18 BRITISH AVONIAN CONODONT FAUNAS 
The outstanding difficulty of detailed correlation of the Avonian with the Car- 
boniferous type sections of the Rheinisches Schiefergebirge has been the absence of 
goniatites in the type Avonian section. A prolecanitid (Protocanites) (identified by 
Professor Frank Hodson) from shales near Abergavenny may have been collected 
from the lithologically similar shales at the top of the Z Zone or from the K Zone. 
The exact locality is not specified on the specimen, which is in the Geological Survey 
Collections (No. G.S.M. 82817) (see also George 1952 : 35). George & Howell (1939) 
have described Prolecanites discoides, Muensteroceras inconstans, and Pericyclus kochi 
from the Upper Caninia Oolite of Three Cliffs Bay, Gower, and these suggest an 
uppermost Tournaisian age for these beds, while the presence of Muensteroceras 
euryomphalus and Merocanites cf. compressus in the overlying Upper Caninia Beds 
suggest a low Viséan age (George & Ponsford, 1935). The traditional Lower-Upper 
Avonian boundary (Dixon & Vaughan, 1912) of the Lower Caninia Zone (C,) and 
Upper Caninia Zone (C2Sj) is thus approximately equivalent to that of the Tour- 
naisian and Viséan (see George 1952, 1955). Smith (1942 : 338) recorded a goniatite 
indicative of a Pz age from the Avonian Tanhouse Beds (D3) of the Yate district in 
Gloucestershire. 
Currie (1954) provided a monographic study of Scottish Carboniferous goniatites 
which allowed her to make correlations with the stages established by Bisat. She 
was able to assign the Upper Limestone Group to the Eg (Arnsbergian) Stage, the 
Limestone Coal Group to the Ej, (Pendleian), both the latter being of Lower 
Namurian age, the Lower Limestone Group to the Pz and the Upper and higher part 
of the Lower Oil Shale Group of the Calciferous Sandstone ‘Series’ to the P; and B 
Stages (Bollandian and Cracoean) of the Middle and Upper Viséan. Bisat’s Bg, Py 
and Pe, goniatite zones are equivalent to Vaughan’s Dibunophyllum Zone, and his 
B, Zone to the main Seminula Zone. Prentice & Thomas (1965 : 43, Fig. 2) have 
given a distribution table of British prolecanitids in which they show a correlation of 
Vaughan’s D-C Zones in North Devon with the European goniatite zones, although 
they provide no detailed discussion of the broader aspects of correlation. 
In spite of these various studies, Lower Carboniferous correlations between Britain 
and continental Europe remain tenuous, the uncertainties arising chiefly from the 
absence of the more stratigraphically useful faunal groups common to the two areas. 
We believe that the closely comparable conodont faunas here described allow a far 
more refined correlation than any yet achieved. 
(d) The stratigraphy of areas from which conodonts are described 
(i). The Avon Gorge, Bristol. 
The Avon Gorge, Bristol, is the type area for the British Avonian. A series of 
steep, river-side cliffs, provide almost continuous exposures of rocks from the upper- 
most Old Red Sandstones at the base, to the highest beds of the D Zone of the 
Carboniferous at the top. 
The lowest beds of the Avonian section are thinly-bedded, grey, brown, green and 
red, marly claystones, thin grits, sandstones and fissile, slightly calcareous shales. 
There are few calcareous deposits, the first limestone occurring 12 ft. above the base 
