78 



THE PRINCIPLES OF SOIL MANAGEMENT 



classes, as they are found in the field. The field classi- 

 fication may not be strictly in accord with the mechani- 

 cal analysis, for the reason that the same essential 

 conditions may result from more than one mixture of 

 groups. By experience much facility in judgment may 

 be attained. 



55 

 50 



3 45 



40 



111 



35 



?30 



Q. 



LLl . >- 

 CO 40 



o'20 

 SJ15 



HI 



810 



o 



3 SANDY y y 



1 FINE 

 GRAVEL 



2 COARSE 

 SAND 



3 MEDIUM 

 SAND 



4 FINE 

 SAND 



6 SILT 



5 VERY 

 FINE 

 SAND 



SOIL SEPARATES 

 Fig. 24. Curves representing the average analysis of seven common 

 field classes of soil 



Taking the soils formed in the same general way, 

 alluvial for example, they are found, to exhibit all 

 gradations of fineness from clay up to the coarsest 

 gravel and stony loams. All these classes constitute 

 a soil series. In the same way, there may be a glacial 

 series or even several of them, lacustrum series, residual 

 series, etc. The river-bottom soils of the Central states 

 are chiefly classified by the Bureau of Soils into the 

 Wabash and Waverly series. Some of the glacial soils 

 into Miami, Volusia, etc.; coastal plain soils into Norfolk 

 (yellow), Orangeburg (red), etc., through all the divis- 

 ions, provinces and groups. 



