The Medina Group comprises 11 facies, which can be organized into three facies associations. The previously defined color-based formations do not conform with lithic correlations except for the Whirlpool and Manitoulin. A formal major revision is being proposed by Brett and others (in press) and Duke and others (in press). The newly revised Medina Group will include the Whirlpool Sandstone at its base (virtually unchanged), the overlying Jolley Cut Formation (a tentative renaming of the Manitoulin), the Balls Falls Formation (new), the Art Park Phosphate Beds (new), the Devils Hole Formation (new), the Grimsby Formation (revised), the Power Glen Formation (revised), the Thorold Formation (revised), the Cambria Formation (new), and the Kodak Formation (resurrected). The Medina unconformably overlies Queenston Shale; unconformably underlies Clinton Group.

Source: GNU records (USGS DDS-6; Reston GNULEX).