Geology of Durness

The photo to the left shows the Moine Thrust where older Lewisian mylonites have been 'pushed' on top of the younger Durine Formation carbonates of the Durness Group (normally younger sediments are found above older ones). At this locality at the western side of sango Bay (below viewpoint), two thrust planes are seen. One seperates the mylonites from a thin slice of 'Far-travelled Quartzite' and the other between this quartzite and the now underlying carbonates. This has resulted in the folding of the carbonates and later reddening has also occurred.

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The Durine Formation is the uppermost and youngest unit within the Durness 'Limestone' as carbonate sedimentation was halted by the movements of the Moine Thrust. This formation is similar to the Croispol Formation, but shows a change into mainly dolostones with thinly interbedded, soft porcelain-like, lighter dolostones and some limestones. These Dolostones commonly contain small, milky white (cloudy) nodular cherts which are thought to have been evaporites once. The sediments are medium-coarse sandy grainstones that show ooidal weathering. Some beds are also very dark grey in colour and parallel lamination is a common feature. Outcrops of this unit in Durine have yielded several specimens of microfossils known as 'conodonts' which can be used to date these rocks as well as predict thermal maturity (conodonts change colour with increasing temperature and are used by geologists to assess past rock temperatures).