CHAPTER 11 

 SOIL'FOBMING PROCESSES 



The forces whicli liave to do with soil formation are largely 

 climatic in nature. They promote the physical and chemical 

 breaking down of rock masses, they intermix there with the 

 decaying organic matter and they shift the products from 

 place to place. Even after the soil is apparently at rest and 

 has become an effective agency in plant production, these 

 same forces are still much in evidence. The physical and 

 chemical evolutions through which mineral and organic mate- 

 rials at or near the earth's surface are passing due to natural 

 forces are spoken of as iveathermg} Erosion and deposition 

 are terms referring to the natural translocations which soils 

 and soil materials are frequently forced to undergo. 



If a soil represents a condition more stable than the rock, 

 the rock change is in that direction. If a soil presents con- 

 stituents or conditions not wholly stable to the forces effective 

 at that particular time, it in turn seeks a change by an altera- 

 tion or an elimination. A cycle of development is thus set 

 up proceeding from youth to adolescence and even into old 

 age. According to conditions, soils may age rapidly or slowly. 

 Rejuvenation may even occur, while cases of arrested develop- 

 ment may exist for short periods. 



10, Soil-fonning processes classified. — While weather- 

 ing, with the changes in form and composition which inva- 

 riably accompany it, profoundly affects topography, it is very 



* The term weathering is somewhat misleading since it comprehends 

 forces other than those generally considered as weather. All of the 

 forces involved, however, depend upon climatic conditions. 



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