BRITISH AVONIAN CONODONT FAUNAS 17 
In this succession, Zones I-3 are generally regarded as Tournaisian, and Zones 
4-6 as Viséan. 
Vaughan’s general zonal scheme has been the subject of much subsequent criticism, 
partly because of the extent to which the distribution of corals and brachiopods is 
influenced by environment, and partly also because of the lack of precision in 
defining boundaries. The K Zone, for example, was coincident with the lithological 
limits of the Lower Limestone Shale, its only fossil of any possible diagnostic value 
being Avonia bassus (George 1952). The faunas of other zones were no less reflec- 
tions of the facies changes represented by successive strata, the zaphrentid corals 
being but one example. In other areas, zonal fossil genera were found beyond the 
limits of these zones. 
It was for these reasons that Kellaway & Welch (1955) suggested the replacement 
of Vaughan’s zones by a succession of lithological units (Fig. 3). The object of these 
was to assist in regional mapping, but such lithological units are of less value in 
correlation than Vaughan’s imperfect faunal zones. Even Kellaway & Welch, 
whose divisions generally correspond with the limits of Vaughan’s faunal zones, 
found lateral transition within this area, the Shirehampton Beds of Bristol passing 
southwards into the base of the Lower Limestone Shale, and northwards and 
westwards into the top of the Portishead Beds. 
Vaughan’s faunal assemblage zones, defined by twin zonal indices, but strength- 
ened and supplemented by other index fossils, still seem to us to represent the most 
satisfactory method of correlation in the field, although we believe that the conodont 
zonation presented in the present paper provides a far more precise alternative for 
those strata in which conodonts are present. 
(c) Previous research on the correlation of the Avoman with the Carboniferous of Europe 
The correlation of the British Avonian with the continental succession has 
presented acute problems. Vaughan (1915) attempted to use the coral-brachiopod 
faunas to correlate with the Belgian succession. He correlated the Lower Tour- 
naisian (Tj) with his Z Zone and the Upper Tournaisian (Tz) with his C Zone 
(including the y horizon), making detailed correlations within the various units. He 
suggested that the faunal overlap (the Suwblaevis Beds and the Marbre Noir Series) 
between the Viséan and Tournaisian in the Dinantian succession was equivalent to 
the Upper Cz and S, Zones, and the Viséan succession above V,, up to and including 
Vocx to the S Zone. He correlated the Lower V2. Beds with the D,, and the Upper 
V2_ with the Dz of the Avon Gorge. Vaughan correlated the Hastiére Limestone 
and Shale, the “‘ Octoplicata’’ Shale, and the base of the Landelies Limestone with 
his 8 horizon, but Paul (1937), on the basis of brachiopod faunas, suggested the 
equivalence of the upper part of K; and of Kg in the Avon Gorge with the Hastiére 
Limestone (Tn;,). He regarded the Hastiére Limestone and the Peracuta Shale 
(Ins) as equivalent to the Gattendorfia Hangenberg Limestone of Germany, but 
Goldring (1958) suggested from their trilobite faunas that both these formations may 
be equivalent to the Lower Limestone Shale (K; and Kg), and he correlated the base 
of the Black Rock Limestone (Z;) with the base of the Landelies Limestone (Tn,,). 
