SOILS IN DRY AREAS 67 



prevent growth in the higher forms of vegetation and in 

 some instances any form of the same. In soils thus 

 saturated, oxygen, so essential to germination and vig- 

 orous growth, is in a great measure excluded. In the ab- 

 sence of this element of the air, microscopic organisms 

 cannot carry on their beneficent work, the decay of 

 plant food is proportionally retarded and the formation 

 of nitrates is proportionately hindered. Moreover, when 

 the seepage waters contain alkali substances, these condi- 

 tions are intensified, and oftentimes to the extent of ex- 

 cluding all kinds of vegetation. Such a condition can- 

 not be remedied until drainage has been effected that 

 will promptly carry away the ingredients that are 

 harmful. ; \ - ; i:| j 



Clay loam soils. These may be defined as soils that 

 contain approximately from 15 to 20 per cent, of clay. 

 They differ from clay soils in the less percentage of the 

 clay which they possess, and from sandy loams in having 

 a lower percentage of sand. They have also less clay 

 than soils that are classed simply as loams. They are 

 relatively high in their percentage of humus. 



It would seem correct to say that clay loam soils pre- 

 vail to a greater extent on the grass-covered bench lands 

 than any other class of soils. This means that they are 

 the principal soils found on the benches of the Plains 

 country. The soils that grow sage brush are also fre- 

 quently of this type. They are also found interspersed 

 to a considerable extent in the Inter-mountain region, 

 and to some extent in the Great Basin. 



The superiority of clay loam soils lies first in the 

 ease with which they may be tilled, second in their mois- 

 ture-holding power, and third in their richness in the 

 elements of plant food. It would not be correct to say 

 that they are the easiest tilled soils in semi-arid areas, 

 but they are relatively easy of tillage, because of the 

 happy blending of the clay and sand particles, more 



