70 ASPECTS OF TROPICAL NATURE 



lowed into vast basins. In the former, particularly on the 

 northern limits of the desert, the rain descending from the 

 gulleys of the Atlas, sometimes forms streams, which are sooa 

 swallowed up by the thirsty sands, or dried by the burning sun- 

 beams. In spite of this short duration, the sudden appearance 

 of these streams is not unfrequently the cause of serious 

 distress to the oases which border the northern limits of the 

 desert. 



For this reason, as soon as the Atlas veils itself with clouds, 

 horsemen from the oases of the Beni Mzab are sent at full 

 speed into the mountains. They form a chain as they proceed, 

 and announce by the firing of their rifles, the approach of the 

 waters. The inhabitants of the oases instantly hurry to their 

 gardens to convey their agricultural implements to a place of 

 safety. A rushing sound is heard ; in a short time the ground is 

 inundated ; and the little village seems suddenly as if by magic 

 transported to the banks of a lake, from which the green tufts 

 of the palm-trees emerge like islands. But this singular 

 spectacle soon passes away like the fantastic visions of the 

 mirage. 



The deeper basins of the Sahara are frequently of great ex- 

 tent, and sometimes contain valuable deposits of salt. Wherever 

 perennial springs rise from the earth, or wherever it has been 

 possible to collect water in artificial wells, green oases, often 

 many a day's journey apart from each other, break the monotony 

 of the desert. They might be compared with the charming 

 islands that stud the vast solitudes of the South Sea ; but they 

 do not appear, like them, as elevations over surrounding plains 

 of sea, but as depressions, where animals and plants find a 

 sufficient supply of water, and a protection, not less necessary, 

 against the terrific blasts of the desert. 



A wonderful luxuriance of vegetation characterises these 

 oases of the wilderness. Under and between the date-palms, 

 that are planted about six paces apart, grow apricot and peach 

 trees, pomegranates and oranges, the henneh, so indispensable 

 to oriental beauty ; and even the apple-tree, the pride of 

 European orchards. The vine twines from one date-palm to 

 another, and every spot susceptible of culture bears corn, par- 

 ticularly dourrah or barley, and also clover and tobacco. With 



