}F. D. Lang — Carboinferous Zones marked by Corals. 435 



Pyripora and for which Canu ^ has proposed the genus Pyriporella. 

 For my own part I find it so veiy difficult to draw any line between 

 the two that I do not think it safe to treat them as generically distinct 

 in the Chalk. 



EXPLANATION OP PLATE XXII. 



(All figures x 12 diams.) 



Fig. 1. Memhranipora pyrigera. Subzone of A. quadratics (I. of W.). 



,,2. ,, ,, ,, Portsdown, Hants. 



,, 3. ,, ,, 0. pilula, West Meon, H&nts. 



,, 4. ,, Zone of M. cor-anguinum, Gravesend. 



,,5. ,, ,, Majsupites, West listed, Hunts. 



,, 6. Membranipora tenebrosa. SubzoneofJ[. g^a^raizts, Shawford, Hants. 



,,7. ,, ,, E. scutatus, var. depressus, 



Newhaven. 



,,8. ,, ,, ,, Eopley, Hants. 



9. Membranipora pellicula. ,, J.. 2Ma<i?-a^7ts, Portsdown, Hants. 



10. 

 11. 

 12. 



13. Membranipora Wither si. 



Hensting, Hants. 

 Portsdown, Hants. 

 Hensting, Hants. 

 Hensting, Hants. 



II. — Caebonipeeous Zones Illtjsxkatkd by Corals : an Exhibit at 



THE jS^atural History Museum. 



By W. D. Lang, M.A., F.G.S. 



IIS" view of the attention lately devoted by geological workers to the 

 British Lower Carboniferous rocks and their fossils, an exhibit 

 has been arranged in the Department of Geology at the J^atural 

 History Museum to illustrate the occurrence in the field of Corals in 

 reference to the division of the Lower Carboniferous rocks into zones. 



As is well known. Dr. A. Vaughan,- the pioneer of modern Lower 

 Carboniferous stratigraphy, divided these rocks into five groups or 

 zones, each named after the genus of Coral or Brachiopod dominant 

 during the time that the zone bearing its name was deposited. 

 A zone is thus seen to be all the material deposited during a given 

 time. The time during which a zone was deposited has been termed 

 by Buckraan a 'hemera',^ a term which has not come into common 

 use, probably because it is as easy and more natural to say, for 

 instance, 'in Caninia tiraQ'' than ' in the hemera of Caninia\ It is 

 true that the former might mean 'during the whole period during 

 which Caninia existed', while 'hemera', as defined, is used for the 

 time during which an organism was dominant ; but in practice such 

 confusion rarely occurs, and, until it is felt, the term 'hemera' is not 

 likely to be generally used. Vaughan further divided his Carboniferous 



■^ Iconographie des Bry. Foss. de V Argentine, pt. ii, p. 234. 



^ Vaughan, " Palseontological Sequence in the Carboniferous Limestone of 

 the Bristol Area " : Quart. Journ. Geol. Soc, vol. Ixi, pp. 181-307, 1905. 



^ Buckman, " The Bajocian of the Sherborne District," Quart. Journ. Geol. 

 Soc, vol. xlix, p. 481, 1893. For a further explanation of the term, see the 

 lucid and amusing article by Buckman, "The term Hemera," Geol. Mag., 

 Dec. IV, Vol. IX, pp. 554-7, 1902, followed by correspondence in Geol. Mag., 

 Dec. IV, Vol. X, 1903. The zone also is discussed in these papers. 



