These three regions are topsoil, subsoil, and bedrock. The topsoil contains any small pieces of bedrock. The smallest pieces are clay. The largest pieces are sand. In between the clay and sand are pieces called silt.
Much humus is found in the topsoil.
There are spaces in the soil filled with air and water. Many decomposers live in the topsoil as well as green plants. The subsoil is more lightly packed with larger pieces of bedrock and very little humus. The bedrock is made of a variety of minerals bound together to form rock. In the next activity you will examine the parts of soil.