Mineralogy of Sky. 183 



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 ex- 

 amination 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 con- 

 sidered 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 diffi- 

 culty 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 ex- 

 tended 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, Airdna- 

 murchan, 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 re- 



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