210 Br. Wheelton Hind — The Toredale Series. 



somewhat approaching that which obtained in the middle of the 

 Carboniferous Series ; but here, as at Coalbrookdale, it is only the 

 Brachiopoda of the lower beds which are present, and this family 

 appears to have comprised the hardiest and most able of all forms of 

 life to assimilate themselves to altered conditions. 



These differences are due to bathymetric conditions, and the over- 

 lapping of the faunas to a return to conditions suitable for each 

 group of organisms. 



In the North Midlands the fossil flora is abundantly present, with 

 the first fauna : present only in the sense of occurring in beds 

 intercalated with the raoUuscan-bearing beds, except in the roof of 

 the Bullion Coal, where there is drifted woody material in abundance. 

 The flora is practically absent in the beds containing the lower 

 fauna. 



In Northumberland and Scotland the peculiar fauna characteristic 

 of those shales which occur below the Millstone Grit in South 

 Yorkshire is absent, although one or two species are quoted, but no 

 reliance can be placed on the nomenclature of the Goniatites at 

 present. 



Aviculopecten papyraceiis, so characteristic of these beds, is quoted 

 by John Young (" the Carb. Foss. of the West of Scotland," p. 47) 

 as rare, and it is noted by the Palaeontologists of the Survey as 

 occurring in shales some distance above the Ell coal (Wishaw 

 district), and in the shale above the Calderwood cement-stone 

 (E. Kilbride district: Mem. Geol. Surv. Scotland, Explanation of 

 Sheet 23) is very much lower down, but in neither case do the 

 other members of the fauna occur. This species is said to occur 

 in the Carboniferous Slate of Clonakilty, co. Cork (Bailey), and in 

 Carboniferous Limestone near Harrogate and Bolland (Phillips) ; 

 but there is the gravest doubt in my mind as to the correctness 

 of this specific determination, for according to my own observations 

 this species is never found in the Carboniferous Limestone, but is 

 characteristic of the Lower Coal-measures and Millstone grits and 

 the shales below them. 



I have shown (Pal. Soc, vol. xlix, Monograph on Carhonicola, 

 Anthracomya, and Naiadites, pp. 82-145) that the genera Carhonicola 

 and Naiadites both occur low down in the Calciferous Sandstone Series 

 of Fifeshire, but that the species are different to those occurring in 

 the Coal-measures ; and I have pointed out that, similar conditions of 

 deposit being suitable, the same genus returned at several horizons. 

 In the slates of South Yorkshire not only do the same genera occur 

 as obtain in the Coal-measures, but a very large number of the same 

 species are common to the two horizons. These shells must have 

 survived in some outside area, during the deposition of the 

 intervening beds in which they are absent, to return when 

 conditions became again suitable for their migration and survival. 

 This theory demands, not that the beds of one deposit are continuous 

 with other beds at two and more widely separated horizons, but 

 that both beds, containing a practically identical fauna, were the 

 result of one successively continuous series of events. This 



