Author Institution: Ohio Department of Natural Resources, Division of Geological SurveyThe Grant Lake Limestone, including, in ascending order, the Bellevue, the Corryville, and the Straight Creek Members, and the Grant Lake Formation, including, in ascending order, the Bellevue, the Corryville, and the Mount Auburn Members, are herein defined as lithostratigraphic units in southwestern Ohio. Regional bedrock mapping, shale-percentage and geophysical logs, and mean shale percentage of lithostratigraphic units demonstrate a progressive change from a limestone-dominant stratigraphic section in the Maysville, KY, region to a shale-dominant stratigraphic section in the Cincinnati, OH, region. The Grant Lake Limestone is redefined to account for the progressive decrease in limestone content observed northwestward away from Maysville, KY. The Grant Lake Formation is introduced to describe the shaledominant lateral equivalent of the Grant Lake Limestone in the Cincinnati, OH, region. The Bellevue Limestone, the Corryville Formation, and the Mount Auburn Formation are reduced to members because, in some cases, they are not mappable at 1:62,500 or smaller scales. The Straight Creek Member is introduced to describe the limestone-dominant lateral equivalent of the shale-dominant Mount Auburn Member. The limestone-dominant and shale-dominant lithologies of the Grant Lake Limestone and the Grant Lake Formation can be recognized in shale-percentage and geophysical logs. Correlation between logs led to recognition of these stratigraphic units in the subsurface of southwestern Ohio
