The Antietam Formation or Antietam Sandstone is a geologic formation in Pennsylvania, Maryland, West Virginia, Virginia, and Tennessee.Antietam Formation in West Virginia, USGSAntietam Formation in Pennsylvania, USGSMaryland Geological Survey, Volume 10, Johns Hopkins Press, 1918 p. 200. In Virginia and Tennessee, it is known as the Erwin Formation. It is largely quartz sandstone with some quartzite and quartz schist. It preserves Skolithos trace fossils dating back to the Cambrian Period. A nevadiid specimen from Tennessee is the earliest known definitive trilobite in the southern Appalachians.
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