278 The Irish Naturalist. November, 



Cambrian age, and not vSilurian, as he had formerly supposed. Those 

 conclusions in the main agreed with the views put forward \yy Mr. 

 Kinahan, to whom the credit of assigning a pre-Cambrian age to the.se 

 green rocks was primarily due. 



Mr. M'Henry said he agreed to the three divisions — Old Red Sand- 

 stone rocks, green rocks, and fossiliferous Silurian rocks. The Pomeroy 

 rocks were mapped as Lower Silurian, but contained, he believed, Wen- 

 lock and Devonian fossils, with a few survivors of the Bala type. Pebbles 

 of the green rocks occurred in the Pomeroy conglomerates. All the green 

 rocks were igneous, except a few baked sediments and chert beds. The 

 line between the schists and the green rocks was a great thrust, which, 

 in his opinion, affected the Old Red Sandstone also. He had followed 

 the thrust south-west as far as Clare Island. The oldest series, in his 

 opinion, was mainly equivalent to the Llandeilo and Bala beds. 



Dr. MatIvEy said in Anglesey the two older series were distinct, and 

 the Arenig contained fragments of the green rocks, showing these to be 

 at any rate not Upper Silurian. 



Professor C01.E said in the central district of Tyrone there were two 

 granites, one of which had made the central zone of gneisses. The 

 gneisses below the green rocks were probably pre-Cambrian. Some of 

 the quartzites and cherts of the west of Ireland might be Silurian, but 

 the evidence was against all the Dalradians being Silurian, as Mr. 

 M'Henry desired to prove. 



Mr. Teali. said he agreed that the disturbance was really to be classed 

 with that which Mr. Barrow had worked out in Forfarshire, and the 

 author of the paper must be right in claiming it as one of the most im- 

 portant disturbances in the British Islands. With regard to Mr. Barrow's 

 views as to the age of the rocks, he had nothing to say ; yet he felt that 

 it was a subject that would have to be considered most carefully. He 

 thought they should hesitate before they classed the jasper and the 

 green rocks as of one age. With Professor Cole's remarks concerning 

 the way in which those questions of age should be determined he 

 thoroughly agreed. It would only be by close and careful work. The}- 

 could not sweep all Dalradian rocks into the Silurian merely on some 

 local bit of evidence. He concurred that chert presented itself in 

 abundance in the Torridon sandstone, and therefore that there were 

 cherts in formation in pre-Cambrian times. 



Professor Watts said he had found true Radiolarian chert pebbles in 

 Ireland, but had not been able to trace them to their source of origin. 



Professor Bi,ake criticised the paper generally. He was impressed 

 with the necessity of detailed work in the classification of the rocks 

 under discussion. If anything revealed that necessity surely it was the 

 difference of opinion that existed between the author of the paper and 

 some of those who had spoken upon it. Great stress was laid by Mr. 

 Mr M'Henry on the nature of the fossils found in the different forma- 

 tions, but he considered that the mixing of fossils alleged in such cases 

 was largely existent in the imaginations of those who had not worked 

 out the stratigraphical problem. 



