2. The probable duration of life in the different epochs. The geologist will tell us not to look at one but at the various families, of all kinds and of all habits, which his science has brought to light, and so many of whose remains he has disinterred from the earth. Every formation abounds with them. They flourished through every epoch. The epochs are many. The tribes which existed and perished in them are many. To allow time for the coming in and the going out, and the fulfillment of their various destinies, what an untold, incalculable amount of ages must have elapsed! Now, give the millions of years supposed, and the wonder some may not hesitate to confess is, that there are so few, and not so many, of the former creatures of the earth which have re-appeared in our geological catalogues. The fossil regions of Great Britain, an epitome of the world, have been well explored, and the statement of fact stands nearly as follows:—Leaving out of consideration all the shelly and lime-building tribes, the numbers of the other families of animals hitherto found and described are, in the various groups of the silurian system, eight genera of only one order of fishes; in the devonian, of two orders, there are under forty genera, and not many more species of fishes, in the carboniferous, of three orders, there are about fifty genera, and a hundred species of fishes; in the permian and triassic, of three orders, there are twenty genera, and fifty species of fishes and reptiles; in the oolitic, of four orders, there are sixty genera, and two hundred and twenty species of fishes, reptiles, and mammals; in the wealden, there are, of three orders, twenty-five genera, and thirty-eight species of fishes and reptiles; in the cretaceous, of six orders, there are fifty genera, and eighty species of fishes, reptiles, and birds; in the tertiaries, of seven orders, the genera are about one hundred and fifty, and two hundred and twenty species of fishes, reptiles, birds, and mammals: thus making in all about four hundred genera, and seven hundred species of the larger families of living creatures during the whole currency of the geological epochs. The current epoch contains, exclusive of microscopic organisms, nearly two millions of species of vegetable and animal bodies existing on the terraqueous globe; and of which there are about eight thousand species of fish alone existing in our present seas.
When we take, instead of Great Britain, the whole explored geological field of the world, the result, so far as the argument is concerned, will be strengthened, not weakened. The formations of other lands are simply, with slight variations, a repetition of our own. The same genera of animals are everywhere prevalent. The specific types are likewise in many instances identical. The silurian organisms of Russia are so like those in our own island, that “no English geologist,” says Murchison, “acquainted with the organic contents of the Wenlock limestone, can view the Calymena Blumenbachii, C. macrophthalma, C. variolaria, and other Trilobites associated with the Leptœna depressa, L. euglypha, Terebratula reticularis, and many corals most familiar to him, without at once recognizing in the upper strata the distinct representative of that British formation.” Various other fossiliferous identities are farther alluded to, when it is added—“In taking leave of Scandinavia, we must specially advert to the close relations which exist between its lower and upper silurian groups, and those of Great Britain and distant parts of the world. Of 133 silurian fossils which we brought back or noted on the spot, at least eighty-four are British, and from twenty-five to twenty-seven are North American species. In this comparison the identity of the upper silurian groups of the Baltic and Great Britain is, indeed, most surprising; for, among seventy-four Scandinavian species, upward of sixty are common to the strata of this age in both countries, and of these, fifteen to sixteen species are also found in the upper silurian rocks of America.” The devonian fossils are equally striking in their resemblances and extensive geographical distribution. Similar representatives are detected, and still more abundantly, in the carboniferous formation—universal specific types of the fauna of the epoch. One remarkable instance has been stated—upon the authority of M. L. Von Buch—that the Leptœna lata, so typical of the silurian rocks of Britain, is specifically the same with the Leptœna sarcinulata, which is no less prevalent in the Russian carboniferous strata, and continued even throughout its uppermost members. Our field of review, therefore, contains a fair proportion of the various fossils of the world, specific and generic. The formations lying before us throughout our base-line, give a true indication of the state and conditions of life during the several epochs, while in number and variety of individual forms they are above the average.
Need it then be urged, that no such incalculable cycles of ages would be required for the whole of this catalogue of animals fulfilling in their several epochs their allotted destiny upon the earth? Compared with the mass of inorganic matter in which they are entombed, their relics are literally as nothing. Only here and there, of certain classes, at remote intervals often, there is a fossil or its impression. And so entire and well-preserved are these organisms, that we have reason to presume there has been no great obliteration, absorption, or utter waste of the races to which they belonged. On the contrary, as their distribution is so persistent in their respective formations throughout the globe,—the same genera and species being common to the four quarters of the world,—the presumption is, that specimens of nearly all the tribes that ever dwelt on the earth or swarmed in its waters have been handed down to us; and thus the number of the actual relics found becomes, as it were, a chronometer or measure of the ages during which they subsisted.
