1. Topsoil: The top layer of soil is the most fertile and contains the highest concentration of organic matter. It is also the most susceptible to erosion.

2. Subsoil: The subsoil is the layer of soil that lies beneath the topsoil. It is less fertile than the topsoil but still contains a significant amount of organic matter.

3. Parent material: The parent material is the layer of soil that lies beneath the subsoil. It is the least fertile layer of soil and is composed of weathered rock or sediment.

4. Bedrock: The bedrock is the solid rock that lies beneath the parent material. It is not a part of the soil but can influence the soil's characteristics.