat, and being a bedded rock we infer that it was laid down layer by layer in the manner of aqueous deposits. On the other hand, its chemical composition is quite different from that of the muds, sands and gravels usually deposited from water. Their special characters are caused by the fact that they have resulted from the slow decay of rocks like these gneisses, under the operation of carbon dioxide and water, whereby the alkaline matter and the more soluble part of the silica have been washed away, leaving a residue mainly silicious and aluminous.[6] Such more modern rocks tell of dry land subjected to atmospheric decay and ram-wash. If they have any direct relation to the old gneisses, they are their grandchildren, not their parents. On the contrary, the oldest gneisses show no pebbles or sand or limestone—nothing to indicate that there was then any land undergoing atmospheric waste, or shores with sand and gravel. For all that we know to the contrary, these old gneisses may have been deposited in a shoreless sea, holding in solution or suspension merely what it could derive from a submerged crust recently cooled from a state of fusion, still thin, and exuding here and there through its fissures heated waters and volcanic products. This, it may be observed here, is just what we have a right to expect, if the earth was once a heated or fluid mass, and if our oldest Laurentian rocks consist of the first beds or layers deposited upon it, perhaps by a heated ocean. It has been well said that "the secret of the earth's hot youth has been well kept." But with the help of physical science we can guess at an originally heat-liquefied ball with denser matter at its centre, lighter and oxidised matter at its surface. We can imagine a scum or crust forming at the surface; and from what we know of the earth's interior, nothing is more likely to have constituted that slaggy crust than the material of our old gneisses. As to its bedded character, this may have arisen in part from the addition of cooling layers below, in part from the action of heated water above, and in part from pressure or tension; while, wherever it cracked or became broken, its interstices would be injected with molten matter from beneath. All this may be conjecture, but it is based on known facts, and is the only probable conjecture. If correct, it would account for the fact that the gneissic rocks are the lowest and oldest that we reach in every part of the earth.

[6] Carbon dioxide, the great agent in the decay of silicious rocks, must then have constituted a very much larger part of the atmosphere than at present.

In short, the fundamental gneiss of the Lower Laurentian may have been the first rock ever formed; and in any case it is a rock formed under conditions which have not since recurred, except locally. It constitutes the first and best example of those chemico-physical, aqueous or aqueo-igneous rocks, so characteristic of the earliest period of the earth's history. Viewed in this way the Lower Laurentian gneiss is probably the oldest kind of rock we shall ever know the limit to our backward progress, beyond which there remains nothing to the geologist except physical hypotheses respecting a cooling incandescent globe. For the chemical conditions of these primitive rocks, and what is known as to their probable origin, I may refer to the writings of my friends, the late Dr. Sterry Hunt and Dr. J. G. Bonney, to whom we owe so much of what is known of the older crystalline rocks[7] as well as of their literature, and the questions which they raise. My purpose here is to sketch the remarkable difference which we meet as we ascend into the Middle and Upper Laurentian.

[7] Hunt, "Essays on Chemical Geology"; Bonney, "Addresses to British Association and Geological Society of London."

In the next succeeding formation, the middle part of the Laurentian of Logan, the Grenville series of Canada, we meet with a great and significant change. It is true we have still a predominance of gneisses which may have been formed in the same manner with those below them; but we find these now associated with great beds of limestone and dolomite, which must have been formed by the separation of calcium and magnesium carbonates from the sea water, either by chemical precipitation or by the agency of living beings. We have also quartzite, quartzose gneisses, and even pebble beds, which inform us of sandbanks and shores. Nay, more, we have beds containing graphite which must be the residue of plants, and iron ores which tell of the deoxidation of iron oxide by organic matters. In short, here we have evidence of new factors in world-building, of land and ocean, of atmospheric decay of rocks, of deoxidizing processes carried on by vegetable life on the land and in the waters, of limestone-building in the sea. To afford material for such rocks, the old Ottawa gneiss must have been lifted up into continents and mountain masses by bendings and foldings of the original crust. Under the slow but sure action of the carbon dioxide dissolved in rainwater, its felspar had crumbled down in the course of ages. Its potash, soda, lime, magnesia, and part Of its silica had been washed into the sea, there to enter into new combinations and to form new deposits. The crumbling residue of fine clay and sand had been also washed down into the borders of the ocean, and had been there deposited in beds. Thus the earth had entered into a new phase, which continues onward through the geological ages; and I place in the reader's hands one key for unlocking the mystery of the world in affirming that this great change took place, this new era was inaugurated in the midst of the Laurentian period, the oldest of our great divisions of the earth's geological history.[8]

[8] I follow the original arrangement of Logan, who first defined this succession in the extensive and excellent exposures of these rocks in Canada. Elsewhere the subject has often been confused and mixed with local details. The same facts, though sometimes under different names, are recorded by the geologists of Scandinavia, Britain, and the United States, and the acceptance of the conclusions of Nicol and Lapworth has served to bring even the rocks of the Highlands of Scotland more into line with those of Canada.

Was not this a fit period for the first appearance of life? should we not expect it to appear, independently of the evidence of the fact, so soon at least as the temperature of the ocean falls sufficiently low to permit its existence?[9] I do not propose to enter here into that evidence. This we shall have occasion to consider in the sequel. I would merely say here that we should bear in mind that in this latter half of the Lower Laurentian, or if we so choose to style it, Middle Laurentian period, we have the conditions required for life in the sea and on the land; and since in other periods we know that life was always present when its conditions were present, it is not unreasonable to look for the earliest traces of life in this formation, in which we find, for the first time, the completion of those physical arrangements which make life, in such forms of it as exist in the sea, possible.

[9] Dana states this at 180°F. for plants and 120° for animals.

This is also a proper place to say something of the disputed doctrine of what is termed metamorphism, or the chemical and molecular changes which old rocks have undergone.

The Laurentian rocks are undoubtedly greatly changed from their original state, more especially in the matters of crystallization and the formation of disseminated minerals, by the action of heat and heated water. Sandstones have thus passed into quartzites, clays into slates and schists, limestones into marbles. So far, metamorphism is not a doubtful question; but when theories of metamorphism go so far as to suppose an actual change of one element for another, they go beyond the bounds of chemical credibility; yet such theories of metamorphism are often boldly advanced and made the basis of important conclusions. Dr. Hunt has happily given the name "metasomatosis" to this imaginary and improbable kind of metamorphism. I would have it to be understood that, in speaking of the metamorphism of the older crystalline rocks, it is not to this metasomatosis that I refer, and that I hold that rocks which have been produced out of the materials decomposed by atmospheric erosion can never by any process of metamorphism be restored to the precise condition of the Laurentian rocks. Thus, there is in the older formations a genealogy of rocks, which, in the absence of fossils, may be used with some confidence, but which does not apply to the more modern deposits, and which gives a validity to the use of mineral character in classifying older rocks which does not hold for later formations. Still, nothing in geology absolutely perishes, or is altogether discontinued; and it is probable that, down to the present day, the causes which produced the old Laurentian gneiss may still operate in limited localities. Then, however, they were general, not exceptional. It is further to be observed that the term gneiss is sometimes of wide and even loose application. Beside the typical orthoclase and hornblendic gneiss of the Laurentian, there are micaceous, quartzose, garnetiferous and many other kinds of gneiss; and even gneissose rocks, which hold labradorite or anorthite instead of orthoclase, are sometimes, though not accurately, included in the term.

The Grenville series, or Middle Laurentian, is succeeded by what Logan in Canada called the Upper Laurentian, and which other geologists have called the Norite or Norian series. Here we still have our old friends the gneisses, but somewhat peculiar in type, and associated with them are great beds and masses, rich in lime-felspar, the so-called labradorite and anorthite rocks. The precise 'origin of these is uncertain, but this much seems clear, namely, that they originated in circumstances in which the great limestones deposited in the Lower or Middle Laurentian were beginning to be employed in the manufacture, probably by aqueo-igneous agencies, of lime-felspars. This proves the Norian rocks to be younger than the Lower Laurentian, and that, as Logan supposed, considerable earth-movements had occurred between the two, implying lapse of time, while it is also evident that the folding and crumpling of the Lower Laurentian had led to great outbursts of igneous matter from below the crust, or from its under part.

Next to the Laurentian, but probably after an interval, the rocks of which are yet scarcely known, we have the Huronian of Logan, a series much less crystalline and more fragmentary, and affording more evidence of land elevation and atmospheric and aqueous erosion than those preceding it. It has extensive beds of volcanic rock, great conglomerates, some of them made up of rounded fragments of Laurentian rocks, and others of quartz pebbles, which must have been the remains of rocks subjected to very perfect decay. The pure quartz-rocks tell the same tale, while slates and limestones speak also of chemical separation of the materials of older rocks. The Huronian evidently tells of previous movements in the Laurentian, and changes which allowed the Huronian to be deposited along its shores and on the edges of its beds. Yet the Huronian itself is older than the Palæozoic series, and affected by powerful earth-movements at an earlier date. Life existed in the waters in Huronian times. We have spicules of sponges in the limestone, and organic markings on the slaty beds; but they are few, and their nature is uncertain.

Succeeding the Huronian, and made up of its débris and that of the Laurentian, we have the great Cambrian series, that in which we first find undoubted evidence of abundant marine life, and which thus forms the first chapter in the great Palæozoic book of the early history of the world. Here let it be observed we have at least two wide gaps in our history, marked by the crumpling up, first, of the Laurentian, and then of the Huronian beds.

After what has been said, the reader will perhaps not be astonished that fierce geological battles have raged over the old crystalline rocks. By some geologists they are almost entirely explained away, or referred to igneous action, or to the alteration of ordinary sediments. Under the treatment of another school they grow to great series of Pre-Cambrian rocks, constituting vast systems of formations, distinguishable from each other chiefly by differences of mineral character. Facts and fossils are daily being discovered, by which these disputes will ultimately be settled.

After the solitary appearance of Eozoon in the Laurentian, and of a few uncertain forms in the Huronian, we find ourselves, in the Cambrian, in the presence of a nearly complete invertebrate fauna of protozoa, polyps, echinoderms, mollusks and Crustacea, and this not confined to one locality merely, but apparently extended simultaneously throughout the ocean, over the whole world. This sudden incoming of animal life, along with the subsequent introduction of successive groups of invertebrates, and finally of vertebrate animals, furnishes one of the greatest unsolved problems of geology, which geologists were wont to settle by the supposition of successive creations. In the sequel I shall endeavour to set forth the facts as to this succession, and the general principles involved in it, and to show the insufficiency of certain theories of evolution suggested by biologists to give any substantial aid to the geologist in these questions. At present I propose merely to notice some of the general principles which should guide us in studying the development of life in geological time, and the causes which have baffled so many attempts to throw light on this obscure portion of our unsolved problems.

It has been urged on the side of rational evolution—and there are both rational and irrational forms of this many-sided doctrine—that this hypothesis does not profess to give an explanation of the absolute origin of life on our planet, or even of the original organization of a single cell, or of a simple mass of protoplasm, living or dead. All experimental attempts to produce by synthesis the complex albuminous substances, or to obtain the living from the non-living, have so far been fruitless, and indeed we cannot imagine any process by which such changes could be effected. That they have been effected we know, but the process employed by their maker is still as mysterious to us as it probably was to him who wrote the words:—"And God said, Let the waters swarm with swarmers." How vast is the gap in our knowledge and our practical power implied in this admission, which must, however, be made by every mind not absolutely blinded by a superstitious belief in those forms of words which too often pass current as philosophy.

But if we are content to start with a number of organisms ready made—a somewhat humiliating start, however—we still have to ask—How do these vary so as to give new species? It is a singular illusion, and especially in the case of men who profess to be believers in natural law, that variation may be boundless, aimless and fortuitous, and that it is by spontaneous selection from varieties thus produced that development arises. But surely the supposition of mere chance and magic is unworthy of science. Varieties must have causes, and their causes and their effects must be regulated by some law or laws. Now it is easy to see that they cannot be caused by a mere innate tendency in the organism itself. Every organism is so nicely equilibrated that it has no such spontaneous tendency, except within the limits set by its growth and the law of its periodical changes. There may, however, be equilibrium more or less stable. I believe all attempts hitherto made have failed to account for the fixity of certain, nay, of very many, types throughout geological time, but the mere consideration that one may be in a more stable state of equilibrium than another, so far explains it. A rocking stone has no more spontaneous tendency to move than an ordinary boulder, but it may be made to move with a touch. So it probably is with organisms. But if so, then the causes of variation are external, as in many cases we actually know them to be, and they must depend on instability with change in surroundings, and this so arranged as not to be too extreme in amount, and to operate in some determinate direction. Observe how remarkable the unity of the adjustments involved in such a supposition!—how superior they must be to our rude and always more or less unsuccessful attempts to produce and carry forward varieties and races in definite directions! This cannot be chance. If it exists, it must depend on plans deeply laid in the nature of things, else it would be most monstrous magic and causeless miracle. Still more certain is this conclusion when we consider the vast and orderly succession made known to us by geology, and which must have been regulated by fixed laws, only a few of which are as yet known to us.

Beyond these general considerations we have others of a more special character, based on palæontological facts, which show how imperfect are our attempts as yet to reach the true causes of the introduction of genera and species.

One is the remarkable fixity of the leading types of living beings in geological time. If, instead of framing, like Haeckel, fanciful phylogenies, we take the trouble, with Barrande and Gaudry, to trace the forms of life through the period of their existence, each along its own line, we shall be greatly struck with this, and especially with the continuous existence of many low types of life through vicissitudes of physical conditions of the most stupendous character, and over a lapse of time scarcely conceivable. What is still more remarkable is that this holds in groups which, within certain limits, are perhaps the most variable of all. In the present world no creatures are individually more variable than the protozoa; as, for example, the foraminifera and the sponges. Yet these groups are fundamentally the same, from the beginning of the Palæozoic until now, and modern species seem scarcely at all to differ from specimens procured from rocks at least half-way back to the beginning of our geological record. If we suppose that the present sponges and foraminifera are the descendants of those of the Silurian period, we can affirm that in all that vast lapse of time they have, on the whole, made little greater change than that which may be observed in variable forms at present. The same remark applies to other low animal forms. In types somewhat higher and less variable, this is almost equally noteworthy. The pattern of the venation of the wings of cockroaches, and the structure and form of land snails, gally-worms and decapod crustaceans were all settled in the Carboniferous age, in a way that still remains. So were the foliage and the fructification of club mosses and ferns. If, at any time, members of these groups branched off, so as to lay the foundation of new species, this must have been a very rare and exceptional occurrence, and one demanding even some suspension of the ordinary laws of nature.

