THE GLACIAL LAKE CHICAGO. 441 



deposits of the succeeding lake stage, are referred by Chamberlin to the same 

 category. 1 



Along the east shore of Lake Michigan evidence of emergence is found 

 in deep channels along the lower courses of the streams tributary to the 

 lake — channels which are in some cases excavated in the till and therefore of 

 later date than the last ice invasion. Attention was called to these chan- 

 nels many }*ears ago by Dr. Alexander Winchell. 2 They were subse- 

 quently discussed by Dr. C. W. Wooldridge. 3 The latter made a special 

 study of the lower course of White River, known as White Lake, and also 

 made a reconnaissance from Grand Traverse Bay to the mouth of Grand 

 River. He made the important discovery that the beds of several of these 

 streams "are excavated in the drift clay and not in the surface sand which 

 overspreads the lower levels in their vicinity." On the borders of White 

 Lake the sand is usually onty a thin deposit 1 to 4 feet in depth and the 

 clay surface reaches a height of 15 to 30 feet above the level of the lake. 

 Similar features are found on Duck Lake, Pentwater Lake, and Manistee 

 Lake. The latter observation carries the emergence well into the northern 

 half of the Lake Michigan Basin. 



The depth to which the erosion extended is difficult to determine, since 

 these channels have no doubt been filled to some extent during the subse- 

 quent emergence. Dr. Wooldridge found a point near the mouth of White 

 Lake in which there is 84 feet (14 fathoms) of water. The U. S. Lake 

 Survey charts show a depth of several fathoms in each of the tributaries of 

 Lake Michigan from Pere Marquette Lake southward to the Kalamazoo 

 River, as follows: 



Depths of lakes tributary to Lake Michigan. 



Fathoms. 



Pere Marquette Lake 7 



Pentwater Lake 8 



White Lake 10 



Muskegon Lake 9 



Spring Lake 7 



Black Lake '. 5 



Kalamazoo River 1 16? 



The above soundings demand an emergence of at least 50 feet above 

 the present shore, even if the bottoms are but slightly filled, and it seems 



1 Wisconsin Geological Survey, Vol. II, pp. 221-224, 229, 230. 



2 Harper's Magazine, July, 1871, p. 284. 



'Amer. Geologist, Vol. I, March, 1888, pp. 143-146. 



■■Possibly the soundings at mouth of Kalamazoo Kiver represent feet instead of fathoms. 



