The part of a soil profile made up of partly weathered rock is called the regolith or C horizon.

Here's a breakdown:

* Regolith: This is the general term for the loose, unconsolidated material that covers bedrock. It includes weathered rock fragments, minerals, and some organic matter.

* C horizon: This is the layer of the soil profile that directly overlies bedrock. It consists primarily of weathered parent material, with little to no organic matter. The C horizon is the transition zone between bedrock and the more developed layers above.

It's important to note that the regolith and C horizon are not always the same. Sometimes, the regolith can extend deeper than the C horizon and include material that is not directly related to the underlying bedrock.