Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/278

 with which we are acquainted, it has occasionally been in a flexible state. Some beds are also to be found there towards the east, on that shoulder of Cairn Gower which hangs towards Loch Lochs, containing rounded pebbles, such as I before described as occurring in it at Jura. The beds in which this variety is found consist indeed entirely of a loose aggregation of large and small rounded gravel. This is only the second instance in which I have noticed a coarse conglomerate mass as forming one of the varieties of quartz rock. The pebbles are of considerable magnitude, and bear just such marks of attrition as do those which have been rolled on a sea shore: if they are not mechanically rounded pebbles I know not where such can be found. I have little doubt that this variety will oftener occur when these rocks shall have been more extensively examined; but I trust this fact is no longer necessary to prove that quartz rock bears the marks of a mixed mechanical origin, and that it thus serves to determine in some measure a corresponding set of circumstances in which the schistose rocks associated with it were formed.

Near Blair it may be observed passing into a regular granite in a very distinct manner. Many of the specimens found were transported stones, but in many other instances, which I have had occasion to notice in a paper on Glen Tilt, the transition from quartz rock to granite is to be seen in situ. I have there also noticed that, which ought for the sake of uniformity to be repeated here, that the beds of quartz rock which are in immediate contact with the granite often pass into it by insensible degrees. It is well known that there is a gradual transition from mica slate into gneiss, and that this rock again by degrees equally evanescent passes into granite. I have shown that quartz rock is here in contact with granite, and it is not therefore surprising that it should, like the mica slate with which it