GLACIAL LAKES 



333 



tration. Our records of this third North American lake stage, 

 referred to as Lake Arkona, are however most imperfect, for the 

 reason that it was followed by a readvance of the ice front which 



FIG. 362. Outline map of Lakes Whittlesey and Saginaw (after Leverett). 



closed the passage around " the thumb " and raised the level of 

 the waters until an outlet was found past the town of Ubly at a 

 lower level than the " Imlay outlet." When the waters of a 



FIG. 363. Map of the glacial Lake Warren, the last of the lakes in the Huron-Erie 

 basin, which discharged through the "Grand River outlet "into the Mississippi 

 (after Leverett). 



lake are thus rising, strong beach formations result, and those of 

 this stage, which is known as the Lake Whittlesey stage, are much 

 the strongest that are found within the Huron-Erie basin. Traced 



