A series of mountain ranges extending southwest to northeast and lying north of the Highland Boundary Fault and southeast of the Great Glen, the Grampians represent the bulk of the Highlands of Scotland. They rise to a height of 1345m (4413 feet) at Ben Nevis in the west (Britain's highest mountain) with other lofty peaks including Ben Macdui (1309m / 4296 feet) and Braeriach (1296 / 4252 feet) in the Cairngorm Mountains. They were formerly known as the Mounth, a name still preserved in the Cairn o' Mounth pass in Aberdeenshire and the plateau called the White Mounth to the south of the River Dee. The term Grampians was first applied by the Aberdeen historian Hector Boece in 1520 in reference to Mons Grampius, the site of Agricola's defeat of the Picts c.84 AD. Older definitions regard the Grampians as mountains of the Central and Eastern Highlands and do not include the western section, thus excluding for example Ben Nevis, the Arrochar Alps and the mountains of Cowal Peninsula.
The Grampians formed as part of the Caledonian Orogeny brought on by the closure of the Iapetus Ocean c.460 million years ago. The rocks represent the roots of the ancient mountains which were formed at this stage, sediments altered by heat and pressure to form the succession of Dalradian schists, phyllites, psammites, pelites and quartzite we see today. This succession is interrupted by igneous intrusions which underlay ancient volcanoes, the most notable of these form the Cairngorm Mountains.
