﻿496 MR. J. T. STOBBS ON THE MAEINE BEDS [Allg. 1905, 



During that period marine conditions were not only more frequent 

 than is generally supposed ; but, what is of the highest importance 

 in stratigraphy, they are proved by the persistence of the beds to 

 have been practically co-extensive with the Coalfield. 



II. The Significance of Marine Horizons in the 

 Coal- Measures. 



The occurrence of marine bands in the Coal-Measures has hitherto 

 been used for the purposes of (a) theoretical subdivision or grouping 

 (as distinct from mapping) and (b) identification of coal-seams. 



(a) Subdivision of the Coal-Measures. 



By the recognition on the part of the earlier workers (notably 

 E.W.Binney and John Phillips) of the marine fossils in beds overlying 

 the Bullion Coal of Lancashire and the Hard Bed of Yorkshire ; and 

 later, thanks to the work of J. W. Salter in South Wales, and to the 

 influence of Warington Smyth, and more especially of Prof. E. Hull, 

 the lower portion of the Coal-Measures has come to be regarded 

 as being essentially marine in character, and on that account dis- 

 tinguishable from the overlying or so-called ' Middle ' Series. 

 Indeed, the well-known grouping of the Coal-Measures into Lower, 

 Middle, and Upper Series was chiefly based on the respectively 

 marine, estuarine, or freshwater character of their mollusca. 



This classification which, confessedly, was mainly adopted for 

 convenience of description, 1 has, through lack of definition, come 

 to be used in the most irregular way by various writers on Coal- 

 Measure geology, and few practical results are due to its adoption. 

 Its weakness is at once revealed when we desire to trace the sub- 

 divisions from one coalfield to another, for then it is discovered that 

 they are incapable of being mapped. Hence, it is of little service 

 to the mining engineer, who, after all, has the strongest claim to 

 utilize the results of the scientific investigation of the Coal-Measures. 

 The confusion that may arise from its application is nowhere more 

 signally shown than by the inclusion of the Pennystone of Coal- 

 brookdale and of South Staffordshire in the Lower or Grannister Series, 

 because of the marine character of the fossils found at that horizon. 2 

 This error was first definitely pointed out by Mr. II. Kidston in 

 1 893, as a result of his study of the fossil flora of the Coal-Measures 

 of South Staffordshire. 3 



A reference to fig. 1 (p. 499) will show that recurrences of marine 

 conditions obtained practically throughout the ' true Coal-Measure ' 

 period, some of which were marked by an exceedingly-rich fauna. 

 These recurrences may be shown to serve a more useful purpose 

 than even that of classification, namely, the recognition of 

 individual horizons over wide areas. 



1 E. Hull, ' The Geology of the Country around Prescot, Lancashire ' Mem. 

 Geol. Surv. 3rd ed. (1882) p. 2. 



2 E. Hull, Quart. Journ. Geol. Soc. vol. sxxiii (1877) pp. 629-30. 



3 Proc. Eoy. Phys. Soc. Edin. vol. xii (1892-94) p. 187. 



