86 NATUEB AND PROPERTIES OF SOILS 



of soils in the field. The soils thus studied are classified into 

 areas having approximately the same crop relations and tillage 

 properties. The location of the areas of each kind of soil is 

 represented on an adequate base map, and their character and 

 chief economic and agricultural relations are described in a 

 printed report accompanying the soil map.^ (See Fig. 18). 



In classifying soils six primary factors are considered. 

 These, beginning with the broadest, are as follows: (1) tem- 

 perature, (2) precipitation, (3) agency of formation, (4) kind 

 of material, (5) special properties other than texture, and 

 (6) texture. It is obvious that certain soils may be of different 

 texture but alike in all other ways. Their climatic environ- 

 ments, mode of formation, rock materials, and specific prop- 

 erties, such as color, drainage, organic condition, and lime 

 content may be approximately the same. Such soils are 

 grouped together as series and the series are named, generally 

 from some town, county, or river of the near vicinity. Thus 

 we have the Norfolk series of the Atlantic coastal plain; the 

 Cecil soils of the Piedmont Plateau ; the Ontario series arising 

 from the calcareous till of central New York state and the 

 Marshall soils of the loessial region of the Middle West. The 

 soils within each series are approximately the same except for 

 class distinction. 



The soil type is the unit of classification and may be defined 

 as an area of soil alike in all characteristics, including crop 

 productiveness. Obviously any soil class of any particular 

 series would be a soil type. Norfolk sandy loam, Ontario loam, 

 and Cecil clay are examples of how soil types are designated. 

 The type designation is especially valuable in soil description 

 since the series name expresses in one word a great number of 

 conditions, which otherwise would require detailed explana- 

 tion. The class name establishes in addition the textural con- 

 dition. 



* For further information consult one of tlie numerous soil survey 

 reports as published by the U. S. Dept. Agr., Bur. of Soils. 



