Vol. 67.] ASSOCIATED EOCKS OF NOETH-EAST MONTGOilEEYSHIEE. 459 



beds yielding Pentamerus undatus. This would indicate an overstep 

 at about the same horizon as in the cases described by the Author. 



The Peesidext (Prof. Watts) pointed out that the Author's map, 

 when compared with that of the Geological Survey and with 

 Murchison's work in the area, showed how much new work had 

 been done by the Author in this district. He recalled that the 

 previous investigator of the area was Mr. Bickerton Morgan, who 

 unfortunately died before he could complete his work. The district 

 was interesting as a link between the little-known region of South 

 Wales on the one hand, and that of Shropshire on the other. He 

 did not recognize any marked resemblance between the igneous 

 rock described by the Author, and the intrusive or interbedded 

 rocks of the Breidden Hills. 



The Authoe said, in reply to Mr. Fearnsides, that the difficulty 

 raised with regard to the Black Shales of Gwern-y-brain seemed 

 to depend upon the identification of the graptolites. The horizon of 

 these shales was certainly higher than that suggested. The com- 

 bined palaeontological evidence tended to confirm that view. It 

 was quite possible that zones representative both of the Ashgillian 

 and of the Lower Yalentian were present ; but, since the beds 

 were very limited both in thickness and in distribution, and since 

 the overlying conglomerate formed the natural base of the Silurian 

 rocks over the rest of the area, the Author had considered the series 

 as one group, which he regarded as corresponding most closely 

 with the Ashgillian. 



In reply to Mr. Thomas, he said that the Pwll-y-glo Beds con 

 tained Orthograptus calcaratus and allied forms, and therefore could 

 be correlated very well with the zones of the Dicranogrcqrtus Shales 

 of South Wales mentioned by that speaker. 



In reply to the President, the Author said that he had in mind 

 the diabases of the Breidden district, and although he did not claim 

 that the Welshpool-Dyke rock was exactly similar to those diabases, 

 it seemed possible that it was a local variation in which the ferro- 

 magnesian mineral was not well developed. 



In conclusion, he thanked the Fellows present for their kind 

 reception of the paper. 



Q. J. G. S. No. 268. 



