186 Dr. Mac Culloch's Supplement to the 



are engaged in investigating the irregular ones. The whole of the 

 original remarks on this quarry must therefore be obliterated from 

 the record. 



There yet remain with respect to the trap rocks of Sky many 

 facts which have resulted from the later more extended examination 

 I bestowed on them. But as these would lead into details inconsistent 

 with the purposes of this paper, and as they are important rather 

 in a general view than as illustrating the history of that island, I 

 shall reserve them for some future communication. 



Having thus made the additions and corrections which appeared 

 of most importance in the geological history of Sky, I shall proceed 

 to enumerate some minerals which were either entirely omitted or 

 but imperfectly seen. 



In the small island of Oransa, and still more conspicuously in an 

 islet adjoining to it, there is to be found a mass of actinolite rock r 

 which can also be traced to the adjoining shore of Sky near to 

 Camiscross. It lies among the gneiss, holding an uniform and parallel 

 course with it, and as the beds of gneiss are here nearly vertical, it 

 presents the appearance of a vein, its edge alone being visible. 

 Nevertheless, its conformity with the gneiss, the analogy which it 

 bears to common hornblende-schist, and its actual gradation into 

 that substance, leave no doubt respecting its true character. The 

 edge of this bed is very irregular, as the bed itself is interrupted and 

 split in various places by intruding laminse of gneiss, thus contract- 

 ing in some places to the breadth of two or three inches, and again 

 enlarging to that of as many feet. It is formed of a confused crys- 

 tallization of actinolite of a pale green colour, the crystals being 

 almost always very minute, and so entangled that the fracture often 

 appears as much granular as it does schistose. It does not present 

 those varieties which occur in the well known rock of Glen Elg, 



