Harlech Grits Group

Harlech Grits Group Stratigraphic range: early Cambrian
Sandstones of the Rhinog Formation, Rhinog Fawr, Snowdonia
Type	Group
Sub-units	Gamlan Formation, Barmouth Formation, Hafotty Formation, Rhinog Formation, Llanbedr Formation, Dolwen Formation
Underlies	Mawddach Group
Overlies	Bryn-teg Volcanic Formation
Thickness	about 2000m
Lithology
Primary	sandstones
Other	mudstones, siltstones, greywacke
Location
Region	northwest Wales
Country	Wales
Type section
Named for	Harlech (town)

The Harlech Grits Group is a lower to middle Cambrian lithostratigraphic group (a sequence of rock strata) in northwest Wales. The name is derived from the town of Harlech in Gwynedd.

Outcrops

The rocks are exposed beneath Harlech and across the Harlech Dome to its east; a broad anticlinal structure which encompasses the Rhinogydd range.^[1]

Lithology and stratigraphy

The Group comprises about 2000m thickness of sandstone, mudstones, siltstones and greywackes laid down in the marine Welsh Basin during the early to mid Cambrian period. The Group comprises (in descending order i.e. oldest last) the Gamlan Formation, the Barmouth Formation,the Hafotty Formation,the Rhinog Formation, the Llanbedr Formation and the Dolwen Formation.^[2]

References