II SOILS 13 



as mica. Sand, however, is principally composed of a Quartz d 



glassy substance known by the names of quartz, flint, silica 



or rock-crystal. It has a gritty feel and it easily scratches 



such hard substances as glass. This property is sometimes 



made use of in the "sand-paper" sold in the shops. 



Sand makes the soil loose, and thus it assists the air and 



water in finding their way through the land, and aids 



the roots of plants in their efforts to penetrate in all 



directions. 



Clay is composed of two chemical bodies known as silica Nature of 

 and alumina in combination with water. When dry it may ^^^^' 

 be made into a powder, and when wet it becomes sticky and 

 is then capable of being moulded into various shapes — and 

 this property is known ^is plasticity. But when clay is burnt 

 it loses its plastic property, for it then becomes hard and 

 brittle. There are various kinds of clay, some quite white, Varieties of 

 from which china ware is made, others yellow, from which *^^^' 

 bricks are made, others again are red and are used to 

 make pots, goglets and other earthen-ware articles. Clay is 

 colder, and it retains much more moisture than sand. 



Lime usually occurs in soils combined with carbonic acid 

 as a carbonate of lime. It came originally from the old 

 hard rocks, but now it occurs in various forms, as chalk. Varieties of 

 lime-stone and coral. It is contained in large quantities in '*'"^' 

 the shells of land snails and of some marine animals besides 

 coral, and many of the lime-stones of the earth are com- 

 posed entirely of these shells and deposits which accumu- 

 lated at the bottom of the sea in past ages. 



Vegetable matter exists in all soils upon which plants have 

 grown. The leaves, roots and stems decay as already shown 

 and form a dark brown substance called Jmmiis or vegetable 

 mould. This occurs abundantly on the surface of the 

 ground in forests and in less quantities in all cultivated lands. 

 In some damp, hollow places where mosses and similar vegetable 

 plants grow abundantly, the soil is composed almost entirely soils. 

 of humus, for the mosses grow up and die and decay, and 



