Bryn Glas Quarry
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Geology & landscape
Mining / Industrial: Quarry · Geological Period: Cambrian, Ordovician
Description
Description A nationally important geological site which is a stratigraphic locality for the Tremadoc-Arenig Series rock section. The basal grit of the Arenig rests with apparent conformity on Tremadoc shales; the junction is lithologically a transitional one with thin, interbedded 'grits' in the upper portion of the Tremadoc. Such conformity is unknown elsewhere in Wales and the Borders where the Ordovician and Cambrian Age rocks are usually unconformable, sometimes with angular discordance. Bryn Glas Quarry exhibits a section of unrivalled importance due to its position in the type area for both the Tremadoc and the Arenig Series. The seemingly conformable sequence makes it a key site for the base of the Ordovician. The site is of no particular biological interest. Remarks: Within the Snowdonia National Park.