3faj)j)ing Soils and AlJaali. 15 



In the humid portions of' the country the description of a soil 

 type covers the materials to a depth of 3 feet, and in the semiarid 

 and arid regions to a depth of 6 feet. The type name covers the 

 entire profile. AVhere there occurs, as a subsoil, material which if 

 exposed at the surface would he. called Fresno sand, for instance, 

 it is not proper to speak of this subsoil as Fresno sand, but as 

 material similar to the Fresno sand. Where this material is cov- 

 ered by a loam or silt loam, for example, within a depth of 3 to 6 

 feet, it loses its identity as the Fresno sand and is an integral part 

 of the new type estaV)lished. 



Correlation of soil types.— It is very desirable, from all points of 

 view, that close attention be paid to the correlation of soils. It is 

 very undesirable to increase the number of soil types more than is 

 necessary, and wherever a soil can consistently be i>ut under an 

 established type it should be done. ^Nluch advance has been made 

 in the past year in this matter of correlation and in using the 

 names of soils to bring out their relations. Several of the original 

 types have been merge<l into others, or have been given new 

 names to bring them into a uniform series, where this could be 

 done without danger of confusion. In doing this the object has 

 been to esta})lish certain series in the different physiographic 

 divisions of the United States, and we are finding that there are a 

 few general classes of soils that are in a way related. 



Due caution must be observed in this matter of correlation, but 

 a greater latitude may be taken in correlating soils of widely sepa- 

 rated areas than at first would appear possible, from the fact that 

 the soil of each area is fully described in all its characteristic and 

 special features. A soil, to be correlated with a type, must con- 

 form to it in certain broad, general features, but it may differ in 

 some unessential details. The descriptions of the soil types given 

 in this publication must not be taken as rigid specifications of 

 the conditions which must be found in certain types in all areas. 

 The description is of necessity general, and in the nature of the 

 case can not be specific in all particulars. 



Every effort has been made to group the soils into series for the 

 purpose of bringing out more clearly the relationship of the dif- 

 ferent types, and their relative agricultural value. The grouping 

 has also been made with a view to reduce the number of local 



