The Story of the Earth and Man

Transcriber’s Note

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Harper & Brothers New York.

THE STORY

OF

THE EARTH AND MAN,

BY

J. W. DAWSON, LL.D., F.K.S., F.G.S.,

PRINCIPAL AND VICE-CHANCELLOR OF McGILL UNIVERSITY, MONTREAL,
AUTHOR OF “ARCHAIA,” “ACADIAN GEOLOGY,” ETC.

NEW YORK:

HARPER & BROTHERS, PUBLISHERS,

FRANKLIN SQUARE

PREFACE

The science of the earth as illustrated by geological research, is one of the noblest outgrowths of our modern intellectual life. Constituting the sum of all the natural sciences in their application to the history of our world, it affords a very wide and varied scope for mental activity, and deals with some of the grandest problems of space and time and of organic existence. It invites us to be present at the origin of things, and to enter into the very workshop of the Creator. It has, besides, most important and intimate connection with the industrial arts and with the material resources at the disposal of man. Its educational value, as a means of cultivating the powers of observing and reasoning, and of accustoming the mind to deal with large and intricate questions, can scarcely be overrated.

But fully to serve these high ends, the study of geology must be based on a thorough knowledge of the subjects which constitute its elementary data. It must be divested as far as possible of merely local colouring, and of the prejudices of specialists. It must be emancipated from the control of the bald metaphysical speculations so rife in our time, and above all it must be delivered from that materialistic infidelity, which, by robbing nature of the spiritual element, and of its presiding Divinity, makes science dry, barren, and repulsive, diminishes its educational value, and even renders it less efficient for purposes of practical research.

That the want of these preliminary conditions mars much of the popular science of our day is too evident; and I confess that the wish to attempt something better, and thereby to revive the interest in geological study, to attract attention to its educational value, and to remove the misapprehensions which exist in some quarters respecting it, were principal reasons which induced me to undertake the series of papers for the Leisure Hour, which are reproduced, with some amendments and extension, in the present work. How far I have succeeded, I must leave to the intelligent and, I trust, indulgent reader to decide. In any case I have presented this many-sided subject in the aspect in which it appears to a geologist whose studies have led him to compare with each other the two great continental areas which are the classic ground of the science, and who retains his faith in those unseen realities of which the history of the earth itself is but one of the shadows projected on the field of time.

To geologists who may glance at the following pages, I would say that, amidst much that is familiar, they will find here and there some facts which may be new to them, as well as some original suggestions and conclusions as to the relations of things, which though stated in familiar terms, I have not advanced without due consideration of a wide range of facts, To the general reader I have endeavoured to present the more important results of geological investigation divested of technical difficulties, yet with a careful regard to accuracy of statement, and in such a manner as to invite to the farther and more precise study of the subject in nature, and in works which enter into technical details. I have endeavoured as far as possible to mention the authors of important discoveries; but it is impossible in a work of this kind to quote authority for every statement, while the omission of much important matter relating to the topics discussed is also unavoidable. Shortcomings in these respects must be remedied by the reader himself, with the aid of systematic text-books. Those who may desire any farther explanation of the occasional allusions to the record of creation in Genesis, will find this in my previously published volume entitled “Archaia.”

J. W. D,

McGill College, Montreal,
January, 1873.

CONTENTS.

LIST OF ILLUSTRATIONS.

CHAPTER I.

THE GENESIS OF THE EARTH.

The title of this work is intended to indicate precisely its nature. It consists of rough, broad sketches of the aspects of successive stages in the earth’s history, as disclosed by geology, and as they present themselves to observers at the present time. The last qualification is absolutely necessary, when dealing with a science whose goal to-day will be its starting point to-morrow, and in whose view every geological picture must have its light and shaded portions, its clear foreground and its dim distance, varying according to the lights cast on them by the progress of investigation, and according to the standpoint of the observer. In such pictures results only can be given, not the processes by which they have been obtained; and with all possible gradations of light and distance, it may be that the artist will bring into too distinct outline facts still only dimly perceived, or will give too little prominence to others which, should appear in bold relief. He must in this judge for himself; and if the writer’s impressions do not precisely correspond with those of others, he trusts that they will allow something for difference of vision and point of view.

The difficulty above referred to perhaps rises to its maximum in the present chapter. For how can any one paint chaos, or give form and filling to the formless void? Perhaps no word-picture of this period of the first phase of mundane history can ever equal the two negative touches of the inspired penman—“without form and void”—a world destitute of all its present order, and destitute of all that gives it life and animation. This it was, and not a complete and finished earth, that sprang at first from its Creator’s hand; and we must inquire in this first chapter what information science gives as to any such condition of the earth.

In the first place, the geological history of the earth plainly intimates a beginning, by utterly negativing the idea that “all things continue as they were from the creation of the world.” It traces back to their origin not only the animals and plants which at present live, but also their predecessors, through successive dynasties emerging in long procession from the depths of a primitive antiquity. Not only so; it assigns to their relative ages all the rocks of the earth’s crust, and all the plains and mountains built up of them. Thus, as we go back in geological time, we leave behind us, one by one, all the things with which we are familiar, and the inevitable conclusion gains on us that we must be approaching a beginning, though this may be veiled from us in clouds and thick darkness. How is it, then, that there are “Uniformitarians” in geology, and that it has been said that our science shows no traces of a beginning, no indications of an end? The question deserves consideration; but the answer is not difficult. In all the lapse of geological time there has been an absolute uniformity of natural law. The same grand machinery of force and matter has been in use throughout all the ages, working out the great plan. Yet the plan has been progressive and advancing, nevertheless. The uniformity has been in the methods, the results have presented a wondrous diversity and development. Again, geology, in its oldest periods, fails to reach the beginning of things. It shows us how course after course of the building has been laid, and how it has grown to completeness, but it contains as yet no record of the laying of the foundation-stones, still less of the quarry whence they were dug. Still the constant progress which we have seen points to a beginning which we have not seen; and the very uniformity of the process by which the edifice has been erected, implies a time when it had not been begun, and when its stones were still reposing in their native quarry.

What, then, is the oldest condition of the earth actually shown to us by geology,—that which prevailed in the Eozoic or Laurentian period, when the oldest rocks known, those constituting the foundation-stones of our present continents, were formed and laid in their places? With regard to physical conditions, it was a time when our existing continents were yet in the bosom of the waters, when the ocean was almost universal, yet when sediments were being deposited in it as at present, while there were also volcanic foci, vomiting forth molten matter from the earth’s hidden interior. Then, as now, the great physical agencies of water and fire were contending with one another for the mastery, doing and undoing, building up and breaking down. But is this all? Has the earth no earlier history? That it must have had, we may infer from many indications; but as to the nature of these earlier states, we can learn from conjecture and inference merely, and must have recourse to other witnesses than those rocky monuments which are the sure guides of the geologist.

One fact bearing on these questions which has long excited attention, is the observed increase in temperature in descending into deep mines, and in the water of deep artesian wells—an increase which may be stated in round numbers at one degree of heat of the centigrade thermometer for every 100 feet of depth from the surface. These observations apply of course to a very inconsiderable depth, and we have no certainty that this rate continues for any great distance towards the centre of the earth. If, however, We regard it as indicating the actual law of increase of temperature, it would result that the whole crust of the earth is a mere shell covering a molten mass of rocky matter. Thus a very slight step of imagination would carry us back to a time when this slender crust had not yet formed, and the earth rolled through space an incandescent globe, with all its water and other vaporisable matters in a gaseous state. Astronomical calculation has, however, shown that the earth, in its relation to the other heavenly bodies, obeys the laws of a rigid ball, and not of a fluid globe. Hence it has been inferred that its actual crust must be very thick, perhaps not less than 2,500 miles, and that its fluid portion must therefore be of smaller dimensions than has been inferred from the observed increase of temperature. Further, it seems to have been rendered probable, from the density of rocky matter in the solid and liquid states, that a molten globe would solidify at the centre as well as at the surface, and consequently that the earth must not only have a solid crust of great thickness, but also a solid nucleus, and that any liquid portions must be of the nature of a sheet or of detached masses intervening between these. On the other hand, it has recently been maintained that the calculations which are supposed to have established the great thickness of the crust, on the ground that the earth does not change its form in obedience to the attraction of the sun and moon, are based on a misconception, and that a molten globe with a thin crust would attain to such a state of equilibrium in this respect as not to be distinguishable from a solid planet. This view has been maintained by the French physicist, Delaunay, and for some time it made geologists suppose that, after all, the earth’s crust may be very thin. Sir William Thomson, however, and Archdeacon Pratt, have ably maintained the previous opinion, based on Hopkins' calculations; and it is now believed that we may rest upon this as representing the most probable condition of the interior of the earth at present. Another fact bearing on this point is the form of the earth, which is now actually a spheroid of rotation; that is, of such a shape as would result from the action of gravity and centrifugal force in the motion of a huge liquid drop rotating in the manner in which the earth rotates. Of course it may be said that the earth may have been made in that shape to fit it for its rotation; but science prefers to suppose that the form is the result of the forces acting on it. This consideration would of course corroborate the deductions from that just mentioned. Again, if we examine a map showing the distribution of volcanoes upon the earth, and trace these along the volcanic belt of Western America and Eastern Asia, and in the Pacific Islands, and in the isolated volcanic regions in other parts of the world; and if we add to these the multitude of volcanoes now extinct, we shall be convinced that the sources of internal heat, of which these are the vents, must be present almost everywhere under the earth’s crust. Lastly, if we consider the elevations and depressions which large portions of the crust of the earth have undergone in geological time, and the actual crumpling and folding of the crust visible in great mountain chains, we arrive at a similar conclusion, and also become convinced that the crust has been not too thick to admit of extensive fractures, flexures, and foldings. There are, however, it must be admitted, theories of volcanic action, strongly supported by the chemical nature of the materials ejected by modern volcanoes, which would refer all their phenomena to the softening, under the continued influence of heat and water, of materials within the crust of the earth rather than under it.[A] Still, the phenomena of volcanic action, and of elevation and subsidence, would, under any explanation, suppose intense heat, and therefore probably an original incandescent condition.

[A] Dr. T. Sterry Hunt, in Silliman’a Journal, 1870.

La Place long ago based a theory of the originally gaseous condition of the solar system on the relation of the planets to each other, and to the sun, on their planes of revolution, the direction of their revolution, and that of their satellites. On these grounds he inferred that the solar system had been formed out of a nebulous mass by the mutual attraction of its parts. This view was further strengthened by the discovery of nebulae, which it might be supposed were undergoing the same processes by which the solar system was produced. This nebular theory, as it was called, was long very popular. It was subsequently supposed to be damaged by the fact that some of the nebulæ which had been regarded as systems in progress of formation were found by improved telescopes to be really clusters of stars, and it was inferred that the others might be of like character. The spectroscope has, however, more recently shown that some nebulæ are actually gaseous; and it has even been attempted to demonstrate that they are probably undergoing change fitting them to become systems. This has served to revive the nebular hypothesis, which has been further strengthened by the known fact that the sun is still an incandescent globe surrounded by an immense luminous envelope of vapours rising from its nucleus and condensing at its surface. On the other hand, while the sun may be supposed, from its great magnitude, to remain intensely heated, and while it will not be appreciably less powerful for myriads of years, the moon seems to be a body which has had time to complete the whole history of geological change, and to become a dry, dead, and withered world, a type of what our earth would in process of time actually become.

Figs. 1 to 5.—Ideal sections illustrating the Genesis of the Earth.

Fig. 1. A vaporous world.

Fig. 2. A world with a central fluid nucleus (b) and a photosphere (a).

Fig. 3. The photosphere darkened, and a solid crust (c) and solid nucleus (d) formed.

Fig. 4. Water (e) deposited on the crust, forming a universal ocean.

Fig. 5. The crust crumpled by shrinkage, land elevated, and the water occupying the intervening depressions.

The figures are all of uniform size; but the circle (A) shows th diameter of the globe when in the state of fig. 1, and that marked (B) its diameter when in the state of fig. 5. In all the figures (a) represents vapour or air; (b) liquid rock; (c) solid rock as a crust; (d) solid nucleus; (e) water.

Such considerations lead to the conclusion that the former watery condition of our planet was not its first state, and that we must trace it back to a previous reign of fire. The reasons which can be adduced in support of this are no doubt somewhat vague, and may in their details be variously interpreted; but at present we have no other interpretation to give of that chaos, formless and void, that state in which “nor aught nor nought existed,” which the sacred writings and the traditions and poetry of ancient nations concur with modern science in indicating as the primitive state of the earth.

Let our first picture, then, be that of a vaporous mass, representing our now solid planet spread out over a space nearly two thousand times greater in diameter than that which it now occupies, and whirling in its annual round about the still vaporous centre of our system, in which at an earlier period the earth had been but an exterior layer, or ring of vapour. The atoms that now constitute the most solid rocks are in this state as tenuous as air, kept apart by the expansive force of heat, which prevents not only their mechanical union, but also their chemical combination. But within the mass, slowly and silently, the force of gravitation is compressing the particles in its giant hand, and gathering the denser toward the centre, while heat is given forth on all sides from the condensing mass into the voids of space without. Little by little the denser and less volatile matters collect in the centre as a fluid molten globe, the nucleus of the future planet; and in this nucleus the elements, obeying their chemical affinities hitherto latent, are arranging themselves in compounds which are to constitute the future rocks. At the same time, in the exterior of the vaporous envelope, matters cooled by radiation into the space without, are combining with each other, and are being precipitated in earthy rain or snow into the seething mass within, where they are either again vaporised and sent to the surface or absorbed in the increasing nucleus. As this process advances, a new brilliancy is given to the faint shining of the nebulous matter by the incandescence of these solid particles in the upper layers of its atmosphere, a condition which at this moment, on a greater scale, is that of the sun; in the case of the earth, so much smaller in volume, and farther from the centre of the system, it came on earlier, and has long since passed away. This was the glorious starlike condition of our globe: in a physical point of view, its most perfect and beautiful state, when, if there were astronomers with telescopes in the stars, they might have seen our now dull earth flash forth—a brilliant white star secondary to the sun.

But in process of time this passes away. All the more solid and less volatile substances are condensed and precipitated; and now the atmosphere, still vast in bulk, and dark and misty in texture, contains only the water, chlorine, carbonic acid, sulphuric acid, and other more volatile substances; and as these gather in dense clouds at the outer surface, and pour in fierce corrosive rains upon the heated nucleus, combining with its materials, or flashing again into vapour, darkness dense and gross settles upon the vaporous deep, and continues for long ages, until the atmosphere is finally cleared of its acid vapours and its superfluous waters.[B] In the meantime, radiation, and the heat abstracted from the liquid nucleus by the showers of condensing material from the atmosphere, have so far cooled its surface that a crust of slag or cinder forms upon it. Broken again and again by the heavings of the ocean of fire, it at length sets permanently, and receives upon its bare and blistered surface the ever-increasing aqueous and acid rain thrown down from the atmosphere, at first sending it all hissing and steaming back, but at length allowing it to remain a universal boiling ocean. Then began the reign of the waters, and the dominion of fire was confined to the abysses within the solid crust. Under the primeval ocean were formed the first stratified rocks, from the substances precipitated from its waters, which must have been loaded with solid matter. We must not imagine this primeval ocean like our own blue sea, clear and transparent, but filled with earthy and saline matters, thick and turbid, until these were permitted to settle to the bottom and form the first sediments. The several changes above referred to are represented in diagrammatic form in figs. 1 to 4.

[B] Hunt, “Chemistry of the Primeval Earth,” Silliman’s Journal, 1858.

In the meantime all is not at rest in the interior of the new-formed earth. Under the crust vast oceans of molten rock may still remain, but a solid interior nucleus is being crystallised in the centre, and the whole interior globe is gradually shrinking. At length this process advances so far that the exterior crust, like a sheet of ice from below which the water has subsided, is left unsupported; and with terrible earthquake-throes it sinks downward, wrinkling up into huge folds, between which are vast sunken areas into which the waters subside, while from the intervening ridges the earth’s pent-up fires belch forth ashes and molten rocks. (Fig. 5.) So arose the first dry land:—

"The mountains huge appear Emergent, and their broad bare backs upheave Into the clouds, their tops ascend the sky, So high as heaved the tumid hills, so low Down sunk a hollow bottom, broad and deep, Capacious bed of waters."

The cloud was its garment, it was swathed in thick darkness, and presented but a rugged pile of rocky precipices; yet well might the “morning stars sing together, and all the sons of God shout with joy,” when its foundations were settled and its corner-stone laid, for then were inaugurated the changes which were to lead to the introduction of life on the earth, and to all the future development of the continents.

Physical geographers have taught us that the great continents, whether we regard their coasts or their mountain chains, are built up on lines which run north-east and south-west, and north-west and south-east; and it is also observed that these lines are great circles of the earth tangent to the polar circle. Further, we find, as a result of geological investigation, that these lines determined the deposition and the elevation of the oldest rocks known to us. Hence it is fair to infer that these were the original directions of the first lines of fracture and upheaval. Whether these lines were originally drawn by the influence of of the seasons on the cooling globe, or by the currents of its molten interior, or of the superficial ocean, they bespeak a most uniform and equable texture for the crust, and a definite law of fracture and upheaval; and they have modified all the subsequent action of the ocean as a depositor of sediment, and of the internal heat as a cause of alteration and movement of rocks. Against these earliest belts of land the ocean first chafed and foamed. Along their margins marine denudation first commenced, and the oceanic currents first deposited banks of sediment; and along these first lines have the volcanic orifices of all periods been most plentiful, and elevatory movements most powerfully felt.

We must not suppose that the changes thus shortly sketched were rapid and convulsive. They must have required periods of enormous duration, all of which had elapsed before the beginning of geological time, properly so called. From Sir William Thomson’s calculations, it would appear that the time which has elapsed from the first formation of a solid crust on the earth to the modern period may have been from seventy to one hundred millions of years, and the whole time from the vaporous condition of the solar system to the present, must of course have been still greater than even this enormous series of ages. Such a lapse of time is truly almost inconceivable, but it is only a few days to Him with whom one day is as a thousand years, and a thousand years as one day. How many and strange pictures does this series of processes call up! First, the uniform vaporous nebula. Then the formation of a liquid nucleus, and a brilliant photosphere without. Then the congealing of a solid crust under dark atmospheric vapours, and the raining down of acid and watery showers. Then the universal ocean, its waves rolling unobstructed around the globe, and its currents following without hindrance the leading of heat and of the earth’s rotation. Then the rupture of the crust and the emergence of the nuclei of continents.

Some persons seem to think that by these long processes of creative work we exclude the Creator, and would reduce the universe into a mere fortuitous concourse of atoms. To put it in more modern phrase, “given a quantity of detached fragments cast into space, then mutual gravitation and the collision of the fragments would give us the spangled heavens.” But we have still to ask the old question, “Whence the atoms?” and we have to ask it with all the added weight of our modern chemistry, so marvellous in its revelations of the original differences of matter and their varied powers of combination. We have to ask, What is gravitation itself, unless a mode of action of Almighty power? We have to ask for the origin of of thousands of correlations, binding together the past and the future in that orderly chain of causes and effects which constitutes the plan of the creation. If it pleased God to create in the beginning an earth “formless and void” and to elaborate from this all that has since existed, who are we, to say that the plan was not the best? Nor would it detract from our view of the creative wisdom and power if we were to hold that in ages to come the sun may experience the same change that has befallen the earth, and may become “black as sackcloth of hair,” preparatory perhaps, to changes which may make him also the abode of life; or if the earth, cooling still further, should, like our satellite the moon, absorb all its waters and gases into its bosom, and become bare, dry, and parched, until there shall be “no more sea” how do we know but that then there shall be no more need of the sun, because a better light may be provided? Or that there may not be a new baptism of fire in store for the earth, whereby, being melted with fervent heat, it may renew its youth in the fresh and heavenly loveliness of a new heaven and a new earth, free from all the evils and imperfections of the present? God is not slack in these things, as some men count slackness; but His ways are not like our ways. He has eternity wherein to do His work, and takes His own time for each of His operations. The Divine wisdom, personified by a sacred writer, may well in this exalt his own office:—

“Jehovah possessed me in the beginning of His way, Before His work of old. I was set up from everlasting, From the beginning, or ever the earth was. When there were no deeps, T was brought forth; When there were no fountains abounding in water. Before the mountains were settled, Before the hills, was I brought forth: While as yet He had not made the earth, Nor the plains, nor the higher part of the habitable world, When He gave the sea His decree, That her waters should not pass His limits; When He determined the foundations of the earth.”

CHAPTER II.

THE EOZOIC AGES.

The dominion of heat has passed away; the excess of water has been precipitated from the atmosphere, and now covers the earth as a universal ocean. The crust has folded itself into long ridges, the bed of the waters has subsided into its place, and the sea for the first time begins to rave against the shores of the newly elevated land, while the rain, washing the bare surfaces of rocky ridges, carries its contribution of the slowly wasting rocks back into the waters whence they were raised, forming, with the material worn from the crust by the surf, the first oceanic sediments. Do we know any of these earliest aqueous beds, or are they all hidden from view beneath newer deposits, or have they been themselves worn away and destroyed by denuding agencies? Whether we know the earliest formed sediments is, and may always remain, uncertain; but we do know certain very ancient rocks which may be at least their immediate successors.

Fig. 6.—The Laurentian nucleus of the American continent.

Deepest and oldest of all the rocks we are acquainted with in the crust of the earth, are certain beds much altered and metamorphosed, baked by the joint action of heat and heated moisture—rocks once called Azoic, as containing no traces of life, but for which I have elsewhere proposed the name “Eozoic,” or those that afford the traces of the earliest known living beings. These rocks are the Laurentian Series of Sir William Logan, so named from the Laurentide hills, north of the River St. Lawrence, which are composed of these ancient beds, and where they are more largely exposed than in any other region. It may seem at first sight strange that any of these ancient rocks should be found at the surface of the earth; but this is a necessary result of the mode of formation of the continents. The oldest rocks, thrown up in places into high ridges, have either not been again brought under the waters, or have lost by denudation the sediments once resting on them; and being of a hard and resisting nature, still remain; and often rise into hills of considerable elevation, showing as it were portions of the skeleton of the earth protruding through its superficial covering. Such rocks stretch along the north side of the St. Lawrence river from Labrador to Lake Superior, and thence northwardly to an unknown distance, constituting a wild and rugged district often rising into hills 4000 feet high, and in the deep gorge of the Saguenay forming cliffs 1,500 feet in sheer height from the water’s edge. South of this great ridge, the isolated mass of the Adirondack Mountains rises to the height of 6,000 feet, rivalling the newer, though still very ancient, chain of the White Mountains. Along the eastern coast of North America, a lower ridge of Laurentian rock, only appearing here and there from under the overlying sediments, is seen in Newfoundland, in New Brunswick, possibly in Nova Scotia, and perhaps farther south in Massachusetts, and as far as Maryland. In the old world, rocks of this age do not, so far as known, appear so extensively. They have been recognised in Norway and Sweden, in the Hebrides, and in Bavaria, and may, no doubt, be yet discerned in other localities. Still, the grandest and most instructive development of these rocks is in North America; and it is there that we may best investigate their nature, and endeavour to restore the conditions in which they were deposited. It has been already stated that the oldest wrinkles of the crust of the globe take the direction of great circles of the earth tangent to the polar circle, forming north-east and south-west, and north-west and south-east lines. To such lines are the great exposures of Laurentian rock conformed, as may be well seen from the map of North America (fig. 6), taken from Dana, with some additions. The great angular Laurentian belt is evidently the nucleus of the continent, and consists of two broad bands or ridges meeting in the region of the great lakes. The remaining exposures are parallel to these, and appear to indicate a subordinate coast-line of comparatively little elevation. It is known that these Laurentian exposures constitute the oldest part of the continent, a part which was land before any of the rocks of the shaded portion of the map were deposited in the bed of the ocean—all this shaded portion being composed of rocks of various geological ages resting on the older Laurentian. It is further to be observed that the beds occurring in the Laurentian bands are crumpled and folded in a most remarkable manner, and that these folds were impressed upon them before the deposition of the rocks next in geological age.

