$34 GEOLOGICAL APPEARANCES 



specks of a reddish felspar, which give their tinge to the whole 

 substance. The coincidence of colour, and that want of a :-: ra- 

 tified structure which is common in granular quartz, made it 

 easily mistaken, on a superficial view, for a gradation from ;.he 

 sienite j but a more minute examination proved the line of junc- 

 tion to be well defined. 



84. Nearer to the bridge, and from fifteen to twenty yards 

 below it, the northern bank is formed by a rock, that rises al- 

 most perpendicularly from the edge of the water. This rock 

 consists principally of the red sienite ; but, near the level of the 

 water, there appears in the face of it (at 7 in the plan) a mass 

 of granular quartz, interstratified with hornblende-slate, about 

 ten feet long, and four thick. The stretch of these strata is 

 nearly the same as that of the strata of limestone in the scar 

 lower down on the other side of the river, about N. 33 d E. 

 But their dip is at an angle of 47° to the north-west, and there- 

 fore in a direction opposite to that of those strata, and oppo- 

 site to the common dip of the strata on the south side of the 

 valley. They dip immediately into the face of the rock, and, 

 as the sienite may be traced completely round them, they are 

 evidently imbedded in it. These strata are traversed by two 

 veins, composed of quartz and red felspar, in large grains, and 

 not intimately mixed. The veins run almost vertically. They 

 are visible for some feet in the sienite beneath the strata, and 

 under the surface of the water, and one of them is continued 

 in the sienite above the strata. There is a shift in one of these 

 veins. 



85. At the bridge the breadth of the river is much contract- 

 ed, and the rocks on both sides rise many feet above it, with 

 precipitous and irregular faces. Those immediately under the 

 bridge, and to the east of it, are free from lichens, and their 

 surfaces either retain that coarse polish, which they received, 



when 





