The BGS Lexicon of Named Rock Units — Result Details

Glyn Dyfrdwy Group [Obsolete Name And Code]

Computer Code: GDGP Preferred Map Code: notEntered
Status Code: Index Level
Age range: Wenlock Epoch (SW) — Ludlow Epoch (SU)
Lithological Description: Slates, slates with thin silty sandstone-bands, alternating bands of cleaved mudstone and uncleaved laminated siltstone, fairly thinly bedded shales and perfectly cleaved silty mudstones.
Definition of Lower Boundary: Drawn at the base of the Pentre-Dwfr Slates where it rests conformably upon the Pen-y-Glog Group, namely the Pen-y-Glog Slates.
Definition of Upper Boundary: Drawn at conformable upward passage of the Glyn Dyfrdwy Group; thin-bedded shales, silty mudstones almost perfectly cleaved to fine-grained uncleaved sandstones and roughly cleaved sandy shales of the Nant-y-Bache Group.
Thickness: 304 metres approx.
Geographical Limits: Llangollen, North Wales.
Parent Unit: Not Entered (?)
Previous Name(s): none recorded or not applicable
Alternative Name(s): Nantglyn Mudstone Formation
Stratotypes:
Type Area  Llangollen area. 
Reference(s):
Cocks, L R M, Holland, C H, Rickards, R B and Strachan, I, 1971. A correlation of Silurian rocks in the British Isles. Geological Society of London, Special Report No.1. 
Wedd, C B, Smith, B and Wills, L J. 1927. The geology of the country around Wrexham, Part 1. Lower Palaeozoic and Lower Carboniferous rocks. Memoir of the Geological Survey of Great Britain. [London: HMSO.] 179pp. 
Wills, L J and Smith, B, 1922. The Lower Palaeozoic Rocks of the Llangollen district with special reference to Tectonics. Quarterly Journal of the Geological Society, Vol.78, p.176-226. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable