They can be arranged in layers or horizons. These horizons constitute a soil profile. The top layer is called topsoil. This is where the accumulation of humus occurs. It is also the layer where the greatest amount of leaching and eluviation occurs.
Capillary action takes place in dry climates.
This layer is of the greatest value for agricultural purposes. The second layer, subsoil, contains material which is the result of leaching and eluviation from the top horizon. Should much of the topsoil disappear, the subsoil usually develops a tough crust called hardpan or iron crust. This layer consists of mantle rock, or parent material, which is virtually unaffected by the soil making process. The lowest layer is the bedrock, or the parent material which is unchanged and unaltered.