SOIL CLASSIFICATION 67 



rocks. These latter constitute soil groups, and, simi- 

 larly, in the transported division there is the sub-division 

 or province of soils deposited in water, and these are 

 further sub-divided into those formed in the ocean, 

 marine; in lakes, lacustrine, and by streams alluvial, 

 each constituting a soil group. Within the soil group 

 the first division is the soil series, based upon the fine- 

 ness of the material, color, drainage and other properties, 

 and each series is made up of soil types, the material 

 in each one being practically identical in all respects. 

 The series and type distinctions will be better under- 

 stood after a consideration of the physical properties 

 of soil. Maps of soils based upon such a classification 

 are constructed by several countries and institutions, 

 the most extensive being' the United States department 

 of Agriculture. These maps are constructed upon dif- 

 ferent scales, but one inch to one mile is the most com- 

 mon. The maps are accompanied by legends and 

 reports, for the proper explanation of the conditions 

 in the area reported upon. 



Chemically, there is also a wide variation among soil 

 materials in the total amount of the elements present. 

 It might be expected that the repeated and long-con- 

 tinued mixing of materials from many kinds of rock 

 would result in a very great uniformity in all soils. 

 This is true of the number of elements present, for no 

 important element is absent from any soil. But the 

 amount may differ greatly. Aside from organic soils 

 (cumulose), the most striking differences occur in sand 

 soils. While the average analyses of many sandstones 

 and sand soils reveals a fair amount of all elements, 