We may perhaps be content on this question to say with Gaudry,[10] that it is not yet possible to "pierce the mystery that surrounds the development of the great classes of animals," or with Prof. Williamson,[11] that in reference to fossil plants "the time has not yet arrived for the appointment of a botanical King-at-arms and Constructor of pedigrees." We shall, however, find that by abandoning mere hypothetical causes and carefully noting the order of the development and the causes in operation, so far as known, we may reach to ideas as to cause and mode, and the laws of succession, even if unable to penetrate the mystery of origins.

[10] "Enchainements du Monde Animal," Paris, 1883.

[11] Address before Royal Institution, Feb., 1883.

Another caution which a palæontologist has occasion to give with regard to theories of life, has reference to the tendency of biologists to infer that animals and plants were introduced under embryonic forms, and at first in few and imperfect species. Facts do not substantiate this. The first appearance of leading types of life is rarely embryonic, or of the nature of immature individuals. On the contrary, they often appear in highly perfect and specialized forms, often, however, of composite type and expressing characters afterwards so separated as to belong to higher groups. The trilobites of the Cambrian are some of them of few segments, and so far embryonic, but the greater part are many-segmented and very complex. The batrachians of the Carboniferous present many characters higher than those of their modern successors and now appropriated to the true reptiles. The reptiles of the Permian and Trias usurped some of the prerogatives of the mammals. The ferns, lycopods and equisetums of the Devonian and Carboniferous were, in fructification, not inferior to their modern representatives, and in the structure of their stems far superior. The shell-bearing cephalopods of the Palæozoic would seem to have possessed structures now special to a higher group, that of the cuttle-fishes. The bald and contemptuous negation of these facts by Haeckel and other biologists does not tend to give geologists much confidence in their dicta.

Again, we are now prepared to say that the struggle for existence, however plausible as a theory, when put before us in connection with the productiveness of animals and the few survivors of their multitudinous progeny, has not been the determining cause of the introduction of new species. The periods of rapid introduction of new forms of marine life were not periods of struggle, but of expansion—those periods in which the submergence of continents afforded new and large space for their extension and comfortable subsistence. In like manner, it was continental emergence that afforded the opportunity for the introduction of land animals and plants. Further, in connection with this, it is now an established conclusion that the great aggressive faunas and floras of the continents have originated in the north, some of them within the arctic circle, and this in periods of exceptional warmth, when the perpetual summer sunshine of the arctic regions coëxisted with a warm temperature. The testimony of the rocks thus is that not struggle but expansion furnished the requisite conditions for new forms of life, and that the periods of struggle were characterized by depauperation and extinction.

But we are sometimes told that organisms are merely mechanical, and that the discussions respecting their origin have no significance any more than if they related to rocks or crystals, because they relate merely to the organism considered as a machine, and not to that which may be supposed to be more important, namely, the great determining power of mind and will. That this is a mere evasion by which we really gain nothing, will appear from a characteristic extract of an article by an eminent biologist in the new edition of the Encyclopedia Britannica, a publication which, I am sorry to say, instead of its proper rôle as a repertory of facts, has admitted partisan papers, stating extreme and unproved speculations as if they were conclusions of science. The statement referred to is as follows:—"A mass of living protoplasm is simply a molecular machine of great complexity, the total results of the working of which, or its vital phenomena, depend on the one hand on its construction, and on the other, on the energy supplied to it; and to speak of vitality as anything but the name for a series of operations is as if one should talk of the horologity of a clock." It would, I think, scarcely be possible to put into the same number of words a greater amount of unscientific assumption and unproved statement than in this sentence. Is "living protoplasm" different in any way from dead protoplasm, and if so, what causes the difference? What is a "machine"? Can we conceive of a self-produced or uncaused machine, or one not intended to work out some definite results? The results of the machine in question are said to be "vital phenomena"; certainly most wonderful results, and greater than those of any machine man has yet been able to construct. But why "vital"? If there is no such thing as life, surely they are merely physical results. Can mechanical causes produce other than physical effects? To Aristotle life was "the cause of form in organisms." Is not this quite as likely to be true as the converse proposition? If the vital phenomena depend on the "construction" of the machine, and the "energy supplied to it," whence this construction and whence this energy? The illustration of the clock does not help us to answer this question. The construction of the clock depends on its maker, and its energy is derived from the hand that winds it up. If we can think of a clock which no one has made, and which no one winds, a clock constructed by chance, set in harmony with the universe by chance, wound up periodically by chance, we shall then have an idea parallel to that of an organism living, yet without any vital energy or creative law; but in such a case we should certainly have to assume some antecedent cause, whether we call it "horologity" or by some other name. Perhaps the term evolution would serve as well as any other, were it not that common sense teaches that nothing can be spontaneously evolved out of that in which it did not previously exist.

There is one other unsolved problem in the study of life by the geologist to which it is still necessary to advert. This is the inability of palæontology to fill up the gaps in the chain of being. In this respect we are constantly taunted with the imperfection of the record, a matter so important that it merits a separate treatment; but facts show that this is much more complete than is generally supposed. Over long periods of time and many lines of being we have a nearly continuous chain, and if this does not show the tendency desired, the fault is as likely to be in the theory as in the record. On the other hand, the abrupt and simultaneous appearance of new types in many specific and generic forms and over wide and separate areas at one and the same time, is too often repeated to be accidental. Hence palæontologists, in endeavouring to establish evolution, have been obliged to assume periods of exceptional activity in the introduction of species, alternating with others of stagnation, a doctrine differing very little from that of special creation, as held by the older geologists.

The attempt has lately been made to account for these breaks by the assumption that the geological record relates only to periods of submergence, and gives no information as to those of elevation. This is manifestly untrue. In so far as marine life is concerned, the periods of submergence are those in which new forms abound for very obvious reasons, already hinted; but the periods of new forms of land and fresh-water life are those of elevation, and these have their own records and monuments, often very rich and ample, as, for example, the swamps of the Carboniferous, the transition from the great Cretaceous subsidence, when so much of the land of the Northern Hemisphere was submerged, to the new continents of the Tertiary, the Tertiary lake-basins of Western America, the Terraces and raised beaches of the Pleistocene. Had I time to refer in detail to the breaks in the continuity of life which cannot be explained by the imperfection of the record, I could show at least that nature in this case does advance per saltum—by leaps, rather than by a slow continuous process. Many able reasoners, as Le Conte, in America, and Mivart and Collard in England, hold this view.

Here, as elsewhere, a vast amount of steady conscientious work is required to enable us to solve the problems of the history of life. But if so, the more the hope for the patient student and investigator. I know nothing more chilling to research, or unfavourable to progress, than the promulgation of a dogmatic decision that there is nothing to be learned but a merely fortuitous and uncaused succession, amenable to no law, and only to be covered, in order to hide its shapeless and uncertain proportions, by the mantle of bold and gratuitous hypothesis.

So soon as we find evidence of continents and oceans we raise the question, Have these continents existed from the first in their present position and form, or have the land and water changed places in the course of geological time? This question also deserves a separate and more detailed consideration. In reality both statements are true in a certain limited sense. On the one hand, any geological map whatever suffices to show that the general outline of the existing land began to be formed in the first and oldest crumplings of the crust. On the other hand, the greater part of the surface of the land consists of marine sediments which must have been deposited when the continents were in great part submerged, and whose materials must have been derived from land that has perished in the process, while all the continental surfaces, except, perhaps, some high peaks and ridges, have been many times submerged. Both of these apparently contradictory statements are true; and without assuming both, it is impossible to explain the existing contours and reliefs of the surface.

In exceptional cases even portions of deep sea have been elevated, as in the case of the Polycistine deposits in the West Indies; but these exceptions are as yet scarcely sufficient to prove the rule.

In the case of North America, the form of the old nucleus of Laurentian rock in the north already marks out that of the finished continent, and the successive later formations have been laid upon the edges of this, like the successive loads of earth dumped over an embankment. But in order to give the great thickness of the Palæozoic sediments, the land must have been again and again submerged, and for long periods of time. Thus, in one sense, the continents have been fixed; in another, they have been constantly fluctuating. Hall and Dana have well illustrated these points in so far as eastern North America is concerned. Prof. Hull of the Geological Survey of Ireland has had the boldness to reduce the fluctuations of land and water, as evidenced in the British Islands, to the form of a series of maps intended to show the physical geography of each successive period. The attempt is probably premature, and has been met with much adverse criticism; but there can be no doubt that it has an element of truth. When we attempt to calculate what could have been supplied from the old Eozoic nucleus by decay and aqueous erosion, and when we take into account the greater local thickness of sediments towards the present sea-basins, we can scarcely avoid the conclusion that extensive areas once occupied by high land are now under the sea. But to ascertain the precise areas and position of these perished lands may now be impossible.

In point of fact we are obliged to believe in the contemporaneous existence in all geological periods, except perhaps the very oldest, of three sorts of areas on the surface of the earth: (1) Oceanic areas of deep sea, which must always have occupied the bed of the present ocean, or parts of it; (2) Continental plateaus sometimes existing as low flats, or as higher table-lands, and sometimes submerged; (3) Areas of plication or folding, more especially along the borders of the oceans, forming elevated lands rarely submerged and constantly affording the material of sedimentary accumulations. We shall find, however, that these have changed places in a remarkable manner, though always in such a way that neither the life of the land nor of the waters was wholly extinguished in the process.

Every geologist knows the contention which has been occasioned by the attempts to correlate the earlier Palæozoic deposits of the Atlantic margin of North America with those forming at the same time on the interior plateau, and with those of intervening lines of plication and igneous disturbance. Stratigraphy, lithology and fossils are all more or less at fault in dealing with these questions, and while the general nature of the problem is understood by many geologists, its solution in particular cases is still a source of apparently endless debate.

The causes and mode of operation of the great movements of the earth's crust which have produced mountains, plains and table-lands, are still involved in some mystery. One patent cause is the unequal settling of the crust towards the centre; but it is not so generally understood as it should be, that the greater settlement of the ocean-bed has necessitated its pressure against the sides of the continents in the same manner that a huge ice-floe crushes a ship or a pier. The geological map of North America shows this at a glance, and impresses us with the fact that large portions of the earth's crust have not only been folded but bodily pushed back for great distances. On looking at the extreme north, we see that the great Laurentian mass of central Newfoundland has acted as a projecting pier to the space immediately west of it, and has caused the gulf of St. Lawrence to remain an undisturbed area since Palæozoic times. Immediately to the south of this, Nova Scotia and New Brunswick are folded back. Still farther south, as Guyot has shown, the old sediments have been crushed in sharp folds against the Adirondack mass, which has sheltered the table-land of the Catskills and of the great lakes. South of this again the rocks of Pennsylvania and Maryland have been driven back in a great curve to the west. Movements of this kind on the Pacific coast of America have been still more stupendous, as well as more recent. Dr. G. M. Dawson[12] thus refers to the crushing action of the Pacific bed on the rocks of British Columbia, and this especially at two periods, the close of the Triassic and the close of the Cretaceous: "The successive foldings and crushings which the Cordillera region has suffered have resulted in an actual change of position of the rocks now composing its western margin. This change may have amounted since the beginning of Mesozoic time to one-third of its whole present width, which would place the line of the coast ranges about two degrees of longitude farther west." Here we have evidence that a tract of country 400 miles wide and consisting largely of mountain ranges and table-lands, has been crushed bodily back over two degrees of longitude; and this applies not to British Columbia merely, but to the whole west coast from Alaska to Chili. Yet we know that any contraction of the earth's nucleus can crumple up only a very thin superficial crust, which in this case must have slid over the pasty mass below.[13] Let it be observed, however, that the whole lateral pressure of vast areas has been condensed into very narrow lines. Nothing, I think, can more forcibly show the enormous pressure to which the edges of the continents have been exposed, and at the same time the great sinking of the hard and resisting ocean-beds. Complex and difficult to calculate though these movements of plication are, they are more intelligible than the apparently regular pulsations of the flat continental areas, whereby they have alternately been below and above the waters, and which must have depended on somewhat regularly recurring causes, connected either with the secular cooling of the earth or with the gradual retardation of its rotation, or with both. There is, however, good reason to believe that the successive subsidences alternated with the movements of plication, and depended on upward bendings of the ocean floor, and also on the gradual slackening of the rotation of the earth. Throughout these changes, each successive elevation exposed the rocks for long ages to the decomposing influence of the atmosphere. Each submergence swept away and deposited as sediment the material accumulated by decay. Every change of elevation was accompanied with changes of climate, and with modifications of the habitats of animals and plants. Were it possible to restore accurately the physical geography of the earth in all these respects, for each geological period, the data for the solution of many difficult questions would be furnished.

[12] Trans. Royal Society of Canada, 1890.

[13] This view is quite consistent with the practical solidity of the earth, and with the action of local expansion by heat, of settlement of areas overloaded with sediment, and of downward sliding of beds. This we shall see in the sequel.

We have wandered through space and time sufficiently for one chapter, and some of the same topics must come up later in other connections. Let us sum up in a word. In human history we are dealing with the short lives and limited plans of man. In the making of worlds we are conversant with the plans of a Creator with whom one day is as a thousand years, and a thousand years as one day. We must not measure such things by our microscopic scale of time. Nor should we fail to see that vast though the ages of the earth are, they are parts of a continuous plan, and of a plan probably reaching in space and time immeasurably beyond our earth. When we trace the long history from an incandescent fire-mist to a finished earth, and vast ages occupied by the dynasties of plant and animal life, we see not merely a mighty maze, an almost endless procession of changes, but that all of these were related to one another by a chain of causes and effects leading onward to greater variety and complexity, while retaining throughout the traces of the means employed. The old rocks and the ancient lines of folding and the perished forms of life are not merely a scaffolding set up to be thrown down, but the foundation stones of a great and symmetrical structure. Is it yet completed? Who can tell? The earth may still be young, and infinite ages of a better history may lie before it.

References[14]:—Presidential Address to the American Association for the Advancement of Science, meeting at Minneapolis, 1883. "The Story of the Earth and Man." Ninth edition, London, 1887.

[14] The references in this and succeeding chapters are exclusively to papers and works by the author, on which the several chapters are based.

[THE IMPERFECTION OF THE GEOLOGICAL RECORD.]

DEDICATED TO THE MEMORY OF
JOACHIN BARRANDE,
One of the most successful Labourers
in the
Completion of the History of Life
in its earlier Stages.

