Vol. 52.] PEOF. E. HELL OX THE GEOLOGY OF THE NILE VALLEY. 315 



In some places, between Silsileh and Assuan, the second terrace 

 seems to merge at the surface into the low terraces of the Nubian 

 Sandstone, the grand escarpment of the Eocene limestone having 

 given place to the Nubian Sandstone. In this district Leith Adams 

 discovered numerous river-shells at a level of at least 120 feet 

 above the highest Nile of the present day. 1 



(/) Old terraces above the First Cataract. — According to Leith 

 Adams, the old terraces now rising far above the highest floods of 

 the Nile at the present day may be traced at intervals along the 

 valley between the First and Second Cataracts. One of the most 

 remarkable instances occurs at Derr, the capital of Nubia, about 

 80 miles below the Second Cataract. Here, above the cultivated 

 terrace liable to floods, rises a cliff of sandstone, above which is a 

 second sloping terrace, rising from 110 to 130 feet above highest 

 Nile, formed of pebbles, among which Adams found numerous 

 specimens of Cyrena flummalis, a shell now abundant in the Nile 

 waters. Some miles farther northward, in the same terrace, the 

 same shell was found in reddish sandy soil, together with Bulimus 

 pullus. Similar terraces were recognized at Gharbea, north of 

 Korosko, at Dakke and Gertassee, rising from 60 to about 100 feet 

 above the highest Nile floods, and containing several species of fresh- 

 water mollusca. 2 These observations are confirmed by Capt. Lyons, 

 who speaks of the large sheets of gravel, which in Nubia extend 

 for a length of 7 or 8 miles along the Nile bank at Debera, 8 miles 

 north of Wadi Haifa, at 100 feet above the present Nile floods, and 

 containing shells, such as jEtheria semilunata, Cyrena jluminalis, 

 Unio, and Paludina. 3 



(g) But these evidences of former higher levels do not cease at 

 the Second Cataract, for Capt. Lyons has shown, 4 by the position and 

 inscriptions on the rocks and temples dating as far back as 2200 B.C., 

 that the river then rose to a maximum of 27 feet above its present 

 flood-level ; the amount of rise decreasing as time went on. Lyons 

 suggests that these variations of the river were caused by earth- 

 movements ; but it seems more probable that they are referable to 

 the same general causes as those which have given rise to the high 

 terraces occurring at intervals down the valley into Lower Egypt. 



Thus we have seen that, throughout a distance of between 600 

 and 700 miles above Cairo, the evidence derived from the terraces 

 is cumulative, and tends to prove that the original surface of the 

 Nile waters stood at a level varying from 50 to 100 feet or more 

 above that of the present day. 



Part III. 



7. Old River-Channels. 



How many channels of the primceval Nile there may be which 

 the river has deserted in consequence of the fall of its surface I 



1 Quart. Journ. Geol. Soc. vol. xx. (1864) p. 9. - Ibid. pp. 13, 14. 



3 Ibid. vol. 1. (1894) p. 543. 4 Ibid. p. 544. 



