258 REPORTS ON THE STATE OF SCIENCE, ETC. 
Orionastrea phillipsi zone... ... O Orionastrea phillipsi 
D; Lonsdaleia duplicata duplicata 
D, Lonsdaleia floriformis floriformis 
D, Dibunophyllum bourtonense and Cyatho- 
Dibunophyllum zone ... 540 ean D 
| phyllum murchisoni 
Major Divisions of the Lower Carboniferous. 
The general equivalence of the Belgian Lower Carboniferous with that of the 
§.W. Province has led to the adoption of Tournaisian and Viséan as time-names for 
the major divisions of the British Lower Carboniferous. The upper limit of the 
Viséan is discussed later, but it approximates to that chosen above as the upper limit 
of the zone D. The Lower Carboniferous of the Bristol district can therefore be 
included in Viséan and Tournaisian, but that of the North of England and the Midland 
Province contains a series of beds with a coral-brachiopod fauna higher in horizon 
than the Viséan of Belgium. The greater part of the Yoredale series and the neigh- 
bouring successions of Cumberland and Durham are of this age. The extension of 
Viséan to include these beds is not advisable, as they may be equivalent to part 
of the Namurian, the next stage in the Belgian succession. The Committee therefore 
recommends the creation of a separate stage approximately equivalent in time-value 
to Viséan and Tournaisian, to include these higher beds. The Committee bases its 
recommendations on the following reasons :— 
(1) The occurrence in the North of England of a series of beds containing a lime- 
stone fauna higher in horizon than the Viséan as developed at Visé. 
(2) The progressive distinction between the limestone fauna of the Yoredalian 
and Viséan. 
(3) The general widespread lithological change which occurs approximately at 
the end of the Viséan (s. str.) in various parts of England. 
This higher subdivision of the Lower Carboniferous has already been suggested, 
and the name ‘ Yoredalian’ was proposed for it by Johns,’ and this was tentatively 
adopted by Vaughan.® Phillips® in 1836 divided on lithological grounds the Lower 
Carboniferous of North Yorkshire into a lower series, which he called the Great Scar 
Limestone, and an upper series which he called the Yoredale series. The approxima- 
tion of the Yoredale series to the proposed upper major division of the Lower 
Carboniferous was the reason for the adoption of the name Yoredalian by Johns and 
Vaughan. This term is eminently suitable for the following reasons: The first 
separation of those higher beds from the rest of the Lower Carboniferous was by 
Phillips, who called them the Yoredale series; the fauna of the Yoredale series is 
mainly a coral-brachiopod fauna, and thus the faunal assemblage defining the Yore- 
dalian is of the same phase as that defining Viséan and Tournaisian ; the series is a 
- complete one conformable with the Viséan ; and finally, beds containing assemblages 
both of Zaphrentid-phase and Goniatite-phase occur in the Yoredales and should 
eventually allow of correlation with the other phasal successions of the Lower 
Carboniferous. The term Yoredalian is therefore adopted and the type succession 
is taken as the Yoredale series of North-West Yorkshire.* 
The Upper Limit of the Visean and the Base of the Yoredalian. 
The upper beds, V.. of the Belgian Survey, of the Viséan at Visé are not suitable 
for direct comparison with the North-West Province succession, because the fauna is a 
knoll fauna of the same type as the brachiopod beds of Derbyshire and the Knolls of 
Craven. At Anhée, however, in the syncline of Namur, the same horizon is repre- 
sented by a coral-brachiopod fauna which compares very well with the fauna of 
? Johns, C., ‘On the Classification of the Lower Carboniferous Rocks,’ Geol. Mag., 
1910, pp. 562-564. 
8 Vaughan, A., ‘Correlation of Dinantian and Avonian,’ Q.J.G.S., vol. Ixxi., 
1915, pp. 1-52. 
ne Phillips, J., ‘Tlustrations of the Geology of Yorkshire.’ Part II. London, 
6. 
* It should be noted that the term Yoredalian does not.imply Yoredale conditions 
of sedimentation ; that is, a lithological succession of shale, sandstone, and limestone 
alternation. 