Nature of the Imperfection—Questions as to its arising from Want of Continuity, from Lack of Preservation, from Imperfect Collecting.—Examples—Land Snails, Carboniferous Batrachians, Palæozoic Sponges, Pleistocene Shells, Devonian and Carboniferous Plants—Comparative Perfection in the Case of Marine Shells, etc.—Possible Cambrian Squids—Questions as to Want of First Chapters of the Record—Practical Conclusions

Cambro-Silurian Sponges restored.—Protospongia, Acanthodictya, Cyathospongia, Lasiothrix, Halichondrites, Palæosaccus, etc., from a single bed of shale in the Quebec Group, Little Metis, Canada ([p. 47]).

[CHAPTER III.]

THE IMPERFECTION OF THE GEOLOGICAL RECORD.

C

Complaints of the imperfection of the geological record are rife among those biologists who expect to find continuous series of fossils representing the gradual transmutation of species. No doubt these gaps are in some cases portentous, and unfortunately they often occur just where it is most essential to certain general conclusions that they should be filled up. Instead, however, of making vague lamentations on the subject, it is well to inquire to what causes these gaps may be due, to what extent they invalidate the completeness of geological history for scientific purposes, and how they may best be filled.

Here we may first remark that it is not so much the physical record of geology that is imperfect as the organic record. Ever since the time of Hutton and Playfair we have learned that the processes of mineral detrition and deposition are continuous, and have been so throughout geological time. The erosion of the land is constantly going on, every shower carries its tribute of earthy matter toward the sea, and every wave that strikes against a beach or cliff does some work toward the grinding of shells, pebbles or stone. Thus, everywhere around our continents there is a continuous deposition of beds of earthy matter, and it is this which, when elevated into new land, has given us our chronological series of geological formations. True, the elevating process is not continuous, but, so far as we know, intermittent; but it has been so often repeated that we have no reason to doubt that the wasting continents afford a complete series of aqueous deposits, since the time when the dry land first appeared.

In recent years the Challenger expedition and similar dredgings have informed us of still another continuity of deposition in the depths of the ocean. There, where no detritus from the land, or only a very little fine volcanic ash or pumice has ever reached, we have, going on from age to age, a deposit of the hard parts of abyssal animals and of those that swim in the open sea; so that if it were possible to bore or sink a shaft in some parts of the ocean, we should find not only a continuous bed, but a continuous series of pelagic life from the Laurentian to the present day. Thus we have continuous physical records, could we but reach or completely put them together, and eliminate the disturbing influence of merely local vicissitudes. It is when we begin to search the geological formations for fossils, that imperfection in our record first becomes painfully manifest.

In the case of many groups of marine animals, as, for example, the shell-fish and the corals, and I may add the bivalve crustaceans, so admirably worked up by my friend Prof. Rupert Jones, we have very complete series. With the and snails the case is altogether different. As stated in another paper of this series, a few species of these animals appear in the later Palæozoic age, and after that they have no successors known to us in all the great periods covered by the Permian, the Trias, and the earlier Jurassic. A few air-breathing water-snails appear in the upper Jurassic, and true land snails are not met with again until the Tertiary. Were there no land snails in this vast lapse of time? Have we two successive creations, so to speak, of these creatures at distant intervals? Were they only diminished in numbers and distribution in the intervening time? Is the hiatus owing merely to the unlikelihood of such shells being preserved? Or is it owing to the lack of diligence and care in collecting?

In this particular case we are, no doubt, disposed to say that the series must have been continuous. But we cannot be sure of this. In whatever way a few species of land snails were so early introduced in the time of the Devonian or of the Coal formation, if from physical vicissitudes or lack of proper pabulum they became extinct, there is no reason known to us why, when circumstances again became favourable, they should not be reintroduced in the same manner as at first, whether by development from allied types or otherwise. The fact that the few Devonian and Carboniferous species are very like those that still exist, perhaps makes against this supposition, but does not exclude it. If we suppose that new forms of life of low grade are introduced from time to time in the course of the geological ages, and if we adopt the Darwinian hypothesis of evolution, we arrive, as Naegeli has so well pointed out, at the strange paradox, that the highest forms of life must be the oldest of all, since they will be the descendants of the earliest of the lower animals, whereas the animals now of low grade may have been introduced later, and may not have had time to improve. But all our attempts to reduce nature to one philosophic expression necessarily lead to such paradoxes.

On the other hand, the chances of the preservation of land snails in aqueous deposits are vastly less than those in favour of the preservation of aquatic species. The first Carboniferous species found[15] had been preserved in the very exceptional circumstances afforded by the existence of hollow trunks of Sigillariæ on the borders of the Coal formation flats, and the others subsequently found were in beds no doubt receiving the drainage of neighbouring land areas. Still it is not uncommon on the modern sea-shore, anywhere near the mouths of rivers, to find a few fresh-water shells here and there. The carbonaceous beds of the Trias, the fossil soils of the Portland series, the estuarine Wealden beds would seem to be as favourably situated as those of the coal formation for preserving land shells, though possibly the flora of the Mesozoic was less suitable for feeding such creatures than that of the Coal period, and they may consequently have become few and local. After all, perhaps more diligent collecting and more numerous collectors might succeed, and may succeed in the future, in filling this and similar gaps.

[15] Pupa vetusta of the Nova Scotia coal formation.

It is a great mistake to suppose that discoveries of this kind are made by chance. It is only by the careful and painstaking examination of much material that the gaps in the geological record can be filled up, and I propose in the sequel of this article to note a few instances, in a country where the range of territory is altogether out of proportion to the number of observers, and which have come within my own knowledge.

It was not altogether by accident that Sir C. Lyell and the writer discovered a few reptilian bones and a land-snail in breaking up portions of the material filling an erect Sigillaria in the South Joggins coal measures. We were engaged in a deliberate survey of the section, to ascertain as far as might be the conditions of accumulation of coal, and one point which occurred to us was to inquire as to the circumstances of preservation of stumps of forest trees in an erect position, to trace their roots into the soils on which they stood, and to ascertain the circumstances in which they had been buried, had decayed, and had been filled with mineral matter. It was in questioning these erect trees on such subjects and this not without some digging and hammering that we made the discovery referred to.

But we found such remains only in one tree, and they were very imperfect, and indicated only two species of batrachians and one land-snail. There the discovery might have rested. But I undertook to follow it up. In successive visits to the coast, a large number of trees standing in the cliff and reefs, or fallen to the shore, were broken up and examined, the result being to discover that, with one unimportant exception, the productive trees were confined to one of the beds at Coal Mine Point, that from which the original specimens had been obtained. Attention was accordingly concentrated on this, and as many as thirty trees were at different times extracted from it, of which rather more than one-half proved more or less productive. By these means bones representing about sixty specimens and twelve species were extracted, besides numerous remains of land shells, millipedes, and scorpions. In this way a very complete idea was obtained of the land life, or at least of the smaller land animals, of this portion of the coal formation of Nova Scotia. It is not too much to say that if similar repositories could be found in the succeeding formations, and properly worked when found, our record of the history of land quadrupeds might be made very complete.

When in 1855 I changed my residence from Nova Scotia to Montreal, and so was removed to some distance from the carboniferous rocks which I had been accustomed to study, I naturally felt somewhat out of place in a Cambro-Silurian district, more especially as my friend Billings had already almost exhausted its fossils. I found, however, a congenial field in the Pleistocene shell beds; more especially as I had given some attention to recent marine animals when on the sea coast. The very perfect series of Pleistocene deposits in the St. Lawrence valley locally contain marine shells from the bottom of the till or boulder clay up to the overlying sands and gravels. The assemblage was a more boreal one than that on the coast of Nova Scotia, though many of the species were the same, and both the climatal and bathymetrial conditions differed in different parts of the Pleistocene beds themselves. The gap in the record here could at that time be filled up only by collecting recent shells. In addition to what could be obtained by exchanging with naturalists who had collected in Greenland, Labrador, and Norway, I employed myself, summer after summer, in dredging both on the south and north shore of the St. Lawrence, until able at length to discover in a living state, but under different conditions as to temperature and depth, nearly every species found in the beds on the land, from the lower boulder clay to the top of the formation, and from the sea-level to the beds six hundred feet high on the hills. Not only so: I could ascertain in certain places and conditions all the peculiar varieties of the species, and the special modes of life which they indicated. Thus, in the cases of the Peter Redpath Museum, and in notes on the Post-pliocene of Canada, the gap between the Modern and the Glacial age was completely filled up in so far as Canadian marine species are concerned. The net result was, as I have elsewhere stated, that no change other than varietal had occurred.

In studying the fossil plants of the Carboniferous, so abundant in the fine exposures of the coal formation in Nova Scotia, two defects struck me painfully. One was the fragmentary and imperfect state of the specimens procurable. Another was the question, What preceded these plants in the older rocks? The first of these was to be met only by thorough exploration. When a fragment of a plant was disclosed it was necessary to inquire if more existed in the same bed, and to dig, or blast away or break up the rock, until some remaining portions were disclosed. In this way it has been possible to obtain entire specimens of many trees of the Carboniferous; and to such an extent has the laborious and somewhat costly process been effectual, that more species of carboniferous trees are probably known in their entire forms from the Coal formations of Nova Scotia than from any other part of the world. I have been amused to find that so little are experiences of this kind known to some of my confrères abroad, that they are disposed to look with scepticism on the information obtained by this laborious but certain process, and to suppose that they are being presented with imaginary "restorations." I think it right here to copy a remark of a German botanist, who has felt himself called to criticise my work: "Dawson's description of the genus (Psilophyton) rests chiefly on the impression made on him in his repeated researches," etc. "He puts us off with an account of the general idea which he has drawn from the study of them." This is the remark of a closet naturalist, with reference to the kind of work above referred to, which, of course, cannot be represented in its entirety in figures or hand specimens.[16]

[16] Solms-Laubach, "Fossil Botany." A pretentious book, which should not have been translated into English without thorough revision and correction.

As to the precursors of the Carboniferous flora, in default of information already acquired, I proceeded to question the Erian or Devonian rocks of Canada, in which Sir William Logan had already found remains of plants which had not, however, been studied or described. Laboriously coasting along the cliffs of Gaspé and the Baie des Chaleurs, digging into the sandstones of Eastern Maine, and studying the plants collected by the New York Survey, I began to find that there was a rich Devonian flora, and that, like that of the Carboniferous, it presented different stages from the base to the summit of the formation. But here a great advance was made in a somewhat unexpected way. My then young friends, the late Prof. Hartt and Mr. Matthew, of St. John, had found a few remains of plants in the Devonian, or at least pre-Carboniferous beds of St. John, which were placed in my hands for description. They were so novel and curious that inquiry was stimulated, and these gentlemen, with some friends of similar tastes, explored the shales exposed in the reefs near St. John, and when they found the more productive beds, broke them up by actual quarrying operations in such a way that they soon obtained the richest Devonian plant collections ever known. I think I may truly say that these young and enthusiastic explorers worked the St. John plant-beds in a manner previously unexampled in the world. Their researches were not only thus rewarded, but incidentally they discovered the first known Devonian insects, which could not have been found by a less painstaking process, and one of them discovered what I believe to be the oldest known land shell. Still more, their studies led to the separation from the Devonian beds of the Underlying Cambrian slates, previously confounded with them; and this, followed up by the able and earnest work of Mr. Matthew, has carried back our knowledge of the older rocks in Canada several stages, or as far as the earliest Cambrian previously known in Europe, but not before fully recognised in America, and has discovered in these old rocks the precursors of many forms of life not previously traced so far back.

The moral of these statements of fact is that the imperfections of the record will yield only to patient and painstaking work, and that much is in the power of local amateurs. I would enforce this last statement by a reference to a little research, in which I have happened to take part at a summer resort on the Lower St. Lawrence, at which I have from time to time spent a few restful vacation weeks. Little Metis is on the Quebec Group of Sir William Logan, that peculiar local representative of the lower part of the Cambro-Silurian and Upper Cambrian formations which stretches along the south side of the St. Lawrence all the way from Quebec to Cape Rosier, near Gaspé, a distance of five hundred miles. This great series of rocks is a jumble of deposits belonging at that early time to the marginal area of what is now the American continent, and indicating the action not merely of ordinary causes of aqueous deposit, but of violent volcanic ejections, accompanied perhaps by earthquake waves, and not improbably by the action of heavy coast ice. The result is that mud rocks now in the form of black, grey, and red shales and slates alternate with thick and irregular beds of hard sandstone, sometimes so coarse that it resembles the angular débris of the first treatment of quartz in a crusher. With these sandstones are thick and still more irregular conglomerates formed of pebbles and boulders of all sizes, up to several feet in diameter, some of which are of older limestones containing Cambrian fossils, while others are of quartzite or of igneous or volcanic rocks.

The whole formation, as presented at Metis, is of the most unpromising character as regards fossils, and after visiting the place for ten years, and taking many long walks along the shore and into the interior, and scrutinising every exposure, I had found nothing more interesting than a few fragments of graptolites, little zoophytes, ancient representatives of our sea mosses, and which are quite characteristic of several portions of the Quebec Group. With these were some marks of fucoids and tracks or burrows of worms. The explorers of the Geological Survey had been equally unsuccessful.

Quite accidentally a new light broke upon these unpromising rocks. My friend, Dr. Harrington, strolling one day on the shore, sat down to rest on a stone, and picked up a piece of black slate lying at his feet. He noticed on it some faintly traced lines which seemed peculiar. He put it in his pocket and showed it to me. On examination with a lens it proved to have on it a few spicules of a hexactinellid sponge—little crosses forming a sort of mesh or lattice-work similar to that which Salter had many years before found in the Cambrian rocks of Wales, and had named Protospongia—the first sponge. The discovery seemed worth following up, and we took an early opportunity of proceeding to the place, where, after some search, we succeeded in tracing the loose pieces to a ledge of shale on the beach, where there was a little band, only about an inch thick, stored with remains of sponges, a small bivalve shell and a slender branching seaweed. This was one small layer in reefs of slate more than one hundred feet thick. We subsequently found two other thin layers, but less productive. Tools and workmen were procured, and we proceeded to quarry in the reef, taking out at low tide as large slabs as possible of the most productive layer, and carefully splitting these up. The results, as published in the Transactions of the Royal Society of Canada,[17] show more than twelve species of siliceous sponges belonging to six genera, besides fragments indicating other species, and all of these living at one time on a very limited space of what is practically a single surface of muddy sea-bottom.[18] The specimens show the parts of these ancient sponges much more perfectly than they were previously known, and indeed, enable many of them to be perfectly restored. They for the first time connect the modern siliceous sponges of the deep sea with those that flourished on the old sea-bottom of the early Cambro-Silurian, and thus bridge over a great, gap in the history of this low form of life, showing that the principles of construction embodied in the remarkable and beautiful siliceous sponges, like Euplectella, the "Venus flower-basket," now dredged from the deep sea, were already perfectly carried out in this far-back beginning of life. This little discovery further indicates that portions of the older Palæozoic sea-bottoms were as well stored with a varied sponge life as those of any part of the modern ocean. I figure[19] a number of species, remains of all of which may be gathered from a few yards of a single surface at Little Metis. The multitude of interesting details embodied in all this it is impossible to enter into here, but may be judged of from the forms reproduced. These examples tend to show that the imperfection of the record may not depend on the record itself, but on the incompleteness of our work. We must make large allowance for imperfect collecting, and especially for the too prevalent habit of remaining content with few and incomplete specimens, and of grudging the time and labour necessary to explore thoroughly the contents of special beds, and to work out all the parts of forms found more or less in fragments.

