Between the two deserts, occupying a breadth of from fifteen to thirty-three miles, lies the depression forming the valley of Egypt. It forms the bed which the river has dug for itself in the soft chalky soil with untiring activity. Formerly, thousands of years ago,--thousands indeterminate,--it poured through the country in riotous cascades, the traces of which are still clearly recognisable in many spots. Gradually the river cleaned out the whole bed and established a regular surface level. When the historical period begins, the creative career of the river has already long been completed; from this time forward, the Nile flows in manifold curves and with numerous tributaries through the wrinkled valley, which it floods to a considerable degree only in midsummer, when the Ethiopian snow melts and seeks an outlet. The fertile land extends precisely as far as the waters of the Nile penetrate, or are guided by the hand of man in the flood season; a sharp line of demarcation separates the black fertile land formed of the muddy deposit left by the river, from the gray-yellow of the bordering desert. The breadth of the fertile territory is variable; on an average it covers eight, rarely more than ten, miles. Only at the mouth of the Nile it expands to the wide marsh lands of the Delta, intersected by numerous swamps and lakes. [Illustration: STATUE OF THE GODDESS SEKHET (Now in the British Museum)] Also on the south the border-land of Egypt has a sharp natural line of demarcation. A little above the 24th degree of latitude, at Gebel Silsilis, the sandstone plateau joins right on the river, higher up covering the whole of Nubia. The narrow neck of river at Gebel Silsilis is the southern boundary of fertile Egypt. A significant saga rising from the Arabian name of the mountain range (Silsilis means “the chain”) tells how once upon a time the stream was cut off by a chain that connected the opposite mountains. About eight miles higher up, at Assuan (Syene) a mountain range of granite and syenite opposes the course of the river like a cross-rail. True, the river has broken through the hard stone, but it has not had the power to rub it away, as it has done with the chalk-stone of Egypt; in numerous rapids it forces a passage between neighbouring rocks and innumerable islands raised from its bed. Without doubt, however, the torrent has continued to make its bed deeper here also. We know from old Egyptian accounts of the Nile levels that about four thousand years ago, at the time of the XIIth Dynasty, the Nile at the fortresses of Semneh and Kumneh, above the second cataract, must have been at least eight metres higher than it is at the present day. This can be explained only by supposing that, since then, the river must have burrowed an equivalent depth in the rocks of the cataract district.