What then are these oldest rocks deposited by the sea—the first-born of the reign of the waters? They are very different in their external aspect from the silt and mud, the sand and gravel, and the shell and coral rocks of the modern sea, or of the more recent geological formations. Yet the difference is one in condition rather than composition. The members of this ancient aristocracy of the rocks are made of the same clay with their fellows, but have been subjected to a refining and crystallizing process which has greatly changed their condition. They have been, as geologists say, metamorphosed; and are to ordinary rocks what a china vase is to the lump of clay from which it has been made. Deeply buried in the earth under newer sediments, they have been baked, until sandstones, gravels, and clays came out bright and crystalline, as gneiss, mica-schist, hornblende-schist, and quartzite—all hard crystalline rocks showing at first sight no resemblance to their original material, except in the regularly stratified or bedded arrangement which serves to distinguish them from igneous or volcanic rocks. In like manner certain finer, calcareous sediments have been changed into Labrador feldspar, sometimes gay with a beautiful play of colour, and what were once common limestones appear as crystalline marble. If the evidence of such metamorphoses is asked for, this is twofold. In the first place, these rocks are similar in structure to more modern beds which have been partially metamorphosed, and in which the transition from the unaltered to the altered state can be observed. Secondly, there are limited areas in the Laurentian itself, in which the metamorphism has been so imperfect as to permit traces of the original character of the rocks to remain. It seems also quite certain, and this is a most important point for our sketch, that the Laurentian ocean was not universal, but that there were already elevated portions of the crust capable of yielding sediment to the sea.

In North America these Laurentian rocks attain to an enormous thickness. This has been estimated by Sir W. E. Logan at 30,000 feet, so that the beds would, if piled on each other horizontally, be as high as the highest mountains on earth. They appear to consist of two great series, the Lower and Upper Laurentian. Even if we suppose that in the earlier stages of the world’s history erosion and deposition were somewhat more rapid than at present, the formation of such deposits, probably more widely spread than any that succeeded them, must have required an enormous length of time.

Geologists long looked in vain for evidences of life in the Laurentian period; but just as astronomers' have suspected the existence of unknown planets from the perturbations due to their attraction, geologists have guessed that there must have been some living things on earth even at this early time. Dana and Sterry Hunt especially have committed themselves to such speculations. The reasons for this belief may be stated thus: (1.) In later formations limestone is usually an organic rock, produced by the accumulation of shells, corals, and similar calcareous organisms in the sea, and there are enormous limestones in the Laurentian, constituting regular beds. (2.) In later formations coaly matter is an organic substance, derived from vegetables, and there are large quantities of Laurentian carbon in the form of graphite. (3.) In later formations deposits of iron ores are almost always connected with the deoxidising influence of organic matters as an efficient cause of their accumulation, and the Laurentian contains immense deposits of iron ore, occurring in layers in the manner of later deposits of these minerals. (4.) The limestone, carbon, and iron of the Laurentian exist in association with the other beds in the same manner as in the later formations in which they are known to be organic.

Fig. 7.—Eozoon Canadense. Dawson.

The oldest known animal. Portion of skeleton, two-thirds natural size,
(a) Tabulated cell-wall, magnified, (b) Portion of canal system, magnified.

In addition to this inferential evidence, however, one well-marked animal fossil has at length been found in the Laurentian of Canada, Eozoon Canadense, (fig. 7), a gigantic representative of one of the lowest forms of animal life, which the writer had the honour of naming and describing in 1865—its name of “Dawn-animal” having reference to its great antiquity and possible connection with the dawn of life on our planet. In the modern seas, among the multitude of low forms of life with which they swarm, occur some in which the animal matter is a mere jelly, almost without distinct parts or organs, yet unquestionably endowed with life of an animal character. Some of these creatures, the Foraminifera, have the power of secreting at the surface of their bodies a calcareous shell, often divided into numerous chambers, communicating with each other, and with the water without, by pores or orifices through which, the animal can extend soft and delicate prolongations of its gelatinous body, which, when stretched out into the water, serve for arms and legs. In modern times these creatures, though extremely abundant in the ocean, are usually small, often microscopic; but in a fossil state there are others of somewhat larger size, though few equalling the Eozoon, which seems to been a sessile creature, resting on the bottom of the sea, and covering its gelatinous body with a thin crust of carbonate of lime or limestone, adding to this, as it grew in size, crust after crust, attached to each other by numerous partitions, and perforated with pores for the emission of gelatinous filaments. This continued growth of gelatinous animal matter and carbonate of lime went on from age to age, accumulating great beds of limestone, in some of which the entire form and most minute structures of the creature are preserved, while in other cases the organisms have been broken up, and the limestones are a mere congeries of their fragments. It is a remarkable instance of the permanence of fossils, that in these ancient organisms the minutest pores through which the semi-fluid matter of these humble animals passed, have been preserved in the most delicate perfection. The existence of such creatures supposes that of other organisms, probably microscopic plants, on which they could feed. No traces of these have been observed, though the great quantity of carbon in the beds probably implies the existence of larger sea-weeds. No other form of animal has yet been distinctly recognized in the Laurentian limestones, but there are fragments of calcareous matter which may have belonged to organisms distinct from Eozoon. Of life on the Laurentian land we know nothing, unless the great beds of iron ore already referred to may be taken as a proof of land vegetation.[C]

[C] It is proper to state here that some geologists and naturalists still doubt the organic nature of Eozoon. Their objections however, so far as stated publicly, have been shown to depend on misapprehension as to the structures observed and their state of preservation; and specimens recently found in comparatively unaltered rocks have indicated the true character of those more altered by metamorphism.

To an observer in the Laurentian period, the earth would have presented an almost boundless ocean, its waters, perhaps, still warmed with the internal heat, and sending up copious exhalations to be condensed in thick clouds and precipitated in rain. Here and there might be seen chains of rocky islands, many of them volcanic, or ranges of bleak hills, perhaps clothed with vegetation the forms of which are unknown to us. In the bottom of the sea, while sand and mud and gravel were being deposited in successive layers in some portions of the ocean floor, in others great reefs of Eozoon were growing up in the manner of reefs of coral. If we can imagine the modern Pacific, with its volcanic islands and reefs of coral, to be deprived of all other forms of life, we should have a somewhat accurate picture of the Eozoic time as it appears to us now. I say as it appears to us now; for we do not know what new discoveries remain to be made. More especially the immense deposits of carbon and iron in the Laurentian would seem to bespeak a profusion of plant life in the sea or on the land, or both, second to that of no other period that succeeded, except that of the great coal formation. Perhaps no remnant of this primitive vegetation exists retaining its form or structure; but we may hope for better things, and cherish the expectation that some fortunate discovery may still reveal to us the forms of the vegetation of the Laurentian time.

It is remarkable that the humbly organized living things which built up the Laurentian limestones have continued to exist unchanged, save in dimensions, up to modern times; and here and there throughout the geological series we find beds of Foraminiferous limestone, similar, except in the species of Foraminifera composing them, to that of the Laurentian. It is true that other kinds of creatures, the coral animals more particularly, have been introduced, and have proved equally efficient builders of limestones; but in the deeper parts of the sea the Foraminifera continue to assert their pre-eminence in this respect, and the dredge reveals in the depths of our modern oceans beds of calcareous matter which may be regarded as identical in origin with the limestones formed in the period which is to us the dawn of organic life.

Many inquiries suggest themselves to the zoologist in connection with the life of the Laurentian period. Was Eozoon the first creature in which the wondrous forces of animal life were manifested, when, in obedience to the Divine fiat, the waters first “swarmed with swarmers,” as the terse and expressive language of the Mosaic record phrases it? If so, in contemplating this organism we are in the presence of one of the greatest of natural wonders—brought nearer than in any other case to the actual workshop of the Almighty Maker. Still we cannot affirm that other creatures even more humble may not have preceded Eozoon, since such humble organisms are known in the present world. Attempts have often been made, and very recently have been renewed with much affirmation of success, to prove that such low forms of life may originate spontaneously from their materials in the waters; but so far these attempts merely prove that the invisible germs of the lower animals and plants exist everywhere, and that they have marvellous powers of resisting extreme heat and other injurious influences. We need not, therefore, be surprised if even lower forms than Eozoon may have preceded that creature, or if some of these may be found, like the organisms said to live in modern boiling springs, to have had the power of existing even at a time when the ocean may have been almost in a state of ebullition. Another problem is that of means of subsistence for the Eozoic Foraminifera. A similar problem exists in the case of the modern ocean, in whose depths live multitudes of creatures, where, so far as we know, vegetable matter, ordinarily the basis of life, cannot exist in a living condition. It is probable, however, from the researches of Dr. Wyville Thompson, that this is to be accounted for by the abundance of life at the surface and in the shallower parts of the sea, and by the consequent diffusion through the water of organic matter in an extremely tenuous state, but yet sufficient to nourish these creatures. The same may have been the case in the Eozoic sea, where, judging from the vast amount of residual carbon, there must have been abundance of organic matter, either growing at the bottom, or falling upon it from the surface; and as the Eozoon limestones are usually free from such material, we may assume that the animal life in them was sufficient to consume the vegetable pabulum. On the other hand, as detached specimens of Eozoon occur in graphitic limestones, we suppose that in some cases the vegetable matter was in excess of the animal, and this may have been either because of its too great exuberance, or because the water was locally too shallow to permit Eozoon and similar creatures to nourish. These details we must for the present fill up conjecturally; bu the progress of discovery may give us further light as to the precise conditions of the beginning of life in the “great and wide sea wherein are moving things innumerable” and which is as much a wonder now as in the days of the author of the “Hymn of Creation”[D] in regard to the life that swarms in all its breadth and depth, the vast variety of that life, and its low and simple types, of which we can affirm little else than that they move.

[D] Psalm civ.

The enormous accumulations of sediment on the still thin crust of the earth in the Laurentian period—accumulations probably arranged in lines parallel to the directions of disturbance already indicated—weighed down the surface, and caused great masses of the sediment to come within the influence of the heated interior nucleus. Thus, extensive metamorphism took place, and at length the tension becoming too great to be any longer maintained, a second great collapse occurred, crumpling and disturbing the crust, and throwing up vast masses of the Laurentian itself, probably into lofty mountains—many of which still remain of considerable height, though they have been subjected to erosion throughout all the extent of subsequent geological time.

The Eozoic age, whose history we have thus shortly sketched, is fertile in material of thought for the geologist and the naturalist. Until the labours of Murchison, Sedgwick, Hall, and Barrande had developed the vast thickness and organic richness of the Silurian and Cambrian rocks, no geologist had any idea of the extent to which life had reached backward in time. But when this new and primitive world of Siluria was unveiled, men felt assured that they had now at last reached to the beginnings of life. The argument on this side of the Question was thus put by one of the most thoughtful of English geologists, Professor Phillips: "It is ascertained that in passing downwards through the lower Palæozoic strata, the forms of life grow fewer and fewer, until in the lowest Cambrian rocks they vanish entirely. In the thick series of these strata in the Longmynd, hardly any traces of life occur, yet these strata are of such a kind as might be expected to yield them.... The materials are fine-grained or arenaceous, with or without mica, in laminae or beds quite distinct, and of various thicknesses, by no means unlikely to retain impressions of a delicate nature, such as those left by graptolites, or mollusks, or annulose crawlers. Indeed, one or two such traces are supposed to have been recognised, so that the almost total absence of the traces of life in this enormous series is best understood by the supposition that in these parts of the sea little or no life existed. But the same remark of the excessive rarity of life in the lower deposits is made in North America, in Norway, and in Bohemia, countries well searched for this very purpose, so that all our observations lead to the conviction that the lowest of all the strata are quite deficient of organic remains. The absence is general—it appears due to a general cause. Is it not probable that during these very early periods the ocean and its sediments were nearly devoid of plants and animals, and in the earliest time of all, which is represented by sediments, quite deprived of such?" These words were written ten years ago, and about the same time were published in America those anticipations of the probability of life in the Laurentian already referred to, and Lyell was protesting against the name Primordial, on the ground that it implied that we had reached the beginning of life, when this was not proved. Yet there were elements of truth in both views. It is true now, as then, that the Primordial seems to be a morning hour of life, having, as we shall see in our next paper, unmistakable signs about it of that approach to the beginning to which Phillips refers. It is also true that it is not so early a morning hour as one who has not risen with the dawn might suppose, since with its apparently small beginnings of life it is almost as far removed from the Eozoon reefs of the early Laurentian on the one hand, as it is from the modern period on the other. The dawn of life seems to have been a very slow and protracted process, and it may have required as long a time between the first appearance of Eozoon and the first of those primordial Trilobites which the next period will introduce to our notice, as between these and the advent of Adam. Perhaps no lesson is more instructive than this as to the length of the working days of the Almighty.

Another lesson lies ready for us in these same facts. Theoretically, plants should have preceded animals; and this also is the assertion of the first chapter of Genesis; but the oldest fossil certainly known to us is an animal. What if there were still earlier plants, whose remains are still to be discovered? For my own part, I can see no reason to despair of the discovery of an Eophytic period preceding the Eozoic; perhaps preceding it through ages of duration to us almost immeasurable, though still within the possible time of the existence of the crust of the earth. It is even possible that in a warm and humid condition of the atmosphere, before it had been caused “to rain upon the earth” and when dense “mists ascended from the earth and watered the whole surface of the ground,”[E] vegetation may have attained to a profusion and grandeur unequalled in the periods whose flora is known to us.

[E] Genesis ii. 5. For a description of this Eophytic period of Genesis, see the Author’s “Archaia,” pp. 160 et seq.

But while Eozoon thus preaches of progress and of development, it has a tale to tell of unity and sameness Just as Eozoon lived in the Laurentian sea, and was preserved for us by the infiltration of its canals with siliceous mineral matters, so its successors and representatives have gone on through all the ages accumulating limestone in the sea bottom. To-day they are as active as they were then, and are being fossilised in the same way. The English chalk and the chalky modern mud of the Atlantic sea-bed, are precisely similar in origin to the Eozoic limestones. There is also a strange parallelism in the fact that in the modern seas Foraminifera can live under conditions of deprivation of light and vital air, and of enormous pressure, under which few organisms of greater complexity could exist, and that in like manner Eozoon could live in seas which were perhaps as yet unfit for most other forms of life.

It has been attempted to press the Eozoic Foraminifers into the service of those theories of evolution which would deduce the animals of one geological period by descent with modification from those of another; but it must be confessed that Eozoon proves somewhat intractable in this connection. In the first place, the creature is the grandest of his class, both in form and structure; and if, on the hypothesis of derivation, it has required the whole lapse of geological time to disintegrate Eozoon into Orbulina, Globigerina, and other comparatively simple Foraminifers of the modern seas, it may have taken as long, probably much longer, to develop Eozoon from such simple forms in antecedent periods. Time fails for such a process. Again, the deep sea has been the abode of Foraminifers from the first. In this deep sea they have continued to live without improvement, and with little material change. How little likely is it that in less congenial abodes they could have improved into higher grades of being; especially since we know that the result in actual fact of any such struggle for existence is merely the production of depauperated Foraminifers? Further, there is no link of connection known to us between Eozoon and any of the animals of the succeeding Primordial, which are nearly all essentially new types, vastly more different from Eozoon than it is from many modern creatures. Any such connection is altogether imaginary and unsupported by proof. The laws of creation actually illustrated by this primeval animal are only these: First, that there has been a progress in creation from few, low, and generalised types of life to more numerous, higher, and more specialised types; and secondly, that every type, low or high, was introduced at first in its best and highest form, and was, as a type, subject to degeneracy, and to partial or total replacement by higher types subsequently introduced. I do not mean that we could learn all this from Eozoon alone; but that, rightly considered, it illustrates these laws, which we gather from the subsequent progress of the creative work. As to the mystery of the origin of living beings from dead matter, or any changes which they may have undergone after their creation, it is absolutely silent.

CHAPTER III.

THE PRIMORDIAL, OR CAMBRIAN AGE.

Between the time when Eozoon Canadense flourished in the seas of the Laurentian period, and the age which we have been in the habit of calling Primordial, or Cambrian, a great gap evidently exists in our knowledge of the succession of life on both of the continents, representing a vast lapse of time, in which the beds of the Upper Laurentian were deposited, and in which the Laurentian sediments were altered, contorted, and upheaved, before another immense series of beds, the Huronian, or Lower Cambrian, was formed in the bottom of the sea. Eozoon and its companions occur in the Lower Laurentian. The Upper Laurentian has afforded no evidence of life; and even those conditions from which we could infer life are absent. The Lowest Cambrian, as we shall see, presents only a few traces of living beings. Still, the physical history of this interval must have been most important. The wide level bottom of the Laurentian sea was broken up and thrown into those bold ridges which were to constitute the nuclei of the existing continents. Along the borders of these new-made lands intense volcanic eruptions broke forth, producing great quantities of lava and scoriæ and huge beds of conglomerate and volcanic ash, which are characteristic features of the older Cambrian in both hemispheres. Such conditions, undoubtedly not favourable to life, seem to have prevailed, and extended their influence very widely, so that the sediments of this period are among the most barren in fossils of any in the crust of the earth. If any quiet undisturbed spots existed in which the Lower Laurentian life could be continued and extended in preparation for the next period, we have yet discovered few of them. The experience of other geological periods would, however, entitle us to look for such oases in the Lower Cambrian desert, and to expect to find there some connecting links between the life of the Eozoic and the very dissimilar fauna of the Primordial.

The western hemisphere, where the Laurentian is so well represented, is especially unproductive in fossils of the immediately succeeding period. The only known exception is the occurrence of Eozoon and of apparent casts of worm-burrows in rocks at Madoc in Canada, overlying the Laurentian, and believed to be of Huronian age, and certain obscure fossils of uncertain affinities, recently detected by Mr. Billings, in rocks supposed to be of this age, in Newfoundland. Here, however, the European series comes in to give us some small help. Gümbel has described in Bavaria a great series of gneissic rocks corresponding to the Laurentian, or at least to the lower part of it; above these are what he calls the Hercynian mica-slate and primitive clay-slate, in the latter of which he finds a peculiar species of Eozoon, which he names Eozoon Bavaricum. In England also the Longmynd groups of rocks in Shropshire and in Wales appears to be the immediate successor to the Upper Laurentian; and it has afforded some obscure “worm-burrows” or, perhaps, casts of sponges or fucoids, with a small shell of the genus Lingulella, and also fragments of crustaceans (Palæeopyge). The “Fucoid Sandstones” of Sweden, believed to be of similar age, afford traces of marine plants and burrows of worms, while the Harlech beds of Wales have afforded to Mr. Hicks a considerable number of fossil animals, not very dissimilar from those of the Upper Cambrian. If these rocks are really the next in order to the Eozoic, they show a marked advance in life immediately on the commencement of the Primordial period. In Ireland, the curious Oldhamia, noticed below, appears to occur in rocks equally old. As we ascend, however, into the Middle and Upper parts of the Cambrian, the Menevian and Lingula flag-beds of Britain, and their equivalents in Bohemia and Scandinavia, and the Acadian and Potsdam groups of America, we find a rich and increasing abundance of animal remains, constituting the first Primordial fauna of Barrande.

The rocks of the Primordial are principally sandy and argillaceous, forming flags and slates, without thick limestones, and often through great thicknesses, very destitute of organic remains, but presenting some layers, especially in their upward extension, crowded with fossils. These are no longer mere Protozoa, but include representatives of all the great groups of animals which yet exist, except the vertebrates. We shall not attempt any systematic classification of these; but, casting our dredge and tow-net into the Primordial sea, examine what we collect, rather in the order of relative abundance than of classification.

Over great breadths of the sea bottom we find vast numbers of little bivalve shells of the form and size of a finger-nail, fastened by fleshy peduncles imbedded in the sand or mud; and thus anchored, collecting their food by a pair of fringed arms from the minute animals and plants which swarm in the surrounding waters. These are the Lingulæ, from the abundance of which some of the Primordial beds have received in England and Wales the name of Lingula flags. In America, in like manner, in some beds near St. John, New Brunswick, the valves of these shells are so abundant as to constitute at least half of the material of the bed; and alike in Europe and America, Lingula and allied forms are among the most abundant Primordial fossils. The Lingulæ are usually reckoned to belong to the great sub-kingdom of mollusks, which includes all the bivalve and univalve shell-fish, and several other groups of creatures; but an able American naturalist, Mr. Morse, has recently shown that they have many points of resemblance to the worms; and thus, perhaps, constitute one of those curious old-fashioned “comprehensive” types, as they have been called, which present resemblances to groups of creatures, in more modern times quite distinct from each other. He has also found that the modern Lingulæ are very tenacious of life, and capable of suiting themselves to different circumstances, a fact which, perhaps, has some connection with their long persistence in geological time. They are in any case members of the group of lamp-shells, creatures specially numerous and important in the earlier geological ages.

Fig. 8.—LIFE IN THE PRIMORDIAL SEA.

On the bottom are seen, proceeding from left to right, Oldhamia antiqua, Lingulæ, Arenicolæ, Oldhamia radiata, Paradoxides, Histioderma, Agnostus, Oldhamia radiata, Algæ, and Lingulæ. In the water are Hymenocaris, different species of Trilobites, and Pteropods.

The Lingulæ are especially interesting as examples of a type of beings continued almost from the dawn of life until now; for their shells, as they exist in the Primordial, are scarcely distinguishable from those of members of the genus which still live. While other tribes of animals have run through a great number of different forms, these little creatures remain the same. Another interesting point is a most curious chemical relation of the Lingula, with reference to the material of its shell. The shells of mollusks generally, and even of the ordinary lamp-shells, are hardened by common limestone or carbonate of lime: the rarer substance, phosphate of lime, is in general restricted to the formation of the bones of the higher animals. In the case of the latter, this relation depends apparently on the fact that the albuminous substances on which animals are chiefly nourished require for their formation the presence of phosphates in the plant. Hence the animal naturally obtains phosphate of lime or bone-earth with its food, and its system is related to this chemical fact in such wise that phosphate of lime is a most appropriate and suitable material for its teeth and bones. Now, in the case of the lower animals of the sea, their food, not being of the nature of the richer land plants, but consisting mainly of minute algæ and of animals which prey on these, furnishes, not phosphate of lime, but carbonate. An exception to this occurs in the case of certain animals of low grade, sponges, etc., which, feeding on minute plants with siliceous cell-walls, assimilate the flinty matter and form a siliceous skeleton. But this is an exception of downward tendency, in which these animals approach to plants of low grade. The exception in the case of Lingulaa is in the other direction. It gives to these humble creatures the same material for their hard parts which is usually restricted to animals of much higher rank. The purpose of this arrangement, whether in relation to the cause of the deviation from the ordinary rule or its utility to the animal itself, remains unknown. It has, however, been ascertained by Dr. Hunt, who first observed the fact in the case of the Primordial Lingulæ, that their modern successors coincide with them, and differ from their contemporaries among the mollusks in the same particular. This may seem a trifling matter, but it shows in this early period the origination of the difference still existing in the materials of which animals construct their skeletons, and also the wonderful persistence of the Lingulæ, through all the geological ages, in the material of their shells. This is the more remarkable, in connection with our own very slender acquaintance with the phenomenon, in relation either to its efficient or final causes.

Before leaving the Lingulæ, I may mention that Mr. Morse informs me that living specimens, when detached from their moorings, can creep like worms, leaving long furrows on the sand, and that they can also construct sand-tubes wherein to shelter themselves. This shows that some of the abundant “worm burrows” of the Primordial may have been the work of these curious little shell-fishes, as well as, perhaps, some of the markings which have been described under the name of Eophyton, and have been supposed, I think incorrectly, to be remains of land plants.

In addition to Lingula we may obtain, though rarely, lamp-shells of another type, that of the Orthids, These have the valves hinged along a straight line, in the middle of which is a notch for the peduncle, and the valves are often marked with ribs or striae. The Orthids were content with limestone for their shells, and apparently lived in the same circumstances with the Lingulæ; and in the period succeeding the Primordial they became far more abundant. Yet they perished at an early stage of the world’s progress, and have no representatives in the modern seas.

