﻿498 MR. J. T. STOBBS ON THE MARINE BEDS [Aug. I905, 



that horizon and has so thickened as to become a payable 

 deposit. Illustrations of this method and its resulting confusion 

 may be cited from all our large coalfields. In contradistinction, 

 marine beds enable correlation to be made with exactness at specific 

 horizons, and form admirable datum-lines for the practical geologist 

 and the mining-engineer. The general impression, however, as to 

 their utility is that their fossils 



' come froin particular beds, of small number, of very trifling thickness, and in 

 all but one case [presumably the Hard Bed] of very little constancy.'" l 



The number of these beds is much greater than was known at the 

 time when the passage just quoted was written, and, although tbey 

 are very thin, that is of no moment if only they be persistent. 

 Jukes, referring to the marine bed in the upper portion of the 

 Pennystone measures of South Staffordshire, states that it is 

 ' confined to a very small district between Oldbury and Portway.' 2 

 On the contrary, it will be shown later that this particular 

 bed extends over a very wide area, but sufficient has now been 

 said in explanation of the general attitude with respect to the 

 importance of these beds. 



Remembering what marine horizons have done for the Hard Bed 

 of Yorkshire and the Bullion Coal of Lancashire, and what our 

 experience of them in North Staffordshire has taught us, there can 

 be no doubt of their excellence as index-beds. If they be used in 

 the way which I have suggested, 3 namely, by selecting them as main 

 lines for the subdivision of the measures in a coalfield, while the 

 intervening beds are traced by other mollusca, entomostraca, etc., 

 the work of correlation will be placed on a sound and scientific basis, 

 and the aid of geology will be more often sought in the everyday 

 problems which confront those who are engaged in the practical 

 work of winning stratified mineral deposits. 



III. The Marine Horizons in the North-Staffordshire 

 Coalfields. 



The known horizons at which marine fossils occur in the Coal- 

 Measures of North Staffordshire are : — 



1. Roof of the Bay or Lady Coal. 



2. The Priorsfield Ironstone-Measures. 



3. The Speedwell and Nettlebank Bed. "1 -r, , ,, rp . , n . , r ~ , 



4. The Florence Colliery-Band. J Below the Twist or Gh^-Mine Coal. 



5. Above the Moss Coal. 



6. Roof of the Single Two-Feet Coal or Moss Cannel. 



7. Above the Seven-Feet Banbury Coal. 



8. The Weston-Sprink Bed. 



9. Below the Four-Feet Coal of Cheadle. 



10. The Knypersley Marine Band. 



11. Near the Crabtree Coal (three horizons). 



1 L. C. Miall, in ' Coal : its History & Uses ' 1878, p. 153. 



2 < The South Staffordshire Coalfield ' Mem. Geol. Surv. 2nd ed. (1859) p. 58. 



3 Trans. Inst. Min. Eng. vol. xxii (1901-1903) p. 234. 



