Weathered Zones of the Drift-Sheets of Illinois

Abstract

A study of the weathered zones of the various drift-sheets of Illinois reveals that they consistently comprise four subdivisions, regardless of topographic or vegetative environment, but that the zones nevertheless show characteristic responses to topographic position and to drainage conditions. In well-drained areas the silttil profile has developed, in poorly drained areas the gumbotil profile has developed, and in partially drained areas the mesotil profile has developed. The Wisconsin and Iowan drift-sheets show immature profiles but the Illinoian and older drift-sheets show, respectively, early-mature to mature profiles. It seems probable that silttil profiles of one area may be correlated with gumbotil profiles of another area. In the older drift-sheets where erosion has worked headward into a broad flat area, the gumbotil profile of weathering may show in its upper portion the beginning of a second profile due to the newer and better drainage conditions. Fossil weathering profiles buried beneath ...