The Plurality of Worlds

by William Whewell

11. But again: on further examination it is found, that we have not merely one series of sedimentary deposits, thus forming our mountains. There are a number of different series of such layers or strata, to be found in different ranges of hills, and in the same range, one series resting upon another. These different series of strata are distinguishable from one another by their general structure and appearance, besides more intimate characters, of which we shall shortly have to speak. Each such series appears to have a certain consistency of structure within itself; the layers of which it is composed being more or less parallel, but the successive series are not thus always parallel, the lower ones being often highly inclined and irregular, while the upper ones are more level and continuous: as if the lower strata had been broken up and thrown into disorder, and then a new series of strata had been deposited horizontally on their fragments. But in whatever way these different sedimentary series succeeded each other, each series must have required, as we have seen, a long period for its formation; and to estimate the length of the interval between the two series, we have, at the present stage of our exposition, no evidence.

12. But the mechanical structure of the strata, the result, as it seems, of aqueous sedimentary deposit, is not the only, nor the most important evidence, with regard to the length of time occupied by the formation of the rocky layers which now compose our mountains. As we have said, they contain shells, and other remains of creatures which live in the sea. These they contain, not in small numbers, scattered and detached, but in vast abundance, as they are found in those parts of the ocean which is most alive with them. There are the remains of oysters and other shell-fish in layers, as they live at present in the seas near our shores; of corals, in vast patches and beds, as they now occur in the waters of the Pacific; of shoals of fishes, of many different kinds, in immense abundance. Each of these beds of shells, of corals, and of fishes, must have required many years, perhaps many centuries, for the growth of the successive individuals and successive generations of which it consists: as long a time, perhaps, as the present inhabitants of the sea have lived therein: or many times longer, if there have been many such successive changes. And thus, while the present condition of the earth extends backwards to a period of vast but unknown antiquity; we have, offered to our notice, the evidence of a series of other periods, each of which, so far as we can judge, may have been as long or longer than that during which the dry land has had its present form.

13. But the most remarkable feature in the evidence is yet to come. We have spoken in general of the oysters, and corals, and fishes, which occur in the strata of our hills; as if they were creatures of the same kinds which we now designate by those names. But a more exact examination of these remains of organized beings, shows that this is not so. The tribes of animals which are found petrified in our rocks are almost all different, so far as our best natural historians can determine, from those which now live in our existing seas. They are different species; different genera. The creatures which we find thus embedded in our mountains, are not only dead as individuals, but extinct as species. They belonged, not only to a terrestrial period, but to an animal creation, which is now past away. The earth is, it seems, a domicile which has outlasted more than one race of tenants.

14. It may seem rash and presumptuous in the natural historian to pronounce thus peremptorily that certain forms of life are nowhere to be found at present, even in the unfathomable and inaccessible depths of the ocean. But even if this were so, the proposition that the earth has changed its inhabitants, since the rocks were formed, of which our hills consist, does not depend for its proof on this assumption. For in the organic bodies which our strata contain, we find remains, not only of marine animals, but of animals which inhabit the fresh waters, and the land, and of plants. And the examination of such remains having been pursued with great zeal, and with all the aids which natural history can supply, the result has been, the proofs of a vast series of different tribes of animals and plants, which have successively occupied the earth and the seas; and of which the number, variety, multiplicity, and strangeness, exceed, by far, everything which could have been previously imagined. Thus Cuvier found, in the limestone strata on which Paris stands, animals of the most curious forms, combining in the most wonderful manner the qualities of different species of existing quadrupeds. In another series of strata, the Lias, which runs as a band across England from N. E. to S. W., we have the remains of lizards, or lacertine animals, different from those which now exist, of immense size and of extraordinary structure, some approaching to the form of fishes (ichthyosaurus); others, with the neck of a serpent; others with wings, like the fabled forms of dragons. Then beyond these, that is, anterior to them in the series of time, we have the immense collection of fossil plants, which occur in the Coal Strata; the shells and corals of the Mountain Limestone; the peculiar fishes, different altogether from existing fishes, of the Old Red Sandstone; and though, as we descend lower and lower, the traces of organic life appear to be more rare and more limited in kind, yet still we have, beneath these, in slates and in beds of limestone, many fossil remains, still differing from those which occur in the higher, and therefore, newer strata.

