Slide 5 of 8
Soils develop into layers. These layers, called horizons, are usually seen along road cuts and other areas where the soil is exposed. In the hypothetical situation, there are four horizons in a soil profile. The thickness of each varies with location, and under disturbed conditions -- heavy agriculture, building sites, or severe erosion, for example -- not all horizons will be present.
O = Organic. It consists of fragments of leaf litter, twigs, roots, and other organic material lying on the surface of the soil. This layer is not present in cultivated fields.
A = Topsoil. It is usually darker than lower layers, loose, and crumbly with varying amounts of organic matter. This is generally the most productive layer of soil.
B = Subsoil. It is usually light colored, dense, and low in organic matter.
C = Parent Material. The unconsolidated organic and mineral material in which soil forms..
R = Bedrock. The solid rock that underlies the soil and other unconsolidated material