The BGS Lexicon of Named Rock Units — Result Details

Yoke House Formation

Computer Code: YKH Preferred Map Code: YkH
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Rhyolitic crystal-lithic tuffs, tuffaceous sandstones and breccio-conglomerates.
Definition of Lower Boundary: The clastic apron deposits lie on Carneddol Rhyolitic Tuff Formation, passing onto Foel Ddu Rhyodacite Tuff Formation. Locally overlies the Penmaen Formation.
Definition of Upper Boundary: The clastic apron deposits pass upwards into dark grey graptolitic mudstones of the Nod Glas Formation, and part of the Carneddol Rhyolitic Tuff Formation.
Thickness: 50-130m
Geographical Limits: Pwllheli area, north-west Wales.
Parent Unit: Llanbedrog Volcanic Group (LIG)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Partial Type Section  Upper part at Cacau Gwynion-isaf. 
Partial Type Section  Lower part of formation at Yoke House. 
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: