176 MISS G. L. ELLES ON" THE RELATION OP THE [MayiO,09, 



two thin flows near the summit of the hill, which are uniformly 

 darker in tone and show distinct phenocrysts. 



(B) Lower or Bodlondeb Ash-Group. — The whole of the 

 top of the hill is occupied by the members of the Bodlondeb Ash- 

 Group, a series of fine and coarse ashes with some shale-bands. The 

 coarser bands contain large fragments of the Banded Lavas and 

 also fragments of shale ; these may be well studied close to the 

 Reservoir ; traced north-eastwards they are seen to be thrown 

 slightly forward by a tear-fault, and like the whole of the Lower 

 Banded Lava-Group disappear beneath Conway Marsh. This Ash- 

 Group, however, reappears at the northern end of Bodlondeb Wood, 

 where it is well exposed both in the wood and on the path, as 

 well as on the shore below. The section is as follows (fig. 2, 

 p. 174) :- 



Thicktiess in feet inches. 



Creamy rhyolites of the Upper Brecciated Group... ? 



Coarse ash , with shale-fragments 2 



Shale-band, with Glyptograptus teretinsculus (His.) . 1 6 



Coarse ash, with large shale-fragmeuls 15 



Eottenbed ? 



Cindery ashes 27 7 



Coarse ashes 9 



(Base not seen.) 



The ashes here contain fewer and smaller rhyolite-fragments, 

 while the slaty matter is more abundant than on Conway Mountain : 

 it is obvious, therefore, that it is passing away from the source of 

 the volcanic material. This is still further emphasized on the 

 eastern bank of the River Conway, where the members of the group 

 are once more exposed after being faulted back some distance to 

 the north-west. They are best seen on the flanks of the small hill 

 north-east of Castell Degamvy ; at this locality the slaty material 

 largely preponderates over the ash, and graptolites are corre- 

 spondingly more abundant. 



This Ash-Group appears to mark the limit between the Lower 

 Banded Rhyolites and the Tipper Brecciated Rhyolites : for the 

 greater part of Conway Mountain is occupied by different members 

 of a series of cream-coloured rhyolites, which exhibit flow-breccia- 

 tion extremely well and are much quartz-veined ; they are some- 

 times platy and occasionally somewhat banded, although never so 

 decidedly as those lavas that belong to the belt below the Bodlondeb 

 Ashes. 



(C) Upper Brecciated Rhyolites. — The Tipper Group of 

 Lavas are characterized by their creamy colour and flow-brecciation : 

 the lowest members appear to have undergone intense silicification ; 

 and among them is a very beautiful nodular rhyolite, with large 

 nodules measuring from 6 to 8 inches in diameter. This band, how- 

 ever, does not exceed 20 feet in thickness ; it is well exposed on 

 the northern slope of the mountain, some little distance below the 



