The Elements of economic geology

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Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Document type:: Monograph

Structure type:: Chapter

Title:: Part III. Earthy minerals

Collection:: Economics Books

CHAPTER XVI THE SOIL DeriniTion AND Funcrion—The soil is the layer of decom- posed rock material charged with organic matter which covers most of the surface of the earth. It forms the basis of vegetation as it can be penetrated by roots and holds stores of plant foods. The study of soils reveals the causes of their fertility or sterility, and has enabled large tracts of useless desert to be rendered of high fertility. The soil is usually brownish or black, and from 6 inches to 2 feet in thickness ; it passes into the underlying rock through the partially decomposed layer, the subsoil—a term however used in civil engineering and public health for the general foundation of a district. Soils are of two chief classes, * sedentary soils ” due to the weathering of rock in situ, and * transported soils composed of materials that have undergone disintegration elsewhere. The decay of rock into soil is due to changes of temperature which break rock to pieces, solution by soil waters, oxidation, the burrowing of animals, the disruptive action of roots, and the solvent action of organic products. The main function of the soil is to convert the inorganic constituents of the air into plant tissues which can be used as food by animals. A soil is also a reservoir of plant foods, which in some circumstances may be its main value, for the deep soils of Manitoba, which contain 20 per cent. of organic matter, can produce wheat for a long period without exhaus- tion; but if a soil be worked simply as a store of plant food, it must be ultimately ruined. The value of a soil may depend on accidental circumstances, such as proximity to a market, local supplies of cheap manure, and freaks of fashion, which render profitable the growth of 190

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