for the mica that characterizes the regular varieties. By degrees the chlorite schist becomes predominant, and at length the felspar is excluded, so that all appearance of gneiss ceases and a simple series of chlorite schist remains. I suppress a detail of the endless varieties found through this series, as such substances can rarely be rendered intelligible in description. But I may add that hornblende schist, so generally found to accompany gneiss, alternates here also with it under many different aspects.
With respect to the position and boundaries of this series, it is found occupying beds of which the elevated edges present a rectilinear direction towards the north-east, dipping to the eastward in an angle which varies between 30 and 50 degrees. Its boundary towards the west lies near the small island Oransa, where it is succeeded immediately by the graywacké schist and the accompanying quartz rock or hard sandstone which were described in the original paper, but which I shall presently describe again in greater detail, having had an opportunity of verifying much of that which was only conjectural, and of extending its limits to a much greater distance than I had foreseen.
Although the boundary of this series, in which gneiss and chlorite slate form the principal parts, is thus defined at the northern end of its western side, no such decided change is perceived at the southern end of the same line, which, if protracted from the place first mentioned near Isle Oransa, would cut a point on the western side of Sleat. The interior of the country is too much encumbered with peat and with vegetation to permit of any decision on a subject so obscure as is the point of change between the gneiss series and the rocks which follow it, and I must therefore limit myself to the appearances which occur on the sea shore, where every change can be traced in the most minute manner. Here