38 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 



Along the sides of the valley, and at a distance more remote from the 

 oued, there are occasional washed-out areas, really box canons, where the 

 banks show a slightly different condition of the hardpan from that just 

 described. Here there may be three strata of hardpan. The uppermost 

 is of the same stratum as the top stratum by the oued, and the second 

 stratum also resembles the lower one just described. There is also a third 

 hardpan stratum of a much different character, in that it has a very large 

 admixture of sand and gravel, and large as well as small stones, making it 

 more easily eroded than either of the upper strata. The soil in which the 

 roots studied were found varied from a fine sand, with waterworn pebbles, 

 near the oued. to a clay mixed with sand nearer the sides of the valley. 

 In places the sand is cemented so as to resemble one of the hardpan strata 

 above described, but it is less hard and apparently is penetrated by water 

 without great difficulty. 



The Oued M'Zab, whose channel is 15 meters more or less in width, is 

 dry most of the year, containing water for only a few hours following the 

 rare storms. Wells are very numerous in the valley and furnish a good 

 supply of water. At the time of my visit to Ghardaia the water lay from 

 10 to 25 meters from the surface, depending on the position of the wells. 

 The depth to water in a single well is said to vary from 1 or 2 meters to 

 15 meters; in other words, the water-table of the valley varies 13 to 15 

 meters between the dry and the moist seasons. No analysis of the water 

 is available, but it is reputed to be noticeably saline near and below the 

 town of Ghardaia, while above the town this quality is not apparent to the 

 taste. The water relations of the plain are much less favorable for plants 

 than those of the M'Zab Valley. In addition to the fact that the soil of 

 this area receives only such water as falls directly on it, there is so little 

 depth that the water escapes shortly after it falls, leaving only the most 

 favorably situated soils, for example, those beneath shallowly placed 

 rocks, or between rocks, or in deeply penetrating cracks or the depressions, 

 with sufficient moisture for long use by plants. The depth to water on the 

 hamada is so great that successful wells have never been dug. 



THE OASIS OF GHARDAIA. 



Each of the cities of the M'Zab has its palm gardens as well as gardens 

 in which grains of various sorts and vegetables are grown. Intensive gar- 

 dening is practised and the fruits of the soil, although won with great labor, 

 are nevertheless not inconsiderable.* 



Perhaps the most palms are to be found about 2 kilometers above 

 Ghardaia, where they are so abundant as to form a small forest. Here, 



* In 1908, according to the Statique generate de l'Alg^rie, there were cultivated in 

 the territory of Ghardaia 572,114 fruit trees, among which were: almond, 5,850; fig, 

 101,722; date palm, 209,898; other sorts of fruits, 211,761. There were also 17,268 hec- 

 tares of grain under cultivation. 



