Page:Popular Science Monthly Volume 73.djvu/215

Rh dominion included the boundary waters not farther west than Kainy Lake, but continued unbroken to Hudson Bay.

A few other general considerations ought to be stated at this point in order to prepare for the discussion of the topic in hand. These are:

1. During the prevalence of the last ice-epoch the state of Minnesota was covered with ice, and all previous inhabitants, whether fauna or flora, were driven southward to more congenial climes.

2. This condition ended between seven and eight thousand years ago. It is not necessary here to rehearse the investigations on which that result is based.

3. Between the ice-fields and the habitable portions of the continent lying to the south was a belt of country, the width of which varied according to the longitude and according to the topography, which was uninhabitable by reason of the severity of the climate. This uninhabitable belt may be compared to a belt in northeastern and northern Canada at the present time which is uninhabitable for the same reason. It was wider, however, than the northern Canadian belt, and less ameliorated along the banks of the rivers. Their waters drained from the northern ice fields, whereas the Canadian rivers carry waters from southern and more temperate latitudes. But like the Canadian belt it was wider toward the west. The ice-margin and the accompanying severity of climate crossed the country from southeast to northwest. The prehistoric isothermals, same as the present, passed northwestwardly.

4. Hence the habitable portions of the United States, until seven or eight thousand years ago when the ice began its retreat, were along the Atlantic seaboard south of New Jersey, a belt along the coast of the Gulf of Mexico, a large interior area without ascertainable limits, and the Pacific coast west of the Sierra Nevada.

5. So far as Minnesota is concerned, and the same is true of much of the northern United States, it seems to be necessary, therefore, to confine all investigation of aboriginal migration to an antiquity not greater than seven or eight thousand years.

6. For Minnesota it is necessary to make a still further restriction, for it was the ice-margin itself that retired seven or eight thousand