18 SAND DUNE REGION OF SAGINAW BAY. 



At the present time the dunes are all stationary, even the newest 

 ones being covered by vegetation. From Sand Point eastward, of the 

 two largest ridges, one — as described by Davis — extends along the 

 landward or southeastern side of the sand area, while the other extends 

 along the northwestern side following the present beach of Saginaw 

 Bay. These two ridges are apparently true sand dunes (with long 

 windward and steep leeward slopes) superimposed upon what was in 

 times past in the case of the southern ridge, or is now in the case of the 

 northern one, the upper beach of Saginaw Bay. 



West of Caseville the inner sand ridge curves eastward, swinging back 

 toward the shore at Bayport, while the outer one, following the shore, 

 curves abruptly to the west and is continued to the end of Sand Point. 

 The base of the Point (the area lying between a line drawn across the 

 Point just west of Orr Lake and the eastern dune ridge) is low and 

 swampy, and relieved l)y only low gravel ridges. These angle off 

 from the outer dune ridge and parallel the eastern one in a general way. 

 On the Point these ridges successively bear more and more to the west- 

 ward, crossing it in a direction diagonal to its length, and are connected 

 at their southern ends by low ridges that run east and west. From 

 about the middle to the end of the Point the dune ridges are higher, 

 liut have about the same arrangement and cross the Point in a more 

 north and south direction. Near the end the high outer dune swings 

 away to the southwest and leaves a wide sand flat (Plate II a), re- 

 placed at the very end by a bay opening to the west, between the 

 dune and the present beach. The outer side of this bay is formed by 

 a sand bar submerged at its outer end, and there is a parallel submerged 

 bar a short distance ofT shore that is continued far out in the bay. 

 Toward the end of the Point the transverse ridges are connected on the 

 south side by a single ridge, l5ut toward its base other ridges now 

 intervene between the present beach .and the one joining the ends of 

 the transverse ridges, and still another is being formed as a southeast- 

 wardly projecting sand spit. Flats similar to the one at the end of 

 Sand Point are found on the west side of Hat Point, Oak Point (II b) 

 and Little Oak Points (Plate III a). 



The topographic conditions briefly outlined above may, I believe, 

 be interpreted as follows: 



1. As the level of the water in the post-glacial lakes fell low enough 



to uncover the sand ridge region, the sand formed by the com- 

 minution of the exposed rock was built up into beaches each one 

 of which represents a halt in the fall of the water level. 



2. In the longer halts opportunity was given for the sand l)lown up by 



the winds from the lieach to be piled into dunes on the upper 

 beach. 



