p.6

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[illustration of strata]

If we adopt the conclusion of Prof. Hall and others ranking the red sandstone of Lake Superior within the Potsdam, and consider the fact that there are outliers of sandstoe still covering the primar beyond the chief line of boundary, we must suppose that there may have been a time when this sandstone extended across the entire breadth of primary rocks as represented by the dotted lines in the figure above. This would indicate that all of Wisconsin may have been submerged beneath the sea of the Potsdam period. Erosions quite as extensive as this supposition would indicate, are known to have taken place in other localities; and when we remember that during all the time of the Devonian, Carboniferous, Cretaceous & all subsequent periods our state was above water & subject to destructive elements, we may readily admit this extended abrasion of the Potsdam Sandstone. Since the commencement of the limestone deposits of the lower Silurian period, it is quite...

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