34 



DATE VARIETIES AND DATE CULTURE IN TUNIS. 



The following table gives the results of mechanical analyses of the 

 samples taken, as furnished by the Bureau of Soils. Descriptions of 

 the localities where each sample was obtained will be found in Table 

 11, on page 37, under corresponding numbers. 



Table 9. — Mechanical analyses of soils of Tozer oasis. 



It will be seen from the above anal3^ses that the typical soil of 

 Tozer oasis is a mixture of fine sand and clay, chiefly remarkable for 

 its small percentage of silt. Soils of this type occur also in the 

 Oued Rirh oases of Algeria. According to Dr. L. J. Briggs, they 

 are seldom found (as soils) in the United States, although subsoils 

 of similar composition are sometimes met with in the Atlantic 

 Coastal Plain. In the field these soils do not impress one as being 

 particularly heavj^, notwithstanding the large amounts of clay they 

 contain. The discrepancy is probably to be explained by the fact 

 that they contain great quantities of lime in the form of calcium 

 carbonate and of gypsum, calcium sulphate. (See Tables 11 and 12.) 

 These salts have a tendency to cement the fine particles of clay into 

 masses that imitate gi^ains of sand and make the soil appear of 

 coarser texture than it is found to be when examined in the labora- 

 tory. In the process of mechanical analysis much of the lime is 

 dissolved and the fine clay particles fall apart. Furthermore, most 

 of the relatively insoluble lime is probably classified as " clay " in 

 computing the results of the mechanical analysis. A similar dis- 

 crepancy between field observations and laboratory analysis was 

 noted by Mr. Thomas H. Means and accounted for in this way in 

 the case of soils from the Oued Rirh oases in Algeria.* 



a See Bui. 80, Bureau of Plant Industry, pp. 41, 42 (1005). Many of the 

 samples described in the table on i)age 42 of that bulletin show a mechanical 

 composition yery similar to the samples from Tozer. 

 92 



