- Cross - sectional soil layers from the surface of the soil down to the bedrock.
- O Horizon: The surface layer of partially and completely undecomposed plant residue such as leaf litter.
- A Horizon: The uppermost layer of the soul commonly known as topsoil. This layer contains a large amount of decomposing organic material known as hummus, and most of the living organisms that dwell in the soil.
- B Horizon: Layer commonly known as the subsoil. Plant roots penetrate this area, but there is much less hummus and more inorganic content than the A Horizon.
- C Horizon: This layer is made predominantly of the Parent Material for the soil. Parent material is the bedrock and large unbroken pieces of rock that are weathered to produce the inorganic components of soil.