62 



SOILS: PROPERTIES AND MANAGEMENT 



loess. 1 Certain characteristics also seem to indicate that 

 the valley adobe might have been deposited by water. 2 

 It appears, therefore, that, while the physical characters 

 of all adobe are somewhat similar, its mode of origin and 

 chemical composition may be variable. Below are the 

 analyses 3 to two typical adobe soils : — 



Si0 2 . . . 



A1 2 3 . . . 



Fe 2 3 . . . 



CaO . . . 



MgO . . . 



K 2 ... 



Na^O . . . 



C0 2 ... 



P 2 O s . . . 

 Organic matter 



Like the loess, adobe is an exceedingly rich soil, but 

 it occurs in an arid or a semiarid region. When irrigated, 

 its fertility seems inexhaustible. It is found in Colorado, 

 Utah, southern California, Arizona, New Mexico, and 

 Texas. It has an especially wide distribution in New 

 Mexico. Like loess its elevation is variable, ranging 

 from sea level in California and Arizona to 6000 feet 

 along the eastern border of the Rocky Mountains. Its 

 maximum thickness cannot be estimated, as it is very 



1 Russell, I. C. Subaerial Deposits of the Arid Regions 

 of North America. Geol. Mag., August, 1889, pp. 342-350. 



2 Hilgard, E. W. Relations of Soil to Climate. U. S. Weather 

 Bur. Bui. 3. 1892. 



3 Merrill, G. P. Rocks, Rock Weathering, and Soils, p. 321. 

 New York. 1896. 