In many parts of the Primordial ocean the muddy bottom swarmed with crustaceans, relatives of our shrimps and lobsters, but of a form which differs so much from these modern shell-fishes that the question of their affinities has long been an unsettled onfi with zoologists. Hundreds of species are known, some almost microscopic in size, others a foot in length. All are provided with a broad flat horseshoe-shaped head-plate, which, judging from its form and a comparison with the modern king-crabs or horseshoe-crabs, must have been intended as a sort of mud-plough to enable them to excavate burrows or hide themselves in the slimy ooze of the ocean bed. On the sides of this buckler are placed the prominent eyes, furnished with many separate lenses, on precisely the same plan with those of modern crustaceans and insects, and testifying, as Buckland long ago pointed out, to the identity of the action of light in the ancient and the modern seas. The body was composed of numerous segments, each divided transversely into three lobes, whence they have received the name of Trilobites, and the whole articulated, so that the creature could roll itself into a ball, like the modern slaters or wood-lice, which are not very distant relatives of these old crustaceans.[F] The limbs of Trilobites were long unknown, and it was even doubted whether they had any; but recent discoveries have shown that they had a series of flat limbs useful both for swimming and creeping. The Trilobites, under many specific and generic forms, range from the Primordial to the Carboniferous rocks, but are altogether wanting in the more recent formations and in the modern seas. The Trilobites lived on muddy bottoms, and their remains are extremely abundant in shaly and slaty beds, though found also in limestone and sandstone. In the latter they have left most curious traces of their presence in the trails which they have produced. Some of the most ancient sandstones have their surfaces covered with rows of punctured impressions (Protichnites, first footprints), others have strange series of transverse grooves with longitudinal ones at the side (Climactichnites, ladder footprints); others are oval burrows, marked with transverse lines and a ridge along the middle (Rusichnites, wrinkle footprints). All of these so nearly resemble the trails and tracks of modern king-crabs that there can be little doubt as to their origin. Many curious striated grooves and bifid marks, found on the surfaces of Primordial beds, and which have been described as plants, are probably only the marks of the oral organs or feet of these and similar creatures, which passed their lives in grubbing for food in the soft, slimy ooze, though they could, no doubt, like the modern king-crabs, swim when necessary. Some still more shrimp-like creatures, Hymenocaris, which are found with them, certainly had this power.

[F] Woodward has recently suggested affinities of Trilobites with the Isopods or equal-footed crustaceans, on the evidence of a remarkable specimen with remains of feet described by Billings.

A lower type of annulose or ringed animal than that of the Trilobites, is that of the worms. These creatures cannot be preserved in a fossil state, except in the case of those which inhabit calcareous tubes: but the marks which their jointed bodies and numerous side-bristles leave on the sand and mud may, when buried under succeeding sediments, remain; and extensive surfaces of very old rocks are marked in this way, either with cylindrical burrows or curious trails with side scratches looking like pinnate leaves. These constitute the genus Crusiana, while others of more ordinary form belong to the genus Arenicolites, so named from the common Arenicola, or lobworm, whose burrows they are supposed to resemble. Markings referable to seaweed also occur in the Primordial rocks, and also some grotesque and almost inexplicable organisms known as Oldhamia, which have been chiefly found in the Primordial of Ireland. One of the most common forms consists of a series of apparently jointed threads disposed in fan-like clusters on a central stem (Oldhamia antiqua). Another has a wider and simpler fan-like arrangement of filaments. These have been claimed by botanists as algæ, and have been regarded by zoologists as minute Zoophytes, while some more sceptical have supposed that they may be mere inorganic wrinklings of the beds. This last view does not, however, seem tenable. They are, perhaps, the predecessors of the curious Graptolites, which we shall have to represent in the Silurian.

Singularly enough, Foraminifera, the characteristic fossils of the Laurentian, have been little recognised in the Primordial, nor are there any limestones known so massive as those of the former series. There are, however, a number of remarkable organisms, which have usually been described as sponges, but are more probably partly of the nature of sponges and partly of that of Foraminifera. Of this kind are some of the singular conical fossils described by Billings as Archæocyathus, and found in the Primordial limestone of Labrador. They are hollow within, with radiating porss and plates, calcareous in some, and in others with siliceous spicules like those of modern sponges. Some of them are several inches in diameter, and they must have grown rooted in muddy bottoms, in the manner of some of the deep-sea sponges of modern times. One species at least of these creatures was a true Foraminifer, allied, though somewhat distantly, to Eozoon. In some parts of the Primordial sandstones, curious funnel-shaped casts in sand occur, sometimes marked with spiral lines. The name Histioderma has been given to some of these, and they have been regarded as mouths of worm-burrows. Others of larger size have been compared to inverted stumps of trees. If they were produced by worms, some of these must have been of gigantic size, but Billings has recently suggested that they may be casts of sponges that lived like some modern species imbedded in the sand. In accordance with this view I have represented these curious objects in the engraving, On the whole, the life of these oldest Palæozoic rocks is not very abundant; but there are probably representatives of three of the great subdivisions of animals or, as some would reckon them, of four the Protozoa, the Radiata (Cœlenterata), the Mollusca, and the Annulosa. And it is most interesting thus to find in these very old rocks the modern subdivisions of animals already represented, and these by types some of them nearly allied to existing inhabitants of the seas I have endeavoured in the engraving to represent some of the leading forms of marine life in this ancient period.

Perhaps one of the most interesting discoveries in these rocks is that of rain-marks and shrinkage-cracks, in some of the very oldest beds—those of the Longmynd in Shropshire. On the modern muddy beach any ordinary observer is familiar with the cracks produced by the action of the sun and air on the dried surfaces left by the tides. Such cracks, covered by the waters of a succeeding tide, may be buried in newer silt, and once preserved in this way are imperishable. In like manner, the pits left by passing showers of rain on the mud recently left bare by the tide may, when the mud has dried, become sufficiently firm to be preserved. In this way we have rain-marks of various geological ages; but the oldest known are those of the Longmynd, where they are associated both with ripple-marks and shrinkage-cracks. We thus have evidence of the action of tides, of sun, and of rain, in these ancient periods just as in the present day. Were there no land animals to prowl along the low tidal flats in search of food? Were there no herbs or trees to drink in the rains and flourish in the sunshine? If there were, no bone or footprint on the shore, or drifted leaf or branch, has yet revealed their existence to the eyes of geologists The beds of the Primordial age exist in England, in Bohemia, in Sweden and Norway, and also in North America. They appear to have been deposited along the shores of the old Laurentian continent, and probably some of them indicate very deep water. The Primordial rocks are in many parts of the world altered and hardened. They have often assumed a slaty structure, and their bedding, and the fossils which they contain, are both affected by this. The usual view entertained as to what is called slaty structure is, that it depends on pressure, acting on more or less compressible material in some direction usually different from that of the bedding. Such pressure has the effect of arranging all the flat particles as scales of mica, etc. in planes parallel to the compressing surface. Hence, if much material of this kind is present in the sediment, the whole rock assumes a fissile character causing it to split readily into thin plates. That such yielding to pressure has actually taken place is seen very distinctly in microscopic sections of some slaty rocks, which often show not only a laminated structure, but an actual crumpling on a small scale, causing them to assume almost the aspect of woody fibre. Such rocks often remind a casual observer of decaying trunks of trees, and sections of them under the microscope show the most minute and delicate crumpling. It is also proved by the condition of the fossils the beds contain. These are often distorted, so that some of them are lengthened and others shortened, and if specimens were selected with, that view, it would be quite easy to suppose that those lengthened by distortion are of different species from those distorted so as to be shortened. Slaty cleavage and distortion are not, however, confined to Primordial rocks, but occur in altered sediments of various ages.

The Primordial sediments must have at one time been very widely distributed, and must have filled up many of the inequalities produced by the rending and contortion of the Laurentian beds. Their thicker and more massive portions are, however, necessarily along the borders of the Laurentian continents, and as they in their turn were raised up into land, they became exposed to the denuding action first of the sea, and afterwards of the rain and rivers, and were so extensively wasted away that only in a few regions do large areas of them remain visible. That of Bohemia has afforded to Barrande a great number of most interesting fossils. The rocks of St. David’s in Wales, those of Shropshire in England, and those of Wicklow in Ireland are also of great interest; and next to these in importance are, perhaps, the Huronian and Acadian groups of North America, in which continent—as for example in Nova Scotia and in some parts of New England—there are extensive areas of old metamorphic rocks whose age has not been determined by fossils, but which may belong to this period.

The question of division lines of formations is one much agitated in the case of the Cambrian rocks. Whether certain beds are to be called Cambrian or Silurian has been a point greatly controverted; and the terms Primordial and Primordial Silurian have been used as means to avoid the raising of this difficulty. Many of our division lines in geology are arbitrary and conventional, and this may be the case with that between the Primordial and Silurian, the one age graduating into the other. There appears to be, however, the best reason to recognise a distinct Cambrian period, preceding the two great periods, those of the second and third faunas of Barrande, to which the term Silurian is usually applied. On the other hand, in so far as our knowledge extends at present, a strongly marked line of separation exists between the Laurentian and Primordial, the latter resting on the edges of the former, which seems then to have been as much altered as now. Still a break of this kind may be, perhaps must be, merely local; and may vary in amount. Thus, in some places we find rocks of Silurian and later ages resting directly on the Laurentian, without the intervention of the Primordial. In any case, where a line of coast is steadily sinking, each succeeding deposit will overlap that which went before; and this seems to have been the case with the Laurentian shore when the Primordial and Silurian were being deposited. Hence over large spaces the Primordial is absent, being probably buried up, except where exposed by denudation at the margin of the two formations.

This occurs in several parts of Canada, while the Laurentian rocks have evidently been subjected to metamorphism and long-continued weathering before the Lower Silurian were deposited; and in some cases the latter rest on weather-worn and pitted surfaces, and are filled with angular bits of the underlying rock, as well as with drift-shells which have been cast on these old Laurentian shores; while in other cases the Silurian rests on smooth water-worn Laurentian rocks, and is filled at the junction with well-rounded pebbles and grains of sand which have evidently been subjected to a more thorough attrition than those of the present beach. With respect to the line of division between the Primordial and the next succeeding rocks, it will be seen that important movements of the continents occurred at the close of the Cambrian, and in some places the Cambrian rocks have been much disturbed before the deposition of the Lower Silurian.

Seated on some ancient promontory of the Laurentian, and looking over the plain which, in the Primordial and Lower Silurian periods was the sea, I have often wished for some shred of vegetable matter to tell what lived on that land when the Primordial surf beat upon its shore, and washed up the Trilobites and Brachiopods of those old seas; but no rock has yet taken up its parable to reveal the secret, and the Primordial is vocal only with the old story: “And God said, Let the waters swarm with swarming living things, and it was so.” So our picture of the period may represent a sea-bottom swarming with animals of low grade, some sessile, some locomotive; and we may merely suppose a distant shore with vegetation dimly seen, and active volcanoes; but a shore on which no foot of naturalist has yet trod to scan its productions. Very different estimates have been formed of the amount of life in this period, according to the position given to its latest limit. Taking some of the more modern views of this subject, we might have included among the Primordial animals many additional creatures, which we prefer noticing in the Silurian, since it may at least be affirmed that their head-quarters were in that age, even if they had a beginning in the Primordial. It may be interesting here, however, to note the actual amount of life known to us in this period, taken in its largest scope. In doing this, I shall take advantage of an interesting table given by Dr. Bigsby,[G] and representing the state of knowledge in 1868, and shall group the species in such a manner as to indicate the relative abundance of distinct types of structure. We find then—

[G] “Thesaurus Siluricus.”

Now in this enumeration we observe, in the first place, a representation of all the lower or invertebrate groups of the waters. We have next the remarkable fact that the Radiata of Cuvier, the lowest and most plant-like of the marine animals, are comparatively slenderly represented, yet that there are examples of their higher as well as of their lower forms. We have the further fact that the crustaceans, the highest marine animals of the annulose type, are predominant in the waters; and that in the mollusks the highest and lowest groups are most plentiful, the middle less so. The whole number of species is small, and this may arise either from our having here reached an early period in the history of life, or from our information being defective. Both are probably true. Still, of the animals known, we cannot say that the proportions of the different kinds depend on defective knowledge. There is no reason, for example, why corals should not have been preserved as well as Trilobites, or why Brachiopods should have been presurved rather than ordinary bivalves. The proportions, therefore, it may be more safe to reason from than the aggregate. In looking at these proportions, and comparing them with those of modern seas, we are struck with the great number of species representing some types either now extinct or comparatively rare: the Trilobites and Brachiopods more particularly. We are astonished at the enormous preponderance of these two groups, and especially of the Trilobites. Further, we observe that while some forms, like Lingula and Nautilus, have persisted down to modern times, others, like the Trilobites and Orthids, perished very early. In all this we can dimly perceive a fitness of living things to physical conditions, a tendency to utilise each type to the limit of its capacities for modification, and then to abandon it for something higher; a tendency of low types to appear first, but to appear in their highest perfection and variety; a sudden apparition of totally diverse plans of structure subserving similar ends simultaneously with each other, as for instance those of the Mollusk and the Crustacean; the appearance of optical and mechanical contrivances, as for example the compound eyes of the Trilobite and the swimming float of the Orthoceras, in all their perfection at first, just as they continue to this day in creatures of similar grade. That these and other similar things point to a uniform and far-reaching plan, no rational mind can doubt; and if the world had stopped short in the Primordial period, and attained to no further development, this would have been abundantly apparent; though it shines forth more and more conspicuously in each succeeding page of the stony record. How far such unity and diversity can be explained by the modern philosophy of a necessary and material evolution out of mere death and physical forces, and how far it requires the intervention of a Creative mind, are questions which we may well leave with the thoughtful reader, till we have traced this history somewhat further.

CHAPTER IV.

THE LOWER AND UPPER SILURIAN AGES.

By English geologists, the great series of formations which succeeds to the Cambrian is usually included under the name Silurian System, first proposed by Sir Roderick Murchison. It certainly, however, consists of two distinct groups, holding the second and third faunas of Barrande. The older of the two, usually called the Lower Silurian, is the Upper Cambrian of Sedgwick, and may properly be called the Siluro-Cambrian. The newer is the true Silurian, or Silurian proper—the Upper Silurian of Murchison. We shall in this chapter, for convenience, consider both in connection, using occasionally the term Lower Silurian as equivalent to Siluro-Cambrian. The Silurian presents us with a definite physical geography, for the northern hemisphere at least; and this physical geography is a key to the life conditions of the time. The North American continent, from its great unbroken area, affords, as usual, the best means of appreciating this. In this period the northern currents, acting perhaps in harmony with old Laurentian outcrops, had deposited in the sea two long submarine ridges, running to the southward from the extreme ends of the Laurentian nucleus, and constituting the foundations of the present ridges of the Roeky Mountains and the Alleghanies. Between these the extensive triangular area now constituting the greater part of North America, was a shallow oceanic plateau, sheltered from the cold polar currents by the Laurentian land on the north, and separated by the ridges already mentioned from the Atlantic and Pacific. It was on this great plateau of warm and sheltered ocean that what we call the Silurian fauna lived; while of the creatures that inhabited the depths of the great bounding oceans, whose abysses must have been far deeper and at a much lower temperature, we know little. During the long Silurian periods, it is true, the great American plateau underwent many revolutions, sometimes being more deeply submerged, and having clear water tenanted by vast numbers of corals and shell-fishes, at others rising so as to become shallow and to receive deposits of sand and mud; but it was always distinct from the oceanic area without. In Europe, in like manner, there seems to have been a great internal plateau bounded by the embryo hills of Western Europe on the west, and harbouring a very similar assemblage of creatures to those existing in America.

Further, during these long periods there were great changes, from a fauna of somewhat primordial type up to a new order of things in the Upper Silurian, tending toward the novelties which were introduced in the succeeding Devonian and Carboniferous. We may, in the first place, sketch these changes as they occurred on the two great continental plateaus, noting as we proceed sucli hints as can be obtained with reference to the more extensive oceanic spaces.

Before the beginning of the age, both plateaus seem to have been invaded by sandy and muddy sediments charged at some periods and places with magnesian limestone; and these circumstances were not favourable to the existence or preservation of organic remains. Such are the Potsdam and Calciferous beds of America and the Tremadoc and Llandeilo beds of England. The Potsdam and Tremadoc are by their fossils included in the Cambrian, and may at least be regarded as transition groups. It is further to be observed, in the case of these beds, that if we begin at the west side of Europe and proceed easterly, or at the east side of America and proceed westerly, they become progressively thinner, the greater amount of material being deposited at the edges of the future continents; just as on the sides of a muddy tideway the flats are higher, and the more coarse sediment deposited near the margin of the channel, and fine mud is deposited at a greater distance and in thinner beds. The cause, however, on the great scale of the Atlantic, was somewhat different, ancient ridges determining the border of the channel. This statement holds good not only of these older beds, but of the whole of the Silurian, and of the succeeding Devonian and Carboniferous, all deposited on these same plateaus. Thus, in the case of the Silurian in England and Wales, the whole series is more than 20,000 feet thick, but in Russia, it is less than 1,000 feet. In the eastern part of America the thickness is estimated at quite as great an amount as in Europe, while in the region of the Mississippi the Silurian rocks are scarcely thicker than in Russia, and consist in great part of limestones and fine sediments, the sandstones and conglomerates thinning out rapidly eastward of the Appalachian Mountains.

In both plateaus the earlier period of coarse accumulations was succeeded by one in which was clear water depositing little earthy sediment, and this usually fine; and in which the sea swarmed with animal life, from the débris of which enormous beds of limestone were formed the Trenton limestone of America and the Bala limestone of Europe. The fossils of this part of the series open up to us the head-quarters of Lower Silurian life, the second great fauna of Barrande, that of the Upper Cambrian of Sedgwick; and in America more especially, the Trenton and its associated limestones can be traced over forty degrees of longitude; and throughout the whole of this space its principal beds are composed entirely of comminuted corals, shells, and crinoids, and studded with organisms of the same kinds still retaining their forms. Out of these seas, in the European area, arose in places volcanic islets, like those of the modern Pacific.

In the next succeeding era the clear waters became again invaded with muddy and sandy sediments, in various alternations, and with occasional bands of limestone, constituting the Caradoc beds of Britain and the Utica and Hudson River groups of America. During the deposition of these, the abounding life of the Siluro-Cambrian plateaus died away, and a middle group of sandstones and shales, the Oneida and Medina of America and the Mayhill of England, form the base of the Upper Silurian.

But what was taking place meanwhile in the oceanic areas separating our plateaus? These were identical with the basins of the Atlantic and Pacific, which already existed in this period as depressions of the earth’s crust, perhaps not so deep as at present. As to the deposits in their deeper portions we know nothing; but on the margin of the Atlantic area are some rocks which give us at least a little information.

In the later part of the Cambrian period the enormous thickness of the Quebec group of North America appears to represent a broad stripe of deep water parallel to the eastern edge of the American plateau, and in which an immense thickness of beds of sand and mud was deposited with very few fossils, except in particular beds, and these of a more primordial aspect than those of the plateau itself. These rocks no doubt represent the margin of a deep Atlantic area, over which cold currents destructive of life were constantly passing, and in which great quantities of sand and mud, swept from the icy regions of the North, were continually being laid. The researches of Dr. Carpenter and Dr. Wyville Thomson show us that there are at present cold areas in the deeper parts of the Atlantic, on the European side, as we have long known that they exist at less depths on the American side; and these same researches, with the soundings on the American banks, show that sand and gravel may be deposited not merely on shallows, but in the depths of the ocean, provided that these depths are pervaded by cold and heavy currents capable of eroding the bottom, and of moving coarse material. The Quebec group in Canada and the United States, and the metalliferous Lower Silurian rocks of Nova Scotia and Newfoundland, destitute of great marine limestones and coral reefs, evidently represent deep and cold-water areas on the border of the Atlantic plateau.

At a later period, the beginning of the Upper Silurian, the richly fossiliferous and exceptional deposits of the Island of Anticosti, formed in the deep hollow of the Gulf of St. Laurence, show that when the plateau had become shallowed up by deposition and elevation, and converted into desolate sand-banks, the area of abundant life was transferred to the still deep Atlantic basin and its bordering bays, in which the forms of Lower Silurian life continued to exist until they were mixed up with those of the Upper Silurian.

If we turn now to these latter rocks, and inquire as to their conditions on our two great plateaus, we shall find a repetition of changes similar to those which occurred in the times preceding. The sandy shallows of the earlier part of this period give place to wide oceanic areas similar to those of the Lower Silurian; In these we find vast and thick coral and shell limestones, the Wenlock of England and Niagara of America, as rich in life as the limestones of the Lower Silurian, and with the generic and family forms similar, but the species for the most part different. In America these limestones were followed by a singularly shallow condition of the plateau, in which the surface was so raised as at times to be converted into separate salt lakes in which beds of salt were deposited. On both plateaus there were alternations of oceanic and shallow conditions, under which the Lower Helderberg and Ludlow beds, the closing members of the Silurian, were laid down. Of the Atlantic beds of this period we know little, except that the great limestones appear to be wanting, and to be replaced by sandy and muddy deposits, in some parts at least of the margins of the area. In some portions also of the plateaus and their margins, extensive volcanic outbursts seem to have occurred; so that the American plateau presented, at least in parts, the aspect of a coral sea with archipelagos of volcanic islands, the ejections from which became mixed with the aqueous deposits forming around them.

Having thus traced the interesting series of geographical conditions indicated by the Silurian series, we may next take our station on one of the submerged plateaus, and inquire as to the new forms of life now introduced to our notice; and in doing so shall include the life of both the Lower and Upper Silurian.

Fig. 9.—Fragment of Lower Silurian Limestone, sliced and magnified ten diameters, showing the manner in which it is made up of fragments of corals, crinoids, and shells. (From a paper oil the Microscopic Structure of Canadian limestone, “Canadian Naturalist.”)

First, we may remark the vast abundance and variety of corals. The polyps, close relatives of the common sea-anemone of our coasts, which build up our modern coral reefs, were represented in the Silurian seas by a great number of allied yet different forms, equally effectual in the great work of secreting carbonate of lime in stony masses, and therefore in the building-up of continents. Let us note some of the differences. In the first place, whereas our modern coral-workers can show us but the topmost pinnacles of their creations, peeping above the surface of the sea in coral reefs and islands, the work of the coral animals of the Silurian has been finished, by these limestones being covered with masses of new sediment consolidated into hard rock, and raised out of the sea to constitute a parfc of the dry land. In the Silurian limestones we thus have, not merely the coral reefs, but the wide beds of comminuted coral, mixed with the remains of other animals, which are necessarily accumulated in the ocean bed around the reefs and islands. Further, these beds, which we might find loose and unconsolidated in the modern sea, have their fragments closely cemented together in the old limestones. The nature of this difference can be well seen by comparing a fragment of modern coral or shell limestone from Bermuda, with a similar fragment of the Trenton limestone, both being sliced for examination under the microscope. The old limestone is black or greyish, the modern one is nearly white, because in the former the organic matter in the animal fragments has been carbonised or converted into coaly and bituminous matter. The old limestone is much more dense and compact, partly because its materials have been more closely compressed by superincumbent weight, but chiefly because calcareous matter in solution in water has penetrated all the interstices, and filled them up with a deposit of crystalline limestone. In examining a slice, however, under the microscope, it will be seen that the fragments of corals and other organisms are as distinct and well preserved as in the crumbling modern rock, except that they are perfectly imbedded in a paste of clear transparent limestone, or rather calcareous spar, infiltrated between them. I have examined great numbers of slices of these limestones, ever with new wonder at the packing of the organic fragments which they present. The hard marble-like limestones used for building in the Silurian districts of Europe and America, are thus in most cases consolidated masses of organic fragments.

In the next place, the animals themselves must have differed somewhat from their modern successors. This we gather from the structure of their stony cells, which present points of difference indicating corresponding difference of detail in the soft parts. Zoologists thus separate the rugose or wrinkled corals and the tabulate or floored corals of the Silurian from those of the modern seas. The former must have been more like the ordinary coral animals; the latter were very peculiar, more especially in the close union of the cells, and in the transverse floors which they were in the habit of building across these cells as they grew in height. They presented, however, all the forms of our modern corals. Some were rounded and massive in form, others delicate and branching. Some were solitary or detached, others aggregative in communities. Some had the individual animals large and probably showy, others had them of microscopic size. Perhaps the most remarkable of all is the American Beatricea,[H] which grew like a great trunk of a tree twenty feet or more in height, its solitary animal at the top like a pillar-saint, though no doubt more appropriate and comfortable; and multitudes of delicate and encrusting corals clinging like mosses or lichens to its sides. This creature belongs to the very middle of the Silurian, and must have lived in great depths, undisturbed by swell or breakers, and sheltering vast multitudes of other creatures in its stony colonnades.

