The horizon that contains large pieces of broken up bedrock is called the R horizon.

Here's a breakdown of why:

* R horizon: This is the bedrock layer, often the very bottom of a soil profile. It's the parent material from which the soil above develops. While not technically soil, the R horizon can be fragmented into large pieces due to weathering and erosion.

* Other horizons:

* O horizon: Organic matter layer (leaf litter, etc.)

* A horizon: Topsoil, rich in organic matter and minerals.

* E horizon: Zone of leaching, where minerals are washed out.

* B horizon: Subsoil, where minerals accumulate.

* C horizon: Weathered parent material, less broken up than the R horizon.

Let me know if you have any other questions!