- As plants grow and die, they contribute organic matter to the soil. This organic matter is decomposed by microorganisms and earthworms, forming the organic matter-rich topsoil.

- The topsoil is usually dark in color due to the presence of organic matter. It also has a loose structure, which allows for easy root penetration and water infiltration.

Horizon B:

- The subsoil, also called Horizon B, is located beneath the topsoil. It is typically lighter in color than the topsoil and has a higher clay content.

- The clay content in the subsoil is a result of the weathering of minerals in the parent material. As these minerals weather, they release ions that are transported downward by water. The ions react with other minerals to form clay minerals.

- The subsoil is often denser and more compacted than the topsoil. This can make it more difficult for roots to penetrate and for water to infiltrate.

The formation of horizons A and B is a continuous process. As organic matter is added to the soil and as minerals are weathered, the horizons will continue to change and develop.