494 



EEV. J. F. BLAKE ON THE 



Star Inn ; but at the farm of Cefn-eth-groen there is a quarry in 

 which a distinct junction may be seen. The actual piece of pelite 

 seen must be an included fragment, since the mass of the rock is 

 away to the west. This patch clings to a vertical surface of the 

 granite on its eastern side (see fig. 11). 



Fig. 11. — Section at Cefn-eth-groen Farm. 



/^ 



1 2 



1. Granite. 



1 

 2. Pelite. 



3. Junction in Map. 4. Farm. 



A little to the south of this we come to the region of Craig-yr- 

 allor. Between that craig and the new Holyhead road is another 

 eminence, called Craig Cocyn. On the surface of this craig the 

 granite is seen in tongues, which enter the dark hornblende-schist. 

 Sometimes these tongues are of the ordinary character, cutting 

 across the edges of the folia of the darker rock ; but at others they 

 seem pulled out into lenticles, which in this case run with the 

 average schistosity (as in fig. 12). Thence we may pass to a more 



Fig. 12. — Granite in Hornblende-schist, Craig Cocyn. 



1. Granite. 



2. Hornblende-schist. 



intimate blending of the two rocks, with the production of a form 

 of banded gneiss. Whether or not we accept Mr. Teall's explanation 

 of the mode of formation of such gneisses, it is to be noted that this, 

 the most mechanical of all explanations, involves an intrusion of the 

 granite to start with. 



Finally, we come to the tongue of " Cambrian " on the map, which 

 crosses the turnpike-road, and in this we observe the same indefinite- 

 ness of granite and pelite as is seen at Llyn Faelog, the more central 

 portion being free from granitic material. 



