486 ON ROCKS IN THE NEIGHBOURHOOD OF BANGOR. 



occurs in all the areas examined. He believed that the existence of 

 the Arvonian would eventually he fully established. He thought 

 that the author's studies would serve to establish a fourth Archaean 

 series in addition to his own. 



Mr. Toplet said it was admitted by the author that the uncon- 

 formity between the Cambrian and underlying beds was compara- 

 tively small and local ; which was a very different conclusion from 

 that previously announced by Dr. Hicks, who required the Cam- 

 brian conglomerate to override some thousands of feet of Pebidian 

 beds within a distance of little more than a mile. 



The Author, in reply to Professor Hughes, said that he thought 

 all the evidence pointed to the Menai and Holyhead schists, with 

 others inland in Anglesey, being approximately of one age. In 

 neighbouring districts and under similar circumstances, he thought 

 lithological correspondence gave a reasonable presumption in favour 

 of a general correspondence in age. In the Bangor district he was 

 fully sensible of the difficulties mentioned by Professor Hughes, 

 especially as regards the conglomerate at Gorphyswfa and the ex- 

 posures between it and the great mass running up from the shore. 

 Still, on the south-east side of the fault, he thought the succession was 

 clear and the improbabilities of the identity of any of the coarser 

 fragmental beds were too great. He said, in reply to Dr. Hicks, 

 that he did not deny that there might be a series in South Wales 

 representing what the speaker called Arvonian ; but in the Caer- 

 narvonshire districts he could not find hallenintas, but there were 

 true acid lavas. With reference to Mr. Topley's remarks, he stated 

 that what he had said was, that he considered there was, under the 

 rocks generally recognized as Cambrian, a series sufficiently distinct 

 stratigraphically and lithologically to justify, in accordance with 

 the usual laws, the giving of a separate name (i. e. Pebidian). 

 Whether Dr. Hicks or Prof. Hughes might or might not have over- 

 estimated the amount of the break, whether they agreed or disagreed, 

 clearly was for them and not for him to settle. Each man, in the 

 matter of mistakes, if he made them, must bear his own burden, as 

 the author had done by his remarks admitting a mistake of his own 

 at Twt Hill, which had been corrected by Prof. Hughes. 





