GLACIAL AND POSTGLACIAL HISTORY OF GREAT LAKES REGION. 323 



LAKE SAGINAW. 



During the later stages of Lake Maumee a small lake appeared in the Saginaw Valley in 

 front of the Saginaw ice lobe and received the drainage of the Imlay outlet river. At first it was 

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

 Maumee. Its outlet was westward through the Grand River channel for a few miles west of 

 Grand Rapids and thence south along the ice front to Lake Chicago. Lake Saginaw was merged 

 with Lake Arkona, restored to independence during Lake Whittlesey, and merged with Lake 

 Warren before its final extinction by the abandonment of its outlet. 



While it existed as an independent body, Lake Saginaw was limited to the Saginaw Valley, 

 which is a part of the basin of Lake Huron. It was also a part of Lake Wayne and later of Lake 

 Lundy, but the outlet was then eastward to the Mohawk near Syracuse, N. Y. 



GLACIAL LAKES IN THE HURON-ERIE-ONTARIO BASIN. 



LAKE ARKONA. V 



The next important step in the ice retreat changed still more profoundly the condition of 

 the glacial lakes. (See fig. 6, p. 370.) The ice withdrew altogether from the "thumb" of Michi- 

 gan, allowing the entire sweep of lake waters to the eastward to fall to the level of Lake Sagi- 

 naw and to merge with that lake. Lake Saginaw had at the same time expanded largely 

 northeastward, and a strait several miles wide had opened past the end of the "thumb." The 

 enlarged lake, which is called Lake Arkona, stretched from the vicinity of Gladwin, Mich., to at 

 least 40 or 50 miles east of Buffalo, N. Y., and covered a considerable part of southern Ontario. 

 Its outlet was westward through the Grand River channel. Its altitude above sea level was 

 at first 710 feet, but by cutting down of the outlet it became reduced to 694 feet. West and 

 northwest of Port Huron are three beach ridges formed by this lake, known as the Arkona beaches. 



LAKE WHITTLESEY. 



After the formation of the Arkona beaches the ice front made a pronounced readvance 

 southward up the slope of the "thumb" to Ubly, building the Port Huron morainic system, cut- 

 ting off the Saginaw Valley, and restoring Lake Saginaw to independence. The advance had 

 no effect on the waters of Lake Saginaw, but it raised those of the lake area east of the " thumb" 

 by about 44 feet, forming a new lake, known as Lake Whittlesey, whose surface stood about 28 

 feet above the highest Arkona beach ridge in the region northwest of Port Huron and 44 feet 

 above the lowest. 



On the northern part of the "thumb" the Arkona beaches were overridden by the ice and a 

 considerable extent of them was buried beneath the terminal moraine or beneath outwash. In 

 the southern part of the Black River valley northwest of Port Huron they were not overridden 

 nor buried but were submerged. Within the valley they are strongly developed gravelly beach 

 ridges and show no modification due to submergence. Outside, on the south, however, they 

 were almost entirely washed away by the storm waves of Lake Whittlesey and in many places 

 are traceable only with much difficulty. Although they were 28 to 44 feet under the water, the 

 storm waves swept their gravels rapidly up the slope and built them into the Whittlesey beach. 



The Whittlesey beach has characters which indicate that it was pushed up the slope as it 

 was made and that it was made rapidly, for it stands very high above the adjacent land and is 

 peculiarly independent of topography, crossing valleys of moderate depth in a direct line like a 

 railroad embankment. 



LAKE WAYNE. 



Below the Arkona beaches lies the Warren beach and next lower the Wayne beach. But the 

 Wayne, like the Arkona and middle Maumee beaches, shows evidence of having been submerged 

 and modified while the Warren beach was being formed above it at the margin of the raised 

 lake. The lake level appears to have dropped abruptly 80 or 85 feet from the Whittlesey beach 



1 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 Lake Arkona, was also limited to the Huron-Erie basin. 



