416 Dr. Mac Culloch on the Geology of 



presence of limestone is discovered in the mass. Ultimately the 

 limestone disappears from the schistus. 



The whiter varieties, which I have described as more rare, are 

 found in contact with a micaceous schistus consisting of thick flexu- 

 ous laminsE of quartz separated by thin layers of mica. Here the 

 gradation from the limestone to the micaceous slate takes place, by 

 an alternation of the layers of mica with the limestone, forming a 

 rock easily mistaken for mica slate, and resembling the Cipolino 

 marble of the Italians. These limestones are no where bituminous, 

 and it is scarcely necessary to say, that I did not observe in them 

 any animal remains. A breccia formed of both the varieties is found 

 here and there, and I obser^'ed detached specimens of a variety filled 

 with minute pores, which although it exhibits no decided animal 

 appearances, has yet a suspicious character. A specimen is before 

 the Society for the examination of those who possess superior expe- 

 rience in these modifications. 



It now remains to determine the place of this limestone in the 

 system of Werner : a determination which probably involves the 

 character of all the limestones so frequent in the Highlands of 

 Scotland, which, like this, are deposited with schistus. The in- 

 stances which occur at Balahulish, at Loch Earn, at Lismore, at Dun 

 MacSniochain, and at numerous other places, are too familiar to be 

 pointed out to those who are acquainted with Scottish mineralogy. 



It is evident that the character of the limestone must, in this case, 

 depend on that of the rocks which it accompanies, and not on the 

 mixture of mica or other foreign minerals which it may contain. 

 If the clay slate and mica slate of Isla are both considered primitive, 

 as they probably will be, then this limestone must also be ranked 

 among the primitive rocks. In all the other instances in which I 

 have observed this kind of limestone, it has appeared to me to ap- 



