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 flexuous laminæ 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 observed 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 experience 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 instances 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-
