The BGS Lexicon of Named Rock Units — Result Details

Mawddach Group

Computer Code: MWG Preferred Map Code: MWG
Status Code: Full
Age range: St David's Series (ED) — Tremadoc Series (O1)
Lithological Description: Mudstone (including dark grey of black mudstone), siltstone and sandstone. For details of specific lithologies refer to entries for the Dol-cyn-Afon, Dolgellau, Ffestiniog Flags, Maentwrog and Clogau formations.
Definition of Lower Boundary: Base of the Clogau Formation as originally proposed, but under discussion.
Definition of Upper Boundary: Top of the Dol-cyn-Afon Formation.
Thickness: c.2400m
Geographical Limits: Harlech Dome and southern Snowdonia.
Parent Unit: Not Applicable (-)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Type Area  From Criccieth east towards Ffestiniog, south to Dolgellau and southwest of Arthog. See also stratotypes for Clogau, Maentwrog, Ffestiniog Flags, Dolgellau and Dol-cyn-Afon formations. 
Allen, P M and Jackson, A A. 1985. Geology of the country around Harlech. Memoir of the British Geological Survey, Sheet 135 with part of Sheet 149 [England and Wales]. [London: HMSO.] 112pp. 
Allen, P M, Jackson, A A and Rushton, A W A. 1981. The stratigraphy of the Mawddach Group in the Cambrian succession of North Wales. Proceedings of the Yorkshire Geological Society, Vol.43, 295-329. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E119 E149 E118