[17] Additional collections made in 1892 show two or three additional species, one of them the type of a new and remarkable genus.

[18] 1889, section iv. p. 39.

[19] Frontispiece to chapter.

The point of all this at present is that patient work is needed to fill up the breaks in our record. A collector passing along the shore at Metis might have picked up a fragment of a fossil sponge, and recorded it as a fossil, or possibly described the fragment. This fact alone would have been valuable, but to make it bear its full fruit it was necessary to trace the fragment to its source, and then to spend time and labour in extracting from the stubborn rock the story it had to tell. Instances of this kind crowd on my memory as coming within my own experience and observation. It is hopeful to think that the record is daily becoming less imperfect; it is stimulating to know that so much is only waiting for investigation. The history never can be absolutely complete. Practically, to us it is infinite. Yet every series of facts known may be complete in itself for certain purposes, however many gaps there may be in the story. Even if we cannot find a continuous series between the snails of the Coal formation or the sponges of the Quebec Group and their successors to-day, we can at least see that they are identical in plan and structure, and can note the differences of detail which fitted them for their places in the ancient or the modern world. Nor need we be too discontented if the order of succession, such as it is, does not exactly square with some theories we may have formed. Perhaps it may in the end lead us to greater and better truths.

Another subject which merits attention here is the evidence which mere markings or other indications may sometimes give as to the existence of unknown creatures, and thus may be as important to us as the footprints of Friday to Robinson Crusoe. As I have been taking Canadian examples, I may borrow one here from Mr. Matthew, of St. John, New Brunswick.

He remarks in one of his papers the manner in which the Trilobites of the early Cambrian are protected with defensive spines, and asks against what enemies they were intended to guard. That there were enemies is further proved by the occurrence of Coprolites or masses of excrement, oval or cylindrical in form, and containing fragments of shells of Trilobites, of Pteropods (Hyolithes) and of Lingula. There must therefore have been marine animals of considerable size, which preyed on Trilobites. Dr. Hunt and myself have recorded similar facts from the Upper Cambrian and Cambro-Silurian of the Province of Quebec. No remains, however, are known of animals which could have produced such coprolites, except, indeed, some of the larger worms of the period, and they seem scarcely large enough. In these circumstances Mr. Matthew falls back on certain curious marks or scratches with which large surfaces of these old rocks are covered, and which he names Ctenichnites or "Comb tracks." These markings seem to indicate the rapid motion of some animal touching the bottom with fins or other organs; and as we know no fishes in these old rocks, the question recurs, What could it have been? From the form and character of the markings Mr. Matthew infers (1) That these animals lived in "schools," or were social in their habits; (2) That they had a rapid, direct, darting motion; (3) That they had three or four (at least) flexible arms; (4) That these arms were furnished with hooks or spines; (5) That the creatures swam with an easy motion, so that sometimes the arms of one side touched the bottom, sometimes those of the other. These indications point to animals allied to the modern squids or cuttle-fishes, and as these animals may have had no hard parts capable of preservation, except their horny beaks, nothing might remain to indicate their presence except these marks on the bottom. Mr. Matthew therefore conjectures that there may have been large cuttle-fishes in the Cambrian. Since, however, these are animals of very high rank in their class, and are not certainly known to us till a very much later period, their occurrence in these old rocks would be a very remarkable and unexpected fact.

A discovery made by Walcott in the Western States since Mr. Matthew's paper was written, throws fresh light on the question. Remains of fishes have been found by the former in the Cambro Silurian rocks nearly as far back as Mr. Matthew's comb-tracks. Besides this, Pander in Russia has found in these old rocks curious teeth, which he refers conjecturally to fishes (Conodonts). Why may there not have been in the Cambrian large fishes having, like the modern sharks, cartilage or gristle instead of bone—perhaps destitute of scales, and with small teeth which have not yet been detected. The fin rays of such fishes may have left the comb tracks, and in support of this I may say that there are in the Lower Carboniferous of Horton Bluff, in Nova Scotia, very similar tracks in beds holding many remains of fishes. Whichever view we adopt we see good evidence that there were in the early Cambrian animals of higher grade than we have yet dreamt of. Observe, however, that if we could complete the record in this point it would only give us higher forms of life at an earlier time, and so push farther back their possible development from lower forms. I fear, indeed, that I can hold out little hopes to the evolutionists that a more complete geological record would help them in any way. It would possibly only render their position more difficult.

But the saddest of all the possible defects of the geological record is that it may want the beginning, and be like the Bible of some of the German historical critics, from which they eliminate as mythical everything before the time of the later Hebrew kings. Our attention is forcibly called to this by the condition of the fauna of the earliest Cambrian rocks. The discoveries in these in Wales, in Norway, and in America show us that the seas of this early period swarmed with animals representing all the great types of invertebrate marine life. We have here highly organized Crustaceans, Worms, Mollusks and other creatures which show us that in that early age all these distinct forms of life were as well separated from each other as in later times, that eyes of different types, jointed limbs with nerves and muscles, and a vast variety of anatomical contrivances were as highly developed as at any subsequent time.[20] To a Darwinian evolutionist this means nothing less than that these creatures must have existed through countless ages of development from their imagined simple ancestral form or forms how long it is impossible to guess, since, unless change was more speedy in the infancy of the earth, the term of ages required must have far exceeded that from the Cambrian to the Modern. Yet, to represent all this we have absolutely nothing except Eozoon in its solitary grandeur, and a few other forms, possibly of Protozoa and worms. An imaginary phylogeny of animal life from Monads to Trilobites would be something as long as the whole geological history. Yet it would be almost wholly imaginary, for the record of the rocks tells little or nothing. In face of such an imperfection as this, geologists should surely be humble, and make confession of ignorance to any extent that may be desired. Yet we may at least, with all humility and self-abasement, ask our critics how they know that this great blank really exists, and whether it may not be possible that the swarming life of the early Cambrian may, after all, have appeared suddenly on the stage in some way as yet unknown to us and to them.

[20] Walcott and Matthew record more than 160 species of 67 genera, including Sponges, Zoophytes, Echinoderms, Brachiopods, Bivalve and Univalve shellfishes, Trilobites and other Crustaceans from the Lower Cambrian of the United States of America and Canada alone; and these are but a portion of the inhabitants of the early Cambrian seas. There is a rich Scandinavian fauna of the same early date, and in England and Wales, Sailer, Hicks and Lapworth have described many fossils of the basal Cambrian. From year to year, also, discoveries of fossil remains are being made, both in America and Europe, in beds of older date than those previously known to be fossiliferous. At present, however, these remains are still few and imperfectly known, and it is not in all cases certain whether the beds in which they occur are pre-Cambrian or belong to the lowest members of that great system. It is unfortunate that so many of the strata between the Laurentian and the Cambrian seem to be of a character little likely to contain fossils; being littoral deposits produced in times of much physical disturbance. Yet there must have been contemporaneous beds of a different character, which may yet be discovered.

References:—"Fossil Sponges from the Quebec Group of Little Metis, Lower St. Lawrence": Transactions Royal Society of Canada, 1890. "Rèsumè of the Carboniferous Land Shells of North America": American Journal of Science, 1880. "Burrows and Tracks of Invertebrate Animals": Journal Geological Society of London, 1890. "Notes on the Pleistocene of Canada": Canadian Naturalist, 1876. "Air-breathers of the Coal Period ": Ibid., 1863.

[THE HISTORY OF THE NORTH ATLANTIC.]

DEDICATED TO THE MEMORY OF
PROF. JOHN PHILLIPS,
OF OXFORD,
One of the most able, earnest, and genial of
English Geologists;
and of other Eminent Scientific Men, now passed away,
who supported him as
President of the British Association, at its
Meeting in Birmingham, in 1865.

Distribution of Land and Water—Causes of Irregularities of the Surface Crust and Interior—Position of Continents—Past History of the Atlantic—Its Relations to Life—Its Future

Map of the North Atlantic, showing depths from 4,000 fathoms upward (after the Challenger Survey).

[CHAPTER IV.]

THE HISTORY OF THE NORTH ATLANTIC.

I

I had the pleasure of being present at the meeting of the British Association at Birmingham, in 1865: a meeting attended by an unusually large number of eminent geologists, under the presidency of my friend Phillips. I had the further pleasure of being his successor at the meeting in the same place, in 1886; and the subject of this chapter is that to which I directed the attention of the Association in my Presidential address. I fear it is a feeble and imperfect utterance compared with that which might have been given forth by any of the great men present in 1865, and who have since left us, could they have spoken with the added knowledge of the intervening twenty years.

The geological history of the Atlantic appeared to be a suitable subject for a trans-Atlantic president, and to a Society which had vindicated its claim to be British in the widest sense by holding a meeting in Canada, while it was also meditating a visit to Australia—a visit not yet accomplished, but in which it may now meet with a worthy daughter in the Australian Association formed since the meeting of 1886. The subject is also one carrying our thoughts very far back in geological time, and connecting itself with some of the latest and most important discussions and discoveries in the science of the earth, furnishing, indeed, too many salient points to be profitably occupied in a single chapter.

If we imagine an observer contemplating the earth from a convenient distance in space, and scrutinizing its features as it rolls before him, we may suppose him to be struck with the fact that eleven-sixteenths of its surface are covered with water, and that the land is so unequally distributed that from one point of view he would see a hemisphere almost exclusively oceanic, while nearly the whole of the dry land is gathered in the opposite hemisphere. He might observe that large portions of the great oceanic areas of the Pacific and Antarctic Oceans are dotted with islands—like a shallow pool with stones rising above its surface—as if the general depth were small in comparison with the area. Other portions of these oceans he might infer, from the colour of the water and the absence of islands, cover deep depressions in the earth's surface. He might also notice that a mass or belt of land surrounds each pole, and that the northern ring sends off to the southward three vast tongues of land and of mountain chains, terminating respectively in South America, South Africa, and Australia, towards which feebler and insular processes are given off by the antarctic continental mass. This, as some geographers have observed,[21] gives a rudely three-ribbed aspect to the earth, though two of the ribs are crowded together, and form the Eurasian mass or double continent, while the third is isolated in the single continent of America. He might also observe that the northern girdle is cut across, so that the Atlantic opens by a wide space into the Arctic Sea, while the Pacific is contracted toward the north, but confluent with the Antarctic Ocean. The Atlantic is also relatively deeper and less cumbered with islands than the Pacific, which has the highest ridges near its shores, constituting what some visitors to the Pacific coast of America have not inaptly called the "back of the world," while the wider slopes face the narrower ocean. The Pacific and Atlantic, though both depressions or flattenings of the earth, are, as we shall find, different in age, character, and conditions; and the Atlantic, though the smaller, is the older, and, from the geological point of view, in some respects, the more important of the two; while, by virtue of its lower borders and gentler slope, it is, though the smaller basin, the recipient of the greater rivers, and of a proportionately great amount of the drainage of the land.[22]

[21] Dana, "Manual of Geology," introductory part. Green, "Vestiges of a Molten Globe," has summed up these facts.

[22] Mr. Mellard Reade, in two Presidential addresses before the Geological Society of Liverpool, has illustrated this point and its geological consequences.

If our imaginary observer had the means of knowing anything of the rock formations of the continents, he would notice that those bounding the North Atlantic are, in general, of great age some belonging to the Laurentian system. On the other hand, he would see that many of the mountain ranges along the Pacific are comparatively new, and that modern igneous action occurs in connection with them. Thus he might see in the Atlantic, though comparatively narrow, a more ancient feature of the earth's surface; while the Pacific belongs to more modern times. But he would note, in connection with this, that the oldest rocks of the great continental masses are mostly toward their northern ends; and that the borders of the northern ring of land, and certain ridges extending southward from it, constitute the most ancient and permanent elevations of the earth's crust, though now greatly surpassed by mountains of more recent age nearer the equator, so that the continents of the northern hemisphere seem to have grown progressively from north to south.

If the attention of our observer were directed to more modern processes, he might notice that while the antarctic continent freely discharges its burden of ice to the ocean north of it, the arctic ice has fewer outlets, and that it mainly discharges itself through the North Atlantic, where also the great mass of Greenland stands as a huge condenser and cooler, unexampled elsewhere in the world, throwing every spring an immense quantity of ice into the North Atlantic, and more especially into its western part. On the other hand, he might learn from the driftage of weed and the colour of the water, that the present great continuous extension and form of the American continent tend to throw northward a powerful branch of the equatorial current, which, revolving around the North Atlantic, counteracts the great flow of ice which otherwise would condemn it to a perpetual winter.

Further, such an observer would not fail to notice that the ridges which lie along the edges of the oceans and the ebullitions of igneous matter which proceed, or have proceeded from them, are consequences of the settling downward of the great oceanic depressions, a settling ever intensified by their receiving more and more of deposit on their surfaces; and that this squeezing upward of the borders of these depressions into folds has been followed or alternated with elevations and depressions without any such folding, and proceeding from other causes. On the whole, it would be apparent that these actions are more vigorous now at the margins of the Pacific area, while the Atlantic is backed by very old foldings, or by plains and slopes from which it has, so to speak, dried away without any internal movement. Thus it would appear that the Pacific is the great centre of earth-movement, while the Atlantic trench is the more potent regulator of temperature, and the ocean most likely to be severely affected in this respect by small changes of its neighbouring land. Last of all, an observer, such as I have supposed, would see that the oceans are the producers of moisture and the conveyors of heat to the northern regions of the world, and that in this respect and in the immense condensation and delivery of ice at its north end, the Atlantic is by far the more active, though the smaller of the two.

