all other animals have been exposed to circumstances productive

of change?

All the ordinary and more observable orders of the inhabitants of the sea, except the cetacea, have been found in the cretaceous formation-zoophytes, radiaria, mollusks, crustacea (in great variety of species), and fishes in smaller variety. Down to this period, the placoid and ganoid fishes had, as far as we have evidence, flourished alone; now they decline, and we begin to find in their place fishes of two orders of superior organization, those which predominate in the present creation. These are osseous in internal structure, with corneous scales. The enaliosaurians disappear in this formation, while the land reptiles, so numerous in the two preceding periods, become much diminished in numbers. Of the latter, one of the most remarkable was the Mosasaurus, which seems to have held an intermediate place

between the monitor and iguana, and to have been about twentyfive feet long, with a tail calculated to assist it powerfully in swimming.

Fuci abounded in the cretaceous seas, and confervæ are found enclosed in flints. Of terrestrial vegetation, as of terrestrial animals, the specimens in the European area are comparatively

rare, rendering it probable that there was little dry land near. The remains are chiefly of ferns, conifers, and cycadeæ, but in the two former cases we have only cones and leaves. There have been discovered many pieces of wood containing holes drilled by the teredo, and thus showing that they had been long drifted about in the ocean before being entombed at the bottom.

The series in America corresponding to this, entitled the Ferruginous Sand formation, presents fossils generally identical with those of Europe, not excepting the fragments of drilled wood: showing that, in this, as in earlier ages, there was a parity of conditions for animal life over a vast tract of the earth's surface. To European reptiles, the American formation adds a gigantic one, styled the Saurodon, from the lizard-like character of its teeth.

We have seen that footsteps of birds have been announced from America, in the new red sandstone. Some similar isolated phenomena occur in the present formation. In the slate of Glaris, in Switzerland, corresponding to the English galt in the chalk formation, the remains of a bird have been found.

ERA OF THE TERTIARY FORMATION.-MAMMALIA

ABUNDANT.

THE chalk-beds are the highest which extend over a considerable space; but in hollows of these beds, comparatively limited in extent, there have been formed series of strata-clays, limestones, marls, alternating-to which the name of the Tertiary Formation has been applied. London and Paris alike rest on basins of this formation, and another such basin extends from near Winchester, under Southampton, and re-appears in the Isle of Wight. A stripe of it passes along the east coast of North America, from Massachusetts to Florida. It is also found in

Sicily and Italy, insensibly blended with formations still in progress. Though comparatively a local formation, it is not of the less importance as a record of the condition of the earth during a certain period.

The hollows filled by the tertiary formation must be considered as the beds of estuaries and gulfs, left at the conclusion of the cretaceous period. We have seen that an estuary, either by the drifting up of its mouth, or a change of level in that quarter, may be supposed to have become an inland sheet of water, and that, by another change of the reverse kind, it may be supposed to have become an estuary again. Such changes the Paris basin appears to have undergone oftener than once; for, first, we have there a fresh-water formation of clay and limestone beds; then a marine-limestone formation; next, a second fresh-water formation, in which the material of the celebrated plaster of Paris (gypsum) is included; then a second marine formation of sandy and limy beds; and finally, a third series of fresh-water strata. Such alternations occur in other examples of the tertiary formation likewise.

The end of the Secondary Formation, which we have just seen take place, presents in some respects a remarkable resemblance to the close of what is called the Palæozoic period in the Permian strata. Looking broadly at the specific forms of the next higher strata, they appear to have undergone a total change. Again do we now witness a difference of the shelly cephalopoda. There is also a gradual reduction, and finally a disappearance, of the specific forms of gasteropods, formerly abundant. It has heretofore been a belief of geologists, that at this point, as at the former, there was an entire renewal of life upon our planet; but several considerations forbid such a conclusion in the second as well as in the first instance. First, the specific forms are not wholly changed, for a few do pass into the next higher strata. Second, there is, in the higher formation, an apparent following of an order applicable to the whole palaeontological history, as something under one law, seeing that birds and mammalia, the

next classes in the vertebrate scale, are then added. In the words of Sir R. Murchison, who believes that a true geological passage may be found between the two formations, the upper secondary rocks-judging from many of their generic forms—“seem to have prepared the way for the sequence of the tertiary strata." For these reasons, the idea of an entire renovation of life at this time what is commonly called a new creation-is not now maintained anywhere with confidence. The more rational explanation of the appearances is one suggested by actual facts observed in the strata; that the final cretaceous beds were deposited in seas more than usually deep, and which were therefore no proper habitat for the animals previously existing; that an interval of time afterwards took place, which is not represented by any strata which have been discovered; and that, by the time the tertiary formation commenced, the usual modifying influences having never ceased, the fauna had undergone such an amount of change as naturalists are accustomed to describe (their language being wholly arbitrary) as a renewal of species.

It is in perfect harmony with this view, that from the commencement of the Tertiaries, and as we ascend in the series, we find more and more specific forms identical with those still existing upon earth, as if we had now reached the dawn of the present state of the zoology of our planet. By the study of the shells alone, Sir C. Lyell has formed a division of the whole term into four sub-periods, to which he has given names with reference to the proportions which they respectively present of surviving species -first, eocene; second, miocene; third, older pliocene; fourth, newer pliocene. This division, however, is to be regarded as not safely applicable to the Tertiaries generally, except as a convenient means of indicating various portions of the series.

The eocene period presents, in three continental groups, 1238 species of shells, of which forty-two, or 3.5 per cent., yet flourish unchanged. Some of these are remarkable enough; but they all sink into insignificance beside the mammalian remains, which

1 Lyell's Elements of Geology.

H

the lower eocene deposits of the Paris basin present to us, showing that the land had now become the theatre of an extensive creation of the highest class of animals. Cuvier ascertained about fifty species of these, all of them long since extinct. About fourfifths are of the order Pachydermata, thick-skinned animals, to which our modern elephant, rhinoceros, horse, and pig, belong. Nearly the whole of these, however, belong to a family which is now confined to South America and Sumatra, namely, the tapir, --an animal of squat figure, and possessing a short proboscis, an inhabitant of the woods, and a herbivore, but of unsocial habits. It is curious to find that a family now so limited in its range, had formerly been distributed over France, England, and other parts of the earth. Naturalists have conferred the names, Palaotherium, Lophiodon, Coryphodon, &c., upon the ancient extinct

FIG. 65.

Skeleton of Palæotherium magnum.

tapirs, which seem chiefly to differ from modern species in a few peculiarities of the constitution of the teeth, and in having three, instead of four, toes upon the fore feet. One British specimen seems to have been about a third larger than the modern animal.

Another section of the Paris eocene remains have served to reconstruct a family to which the general name Anoplotherium has been given, from regard to its deficiency of all offensive or