78 



PETROLOGY AND PEDOLOGY: 



TABLE 5.5 CHARACTERISTICS OF SOIL BY TEXTURAL CUSSES 



Classes 



Composition (%) 



Dry Sample 



Form 



Texture 



Physical Characteristics^ 



Moist Ball 



Handling 



Consistency 



Ribbon 



U 



E - - 

 a t- irt 



O CO w 



>. — 



Sand 85-100 0-15 0-10 



Loamy sand 70-90 0-30 0-15 



Sandy loam 43-85 0-50 0-20 



Loam 23-52 28-50 7-27 



Siltyloam 0-50 50-88 0-27 



Clay loam 20-45 15-53 0-27 



Silty clay loam 0-20 40-73 27-40 



Sandy clay loam 45-80 0-28 20-35 



Clay 0-45 0-40 40-100 



Sandy clay 45-65 0-20 35-55 



Silty clay 0-20 40-60 40-60 



Silt 0-12 88-100 0-12 



* 



*b 



+ 

 * 



+ 



+ 



'* indicates usual; +, secondary; ?, questionable. 

 With slick, buttery, or velvety feel. 



system must be natural in the sense that it depicts the 

 factors of soil formation. This means that any ac- 

 ceptable classification scheme must emphasize cli- 

 mate and vegetation. Therefore, any map of the 

 distribution of natural soil categories is a generalized 

 presentation of climate and vegetation (Figures 5.2, 

 5.3, 5.4, and 5.5). Although a natural classification 

 of soils, and therefore a soil map, might seem easy 

 to accomplish, in actual practice even the natural 

 system is hard to produce. 



The natural system presented here is discussed in 



some detail in the 1938 Yearbook of Agriculture, 

 Soils and Men. It is a natural system because it 

 stresses the factors of soil formation, especially 

 climate, vegetation, parent material, and topography. 

 Categories. The largest category of soil classifica- 

 tion is the order. Further subdivisions are sub- 

 orders, soil groups, families, series, and types. Here, 

 our purposes are satisfied by considering the three or- 

 ders (zonal, intrazonal, and azonal) and subunits that 

 approximate the suborders. The subunits under their 

 respective orders are indicated in Table 5.6. 



TABLE 5.6 CLIMATE AND SOIL CLASSIFICATION 



