A distinct layer of soil, more or less parallel with the soil surface, having similar properties such as color, texture and permeability; the soil profile is subdivided into the following major horizons: A-horizon, characterized by an accumulation of organic material; B-horizon, characterized by relative accumulation of clay iron, organic matter or aluminum; C-horizon, the undisturbed and unaltered parent material. (Some soils have an E-horizon, characterized by leaching of organic and other material.)