Introduction In the summer of 1880 I commenced an investigation into the relations between the fossiliferous limestone of Darness and the great gneissie series which was alleged to overlie it. A portion of my first results I communicated to the Society in a paper in which I endeavoured to show that the sections at Durness and in Assynt did not display a true ascending series, the limestone in both localities being separated by a fault from the rock which was supposed to conformably succeed it. On the relation of the limestone to the quartzite I formed no opinion ; but in the two sections described I found them brought together by faults. As the quartzite passed with apparent conformity below the eastern gneiss on the east of Loch Erriboll, I hinted, in accordance with the views of Murchison, which I had not then seen reason to abandon, that the quartzite might belong to the metamorphic series. From these limited observations I carefully abstained from drawing a general conclusion ; and I was convinced that no satisfactory result could be achieved without a detailed survey. Accordingly I devoted a fortnight in 1881, and two months in 1882, to the districts which appeared most promising ; and I have now the honour to submit the conclusions to which I have been led. The published theories on the relation between the Durness limestone and the eastern gneiss are the following :— 1. 1. That the eastern gneiss conformably overlies the limestone