Occasional Papers of the Museum of Zoology 13, 



that forms the outlet is ahnost choked by muck washed in 

 from the lake, except in a few places where the current is swift 

 enough to expose a sandy bottom. Sphccrinm sulcatum was 

 much more abundant in the outlet than in the lake itself. 



Jackson Lake 



Habitat 10. Jackson Lake and Outlet. This lake is about 

 200 yards long by about 75 wide, and is in a hollow behind 

 the hill formed by the rock ridge at the Rock Dam. When 

 studied the water was only two or three feet deep in the deepest 

 portion, as the basin is almost completely filled with soft, very 

 finely divided, marly muck ; this material must reach a con- 

 siderable depth at the center, as the marly muck is six feet in 

 depth a yard from the shore. Around the lake was a quite high 

 and dry grass swamp, the flora of which resembled that of 

 stream banks rather than that of the true bog lakes ; along the 

 edge there was a considerable growth of Chara in shallow 

 water and the yellow water lilies were very abundant near 

 the middle. 



Several small spring brooks empty into the lake and it£t 

 short but quite large outlet drains into the Sturgeon River 

 From all appearances, this outlet had formerly been quite 

 deep with a rocky bottom, but the marly muck has almost 

 entirely filled it and the conditions are very simlar to the lake 

 itself. The living shells were mostly obtained at the entrance 

 into the outlet, as this was the only place where it was pos- 

 sible to reach water of any depth. Many dead shells were 

 found mixed in the mud ; all of these types were probably 

 inhabitants of the lake itself at some time, and many of them 

 may have still been living near the center. 



