The BGS Lexicon of Named Rock Units — Result Details

Snowdon Volcanic Group

Computer Code: SV Preferred Map Code: SVG
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Acidic ash-flow tuffs with a major basaltic division.
Definition of Lower Boundary: At base of volcanic formations resting on sedimentary rocks of Cwm Eigiau Formation.
Definition of Upper Boundary: At base of Cadnant Shales Formation.
Thickness: Not exceeding 1800 metres.
Geographical Limits: Snowdonia.
Parent Unit: Not Applicable (-)
Previous Name(s): Crafnant Volcanic Group [Obsolete Name And Code: See SV] (CV)
Snowdon Volcanic Series (-4910)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Snowdon. Note: see also stratotypes of constituent (Upper Rhyolitic Tuff; Lower Rhyolitic Tuff; Bedded Pyroclastic; Pitts Head Tuff; Dolgarrog Volcanic; Upper, Middle and Upper Crafnant Volcanic; Tal y Fan; Yr Arddu Tuffs) volcanic formations. 
Reference(s):
Williams, D, 1930. The geology of the country between Nant Peris and Nant Ffrancon (Snowdonia). Quarterly Journal of the Geological Society, Vol.86, p.193, 202-212, map. 
Williams, H and Bulman, O M B, 1931. The geology of the Dolwyddelan Syncline, North Wales. Quarterly Journal of the Geological Society of London, Vol.87, p.429, 434-443. 
Rast, N and others, 1958. Sub-Aerial volcanicity in Snowdonia. Nature. London, Vol.181, p.508. 
Oliver, R L, 1954. Welded tuffs in the Borrowdale Volcanic Series, English Lake District, with a note on similar rocks in Wales. Geological Magazine, Vol.91, p.478. 
Williams, H. 1927. The geology of Snowdon, North Wales. Quarterly Journal of the Geological Society, Vol.83, p.353, 363-389. 
Howells, M F, Reedman, A J and Campbell, S D G, 1991. Ordovician (Caradoc) marginal basin volcanism in Snowdonia (north-west Wales). (London: HMSO for the British Geological Survey). 
Shackleton, R M. 1959. The stratigraphy of the Moel Hebog district between Snowdon and Tremadoc. Liverpool and Manchester Geological Journal, Vol.2, 216-252. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E119 E106 E107