KINDS OF SOIL 



51 



composed chiefly of yellowish or grayish sand, or 

 sandy clays blown by the wind, and extending over 

 portions of Nebraska, Colorado, Wyoming, and 

 Utah. The "Pine Barrens" of Michigan and of 

 the Atlantic Coast are other illustrations of drift 

 soils worthless for agricultural purposes. 



COMPOSITION OF SOILS 



With respect to composition, all soils are made of 

 four ingredients sand, silt, clay and humus. No 

 one of these ingredients alone makes a valuable soil, 

 nor is it possible to find any soil composed entirely 

 of a single grade. The most valuable soils the 

 loams are a mixture of the four ingredients. 



The basis upon which the four ingredients of 

 soils are separated is the size of the grains, and here 

 an arbitrary division is made. This is called a 

 "mechanical" analysis" of the soil as distinguished 

 from a chemical analysis, described in Chapter 

 XI. The coarser materials are screened from the 

 soil by passing it through several sieves, with 

 meshes of different sizes. Fine sand, silt, and clay 

 are separated by allowing them to settle in water, 

 the fine sand settling first, then the silt and finally 

 the clay. The approximate size of the different 

 ingredients is: 



Coarse sand 

 Medium sand 

 Fine sand . 

 Very fine sand 

 Silt . . . 

 Fine silt. . 

 Clay. . . 



-fa to ir 



7U 



i 



to 

 to 

 to 



jnnnr to 

 - 1 to 



TT 

 TtVlF 



of an inch in diameter 



T5T 

 1 



Sand is made chiefly of particles of quartz, and 



