﻿Vol. 64.] CAEBONIFEROFS LIMESTONE OF THE MIDLAND AEEA. 49 



in the Midland area of Carboniferous Limestone have long been 

 famous for the beautiful specimens which they have yielded. The 

 chief localities of these beds are as follows, taken in order from 

 north to south : — Treak Cliff, west of Castleton ; Park Hill, north 

 of Longnor ; Narrowdale, north of Wetton ; and Thorpe Cloud, at 

 the mouth of Dove Dale. The first-named of these lies at the 

 northern extremity, and the last-named on the southern margin, of 

 the limestone-area : all of them lie within the western part of the 

 area. As a rule, these ' brachiopod-beds ' form part of a thick 

 series of Avhite limestones, the structural relations of which are 

 obscure ; and I am not aware of any instance in which their 

 horizon can be demonstrated by elementary stratigraphical reason- 

 ing. ]!^evertheless, the following evidence appears to me to fix 

 their horizon with some certainty : — 



(i) The ' brachiopod-beds ', which are very rich in species and 

 individuals, contain in abundance, not only certain species of 

 brachiopods which are rare in the normal Lonsdalia-suhzone of the 

 area, but also certain other species which I have not recorded in 

 the normal Lonsdalia-suhzone. But • all those species of 

 brachiopods that a,re found in the normal Lonsdalia- 

 suhzone occur, at one or more localities, in the 

 ' brachiopod-beds'. 



(ii) Although corals are generally rare in the ' brachiopod-beds ', 

 I have found, in these beds at Park Hill, Lithostrotion Martini in 

 abundance, associated with L. Flemingi, OampopJiyllum derhiense, 

 and a large species of Carcinophyllum — an assemblage of corals 

 which would indicate D... 



This evidence indicates, with tolerable certainty, that the 

 ' brachiopod-beds ' form an abnormal phase, which locally replaces 

 the normal Lonsdalia-snhzone. In support of this conclusion, 

 arrived at by considering the faunal assemblage of the beds, we 

 have the following important negative evidence: — The normal 

 Lonsdalia-snhzone is apparently never developed in 

 the immediate neighbourhood of the 'brachiopod-beds'. 



As examples of D.^ brachiopods which attain a greater abundance 

 in the ' brachiopod-beds ', the following may be mentioned : — 

 Dielasma hastata, Mariinia lineaia, M. ovalis, Spirifer duj^Ucicosta, 

 Piignax acuminatus, P. pugnus^ Schizophoria resupinata, Prodiictus 

 longispinus^ Pr. Jimhriatus, and Pr. Martini. 



The ' brachiopod-beds ', which are confined to the western part of 

 the area, indicate the localized prevalence of conditions especially 

 favourable to brachiopod-life, and at the same time, apparently, 

 unfavourable to coral-life. It would appear that these conditions 

 prevailed, to some extent, over an area considerably larger than 

 that actually covered by the ' brachiopod-beds '. Por example, 

 throughout Dove Dale, and in the neighbourhood of Alstonfield 

 and Wetton, that is, in the vicinity of the ' brachiopod-beds ' of 

 Thorpe Cloud and Narrowdale, there appears to be an extensive 



Q. J. G. S. No. 253. E 



