CHAPTER II 



GEOLOGICAL FORMATION AND CLASSIFICATION OF 



SOILS 



53. Agricultural Geology. The geological study of 

 a soil concerns itself with the past history of that soil, 

 the materials out of which it has been produced, together 

 with the agencies which have taken part in its forma- 

 tion and distribution. Geologically, soils are classified 

 according to the period in the earth's history when 

 formed, and also according to the agencies which have 

 distributed them. The principles of soil formation and 

 distribution should be understood, because of their im- 

 portant bearing upon fertility. Agricultural geology 

 forms a separate branch of agricultural science ; in this 

 work only a few topics especially relating to soils are 

 treated. 



54. Formation of Soils. Geologists state that the 

 surface of the earth was at one time solid rock. It is 

 held that soils have been formed from rock by the 

 joint action of the various agents : (i) heat and cold, 

 (2) water, (3) gases, (4) micro-organisms and other forms 

 of vegetable and animal life, and (5) wind. One of the 

 best evidences that soil is derived from rock is that there 



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