The BGS Lexicon of Named Rock Units — Result Details

Craig Hen-Gae Member

Computer Code: CNE Preferred Map Code: notEntered
Status Code: Full
Age range: Longvillian Substage (OL) — Longvillian Substage (OL)
Lithological Description: Black hemipelagic mudstones, thinly interbedded with grey turbiditic mudstones and siltstones.
Definition of Lower Boundary: Conformably overlies the main part of the Ceiswyn Formation, the boundary being taken where laminated hemipelagic mudstones become equal or dominant in the sequence.
Definition of Upper Boundary: Conformably overlain by the Nod Glas Formation, the boundary being taken where the turbidite mudstone disappears and the sequence consists wholly of black, graptolitic, pelagic mudstone.
Thickness: 200 to 300m
Geographical Limits: Cadair Idris district, North Wales.
Parent Unit: Ceiswyn Formation (CSW)
Previous Name(s): Upper Ceiswyn Beds (-150)
Alternative Name(s): Gelli-Grin Calcareous Ash Formation
Stratotypes:
Partial Type Section  Craig Hen-gae, 1.5km westnorthwest of Aberllefenni. Pratt et al. 1995. 
Reference(s):
Lockley, M G. 1980. The geology of the Llanuwchllyn to Llanmawddwy area, south Gwynedd, North Wales. Geological Journal, Vol.15, 21-41. 
Pugh, W J. 1928. The geology of the district around Dinas Mawddwy (Merioneth). Quarterly Journal of the Geological Society of London. Vol.84, 345-381. 
Bassett, D A, Whittington, H B and Williams, A. 1966. The stratigraphy of the Bala district, Merionethshire. Quarterly Journal of the Geological Society of London, Vol.122, 219-271. 
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 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E149