SOIL CLASSIFICATION 



39 



based on soil texture and is determined in the laboratory by separating 

 a sample into seven portions, or grades. Each portion contains soil 

 particles ranging in diameter between fixed limits. This process consti- 

 tutes a mechanical analysis. In such an analysis the groups and their 

 diameters are as follows: 



Groups. 



Diameter in mm 



1. Fine gravel 2.000-1 .000 



2. Coarse sand 1 .000-0.500 



3. Medium sand 0.500-0.250 



4. Fine sand ; 0.250-0. 100 



5. Very fine sand 0. 100-0.050 



6. Silt 0.050-0.005 



7. Clay 0.005-0.000 



Number of Par- 

 ticles in 1 Gram. 



252 



1,723 



13,500 



132,600 



1,687,000 



65,100,000 



45,501 ),()()( ),()()() 



Fifteen types of soil are possible within any soil series. The relative 

 proportions of the several soil separates, given in the table above, de- 

 termine the type. The twelve most important of these are known as 



Per Cent of Gravel, Sand,5ilt, and Clay in 20 Grams of Subsoil. 



Gravel 



Coarse 

 sand 



3.26 



Medium 

 sand 



9.92 



Fine 

 sand 



22.62 



Very fine 

 sand 



45.47 



.1-05 

 mm. 



Silt 



10.41 



Fine 

 silt 



1.36 



Clay 



2.32 



DIAMETER OF THE GRAINS IN MILLIMETERS. 



The Soil Separates as Made by Mechanical Analysis, 

 Showing the Makeup of a Typical Soil. 1 



coarse sand, medium sand, fine sand, coarse sandy loam, medium sandy 

 loam, fine sandy loam, loam, silt loam, clay loam, sandy clay, silt clay and 

 clay. They range from light to heavy in the order named, and, except 



1 Courtesy of Orange Judd Company. From "Soils and Crops," by Hunt and Burkett. 



