Bedrock Topography and Pleistocene Glacial Lobes in Central United States

Comparison of a generalized 250-foot contour map of the bedrock surface and the glacial map of central United States shows that the Pleistocene glacial lobes were closely controlled by bedrock lowlands even in areas of relatively thick drift and that positions of ice centers and deflection by adjoining lobes were of secondary importance. The implications of these relations in the study of glacial centers and possible flow units within glacial lobes are considered, and an interpretation of preglacial drainage, based on the bedrock-surface map, is proposed.