The underlying geology of most of Caithness is old red sandstone to an estimated depth of over 4,000 metres. This consists of the cemented sediments of Lake Orcadie, which is believed to have stretched from Shetland to Grampian during the Devonian period, about 370 million years ago. Fossilised fish and plant remains are found between the layers of sediment. Older metamorphic (granite) rock is apparent in the Scaraben and Ord area, in the relatively high southwest area of the county. Caithness' highest point (Morven) is in this area.