Subsoil is the layer of
soil under the
topsoil on the surface of the ground. Like topsoil it is composed of a variable mixture of small particles such as
sand,
silt and/or
clay, but it lacks the
organic matter and
humus content of topsoil. Below the subsoil is the substratum, which can be residual
bedrock, sediments, or
aeolian deposits. As it is lacking in dark humus, subsoil is usually paler in colour than the overlying topsoil. It may contain the deeper roots of some plants, such as trees, but a majority of plant roots lie within the surface topsoil.