TEXTURE OF SOILS. 33 



The gardens are divided into small plots by means of banks of 

 earth, to facilitate irrigation, as in the basin method used in the 

 United States. The water from the ditch (seguia) is turned into 

 the nearest plot through a breach made in its bank, the ditch being 

 dammed at that point with a few spadefuls of earth. When the soil 

 is sufficiently saturated, the farther bank is cut, allowing the water 

 to pass on into the plot beyond ; and so on, until the whole garden has 

 been irrigated. In this way not only the date palms, but the other 

 fruit trees and the small crops among them that occupy a portion 

 of every garden, are irrigated simultaneously. 



DRAINAGE SYSTEM. 



Owing to the situation of the oases on the edge of the Shott Jerid 

 and the great amount of water used in irrigation, its soils would be 

 completely water-logged were it not for the excellent provision that 

 has been made for drainage. Each garden is provided with open 

 drainage ditches, or " khandaks," these being generally about 166 

 feet apart and about 5 feet deep. They are constructed at the ex- 

 pense of the proprietor of the garden, the work of keeping them 

 open devolving upon his tenant. Several of these smaller drains 

 unite to form a large ditch, which is kept up by an association of the 

 proprietors whose gardens are served by it, each contributing in 

 proportion to the size of his water right. Finally, at Tozer. all 

 the drainage ditches empty into a main one called the " Khandak-el- 

 Kebir." which runs along the southern side of the oasis and carries 

 its drainage water to the Shott Jerid. In former times, when Tozer 

 was frequently raided by the savage nomadic tribes of the desert, 

 this large drainage ditch also served the inhabitants as a moat for 

 the defense of the oasis. Not only is this excellent drainage system 

 useful for ridding the oasis of surplus water, but it renders inesti- 

 mable service in preventing the harmful accumulation of salts or 

 "alkali." (See p. 36.) 



SOILS OF THE JERID REGION. 

 TEXTURE. 



As the soils of the Jerid region only were investigated, the discus- 

 sion which follows relates only to that group of oases. All samples 

 for analysis were collected at Tozer, but the composition of the soils 

 of the other three oases is probably similar, except that those of 

 Nefta apparently contain a higher percentage of sand. The date 

 palm is said to grow most rapidly and vigorously in the soils that are 

 richest in clay, although yielding a better quality of fruit in the 

 sandier soils. 



30618 No. 9206 3 



