Recent literature reveals that the term 'zone' includes a multitude of uses both descriptive and interpretive, and, despite the fact that the word 'zone' may apply to different phenomena, no common understanding of its several possible meanings is apparent, although several were discussed by the American Commission on Stratigraphic Nomenclature and the International Subcommission on Stratigraphic Terminology. Attention here is focused on some long and widely used meanings of 'zone' not discussed in reports of the above committees. Correlations of British and North American Early and Middle Ordovician graptolite zones are proposed and recommendation for study of wider latitude in use of term 'zone' is made.

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