IOO PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [May 1 894,. 



The general succession is argued to be the same in the isolated 

 portion south-east of Bangor, as in the main mass. Not having 

 been able to make things fit in with the existing Survey map, he 

 offers one of his own, which he does not bring forward as absolutely 

 correct ; doubts may affect the surface-distribution, but of the vertical 

 succession, he claims, there can be no doubt whatever. The presence 

 of the summit-beds of Blake's Cambrian would seem to depend on 

 whether the Bronllwyd Grit, which he regards as belonging to the 

 overlying group, rests conformably or unconformably on the under- 

 lying rocks. Amongst his conclusions he regarded it as proved that 

 the rocks to the west of the felsite belong to the lower part of the 

 series, and those to the east to the upper, both being determined in 

 areas where the felsite is absent, and hence it appears probable that 

 the felsite mass is a volcanic complex belonging to the middle of the 

 Cambrian period. 



In his last paper ' On the Pelsites and Conglomerates between 

 Bethesda and Llanllyfni,' Prof. Blake, in support of his previous 

 argument, asserts that the felsites occur on so many horizons that 

 they could only be one mass if they were intrusive. He regards it 

 as having been abundantly shown that the conglomerates, derived 

 from these felsites — at all events on the east side of the faulted 

 Silurian strip — do not lie at the base of the Cambrian series, fie 

 allows, however, that it is another thing to demonstrate that any 

 of them are of later age than the workable slates — and to this he 

 now limits himself. Such a contention cannot be demonstrated 

 off-hand ; the proofs as to the relations of the conglomerates to the 

 felsites require, he says, a careful consideration of the whole 

 obtainable evidence, and this is so interwoven that it is necessary 

 to take the localities in geographical order and exhaust the evidence 

 in each. Of course we cannot follow Prof. Blake, on the present 

 occasion, across country generally, but his reading of the Moel 

 Tryfaen section presents features of considerable novelty. He 

 evidently expects that this will give the coup de grace to the idea of 

 pre-Cambrians occurring in this district. It is clear that previous 

 observers have been hasty in assuming that the great crags of con- 

 glomerate on the summit are really represented in the interior of that 

 mountain. Por the first time we have something like a section as 

 afforded by the adit : the length is a little over a quarter of a mile - 7 

 the average dip of the beds about 60°. The Author shows that, 

 next the Purple Slates, there is a conglomerate of quartz-pebbles in a 

 gritty green matrix, say 4 feet thick, and that all the rest consists 



