324 



THE FORMATION OF SOILS. 



azote, which they may require, supply this deficiency. In propor- 

 tion as soils possess a due degree of tenacity, and power of retaining 

 or absorbing heat and moisture, the necessity for a supply of manure 

 is diminished ; and, in some instances, the earths are so fortunately 

 combined, as to render all supply of artificial manure unnecessary. 

 He who possesses on his estate the three earths, — clay, sand, and 

 lime, — of a good quality, with facilities for drainage or irrigation, has 

 all the materials for permanent improvement ; the grand desiderata 

 in agriculture being to render wet lands dry, to supply dry lands with 

 sufficient moisture, to make adhesive soils loose, and loose soils suffi- 

 ciently adhesive. 



The intermixture of soils, where one kind of earth is either redun- 

 dant or deficient, is practised in some countries with great advantage. 

 Part of Lancashire is situated on the red sandstone described in the 

 sixth chapter. This rock, being composed principally of siliceous 

 earth and the oxide of iron, forms of itself very unproductive land : 

 but, fortunately, in many situations, it contains, near the surface, de- 

 tached beds of calcareous marl. By an intermixture of this marl 

 with the soil, it is converted into fertile land, and the necessity for 

 manure is superseded. The effect of a good marl applied liberally 

 to this land, lasts for more than twenty years. In some lands, a mix- 

 ture of light marl which contains scarcely a trace of calcareous earth, 

 is found of great service. The good effect of this appears to depend 

 on its giving to the sandy soil a sufficient degree of tenacity. The 

 sterile and gravelly soils in Wiltshire have been recently rendered 

 productive, by mixing them with chalk ; the most liberal application 

 of manure having been found ineffective, or injurious. In stiff clay 

 soils, where lime is at a great distance, the land might, frequently, be 

 improved by an intermixture with siliceous sand. A proper knowl- 

 edge of the quality of the sub-soil, and the position of the sub-strata, 

 is necessary to ascertain the capability of improvement which land 

 may possess. It may frequently happen, that a valuable stratum of 

 marl or stone, which lies at a great depth in one situation, may rise 

 near the surface in an adjoining part of the estate, and might be 

 procured with little expense. 



Lime is the only earth which has been generally used to intermix 

 with soils, and has been considered as a manure ; but its operation, 

 as such, is very imperfectly understood. Burnt lime, when caustic, 

 destroys undecomposed vegetable matter, and reduces it to mould, — 

 so far its use is intelligible. It combines, also, with vegetable or min- 

 eral acids in the soil, which might be injurious to vegetation, — here 

 its operation is likewise intelligible : but if we assert, that when burnt 

 lime has absorbed carbonic acid and become mild, it gives out its 

 carbon again to the roots of plants, we assume a fact, which we have 

 neither experiments nor analogies to support. The utility of lime 

 in decomposing vegetable matter and neutralizing acids is obvious : 

 but its other uses are not so evident : except we admit that it acts 