Look again at the demands of geology. Upward of sixteen millions of years[14] are supposed to have elapsed since the creation of life upon the earth. The lowest of the rocks, in which that life has found its grave, have been reached. Their contents, upward, have been examined and catalogued. How many generations of animals must have subsisted within that period? How many individual skeletons must have been entombed and preserved, seeing that things of the filmiest texture, plants and animals, have been inclosed and handed down to us entire? Quadruple the ages of every one of the existing denizens of sea and land, and still, what countless millions of generations, succeeding each other, have lived and died during the eras that were to run? Geology presents us with her list, her whole lengthened organic roll, of scarcely four hundred generic, and less than eight hundred specific forms, gathered out of all the past cemeteries of the dead. The cemeteries themselves, of such vast walls and dimensions, may, according to the present mordant powers of the elements and the capacity of rivers for the transport of mud, have required the calculations usually assigned for their erection. But where, the question will ever recur, where is there anything like a corresponding amount of animal exuviæ apart from the calcareous supplies, to be found in the successive formations, conforming in any approximation to the existing powers and capacities of parturient nature? The fossil remains, inclosed from the beginning to the end of the inconceivable cycles of time, are the remains only of a few great families: their skeletons are admirably preserved, or their casts are minutely and accurately engraven on the rock; and do they not look as if they were the identical individuals which rose in the dawn and were buried in the setting of their own geological epoch!
If we go still farther into details, the results will be found startling enough. Let us select one of the periods, the old red sandstone, for illustrating our views. The period assigned for this formation embraces a term of about, we shall suppose, according to the geological distribution of time, a million or two of years. This formation consists of three great subdivisions, every one of which contains their distinct specific forms, and hence their separation into the lower, middle, and upper groups. This was pre-eminently the fish epoch—finners which roamed in undisturbed possession of every sea on the surface of the globe. Dropping into the waters, and speedily silted up in the sands, the skeletons were in the best of all possible circumstances for preservation; and accordingly, the specimens of the period constitute the wonder of the geologist, for their enameled freshness and perfect outline of figure. The productiveness of fish is prodigious, the cod-fish multiplying at the rate of three millions and a-half, mackerel at about half a million, and most of the other tribes at a corresponding high ratio. Count now how many generations, of every one of the species of the separate groups of the old red sandstone series, would exist and multiply during a period of so many hundred thousand years. The modern epoch and its breeders have scarcely reached their six thousand. When six times six have been added, and sixty times more have been added to these, they will still be a third short of the term allotted to the favored denizens of the olden time. And where, amidst the well-protected few that have yielded up their remains, are the traces of the myriads upon myriads that perished and were buried along with them? To the genus Homo, the head of creation, few think of the earth, as it now is, being the abode for periods reckoned by millions of years. Nay, within his as yet brief period, how many of his cotemporaries have already passed from the stage, extirpated, many of them, by his own direct agency? The dodo, and his fellow islander the solitaire, and other brevipennate birds,—probably, too, the elk and the urus,—certainly from this island the beaver, the wolf, and the bear, and just as certainly, at no distant day, the extinction of many other races will follow in the onward progress of civilization. But as now, so in all past ages, superior power, or a more dextrous instinct, have led to their extirpation. Their destiny was fulfilled, and the race perished. And as we are reasoning upon the known laws of nature, whence the geologist only seeks a footing for his vast cycles of time, so, we venture to affirm, is he bound to abide by the test of his own selection, and to read therein the terms of life granted to the families of earth. The modern epoch shows the outgoing of genera as well as of species within the limited compass of a few thousand years—gives reasonable indications of the probable extinction, speedily and at no distant period, of hundreds of others,—these families possessed, all of them, of as enduring structures, and of higher types of existence, than those of the older epochs,—and, therefore, upon every fair ground of analogy, are we justified in concluding that there can be no such diversity of ages, under one and the same system of nature, as that of hundreds of thousands of years to the living tribes of earth.
