MICHIGAN ACADEMY OP SCIENCE. 25 



extent of the ancient water bodies. These include bars of gravelly 

 material thrown up by waves along the old shores, and abrupt banks 

 formed where the waves cut back into the bordering land ; also deposits 

 with the delta form and structure laid down Mhere streams entered the 

 old lakes. The beaches of a given lake lead into the head of its outlet at 

 a level corresponding to the ordinary stage of water in the outlet. In 

 some cases, however, the outlet experieaced considerable deepening dur- 

 ing the life of the lake and one finds later beaches opening into it at 

 levels corresponding to this deei>ening. 



THE SUCCESSION OF LAKES. 



It is evident that Avhen the ice sheet extended out to or beyond the 

 divide between the Great Lakes and the Mississippi drainage there 

 would be a direct discharge along valleys into the Mississipiji and no 

 lakes would be present. But as soon as the ice had shrunk back inside 

 the divide to where the land sloped toward the ice border lakes would 

 begin forming. There would be at first small bodies of vrater at numer- 

 ous points along the borders of the basin, either discharging directly 

 across the rim by independent outlets or having connection by border 

 drainage along the ice edge to some low place on the rim of the basin. 

 With the shrinking of the ice the small lakes which at first were inde- 

 pendent, or were connected by border drainage channels would become 

 confluent and take the level of the lowest water level of the series. 



Inasmuch as the melting of the ice uncovered the southern and south- 

 western borders of the lake basins earliest, it is here that we find the 

 beginnings of the lakes. These basins extend somewhat farther out than 

 the present Great Lakes, and it is in these extensions that the first 

 ponding oecurred ; in some cases while the whole area now occupied by 

 water was occupied by the ice. 



It is scarcely possible as yet to determine in which basin the ponding 

 of water took place earliest. Mapping of moraines has been carried far 

 enough to indicate that tliere was no great ditference in the dates- of 

 the beginning of the lakes in the southwest ends of the Superior, Green 

 Bay, Lake Michigan, and Lake Erie basins, whereas the lakes formed in, 

 the Huron and Ontario basins were much later. A lake in the Saginaw 

 basin southAvest of Lake Huron was earlier than in the southern end 

 of Lake LIurou. The lake in the Ontario basin came in the latest of 

 any in the large basins, being situated farthest northeast and conse- 

 quently nearest the center of dispersion of the ice. 



SUPERIOR BASIX. 



The earliest part of the drainage basin of Lake Superior to be vacated 

 by the ice seems to have been in the district now drained by St. Louis 

 River. As noted by Winchell,^ the ponded Avaters in the southwest parL 

 of this river basin were at one time discharged southwestward to the 

 Mississippi from an altitude about TOO feet above Lake Superior, as 

 indicated in Fig. 1. The name Lake I']»ham has been given to this 

 small and transient water body. With tlu^ shrinking of the ice border 

 a lower jiassage, about 5.30 feet above Lake Superior was opened from 



iBull. Geol. Soc. Am. Vol. 12, 1901, p. 124. 

 4 



