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
