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Published online by Cambridge University Press: 14 March 2018
The blue substance first came under my observation many years ago in one of the Slickensides, in the first quarry opened for the supply of Abriachan granite, and situated by the side of the road leading to Abriachan,-a somewhat isolated district amongst the hills overlooking Lock Ness.
It was then seen in purplish-blue spots, dotting here and there the surface of the rocks which had been exposed to considerable weathering, and over which water had poured freely.