IN GLEN TILT. 333 



remarkable correspondence in their outlines on the opposite 

 sides of these veins ; but there is a distinct correspondence in 

 those divided by the small vein. 



80. Adjoining to this projecting rock, but nearer to the bank, 

 are several masses of gneiss. Along the lines of junction be- 

 tween the gneiss and the sienite, there is sometimes an appear- 

 ance of gradation, owing to a large proportion of felspar in the 

 gneiss, and an irregular structure in its stratification. We be- 

 lieve there are instances, in which they may be justly said to 

 graduate into each other, but more commonly the line of junc- 

 tion is pretty well defined. 



81. Among the rocks immediately to the eastward, we ob- 

 served an imbedded mass, which, from its general aspect, 

 might be considered as a granular limestone, but exhibited in 

 some parts a singular siliceous character, especially near its junc- 

 tion with the sienite, though the line of junction is precise- 

 ly marked. This character consists in a fracture that is rather 

 splintery than foliated, a hardness so considerable as to yield 

 with difficulty to the knife, and a greasy lust-re. Yet its de- 

 composed surface shows that it contains carbonate of lime, and 

 it effervesces when pulverised. Its colour is a light greenish- 

 grey. 



82. Not far from this, there is a vein of limestone, less than 

 an inch in thickness, running between two masses of sienite, 

 and connected with an imbedded mass of limestone. The im- 

 bedded mass and the vein have similar oryctognostic charac- 

 ters. The fracture approaches more to the foliated, than that 

 of the substance last described, and the hardness is less. The 

 lustre is greasy, and the stone appears to contain a good deal 

 of magnesia, but not a large proportion of silex. 



83. A part of these rocks (near 6 in the plan) is formed by 

 some large masses of granular quartz, containing numerous 



Vol. VII. P. II. . U u specks 



