86 Reports and Proceedings — Geological Society of London. 



the other. Thus, twin earthquakes are due to a single generative- 

 effort ; and they are caused, it is urged, by the growth of a crust- 

 fold cut transversely by a fault. If the movement is such that the 

 anticline of the fold is made more anticlinal and the syncline more 

 synclinal, the middle limb will remain practically undisturbed ; so 

 that, by a single effort, there will be two impulses in detached foci 

 situated at diffei'ent depths. The average distance between successive 

 anticlines and synclines in France along several lines lies between 

 9 and 12 miles, which agrees closely with the average distance 

 between the epicentres of twin earthquakes. 



II.— January 4th, 1905.— J. E. Marr, Sc.D., F.R.S., President, in 

 the Chair. The following communications were read : — 



1. "The Marine Beds in the Coal-measures of North Stafford- 

 shire." By John T. Stobbs, Esq., F.G.S. With Notes on their 

 Paleontology by Wheelton Hind, M.D., B.S., F.R.C.S., F.G.S. 



Owing to the disposition of the rocks and other causes, the 

 stratigraphical position of the marine beds can be located with 

 exactness in situ, and a large quantity of material can be obtained 

 for examination. The horizons can be utilized for the identification 

 of coal-seams and for the subdivision of the Coal-measures, as they 

 are remarkably persistent, and can be frequently traced not only 

 over the North Staffordshire field but in adjacent coalfields. The 

 known horizons at which marine fossils have been obtained are the 

 following, given in descending order : — 



11. The roof of the Bay or Lady Coal. 

 10. The Priorsfield Ironstone Measures. 



9. The Speedwell and Nettlebauk Bed. \ Below the Twist or 



8. The Florence Colliery Band. ] Gin Mine Coal. 



7. Above the Moss Coal. 



6. The roof of the Moss Cannel or Single 2 -foot Coal. 



5. Above the 7-foot Banbury Coal. 



4. Beneath the 4-foot Coal of Cheadle. 



3. The KnjiDorsley Band. 



2. Near the Crabtree Coal (three horizons). 

 And also 1. The Weston- Sprink Bed. 

 A map of the distribution of these beds is given, each one is 

 described in detail, and a list of fossils found from the various 

 exposures is tabulated. The Speedwell and Nettlebank Bed appears 

 to be the most important marine bed in the coalfield ; it is remark- 

 ably rich in species and individuals, and occurs in the upper portion 

 of the true Coal-measures. Further, it proves the identity of the 

 Twist coal of the Norton area with the Gin Mine of Longton. 

 Lithologically, the marine beds are undistinguishable from the 

 beds with which they are interstratified ; but the fossils are 

 usually in a good state of preservation and not confined to one 

 particular bedding-plane ; the individuals are likewise numerous. 

 The marine mollusca are, however, sharply separated from the 

 fresh-water forms, and no intermingling occurs. It is remarkable 

 that several of the marine shales immediately succeed the coal- 

 seams. A detailed table of the beds in North Staffordshire is 



