556 MULL. GEOLOGY. 



ginal straight direction; the ends of the strata in some 

 cases, and in others their sides being united to it, and so 

 1: mly adherent that they can scarcely be separated. In 

 others, a disturbance takes place in their even direction, 

 particularly where veins are found passing from the granite 

 through them. These veins are of various sizes, and 

 ramify in a manner too well known to need description. 

 At the places of contact there may often be observed frag- 

 ments of the different stratified rocks, detached from the 

 main body and imbedded in the granite. These are of 

 different dimensions, from that of an inch or less, to many 

 feet ; and they are in some instances so distinct that the 

 parts whence they were separated may be traced, and the 

 fragments re-united by the imagination. A diagram is 

 subjoined for the illustration of this important pheno- 

 menon *, which occurs also in many other parts of Scot- 

 land ; among others in Glenco, in Rannoch, and in 

 Braemar. 



The last remarkable circumstance is the change which 

 the stratified rocks undergo at these points of contact. 

 In these places the quartz rock becomes red, and is found 

 to contain felspar in large proportion, often putting on 

 the appearance of fine grained gneiss; and it frequently 

 also passes into the granite by a transition nearly imper- 

 ceptible. The micaceous schist in the same situations 

 becomes a real gneiss, not to be distinguished in hand 

 specimens from the most regular rocks of this class. 

 These changes are however extremely partial, commonly 

 extending but a few inches, rarely to a few feet beyond 

 the junction, and vanishing gradually as they recede from 

 it: this phenomenon also occurs in similar situations in 

 Glen Tilt. 



Although unwilling to repeat the trite arguments derived 

 from the nature of granite veins, I cannot avoid remark- 

 ing the strong support they receive from the circumr 



* Plate XXVI. fi.','. 



