CHAPTER II 



GEOLOGICAL FORMATION AND CLASSIFICATION OF SOILS 



47. 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 a part in 

 its formation 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 soil distribution should be understood, 

 because they have such an important bearing upon 

 soil fertility. Agricultural geology is of itself a 

 separate branch of agricultural science. In this work, 

 only a few of the topics which are of most importance 

 in agriculture are treated and only in a general way. 



48. Formation of Soils. Geologists state that the 

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

 now 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 

 vegetable life. One of the best evidences that soil is 

 derived from rock is that there are frequently found 

 in fields pieces of rock which are actually rotten, and, 

 when crushed, closely resemble the prevailing soil of 

 the field. This is particularly true of clay soils where 

 fragments of disintegrated feldspar are found which, 

 when crushed, resemble the soil in which the feldspar 



