IN GLEN TILT. 



S3* 



the top of the rock, in an area of about ten feet by eight there 

 is one having its stretch N. 143^ E., and its dip south-west at 

 an angle of 40° ; a second having its stretch N. 36° E., and its 

 dip north- west at an angle of 55° ; a third, which appears to 

 ha e been once united to the last, stretching N. 13° E., and 

 dipping west at an angle of 58°; and a fourth, stretching 

 N. 1G8* E., and dipping north at an angle of 55°. The obser- 

 vations were taken in an order from the west to the east side 

 of the rock. Of the four masses, the first and last extend to 

 an unknown depth into the rock below ; but the second and 

 third rest entirely upon the sienite. Veins of sienite and fel- 

 spar, and of gradations between them, are frequent in most of' 

 the larger masses, and many of them may be traced to be con- 

 tinuous with the main rock of sienite below. In the small 

 veins there is generally white felspar intermixed with the red. 

 As in the rock last described, there are small veins of felspar 

 mixed with hornblende, running sometimes parallel, and some- 

 times transverse, to the planes of the strata. The veins also re- 

 semble those in the rock at 8 in their reticulation, in the great 

 irregularities of their direction and outlines, and in having 

 their lines of junction commonly distinct. There is here too 

 the same marked difference in the general aspect of the sub- 

 stances of the sienite and the hornblende-slate. Sometimes 

 perhaps the parts in contact are blended, but this is rare. 

 They are usually bounded by lines that are well defined, and 

 some of the imbedded pieces are remarkable for the sharp- 

 ness of the angles, which they exhibit in the common sec^ 

 tion of them and the sienite, afforded by the surface of the 

 rock. 



8a At the bridge, the channel of the river makes a sharp 

 turn to the eastward. The rocks about the bridge are chiefiy 

 formed of the main body of the sienite j but, near the fall, this is 



succeeded 



