INTRODUCTION. 
9 
proportion of the soil grains have the same size or texture. 
Thus we may have different kinds of clays, loams, sands, etc., 
and the class to which any soil will belong depends upon the 
size of the individual soil grains of which it is composed, and 
not upon its color, origin, topographic position, or agricultural 
value. 
■Soils Containing Less Than 20% Silt and Clay 
Coarse sand.—Over 25% fine gravel and coarse sand, and less than 
50% of any other grade of sand. 
Sand.—Over 25% fine gravel, coarse and medium sand, and less than 
50% fine sand. 
Fine sand.—Over 50% fine sand, or less than 25% fine gravel, coarse 
and medium sand. 
Very fine sand.—Over 50% very fine sand. 
Soils Containing Between 20-50% of Silt and Clay 
Sandy loam.—Over 25% fine gravel, coarse and medium sand. 
Fine sandy loam.—Over '50% fine sand, or less than 25% fine gravel, 
coarse and medium sand. 
Sandy clay.—Less than 20% silt. 
Soils Containing over 50% of Silt and Clay. 
* 
Loam.—Less than 20% clay, and less than 50% silt. 
Silt loam.—Less than 20% clay, and over 50% silt. 
Clay loam.—Between 20 and 30% clay, and less than 50% silt. 
Silty clay loam.—Between 20 and 30% clay, and over 5»0% silt. 
Clay.—Over 30% clay. 
Soils may may be grouped in another way. Where soils are 
closely related through similar sources of the material from 
which derived, mode of origin, topographic position, etc., so 
that the different soils constitute merely a graduation in text¬ 
ure of otherwise uniform material, such a group is called a soil 
series. It corresponds to the family which is made up of dif¬ 
ferent individuals having the same parentage. The Miami 
series, for examples, includes light colored, glacial material 
where the soils have been derived largely from the underlying 
limestone, and the soils in the series range in texture from a clay 
loam to sand and gravel. The Plainfield series includes light 
colored soils in regions where no limestone is present, where the 
parent rock was largely sandstone, and where the material oc¬ 
curs as outwash plains or stream terraces. The soils in this 
series also have a wide range in texture. The name used for a 
soil series usually indicates the locality where that particular 
series was first recognized and mapped by the Soil Survey. 
