314 ANNUAL REPOET SMITHSONIAN INSTITUTION, 1912. 



earlier, higher outlet. Perhaps this accounts for the faintness of 

 some of the beaches immediately above the Algonquin beach in the 

 Lake Superior basin; they may have been submerged and obliterated 

 after they were made. 



On the east side, the retreating ice front finally reached the straits 

 of Mackinac, where an opening allowed the waters of Lake Chicago to 

 unite with those of the Lake Huron basin. Whether this merging 

 of the waters in the Lake Mich^an and Lake Huron basins occurred 

 before or after the opening of the Trent Valley outlet at Khkfield, 

 Ontario, is not certainly known. 



GLACIAL LAKES IN GREEN BAY BASIN. 



Very little has been written concerning the glacial lakes m the 

 Green Bay-Lake Wmnebago valley and their extent has been as yet 

 only partially worked out. Upham published a paper in 1903 ^ 

 suggesting the name Glacial Lake Jean Nicolet for a lake that 

 discharged from the Fox Kiver dramage past Portage, Wis., to the 

 Wisconsin Valley. This paper was not based on any field work, 

 except a visit to the outlet, and the existence of the lake was inferred 

 partly from the presence of the outlet chaimel and partly from 

 Chamberlin's ^ description of the red clays in the Green Bay basin as 

 lacustrine. As noted above, studies recently carried on by Alden for 

 the United States Geological Survey have shown that the red clay 

 was largely worked over and formed mto morainal ridges and till 

 sheets by a readvance of the ice so that the limits of the red clay in 

 the Green Bay basin mark a glacial instead of a lake border. Alden's 

 studies have also shown that the lake history in this basin was some- 

 what different from that set forth by Upham. There was first a lake 

 that discharged from the district south of Lake Wmnebago south- 

 ward past Horicon into Kock River. This lake persisted until the 

 ice which formed the moraines at the head of Lake Winnebago had 

 receded far enough northward to open a passage westward from 

 Oshkosh to the headwater part of Fox River. Then the discharge 

 was shifted past Portage to the Wisconsin Valley. Later, when the 

 melting of the ice cleared the Green Bay peninsula the waters lowered 

 to the Lake Winnebago level and to a lake ui the Green Bay basm by 

 discharging eastward into Lake Chicago. A similar series of events 

 accompanied the preceding recession of the ice front, and also, in 

 reverse order, the readvance of the ice which formed the red till 

 moraines.^ In the present incomplete state of the study one can 

 hardly forecast the full succession oi events in this basin, but it is 

 evidently so different from Upham'e conception that it seems best 

 to leave the naming of these lakes until a later time. 



1 Amer. Geol., vol. 32, 1903, pp. 105-115 and 330-331. 



« Geology of Wisconsin, vol. 2, 1877, pp. 221-228; pi. 2, Geology Atlas of Wisconsin, 1881. 



» Alden, Wm. C, personal communi cation. , 



