SOILS 7 



Sand. This is principally" composed of quart/, Hint, or silica. 

 It imparts a loose porous consistency to the soil, 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. In agricul- 

 tural and horticultural practices, sand is frequently added to the 

 soil so as to render it porous and " sweet." Thus in potting com- 

 posts, sand is usually a necessary constituent. 



Clay is composed of two chemical bodies, known as silica 

 and alumina, in combination with water. When wet, it is sticky 

 and plastic; but when burnt, as was formerly done in the culti- 

 vation of stiff soils, it loses its plastic property and becomes brittle. 

 Liming has also this effect on clay soil, depriving it of its sticky, 

 binding nature. There are various kinds of clay, some white, 

 from which china-ware is made ; others yellow, from which 

 are made bricks, pots, chatties and other earthenware articles. 

 Clay is colder, and retains much more moisture than sand. A 

 certain proportion of clay is a highly desirable constituent in all 

 soils, and no land can be efficiently and economically worked 

 unless clay be present to an appreciable extent. 



Lime. This usually occurs in soils combined with carbonic 

 acid as a carbonate of lime in various forms, as chalk, lime-stone, 

 and coral. It is present in large quantities in the shells of land- 

 snails and some marine animals, besides coral. Ceylon soils 

 generally are lacking in lime, which when present usually occurs 

 in the form of dolomite. 



Humus or vegetable-mould is formed by decayed vegetable 

 matter, such as leaves, roots, stems, etc., and exists to some extent 

 in all cultivated soils as a dark brown substance. It often occurs 

 abundantly on the surface of the ground in forests. Humus 

 may be said to be the most important constituent of all soils for 

 the planter or gardener. It has a great influence on the capacity of 

 soils for retaining moisture, renders their cultivation easier, and 

 encourages the activity of soil bacteria. Soils which are deficient 

 in humus are liable to cake and become very hard in dry weather, 

 and quickly lose their heat in cool weather. (See under Manures). 



Leaf-mould may be distinguished from humus as being 

 composed almost entirely of decayed leaves ; it is a valuable 

 ingredient in composts for pot-plants, tender seedlings, etc. 



Stones are simply particles of the original rock from which 

 the soil was formed. If they do not exist in too great a number 



