The soil : an introduction to the scientific study of the growth of crops / by A.D. Hall.

  • Hall, A. Daniel (Alfred Daniel), Sir, 1864-1942.
Date:
1903
Catalogue details

Licence: In copyright

Credit: The soil : an introduction to the scientific study of the growth of crops / by A.D. Hall. Source: Wellcome Collection.

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    CHAPTER I THE ORIGIN OF SOILS Sedentary Soils, and Soils of Transport—Weathering—The Com- position of Rock-forming Minerals and their Weathered Products—Distinction between Soil and Subsoil—General Classification of Soils. TlIE study of soils must begin with some knowledge of their origin and their relationship to the rocks that underlie them, out of which, in most cases, they have been formed. Perhaps the best way of arriving at an idea of the natural processes which result in soil, is to visit a river valley and examine, first a quarry on the flanks of the hills, and then one of the cuttings for gravel or brick-earth, which often lie a little above the river level. The face of the quarry shows at a depth of 10 feet or so from the surface the massive rock, unaltered as yet by any action of the weather. Closer examination, however, shows that even at this depth the rock is not quite solid ; if it be a stratified rock the planes of bedding are apparent, along which the rock can be split. Joints again traverse the rock at right angles to the bedding planes, and along both joints and bed- ding planes it is evident that water makes its way, for the edges of the cracks are slightly altered and dis- coloured. Nearer the surface, the cracks and lines of o