336 



MISS C. A. RAISIN ON THE LOWER LIMIT OF 



the rock which is nearest to the fclsite ; for at Brynderw, where 

 the valley is narrower, we find a banded gritty rock with pebbles ; 

 and the knoll of argillite itself in the field west of the main road 

 has at its southern side {i. e., nearer to the felsite) a curious 

 purplish rock, which is fragmental and apparently of an ashy 

 nature. 



(b) Quarry at Bryn Efail. 



AVe come, however, to the section upon which Mr. Blake most 

 relies. This is afforded by a quarry, which, to quote his phrase, 

 is " exactly on the letter E of the word Efail." That letter, as 

 shown on the Survey map, falls on a flat alluvial plain ; there is, 



Fig. 2. — Plan of Quarry at Bryn Efail. (Scale | inch = 40 feet.) 





Quartz-felsite, This inchxdes the "porphyry" (1) and some or all of 

 the " grit " (3) of Mr. Blake. 



Greenstone. This includes the greenstone (4) and most of the *' slate ' 

 (2) of IVfi-. Blake 



,^^^y^ Dyke of fine-grained felsite. 



+ Position of specimens, whence slides have been cut, showing felsite or 



diabase, or both. 

 J« Slide which simulates a grit of felsite-fragments. 



The parts left blank are covered* with grass. 



however, a quarry " on the west side of the road " to the north-east 

 of the mineral railway, nearly in the angle formed by the two, 

 which, as there is no other in the neighbourhood, I assume to be the 

 one intended, especially as it agrees in its topographical features 



