Soil Horizons

As soils form, they develop characteristic horizons. The specific composition of those horizons depends greatly on climate, vegetation, and parent material.

O Horizon: Humus. Mostly organic material

A Horizon: Topsoil. A layer of organic materials and minerals mixed together. (Usually the layer mixed by plowing or tilling)

B Horizon: Subsoil. Composed primarily of mineral material with very little organic material mixed in.

C Horizon: The least weathered layer. Made up of primarily the parent material.

D Horizon: Bedrock