The oldest rocks in Britain are found in NW Scotland and the western isles. This ancient Lewisian gneiss is almost 3,000 million years old!
The Scottish Highlands are mainly formed from metamorphic rocks formed around 400-450 million years ago. Ben A’an shows foliated mica-schists exposed at the top.
These slates in north Wales are about 400 million years old. They split easily into thin sheets, used for roofs. This quarry now stores water for a hydro-electric scheme.
Working slate quarry at Delabole, Cornwall. These slates formed from mudstones on the sea floor 300 million years ago.
There are many granite intrusions in northern and western Britain, most of which have metamorphosed the surrounding rock.