Soil consists of different layers that are often called horizons. There are three main soil horizons called A, B and C as well as an organic layer (O) on top of the soil (O) and bedrock (R) below:
O: This is a layer of organic matter that is about 2 inches thick and is made up of dead plant material such as leaves and twigs.
A: This upper soil horizon is also called Topsoil. It is only between 5 to 10 inches thick and consists of organic matter and minerals. This is the soil layer where plants and organisms primarily live.
B: This layer is also called Subsoil. It is mostly made of clay, iron minerals as well as organic matter, which has been washed down to this horizon by rainwater.
C: The C horizon is the parent material from which the upper soil layers developed. It consists primarily of large rocks.
R: This is the bedrock and is located several feet under the surface. The bedrock is made up of a solid mass of rock.