THE AVONIAN OF THE AVON GORGE 
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and our examination cannot be resumed, along the riverside, 
until we have passed the engine shed. From this point, the 
rocks of the subzone Di are exposed in low and discontinuous 
masses by the side of the towing path, as far as the level crossing 
which leads to the New Zig-zag (a steep path which winds its 
way up the side of the gorge, in a narrow depression of the surface 
of the Downs). 
The whole of this subzone can, however, be more 
satisfactorily examined along the side of the Hot- 
well- Avonmouth line which emerges from a short tunnel close 
to Point Villa, and runs along the side of the section to the end 
of the Carboniferous Limestone sequence. 
The upper portion of the subzone, near the mouth of the 
tunnel, consists of shales, limestones and grits. The rock- 
characters indicate considerable variation of level, but of less 
amount than in the case of the D 2 beds. 
The lower portion of the D^ subzone can be examined by the 
side of the line, just south of the New Zig-zag level crossing ; 
it consists of thick -bedded, fossiliferous limestones which, like 
most of the Dihunophyllum beds in the Bristol Area, are stained 
red. To the north of the New Zig-zag, the surface of the ground 
rises rapidly, on a dip slope, until it reaches a height of 200 feet 
above the towing path. The limestones forming this slope con- 
stitute the base of the Dibunoyhyllum-ZonQ ; they are highly 
fossiliferous and can be examined by ascending the New Zig-zag 
Path and clambering up the slope on the left-hand side. 
The rubbly limestones which recur so frequently throughout 
the Dibuno'phyllum-Zone may be studied either at ‘ Pound Point ’ 
or in the exposures of the same beds along the Bridge Valley 
Road, between the large mass of Dolomitic Conglomerate, at the 
bend of the road, and the ‘ Great Fault ’ at its foot. 
Examined in a clean cut face, the rock is seen to be made 
up of large numbers of rounded portions composed of com- 
paratively pure limestone, separated by softer material which 
is usually very rich in iron ; to this structure the face owes its 
