Study of a cherty, red, residual soil found in Madison County, Ohio, has resulted in the reconstruction of the chemical and environmental conditions necessary for its formation and the postulation of its probable age. The soil exists in solution pits and fractures in the limestone, overlain by Wisconsin drift. Studies of field relations and insoluble residues show the limestones to be the source rock. Soil and mineral analyses, considered on the basis of weathering necessary to alter the source minerals to minerals in the soil, indicate that the soil must have formed in a warm climate with heavy seasonal rainfall in an area of moderate relief. The relation of these conditions to the geologic history of the area suggests that the soil formation is of pre-Pleistocene age.