The basement is formed by Archaean and Paleoproterozoic gneisses of the Lewisian complex , unconformably overlain by the Neoproterozoic Torridonian sediments , which in turn are unconformably overlain by a sequence of Cambro -- Ordovician sediments .
The basement rock is formed by Archaean and Paleoproterozoic gneisses of the Lewisian complex . They are overlaid unconformably overlain by the Neoproterozoic Torridonian sediments .