Of the Veins or Shoots of Granite, which traverse the Grauwacke Formation.
The last place in Cornwall where I met with veins or shoots of granite in the grauwacke, was at Mousehole near Penzance. As the attention of geologists, particularly the supporters of the Huttonian Theory, has been strongly directed to facts of this sort, I shall briefly state the observations I have made on this subject, confining myself to what I saw in Devonshire and Cornwall:[1] not that I am unacquainted with some of those places on the continent where similar facts have been pointed out,[2] but because I found them exhibited in this part of England in a manner much more striking and less difficult of apprehension.
1. We never find these veins or shoots of granite but at the point of junction of that rock with the grauwacke, whether that junction be in high situations or on the sea shore.
2. These veins are not independent or insulated, but by following their course we can always trace them to a main body of granite, without any interruption of continuity intervening between them.
- ↑ There is a remarkable example of this occurrence of granite veins at the junction with the grauwacke, in New Galloway in Dumfries-shire, on one of the estates of Sir James Hall. Vide third vol. of the Transactions of the Royal Society of Edin. Sir James Hall had a very interesting model of the place made on a pretty large scale, which he has deposited in the collection of the Geological Society.
Mr. Playfair also mentions some other facts of this sort, which he has observed in the course of his travels in England and Scotland. Illustrations of the Huttonian Theory, from p. 307 to 320.
- ↑ Voyages dans les Alpes, § 598, 599, 601.