So much could be learned by an extra-mundane observer; but unless he had also enjoyed opportunities of studying the rocks of the earth in detail and close at hand, or had been favoured by some mundane friend with a perusal of "Lyell's Elements," or "Dana's Manual," he would not be able to appreciate as we can the changes which the Atlantic has seen in geological time, and in which it has been a main factor. Nor could he learn from such superficial observation certain secrets of the deep sea, which have been unveiled by the sounding lead, the inequalities of the ocean basin, its few profound depths, like inverted mountains or table-lands, its vast nearly flat abyssmal floor, and the sudden rise of this to the hundred fathom line, forming a terrace or shelf around the sides of the continents. These features, roughly represented in the map prefixed, he would be unable to perceive.

Before leaving this broad survey, we may make one further remark. An observer, looking at the earth from without, would notice that the margins of the Atlantic and the main lines of direction of its mountain chains are north-east and south-west, and north-west and south-east, as if some early causes had determined the occurrence of elevations along great circles of the earth's surface tangent to the polar circles.

We are invited by the preceding general glance at the surface of the earth to ask certain questions respecting the Atlantic, (1) What has at first determined its position and form? (2) What changes has it experienced in the lapse of geological time? (3) What relations have these changes borne to the development of life on the land and in the water? (4) What is its probable future?

Before attempting to answer these questions, which I shall not take up formally in succession, but rather in connection with each other, it is necessary to state, as briefly as possible, certain general conclusions respecting the interior of the earth. It is popularly supposed that we know nothing of this beyond a superficial crust perhaps averaging 50,000 to 100,000 feet in thickness. It is true we have no means of exploration in the earth's interior, but the conjoined labours of physicists have now proceeded sufficiently far to throw much inferential light on the subject, and to enable us to make some general affirmations with certainty; and these it is the more necessary to state distinctly, since they are often treated as mere subjects of speculation and fruitless discussion.

(1) Since the dawn of geological science, it has been evident that the crust on which we live must be supported on a plastic or partially liquid mass of heated rock, approximately uniform in quality under the whole of its area. This is a legitimate conclusion from the wide distribution of volcanic phenomena, and from the fact that the ejections of volcanoes, while locally of various kinds, are similar in every part of the world. It led to the old idea of a fluid interior of the earth, but this seems now generally abandoned, and this interior heated and plastic layer is regarded as merely an under-crust, resting on a solid nucleus.[23]

[23] I do not propose to express any definite opinion as to this question, as either conclusion will satisfy the demands of geology. It would seem, however, that astronomers now admit a slight periodical deformation of the crust. See Lord Kelvin's Anniversary Address to Royal Society, 1892.

(2) We have reason to believe, as the result of astronomical investigations,[24] that, notwithstanding the plasticity or liquidity of the under-crust, the mass of the earth—its nucleus as we may call it—is practically solid and of great density and hardness. Thus we have the apparent paradox of a solid yet fluid earth; solid in its astronomical relations, liquid or plastic for the purposes of volcanic action and superficial movements.

[24] Hopkins, Mallet, Lord Kelvin, and Prof. G. H. Darwin maintain the solidity and rigidity of the earth on astronomical grounds; but different conclusions have been reached by Fisher, Hennesey, Delaunay, and Airy. In America, Hunt, Barnard and Crosby, Button, Le Conte and Wadsworth have discussed these questions. Bonney has suggested that a mass may be slowly mobile under long-continued pressure, while rigid with reference to more sudden movements.

(3) The plastic sub-crust is not in a state of dry igneous fusion, but in that condition of aqueo-igneous or hydrothermic fusion which arises from the action of heat on moist substances, and which may either be regarded as a fusion or as a species of solution at a very high temperature. This we learn from the phenomena of volcanic action, and from the composition of the volcanic and plutonic rocks, as well as from such chemical experiments as those of Daubrée, and of Tilden, and Shenstone.[25] It follows that water or steam, as well as rocky matter, may be ejected from the under-crust.

[25] Phil. Trans., 1884. Also Crosby in Proc. Boston Soc. Nat. Hist., 1883.

(4) The interior sub-crust is not perfectly homogeneous, but may be roughly divided into two layers or magmas, as they have been called; an upper, highly silicious or acidic, of low specific gravity and light-coloured, and corresponding to such kinds of plutonic and volcanic rocks as granite and trachyte; and a lower, less silicious or more basic, more dense, and more highly charged with iron, and corresponding to such igneous rocks as the dolerites, basalts, and kindred lavas. It is interesting here to note that this conclusion, elaborated by Durocher and Von Waltershausen, and usually connected with their names, appears to have been first announced by John Phillips, in his "Geological Manual," and as a mere common sense deduction from the observed phenomena of volcanic action and the probable results of the gradual cooling of the earth. It receives striking confirmation from the observed succession of acidic and basic volcanic rocks of all geological periods and in all localities. It would even seem, from recent spectroscopic investigations of Lockyer, that there is evidence of a similar succession of magmas in the heavenly bodies, and the discovery by Nordenskiöld of native iron in Greenland basalts, affords a probability that the inner magma is in part metallic, and possibly, that vast masses of unoxidised metals exist in the central portion of the earth.

(5) Where rents or fissures form in the upper crust, the material of the lower crust is forced upward by the pressure of the less supported portions of the former, giving rise to volcanic phenomena either of an explosive or quiet character, as may be determined by contact with water. The underlying material may also be carried to the surface by the agency of heated water, producing those quiet discharges which Hunt has named crenitic. It is to be observed here that explosive volcanic phenomena, and the formation of cones, are, as Prestwich has well remarked, characteristic of an old and thickened crust; quiet ejection from fissures and hydro-thermal action may have been more common in earlier periods and with a thinner over-crust This is an important consideration with reference to those earlier ages referred to in chapter second.

(6) The contraction of the earth's interior by cooling and by the emission of material from below the over-crust, has caused this crust to press downward, and therefore laterally, and so to effect great bends, folds, and plications; and these, modified subsequently by surface denudation, and the piling of sediments on portions of the crust, constitute mountain chains and continental plateaus. As Hall long ago pointed out,[26] such lines of folding have been produced more especially where thick sediments had been laid down on the sea-bottom, and where, in consequence, internal expansion of the crust had occurred from heating below. Thus we have here another apparent paradox, namely, that the elevations of the earth's crust occur in the places where the greatest burden of detritus has been laid down upon it, and where, consequently, the crust has been softened and depressed. We must beware, in this connection, of exaggerated notions of the extent of contraction and of crumpling required to form mountains. Bonney has well shown, in lectures delivered at the London Institution, that an amount of contraction, almost inappreciable in comparison with the diameter of the earth, would be sufficient; and that, as the greatest mountain chains are less than 1/600th of the earth's radius in height, they would, on an artificial globe a foot in diameter, be no more important than the slight inequalities that might result from the paper gores overlapping each other at the edges. This thinness of the crushed crust agrees with the deductions of physical science as to the shallowness of the superficial layer of compression in a cooling globe. It is perhaps not more than five miles in thickness. A singular proof of this is seen by the extension of straight cracks filled with volcanic rock in the Laurentian districts of Canada.[27] The beds of gneiss and associated rocks are folded and crumpled in a most complex manner, yet they are crossed by these faults, as a crack in a board may tear a sheet of paper or a thin veneer glued on it. We thus see that the crumpled Laurentian crust was very thin, while the uncrushed sub-crust determined the line of fracture.

[26] Hall (American Association Address, 1857, subsequently republished, with additions, as "Contributions to the Geological History of the American Continent"), Mallet, Rogers, Dana, La Conte, etc.

[27] As, for instance, the great dyke running nearly in a straight line from near St. Jerome along the Ottawa to Templeton, on the Ottawa, and beyond, a distance of more than a hundred miles.

(7) The crushing and sliding of the over-crust implied in these movements raise some serious questions of a physical character. One of these relates to the rapidity or slowness of such movements, and the consequent degree of intensity of the heat developed, as a possible cause of metamorphism of rocks. Another has reference to the possibility of changes in the equilibrium of the earth itself, as resulting from local collapse and ridging. These questions in connection with the present dissociation of the axis of rotation from the magnetic poles, and with changes of climate, have attracted some attention,[28] and probably deserve further consideration on the part of physicists. In so far as geological evidence is concerned, it would seem that the general association of crumpling with metamorphism indicates a certain rapidity in the process of mountain-making, and consequent development of heat; and the arrangement of the older rocks around the Arctic basin forbids us from assuming any extensive movement of the axis of rotation, though it does not exclude changes to a limited extent.

[28] See recent papers of Oldham and Fisher, in Geological Magazine, and Philosophical Magazine, July, 1886. Also Péroche, "Revol. Polaires." Paris, 1886.

(8) It appears from the above that mountains and continental elevations may be of three kinds, (a) They may consist of material thrown out of volcanic rents, like earth out of a mole burrow. Mountains like Vesuvius and Ætna are of this kind. (b) They may be parts of wide ridges or chains variously cut and modified by rains and rivers. The Lebanon and the Catskill Mountains are cases in point, (c) They may be lines of crumpling by lateral pressure. The greatest mountains, like the Cordillera, the Alps, and the Appalachians are of this kind, and such mountains may represent lateral pressure occurring at various times, and whose results have been greatly modified subsequently.

I wish to formulate these principles as distinctly as possible, and as the result of all the long series of observations, calculations, and discussions since the time of Werner and Hutton, and in which a vast number of able physicists and naturalists have borne a part, because they may be considered as certain deductions from our actual knowledge, and because they lie at the foundation of a rational physical geology.

We may roughly popularise these deductions by comparing the earth to a drupe or stone-fruit, such as a plum or peach somewhat dried up. It has a large and intensely hard stone and kernel, a thin pulp made up of two layers, an inner, more dense and dark-coloured, and an outer, less dense and lighter-coloured. These constitute the under-crust. On the outside it has a thin membrane or over-crust. In the process of drying it has slightly shrunk, so as to produce ridges and hollows of the outer crust, and this outer crust has cracked in some places, allowing portions of the pulp to ooze out—in some of them its lower dark substance, in others, its upper and lighter material. The analogy extends no farther, for there is nothing in our withered fruit to represent the oceans occupying the lower parts of the surface, or the deposits which they have laid down.

Here a most important feature demands attention. The rain, the streams, and the sea are constantly cutting down the land and depositing it in the bed of the waters. Thus weight is taken from the land, and added to the sea bed. Geological facts, such as the great thickness of the coal measures, in which we find thousands of feet of sediment, all of which must have been deposited in shallow water, and the accumulation of hundreds of feet of superficial material in deltas at the mouth of great rivers, show that the crust of the earth is so mobile as to yield downward to every pressure, however slight.[29] It may do this slowly and gradually, or by jumps from time to time; and this yielding necessarily tends to squeeze up the edges of the depressed portions into ridges, and to cause lateral movement and ejection of volcanic matter at intervals.

[29] Starkie Gardiner, Nature, December, 1889.

Keeping in view these general conclusions, let us now turn to their bearing on the origin and history of the North Atlantic.

Though the Atlantic is a deep ocean, its basin does not constitute so much a depression of the crust of the earth as a flattening of it, and this, as recent soundings have shown, with a slight ridge or elevation along its middle, and banks or terraces fringing the edges, so that its form is not so much that of a basin as that of a shallow elongated plate with its middle a little raised. Its true margins are composed of portions of the over-crust folded, overlapped and crushed, as if by lateral pressure emanating from the sea itself. We cannot, for example, look at a geological map of America without perceiving that the Appalachian ridges, which intervene between the Atlantic and the St. Lawrence valley, have been driven bodily back by a force acting from the east, and that they have resisted this pressure only where, as in the Gulf of St. Lawrence and the Catskill region of New York, they have been protected by outlying masses of very old rocks, as, for example, by that of the island of Newfoundland and that of the Adirondack Mountains. The admirable work begun by my friend and fellow-student, Professor James Nicol, followed up by Professor Lapworth, and now, after long controversy, fully confirmed by the recent observations of the Geological Survey of Scotland, has shown the most intense action of the same kind on the east side of the ocean in the Scottish highlands; and the more widely distributed Eozoic and other old rocks of Scandinavia may be appealed to in further evidence of this.[30]

[30] Address to Geological Section, Brit. Assoc., by Prof. Judd, Aberdeen Meeting, 1885. According to Rogers, the crumpling of the Appalachians has reduced a breadth of 158 miles to about 60. Geikie, Address, Geological Society, 1891-2.

If we now inquire as to the cause of the Atlantic depression, we must go back to the time when the areas occupied by the Atlantic and its bounding coasts were parts of the shoreless sea in which the earliest gneisses or stratified granites of the Laurentian age were being laid down in vastly extended beds. These ancient crystalline rocks have been the subject of much discussion and controversy, to which reference has been made in a previous chapter.

It will be observed, in regard to these theories, that they do not suppose that the old gneiss is an ordinary sediment, but that all regard it as formed in exceptional circumstances, these circumstances being the absence of land and of subaërial decay of rock, and the presence wholly or principally of the material of the upper surface of the recently hardened crust. This being granted, the question arises, Ought we not to combine the several theories as to the origin of gneiss, and to believe that the cooling crust has hardened in successive layers from without inward; that at the same time fissures were locally discharging igneous matter to the surface; that matter held in suspension in the ocean and matter held in solution by heated waters rising from beneath the outer crust were mingling their materials in the deposits of the primitive ocean?[31] It would seem that the combination of all these agencies may safely be evoked as causes of the pre-Atlantic deposits. This is the eclectic position I have maintained in a previous chapter, and which I hold to be in every way the most probable.

[31] Hunt, Transactions Royal Society of Canada, 1885.

