Soil layers, also called horizons, differ in composition and depth and are defined according to location , The soil profile shown here represents a clayey soil common in parts of the southeastern United States.
HORIZON O : Up to I inch thick. Decomposing material such as leaf litter and humus, on its way to becoming topsoil.
HORIZON A: 6 to 8 inches thick. The dark topsoil contains organic material and animals ranging from microscopic bacteria to worms and burrowing shrews.
HORIZON E: A few inches thick. Lighter in color than Horizon A as a result of minerals leaching downward.
HORIZON B: 1.5 to 2 feet thick. High iron content turns this layer red. Also called subsoil.
HORIZON C: Soil is born here, where water and temperature join to break bedrock. volcanic ash, or sediment down into smaller particles. Little organic material is found here.
HORIZON R: (not seen in the image) Solid bedrock, unweathered, beneath the other layers.