PHYSICAL COMPOSITION AND CLASSICS OF SOILS 95 



contain all the possible physical classes of soils already mentioned. 

 Comparatively few soil series, however, are complete. 



In establishing soil types and soil series, the texture of the soil, 

 its mechanical composition, its origin, the topography of the soil, 

 native vegetation, color, depth, drainage, and all other factors 

 which influence the relation of the soil to the crop, are considered, 

 as far as possible. Both the surface soil, and the subsoil should 

 be considered. All the types in a given locality have been formed 

 by the same general processes, and will naturally grade into one 

 another. In humid regions, the description of a type covers the 

 material to an average depth of three feet; in arid regions to a 

 depth of six feet. Minor variations of texture, structure, organic 

 matter content, or succession of materials, which occur in sections 

 representing 10 acres or less, are described as phases by the field 

 agents of the Bureau of Soils. There is some local variation in 

 types. Differences in agricultural value may be due to differences 

 in treatment of the same soil. 



The soil name of a type does not mean that it belongs to that 

 class necessarily. For example, Norfolk sandy loam may be a 

 coarse to medium yellow or gray sand or light sandy loam. 



Pippin 1 suggests the following scheme of soil classification. 

 The broadest division is based on temperature, into (I) tem- 

 perate, (II) subtropical, (III) tropical regions. Each of these is 

 sub-divided into (A) humid, (B) semi-arid, (C) arid sections 

 based on rainfall. The next two sub-divisions are into divisions 

 and provinces according to mode of formation; (a) sedentary, 

 soils sub-divided into (a ) residual soils and (a 2 ) cumulose soils 

 and (b) transported soils, sub-divided into (& x ) colluvial, (b. 2 ) 

 wind borne, (A,) transported by water; namely, (b 3a } ocean, 

 ( 3 *) lakes, (b y ) rivers. The soils of different origin are next 

 divided into groups based on the source of material (i) acid and 

 basic igneous rock; (2) shale and slate; (3) sandstone and 

 quartzite; (4) limestone and marble rock: (5) muck, peat, and 

 swamps (cumulose soil). The next sub-division is into series, 

 based on color, organic matter, drainage, lime content, and special 

 1 Proc. Am. Soc. Agron., 1911, p. 88. 