15. We have no intention of instituting any definite calculation with regard to the periods of time which this succession of forms of organic life may have occupied. This, indeed, the boldest geological speculators have not ventured to do. But the scientific discoveries thus made, have a bearing upon the analogies of creation, quite as important as the discoveries of astronomy. And therefore we may state briefly some of the divisions of the series of terrestrial strata which have suggested themselves to geological inquirers. At the outset of such speculations, it was conceived that the lower rocks, composed of granite, slate, and the like, had existed before the earth was peopled with living things; and that these, being broken up into inclined positions, there were deposited upon them, as the sediment of superincumbent waters, strata more horizontal, containing organic remains. The former were then called Primitive or Primary, the latter, Secondary rocks. But it was soon found that this was too sweeping and peremptory a division. Rocks which had been classed as Primary, were found to contain traces of life; and hence, an intermediate class of Transition strata was spoken of. But this too was soon seen to be too narrow a scheme of arrangement, to take in the rapidly-accumulating mass of facts, organic and others, which the geological record of the earth's history disclosed. It appeared that among the fossil-bearing strata there might be discerned a long series of Formations: the term Formation being used to imply a collection of successive strata, which, taking into account all the evidence, of materials, position, relations, and organic remains, appears to have been deposited during some one epoch or period; so as to form a natural group, chronologically and physiologically distinct from the others. In this way it appeared that, taking as the highest part of the Secondary series, the beds of chalk, which, marked by characteristic fossils, run through great tracts of Europe, with other beds, of sand and clay, which generally accompany these; there was, below this Cretaceous Formation, an Oolitic Formation, still more largely diffused, and still more abundant in its peculiar organic remains. Below this, we have, in England, the New Red Sandstone Formation, which, in other countries, is accompanied by beds abundant in fossils, as the Muschelkalk of Germany. Below this again we have the Coal Formation, and the Mountain Limestone, with their peculiar fossils. Below these, we have the Old Red Sandstone or Devonian System, with its peculiar fishes and other fossils. Beneath these, occur still numerous series of distinguishable strata; which have been arranged by Sir Roderick Murchison as the members of the Silurian formation; the researches by which it was established having been carried on, in the first place, in South Wales, the ancient country of the Silures. Including the lower part of this formation, and descending still lower in order, is the Cambrian formation of Professor Sedgwick. And since the races of organic beings, as we thus descend through successive strata, seem to be fewer and fewer in their general types, till at last they disappear; these lower members of the geological series have been termed, according to their succession, Palæozoic, Protozoic, and Hypozoic or Azoic. The general impression on the minds of geologists has been, that, as we descend in this long staircase of natural steps, we are brought in view of a state of the earth in which life was scantily manifested, so as to appear to be near its earliest stages.

16. Each of these formations is of great thickness. Several of the members of each formation are hundreds, many of them thousands of feet thick. Taken altogether, they afford an astounding record of the time during which they must have been accumulating, and during which these successive groups of animals must have been brought into being, lived, and continued their kinds.

17. We must add, that over the Secondary strata there are found, in patches, generally of more limited extent, another, and of course, newer mass of strata, which have been termed Tertiary Formations. Of these, the strata, near and under Paris, lying in a hollow of the subjacent strata, and hence termed the Paris Basin, attracted prominent notice in the first place. And these are found to contain an immense quantity of remains of animals, which, being well preserved, and being subjected to a careful and scientific scrutiny by the great naturalist George Cuvier, had an eminent share in establishing in the minds of Geologists the belief of the extinct character of fossil species, and of the possibility of reconstructing, from such remains, the animals, different from those which now live, which had formerly tenanted the earth.

18. We have, in this enumeration, a series of groups of strata, each of which, speaking in a general way, has its own population of animals and plants, and is separated, by the peculiarities of these, from the groups below and above it. Each group may, in a general manner, be considered as a separate creation of animal and vegetable forms—creatures which have lived and died, as the races now existing upon the earth live and die; and of which the living existence may, and according to all appearance must, have occupied ages, and series of ages, such as have been occupied by the present living generations of the earth. This series of creations, or of successive periods of life, is, no doubt, a very striking and startling fact, very different from anything which the imagination of man, in previous stages of investigation of the earth's condition, had conceived; but still, is established by evidence so complete, drawn from an examination and knowledge of the structures of living things so exact and careful, as to leave no doubt whatever of the reality of the fact, on the minds of those who have attended to the evidence; founded, as it is, upon the analogies, offices, anatomy, and combinations of organic structures. The progress of human knowledge on this subject has been carried on and established by the same alternations of bold conjectures and felicitous confirmations of them,—of minute researches and large generalizations,—which have given reality and solidity to the other most certain portions of human knowledge. That the strata of the earth, as we descend from the highest to the lowest, are distinguished in general by characteristic or organic fossils, and that these forms of organization are different from those which now live on the earth, are truths as clearly and indisputably established in the minds of those who have the requisite knowledge of geology and natural history, as that the planets revolve round the sun, and satellites round the planets. That these epochs of creation are something quite different from anything which we now see taking place on the earth, no more disturbs the belief of those facts, which scientific explorers entertain, than the seemingly obvious difference between the nebulæ which are regarded as yet unformed planetary systems, and the solar system to which our earth belongs, disturbs the belief of astronomers, that such nebulæ, as well as our system, really exist. Indeed we may say, as we shall hereafter see, that the fact of our earth having passed through the series of periods of organic life which geologists recognize, is, hitherto, incomparably better established, than the fact that the nebulæ, or any of them, are passing through a series of changes, such as may lead to a system like ours; as some eminent astronomers in modern times have held. In this respect, the history of the world, and its place in the universe, are far more clearly learnt from geology than from astronomy.

