188 



NORTH-EAST AFEICA. 



gypsum cliffs, liere and there intersected by wadies. Their summits are crowned 

 with feathery diim palms, and from their sides flow perennial springs. A verdant 

 circle thus surrounds this desert waste, where nothing is visible but a few acacias 

 and brushwood. At some distance from the cliffs are saline efflorescences, which 

 become gradually solidified towards the middle of the plains, where they acquire 

 the consistency of slabs some two feet thick. Here and there they present a greyish 

 tesselated appearance, the interstices being filled with dazzling white crystals. At 

 the lowest level of the depression, between the Ansali promontory and Mount 

 Ortoaleh, are collected the waters of Lake Alalbed, or Allolebed, whose size varies 

 according to the quantity of water brought down by the torrents. Its mean 

 depth is said scarcely to exceed 40 inches. The dessication of the old bay of 



Fig. 46. — Lake of Alalbed. 

 Scale 1 : 1,500,000. 



r% i-frTlK 



5g°50 



40° 50' 



30 Miles. 



Ansali may be explained by a gradual upheaval of the coast west of the Red Sea, 

 as well as on the east side in Arabia. The coral banks and recent shells found at 

 the north of the plain attest the presence of marine waters on the now upheaved 

 depression between the plain of Bagad and Auwakil Bay. The rivers flowing 

 from the Abyssinian chain are not sufficiently copious to repair the loss by 

 evaporation, and thus the old lake, formerly of some extent, has gradually become 

 a shallow swamp. The Taltals, who inhabit the surrounding district, assure the 

 Abyssinians, possibly to protect themselves from their visits, that the lake 

 occasionally " walks away " from its old bed in search of a new one ; and woe to 

 the caravans overtaken by this sudden inundation ! Besides, even at some 

 distance from the lake, travellers run the risk of sinking into the treacherous 

 soil, and whole companies of men and beasts are said to have thus disappeared. 



