GEOLOGICAL CLASSIFICATION OF SOILS 65 



long. In sucli proportions they become a grave menace to 

 agriculture, not only because they are an absolutely valueless 

 medium for plant growth, but also because they cover fertile 

 lands and entirely blot out all vegetation. 



From early geologic times deposits of the very fine material, 

 that is continually being ejected from volcanoes, have been 

 distributed over the earth's surface. These deposits are 

 usually flour-like, and while at one time they probably cov- 

 ered many square miles of territory, they have succumbed 

 very largely to erosion and denudation, and only remnants 

 are found at the present time. Such material may be found 

 in Montana, Nebraska, and Kansas, ^olian deposits of this 

 character are usually rather porous and light, and are likely 

 to be highly siliceous. They are not of great agricultural 

 importance, except in certain localities. 



37. Eesume. — The geological classification of soils pro- 

 vides a logical basis for the discussion of the formation, char- 

 acter, and agricultural value of soils in general. A detailed 

 consideration on any other basis would lead to endless con- 

 fusion and repetition. In classifying soils a study must be 

 made not only of the past effects but of the present influences 

 of the soil-forming processes, and while the conclusions and 

 observations are apparently purely agricultural in nature, 

 they really spring from a geochemical foundation. 



With such a classification at hand one cannot fail to under- 

 stand the occurrence of so many distinct and different types 

 of soil. It is really difficult to see why soils do not present 

 greater differences and why transition types do not utterly 

 prevent clean-cut field distinctions. In such soil study the 

 all-important character of climatic control must always be 

 remembered. Weathering is strictly a climatic influence and 

 crop adaptation is usually dominated by climate rather than 

 by soil. 



