Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/193

 is also remarkable for a schistose fracture parallel to the axis of the columns. It is accompanied by a small and very unintelligible fragment of limestone breccia, which appears here totally out of its place, and unconnected with the surrounding rocks.

I formerly represented the difficulties which impede the examination of the Cuchullin hills. Since that period I have obtained access to a larger portion of them, but still there is much unseen, probably inaccessible to human footsteps. That portion however is important, and I shall here describe it, although much remains to be done before the history of this division of Sky can be considered complete.

I remarked in the former paper that hypersthene was found united to felspar and hornblende in the rocks which surround Coruisk, but in the same place I also stated that a large portion of these rocks consisted of common greenstone. I have now reason to think this observation incorrect, and that the only greenstones (formed of felspar and hornblende) are found in veins. The difficulty of distinguishing between hornblende and hypersthene when the parts are very minute, was another cause of error, which a more intimate acquaintance with the place and a far more extended examination of specimens have enabled me to correct. In thus correcting my own errors I shall also correct those of other observers, since I may point out a well known district, Airdnamurchan, where the same rock as that of the Cuchullin hills has been hitherto mistaken for greenstone.

Although the hills themselves which encircle the romantic valley and water of Coruisk are utterly inaccessible on this side, yet it is easy every where to examine their bases, while the continuity of the beds or sheets of rock, from the foot to the very summit of the ridge, and its remarkable external characters, leave no doubt respecting