64 MR ROBERT KIDSTON ON THE 



1. Upper Measures, consisting chiefly of red " marls" or clays, with a few thin bands 



of coal, and some grey binds and sandstones in the upper part, containing an 

 ironstone called the Top red mine, 18 inches thick at Silverdale. 

 Thickness very uncertain ; probably about 1000 feet. 



2. Pottery Coals and Ironstone Measures, containing eight to thirteen seams of 



coal of above 2 feet thick, mostly inferior, and suitable only to pottery purposes, 

 and ten or twelve workable measures of ironstone. 



Thickness 1000 to 1420 feet down to Ash or Rowhurst coal. 



3. Lower Thick Measures, containing the chief furnace coals, from the Ash to the 



Winpenny inclusive, seventeen or eighteen seams above 2 feet thick. Ironstone 

 scarce, or almost absent. 



Thickness 1400 to 2400 feet. 



4. Lowest Measures, including thin seams generally known as the Wetley Moor, 



Biddulph, or " Wild " coals, from two to four in number. 

 Thickness about 800 feet. 

 This would give a total, down to the upper bed of Millstone Grit, variable in different 

 parts of the field, of from 4200 to 5620 feet. # 



Professor Hull t gives the following divisions : — 



Permian Rocks. — Red and purple sandstones, marls, and cornstones (with plants); 

 strata slightly unconformable to the Coal Measures. 

 Greatest thickness 600 feet. 

 Coal Measures. — I. Upper. — Brown sandstones, greenish conglomerate (like the vol- 

 canicashes of South Staffordshire), with thick beds of red and purple mottled clays ; 

 thin coals and a bed of Spirorbis limestone at Fenton, Longton, Shelton, &c. 

 Greatest thickness 1000 feet. 

 II. Middle. — Sandstone, shales, with ironstone, and about forty coal seams. 



Greatest thickness 4000 feet. 

 III. Lower. — Black shales and flags, with Wetley Moor thin coals, and red iron- 

 stone of the Churnet Valley (Goniatites, Aviculopecten). 

 Greatest thickness 1000 feet. 

 Millstone Grit. — Coarse grits, shales, and flags. 



Greatest thickness 1000 feet. 

 Yoredale Rocks. — Black shales, &c, with marine fossils. 



Greatest thickness 3100 feet. 

 Carboniferous Limestone. — 4000 to 5000 feet. 



In the excellent memoir published by Mr John Ward, j F.G.S. ("The Geological 



*Loc. cit., ].. 258. 



t Tlie Coal Fields of Great Britain, 4th ed. (1881), p. 183. 



% "The Geological Features of the North Staffordshire Coal Fields; their Organic Remains, their Range and 

 Distribution ; with a Catalogue of the Fossils of the Carboniferous System of North Staffordshire," Trans. North 

 Staffordshire Institute of Mining and Mechanical Engineers, vol. x. pp. 1-189, with 9 plates, 1890. 



