SOILS. 15 



the sub-soil is readily distinguishable by the eye from the 

 upper stratum or soil, by the absence of animal or vegetable 

 matter in a decomposed or decomposing state. 



Sub-soils may either consist of loose earthy matter, like the 

 soil, or they may consist of rock sub-soils, therefore may be 

 divided into two classes, the rocky and the earthy. The 

 rocky consists of granite, sandstone, limestone, chalk, and the 

 other mountain rocks of a country. When readily penetrated 

 by water falling on the soil, they are termed free or porous; 

 but when they resist the entrance of water they are called close 

 or retentive. 



The earthy sub-soils may, in like manner, be divided into 

 the close or retentive, and the free or porous. The retentive 

 are those which, from containing a large proportion of clay, 

 are tenacious and cohesive in their parts; that is, tending to 

 unite in a mass and resist separation. They also resist in a 

 great measure the entrance or passage of fluids. The porous 

 are those which, having less of clay in their composition, are 

 more readily penetrated by water, by which means all super- 

 fluous moisture may be absorbed. 



On the nature of the under stratum depends much of the 

 value of the surface soil, says Mr. LOUDON, and on various 

 accounts its properties merit peculiar attention. He says, that 

 by examining the sub-soil, information may be obtained in re- 

 gard to the soil itself; for, although the substances in the soil 

 are by various mixtures in the course of cultivation necessarily 

 altered, the materials of the soil are in most cases identified 

 with or similar to those which enter largely into the composi- 

 tion of the sub-soil. "Disorders in the roots of plants are gene- 

 rally owing to a wet or noxious sub-soil." 



There are only four kinds of simple primitive earths, which 

 enter into the composition of soil.* These are clay, sanely 

 lime and magnesia. These, variously combined, and in dif- 

 ferent proportions, so far as earth is concerned, constitute all 

 the vast varieties of soil, such as wet, dry, warm, cold, light, 

 heavy, barren or fruitful. 



The clayey soils have, as their distinguishing character, the 

 adhesiveness of their parts; and this property alone will enable 

 even the inexperienced to recognise them without difficulty. 

 Clay, known as aluminous or argillaceous earth, as an ingre- 

 dient of soil, has the four following properties by which it 

 exerts a powerful effect upon vegetation. First, it greatly 

 absorbs and retains moisture. Secondly, when thoroughly 



* There are also other earths known in chemistry, but not in agriculture, as 

 they are found only in certain substances, in small quantities, and do not form 

 the constituent properties or parts of any soil. 





