36 AGRICULTURAL EXPLORATIONS IN ALGERIA. 



Algeria, large areas of once fertile .soil have in consequence become 

 subirrigated and salty. In many cases considerable tracts have had 

 to be abandoned for this reason. ^ 



HIGH PLATEAU REGION. 



A very insignificant area is irrigated in the high plateau reg'ion. 

 There are almost no running streams, except after an occasional heavy 

 rain in winter. The water of the chotts or lakes that fill the depres- 

 sions is far too salty to be used for irrigating purposes. Here and 

 there a small patch of grain, forage plants, or garden vegeta))les is 

 watered from a well, but artesian water seems to be generally lacking. 



DESERT REGION. 



Oases of greater or less extent occur in all parts of the Sahara. They 

 are particularly numerous, however, in the lower eastern portion. In 

 the region known as the Oued Rirh, a larger percentage of the total 

 area is occupied by cultures than anywhere else in the desert. The oases 

 (see PI. I), almost without exception, are probably of artificial origin. 

 The date palm, to which they owe their life, is believed to have been 

 introduced into Algeria by man. In some places near the base of the 

 mountains, as in the region of the Zibans, there is flowing water on 

 the surface of the ground which can be diverted directly into canals. 

 At most, a few rude dams arc needed to raise its level a few inches. 

 Elsewhere wells must be dug and the water nuist generally be raised 

 by hand or by the noria in order to water the crops. The source of the 

 water thus utilized is to be looked for in the high mountains adjacent to 

 the Sahara, where the rainfall is much heavier than in the desert itself. 

 This water fiows down to the lower levels, at first over the surface of 

 the frround, then beneath it. Subterranean streams of considera])le 







volume nuist occur in the eastern part of the Sahara. There is no 

 foundation for the idea sometimes entertained that the oases are nat- 

 ural subirrigated spots in the desert. Most of the desert soils are too 

 saline to permit of subirrigation without injury to the crops. As a 

 matter of fact, agriculture would be almost impossible in the Sahara 

 were not careful provision made for drainage. 



From very ancient times irrigation has )»een practiced in the desert. 

 When the Romans governed northern Africa the area under cultiva- 

 tion in the Sahara was much larger than it is to-day. By many centu- 

 ries of practice the natives of the Sahara have acquired great skill in 

 procuring and managing water for irrigation. The art of well boring, 

 as originally practiced in the Oued Rirh, is a dangerous one. The 

 work is begun by scooping out a hole in the sand, the sides of which 

 are incased with wood as fast tis the digging proceeds. Finally, a 

 layer of rock or of stiff clay, overlying the sheet of water, is reached. 



