Subsoil: layer of soil under topsoil on the surface of the ground
Topsoil: fertile, upper part of soil
Regolith: unconsolidated residual or transported material that overlies the solid rock on the earth
Bedrock: lies under regolith, can be 100 meters undersurface.
Order of surface: Topsoil --> Subsoil --> Regolith --> Bedrock
Your answer is bedrock