ORIGIN AND KINDS OP SOILS. 47 



a plastic mass, or consolidated by pressure, whether in a moist or dry state, 

 so as to form a compact solid body. Hence all sandy soils are loose, never 

 present a firm surface, and are never covered with a compact clothing of 

 grass or other herbaceous plants. Such soils, from being without cohesion, 

 are incapable of retaining moisture ; and as they are readily permeable by 

 both moisture and air, they powerfully promote the putrefaction of organic 

 matter, whilst they as readily permit it to be washed away from them by 

 rains, or to escape in the form of gas. Hence, in manuring sandy soils no 

 more should be applied at once than what can be consumed by the crop of 

 the current year ; and hence, also, they should be cultivated to a greater 

 depth than other soils, in order that there may be a greater mass of material 

 for retaining moisture. One great advantage of a sandy soil over all others 

 is its natural warmth. This arises from its greater looseness and porosity, 

 in consequence of which the atmosphere penetrates into it more rapidly, and 

 to a greater depth, than in the case of any other soil. Hence, in the absence 

 of sunshine, a sandy soil will be raised to the temperature of the atmosphere, 

 to the depth of several inches, by the mere penetration of the air among its 

 particles ; while a firm compact soil, the earthy basis of which is clay or 

 chalk, could not be heated to the same depth without the direct influence of 

 the sun's rays. Sandy soils are also more easily penetrated by water than 

 any others, and hence they are sooner raised or lowered to the temperature 

 of the rains which fall on them than a clayey or calcareous soil. As the 

 water never rests on sandy soils, they are never cooled down by evaporation ; 

 the reverse of which is the case with clayey and calcareous surfaces. Sandy 

 soils being much less cohesive than soils in which clay or lime prevails, they 

 are much more easily laboured ; and being always loose and friable on the 

 surface, they are better adapted for the germination of seeds. Sandy soils 

 may be made to approach alluvial soils by the addition of clay and calcareous 

 earth, either taken from clayey or calcareous surfaces, or from subsoils in 

 which these earths abound ; but the former source is greatly preferable, from 

 the earths being already in combination with organic matter. * 



154. Whatever has been said of sandy soils is applicable to gravelly soils ; 

 in some particulars in a greater, and in some in a lesser degree. The small 

 stones of which the greater part of gravel consists, being better conductors of 

 heat than the particles of sand, it follows that gravels are both easier heated 

 and easier cooled than sands ; they are also more readily penetrated by rain, 

 and more readily dried by filtration and evaporation. Like sands, they are 

 improved by the addition of clay and chalk, or by alluvial soil ; and they 

 require also to be cultivated to a greater depth than clays or chalks. A gra- 

 velly soil isolated so as not to be supplied with water from higher grounds, is 

 of all others the most suitable for a suburban villa (Sub. Arch, and Land- 

 scape Gard. p. 16) ; and therefore, though not so suitable for a kitchen-garden 

 as a sandy or loamy soil, yet as a sufficient portion of soil, whatever may be 

 its earths, may always be improved so as to render it fit for the cultivation 

 of vegetables, a gravelly or sandy soil for building on should never be rejected. 



155. Clayey Soil. Alumina, which is the basis of clayey soil, is the most 

 frequent of earths next to sand. It is found nearly pure in the ruby and 

 sapphire ; tolerably so in the blue or London clay, but more so in the white 

 plastic clay, which is found between the London clay and the upper chalk, 

 and which is used for making tobacco-pipes. This soil relatively to water is 

 the very reverse of sand ; for while in nature, sand and water are never found 



