THE SOIL 103 



again, even large blocks of stone are in the course of 

 time reduced to small fragments. 



It requires little observation to see that the particles 

 of which the soil is composed vary greatly in size. This 

 variation is of great importance, agriculturally, for the 

 nature of the soil is greatly influenced by the preponder- 

 ance of large or small particles. By stirring up a small 

 quantity of soil with water and pouring it away, 

 repeating the operation until the water comes away 

 clear, the fine and coarse particles may be separated 

 from one another ; and by stirring up the water 

 containing the finer particles, and pouring away again, 

 a further separation may be made into fine and very 

 fine particles. It will be noticed that the water remains 

 muddy for a long time, indicating the presence of 

 particles of an extreme degree of fineness ; these very 

 fine particles are clay. This method, carried out with 

 certain precautions, is largely employed in ascertaining 

 the proportions of particles of various sizes existing in 

 soils, and yields information of considerable value to the 

 farmer. 



The particles are classed as gravel, sand, silt and clay. 



Soils are classed as gravelly, sandy, or clayey, 

 according to which of these constituents predominates. 

 Gravelly or sandy soils are often spoken of as " light," 

 not because they weigh relatively less than other soils, 

 but because they offer little resistance to implements of 

 tillage (such as ploughs, spades, and forks) ; that is to say, 

 they are light or easy to work. Clay soils, on the other 

 hand, are often called " heavy," because of the difficulty 

 with which the implements pass through them. 



