SOILS OF THE SFAX KEGION. 



17 



TOPOGRAPHY AND SOILS. 

 TOPOGRAPHY AND NATURAL VEGETATION. 



The portion of southern Tunis in which dry-land olive culture 

 reached its highest development in ancient times is that where 

 Quaternary deposits form the surface covering. The district around 

 Sfax that is now occupied by olive orchards is a slightly rolling plain 

 of low elevation, extending from the coast toward the base of the 

 high table-land that occupies central Tunis. In its natural condition 

 it is a steppe, in many ways like the great plains east of the Rocky 

 Mountains, and especially like parts of western Texas and eastern 

 New Mexico. It bears a scattered vegetation, a conspicuous feature 

 of which is the Christ thorn (Zizyphus spina- christi) , a spreading 

 thorny bush with most of the trunk underground, thus resembling the 

 mesquite (Prosopis juliflora) as it grows in eastern New Mexico. 

 Like the mesquite, the Christ thorn generally occupies the summits 

 of small mounds, which it has probably helped to form by catching 

 and holding wind-blown soil. While its stems are usually only 4 or 5 

 feet high above ground, its roots are said often to penetrate to a 

 depth of 12 feet or more. The presence of this shrub makes the 

 clearing of the land difficult and expensive. Sagebrush ( a species of 

 Artemisia) and coarse bunch- grass make up the bulk of the natural 

 vegetation. 



SOILS. 



The soil that is considered most desirable for olive culture is bright 

 red in color. It is generally of considerable depth, but at some places 

 within 20 miles of Sfax hardpan is said to be encountered only 24 

 inches below the surface. To an average depth of 7 feet the soil 

 appears to be generally rather uniform in texture, but below this 

 strata of fine material alternate with layers of coarse sand and gravel. 

 As regards water content, it is stated a that when the surface soil was 

 air dry, at a depth of 8 inches the moisture content was found to be 6 

 per cent, at 20 inches 10 per cent, and at 40 inches 14 per cent. This 

 would indicate a distribution of soil moisture to which only trees and 

 deep-rooted perennials could adapt themselves. It is said & that 

 even after several months without rain the soil at a depth of 8 inches 

 contains enough moisture to stick together when squeezed in the 

 hand. At the end of January, 1905, however, when heavy rains had 

 followed a prolonged drought, the writer observed that while the 



a Bourde, P. Rapport sur les Cultures Fruitieres * * * dans le Centre 

 de la Tunisie, 2d edition, 1899, pp. 13, 14. 



6 Bertainchand. Note Explicative sur la Carte Agronomique et Hydrologique 

 * * * des Terres de la Region de Sfax, Paris, 1896, p. 16. 



26017— Bull. 125—08 3 



