Definition: Gently undulating land surfaces cut indiscriminately across underlying geology - the end-product of a long period of erosion.

Alain Godard (1965) recognises four cross-cutting erosion surfaces in Caithness:

• sub-Devonian surfaces
• the Surfaces intermédiaire and écossaise of mid-Tertiary age
• the late Tertiary "Niveau Pliocene", dominating the plain of Caithness.

These surfaces form the main relief elements in the county and remain recognisable despite variable amounts of glacial erosion. Each reflects millions of years of erosion and each has been uplifted and deformed since its formation.