116 
THE AVONIAN OF THE AVON GORGE 
area during Seminula-t\m.Q in the shape of a horse-shoe, and 
ceased somewhat suddenly at a certain distance from the shore- 
line.] 
The groups which are unrepresented in the S2 fauna either 
migrated from the Province during Si time, before the estab- 
lishment of the new conditions, or lived on in the area until 
they suffered local extinction. {Productus aff. semireticulatus, 
mut. Si, in its profusion of spines and in its marginal exten- 
sions, exhibits very convincingly the moribund characters 
which prognosticate approaching extinction). 
Local detail: — 
North of the Great Fault, only the base of the S2 
subzone can be examined on the Clifton side of the 
Avon, and this portion of the series is represented by the thick 
Seminula-Oolite at the southern end of the Great Quarry. 
Seminula ficoides, Lithostrotion Martini, Chonetes cf. 'papil- 
ionacea, Syringo'pora cf. distans and Productus corrugato-hemi- 
sphericus build up distinct and recurring seams. 
Carcinophyllum and the Bryozoan, ^Chaetetes cf . radians,’’ can 
always be detected by careful searching. 
Cyrtina carhonaria, which is so extremely abundant at the 
base of S2 in certain parts of the South-Western Province (e.g. 
Wickwar), has not been recorded from the Avon section. 
In the repetition of the series, south of the Great 
Fault, the entire S2 subzone is splendidly exposed 
between the bottom of Bridge Valley Koad and a point a few 
yards north of the foot of the Old Zig-zag. The repeated seams 
of Lithostrotion, Seminula, Productus and Chonetes can be 
readily examined, but very few other fossils have, as yet, been 
recorded. 
Plate XL 
Dihunophyllum-ZoiiQ : D = 
Zonal Index : — The Dihunophyllum group of the 
Clisiophyllidan Corals. 
