Here's a breakdown:

* A horizon: Topsoil - rich in organic matter, dark in color

* B horizon: Subsoil - enriched with minerals and clay leached from the A horizon, often lighter in color

* C horizon: Parent material - the bedrock or geological material from which the soil formed

* O horizon: (Optional) Organic layer - found in forest soils, composed of decaying plant matter

Let me know if you have any other soil questions!