314 GEOLOGICAL APPEAPANCES 



ridge, formed on one side by the slope he had passed over, 

 and, on the other, by the declivity of a deep ravine, through 

 which flows a stream that rises in the higher part of Ben y 

 Gloe, and joins the Tilt about three quarters of a mile above 

 the bridge, by a course almost due north, while that of the Tilt 

 is to the south-west. On this ridge he fo nd mica-slate, 

 stretching N. 38" E., and dipping to the south-east at an angle 

 of about 35°. 



27. In the direction of south, and perhaps a little west, 

 from this spot, and at the distance of about a quarter of a mile, 

 is a conical eminence, of considerable height, forming the point 

 of Cairn Toorchie. All the way to its summit, he observed 

 the rock to be a granular quartz, in which there occur thin lay- 

 ers of felspar and mica ; and thus the stone is a gradation into 

 gneiss. The granular quartz lies above the mica- slate last 

 mentioned, and, as far as he could judge, has the same stretch 

 and dip. Another high and bare point, at the distance of about 

 half a mile on the other side of the ravine, appeared pretty 

 evidently to consist of a similar rock. 



28. Mr Playfair descended towards the north, along the 

 sloping edge of the ridge, by the side of the ravine, and, in 

 the course of his walk, went more than once to the bottom of 

 the ravine, in order to examine the rock. At first, he found 

 mica-slate upon the ridge, and, in the bottom of the ravine, 

 granular quartz. Lower down, there was granular limestone 

 upon the ridge, of the same characters with that which he had 

 seen in ascending the steep declivity above the bridge, and he 

 had no doubt that it extended all the way to the side of the 

 Tilt. The rock, on this part of the ridge, is indeed generally 

 covered with a thick coat of earth ; but, in the bottom of the 

 ravine, for several hundred yards before it opens upon Glen 

 Tilt, there is limestone, which many falls in the stream have 

 worn down, and scooped out, into a variety of irregular forms. 



We 



