- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
Seven graptolite assemblages from the upper member of the Silurian Perham Formation in northern Presque Isle quadrangle, Maine, include 14 species of Monograptus, which are described. The monograptid assemblages indicate Early Ludlovian age, as they are closely similar to those of the M. nilssoni and M. scanicus zones of the lower part of the Ludlow Series in its type exposure in Wales. These two zones cannot be validly distinguished in Britain outside the type area, and have not been recognized as separate zones elsewhere, and so can be considered as one zone. The Maine graptolite-bearing beds are correlated also with the M. nilssoni and M. bohemicus zones of the Cape Phillips Formation in the Canadian Arctic.