Igo BOTANICAL GAZETTE [MARCH 
Bay would become a lake if the water level should sink 5-6 m.; 
Pickerel Cove is a similar case; and the inland portion of Rock 
Harbor is nearly closed at its narrowest point by a sand bar that 
has been built almost to the surface. 
Several of the lakes of Isle Royale are of respectable size. 
Siskowit Lake, the largest, is more than 10 km. long and 2.5 km. 
wide (fig. 31). The majority are small, many being mere ponds. 
All the lakes, and the harbors as well, are tending toward 
extinction through down-cutting of outlets, sedimentation, and 
vegetation. Down-cutting of outlets has as yet accomplished very 
agi 
Fic. 31.—Siskowit Lake: the largest of the Isle Royale lakes 
little. The large lakes like Siskowit are being filled by sedimenta- 
tion with extreme slowness, because of the small size of the streams, 
their slight gradient, and the thick covering of vegetation which 
almost inhibits erosion of the land surfaces. It is impossible for bog 
vegetation to obtain a foothold in the large lake basins except here 
and there in very sheltered spots, because of vigorous wave and ice 
action (HoLT 33, p. 218). They will therefore remain much as they 
are for a long time. In the small lakes, on the other hand, where 
wave and ice action are not severe, invasion by bog vegetation is 
in active progress. 
