Thus the Driftless area is in strong contrast with the immature drift topography about it, where lakes and waterfalls are common.
"The Elements of Geology"
William Harmon Norton
South of the Driftless area the Mississippi valley was invaded at different times by ice sheets from the west,-the Kansan and the Iowan,-and again by the Illinoian ice sheet from the east.
"The Elements of Geology"
William Harmon Norton