THE BAYUDA STEPPE. 289 



commanded by ttese heights is a mountainous country covered with hollows, or a 

 few groves of green mimosas during the rainy season, and bounded to the west 

 between Khartum and Ambukol by the depression of the Wady Mokattam, or the 

 " Yalley of Inscriptions," into which probably flowed an ancient arm of the Nile. 

 The whole region, though much less barren than the atmur of Eastern Nubia, is 

 termed the steppe or desert of Bayuda. Gekdul and Magaga, whose highest 

 point, Ussub-Ommaneh, is a cupola of red porphyry, or erupted masses, around 

 which the sandstone rocks, probably liquefied by the outpourings of lava, have 

 spread over the sands in sheets of siliceous scoriae. According to Russegger, it is 

 owing to the eruption of these ancient volcanoes that the Nile, formerly flowing to 

 the west, was compelled to turn eastwards in order to effect its great bend of over 

 480 miles. In the western part of the steppe the ferruginous sands of the moun- 

 tains, washed down by the rains, have covered the soil in thick layers. Here and 

 there the sand has collected in the hollows where the wadies have deposited their 

 alluvia ; the surface of the plain is thus streaked with long bands of diverse colours 

 of the strangest appearance. 



The Jebel-Simrieh, formed of pink sandstone, and other hills to the west of the 

 depression of the " Valley of Inscriptions," are less elevated than Magaga, and 

 like it are not very long ; the valley of the "VVady-Melek, whose bed, during the 

 floods, gives passage to the waters of Dar-F6r, bounds these mountains on the west. 

 On the banks of the Nile itself, in the space comprised between Marawi and New 

 Dongola, there are nothing but sandstone cliffs, the crystalline rocks reappearing 

 only at the Third Cataract. Here the heights on the left bank form part of the 

 chains which rise in Eastern Nubia ; to the west they soon become lost under the 

 sands, being succeeded by oases at a short distance from the river and parallel with 

 it. In this respect the western zone of the Nubian region forms a complete 

 contrast to the tracts beyond the Nile. To the north of Wady-Halfa, and nearly 

 opposite the colossi of Ibsambul, lies a deep valley overlooked by the black or 

 reddish walls of ancient volcanoes. This is the Wady-Jehenna, or " Valley of 

 Gehenna," a terrible region which the Arabs shun as if it were still burning. 



In Western as well as in Eastern Nubia, the sandstones rapidly crumble away 

 under the influence of the wind, rain, and heat, and change into loose sand which 

 the aerial currents reform into dunes or taluses. In many respects the sands of 

 Africa recall the snows of the great Alps ; like the snowfields they collect in the 

 depressions and crevasses of the rocks, glide over the ravines in avalanches, crown 

 the needle-like points of the peaks, and here and there project over the precipices, 

 forming narrow strips which give way at the slightest shock. Between the dunes 

 and the populations of the oases on the edge of the desert the struggle is incessant ; 

 the sands, borne forward by the winds, surround the trees, cover up cultivations, 

 block up the fountains, and encroach upon the inhabitable domain. But on his 

 side the peasant utilises the sand by mixing it with his soil. The extent of ground 

 he can render productive depends entirely upon the quantity of water at his 

 disposal. 



19— AF. 



