﻿264 DK. A. VATTGHAN ON THE PAL^ONTOLOGICAL [May I905, 



Cliothyris : it is doubtful whether the form found in S x really belongs to 

 this genus. 



Syringothyris aff. laminosa is found rarely in S 15 but is essentially character- 

 istic of the top of the Tournaisian. 



Prom the foregoing analysis, it seems to me beyond question that, 

 in the Bristol area, the division of the Carboniferous Limestone into 

 an upper and a lower part is thoroughly justified on purely-palaeonto- 

 logical grounds, and is also of great practical utility. In recognition 

 of the great amount of exact work done by Belgian geologists, in 

 elucidating the palseontological sequence in the Carboniferous Lime- 

 stone of their own country, we are, I think, bound to accept the 

 names which they have adopted for the two divisions. 



On the other hand, the designation Dinantian, as including the 

 whole of the Carboniferous Limestone, seems hardily justified by 

 the continuity or clearness of the sequence in the district which 

 has suggested the title. It cannot, however, be denied that it would 

 be extremely convenient to have a single designation (other than a 

 misleading lithological term) which should include the ' Lower 

 Limestone-Shales ' at the base and the ' Upper Limestone-Shales ' 

 at the top, as well as the main mass of limestone. 



[As I have pointed out above, the detailed examination of the 

 faunal sequence in the Bristol area demands that the division-line 

 between a lower series (Tournaisian) and an upper (Yisean) should 

 be drawn at the top of the Syringothyris-Zone. But, if I am 

 correct in correlating the Lower Yisean of the Belgian Geological 

 Survey with the Syringothyris-Zone of the Bristol area, the terms 

 Tournaisian and Yisean, as employed by me in this paper, do 

 not bear their original connotation : the zone C being included in the 

 Yisean by Belgian geologists, and in the Tournaisian on my system. 



Under these circumstances, it seems better to avoid all chance of 

 confusion by employing new indices for the whole of the Carboni- 

 ferous-Limestone Series as developed in the South- West of England 

 and in South Wales, as well as for its two great divisions. 



I consequently suggest the following classification : — 



f KlDWELLTAN 



f Dibunophyllum. 

 " \ Seminula. 



Avonian A f Syringothyris. 



Clevedonian ... < Zaphrentis. 

 ^ [ Cleistopora. 



Avonian, as synonymous with Lower Carboniferous, seems 

 warranted by the completeness of the sequence in. the Avon section 

 (Bristol) and by the fact that the Avon Gorge has been recognized as 

 a classical section, since its minute description in Trans. Geol. Soc. 

 ser. 1, vol. iv (1811-17) p. 197 & vol. v (1818-21) p. 95, by George 

 Cumberland. 



Clevedonian satisfactorily connotes the Lower Avonian, since, 

 in the neighbourhood of Clevedon (Somerset) : — 



(1) The zones of Cleistopora, Zaphrentis, and Syringothyris are all well- 



displayed; and 



(2) The Upper Avonian is practically absent. 



