8 SOILS 



(10X of small stones not being considered harmful) they serve a 

 useful purpose in the soil, as they render it lighter in character, 

 affording porosity and assisting in the retention of moisture. The 

 stones are weathered by the atmosphere and other agencies, in the 

 same way as the rocks from which the soil was made, so that 

 their gradual wasting away adds material to the soil. 



CLASSIFICATION OF SOILS. 



Soils are classified in accordance with their physical or 

 chemical composition, and are divided into classes, sub-classes, etc., 

 according to the proportion of clay, sand, lime and humus they 

 contain. The principal classes are: 



Clay or argillaceous soils. These contain over 50 per cent, 

 of clay. They are heavy and dense, very retentive of water, 

 are cold and difficult to work, and require to be well-drained in 

 order to be properly cultivated. In periods of drought, plants on 

 clay soils are apt to suffer, as the roots cannot penetrate into stiff 

 clays, or obtain water from the subsoil. Though such soils may 

 contain an abundance of mineral food for plants, it is often 

 rendered unavailable by their stiff texture. This may, however, 

 be corrected by the addition of sand, lime, or suitable manures, and 

 by drainage. Clay soils of moderate texture have, nevertheless, 

 very important advantages in the tropics, owing to their power of 

 retaining soluble manures and moisture. . (See under Clay}. 



Loamy soils are composed of 30 to 50 per cent, of clay, 

 under 5 pe>' cent. ( if any) of lime, and the remainder of sand and 

 vegetable mould. 



Sandy loams contain from 20 to 30 per cent, of clay, and 

 may be with or without lime. 



Loamy sands comprise 10 to 20 per cent, of clay ; lime may 

 be present or absent. 



Sandy soils. These contain not less than 70 per cent, of 

 quartz sand ; they have little cohesion, are very porous, and 

 contain little nourishment for plants. Such soils can be improved 

 by the addition of clay, marl or chalk. 



Marly soils. These contain from 5 to 20 per cent, of lime, 

 and may partake of the characters of the first four classes, or of the 

 eighth. 



Calcareous soils contain over 20 per cent, of lime, and 

 may partake of the characters of a loamy soil with 30 to 50 per cent. 



