THE AVONIAN OF THE AVON GORGE 
107 
Horizon ^ 
Diagnosis : — 
Spiriferina cf. octoplicata, the index fossil of the Upper 
Zone, occurs in association with Zaphrentis 
Phillipsi, the index of the Zaphrentis-ZonQ. 
Fauna: — 
This horizon, though characterized by a fauna essentially the 
same as that of the Zaphrentis-ZoxiQ, contains one or two sur- 
vivors from the fauna peculiar to the Cleistopora-Zone. 
Local detail : — 
In the Avon Section, this extremely fossiliferous level forms 
the base of the Black Rock Limestone-massif and, on the Clifton 
side of the river, it can only be examined in Press’ Quarry. 
The Brachiopods, with the two principal exceptions men- 
tioned below, are characteristic Lowev- Zaphrentis forms and in 
fact, at Horizon /3, the Zi fauna is already typically developed ; 
hence it is unnecessary to enumerate the forms which are most 
abundant since they are equally abundant throughout Zi and 
'will be sufficiently dealt with in the general account of that 
sub zone which immediately follows. 
The two Brachiopods worthy of special notice are Spiriferina 
cf. octoplicata and Athyris Royssii, mut. /3. 
In the Bristol Area, Spiriferina cf. octoplicata is not found 
above Horizon /3 ; it is the index fossil of K 2 , but reaches its 
maximum abundance at, or just below, Horizon p. 
Athyris Royssii, mut. fl agrees very closely, in range and 
distribution, with Spiriferina cf. octoplicata it is an abundant 
and characteristic fossil at Horizon f^ and is common through- 
out K 2 , but it ranges on into the Zi subzone. 
The only coral which occurs at this horizon is Zaphrentis aff . 
Phillipsi which here makes its earliest appearance ; it is not 
uncommon and good specimens, showing the calyx, can be 
picked out of the weathered partings. 
Cups and stems of Crinoids, spines and plates of a Palechinid, 
