GEOGRAPHICAL CHARACTERISTICS OF ALGERIA. 5 



be found along the oueds and the nearby flood-plains. Here the water 

 relations are the most favorable and the oueds constitute highways along 

 which plants venture into the desert from the more hvimid regions. 



Very little study appears to have been given the soils of Algeria. It has 

 been stated that there are vast areas of light, sandy soils, and also exten- 

 sive tracts of marls, clays, and alluvial soils.* Gypsum is an important 

 element in the soils, both those of the oases and probably of the open 

 desert also; it occurs in great quantity in the large chotts of the desert, 

 along with common salt and other salts. In the soils of the oases it acts 

 as a cementing material, "uniting the finer soil-grains into aggregates 

 which give the soil a much more sandy appearance than would be suspected 

 from the results of mechanical analysis." At Laghouat and at Ghardaia 

 a light-colored, hard substance, closely resembling the "caliche" of the 

 southwestern United States, was seen incrusting stones, filling cracks in 

 rocks and crevices between rocks, and in places forming a stratum, hori- 

 zontally placed (15 cm. more or less in thickness) underneath the superficial 

 soils. This is extremely hard and can be broken or cut with difficulty. 

 In the valley of the M'Zab, where it constitutes a heavy substratum, it 

 appears to be impervious to water. This hardpan is used as threshing 

 floors by removing the superficial soils. 



An unexpectedly small amount of sand was observed over the route 

 traversed. Near the southern edge of the High Plateau a sand belt was 

 encountered and a long stretch of low dunes was seen leading to the east- 

 ward, which were said to reach nearly to Bou Saada; and again at Laghouat 

 there are dunes to the east of town as well as to the west. Low dunes 

 were seen in the valley of the Oued M'Zab, and sand mountains, possibly 

 250 meters high, were passed on the way from Ghardaia to Ouargla. Be- 

 tween Ouargla and Touggourt, also, sand was encountered and the way 

 lay across about 1 2 miles of low dunes ; to the north of Touggourt dunes 

 are also to be seen; and finally, some sand is to be found in the neighbor- 

 hood of Biskra. Although, thus, relatively little sand was met, much of 

 the entire portion of southern Algeria is covered by sand. Large areas of 

 sand-covered country lie to the east of the Oued Rirh, and especially south- 

 east of Touggourt, and also to the west of Ghardaia there is said to be a 

 large dune-covered territory. For the most part, however, the surface of 

 the plains crossed is covered with large or small stones, mingled with which, 

 or beneath which, there is a rather fine clay-like soil. This constitutes the 

 hamada, or stony desert, of which the largest portion of the surface of the 

 Sahara is probably composed. Where stones are largely absent and the 

 soil is fine, usually of flu\'ian origin, the formation is known as "reg." Reg 

 desert was encountered at and north of Ouargla, in the drainage of the 

 Igharghar or its tributaries, and south of Biskra. The latter may not, 



*Kearney and Means, Agricultural explorations in Algeria, Bui. No. 80, Bur. Plant 

 Ind., U. S. Dept. Agric, 1905. 



