1862.] HULL CARBONIFEROUS STRATA, 139 



(6.) Distribution of the " Sedimentaxy^^ Strata of the Oarhoniferous 

 Period. — The isometric lines on the Map will indicate better than 

 any description the development of the grits, sandstones, and shales, 

 from the north towards the south, collected from the most reliable 

 sources. We shall commence with South Staffordshire. 



South Staffordshire. — As is well known, the Lower Carboniferous 

 Bocks, including the Millstone-grit, are absent here, for the same 

 reason that the limestone is absent, namely, that this was a district 

 of land forming a portion of the northern side of the barrier at this 

 period. As the land became submerged during the Coal-period, the 

 sea gradually encroached, and spread the Coal-measures as far south 

 as the Lickey. Notwithstanding the uneven nature of the Silurian 

 sea-bottom on which the Coal-measures were spread, we feel certain 

 that near Dudley there exists the full series of the Coal-formation, 

 as proved by the fossil shells from the ironstones, which are iden- 

 tical with those from the Lower Coal-measures of Coalbrook-Dale 

 and Lancashii'e *. Here the combined thickness of the lower, 

 middle, and upper Coal-measures (as determined by Mr. Jukes) is 

 1810 feet, which becomes considerably expanded north of Wolver- 

 hampton. This northerly expansion is remarkably exemplified in 

 the case of the " thick coal " of Dudley, which, forming at that place 

 one solid seam 10 yards in thickness, becomes split up into nine 

 distinct seams by the intercalation of 420 feet of strata over the 

 northern area of the coal-field. 



In the Warwickshire Coal-Jleld we find the Coal-series attaining, 

 according to Mr. Howell f, a combined thickness of 2950 feet, in 

 addition to which the Millstone-grit and Limestone- shale is 500 feet. 

 The main coal here also presents an example of the thinning of the 

 strata towards the south ; for, at the north side of the field, this 

 seam is spht into five beds by the intervention of 120 feet of strata. 



In the Leicestershire Coal-field, the Coal-series attains a thick- 

 ness of about 2500 feet, while the Millstone-grit and Limestone-shale 

 never exceeds 150 feet. The " main coal '* of Moira offers another 

 illustration in addition to those mentioned above of southerly at- 

 tenuation X' 



The three coal-fields of South Staffordshire, Warwickshire, and 

 Leicestershire, presenting, as they do, a somewhat similar develop- 

 ment of sedimentary strata, lie in the direction of the same series of 

 isometric lines, and are to be compared vn.th the coal-fields of North 

 Staffordshire, Notts, and Derbyshire, immediately to the north of 

 them. 



North Staffordshire. — The development of the strata in this coal- 

 field, as compared with that in any of the three just described, is 



* The following are some of these, determiaed by Mr. Salter : — JDiscina nitida, 

 Producta scabricula, Lingula ellijptica. — Mr. Jukes's Memoir, 2nd edit. p. 27. 

 The presence of these Lower Coal-measures is distinctly stated by Sir R. Mur- 

 chison in his original description of this coal-field (Proc. Geol. Soc. vol. ii. p. 407). 



t " Memoir on the Warwickshire Coal-field," Mem. Geol. Surv. 1859. 



X Memoir by the Author, " On the Greology of Ashby-de-la-Zouch," &c., Mem. 

 Geol. Surv. 1860. 



