304 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1912. 



east of Imlay and thence westward into the Saginaw basin, but if so 

 was overridden and obliterated by a readvance of the ice. 



Third stage. — ^Wlien the ice front readvanced it closed the outlet 

 for the second stage, and moved westward to a position close along 

 the east side of the gTeat Imlay outlet channel, which passes north- 

 ward just east of Imla}^. This channel shows evidence of having 

 been crowded westward by the moraine along its east side. At this 

 stage Lake Maumee was almost high enough to overflow at Fort 

 Wayne. 



Wlien the ice retreated from this last position it opened a very 

 temporary outlet across Tuscola County, Mich., but it did not open 

 a permanent new outlet until it had retreated many miles to the 

 north, toward the north end of the Saginaw peninsula, or "thumb." 

 The opening then made, however, allowed the lake waters to fall 

 quite suddenly to a much lower level. 



At this stage Lake Maumee reached its greatest extent, stretcliing 

 from^ New Haven, Ind., to a point several miles north of Imlay, 

 Mich., and on its south side to a point a little cast of Girard, Pa. 

 (fig. 2, ice border at M). In its horizontal part the tliird beach is 

 760 feet above sea level. The fronts of the contemporary ice lobes 

 were probably a few miles east of Detroit for the Lake Huron lobe 

 and perhaps 40 or 50 miles east of Toledo in Lake Erie. At its front 

 the ice was therefore standing in water 150 to 200 feet deep. 



LAKE SAGINAW. 1 



During the later stages of Lake Maumee a lake appeared in the 

 Saginaw Valley in front of the Saginaw ice lobe (fig. 2), and the 

 Imlay outlet river emptied into it. At fu'st it was narrow and 

 crescent-shaped, but it grew larger and wider before the end of Lake 

 Maumee. Its outlet was through the Grand River channel to glacial 

 lake Chicago, a little west of Grand Rapids. Lake Saginaw was 

 merged with Lake Arkona, restored to independence during the time 

 of Lake Wliittlesey, and merged with Lake Warren before its final 

 extinction by the abandonment of its outlet. 



GLACIAL LAKES OF THE HUKON-ERIE-ONTAKIO BASIN. 



LAKE ARK0NA.2 



The next important stage of the ice retreat caused a still more 

 profound change in the status of the glacial lakes. The ice with- 

 drew altogether from the "thumb" of IVIichigan, so that the entire 

 sweep of the lake waters to the eastward was allowed to fall to the 

 level of Lake Saginaw and merge with that lake. Lake Saginaw 



1 When it existed as au independent body, Lake Saginaw was limited to the Saginaw Valley. 



2 The lakes preceding Lake Arkona were confined to the Huron-Erie basin and did not include any 

 part of the basin of Lake Ontario; Lake Whittlesey, following I>ake Arkona, was also limited to the 

 liuron-Erie basin. 



