highest mountain of the British Isles, in the Highland council area, Scotland. Its summit, reaching an elevation of 4,406 feet (1,343 metres), is a plateau of about 100 acres (40 hectares), with a slight slope to the south and a sheer face to the northeast. Snow lies in some parts all year, and permafrost conditions are almost reached. The mountain consists of a superstructure of volcanic rocks surmounting the ancient schists, with granites intruded, of the Highlands.