The fossil fish are Ganoids, some of them of the genus Catopterus, others belonging to the liassic genus Tetragonolepis (Æchmodus), see [Fig. 376.] Two species of Entomostraca called Estheria are in such profusion in some shaly beds as to divide them like the plates of mica in micaceous shales (see Fig. 409).

These Virginian coal-measures are composed of grits, sandstones, and shales, exactly resembling those of older or primary date in America and Europe, and they rival, or even surpass, the latter in the richness and thickness of the coal-seams. One of these, the main seam, is in some places from 30 to 40 feet thick, composed of pure bituminous coal. The coal is like the finest kinds shipped at Newcastle, and when analysed yields the same proportions of carbon and hydrogen—a fact worthy of notice, when we consider that this fuel has been derived from an assemblage of plants very distinct specifically, and in part generically, from those which have contributed to the formation of the ancient or palæozoic coal.

Triassic Mammifer.—In North Carolina, the late Professor Emmons has described the strata of the Chatham coal-field, which correspond in age to those near Richmond, in Virginia. In beds underlying them he has met with three jaws of a small insectivorous mammal which he has called Dromatherium sylvestre, closely allied to Spalacotherium. Its nearest living analogue, says Professor Owen, “is found in Myrmecobius; for each ramus of the lower jaw contained ten small molars in a continuous series, one canine, and three conical incisors—the latter being divided by short intervals.”

Low Grade of Early Mammals favourable to the Theory of Progressive Development.—There is every reason to believe that this fossil quadruped is at least as ancient as the Microlestes of the European Trias described in [p. 368]; and the fact is highly important, as proving that a certain low grade of marsupials had not only a wide range in time, from the Trias to the Purbeck, or uppermost oolitic strata of Europe, but had also a wide range in space, namely, from Europe to North America, in an east and west direction, and, in regard to latitude, from Stonesfield, in 52° N., to that of North Carolina, 35° N.

If the three localities in Europe where the most ancient mammalia have been found—Purbeck, Stonesfield, and Stuttgart—had belonged all of them to formations of the same age, we might well have imagined so limited an area to have been peopled exclusively with pouched quadrupeds, just as Australia now is, while other parts of the globe were inhabited by placentals; for Australia now supports one hundred and sixty species of marsupials, while the rest of the continents and islands are tenanted by about seventeen hundred species of mammalia, of which only forty-six are marsupial, namely, the opossums of North and South America. But the great difference of age of the strata in each of these three localities seems to indicate the predominance throughout a vast lapse of time (from the era of the Upper Trias to that of the Purbeck beds) of a low grade of quadrupeds; and this persistency of similar generic and ordinal types in Europe while the species were changing, and while the fish, reptiles, and mollusca were undergoing great modifications, would naturally lead us to suspect that there must also have been a vast extension in space of the same marsupial forms during that portion of the Secondary or Mesozoic epoch which has been termed “the age of reptiles.” Such an inference as to the wide geographical range of the ancient marsupials has been confirmed by the discovery in the Trias of North America of the above-mentioned Dromatherium. The predominance in earlier ages of these mammalia of a low grade, and the absence, so far as our investigations have yet gone, of species of higher organisation, whether aquatic or terrestrial, is certainly in favour of the theory of progressive development.

[1] Dr. Wright, on Lias and Bone Bed, Quart. Geol. Journ., 1860, vol. xvi.

[2] Buckland, Proc. Geol. Soc., vol. ii, p. 439; and Murchison and Strickland, Geol. Trans., Second Series., vol. v, p. 347.

[3] Principles of Geology, chap. xxvii.

[4] Monog. des Bunter-Sandsteins.

[5] Reaches its maximum in the Trias, but passes down to older rocks.