These soils are formed on Devonian granites and granodiorites with decomposing rock generally occurring before 2 metres. At the surface, the soils are dark brownish grey or grey sandy loams. Occasionally, there are sandy clay loams with the sand fraction generally containing coarse angular sand and small gravel. At about 20 cm, yellowish or greyish brown similarly textured soils can be found. Below this, yellowish brown to reddish brown sandy clay loams occur if the soils are shallow, or sandy clays if otherwise.
In the valleys, the soils are generally deeper than 2 metres and mainly comprise clayey fine gravels and coarse angular sands. A cemented zone generally occurs at about 90 cm.