The BGS Lexicon of Named Rock Units — Result Details

Hell's Mouth Formation

Computer Code: HMG Preferred Map Code: HM
Status Code: Full
Age range: Comley Series (EC) — St David's Series (ED)
Lithological Description: Laterally-persistent coarse- to medium-grained green sandstones, interbedded with green and grey siltstones.
Definition of Lower Boundary: Base not exposed; possibly rests unconformably on Neoproterozoic rocks.
Definition of Upper Boundary: Conformably overlain by manganiferous siltstones of the Trwyn y Fulfran Formation.
Thickness: >190m
Geographical Limits: Pwllheli area, northwest Wales.
Parent Unit: Harlech Grits Group (HGG)
Previous Name(s): Hell's Mouth Grits (-3473)
Alternative Name(s): Rhinog Formation
Type Section  Trwyn y Ffosle cliff section, from sea level to the base of the overlying Trwyn-y-Fulfran Formation. 
Young, T P, Martin, F, Dean, W T and Rushton, A W A. 1994. Cambrian stratigraphy of St Tudwal's Peninsula, Gwynedd, northwest Wales. Geological Magazine, Vol.131, 335-360. 
1:50K maps on which the lithostratigraphical unit is found, and map code used: