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.

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 then 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 then 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 then at present, the formation of such deposits, probably more widely spread then 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.

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 equaling 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 then 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 then 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 then 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 then 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 then 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.