Ch. VII.] THE GRANITIC AND SCHISTOSE HOCKS. 135 



Such is the nature of the junction of granite with the 

 primary slates. Many of the appearances which it presents 

 might be expected, when it is remembered that these slates do 

 not differ much in composition from the granite; and it 

 therefore becomes an interesting enquiry what would be the 

 result if granite were thus to be united with a stratified rock 

 of a different nature. This desideratum is, indeed, already 

 supplied by the exhibition, in several countries, of the inter- 

 ference of granite with calcareous rocks. 



The junction of granite and limestone is beautifully ex- 

 hibited at Glen Tilt, in Scotland, and has been carefully 

 examined and minutely described by Dr. Macculloch : indeed, 

 his whole account of Glen Tilt * is so very interesting, and so 

 replete with excellent details, showing the nature of the strati- 

 fied rocks, both at a distance from, and in immediate contact 

 with, the granite, that we propose to make some lengthened 

 extracts. 



The granite which forms the right ridge of Glen Tilt ap- 

 pears to be a continuation of the great central granite of the 

 Grampians, constituting its termination in a southern direc- 

 tion. The varieties of this granite are mixtures of quartz, 

 felspar, and mica ; differing, however, as much in colour and 

 texture as they do in structure. To these minerals horn- 

 blende is often added, sometimes to the exclusion of the mica. 

 These syenitic granites are almost invariably grey, or even 

 black, from the predominance of the hornblende : their texture 

 is as various as their colour, the crystals of hornblende being 

 sometimes very large, and imbedded, as it were, in a paste of 

 quartz and felspar ; while in other extreme cases the mixture 

 of the several ingredients is so fine, that the constituents can 

 scarcely be discerned ; and it is only to be distinguished from 

 greenstones of the trap family by tracing it for some space 

 until it passes into well-characterised granite. The chief 

 varieties of syenitic granite are found on the slopes which 



* Geol. Trans., vol. iii. p. 259. et seq. 

 K 4 



