THE SOIL PARTICLE 103 



tions in air and water movements. The chemical phases 

 of such an interpretation are also worthy of considera- 

 tion, as the proportion of the various separates determines 

 whether the essential plant-food elements will be present 

 in sufficient quantities to permit normal crop growth. 

 Thus in a general way the mechanical analysis of a soil 

 not only enlightens us as to the general properties of a 

 given soil, but is to some extent a criterion of agricultural 

 value and crop adaptation. Some authors l maintain 

 that in the investigation of any soil a mechanical analysis 

 should first be made, as such an analysis throws so much 

 light on the general qualities of a soil. 



77. Soil class. — Class is a term used in relation to 

 the texture, or size of particles, of a soil. Class differs 

 from texture, however, in that it has reference rather to 

 the particular properties exhibited by a soil than to any 

 absolute grain size. As soils are not made up of particles 

 of the same size, a blanket term is needed which will not 

 only give an idea of the texture of the soil, but also name 

 it in such a manner as to reveal general peculiarities and 

 properties. We may have any number of classes, de- 

 pending on the sizes of the soil grains carried. 



These class names have originated through long cen- 

 turies of agricultural operations, but of late they have 

 been more or less standardized because of the necessity 

 of a definite nomenclature. In general the names used 

 for the soil classes are the same as are used in mechanical 

 analyses to designate the soil separates. This is rather 

 unfortunate, but it obviates the increase of technical terms 

 and a little care will prevent confusion in this regard. 



Another word introduced by common usage is loam. 



iHall, A. D., and Russell, E. J. Soil Surveys and Soil 

 Analyses. Jour. Agr. Science, Vol. IV, Part 2, p. 199. 1911. 



