Читать книгу The Pleistocene of North America and its vertebrated animals - Oliver Perry Hay - Страница 23

In Maryland and the District of Columbia there have been recognized three Pleistocene terraces (Shattuck, as cited above). The uppermost is the Sunderland, the next the Wicomico, the lowest the Talbot. These are not correlated by Shattuck definitely with glacial divisions of the Pleistocene, but the Sunderland is the oldest, while the Talbot is regarded the most recent, probably about the age of the last glacial stage, the Wisconsin.

When the writer began his study of the Pleistocene he accepted the theory proposed by McGee and the Maryland geologists, and traces of this acceptance may be found in this work; but he is now convinced of its falsity. It is hardly to be believed that the coastal region could have been occupied, even at intervals, since the late Pliocene, when the depression is supposed to have been at least 500 feet, and 200 feet during the Sunderland, down to the end of the Wicomico and even the Talbot, without its having left other traces of marine occupation than the supposed terraces and escarpments. There ought to appear somewhere in the long border from New Jersey to Mexico abundant and extensive deposits of stratified materials, clays, sands, and gravels. Such deposits appear to be relatively rare.

A still more serious objection to the theory of submergence beneath marine waters is the absence of marine fossils. In the materials forming these terraces one might with confidence expect to find at least marine mollusks, mussels, clams, and beds of oysters; probably also remains of fishes, of porpoises, and of whales. Leaving out of consideration the Talbot terrace, which is near sea-level (Shattuck, op. cit., p. 10), the supporters of the theory under consideration admit that not in the Lafayette, nor the Sunderland, nor the Wicomico, have any traces of such fossils been met with. On the other hand, all over these terraces are found remains of land animals and plants. Mastodons, elephants, and horses are by no means rare. Conditions favorable for the preservation of teeth of proboscideans must have been quite as well adapted to preserve shells of oysters. In the Sunderland and Wicomico a few land plants have been secured, an abundance of them in the Talbot. Map No. 39 shows the distribution of Pleistocene mammals, mollusks, and plants on the Coastal Plain of North Carolina.

It seems evident, therefore, that the sea has had nothing to do with the formation of the Lafayette, the Sunderland, and the Wicomico terraces, and little with that of the Talbot. It was natural that the advocates of this theory of the formation of these terraces during the Pleistocene should distribute them somewhat impartially over the time of this epoch, assigning the Talbot to a late interval. On page 11 the writer has called attention to the fact that in many places along the coast from southeastern Texas to New Jersey, at or near sea-level, there are beds which contain a vertebrate fauna of the Aftonian or first interglacial stage. Probably nowhere do these beds have any large amount of later materials overlying them; it is often extremely little. So far as the writer can judge, this means that all the terraces and escarpments were produced before the time of the first interglacial; not since that distant time has there occurred along the Gulf or Atlantic coasts south of New Jersey any considerable elevation or depression of the Coastal Plain.