11] STUDY OF SOUTHERN WISCONSIN FISHES— CAHN 11 



At this time the invasion came from the Labrador glaciers and the move- 

 ment was in a southerly direction, with a slight westerly trend. The 

 movement of the ice sheet followed in a general way the already formed 

 basins of the Great Lakes, and overflowed into the surrounding country 

 (Fig. 9). As a result of this guiding of the course of the glacier, the ice mass 

 assumed a lobate form, coinciding roughly with the general shore line of 

 the basin down which it flowed. Thus the glacier that came down the basin 

 of Lake Michigan, known as the Michigan glacier, put out a lobe, or sub- 

 glacier, which traveled down the basin formed by Green Bay, and is known 

 as the Green Bay glacier, while the ice mass occupying the basin of Lake 

 Superior sent out smaller lobes which followed roughly the larger bays of 

 its shore line. Following the outline of the glacier westward, one finds a 

 series of smaller lobes and glaciers, the Langlade, Wisconsin Valley, Chip- 

 pewa and Superior off-shoots which, however, did not reach far into the 

 state, and which are of no significance in so far as the present paper is 

 concerned. 



By referring to figure 9 it will be seen at once that the edges of the 

 Michigan glacier and the Green Bay glacier came in contact for quite a 

 distance. As a result of this contact, and because each glacier was acting 

 as an independent unit, the adjacent lateral moraines also came together 

 and were built up side by side as a continuous ridge, forming a medial 

 moraine which, because of its very broken and uneven appearance, is of the 

 type known as a kettle moraine, extending as a ridge of glacial deposit 

 down the middle of the apparently united ice mass. In this manner was 

 formed the ridge of broken hills, over one hundred and fifty miles in length, 

 which crosses Waukesha county in a northeast-southwest direction, 

 forming the most important topographic feature of the landscape. Within 

 the county the highest point in this ridge is Government Hill, with an 

 elevation of 1,233 feet. With the retreat of the glacier, not only was this 

 great moraine left stranded, but great blocks of ice were broken off and 

 remained imbedded in this moraine area. These melted with the advance 

 of the warmer climate accompanying the retreat of the main body of the 

 ice, and left innumerable depressions varying in size from "pot-holes" 

 a few yards in diameter to lake basins having an area of over a thousand 

 acres. Some of these depressions filled with water, the source of which was 

 surface drainage and a multitude of springs, and formed the abundant 

 lakes of the district. In this manner all the lakes of the county were formed, 

 with the exception of Pewaukee lake, which lies outside the area of the 

 kettle moraine. This lake differs, then, from the others in that it lies in the 

 area of the ground moraine, and occupies a shallow valley which resulted 

 from the failure of the glacier to fill in this basin with ground moraine 

 deposits. At the same time that the lake basins were being laid out, the 

 general plan of the river systems were being formed, with the natural result 



