GeoGraph - photograph every grid square

Strata near the top of the Bannau Sir Gaer cliffs

Crumbly brownstones with a topping of less brittle grey mudstone. The rocks of the cliff face on the Bannau Sir Gaer escarpment belong to the Devonian Brownstones formation. It contains layers of sandstone and coarser mudstone in narrow bands. The top layer south of the escarpment belongs to the Plateau Beds formation (later Devonian), which is a finer, harder sandstone. Some geological background about the area can be found at Link .