Wisconsin Kettle Moraine. 229 



stretch away in that direction to the moraine, and, mingling with 

 it, pass onward to an equal distance beyond. At the same time 

 there is abundant evidence from the material of the drift, from the 

 surface contour and from striation, recently observed by Mr. I. M, 

 Buell, that the westerly movement of the Lake Michigan glacier, 

 near the Illinois line, extended to the west side of Rock River, 

 and that the line of junction of the two glaciers was on the west 

 side of that stream. It appears then, that in this region, the move- 

 ments were in the same general direction before and after the 

 formation of the moraine, but that there were changes in the de- 

 tails, and that the relative size and position of the glaciers were 

 somewhat different, the Green Bay glacier being relatively smaller 

 in the earlier epoch. Testimony of similar general import, but 

 less specific, may be gleamed from the reports of the other states 

 involved. 



Method of Formation. — If, then, the glacial movements were the 

 same, in general, before and after the formation of the moraine, 

 and yet the minor movements and relative size of the glaciers 

 somewhat different, how was the moraine formed ? A halt in the 

 retreat of the glaciers, by which their confluent margin should re- 

 main stationary for a period, would doubtless cause an unusual 

 accumulation of debris, but this would fail to account for the 

 varying width or irregularities of the moraine. The structure of 

 the range 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 immense ridges. If this process be repeated 

 several times paralled ranges will be accounted for, and the irreg- 

 ularities incident to such advance and retreat will explain the 

 complexity of the range. "Where the later advances were equal 

 to the earlier ones, the accumulation 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 accumulations, bat would in 

 general be more or less trough-like in character. Where tongues 

 of ice were thrust into the accumulated material an irregular or 