Let us suppose, then, the floor of old ocean covered with a flat pavement of gneiss, or of that material which is now gneiss, the next question is, How and when did this original bed become converted into sea and land? Here we have some things certain, others most debatable. That the cooling mass, especially if it was sending out volumes of softened rocky material, either in the form of volcanic ejections or in that of matter dissolved in heated water, and piling this on the surface, must soon become too small for its shell, is apparent; but when and where would the collapse, crushing and wrinkling inevitable from this cause begin? The date is indicated by the lines of old mountain chains which traverse the Laurentian districts; but the reason why is less apparent. The more or less unequal cooling, hardening and conductive power of the outer crust we may readily assume. The driftage unequally of water-borne detritus to the south-west by the bottom currents of the sea is another cause, and, as we shall soon see, most effective. Still another is the greater cooling and hardening of the crust in the polar regions, and the tendency to collapse of the equatorial protuberance from the slackening of the earth's rotation. Besides these, the internal tides of the earth's substance at the times of solstice would exert an oblique pulling force on the crust, which might tend to crack it along diagonal lines. From whichever of these causes, or the combination of the whole, we know that, within the Laurentian time, folded portions of the earth's crust began to rise above the general surface, in broad belts running from north-east to south-west, and from north-west to south-east, where the older mountains of Eastern America and Western Europe now stand, and that the subsidence of the oceanic areas, allowed by this crumpling of the crust, permitted other areas on both sides of the Atlantic to form limited table-lands. This was the commencement of a process repeated again and again in subsequent times, and which began in the middle Laurentian, when for the first time we find beds of quartzite, limestone, and iron ore, and graphite beds, indicating that there was already land and water, and that the sea, and perhaps the land, swarmed with forms of animal and plant life, unknown, for the most part, now. Independently of the questions as to the animal nature of Eozoon, I hold that we know, as certainly as we can know anything inferentially, the existence of these primitive forms of life. If I were to conjecture what were these early forms of plant and animal life, still unknown to us by actual specimens, I would suppose that, just as in the Palæozoic, the acrogens culminated in gigantic and complex forest trees, so in the Laurentian, the algæ, the lichens, and the mosses grew to dimensions and assumed complexity of structure unexampled in later times, and that, in the sea, the humbler forms of Protozoa and Sea Mosses were the dominant types, but in gigantic and complex forms. The land of this period was probably limited, for the most part, to high latitudes, and its aspect, though more rugged and abrupt, and of greater elevation, must have been of that character which we still see in the Laurentian hills. The distribution of this ancient land is indicated by the long lines of old Laurentian rock extending from the Labrador coast and the north shore of the St. Lawrence, and along the eastern slopes of the Appalachians in America, and the like rocks of the Hebrides, the Western Highlands, and the Scandinavian mountains. A small but interesting remnant is that in the Malvern Hills, so well described by Holl. It will be well to note here, and to fix on our minds, that these ancient ridges of Eastern America and Western Europe have been greatly denuded and wasted since Laurentian times, and that it is along their eastern sides that the greatest sedimentary accumulations have been deposited.

From this time dates the introduction of that dominance of existing causes which forms the basis of uniformitarianism in geology, and which had to go on with various and great modifications of detail, through the successive stages of the geological history, till the land and water of the northern hemisphere attained to their present complex structure.

So soon as we have a circumpolar belt or patches of Eozoic[32] land and ridges running southward from it, we enter on new and more complicated methods of growth of the continents and seas. Portions of the oldest crystalline rocks, raised out of the protecting water, were now eroded by atmospheric agents, and especially by the carbonic acid, then existing in the atmosphere perhaps more abundantly than at present, under whose influence the hardest of the gneissic rocks gradually decay. The arctic lands were subjected, in addition, to the powerful mechanical force of frost and thaw. Thus every shower of rain and every swollen stream would carry into the sea the products of the waste of land, sorting them into fine clays and coarser sands; and the cold currents which cling to the ocean bottom, now determined in their courses, not merely by the earth's rotation, but also by the lines of folding on both sides of the Atlantic, would carry south-westward, and pile up in marginal banks of great thickness the débris produced from the rapid waste of the land already existing in the Arctic regions. The Atlantic, opening widely to the north, and having large rivers pouring into it, was, especially, the ocean characterised, as time advanced, by the prevalence of these phenomena. Thus, throughout the geological history it has happened that, while the middle of the Atlantic has received merely organic deposits of shells of foraminifera and similar organisms, and this probably only to a small amount, its margins have had piled upon them beds of detritus of immense thickness. Professor Hall, of Albany, was the first geologist who pointed out the vast cosmic importance of these deposits, and that the mountains of both sides of the Atlantic owe their origin to these great lines of deposition, along with the fact, afterwards more fully insisted on by Rogers, that the portions of the crust which received these masses of débris became thereby weighted down and softened, and were more liable than other parts to lateral crushing.

[32] Or Archæan, or pre-Cambrian, if these terms are preferred.

Thus, in the later Eozoic and early Palæozoic times, which succeeded the first foldings of the oldest Laurentian, great ridges were thrown up, along the edges of which were beds of limestone, and on their summits and sides, thick masses of ejected igneous rocks. In the bed of the central Atlantic there are no such accumulations. It must have been a flat, or slightly ridged, plate of the ancient gneiss, hard and resisting, though perhaps with a few cracks, through which igneous matter welled up, as in Iceland and the Azores in more modern times. In this condition of things we have causes tending to perpetuate and extend the distinctions of ocean and continent, mountain and plain, already begun; and of these we may more especially note the continued subsidence of the areas of greatest marine deposition. This has long attracted attention, and affords very convincing evidence of the connection of sedimentary deposit as a cause with the subsidence of the crust.[33]

[33] Dutton in Report of U.S. Geological Survey, 1891. From facts stated in this report and in my "Acadian Geology," it is apparent that in the Western States and in the coal fields of Nova Scotia, shallow-water deposits have been laid down, up to thicknesses of 10,000 to 20,000 feet in connection with continuous subsidence. See also a paper by Ricketts in the Geol. Mag., 1883.

We are indebted to a French physicist, M. Faye, for an important suggestion on this subject. It is that the sediment accumulated along the shores of the ocean presented an obstacle to radiation, and consequently to cooling of the crust, while the ocean floor, unprotected and unweighted, and constantly bathed with currents of cold water having great power of convection of heat, would be more rapidly cooled, and so would become thicker and stronger. This suggestion is complementary to the theory of Professor Hall, that the areas of greatest deposit on the margins of the ocean are necessarily those of greatest folding and consequent elevation. We have thus a hard, thick, resisting ocean bottom, which, as it settles down toward the interior, under the influence of gravity, squeezes upwards and folds and plicates all the soft sediments deposited on its edges. The Atlantic area is almost an unbroken cake of this kind. The Pacific area has cracked in many places, allowing the interior fluid matter to exude in volcanic ejections.

It may be said that all this supposes a permanent continuance of the ocean basins, whereas many geologists postulate a mid-Atlantic continent to give the thick masses of detritus found in the older formations both in Eastern America and Western Europe, and which thin off in proceeding into the interior of both continents. I prefer, as already stated, to consider these belts of sediment as the deposits of northern currents, and derived from arctic land, and that, like the great banks off the American coast at the present day, which are being built up by the present arctic current, they had little to do with any direct drainage from the adjacent shore. We need not deny, however, that such ridges of land as existed along the Atlantic margins were contributing their quota of river-borne material, just as on a still greater scale the Amazon and Mississippi are doing now, and this especially on the sides toward the present continental plateaus, though the greater part must have been derived from the wide tracts of Laurentian land within the Arctic Circle, or near to it. It is further obvious that the ordinary reasoning respecting the necessity of continental areas in the present ocean basins would actually oblige us to suppose that the whole of the oceans and continents had repeatedly changed places. This consideration opposes enormous physical difficulties to any theory of alternations of the oceanic and continental areas, except locally at their margins.

But the permanence of the Atlantic depression does not exclude the idea of successive submergences of the continental plateaus and marginal slopes, alternating with periods of elevation, when the ocean retreated from the continents and contracted its limits. In this respect the Atlantic of to-day is much smaller than it was in those times when it spread widely over the continental plains and slopes, and much larger than it has been in times of continental elevation. This leads us to the further consideration that, while the ocean beds have been sinking, other areas have been better supported, and constitute the continental plateaus; and that it has been at or near the junctions of these sinking and rising areas that the thickest deposits of detritus, the most extensive foldings, and the greatest ejections of volcanic matter have occurred. There has thus been a permanence of the position of the continents and oceans throughout geological time, but with many oscillations of these areas, producing submergences and emergences of the land. In this way we can reconcile the vast vicissitudes of the continental areas in different geological periods with that continuity of development from north to south, and from the interiors to the margins, which is so marked a feature. We have, for this reason, to formulate another apparent geological paradox, namely, that while, in one sense, the continental and oceanic areas are permanent, in another, they have been in continual movement. Nor does this view exclude extension of the continental borders or of chains of islands beyond their present limits, at certain periods; and indeed, the general principle already stated, that subsidence of the ocean bed has produced elevation of the land, implies in earlier periods a shallower ocean and many possibilities as to volcanic islands, and low continental margins creeping out into the sea; while it is also to be noted that there are, as already stated, bordering shelves, constituting shallows in the ocean, which at certain periods have emerged as land.

We are thus compelled, as already stated, to believe in the contemporaneous existence in all geological periods, except perhaps the earliest of them, of the three distinct conditions of areas on the surface of the earth, defined in chapter second oceanic areas of deep sea, continental plateaus and marginal shelves, and lines of plication and folding.

In the successive geological periods the continental plateaus, when submerged, owing to their vast extent of warm and shallow sea, have been the great theatres of the development of marine life and of the deposition of organic limestones, and when elevated, they have furnished the abodes of the noblest land faunas and floras. The mountain belts, especially in the north, have been the refuge and stronghold of land life in periods of submergence; and the deep ocean basins have been the perennial abodes of pelagic and abyssal creatures and the refuge of multitudes of other marine animals and plants in times of continental elevation. These general facts are full of importance with reference to the question of the succession of formations and of life in the geological history of the earth.

So much space has been occupied with these general views, that it would be impossible to trace the history of the Atlantic in detail through the ages of the Palæozoic, Mesozoic, and Tertiary. We may, however, shortly glance at the changes of the three kinds of surface already referred to. The bed of the ocean seems to have remained, on the whole, abyssal; but there were probably periods when those shallow reaches of the Atlantic which stretch across its most northern portion, and partly separate it from the Arctic basin, presented connecting coasts or continuous chains of islands sufficient to permit animals and plants to pass over.[34] At certain periods also there were, not unlikely, groups of volcanic islands, like the Azores, in the temperate or tropical Atlantic. More especially might this be the case in that early time when it was more like the present Pacific; and the line of the great volcanic belt of the Mediterranean, the mid-Atlantic banks, the Azores and the West India Islands point to the possibility of such partial connections. These were stepping stones, so to speak, over which land organisms might cross, and some of these may be connected with the fabulous or pre-historic Atlantis.

[34] It would seem, from Geikie's description of the Faroe Islands, that they may be a remnant of such connecting land, dating from the Cretaceous or Eocene period.

In the Palæozoic period, the distinctions already referred to, into continental plateaus, mountain ridges, and ocean depths, were first developed, and we find, already, great masses of sediment accumulating on the seaward sides of the old Laurentian ridges, and internal deposits thinning away from these ridges over the submerged continental areas, and presenting dissimilar conditions of sedimentation. It would seem also that, as Hicks has argued for Europe, and Logan and Hall for America, this Cambrian age was one of slow subsidence of the land previously elevated, accompanied with or caused by thick deposits of detritus along the borders of the subsiding shore, which was probably covered with the decomposing rock arising from long ages of subaërial waste.

In the coal formation age its characteristic swampy flats stretched in some places far into the shallower parts of the ocean.[35] In the Permian, the great plicated mountain margins were fully developed on both sides of the Atlantic. In the Jurassic, the American continent probably extended farther to the sea than at present. In the Wealden age there was much land to the west and north of Great Britain, and Professor Bonney has directed attention to the evidence of the existence of this land as far back as the Trias, while Mr. Starkie Gardiner has insisted on connecting links to the southward, as evidenced by fossil plants. So late as the Post-glacial, or early human period, large tracts, now submerged, formed portions of the continents. On the other hand, the interior plains of America and Europe were often submerged. Such submergences are indicated by the great limestones of the Palæozoic, by the chalk and its representative beds in the Cretaceous, by the Nummulitic formation in the Eocene, and lastly, by the great Pleistocene submergence, one of the most remarkable of all, one in which nearly the whole northern hemisphere participated, and which was probably separated from the present time by only a few thousands of years.[36] These submergences and elevations were not always alike on the two sides of the Atlantic. The Salina period of the Silurian, for example, and the Jurassic, show continental elevation in America not shared by Europe. The great subsidences of the Cretaceous and the Eocene were proportionally deeper and wider on the eastern continent, and this and the direction of the land being from north to south, cause more ancient forms of life to survive in America. These elevations and submergences of the plateaus alternated with the periods of mountain-making plication, which was going on at intervals, at the close of the Eozoic, at the beginning of the Cambrian, at the close of the Siluro-Cambrian, in the Permian, and in Europe and Western America in the Tertiary. The series of changes, however, affecting all these areas was of a highly complex character in detail.[37]

[35] I have shown the evidence of this in the remnants of Carboniferous districts once more extensive on the Atlantic coast of Nova Scotia and Cape Breton ("Acadian Geology").

[36] The recent surveys of the Falls of Niagara coincide with a great many evidences to which I have elsewhere referred in proving that the Pleistocene submergence of America and Europe came to an end not more than ten thousand years ago, and was itself not of very great duration. Thus in Pleistocene times the land must have been submerged and re-elevated in a very rapid manner.

[37] "Acadian Geology."

We may also note a fact which I have long ago insisted on,[38] the regular pulsation of the continental areas, giving us alternations in each great system of deep-sea and shallow-water beds, so that the successive groups of formations may be divided into triplets of shallow-water, deep-water, and shallow-water strata, alternating in each period. This law of succession applies more particularly to the formations of the continental plateaus, rather than to those of the ocean margins, and it shows that, intervening between the great movements of plication there were subsidences of those plateaus, or elevations of the sea bottom, which allowed the waters to spread themselves over all the inland spaces between the great folded mountain ranges of the Atlantic borders.

[38] "Acadian Geology."

In referring to the ocean basins we should bear in mind that there are three of these in the northern hemisphere the Arctic, the Pacific, and the Atlantic. De Ranee has ably summed up the known facts as to Arctic geology in a series of articles in Nature, from which it appears that this area presents from without inwards a succession of older and newer formations from the Eozoic to the Tertiary, and that its extent must have been greater in former periods than at present, while it must have enjoyed a comparatively warm climate from the Cambrian to the Pleistocene period. The relations of its deposits and fossils are closer with those of the Atlantic than with those of the Pacific, as might be anticipated from its wider opening into the former. Blandford has recently remarked on the correspondence of the marginal deposits around the Pacific and Indian oceans,[39] and Dr. Dawson informs me that this is equally marked in comparison with the west coast of America, but these marginal areas have not yet gained much on the ocean. In the North Atlantic, on the other hand, there is a wide belt of comparatively modern rocks on both sides, more especially toward the south and on the American side; but while there appears to be a perfect correspondence on both sides of the Atlantic, and around the Pacific respectively, there seems to be less parallelism between the deposits and forms of life of the two oceans, as compared with each other, and less correspondence in forms of life, especially in modern times. Still, in the earlier geological ages, as might have been anticipated from the imperfect development of the continents, the same forms of life characterise the whole ocean from Australia to Arctic America, and indicate a grand unity of Pacific and Atlantic life not equalled in later times,[40] and which speaks of true contemporaneity rather than of what has been termed homotaxis or mere likeness of orders.

