Dr. Mac CvLLOCU on the Geology of Glen Tilt, 279 



granite, is that of one solitary and small vein, of a grey colour, which 

 intersects the schist immediately above the bridge ; the disturbance 

 however produced by it is trifling. Another disturbance, although 

 small in extent, is very remarkable, though not unique, since I 

 have found a similar occurrence in lona. Below the bridge on 

 the left bank a bed of white marble is seen surmounted by a bed of 

 hornblende schist. This is followed by a second bed of the marble 

 about two feet in thickness, of which the greater part is suddenly 

 cut off at right angles to the bed by a second mass of hornblende 

 schist, while the lower part continues in the same direction, but 

 bent, and of the breadth of only two or three inches. The lower 

 part of the mass of hornblende schist, which thus intersects the 

 marble, is also protracted in a thin plane continuous with the thin 

 part of the marble and lying above it, while the upper side of the same 

 becomes continuous with a regular and thick bed of the schist. 

 Between these two portions of the schist there is interposed a thick 

 bed of the marble, which is therefore included on three sides with- 

 in the hornblende schist, its outer extremity being cut through at 

 right angles by the schist. As the beds dip into the hill, the 

 further progress of this extraordinary arrangement cannot be 

 traced. A drawing accompanies this description, which words 

 can scarcely render intelligible.* The appearance now described 

 is interesting, since it is connected with phenomena of no very 

 uncommon occurrence, which have given rise to much controversy. 

 It is evident that both the prolongation of the limestone and that of 

 the schist bear a great resemblan<;e to the veins, which, in the case 

 of granite, may be traced from a mass of that substance into the 

 neighbouring rocks: yet there is no doubt that both the lime- 



* Vide Plate 22. 



