4 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 



to efficient subdrainage. In the region of the dayas the surface falls away 

 to the south or the southeast until the region of the Chebka is reached, 

 which extends to the territory of the Beni M'Zab. In the Chebka low and 

 flat-topped mountains are so irregularly disposed as to give rise to the 

 name, meaning a net; they are separated by valleys, narrow toward the 

 northern portion of the region, but expanding into small plains as one 

 proceeds towards Ghardaia. Ghardaia, the country of the Beni M'Zab, 

 marks the southern limit of the Chebka. At Ghardaia the altitude is 

 1, 600 feet. Between Ghardaia and Ouargla are undulating stony plains, 

 the Gantara (hamada), large salt spots, the chotts, and a prominent range 

 of sand mountains, areg desert, possibly 1,000 feet high. At the eastern 

 edge of the Gantara the general level of the country drops suddenly 

 about 200 feet to the Ouargla plain (reg desert), with an altitude less 

 than 500 feet; this is an eroded flood-plain of the Oued Igharghar or its 

 tributaries. 



There are no navdgable rivers in Algeria. The most important river is 

 the Chelif, which takes its origin in the Saharan Atlas, crosses the High 

 Plateau, breaks through the Atlas of the Tell, and, ttuning westward, 

 traverses obliquely the Tell for a distance of about 108 miles before dis- 

 charging into the sea. The Chelif is the only stream which rises in the 

 Saharan Atlas and pierces the northern range. To the south of the Saharan 

 Atlas are several important oueds. One, the Oued Djedi, rises near Aflou 

 and goes easterly, past Laghouat, until it reaches the Chott Melrir, south 

 of Biskra; two others, the M'Zab and the Nessa, drain the region of the 

 Chebka, and taking an easterly or a southeasterly direction reach the Oued 

 Rirh or its upper extension. The Oued Rirh constitutes the northern por- 

 tion of the great Oued Igharghar, or a tributary of this oued, and extends 

 about 60 miles north from Touggourt to the Chott Merouan. The region 

 of the Oued Rirh is of great economic importance from the production of 

 dates, made possible through the development of artesian wells by the 

 French government. The oueds as a whole are very like the arroyos of 

 the southwestern portion of the United States, in that they carry water 

 for a small portion of the year only, when the torrential rains fill them 

 with a muddy, rushing flood. 



In the plains adjacent to the oueds, at Ghardaia especially, the natives 

 usually dig their wells, from which water for domestic as well as for irri- 

 gating purposes is obtained. The flood-water of the oueds is also diverted 

 into ditches, or impounded for later use, although the latter has not met 

 with uniform success. The depths at which water has been found vary 

 greatly. At Ouargla the water lies within 3 feet of the surface, although 

 there are also very deep artesian wells, and at Ghardaia it varies from 10 

 to 50 feet or more. At the daya of Tilrempt the water in the deepest wells 

 stands as deep as 300 feet; it is drawn in a very primitive fashion for pur- 

 poses of watering flocks and for the bordj. The heaviest vegetation is to 



