96 
THE AVONIAN OP THE AVON GORGE 
scenery of the Gully that its local title, ‘ Gully Oolite,’ is well 
deserved. Since, however, it is essential to emphasize the 
zonal position of any particular rock-type, in order to distinguish 
it from the same rock-type occurring at a different level, I have 
named this Oolite the ‘ Guwmm- Oolite.’ (Compare the terms 
‘ /ummosu-dolomite,’ ‘ Seminula-OolitQ.'^) 
We now enter the Black Eock Quarry by scrambling 
through into it from the bottom of the Gully Path (keeping along 
the right-hand side of the fence which bounds the railroad). 
[The limestone-massif which bounds the Gully on the north is 
known as the ‘ Black Eock ’ ; the top of this mass is flat and 
forms the plateau of the Durdham Downs, its river edge is 
known as the ‘ Sea Wall ’ and, from this edge, there is a pre- 
cipitous descent into the ‘ Black Eock Quarry.’ To the south 
of the massif lies the Gully, and to the north lies the lower ground 
of the ‘ Lower Limestone Shales.’] 
The thick bed which underlies the north slope of the Gully 
can be examined between the Gully and the Black Eock Quarry. 
It is a dull, yellowish-brown dolomitic limestone and forms 
the base of the ‘ ^ummosu-dolomites ’ ; as seen in the face of 
the quarry, it forms a conspicuous cap, distinct in colour and 
texture from the pure limestones beneath. 
With this bed we reach the bottom of the Syringoihyris-TjOxiQ 
which we have been examining ever since we left the Great Quarry. 
Eeviewing the whole zone, it is clear that the circumstances 
of deposit were peculiar and comparatively local. 
Judging by similar deposits of recent age, the Gamma- Oolite 
indicates perfectly clear and shallow water conditions such as 
are associated with the growth of coral reefs. Further, deposi- 
tion must have been sufficiently continuous to prevent the forma- 
tion of well marked bedding planes and consequently, when the 
mass consolidated, the cross joints traversed the whole mass. 
The dolomites point to the same conditions, for it is probable 
that the doloniitization which affects recent coral masses is 
