THE CARBONIFEROUS SYSTEM 255 



In Pembrokeshire all the zones are well developed, and are 

 tiiiely rxliiliitfl in tin: coast sections. At Skrinkle Haven the 

 junction of Old Red Sandstone and basal Carboniferous is well 

 shown ; the central beds constitute the Tenby anticline, and the 

 " Pendleside " Beds are found north of that place, where they 

 consist of black carbonaceous shales with large ellipsoidal concre- 

 tions, locally known as bullions. These beds contain Glyphioceras 

 diadema, Pterinopecten papyraceus, and Posidoniella membranacea. 



2. North Wales, Stafford, and Derby 



The great difference between the limestone series of this area 

 and that of South Wales and Gloucestershire is that it belongs 

 entirely to the Visean stage, the basal beds being on the horizon 

 of the upper part of the Seminula zone ; so that there is no 

 representative of the Tournaisian stage. 



The lithological divisions were studied and described by Mr. G. 

 H. Morton and Dr. A. Strahan, while the palaeontological zones have 

 recently been worked out by Dr. W. Hind and Mr. J. T. Stobbs. 3 

 The most complete sequence is found in Flintshire, and this is 

 given in the following table : 



Lithological Divisions. Zones. Thickness. 



1000 



} Lower Dibun.p,,y,,u m } 1,00 



seminula ) 



About 3000 



The absence of Caninia makes it fairly certain that only the 

 top of the Seminula zone comes into the succession. The lower 

 p.irt of the Dibuuopliyllum zone is marked by the presence of 

 that genus with Cyathophyllum Murchisoni, Productus hemisphericus, 

 and P. cora. The higher part contains all the typical fossils of its 

 Bristol equivalent, and the species of Lithostrotion are common, 

 as are also several species of Spirifer and Schizophora resupinata. 

 The sandy beds at the top of this zone consist of compact fine- 

 grained sandstone, each bed having a medial band of grey or black 

 chert which is full of sponge spicules. These beds and the Aberdo 

 limestone are regarded as a separate sub-zone characterised by the 

 coral Cyathaxonia and Productus longispina. They form a passage 

 into the overlying stage. 



