been greatly modified by recent discoveries. The inference as to the non-existence of fishes, resting, as it did, upon negative evidence has been entirely subverted. It is now ascertained that their remains occur in strata of all ages, each group of strata being characterized, according to M. Agassiz, by peculiarities in the structure of its fishes; and though the remains of reptiles have not yet been found so low as the coal formation they have been traced down to the magnesian limestone, immediately above it; which gives to them a higher antiquity than till lately they were supposed to possess. Again, with respect to the remains of warmblooded animals, five jaws, belonging to at least two species of a small animal resembling the didelphys, or opossum, and about the size of a mole, have been found in the calcareous slate of Stonesfield, in Oxfordshire, a stratum considerably below the chalk. One fact of this kind is of more value than a host of negative evidence, and it is triumphantly appealed to by those geologists who contend for the uniformity of the course of nature from the earliest epochs to the present time. It is evident, they say, that some of our oldest rocks have been derived from the waste of pre-existing land; and, as that land appears to have been clothed with its appropriate vegetation, we have no right to suppose that it was destitute of its appropriate animals. A great ocean like the Pacific, interspersed, like it, with small islands appears to have prevailed, during the formation of the older strata, over that part of the Northern Hemisphere in which are situated those countries whose geology has been most explored. Small oceanic islands do not, at the present day, contain many mammalia, while they are wholly destitute of the larger kinds; and the discovery of such remains, in an oceanic sediment, after its conversion into dry land, must be an event of very rare occurrence, for however abundant mammalia might be on some distant continent, by the rivers of which their carcases would be drifted down, yet before they could be floated out far to sea, they would be almost certain to be devoured by the carnivorous monsters of the deep; and even supposing them to escape this fate, the chances are very much against the discovery of the spot where these rare remains are concealed after the bed of the ocean shall be laid dry.

Allowing to this argument its due weight, we must observe, that there are certain tribes of mammalia (as the whale and the seal) which are peculiar to the sea; and the imbedding of their remains in the sediment of a great ocean would be no uncommon event. Yet no traces of their remains have hitherto been found in the strata below the chalk*. The absence therefore of the remains of marine, as well as of terrestrial, mammalia, appears favourable to the conclusion, that this order of animals was not created until an epoch comparatively recent, though that epoch is proved, by the Didelphoid remains of Stonesfield, to have been more remote than we formerly supposed. We must, likewise, observe that there is a local deposit, older than the chalk, but more recent than the Stonesfield slate, principally confined to the Weald of Kent and Sussex, and thence named the Wealden, which, from its assemblage of fossils, (derived, with few exceptions, from land and fresh water) appears

*The bones found in the Wealden, and to

described by Dr. Buckland as belonging M. Cetacea, are referred by Cuvier and

Mantell to some unknown Saurian.

to have been deposited at the mouth of a river; and, from the extent of the formation, that river must have drained some large continent. Here, then, we ought to find the remains of mammalia if that class of animals were as abundant in the world then as they were at a subsequent period. But though this deposit has long been under the examination of an eminent geologist, celebrated for his skill in comparative anatomy, not a trace of such remains has yet been discovered. On the contrary, the Wealden exhibits a most curious group of animals as inhabiting the shores and waters of the river which drifted down their remains, and indicates an extraordinary developement, during that era, of the saurian, or lizard family. They seem to have possessed earth, and sea, and air. Inhabiting the sea, there was the ichthyosaurus, a creature intermediate between a crocodile and a fish,—having the snout of a dolphin, the head and teeth of a crocodile, the doubly concave vertebræ of a fish, fitting it for rapid motion through the water, and, instead of fins or feet, it had four paddles, like those of a turtle; while nearly allied to it in structure was the plesiosaurus, one species of which had a long neck like the body of a serpent. These creatures appear, from their structure, to have been confined to the sea, and never to have appeared on dry land; but there were amphibious saurians, of the crocodile and alligator families, frequenting the rivers and estuaries, in company with tortoises and turtles; and there were pterodactyles, or flying saurians, together with a great variety of gigantic terrestrial saurians, the lord of whom appears to have been the iguanodon, a creature pronounced by Cuvier to be the most extraordinary that had ever come under his consideration. It was an herbivorous lizard, of colossal proportions, for it must have been seventy feet long, and nine feet high. In some respects its teeth bore an analogy to those of the iguana, a small species now inhabiting the West Indies; but it differed from all other herbivorous lizards, either fossil or recent, in having chewed its food, as appears by the manner in which its teeth were worn, whereas other herbivorous lizards nip or crop theirs, and swallow it without mastication. In short, during the Wealden era, there were lizards twice the size of the largest elephant or rhinoceros, approaching them in the character of their dentition, and apparently occupying their place in the economy of nature.

