Page:Popular Science Monthly Volume 23.djvu/347

Rh Herodotus for the filling up of the Arabian Gulf—twenty thousand years—is very much below the time required for the formation of the delta.

Thus far we have traced the unwritten history of Egypt, and the gulf of the Mediterranean, postulated by Herodotus, is not yet in sight. Nevertheless, at a much more remote epoch—in that called miocene by geologists—the gulf was assuredly there.

Near the tombs of the Caliphs at Cairo (according to Schweinfurth, two hundred feet above the level of the Mediterranean), in the neighborhood of Sakkarah and in that of the great pyramids, the limestone rocks, which look so like a sea-shore, were found by Professor Fraas to display the remains of a veritable coast-line. For they exhibit the tunnels of boring marine mollusks (Pholades and Saxicavæ), and they are incrusted with acorn-shells, as if the surf had only lately ceased to wash them. At the feet of these former sea-cliffs lie ancient sandy beaches, containing shells of oysters, scallops, and other marine mollusks, with the skeletons of sea-urchins. The specific characters of these marine organic remains leave no doubt that they lived during the miocene, or middle tertiary, epoch. Marine beds of the same age occur at Ain Musa, between Cairo and Suez.

There can be no question, therefore, that, in the miocene epoch, the valley of the delta was, as Herodotus thought it must have been, a gulf of the sea. And, as no trace of marine deposits of this, or of a later age, has been discovered in Upper Egypt, it must be assumed that the apex of the delta coincides with the southern limit of the ancient gulf.

Moreover, there is some curious evidence in favor of the belief that, at this period, however remote as measured by our standards of time, the Nile flowed down from Central Africa as it flows now, but probably in much larger volume. Every visitor to Cairo makes a pilgrimage to the "petrified forest," which is to be seen in the desert a few miles to the northeast of that city. And indeed it is a spectacle worth seeing. Thousands of trunks of silicified trees, some of them twenty or thirty feet long, and a foot or two in diameter, lie scattered about and partly imbedded in the sandy soil. Not a trunk has branches, or roots, or a trace of bark. None are upright. The structure of wood, which has not had time to decay before silicification, is usually preserved in its minutest details. The structure of these trunks is often obscure, as if they had decayed before silicification; and they are often penetrated, like other decayed wood, by fungi, which, along with the rest, have been silicified.