l6 SOILS AND FERTILIZERS 



content of soils. In the wheat lands of the Red 

 River Valley of the North, the particles are small and 

 spherical, being formed largely from limestone rock, 

 while the subsoil of the western prairie regions is 

 composed largely of angular silt particles, which are 

 intermingled with clay, forming a mass containing 

 only a minimum of inter soil spaces. The silt particles 

 being angular and imbedded in the clay, the soil has 

 more the character of clay than of silt. While these 

 two soils are unlike in physical composition, the form 

 and arrangement of the particles give each nearly the 

 same water-holding power. On account of a differ- 

 ence in the form and arrangement of the soil particles 

 two soils may have the same mechanical composition, 

 and yet possess materially different physical proper- 

 ties. In some soils 10 per cent, of clay is of more 

 value agriculturally than in other soils. Ten per cent, 

 of clay associated with 60 or 70 per cent, of silt,, 

 makes a good grain soil, while 10 per cent, of clay 

 associated largely with sand makes a soil poorly suited 

 to grain culture. 



The classification of the soil particles into sand, silt, 

 and clay is purely an arbitrary one. Various authors 

 use these terms in different ways, and when compar- 

 ing soils, reported in different works, one may avoid 

 confusion by omitting the names and noting only the 

 sizes of the particles. A division has recently been 

 suggested by Hopkins 7 in which the square root is 



