W. A. E. UssJier — Falceozoic Rocks of Devon and Somerset. 441 



Tygwyn and Ysyuborwen, about half a mile N.E, of Carnarvon. 

 The brown grit and sandstones, however, are well exposed about 

 three miles to the N.E. at Carreg Goch, dipping at a high angle to 

 the S.S.E., and apparently dipping under black shales. Still farther 

 north-east, but south of Llanddeiniolen, similar beds are seen con- 

 taining hard bauds of quartz pebbles, dijDping as before S.S.E., and 

 succeeded by black shaly beds. North of Llandeinidlen the con- 

 glomerate becomes felsitic. The actual base of the series is not 

 seen, the lowest bed exposed being a grit of quartz and felsite 

 passing up into a conglomerate composed of felsite pebbles. 



This seems to furnish a parallel instance to that at Penygi'aig and 

 Penlon, in Anglesea, referred to above, where two conglomerates 

 occur, a quartz conglomerate below, and a felsite conglomerate 

 above separated by quartz sandstones. 



There is, therefore, nothing exceptional in the fact that a con- 

 glomerate exhibits very different lithological characters in different 

 parts of even a limited area. If anything more is needed to show 

 that the lithological difference between the conglomerates of Twt 

 Hill and Bangor is no valid argument against the Cambrian age of 

 the former, I need only state that on the shore of the Menai Straits, 

 near Garth Ferry, Bangor, a baud of quartz conglomerate occurs 

 high up in the Cambrian, which lithologicaily so closely resembles 

 the Twt Hill conglomerate, that if a number of unlabelled specimens 

 from the two places were mixed together, it would be extremely 

 difficult, if not imj^ossible, to re-sort them. The sandstones in which 

 the conglomeratic band occurs may be traced down some 400 or 500 

 feet into the felsitic conglomerate which forms the base of the series 

 in that area. 



It appears therefore that whatever objections there may be to 

 regarding the Twt Hill conglomerate as the base of the Cambrian 

 in the Carnarvon area, the stratigraphical evidence, as Prof. Hughes 

 has already shown by careful mapping, is all in favour of that view. 

 The identity of sequence in Anglesea and at Carnarvon constitutes 

 an ai'gument of the greatest weight, which no lithological difference 

 such as the conglomerates of Bangor and Carnarvon display could 

 counter-balance, even if it had not been possible to parallel these 

 with similar differences in other areas where no doubts as to the 

 stratigraphical position of the various beds exist. 



IV. — On the Paleozoic Eocks of North Devon and West 



Somerset. 

 By W. A. E. ITssHER, F.G.S. 



THE Palaeozoic rocks of North Devon and West Somerset, present- 

 ing so complete a change in stratigraphical sequence and 

 Iseontological and lithological characters from those forming the 

 Coal-basins of Somerset and South Wales and their environs, have 

 long attracted the attention of geologists. The bibliography of the 

 subject, which has since attained such formidable dimensions and 

 embraces so many stars in the geological firmament, had been swelled 

 by the contributions of early theorists ; and ere the term Grauwacke 



