Cwmystwyth Grits Group

The Cwmystwyth Grits Group is a Silurian lithostratigraphic group (a sequence of rock strata) in mid Wales. The name is derived from the village of Cwmystwyth near Devil's Bridge in Ceredigion. The Group comprises the Blaen Myherin Mudstones Formation, the Glanyrafon Formation (upper and lower tongues), the Caerau Mudstones Formation, the Rhuddnant Grits Formation (including the Llyn Teifi Member) and the Pysgotwr Grits Formation.^[1][2]

Cwmystwyth Grits Group
Stratigraphic range: early Silurian (Llandovery)
Type	Group
Underlies	Dolgau Mudstones Formation
Overlies	Claerwen Group
Lithology
Primary	sandstones
Other	mudstones
Location
Region	mid Wales
Country	Wales
Type section
Named for	Cwmystwyth (village)

Outcrops

The rocks are intermittently exposed in mid Wales between Cwmystwyth, Llanidloes and Claerwen reservoir.^[3]

Lithology and stratigraphy

The Group comprises hundreds of metres thickness of sandstones with subordinate mudstone turbidites laid down in the marine Welsh Basin during the Llandovery epoch.