HydrograpMcal System of Algeria. 375 



and the Mountain of Lions in the plain of Oran. Rivers tra- 

 verse these without draining them, and any depressions in 

 their surface are occupied by marshes and shallow lakes, 

 either fresh or salt*. 



The region of the High Plateaux extends longitudinally 

 from the east to the west, south-west of Algeria, and is formed 

 by vast plains separated by parallel ranges of mountains. 



These terraces increase in height as they recede from the 

 Tell, and again decrease as they approach the Sahara, thus 

 forming a double series of gradients, of which the highest is 

 3000 or 3800 feet above the level of the sea, much higher, in- 

 deed, than the summits of the hills which bound it. 



The spurs or projections from the mountains cut up each of 

 these stages into a series of basins, more or less elongated, 

 sometimes circular, like the Hodua, in which the depressions 

 are occupied by lakes, generally salt, known by the name of 

 Chotts or SebWias. 



This region is subject to alternations of intense cold and 

 extreme heat ; rain waters it less copiously than the Tell ; 

 instead of sea-breezes it receives the hot blast of the desert- 

 wind ; and it is entirely devoid of trees, save on the southern 

 side of the high mountain-ranges. 



During seasons of abundant rain, however, and in places 

 capable of irrigation, it produces abundant crops of cereals ; 

 but otherwise it presents to the weary eye of the traveller an 

 unbroken stretch of stunted scrub and salsolaceous plants, on 

 which browse the sheep and camel, the wealth of the wander- 

 ing Arab. 



Here and there a stream of water escapes from the moun- 

 tains to be lost in the Chotts ; sometimes, however, they are 

 absorbed by irrigation in the upper part of their short course ; 

 so that for a considerable part of the year the lower part of 

 the beds are entirely dry. 



The disposition of the soil in enclosed basins, and the exis- 

 tence of veins of permeable rock of a concave form, gave rise 

 to the supposition that there existed subterranean sheets of 

 water in several parts of the High Plateaux. Acting on this 

 theory, artesian wells were sunk ; and in many instances these 

 brought to the surface copious supplies of water, which here 

 is verdure and life. 



* The lakes of Houlaeira and Tonga, near La Calle, are sheets of fi'esh 

 water, as were those of Oued-el-Maiz in the plain of Bone, and Lake 

 Halloula in the Metidja, now dry. The lake of Mezerguin near Oran is 

 salt, and that of Fezzura near Bone is brackish. The last, in the time of 

 the Romans, poured the excess of its waters into the Seybouse by means 

 of a canal, the remains of which still exist. 



29* 



