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. 
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 Unpublished PhD thesis, University of Liverpool.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. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E120 E121 E137