Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/751

Rh 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. t ' Iron-ores of Great Britain,' part iv. { Prestwich, loc. cit.
 * Trans. Geol. Soc. 2nd ser. vol. v. p. 413, and pi. xxxix.