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the sandstones in the valley of the Connecticut River, which contain so many footprints of birds, are to be regarded as underlying the Lias, the likelihood is that their age is triassic. Land plants, molluscs, fishes, and reptiles have also left numerous traces of their presence in the strata of the trias. The most remarkable reptilian form of the triassic age was a great aquatic lizard, which has been named Nothosaurus, or spurious lizard — a name indicative of the uncertain place at first assigned to it in the zoological scale.
Next in the ascending order comes the Oolite, named by Sir Charles Lyell the Jurassic, from having its typical rocks on the continent of Europe, in the Jura mountains. It contains many well-marked varieties of strata, which are all included under
Fig. 40. the general divisions Lias, Oolitelower, middle, and upper—and Wealden, and is between two and three thousand feet thick, fig. 39. This series abounds in fossils, land plants of many entirely new genera, marine and fresh-water shells,uncouth-looking amphibious flying reptiles, and great carnivorous land lizards. If we asso
Pycnodus rhombus-Oolite. ciate the American sandstones referred to with this series, huge wingless birds must have frequented the borders of its quiet lakes, or strolled along the sea-washed margins of its sandy shores.
It is, moreover, especially worthy of notice, in connection with the most recent and able exposition of the age theory of creation, that in what is known as the middle Purbeck layers, lying at the top of the great Oolite division, remains have recently been discovered of species of the higher type of mammals, namely, the placentals, or those born with all their parts complete, and suckled from true breasts, as our dog and cat are, and distinguished from the lower type, or the marsupials, which after birth are nourished in a marsupium or pouch, like the kangaroo and opossum of the present epoch. Figs. 2 and 3, on Plate II., represent two of the ammonites of the Oolite. Trigonia, fig. 1, ranges from the trias to the chalk. It resembles the common mussel in the mode in which its shells are closed. This bivalve ceases as a fossil with the close of the chalk, and reappears in certain similar recent forms in the waters of the Pacific. Gryphæa, fig. 7, is closely allied to the common oyster. It is characterized by a hinge knob strongly
incurved, and by the disproportionate size of its left valve. The right one is much more like a lid than a true valve. Pholadomya, fig. 6, has two equal valves—narrow at the hinge, broad and gaping at the front. Figs. 4 and 5 represent sea urchins of the Oolite period.
The reptiles of the Oolite present several remarkable forms; such as the Pliosaurus which takes its name from its strongly marked lizard-like features and is distinguished from another gigantic sea-lizard, and the Ichthyosaurus, so called from its resemblance to the fish type of life.
The Chalk or cretaceous system lies above the Oolite. Representatives of all the forms of life met with in the underlying system abound
in this formation, except Fig. 41.
those of mammals and birds. If traces of these have been found, they are so faint and indistinct as to be unworthy of being set down as characteristic forms. The
great majority of the generic forms of life of the chalk became extinct at the close of that epoch. This remark, indeed, is applicable to the fossils of all the great Fig. 42.
formations. The chalk yields a great number of beautiful forms. —(Plate II., figs. 1-12—Chalk fossils.) The representatives of several of these in lower and older strata have been noticed. Fig. 11, Belemnites, is highly characteristic of the Oolite and chalk. It has served the same purpose in some of the forms of life kindred to the recent cuttle-fish, as the so-called "pen" of the cuttle
fish does to it. Cycadeoidea megaphylla— Wealden.
The last series in the ascending order is the Tertiary. In this many forms occur which are ranked among living species, or are identical with them. This fact led Sir Charles Lyell to the now universally accepted classification of the strata of the tertiary system. The lowest layers are distinguished by the appellation Eocene, or the dawn of recent species, because only a few of these
are found in them. The layers immediately overlying are named Miocene, or less recent, because, while recent forms are more numerous
Plesiosaurus Hawkinsii – Owen. than in the former, they are in a minority when compared with those now extinct. Above these occur the strata included under the Pliocene, in which recent shells are found in greater numbers than those now extinct. The topmost strata are denominated Pleistocene, because the molluscs of this group are for the most part the same as those which now, or very recently, inhabited our waters.—(See Plate II., Tertiary fossils, figs. 1–12.) A glance at these will be sufficient to show that the molluscan life of the tertiary period supplies many more points at which the truly geological
Fig. 44. period comes in contact with our own. The Voluta, fig. 1, Dentalium, fig. 2, Turbo, fig. 7, Cypria, fig. 11, &c., look as if their originals had been picked up on our own sea-shore.
The mammalian remains of the tertiaries have had much attention directed to them recently. At the commencement of the tertiary epoch we meet with the bones of the noted Palæothere, so called from its having been regarded at the time of its discovery as the most ancient wild animal (fig. 44)
The above cut represents Cuvier's outline of the restored Palæo
therium. The ten or twelve species which have been found in the tertaries, vary in size from that of a horse to that of a dog. Its place in the zoological scale is likely between the living rhinoceros and the tapir. Its nasal bones show that it must have possessed a short proboscis, like the latter.
Other mammalia of the tertiary series exhibit many novel forms. The huge size of the tertiary Pachydermata, or thick-skinned animals, their structural adaptations to the circumstances of their position and Fig. 55.
habits, and the missing links in the geological scale supplied by them have invested them with great interest to the student of science. Regarded as the predecessors of the elephant, the rhinoceros, the hippopotamus, &c., to which in structure they have many resemblances, much light is shed on their habits by our acquaintance with these corresponding forms of life of the present epoch. The name given to one of them still indicates the feelings of surprise with which it was regarded by naturalists when discovered—Dinotherium, or terrible wild beast. In
1836 an entire head of this mamSkull of Dinotherium.
mal was found in the miocene tertiary in Germany, and since that period other remains have been found in France, in Switzerland, and in Perim island, Gulf of Cambay.
In general bodily outline, and especially in the form of some of its teeth, the Dinotherium bears a great resemblance to the South American Tapir. Even Cuvier at first considered it a gigantic species of Tapir. It has far closer affinities with certain herbivorous Cetacea, with the Manatee for example, an aquatic mammal ranked with the whales, but differing widely from them, both in habits and in some aspects of structure. The lower jaw, however, exhibits peculiarities which distinguish the Dinotherium from all other animals. Two great tusks are placed at the front extremity of the lower jaw. This feature in its structure would have greatly interfered with its comfort, had the Dinotherium been a land mammal. But as it must have frequented the lakes and the sluggish rivers of the miocene period, the enormous tusks would