An extensive geological discontinuity of the NW Highlands, the Moine Thrust is the easternmost and oldest of a series of low-angle faults which comprise a thrust zone, up to 6 miles (10 km) in width, within which older sheets of rock (or nappes) are piled up over younger sequences. The thrust trends south southwest for 120 miles (192 km) from Loch Eriboll in the north, past Glencoul, Knockan Crag, Ullapool, Kinlochewe, Kishorn, Lochalsh to the Sleat peninsula of Skye.
Formed during the Caledonian mountain building episode between 430 and 500 million years ago, the structure generally involves Pre-Cambrian schists and gneisses being pushed above a sequence of limestones, quartzites and shales of Cambrian and Ordovician age, but has been much complicated by later deformation. The thrust zone defines the western margin of the Caledonian mountain belt in Europe.
Since the thrust belt was first identified in the late 19th century, it has become a classical site for the study of structural geology and its mode of formation has been re-interpreted several times as understanding of the science developed.