[39] Journal of Geological Society, May, 1886. Blandford's statements respecting the mechanical deposits of the close of the Palæozoic in the Indian Ocean, whether these are glacial or not, would seem to show a correspondence with the Permian conglomerates and earth-movements of the Atlantic area; but since that time the Atlantic has enjoyed comparative repose. The Pacific seems to have reproduced the conditions of the Carboniferous in the Cretaceous age, and seems to have been less affected by the great changes of the Pleistocene.

[40] Daintree and Etheridge, "Queensland Geology," Journal Geological Society, August, 1872; R. Etheridge, Junior, "Australian Fossils," Trans. Phys. Soc..Edin., 1880.

We may pause here for a moment to notice some of the effects of Atlantic growth on modern geography. It has given us rugged and broken shores, composed of old rocks in the north, and newer formations and softer features toward the south. It has given us marginal mountain ridges and internal plateaus on both sides of the sea. It has produced certain curious and by no means accidental correspondences of the eastern and western sides. Thus the solid basis on which the British Islands stand may be compared with Newfoundland and Labrador, the English Channel with the Gulf of St. Lawrence, the Bay of Biscay with the Bay of Maine, Spain with the projection of the American land at Cape Hatteras, the Mediterranean with the Gulf of Mexico. The special conditions of deposition and plication necessary to these results, and their bearing on the character and productions of the Atlantic basin, would require a volume for their detailed elucidation.

Thus far our discussion has been limited almost entirely to physical causes and effects. If we now turn to the life history of the Atlantic, we are met at the threshold with the question of climate, not as a thing fixed and immutable, but as changing from age to age in harmony with geographical mutations, and producing long cosmic summers and winters of alternate warmth and refrigeration.

We can scarcely doubt that the close connection of the Atlantic and Arctic oceans is one factor in those remarkable vicissitudes of climate experienced by the former, and in which the Pacific area has also shared in connection with the Antarctic Sea. No geological facts are indeed at first sight more strange and inexplicable than the changes of climate in the Atlantic area, even in comparatively modern periods. We know that in the early Tertiary temperate conditions reigned as far north as the middle of Greenland, and that in the Pleistocene the Arctic cold advanced until an almost perennial winter prevailed half way to the equator. It is no wonder that nearly every cause available in the heavens and the earth has been invoked to account for these astounding facts. I shall, I trust, be excused if, neglecting most of these theoretical views, I venture to invite attention, in connection with this question, chiefly to the old Lyellian doctrine of the modification of climate by geographical changes. Let us, at least, consider how much these are able to account for.

The ocean is a great equalizer of extremes of temperature. It does this by its great capacity for heat, and by its cooling and heating power when passing from the solid into the liquid and gaseous states, and the reverse. It also acts by its mobility, its currents serving to convey heat to great distances, or to cool the air by the movement of cold icy waters. The land, on the other hand, cools or warms rapidly, and can transmit its influence to a distance only by the winds, and the influence so transmitted is rather in the nature of a disturbing than of an equalizing cause. It follows that any change in the distribution of land and water must affect climate, more especially if it changes the character or course of the ocean currents.

Turning to the Atlantic, in this connection we perceive that its present condition is peculiar and exceptional. On the one hand it is widely open to the Arctic Sea and the influence of its cold currents, and on the other it is supplied with a heating apparatus of enormous power to give a special elevation of temperature, more particularly to its eastern coasts. The great equatorial current running across from Africa is on its northern side embayed in the Gulf of Mexico, as in a great cauldron, and pouring through the mouth of this in the Bahama channel, forms the gulf stream, which, widening out like a fan, forms a vast expanse of warm water, from which the prevailing westerly winds of the North Atlantic waft a constant supply of heated moist air to the western coasts of Europe, giving them a much more warm and uniform climate than that which prevails in similar latitudes in Eastern America, where the cold Arctic currents hug the shore, and bring down ice from Baffin's Bay. Now all this might be differently arranged. We shall find that there were times, when the Isthmus of Panama being broken through, there was no Gulf Stream, and Norway and England were reduced to the conditions of Greenland and Labrador, and when refrigeration was still further increased by subsidence of northern lands affording freer sweep to the Arctic currents. On the other hand, there were times when the Gulf of Mexico extended much farther north than at present, and formed an additional surface of warm water to heat all the interior of America, as well as the Atlantic. Geographical changes of these kinds, have probably given us the glacial period in very recent times, and at an earlier era those warm climates which permitted temperate vegetation to flourish as far north as Greenland. These are, however, great topics, which must form the subject of other chapters.

I am old enough to remember the sensation caused by the delightful revelations of Edward Forbes respecting the zones of animal life in the sea, and the vast insight which they gave into the significance of the work on minute organisms previously done by Ehrenberg, Lonsdale and Williamson, and into the meaning of fossil remains. A little later the soundings for the Atlantic cable revealed the chalky foraminiferal ooze of the abyssal ocean. Still more recently, the wealth of facts disclosed by the Challenger voyage, which naturalists have scarcely yet had time to digest, have opened up to us new worlds of deep-sea life.

The bed of the deep Atlantic is covered, for the most part, by a mud or ooze, largely made up of the débris of foraminifera and other minute organisms mixed with fine clay. In the North Atlantic the Norwegian naturalists call this the Biloculina mud. Farther south, the Challenger naturalists speak of it as Globigerina ooze. In point of fact it contains different species of foraminiferal shells, Globigerina and Orbulina being in some localities dominant, and in others, other species; and these changes are more apparent in the shallower portions of the ocean.

On the other hand, there are means for disseminating coarse material over parts of the ocean beds. There are, in the line of the Arctic current, on the American coast, great sand banks, and off the coast of Norway, sand constitutes a considerable part of the bottom material. Soundings and dredgings off Great Britain, and also off the American coast, have shown that fragments of stone referable to Arctic lands are abundantly strewn over the bottom, along certain lines, and the Antarctic continent, otherwise almost unknown, makes its presence felt to the dredge by the abundant masses of crystalline rock drifted far from it to the north. These are not altogether new discoveries. I had inferred, many years ago, from stones taken up by the hooks of fishermen on the banks of Newfoundland, that rocky material from the north is dropped on these banks by the heavy ice which drifts over them every spring, that these are glaciated, and that after they fall to the bottom sand is drifted over them with sufficient velocity to polish the stones, and to erode the shelly coverings of Arctic animals attached to them.[41] If, then, the Atlantic basin were upheaved into land, we should see beds of sand, gravel and boulders with clay flats and layers of marl and limestone. According to the Challenger reports, in the Antarctic seas S. of 64 there is blue mud, with fragments of rock, in depths of 1,200 to 2,000 fathoms. The stones, some of them glaciated, were granite, diorite, amphibolite, mica schist, gneiss and quartzite. This deposit ceases and gives place to Globigerina ooze and red clay at 46° to 47° S., but even farther north there is sometimes as much as 49 per cent, of crystalline sand. In the Labrador current a block of syenite, weighing 400 lbs., was taken up from 1,340 fathoms, and in the Arctic current, 100 miles from land, was a stony deposit, some stones being glaciated. Among these were smoky quartz, quartzite, limestone, dolomite, mica schist, and serpentine; also particles of monoclinic and triclinic felspar, hornblende, augite, magnetite, mica and glauconite, the latter, no doubt, formed in the sea bottom, the others drifted from Eozoic and Palæozoic formations to the north.[42]

[41] "Notes on Post-Pliocene of Canada," 1872.

[42] General Report, "Challenger" Expedition.

A remarkable fact in this connection is that the great depths of the sea are as impassable to the majority of marine animals as the land itself. According to Murray, while twelve of the Challenger's dredgings, taken in depths greater than 2,000 fathoms, gave 92 species, mostly new to science, a similar number of dredgings in shallower water near the land, give no less than 1,000 species. Hence arises another apparent paradox relating to the distribution of organic beings. While at first sight it might seem that the chances of wide distribution are exceptionally great for marine species, this is not so. Except in the case of those which enjoy a period of free locomotion when young, or are floating and pelagic, the deep ocean sets bounds to their migrations. On the other hand, the spores of cryptogamic plants may be carried for vast distances by the wind, and the growth of volcanic islands may effect connections which, though only temporary, may afford opportunity for land animals and plants to pass over.

With reference to the transmission of living beings across the Atlantic, we have before us the remarkable fact that from the Cambrian age onwards there were, on the two sides of the ocean, many species of invertebrate animals which were either identical or so closely allied as to be possibly varietal forms, indicating probably the shallowness of the ocean in these periods. In like manner, the early plants of the Upper Silurian, Devonian, and Carboniferous present many identical species; but this identity is less marked in more modern times. Even in the latter, however, there are remarkable connections between the floras of oceanic islands and the continents. Thus the Bermudas, altogether recent islands, have been stocked by the agency chiefly of the ocean currents and of birds, with nearly 150 species of continental plants; and the facts collected by Helmsley as to the present facilities of transmission, along with the evidence afforded by older oceanic islands which have been receiving animal and vegetable colonists for longer periods, go far to show that, time being given, the sea actually affords facilities for the migration of the inhabitants of the land, comparable with those of continuous continents.

In so far as plants are concerned, it is to be observed that the early forests were largely composed of cryptogamous plants, and the spores of these in modern times have proved capable of transmission from great distances. In considering this, we cannot fail to conclude, that the union of simple cryptogamous fructification with arboreal stems of high complexity, so well illustrated by Dr. Williamson, had a direct relation to the necessity for a rapid and wide distribution of these ancient trees. It seems also certain that some spores, as, for example, those of the Rhizocarps,[43] a type of vegetation abundant in the Palæozoic, and certain kinds of seeds, as those named Æthoetesta and Pachytheca, were fitted for flotation. Further, the periods of Arctic warmth permitted the passage around the northern belt of many temperate species of plants, just as now happens with the Arctic flora; and when these were displaced by colder periods, they marched southward along both sides of the sea on the mountain chains.

[43] See paper by the author on Palæozoic Rhizocarps, Chicago Trans., 1886.

The same remark applies to northern forms of marine invertebrates, which are much more widely distributed in longitude than those farther south. The late Mr. Gywn Jeffreys, in one of his latest communications on this subject, stated that 54 per cent, of the shallow-water mollusks of New England and Canada are also European, and of the deep-sea forms, 30 out of 35; these last, of course, enjoying greater facilities for migration than those which have to travel slowly along the shallows of the coast in order to cross the ocean and settle themselves on both sides. Many of these animals, like the common mussel and sand clam, are old settlers which came over in the Pleistocene period, or even earlier. Others, like the common periwinkle, seem to have been slowly extending themselves in modern times, perhaps even by the agency of man. The older immigrants may possibly have taken advantage of lines of coast now submerged, or of warm periods, when they could creep round the Arctic shores. Mr. Herbert Carpenter and other naturalists employed on the Challenger collections have made similar statements respecting other marine invertebrates, as, for instance, the Echinoderms, of which the deep-sea crinoids present many common species, and my own collections prove that many of the shallow-water forms are common. Dall and Whiteaves[44] have shown that some mollusks and Echinoderms are common even to the Atlantic and Pacific coasts of North America; a remarkable fact, testifying at once to the fixity of these species and to the manner in which they have been able to take advantage of geographical changes. Some of the species of whelks common to the Gulf of St. Lawrence and the Pacific are animals which have no special locomotive powers, even when young, but they are northern forms not proceeding far south, so that they may have passed through the Arctic seas. In this connection it is well to remark that many species of animals have powers of locomotion in youth which they lose when adult, and that others may have special means of transit. I once found at Gaspé a specimen of the Pacific species of Coronula, or whale-barnacle, the C. reginæ of Darwin, attached to a whale taken in the Gulf of St. Lawrence, and which had possibly succeeded in making that passage around the north of America which so many navigators have essayed in vain.[45]

[44] Dall, Report on Alaska; Whiteaves, Trans. R. S. C.

[45] I am informed, however, that the Coronula is found also in the Biscayan whales.

But it is to be remarked that while many plants and marine invertebrates are common to the two sides of the Atlantic, it is different with land animals, and especially vertebrates. I do not know that any palæozoic insects or land snails or millipedes of Europe and America are specifically identical, and of the numerous species of batrachians of the Carboniferous and reptiles of the Mesozoic, all seem to be distinct on the two sides. The same appears to be the case with the Tertiary mammals, until in the later stages of that great period we find such genera as the horse, the camel, and the elephant appearing on the two sides of the Atlantic; but even then the species seem different, except in the case of a few northern forms.

Some of the longer-lived mollusks of the Atlantic furnish suggestions which remarkably illustrate the biological aspect of these questions. Our familiar friend the oyster is one of these. The first-known oysters appear in the Carboniferous in Belgium and in the United States of America. In the Carboniferous and Permian they are few and small, and they do not culminate till the Cretaceous, in which there are no less than ninety-one so-called species in America alone; but some of the largest known species are found in the Eocene. The oyster, though an inhabitant of shallow water, and very limitedly locomotive when young, has survived all the changes since the Carboniferous age, and has spread itself over the whole northern hemisphere,[46] though a warm water rather than Arctic type.

[46] White, Report U. S. Geol. Survey, 1882-3.

I have collected fossil oysters in the Cretaceous clays of the coulées of Western Canada, in the Lias shales of England, in the Eocene and the Cretaceous beds of the Alps, of Egypt, of the Red Sea coast, of Judea, and the heights of Lebanon. Everywhere and in all formations they present forms which are so variable and yet so similar that one might suppose all the so-called species to be mere varieties. Did the oyster originate separately on the two sides of the Atlantic, or did it cross over so promptly that its appearance seems to be identical on the two sides? Are all the oysters of a common ancestry, or did the causes, whatever they were, which introduced the oyster in the Carboniferous act over again in later periods? Who can tell? This is one of the cases where causation and development—the two scientific factors which constitute the basis of what is called evolution—cannot easily be isolated. I would recommend to those biologists who discuss these questions to devote themselves to the oyster. This familiar mollusk has successfully, pursued its course, and has overcome all its enemies, from the flat-toothed selachians of the Carboniferous to the oyster dredges of the present day, has varied almost indefinitely, and yet has continued to be an oyster, unless, indeed, it may at certain portions of its career have temporarily assumed the guise of a Gryphæa or an Exogyra. The history of such an animal deserves to be traced with care, and much curious information respecting it will be found in the report which I have cited in the note.

