Lithologic similarities between the Salem Limestone and the subjacent Harrodsburg Limestone, redefined here, indicate a close relationship between these formations, which are assigned to a new rock unit, the Sanders Group (middle Mississippian). The Harrodsburg Limestone is redefined to exclude a dissimilar unit, the Ramp Creek Limestone Member, which is reassigned to the highest formation (Muldraugh) of the Borden Group; thus the Borden Group is modified by the addition of the Ramp Creek. The Ramp Creek is expanded to include subjacent rocks of similar lithologies that were formerly classed as parts of the Edwardsville Formation. The Leesville and Guthrie Creek Members are retained as parts of the Harrodsburg Limestone. The name Muldraugh Formation, excluding here the Leesville and Guthrie Creek Members of former usage in Kentucky, is introduced for the uppermost formation of the Borden Group in Indiana. The Muldraugh includes the Ramp Creek Limestone Member and the redefined Edwardsville Member and the Floyds Knob Limestone Member; the Floyds Knob and Edwardsville, formerly classified as formations, have widespread but thin carbonate rocks that are intercalated with calcareous, quartzose, and argillaceous rocks very similar lithologically to those of the revised Ramp Creek.