The geology of Cornwall, England, is dominated by its granite backbone, part of the Cornubian batholith, formed during the Variscan orogeny. Around this is an extensive metamorphic aureole (known locally as killas) formed in the mainly Devonian slates that make up most of the rest of the county. There is an area of sandstone and shale of Carboniferous age in the north east, and the Lizard peninsula is formed of a rare section of uplifted oceanic crust.