The BGS Lexicon of Named Rock Units — Result Details

Lower Rhyolitic Tuff Formation

Computer Code: LR Preferred Map Code: LR
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Acid ash-flow tuff, welded and non-welded, volcanic breccias and rhyolite intrusions.
Definition of Lower Boundary: Overlies sandstones and silty mudstones of Cwm Eigiau Formation.
Definition of Upper Boundary: Overlain by basic volcanic deposits of Bedded Pyroclastic Formation.
Thickness: 600m
Geographical Limits: Central Snowdonia.
Parent Unit: Snowdon Volcanic Group (SV)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Lliwedd, Snowdon. 
Reference(s):
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). 
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:
E106 E119