[H] First described by Mr. Billings. It has been regarded as a plant, and as a cephalopod shell; but I believe it was a coral allied to Cystiphyllum.

Fig. 10.—LIFE IN THE SILURIAN AGE.

On the bottom are seen, proceeding from left to right, Corals (Stenopora and Beatricea) and a Gasteropod; Orthoceras; Coral (Patria); Crinoids, Lingulæ, and Cystideans; a Trilobite and Cyrtolites. In the water is a large Pterygotus, and under it a Trinucleus. Furthere on, are Cephalopods, a Heteropod, and Fishes. At the surface, Phyllograptus, Graptolithus, and Bellerophon. On the Land, Lepidodendron, Psilophyton, and Prototaxites.

Lastly, the Silurian corals nourished in latitudes more boreal than their modern representatives. In both hemispheres as far north as Silurian limestones have been traced, well-developed corals have been found. On the great plateaus sheltered by Laurentian ridges to the north, and exposed to the sun and to the warmer currents of the equatorial regions, they nourished most grandly and luxuriantly: but they lived also north of the Laurentian bands in the Arctic Sea basins, though probably in the shallower and more sheltered parts. Undoubtedly the geographical arrangements of the Silurian period contributed to this. We have already seen how peculiarly adapted to an exuberant marine life were the submerged continents of the period; and there was probably little Arctic land producing icebergs to chill the seas. The great Arctic currents, which then as now flowed powerfully toward the equator, must have clung to the deeper parts of the ocean basins, while the return waters from the equator would spread themselves widely over the surface; so that wherever the Arctic Seas presented areas a little elevated out of the cold water bottom, there might be suitable abodes for coral animals. It has been supposed that in the Silurian period the sea might have derived some appreciable heat from the crust of the earth below, and astronomical conditions have been suggested as tending to produce changes of climate; but it is evident that whatever weight may be due to these causes, the observed geographical conditions are sufficient to account for the facts of the case. It is also to be observed, that we cannot safely infer the requirements as to temperature of Silurian coral animals from those of the tenants of the modern ocean. In the modern seas many forms of life thrive best and grow to the greatest size in the colder seas; and in the later tertiary period there were elephants and rhinoceroses sufficiently hardy to endure the rigours of an Arctic climate. So there may have been in the Silurian seas corals of much less delicate constitution than those now living.

Next to the corals we may place the crinoids, or stone-lilies—creatures abounding throughout the Silurian seas, and realizing a new creative idea, to be expanded in subsequent geological time into all the multifarious types of star-fishes and sea-urchins. A typical crinoid, such as the Glyptocrinus of the Lower Silurian, consists of a flexible jointed stem, sometimes several feet in length, composed of short cylindrical discs, curiously articulated together, a box-like body on top made up of polygonal pieces attached to each other at the edges, and five radiating jointed arms furnished with branches and branchlets, or fringes, all articulated and capable of being flexed in any direction. Such a creature has more the aspect of a flower than of an animal; yet it is really an animal, and subsists by collecting with its arms and drifting into its mouth minute creatures floating in the water. Another group, less typical, but abundantly represented in the Silurian seas, is that of the Cystideans, in which the body is sack-like, and the arms few and sometimes attached to the body. They resemble the young or larvaa of crinoids. In the modern seas the crinoids are extremely few, though dredging in very deep water has recently added to the number of known species; but in the Silurian period they had their birth, and attained to a number and perfection not afterwards surpassed. Perhaps the stone-lilies of the Upper Silurian rocks of Dudley, in England, are the most beautiful of Palæozoic animals. Judging from the immense quantities of their remains in some limestones, wide areas of the sea bottom must have been crowded with their long stalks and flower-like bodies, presenting vast submarine fields of these stony water-lilies.

Passing over many tribes of mollusks, continued or extended from the Primordial—and merely remarking that the lamp-shells and the ordinary bivalve and univalve shell-fishes are all represented largely, more especially the former group, in the Silurian—we come to the highest of the Mollusca, represented in our seas by the cuttle-fishes and nautili, creatures which, like the crinoids, may be said to have had their birth in the Silurian, and to have there attained to some of their grandest forms. The modern pearly nautilus shell, well known in every museum, is beautifully coiled in a disc-like form, and when sliced longitudinally shows a series of partitions dividing it into chambers, air-tight, and serving as a float to render the body of the creature independent of the force of gravity. As the animal grows it retracts its body toward the front of the shell, and forms new partitions, so that the buoyancy of the float always corresponds with the weight of the animal; while by the expansion and contraction of the body and removal of water from a tube or syphon which traverses the chambers, or the injection of additional water, slight differences can be effected, rendering the creature a very little lighter or heavier than the medium in which it swims. Thus practically delivered from the encumbrance of weight, and furnished with long flexible arms provided with suckers, with great eyes and a horny beak, the nautilus becomes one of the tyrants of the deep, creeping on the bottom or swimming on the surface at will, and everywhere preying on whatever animals it can master. Fortunately for us, as well as for the more feeble inhabitants of the sea, the nautili are not of great size, though some of their allies, the cuttle-fishes, which, however, want the floating apparatus, are sufficiently powerful to be formidable to man. In the Silurian period, however, there were not only nautili like ours, but a peculiar kind of straight nautilus—the Orthoceratites—which sometimes attained to gigantic size. The shells of these creatures may be compared to those of nautili straightened out, the chambers being placed in a direct line in front of each other. A great number of species have been discovered, many quite insignificant in size, but others as much as twelve feet in length and a foot in diameter at the larger end. Indeed, accounts have been given of individuals of much larger growth. These large Orthoceratites were the most powerful marine animals known to us in the Silurian, and must have been in those days the tyrants of the seas.[I]

[I] Zoologists will observe that I have, in the illustrations given the Orthoceras the arms rather of a cuttle-fish than of a nautilus. The form of the outer chamber of the shell, I think, warrants this view of the structure of the animal, which must have been formed on a very comprehensive type.

Among the crustaceans, or soft shell-fishes of the Silurian, we meet with the Trilobites, continued from the Primordial in great and increasing force, and represented by many and beautiful species; while an allied group of shell-fishes of low organization but gigantic size, the Eurypterids, characteristic of the Upper Silurian, were provided with powerful limbs, long flexible bodies, and great eyes in the front of the head, and were sometimes several feet in length. Instead of being mud grovellers, like the Trilobites and modern king-crabs, these Eurypterids must have been swimmers, careering rapidly through the water, and probably active and predaceous. There were also great multitudes of those little crustaceans which are inclosed in two horny or shelly valves like a bivalve shell-fish, and the remains of which sometimes fill certain beds of Silurian shale and limestone.

No remains found in the Silurian rocks have been more fertile sources of discussion than the so-called Graptolites, or written stones—a name given long ago by Linnæus, in allusion to the resemblance of some species having rows of cells on one side, to minute lines of writing. These little bodies usually appear as black coaly stains on the surface of the rock, showing a slender stem or stalk, with a row of little projecting cells at one side, or two rows, one on each side. The more perfect specimens show that, in many of the species at least, these fragments were branches of a complex organism spreading from a centre; and at this centre there is sometimes perceived a sort of membrane connecting the bases of the branches, and for which various uses have been conjectured. The branches themselves vary much in different species. They may be simple or divided, narrow, or broad and leaf-like, with one row of cells, or two rows of cells. Hence arise generic distinctions into single and double graptolites, leaf and tree graptolites, net graptolites, and so on. But while it is easy to recognise these organisms, and to classify them in species and genera, it is not so easy to say what their affinities are with modern things. They are exclusively Silurian, disappearing altogether at the close of this period, and, so far as we know, not succeeded by any similar creatures serving to connect them with modern forms. Hence the most various conjectures as to their nature. They have been supposed to be plants, and have been successively referred to most of the great divisions of the lower animals. Most recently they have been regarded by Hall, Nicholson,[J] and others, who have studied them most attentively, as zoophytes or hydroids allied to the Sertularise, or tooth-corallines and sea-fir-corallines of our coasts, to the cell-bearing branches of which their fragments bear a very close resemblance. In this case, each of the little cells or teeth at the sides of the fibres must have been the abode of a little polyp, stretching out its tentacles into the water, and enjoying a common support and nutrition with the other polyps ranged with it. Still the mode of life of the community of branching stems is uncertain. In some species there is a little radicle or spike at the base of the main stem, which may have been a means of attachment. In others the hollow central disk has been conjectured to have served as a float. Occurring as the specimens do usually in shales and slates, which must have been muddy beds, they could not have been attached to stones or rocks, and they must have lived in clear water, either seated on the surface of the mud, attached to sea-weeds, or floating freely by means of hollow disks filled with air. After much thought on their structure and mode of occurrence, I am inclined to believe that in their younger stages they were attached, but by a very slender thread; that at a more advanced stage they became free, and acquiring a central membranous disk filled with air, floated by means of this at the surface, their long branches trailing in the waters below. They would thus be, with reference to their mode of life, though not to the details of their structure, prototypes of the modern Portuguese man-of-war, which now drifts so gaily over the surface of the warmer seas. I have represented them in this attitude; but in case I should be mistaken, the reader may imagine it possible that they may be adhering to the lower surface of floating tangle. The head-quarters of the Graptolites seem to be in the upper part of the Cambrian, and in the Siluro-Cambrian, and they are widely distributed in Europe, in America, and in Australia. This very wide distribution of the species is probably connected with their floating and oceanic habits.

[J] See also an able paper by Carruthers, in the Geological Magazine, vol. v., p. 64.

Lastly, just as the Silurian period was passing away, we find a new thing in the earth—vertebrate animals, represented by several species of shark-like fishes, which came in here as forerunners of the dynasty of the vertebrates, which from that day to this have been the masters of the world. These earliest vertebrates are especially interesting as the first known examples of a plan of structure which culminates only in man himself. They appear to have had cartilaginous skeletons; and in this and their shagreen-like skin, strong bony spines, and trenchant teeth, to have much resembled our modern sharks, or rather the dog-fishes, for they were of small size. One genus (Pteraspis), apparently the oldest of the whole, belongs, however, to a tribe of mailed fishes allied to some of those of the old red sandstone. In both cases the groups of fishes representing the first known appearance of the vertebrates were allied to tribes of somewhat high organization in that class; and they asserted their claims to dominancy by being predaceous and carnivorous creatures, which must have rendered themselves formidable to their invertebrate contemporaries. Coprolites, or fossil masses of excrement, which are found with them, indicate that they chased and devoured orthoceratites and sea-snails of various kinds, and snapped Lingulæ and crinoids from their stalks; and we can well imagine that these creatures, when once introduced, found themselves in rich pasture and increased accordingly. Space prevents us from following further our pictures of the animal life of the great Silurian era, the monuments of which were first discovered by two of England’s greatest geologists, Murchison and Sedgwick. How imperfect such a notice must be, may be learned from the fact that Dr. Bigsby, in his “Thesaurus Siluricus” in 1868, catalogues 8,897 Silurian species, of which only 972 are known in the Primordial.

Our illustration, carefully studied, may do more to present to the reader the teeming swarms of the Silurian seas than our word-picture, and it includes many animal forms not mentioned above, more especially the curved and nautilus-like cuttle-fishes, those singular molluscous swimmers by fin or float known to zoologists as violet-snails, winged-snails or pteropods, and carinarias; and which, under various forms, have existed from the Silurian to the present time. The old Lingulæ are also there as well as in the Primordial, while the fishes and the land vegetation belong, as far as we yet know, exclusively to the Upper Silurian, and point forward to the succeeding Devonian. We know as yet no Silurian animal that lived on the land or breathed air. But our knowledge of land plants, though very meagre, is important. Without regarding such obscure and uncertain forms as the Eophyton of Sweden, Hooker, Page, and Barrande have noticed, in the Upper Silurian, plants allied to the Lycopods or club-mosses. I have found in the same deposits another group of plants allied to Lycopods and pill-worts (Psilophyton), and fragments of wood representing the curious and primitive type of pine-like trees known as Prototaxites. These are probably only a small instalment of Silurian land plants, such as a voyager might find floating in the sea on his approach to some unknown shore, which had not yet risen above his horizon. Time and careful search will, no doubt, add largely to our knowledge.

In the Silurian, as in the Cambrian, the head-quarters of animal life were in the sea. Perhaps there was no animal life on the land; but here our knowledge may be at fault. It is, however, interesting to observe the continued operation of the creative fiat, “Let the waters swarm with swarmers” which, beginning to be obeyed in the Eozoic age, passes down through all the periods of geological time to the “moving things innumerable” of the modern ocean. Can we infer anything further as to the laws of creation from these Silurian multitudes of living things? One thing we can see plainly, that the life of the Silurian is closely related to that of the Cambrian. The same generic and ordinal forms are continued. Even some species may be identical. Does this indicate direct genetic connection, or only like conditions in the external world correlated with likeness in the organic world? It indicates both. First, it is in the highest degree probable that many of the animals of the Lower Silurian are descendants of those of the Cambrian. Sometimes these descendants may be absolutely unchanged. Sometimes they may appear as distinct varieties. Sometimes they may have been regarded as distinct though allied species. The continuance in this manner of allied forms of life is necessarily related to the continuance of somewhat similar conditions of existence, while changes in type imply changed external conditions. But is this all? I think not; for there are forms of life in the Silurian which cannot be traced to the Cambrian, and which relate to new and even prospective conditions, which the unaided powers of the animals of the earlier period could not have provided for. These new forms require the intervention of a higher power, capable of correlating the physical and organic conditions of one period with those of succeeding periods. Whatever powers may be attributed to natural selection or to any other conceivable cause of merely genetic evolution, surely prophetic gifts cannot be claimed for it; and the life of all these geological periods is full of mute prophecies to be read only in the light of subsequent fulfilments.

The fishes of the Upper Silurian are such a prophecy. They can claim no parentage in the older rocks, and they appear at once as kings of their class. With reference to the Silurian itself, they are of little consequence; and in the midst of its gigantic forms of invertebrate life they seem almost misplaced. But they predict the coming Devonian, and that long and varied reign of vertebrate life which culminates in man himself. No such prophetic ideas are represented by the giant crustaceans and cuttle-fishes and swarming graptolites. They had already attained their maximum, and were destined to a speedy and final grave in the Silurian, or to be perpetuated only in decaying families whose poverty is rendered more conspicuous by the contrast with the better days gone by. The law of creation provided for new types, and at once for the elevation and degradation of them when introduced; and all this with reference to the physical conditions not of the present only but of the future. Such facts, which cannot be ignored save by the wilfully blind, are beyond the reach of any merely material philosophy.

The little that we know of Silurian plants is as eloquent of plan and creation as that which we can learn of animals. I saw not long ago a series of genealogies in geological time reduced to tabular form by that ingenious but imaginative physiologist, Haeckel. In one of these appeared the imaginary derivation of the higher plants from Algæ or sea-weeds. Nothing could more curiously contradict actual facts. Algæ were apparently in the Silurian neither more nor less elevated than in the modern seas, and those forms of vegetable life which may seem to bridge over the space between them and the land plants in the modern period, are wanting in the older geological periods, while land plants seem to start at once into being in the guise of club-mosses, a group by no means of low standing. Our oldest land plants thus represent one of the highest types of that cryptogamous series to which they belong, and moreover are better developed examples of that type than those now existing. We may say, if we please, that all the connecting links have been lost; but this is begging the whole question, since no thing but the existence of such links could render the hypothesis of derivation possible. Further, the occurrence of any number of successive yet distinct species would not be the kind of chain required, or rather would not be a chain at all.

Yet in some respects development is obvious in creation. Old forms of life are often embryonic, or resemble the young of modern animals, but enlarged and exaggerated, as if they had overgrown themselves and had prematurely become adult. Old forms are often generalized, or less specific in their adaptations than those of modern times. There is less division of labour among them. Old forms sometimes not only rise to the higher places in their groups, but usurp attributes which in later times are restricted to their betters. Old forms are often gigantic in size in comparison with their modern successors, which, if they could look back on their predecessors, might say, “There were giants in those days.” Some old forms have gone onward in successive stages of elevation by a regular and constant gradation. Others have remained as they were through all the ages, Some have no equals in their groups in modern days. All these things speak of order, but of order along with development, and this development not evolution; unless by this term we understand the emergence into material facts of the plans of the creative mind. These plans we may hope in some degree to understand, though we may not be able to comprehend the mode of action of creative power any more than the mode in which our own thought and will act upon the machinery of our own nerves. Still, the power is not the less real, that we are ignorant of its mode of operation. The wind bloweth whither it listeth, and we feel its strength, though we may not be able to calculate the wind of to-morrow or the winds of last year. So is the Spirit of God when it breathes into animals the breath of life, or the Almighty word when it says, “Let the waters bring forth.”

CHAPTER V.

THE DEVONIAN AGE.

Paradoxical as it may appear, this period of geological history has been held as of little account, and has even been by some geologists regarded as scarcely a distinct age, just because it was one of the most striking and important of the whole. The Devonian was an age of change and transition, in both physical and organic existence; and an age which introduced, in the Northern hemisphere at least, more varied conditions of land and water and climate than had previously existed. Hence, over large areas of our continents, its deposits are irregular and locally diverse; and the duration and importance of the period are to be measured rather by the changes and alterations of previous formations, and the ejection of masses of molten rock from beneath, than by a series of fossiliferous deposits. Nevertheless, in some regions in North America and Eastern Europe, the formations of this era are of vast extent and volume, those of North America being estimated at the enormous thickness of 15,000 feet, while they are spread over areas of almost continental breadth.

At the close of the Upper Silurian, the vast continental plateaus of the northern hemisphere were almost wholly submerged. No previous marine limestone spreads more widely than that of the Uppei Silurian, and in no previous period have we much less evidence of the existence of dry land; yet before the end of the period we observe, in a few fragments of land plants scattered here and there in the marine limestones—evidence that islands rose amid the waste of waters. As it is said that the sailors of Columbus saw the first indications of the still unseen Western Continent in drift canes, and fragments of trees floating in mid ocean, so the voyager through the Silurian seas finds his approach to the verdant shores of the Devonian presaged by a few drift plants borne from shores yet below the horizon. The small remains of land in the Upper Silurian were apparently limited to certain clusters of islands in the north-eastern part of America and north-western part of Europe, with perhaps some in the intervening Atlantic On these limited surfaces grew the first land plants certainly known to us—herbs and trees allied to the modern club-mosses, and perhaps forests of trees allied to the pines, though of humbler type; and this wide Upper Silurian sea, with archipelagos of wooded islands, may have continued for a long time. But with the beginning of the Devonian, indications of an unstable condition of the earth’s crust began to develop themselves. New lands were upheaved; great shallow, muddy, and sandy flats were deposited around them the domains of corals and sea-weeds were contracted and on banks, and in shallows and estuaries, there swarmed shoals of fishes of many species, and some of them of most remarkable organization. On the margins of these waters stretched vast swamps, covered with a rank vegetation.

But the period was one of powerful igneous activity. Volcanoes poured out their molten rocks over sea and land, and injected huge dykes of trap into the newly-formed beds. The land was shaken with earthquake throes, and was subject to many upheavals and subsidences. Violent waves desolated the coasts, throwing sand and gravel over the flatk, and tearing up newly-deposited beds; and poisonous exhalations, or sudden changes of level, often proved fatal to immense shoals of fishes. This was the time of the Lower Devonian, and it is marked, both in the old world and the new, by extensive deposits of sandstones and conglomerates.

But the changes going on at the surface were only symptomatic of those occurring beneath. The immense accumulations of Silurian sediment had by this time so overweighted certain portions of the crust, that great quantities of aqueous sediment had been pressed downward into the heated bowels of the earth, and were undergoing, under an enormous weight of superincumbent material, a process of baking and semi-fusion. This process was of course extremely active along the margins of the old Silurian plateaus, and led to great elevation of land, while in the more central parts of the plateaus the oceanic conditions still continued; and in the Middle Devonian, in America at least, one of the most remarkable and interesting coral limestones in the world—the corniferous limestone—was deposited. In process of time, however, these clear waters became shallow, and were invaded by muddy sediments; and in the Upper Devonian the swampy flats and muddy shallows return in full force, and in some degree anticipate the still greater areas of this kind which existed in the succeeding Coal formation.

Such is a brief sketch of the Devonian, or, as it may be better called in America, from the vast development of its beds on the south side of Lake Erie, the Erian formation. In America the marine beds of the Devonian were deposited on the same great continental plateau which supported the seas of the Upper and Lower Silurian, and the beds were thicker towards the east and thinned towards the west, as in the case of the older serios. But in the Devonian there was much, land in the north-east of America; and on the eastern margin of this land, as in Gaspé and New Brunswick, the deposits throughout the whole period were sandstones and shales, without the great coral limestones of the central plateau. Something of the same kind occurred in Europe, where, however, the area of Devonian sea was smaller. There the fossiliferous limestones of the Middle Devonian in Devon, in the Eifel district, in France and in Russia, represent the great corniferous limestone of America; while the sandstones of South Wales, of Ireland, and of Scotland, resemble the local conditions of Gaspé and New Brunswick, and belonged to a similar area in the north-west of Europe, in which shallow water and land conditions prevailed during the whole of the Devonian, and which was perhaps connected with the corresponding region in Eastern America by a North Atlantic archipelago, now submerged. This whole subject is so important to the knowledge of the Devonian, and of geology in general, that I may be pardoned for introducing it here in a tabular form, taking the European series from Etheridge’s excellent and exhaustive paper in the “Journal of the Geological Society.”

DEVONIAN OF ERIAN.

DIVISIONS.		CENTRAL AREAS.
		Devon.	Rhen. Prussia.	New York.
Upper		Pilton group:— Brown calcareous shales, brown and yellow sandstone. Land plants and marine shells.	Clymenia, Cypridina, etc. Shales, limestones, and sandstones. Plants and marine shells.	Chemung and Portage. Sandstones and shales. Plants and marine shells.
Middle		Ilfracombe group:— Grey and red sandstones and flags, calcareous slates and limestones, with corals, etc.	Eifel limestone, Calceola shales, etc. Corals, shells, etc.	Hamilton shales, and Corniferous or cherty limestone. Many corals and shells, also plants.
Lower		Lynton group:— Bed and purple sandstones. Marine shells, etc.	Coblentz and Wisseubach shales, Rhenish greywacke, Spinier sandstone. Marine shells.	Schoharie and Caudagalli grits. Oriskany sandstones. Marine shells.
DIVISIONS.		MARGINAL AREAS.
		Scotland.	Ireland.	Gaspé and New Brunswick.
Upper		Yellow and red sandstones. Fishes and plants.	Yellow and red sandstones, etc. Plants, fishes, etc.	Red and grey sandstones, grits and shales, and conglomerates of Gaspé and Miapeck. Plants.
Middle		Red shales and sandstones, and conglomerates. Caithness flags. Fishes and plants.	Grits and sandstones of Dingle.	Grey and Red sandstones, and grey and dark shales. Gaspé and St. John. Many plants and fishes.
Lower		Flagstones, shales and conglomerates. Fishes and plants.	Glengariff grits, etc.	Sandstone and conglomerate. Gaspé and St. John. Plants and fishes.

A glance at this table suffices to show that when we read Hugh Miller’s graphic descriptions of the Old Red Sandstone of Scotland, with its numerous and wonderful fishes, we have before us a formation altogether distinct from that of Devonshire or the Eifel. But the one represents the shallow, and the other the deeper seas of the same period. We learn this by careful tracing of the beds to their junction with, corresponding series, and by the occasional occurrence of the characteristic fishes of the Scottish strata in the English and German beds. In like manner a geologist who explores the Gaspé sandstones or the New Brunswick shales has under his consideration a group of beds very dissimilar from that which he would have to study on the shores of Lake Erie. But here again identity of relations to the Silurian below and the carboniferous above, shows the contemporaneousness of the beds, and this is confirmed by the occurrence in both series of some of the same plants and shells and fishes.

