Egypt may be said to have no prehistoric period, and our task with it will be limited to showing that its written history scarcely goes back as far as many Egyptologists suppose and confidently affirm, and that beyond this it has as yet afforded nothing. Egypt, in short, old though it seems, is really a new country. When its priests, according to Plato, taunted Solon with the newness of the Greeks and referred to the old western empire of Atlantis, they were probably trading on traditions of antediluvian times, which had no more relation to the actual history of the Egyptian people than to that of the Greeks. The limestones and sandstones which bound the Nile valley, sometimes rising in precipitous cliffs from the bank of the stream, sometimes receding for many miles beyond the edge of the green alluvial plain, are rocks formed in cretaceous and early tertiary times under the sea, when all Northern Africa and Western Asia were beneath the ocean. When raised from the sea-bed to form land, they were variously bent and fractured, and the Nile valley occupies a rift or fault, which, lying between the hard ridges of the Arabian hills on the east and the more gentle elevations of the Nubian desert on the west, afforded an outlet for the waters of interior Africa and for the great floods which in the rainy season pour down from the mountains of Abyssinia. This outlet has been available and has been in process of erosion by running water from a period long anterior to the advent of man, and with this early pre-human history belonging to the miocene and pliocene periods of geology we have no need to meddle, except to state that it was closed by a great subsidence, that of the pleistocene or glacial period, when the land of North Africa and Western Asia was depressed several hundred feet, when Africa was separated from Asia, when the Nile valley was an arm of the sea, and when sea-shells were deposited on the rising grounds of Lower Egypt at a height of two hundred feet or more.[64] Such raised beaches are found not only in the Nile valley but on the shores of the Red Sea, and, as we shall see, along the coast of Palestine; but, so far as known, no remains of man have been found in connection with them. This great depression must, however, geologically speaking, have been not much earlier than the advent of man, since in many parts of the world we find human remains in deposits of the next succeeding era. [64] Hull, _Geology of Palestine and adjacent Districts_, Palestine Exploration Fund. Dawson, _Modern Science in Bible Lands_, p. 311 and Appendix. References will be found in these works to the labours of Fraas, Schweinfurth, and others.