1852.] SHARPE ON QUARTZ ROCK. 121 



nating with quartzose conglomerate and limestone, that they constitute 

 together one deposit which he calls the "Quartz-series." This series 

 is overlaid by red sandstone, and itself overlies the red sandstone of 

 Assynt. Mr. Cunningham regards all the limestones of the west of 

 Sutherland as belonging to the Quartz-series, and he states that the 

 great mass of limestone of Assynt underlies the quartz-system of Ben 

 More, and overlies that of Canisp*. From the remarks of this ex- 

 cellent observer, we may safely conclude that the quartz-rock and 

 limestone of the west of Sutherland are part and parcel of the Old 

 Red Sandstone Formation, with which it is thus intimately con- 

 nected. 



I have mentioned in my paper " On the Southern Border of the 

 Highlands" (see p. 128) that the limestone of Aberfoyle is associated 

 with beds of quartz-rock in the midst of a formation of red conglo- 

 merate which preserves its original character both above and below 

 the metamorphic beds of quartz-rock. This is analogous on a small 

 scale to the larger phsenomena of Sutherland described by Mr. Cun- 

 ningham. The explanation is easily found : the limestone acting as 

 a flax assisted the reduction of the beds with which it was in contact, 

 which were altered into quartz-rock, while the beds below, being less 

 fusible, retained nearly their original characters, although, from being 

 nearer to the source of heat, they were probably exposed to a higher 

 temperature than the upper beds which we find altered. Similar su- 

 perpositions of altered upon unaltered beds have been described by 

 various authors, and the principle is now familiar to us. 



To return to the north-west of Scotland. It will be seen in Mac- 

 Culloch's map of Scotland that large masses of quartz-rock extend in 

 a broken line from Sutherland down the west of Ross-shire into Skye, 

 either separating the Old Red Sandstone from the Gneiss, or forming 

 detached outliers on the Gneiss ; and beds of limestone are marked in 

 several places on that side of these masses of quartz-rock which is 

 nearest to the Gneiss, that is to say, in the lower portion of them. 

 Their position is so analogous to that of the quartz-rock of Suther- 

 land, that we may, without danger, regard them as continuations of 

 it, and class them in the Old Red Sandstone. I had an opportunity 

 of confirming this view with regard to the hills of quartz-rock at the 

 head of Loch Maree, which are part of the line in question. The 

 lower part of these hills consists of a series of thin-bedded quartz-rock, 

 separated by layers of micaceous schist, with a dip of S.E. 15°, and 

 overlaid by a great thickness of semi-granular quartz-rock without 

 mica, dipping S. 30°. The granular structure of the upper portion 

 of quartz-rock shows it to have been originally a sandstone, since al- 

 tered by plutonic action, and its position relatively to the Old Red 

 Sandstone, at the foot and sides of the same lake, which is in many 

 places partially altered into quartz, and which forms hills almost con- 

 tinuous with those of the quartz-rock, left me no doubt that the two 

 belonged to the same formation. The lower portion of the quartz- 

 rock admits of more doubt. It has no distinct granular character, 

 and from its alternating with thin beds of micaceous schist cannot be 

 * Op. cit. pp. 92, 93, and 94. 



