1899] DUNE FLORAS OF LAKE MICHIGAN 105. 
crowned by established dunes. Only rarely are these dunes in 
action at the present time, and, where such action is observed, it 
is clearly due to the rejuvenation of dunes that had become 
established. The origin of these perched dunes is obscure and 
hardly within the province of this paper. The formation of 
dunes at the summit of a bluff is not unknown. A wind laden 
with sand may sweep up the slopes of a hill. As it reaches the 
summit its path is no longer narrowly restricted, and as it spreads 
out, its energy is dissipated and its load deposited. - However, 
no such action was anywhere observed; on the contrary, at many 
points the wind is removing the dunes from just such locations. 
Consequently the author rather inclines to the belief that these 
perched dunes represent an earlier phase of dune formation, 
when lake or wind conditions were different from the present. 
Another possible mode of origin will be discussed in connection 
with the rejuvenated dunes. 
The greatest altitude reached by the clay and gravel bluffs is 
at Empire, a few miles south of Glen Haven; at this point a 
height of 128 meters is attained. There is a high degree of 
oscillation in the altitudes even within a few meters. Where the 
clay bluffs are highest, the perched dunes are seldom as high as 
where the bluffs are lower. The greatest observed height of the 
perched dunes above the top of the clay was 60 meters. The 
Steatest total observed height above the lake at Empire was 162 
meters; at Frankfort 153 meters. South of Frankfort and north 
of Glen Haven the altitudes are much less. At Charlevoix and 
Petoskey there are no cliffs; the dunes are low and superposed. 
directly upon the beach. 
The islands in the north end of the lake are of great interest 
Pe student of dunes, since they are exposed to winds noe 
he rt the position of the dunes thus indicates the direc- 
_ he dune-forming winds. In all cases the chief dune 
cS is on the west coast, and the most conspicuous active 
ee ae woe restricted to a narrow area at or near the south- 
ne — of each island. Observation from the iteamboat 
© presence of such dunes on South Manitou, South 
d 
