IN GLEN TILT. 835 



when formerly cut through and rounded off by the stream, or 

 have had it occasionally refreshed by the action of the water in 

 time of floods. They are thus well prepared to show the con- 

 trasted colours of the red sienite, and the blackish hornblende- 

 slate, and to render the phenomena attending the junction of 

 these substances extremely distinct. 



86. From the east side of the bridge, there may be seen ly- 

 ing; under the road that leads to it from the northern bank, a 

 large body of granular limestone, mixed with felspar, and pe- 

 netrated by chlorite, and often approaching in its characters to 

 a serpentine. The position of the mass, with respect to its 

 stratification, cannot, I think, be well determined ; but I was 

 inclined to consider its stretch as parallel to that of some stra- 

 ta, which rise, a few feet to the eastward of it, on the other 

 side of an intervening chasm, and the stretch of these is 

 N. 115° E. Veins of the sienite appear in the limestone. A 

 part of the main body of sienite also lies over it, and the plane 

 of their junction dips towards the southern bank. 



87. The rock, in which the sienite thus lies over the lime- 

 stone from the south, terminates towards the river (at 8) in a 

 bold projection, affording a distinct section on its top, and on 

 the three sides of its perpendicular face. Its substance is a 

 part of the main body of the sienite, but it contains many im- 

 bedded masses, of various sizes, particularly about its summit. 

 Two of them are of granular quartz, and the lines of junction 

 between these and the sienite are perfectly distinct. In the 

 rest we observed nothing but hornblende-slate, consisting en- 

 tirely of pure black hornblende, except that it is here and there 

 interstratified with a small quantity of red felspar. The angles 

 of the imbedded masses are always quite sharp, even when the 

 mass does not exceed half an inch in its largest dimension. 

 In these masses there are numerous veins, of which the sub- 



U u 2 stance 



