The following are some commonly used soil designations, their definitions and basic properties:
Bentonite: Decomposed volcanic ash containing a high percentage of clay mineral— montmorillonite. It exhibits high degree of shrinkage and swelling.Black cotton soil: Black soil containing a high percentage of montmorillonite and colloidal material; exhibits high degree of shrinkage and swelling. The name is derived from the fact that cotton grows well in the black soil.Boulder clay: Glacial clay containing all sizes of rock fragments from boulders down to finely pulverised clay materials. It is also known as ‘Glacial till’.Caliche: Soil conglomerate of gravel, sand and clay cemented by calcium carbonate.Hard pan: Densely cemented soil which remains hard when wet. Boulder clays or glacial tills may also be called hard-pan— very difficult to penetrate or excavate.Laterite: Deep brown soil of cellular structure, easy to excavate but gets hardened on exposure to air owing to the formation of hydrated iron oxides.Loam: Mixture of sand, silt and clay size particles approximately in equal proportions; sometimes contains organic matter.Loess: Uniform wind-blown yellowish brown silt or silty clay; exhibits cohesion in the dry condition, which is lost on wetting. Near vertical cuts can be made in the dry condition.Marl: Mixtures of clacareous sands or clays or loam; clay content not more than 75% and lime content not less than 15%.Moorum: Gravel mixed with red clay.Top-soil: Surface material which supports plant life.Varved clay: Clay and silt of glacial origin, essentially a lacustrine deposit; varve is a term of Swedish origin meaning thin layer. Thicker silt varves of summer alternate with thinner clay varves of winter.
