The BGS Lexicon of Named Rock Units — Result Details

Grey Friar Tuff Member

Computer Code: GY Preferred Map Code: Gy
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Massive, dacitic lapilli-tuff; contains significant quantities of lithic clasts, mainly of siltstone and sandstone derived from the subvolcanic, Skiddaw Group, basement.
Definition of Lower Boundary: Base of dacitic lapilli tuff. Unconformable, locally overlies Great Whinscale Dacite and elsewhere un-named basaltic andesite and andesite in the Birker Fell Andesite Formation.
Definition of Upper Boundary: Overlying parts of Birker Fell Andesite Formation, usually volcaniclastic sandstone or andesite.
Thickness: 0 - 50m
Geographical Limits: Cockley Beck Fell - Grey Friar - Seathwaite Tarn - Troutal Fell, Cumbria.
Parent Unit: Birker Fell Andesite Formation (BFA)
Previous Name(s): Tongue House Member [Obsolete Name: Replaced By LIT, GWD, GY] (TNM)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Grey Friar - Seathwaite Tarn. 
Reference(s):
Millward, D, Johnson, E W, Beddoe-Stephens, B, Young, B, Kneller, B C, Lee, M K, Fortey, N J, Allen, P M, Branney, M J, Cooper, D C, Hirons, S, Kokelaar, B P, Marks, R J, McConnell, B J, Merritt, J W, Molyneux, S G, Petterson, M G, Roberts, B, Rundle, C C, Rushton, A W A, Scott, R W, Soper, N J and Stone, P. 2000. Geology of the Ambleside district. Memoir of the British Geological Survey, England and Wales, Sheet 38. 
Petterson, M G, Beddoe-Stephens, B, Millward, D and Johnson, E W, 1992. A pre-caldera plateau-andesite field in the Borrowdale Volcanic Group of the English Lake District. Journal of the Geological Society, London, Vol. 149, 889-906. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E038