650 EDWAKD HULL ON THE CLASSIFICATION 



On the other hand, Stages E, D, and C form one natural group, 

 somewhat similar in mineral composition, and palseontologically 

 connected throughout by marine molluscan forms. Their association 

 under the term " Middle Carboniferous," seems to be a proper 

 way in which to recognize this relationship. 



Lastly, it is proposed to retain Stages A and B in the Lower 

 Carboniferous group as generally accepted — representing the pre- 

 dominance of marine conditions, and of mineral characters generally 

 differing from those of the overlying beds. 



Discussion. 



Prof. Ramsay, after referring to the exceptional opportunities 

 which Prof. Hull had enjoyed of becoming intimately acquainted 

 with the Carboniferous rocks of these islands, remarked that in the 

 present paper he had correlated these beds with singular ability, 

 but added that, for his own part, he was averse to drawing hard 

 and fast lines without any distinctly evident unconformity. There 

 was, however, evidence of great up-and-down physical changes, 

 slowly substituting estuarine for marine conditions, and vice versa ; 

 and these were associated with small palaeontological breaks. He 

 did not feel sure that the Scaur Limestone of the north-east is the 

 entire representative of the Lower Carboniferous Limestone of 

 Derbyshire. He thought that the only philosophical way of map- 

 ping the Carboniferous deposits of England was upon lithological 

 principles, colouring the sandstones, limestones, &c. separately, and, 

 when coal-beds occur, indicating the underclays &c. In this way a 

 good physical map of the whole series would be obtained. Prof. 

 Ramsay also stated that he had been informed by a Russian gentle- 

 man that the Scotch Coal-measures are identical with those of 

 Southern Russia. 



Prof. "W. Boyd Dawkins, referring to the break which Prof. Hull 

 had put at the top of the Gannister series, stated that he was unable 

 to recognize any decided physical or palseontological break at this 

 point. Taking Lancashire and the north, the Coal series appears to 

 be continuous. Erom the presence of remains of sharks he inferred 

 that the upper deposits were not exclusively estuarine or freshwater, 

 but at least partly marine. 



Prof. Hughes objected to the assumption of a sharp line of 

 demarcation at the top of the Mountain Limestone. He doubted 

 the identification of the so-called Irish Yoredale beds with those of 

 Yoredale, and stated that the latter in the typical locality thin out 

 from 2200 to 609 feet within a short distance. In the Carboniferous 

 series we have local alternations of marine and freshwater condi- 

 tions ; and such a correlation as had been attempted by the author, 

 implying synchronism in England, Scotland, and Ireland, did not 

 seem to him to be useful. 



Prof. Peestwich did not doubt the correctness of Prof. Hull's 



Addresses to the Geological Society of London, Quart. Journ. Geol. Soc. vols, 

 xix. and xx. 



