Correlations, based on conodonts, between the Lexington, Kope and Clays Ferry Formations of the Cincinnati Region (Ohio, Kentucky, Indiana) and formations of the Trenton Group of New York and Ontario indicate that the base of the typical Edenian Stage and the top of the typical Shermanian Stage are at essentially the same biostratigraphic level. Hence, it can be shown that the upper part of the Trenton Group (Rust Member of Denley Limestone; Steuben and Hillier Limestones of Kay, 1968) is the same age as Edenian and lower Maysvillian strata in the type section of the Cincinnatian Series, and that the Edenian Stage (Cincinnatian) does not succeed the Cobourgian Stage (Champlainian) as has long been assumed. In fact, uppermost Cobourgian strata in New York are of demonstrably early Maysvillian age.

Concepts of and names for Cincinnatian stages have not changed since at least 1915, but there are several systems of and no agreement on nomenclature for upper Champlainian time-stratigraphic units in New York and Ontario; also, none of the upper Champlainian stadial names in current use has priority over Edenian (1873), Maysvillian (1905) or Richmondian (1897). Thus, we propose that the top of the Champlainian Series be drawn at the top of the Shermanian Stage and that this be succeeded in the standard time-stratigraphic classification of the North American Ordovician by Edenian, Maysvillian, and Richmondian Stages, included col lectively in the Cincinnatian Series.

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