THE SOIL SURVEY 725 



in other areas another element is dominant. To this 

 extent the classification deviates from the ideal system 

 outlined above. 



625. The soil type and series. How characterized and 

 named. The two predominant divisions of soil are the 

 soil type and the soil series. The soil type is the unit 

 of field study and classification, and corresponds to a 

 species of plant or animal in biological classification. It 

 includes all those areas of soil that are essentially alike 

 in all properties texture, color, chemical nature, struc- 

 tural properties, source of material, and mode of forma- 

 tion. In other words, soils of the same type are as nearly 

 alike as field identification will admit. The soil series is 

 a group of types differing only in the texture of the differ- 

 ent members. This may be said to correspond to the 

 genera in biological classification. 



A name is given to each series of soil for purposes of 

 easy identification, and to this name the class designation 

 is added, thereby fixing the identity of the type. For 

 example, the Miami series includes certain light-colored, 

 timbered, glacial soils of the East Central States. The 

 Hagarstown series includes certain light brown to reddish 

 residual limestone soils, found in the blue-grass region of 

 Kentucky and adjacent states. The Norfolk series in- 

 cludes lemon yellow, marine-deposited soils of the coastal 

 plain of the Atlantic and Gulf regions. Clay loam would 

 refer to a particular texture of any of these series, as the 

 Miami clay loam, for example, thus completing the type 

 name of a soil, which is made up of the series name and 

 the class designation. 



The common practice is to select for the series desig- 

 nation some geographical name in the region where the 

 soil is first identified or is best developed. The word 



