276 BRITISH AVONIAN CONODONT FAUNAS 
Mid-Avonian unconformity in some places in the North Crop, and the absence of 
conodonts in others, does not allow comparisons of the middle part of the succession, 
although the uppermost Z of the Avon Gorge is younger than that of the North Crop. 
The base of the Dg Subzone corresponds in both the Avon Gorge and the North 
Crop. Few Dz or Dg conodonts have been recovered from the Avon Gorge (Figs. 
67-69). 
Shropshire 
The lowest K strata at Farlow appear to be younger than those of the Avon Gorge, 
or the North Crop. The Shropshire K Zone strata represent a very condensed 
deposit. The higher part of the K Zone at Farlow is equivalent to the Lower Z of the 
Avon Gorge. The Z Zone at Farlow represents the Spathognathodus costatus costatus— 
Gnathodus delicatus Zone. 
Yorkshire 
The lowermost Yoredale limestones (the Gayle and the Hawes) have yielded few 
conodonts. The overlying Hardraw Scar Limestone and Simonstone Limestone fall 
within the Gnathodus mononodosus Assemblage Zone, and the Middle and Five Yard 
Limestones within the Gnathodus girtyi collinsont Assemblage Zone. 
Scotland 
A correlation is suggested between the Fife, Midlothian, Ayrshire, Dunbar and 
Glengarnock successions, and between these and the South Western Province. The 
Scottish sections all fall within the Gnathodus mononodosus or Gnathodus girtyi 
collinsont Zones, except for the lowest part of the Ayrshire succession and the Lower 
Algal “ Series’ of Roxburghshire. Details of the correlations are given in Fig. 15. 
(h) Intercontinental correlation 
A critical review of North American and European Lower Carboniferous conodont 
faunas is given (p. 52), and the correlation of these with the British Avonian is 
summarized in Figs. 12, 16. The K Zone of the Avonian, represented by the two 
lowest conodont zones and by the lower part of the Spathognathodus cf. S. robustus— 
S. tridentatus Zone, is probably equivalent to the Lower Hannibal—Upper Chouteau 
succession of the Mississippi Valley (Cu I-Cu II «). This would imply a very con- 
siderable unconformity below the “‘ Sedalia Formation ”’ (Lower Cu II $-y) which is 
correlated with the Polygnathus lacinatus Zone of the Upper Zz Beds. An alternative 
correlation, based upon the first appearance of Gnathodus delicatus, would equate the 
Spathognathodus costatus costatus—Gnathodus delicatus Zone of the Middle Z Zone 
with the Upper Chouteau (Cu II «) (p. 56). The highest Z Zone is equivalent to 
the Fern Glen and lower part of the Burlington Formations (Middle Cu II 6-y). 
The C; Subzone of the Avonian is of Upper Cu II B—y—Lower Cu II 3 (Middle and 
Upper Burlington) age, and the CgS; and Seg Subzones of Upper Cu II 8 age. 
(Keokuk to Lower St. Louis). 
The D; Subzone is of Cu III « age, the Dz Subzone of Cu III «Cu III 8 age, and 
the D3 Subzone of Cu III B-y age. 
