286 



NORTH-EAST AFRICA. 



Fig. 91.— KoRosKo Desert. 

 Scale 1 : 2,800,000. 



QQ° 



*-v"'"'Bab.el-Ko 



P2° 



sko 



bbu Rakib 



'^adi Marîsha 



scattered by thousands in the desert. They are small sandstone hills merely 

 rising some 60 feet above the plain, but at some points attaining a relative elevation 

 of 660 feet, or from 1,630 to 2,000 feet above the sea. The granite heights in the 

 interior reach an altitude of over 2,160 feet, some of the peaks even rising to 

 nearly 3,300 feet. 



The sandstone rocks of Nubia present 

 the most diverse forms. Some stand out 

 like regular towers, others in the form 

 of pyramids, whilst others again, whose 

 central portion has disappeared, re- 

 semble volcanic cones. Consisting of 

 horizontal layers of quartzose sandstone 

 of varying density, they offer more or 

 less resistance in different places. In 

 one place the summit crumbles away, 

 elsewhere the base leaving the crest 

 crowned as if with a table ; several rocks 

 are also pierced with openings through 

 which light is visible. The very names 

 that the nomads and caravan leaders 

 give to these sandstone heights are a 

 proof of the variety of their forms. 

 They imagine they see in them j^alaces, 

 animals, and processions of warriors. 

 Thanks to these fantastic outlines, the 

 guides of the caravans can always de- 

 termine their whereabouts in these 

 endless labyrinths of breaches winding 

 between the rocks. The various colours 

 of the stone also assist them in finding 

 their way. Certain strata are shaded 

 with green, yellow, pink, or blue ; whilst 

 others, in which ferruginous sands pre- 

 dominate, are of a brilliant red. Jasper, 

 chalcedony, and siliceous crystals are 

 embedded in the walls. But on each 

 journey the guide finds some changes. 

 The sands produced by the disinte- 

 gration of the rocks shift their position 

 according to the direction of the wind, 

 which carries it in a cloud above the 

 crests, and scatters it now on one side, now on another, forming rounded heaps 

 which blend in graceful curves with the coarser sands at the base. Shifting dunes 

 of sand, some of which are as much as 166 feet high, move here and there through- 



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D/e6e/ Go^eJbat^-^" Taboun 



Abbu:lnteh-ChourrQut 



■ D/ei> e/ Af.a^hén'^h^ 



60 Miles. 



