THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE III. VOL. III. 



No. XII.— DECEMBER, 1886. 



OZRIG-IZCsT^-Xi ARTICLES. 



I. — On the Structure and Organisms of the Lower Lime- 

 stone Shales, Carboniferous Limestone and Upper Lime- 

 stones of the Forest of Dean. 



By Edward Wethered, F.G.S., F.C.S., F.E.M.S. 

 (PLATES XIV. & XV.) 



OIR ANDREW RAMSAY Las described 1 the Coal-fields of the 

 O Forest of Dean, Somersetshire, and Bristol as outliers of the 

 great Coal-fields of South Wales ; there is, however, a marked thinning 

 out in the thickness of the Carboniferous rock in the Forest of Dean 

 as compared with the development of those rocks in South Wales 

 and Bristol. At Clifton, near Bristol, the total thickness of the 

 Carboniferous Limestone is about 2900 feet, at the northern end ot 

 the Forest of Dean Coal-field it is about 600 feet. 



Professor Edward Hull has given 2 a comprehensive idea of the 

 several divisions of the Carboniferous series as represented by typical 

 developments in England. He has divided the series into three 

 divisions, which he has again subdivided into stages marked by 

 letters. The following is Professor Hull's classification, but I have 

 omitted details which do not concern this paper. 



The British Carboniferous Series. Beds in Descending Order. 



Essentially Fresh- j Stage G. Upper Coal-Measures, 

 water and \ 

 Estuarine Beds. I Stage F. Middle Coal-Measures. 



f Stage E. Gannister Beds (Phillips), or Lower Coal-measures. 

 Essentially j Stage D. Millstone-grit Series. Coarse grits, flagstones, and 



Marine. <( shales, with a few thin coal-seams. 



j Stage C. Voredale Series. Shales and grits, passing down- 

 l wards into dark shales and earthy limestones, 



f Stage B. Carboniferous Limestone. Massive Limstone, pass- 

 ing northwards into several beds, with intervening 

 Essentially Marine, -^ shales and grits, 



except Stage A | Stage A. Lower Limestone Shales and Calciferous Sandstone. 

 in Scotland. (_ Dark shales in some places ; grits, conglomerates, 



and red sandstones and shales in the northern 

 district. 



Freshwater Beds i Base * ^PP er 01( * Re ^ Sandstone. Yellow sandstones and 

 I conglomerates. 



In the Forest of Dean stage A is represented resting on a succes- 

 sion of many-coloured calciferous sandy beds and shales, very much 



1 Physical Geology and Geography of Great Britain, fifth edition, pp. 34, 35. 

 Also, Mem. Geol. Survey, vol. i. p. 303. 



2 Quart. Journ. Geol. Soc. vol. xxxiii. p. 615, 1877. 



DECADE III. — VOL. III. — NO. XII. 34 



