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ascend nearer the surface of the earth, in our investigation of the Tertiary depositions, we mark particularly the petrified remains of existing genera, though the species themselves are extinct. For instance, there is the Dinotherium, a gigantic herbivorous animal, nearly eighteen feet high, allied to the aquatic family of the Tapirs, and provided with tusks, by which, during sleep, the animal might be hooked to the banks and margins of rivers and lakes, and by whose assistance, when awake, it might procure and separate its food.

There is also the Megatherium of Paraguay, similar in organization to the family of the Sloths, possessing the same peculiarities of structure which in the sloth seem to be in such contradiction to the rules of co-existence which are established among the rest of the Animal Kingdom, that even Cuvier himself was induced to declare, "that in the creation of the genus to which it belongs, Nature seems to have amused herself by producing something imperfect and grotesque." But the study and researches of later naturalists have established the truth that the seeming incongruities and anomalies in the structure of the existing Sloth and the extinct Megatherium are in wise adaptation to their wants and require

ments; and that so far from imperfection obtaining among their various parts, there may be traced therein the same harmonious symmetry which pervades the rest of the Animal Kingdom.

Another gigantic species of Mammalia, now extinct, but belonging to existing genera, is the great Mastodon, known under the appellation of the Animal of the Ohio. Its remains are found over the greater part of North America, and in some parts in such abundance, that to one of its localities has been applied the somewhat inelegant soubriquet of "bigbone lick." Professor Cuvier, after a careful and minute examination of its structure, came to the conclusion that this great Mastodon, or animal of the Ohio, resembled the elephant in its anatomical construction; that it had most probably a trunk; that though its height did not surpass that of the elephant, yet that it was longer in proportion, and its limbs thicker; and that it fed much in the same way as the Hippopotamus.

There are also many other extinct animals among the deposites of this series which have their similitudes in the present time among existing species. The Tapirus and the Chalicotherium were allied to the family of the Tapirs, only exceeding them greatly in size. The Hippo

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therium strongly resembled the horse, and the Felis, Machairodus and Agnotherium have their antitypes in the cat, the bear, and the dog. And as we ascend to each successive epoch in the four several divisions of the Tertiary system, we perceive an augmenting proportion of those fossils which may be referred to existing species and genera; colossal forms of Mammalia existed in great abundance; the seas, rivers, and lakes were, as before, crowded with their minute and unnumbered inhabitants; the extensive family of the monkey tribe were then, for the first time, ushered into existence; many species of birds analogous to those at present existing were created; and in fact, so closely do the organic remains of this series approximate to existing genera and species, that the zoology of the Tertiary period requires but few modifications to be an equally close and accurate description of the zoology of the present.

And while, as a distinctive characteristic of this era, we mark an enormous multiplication and increase among the Terrestrial Mammalia, with forms, habits, and instincts approximating closely to the existing forms of animated Nature, we also see that, in the lower orders of the scale of being, the creative energy of the Deity was continually put forth to stock with life and animation both earth, air, and sea. Indeed so vast

are the accumulations of marine and fresh-water shells peculiar to this epoch, amounting, we believe, to the number of three thousand species, that many beds of solid rock are, like those of the Secondary and Transition periods, made up entirely of their remains; and, from the mode of their aggregation, are regarded by Geologists as evidencing most satisfactorily the existence of an immense lapse of ages during their formation. To mention one instance out of many, we may remark, that in the great fresh-water deposites of Central France, the single district of Auvergne alone presents an area of twenty miles in width. and eighty in length, extending to at least seven hundred feet in thickness, which, according to Mr. Lyell, is mainly attributable to the presence of countless myriads of microscopic exuvia of the Cypris, a species of the Infusoria, of which the formations are principally composed, and which gave rise to divisions in the marl as thin as paper; and connecting this fact with the known habits of these animals to change their skin, he with justice remarks that a more convincing proof of the tranquillity of the waters, and of the slow and gradual process by which the lake was filled up with fine mud, cannot be ascertained.*

*Lyell's Principles of Geology, vol. iv. p. 88.

One of the most celebrated rocks, lately discovered to be

BILIN TRIPOLI.

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We have not time to dwell more at length, or in greater detail, upon the fossil remains of antiquity, with which the interior of the earth abounds, as we have several important general inferences to establish, which will occupy us for the remainder of the lecture. The view we have taken has, we are conscious, been very limited and imperfect, partly from our own inability rightly to condense the varied materials we have before us, and partly, we may add, from the vastness and extent of the subject itself. Still, if it lead you to search and investigate for yourselves-if it create in any of you a wish to know more of so interesting a science-to be made more fully acquainted with its thousand phenomena, and to enter more deeply into the sublime and beautiful facts which

made up entirely of millions of these Infusoria, is the Bilin Tripoli of Bohemia, denominated by Werner polishing slate, on account of the purposes to which it was and still is applied, viz. that of polishing stones and metals. It was formerly supposed to be a silicious shale, hardened by heat, but Professor Ehrenberg proved that this supposition was entirely erroneous, and stated that it consisted of myriads of microscopic animalcules, minute to an inconceivable degree. It is difficult to convey an idea of their extreme minuteness, but Ehrenberg has computed that forty-one thousand millions of the Gaillonella Distans are required to make up the dimensions of a cubic inch, and thus has unfolded to us the astonishing fact, that as there is a system in every star, so there is a world in every atom.