152 Wisconsin Academy of Sciences, Arts, and Letters. 



Swan lake, east of tlie portage, and the deep holes in Big Slough 

 appear to be remnants of this lake. The ban-ier has been 

 broken down, and much of the filling up has been done by 

 glacial action, as here is near the western boundary of that 

 action. "Where the eastern boundary of this lake was located 

 we may 'never know, since all monuments of its former exist- 

 ence may have been swept away by the glacial action, which 

 spread over that whole region. For the same reason it will be 

 difficult to accurately determine the former character of the 

 lakes and valley of the Upper Fox and Wolf rivers ; whether 

 they are remnants of one immense lake or parts of several, or 

 whether they were deep cavities in the ancient Potsdam sand 

 rocks or scooped out during the glacial period, we may never 

 be able to detemiine with any degTce of exactitude. 



Lake Winnebago was once much larger than at present. 

 The ancient boundaries may be readily traced, at about the 

 same level as the present clay banks at Appleton, which have 

 been cut through with the entire channel of the lower Fox 

 since the drift period, and the clay deposits. That higher 

 lake level may have been sufficient to have mingled the waters 

 of Lake Winnebago with the Horicon, during the existence of 

 the present fauna, since the fishes of Lake Winnebago and 

 Eock river, with few exceptions, are identical even to varieties. 



The extensive lakes found in the drift, with the adjacent 

 wet meadows and swamps, owe ther origin to the glacial action, 

 and their drainage has been the work of water, and in most 

 cases so gradual, yet continuous, that the ancient beaches have 

 been obliterated, if ever fornied. These will each present 

 peculiar characteristics, and must be studied as individuals, 

 and not as a whole system. 



The Upper and Lower Dells of the Wisconsin present us 

 with the result of the action of water in slowly cutting down 

 the sand rock, and emptying one of the most extensive of the 

 Wisconsin lakes. This lake, and the water-worn outlet was 

 -exterior to the drift range, and was one of the largest fresh- 



