Definition for Bedrock
From Biology Forums Dictionary
In geology, bedrock is the lithified rock that lies under the loose softer material (regolith) at the surface of the Earth or other terrestrial planet. The broken and weathered regolith includes soil and subsoil.
The surface of the bedrock beneath soil cover is known as rockhead in engineering geology and its identification by digging, drilling or geophysical methods is an important task in most civil engineering projects. Superficial deposits (also known as drift) can be extremely thick, such that the bedrock lies hundreds of meters below the surface.