BRITISH AVONIAN CONODONT FAUNAS 15 
Carboniferous. Although Vaughan (1905) established a series of coral-brachiopod 
zones for the succession, these were later found to be of only local value in correlation 
(see George 1952, 1958 for a critical review), so that other type sections have been 
recognized for other areas of Britain (e.g. Walker 1964). The accepted international 
type section for the Lower Carboniferous is that in West Germany. 
The rocks of the Avon Gorge comprise some 3,000 ft. of strata, consisting pre- 
dominantly of carbonates, but with subordinate shales and sandstones. Vaughan 
(1905) subdivided these into five faunal zones, four of which were divided into two 
subzones (Fig. 2). Vaughan pointed out that the Dinantian was approximately, but 
not exactly, equivalent to his Avonian, which he subdivided into the underlying 
Clevedonian (C, Z, K) and the Kidwellian (D and S Zones), rather than using the 
equivalent Tournaisian and Viséan. Vaughan modified his classification in later 
publications (1906, 1915 : Dixon & Vaughan 1911, Reynolds & Vaughan Ig1r). 
The modifications involved the inclusion of the Modiola phase as the basal subzone 
of K (Km), the varying position of horizon y (included in Z in 1905 ; in C in IgiI ; 
included as the major part of C in Burrington Combe in 1911), and the development 
of the Caninia Zone (1906, 1911). Other authors also proposed subsequent amend- 
ments, Dixey & Sibly (1918) subdividing the C Zone in South Wales, and Hudson & 
Dunnington (1945) placing the Caninia Oolite in the Upper C Zone. 
The present standard coral-brachiopod zonation of the Avonian (modified after 
George 1958) is as follows : 
Symbols 
6 DIBUNOPHYLLUM ZONE D Vaughan (1905) Subzones 
De and D,. 
5 SEMINULA ZONE Se Vaughan (1905) ‘‘ Main 
Seminula Zone’’ of Dixey 
& Sibly (1918). 
4 UPppeR CANINIA ZONE CoSa1 Dixey & Sibly (1918). 
This includes part of Vau- 
ghan’s (1905) Syringothyris 
Zone and the overlying 
Lower Seminula Zone (Sj). 
The lower limit of this zone 
is placed at the top of the 
Caninia Oolite. 
3. Lower CaNnInIA ZONE Cy Dixey & Sibly (1918), with 
horizon y at the base. 
2 ZAPHRENTIS ZONE Z Vaughan (1905) Subzones 
Z2 and Zit. 
I CLEISTOPORA ZONE K M and K Zones of Vaughan 
(1905) and the K Zone of 
Sibly (1906). 
