76 



THE PRINCIPLES OF SOIL MANAGEMENT 



A mixture of all the groups without the preponderance 

 of the properties of any one group constitutes a loam 

 soil. 



For purposes of a soil survey, a classification is made 

 that permits of finer distinctions. The textures which 

 have been recognized are given in the table opposite, 

 together with the limits in mechanical composition 



Fig. 23. Heavy clay, showing the mechanical composition. For explanation, 

 see Fig. 21. Compare with Figs. 21, 22. 



which they represent. It is of course, impossible to fix 

 all of the limits in such a classification, and therefore 

 only certain groups are specified. This scheme has 

 been devised by the United States Bureau of Soils in 

 its soil-survey work. 



All those soils having the same general texture, 

 although they may have been derived in a very different 

 way, constitute a soil class. Thus there is the sandy 

 loam class, the silt class, the clay class, etc. The fol- 

 lowing curves exhibit the average composition of several 



