SANDS OF EGYPT. Bot 
with respect to the advancement of the sands; for their pro- 
gress was so slowas hardly to be perceptible in the course of a 
single reign, and long experience has shown that, from the na- 
tural effect of the inundations, the cultivable soil of the valley 
is, on the whole, trenching upon the domain of the desert, not 
retreating before it. 
The oases of the Libyan, as well as of many Asiatic deserts, 
have no such safeguards. The sands are fast encroaching upon 
them, and threaten soon to engulf them, unless man shall 
resort to artesian wells and plantations, or to some other ef- 
ficient means of checking the advance of this formidable 
enemy, in time to save these islands of the waste from final de- 
struction. 
Accumulations of sand are, in certain cases, beneficial as a 
protection against the ravages of the sea; but, in general, the 
vicinity, and especially the shifting of bodies of this material, 
are destructive to human industry, and hence, in civilized 
countries, measures are taken to prevent its spread. This, 
however, can be done only where the population is large and 
enlightened, and the value of the soil, or of the artificial erec- 
tions and improvements upon it, is considerable. Hence in 
the deserts of Africa and of Asia, and the inhabited lands 
which border on them, no pains are usually taken to check the 
drifts, and when once the fields, the houses, the springs, or the 
canals of irrigation are covered or choked, the district is aban- 
doned without a struggle, and surrendered to perpetual deso- 
lation.* 
* In parts of the Algerian desert, some efforts are made to retard the ad- 
vance of sand dunes which threaten to overwhelm villages. ‘‘ At Debila,” 
says Laurent, ‘‘ the lower parts of the lofty dunes are planted with palms, 
. « but they are constantly menaced with burial by the sands. The only 
remedy employed by the natives consists in little dry walls of crystallized 
gypsum, built on the crests of the dunes, together with hedges of dead palm- 
leaves. These defensive measures are aided by incessant labor ; for every 
day the people take up in baskets the sand blown over to them the night 
before and carry it back to the other side of the dune.”—Mémoires sur le 
Sahara, p. 14, 
