1904] WELD: BOTANICAL SURVEY OF HURON VALLEY 51 
peat the lake first disappears from the center, then the bog, and 
so on until a tamarack woods fills the basin. Into this pure 
growth of tamarack there come in slowly elm, ash, maple, birch, 
basswood, and their accompanying undergrowth. Aswamp near 
Cavenaugh Lake was observed where elms and ash a foot and a 
half in diameter had come in, overtopped the tamaracks, and 
killed them. This swamp had a very leafy undergrowth. Thus 
the final stage is a damp, rich-woods flora of soft woods; never 
does a hard-wood flora take possession, as far as my observations 
in this region extend, although an occasional oak or juniper may 
be found. 
The history just outlined has been greatly modified in indi- 
vidual cases, as the remarkable differences between the first and 
second lakes plainly show, and future investigations should take 
full account of such differences. Thus far, critical comparisons 
of the flora of different lakes and bogs and the conditions affect- 
ing their plant life are wanting. The distribution of their phyto- 
plankton presents many unexplained facts, and the factors deter- 
mining the peculiarities of bog xerophytes are still an unsolved 
riddle. The deposition of peat is progressing with varying 
rapidity in numerous bogs and swamps in southern Michigan, 
but the processes involved in its formation and affecting not 
merely its fuel value but its fitness for further plant growth, and 
hence the composition of succeeding plant societies, are still 
very imperfectly known. The valley of the Huron River, with 
its great number of lakes and variety of conditions, offers a 
favorable area for more extended study of these problems. 
SUMMARY. 
1. These lakes were formed in the moraine at the front of 
the ice sheet when the Erie lobe extended 3 miles (5*") west of 
Ann Arbor. The present outlets follow the glacial drainage to 
the west into the Huron River, which then flowed west into Lake 
Michigan. 
2. The third lake never was connected with the others. The 
first and second were once one, with an island in the center. 
Subsequent lowering of water and filling of channels has made 
two lakes. 
