978 PROFESSOR J. PRESTWTCH ON THE EVIDENCES OF A SUBMERGENCE 
also forms a perfectly hard conglomerate, as do some of the recent breccias in Greece. 
Besides, the deposit is said to have been washed down a valley and “ spread out on 
the plain in a fan-shape between the gorge of the valley and the Nile,” which is not 
the usual form assumed by the Bubble-drift. It seems more probably to be a detrital 
bed carried down from the adjacent hills at a time when a heavy seasonal rainfall, like 
that which now takes place in Abyssinia, prevailed in this part of Egypt, and is not 
necessarily of geological antiquity. 
In the many accounts we have of the geology of Egypt no mention is made of any 
deposit that corres 2 :)onds with the Ossiferous Breccias and Fissures of the Mediterranean 
coasts, though limestone rocks have been largely exploited and exhibit great lengths 
of mural escarpments. It would seem that these proofs of submergence are wanting 
in Egypt. The earlier stages, however, or those corresponding with the period of 
some of the high-level beaches of the Mediterranean are represented in Egypt by 
the terraces of the Lower Nile valley, described by Sir J. W. Dawson.* One of 
these terraces on the Mokattam Hill, near Cairo, is about 200 feet above the sea 
level, and associated with it have been found recent species of Ostrea, Pecten, 
Terehratula, Litliodomiis, and Balanus. Other terraces are mentioned higher up 
the valley, and likewise in the neighbourhood of Alexandria. 
The Mokattam beach possibly corresponds also with the river terrace above Assouan, 
about 120 feet above the level of the Nile, described by Dr. Leith Adams.+ In the 
river drift on this terrace he found several freshwater shells, and amongst others the 
Corhicula Jluminalis so common in pre-glacial and post-glacial times in England. If, 
as in Western Europe, the valley gravels and Baised Beaches had been covered by a 
Bubble-drift, it should have shown in some of these sections, but none have been 
recorded. 
Again, in the European area, the Quaternary deposits are separated from the alluvium 
of modern or Neolithic date by beds of coarse gravel, as in the valleys of the Thames 
and Somme, or by the stanniferous gravel in the valleys of Cornwall. In the valley 
of the Nile no such drift beds have been found at the base of the alluvium of that 
river, though the numerous deep boringsj that have been made, both below and 
above Cairo, offered unusual facilities for their detection. In all cases, where the 
boring was of sufficient depth, the alluvium, was found “ to consist of variable propor¬ 
tions of blown sand and alluvial mud,” and nothing to represent a Bubble-drift was 
met with. Nor were any marine beds encountered. 
We may, therefore, assume that before the deposit of the alluvium over the Nile 
valley, a land surface existed which would seem to have subsided gradually to an 
extent corresponding with the thickness of the Nile sediments. Although, therefore, 
* ‘ Geol. Mag.,’ Dec. iii., vol. 1, p. 289, 1884 ; and “Egypt and Syria,’’ chapters 2 and 4, 1887. 
t ‘ Quart. Jonrn. Geol. Soc.,’ vol. 20, p. 6, 1864. 
^ Leonard Hornkr m ‘Phil. T vans.’ for 1855, Part I., p. 105, and for 1858, Part II., ^3. 63, and 
Prof. Judd, in ‘ Roy. Soc. Proc.,’ vol. 39, p. 213, 1885. 
