The BGS Lexicon of Named Rock Units — Result Details

Cefn Hir Member

Computer Code: CFH Preferred Map Code: Cfn
Status Code: Full
Age range: Llanvirn Series (OE) — Llanvirn Series (OE)
Lithological Description: Mafic and felsic tuffs and tuffites with interbedded mudstones and rare pillowed basalts.
Definition of Lower Boundary: Conformable within the mudstones of the Cregennen Formation.
Definition of Upper Boundary: Conformable within the mudstones of the Cregennen Formation and locally overlain conformably by the mafic lavas and tuffs of the Llyn y Gafr Volcanic Formation.
Thickness: To 90m
Geographical Limits: Cadair Idris district.
Parent Unit: Cregennen Formation (CREN)
Previous Name(s): Cefn Hir Ashes. (-766)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  The crags of Pared-y-Cefn Hir, east of Arthog. Pratt, W T, Woodhall, D G and Howells, M F. 1995. 
Reference(s):
Cox, A H, and Wells, A K. 1927. The geology of the Dolgelley district, Merionethshire. Proceedings of the Geologists' Association, Vol.38, 265-318. 
Pratt, W T, Woodhall, D G and Howells, M F. 1995. Geology of the country around Cadair Idris. Memoir of the British Geological Survey, Sheet 149. (England and Wales). (London: HMSO), 111pp 
Jones, B, 1933. The geology of the Fairbourne-Llwyngwril district, Merioneth. Quarterly Journal of the Geological Society, Vol.89, 145-171. 
Cox, A H, and Wells, A K. 1921. The Lower Palaeozoic rocks of the Arthog-Dolgellau district (Merionethshire). Quarterly Journal of the Geological Society, London, Vol.76, p. 254-324. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E149