126 



THE RELATIVE POSITION OF THE 



[Ch. VII 



cretions are aggregated together : a subject which lias not as 

 yet sufficiently occupied the attention of the geologist. 



In the last chapter, we gave a sketch of the structure of 

 the granite and of the slate ; we now propose to offer a few 

 examples of the structure of these rocks at their junction, 

 which occur in the Land's End district, where the union of 

 these rocks is so instructively displayed. 



Thus, in the first place, at Polmear Cove, on the north 

 coast, the slate reposes on the granite at an angle of about 

 45; and these rocks, at their junction, not only form parts 

 of the same concretions, but also of the same beds ; the under 

 part consisting of granite, the upper of slate, owing to both 

 rocks possessing the same rhomboidal structure ; as may be 

 seen in the annexed diagram. 



Fig. 6. 



Junction of Granite and Slate at Polmear Cove, Cornwall. 

 (Cliff Section.) 



In this place, the beds of granite are often separated from 

 each other by thin parallel layers, or veins, of shorl-rock ; 

 so that the beds are more distinctly developed, in the direc- 

 tion of the greater angle, whilst the laminae of the slate follow 

 the lesser : these beds also decline in the direction of their 

 strike towards the sea, and along this slope the waves are 

 gradually removing the slate. At St. Michael's Mount, and 

 at Mousehole, the slate rests on the granite at a less angle ; 

 otherwise the appearance is the same as that of Polmear, 



