[facedown]

The geology is complex, but it boils down to this: Relieved of billions of tons of glacial weight, the land has risen much as a cushion regains its shape after someone gets up from a couch.

This is utterly laughable.

[HiTech RedNeck]

Perhaps a new name is needed for such land: permamush?

[driftless2]

"utterly laughable"

No it's not. It's called isostatic rebound, and it's something I learned in college. Look at a relief map of North America. You will see that most of the natural lakes on the continent occur in the northern regions. There are relatively few natural lakes south of the Great Lakes. There used to be huge lakes created by melting glaciers including Lake Agassiz which was situated somewhat to the west of Lake Superior. It is now almost entirely gone. Canada had gigantic volumes of water. As the land rises, much of this water will run off.