253 



FOSSIL MOLLUSCAN ZONES IN THE CARBONIFEROUS 

 ROCKS OF THE MIDLANDS. 



PART I. 



(plates XXI., XXII,) 



WHRELTON HIND, M.D., B.S., F.R.C.S., F.G.S. 



It has long- been a reflection on the students of the g-eology of 

 the Carboniferous Rocks of the North Midlands of England that 

 they had not worked out any life zones in these rocks. Of late 

 years, however, much has been done, and to-day I hope I may 

 say that at least the broad lines of Zonal division of the whole 

 Carboniferous series has been laid down. Following up the 

 idea which led me to show, in a graphic manner, the distribution 

 of the mollusca of the coal measures, in my Monograph on 

 (\irbojiicoln, A^aidditcs, and Anfliraconiya^ I, in conjimction with 

 my friend Mr. Stobbs, published a Fossil Chart for the North 

 Staffordshire Coal Field. Since that time we have made many 

 observations on the distribution of these shells in other coal 

 fields, and we believe that this succession of fossils is fairly 

 constant in all of them. Two distinct faunas, one characterised 

 by the genera Cai'bonicola, Anihracomya^ and Naiadites, and the 

 other by Pterinopccfen papyroceus and various small cephalopods, 

 occur in the coal measures, but never intermingle. We regard 

 the species of the former as exact zonal indices, and make use 

 of marine bands occurring in a definite relation between any two 

 of the zones as aftording- detailed evidence of definite horizons. 



That the genera Carbonicola, Anthracotnya, and Naiadites 

 denote fresh water, or possibly slightly brackish water condi- 

 tions, we assume from the eroded conditions of the umbones due 

 to solution of the CaCO.^ of the shell in water charged with 

 Co.j. This view is strengthened by the negative fact that no 

 known marine species occur with them. Lastly, the Carbonicola 

 and Anthracomya belong to the Unionidoe^ which have a fresh 

 water habitus now. 



In the North Staffordshire coal field we find that in the upper- 

 most beds, 'the Keele series,' no mollusca occur. These beds 

 are probably the equivalent of the Radstock series of the Bristol 

 Coal Field, judging from the plants which are found in them. 

 The shell which is found in the lower part of the Newcastle 

 series of North Staffordshire is very small, and has not a wide 

 vertical range, but it is fairly common in certain calcareous 

 beds in the series. This shell is Anthracoinya calcifera [Quar. 

 Jour. Gcol. Soc, Vol. LV., p. 365, pi. xxv., figs. 14-20), and 



3906 August I. 



