256 REPORTS ON THE STATE OF SCIENCE, ETC. 
Lower Carboniferous Zonal Nomenclature. — Report of 
Commuttee (Professor P. F. Kenpatt, Chairman; Mr. R. G. 
S. Hupson, Secretary; Mr. W. 8. Bisat, Mr. R. G. Carrutuers, 
Mr. E. E. L. Drxon, Professor E. J. Garwoop, Miss E. GoopyeEar, 
Mr. S. E. Hotirneworts, Mr. J. W. Jackson, Dr. G. W. LEr, Miss 
H. M. Murr-Woop, Mr. D. Parxinson, Mr. J. Prineie, Professor 
S. H. Reynotps, Principal T. F. Srsty, Dr. Bernarp Suirs, Dr. 
Sranuey Smits, Mr. L. Smytu, Mr. L. H. Tonks, Mr. F. M. Trotter, 
Mr. W. B. Wricut) appointed to attempt to obtain agreement regarding 
the significance to be attached to Zonal Terms used in connexion with 
the Lower Carboniferous. (Drawn up by the Secretary.) 
THe work of the above Committee has been chiefly concerned with the upper beds 
of the Lower Carboniferous, and more especially with the definition and limitation 
of the Dibunophyllum zone. There is general agreement among the members of the 
Committee as to the need for a definite upper limit to the Dibunophyllum zone and 
also for a time-division of the Lower Carboniferous for those beds above the Viséan,* 
and it is chiefly with these aspects that this report deals. 
The Upper Limit of the Zone D. 
The zonal divisions of the Lower Carboniferous were based on the faunal succession 
of the beds exposed in the Avon Gorge and were originally defined by the dominance 
of some particular genus or species. They are now regarded as characterised by 
coral-brachiopod faunal assemblages, which are usually referred to by an index letter 
such as Z, C, S, or D. In addition to the index letter, the zone is often distinguished 
by an index fossil. In practically all cases this index fossil is not limited to that 
particular zone, but is found below and often above. It should, however, attain its 
maximum development at that horizon. The definition of the zone is based on the 
occurrence of a number of fossil forms, generally corals and brachiopods, which 
attain their maximum at that particular horizon. The horizontal distribution of 
these forms often leads to the absence of one or two of them in some particular area— 
in some cases the form chosen as an index fossil is absent—but in general the sum of 
the forms which have their maximum development‘at that level will determine its 
zonal horizon. 
The upper zone D was originally defined as co-extensive with the occurrence of 
Dibunophyllum. No definite upper limit was suggested for this zone, as the limestone 
containing the coral-brachiopod fauna is replaced at Bristol by a sandstone facies 
containing practically no fossils. The persistence elsewhere, and more particularly 
in the North of England, of the coral-brachiopod fauna to higher zones than in the 
S.W. Province has led the upward:extension of the zone D far beyond the original 
zone of Vaughan and has been the cause of much confusion. It is therefore proposed 
that the zone D should be limited and defined by a faunal assemblage, as are most 
of the lower zones, and not by the occurrence of Dibunophyllum, and that this faunal 
assemblage should be approximately that contained in those beds originally defined 
as D in the 8.W. Province.? 
This limitation of the zone D is facilitated by the fact that where, as in the North 
of England, the beds above D contain a normal limestone fauna, that fauna is charac- 
terised by the maximum development of genera and species either unknown or rare 
in the D zone below. This fauna has been described from various districts in the 
North of England.* It contains as one of its distinguishing elements the maximum 
1 Sub-report I., E. E. L. D. 
2 Vaughan, A., ‘The Palzontological Sequence in the Carboniferous Limestone 
of the Bristol Area,’ Q.J.G.S., vol. lxi., 1905, pp. 197-199, and later papers. 
3 Garwood, E. J., and Goodyear, E., ‘The Lower Carboniferous Succession in 
the Settle District,’ Q.J.G.S., vol. lxxx., 1924, pp. 184-273. 
3 Edmunds, C., ‘The Carboniferous Limestone Series of West Cumberland,’ 
Geol. Mag., 1922, pp. 74-83 and 117-131. 
3? Hudson, R. G.8., ‘ Faunal Horizons in the Lower Carboniferous of N.W. York- 
shire,’ Geol. Mag., 1925, pp. 181-186. 
