The BGS Lexicon of Named Rock Units — Result Details

Lower Acid Volcanic Group

Computer Code: LAV Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Arenig Series (OR) — Abereiddian Stage (O2)
Lithological Description: Tuffs and rhyolitic lavas (the latter may be recrystallized acid tuffs) interbedded slates also occur.
Definition of Lower Boundary: Drawn at base of mainly tuffs of Lower Acid Volcanic Group which rest conformably on grits and sandy flags of the Basement Group.
Definition of Upper Boundary: Drawn at conformable upward passage from mainly tuffs of Lower Acid Volcanic Group to the Moelyn Slates of the 'Bifidus' Beds.
Thickness: Approx. 150 to 300 metres.
Geographical Limits: Mid-Wales and Marches.
Parent Unit: Not Entered (?)
Previous Name(s): Mynydd Y Gader Rhyolitic Group (-2281)
Lower Acid Rhyolitic Group (-3512)
Mynydd Y Gader Volcanic Group (-4746)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Dolgellau-Cader Idris district, Gwynedd. 
Reference(s):
Davies, R G, 1959. The Cader Idris Granophyre and its associated rocks. Quarterly Journal of the Geological Society, London. Vol.115, 189-216. 
Cox, A H and Wells, A K, 1916. The Ordovician sequence in the Cader Idris district (Merioneth). British Association for the Advancement of Science Report for 1915 (Manchester), p.424. 
Jones, B, 1933. The geology of the Fairbourne-Llwyngwril district, Merioneth. Quarterly Journal of the Geological Society, Vol.89, 145-171. 
Lake, P and Reynolds, S H, 1912. The geology of Mynydd-y-Gader, Dolgelly. Quarterly Journal of the Geological Society of London, Vol.68, 345-363. 
Cox, A H and Wells, A K, 1927. The geology of the Dolgelley district, Merionethshire. Proceedings of the Geologists' Association, Vol.38, 265-318. 
Lake, P and Reynolds, S H. 1896. The Lingula Flags and igneous rocks of the neighbourhood of Dolgelly. Quarterly Journal of the Geological Society of London, Vol.52, 511-527. 
Cox, A H, and Wells, A K, 1921. The Lower Palaeozoic rocks of the Arthog-Dolgellau district (Merionethshire). Quarterly Journal of the Geological Society, London, Vol.76, p. 254-324. 
Wells, A K. 1925. The geology of the Rhobell Fawr district (Merioneth). Quarterly Journal of the Geological Society of London, Vol.81, 463-538. 
Cox, A H. 1925. The geology of the Cadair Idris Range, (Merioneth). Quarterly Journal of the Geological Society of London, Vol.81, p.539-592. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable