Foula is the most westerly of the Shetland Islands, which are situated to the north of the Scottish mainland and Orkney. It lies 20 km west of the Shetland mainland and is the most isolated inhabited island in the UK. The island is formed of Old Red Sandstone with a low-lying eastern side rising steeply to a central ridge and terminating on the western coast in sea-cliffs, including the second highest sea-cliff in the UK (The Kame at 317 m a.s.l). The cool oceanic climate has produced extensive peat formation and much of the island is covered in different types of bog vegetation, largely dominated by Hare's-tail Cottongrass Eriophorum vaginatum and Crowberry Empetrum nigrum, although with very little Heather Calluna vulgaris. At higher altitudes the vegetation becomes sub-maritime, whilst near cliff-tops it is highly spray-influenced. The island is important for a wide range of breeding seabirds, with different species nesting in different parts of the island. It is one of only seven known nesting localities in the EU for Leach's PetrelOceanodroma leucorhoa. The seabirds feed outside the SPA in nearby waters, as well as more distantly in the North Atlantic.