THE NEIGHBOURHOOD OF BANGOR. 



485 





No. I. 



No. II. 



No. III. 



No. IV. 



so 2 



72-57 



1364 



2-28 



slight trace 



100 



•64 



617 



2-07 



110 



72-18 



14-46 



1-78 



•91 



6-92 

 trace 

 610 

 192 



1-47 



83-802 



7-686 



•111 



•408 



'•896 



■ -109 



2-161 



4-229 



•191 



•301 



79-72 

 9-65 

 5-69 



"t 



t 



1-93 

 3-54 



AL0 



IT 2~3 



Fe„0, 



FeO 



BaO 



CaO 



MgO 



K 



Na 



FeS 



Loss on ignition . . . 



99-47 



99-74 



100-000* 



100-53 



No. I. By J. J. H. Teall, Esq., F.G.S. 



No. II. By J. A. Phillips, Esq., F.R.S., Quart. Journ. Geol. Soo. xxxiii. 

 p. 457. Cf. the analyses there given of modern " perlites." 

 No. III. By J. Hughes, Esq., F.O.S., Quart, Journ. Geol. Soc. xxxi. p. 400. 

 No. IV. By F. H. Hatch, Esq. 



Discussion. 



Prof. Hughes remarked on the confusion among the Archaean 

 rocks arising from their classification according to similarity of cha- 

 racter, previous to exact determination of their relations to one 

 another in each area. He could not agree with the author in saying 

 that any of the beds east of Brithdir now described were identical 

 with those of Holyhead and Amlwch. He had failed to find any 

 break or unconformity in the British Archaean. He could not agree 

 with the author as to the succession of grits and conglomerates in- 

 dicated, as he took the strike to be in some cases at right angles to 

 that assumed by the author ; so that the author's bands, according 

 to him, were in one part to be referred to the Cambrian conglo- 

 merate and in another part of the same band to the Bangor series. 

 Noticing the frequency with which volcanic series, when traced along 

 the strike, pass into ordinary sedimentary rocks, he thought that 

 the relation of the Pebidian to beds not of volcanic origin in ad- 

 joining areas might be regarded as still an open question. 



Mr. Teall stated that his analysis had been made quite inde- 

 pendently of that of Mr. Phillips. 



Dr. Hicks remarked on the discordance of strike of the Pebidian 

 rocks from that of the beds above and below. The granitoid, felsitic, 

 and volcanic groups of Prof. Hughes agreed fairly well with his 

 Dimetian, Arvonian, and Pebidian ; but neither of these is fully re- 

 presented here. Unquestionably the Cambrian conglomerates over- 

 lap each group with a marked unconformity, and are mainly made 

 up of fragments derived from the groups below. This unconformity 



* Including "089 phosphoric acid, '017 of sulphuric acid, and a trace of 

 carbonic acid. 



t Traces, amount not estimated. 



Q.J.G.S. No. 155. 2 m 



