18 AGRICULTURE IN THE SAHARA DESERT. 



SOILS. 



The soil of the whole Oued Souf region is a fine-grained, light- 

 yellow quartz sand, Avliich is practically uniform in character to a con- 

 siderable depth.* Here and there beds of a coarse, rather soft, gyp- 

 seous rock occur at a depth, it is said, of 10 to 20 feet and in strata 

 1.5 to 10 feet thick. The crystals of which this rock is composed 

 are very large, often 1 foot long. They are often aggregated into 

 masses which, on account of their shape, are known as " Souf roses." ^ 

 It is therefore a fair inference that the Souf soils are sufficiently 

 rich in lime. They are very poor in organic matter and doubtless in 

 nitrogen. Other data as to their composition are wanting. 



In the eastern part of the region the soil of all the gardens is said 

 to be somewhat saline, and the writer was told that there is even a 

 small sebka (salt pond) in that section, although he saw nothing of 

 these conditions. There is said to be nowhere enough salt to injure 

 seriously the palms themselves, but the yields of fruit are diminished 

 by this cause, and the dates are somewdiat smaller and of slightly 

 inferior quality. Consequently, palms in full bearing in the gardens 

 west of El Oued are worth from two to ten times as much as those 

 in the gardens east of that town. The Souafas do not pretend to 

 distinguish some varieties of the date palm as being more resistant 

 to salt than others, as do the inhabitants of the Djerid oases, where 

 the salinity of the soil is often very pronounced. Neither have they 

 adopted any special methods of preparing and handling salt land 

 by drainage, flooding, or otherwise, as is the case in the Tunisian 

 oases. It is fortunate for the Souafas that their soils are not saline, 

 or but very slightly so, as it is hard to see how they could possibly 

 reclaim strongly saline lands in view of the conditions of water sup- 

 ply in their country. 



THE DATE GARDENS. 



Let us now have a closer look at the gardens. (PI. Ill, figs. 1 

 and 2.) The craterlike basins which they occupy are generally cir- 

 cular or nearly so, and from 35 to 50 feet deep. The bottom is 

 entirely given up to the palms. Descending to the floor of the basin, 



aAccoi'ding to .Jus this hard quartz sand extends to a depth of 3.5 to 4.5 feet ; 

 next there are from 7 to 8.5 feet of a " reddish gypseous sand ; " and then 3 to 

 3.5 feet of either " a fine quai'tz sand " or " a yellow gypseous sand." 



6 The composition of this rock, as given by Jus (ibid., p. GO), is: 



Per cent. 



Quartz sand 37. OO 



Clay __'_ 5. 10 



Gypsum 41. 40 



Carbonate of lime '_ 3. 20 



Carbonate of maffnesisi 1. 50 



Water '___ n. 43 



