HAWKSHAW FIEST CATARACT. 



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(specimen 112). The desert to the westward seems to consist entirely 

 of low hills of sandstone, the intervening valleys heing filled with sand 

 of a rich yellow colour composed of rounded grains of quartz. 



The sandstone on the exposed sides of these hills yields easily to the 

 action of the weather, presenting a branched and almost coralline 

 appearance in situations exposed to the wind. 

 Hesseh is the only island of the Cataract on which 

 sandstone occurs ; it is there seen capping a rocky 

 eminence at the northern extremity of the island 

 (see PL lY.). 



On the eastern side of the Cataract the crystal- 

 line rocks appear in the form of hornblende- and 

 mica-schists, and at about four miles below As- 

 souan are overlain by sandstone, which caps all 

 the hills for many miles to the eastward, forming 

 a layer often not more than a few feet thick on the 

 top of the syenite. The latter appears in most of 

 the hollows and valleys in bare coarse-grained 

 bosses, rapidly decomposing and scahng off in layers, 

 or else is covered with sand strewed with pebbles 

 of quartz and chalcedony, these being derived from 

 the sandstone, which wastes quite as fast. 



To the eastward of the Eirst Cataract there is a 

 wide valley, which may be seen on the map, com- 

 mencing at Philae aod joining the Nile vaUey 

 again about four miles below Assouan. As it has 

 more than once been suggested that the course of 

 the Nile was formerly along this valley, it may be 

 of interest to state that the level of the highest 

 point of this valley (R on map) is 1 00 feet above 

 the level of high Nile at Philae ; the total length of 

 the valley is 7 J miles. At this point, R, a pit 

 16 feet deep has been dug through a sandy deposit. 



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containing branched concretions of lime. As rock 



in the form of hornblende-schist and greenstone 

 occurs on both sides of this valley, and at no great 

 distance from the pit, this deposit of sand pro- 

 bably extends to no great depth, though we have 

 seen that to the west of Hesseh the Nile flows 

 through a narrow channel of very great depth; 

 the river is not, however, entirely confined to that 

 channel. The section along this valley (of which 

 an accurate one was taken) seems to favour the idea 

 that the Nile did formerly flow through it ; for to 

 the north of its summit the valley (see the section) 

 is, for the last three miles and a half, below the level of high Nile at 

 Philse, whilst the portion to the south is considerably above that level, 

 and is covered with a considerable thickness of deposit from the Nile. 

 It is in this part of the valley that the section of Nile deposit 30 

 feet thick, described by Dr. Leith Adams, in a paper printed in the 



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