44 Reports and Proceedings — Oeol. Soc. London. 



at different points. He contended that, instead of being an intrusive 

 granite, as supposed by the officers of the Survey, it was in all 

 probability the oldest rock in Anglesey. The basal Cambrian 

 conglomerate in contact with it is in an unaltered condition, and 

 at Llanfaelog contains an extraordinary proportion of well-rolled 

 pebbles, identical in mineral composition with the so-called granite 

 immediately below. Fragments of all the varieties of rock found 

 in the granitoid axis are recognizable in the conglomerate, and in 

 pi-ecisely the same condition as in the parent rock. Fragments of 

 the various schists of the area were also present ; so that he thought 

 there cannot be the shadow of a doubt that the so-called granite 

 and the metamorphic schists are older than the conglomerate, and 

 therefore Pre-Cambrian. The view maintained by the Survey 

 that the schists are altered Cambrian and Silurian strata, and the 

 granitoid rock an intrusive granite of Lower Silurian age, is 

 consequently quite untenable. 



In Caernarvonshire equally conclusive evidence was obtained from 

 many areas. Fragments of the Dimetian (Twt-Hill type) occurred 

 abundantly in the basal Cambrian Conglomerates at Dinas Dinorwig, 

 Pont Rothel, Moel Tryfaen, and Glyn Lifon. Quartz-felsite pebbles 

 in every respect identical with the varieties found in the so-called 

 intrusive ridges between Bangor and Caernarvon, and to the north 

 and south of Llj^n Padarn, were found on the shores of the Menai 

 Straits, in the railway-cutting at Bangor, at Llandeiniolen, Dinas 

 Dinorwig, Llyn Padarn, and elsewhere. This evidence, supplemen- 

 tary to that previously furnished by Prof. Hughes, Prof. Bonney, and 

 the author, is conclusive as to these areas, since the basal Cambrian 

 conglomerates, which are in contact with these supposed intrusive 

 masses, are composed almost entirely of rocks identical with the 

 latter ; and this could not possibly be the case if the granitoid masses 

 had been intruded among the conglomerates after their deposition. 



2. " On some Eock-specimens collected by Dr. Hicks in Anglesey 

 and N.W. Caernarvonshire." By Prof. T. G. Bonney, D.Sc, F.R.S. 

 The author stated that pebbles in the blocks of conglomerate 

 collected by Dr. Hicks to the north of Llanfaelog were practically 

 undistinguishable macroscopically and microscopically from the 

 granitoid and gneissic rocks which occur in situ between that place 

 and Ty Croes, and that the matrix contained smaller fragments, 

 probably from the same rock, with schist bearing a general i-e- 

 semblance to members of the group of schists so largely developed 

 in Anglesey, and with grits, argillites, etc. Pebbles of granitoid 

 aspect in the Cambrian conglomerate near Dinas Dinorwig, etc., 

 bear a very close resemblance to the Twt-Hill rock, and are 

 associated with abundant rolled fragments of rhyolite resembling 

 those already described from the Cambrian conglomerate and the 

 underlying conglomeratic beds and rhyolites. Two pebbles of rather 

 granitoid aspect in the Cambrian conglomerate by the shore of the 

 Menai Straits, near Garth, prove to be spherulitic felsite, somewhat 

 resembling that already described by the author from Tan-y-maes. 

 He pointed out that the evidence of these specimens collected by 



