1979. 2014-09-10T17:26:37Z. 2021-06-01T21:36:14Z. Weir, Gordon W. (Gordon Whitney), 1922-2011. U.S. Geological Survey. English. Public. Kentucky and Kentucky. Ordovician and From 425 to 500 million years ago.
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1945. 2018-02-20T15:02:08Z. 2018-02-20T15:02:08Z. Cohee, George Vincent, 1907-. U.S. Geological Survey. English. cartographic image. Public. Michigan Basin (Mich. and Ont.), North America, and Michigan Basin. Ordovician, Cambrian, and From 425 to 570 million years ago.
2008. 2008-11-11T15:36:27Z. 2012-04-26T14:16:08Z. Ryder, Robert T. U.S. Dept. of the Interior, U.S. Geological Survey ; For sale by U.S. Geological Survey, Information Services. English. Public. Appalachian Basin and Appalachian Basin. Cambrian and Ordovician.
1948. 2018-01-30T14:30:37Z. 2018-01-30T14:30:37Z. Cohee, George Vincent, 1907-. U.S. Geological Survey. English. cartographic image. Public. Michigan Basin (Mich. and Ont.), North America, and Michigan Basin. Ordovician, Silurian, and From 405 to 500 million years ago.