A soil horizon is a particular layer of soil parallel to the surface. Its physical characteristics are different from the layers above and below it. The following are the main soil horizons:
The O Horizon is the organic layer of soil, comprising mainly of decomposing organic material (humus).
The A Horizon is the layer of topsoil. It is here that most organisms, such as worms, are found.
The B Horizon is known as subsoil and is rich in iron and aluminum.
The C Horizon is the subratutm and contains large clumps of soil and bedrock.