﻿Vol. 64.] CAEBONIFBROUS LIMESTONE OF THE MIDLAND AHEA. 53 



Chonetes cf. Jiardrensis occurs commonly in the shales of this 

 subzone. 



All the other brachiopods recorded in the fauna! list are rare. 



Other groups : 



Ostracods occur commonly in the shales and limestones in the 

 upper beds of the subzone. 



Polyzoa,^ which include species of Polyj^ora, Penniretepora, 

 and Rhabdomeson^ are highly abundant locally. 



The lamellibranchs and cephalopods, occurring in the passage- 

 beds included in this subzone, and representing the first ap- 

 pearance of the fauna of the Pendleside Series, are recorded in 

 the subsequent descriptions of certain sections of the subzone 

 (pp. 57-63). 



lY. Description of certain Sections of the Z^ojv^amz/^-Scjbzone : 

 Variation of the Litholoohcal Facies. 



Without attempting a detailed account of the very numerous 

 good exposures of the Lonsdalia-B^xhzonQ which are to be found 

 within the area, I may briefly describe certain of the more 

 extensive sections of that subzone. This description will serve 

 to exemplify the changes in the lithological facies of the subzone 

 which occur within the area. 



(A) Sections in the Eastern Part of the Area. 

 (i) The typical section. 



In the typical section, already described (pp. 37-42), D^ is seen 

 only in the eastern limb of the anticline, being faulted out on the 

 western side. The subzone here exhibits a remarkable lithological 

 facies. A series of cherty limestones, about 450 feet thick, 

 here forms the lower part of D^ and the whole of D^, the latter 

 subzone comprising not much less than 400 feet of beds. This 

 cherty series consists very largely of dark-grey or black limestones, 

 as a rule thinly bedded, and often compact in texture, with black 

 shaly partings frequently developed. Beds of lighter colour occur, 

 however, and iu the lower part of D,, a conspicuous development 

 of massive white limestones forms a break in the cherty series. 

 The chert is abundantly developed, and, in addition to forming 

 nodular and lenticular masses of no great size, frequently occurs 

 in large ramifying masses, and in well-defined bands of considerable 

 horizontal extent. 



This section shows a much greater development of the cherty 

 series than is found elsewhere in the eastern part of the area, as 

 the following details of certain sections will show. 



^ Mr. W. D. Lang, M.A., F.G.S., very kindly determined my specimens of 

 Polvzoa. 



