The Student's Elements of Geology

by Sir Charles Lyell

According to Professor Hitchcock, the footprints of no less than thirty-two species of bipeds, and twelve of quadrupeds, have been already detected in these rocks. Thirty of these are believed to be those of birds, four of lizards, two of chelonians, and six of batrachians. The tracks have been found in more than twenty places, scattered through an extent of nearly 80 miles from north to south, and they are repeated through a succession of beds attaining at some points a thickness of more than 1000 feet.[^[7]]

The bipedal impressions are, for the most part, trifid, and show the same number of joints as exist in the feet of living tridactylous birds. Now, such birds have three phalangeal bones for the inner toe, four for the middle, and five for the outer one (see Fig. 408); but the impression of the terminal joint is that of the nail only. The fossil footprints exhibit regularly, where the joints are seen, the same number; and we see in each continuous line of tracks the three-jointed and five-jointed toes placed alternately outward, first on the one side, and then on the other. In some specimens, besides impressions of the three toes in front, the rudiment is seen of the fourth toe behind. It is not often that the matrix has been fine enough to retain impressions of the integument or skin of the foot; but in one fine specimen found at Turner’s Falls, on the Connecticut, by Dr. Deane, these markings are well preserved, and have been recognised by Professor Owen as resembling the skin of the ostrich, and not that of reptiles.

The casts of the footprints show that some of the fossil bipeds of the red sandstone of Connecticut had feet four times as large as the living ostrich, but scarcely, perhaps, larger than the Dinornis of New Zealand, a lost genus of feathered giants related to the Apteryx, of which there were many species which have left their bones and almost entire skeletons in the superficial alluvium of that island. By referring to what was said of the Iguanodon of the Wealden, the reader will perceive that the Dinosaur was somewhat intermediate between reptiles and birds, and left a series of tridactylous impressions on the sand.

To determine the exact age of the red sandstone and shale containing these ancient footprints, in the United States, is not possible at present. No fossil shells have yet been found in the deposit, nor plants in a determinable state. The fossil fish are numerous and very perfect; but they are of a peculiar type, called Ischypterus, by Sir Philip Egerton, from the great size and strength of the fulcral rays of the dorsal fin, from ischus, strength, and pteron, a fin.

The age of the Connecticut beds cannot be proved by direct superposition, but may be presumed from the general structure of the country. That structure proves them to be newer than the movements to which the Appalachian or Allegheny chain owes its flexures, and this chain includes the ancient or palæozoic coal-formation among its contorted rocks.

Coal-field of Richmond, Virginia.—In the State of Virginia, at the distance of about 13 miles eastward of Richmond, the capital of that State, there is a coal-field occurring in a depression of the granite rocks, and occupying a geological position analogous to that of the New Red Sandstone, above-mentioned, of the Connecticut valley. It extends 26 miles from north to south, and from four to twelve from east to west.

The plants consist chiefly of zamites, calamites, equiseta, and ferns, and, upon the whole, are considered by Professor Heer to have the nearest affinity to those of the European Keuper.

The equiseta are very commonly met with in a vertical position more or less compressed perpendicularly. It is clear that they grew in the places where they are now buried in strata of hardened sand and mud. I found them maintaining their erect attitude, at points many miles apart, in beds both above and between the seams of coal. In order to explain this fact, we must suppose such shales and sandstones to have been gradually accumulated during the slow and repeated subsidence of the whole region.