IN GLEN TILT. 313' 



mile above Forest Lodge, a spot remarkable for its distinct ex- 

 hibition of a junction between the strata and the sienite, in the 

 bed of the river. The southern bank of the river is here the foot 

 of a declivity, several hundred feet in height, and excessive- 

 ly steep, on which the rock appears only at intervals. 



24. In the ascent of this declivity, Mr Playfair saw nothing 

 but granular limestone, to the height of perhaps more than 

 three hundred feet. 1 he beds of the limestone dip southerly, 

 into the face of the mountain. Over the limestone is a bed of 

 porphyry, twelve or fifteen feet thick. The base of the por- 

 phyry is a grey compact felspar, and contains numerous small 

 and imperfect crystals, of a reddish felspar, hornblende, and 

 mica. At the foot of the declivity, and close to the bridge, there 

 are lying many blocks of a porphyry, which has a base of grey 

 compact felspar, and is singular for containing distinct crys- 

 tals, not only of white felspar and quartz, but also of mica in 

 thin hexagonal plates. From the sharp angles of the blocks, 

 they must be supposed to have fallen from the declivity above; 

 but whether they are a variety of the bed just mentioned, or 

 from another rock, we found no opportunity to determine. 



25. Above the porphyry is mica-slate, alternating with beds 

 of granular limestone ; and Mr Playfair observed granular 

 limestone upon the brow of this steep face, where it changes 

 to a more gentle slope. This is the highest point that is vi- 

 sible from the Glen below, and, by comparing its level with 

 that of another on the same face, immediately above the 

 Lodge, the height of which was afterwards determined by tri- 

 gonometrical measurement, he computed it to be about eight 

 hundred feet above the Tilt. 



26. From hence the ascent is more gentle for a considerable 

 distance, and the ground is covered with lono- heath. The 

 rock is rarely seen ; but what appears is mica-slate. The 

 line in which Mr Playfair ascended, conducted him to a 



ridge, 



