568 THE CARBONIFEROUS SUCCESSION IN GOWER. [Nov. I9II, 



was most pronounced, but the upward limit of a ' Posidonomya 

 Zone' was extremely vague. 



The President (Prof. Watts) congratulated the Authors on the 

 number of issues that they had raised, and on the discussion to 

 which the paper had given rise. He agreed with Dr. Strahan that 

 the South Wales limestone outcrops afford an unrivalled opportunity 

 for the study of the broad variations occurring in a formation 

 throughout its geographical extent : the extent and continuity of 

 the South Wales sequence being far more favourable than the 

 meagre outcrops north of the Midland barrier. He referred to 

 the difficulty in finding modem parallels for the lagoon conditions 

 postulated in the paper, which required wide extent of shallow 

 water, abundance of organisms, and yet freedom from clastic 

 material. Coral-reefs presented almost the only example of such 

 conditions to be observed at the present day. He deprecated too 

 much controversy on the application of Belgian subdivisions to 

 British strata, until the exact extent and character of these 

 subdivisions had been again checked in their coustry of origin. 



Mr. R. H. Tiddeman said that he was much pleased with a paper 

 which dealt with so many points of interest. He agreed with the 

 Authors that many of the limestones of Gower had been formed in 

 shallow waters ; indeed, when mapping the ground, he thought it 

 probable that the oolites had been formed under aeolian conditions. 

 Eeferring to the term » lagoon ' so much employed, he wished to 

 ask Mr. Dixon whether he had seen anything in the area at all 

 resembling a barrier-reef or reef-knolls, such as the speaker had 

 found in the North of England : he himself had failed to see any- 

 thing similar in Gower. He was satisfied with the identification 

 of the ' Black Lias ' of Oystermouth with the Bishopston white 

 rottenstones, and mentioned that the former, when exposed for a 

 short time to the weather, became covered with a white powder. 

 He believed that the shales above the cherts represented the 

 'Bowland Shales' (of Phillips), a name which had priority over 

 the Pendleside Shale of a later author. 



Mr. A. L. Leach remarked that the rocks formed under ' shallow- 

 water ' conditions appeared to be of great importance in the area 

 described by the Authors, but the application of the definite term 

 ' lagoon-phase ' to the conditions under which these sediments 

 were deposited seemed to need further justification. The Authors 

 apparently did not claim a coral-reef origin for any of the rocks 

 described, and the oceanic atoll-lagoons were therefore rightly 

 excluded, as also those coastal lagoons which were bounded seawards 

 by coral-reefs, since neither in Gower nor, so far as his observations 

 went, in Pembrokeshire, were there any limestones of coral-reef 

 origin. Lagoons bounded seawards by islets or by submarine banks 

 were, he thought, usually associated with river-mouths, and were 

 necessarily adjacent to land. Deposits formed in such lagoons 

 would show, he thought, some unconformity with the boundary- 

 deposits, and moreover terrigenous material would probably be 

 present. He had not observed any deposits in the adjacent Pem- 

 brokeshire area that could be assigned to lagoons of this type. 



