Geology of Snowdonia National Park
The geology of Snowdonia National Park in North Wales is dominated by sedimentary and volcanic rocks from the Cambrian and Ordovician periods with intrusions of Ordovician and Silurian age. There are Silurian and Cenozoic sedimentary rocks on the park's margins.
Source: Wikipedia — Geology of Snowdonia National Park (CC BY-SA 4.0)