It will further be observed that it is in the middle that the greatest difference occurs. Sand and mud and pebble-banks were almost universal over our two great continental plateaus in the Older and Newer Devonian. But in the Middle there were in some places deeper waters with coral reefs, in others shallow flats and swamps rich in vegetation. Herein we see the greater variety and richness of the Devonian. Had we lived in that age, we should not have seen great continents like those that now exist, but we could have roamed over lovely islands with breezy hills and dense lowland jungles, and we could have sailed over blue coral seas, glowing below with all the fanciful forms and brilliant colours of polyp life, and filled with active and beautiful fishes. Especially did all these conditions culminate in the Middle Devonian, when what are now the continental areas of the northern hemisphere must have much resembled the present insular and oceanic regions of the South Pacific.

Out of the rich and varied life of the Devonian I may select for illustration its corals, its crustaceans, its fishes, its plants, and its insects.

Fig. 11.—CORALS, FISHES, AND CRUSTACEANS OF THE DEVONIAN

In the foreground are Corals of the genera Favosites, Michelina, Phillipsatrea, Zaphrentis, Blothrophyllum, and Syringopora, and the seaweed Spirephyton; also Fishes of the genera Cephalaspis and Pterichthys. Above are Pterygotus and Dinichtys, with Fishes of the genera Diplacanthus, Osteolepis, Holoptychius, Pteraspis, Coccosteus, etc. The distant land had Lepidodendra, Pines and Tree-ferns.

The central limestones of the Devonian may be regarded as the head-quarters of the peculiar types of coral characteristic of the Palæozoic age. Here they were not only vastly numerous, but present some of their grandest and also their most peculiar forms. Edwards and Haime, in their “Monograph of British Fossil Corals” in 1854, enumerate one hundred and fifty well-ascertained species, and the number has since been largely increased; I have no doubt that my friend Dr. Bigsby, in his forth-coming “Thesaurus Devonicus,” will more than double it. In the Devonian limestones of England, as for instance at Torquay, the specimens, though abundant and well preserved as to their internal structure, are too firmly imbedded in the rock to show their external forms. In the Devonian of the continent of Europe much finer specimens occur; but, perhaps, in no part of the world is there so clear an exhibition of them as in the Devonian limestones of the United States and Canada. Sir Charles Lyell thus expresses his admiration of the exposure of these corals, which he saw at the falls of the Ohio, near Louisville. He says, "Although the water was not at its lowest, I saw a grand display of what may be termed an ancient coral-reef, formed by zoophytes which flourished in a sea of earlier date than the Carboniferous period. The ledges of horizontal limestone, over which the water flows, belong to the Devonian group, and the softer parts of the stone have decomposed and wasted away, so that the harder calcareous corals stand out in relief. Many branches of these zoophytes project from their erect stems precisely as if they were living. Among other species I observed large masses, not less than five feet in diameter, of Favosites Gothlandica, with its beautiful honeycomb structure well displayed. There was also the cup-shaped Cyathophyllum, and the delicate network of Fenestella, and that elegant and well-known European species of fossil, the chain coral, Catenipora escharoides, with a profusion of others which it would be tedious to all but the geologist to enumerate. Although hundreds of fine specimens have been detached from these rocks to enrich the museums of Europe and America, another crop is constantly working its way out under the action of the stream, and of the sun and rain in the warm season when the channel is laid dry."[K] These limestones have been estimated to extend, as an almost continuous coral reef, over the enormous area of five hundred thousand square miles of the now dry and inland surface of the great American continental plateau. The limestones described by Sir Charles are known in the Western States as the “Cliff limestone.” In the State of New York and in Western Canada the “Corniferous limestone,” so called from the masses of hornstone, like the flint of the English chalk, contained in it, presents still more remarkable features. The corals which it contains have been replaced by the siliceous or flinty matter in such a manner that, when the surrounding limestone weathers away, they remain projecting in relief in all the beauty of their original forms. Not only so, but on the surface of the country they remain as hard siliceous stones, and may be found in ploughing the soil and in stone fences and roadside heaps, so that tons of them could often be collected over a very limited space. When only partly disengaged from the matrix, the process may be completed by immersing them in a dilute acid. The beauty of these specimens when thus prepared is very great not at all inferior to that of modern corals, which they often much resemble in general form, though differing in details of structure. One of the most common forms is that of the Favosites, or honeycomb coral, presenting regular hexagonal cells with transverse floors or tabulæ. Of these there are several species, usually flat or massive in form; but one species, F. polymorpha, branches out like the modern stag-horn corals. Another curious form, Michelina, looks exactly like a mass of the papery cells of the great American hornet in a petrified state, and the convex floors simulate the covers of the cells, so that it is quite common to find them called fossil wasps' nests. Some of the largest belong to the genus Phillipsastrea or Smithia, which Hugh Miller has immortalized by comparing its crowded stars, with confluent rays, to the once-popular calico pattern known as “Lane’s net”—a singular instance of the accidental concurrence of a natural and artificial design. Another very common type is that of the conical Zaphrentis, with a deep cut at top to lodge the body of the animal, whose radiating chambers are faithfully represented by it’s delicate lamellæ. Perhaps the most delicate of the whole is the Syringopora, with its cylindrical worm-like pipes bound together by transverse processes, and which sometimes can be dissolved out in all its fragile perfection by the action of an acid on a mass of Corniferous limestone filled with these corals in a silicified state.

[K] “Travels in North America.” second series.

These Devonian corals, like those of the Silurian, belong to the great extinct groups of Tabulate and Rugose corals; groups which present, on the one hand, points of resemblance to the ordinary coral animals of the modern seas, and, on the other, to those somewhat exceptional corals, the Millepores, which are produced by another kind of polyp, the Hydroids. Some of them obviously combine properties belonging to both, as, for example, the radiating partitions with the arrangement of the parts in multiples of four, the horizontal floors, and the external solid wall; and this fact countenances the conclusion that in these old corals we have a group of high and complex organization, combining properties now divided between two great groups of animals, neither of them probably, either in their stony skeletons or the soft parts of the animal, of as high organization as their Paleozoic predecessors. This sort of disintegration of composite types, or dissolution of old partnerships, seems to liave been no unusual occurrence in the history of life.[L]

[L] Verril has suggested that the Tabulata may be divided into two groups, one referable to Actinoids, the other to Hydroids.

If the Devonian witnessed the culmination of the Palæozoic corals, its later stages saw the final decadence of the great dynasty of the Trilobites. Of these creatures there are in the Devonian some large and ornate species, remarkable for their spines and tubercles; as if in this, the latter day of their dominion, they had fallen into habits of luxurious decoration unknown to their sterner predecessors, and at the same time had found it necessary to surround their now disputed privileges with new safeguards of defensive armour. Not improbably the decadence of the Trilobites may have been connected with the introduction of the numerous and formidable fishes of the period.

But while the venerable race of the Trilobites was preparing to fight its last and unsuccessful battle, another and scarcely less ancient tribe of crustaceans, the Eurypterids, already strong in the Silurian, was armed with new and formidable powers. The Pterygotus anglicus, which should have been named scoticus, since its head-quarters are in Scotland, was in point of size the greatest of known crustaceans, recent or fossil. According to Mr. Henry Woodward, who has published an admirable description and figures of the creature in the Palæontographical Society’s Memoirs, it must have been six feet in length, and nearly two feet in breadth. Its antennæ were, unlike the harmless feelers of modern Crustacea, armed with powerful claws. Two great eyes stood in the front of the head, and two smaller ones on the top. It had four pairs of great serrated jaws, the largest as wide as a man’s hand. At the sides were a pair of powerful paddles, capable of urging it swiftly through the water as it pursued its prey; and when attacked by any predaceous fish, it could strike the water with its broad tail, terminated by a great flat “telson,” and retreat backward with the rapidity of an arrow. Woodward says it must have been the “shark of the Devonian seas;” rather, it was the great champion of the more ancient family of the lobsters, set to arrest, if possible, the encroachments of the coming sharks.

The Trilobites and Eurypterids constitute a hard case for the derivationists. Unlike those Melchisedeks, the fishes of the Silurian, which are without father or mother, the Devonian crustaceans may boast of their descent, but they have no descendants. No distinct link connects them with any modern crustaceans except the Limuli, or horse-shoe crabs; and here the connection is most puzzling, for while there seems some intelligible resemblance between the adult Eurypterids and the horse-shoe, or king-crabs, the latter, in their younger state, rather resemble Trilobites, as Dr. Packard has recently shown. Thus the two great tribes of Eurypterids and Trilobites have united in the small modern group of king-crabs, while on the other hand, there are points of resemblance, as already stated, between Trilobites and Isopods, and the king-crabs had already begun to exist, since one species is now known in the Upper Silurian. So puzzling are these various relationships, that one naturalist of the derivationist school has recently attempted to solve the difficulty by suggesting that the Trilobites are allied to the spiders! Thus nature sports with our theories, showing us in some cases, as in the corals and fishes, partnerships split up into individuals, and in others distinct lines of being converging and becoming lost in one slender thread. Barrande, the great palæontologist of Bohemia, has recently, in an elaborate memoir on the Trilobites, traced these and other points through all their structures and their whole succession in geological time thereby elaborating a most powerful inductive argument against the theory of evolution, and concluding that, so far from the history of these creatures favouring such a theory, it seems as if expressly contrived to exclude its possibility.

But, while the gigantic Eurypterids and ornate Trilobites of the Devonian were rapidly approaching their end, a few despised little crustaceans,—represented by the Amphipeltis of New Brunswick and Kampecaris of Scotland,—were obscurely laying the foundation of a new line of beings, that of the Stomapods, destined to culminate in the Squillas and their allies, which, however different in structure, are practically the Eurypterids of the modern ocean. So change the dynasties of men and animals.

"Thou takest away their breath, they die, They return to their dust; Thou sendest forth Thy Spirit, They are created; Thou renewest the form of the earth."

The reign of fishes began in the Upper Silurian, for in the rocks of this age, more especially in England, several species have been found. They occur, however, only in the newer beds of this formation, and are not of large size, nor very abundant. It is to be observed that, in so far as the fragments discovered can be interpreted, they indicate the existence already of two distinct types of fishes, the Ganoids, or gar-fishes, protected with bony plates and scales, and the Placoids, or shark-like fishes; and that in the existing world these fishes are regarded as occupying a high place in their class. Further, these two groups of fishes are those which throughout a large portion of geological time continue to prevail to the exclusion of other types, the ordinary bony fishes having been introduced only in comparatively recent periods. With the Devonian, however, there comes a vast increase to the finny armies; and so characteristic are these that the Devonian has been called the age of fishes par excellence, and we must try, with the help of our illustration, to paint these old inhabitants of the waters as distinctly as we can. Among the most ancient and curious of these fishes are those singular forms covered with broad plates, of which the Pteraspis of the Upper Silurian is the herald, and which are represented in the Lower Devonian by several distinct genera. Of these, one of the most curious is the Cephalaspis, or buckler-head, distinguished by its broad flat head, rounded in front and prolonged at the sides into two great spines, which project far beyond the sides of the comparatively slender body. This fish, it may be mentioned, is the type of a family highly characteristic of the Lower Devonian, as well as of the Upper Silurian, and all of which are provided with large plate-like cephalic coverings, sometimes with a long snout in front, and, in so far as is known, a comparatively weak body and tail. They were all probably ground-living creatures, feeding on worms and shell-fishes, and “rooting” for these in the mud, or burrowing therein for their safety. In these respects they have a most curious analogy to the Trilobites, which in habits they must have greatly resembled, though belonging by their structure to an entirely different and much higher class. So close is this resemblance, that their head-shields used to be mistaken for those of Trilobites. The case is one of those curious analogies which often occur in nature, and which must always be distinguished from the true affinities which rest on structural resemblances. Another group of small fishes, likewise cuirassed in bony armour of plates, may be represented by the Pterichthys, with its two strong bony fins at the sides, which may have served for swimming, but probably also for defence, and for creeping on or shovelling up the mud at the bottom of the sea. But, besides the Ganoids which were armed in plated cuirasses, there were others, active and voracious, clad in shining enamelled scales, like the bony pikes of the American rivers and the Polypterus of the Nile. Some of these, like the Diplacanthus, or “double-spine” were of small size, and chiefly remarkable for their sharp defensive bony spines. Others, like Holoptychius (wrinkled-scale) and Osteolepis (bone-scale), were strongly built, and sometimes of great size. One Russian species of Asterolepis (star-scale) is supposed to have been twenty feet in length, and furnished with strong and trenchant teeth in two rows. These great fishes afford a good reason for the spines and armour-plates of the contemporary trilobites and smaller fishes. Just as man has been endeavouring to invent armour impenetrable to shot, for soldiers and for ships, and, on the other hand, shot and shells that can penetrate any armoury so nature has always presented the spectacle of the most perfect defensive apparatus matched with the most perfect weapons for destruction. In the class of fishes, no age of the world is more eminent in these respects than the Devonian.[M] In addition to these fishes, there were others, represented principally by their strong bony spines, which must have been allied to some of the families of modern sharks, most of them, however, probably to that comparatively harmless tribe which, furnished with flat teeth, prey upon shell-fishes. There are other fishes difficult to place in our systems of classification; and among these an eminent example is the huge Dinichthys of Newberry, from the Hamilton group of Ohio. The head of this creature is more than three feet long and eighteen inches broad, with the bones extraordinarily strong and massive. In the upper jaw, in addition to strong teeth, there were in front two huge sabre-shaped tusks or incisors, each nearly a foot long; and corresponding to these in the massive lower jaw were two closely joined conical tusks, fitting between those of the upper jaw. No other fish presents so frightful an apparatus for destruction; and if, as is probable, this was attached to a powerful body, perhaps thirty feet in length, and capable of rapid motion through the water, we cannot imagine any creature so strong or so well armed as to cope with the mighty Dinichthys.

[M] Many of these were discovered and successfully displayed and described by Hugh Miller, and are graphically portrayed in his celebrated work on the “Old Red Sandstone,” published in 1841.

The difference between the fishes of the Devonian and those of the modern seas is well marked by the fact that, while the ordinary bony fishes now amount to probably 9,000 species, and the ganoid fishes to less than thirty, the finny tribes of the Devonian are predominantly ganoids, and none of the ordinary type are known. To what is this related, with reference to conditions of existence? Two explanations, different yet mutually connected, may be suggested. One is that armour was especially useful in the Devonian as a means of defence from the larger predaceous species, and the gigantic crustaceans of the period. That this was the case may be inferred from the conditions of existence of some modern ganoids. The common bony pike of Canada (Lepidosteus), frequenting shallow and stagnant waters, seems to be especially exposed to injury from its enemies. Consequently, while it is rare to find an ordinary fish showing any traces of wounds, a large proportion of the specimens of the bony pike which I have examined have scars on their scales, indicating injuries which they have experienced, and which possibly, to fishes not so well armed, might have proved fatal. Again, in the modern Amia, or mud-fish, in the bony pike and Polypterus, there is an extremely large air-bladder, amply supplied with blood-vessels, and even divided into cells or chambers, and communicating with the mouth by an “air-duct.” This organ is unquestionably in function a lung, and enables the animal to dispense in some degree with the use of its gills, which of course depend for their supply of vital air on the small quantity of oxygen dissolved in the water. Hence, by the power of partially breathing air, these fishes can live in stagnant and badly aerated waters, where other fishes would perish. In the case of the Amia, the grunting noises which it utters, its habit of frequenting the muddy creeks of swamps, and its possession of gill-cleaners, correspond with this view. It is possible that the Devonian fishes possessed this semi-reptilian respiration; and if so, they would be better adapted than other fishes to live in water contaminated with organic matter in a state of decay, or in waters rich in carbonic acid or deficient in oxygen. Possibly the palæozoic waters, as well as the palæozoic atmosphere, were less rich in pure oxygen than those of the present world; and it is certain that, in many of the beds in which the smaller Devonian fishes abound, there was so much decaying vegetable matter as to make it probable that the water was unfit for the ordinary fishes. Thus, though at first sight the possession of external armour and means to respire air, in the case of these peculiar fishes, may seem to have no direct connection with each other, their obvious correlation in some modern ganoids may have had its parallel on a more extensive scale among their ancient relatives. Just as the modern gar-fish, by virtue of its lungs, can live in stagnant shallows and hunt frogs, but on that account needs strong armour to defend it against the foes that assail it in such places; so in the Devonian the capacity to inhabit unaërated water and defensive plates and scales may have been alike necessary, especially to the feebler tribes of fishes. We shall find that in the succeeding carboniferous period there is equally good evidence of this.

We have reserved little space for the Devonian plants and insects; but we may notice both in a walk through a Devonian forest, in which we may include the vegetation of the several subordinate periods into which this great era was divisible. The Devonian woods were probably, like those of the succeeding carboniferous period, dense and dark, composed of but few species of plants, and these somewhat monotonous in appearance, and spreading out into broad swampy jungles, encroaching on the shallow bays and estuaries. Landing on one of these flats, we may first cast our eyes over a wide expanse, covered with what at a distance we might regard as reeds or rushes. But on a near approach they appear very different; rising in slender, graceful stems, they fork again and again, and their thin branches are sparsely covered with minute needle-like leaves, while the young shoots curl over in graceful tresses, and the older are covered with little oval fruits, or spore-cases; for these plants are cryptogamous, or flowerless. This singular vegetation stretches for miles along the muddy flats, and rises to a height of two or three feet from a knotted mass of cylindrical roots or root-stocks, twining like snakes through and over the soil. This plant may, according as we are influenced by its fruit or structure, be regarded as allied to the modern club-mosses or the modern pill-worts. It is Psilophyton, in every country one of the most characteristic plants of the period, though, when imperfectly preserved, often relegated by careless and unskilled observers to the all-engulfing group of fucoids. A little further inland we see a grove of graceful trees, forking like Psilophyton, but of grander dimensions, and with the branches covered with linear leaves, and sometimes terminated by cones. These are Lepidodendra, gigantic club-mosses, which were developed to still greater dimensions in the coal period. Near these we may see a still more curious tree, more erect in its growth, with rounded and somewhat rigid leaves and cones of different form, and with huge cable-like roots, penetrating the mud, and pitted with the marks of long rootlets. This is Cyclostigma, a plant near to the Lepidodendron, but distinct, and peculiar to the Devonian. Some of its species attain to the dimensions of considerable trees; others are small and shrubby. Another small tree, somewhat like the others, but with very long shaggy leaves, and its bark curiously marked with regular diamond-shaped scars, is the Leptophleum. All these plants are probably allied to our modern club-mosses, which are, however, also represented by some low and creeping species cleaving to the ground. A little further, and we reach a dense clump of Sigillariæ, with tall sparsely forking stems, and ribbed with ridges holding rows of leaf-scars a group of plants which we shall have further occasion to notice in the coal formation; and here is an extensive jungle of Calamites, gigantic and overgrown mares'-tails, allies of the modern equisetums.

Fig. 12.—VEGETATION OF THE DEVONIAN.

To the left are Calamites; next to these, Leptophleum; in the centre are Lepidodendron, Sigillaria, and a Pine. Below are Psilophyton, Cordaites, Ferns, and Asterophyllites.

Amidst these trees, every open glade is filled with delicate ferns of marvellous grace and beauty; and here and there a tree-fern rears its head, crowned with its spreading and graceful leaves, and its trunk clad with a shaggy mass of aërial roots—an old botanical device, used in these ancient times, as well as now, to strengthen and protect the stems of trees not fitted for lateral expansion. Beyond this mass of vegetation, and rising on the slopes of the distant hills, we see great trees that look like pines. We cannot approach them more nearly; but here on the margin of a creek we see some drift-trunks, that have doubtless been carried down by a land flood. One of them is certainly a pine, in form and structure of its wood very like those now living in the southern hemisphere; it is a Dadoxylon. Another is different, its sides rough and gnarled, and marked with huge irregular ridges; its wood loose, porous, and stringy, more like the bark of modern pines, yet having rings of growth and a true bark of its own, and sending forth large branches and roots. It is the strange and mysterious Prototaxites, one of the wonders of the Devonian land, and whose leaves and fruits would be worth their weight in gold in our museums, could we only procure them. A solitary fragment further indicates that in the yet unpenetrated solitudes of the Devonian forests there may be other trees more like our ordinary familiar friends of the modern woods; but of these we know as yet but little. What inhabitants have these forests? All that we yet know are a few large insects, relatives of our modern May-flies, flitting with broad veined wings over the stagnant waters in which their worm-like larvæ dwell, and one species at least assuming one of the properties of the grasshopper tribe, and enlivening the otherwise silent groves with a cricket-like chirp, the oldest music of living things that geology as yet reveals to us; and this, not by the hearing of the sound itself, but by the poor remains of the instrument attached to a remnant of a wing from the Devonian shales of New Brunswick.

A remarkable illustration of the abundance of certain plants in the Devonian, and also of the slow and gradual accumulation of some of its beds, is furnished by layers of fossil spore-cases, or the minute sacs which contain the microscopic germs of club-mosses and similar plants. In the American forests, in spring, the yellow pollen-grains of spruces and pines sometimes drift away in such quantities in the breeze that they fall in dense showers, popularly called showers of sulphur; and this vegetable sulphur, falling in lakes and ponds, is drifted to the shore in great sheets and swathes. The same thing appears to have occurred in the Devonian, not with the pollen of flowering plants, but with the similar light spores and spore-cases of species of Lepidodendron and allied trees. In a bed of shale, at Kettle Point, Lake Huron, from 12 to 14 feet thick, not only are the surfaces of the beds dotted over with minute round spore-cases, but, on making a section for the microscope, the substance of each layer is seen to be filled with them; and still more minute bodies, probably the escaped spores, are seen to fill up their interstices. The quantity of these minute bodies is so great that the shale is combustible, and burns with much flame. A bed of this nature must have been formed in shallow and still water, on the margin of an extensive jungle or forest; and as the spore-cases are similar to those of the Lepidodendra of the coal-measures, the trees were probably of this kind. Year after year, as the spores became ripe, they were wafted away, and fell in vast quantities into the water, to be mixed with the fine mud there accumulating. When we come to the coal period, we shall see that such beds of spore-cases occur there also, and that they have even been supposed to be mainly instrumental in the accumulation of certain beds of coal. Their importance in this respect may have been exaggerated, but the fact of their occurrence in immense quantities in certain coals and shales is indisputable.

This is but a slender sketch of the Devonian forests: but we shall find many of the same forms of plants in the carboniferous period which succeeds. With one thought we may close. We are prone to ask for reasons and uses for things, but sometimes we cannot be satisfied. Of what use were the Devonian forests? They did not, like those of the coal formation, accumulate rich beds of coal for the use of man. Except possibly a few insects, we know no animals that subsisted on their produce, nor was there any rational being to admire their beauty. Their use, except as helping us in these last days to complete the order of the vegetable kingdom as it has existed in geological time, is a mystery. We can but fall back on that ascription of praise to Him “who liveth for ever and ever,” on the part of the heavenly elders who cast down their crowns before the throne and say, “Thou art worthy, Lord, to receive the glory, and the honour, and the might; because Thou didst create all things, and by reason of Thy will they are and were created.”

CHAPTER VI.

THE CARBONIFEROUS AGE.

That age of the world’s history which, from its richness in accumulations of vegetable matter destined to be converted into coal, has been named the Carboniferous, is in relation to living beings the most complete and noble of the Palæozoic periods. In it those varied arrangements of land and water which had been increasing in perfection in the previous periods, attained to their highest development. In it the forms of animal and plant life that had been becoming more numerous and varied from the Eozoic onward, culminated. The Permian which succeeded was but the decadence of the Carboniferous, preparatory to the introduction of a new order of things. Thus the Carboniferous was to the previous periods what the Modern is to the preceding Tertiary and Mesozoic ages the summation and completion of them all, and the embodiment of their highest excellence. If the world’s history had closed with the Carboniferous, a naturalist, knowing nothing further, would have been obliged to admit that it had already fulfilled all the promise of its earlier years. It is important to remember this, since we shall find ourselves entering on an entirely new scene in the Mesozoic period, and since this character of the Carboniferous, as well as its varied conditions and products, may excuse us for dwelling on it a little longer than on the others, On the other hand, the immense economic importance of the coal formation, and the interesting points connected with it, have made the Carboniferous more familiar to general readers than most other geological periods, so that we may select points less common and well-known for illustration. Popular expositions of geology are, however, generally so one-sided and so distorted by the prevalent straining after effect, that the true aspect of this age is perhaps not much better known than that of others less frequently described.

