98 NATURE TEACHING. 



ascertaining the proportions of particles of 

 various sizes existing in soils and yields infor- 

 mation of considerable value to the farmer. 

 The. particles are classed as gravel, sand, 

 silt and clay. 



4. Soils are classed as gravelly, sandy, or 

 clayoy, 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 imple- 

 ments pass through them. 



WATER IN SOILS. 



1. Sandy or light soils differ in a marked 

 degree from clayey or heavy soils as regards 

 their relation to water. Water drains through 

 sand with ease while it passes through clay 

 soils with difficulty. When water falls, or is 

 poured upon soil, which is then allowed to 

 drain, a certain quantity of the water is 

 retained by the soil, and does not drain out. 

 Sandy soils retain only a small amount of 

 water and clayey soils a great deal. Thus 



