The Carboniferous Succession below tJte Coal-Mensures. 387 



The choice of the terms is indefinite, for it wouhl lead one to expect 

 the existence of a Lower Grey and an Upper Brown. As far as tlie 

 nomenclature goes, it would have been much simpler to have inserted 

 the word 'or' between the horizon and its indicative colour. 



Moreover, the beds which lie on the Upper Grey Limestone he 

 unfortunately termed 'Upper Black Limestone,' and to this the great 

 source of error in the conception of the sequence, which the officers 

 of the Geological Survey accepted from him, is almost entirely due. 

 There are two or more horizons in North Wales at which Black 

 Limestones occur, just as obtains in Derbyshire, each of which is 

 characterised by a totally different fauna. 



The lower set of Black Limestones is worked for hydraulic 

 cement, and is locally misnamed 'Aberdo' Limestone. They are 

 characterised by a fauna typical of the uppermost beds of the 

 Carboniferous Limestone, and contain such characteristic fossils as 

 Productus giganteus, Lonsdaleia rugosa, L. floriformis, Cyathophyllum 

 regium, Amplexi-zayhrentis sp., and C'yathaxonia sp. These corals are 

 only known in beds which form the uppermost division of the 

 Dibnnophyllum zone of the south-west of England. 



The other set of Black Limestones do not yield a hydraulic lime, 

 have peculiar physical characters, weather and fracture in a manner 

 altogether different from tlie 'Aberdo' stone, and contain a typical 

 Pendleside fauna, Fterinopecten papyraceus, Posidonomyn JBecheri, 

 which at once definitely determines the age of the beds to be later 

 than the Carboniferous Limestone Series, and therefore the equivalent 

 of the Pendleside Series of the Midlands. Mr. Morton's lists show 

 that he recognised the fact that Cyathophyllum regium and Lonsdaleia 

 floriformis only occur in the Upper Grey Limestone in every locality 

 which he examined. 



Another important horizon seems to be indicated from Morton's 

 lists. The base of the Lower Brown Limestone is characterised by 

 the presence of that peculiar shell Daviesiella (Prodtietns) Llangol- 

 lensis, which appears under the name of Productus comoides in his 

 lists. We found these two important facts of distribution to be 

 universally true. 



The Middle White Limestones we found to be characterised by 

 the presence of Dibunophyllum and Cyathophyllum Murchisoni, 

 fossils which indicate, in the Bristol area, the lite zone which 

 immediately underlies the Lonsdaleia beds. These two life zones 

 have been named by Dr. Vaughan the Upper and Lower Dibuno- 

 phyllum zones respectively. To a certain extent, therefore, Morton's 

 division of the Limestone Series of North Wales does correspond 

 with that indicated by the palfeontological succession. 



The Lower Brown Limestone is the lowest member of the series 

 in North Wales, excepting the basement conglomerate, when present, 

 and appears to correspond with the junction of the Upper Seminula 

 and Lower Dibunophyllum beds of the Bristol area. The Middle 

 White Limestones are practically the equivalents of the Lower 

 Dihnnophyllmn zone of Bristol, but probably a portion of the Upper 

 Grey measures belong to this division. Part of the Upper Grey, the 



