veins in their course, and even crossing the layers at considerable angles. A rock observable at Garviemore illustrates this accident well. Here the transit of the granite vein through the schist is at right angles, and is attended with a flexure of the layers on each side of the vein, in a curve directed from the thickest to the thinnest part of it. At each side of the vein the granite passes from it between the laminæ of the schist, producing a partial effect similar to the more extensive one above described, and which has doubtless owed its origin to a similar cause.
The other case which I reserved for consideration, is that where similar beds of granite are found alternating with, and graduating into quartz rock. This alternation is visible in the bed of the river not far from the entrance of the Mark. But a much better instance occurs in the hill of Grianan on the right of Glen Tilt, where the transition from the quartz rock to the granite is so perfect that the boundary cannot be defined. I have met with similar appearances in the vicinity of Dalnacardoch.
In a paper which I presented to the Society last year, I described among several varieties of quartz rock, that, perhaps the most common of all, in which grains of felspar are found mixed with grains of quartz, neither of them being crystallized; and I then pointed out the distinction between this rock and granite, attempting to shew that it was a recomposed rock, and that it had been formed from the wearing of more ancient granites. Among the several transitions of quartz rock into mica slate, clay slate, &c. I did not notice this transition into real granite, as I had not then met with this appearance: it will add one to the number of those transitions. It will at the same time be obvious, that it can in no respect affect the account which I then gave of the nature and connections of quartz rock. On the contrary, as I have shewn that this rock belongs
