SHIRAS EXPEDITIONS TO WHITEFISH POINT. 129 



up in these channels that would Avash much of this material into the 

 lake. A rapid accumulation of muck over a plant association would 

 obliterate it, and the looseness of the soil would prevent plants again 

 taking root. Thus regions like Stations 52 and 55 could be produced. 

 In more open parts of the lakes, this light muck may be carried and 

 very generally distributed by wind-made water currents. Beaver Lake 

 and Spruce Lake hav(^ muck practically over their entire bottoms. It 

 is possible that currents sweep this away completely in some cases, thus 

 returning the shoals to a primitive type, that is, with sandy bottoms 

 and no plants, but a continued accumulation of organic debris in these 

 lakes must in time bring about a firm substratum, peaty in nature, that 

 will support plants readily. The marsh, then, can rapidly encroach on 

 the lake, and the last stage as a fish environment would thus be reached. 

 Beaver channels and pools Avill finally give way to the marsh if man 

 destroys these animals, as he is rapidly doing at present. Spruce 

 swamps encroach on the open marsh and, in places, they have reached, 

 the edges of the lake producing conditions for fish life which are different 

 from those of other parts of the lake (Plate XXII A). 



The probable developmental relation of these fish habitats to each 

 other is showi in the diagram below. 



"to'^ 



Wooded Swamp 



I 



Sedge Maroh 



1 I 



Muck covered Bottom Areas without Plants 



quatio Plant Associations 



Deep areas without Plants - ^ > Shoala wi-'uhout Plants 



Diagram showing probable developmental relation of fish habitats near Vermilion, 



Michigan. 



A classification of the fish habitats in the marsh lakes may be made 

 as follows : 



Deep Water Areas; five to seven feet. Natural depressions, deep 

 channels, beaver excavations, etc. 

 With few or no visible plants 

 With stonewort association 

 With pond weed association 

 With water-lily association 

 17 



