124 
THE AVONIAN OF THE AVON GORGE 
examples of Cyathofhyllum Murchisoni attain a length of 2 
feet. 
. s,. 
PI t XII below the beds there is a good 
exposure of the ‘ Concretionary Beds ’ which form 
the uppermost part of the Seminula-Zone. These beds are well 
exposed on the broad slope which here rises steeply from the 
towing-path. Although there is no stratigraphical break between 
the base of Di and the top of S 2 , yet the faunal break (as also 
the lithological break) is remarkably striking and, at first sight, 
well-nigh complete. In the Avon sequence, the Di beds, with 
their rich coral fauna, are underlain by the S 2 ‘ Concretionary 
Beds ’ which contain few fossils beyond recurrent seams of 
Seminula. (Although the sharpness of the faunal break between 
the Dihunofhyllum and Seminula-ZowQ^ is seen to be less perfect 
the more closely we examine any one locality, and the more 
widely we extend our observations, it yet remains a striking 
feature of the sequence throughout the South-Western Province 
and undoubtedly indicates a very considerable change of con- 
ditions.) 
The only other points worthy of special note with regard to 
the ‘ Concretionary Beds ’ at the top of S 2 are ; — 
(1) The ‘ Cotham Marble ’ structure, which causes certain of 
the limestone beds to appear as if mottled by irregular black 
patches. 
(2) The abundance of Seminula ficoides and its variants, which 
occur in repeated seams. 
Quarry 5, which lies north of the slope, exhibits upper 
S 2 -beds which present no special features worthy of more 
than the briefest examination. 
Seminula ficoides and Lithostrotion Martini are both abundant. 
(Certain of the beds in this quarry, and in the tunnel immediately 
south of it, are crowded with Seminula ficoides^ and rock speci- 
mens from these beds, when cut and polished, afford the best 
