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layers created as a result of natural differentiation during soil formation; they are also called genetic horizons. All the soil horizons together form the soil profile. Each horizon is more or less homogeneous in granulometric, mineral and chemical composition, physical properties, texture, and color. It can also be divided into subhorizons. Soil horizons are designated by the letters A, B, and C. A designates the horizon of humus accumulation and also the eluvial horizon; B the illuvial, or metamorphic horizon; and C the parent material. The A horizon in turn is subdivided into A0, indicating forest litter or steppe matting; A1, the humus subhorizon; and A2, the podzolic subhorizon. An Ap horizon is formed in plowed soils.