360 PLEISTOCENE OP INDIANA AND MICHIGAN. 



Maumee, Arkona, Whittlesey, Wayne, Warren, and Lundy. In its relations to these lakes 

 it illustrates in a wonderful way the vicissitudes of lake waters controlled by an ice sheet with 

 periodic oscillations of front during retreat. The Lundy beach is described on pages 400-406. 



ICE BARRIERS OF LAKE SAGINAW. 



The first appearance of Lake Saginaw was probably during the back-step halt immediately 

 preceding the building of the Owosso moraine, or possibly during the back step next following. 

 (See p. 243 and fig. 1, p. 258.) This first stage and all the succeeding independent stages of- 

 Lake Saginaw were contemporaries or time equivalents of the later stages of Lake Maumee 

 and of Lake Whittlesey. The ice lobe that formed the successive barriers of Lakes Maumee 

 and Whittlesey in the Huron-Erie lowland extended also to the Saginaw Valley and formed 

 barriers for Lake Saginaw. Several positions of the barriers are shown diagrammatically in 

 fio-ure 6 (p. 370) . Considerable parts of these barriers are represented by moraines which have 

 been studied and mapped. The barriers of the remaining stages when Lake Saginaw was 

 merged with the Huron-Erie waters to the east (Lake Arkona and its successors down to Early 

 Lake Algonquin) are also shown conjecturally in figure 6. 



GRAND RIVER CHANNEL. 



HISTORY. 



The Grand River channel was the outlet of Lake Saginaw throughout most of the lake's 

 history, even through part of the time when it was merged with the much larger glacial lakes 

 of the Huron-Erie basin. A descriptive account of it, with some account of its early drainage 

 and earlier development, has already been given. (See pp. 255-260.) Its later development, 

 during its long service as a great outlet river, is discussed below. 



The Grand River channel was in use a much longer time than any other channel in Michi- 

 gan. It began to carry the lake waters when the outlet of Lake Maumee first opened near 

 Imlay, before the beginning of Lake Saginaw. Later it received the discharge from Lake 

 Maumee through the first Lake Saginaw. Next it received the overflow of the merged Lakes 

 Arkona and Saginaw. Later, when by a readvance of the ice Lake Saginaw was restored to 

 independent existence, it received the waters of Lakes Whittlesey and Saginaw. Only when 

 the ice retreated from the Port Huron morainic system and Lake Saginaw merged again 

 eastward and became part of Lake Wayne was the Grand River channel for the first time 

 in its existence temporarily abandoned, the waters of the merged lakes draining eastward to 

 the vicinity of Syracuse, N. Y. Through all previous changes, apparently without break or 

 intermission from the first opening of the Imlay outlet, it had carried the overflow. 



Later theice readvanced, closing the eastern outlet past Syracuse, and inaugurating Lake 



Warren, which discharged through the Grand River channel. The Warren beaches lie 20 to 



25 feet above the broad, swampy, dune-covered divide at the head of the channel north of 



Bannister. 



DEEPENING. 



Chamberlin has accounted for successive steps in the lowering of the level of glacial Lake 

 Chicago by a process of s toping in the bed of the outlet of that lake. The Grand River channel 

 led to Lake Chicago below Grand Rapids, and the river which flowed through this channel had 

 Lake Chicago for its base level of erosion. It would seem certain that a relatively sudden 

 lowering of Lake Chicago would introduce a process of stoping in the Grand River channel. 

 Possibly this accounts for the principal lower terraces in the valley, especially for one that seems 

 rather persistent at a height of 35 to 40 feet above the general channel floor. This terrace seems 

 to represent a relatively stable condition of the outlet river and a long duration of flow with 

 comparatively little deepening. It is to be noted, further, that this terrace appears to be the 

 one that is most closely related to the Arkona beaches. These beaches in the Saginaw basin 

 are very mature, and though they are generally double near the head of the outlet, they differ 

 in altitude by less than 10 feet, generally by not more than 5 to 7 feet. From their mature 



