extinct volcanoes of Kenya and Kilimanjaro, and on the highest peaks of the Atlas range far away in the west of Morocco.[131] The lower valley of the Nile, the country which we know as Egypt, has undergone fluctuations of level since the beginning of the Tertiary Epoch. In the secondary ages the last five hundred miles of the Nile valley lay for a period of immense duration under the waters of the ocean, where the limestone deposits were formed. In Eocene times this limestone bed was slowly raised to the altitude of a tableland above the Mediterranean, but always cut off from the direction of the Red Sea by the continuous range of mountains which we know as the Nubian Alps. It is possible that the drainage of the Central African rift valleys and lakes and snow-mountains may, by the uprising of this tableland, have been severed from its natural escape to the Mediterranean, and that the Nile ran to waste in what is now the Libyan Desert. No doubt the Nile formed lake after lake, and the overflow from these lakes slowly bored a passage through the limestone tableland. Then in Miocene times took place a further rise in the range of the Nubian Alps and the adjoining land, which caused fractures to occur in the limestone formation. Of this the Nile took advantage, though it filled up the rifts to some extent with its debris. The Nile cut at one time a very deep bed through the limestone; but then occurred fluctuations in level, a sinking of the Nile valley which once more brought the waters of the Mediterranean far inland, and covered the channel of the Nile with rubble washed in by the sea. Previous to this the cracks and folds which had occurred through the upheaval of the eastern highlands had evidently caused volcanic disturbances by the water of the Nile reaching through these cracks the heated strata below. The volcanic outbursts left behind beds of basalt through which the persistent Nile again cut a channel. In the later Tertiary ages Egypt was a country of abundant rainfall, the very reverse of the absolute desert of to-day. Heavy rains carved and scarped the surface of the country and nourished a luxuriant forest. At this period the lands lying to the west of Egypt, in what is now known as the Libyan Desert, were probably a bay of the Mediterranean.