240 T. m'ke:xny hughi^is on the geology of a.>'glesey. 



He thought the northern region of Anglesey represented the Cam- 

 brian grits and slates of Caernarvonshire and Merionethshire; in 

 the Anglese)^ district there was no trace of volcanic matter. The 

 metamorphosis of the Anglesey rock was very great, as had long 

 ago been noted by Sir H. De la Beche. He described the nature 

 of the alteration these rocks had undergone. He held that the 

 strike of the strata and other evidence proved faults in the districts 

 where Prof. Hughes doubted their existence. 



Dr.* Hicks expressed his agreement with most of the remarks of 

 Prof. Eamsay. He thought that the rocks were metamorphic ; and 

 that was proved by the specimens which Prof. Hughes had brought 

 forward. He instanced cases of contortion alone not disturbing 

 the general character of a rock. In this district all the rocks were 

 highly altered ; and he could not believe they were Bala beds, but 

 that they were of Pre-Cambrian age. But he quite agreed with 

 Prof. Hughes in his recognition of the Tremadoc rocks. They 

 were, perhaps, a little nearer to the Lingula-flags. Paults of the 

 kind required by the ordinary theory were common in them. 



Prof. BoNis^EY said that he thought much more convincing evi- 

 dence was required before these schists, which he held to be truly 

 metamorphic, could be regarded as altered Bala rocks ; mere re- 

 semblance did not suffice; and such examination as he had made 

 had led him to an entirely different conclusion from Prof. Hughes. 

 It was very improbable that beds so much altered should overlie so 

 great a thickness of comparatively unaltered beds. 



Mr. Keeping mentioned some instances in the beds of Llandovery 

 age, near Aberystwith, which indicated a structure similar to 

 that described by the author ; and expressed his doubts whether the 

 schists were of Pebidian age. He thought there was much paralleHsm 

 between the Lleyn peninsula and the island of Anglesey. 



The President said that as regards the Lower Silurian rocks 

 of Anglesey Prof. Hughes had added much to our knowledge. 

 Neseuretus ramseyensis was a distinctively Tremadoc form ; and 

 OrtJiis carausii was quite distinct from 0. calligramma^ and also 

 marked a Tremadoc horizon. He thought Mr. LajDWorth's deter- 

 mination of Arenig Graptolites also might be thoroughly trusted. 

 It was also possible that representatives of the Lower Llandovery 

 beds might be present. 



Prof. Hughes, in reply, said he was glad to have his views as to 

 the unconformity near Treiorwerth confirmed by Prof. Pamsay, as 

 it was in that area he suspected the overlap of ihe May-Hill beds. 

 In the absence of fossils through a great thickness of sedimen- 

 tary rock, the Gnarled Schists (unpromising rocks for search) agreed 

 with the green slates of ChapeLle-dale. He had not seen any thing 

 in the arrangement of the contorted laminae in adjoining beds which 

 could not be better explained by crushing than by foliation. He did 

 not suggest that they were metamorphosed rocks, but sedimentary 

 rocks outside the volcanic area altered by mechanical action ; and he 

 did not think that there was any thing in the minute structure or 

 constituents of any part of the series inconsistent with this view. 



