GEOLOGICAL HISTORY OF EGYPT AND THE NILE VALLEY. 329 
to a depth of over 200 feet, at a very recent period* (see 
Figs. 2 and 3). 
Thus after the general elevatory movement of the Miocene 
and early Plocene periods above described, a movement of 
depression in later Pliocene times set in, and the ocean 
waters gradually spread over the deeply eroded plain at the 
Nile mouth. As the land continued to sink, the sea would 
continue to wear down the cliffs and carry away exposed 
rock masses, and thus ultimately Lower Egypt became a 
wide gulf, imto which the Nile Valley opened out northwards, 
until the waters reached the level indicated by the shell 
beds of Mokattam and Ghizeh. 
The submergence of Lower Egypt and the Mediterranean 
coasts could not but make itself felt far up the Nile Valley. 
The sea must have sent an arm into the channel, while the 
waters of the river still higher would be pent up and rise to 
higher levels. 
The effect of this inundation may be clearly recognised in 
the terraces which occur on both banks of the river from 
below the First, to above the Second, Cataract, and in the 
caves marking higher levels of the river margin. These occur 
both in the limestone and Nubian sandstone, and are from 
60 to 70 feet above the highest Nile. The terraces, consist- 
ing of gravel and alluvial matter, with fluviatile shells, have 
been described by the late Dr. Leith Adams.t These old 
terraces with fresh-water shells were observed at levels of 
110 to 130 feet above the highest inundations of the present 
river; as, for example, at Derr, the capital of Nubia, and at 
Abusir, Gharbea, north of Koroske, &e. The shells in these 
terraces belong to fresh-water species, such as Cyrena flumi- 
nalis, Unio pictorum, Paludina bulimoides, and Bulimus pulus. 
The tooth of a Hippotamus considered by Dr. Falconer to be 
that of Hl. amphibius, the existing species of the country, 
was dug out of one of these terraces by Dr. Adams. 
* These raised beaches were recognised by the author at Akabah, Wady 
esh Sheriah, near Gaza, at E] Mejdel and Esdud, in Palestine, &e. Dr. J. 
Walther describes two coral reefs of modern date on the shores of the Red 
Sea near Tor at levels of 230 and about half this height above the surface, 
Die Korallenriffe d.Sinai halbinsel, ch. vi. 
+ Quart. Journ. Geol. Soc., vol. xx, p.6. These terraces are also de- 
scribed by Sir J. W. Dawson. It may be presumed that the numerous 
hammerstones and worked flakes found by Surgeon-Major S. Archer at 
Wady Halfa during the recent Soudan Campaign, and described by Dr. 
J.S. Hyland, come from these terraces, but this is not very clear from the 
description itself. See Scientifie Proceedings Royal Dublin Society, Feb., 
1890. 