When such premises are made the grounds of such inferences, and, again, when the geologist reiterates the statement that these great periods of time correspond wonderfully with the gradual increase of animal life, and the successive creation and extinction of numberless orders of being, and with the incredible quantity of organic remains buried in the crust of the earth, we have just to remind him that betwixt great periods of time, and the gradual increase of animal life, there is no necessary connection. However long and indefinite the time connected with the rocky formations, certain it is that the successive organic tribes were created within a period that admits, and can admit, of no calculation whatever, not even of any analogical illustration from experience or the known laws of nature. The species, however numerous, of every epoch were called at once into being, not gradually but instantly, by the fiat of an all-creative act. Their multiplication and increase depended upon the law of their nature; but how long they were to be privileged to multiply, in one unvarying specific form, according to that law, is a point that comes legitimately within the range of experience and the calculations of existing life. Let not things which differ, therefore, be mixed together. The organic and the inorganic types, in the act of formation, cannot be compared. And no argument can be adduced from the fact of the mere numbers of animal species, or of their individual increase, in support of the assumed length of any geological epoch. Species as well as individuals have perished, and gone out within the narrow limits of our own epoch, and yet have multiplied in progeny through countless myriads.
The same course of argument applies to every one of the formations, to some of them of vast thickness, even more conclusively, where we find the same species persistent throughout the group, and the same genus often extending over two or three entire formations, embracing periods of geological time of as many millions of years. Thus the Leptœna lata of the Silurian age lives on to the close of the Carboniferous; the trilobite, earliest of living creatures, has its representatives still in our modern seas; the mail-clad holoptychius existed through the whole of the Devonian and Carboniferous eras; and equally remarkable is the fact that the Onchus Marchisoni, the oldest fish yet detected in the rocks of the earth, is a creature more allied to the existing genus Spinax (the dog-fish) than to any other family of relics inclosed in all the intermediate ascending series of deposits. Among the infusoria it is ascertained that there’ are two kinds of living Gallionellæ identical with the fossil species in the Richmond clays of Virginia; while again, in geological botany, we have all the types of the coal formation still flourishing with the sane gigantic forms in the continents and islands washed by the Pacific.
3. The superficial Accumulations. The argument of the geologists, for their indefinite periods of time, proceeds mainly upon the assumption that the present and the past operations of the laws of nature are nearly uniform; or, in other words, that the existing rate of increment of detrital and alluvial matter, in seas, deltas, and rivers, is to be taken as the standard throughout the various geological epochs. Tried by the test of the superficial accumulations, the subject is brought within a manageable compass, the definite is substituted for the indefinite, and the scale of accumulative power in the ancient will be in the ratio of its erosive and transporting agency in the modern epoch. The products of volcanoes also fall to be considered in estimating the effects of causes now in operation.
The bowlder clay comes first and legitimately within the scope of this estimate; for, whatever theory of its formation be adopted, whether by the sudden submergence of a vast arctic continent and consequent upbreaking of the icy regions of the polar seas, by the sweep of a universal deluge, or a violent upheaval of the bed of the ocean, certain it is that the materials were brought together by rapid spasmodic action. This deposit covers the whole of Northern Europe, much of Asia, and extends over the vast continent of North America, as far as the 42° of latitude: it varies from a hundred to several hundred feet in depth: and thus, so far as quantity and extent of superficial area are concerned, the bowlder clay formation may be compared with any of the older rocky formations of the interior. But no geologist has ventured to speculate about an indefinite cycle of years, as the condition of the planet during the drift and accumulation of these rude and plastic materials.
The sands and gravels which succeed are likewise of great depth, spread over extensive valleys, and rise on the acclivities of hills five and six hundred feet above the level of the sea. This may be regarded, all of it, as the collect of the current epoch; and within the period of civilization and history and the arts, what sand-floods have been carried to every quarter of the globe, covering entire regions, devastating cities, and obliterating the very traces of man’s dominion over countries once subject to his use. Nor would fossils be wanting to complete the analogy, as the dunes along the shores of every continent, and especially on the coast of the North Sea in Norway, Denmark, Holland and Belgium, only require consolidation in order to represent with living instead of extinct species, the fossiliferous deposits of anterior times; more particularly the Molasse and Nagelflue of the Swiss Alps. Near Tours, in France, there is a bed of oyster-shells which is twenty-seven miles long, with a corresponding breadth, and twenty feet thick. And in the United States there are beds far exceeding this: a stratum, nearly continuous, has been traced from the Eutaw Springs in South Carolina, to the Chickasaw country—being six hundred miles in length by ten to a hundred miles in breadth.