106 BOTANICAL GAZETTE [FEBRUARY 
Fox, and High islands. The dunes on North Manitou and 
Beaver islands were visited. On North Manitou there are promi 
nent areas of dune activity along the southwest coast, the dunes 
being superposed on bluffs of clay or gravel. There is a flat- 
topped terrace here, like that at Glen Haven, but in miniature, 
the height being only 15 meters and the area scarcely halfa 
hectare; the dune perched on this bluff has been rejuvenated | | 
and carried inland a few meters, the greatest altitude being 45 
meters above the lake. There are also small wandering dunes 
superposed directly upon the beach. On the west coast the 
bluffs are steeper and much higher, at times perhaps 60 meters 
above the lake; the summits are occasionally crowned by estab- 
lished dunes. On Beaver island the southwest coast was not 
visited, but there are rejuvenated dunes at various points along 
the west coast, sometimes 45 meters in height; these dunes are 
superposed upon the beach. The beach dunes here are exceed 7 
ingly varied and extensive. As previously stated, there are low | 
beach dunes along the east coast of Beaver island. On Mack- 
inac island there are steep clay bluffs, but no dunes. Thus, the | 
islands plainly show that westerly winds, and especially winds | 
from the southwest, are the chief dune formers. . 
Surveying the lake region as a whole, the dunes are created 
and shaped almost entirely by westerly winds. In the southe™ 
portions of the lake, the northwest winds have the greater sweep ‘ 
and are the chief dune-formers. Northward the southwest Wi a | 
are the chief factors in determining the location of dunes. 
intermediate localities all westerly winds contribute about equal) 7 
to dune formation, and there is progressive movement of acti 5 
dunes to the eastward of 
III. The ecological factors. 
The distribution of the plants in the various dune ass 
is governed by physical and biotic agencies which will bee 
sidered somewhat in detail in another place. At this | 
seems advisable to give a general survey of these factors ® 
ally in so far as they affect the distribution of plant soc” ” 
the region as a whole. | 
ociatio® | 
