498 Di\ WItcclton Unid ^- John T. Stohh— 



Ehyl, Abergele, and Colwyn," p. 9). where it occurs with Arcliceo- 

 siijiUaria Vamixemi, Gijpp., and other phmt-reiuains. This shell 

 was evidently alluded to as Athyris J?()//.s\sj/ in the nienioir. 



Tlie absence of" Cauinta makes it definite that only the top of the 

 Semiitnla beds, if any, can be present. In the Bristol area Semiiinla 

 is still present in the Lower Dilini02)hi/I(nm zone. It is therefore 

 certain that the lowest limestones of tlie North Wales sequence 

 cannot be lower than the jiniction of the Semiiinla and Dibunojihyllinn 

 zones of Bristol. 



In North Wales Daviesiella (Procfuctns) LlaiigoUensts characterises 

 the lowest beds of limestone at Llangollen and Minera, but it is 

 found some little distance above the base, and associated with 

 jSt')»i'H(//(i at Llaiidulas. The internal characters of Dariesiella (/'.) 

 Zlaiiijollensis closely resemble those of Chouetes aff. comoides, 

 Vanghan, which that writer proposes to call Chonett-productus. 

 It is important to note that the one species in North Wales and the 

 other in Bristol occur apparently at the same level, i.e. practicallj'^ 

 at the junction of the Upper Seminuhi and Lower DihitnophyUum 

 zones. 



Hence we arrive at the important conclusion that the whole of 

 the Tournaisian Series as represented in the Bristol area, and nearly 

 all. if not all, of the Semiiiidti beds, were not deposited in North 

 Wales, and we may reasonably infer that this area was not 

 submerged during the time that these beds were being laid down 

 in the south-w^est of England. This fact is of great importance, and 

 clears away many of the great difficulties that the distribution of the 

 Carboniferous corals in the Pennine area and the Lower Limestone 

 Series of Scotland apparently opposed at first to Dr. Vaughan's 

 conclusions. It was a well-known fact that the more highly evolved 

 corals, the Dibunophyllids, Clisiophyllids, and Loitsdaleia, in fact 

 the upper coral fouua, were found at the base of the Carboniferous 

 Limestone, Westmoreland (Shap) and in the Lower Limestone 

 Series of Scotland. It was also puzzling why the lower faunas of 

 the Bristol area had not been found in the Midlands. The succession 

 of the Lower Carboniferous rocks of North Wales evidently 

 furnishes a very simple solution of the problem, and that the whole of 

 the Carboniferous Limestone Series of the Pennine area and Scotland 

 belong to the Dibunophi/Unm and Seininida zones, witli the possible 

 exception of the Basement beds below the Ash Fell Series of 

 Westmoreland. Hence the contention of Dr. W. Hind that the 

 limestones of the Pennine area are characterised by Prodncttts 

 gigauteus and its varietal forms is practically correct (^Gkol. Mag., 

 Dec. IV, Vol. V, p. 69). 



In the Bristol area Dr. Vanghan estimates the DibitnoplujUum 

 zone to be 400 feet thick. It is probably about 500 feet thick in 

 North Wales, but in the IMidlands may be from 1,500 to 2,000 feet 

 thick. 



The Dihunophi/Utnn zone of North Wales can be everywhere 

 divided into an upper and a lower sub-zone as at Bristol, but certain 

 local differences are present. 



