/ 



128 



BOTANICAL GAZETTE 



[august 



sluggish outlet at the southwestern corner of the lake. The 

 border swamp is interrupted on the south side of the lake by the 

 former delta of the brook entering at that place. The delta 

 rises several feet above the level of the surrounding shore and 

 differs from it very markedly in vegetation [fig^ /). 



Fig. I. — South shore of the lake, part of the former delta plain in the foreground. 



i 



• The lake basin proper is surrounded by a shallow marginal 

 rim varying from forty to seventy-five feet in width and descend- 

 ing from the water*s edge at one side to eighteen or twenty feet 

 below the surface at the other. This marginal rim owes its 

 existence primarily to organic factors which are still at work 

 modifying and extending it. The soil for several feet in depth 

 is largely composed of organic material which presents the 

 usual successive gradations from vegetable detritus to muck and 

 peat. The bottom descends very rapidly from this rim to form 

 the main central basin, which averages more than fifty feet in 



