SAND DUNE REGION OF SAGINAW BAY. 25 



occur along the landward side of the inner dune ridge. It is about 

 two and one-half miles long by one mile wide. The bottom consists 

 of deep deposits of peat and marl, and the depth of water is, in summer, 

 but a few inches over most of the lake, although along the north side 

 of the middle there is a channel from three to five feet deep. There is a 

 rich aquatic vegetation, consisting mostly of pond weeds, over most of 

 the bottom. The plants whose stems and leaves mostly float upon, or are 

 often tlirust above the water, grow in patches. These patches we 

 found to consist of such forms as potamogetons, pickerel-weed, tape- 

 grass, water-shield, bur-reed (Sparganium eurycarpum), pond-lilies, 

 great bulrush, etc. In places the peat has been l^uilt up so that it \nll 

 support bog plants, and bog-islands have been formed "with a flora 

 the same as in the tamarack swamps about the margin of the lake. 

 (Plates IX, X a.) 



The aquatic invertebrate collections of Rush Lake have not been 

 studied, with the exception of the mollusks. The painted tm-tle and 

 bull frog were found here, and the following fish: yellow catfish, long- 

 jawed catfish, blunt-nosed minnow, golden shiner, Cayuga minnow, 

 grass pike, sun fish, perch, and spindle darter. 



Streams: The Pigeon River was the only stream studied that heads 

 back in the "hill district" of the central part of the county. Flowing 

 across the intervening plain it enters the sand region and empties into 

 Saginaw Bay at Caseville. As it crosses the plain district it is little 

 more than a meandering creek, with a bottom of clay and gravel. After 

 entering the sand region it becomes much more winding, as it is nearly 

 at base level. It also becomes wider and deeper (up to six feet) which 

 with the feeble current permits a rich growth of aquatic plants. (Plates 



X b, XI b.) 



Within the sand region (at Caseville) the river is a sluggish meandering 

 stream ^\ith a mud bottom, and considerable aquatic vegetation in 

 places. One of the curves has been cut off as an ox-bow pond. (Plate 



XI a.) The conditions in this pond apparently differ little from those 

 of the river except that the quiet water permits a greater development 

 of vegetation. Zones of rushes surround it and beds of yellow and 

 white waterlilies and Sparganium eurycarpum occur in the open water. 



The only animal groups studied in these habitats were the fish and 

 mollusks. The fish found in the river are: dog-fish, yellow catfish, 

 black bullhead, common sucker, mullet, silver fin (one specimen), 

 grass pike, calico bass, rock bass, sun-fish, black bass, large-mouthed 

 black bass, wall-eyed pike, perch, log perch, black-sided darter, Iowa 

 darter, and spindle darter. Those found in the ox-bow pond are: 

 bullhead, golden shiner, red-fin dace, little pickerel, grass pike, rock 

 bass, and large-mouthed black bass. 



