Ch. VII.] THE GRANITIC AND SCHISTOSE ROCKS. 139 



and, when this is the case, its beds sometimes exhibit 

 all the constituents of granite, so disposed as to resemble the 

 foliated texture of gneiss, and, in some instances, a perfect 

 granite ; and, when this is the case, this quartz rock is fol- 

 lowed by a schist, which seems intermediate between gneiss 

 and mica-slate, having the aspect of the latter with its shining 

 surface, and even foliated structure, but showing in its cross 

 fracture the grains of felspar which belong to the former. 

 This granitic variety of quartz-rock occurs at a considerable 

 distance from the mass of granite, and the schistose beds are 

 straight and undisturbed. 



Such is the nature of the granite and the adjacent schistose 

 rocks at Glen Tilt ; and, before proceeding to point out their 

 analogy to the primary formation of Cornwall, there are 

 some phenomena exhibited by these rocks which require to be 

 noticed. 



It has been already remarked, that, at a distance from the 

 granite, the alternations between the limestone, schist, and 

 quartz-rock are regular and well-defined: but when the 

 granite is approached, the lines of stratification become irre- 

 gular, and the dip of the strata is in almost every direction ; 

 and immediately adjoining the granite there is a general 

 mixture of all the stratified rocks, and a total discomposure 

 of their regularity, which is increased by the presence of 

 elongated and detached portions of the granite. It is worthy 

 of remark, that at the junction the strata are not continuously 

 in contact with the granite : on the contrary, it is sometimes 

 the schist, sometimes the quartz-rock, sometimes the limestone, 

 or there is a want of conformity between the granite and the 

 rocks which lie above it. 



The granite and the strata in the bed of the Tilt have 

 frequently the appearance of alternating together ; but all the 

 circumstances are nowhere so clearly exposed to view as to 

 warrant a positive conclusion. Dr. Macculloch is of opinion, 

 that "those parts of the granite which seem to alternate with 

 these strata can only be considered as portions of veins, the 



