GRANITE IN ARRAN. 241 



remarks l that the granite of Goat Fell and the principal mountains is 

 a large-grained variety, in which felspar predominates and mica is 

 comparatively rare. Some of the felspar is light-brown, other crystals 

 are pure white, and a third is glassy, so as to resemble quartz. The 

 quartz too is very variable, being white, pale yellow, grey, light or 

 dark brown, and sometimes almost black. This mineral frequently 

 occurs in hexagonal prisms in cavities in the rock. There are large 

 areas in the interior between Ben Ghnuis and Ben Mhorroinn 

 which consist of a fine-grained granite, and in some of the veins the 

 texture is so fine that the rock might be mistaken in hand-specimens 

 for a sandstone. 



In veins the quartz and mica sometimes disappear, leaving the 

 rock in the form of a compact felspar. The mica is in very small 

 black scales. Frequently the granite rises in perpendicular cliffs 





Fig. 54. From the top of Goat Fell (Arran). 



which are well seen on Goat Fell, the west side of Ben Ghnuis, and 

 on the peak of Caisteal Abhael. The junction of the granite and 

 slate is seen in Glen Kosa and Glen Sannox, the slate being pene- 

 trated by veins. A mass of fine-grained granite forming part of the 

 hills which surround Glen. Dubh at the upper part of Glen Cloy, 

 contains a large proportion of reddish felspar. It is partly surrounded 

 by syenite and porphyry, and the syenite has metamorphosed the 

 sandstone into quartz rock. 



Alterations of Stratified Rocks in Arran. No new minerals are 

 produced in the slate where the granite touches it, nor in the red 

 sandstones where they are hardened by the basaltic dykes. This 

 hardening is very various in degree, and the causes of these differences 

 are not very evident even upon the examination of many cases. The 



1 " Geology of the Isle of Arran from Original Survey," 1841. 

 VOL. I. Q 



