The BGS Lexicon of Named Rock Units — Result Details

Tryfan Grit Group (A) [Obsolete Name And Code: Use FA]

Computer Code: ACTG Preferred Map Code: notEntered
Status Code: Index Level
Age range: Comley Series (EC) — Comley Series (EC)
Lithological Description: Coarse quartzo-feldspathic grits and medium-grained lithic sandstones and siltstones.
Definition of Lower Boundary: Drawn at base of grits of the Tryfan Grits Group where it rests conformably on acid tuffs, ignimbrites and ashes of the Clogwyn Volcanic Group.
Definition of Upper Boundary: Drawn at unconformable upward passage from sandstones and siltstones of the Tryfan Grit Group to conglomerate of the Cilgwyn Conglomerate.
Thickness: Approximately 300 metres.
Geographical Limits: Gwynedd, Wales.
Parent Unit: Not Entered (?)
Previous Name(s): Tryfan Group (-4420)
Alternative Name(s): Fachwen Formation
Type Area  Nantlle, Gwynedd, Wales. 
Morris, T O and Fearnsides, W G, 1926. The stratigraphy and structure of the Cambrian Slate Belt of Nantlle, (Caernarvonshire). Quarterly Journal of the Geological Society of London, Vol.82, p.250-303. 
Wood, D S, 1969. The base and correlation of the Cambrian rocks of north Wales, "in" Wood, A. The Pre-Cambrian and Lower Palaeozoic rocks of Wales. University of Wales Press, Cardiff, p.47-66. 
Cattermole, P and Jones, A. 1970. The geology of the area around Mynydd Mawr, Nantlle, Caernarvonshire. Geological Journal, Vol.7, 111-128. 
Morris, T O, "In" Greenly, E, 1945. The Arvonian rocks of Arvon. Quarterly Journal of the Geological Society of London, Vol.100, p.269-284. 
Smith, B and George, T N. 1961. North Wales. British Regional Geology. (London: H.M.S.O.). 97pp. 
Cowie, J W, Rushton, A W A and Stubblefield, C J, 1972. A correlation of Cambrian rocks in the British Isles. Special Report of the Geological Society of London, No.2, p.26. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable