128 PAPERS ON ZOOLOGY OF MICHIGAN. 



a thick stratum of loose, buoyant muck, barren of visible growing 

 vegetation. Where this deposit is absent, the clean yellow sand sup- 

 ports few plants; but where a little humus is present, there is often a 

 growth of submerged aquatic plants, principally stoneworts, pond- 

 weeds, bladderworts, water weeds, and water lilies. The marshy 

 shores have, as a rule, either sedge growths (Plate XXIIB) or partly 

 submerged patches of sweet gale (XXI A). Cat-tails, bulrushes, smart- 

 weeds, and some other plants characterize the open marsh region. In 

 a number of places, the wooded swamps extend to the lake margin 

 (Plate XXIIA). The water of these marsh lakes is without evident 

 turbidity, but is slightly browTi stained. In temperature it was found 

 commonly to be about that of the air, and the readings made were not 

 far from 70° F. 



Although fish are numerous in these lakes they are not found in all of 

 them or in all parts of any one of them. They have a marked tendency 

 to dwell near the shore, although bottom and water conditions in mid- 

 lake are very similar to those about the margin, except for those pro- 

 duced by the shore features. Muck bottoms are evidentty much pre- 

 ferred to the sandy ones. On account of these restrictions in dis- 

 tribution, very definite fish habitats could be found. A consideration 

 of the important types of these ^vill now be made. It is very difficult 

 and apparently impossible to work out these habitats in a successional 

 way, on account of complications in their history, brought about by 

 dams, channels, and other structures built by beavers and man and by 

 the removal of beaver dams by man, when their presence interfered 

 with cranberry culture and other interests, but in general the habitats 

 have developed as follows. When the water receded from the Nipissing 

 to the Lake Superior level and the sand ridges were formed, the inter- 

 vening depressions were capable of containing water in sufficient 

 amounts in some cases to form small lakes. Wind and water borne 

 sand and accumulating humus tended to make these lakes shallower. 

 Beavers, however, converted parts of their shoals into deep water 

 areas by digging channels. Similar work may have been done by water 

 currents. Marshes followed the shoals by the encroachment of plants 

 on them, ])ut in places there is a reversion to lake conditions by the 

 formation of channels and pools in marshes by beavers and sometimes 

 this occurs temporarily when the marshes are flooded by man to pro- 

 tect or harvest cranberries. These operations appear to be the chief 

 source of the muck deposits over the sand bottom in these lakes. A 

 considerable amount of this light black soil could be transferred by 

 beavers from the marshes while making their channels or while using 

 them as runways, and when the lakes are lowered by opening the 

 sluices in dams for flooding cranberry marshes, currents might be set 