But in these respects the oyster, is merely an example of many forms. Similar considerations apply to all those Pliocene and Pleistocene mollusks which are found in the raised sea bottoms of Norway and Scotland, on the top of Moel Tryfaen, in Wales, and at similar great heights on the hills of America, many of which can be traced back to early Tertiary times, and can be found to have extended themselves over all the seas of the northern hemisphere. They apply in like manner to the ferns, the conifers, and the broad-leaved trees, many of which we can now trace without specific change to the Eocene and Cretaceous. They all show that the forms of living things are more stable than the lands and seas in which they live. If we were to adopt some of the modern ideas of evolution, we might cut the Gordian knot by supposing that, as like causes produce like effects, these types of life have originated more than once in geological time, and need not be genetically connected with each other. But while evolutionists repudiate such an application of their doctrine, however natural and rational, it would seem that nature still more strongly repudiates it, and will not allow us to assume more than one origin for one species. Thus the great question of geographical distribution remains in all its force; and, by still another of our geological paradoxes, mountains become ephemeral things in comparison with the delicate herbage which covers them, and seas are in their present extent but of yesterday, when compared with the minute and feeble organisms that creep on their sands or swim in their waters.

The question remains: Has the Atlantic achieved its destiny and finished its course, or are there other changes in store for it in the future? The earth's crust is now thicker and stronger than ever before, and its great ribs of crushed and folded rock are more firm and rigid than in any previous period. The stupendous volcanic phenomena manifested in Mesozoic and early Tertiary times along the borders of the Atlantic have apparently died out. These facts are in so far guarantees of permanence. On the other hand, it is known that movements of elevation, along with local depression, are in progress in the Arctic regions, and a great weight of new sediment is being deposited along the borders of the Atlantic, especially on its western side; and this is not improbably connected with the earthquake shocks and slight movements of depression which have occurred in North America. It is possible that these slight and secular movements may go on uninterruptedly, or with occasional paroxysmal disturbances, until considerable changes are produced.

It is possible, on the other hand, that after the long period of quiescence which has elapsed, there may be a new settlement of the ocean bed, accompanied with foldings of the crust, especially on the western side of the Atlantic, and possibly with renewed volcanic activity on its eastern margin. In either case, a long time relatively to our limited human chronology may intervene before the occurrence of any marked change. On the whole, the experience of the past would lead us to expect movements and eruptive discharges in the Pacific rather than in the Atlantic area. It is therefore not unlikely that the Atlantic may remain undisturbed, unless secondarily and indirectly, until after the Pacific area shall have attained to a greater degree of quiescence than at present. But this subject is one too much involved in uncertainty to warrant us in following it farther.

In the meantime the Atlantic is to us a practically permanent ocean, varying only in its tides, its currents, and its winds, which science has already reduced to definite laws, so that we can use if we cannot regulate them. It is ours to take advantage of this precious time of quietude, and to extend the blessings of science and of our Christian civilisation from shore to shore, until there shall be no more sea, not in the sense of that final drying-up of old ocean to which some physicists look forward, but in the higher sense of its ceasing to be the emblem of unrest and disturbance, and the cause of isolation.

I must now close this chapter with a short statement of some general truths which I have had in view in directing attention to the geological development of the Atlantic. We cannot, I think, consider the topics to which I have referred without perceiving that the history of ocean and continent is an example of progressive design, quite as much as that of living beings. Nor can we fail to see that, while in some important directions we have penetrated the great secret of nature, in reference to the general plan and structure of the earth and its waters, and the changes through which they have passed, we have still very much to learn, and perhaps quite as much to unlearn, and that the future holds out to us and to our successors higher, grander, and clearer conceptions than those to which we have yet attained. The vastness and the might of ocean and the manner in which it cherishes the feeblest and most fragile beings, alike speak to us of Him who holds it in the hollow of His hand, and gave to it of old its boundaries and its laws; but its teaching ascends to a higher tone when we consider its origin and history, and the manner in which it has been made to build up continents and mountain-chains, and, at the same time, to nourish and sustain the teeming life of sea and land.

References:—Presidential Address to the British Association for the Advancement of Science, Birmingham, 1886. "Geology of Nova Scotia, New Brunswick, and Prince Edward Island." Fourth Edition, London, 1891.

[THE DAWN OF LIFE.]

DEDICATED TO THE MEMORY OF
SIR WILLIAM E. LOGAN,
The unwearied Explorer of the Laurentian Rocks,
and the Founder
of the
Geological Survey of Canada.

What Are the Oldest Rocks, and where?—Conditions of their Formation—Indications of Life—What its probable Nature

Nature-print of Eozoon, showing laminated, acervuline, and fragmental portions.

This is printed from an electrotype taken from an etched slab of Eozoon, and not touched with a graver except to remedy some accidental flaws in the plate. The diagonal white line marks the course of a calcite vein.

[CHAPTER V.]

THE DAWN OF LIFE

D

Do we know the first animal? Can we name it, explain its structure, and state its relations to its successors? Can we do this by inference from the succeeding types of being; and if so, do our anticipations agree with any actual reality disinterred from the earth's crust? If we could do this, either by inference or actual discovery, how strange it would be to know that we had before us even the remains of the first creature that could feel or will, and could place itself in vital relation with the great powers of inanimate nature. If we believe in a Creator, we shall feel it a solemn thing to have access to the first creature into which He breathed the breath of life. If we hold that all things have been evolved from collision of dead forces, then the first molecules of matter which took upon themselves the responsibility of living, and, aiming at the enjoyment of happiness, subjected themselves to the dread alternatives of pain and mortality, must surely evoke from us that filial reverence which we owe to the authors of our own being; if they do not involuntarily draw forth even a superstitious adoration. The veneration of the old Egyptian for his sacred animals would be a comparatively reasonable idolatry, if we could imagine any of these animals to have been the first that emerged from the domain of dead matter, and the first link in a reproductive chain of being that produced all the population of the world. Independently of any such hypotheses, all students of nature must regard with surpassing interest the first bright streaks of light that break on the long reign of primeval night and death, and presage the busy day of teeming animal existence.

No wonder, then, that geologists have long and earnestly groped in the rocky archives of the earth in search of some record of this patriarch of the animal kingdom. But after long and patient research there still remained a large residuum of the oldest rocks destitute of all traces of living beings, and designated by the hopeless name "Azoic,"—the formations destitute of remains of life, the stony records of a lifeless world. So the matter remained till the Laurentian rocks of Canada, lying at the base of these old Azoic formations, afforded forms believed to be of organic origin. The discovery was hailed with enthusiasm by those who had been prepared by previous study to receive it. It was regarded with feeble and not very intelligent faith by many more, and was met with half-concealed or open scepticism by others. It produced a copious crop of descriptive and controversial literature, but for the most part technical, and confined to scientific transactions and periodicals, read by very few except specialists. Thus, few even of geological and biological students have clear ideas of the real nature and mode of occurrence of these ancient organisms, if organisms they are, and of their relations to better known forms of life; while the crudest and most inaccurate ideas have been current in lectures and popular books, and even in text-books.

This state of things has long ceased to be desirable in the interests of science, since the settlement of the questions raised is in the highest degree important to the history of life. We cannot, it is true, affirm that Eozoon is in reality the long-sought prototype of animal existence; but it was for us, at least until recently, the last organic foothold, on which we can poise ourselves, that we may look back into the abyss of the infinite past, and forward to the long and varied progress of life in geological time. Now, however, we have announcements to be referred to in the sequel of other organisms discovered in the so-called Archæan rocks; and it is not improbable that these will rapidly increase. The discussion of its claims has also raised questions and introduced new points, certain, if properly entered into, to be fruitful of interesting and valuable thought, and to form a good introduction to the history of life in connection with geology.

As we descend in depth and time into the earth's crust, after passing through nearly all the vast series of strata constituting the monuments of geological history, we at length reach the Eozoic or Laurentian rocks,[47] deepest and oldest of all the formations known to the geologist, and more thoroughly altered or metamorphosed by heat and heated moisture than any others. These rocks, at one time known as Azoic, being supposed destitute of all remains of living things, but now more properly Eozoic, are those in which the first bright streaks of the dawn of life make their appearance.

[47] Otherwise named "Archæan."

The name Laurentian, given originally to the Canadian development of these rocks by Sir William Logan, but now applied to them throughout the world, is derived from a range of hills lying north of the St. Lawrence valley, which the old French geographers named the Laurentides. In these hills the harder rocks of this old formation rise to considerable heights, and form the highlands separating the St. Lawrence valley from the great plain fronting on Hudson's Bay and the Arctic Sea. At first sight it may seem strange that rocks so ancient should anywhere appear at the surface, especially on the tops of hills; but this is a necessary result of the mode of formation of our continents. The most ancient sediments deposited in the sea were those first elevated into land, and first altered and hardened. Upheaved in the folding of the earth's crust into high and rugged ridges, they have either remained uncovered with newer sediments, or have had such as were deposited on them washed away; and being of a hard and resisting nature, they have remained comparatively unworn when rocks much more modern have been swept off by denuding agencies.[48]

[48] This implies the permanence of continents in their main features, a doctrine the writer has maintained for thirty years, and which is discussed elsewhere.

But the exposure of the old Laurentian skeleton of mother earth is not confined to the Laurentide Hills, though these have given the formation its name. The same ancient rocks appear in the Adirondack mountains of New York, and in the patches which at lower levels protrude from beneath the newer formations along the American coast from Newfoundland to Maryland. The older gneisses of Norway, Sweden, and the Hebrides, of Bavaria and Bohemia, of Egypt, Abyssinia and Arabia, belong to the same age, and it is not unlikely that similar rocks in many other parts of the old continent will be found to be of as great antiquity. In no part of the world, however, are the Laurentian rocks more extensively distributed or better known than in Canada; and to this as the grandest and most instructive development of them we may more especially devote our attention.

The Laurentian rocks, associated with another series only a little younger, the Huronian, form a great belt of broken and hilly country, extending from Labrador across the north of Canada to Lake Superior, and thence bending northward to the Arctic Sea. Everywhere on the lower St. Lawrence they appear as ranges of billowy rounded ridges on the north side of the river, and as viewed from the water or the southern shore, especially when sunset deepens their tints to blue and violet, they present a grand and massive appearance, which, in the eye of the geologist, who knows that they have endured the battles and the storms of time longer than any other mountains, invests them with the dignity which their mere elevation would fail to give. ([Fig. 1.]) In the isolated mass of the Adirondacks, south of the Canadian frontier, they rise to a still greater elevation, and form an imposing mountain group, almost equal in height to their somewhat more modern rivals, the White Mountains, which face them on the opposite side of Lake Champlain.

The grandeur of the old Laurentian ranges is, however, best displayed where they have been cut across by the great transverse gorge of the Saguenay, and where the magnificent precipices, known as Capes Trinity and Eternity, look down from their elevation of 1,500 feet on the fiord, which at their feet is more than 100 fathoms deep. The name Eternity applied to such a mass is geologically scarcely a misnomer, for it dates back to the very dawn of geological time, and is of hoar antiquity in comparison with such upstart ranges as the Andes and the Alps. (See [Frontispiece].)

On a nearer acquaintance, the Laurentian country appears as a broken and hilly upland and highland district, clad in its pristine state with magnificent forests, but affording few attractions to the agriculturist, except in the valleys, which follow the lines of its softer beds, while it is a favourite region for the angler, the hunter, and the lumberman. Many of the Laurentian townships of Canada are, however, already extensively settled, and the traveller may pass through a succession of more or less cultivated valleys, bounded by rocks or wooded hills and crags, and diversified by running streams and romantic lakes and ponds, constituting a country always picturesque and often beautiful, and rearing a strong and hardy population. To the geologist it presents in the main immensely thick beds of gneiss, bedded diorite and quartzite, and similar crystalline rocks, contorted in the most remarkable manner, so that if they could be flattened out they would serve as a skin much too large for mother earth in her present state, so much has she shrunk and wrinkled since those youthful days when the Laurentian rocks were her outer covering.

Fig. 1.—Laurentian Hills opposite Kamouraska, Lower St. Lawrence. The islands in front are Cambro-Silurian.

Fig. 2.—Section from Petite Nation Seigniory to St. Jerome (60 miles). After Sir W. E. Logan.
(a b) Upper Laurentian. (c) Fourth Gneiss. (d′) Third Limestone. (d) Third Gneiss. (e′) Second Limestone. (x) Porphyry. (y) Granite.

I cannot describe such rocks, but their names, as given in the section, [Fig. 2], will tell something to those who have any knowledge of the older crystalline materials of the earth's crust. To those who have not, I would advise a visit to some cliff on the lower St. Lawrence, or the Hebridean coasts, or the shore of Norway, where the old hard crystalline and gnarled beds present their sharp edges to the ever raging sea, and show their endless alternations of various kinds and colours of strata, often diversified with veins and nests of crystalline minerals. He who has seen and studied such a section of Laurentian rock cannot forget it.

The elaborate stratigraphical work of Sir William Logan has proved that these old crystalline rocks are bedded or stratified, and that they must have been deposited in succession by some process of aqueous action. They have, however, through geological ages of vast duration been subjected to pressure and chemical action, which have, as stated in a previous chapter, much modified their structure, while it is also certain that they must have differed originally from the sands, clays and other materials laid down in the sea in later times.

It is interesting to notice here that the Laurentian rocks thus interpreted show that the oldest known portions of our continents were formed in the waters. They are oceanic sediments deposited perhaps when there was no dry land, or very little, and that little unknown to us, except in so far as its débris may have entered into the composition of the Laurentian rocks themselves. Thus the earliest condition of the earth known to the geologist is one in which old ocean was already dominant on its surface; and any previous condition when the surface was heated, and the water constituted an abyss of vapours enveloping its surface, or any still earlier condition in which the earth was gaseous or vaporous, is a matter of mere inference, not of actual observation. The formless and void chaos is a deduction of chemical and physical principles, not a fact observed by the geologist. Still we know, from the great dykes and masses of igneous or molten rock which traverse the Laurentian beds, that even at that early period there were deep-seated fires beneath the crust; and it is quite possible that volcanic agencies then manifested themselves, not only with quite as great intensity, but also in the same manner, as at subsequent times. It is thus not unlikely that much of the land undergoing waste in the earlier Laurentian time was of the same nature with recent volcanic ejections, and that it formed groups of islands in an otherwise boundless ocean.

However this may be, the distribution and extent of these pre-Laurentian lands is, and probably ever must be, unknown to us; for it was only after the Laurentian rocks had been deposited, and after the shrinkage and deformation of the earth's crust in subsequent times had bent and contorted them, that the foundations of the continents were laid. The rude sketch map of America given in [Fig. 3] will show this, and will also show that the old Laurentian mountains mark out the future form of the American continent.

Fig. 3.—The Laurentian Nucleus of the American Continent, after Dana.