Swallow, Meek, and Hall. The Permian rocks west of the Mississippi have more recently been subjected to thorough investigations by Swallow, Meek, Hayden, and Shumard; and though much of what was first regarded as Permian is now proven to belong to the period of the coal-measures, we know that this group of sediments is developed in America on a scale little less magnificent than in the ancient Russian kingdom of Perm, which gave its name to the group.

CHAPTER XVI.

THE REIGN OF REPTILES.

WE

E now enter upon a new Age in the history of the world. The reptilian army has arrived and taken absolute possession of the land and the sea. The highest of these monarch reptiles, in respect to organization, are some lizard-like creatures as much at home in the sea as upon the land. But especially does the great deep swarm with huge beings having the body of a lizard, the immense jaws and sharp, conical teeth of a crocodile, the bi-concave vertebræ of a fish, and the short, flat paddles of a whale. What a synthesis of characters is here! The type of the age is expressed in the lacertiform trunk and tail. Crocodiles had not yet existed; but the jaws of these monsters seem like an experiment preparatory to the supply of quantities of those savage brutes. Mammals were yet in the distant future; but here, in the paddles of these Enaliosaurs. is a prophecy of coming cetacea-the form which the mammalian type assumes at the point where it comes in contact with the type of fishes. The reign of fishes is past; but here, in the bi-concave vertebræ of these sea-monsters is preserved a reminiscence of the last sovereigns.

This, the Triassic Age, was peculiarly the reign of Labyrinthodont saurians. Thirty-five years ago the tracks of these anomalous creatures were first noticed upon some red sandstone in Saxony, and they have since been discovered in other parts of the world. The peculiarity of these footprints consists in their hand-like form, and in the occurrence of a series of larger and smaller in connection with

each other. The latter circumstance led to the opinion that the posterior limbs of the reptile were much stouter than the anterior, as in the kangaroo and frog. When the bones of these animals were brought to light, geologists had the opportunity to certify themselves that these problematical hand-prints were impressed by reptilian instead of mammalian quadrupeds; and that while the weight of characters allied them to true reptiles, they nevertheless. possessed strong analogies with Batrachians, and probably simulated the form and habits of the frog-though in truth we should say that the frog was subsequently fashioned in the similitude of a Labyrinthodont. The head was helmeted by a pair of broad, bony plates, through which were openings for the eyes; and some parts of the body were covered, especially in the later ages, by a similar armor. The striking characteristic of these ancient reptiles, from which they receive their name, is seen when a very thin transverse section or slice of one of the teeth is viewed under the microscope. The external coating of the tooth, called cement, is folded inward in folds which reach to the central cavity, and in their course are inflected into a labyrinth of subordinate lateral folds. Some of these frog-like quadrupeds seem to have attained the size of an ox. It is likely that they were the representatives of the class of Batrachians in those early periods, as no other Batrachia are known in the Trias; and those before alluded to from the coal-measures are known likewise to have possessed the peculiar cephalic plates of the Labyrinthodonts.

The Triassic Age witnessed also the advent of multitudes of marine saurians of the family of Ichthyosaurs, having enormous cavities in their craniums for the lodgment of the eyes. This type of reptiles is restricted to this single age of the world. Here also crawled reptiles resembling gigantic lizards, semi-aquatic or purely terrestrial in

their habits, having feet for walking instead of flat, oarlike extremities for swimming.

These forms all disappeared with the dawn of a new era. Their bones lie buried in the geological cemeteries of Europe. It is almost incredible that information so exact can be drawn from the few scattered fragments which have been brought to light; but such is the unity and persistence of plan which runs through the different classes of the animal kingdom, that a single tooth, whether of a living or extinct species, will often suffice to enable the expert to disclose all the zoological relationships of the animal to which it belonged, to delineate its form, and size, and habits of life; as the architect from a single capital rescued from a ruined edifice can declare not only the general style of the entire architecture, but can reproduce the size and proportions of the temple whose spirit and method it embodies. Not less sublime than the work of the astronomer, who sits in his observatory, and, by the use of a few figures, determines the existence and position in space of some far-off, unknown orb, is that of the paleontologistthe astronomer of time-worlds-who, from the tooth of a reptile, or the bony scale of a fish found thirty feet deep in the solid rock, declares the existence, ages ago, of an animal form which human eyes never beheld-a form that passed totally out of being uncounted centuries before the first intelligent creature was placed upon our planet-and by laws as unerring and uniform as those of the mathematics, proceeds to give us the length and breadth of the extinct form; to tell us whether it lived upon dry land, in marshes, or in the sea; whether a breather of air or water, and whether subsisting upon vegetable or animal food. It is this unity of the laws of animal life and organization running through the whole chain of existence, whether past or present, whether extinct or recent, that constitutes the

sublime philosophy of paleontological studies, and assures us that one enduring and infinite Intelligence has planned and executed every part of creation.

Crowds of reptile forms have passed before our view, but we have only just arrived at the culmination of the reign of reptiles-the Herpetarchy of the world's history. The Jurassic Age followed the Triassic. Before this time the Trilobites of the Paleozoic Ages were known only in history. The plain-chambered shells had been followed by lobulate-chambered shells-the Goniatites-and these were now, to a great extent, superseded by the Ammonites, a family of chambered shells with dorsal siphons and extremely complicated partitions between the chambers. So the complexity of Nature's products increased with her Most of the Ammonites were closely coiled. In their modifications and decorations the exuberance of Nature effloresced in hundreds of distinct species. Six hundred representatives of this peculiarly European family are exhibited in the museum of the University of Michigan-one of the results of the tireless industry of Dr. C. Rominger. The land was clothed with a vegetation quite similar to that of the present day; but the climate was yet warmer than at present, and many types of plants and animals, which to-day are confined within the tropics, were then enabled to range to the Arctic circle (Fig. 70).

age.

The great feature of the age was its reptiles. These were represented in all their orders except serpents. Batrachians also existed, if we may judge from some remains found in North Carolina and Pennsylvania in sandstones accumulated probably during this age. These remains belong to the genus Composaurus, and reveal, like the Carboniferous Batrachians, some relationship with the Labyrinthodonts. Better characterized Labyrinthodonts have. been described under the name of Centemodon, from the