LATER MORAINES OF LAKE MICHIGAN, SAGINAW, AND HURON-ERIE LOBES. 257 



had a small lakelike expansion just west of Duplain. In the east side of this a large gravel deposit 

 occupies the position of a delta, but seems rather to have been an island-like obstacle in the flow 

 of the river, the current dividing around it with the larger part passing around the north side. 

 It is oval in form and stands 10 to 15 feet above the swamp. Along its west and north sides 

 a prominent gravel ridge runs like a parapet and closely resembles a beach ridge made by waves; 

 from this there is a steep descent into the swamp which stretches away to the west. A narrower 

 channel passes around its south side. This deposit seems more like a kame than any other 

 type — a kame deposited in a small reentrant of the ice front and shaped partly by the ice with 

 which it was in contact and perhaps partly by the later river current. It seems impossible to 

 explain its peculiarities on the supposition that it is simply a delta. 



Southeast of Maple Rapids the river appears to have entered a shallow basin and deposited 

 a thin gravelly delta. East of Maple Rapids and resting against the front of the Flint moraine 

 another bed of gravel, much coarser and thicker, appears to have been shed directly from the 

 ice front or else brought in from the east along the eroded bluff. For several miles west of 

 Duplain the Flint moraine is represented by only a few scattered knolls; either it was not formed 

 or else it was washed away by the outlet river. In this interval the channel is nearly all a swamp. 



With the advent of the outlet river the increase of volume must have been sudden and 

 great, so that the preexisting river bed along the line of drainage westward was much too small. 

 In its first rush the great river must have torn away the banks of the then existing channel and 

 made a new bed suited to its volume. In doing this it must have swept along a great amount of 

 sediment, and it may possibly have deposited the gravel on the bluff south of Matherton, south 

 of Ionia, and 2 miles west of Lyons in its first rush. The deposit south of Matherton in particular 

 might have had such an origin ; the others are thin and flat and appear to have been laid down 

 by small rather than great volumes of water. 



RELATION OP THE GRAND RIVER CHANNEL TO THE COURSE OF THE MORAINES. 



Early moraines. — As already noted (p. 256), the early moraines show scarcely any tendency 

 to project westward out of their even curves where they cross the Grand River channel. Except 

 in the case of the Lansing moraine at Lansing, no very pronounced evidence of readvance has 

 been found among them; and if the Lansing moraine is the foremost one of a distinct group its 

 readvance may not signify a normal habit for the slender moraines in general but may mark 

 only a readvance after a relatively long backstep in the general glacial retreat. 



Oivosso moraine. — East of Maple Rapids, however, there seems to be no escape from the 

 conclusion that there was some readvance. The Flint moraine, like all the older moraines of 

 the deployed group, comes up to the Grand River channel on the south side without showing the 

 slightest evidence that any channel or depression was present to influence the movement of the 

 ice, and it seems to pass on to the north with the same general trend. East of the Flint moraine, 

 however, another moraine runs eastward past Union Home and Eureka, forming a high bluff 

 along the south side of Maple River where the head of the Grand River channel widens to the 

 east. (See fig. 1, p. 258.) This fragment is of irregular form and is out of adjustment with the 

 Flint moraine. It runs westward into the head of the channel. 



On the north side of the channel a strong, continuous moraine runs south from Ithaca, turn- 

 ing southwestward into the head of the channel, to a point opposite Maple Rapids. (See fig. 1.) 

 This part of the moraine projects westward through the Flint moraine, as though a depression 

 had led the ice to flow a mile or two farther west during the building of the Owosso moraine than 

 it did during the building of the Flint moraine. Such' a depression can be accounted for only as 

 the work of the Imlay outlet river immediately before the readvance to the Owosso moraine, 

 and the sharp ice tongue which pushed its point westward to Maple Rapids can hardly be 

 explained except on the supposition that its axis followed a pronounced depression. 



The events leading to this result are conceived to have been about as follows: When the ice 

 withdrew from the Flint moraine to some point a little farther east than Eureka, the Imlay out- 

 let river rushed in westward along the front of the ice and cut the channel back several miles 

 34407°— 15 17 



