OF THE CARBONIFEROUS SERIES. 643 



2. That all the genera, and about 40 species, ascend upwards 



from the Carboniferous Limestone into Stage E. 



3. That only 6 species pass up into Stages F and G. 



4. That about 18 species are peculiar to Stage E. 



5. And that 5 are peculiar to Stages E and G. (Table IV.) 



The number of genera and species in Stage E is probably greater 

 than is here stated ; for it is exclusive of some forms of bivalves from 

 the Pennystone of Coalbrook Dale, figured by Professor Prestwich in 

 his well-known memoir on that coal-field, and classed under the 

 head of the genus Unio*. But it seems more probable that they 

 belong to the marine genus Myacites, or some similar form, as it is 

 in the last degree improbable that shells of a freshwater genus should 

 be associated in the same bed with such forms as Productus, Spirifer, 

 Orthoceras and Nautilus. These bivalves (the Anthracosice of King) 

 are the bane of palaeontologists ; and after a long consideration of 

 their relationship to other fossils in Carboniferous strata, and their 

 ever- varying forms, I have come to the conclusion that either they 

 were capable of inhabiting both lakes and estuaries on the one hand 

 and the open sea on the other, or else that the marine and freshwater 

 forms are so similar in appearance that they ean only be identified 

 by reference to those which may occur along with them in the same 

 bed. Thus, when (as in Coalbrook Dale and Lancashire) we find them 

 associated with undoubted marine forms we can only conclude that 

 they themselves were inhabitants of the sea ; but if they happen to 

 occur unaccompanied by such well-recognized forms, then we may 

 assume that they represent lacustrine or estuarine conditions, the 

 probability being that, had the strata been formed under the sea, 

 marine shells would have been preserved along with those of this 

 genus. 



The most striking fact brought to light in the above census is the 

 essentially marine character of the fauna in Stage E, which is clearly 

 representative of that of the Carboniferous-Limestone period. In 

 this it is distinguished from that of Stages E and G, in which, with 

 the exception of two or three marine bands occurring throughout a 

 series of (in some districts) 5000 to 6000 feet of strata, the beds are 

 destitute of recognized marine forms. If any one will carefully 

 peruse the list of species drawn up by the late Mr. Salter from the 

 Upper and Middle Coal-measures of North Staffordshire t, and com- 

 pare it with that from the Gannister beds of the same coal-field, or of 

 the Pennystone bands of Coalbrook Dale J, he cannot fail to be struck 

 with the change in the character of the fauna — the contrast bearing 

 comparison with that between the faunas of the Portland Oolite and the 

 Purbech beds of the south of England. 



* Trans. Geol. Soc. 2nd ser. vol. v. p. 413, and pi. xxxix. 

 t ' Iron-ores of Great Britain,' part iv. 

 { Prestwich, loc. cit. 



