22 BRITISH AVONIAN CONODONT FAUNAS 
4. The Zz Limestone traverse in Quarry 2. Leigh Woods side of the Gorge. 
(ST 558 745). 
Sample numbers Z21-Z38. 
5. The Laminosa Dolomite traverse in the Railway cutting, Leigh Woods side of 
the Gorge, between Quarry 2 and Quarry 3. (ST 559 745). 
Sample numbers C1-C11. 
6. The Laminosa Dolomite and Caninia Oolite traverse in Quarry 3. Leigh 
Woods side of the Gorge. (ST 560 744). 
Sample numbers C12—C25. 
7. The Caninia Dolomite traverse along the roadside on the Clifton side of the 
Gorge, between the Caninia Oolite Quarry to the North and the Great Quarry to 
the South. (ST 562 746). 
Sample numbers C26—C48. 
8. The S; and lower Sz traverse in the Great Quarry on the Clifton side of the 
Gorge. (ST 563 740). 
Sample numbers S1-S30. 
9. The Sg and Concretionary Bed riverside traverse, south of Quarry 4. Leigh 
Woods side of the Gorge. (ST 562 737). 
Sample numbers S31-S72. 
to. The D Zone traverse at the roadside, north of and a short distance to the 
south of Bridge Valley Road on the Clifton side of the Gorge. (ST 564 734). 
Sample numbers D1—D27. 
(ii) South Wales 
Rocks of Lower Carboniferous age form an extensive rim around the margins of the 
South Wales Coalfield, where they overstep the Old Red Sandstone. The thickest 
and most complete sequence is developed on the southern margin of the Coalfield in 
Pembrokeshire, Gower and the Vale of Glamorgan. The application of Vaughan’s 
zonal scheme has shown that in this area the complete succession is present, the total 
thickness being in excess of 4,000 ft. in parts of Pembrokeshire and some 3,500 ft. in 
Gower, but thinning gradually eastwards. There is a broadly comparable litho- 
logical sequence to that of the Bristol area, comprising a lower limestone and shale 
sequence, followed by bioclastic limestones and oolites, but including varying 
developments of shales and pseudobreccias in the highest parts, and dolomites in the 
C and Z Zones in the east. On the North Crop of the coalfield the thickness is much 
reduced, however, partly as a result of original depositional thinning against the 
margins of a northerly landmass, partly because of intra-Avonian unconformities, 
and partly because of truncation below the transgressive unconformable base of the 
overlying Millstone Grit. The intra-Avonian unconformity cuts out much of the C 
and S Zones in places. 
Our collections were made chiefly from the North Crop of the Coalfield, though 
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