SOILS OF THE ARID AND HUMID REGIONS. 



387 



It is a well-known fact that on the " sands of the desert " when 

 either irrigated, or wetted by rain, vegetation at once springs 

 up with remarkable luxuriance, even on sand drifts; and this 

 productiveness appears to be quite as lasting as that of 



strong 



clay soils of the humid regions. 



This difference is curiously illustrated on the southern edge of the 

 "black adobe" or prairie soil area which surrounds Stockton, Cal. 

 Here we find on the opposite sides of a small stream (French Camp 

 slough) the two extremes, of heavy clay and the sandy soils which for 

 many years made Stanislaus county the " banner " county for wheat. 

 The grain product of both banks ranked alike in quantity and quality 

 in average years ; but in extreme seasons sometimes one, sometimes the 

 other failed, according to the weather conditions which favored one or 

 the other soil. No one would think of sowing wheat on so sandy a 

 soil in the humid States. 



TABLE ILLUSTRATING DIFFERENCE IN SANDS OF THE HUMID AND ARID REGIONS. 



It thus appears that while in the Mississippi soil, solubility of 

 plant-food practically ceased at grain-diameter of .036 mm, in 



1 Analyses by R. H. Loughridge. 2 Analyses by L. M. Tolman. 8 Analyses bj 

 E. H. Lea. 



