The monograptid fauna extends almost to the top of the Lower Devonian in the Old World, but monograptids do not occur in the Lower Devonian succession of New York or elsewhere in the central or southern Appalachians. Monograptid occurrences in the northern Appalachians are too sparse to demonstrate equivalence of any Old World graptolite zone with a definite level in the New York succession.
Three Lower Devonian graptolite zones occur in sequence interbedded with shelly and conodont-bearing carbonate rocks in central Nevada. The Nevada succession, coupled with an auxiliary succession at Royal Creek, Yukon Territory, Canada, can be correlated with the Appalachian Lower Devonian standard according to New York terminology, principally on the basis of brachiopods and conodonts. Allowing for relatively small, eventually correctable errors of inexactness, the Monograptus uniformis Zone correlates with the Coeymans Limestone, the M. praehercynicus Zone with the New Scotland Formation, and the M. hercynicus Zone with the Becraft Limestone. The position of the Monograptus yukonensis Zone corresponds to the Oriskany-Esopus interval.
These correlations will provide the basis for a continent-wide evaluation of paleogeography and tectonism in terms of chronostratigraphic units smaller than series for the first time.