Hind: Carboniferous Geology. 



153 



absence of the whole of the Visean group of the Carboniferous 

 Limestone, 



NORTH WALES. - 



Mr. Stobbs and I have shewn that the Carboniferous Lime- 

 stone Succession in North Wales approximates much more 

 to the Midland type than to that of the Bristol area. The 

 principal point of importance that we made out was the absence 

 of the whole of the lower part of the Bristol sequence, the 

 basement conglomerate being succeeded by Limestones of 

 various horizons in the Visean ; and that in the most extreme 

 cases, only about 500 feet of Seminula beds are represented. 

 We were able to shew that the lowest Limestones of North 

 Wales are characterised when present, by the presence of 

 Daviesiella Llangollensis. 



In certain localities Craignant, Llannt, Bron y Garth, 

 Hafod near Corwen, Fron y Cysyllte, the Seminula beds are 

 absent, and there is an overlap of Dihunophylhim beds, which 

 rest unconformably on Silurian and Ordovician rocks. 



Towards the top of the Dibunophyllum zone the beds be:ome 

 cherty in places, and a sub-zone distinguished by the presence 

 of Cyathaxonia and Amplexi-zaphrentis is developed. 



The Limestones are succeeded at Teilia and Prestatyn by 

 the Teilia beds, a series ef thin limestones and shales, con- 

 taining a typical Pendleside fauna and flora, and probabl}^ in 

 places, some of the regularly and thinly bedded Pendleside 

 Limestone have been replaced by Cherts. 



The Cherts of North Wales, therefore, are in the upper part 

 of the Dibunophyllum and Cyathaxonia zones, and in the 

 lower part of the Pendleside Series. 



At Allinson's quarry, near Oswestry Racecourse, and near 

 Bwlch Gwyn, north of Minera and at Halkin Mountain, the 

 cherts contain corals, Cyathaxonia and Brachiopoda, and are 

 certainly part of the Carboniferous Limestone. 



The succession in North Wales may be explained as follows : 



Coal Measures belonging to the Lower Coal Measures of Lanca- 

 shire, about the Arley Seam, and with the marine beds of Gas- 

 triocevas listen in any area. 



Sandy Shales. 



Pendleside Series of Teilia and Holywell. .' 

 Cyathaxonia beds. . . 



Upper Dibunophyllum. 

 Lower Dibunophyllum. 



Seminula beds. , , 



Basement Conglomerate. 



The Pendleside Series of Teilia and the Holyw^ell and 



9019 April I. 



