This is the top layer of soil. It is usually the most fertile, being dark in colour and crumbly.
If you dig into undisturbed garden soil, you'll find it has a clear structure. The upper layer or topsoil, which can vary widely in depth, is normally dark, a sign that it is rich and full of plant foods. Garden plants grow best in topsoil that is well broken up, fertile and able to hold moisture. Regular cultivation aims to maintain and improve these qualities. After a number of years, very high quality topsoil can be produced. Keen gardeners have been known to take it with them when moving house.