﻿640 THE GEOLOGY OP ARENIG EAWR AND MOEL LLYENANT. [Allg. I905, 



beds had been entirely removed by denudation in the area mapped, 

 they were unable to determine the age of the unconformity. The 

 Author's observations rendered it highly probable that it was the 

 same unconformity as that which he had described at the base of 

 the Arenig Series. In conclusion, the speaker desired to add his 

 thanks to those of the previous speakers, for the very careful and 

 valuable piece of work which the Author had brought before the 

 Society. 



Mr. H. H. Thomas congratulated the Author, on behalf of his 

 eolleague, Mr. T. C. Can trill, and himself, on the excellence and 

 general utility of his work ; for it was always desirable to have a 

 classical area competently revised, with the help of modern methods 

 of research. He remarked on the striking similarity, both litho- 

 logical and faunal, between most of the members of the Arenig and 

 Llandeilo rocks of the Arenig district and similar horizons in South 

 Wales, over that part remapped by the Geological Survey in the past 

 three years (Llandeilo to Whitland). He considered that in the 

 two areas it would be quite possible to correlate the Arenig and 

 Llandeilo rocks, bed for bed. In South Wales there was no uncon- 

 formity at the base of the Arenig Series. 



The President said that there appeared to be differences of 

 opinion on some points among previous speakers, as to matters 

 of detail, but all were agreed as to the value of the paper. He was 

 glad to add his testimony on this, to that of the other Fellows 

 who had taken part in the discussion. 



The Author thanked the President and Fellows for their kind 

 reception of his paper. In reply to the President, he suggested that 

 the Rvlensus-'Flags included a representative of the highest part of 

 the ' Many-branching graptolite '-fauna of the Lakes and elsewhere. 

 With the President and Prof. Watts, he too was not satisfied as 

 to the entire absence of the Upper Llandeilo Beds, but had hunted 

 for them in vain all over the district discussed. He remarked that 

 Upper Llandeilo Shales were exceedingly well developed in the 

 district west of Tremadoc and all along the north-western margin of 

 Snowdonia, but even there were locally quite pinched out. He 

 hoped to clear up the matter by future work in the intervening 

 districts. In reply to Mr. Young, he said that he had used the word 

 laccolite to describe rather large cake- like masses of intrusive 

 igneous rock, the general extent of which coincided with the bedding- 

 planes of the neighbouring sediments, and the thickness of which was 

 considerable (about J-q) compared with their linear extent. He 

 particularly thanked Prof. Watts and Messrs. Lake and Thomas for 

 their useful and valuable hints as to the correlation of the beds of 

 the Arenig district with those of other areas. 



