﻿Vol. 6 1.] THE MARINE BEDS IN THE COAL-MEASUKES. 519 



Ifc should be mentioned that the highest and lowest horizons 

 marked by /S^n>r&is-Limestones in the foregoing succession have 

 been traced over practically the whole Coalfield, wherever they have 

 not been removed by denudation. 



VII. Correlation of various Coalfields dy the Use of 

 Marine Horizons. 



The existence of these definite horizons may be of service, not 

 only for correlating the seams in .any one coalfield, but they also 

 offer the best means of correlating one coalfield with another. 

 There can be little doubt that, at the time of their deposition, they 

 formed absolutely the same plane-surface corresponding to sea-level, 

 and in this respect they are of greater value than the freshwater 

 molluscan zones of the Coal-Measures. With reference to the 

 latter, we cannot overestimate the valuable work done by 

 Dr. Wheelton Hind in establishing the order of succession of these 

 mollusca 5 for, after scores of opportunities of testing their merits, 

 their first failure in North Staffordshire has yet to be experienced. 

 In comparison, however, the marine bands are more easily dis- 

 tinguished by practical mining-men, and they mark with greater 

 precision a definite plane of deposit over wide areas of country. 

 Their supreme adaptability, when present, for this purpose was 

 recognized by earlier workers, who unfortunately assumed that 

 marine bands were of rare occurrence, at any rate, in the most 

 valuable portion of the Coal-Measures. The following instances, 

 however, of attempts to correlate different Coalfields by these 

 horizons may be enumerated, namely : — 



(1) The Pecten, Hard, or Gannister Coal of Yorkshire was con- 

 sidered identical with the Bullion Coal of Lancashire by E. W. 

 Binney, 1 and the latter was correlated with the Crabtree Coal of 

 North Staffordshire by Warington Smyth. 2 Prom the fauna and 

 the position of these coals in the sequence, this identification may 

 be considered as established (line C, fig. 3, p. 518). 



(2) The Pennystone of South Staffordshire, in the opinion of 

 J. W. Salter, 3 was the equivalent of the Pennystone of Coalbrook- 

 dale, because of the character of the marine mollusca found in 

 connection with those deposits. It was adopted as a datum-line for 

 the correlation of these coalfields by S. Bowkley 4 and Mr. Daniel 

 Jones 5 ; and this met with the approval of Sir Andrew Ramsay. 6 



(3) The Bay Coal and Priorsfield horizons of North Staffordshire 

 were regarded as correlative of Green's marine bed at Ashton- 

 under-Lyne by the late Robert Etheridge, 7 but with this view I 



1 Trans. Manch. Geol. Soc. vol. iv (1862-64) p. 18. 



2 'The Iron-Ores of Great Britain ' pt. iv, Mem. Geol. Surv. 1862, p. 264. 



3 ' The South Staffordshire Coalfield ' 2nd ed. Mem. Geol. Surv. 1859, p. 27. 



4 Trans. S. Midland Inst. vol. ii, p. 65. 



5 Eep. Roy. Coal-Comm. vol. i (1871) pp. 121-22. 



6 'The South Staffordshire Coalfield' 2nd ed. Mem. Geol. Surv. 1859, p. 58. 



7 ' Geology of the Country round Stockport, Macclesfield, &c.' Mem. Geol. 

 Surv. 1866, p. 94. 



