Arkle is a mountain in Sutherland, in the far north-west corner of the Scottish Highlands. Like its sister Foinaven, the mountain is made up of glistening white Cambrian quartzite, laid down around 530 million years ago on an uneven basement of much older Lewisian gneiss. The quartzite, and the Torridonian sandstone which makes up many of the other mountains in the area, have been dissected by rivers and glaciers, leaving a series of isolated peaks, such as Suilven, Quinag and Stac Pollaidh, standing above the "knock and lochan" landscape of small hills and lakes that is typical of the Lewisian gneiss.