I shall continue to describe this rock as far as I have traced it, since if not strictly a part of the professed object of this paper, it will, in addition to the contribution which it forms to the mineral topography of the country, either assist future geologists in connecting their own observations, or present them, in a tract among the most desert and difficult of access in Scotland, with a point of departure from whence they may prolong their observations over the adjoining country.
In leaving Balahulish to proceed westward we almost immediately lose sight of the granite, which occupies here only the lowest position, and is scarcely to be found above the level of the sea, The schistose rocks which cover it do not however accompany us long, being succeeded at the mouth of Glenco by a mass of rocks appertaining to the porphyry family, which I shall recur to when I have traced the granite. This becomes again visible as we approach the King's house, and, quitting the rugged hills which separate Glenco from Loch Etive and from Loch Leven, enter upon the wide, trackless, and solitary moor of Rannoch. This extensive and barren tract is elevated at a very considerable height above the sea, and, although unascertained, it probably does not fall much short of a thousand feet. Its surface in a general sense is flat, when compared with the ordinary aspect of a Highland moor, yet it is diversified by low rocky hills and undulations, covered with a deep peat which conceals the subjacent rock. There are notwithstanding abundant indications of its nature in the beds of the streams which flow over it, by which the naked rock is completely exposed to view, while every protuberance which time or accident has laid bare, and the detached blocks that are strewed over its surface, confirm its identity with the granite of Glenco. It can be thus traced to the head of Loch Rannoch, a distance estimated