The foregoing discussion of glaciers and their deposits is greatly
simplified. For some time geologists of the Illinois Geological Survey
have been mapping the moraines, valley trains, outwash plains, and other
glacial deposits of the state. Because the Illinoian and Wisconsinan
glaciers advanced and retreated several times, they built many moraines.
The Survey has made a map (fig. 18) that shows the complexity of the
moraines left by the Wisconsinan glacier. They are roughly concentric,
indicating that the general shape of the glacier front remained about
the same.