SOILS. 41 



HIGH PLATEAU REGION. 



The soils of this region, derived larg-ely from cretaceous and ter- 

 tiary rocks, are in great part alhiviai deposits washed down from the 

 neighboring mountains. Particularly in eastern Algeria, soils very 

 rich in phosphates occur. These would be extremely fertile if water 

 wherewith to irrigate them were available. Calcareous hardpan undei'- 

 lies a great deal of the surface of the high plateau. Where this 

 impervious layer is quite near the surface the vegetation is sparse and 

 woody plants are absent. 



The high plateau soils grade from stony soils on the lower slopes of 

 the mountains, through sandy loams and loams, to heavy clay loams 

 and clays in the bottoms of the depressions. These depressions, known 

 among the Arabs as "" chotts," are a conspicuous feature of the steppes. 

 AVhile occasionally liUed with water, the bottom is commonly dry and 

 covered with a layer of salt. The chotts greatly resemble the "" playa " 

 lakes of the (xreat Basin region in Utah and Nevada and of the " bol- 

 son" plains of the southwestern United States and Mexi(;o. The soil 

 in the bottom of the chotts is always heavy and impervious. 



DESERT REGION. 



The soils of the western part of the Algerian Sahara — which is of 

 very little agricultural importance — more or less resemble those of 

 the very arid parts of the high plateau. In the eastern part of the 

 desert, where numerous oases occur, the character of the soil becomes 

 a matter of greater practical interest. The combined area of all the 

 oases amounts to but a small fraction of 1 per cent of the total surface 

 of the desert. The limited localities where oases occur are determined 

 by the presence of water rather than ])y an}^ exceptional fertility of 

 the soil. As a matter of fact, there are vast tracts in the Sahara which 

 are, probably, naturally more fertile than the oases and require only 

 water to make them extremeh' productive. 



The field observations made by the writers were confined to a num- 

 ber of typical areas in the Oued Kirh country. There are found the 

 most important oases that are easily accessible from the Mediterranean 

 coast. They are situated in what is prol)al)ly the hottest part of the 

 desert and their elevation above sea level is only a few feet. In fact, 

 several of the oases occur in a part of the basin that is below sea level. 



As a rule the soils of the oases in the eastern Sahara are light in 

 texture. Sandy loams and sands predominate, though here and there 

 are found soils heavy enough to be classed as true loams. Gypsum is 

 an important. constituent of nearly all the soils examined, in some 

 cases the subsoil being pi'acticall}' pure gypsum. This often acts as a 

 cementing material, uniting the tiner soil grains into aggregates which 

 give the soil a much more sand}' appearance than would be suspected 



