Wisconsin Kettle Moraine. 233 



to be accumulated during the accumulation of the moraine, and 

 through the agency of glacial floods ; while it is even more cer- 

 tain, that other vegetal deposits accumulated much subsequently^ 

 as those found in the red clays of Wisconsin, which are lacustrine 

 deposits of the great lakes formed after the recession of the glacier. 

 It would be too much to assume that all plant remains, found 

 south of the moraine, antedate its formation, but it is safe to 

 affirm that, with only phenomenal exceptions, e. g., such as escaped 

 glacial abrasion, all north of it are more recent. 



The bearing of these definite determinations of the glacial outlines 

 and movements upon the question of the origin of the remarkable 

 driftless area of Wisconsin, Minnesota, Iowa and Illinois (see map) 

 was early perceived, and it was clearly foreseen that this line of 

 investigation promised a demonstrative solution of the problem. 

 The driftless area manifestly owes its origin to the divergence of 

 the glaciers through the Lake Superior channel, on the one hand, 

 and that of Grreen Bay and Lake Michigan, on the other, and to 

 the obstacle presented by the highlands of northern Wisconsin 

 and Michigan. This obstacle the glacier surmounted, and passed 

 some distance down the southern slope, but apparently not in 

 sufficient thickness to overcome the melting and wasting to which 

 it was subjected, and so it terminated midway the slope. But 

 the deep, massive ice currents of the great channels pushed far 

 on to the south, converging toward each other ; and, if they did 

 not actually unite, at least commingled their debris south of the 

 driftless area.-^ An instance closely similar to this, considered 

 from a dynamical point of view, may be seen, at the present 

 termination of the Viesch glacier, and illustrations of the general 

 principles involved in the explanation may be seen in connection 

 with several other Alpine glaciers. 



If the evidence adduced to show that the Kettle moraine was 

 due to an advance of the glaciers be trustworthy, then, to the 

 extent of that advance, whether much or little, the moraine marks 

 a secondary period of glaciation, with an interval of deglaciation 



1 Compare N. H. Winchell In An. Kep., Qeol. of Minn., 1876, and R. D. Irvin?, Geol. of 

 Wis., Vol. II, 1877, whose Tiews are closely analogous to the above and each to the other but 

 are not strictly identical. See, alao, J. D. Dana, Am. Jour. Sci., April, 1878. 



