p.10

The condition of the country now entranced within the limits of Wisconsin, five hundred years ago may have been quite different from the present.
It is quite certain that the prairies then covered a much large portion of the state than at present.
The largest trees are probably not more than 500 years old.
Large tracts are now covered with forests of young trees, where there are no traces of an antecedent growth.
The state is subject to sudden gusts of wind sweeping through the forest turning up the trees by the roots.
The earth turned up with the roots falls upon the decay of the roots forming an elongated mound by the side of a depression at the place where the tree stood.
Now as there has been no change of climate, it is clear that