Let us first consider the Carboniferous geography of the northern hemisphere; and in doing so we may begin with a fact concerning the preceding age. One of the most remarkable features of the Newer Devonian is the immense quantity of red rocks, particularly red sandstones, contained in it. Ked sandstones, it is true, occur in older formations, but comparatively rarely; their great head-quarters, both in Europe and America, in so far as the Palæozoic is concerned, are in the Upper Devonian. Now red sandstone is an infallible mark of rapid deposition, and therefore of active physical change. If we examine the grains of sand in a red sandstone, we shall find that they are stained or coated, externally, with the peroxide of iron, or iron rust; and that this coating, with perhaps a portion of the same substance in the intervening cement, is the cause of the colour. In finer sandstones and red clays the same condition exists, though less distinctly perceptible. Conrrequently, if red sands and clays are long abraded or scoured in water, or are subjected to any chemical agent capable of dissolving the iron, they cease to be red, and resume their natural grey or white colour. Now in nature, in addition to mechanical abrasion, there is a chemical cause most potent in bleaching red rocks, namely, the presence of vegetable or animal matter in a state of decay. Without entering into chemical details, we may content ourselves with the fact that organic matter decaying in contact with peroxide of iron tends to take oxygen from it, and then to dissolve it in the state of protoxide, while the oxygen set free aids the decay. Carrying this fact with us, we may next affirm that iron is so plentiful in the crust of the earth that nearly all sands and clays when first produced from the weathering of rocks are stained with it, and that when this weathering takes place in the air, the iron is always in the state of peroxide. More especially does this apply to the greater number of igneous or volcanic rocks, which nearly always weather brown or red. Now premising that the original condition of sediment is that of being reddened with iron, and that it may lose this by abrasion, or by the action of organic matter, it follows that when sand has been produced by decay of rocks in the air, and when it is rapidly washed into the sea and deposited there, red beds will result. For instance, in the Bay of Fundy, whose rapid tides cut away the red rocks of its shores and deposit their materials quickly, red mud and sand constitute the modern deposit. On the other hand, when the red Band and mud are long washed about, their red matter may disappear; and when the deposition is slow and accompanied with the presence of organic matter, the red colour is not only removed, but is replaced by the dark tints due to carbon. Thus, in the Gulf of St. Lawrence, where red rocks similar to those of the Bay of Fundy are being more slowly wasted, and deposited in the presence of sea-weeds and other vegetable substances, the resulting sands and clays are white and grey or blackened in colour. An intermediate condition is sometimes observed, in which red beds are stained with grey spots and lines, where sea-weeds or land-plants have rested on them. I have specimens of Devonian red shale with the forms of fern leaves, the substance of which has entirely perished, traced most delicately upon them in greenish marks.

It follows from these facts that extensive and thick deposits of red beds evidence sub-aërial decay of rocks, followed by comparatively rapid deposition in water, and that such red rocks will usually contain few fossils, not only because of their rapid deposition, but because the few organic fragments deposited with them will probably have been destroyed by the chemical action of the superabundant oxide of iron, which, so to speak, “iron-moulds” them, just as stains of iron eat holes out of linen. Now when Sir Roderick Murchison tells us of 10,000 feet in thickness of red iron-stained rocks in the old red sandstone of England, we can see in this the evidence of rapid aqueous deposition, going on for a very long time, and baring vast areas of former land surface. Consequently we have proof of changes of level and immense and rapid denudation—a conclusion further confirmed by the apparent unconformity of different members of the series to each other in some parts of the British Islands, the lower beds having been tilted up before the newer were deposited. Such was the state of affairs very generally at the close of the Devonian, and it appears to have been accompanied with some degree of subsidence of the land, succeeded by re-elevation at the beginning of the Carboniferous, when many and perhaps large islands and chains of islands were raised out of the sea, along whose margins there were extensive volcanic eruptions, evidenced by the dykes of trap traversing the Devonian, and the beds of old lava interstratified in the lower part of the Carboniferous, where also the occurrence of thick beds of conglomerate or pebble-rock indicates the tempestuous action of the sea.

But a careful study of the Lower Carboniferous beds, where their margins rest upon the islands of older rocks, shows great varieties in these old shores. In some places there were shingly beaches; in others, extensive sand-banks; in others, swampy flats clothed with vegetation, and sometimes bearing peaty beds, still preserved as small seams of coal. The bays and creeks swarmed with, fishes. A few sluggish reptiles crept along the muddy or sandy shores, and out sea-ward were great banks and reefs of coral and shells in the clear blue sea. The whole aspect of nature, taken in a general view, in the Older Carboniferous period, must have much resembled that at present seen among the islands of the southern hemisphere. And the plants and animals, though different, were more like those of the modern South Pacific than any others now living.

As the age wore on, the continents were slowly lifted out of the water, and the great continental plateaus were changed from coral seas into swampy flats or low uplands, studded in many places with shallow lakes, and penetrated with numerous creeks and sluggish streams. In the eastern continent these land surfaces prevailed extensively, more especially in the west; and in America they spread both eastward and westward from the Appalachian ridge, until only a long north and south Mediterranean, running parallel to the Rocky Mountains, remained of the former wide internal ocean. On this new and low land, comparable with the “Sylvas” of the South American continent, flourished the wondrous vegetation of the Coal period, and were introduced the new land animals, whose presence distinguishes the close of the Palæozoic.

After a vast lapse of time, in which only slow and gradual subsidence occurred, a more rapid settlement of the continental areas brought the greater part of the once fertile plains of the coal formation again under the waters; and shifting sand-banks and muddy tides engulfed and buried the remains of the old forests, and heaped on them a mass of sediment, which, like the weights of a botanical press, flattened and compressed the vegetable débris preserved in the leaves of the coal formation strata. Then came on that strange and terrible Permian period, which, like the more modern boulder-formation, marked the death of one age and the birth of another.

The succession just sketched is the normal one; but the terms in which it has been described show that it cannot be universal. There are many places in which the whole thickness of the Carboniferous is filled with fossils of the land, and of estuaries and creeks. There are places, on the other hand, where the deep sea appears to have continued during the whole period. In America this is seen on the grandest scale in the absence of the marine members along the western slopes of the Appalachians, and the almost exclusive prevalence of marine beds in the far west, where the great Carboniferous Mediterranean of America spread itself, and continued uninterruptedly into the succeeding Permian period.

In our survey of the Carboniferous age, though there are peculiarities in the life of its older, middle, and newer divisions, we may take the great coal measures of the middle portion as the type of the land life of the period, and the great limestones of the lower portion as that of the marine life; and as the former is in this period by far the most important, we may begin with it. Before doing so, however, to prevent misapprehension, it is necessary to remind the reader that the Flora of the Middle Coal Period is but one of a succession of related floras that reach from the Upper Silurian to the Permian. The meagre flora of club-mosses and their allies in the Upper Silurian and Lower Devonian was succeeded by a comparatively rich and varied assemblage of plants in the Middle Devonian. The Upper Devonian was a period of decadence, and in the Lower Carboniferous we have another feeble beginning, presenting features somewhat different from those of the Upper Devonian. This was the time of the Culm of Germany, the Tweedian formation of the North of England and South of Scotland, and the Lower Coal formation of Nova Scotia. It was a period eminently rich in Lepidodendra. It was followed by the magnificent flora of the Middle Coal formation, and then there was a time of decadence in the Upper Coal formation and only a slight revival in the Permian.

In the present condition of our civilization, coal is the most important product which the bowels of the earth afford to man. And though there are productive beds of coal in most of the later geological formations, down to the peats of the modern period, which are only unconsolidated coals, yet the coal of the Carboniferous age is the earliest valuable coal in point of time, and by far the most important in point of quantity. Mineral coal may be defined t o be vegetable matter which has been buried in the strata of the earth’s crust, and there subjected to certain chemical and mechanical changes. The proof of its vegetable origin will grow upon us as we proceed. The chemical changes which it has undergone are not very material. Wood or bark, taken as an example of ordinary vegetable matter, consists of carbon or charcoal, with the gases hydrogen and oxygen. Coal has merely parted with a portion of these ingredients in the course of a slow and imperfect putrefaction, so that it comes to have much less oxygen and considerably less hydrogen than wood, and it has been blackened by the disengagement of a quantity of free carbon. The more bituminous flaming coals have a larger amount of residual hydrogen. In the anthracite coals the process of carbonisation has proceeded further, and little remains but charcoal in a dense and compact form. In cannel coals, and in certain bituminous shales, on the contrary, the process seems to have taken place entirely under water, by which putrefaction has been modified, so that a larger proportion than usual of hydrogen has been retained. The mechanical change which the coal has experienced consists in the flattening and hardening effect of the immense pressure of thousands of feet of superincumbent rock, which has crashed together the cell-walls of the vegetable matter, and reduced what was originally a pulpy mass of cellular tissue to the condition of a hard laminated rock. To understand this, perhaps tha simplest way is to compare under the microscope a transverse section of recent pine-wood with a similar section of a pine trunk compressed into brown coal or jet. In the one the tissue appears as a series of meshes with thin woody walls and comparatively wide cavities for the transmission of the sap. In the other the walls of the cells have been forced into direct contact, and in some cases have altogether lost their separate forms, and have been consolidated into a perfectly compact structureless mass.

With regard to its mode of occurrence, coal is found in beds ranging in vertical thickness from less than an inch to more than thirty feet, and of wide horizontal extent. Many such beds usually occur in the thickness of the coal formation, or “coal measures,” as the miners call it, separated from each other by beds of sandstone and compressed clay or shale. Very often the coal occurs in groups of several beds, somewhat close to each other and separated from other groups by “barren measures” of considerable thickness. In examining a bed of coal, where it is exposed in a cutting or shore cliff, we nearly always find that the bed below it, or the “underclay,” as it is termed by miners, is a sort of fossil soil, filled with roots and rootlets. On this rests the coal, which, when we examine it closely, is found to consist of successive thin layers of hard coal of different qualities as to lustre and purity, and with intervening laminae of a dusty fibrous substance, like charcoal, called “mother coal” by miners, and sometimes mineral charcoal. Thin partings of dark shale also occur, and these usually present marks and impressions of the stems and leaves of plants. Above the coal is its “roof” of hardened clay or sandstone, and this generally holds great quantities of remains of plants, and sometimes large stumps of trees with their bark converted into coal, and the hollow once occupied with wood filled with sandstone, while their roots spread over the surface of the coal. Such fossil forests of erect stumps are also found at various levels in the coal measures, resting directly on under-clays without any coals. A bed of coal would thus appear to be a fossil bog or swamp.

This much being premised about the general nature of the sooty blocks which fill our coal-scuttles, we may now transport ourselves into the forests and bogs of the coal formation, and make acquaintance with this old vegetation, while it still waved its foliage in the breeze and drank in the sunshine and showers. We are in the midst of one of those great low plains formed by the elevation of the former sea bed. The sun pours down its fervent rays upon us, and the atmosphere, being loaded with vapour, and probably more rich in carbonic acid than that of the present world, the heat is as it were accumulated and kept near the surface, producing a close and stifling atmosphere like that of a tropical swamp. This damp and oppressive air is, however, most favourable to the growth of the strange and grotesque trees which tower over our heads, and to the millions of delicate ferns and club-mosses, not unlike those of our modern woods, which carpet the ground. Around us for hundreds of miles spreads a dense and monotonous forest, with here and there open spaces occupied by ponds and sluggish streams, whose edges are bordered with immense savannahs of reed-like plants, springing from the wet and boggy soil. Everything bespeaks a rank exuberance of vegetable growth; and if we were to dig downward into the soil, we should find a thick bed of vegetable mould evidencing the prevalence of such conditions for ages. But the time will come when this immense flat will meet with the fate which in modern times befell a large district at the mouth of the Indus. Quietly, or with earthquake shocks, it will sink under the waters; fishes and mollusks will swarm where trees grew, beds of sand and mud will be deposited by the water, inclosing and preserving the remains of the vegetation, and in some places surrounding and imbedding the still erect trunks of trees. Many feet of such deposits may be formed, and our forest surface, with its rich bed of vegetable mould, has been covered up and is in process of transformation into coal; while in course of time the shallow waters being filled up with deposit, or a slight re-elevation occurring, a new forest exactly like the last will flourish on the same spot. Such changes would be far beyond the compass of the life even of a Methuselah; but had we lived in the Coal period, we might have seen all stages of thesa processes contemporaneously in different parts of either of the great continents.

But let us consider the actual forms of vegetation presented to us in the Coal period, as we can restore them from the fragments preserved to us in the beds of sandstone and shale, and as we would have seen them in our imaginary excursion through the Carboniferous forests. To do this we must first glance slightly at the great subdivisions of modern plants, which we may arrange in such a way as to give an easy means for comparison of the aspects of the vegetable kingdom in ancient and modern times. In doing this I shall avail myself of an extract from a previous publication of my own on this subject.

"The modern flora of the earth admits of a grand twofold division into the Phænogamous, or flowering and seed-bearing plants, and the Cryptogamous, or flowerless and spore-bearing plants. In the former series, we have, first, those higher plants which start in life with two seed-leaves, and have stems with distinct bark, wood, and pith—the Exogens; secondly, those similar plants which begin life with one seed-leaf only, and have no distinction of bark, wood, and pith, in the stem—the Endogens; and, thirdly, a peculiar group starting with two or several seed-leaves, and having a stem with bark, wood, and pith, but with very imperfect flowers, and wood of much simpler structure than either of the others—the Gymnosperms. To the first of these groups or classes belong most of the ordinary trees of temperate climates. To the second belong the palms and allied trees found in tropical climates. To the third belong the pines and cycads. In the second or Cryptogamous series we have also three classes,—(1.) The Acrogens, or ferns and club-mosses, with stems having true vessels marked on the sides with cross-bars—the Scalariform vessels. (2.) The Anophytes, or mosses and their allies, with stems and leaves, but no vessels. (3.) The Thallophytes, or lichens, fungi, sea-weeds, etc., without true stems and leaves.

"In the existing climates of the earth we find these classes of plants variously distributed as to relative numbers. In some, pines predominate. In others, palms and tree-ferns form a considerable part of the forest vegetation. In others, the ordinary exogenous trees predominate, almost to the exclusion of others. In some Arctic and Alpine regions, mosses and lichens prevail. In the Coal period we have found none of the higher Exogens, though one species is known in the Devonian, and only a few obscure indications of the presence of Endogens; but Gymnosperms abound, and are highly characteristic. On the other hand, we have no mosses or lichens, and very few algæ, but a great number of ferns and Lycopodiaceæ or club-mosses. Thus the coal formation period is botanically a meeting-place of the lower Phænogams and the higher Cryptogams, and presents many forms which, when imperfectly known, have puzzled botanists in regard to their position in one or other series. In the present world, the flora most akin to that of the Coal period is that of moist and warm islands in the southern hemisphere. It is not properly a tropical flora, nor is it the flora of a cold region, but rather indicative of a moist and equable climate. In accordance with this is the fact that the equable but not warm climate of the southern hemisphere at present (which is owing principally to its small extent of land) enables sub-tropical plants to extend into high latitudes. In the Coal period this uniformity was evidently still more marked, since we find similar plants extending from regions within the Arctic circle to others near to the tropics. Still we must bear in mind that we may often be mistaken in reasoning as to the temperature required by extinct species of plants differing from those now in existence. Further, we must not assume that the climatal conditions of the northern hemisphere were in the Coal period at all similar to those which now prevail. As Sir Charles Lyell has argued, a less amount of land in the higher latitudes would greatly modify climates, and there is every reason to believe that in the Coal period there was less land than now. It has been shown by Tyndall that a very small additional amount of carbonic acid in the atmosphere would, by obstructing the radiation of heat from the earth, produce almost the effect of a glass roof or conservatory, extending over the whole world. There is much in the structure of the leaves of the coal plants, as well as in the vast amount of carbon which they accumulated in the form of coal, and the characteristics of the animal life of the period, to indicate, on independent grounds, that the Carboniferous atmosphere differed from that of the present world in this way, or in the presence of more carbonic acid a substance now existing in the very minute proportion of one-thousandth of the whole by weight, a quantity adapted to the present requirements of vegetable and animal life, but probably not to those of the Coal period."

Returning from this digression to the forests of the Coal period, we may first notice that which is the most conspicuous and abundant tree in the swampy levels—the Sigillaria or seal-tree, so called from the stamp-like marks left by the fall of its leaves—a plant which has caused much discussion as to its affinities. Some regard it as a gymnosperm, others as a cryptogam. Most probably we have under this name trees allied in part to both groups, and which, when better known, may bridge over the interval between them. These trees present tall pillar-like trunks, often ribbed vertically with raised bands, and marked with rows of scars left by the fallen leaves. They are sometimes branchless, or divide at top into a few thick limbs, covered with long rigid grass-like foliage. On their branches they bear long slender spikes of fruit, and we may conjecture that quantities of nut-like seeds scattered over the ground around their trunks are their produce. If we approach one of these trees closely, more especially a young specimen not yet furrowed by age, we are amazed to observe the accurate regularity and curious forms of the leaf-scars, and the regular ribbing, so very different from that of our ordinary forest trees. If we cut into its stem, we are still further astonished at its singular structure. Externally it has a firm and hard rind. Within this is a great thickness of soft cellular inner bark, traversed by large bundles of tough fibres. In the centre is a core or axis of woody matter very slender in proportion to the thickness of the trunk, and still further reduced in strength by a large cellular pith. Thus a great stem four or five feet in diameter is little else than a mass of cellular tissue, altogether unfit to form a mast or beam, but excellently adapted, when flattened and carbonised, to blaze upon our winter hearth as a flake of coal. The roots of these trees were perhaps more singular than their stems; spreading widely in the soft soil by regular bifurcation, they ran out in long snake-like cords, studded all over with thick cylindrical rootlets, which spread from them in every direction. They resembled in form, and probably in function, those cable-like root-stocks of the pond-lilies which run through the slime of lakes, but the structure of the rootlets was precisely that of those of some modern Cycads. It was long before these singular roots were known to belong to a tree. They were supposed to be the branches of some creeping aquatic plant, and botanists objected to the idea of their being roots; but at length their connection with Sigillaria was observed simultaneously by Mr. Binney, in Lancashire, and by Mr. Kichard Brown, in Cape Breton, and it has been confirmed by many subsequently observed facts. This connection, when once established, further explained the reason of the almost universal occurrence of Stigmaria, as these roots were called, under the coal beds; while trunks of the same plants were the most abundant fossils of their partings and roofs. The growth of successive generations of Sigillariæ was, in fact, found to be the principal cause of the accumulation of a bed of coal. Two species form the central figures in our illustration.

Fig. 13.—GROUP OF CARBONIFEROUS PLANTS,
RESTORED FROM ACTUAL SPECIMENS.

(a) Calamites (type of C. Suckovii). (b) Lepidofloios, or Ulodendron. (c) Sigillaria (type of S. reniformis). (d) (type of S. elegans). (e) Lepidodendron (type of L. corrugatum). (f) Megaphyton (type of M. magnificum). (g) Cordaites, or Pychnophyllum (type of C. borassifolia).

Along with the trees last mentioned, we observe others of a more graceful and branching form, the successors of those Lepidodendra already noticed in the Devonian, and which still abound in the Carboniferous, and attain to larger dimensions than their older relations, though they are certainly more abundant and characteristic in the lower portions of the carboniferous. Relatives, as already stated, of our modern club-mosses, now represented only by comparatively insignificant species, they constitute the culmination of that type, which thus had attained its acme very long ago, though it still continues to exist under depauperated forms. They all branched by bifurcation, sometimes into the most graceful and delicate sprays. They had narrow slender leaves, placed in close spirals on the branches. They bore their spores in scaly cones. Their roots were similar to Stigmaria in general appearance, though differing in details. In the coal period there were several generic forms of these plants, all attaining to the dimensions of trees. Like the Sigillariæ, they contributed to the materials of the coal; and one mode of this has recently attracted some attention. It is the accumulation of their spores and spore-cases already referred to in speaking of the Devonian, and which was in the Carboniferous so considerable as to constitute an important feature locally in some beds of coal. A similar modern accumulation of spore-cases of tree-ferns occurs in Tasmania; but both in the Modern and the Carboniferous, such beds are exceptional; though wherever spore-cases exist as a considerable constituent of coal, from their composition they give to it a highly bituminous character, an effect, however, which is equally produced by the hard scales supporting the spores, and by the outer epidermal tissues of plants when these predominate in the coal, more especially by the thick corky outer bark of Sigillaria. In short, the corky substance of bark and similar vegetable tissues, from its highly carbonaceous character, its indestructibility, and its difficult permeability by water carrying mineral matter in solution, is the best of all materials for the production of coal; and the microscope shows that of this the principal part of the coal is actually composed.

In the wide, open forest glades, tree-ferns almost precisely similar to those of the modern tropics reared their leafy crowns. But among them was one peculiar type, in which the fronds were borne in pairs on opposite sides of the stem, leaving when they fell two rows of large horseshoe-shaped scars marking the sides of the trunk. Botanists, who have been puzzled with these plants almost as much as with the Stigmaria, have supposed these scars to be marks of branches, of cones, and even of aërial roots; but specimens in my collection prove conclusively that the stem of this genus was a great caudex made up of the bases of two rows of huge leaves cemented together probably by intervening cellular tissue. As in the Devonian and in modern times, the stems of the tree-ferns of the Carboniferous strengthened themselves by immense bundles of cord-like aërial roots, which look like enormous fossil brooms, and are known under the name Psaronius.

We have only time to glance at the vast brakes of tall Calamites which fringe the Sigillaria woods, and stretch far sea-ward over tidal flats. They were allied to modern Mares' Tails or Equisetums, but were of gigantic size, and much more woody structure of stem. The Calamites grew on wet mud and sand-flats, and also in swamps; and they appear to have been especially adapted to take root in and clothe and mat together soft sludgy material recently deposited or in process of deposition. When the seed or spore of a Calamite had taken root, it probably produced a little low whorl of leaves surrounding one small joint, from which another and another, widening in size, arose, producing a cylindrical stem, tapering to a point below. To strengthen the unstable base, the lower joints, especially if the mud had been accumulating around the plant, shot out long roots instead of leaves, while secondary stems grew out of the sides at the surface of the soil, and in time there was a stool of Calamites, with tufts of long roots stretching downwards, like an immense brush, into the mud. When Calamites thus grew on inundated flats, they would, by causing the water to stagnate, promote the elevation of the surface by new deposits, so that their stems gradually became buried; but this only favoured their growth, for they continually pushed out new stems, while the old buried ones shot out bundles of roots instead of regular whorls of leaves.

The Calamites, growing in vast fields along the margins of the Sigillaria forests, must have greatly protected these from the effects of inundations, and by collecting the mud brought down by streams in times of flood, must have done much to prevent the intrusion of earthy deposits among the vegetable matter. Their chief office, therefore, as coal-producers, seems to have been to form for the Sigillaria forests those reedy fringes which, when inundations took place, would exclude mud, and prevent that mixture of earthy matter in the coal which would have rendered it too impure for use. Quantities of fragments of their stems can, however, be detected by the microscope in most coals.

The modern Mares' Tails have thin-walled hollow stems, and some of the gigantic calamites of the coal resembled them in this. But others, to which the name Calamodendron, or Reed-tree, has been given, had stems with thick woody walls of a remarkable structure, which, while similar in plan to that of the Mares' Tails, was much more perfect in its development. Professor Williamson has shown that there were forms intervening between these extremes; and thus in the calamites and calamodendrons we have another example of the exaltation in ancient times of a type now of humble structure; or, in other words, of a comprehensive type, low in the modern world, but in older periods taking to itself by anticipation the properties afterward confined to higher forms. The gigantic club-mosses of the Coal period constitute a similar example, and it is very curious that both of these types have been degraded in the modern world, though retaining precisely their general aspect, while the tree-ferns contemporary with them in the Palæozoic still survive in all their original grandeur.

