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
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