GLACIAL LAKES TAYLOR. 315 



GLACIAL LAKES IN THE BASIN OF LAKE SUPERIOR. 



From tho first small lakes at the extreme western end of 

 tlae Lake Superior basin the glacial waters expanded in a manner 

 similar to those just described for the Lake Erie and Lake Michigan 

 basins. In the earlier stages, while the lakes were small, there were 

 slight changes m outlet and level, though the early stages had outlet 

 directly or indirectly to the St. Croix Valley. 



LAKE DULUTH. 



Finally came Lake Duluth with its outlet southward thi'ough the 

 Brul6 and St. Croix Valleys. Lake Duluth endured for a much 

 longer time than the earlier lakes, and at its lower levels expanded 

 to a lake of large size, formmg beaches found even on the outer part 

 of the Keweenaw peninsula. Its outlet was cut down about 40 feet, 

 lowermg the level of the lake and causing the formation of later 

 beaches below the highest. 



Several lower beaches which have been traced by Mr. Leverett 

 seem to lie too low for waters discharging through the St. Croix 

 outlet, and hence may not belong to Lake Duluth, These suggest a 

 place of overflow to the east and south, around the hills south of 

 Marquette. The outlet mdicated by these beaches has not yet been 

 determined. These are rather weak beaches, and suggest the possi- 

 bility of submergence in consequence of a readvance of the ice after 

 they were made. There is independent evidence of such a readvance. 



GLACIAL LAKES IN THE SUPERIOR-MICHIGAN-HURON BASIN. 



LAKE ALGONQUIN.' 



In the outline given above the succession of lakes in each of the 

 upper three bashis — those of Lakes Huron, Michigan, and Superior — 

 were given down to the time when the glacial waters ui all three 

 basins were about to merge uito one great lake. This larger body 

 is called Lake Algonqum, and its upper beach is one of the strongest 

 and most persistent shore Imcs m the Great Lakes region. At its 

 greatest extent, as shown in figure 7, this lake covered an area con- 

 siderably larger than all three of the present upper Great Lakes. 



Wlien the lake waters fell away to lower levels from Lake Warren 

 they uncovered ior the first time the low lands between Lakes Huron 

 and Erie. This low land divided the waters mto two separate lakes 

 and inaugurated for the first lime the flow of the St. Clan- and 

 Detroit Rivers. 



Lake Algonquin may be divided into four stages: (1) Early Lake 

 Algonquin, confined to the south part of the Lake Huron basin, 

 outlet at Port Huron; (2) Kirkfield stage, covered all of the upper 



» Spencer, J. W., Am. Jour. Sci., 3, vol. 41, Jan. 1S91, pp. 12-21. Goldthwalt, J. W., Bull. Geol. Soc. 

 Am., vol. 21, 1909, pp. 227-2-lS. 