But whether mammalia existed during the earliest epochs of the world of which we possess geological monuments, and were contemporary with those marine animals imbedded in the lower strata, though, for the reasons above stated, their remains have not yet been discovered; or whether they were not created till a later period, though still before the deposition of the chalk, it is certain that during the tertiary era, when their remains were abundantly entombed in the strata, we can trace the introduction of new races even of them. The remains of the land qua

drupeds imbedded in the olden tertiary strata, are exclusively those of extinct genera. In the deposits of a more recent period we meet, in these northern latitudes, with the remains of extinct species of genera now existing, but existing only in warm climates, such as the elephant, rhinoceros, hippopotamus, &c. These are found to be gradually intermixed (in the ascending order of the strata) with the bones of mammalia, identical in species with those now living under the present climates of Furope; till at length we come to peat bogs and alluvial deposits, in

which human remains occur, mixed with those of animals now living in the countries where the remains are found, together with a few which have become locally extinct, within the historic period. The animals that have become locally extinct in Britain are, the wolf, the beaver, and the wild boar. The great fossil elk of Ireland, now universally extinct, perhaps continued to exist in that country after it was inhabited by man. It is doubtful whether the elephants, hyænas, tigers, &c., whose remains are so abundant in gravel and in caves, inhabited Europe after the human era. In those cases where their bones occur in caverns, mixed with the bones and works of men, there is often evidence that the latter were introduced after the former; and in no case is there clear evidence that they were deposited simultaneously. It is a very remarkable circumstance, that not a single bone of any of the monkey tribe has yet been found in a fossil state, though so many bones of elephants and other inhabitants of the same climate as the monkey, have been disinterred in Europe. This would almost lead to the conclusion that the class of animals most resembling man in organization were created nearly at the same time with him. It is needless to adduce proofs of the recent introduction of man upon the earth. It is a fact admitted by all geologists, even by those who contend that the existing order of things is but the last link of a chain of events derived from laws now in daily operation. The most able and strenuous advocate of this doctrine asserts, that the real difficulty consists in tracing back the signs of man's existence upon the earth to that comparatively modern period when species, his contemporaries, began to predominate.

The absence of human remains from the older strata cannot be accounted for as in the case of the quadrupeds of the land, by the rare occurrence of the circumstances which would cause them to be imbedded in submarine sediment. "No inhabitant of the land," says Mr. Lyell, exposes himself to so many dangers on the waters as man, whether in a civilized or a savage state; and there is no animal, therefore, whose skeleton is so liable to become imbedded in lacustrine and submarine deposits: nor can it be said that his remains are more perishable than those of other animals; for in ancient fields of battle, as Cuvier has observed, the bones of men have suffered as little decomposition as the bones of horses, which were buried in the same grave. But even if the more solid parts of our species had disappeared, the impression of their form would have remained engraven on the rocks, as have the traces of the tenderest leaves of plants, and the soft integuments of many animals. Works of art, moreover, composed of the most indestructible materials, would have outlasted almost all the organic remains of sedimentary rocks. Edifices, and even entire cities, have, within the times of history, been buried under volcanic ejections, submerged beneath the sea, or ingulfed by earthquakes; and had these catastrophes been repeated through an indefinite lapse of ages, the high antiquity of man would have been inscribed in far more legible characters on the frame-work of the globe, than are the forms of the ancient vegetation, which once covered the islands of the northern ocean, or of the gigantic reptiles which, at still later periods, peopled the seas of the northern hemisphere*."

