216 Mr Anderson on the Quartz District 



north side of the lake, veins of granite are seen traversing the 

 quartz. In the conglomerate, also, large fragments of granite 

 occur, though these are but rarely seen in the compact homo- 

 geneous quartz-rock. 



The granitic mountain on the north side of Loch Ness, to 

 which I have alluded, is a variety approaching very near to 

 the character of quartz-rock, being, like it, naturally resolved 

 into short angular and rhomboidal fragments, of a tabular ap- 

 pearance, while its structure is finer than we generally meet 

 with in granitic rocks. In the neighbourhood of the same 

 mountain, we also find the more common variety of the 

 quartz-rock, while its alliance to this variety of small-grained 

 granite, which it so nearly resembles, is confirmed by the pas- 

 sage through each of veins of an undoubted large-grained 

 granite. 



This red quartz-rock likewise contains cavities encrusted 

 with small rock-crystals ; and, associated with these, I dis- 

 covered particles of galena, copper-glance, and antimony. 



5. The other primitive rock to be noticed is gneiss, with 

 which, as I have stated, the quartz-rock of this district is con- 

 nected. Gneiss occurs chiefly on the north side of the lake, 

 extending from thence as far as Ross-shire. 



The changes induced on the quartz-rock by its contact with 

 gneiss, are shortly these : — There is, first, an increase ©f mica, 

 which adds to its schistose tendency, and gives it a grey or 

 blue colour. Secondly, the gneiss is disturbed in the regu- 

 larity of its stratification, for I observed it to deviate from 

 an inclined or vertical position into a horizontal one. Lastly, 

 both the gneiss and the quartz-rock are mutually intersected 

 by granite veins, and imbedded masses of various sizes, con- 

 sisting of hornblende, often beautifully crystallized, in which 

 garnets are sometimes found. 



6. This concludes my account of the important relations of 

 quartz-rock to gneiss and granite. I shall now describe brief- 

 ly its connections with sandstone. 



On the north side of Loch Ness, granite is succeeded to- 

 wards the east by quartz-rock, intermixed with gneiss ; and to 

 these are joined a lower sandstone ridge, on the last of which, 



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