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Sango Bay & Smoo Cave

Durness, Highlands, Scotland

Smoo Cave

The Durness area on the north coast of Sutherland is of historical importance for establishing the geological structure of NW Scotland. 

Smoo Cave

The dominant bedrock here is carbonate of the Durness Group – of Cambro-Ordovician age. It is these that give rise to the dramatic coastal karst scenery at Smoo Cave. However, the most important outcrops for understanding the tectonic evolution of NW Scotland lie directly in front of the village, in the stunning coves of Sango Bay. 

The bay itself is bounded to the east by a spectacular fault scarp. This is one of several normal faults that probably developed during the Permo-Triassic and relate to the onshore formation of the West Orkney Basin. 

The faults display stunning breccias and other fault rocks which give insight into tectonic processes. The faults down throw highly sheared rocks, probably derived from Lewisian gneiss that once overlay the region as part of the Moine Thrust Sheet.

These units have been carried from original positions far to the east, and represent the preserved outliers of thrust sheets that otherwise are restricted to the east of Loch Eriboll. The sheared materials include the dramatic crenulated schists – termed colloquially by the Survey geologists in the 1880s “oyster-shell rock”. 

The tectonic contact at the base of these highly deformed strata lies on the promontory in the middle of Sango Bay. This is the Moine Thrust, decorated with a thin slice of “far-travelled” Lower Cambrian quartzite and carried onto the Durness carbonates. 

These outcrops are part of the NW Highlands Geopark.

Text: Professor Rob Butler

100 Great Geosites

Related Links

Further Reading

Butler, R.W.H. 2009. Sango Bay. In: Lewisian, Torridonian and Moine rocks of Scotland. (edited by Mendum, J. R, Barber, A. J., Butler, R. W. H., Flinn, D., Goodenough, K. M., Krabbendam, M., Park, R. G. and Stewart, A. D.) Geological Conservation Review Series, volume 34, Joint Nature Conservation Committee, Peterborough, pp. 721.

Images (top to bottom):

  • The Entrance to Smoo Cave © Florian Fuchs (source Wikimedia Commons) Creative Commons Attribution 3.0 Unported license
  • Sango Bay © Mark Godden
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