It can scarcely, we think, be denied that the facts above enumerated point to something very like a progressive developement of organic life; though they will not support the doctrine to the extent contended for a few years ago, and though the terms in which it was announced might be open to objection. It is possible to repudiate the monstrous and absurd notions of Lamarck, respecting the transmutation of one species into another, it is possible to admit that fishes, reptiles, and mammalia occur, respectively, in older strata than was supposed at the time Sir Humphry Davy wrote his Consolations in Travel,—we may admit the absence from the coal strata of fungi, lichens, and mosses, which are the simplest forms of flowerless vegetation, and the presence of ferns and Lycopodiacea, which are the most highly organized of the cryptogamic* plants, we may admit that the monocotyledons† of the same period consisted of the most highly-developed of that class of plants, and that it was not destitute of its dicotyledons. It may be true that an orthoceratite or a nautilus, though they have no back-bone, are, for the purposes for which they were designed, as perfect in their organization as an elephant or a crocodile; and that palms and bread-corn, though they have but one seed-lobe, are not inferior in dignity to an oak and a nettle which have two: and yet, admitting all this, we may contend with Professor Sedgwick, that a doctrine may be abused and yet contain the elements of truth,—that it is one thing to refute it, and another to point out the errors and overcharged statements of its supporters. "With reference," he says "to the functions of the individual, one organic structure is as perfect as another; but I think that in the repeated, and almost entire, changes of organic types in the successive formations of the earth,-in the absence of mammalia in the older, and their rare occurrence (and then in forms entirely unknown to us) in the newer secondary groups,-in the diffusion of warm-blooded quadrupeds (frequently of unknown genera) through the older tertiary systems,—in their abundance (and frequently of known genera) in the upper portion of the same series,—and, lastly, in the recent appearance of man on the surface of the earth, now universally admitted, in one word, from all these facts combined we have a series of proofs, the most emphatic and convincing, that the existing order of Nature is not the last of an uninterrupted succession of mere physical events, derived from causes now in daily operation, but on the contrary, that the approach to the present system has been gradual, and that there has been a progressive developement of organic structure, subservient to the purposes of life §."

While these changes were taking place in the organic world, changes as great were taking place in the inorganic. Land was converted into sea, and sea into land, and land again into sea. The same portions of the earth's surface have been subject to repeated oscillations, so as to be alternately above and below the ocean level. We have already alluded to the indications of a change of climate, discoverable in the crust of the globe. We shall not at present enter into a detail of all the evidence on which this rests; suffice it to say, that from the testimony of the imbedded organic remains, it appears that, during the formation of the

* Plants whose fructification is concealed. + Plants having only one seed-lobe.

Plants having two seed-lobes.
§ Sedgwick's Anniversary Address.

older strata, a tropical, if not an ultra-tropical, climate prevailed over the northern hemisphere, and that even at a period so comparatively recent as the commencement of the tertiary series, a very high temperature existed over what are now the cool regions of Europe; when a great part of England was yet beneath the waves, when her mountain-chains formed a cluster of spice islands, haunted by the crocodile and the turtle, and when, on the spot where London now stands, the nautilus of the tropics, spreading his sail to the breeze, was the only representative of the fleets that crowd her port. But if the earth's crust furnishes us with evidence, that great and repeated changes have taken place in the organic and inorganic world, it furnishes us with proofs no less clear, that great epochs of time elapsed while these changes were in progress,— epochs so great that we are tempted to connect them with the secular periods of astronomy to which we have before alluded. There is, however, this difference between the phenomena of astronomy and geology; that in the former we have a series of events recurring, in a fixed order, after the lapse of fixed intervals of time, whereas in geology (if we except the interchange between land and sea, and the recurrence of volcanic action after long intervals of repose) we have no evidence of the repetition of a single phenomenon, much less have we evidence of geological cycles, in which the same events are repeated, again and again, in a stated order, and at stated intervals. We have proofs of a change from a hot to a colder climate; but we have no proofs of a change from a cold climate to a hotter. Whole orders of fishes characteristic of the older strata become extinct, and are succeeded by new races, which in their turn give place to others. This class of vertebrated animals affords an unbroken record, from the earliest to the most recent geological epoch, and the changes which occur in it are more rapid than those which take place among invertebrate animals; but, as we ascend in the series of strata, we meet with no instance of the revival of any of the extinct genera or species. By means of a series of geological monuments, we can trace the commencement and decay of the family of the Ichthyosauri; but once extinct they reappear no more, except in the humorous sketch of Mr. Delabeche*: and, lastly, man becomes an inhabitant of the earth, but there is not a particle of evidence that the race had previously existed, though at some very remote period, and had been destroyed to revive on the completion of a great geological cycle. Again, to use the language of Professor Sedgwick, "each formation of geology may have required a very long period for its complete developement: but, after all, the successive formations about which we speculate, however complex in their subdivisons, are few in number; and after deciphering a series of monuments, we reach the dark ages of our history, when having no longer any characters to guide us, we may indulge at will in the creations of our fancy. We may imagine indefinite cycles, and an indefinite succession of phenomena, and in the physical Allusion is here made to a lithographic | brethren, on a human skull, which he prosketch from the pencil of that gentleman, nounces to belong to one of the inferior entitled, "Reappearance of Ichthyosauri animals, on account of the insignificance of -man only found in a fossil state;" in the teeth, and the trifling powers of the which Professor Ichthyosaurus is repre- jaw, expressing wonder how the creature sented lecturing to an audience of his procured its food.