1852.] SHARPE ON QUARTZ ROCK. 123 



chasm cut through it to the mica-schist by the waters of the Conny, 

 a little above their junction with the Dee. There are here exposed 

 above 200 feet of thin-bedded quartz-rock, regularly stratified, with a 

 dip of 10° to the S., and alternating, towards the base, with thin beds 

 of micaceous schist. 



As all the masses of limestone above-mentioned have much the 

 same character with well-marked stratification, and all occur in the 

 lower members of the quartz-rock formation, we must class them to- 

 gether, and they would alone establish the stratified and sedimentary 

 origin of the quartz-rock, which is confirmed by the granular struc- 

 ture of most of its beds indicating that it is an altered sandstone. 

 It is exceedingly probable that most of the bands of limestone which 

 figure in so strange a manner in MacCulloch's map among the gneiss 

 and mica-schist of the southern part of the Highlands, will prove to 

 belong to outlying masses of quartz-rock, which have been confounded 

 with the crystalline rocks on which they rest. 



I met with such an outlier of quartz-rock, accompanied with lime- 

 stone, on the north side of Loch Earn, about a mile below the head 

 of the lake. The limestone is worked in a large quarry visible from 

 the road ; it consists of many beds, of which the upper 50 feet are 

 very siliceous, and about 20 feet are tolerably pure limestone of a 

 grey colour and semicrystalline structure. Below it are about 100 

 feet of quartz-rock, resting unconformably on contorted mica-schist, 

 and above the limestone is also quartz-rock which is overlaid by a great 

 mass of trap. The partings both of the limestone and of the upper 

 and lower portions of the quartz-rock are micaceous. The nearest 

 spot to this in which quartz-rock is marked on the map is fifteen 

 miles off to the north ; but I expect that many other masses of the 

 same formation will be found in this part of the country, as I heard 

 of limestone-quarries in several places, whose occurrence I could only 

 explain on such a supposition. 



MacCulloch has laid down a band of quartz-rock, running between 

 the mica-schist and the gneiss, from Glen Urchay, through Glen Lyon 

 and Schiehallion, to Glen Tumel, of which I have only seen some 

 portions. In Glen Urchay and about Tyndrum the rock is a quartzose 

 variety of gneiss, with a foliation conformable to that of the neigh- 

 bouring gneiss and mica-schist. I did not visit Glen Lyon, but from 

 MacCulloch's remark that "the boundary of almost the whole of the 

 northern side, as far at least as from Meggarney to Fortingall, con- 

 sists of a sort of compact sandstone or granular quartz *," we may 

 conclude that there are in that neighbourhood some deposits of sedi- 

 mentary quartz-rock or metamorphosed sandstone. The upper part 

 of SchiehaUion has been described by Dr. Playfair as consisting of 

 " pure quartz, granular quartz, quartzy sandstone with mica, indu- 

 rated sandstone, grey sandstone, containing mica in thin layers," &c.f , 

 which sufficiently indicate that this mass of quartz-rock is an altered 

 sandstone, and does not belong to the mica-schist which forms the 

 surrounding country. The occurrence of distinctly stratified lime- 



* MacCulloch on Quartz-Kock, Geol. Trans, vol. ii. p. 469. 



t Lithological Survey of Schiehallion, Phil. Trans, for 1810, pp. 352 and 358. 



