The BGS Lexicon of Named Rock Units — Result Details

Pitts Head Tuff Formation

Computer Code: PT Preferred Map Code: PT
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Acid ash-flow tuff; variably welded, rhyolitic. Two main facies - intra caldera tuffs and out-flow tuffs.
Definition of Lower Boundary: Overlies sandstones and mudstones of the Cwm Eigiau Formation.
Definition of Upper Boundary: Overlain by sandstones and siltstones of the Cwm Eigiau Formation or tuffs of the Lower Rhyolitic Tuff Formation.
Thickness: 700m intra caldera facies, 0-100m outflow facies
Geographical Limits: From Llwyd Mawr to Dolgarrog, central Snowdonia.
Parent Unit: Snowdon Volcanic Group (SV)
Previous Name(s): Pitts Head "Tuffs" (-3625)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Outflow facies, west flanks of Moel Hebog. 
Partial Type Section  Intra caldera facies. Llwyd Mawr - Cwm Silyn. 
Reference(s):
Reedman, A J, Howells, M F, Orton, G and Campbell, S D G, 1987. The Pitts Head Tuff Formation: a subaerial to submarine welded ash-flow tuff of Ordovician age, North Wales. Geological Magazine, Vol.124, 427-439. 
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:
E119 E106 E134