The Foerstia zone of the Ohio and Chattanooga shales : an explanation for the stratigraphic zonation of the fossils and a report on a newly discovered occurrence of the Foertia zone in western Ohio / by J.M. Schopf and J.F. Schwietering.
Publication Info.
[Washington, D.C.] : United States Department of the Interior, Geological Survey, 1970.
Washington : United States Government Printing Office