CHAPTER XX!. 



GLACIAL LAKE ALGONQUIN. 

 By Frank B. Taylor. 



HISTORICAL OUTLINE. 



OUTLETS AND STAGES. 



Lake Algonquin was the largest of the glacial lakes and marked the culmination of the 

 waters controlled by the retreating ice sheet. The glacial lakes began separately in the Erie, 

 Saginaw, Michigan, Green Bay, and Lake Superior basins, but after many changes all, except 

 that which lay in the basin of Lake Erie, were combined in Lake Algonquin. (See PL XXI.) 



Lake Algonquin has a very complex history, for at different times it had outlets at five 

 different places and was affected, especially in the latter part of its existence, by extensive 

 differential uplifts of the land. The uplifting movements were strongest in the north, the 

 direction of maximum rise being a little east of north in the central part of the area and about 

 north-northeast in the eastern and western parts. The establishment of the first outlet and two 

 later changes of outlet were caused by the uncovering of lower points of discharge by the retreat- 

 ing ice sheet; one change was caused by differential uplift and one change was caused by the 

 merging of Lake Algonquin with another lake at about the same level. Besides these, there 

 were several temporary and transitional stages during which two or three outlets were active 

 at once while the discharge was shifting from one outlet to another. The changes of Lake 

 Algonquin can perhaps be understood best by considering them in terms of the different lake 

 basins occupied at the successive stages and by noting the location of the outlet at each stage. 

 This method furnishes a natural basis for dividing Lake Algonquin into four stages. 



The introductory stage of Lake Algonquin was short and was followed by one or two 

 transitional steps or substages in which different lake basins and different outlets were involved. 

 These steps of transition are mainly matters of inference and are not based on observation. 

 Nevertheless, their existence is not to be doubted. The first stage occupied only the south 

 part of the basin of Lake Huron, including Saginaw Bay. It received tributary drainage from 

 smaller lakes in the south part of the Georgian Bay and Lake Simcoe basins. Its existence is 

 based on evidence of the establishment and erosion of its outlet through the distributaries of 

 the St. Clair River at St. Clair, and on characters of the Niagara River and gorge. The steps 

 of transition following this are simply physical and logical necessities, made so by the con- 

 ditions of development from the first stage to the later fully developed Lake Algonquin, which 

 included all three of the upper Great Lake basins. 



The first stage, known as Early Lake Algonquin, covered only the south part of Lake 

 Huron (including Saginaw Bay) and did not cover any part of the present Georgian Bay or of 

 the Lake Michigan or Lake Superior basins, its contemporaries in the Michigan and Superior 

 basins being still Lake Chicago and Lake Duluth respectively. The outlet was at Port Huron 

 and the overflow passed south through St. Clair and Detroit rivers to the basin of Lake Erie. 



When the ice sheet drew away from the high ground northwest of Alpena, Mich., it allowed 

 glacial Lake Chicago in the basin of Lake Michigan to unite with Early Lake Algonquin. If 

 this occurred, as it most probably did, before the opening of the Kirkfield outlet in Ontario, the 

 two lakes were probably already at very nearly the same level at the time of union, and no 

 considerable change of altitude occurred in either, the overflow probably being divided between 

 the two original outlets at Port Huron and Chicago. If this was the order of events the united 

 lake succeeded Early Lake Algonquin. 



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