58 DRY-FAKMING 



ably been formed under abnormal conditions, as in 

 high mountain valleys, or under i)rehistoric humid 

 climates. 



Sand. — The sand-forming rocks that are not 

 capable of clay production usually consist of uncom- 

 bined silica or cjuartz, which when pulverized by the 

 soil-forming agencies give a c(jmparatively barren 

 soil. Thus it has come about that ordinarily a clayey 

 soil is considered "strong" and a sandy soil "weak." 

 Though this distinction is true in humid climates, 

 where clay formation is rapid, it is not true in arid 

 climates, where true claj^ is formed very slowly. 

 Under conditions of deficient rainfall, soils are nat- 

 urally less clayey, but as the sand and silt particles 

 are produced from rocks which under humid condi- 

 tions would yield clay, arid soils are not necessarily 

 less fertile. 



Experiment has shown that the fertility in the 

 sandy soils of arid sections is as large and as available 

 to plants as in the clayey soils of humid regions. 

 Experience in the arid section of America, in Egypt, 

 India, and other desert-like regi(jns has further 

 proved that the sands of the deserts produce excel- 

 lent crops whenever water is a])plied to them. The 

 prospective dry-farmer, therefore, need not be afraid 

 of a somewhat sandy soil, provided it has been formed 

 under arid conditions. In truth, a degree of sandi- 

 ness is characteristic of dry-farm soils. 



The humus content forms anothei- characteristic 



