292 Frof, J. W. Dawson— Geology of ihe Nile- Valley. 



reasons stated elsewhere, however, I doubt very much whether they 

 can be attributed to man.^ 



We may also connect this recent submergence with the sandstones 

 and raised beaches holding modern shells in the vicinity of Alex- 

 andria and of the Eed Sea, and also the similar sandstones of the 

 maritime plains of Syria, which near Jaffa and at Beyrout attain to 

 elevations of about 200 feet. We thus have evidence of a very 

 extensive Pleistocene submergence, extending all around the eastern 

 end of the Mediterranean. It is limited in date- by the Middle Tertiary 

 on the one hand, and by the elevated land of the Post-glacial on the 

 other, and was not improbably coincident with that great submer- 

 gence of the Pleistocene which aifects so generally the Northern 

 hemisphere. 



There is, I thint, evidence at Cairo that this submergence was in 

 its earlier period of still greater magnitude. The elevation of the 

 Mokattam Hill is 640 feet, and it consists of horizontal Eocene 

 deposits, the lower part of which are for the most part pure marine 

 limestones, while about one-third of the upper part consists of coarse 

 brown limestone with marly beds and clays. At the height of 

 about 500 feet, and near the junction of these two members, there is 

 a broad flat terrace, especially on the western side ; and though no 

 marine shells have been found in this, it is scarcely possible to pass 

 along it and examine its bounding cliffs, without being convinced 

 that it has been produced by surf erosion. The continuation of this 

 terrace may be observed here and there along the Nile as far as 

 Assouan, beyond which place I had less opportunity to trace it. 

 With this second terrace, older no doubt than that at a lower level, 

 I would connect the denudation of the probably Miocene sandstones 

 containing silicified trees of which Gebel Ahmeen, near Cairo, is a 

 remnant, and also the denudation of the Judaean Hills and the lower 

 slopes of Lebanon, and the higher marine terraces of the Red Sea. 



In contrast with these evidences of subsidence, I may now refer to 

 the fact that at a later date, and more immediately preceding the 

 historic period, the land of Egypt was probably higher than at 

 present. The occurrence of patches of sand projecting through the 

 Nile mud of the delta, and the fact ascertained by the recent borings 

 by Col. Ardagh, that at a depth of 30 to 40 feet the alluvial mud 

 rests on desert sand, show that in post-Glacial or early modern 

 times the plain of the delta was a part of the desert, through which 

 the Nile probably ran in a narrow and deep channel, and more to 

 the eastward than at present.^ A subsequent slight depression near 

 the beginning of the historical period placed it in a position to 

 receive and retain the inundation mud. This, with the further pro- 

 tection aflbrded by the line of raised beaches along its northern 

 edge, rendered the formation of the delta easy, and enabled its 

 alluvial soil to be deposited in a much shorter time than would have 

 been required had the Nile poured its deposits into a maritime bay 

 of any considerable depth, and unsheltered oh its leeward side. 



1 Trans. Victoria Institute, 1884. 



2 The fresh-water deposits found in the central part of the Isthmus of Suez may 

 belong to this period. 



