The Sahara: 31 
and their ice and extend the borders of their empire.* But when the 
desert was dry, what an effect must have been produced by the first 
visit -of the ‘foehn’ to the enormous glaciers of our Alps! What 
torrents!—what deluges of water!—what ravages, especially on the 
southern slope! and now how easy to comprehend the erosion of the 
mountains and the levelling of the plain of Lombardy subjected to 
these rude assaults and covered with erratic débris ! T 
The Oases.—Wherever in the arid burning Sahara a thread of 
water appears, a precious tree, the Date-palm, grows and prospers. 
An Arab proverb says ‘the Date must have its feet in water and 
its head in fire.’ Wherever water moistens the soil the date-palms 
raise their graceful columns, waving in the wind their plume of 
verdure and promising to man shelter from the sun and food for his 
subsistence. These trees are the wealth of the desert, and the Oases 
are merely forests of palms rendered possible by the presence of 
water. This water may have a triple origin ; it may be furnished 
either by springs or by artesian wells, or from having been dug out 
from a water-bearing stratum. Hence the three types of oases— 
Ist. Those watered by streams from the mountains; 2nd. Those 
supplied with water from the artesian wells, the products of a very 
ancient industry ; 8rd. The Oases without water, of which those of 
Souf are an example. 
The oases of the first category are fed either by the streams from 
the mountains, or from subterranean springs, which are found in 
great and almost constant abundance, like the Reuss, the Noirague, 
and the Serriéres, which are produced by the same cause, namely, 
the infiltration of the rain-water through the fissures of the lime-- 
stone in the mountains. They are found at the foot of the Aurés, 
where they form the Oasis of Zibans; and some of them are warm, 
their temperature rising to 30° Centigrade. 
Oases of Artesian Wells.—At a depth of about 160 feet, there is 
a sheet of water which springs to the surface when the intervening 
soil is pierced. Many of the oases, and particularly that of Tug- 
curt, have no water but that of the wells; and these appear to be 
very ancient. It is indeed no light undertaking for the Arabs to 
dig a well. They club together, and employ forced labour; but 
notwithstanding, it often happens that years pass before they reach 
* See Prof. E. Suess on the evidences of a post-pliocene sea on the site of the 
Sahara; Trans. Roy. Imp. Geol. Institute of Vienna, Jan. 1863.—A.C. R. 
{ In 1851 I published a paper in the Journal of the Geological Society on glacial 
phenomena, only part of which was printed, the remainder having been considered 
by the Council as too wild for publication in the Journal; and I therein stated, on 
the authority of the late Professor E. Forbes, that the Sahara ‘formed an extension 
of the sea in which the Sicilian Pleistocene beds were formed;’ but I am at this 
distance of time unable to recollect on what data he grounded this opinion. The 
diminution of the Alpine glaciers, both on the south and north sides of the chain, is 
however connected with phenomena of a much more general kind, which accom- 
panied or caused the close of the ‘Glacial Period’ in both hemispheres, and we 
suspect of a kind not necessarily connected with any local phenomenon lke the 
formation of the Sahara, however important that might have been in modifying 
part of the general result.— A. C. R. 
