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soil profile 
Soil usually has four main layers; it varies in total thickness from several centimeters to several meters, depending on the area.
bedrock
Rock that forms the bottom layer of soil; its physical and chemical breakdown enables the upper layers to develop.
subsoil
Third layer of soil to which the roots extend; contains little organic matter but many nutrients leached from the topsoil.
plant litter
Upper layer of soil, composed of recently fallen animal and vegetable scraps or those in the early stages of decomposition.
topsoil
Second layer of soil, dark in color and rich in organic matter; it contains almost all of the soil’s animal and vegetable life.
