Ordovician volcanic rocks
Volcanoes are represented by pillow lavas and red jasper around the eastern end of Lough Nafooey and on Knockkilbride. Pillow lavas are formed when blobs of lava are chilled by the water into which they were erupted. Coarse breccias of mixed volcanic rocks and jasper occur with the pillow lavas. Lava domes of pale-coloured rhyolite studed with quartz crystals occur in Glensaul and between Tourmakeady and Srah.