The Last Submergence of the Appalachian Basin - The Pennsylvanian age Ames Limestone represents the last submergence of the Appalachian Basin by marine waters. This limestone crops out throughout southwestern Pennsylvania, northern West Virginia, and eastern Ohio. Lewis passed this site along the Ohio River near Wellsburg, West Virginia on his way to St. Louis. Today, nearly one mile away, is the grave of Sergeant Patrick Gass, the last member of the Corps of Discovery to pass away, in 1870 (inset). (Lewis, 9/7/1803)