Horizon A
This humus-rich layer is often referred to as "topsoil" or "top layer soil." Its color is usually dark brown due to its high organic matter content. Its fertility promotes plant growth, and its aeration is ensured by burrowing fauna. In civil engineering, it corresponds to the earthy materials from the upper soil layer.
Horizon B
Poor in humus but rich in minerals, this layer is generally lighter in color than Horizon A. Residues from the upper layers accumulate here. In civil engineering, it corresponds to the earthy materials from the underlying soil layer.
Horizon C
This layer corresponds to the parent rock on which the soil rests. It is either loose or consolidated and contains almost no organic matter, marking the limit of vegetation root penetration. In civil engineering, it corresponds to the excavation materials.