OF THE CAKBONIFEROTJS SEHIES. 629 



The thinness of Stage A is accounted for by the supposition of 

 the proximity of land at this period. The Old Red Sandstone is hut 

 sparingly represented. 



(5) CoalbrooJc-Dale Coal-field. 



The observations of Prof. Prestwich, followed more recently by 

 those of Mr. Marcus "W. T. Scott*, Mr. Randall f , and Mr. D. JonesJ, 

 show that, after the Lower and Middle Measures (Stages E and P) 

 had been deposited, a considerable amount of denudation took place 

 along the centre of the field, and that in the hollow thus formed the 

 Upper Measures (Stage G) were deposited. There is therefore a 

 considerable break between Stage G and those below it. 



General Section. 



Thickness — feet. 

 Stage G. Upper Coal-measures. — Mottled clays and greenish grits ; calca- 

 reous breccia with band of compact limestone. Spirorbis carbonarius 300 



Stage F. Coal-measures. — Yellow sandstones, shales, and clays, with ^ 

 ironstones and coal-seams. Fish-remains, Anthracosia 



Stage E §. Gannister Beds (or Penny stone Series). — Sandstones, shales, 



with coal and ironstone (Pennystone- and Orowshaw-bands ||). Cms- r f OUO 

 tacea, Limulus; Mollusca, Nautilus, Orthoceras, Bellerophon, Conu- 

 laria, Spirifer bisulcatics, Productus scabriculus, Aviculopccten, Lin- 

 gula, Bhynchonella j 



Stages D, C, & B are bat poorly represented, and Stage A not 

 at all. This is owing to the proximity to the marginal land and the 

 existence of terrestrial conditions during the early portion of the 

 Carboniferous period %. Having dealt with this subject on former 

 occasions, I do not consider it necessary to enter upon the physical 

 geology of the Carboniferous beds in this district at the present 

 time, further than to observe that in the " Chance Pennystone " 

 (which occurs probably in Stage F, but of which there is some un- 

 certainty) we have an accidental marine band with Productus sca- 

 bricidus, as described by Prof. Prestwich, lying 200 feet above the 

 " Pennystone " bed. 



* Quart. Journ. Geol. Soc. vol. xvii. p. 457. 



t Letters in the Mining Journ. 1871. \ Geol. Mag. vol. viii. p. 200. 



§ The fossils have been enumerated in detail by Prof. Prestwich in Lis ori- 

 ginal paper, Geol. Trans. 2nd ser. vol. v. 1840. Amongst them the genus " Unio " 

 is mentioned ; but there can be little doubt that the bivalves included under this 

 head are really not Uniones ; their association with the marine genera makes 

 it highly improbable. In this view Mr. Baily concurs. 



|| The position of the " Pennystone" ironstone is (according to Mr. D. Jones) 

 just above " the stinking " coal in the lower part of the measures. 



^[ This subject is explained at some length in the Memoir " On the Triassic 

 and Permian Bocks of the Central Counties," Mem. Geol. Surv. p. 109, and in 

 ' The Coal-fields of Great Britain,' 3rd edit. p. 462. It is owing to the same 

 cause that Stages A, B, C, D are absent in South Staffordshire. 



Q.J. G.S. No. 132. 2t 



