This geological board describes the origin and importance of the Great Glen.

The Highlands are divided by the Great Glen into the Northern Highlands and the Grampian Highlands.  The Northern Highland terrane is composed of Moine Supergroup, rocks that were originally laid down as sandstones and mudstones around 950 million yeas ago. 

The Grampian Highlands are formed from the Dalradian Supergroup; rocks formed in shallow seas between 800-500 million years ago.

These two ‘terranes’ were initially separated but were later brought together by the collision of two tectonic plates, Laurentia and Avatonia, about 430 million years ago.  This resulted in a mountain building and metamorphism of these rocks. The Great Glen fault (a strike slip fault) continued to move periodically for 50 million years ((in both dextral and sinistral directions), transforming and sculpturing the landscape. 

Take time to survey the Northern Highland terrane in front of the board, and the Grampian Highlands behind.

The board is located in the a layby (northbound)  just north of Letterfinlay on the banks of Loch Lochy.

A great introduction to the impact of tectonic plate collisions of the geology and topography of Lochaber.