922] WATERMAN—PLANT COMMUNITIES 27 
Each of these formations, although differently situated (one 
in the heart of the sand ridges, the other between two lakes), seems 
to indicate the same physiographic change, that is, a sudden lower- 
ing of the water table by several feet. This change might be 
referred to the activities of the first white settlers about fifty years 
ago. The Long Lake area is very close to Crystal Lake, and might 
have been partially drained by seepage when Crystal Lake level 
was lowered in 1871 (10). A low terrace on the south bank of Long 
Lake adds weight to this hypothesis. The other meadow must 
have come very close to Platte River at its eastern extremity, and 
may have been lowered in connection with the first lumbering opera- 
tions at about the same time. : 
Another explanation of the lowering of the water is based on 
diastrophic changes. Observations on the shore of Lake Michigan, 
both on the Michigan side and on the Green Bay Peninsula opposite, 
indicate that fifty years ago the lake was several feet higher than 
the highest levels of recent years, and this fall of level might have 
affected the level of Platte River in its lower reaches (fig. 12). 
There are also extensive meadows bordering Platte River and the 
sluggish stream connecting Platte and Little Platte Lakes, whose 
origin may be connected with the lowering of water levels at 
about the same time. Further study, both of the floristic content 
and of the nature of the substratum, is necessary before definite 
conclusions can be reached. There is no indication of any migra- 
tion of trees into a grass meadow with solid grass mat, whether 
large or small, but there seems to be some evidence that they can 
come in on a floating mat of the swamp type. . Further investigation 
may show that the latter case is really a bog mat, in which event 
it would not be available as evidence, and the presence of trees 
would be quite in accordance with the rule for bog mats. 
Boc typr.—Here the fourth stage develops as a bog mat com- 
posed of sphagnum and the usual accompanying bog plants. In 
several cases this has developed into an ericad heath composed 
largely of Chamaedaphne, Andromeda, occasionally Ledum and 
similar shrubs, including Betula pumila, and scattered trees of 
Larix, Picea mariana, and occasionally Pinus Strobus and P. resi- 
nosa. In other cases the tamaracks with some bog shrubs and 
