56 SOILS AND FERTILIZERS 



CHEMICAL COMPOSITION OF ROCKS" 



67. Value of Geological Study of Soils. Agri- 

 cultural geology is a valuable aid in studying soil 

 problems, but like other sciences it is incapable alone 

 of solving all of the problems of soil fertility. 

 Means have not as yet been devised for accurately de- 

 termining the extent of rock disintegration and the 

 rapidity with which it has taken place or the extent 

 to which disintegrated minerals have been removed 

 from rocks by leaching and other agencies. It is 

 known that the rate of weathering of soils is influenced 

 by various factors, as origin, texture, composition, 

 humidity and other climatic conditions, presence of de- 

 caying organic matter, micro-organisms, mechanical 

 treatment and manipulation of the soil, fertilizers, 

 sun light and vegetation. Some of these agencies for 

 soil disintegration are under the control of the farmer 

 and are utilized by him in rendering plant food avail- 

 able. 



