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PALAEONTOLOGY 



11. ORDOVICIAN GRAPTOLITE ZONES. 



After Lapworth, Elles and Wood. 



NOTE. Zones marked * occur in the same sequence in Scandinavia as in Britain, 

 and those marked f in North America. The identity of other zones may be masked 

 by difference of name; or greater or lesser thickness of sediment or abundance of 

 fossils may lead to a larger or smaller number of zones being recognized ; or zones 

 may be wanting through non-sequence. 



