148 Geological Society : — 



communication special attention is paid to the alteration of a group 

 of basic volcanic rocks by the granite. 



May 10th.— "W. H. Hudleston, Esq., M.A., F.R.S., 



President, in the Chair. 



The following communications were read : — 



1. " The Felsites and Conglomerates between Bethesda and 

 LlanUyfni, North Wales." By Prof. J. P. Blake, M.A., F.G.S. 



The author brought forward fresh evidence in support of the 

 views he had previously expressed as to the Cambrian age of these 

 felsites, and as to the unconformity of the conglomerates on the 

 Purple Slates. 



A new tunnel-section at Penrhyn Quarry was described, in which 

 felsite was followed by St. Ann's Grit with a conglomerate-band, and 

 there lying in the midst of the Cambrian Series. After a word or 

 two on the conglomerate on Hoel Rhiw-wen, the sections on either 

 side of Llyn Padarn were discussed in detail, and it was shown that 

 the distribution of the rocks on the surface of the country could only 

 be explained by the unconformable position of the conglomerates and 

 grits, which, moreover, lie nearly horizontal. 



After a discussion of the conglomerates of Bettws-Garmon, a 

 detailed section of the adit at Moel Tryfaen was given, in which it 

 was shown that there was only a 3 ft. 6 in. band of conglomerate 

 next the Purple Slates, followed by 1350 feet of Banded Slates and 

 Laminated Grits with four distinct intercalated bands of felsite ; 

 and it was argued that the conglomerate on the summit, 55 yards 

 across, could scarcely be represented by this thin band. Finally, 

 the distribution of rocks on Mynydd-y-Celgwyn was shown to be 

 satisfactorily explained by unconformity. 



Incidentally it was mentioned that a band of rock in the felsite 

 at Llyn Padarn, which had been considered to be a deposited slate, 

 was in reality an intrusive igneous rock. 



The conglomerates described were considered to be an overlap of 

 the Bronllwyd Grit. 



2. " The Llandovery and Associated Rocks of the Neighbourhood 

 of Corwen." By Philip Lake, Esq., M.A., F.G.S., and Theo. T. 

 Groom, Esq., B.Sc, F.G.S. 



The area described forms a part of the northern slope of the 

 Berwyn Hills, and stretches along the southern bank of the Dee from 

 Corwen to Pen-y-glog. The beds of the Berwyns are here thrown 

 into a series of folds which run nearly E.-W. ; and the northerly 

 limbs of these folds are long and low, while the southerly limbs are 

 short and steep. The folds are cut through by a number of faults 

 which run nearly E.-W., generally along the crests of the anticlinals, 

 and these invariably throw down towards the north. The southern 

 bank of the Dee Valley is here formed by these faults. 



A second series of faults running about 20° W. of N. to 20° E. of 

 S. is of later date. One of these, near Corwen, presents some 



