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MK. E. KIDSTON ON THE DIVISIONS OF THE [May I905, 



to which I applied the name of Transition Series have proved to 

 be a most important group, not only in the Potteries Coalfield, but 

 iu other areas of the Midland Counties of England. 



In 1895, the Geological Survey commenced a re-survey of the 

 Potteries Coalfield, and in 1902 the Memoir of ' The Geology of 

 the Country around Stoke-upon-Trent ' was published. 1 Here, for the 

 first time, 2 Mr. Walcot Gibson gives a full account of the rocks 

 lying above the Middle Coal-Measures of the Potteries Coalfield, 

 and accepts as their base the Bassey-Mine Ironstone. This brings 

 down the dividing-line between the Middle Coal-Measures and the 

 overlying strata 36 feet; but Mr. Gibson considers the Bassey- 

 Mine Ironstone a more convenient line of division than the 

 Spir or b is- Limestone previously accepted, and this ' line ' has 

 now been adopted. 



The following are the subdivisions of the rocks overlying the 

 Middle Coal-Measures of North Staffordshire, as tabulated by 

 Mr. Walcot Gibson (Mem. Geol. Surv. jam tit. p. 37) : — 



Name of 

 Subdivision. 



Characters. 



Thickness. 



Keele Group. 



Red and purple sandstones and marls. Oc- 

 casional seams of coal. Thin blaclc and 

 grey limestones, and subordinate bands of 

 grey sandstone and shale. Base, entomo- 

 stracan shale. 



Over 700 feet at 

 Keele Park. 

 Summit nowhere 

 visible, unless at 

 Moddershall. 



Newcastle- 



undee-Lyme 



Group. 



Grey sandstones and shales, with four thin 

 seams of coal. Base, entomostracan lime- 

 stone. 



300 feet. 



Etruria- 

 Marl Group. 



Chiefly mottled red and purple marls and 

 clays. Thin beds of green grit very charac- 

 teristic. Limestone-bands near the summit 

 and base. Lenticular mass of grey sand- 

 stone overlying a laminated ironstone and 

 thin coal 150 feet above the base (Chester- 

 ton only). Base, often a greenish fine- 

 grained sandstone. 



800 to 1100 feet. 



Blackband 

 Group. 



Chiefly sandstones, marls, and clays. Some 

 lenticular bands of grey grit and slightly- 

 mottled marls. Numerous thin seams of 

 coal and Blackband ironstones. Thin 

 bands of limestone throughout the series, 

 one of which is constant at 36 to 40 feet 

 above the Bassey-Mine Coal. 



300 to 450 feet. 



Since my last notes on the fossil flora of the Potteries Coalfield 

 were published in 1897, the fossil plants from this group have been 



1 Mem. Geol. Suvv. 1902, ' The Geology of the Country around Stoke-upon- 

 Trent. (Explanation to Sheet 123.) ' By Walcot Gibson & C. B. Wedd ; with 

 Notes by George Barrow. 



2 A preliminary account of these rocks was given by Mr. Gibson, in his 

 paper, ' On the Character of the Upper Coal-Measures of North Staffordshire, 

 Denbighshire, South Staffordshire, & Nottinghamshire ; & their Relation to 

 the Productive Series' Quart. Journ. Geol. Soc. vol. lvii (1901) p. 251. 



