The BGS Lexicon of Named Rock Units — Result Details

Foel Ddu Rhyodacite Formation

Computer Code: FDR Preferred Map Code: FD
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Rhyodacitic lavas and tuffs.
Definition of Lower Boundary: Overlies Penmaen Tuff Formation comprising lava flows and tuffs of intermediate composition, plus associated sediments.
Definition of Upper Boundary: Overlain by crystal-lithic tuffs with variable characteristics, of the Carneddol Rhyolitic Tuff Formation.
Thickness: <100m to >250m
Geographical Limits: Pwllheli area, northwest Wales.
Parent Unit: Llanbedrog Volcanic Group (LIG)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Reference Section  Between Garn Saethon and Glan-y-gors. 
Young, T P, Gibbons, W and McCarroll, D. 2002. Geology of the country around Pwllheli. Memoir of the British Geological Survey, Sheet 134 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used: