Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/274

 manner. Such is the ordinary view which has been taken by one class of observers of this rock, as well as of all the other rocks seen in Glen Tilt. They have been looked upon as mere masses of schist intersected by veins of granite, the larger bodies of granite being considered as veins, the origin and direction of which were unknown, and the smaller ones as ramifications proceeding from them. A different class of observers, seeing in this imagined schist nothing but its approximate position with granite, have considered it as offering an example of the alternation of these two rocks. In whatever way the different theories may be affected by these distinct views of this case, I have no inclination at present to enquire. If one of them be incorrect, the other is imperfect, and the object of this paper is rather to give a more full account of the appearances to be observed in this place, than to renew a controversy on the same grounds on which it has already been agitated.

Independently of such considerations, the disposition of the rocks at this place, as well as in other parts of the Tilt, are so curious, and as yet so solitary and new, as to render them highly attractive and well worthy of record. It will however be seen hereafter, that the history of these several appearances, even if it should not be supposed to add any strength to the general theory respecting the posteriority of granite, serves at least to give us an accurate idea of the real structure of the valley itself.

The remarkable novelty here visible, and in which the junction of the granite with the superincumbent rocks differs from all similar junctions formerly described, is that of the interference of granite and limestone. The granite veins which traverse the schist, pass equally into the limestone which accompanies it. These veins are occasionally of large size. In this case they can sometimes be traced into