The BGS Lexicon of Named Rock Units — Result Details

Llanberis Slates Formation

Computer Code: LLBS Preferred Map Code: LlbS
Status Code: Full
Age range: Comley Series (EC) — Comley Series (EC)
Lithological Description: Purple and blue-grey silty mudstones and subordinate coarse-grained turbiditic sandstones.
Definition of Lower Boundary: On felsic tuff of the Bangor Formation or a conformable contact with sandstone of the Fachwen Formation.
Definition of Upper Boundary: Silty mudstones of the Formation are sharply but generally conformably overlain by coarse-grained or conglomeratic sandstones of the Bronllwyd Grit Formation.
Thickness: c.1000m
Geographical Limits: Northern Snowdonia.
Parent Unit: Harlech Grits Group (HGG)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Padern Country Park, Quarry Nature Trail. [SH 586 603]. 
Partial Type Section  Penrhyn slate quarry, Bethesda. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E119 E106 E118