Barely in the swampy flats, perhaps more frequently in the uplands, grew great pines of several kinds; trees capable of doing as good service for planks and beams as many of their modern successors, but which lived before their time, and do not appear even to have aided much in the formation of coal. These pines of the Coal-period seem to have closely resembled some species still living in the southern hemisphere; and, like the ferns, they present to us a vegetable type which has endured through vast periods of time almost unchanged. Indeed, in the Middle Devonian we have pines almost as closely resembling those of the Modern world as do those of the Coal period. It is in accordance with this long duration of the ferns and pines, that they are plants now of world-wide distribution—suited to all climates and stations. Capacity to exist under varied conditions is near akin to capacity to survive cosmical changes. A botanist in the strange and monstrous woods which we have tried to describe, would probably have found many curious things among the smaller herbaceous plants, and might have gathered several precursors of the modern Exogens and Endogens which have not been preserved to us as fossils, or are known only as obscure fragments. But incomplete though our picture necessarily is, and obscured by the dust of time, it may serve in some degree to render green to our eyes those truly primeval forests which treasured up for our long winter nights the Palæozoic sunshine, and established for us those storehouses of heat-giving material which work our engines and propel our ships and carriages. Truly they lived not in vain, both as realizing for us a type of vegetation which otherwise we could not have imagined, and as preparing the most important of all the substrata of our modern arts and manufactures. In this last regard even the vegetable waste of the old coal swamps was most precious to us, as the means of producing the clay iron ores of the coal measures. I may close this notice of the Carboniferous forests with a suggestive extract from a paper by Professor Huxley in the Contemporary Review:—

"Nature is never in a hurry, and seems to have had always before her eyes the adage, ‘Keep a thing long enough, and you will find a use for it.’ She has kept her beds of coal for millions of years without being able to find much use for them; she has sent them down beneath the sea, and the sea-beasts could make nothing of them: she has raised them up into dry land and laid the black veins bare, and still for ages and ages there was no living thing on the face of the earth that could see any sort of value in them; and it was only the other day, so to speak, that she turned a new creature oat of her workshop, who by degrees acquired sufficient wits to make a fire, and then to discover that the black rock would burn.

"I suppose that nineteen hundred years ago, when Julius Cæsar was good enough to deal with Britain as we have dealt with New Zealand, the primeval Briton, blue with cold and woad, may have known that the strange black stone, of which he found lumps here and there in his wanderings, would burn, and so help to warm his body and cook his food. Saxon, Dane, and Norman swarmed into the land. The English people grew into a powerful nation, and Nature still waited for a return for the capital she had invested in the ancient club-mosses. The eighteenth century arrived, and with it James Watt. The brain of that man was the spore out of which was developed the steam-engine, and all the prodigious trees and branches of modern industry which have grown out of this. But coal is as much an essential condition of this growth and development as carbonic acid is for that of a club-moss. Wanting the coal, we could not have smelted the iron needed to make our engines, nor have worked our engines when we had got them. But take away the engines, and the great towns of Yorkshire and Lancashire vanish like a dream. Manufactures give place to agriculture and pasture, and not ten men could live where now ten thousand are amply supported.

“Thus all this abundant wealth of money and of vivid life is Nature’s investment in club-mosses and the like so long ago. But what becomes of the coal which is burnt in yielding the interest? Heat comes out of it, light comes out of it, and if we could gather together all that goes up the chimney and all that remains in the grate of a thoroughly-burnt coal fire, we should find ourselves in possession of a quantity of carbonic acid, water, ammonia, and mineral matters, exactly equal in weight to the coal. But these are the very matters with which Nature supplied the club-moss which made the coal. She is paid back principal and interest at the same time; and she straightway invests the carbonic acid, the water, and the ammonia in new forms of life, feeding with them the plants that now live. Thrifty Nature! surely no prodigal, but most notable of housekeepers!”

All this is true and admirably put. Its one weak point is the poetical personification of Nature as an efficient planner of the whole. Such an imaginary goddess is a mere superstition, unknown alike to science and theology. Surely it is more rational to hold that the mind which can utilize the coal and understand the manner of its formation, is itself made in the image and likeness of the Supreme Creative Spirit, in whom we live and move and have our being, who knows the end from the beginning, whose power is the origin of natural forces, whose wisdom is the source of laws and correlations of laws, and whose great plan is apparent alike in the order of nature of the Palæozoic world and of the modern world, as well as in the relation of these to each other.

In the Carboniferous, as in the Devonian age, insects existed, and in greater numbers. The winged insects of the period, so far as known, belong to three of the nine or ten orders into which modern insects are usually divided. Conspicuous among them are representatives of our well-known domestic pests the cockroaches, which thus belong geologically to a very old family. The Carboniferous roaches had not the advantage of haunting our larders, but they had abundance of vegetable food in the rank forests of their time, and no doubt lived much as the numerous wild out-of-door species of this family now do. It is, however, a curious fact that a group of insects created so long ago, should prove themselves capable of the kind of domestication to which these creatures attain in our modern days; and that, had we lived even so far back as the coal period, we might have been liable to the attacks of this particular kind of pest. Another group, represented by many species in the coal forests, was that of the May-flies and shad-flies, or ephemeras, which spend their earlier days under water, feeding on vegetable matter, and affording food to many fresh-water fishes—a use which they no doubt served in the coal period also. Some of them were giants in their way, being probably seven inches in expanse of wing, and their larvæ must have been choice morsels to the ganoid fishes, and would have afforded abundant bait had there been anglers in those days. Another group of insects was that of the weevils, a family of beetles, whose grubs must have found plenty of nuts and fruits to devour, without attracting the wrathful attentions of any gardener or orchardist.

A curious and exceptional little group of creatures in the present world is that of the galley-worms or millipedes; wingless, many-jointed, and many-footed crawlers, resembling worms, but more allied to insects. These animals seem to have swarmed in the coal forests, and perhaps attained their maximum numbers and importance in this period, though they still remain, a relic of an ancient comprehensive type. I have myself found specimens referred by Mr. Scudder, a most competent entomologist, to two genera and five species, in a few decayed fossil stumps in Nova Scotia, and several others have been discovered in other parts of the world. It is not wonderful that animals like these, feeding on decayed vegetable matter, should have flourished in the luxuriant Sigillaria swamps. A few species of scorpions and spiders, very like those of the modern world, have been found in the coal measures, both in Europe and America; so that while we know of no enemy of the Devonian insects except the fishes, we know in addition to these in the Carboniferous the spiders and their allies, and the smaller reptiles or batrachians to be noticed in the sequel. With reference to the latter, it is a curious fact that one of the first fragments of a winged insect found in the coal-fields of America was a part of a head and some other remains contained in the coprolites or excrementitious matter of one of the smaller fossil reptiles. It is perhaps equally interesting that this head shows one of the compound facetted eyes as perfectly developed as those of any modern Neuropter, a group of insects remarkable even in the present world for their large and complex organs of vision. We may pause here to note that, just as in the Primordial we already have the Trilobites presenting all the modifications of which the type is susceptible, so in the Carboniferous we have in the case of the terrestrial articulates a similar fact—highly specialised forms like the beetles, the spiders, and the scorpions, already existing along with comprehensive forms like the millipedes. Let us formulate the law of creation which the Primordial trilobites, the Devonian fishes, and the Carboniferous club-mosses and insects have taught us: it is, that every new type rapidly attains its maximum of development in magnitude and variety of forms, and then remains stationary, or even retrogrades, in subsequent ages. We may connect this with other laws in the sequel.

In the coal measures we also meet, for the first time in our ascending progress, the land snails so familiar now in every part of the world, and which are represented by two little species found in the coal formation of Nova Scotia. The figures of these must speak for themselves; but the fact of their occurrence here and the mode of their preservation require some detailed mention. The great province of the Mollusks we have carried with us since we met with the Lingulæ in the Primordial, but all its members have been aquatic, and probably marine. For the first time, in the Carboniferous period, snails emerge from the waters, and walk upon the ground and breathe air; for, like the modern land snails, these creatures no doubt had air-sacks instead of gills. They come suddenly upon us—two species at once, and these representing two distinct forms of the snail tribe, the elongated and the rounded. They were very numerous. In the beds where they occur, probably thousands of specimens, more or less perfect, could be collected. Were they the first-born of land snails? It would be rash to affirm this, more especially since in all the coal-fields of the world no specimens have been found except at one locality in Nova Scotia;[N] and in all the succeeding beds we meet with no more till we have reached a comparatively modern time. Yet it is very unlikely that these creatures were in the coal period limited to one country, and that, after that period, they dropped out of existence for long ages, and then reappeared. Still it may have been so.

[N] Bradley has recently announced the discovery of other species in the coal-field of Illinois

THE TWO OLDEST LAND SNAILS.

Fig. 14.—Pupa Vetusta, Dawson.

(a) Natural size, (b) Enlarged, (c) Apex, enlarged, (d) Sculpture, magnified.

Fig. 15.—Conulus Priscus, Carpenter.

(a) Specimen enlarged, (b) Sculpture, magnified.

There are cases of geographical limitation quite as curious now. Here again another peculiarity meets us. If these are really the oldest land snails, it is curious that they are so small,—so much inferior to many of their modern successors even in the same latitudes. The climate of the coal period must have suited them, and there was plenty of vegetable food, though perhaps not the richest or most tender. There is no excuse for them in their outward circumstances. Why, then, unlike so many other creatures, do they enter on existence in this poor and sneaking way. We must here for their benefit modify in two ways the statement broadly made in a previous chapter, that new types come in under forms of great magnitude. First, we often have, in advance of the main inroad of a new horde of animals, a few insignificant stragglers as a sort of prelude to the rest—precursors intimating beforehand what is to follow. We shall find this to be the case with the little reptiles of the coal, and the little mammals of the Trias, preceding the greater forms which subsequently set in. Secondly, this seems to be more applicable in the case of land animals than in the case of those of the waters. To the waters was the fiat to bring forth living things issued. They have always kept to themselves the most gigantic forms of life; and it seems as if new forms of life entering on the land had to begin in a small way and took more time to culminate.

The circumstances in which the first specimens of Carboniferous snails and gally-worms were found are so peculiar and so characteristic of the coal formation, that I must pause here to notice them, and to make of them an introduction to the next group of creatures we have to consider. In the coal formation in all parts of the world it is not unusual, as stated already in a previous page, to find erect trees or stumps of trees, usually Sigillariæ, standing where they grew; and where the beds are exposed in coast cliffs, or road cuttings, or mines, these fossil trees can be extracted from the matrix and examined. They usually consist of an outer cylinder of coal representing the outer bark, while the space within, once occupied by the inner bark and wood, is filled with sandstone, sometimes roughly arranged in layers, the lowest of which is usually mixed with coaly matter or mineral charcoal derived from the fallen remains of the decayed wood, a kind of deposit which affords to the fossil botanist one of the best modes of investigating the tissues of these trees. These fossil stumps are not uncommon in the roofs of the coal-seams. In some places they are known to the miners as “coal pipes,” and are dreaded by them in consequence of the accidents which occur from their suddenly falling after the coal which supported them has been removed. An old friend and helper of mine in Carboniferous explorations had a lively remembrance of the fact that one of these old trees, falling into the mine in which he was working, had crushed his leg and given him a limp for life; and if he had been a few inches nearer to it would have broken his back.

The manner in which such trees become fossilized may be explained as follows:—Imagine a forest of Sigillariæ growing on a low flat. This becomes submerged by subsidence or inundation, the soil is buried under several feet of sand or mud, and the trees killed by this agency stand up as bare and lifeless trunks. The waters subside, and the trees rapidly decay, the larvæ of wood-boring insects perhaps aiding in the process, as they now do in the American woods. The dense coaly outer bark alone resists decomposition, and stands as a hollow cylinder until prostrated by the wind or by the waters of another inundation, while perhaps a second forest or jungle has sprung up on the new surface. When it falls, the part buried in the soil becomes an open hole, with a heap of shreds of wood and bark in the bottom. Such a place becomes a fit retreat for gally-worms and land-snails; and reptiles pursuing such animals, or pursued by their own enemies, or heedlessly scrambling among the fallen trunks, may easily fall into such holes and remain as prisoners. I remember to have observed, when a boy, a row of post-holes dug across a pasture-field and left open for a few days, and that in almost every hole one or two toads were prisoners. This was the fate which must have often befallen the smaller reptiles of the coal forests in the natural post-holes left by the decay of the Sigillariæ. Yet it may be readily understood that the combination of circumstances which would effect this result must have been rare, and consequently this curious fact has been as yet observed only in the coal formation of Nova Scotia; and in it only in one locality, and in this in one only out of more than sixty beds in which erect trees have been found. But these hollow trees must be filled up in order to preserve their contents; and as inundation and subsequent decay have been the grave-diggers for the reptiles, so inundations filled up their graves with sand, to be subsequently hardened into sandstone, burying up at the same time the newer vegetation which had grown upon the former surface. The idea that something interesting might be found in these erect stumps, first occurred to Sir C. Lyell and the writer while exploring the beautiful coast cliffs of Western Nova Scotia in 1851; and it was in examining the fragments scattered on the beach that we found the bones of the first Carboniferous reptile discovered in America, and the shell of the oldest known land snail.

These were not, however, the earliest known instances of Carboniferous reptiles. In 1841, Sir William Logan found footprints of a reptile at Horton Bluff, in Nova Scotia, in rocks of Lower Carboniferous age. In 1844, Von Dechen found reptilian bones in the coal-field of Saarbruck; and in the same year Dr. King found reptilian footprints in the Carboniferous of Pennsylvania. Like Robinson Crusoe on his desert island, we saw the footprints before we knew the animals that produced them; and the fact that there were marks on a slab of shale or sandstone that must have been made by an animal walking on feet, was as clear and startling a revelation of the advent of a new and higher form of life, as were the footprints of Man Friday. Within the thirty years since the discovery of the first slab of footprints, the knowledge of coal formation reptiles has grown apace. I can scarcely at present sum up exactly the number of species, but may estimate it at thirty-five at least. I must, however, here crave pardon of some of my friends for the use of the word reptile. In my younger days frogs and toads and newts used to be reptiles; now we are told that they are more like fishes, and ought to be called Batrachians or Amphibians, whereas reptiles are a higher type, more akin to birds than to these lower and more grovelling creatures. The truth is, that the old class Reptilia bridges over the space between the fishes and the birds, and it is in some degree a matter of taste whether we make a strong line at the two ends of it alone, or add another line in the middle. I object to the latter course, however, in the period of the world’s history of which I am now writing, since I am sure that there were animals in those days which were batrachians in some points and true reptiles in others; while there are some of them in regard to which it is quite uncertain whether they are nearer to the one group or the other. Although, therefore, naturalists, with the added light and penetration which they obtain by striding on to the Mesozoic and Modern periods, may despise my old-fashioned grovellers among the mire of the coal-swamps, I shall, for convenience, persist in calling them reptiles in a general way, and shall bring out whatever claims I can to justify this title for some of them at least.

Perhaps the most fish-like of the whole are the curious creatures from the coal measures of Saarbruck, first found by Yon Dechen, and which constitute the genus Archegosaurus. Their large heads, short necks, supports for permanent gills, feeble limbs, and long tails for swimming, show that they were aquatic creatures presenting many points of resemblance to the ganoid fishes with which they must have associated; still they were higher than these in possessing lungs and true feet, though perhaps better adapted for swimming than even for creeping.

From these creatures the other coal reptiles diverge, and ascend along two lines of progress, the one leading to gigantic crocodile-like animals provided with powerful jaws and teeth, and probably haunting the margins of the waters and preying on fishes; the other leading to small and delicate lizard-like species, with well-developed limbs, large ribs, and ornate horny scales and spines, living on land and feeding on insects and similar creatures.

Fig. 16.—RESTORATIONS OF BAPHETES, DENDRERPETON. HYLONOMUS, AND HYLERPETON, WITH CARBONIFEROUS PLANTS IN THE DISTANCE.

In the first direction we have a considerable number of species found in the Jarrow coal-field in Ireland, and described by Professor Huxley. Some of them were like snakes in their general form, others more like lizards. Still higher stand such animals as Baphetes and Eosaurus from the Nova Scotia coal-field and Anthracosaurus from that of Scotland. The style and habits of these creatures it is easy to understand, however much haggling the comparative anatomists may make over their bones. They were animals of various size, ranging from a foot to at least ten feet in length, the body generally lizard-like in form, with stout limbs and a flattened tail useful in swimming. Their heads were flat, stout, and massive, with large teeth, strengthened by the insertion and convolution of plates of enamel. The fore limbs were probably larger than the hind limbs, the better to enable them to raise themselves out of the water. The belly was strengthened by bony plates and closely imbricated scales, to resist, perhaps, the attacks of fishes from beneath, and to enable them without injury to drag their heavy bodies over trunks of trees and brushwood, whether in the water or on the land. Their general aspect and mode of life were therefore by no means unlike those of modern alligators; and in the vast swamps of the coal measures, full of ponds and sluggish streams swarming with fish, such creatures must have found a most suitable habitat, and probably existed in great numbers, basking on the muddy banks, surging through the waters, and filling the air with their bellowings. The most curious point about these creatures is, that while rigid anatomy regards them as allied in structure more to frogs and toads and newts than to true lizards, it is obvious to common sense that they were practically crocodiles; and even anatomy must admit that their great ribs and breastplates, and powerful teeth and limbs, indicate a respiration, circulation, and general vitality, quite as high as those of the proper reptiles. Hence, it happens that very different views are stated as to their affinities; questions into which we need not now enter, satisfied with the knowledge of the general appearance and mode of life of these harbingers of the reptilian life of the succeeding geological periods.

In the other direction, we find several animals of small size but better developed limbs, leading to a group of graceful little creatures, quite as perplexing with regard to affinities as those first mentioned, but tending towards the smaller lizards of the modern world. At the top of these I may place the genus Hylonomus from hollow fossil trees of Nova Scotia, of which two species are represented as restored in our illustration. In these restorations I have adhered as faithfully as possible to the proportions of parts as seen in my specimens. Imagine a little animal six or seven inches long, with small short head, not so flat as those of most lizards, but with a raised fore-head, giving it an aspect of some intelligence. Its general form is that of a lizard, but with the hind feet somewhat large, to aid it in leaping and standing erect, and long and flexible toes. Its belly is covered with bony scales, its sides with bright and probably coloured scale armour of horny consistency, and its neck and back adorned with horny crests, tubercles, and pendants. It runs, leaps, and glides through the herbage of the coal forests, intent on the pursuit of snails and insects, its eye glancing and its bright scales shining in the sun. This is a picture of the best known species of Hylonomus drawn from the life. Yet the anatomist, when he examines the imperfectly-ossified joints of its backbone, and the double joint at the back of its skull, will tell you that it is after all little better than a mere newt, an ass in a lion’s skin, a jackdaw with borrowed feathers, and that it has no right to have fine scales, or to be able to run on the land. It may be so; but I may plead in its behalf, that in the old coal times, when reptiles with properly-made skeletons had not been created, the next best animals may have been entitled to wear their clothes and to assume their functions as well. In short, functionally or officially, our ancient batrachians were reptiles; in point of rank, as measured by type of skeleton, they belonged to a lower grade. To this view of the case I think most naturalists will agree, and they will also admit that the progress of our views has been in this direction, since the first discovery of Carboniferous air-breathing vertebrates. In evidence of this I may quote from Professor Huxley’s description of his recently found species,[O] After noticing the prevalent views that the coal reptiles were of low organization, he says: “Discoveries in the Nova Scotia coal-fields first shook this view, which ceased to be tenable when the great Anthracosaurus of the Scotch coal-field was found to have well-ossified biconcave vertebrae.”

[O] Geological Magazine, vol. iii.

The present writer may, however, be suspected of a tendency to extend forms of life backward in time, since it has fallen to his lot to be concerned in this process of stretching backward in several cases. He has named and described the oldest known animal. He has described the oldest true exogen, and the oldest known pine-tree. He was concerned in the discovery of the oldest known land snails, and found the oldest millipedes. He has just described the oldest bituminous bed composed of spore-cases, and he claims that his genus Hylonomus includes the oldest animals which have a fair claim to be considered reptiles. Still this discovery of old things comes rather of fortune and careful search than of a desire to innovate; and a distinction should be drawn between that kind of novelty which consists in the development of new truths, and that which consists in the invention of new fancies, or the revival of old ones. There is too much of this last at present; and it would be a more promising line of work for our younger naturalists, if they would patiently and honestly question nature, instead of trying to extort astounding revelations by throwing her on the rack of their own imaginations.

We may pause here a moment to contemplate the greatness of the fact we have been studying the introduction into our world of the earliest known vertebrate animals which could open their nostrils and literally “breathe the breath of life.” All previous animals that we know, except a few Devonian insects, had respired in the water by means of gills or similar apparatus, Now we not only have the little land snails, with their imperfect substitutes for lungs, but animals which must have been able to draw in the vital air into capacious chambered lungs, and with this power must have enjoyed a far higher and more active style of vitality; and must have possessed the faculty of uttering truly vocal sounds. What wondrous possibilities unknown to these creatures, perhaps only dimly perceived by such rational intelligences as may have watched the growth of our young world, were implied in these gifts. It is one of the remarkable points in the history of creation in Genesis, that this step of the creative work is emphatically marked. Of all the creatures we have noticed up to this point, it is stated that God said, “Let the waters bring them forth”—but it is said that “God created” great reptiles (tanninim).[P] No doubt these “great tanninim” culminate in the succeeding Mesozoic age, but their first introduction dates as far back as the Carboniferous; and this introduction was emphatically a creation, as being the commencement of a new feature among living beings. What further differences may be implied in the formulæ, “Let the waters produce” and “God created,” we do not know; very probably he who wrote the words did not fully know. But if we could give a scientific expression to this difference, and specify the cases to which its terms apply, we might be able to solve one of the most vexed questions of biology.

[P] Not “whales,” as in our version.

Let us observe, however, that even here, where, if anywhere, we have actual creation, especial pains are taken to bridge over the gap, and to prevent any appearance of discontinuity in the work. The ganoid fishes of the coal period very probably had, like their modern congeners, well-developed air-bladders, serving to some extent, though very imperfectly, as lungs. The humbler and more aquatic reptiles of the period retained the gills, and also some of the other features of the fishes; so that, like some modern creatures of their class, they stood, as to respiration, on two stools, and seemed unwilling altogether to commit themselves to the new mode of life in the uncongenial element of air. Even the larger and more lizard-like of the coal reptiles may—though this we do not certainly know, and in some cases there are reasons for doubting it—have passed the earliest stage of their lives in the water as gilled tadpoles, in the manner of our modern frogs. Thus at the very point where one of the greatest advances of animal life has its origin, we have no sudden stop, but an inclined plane; and yet, as I have elsewhere endeavoured to show by arguments which cannot be repeated here,[Q] we have not a shadow of reason to conclude that, in the coal period, fishes were transmuted into reptiles.

[Q] “Air-breathers of the Coal Period,” p. 77.

But the reader may be wearied with our long sojourn in the pestilential atmosphere of the coal swamps, and in the company of their low-browed and squalid inhabitants. Let us turn for a little to the sea, and notice the animal life of the great coral reefs and shell beds preserved for us in the Carboniferous limestone. Before doing so, one point merits attention. The coal formation for the first time distinctly presents to us the now familiar differences in the inhabitants of the open sea and those of creeks, estuaries and lakes. Such distinctions are unknown to us in the Silurian. There all is sea. They begin to appear in the Devonian, in the shallow fish-banks and the Anodon-like bivalves found with fossil plants. In the coal period they become very manifest. The animals found in the shales with the coal are all, even the aquatic ones, distinct from those of the open seas of the period. Some of them may have lived in salt or brackish water, but not in the open sea. They are creatures of still and shallow waters. It is true that in some coal-fields marine beds occur in the coal measures with their characteristic fossils, but these are quite distinct from the usual animal remains of the coal-fields, and mark occasional overflows of the sea, owing to subsidence of the land. It is important to notice this geographical difference, marking the greater specialisation and division of labour, if we may so speak, that was in the process of introduction.

