The BGS Lexicon of Named Rock Units — Result Details

Long Top Tuff Member

Computer Code: LTT Preferred Map Code: LTT
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Bedded units of massive, eutaxitic rhyolitic tuff and lapilli-tuff. Intercalations of bedded and laminated tuff widespread. Localized units of pyroclastic breccia.
Definition of Lower Boundary: Base of rhyolitic pyroclastic rocks. Unconformable, on slumped surface of Whorneyside Tuff Formation and locally on the underlying Birker Fell Andesite Formation, but locally interbedded.
Definition of Upper Boundary: Defined by the bases of overlying Crinkle Tuff Member of the Airy's Bridge Tuff Formation.
Thickness: 0 - 310m
Geographical Limits: Crinkle Crags and Scafell area, extending to Coniston Fells, Duddon Valley, Eskdale, Wasdale, Borrowdale and Langdale.
Parent Unit: Airy's Bridge Tuff Formation (AIB)
Previous Name(s): Long Top Member (-2303)
Long Top Tuffs (-2304)
Alternative Name(s): none recorded or not applicable
Type Area  Long Top, Crinkle Crags. 
Oliver, R L, 1961. The Borrowdale Volcanic and associated rocks of the Scafell area, English Lake District. Quarterly Journal of the Geological Society of London, Vol 117, p. 377-417 
Branney, M J, Davis, N C, Kokalaar, B P and McConnell, B J. 1993. The Airy's Bridge Formation in the central Fells. British Geological Survey Technical Report WA/93/41 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E038 E029