The BGS Lexicon of Named Rock Units — Result Details

Moelwyn Volcanic Formation

Computer Code: MV Preferred Map Code: Mv
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Volcaniclastic debris-flow deposits, felsic tuffs and tuffites.
Definition of Lower Boundary: Conformable within silty mudstones of the undivided Nant Ffrancon Subgroup.
Definition of Upper Boundary: Conformable within silty mudstones of the undivided Nant Ffrancon Subgroup.
Thickness: Upper up to 200mwith a Lower and Upper Member each up to 100m
Geographical Limits: South central Snowdonia.
Parent Unit: Nant Ffrancon Subgroup (NFR)
Previous Name(s): Y Glog Volcanic Series (-1714)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Upper Member: Cefn Fedw. 
Reference Section  Moelwyn Mountains, above Tan y Grisiau Dam. 
Partial Type Section  Lower Member: screes behind Glan Y Morfa. 
Reference(s):
Shackleton, R M. 1959. The stratigraphy of the Moel Hebog district between Snowdon and Tremadoc. Liverpool and Manchester Geological Journal, Vol.2, 216-252. 
Howells, M F and Smith, M. 1997. Geology of the country around Snowdon. Memoir of the British Geological Survey, Sheet 119 (England and Wales). (London: The Stationery Office). 104pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E119