The sea of the Carboniferous period presented in the main similar great groups of animals to those of the Devonian, represented however by different species. We may notice merely some of the salient points of resemblance or difference. The old types of corals continue in great force; but it is their last time, for they rapidly decay in the succeeding Permian and disappear. The Crinoids are as numerous and beautiful as in any other period, and here for the first time we meet with the new and higher type of the sea-urchin, in large and beautiful species. One curious group, that of the Pentremites, a sort of larval form, is known here alone. Among the lamp-shells we may note, as peculiarly and abundantly Carboniferous, those with one valve very convex and the other very concave and anchored in the mud by long spines instead of a peduncle attached to stones and rocks.[R] There are many beautiful shells allied to modern scallops, and not a few sea-snails of various sorts. The grand Orthoceratites of the Silurian diminish in size preparatory to their disappearance in the Permian, and the more modern type of Nautilus and its allies becomes prevalent. Among the Crustaceans we may notice the appearance of the Limulus, or king-crab, of which the single little species described by Woodward from the Upper Silurian may be regarded as merely a prophecy. It is curious that the Carboniferous king-crabs are very small, apparently another case of a new form appearing in humble guise; but as the young of modern king-crabs haunt creeks and swampy flats, while the adults live in the sea, it may be that only the young of the Carboniferous species are yet known to us, the specimens found being mostly in beds likely to be frequented by the young rather than by the full-grown individuals.

[R] The Productidæ.

The old order of the Trilobites, which has accompanied us from Primordial times, here fails us, and a few depauperated species alone remain, the sole survivors of their ancient race—small, unornamented, and feeble representatives of a once numerous and influential tribe. How strange that a group of creatures so numerous and apparently so well adapted to conditions of existence which still continue in the sea, should thus die out, while the little bivalved crustaceans, which began life almost as far back and lived on the same sea-floors with the Trilobites, should still abound in all our seas; and while the king-crabs, of precisely similar habits with the Trilobites, should apparently begin to prosper. Equally strange is the fate of the great swimming Eurypterids which we saw in the Devonian. They also continue, but in diminished force, in the Carboniferous, and there lay down for ever their well-jointed cuirasses and formidable weapons, while a few little shrimp-like creatures, their contemporaries, form the small point of the wedge of our great tribes of squillas and crabs and lobsters. Some years ago the late lamented palæontologist, Salter, a man who scarcely leaves his equal in his department, in conjunction with Mr. Henry Woodward, prepared a sort of genealogical chart of the Crustacea on which these facts are exhibited. Some new species have since been discovered, and a little additional light about affinities has been obtained; but taken as it stands, the history of the Crustacea as there shown in one glance, has in it more teaching on the philosophy of creation than I have been able to find in many ponderous quartos of tenfold its pretensions. Had Salter been enabled, with the aid of other specialists like Woodward, to complete similar charts of other classes of invertebrate animals, scientific palaeontology in England would have been further advanced than it is likely to be in the next ten years.

To return to our Trilobites: one of the most remarkable points in their history is their appearance in full force in the Primordial. In these rocks we have some of the largest in size—some species of Paradoxides being nearly two feet long, and some of the very smallest. We have some with the most numerous joints, others with the fewest; some with very large tails, others with very small; some with no ornamentation, others very ornate; some with large eyes, others with none that have been made out, though it is scarcely probable that they were wholly blind. They increased in numbers and variety through the Silurian and Devonian, and then suddenly drop off at the end of the Lower Carboniferous. Throughout their whole term of existence they kept rigidly to that type of the mud-plough which the king-crab still retains, and which renders the anterior extremity so different from that of the ordinary Crustacea. They constitute one of the few cases in which we seem to see before us the whole history of an animal type; and the more we look into that history, the more do we wonder at their inscrutable introduction, the unity and variety mingled in their progress, and their strange and apparently untimely end. I have already referred (page 95) to the use which Barrande makes of this as an argument against theories of evolution; but must refer to his work for the details.

One word more I must say before leaving their graves. I have reason to believe that they were not only the diggers of the burrows, and of the ladder-tracks and pitted tracks[S] of the Silurian and Primordial, but that with the strokes of their rounded or spinous tails, the digging of their snouts, and the hoe-work of their hard upper lips, or Hypostomes, they made nearly all those strange marks in the Primordial mud which have been referred to fucoids, and even to higher plants. The Trilobites worked over all the mud bottoms of the Primordial, even in places where no remains of them occur, and the peculiarities of the markings which they left are to be explained only by a consideration of the structures of individual species.

[S] Climactichnites and Protichnites.

I had almost lost sight of the fishes of the Carboniferous period, but after saying so much of those of the Devonian, it would be unfair to leave their successors altogether unnoticed. In the Carboniferous we lose those broad-snouted plate-covered species that form so conspicuous a feature in the Devonian; and whatever its meaning, it is surely no accident that these mud-burrowing fishes should decay along with those crustacean mud-burrowers, the Trilobites. But swarms of fishes remain, confined, as in the Devonian, wholly to the two orders of the Gar-fishes (Ganoids) and the sharks (Placoids). In the former we have a multitude of small and beautiful species haunting the creeks and ponds of the coal swamps, and leaving vast quantities of their remains in the shaly and even coaly beds formed in such places. Such were the pretty, graceful fishes of the genera Palæoniscus and Amblypterus. Pursuing and feeding on these were larger ganoids, armed with strong bony scales, and formidable conical or sharp-edged teeth. Of these were Rhizodus and Acrolepis. There were besides multitudes of sharks whose remains consist almost wholly of their teeth and spines, their cartilaginous skeletons having perished. One group was allied to the few species of modern sharks whose mouths are paved with flat teeth for crushing shells. These were the most abundant sharks of the Carboniferous—slow and greedy monsters, haunting shell banks and coral reefs, and grinding remorselessly all the shell-fishes that came in their way. There were also sharks furnished with sharp and trenchant teeth, which must have been the foes of the smaller mailed fishes, pursuing them into creeks and muddy shallows; and if we may judge from the quantity of their remains in some of these places, sometimes perishing in their eager efforts. On the whole, the fishes of the Carboniferous were, in regard to their general type, a continuation of those of the Devonian, but the sharks and the scaly ganoids were relatively more numerous. They differed from our modern fishes in the absence of the ordinary horny-scaled type to which all our more common fishes belong, and in the prevalence of that style of tail which has been termed “heterocercal,” in which the continuation of the backbone forms the upper lobe of the tail, a style which, if we may judge from modern examples, gives more power of upward and downward movement, and is especially suitable to fishes which search for food only at the bottom, or only above the surface of the waters.

Most reluctantly I must here leave one of the most remarkable periods of the world’s history, and reserve to our next chapter the summation of the history of the older world of life in its concluding stage, the Permian.

CHAPTER VII.

THE PERMIAN AGE AND CLOSE OF THE PALÆOZOIC.

The immense swamps and low forest-clad plains which occupied the continental areas of the Northern Hemisphere, and which we now know extended also into the regions south of the equator, appear at the close of the Carboniferous age to have again sunk beneath the waves, or to have relapsed into the condition of sand and gravel banks; for a great thickness of such deposits rests on the coal measures and constitutes the upper coal formation, the upper “barren measures” of the coal-miners. There is something grand in the idea of this subsidence of a world of animal and vegetable life beneath the waters. The process was very slow, so slow that at first vegetable growth and deposition of silt kept pace with it; and this is the reason of the immense series of deposits, in some places nearly 15,000 feet thick, which inclose or rest upon the coal beds; but at length it became more rapid, so that forests and their inhabitants perished, and the wild surf drifted sand and pebbles over their former abodes. So the Carboniferous world, like that of Noah, being overflowed with water, perished. But it was not a wicked world drowned for its sins, but merely an old and necessarily preliminary system, which had fully served its purpose; and, like the stubble of last year, must be turned under by the plough that it may make way for a new verdure. The plough passed over it, and the winter of the Permian came, and then the spring of a new age.

The Permian and the succeeding Triassic are somewhat chilly and desolate periods of the earth’s history. The one is the twilight of the Palæozoic day, the other is the dawn of the Mesozoic. Yet to the philosophical geologist no ages excel them in interest. They are times of transition, when old dynasties and races pass away and are replaced by new and vigorous successors, founding new empires and introducing new modes of life and action.

Three great leading points merit our attention in entering on the Permian age. The first is the earth-movements of the period. The second is the resulting mineral characteristics of the deposits formed. The third is the aspect of the animal and vegetable life of this age in their relation more especially to those which preceded.

DIAGRAM OF FOLDINGS OF THE CRUST IN THE PERMIAN PERIOD.
(The vertical scale of heights and depressions exaggerated more than six times.)
The lower figure shows a portion of folded strata in the Appalachians—after Rogers.

With respect to the first point above named, the earth’s crust was subjected in the Permian period to some of the grandest movements which have occurred in the whole course of geologic time, and we can fix the limits of these, in Europe and America at least, with some distinctness. If we examine the Permian rocks in England and Germany, we shall find that everywhere they lie on the upturned edges of the preceding Carboniferous beds. In other words, the latter have been thrown into a series of folds, and the tops of these folds have been more or less worn away before the Permian beds were placed on them. But if we pass on to the eastward, in the great plain between the Volga and the Ural mountains, where, in the “ancient kingdom of Perm,” the greatest known area of these rocks is found, an area equal in extent to twice that of France, and which Sir R. I. Murchison, who first proposed the name, took as the typical district, we find, on the contrary, that the Permian and Carboniferous are conformable to one another. If now we cross the Atlantic and inquire how the case stands in America, we shall find it precisely the same. Here the great succession of earth-waves constituting the Appalachian Mountains rises abruptly at the eastern edge of the continent, and becomes flatter and flatter, until, in the broad plains west of the Mississippi, the Permian beds appear, as in Russia, resting upon the Carboniferous so quietly that it is not always easy to draw a line of separation between them. As Dana has remarked, we find at the western side of Europe and the eastern side of America, great disturbances inaugurating the Permian period; and in the interior of both, in the plains between the Volga and the Ural in one, and between the Mississippi and Rocky Mountains in the other, an entire absence of these disturbances. The main difference is, that in eastern America the whole Carboniferous areas have apparently been so raised up that no Permian was deposited on them, while in Europe considerable patches of the disturbed areas became or remained submerged. Another American geologist has largely illustrated the fact that the movements which threw up the Appalachian folds were strongest to the eastward, and that the ridges of rock are steepest on their west sides, the force which caused them acting from the direction of the sea. It seems as if the Atlantic area had wanted elbow-room, and had crushed up the edges of the continents next to it. In other words, in the lapse of the Palæozoic ages the nucleus of the earth had shrunk away from its coating of rocky layers, which again collapsed into great wrinkles.

Such a process may seem difficult of comprehension. To understand it we must bear in mind some of its conditions. First, the amount of this wrinkling was extremely small relatively to the mass of the earth. In the diagram on page 162 it is greatly exaggerated, yet is seen to be quite insignificant, however gigantic in comparison with microscopic weaklings like ourselves. Secondly, it was probably extremely slow. Beds of solid rock cannot be suddenly bent into great folds without breaking, and the abruptness of some of the folds may be seen from our figure, copied from Rogers (page 162), of some of the foldings of the Appalachian Mountains. Thirdly, the older rocks below the Carboniferous and the Devonian must have been in a softened and plastic state, and so capable of filling up the vacancies left by the bending of the hard crust above. In evidence of this, we have in the Lower Permian immense volcanic ejections—lavas and other molten rocks spewed out to the surface from the softened and molten masses below. Fourthly, the basin of the Atlantic must have been sufficiently strong to resist the immense lateral pressure, so that the yielding was all concentrated on the weaker parts of the crust near the old fractures at the margins of the great continents. In these places also, as we have seen in previous papers, the greatest thickness of deposits had been formed; so that there was great downward pressure, and probably, also, greater softening of the lower part of the crust. Fifthly, as suggested in a previous chapter, the folding of the earth’s crust may have resulted from the continued shrinkage of its interior in consequence of cooling, leading after long intervals to collapse of the surface. Astronomers have, however, suggested another cause. The earth bulges at the equator, and is flattened at the poles in consequence of, or in connection with, the swiftness of its rotation; but it has been shown that the rotation of the earth is being very gradually lessened by the attraction of the moon.[T] Pierce has recently brought forward the idea[U] that this diminution of rotation, by causing the crust to subside in the equatorial regions and expand in the polar, might produce the movements observed; and which, according to Lesley, have amounted in the whole course of geological time to about two per cent, of the diameter of our globe. We thus have two causes, either of which seems sufficient to produce the effect.

[T] Sir William Thomson, who quotes Adams and Delaunay.

[U] “Nature,” February, 1871.

Viewed in this way, the great disturbances at the close of the Palæozoic period constitute one of the most instructive examples in the whole history of the earth of that process of collapse to which the crust was subject after long intervals, and of which no equally great instance occurs except at the close of the Laurentian and the close of the Mesozoic. The mineral peculiarities of the Permian are also accounted for by the above considerations. Let us now notice some of these. In nearly all parts of the world the Permian presents thick beds of red sandstone and conglomerate as marked ingredients. These, as we have already seen, are indications of rapid deposition accompanying changes of level. In the Permian, as elsewhere, these beds are accompanied by volcanic rocks, indicating the subterranean causes of the disturbances. Again, these rocks are chiefly abundant in those regions, like Western Europe, where the physical changes were at a maximum. Another remarkable feature of the Permian rocks is the occurrence of great beds of magnesian limestone, or dolomite. In England, the thick yellow magnesian limestone, the outcrop of which crosses in nearly a straight line through Durham, Yorkshire, and Nottingham, marks the edge of a great Permian sea extending far to the eastward. In the marls and sandstones of the Permian period there is also much gypsum. Now, chemistry shows us that magnesian limestones and gypsums are likely to be deposited where sea water, which always contains salts of magnesia, is evaporating in limited or circumscribed areas into which carbonate of lime and carbonate of soda are being carried by streams from the land or springs from below;[V] and it is also to be observed that solutions of sulphuric acid, and probably also of sulphate of magnesia, are characteristic products of igneous activity. Hence we find in various geological periods magnesian limestones occurring as a deposit in limited shallow sea basins, and also in connection with volcanic breccias. Now these were obviously the new Permian conditions of what had once been the wide flat areas of the Carboniferous period. Still further, we find in Europe, as characteristic of this period, beds impregnated with metallic salts, especially of copper. Of this kind are very markedly the copper slates of Thuringia. Such beds are not, any more than magnesian limestones, limited to this age; but they are eminently characteristic of it. To produce them it is required that water should bring forth from the earth’s crust large quantities of metallic salts, and that these should come into contact with vegetable matters in limited submerged areas, so that sulphates of the metals should be deoxidized into sulphides. A somewhat different chemical process, as already explained, was very active in the coal period, and was connected with the production of its iron ores; but, in the Permian, profound and extensive fractures opened up the way to the deep seats of copper and other metals, to enrich the copper slate and its associated beds. It is also to be observed that the alkaline springs and waters which contain carbonate of soda, very frequently hold various metallic salts; so that where, owing to the action of such waters, magnesian limestone is being deposited, we may expect also to find various metallic ores.

[V] Hunt, “Silliman’s Journal,” 1859 and 1863.

Let us sum up shortly this history. We have foldings of the earth’s crust, causing volcanic action and producing limited and shallow sea-basins, and at the same time causing the evolution of alkaline and metalliferous springs. The union of these mechanical and chemical causes explains at once the conglomerates, the red sandstones, the trap rocks, the magnesian limestones, the gypsum, and the metalliferous beds of the Permian. The same considerations explain the occurrence of similar deposits in various other ages of the earth’s history; though, perhaps, in none of these were they so general over the Northern Hemisphere as in the Permian.

From the size of the stones in some of the Permian conglomerates, and their scratched surfaces, it has been supposed that there were in this period, on the margins of the continents, mountains sufficiently high to have snow-clad summits, and to send down glaciers, bearing rocks and stones to the sea, on which may have floated, as now in the North Atlantic, huge icebergs.[W] This would be quite in accordance with the great elevation of land which we know actually occurred; and the existence of snow-clad mountains along with volcanoes would be a union of fire and frost of which we still have examples in some parts of the earth’s surface, and this in proximity to forms of vegetable life very similar to those which we know existed in the Permian.

[W] Ramsay has ably illustrated this in the Permian conglomerates of England.

With the exception of a few small and worthless beds in Russia, the Permian is not known to contain any coal. The great swamps of the coal period had disappeared. In part they were raised up into rugged mountains. In part they were sunken into shallow sea areas. Thus, while there was much dry land, there was little opportunity for coal production, or for the existence of those rank forests which had accumulated so much vegetable matter in the Carboniferous age. In like manner the fauna of the Permian waters is poor. According to Murchison, the Permian limestones of Europe have afforded little more than one-third as many species of fossils as the older Carboniferous. The fossils themselves also have a stunted and depauperated aspect, indicating conditions of existence unfavourable to them. This is curiously seen in contrasting Davidson’s beautiful illustrations of the British Lamp-shells of the Permian and Carboniferous periods. Another illustrative fact is the exceptionally small size of the fossils even in limestones of the Carboniferous period when these are associated with gypsum, red sandstones, and magnesian minerals; as, for instance, those of some parts of Nova Scotia. In truth, the peculiar chemical conditions conducive to the production of magnesian limestones and gypsum are not favourable to animal life, though no doubt compatible with its existence. Hence the rich fauna of the Carboniferous seas died out in the Permian, and was not renewed; and the Atlantic areas of the period are unknown to us. They were, however, probably very deep and abrupt in slope, and not rich in life. This would be especially the case if they were desolated by cold ice-laden currents.

During the Permian period there was in each of our continental areas a somewhat extensive inland sea. That of Western America was a northward extension of the Gulf of Mexico. That of Eastern Europe was a northward extension of the Euxine and Caspian. In both, the deposits formed were very similar—magnesian limestones, sandstones, conglomerates, marls, and gypsums. In both, these alternate in such a way as to show that there were frequent oscillations of level, producing alternately shallow and deep waters. In both, the animal remains are of similar species, in many instances even identical. But in the areas intervening between these sea basins and the Atlantic the conditions were somewhat different. In Europe the land was interrupted by considerable water areas, not lakes, but inland sea basins; sometimes probably connected with the open sea, sometimes isolated. In these were, deposited the magnesian limestone and its associated beds in England, and the Zechstein and Rotheliegende with their associates in Germany. In America the case was different. In all that immense area which extends from the Atlantic to the plains east of the Mississippi, we know no Permian rocks, unless a portion of those reckoned as Upper Carboniferous, or Permo-carboniferous in Northern Nova Scotia, and Prince Edward Island, should be included in this group. If such existed, they may possibly be covered up in some places by more modern deposits, or may have been swept away by denudation in the intervening ages; but even in these cases we should expect to find some visible remains of them. Their entire absence would seem to indicate that a vast, and in many parts rugged and elevated, continent represented North America in the Permian period. Yet if so, that great continent is an absolute blank to us. We know nothing of the animals or plants which may have lived on it, nor do we even know with certainty that it had active volcanoes, or snow-clad mountains sending down glaciers.

Our picture of the Permian World has not been inviting, yet in many respects it was a world more like that in which we live than was any previous one. It certainly presented more of variety and grand physical features than any of the previous ages; and we might have expected that on its wide and varied continents some new and higher forms of life would have been introduced. But it seems rather to have been intended to blot out the old Palæozoic life, as an arrangement which had been fully tried and served its end, preparatory to a new beginning in the succeeding age.

Still the Permian has some life features of its own, and we must now turn to these. The first is the occurrence here, not only of the representatives of the great Batrachians of the coal period, but of true reptiles, acknowledged to be such by all naturalists. The animals of the genus Protorosaurus, found in rocks of this age both in England and Germany, were highly-organised lizards, having socketed teeth like those of crocodiles, and well-developed limbs, with long tails, perhaps adapted for swimming. They have, however, biconcave vertebras like the lizard-like animals of the coal already mentioned, which, indeed, in their general form and appearance, they must have very closely resembled. The Protorosaurs were not of great size; but they must have been creatures of more stately gait than their Carboniferous predecessors, and they serve to connect them with the new and greater reptiles of the next period.

Another interesting feature of the Permian is its flora, which, in so far as known, is closely related to that of the coal period, though the species are regarded as different; some of the forms, however, being so similar as to be possibly identical. In a picture of the Permian flora we should perhaps place in the foreground the tree-ferns, which seem to have been very abundant, and furnished with dense clusters of aërial roots to enable them to withstand the storms of this boisterous age. The tree-ferns, now so plentiful in the southern hemisphere, should be regarded as one of the permanent vegetable institutions of our world—those of the far-back Lower Devonian, and of all intervening ages up to the present day, having been very much alike. The great reed-like Calamites have had a different fate. In their grander forms they make their last appearance in the Permian, where they culminate in great ribbed stems, sometimes nearly a foot in diameter, and probably of immense height. The brakes of these huge mares'-tails which overspread the lower levels of the Permian in Europe, would have been to us what the hayfields of Brobdingnag were to Gulliver. The Lepidodendra also swarmed, though in diminished force; but the great Sigillarise of the coal are absent, or only doubtfully present. Another feature of the Permian woods was the presence of many pine-trees different in aspect from those of the coal period. Some of these are remarkable for their slender and delicate branches and foliage.[X] Others have more dense and scaly leaves, and thick short cones.[Y] Both of these styles of pines are regarded as distinct, on the one hand, from those of the coal formation, and on the other from those of the succeeding Trias. I have shown, however, many years ago, that in the upper coal formation of America there are branches of pine-trees very similar to Walchia, and, on the other hand, the Permian pines are not very remote in form and structure from some of their modern relations. The pines of the first of the above-mentioned types (Walchia) may indeed be regarded as allies of the modern Araucarian pines of the southern hemisphere, and of the old conifers of the Carboniferous. Those of the second type (Ulmannia) may be referred to the same group with the magnificent Sequoias or Redwoods of California.

[X] Walchia.

[Y] Ulmannia.

It is a curious indication of the doubts which sometimes rest on fossil botany, that some of the branches of these Permian pines, when imperfectly preserved, have been described as sea-weeds, while others have been regarded as club-mosses. It is true, however, that the resemblance of some of them to the latter class of plants is very great; and were there no older pines, we might be pardoned for imagining in the Permian a transition from club-mosses to pines. Unfortunately, however, we have pines nearly as far back in geological time as we have club-mosses; and, in so far as we know, no more like the latter than are the pines of the Permian, so that this connection fails us. In all probability the Permian forests are much less perfectly known to us than those of the coal period, so that we can scarcely make comparisons. It appears certain, however, that the Permian plants are much more closely related to the coal plants than to those of the next succeeding epoch, and that they are not so much a transition from the one to the other as the finishing of the older period to make way for the newer.

But we must reserve some space for a few remarks on the progress and termination of the Palæozoic as a whole, and on the place which it occupies in the world’s history. These remarks we may group around the central question, What is the meaning or value of an age or period in the history of the earth, as these terms are understood by geologists? In most geological books terms referring to time are employed very loosely. Period, epoch, age, system, series, formation, and similar terms, are used or abused in a manner which only the indefiniteness of our conceptions can excuse.

A great American geologist[Z] has made an attempt to remedy this by attaching definite values to such words as those above mentioned. In his system the greater divisions of the history were “Times:” thus the Eozoic was a time and the Palæozoic was a time. The larger divisions of the times are “Ages:” thus the Lower and Upper Silurian, the Devonian, and the Carboniferous are ages, which are equivalent in the main to what English geologists call Systems of Formations. Ages, again, may be divided into “Periods:” thus, in the Upper Silurian, the Ludlow of England, or Lower Helderberg of America, would constitute a period. These periods may again be divided into “Epochs,” which are equivalent to what English geologists call Formations, a term referring not directly to the time elapsed, but to the work done in it. Now this mode of regarding geological time introduces many thoughts as to the nature of our chronology and matters relating to it. A “time” in geology is an extremely long time, and the Palæozoic was perhaps the longest of the whole. By the close of the Palæozoic nine-tenths of all the rocks we know in the earth’s crust were formed. At least this is the case if we reckon mere thickness. For aught that we know, the Eozoic time may have accumulated as much rock as the Palæozoic; but leaving this out of the question, the rocks of the Palæozoic are vastly thicker than those of the Mesozoic and Cainozoic united. Thus the earth’s history seems to have dragged slowly in its earlier stages, or to have become accelerated in its latter times. To place it in another point of view, life changes were greater relatively to merely physical changes in the later than in the earlier times.

[Z] Dana.