Sir J. W. Dawson — Geology of the Nile Valley. 483 



and in the subsequent elevation whicli immediately preceded the 

 Modern age. 



The Historical period has been characterized by the deposition of 

 much fluviatile sediment, especially in the Delta, and probably by a 

 slight depression of the Mediterranean coast, accompanied by a corre- 

 sponding slight elevation between Cairo and the Gulf of Suez. 

 From the close of the Pleistocene period, however, the central part 

 of the Isthmus of Suez would appear to have been land, since it 

 consists of fluviatile and lacustrine deposits, formed by the Pliocene 

 or Post-Glacial Nile, and is uncovered by the modern beds which 

 lie on either side, and contain respectively the shells of the Red Sea 

 and of the Mediterranean. 



9. The remains of Man discovered in the Nile Valley are all 

 superficial and modern, unless we except the supposed implements 

 found by General Pitt Rivers in the old indurated gravels near 

 Thebes, which are probably of Pleistocene age. I have, however, 

 elsewhere shown that there is no certainty as to the human origin 

 of the flakes found in these beds.' Of the mode of occurrence and 

 relations of the flint implements found on the surface in various 

 parts of the Valley of the Nile, a very good account is given by Mr. 

 Jukes-Browne, in his papers in the Cambridge Antiquarian Society's 

 communications, and in the Journal of the Anthropological Institute. 

 The same conclusions apply to the flint implements found on the 

 surface in Judea and at Beyrout, though there are remains of greater 

 antiquity in the older cave-breccias of the Lebanon. 



10. It thus appears that the position of the Valley of the Nile was 

 primarily determined by that of the ridges of old crystalline rocks 

 which caused the flow of drainage to the North, and prevented 

 direct communication with the depression of the Red Sea. It was 

 also influenced by the fractures and faults above referred to, as 

 occurring in the elevation of the Eocene beds, and which produced 

 lines of weakness along the course of the present valle3^ Much of 

 the actual cutting of the valley must have been effected by the sea 

 in times of Pleistocene submergence, and it must have been at this 

 time that the extensive removal of the softer parts of the Miocene 

 sandstone, evidenced by the loose trees of the petrified forests, oc- 

 curred. At this time also, many inland cliffs and wadys must have 

 been cut, and beds of gravel deposited. To this period we may also 

 refer the scattering of boulders from the eastern crystalline moun- 

 tains over the Lybian desert, as seen for example at Denderah. 

 This transport of boulders would indeed seem to imply the action of 

 floating ice in some part of the Pleistocene period, though it is 

 possible that they may have been pushed by the waves along coast- 

 lines which have since disappeared. Lastly, from the first elevation 

 of the Eocene beds, the river itself has been extensively modifying 

 its bed, both by erosion and deposition. It is difficult in all cases to 

 separate the effects of the river erosion and that of its lateral torrents 

 from those of the previous submergence. It is certain, however, 

 that the river action is capable of undermining and gradually cutting 



1 Transactions Victoria Inst. 1884. 



