630 DESERT VALLEYS. 
been laid bare by the destruction of the native forests.* In 
China, too, rock has been artificially covered with earth to an 
extent which gives such operations a real geographical import- 
ance, and the accounts of the importation of earth at Malta, 
and the fertilization of the rocks on Mount Sinai with slime 
from the Nile, may be not wholly without foundation. 
Valleys in Deserts. 
In the latter case, indeed, river sediment might be very use- 
ful as a manure, but it could hardly be needed as a soil; for 
the growth of vegetation in the wadies of the Sinaitic Penin- 
sula shows that the disintegrated rock of its mountains requires 
only water to stimulate it to considerable productiveness. The 
wadies present, not unfrequently, narrow gorges, which might 
easily be closed, and thus accumulations of earth, and reser- 
voirs of water to irrigate it, might be formed which would 
convert many a square mile of desert into flourishing date 
gardens and cornfields. Tor example, not far from Wadi 
Feiran, on the most direct route to 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 little labor or expense. Aboye this pass is a wide 
and nearly level expanse, filled up to a certain regular 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. 
Lifects of Mining. 
The excavations made by man, for mining and other pur- 
poses, may occasion disturbance of the surface by the subsi- 
dence of the strata above them, as in the case of the mine of 
Fahlun, in Sweden, but such accidents have generally been too 
* MANTEGAZZA, Lio de la Plata e Tenerijfa, p. 567. 
