The backbone of the Wicklow Mountains consists of a large mass of Granite which was forced up to the surface of the earth around 400 million years ago. The hot molten Granite crushed and baked the overlying Schists and Slates to form Mica-Schists. Much of the mining activity occured where the Granite and Copper-Schists meet as the holds high concentrating of Lead, Tin, and Zinc, with some iron and Copper.