14 SOILS AND FERTILIZERS 



14. The action of wind. — That wind has been an active 

 factor in the transporation of soil is evident to any one 

 who has lived in an arid or semi-arid region, where dust 

 storms are not infrequent. In a humid region the move- 

 ment of soil by wind is not so patent, but even there, espe- 

 cially along the seacoast, there is some movement of this 

 kind. There is also an erosive action produced by wind, but 

 this has not been very important. However, in arid regions 

 the sand-bearing wind has been instrumental in wearing 

 away large surfaces of rock, the eroded portions of which 

 have helped to form soil. 



The most important result of wind action has been the 

 production of loessial soils, which are found in parts of Wis- 

 consin, Illinois, Iowa, Missouri, Nebraska and Kansas, 

 also in the valley of the Rhine and in parts of China. An- 

 other result is the production of adobe soils, which are found 

 in mountain sections of western and southwestern United 

 States. While these soils do not owe their present location 

 entirely to the action of wind, that element has played a 

 large part in removing them from other regions and depos- 

 iting them where they now are. 



15. Action of gases. — Of the gases that compose the 

 normal atmosphere, oxygen and carbon dioxide are instru- 

 mental in decomposing rock and soil. They unite chemi- 

 cally with some of the substances composing rocks, and 

 when the new compound thus formed is more soluble than 

 the original substance, the resistance of the rock to water 

 is decreased. This is a very constant operation, and as air 

 penetrates deeply into soil and into the pores of rock its 

 action is widespread. 



16. Action of plants and animals. — Some of the lower 

 forms of plants, of which lichens are a notable example, 

 are able to live on the bare surfaces of rock, fastening them- 

 selves to the small crevices and pores and in the process of 



