The BGS Lexicon of Named Rock Units — Result Details

Bronllwyd Grit Formation

Computer Code: BGR Preferred Map Code: BGr
Status Code: Full
Age range: Comley Series (EC) — Merioneth Series (EM)
Lithological Description: Comprises thick bits of coarse-grained green-grey massive sandstone, and interbedded mudstone, which is locally manganiferous, and local conglomerates.
Definition of Lower Boundary: Sharply defined but generally conformable base of coarse conglomeratic sandstone overlying the mudstones of the Llanberis Slates Formation.
Definition of Upper Boundary: Gradational into basal mudstones of the Marchlyn Formation.
Thickness: 500m
Geographical Limits: Northern Snowdonia, North Wales.
Parent Unit: Harlech Grits Group (HGG)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Clogwyn Mawr. 
Partial Type Section  Roadside exposures towards the southeast end of Llyn Peris, near Llanberis, North Wales. 
Reference(s):
Howells M F, Reedman A J and Leveridge B E. 1985. Geology of the country around Bangor: Explanation for 1:50 000 geological sheet 106 (England and Wales). British Geological Survey Sheet Explanation. [London: HMSO.] 34pp. 
Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E119 E106 E118