﻿522 MR. J. T. ST0BBS ON THE MARINE BEDS [Aug. I905, 



section by fig. 3, has been frequently noted within narrow vertical 

 limits, as in the case of the Warwickshire Coalfield from Tamworth 

 to Bedworth, and of South Staffordshire from Cannock Chase to 

 Dudley — indeed, this is shown quite diagram matically in the Thick 

 Coal itself, while the evidence for it in North Staffordshire has 

 been referred to in this paper (p. 505). The remarkable persistence 

 of seams of coal in comparison with the general thinning-out of 

 the Coal-Measures is worthy of special attention. This collective 

 decrease in thickness is clearly shown in fig. 3 (p. 518), which 

 indicates that the strata between the lines A and B have been most 

 affected by this process. 



VIII. Conclusion. 



These marine beds, which have been described at length in the 

 foregoing pages, are seen to be true zoological zones, indicative of 

 special conditions of deposit: they are persistent, and their contained 

 fossils are abundant aud easily recognized. 



Recent work has shown that they are more numerous in the Coal- 

 Measures than has been hitherto suspected. They are generally to 

 be met with in shaft-sinkings, borings, and cross-measure drifts, if 

 carefully looked for: in such circumstances, however, the discoverer 

 should not rest satisfied until he has personally located the horizon 

 in situ. 



In accounting for the presence of these bands among strata of 

 freshwater origin, it is not necessary to assume vertical oscillation 

 of the ground, for they are sufficiently explained by the occasional 

 recurrence of somewhat excessive subsidences during a general and 

 prolonged movement of depression. Thus, inroads of the sea would 

 be permitted over an extensive area, which we may consider was 

 land-locked. This area embraced the sites of the coalfields of 

 Lancashire, Yorkshire, Derbyshire and Nottinghamshire, Leicester- 

 shire, Warwickshire, North and South Staffordshire, and Shropshire, 

 the measures in which were laid down as continuous deposits ; for 

 the existence of these marine beds renders untenable the theory 

 that each coalfield was a 'separate area of deposition.' 



Furthermore, these recurrences of marine conditions cannot be 

 regarded as more characteristic of the lowest portion of the Coal- 

 Measures, for the richest horizon of all is the Gin-Mine or Penny- 

 stone Bed, which is high up in the ' true Coal-Measures.' 



While the stratigraphy of nearly every formation has been 

 based on palseontological data, it is to be regretted that (in this 

 respect) the Coal-Measures have been comparatively neglected ; but 

 increased attention is now being given to the abundant material at 

 our disposal. 



In conclusion, I desires to express my indebtedness to Messrs. 

 G. A. Mitcheson, F.G.S., and J. Lockett for allowing me to 

 examine in situ, and to collect from, several marine horizons at 

 collieries under their charge; to Mr. E. P. Turner for preparing 



