Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/74

 or fragment and without symptom of vegetable life, from the borders of the lake to the summits of the mountains. Of its interior extent I have no means of judging, since it is inaccessible. This rock is composed fundamentally of felspar and hornblende, the parts being always distinct and crystallized in various sizes, so as to form varieties more or less coarse. The felspar predominates in the compound, and is either glassy or inclining to that variety; at times indeed quite opake. To these is superadded hypersthene, but it is neither so abundant as the hornblende, nor is it found so generally dispersed through the rocks. It is traversed by veins of basalt, and by veins containing hypersthene in a larger and more distinct form.

The other rocks which are found in the Cuchullin hills may all be comprehended under the general term of clinkstone. I find it impossible even to conjecture the relative spaces which are occupied by the rocks of this division and the greenstones, but I have already said that the greenstones appeared to me most prevalent. In the southern parts of the Cuchullin they undoubtedly are so, but I am inclined to think that in Blaven, and in those hills which contain the light coloured syenite mixed with darker coloured rocks and which are as I have already noticed so easily distinguished at a distance, the dark rocks will be chiefly found to consist of clinkstone. The varieties which occur are as numerous as they usually are in the different situations in the western islands where this rock is found, with the single exception of Arran, which presents an infinite and instructive variety of them in all their modifications and transitions. In general the clinkstone is simple in its composition, and of a dark lead blue, which sometimes assumes a brighter hue, and occasionally passes through various tints to a pale whitish gray or ash-icolour. In many places it is porphyritic, the porphyries