SKETCH OF THE GEOLOGICAL HISTORY OF THE BRISTOL DISTRICT. 9 
Dr. Vaughan’s primary divisions of the Carboniferous Limestone 
series are as follows : — 
Upper Carboniferous Limestone, 
or Visean 
Lower Carbonifeious Limestone,) 
or Tournaisian | 
Dibunophyllum Zone. 
Seminula Zone. 
Syringothyris Zone. 
Zaphrentis Zone. 
Cleistopora Zone. 
u 
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