The BGS Lexicon of Named Rock Units — Result Details

Pen-Y-Graig Tuff Member

Computer Code: PGT Preferred Map Code: Pngr
Status Code: Full
Age range: Longvillian Substage (OL) — Longvillian Substage (OL)
Lithological Description: Laterally discontinous acid tuff. (coarse ash of Wedd et al., 1929).
Definition of Lower Boundary: Base of tuff succeeds siltstones of the Bryn Siltstone Formation.
Definition of Upper Boundary: Uncomformably overlain by Ashgill, grey-green muds of the Dolhir Formation.
Thickness: To 7m
Geographical Limits: North side of Berwyn Hills of Oswestry (137) and Wrexham (121). Overstepped by Dolhir Formation.
Parent Unit: Bryn Siltstone Formation (BSI)
Previous Name(s): Pen Y Graig Ash (-1119)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Oswestry, Sheet 137. 
Type Area  Outcrops at Pen-y-graig. 
Reference(s):
Groom, T and Lake, P. 1908. The Bala and Llandovery rocks of Glyn Ceiriog (North Wales). Quarterly Journal of the Geological Society, Vol.64/4, p.546-595. 
Wedd, C B, Smith, B, King, W B R and Wray, D A. 1929. Geology of the country around Oswestry. Memoir of the Geological Survey of Great Britain, Sheet 137. 
Brenchley, PJ. 1966. The Caradoc rocks of the north and west Berwyns, North Wales. Unpublished PhD thesis, University of Liverpool. 
Brenchley, P J, 1978. The Caradocian rocks of the North and West Berwyn Hills. Geological Journal, Vol.13, 137-164. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E120 E121 E137