 The superficial rock of Orkney is almost entirely Old Red Sandstone, mostly of Middle Devonian age. As in the neighbouring mainland county of Caithness, this sandstone rests upon the metamorphic rocks of the Moine series, as may be seen on the Orkney Mainland, where a narrow strip of the older rock is exposed between Stromness and Inganess, and again on the small island of Graemsay.
