60 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 



are called Ed Delouatt. To the south of Biskra, as has already been 

 stated, there extends a vast plain, the reg, which dips gently to the south 

 and drains into the Chott Melrirh, 50 kilometers or more distant. The 

 situation of Biskra relative to the mountains on the one side and the desert 

 on the other, together with its altitude, governs the climate of the place. 

 Except Laghouat no vicinity in the desert proper was seen with so great 

 an amount of precipitation (about 200 mm.) as Biskra, which is indicated 

 by the relatively rich flora. One who has seen only Biskra can not draw 

 conclusions regarding the vegetation or the conditions of plant life of those 

 portions of the Sahara that lie farther to the south, where much more 

 intense conditions of aridity obtain. 



The soils of the vicinity of Biskra are various. That of the low hills 

 between the town and the Djebel Bou Rhezal is only a few centimeters in 

 thickness, but in the washes from the hills it is a meter or more. Here the 

 soil is a sandy loam with an admixture of small stones and pebbles. On 

 the fiat ground to the north and to the south of these hills it is of a finer 

 texture, approaching the adobe of the southwestern United States. On the 

 reg to the south of the oasis the soil is also fine, and in some places, if not 

 underlying the plain as a whole, there are strata of gravel at varying depths 

 beneath the surface. This soil in places carries considerable salts. It dries 

 to a powder during the long dry seasons and is easily blown by the winds. 

 Owing to outcropping rock, the south face of the Bou Rhezal Mountains 

 has but scant soil, but that of the northern side resembles the soil of the 

 low hills to the south, which has already been characterized. Near the 

 town are dunes of good size. Especially to the southwest the sand banks 

 against Ed Delouatt hills is in large amount. In the opposite direction, 

 but farther from the oasis, the dunes are fairly extensive. 



The Oued Biskra is of great importance to the oasis, since it carries water 

 for several weeks of the year and furnishes water for irrigation. Its channel 

 lies about 3 meters, or possibly more, below the general level of the oasis, 

 and possibly in earlier times may not have been so well defined as at present, 

 spreading its waters over its flood-plain during high water. The oued is 

 made up of several tributary oueds which cross the plain north of Djebel 

 Bou Rhezal, unite where there is a pass in these mountains, and finally 

 debouch on the reg to the south of the town, where the channel becomes 

 continually less well defined. Another oued takes its origin in the Bou 

 Rhezal I^.Iountains in several independent branches which unite at a pass 

 in Ed Delouatt hills and extend for a distance of 15 kilometers or more into 

 the reg. One of the feeders of this oued is from hot springs, Hamman es 

 Salahine, about 8 kilometers northwest of Biskra. 



PLANT HABITATS OF THE BISKRA REGION. 



From the preceding sketch of the leading topographical conditions of 

 the vicinity of Biskra it will be seen that the plant habitats are more diverse 

 than at any other place visited. For the present purpose the habitats may 



