1. Stratigraphic framework of Cambrian and Ordovician rocks in the central Appalachian basin from Richland County, Ohio to Rockingham County, Virginia Yale Public content 1991. 2002-06-01T04:00:00Z. 2002-06-01T04:00:00Z. Geological Survey (U.S.). The Survey ; For sale by Map Distribution. English. Public. Appalachian Basin. Cambrian and Ordovician.