Soil Horizon

A layer of soil that is nearly parallel to the land surface and is different from layers above and below in terms of composition (e.g., organic matter, mineral content) and other characteristics (e.g., color, texture). The major soil horizons in descending order from the surface of the earth include the O (organic) horizon, the A (topsoil) horizon, the B (subsoil) horizon, the C (mineral) horizon and the R (bedrock) horizon. Geologists and Soil Scientists also recognize many sub-horizons designated by lowercase letters. <