214 GEOLOGY OF EASTERN WISCONSIN. 



quartzite in the towns of Portland and "Waterloo, stretches directly 

 across the Eange and onward into Illinois. It seems evident, then, 

 that before the formation of the Kettle Kange, the glacial movements 

 were essentially the same as they were subsequent to its formation, 

 and that it-s accumulation was due to unusual conditions affecting the 

 rate of the recession of the glaciers. The structure of the Eange 

 seems to indicate an alternating retreat and advance of the ice-mass. 

 During the former, debris was thrust out at the foot of the melting 

 mass, which, when the glacier advanced, was plowed up into im- 

 mense ridges. 



If this process be supposed to be repeated several times, parallel 

 ranges will be accounted for, and the irregularities incident to such 

 retreat and advance will explain the complexity of the Kange. Where 

 the later advances were equal to the earlier ones, the whole accumula- 

 tion of drift material would be forced into a single massive ridge. 

 Where any advance failed to equal a former one, an interval between 

 the accumulations of the two would result, giving rise to a depression 

 whose form would depend upon the relations of the two accumula- 

 tions, but would, in general, be more or less trough-like in character. 

 Where tongues of ice were thrust into the accumulated material, a 

 •serrated edge or projecting spurs and corresponding indentures would 

 result. If masses of the ice became incorporated within the drift, as 

 has been suggested, their subsequent melting would give rise to a de- 

 pression constituting one form of the kettles which characterize the 

 range. The suggestion just made, with reference to the irregular ad- 

 vance of the ice mass, accounts for other forms, and at the same time 

 for the irregular hills, mounds and ridges that are so conspicuous a 

 feature of the Kange. 



Certain of the "kettles " may have an origin diverse from either of 

 the causes above suggested. A portion of the material of the forma- 

 tion is a loose quicksand, easily removed by the action of water. The 

 irregular surface of the Kange, and its porous character, facilitate the 

 collection of water, which issues from its base in numerous perennial 

 springs; indeed, in some cases, brooks of no inconsiderable size flow 

 full-fledged from its base. These are entirely competent to carry 

 away, through their underground channels, quicksand and similar 

 material, thus undermining the surface and causing a depression. It 

 may be prudent to remark in this connection, that depressions alto- 

 gether similar to many of those under consideration occur within 

 eastern Wisconsin, which are manifestly due to very different causes. 

 One of these is the well known formation of sink-holes in limestone 

 districts, by the dissolving out and removal of the rocks by under- 



