604 DESEET VALLEYS. 



covered with soil painfully scooped out from fissures in and be- 

 tween the rocks which have been laid bare by the destruction of 

 the native forests.* In China, too, rock has been artificially cov- 

 ered with earth to an extent which gives such operations a real 

 geographical importance, and the accounts of the importation of 

 earth at Malta, and the fertihzation of the rocks on Mount Sinai 

 with sHme from the !Nile, may be not whoUy without foundation. 



Valleys m Deserts. 



In the latter case, indeed, river sediment might be very useful 

 as a manure, but it could hardly be needed as a soil ; for the 

 growth of vegetation in the wadies of the Sinaitic Peninsula 

 shows that the disintegrated rock of its mountains requires only 

 water to stimulate it to considerable productiveness. The wadies 

 not unfrequently present narrow gorges which might easily be 

 closed, and thus accumulations of earth, and reservoirs of water to 

 irrigate it, might be formed which would convert many a square 

 mUe of desert into fiom-ishing date-gardens and corn-fields. For 

 example, not far from Wadi Feirau, on the most direct route ta 

 Wadi Esh-Sheikh, is a very narrow pass called by the Arabs El 

 Bueb (El Bab) or, The Gate, which might be securely closed to a 

 very considerable height, with httle labor or expense. Above this 

 pass is a wide and nearly level expanse, filled up to a certain regu- 

 lar level with deposits brought down by torrents before the Gate, 

 or Bueb, was broken through, and they have now worn down a 

 channel in the deposits to the bed of the wadi. If a dam were 

 constructed at the pass, and reservoirs built to retain the winter 

 rains, a great extent of valley might be rendered cultivable. 



Effects of Minmg. 



The excavations made by man, for mining and other purposes, 

 may occasion disturbance of the surface by the subsidence of the 

 strata above them, as in the case of the mine of Fahlun, in Swe- 

 den, but such accidents have generally been too inconsiderable in 



* Manteqazza, Biodela Plata, e Teneriffa, p. 567. 