19. But with regard to this series of Organic Creations, if, for the sake of brevity, we may call them so; we may naturally ask, in what manner, by what agencies, at what intervals, they succeeded each other on the earth? Now, do the researches of geologists give us any information on these points, which may be brought to bear upon our present speculations? If we ask these questions, we receive, from different classes of geologists, different answers. A little while ago, most geologists held, probably the greater number still hold, that the transitions from one of these periods of organic life to another, were accompanied generally by seasons of violent disruption and mutation of the surface of the earth, exceeding anything which has taken place since the surface assumed its present general form; in the same proportion as the changes of its organic population go beyond any such changes which we can discern to be at present in operation. And there were found to be changes of other kinds, which seemed to show that these epochs of organic transition had also been epochs of mechanical violence, upon a vast and wonderful scale. It appeared that, at some of these epochs at least, the strata previously deposited, as if in comparative tranquillity, had been broken, thrust up from below, or drawn or cast downwards; so that strata which must at first have been nearly level, were thrown into positions highly inclined, fractured, set on edge, contorted, even inverted. Over the broken edges of these strata, thus disturbed and fractured, were found vast accumulations of the fragments which such rude treatment might naturally produce; these fragmentary ruins being spread in beds comparatively level, over the bristling edges of the subjacent rocks, as if deposited in the fluid which had overwhelmed the previous structure; and with few or no traces of life appearing in this mass of ruins; while, in the strata which lay over them, and which appeared to have been the result of quieter times, new forms of organic life made their appearance in vast abundance. Such is, for example, the relation of the coal strata in a great part of England; broken into innumerable basins, ridges, valleys, strips, and shreds, lying in all positions; and then filled into a sort of level, by the conglomerate of the magnesian limestone, and the superincumbent red sandstone and oolites. In other cases it appeared as if there were the means of tracing, in these dislocations, the agency of igneous stony matter, which had been injected from below, so as to form mountain-chains, or the cores of such; and in which the period of the convulsion could be traced, by the strata to which the disturbance extended; those strata being supposed to have been deposited before the eruption, which were thrust upwards by it into highly-inclined positions; while those strata which, though near to these scenes of mechanical violence, were still comparatively horizontal, as they had been originally deposited, were naturally inferred to have been formed in the waters, after the catastrophe had passed away. By such reasonings as these, M. Elie de Beaumont has conceived that he can ascertain the relative ages (according to the vast and loose measurements of age which belong to this subject) of the principal ranges of mountains of the earth's surface.

20. Such estimations of age can, indeed, as we have intimated, be only of the widest and loosest kind; yet they all concur in assigning very great and gigantic periods of time, as having been occupied by the events which have formed the earth's strata, and brought them into their present position. For not only must there have been long ages employed, as we have said, while the successive generations of each group of animals lived, and died, and were entombed in the abraded fragments of the then existing earth; but the other operations which intervened between these apparently more tranquil processes, must also have occupied, it would seem, long ages at each interval. The dislocation, disruption, and contortion of the vast masses of previously existing mountains, by which their framework was broken up, and its ruins covered with beds of its own rubbish, many thousand feet thick, and gradually becoming less coarse and smoother, as the higher beds were deposited upon the lower, could hardly take place, it would seem, except in hundreds and thousands of years. And then again, all these processes of deposition, thus arranging loose masses of material into level beds, must have taken place in the bottom of deep oceans; and the beds of these oceans must have been elevated into the position of mountain ridges which they now occupy, by some mighty operation of nature, which must have been comparatively tranquil, since it has not much disturbed those more level beds; and which, therefore, must have been comparatively long continued. If we accept, as so many eminent geologists have done, this evidence of a vast series of successive periods of alternate violence and repose, we must assign to each such period a duration which cannot but be immense, compared with the periods of time with which we are commonly conversant. In the periods of comparative quiet, such as now exist on the earth's surface, and such as seem to be alone consistent with continued life and successive generation, deposits at the bottom of lakes and seas take place, it would seem, only at the rate of a few feet in a year, or perhaps, in a century. When, therefore, we find strata, bearing evidence of such a mode of deposit, and piled up to the amount of thousands and tens of thousands of feet, we are naturally led to regard them as the production of myriads of years; and to add new myriads, as often as, in the prosecution of geological research, we are brought to new masses of strata of the like kind; and again, to interpolate new periods of the same order, to allow for the transition from one such group to another.