370 GEOLOGICAL APPEARANCES 



About four miles from the road, we found mica-slate, stretching 

 N. 8° E., and dipping eastward 23°. 



About two miles to the north-east of this, lies Ben y Chat, the 

 nearest of that group of mountains, which spreads between the Bruar, 

 the Tarff, and the Tilt; but we found no opportunity of extending our 

 examination farther towards it. Among the rolled stones in, and near, 

 the bed of the Bruar, we saw a few blocks of sienite, both grey and 

 red, and one large block of granite. 



The course of the river Garry, above its junction with the Bruar, 

 lies a good deal farther to the west of Blair. In following it up, along 

 the road to Dalnacardoch, for between six and seven miles from 

 Blair, we had frequent opportunities of seeing a fine section of the 

 rock in the channel. The banks are abrupt, and the stream crosses 

 the strata almost at right angles to their stretch. Our examination of 

 them was very cursory ; but they seemed to be chiefly mica- slate, and 

 pretty uniform in their stretch and dip. About five miles from Blair, 

 the stretch was N. 18° E., and the dip easterly £8°. Six miles 

 and a half from Blair, the stretch was N. 29° E., and the dip easter- 

 ly 29°. 



From a comparison of the observations in the beds of the Tilt, the 

 Banavie, the Bruar, and the Garry, it appears that the strata, which 

 would be crossed by a line passing through Blair a little to the north 

 of west, and extending about seven miles in that direction from the 

 Tilt, are conformable in dipping towards the south-east ; but vary in 

 the extreme differences of their stretch about forty degrees. 



The strata in the channel of the Garry are intersected by veins, or 

 dykes, of porphyry. About five miles from Blair, there is a remark- 

 able one crossing the river, and between twenty and thirty yards 

 broad. The base of this porphyry is a reddish brown compact felspar, 

 in which there are imbedded small crystals of white felspar, and very 

 imperfect crystals of hornblende. Where the porphyry joins to the 

 mica-slate, the colour of the base changes to black by a gradation 

 in the course of a few inches. Of this circumstance I can offer no ex- 

 planation. 



Six miles and a half from Blair, there is a bed of porphyry perfectly 

 parallel to the strata, and uniform in its thickness, which is several 



feet. 



