ON LOWER CARBONIFEROUS ZONAL NOMENCLATURE, 259 
the D, sub-zone (as defined above). Above the Viséan in both areas is the Namurian, 
the lower half of which is the Assise de Chokier (H,,, zone or G. diadema) with 
G. spirale ? at its base. At Visé, as elsewhere in the Liége district, H,, rests possibly 
unconformably on the Viséan, while at Anhée the succession is apparently an 
unbroken one. Delépine?® considers the lower part of H,, equivalent to the Yoredales 
and conformable with the limestone below, but does not discuss the advisability of 
its inclusion in the Viséan. If this present limitation of the Viséan, as in Belgium, 
is transferred to the English succession, the top of D, becomes the top of the Viséan 
and therefore the base of the Yoredalian. 
It has not, however, been possible to obtain agreement among members of the 
Committee as to the exact horizon of the base of the Yoredalian. There are three 
proposals :— 
(1) The base of the Yoredalian should be placed at the top of the Dibunophyllum 
zone. No definition of the Viséan is then needed. 
(2) The base of the Yoredalian should be placed at the top of D, and D, should 
be included in the Yoredalian. The division then corresponds to the division by 
Phillips between the Yoredale series and the Great Scar series, and moreover the base 
of the Yoredalian then corresponds to the base of the zone G. crenistria (the zone P 
as defined by Bisat) and in many areas corresponds with the oncoming of the Culm 
facies. 
(3) The base of the Yoredalian should be at the base of D,. The division is then 
marked by the Girvanella band, first recognised by Garwood and since mapped over 
the greater part of the North of England. 
The Committee recommends that for the time being the base of the Yoredalian 
should be taken as the top of D,. The application of this zonal scheme to the success- 
ion in various areas in England is shown in Tables I and II. 
The Subdivision and Upper Limit of Yoredalian. 
The establishment of Yoredalian is the result of work on the higher beds of the 
Lower Carboniferous of the North of England and depends on the persistence of the 
standard limestone fauna in these beds. The subdivision and definition of an upper 
limit of Yoredalian depends, therefore, on the faunal grouping of this upper series. 
Pending further work now in progress, no attempt has been made to show this sub- 
division of the Yoredalian beyond the definition of the zone O at its base. The beds, 
such as the Undersett and the Main Limestone, have a coral-brachiopod fauna which 
is a continuation of that of the Lower Yoredalian and should be included in the 
Yoredalian. The further extension of Yoredalian to include such beds as that of the 
Fell Top Limestone characterised by Avulina rotiformis or the separation of these 
beds as a further division of the Carboniferous is left for further consideration. 
Phasal Faunas. 
The Lower Carboniferous is often of such a facies that the coral-brachiopod fauna 
(standard limestone fauna) is replaced by a faunal phase characterised either by 
goniatites and lamellibranchs (Culm fauna) or by a Zaphrentid or reef phase. The 
standard limestone fauna may be replaced by Culm phase or the reef phase only in 
certain beds, as at Loughshinny and in the Midland Province, or it may be completely 
replaced, as in the Lower Bolland shales at Pendle. The zonal scheme outlined 
above is readily applicable only where there is a coral-brachiopod faunal succession. 
The occurrence of the Culm phase necessitates, for the time being, two parallel 
and contemporaneous sets of zones, the one set based on the standard limestone 
fauna and the other, as outlined by Bisat,!! on the goniatites. It remains to be seen 
how the limits between the goniatite zones compare with those between the standard 
limestone zones. , 
10 Delépine, G., ‘Les formations supérieures du Calcaire carbonifére de Visé,’ 
Ann. de la Soc. sci. de Bruxelles, 1921, p. 114. 
1 Bisat, W.S., ‘The Carboniferous Goniatites of the North of England and their 
Zones.’ Proc. Y.G.S., vol. xx., pt. I. 1924. 
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