Hebridean Terrane
The basement rock is formed by Archaean and Paleoproterozoic gneisses of the Lewisian complex. They are overlaid unconformably by the Neoproterozoic Torridonian sediments. This in turn is unconformably overlain by a sequence of Cambro–Ordovician sediments. It formed part of the Laurentian foreland during the Caledonian continental collision.