122 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 21, 



distinguished from gneiss, to which formation I believe that it belongs. 

 The want of conformity between the two portions makes this view 

 more probable ; but I leave the point doubtful, since I met with 

 quartz-rock elsewhere of truly sedimentary origin, in which the beds 

 were separated by thin beds of a micaceous schist. 



I also examined several portions of the great deposit of quartz-rock 

 which, reaching from Braemar to Blair Athol, forms an important 

 part of the range of the Grampians. In the neighbourhood of Castle- 

 ton Braemar, MacCuUoch has laid down in the gneiss several patches 

 of limestone nearly on the same line of strike as that of Glen Tilt, 

 which is mapped as separating quartz-rock from granite. But the 

 limestones of Castleton have in reality no connexion with the gneiss ; 

 they occur in the quartz-rock about 100 or 200 feet above its base. 

 The lower members of the quartz-rock, consisting of beds of granular 

 quartz, separated by thin beds of micaceous schist, have been mistaken 

 for gneiss, to which they are quite unconformable ; and the gneiss is 

 represented as covering far too large a surface of the country. The 

 contortions of the folia of gneiss, and their steeper inclination contrast 

 with the regularity and comparative horizontality of the quartz-rock, 

 making it easy to separate them ; and the stratified structure of the 

 limestone completes the evidence of the sedimentary nature of the 

 formation of quartz-rock of which it is a part. 



There are here between 20 and 30 feet of limestone, more or less 

 mixed up with siliceous grains, and consisting of well-marked beds, 

 divided by light and dark grey bands, parallel to the bedding. In 

 the immediate neighbourhood of Castleton, the limestone and the 

 beds of quartz-rock, with which it is associated, have been disturbed 

 and broken up by the eruption of a mass of granite, on which the old 

 castle of Mar stands ; hence there appear to be several beds of hme- 

 stone, which are, however, all parts of one bed. The same limestone 

 is worked in Glen Ey, about two miles south of the junction of the 

 Ey and the Conny, where it also occurs near the base of the quartz- 

 rock. This locality lies nearly in a line between Castleton to Glen 

 Tilt, and helps to connect together the limestones of those two 

 places. 



For well-known reasons I was unable to visit Glen Tilt, but I have 

 no hesitation in classing the limestone of that Glen with the bed just 

 described, since MacCuUoch remarks that it is " interstratified with 

 quartz-rock and with different varieties of schist *." 



In ascending Glen Clunie from Castleton, we pass for some miles 

 over quartz-rock, but about five miles higher up mica-schist appears 

 in the bottom of the Glen, and the lower beds of the quartz-rock are 

 again brought to view : here also limestone has been worked by the 

 farmers in the lower part of the quartz-rock. On the southern edge 

 of this great quartzose deposit in Glen Beg, an upper branch of Glen 

 Shee, we find on the right side of the Glen a similar limestone a little 

 above the base of the quartz-rock, but in a spot which MacCuUoch 

 has coloured as mica-schist. 



The lowest part of the quartz-rock is well laid open in the beautiful 

 * " MacCuUoch on Glen Tilt," Trans. Geol. Soc. vol. iii. p. 271. 



