Glencoul Thrust

A significant and very obvious geological discontinuity whereby a block of older metamorphic Lewisian Gneiss has been pushed above a sliver of younger Cambrian sediments, itself naturally, but unconformably, lying on top of Lewisian basement rocks. The thrust crosses Loch Glencoul in the Assynt district of NW Sutherland, and is easily observed from the A894 road, looking north across the loch to the Aird da Loch peninsula, where it appears as a crag with a distinct difference in colour between the different rock units. It lies to the west of the more famous Moine Thrust, but both form part of a thrust belt associated with the Caledonian mountain building episode between 430 and 500 million years ago. One of the first of this type of structure to be identified anywhere in the world, the Glencoul Thrust was recognised in 1883 by English geologist Charles Callaway (1838 - 1915). Callaway realised that significant earth movement must have been involved in bringing older metamorphic rocks, which had been altered by heat and pressure deep within the earth, above younger and unaltered sediments. The area was subsequently mapped and further interpreted by a team led by the notable field geologists Ben Peach (1842 - 1926) and John Horne (1848 - 1928). Archibald Geikie (1835 - 1924) was also involved, as Director General of the Geological Survey, and coined the term "thrust" in a paper in Nature in 1884.

Interpretation boards are provided at a viewpoint on the roadside by Scottish Natural Heritage as part of the NW Highlands Geopark.


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