The BGS Lexicon of Named Rock Units — Result Details

Cwar Glas Member

Computer Code: CWGL Preferred Map Code: notEntered
Status Code: Full
Age range: Ludlow Epoch (SU) — Ludlow Epoch (SU)
Lithological Description: Greenish grey mudstones and siltstones with abundant thin to medium bedded fine-grained sheet sandstones. Scattered burrows. Packets of thicker bedded green grey and purple fine-grained sandstone with hummocky cross statification and parallel lamination occur throughout the member. In the west of the outcrop the member becomes predominantly sandstone.
Definition of Lower Boundary: Taken at the base of the first packet of thick bedded fine-grained sandstone with hummocky cross statification and parallel lamination of the Cwar Glas Member above the mudstones and siltstones with abundant thin to medium bedded fine-grained sheet sandstones of the Hafod Fawr Formation.
Definition of Upper Boundary: Taken at the incoming of low angle cross bedded lilac coloured conglomerates, conglomeratic quartzites and coarse-grained quartzites of the Mynydd Myddfai Formation above the thick bedded greenish grey and purple fine-grained sandstones of the Cwar Glas Member of the Hafod Fawr Formation.
Thickness: 0 to 66m
Geographical Limits: Northeast Carmarthenshire (SN 73 24), South Wales.
Parent Unit: Hafod Fawr Formation (HAFOD)
Previous Name(s): Carn Powell Facies (-2132)
Grammysia Beds (-1468)
Carn Powell Facies (Of Black Cock Beds) (-4576)
Grammysia Bed (-4577)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Banks and bed of the Afon Sawdde opposite Cwar Glas (quarries) between 400 and 320m downstream of Pont ar Llechau, Llangadog, Carmarthenshire. Most of the Member is exposed, including the lower boundary with the lower part of the Hafod Fawr Formation. The upper boundary with the Mynydd Myddfai Formation is not exposed, being obscured by a 2m walled section of the river bank. 
Reference(s):
Potter, J F and Price, J H. 1965. Comparative sections through rocks of Ludlovian-Downtonian age in the Llandovery and Llandeilo districts. Proceedings of the Geologists' Association, Vol.76, 379-402. 
Schofield, D I, Davies, J R, Jones, N S, Leslie, A B, Waters, R A, Williams, M, Willson, D, Venus, J and Hillier, R D. In press. Geology of the Llandovery district - a brief explanation of the geological map. Sheet Explanation of the British Geological Survey. 1:50 000 Sheet 212 Llandovery (England and Wales). 
Stamp, L D. 1923. The base of the Devonian, with special reference to the Welsh Borderland. Geological Magazine, Volume 60, 276-410. 
Strahan, A, Cantrill, T C, Dixon, E E L and Thomas, H H. 1907. Geology of the South Wales Coalfield, Part VII, the country around Ammanford. Memoir of the Geological Survey of England and Wales, Sheet 230 (England and Wales). (London: HMSO.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable