The BGS Lexicon of Named Rock Units — Result Details

Upper Crafnant Volcanic Formation

Computer Code: UCV Preferred Map Code: UCV
Status Code: Full
Age range: Woolstonian Substage (OS) — Woolstonian Substage (OS)
Lithological Description: Massive, acidic, grey, muddy, crystal tuffite.
Definition of Lower Boundary: Rests on mudstone and siltstone of the Middle Crafnant Volcanic Formation.
Definition of Upper Boundary: Overlain by Nod Glas (= Cadnant Shales).
Thickness: 60-150m
Geographical Limits: Eastern Snowdonia, around Betws-y-Coed. Farther north it is not readily separated from the Middle Crafnant Volcanic Formation.
Parent Unit: Snowdon Volcanic Group (SV)
Previous Name(s): Upper Tuff Bed (-1251)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Gwydir Forest. 
Reference(s):
Howells, M F, Leveridge, B E, Evans, C D R and Nutt, M J C, 1981. Classical areas of British Geology. Dolgarrog. Description of 1:25 000 Sheet SH76. London: HMSO for Institute of Geological Sciences. 
Howells, M F, Francis, E H, Leveridge, B E and Evans, C D R, 1978. Classical areas of British Geology. Capel Curig and Betws-y-Coed. Description of 1:25 000 Sheet SH75. London: HMSO for Institute of Geological Sciences. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E106 E107