The Clwyd Limestone Group is a stratigraphic unit (a defined sequence of rock layers) of to Brigantian age (Lower Carboniferous) found in north Wales. It forms part of the Carboniferous Limestone Supergroup. Its most extensive outcrop is along the length of the Clwydian Range, immediately to the east of its crest, between Llandegla and Prestatyn. A further though more fragmented outcrop extends in an arc along the western margins of the Vale of Clwyd north from Rhyd-y-meudwy, west of Ruthin and then northwest to meet the coast at Llanddulas. It is prominently exposed at the Great Orme and Little Orme near Llandudno and again in three areas of eastern and southern Anglesey, together with a small area to the south of the Menai Strait between Bangor and Y Felinheli. The outcrop also extends