GLACIAL LAKES TAYLOR, 313 



igaii, and the Nipissing beach, about 15 feet above the lake. The 

 summit m the Chicago outlet m the southwest part of the city is 

 only 8 feet above Lake Michigan and is a broad, flat region much 

 obstructed by low, sandy ridges. The Toleston beach passes over 

 this broad divide at a level high enough to have jDermitted Lake 

 Chicago to discharge over it, even when receiving the discharge of 

 Lake Whittlesey or Lake Warren. Nevertheless, the Toleston beach 

 seems to be continuous with the Algonqum beach, which is present 

 in all of the upper three lake basins, and part of the overflow of 

 Lake Algonquin may have been by way of Chicago for a time. 

 When the Huron-Erie waters were discharging eastward past Syra- 

 cuse, the volume of discharge at Chicago was largely dhnuiished and 

 the lake stood slightly lower. 



Wlien the ice lobe m the Lake Micliigan basm retreated mto the 

 northern part of that basui, it uncovered ground of critical interest 

 on both sides. On the west side the glacial waters of the Lake 

 Superior basin had been held up to a liigher level than those of Lake 

 Chicago, and when an opening occurred around the hills southeast 

 of Marquette these waters were dramed southward along the western 

 edge of the Green Bay lobe of the ice sheet and ultimately into Lake 

 Chicago. 



Bordering the west shore of Lake Michigan and extending into the 

 Green Bay-Lake Winnebago trough and the Fox and Wolf River 

 valleys is an extensive deposit of red clay, partly laminated, partly 

 pebbly and massive, which was described by Chamberlin^ m his 

 Geology of eastern Wisconsm. Later study of this deposit by Alden,^ 

 under the direction of Chamberlm, shows that the larger part of this 

 deposit, the massive pebbly clay, is to be interpreted as glacial till 

 which was laid down durmg a readvanco of the glacier in the Lake 

 ^lichigan basm as lar south as Llilwaukee and of the Green Bay lobe 

 in the Green Bay-Lake Wimiebago trough to a point south of Fond 

 du Lac, Wis. The ice also crowded westward in the Fox and Wolf 

 River valleys. The red silt composmg the lammated clay and the 

 matrix of the massive pebbly clay is thought to have come from the 

 Lake Superior region, beuig brought into the Green Bay and Lake 

 Michigan basins by the openmg of a southward outlet southeast of 

 Marquette. The first opening of this outlet must have been at or 

 near the climax of the stadial retreat immediately before the read- 

 vance to the Ihst red till moraine. The phenomena indicate a 

 readvance over a relatively wide interval, and it seems certain that if 

 a lower outlet had been opened by the retreat, it was closed agam by 

 the readvance and the level of the glacial v/aters m the western half 

 of the Lake Superior basin were raised again to the level of some 



* Geology of Wisconsin, vol. 2, pp. 221-228. » Alden, Wm. C, personal communication. 



