1899 | DUNE FLORAS OF LAKE MICHIGAN IOI 
several established dunes which are more than 36 meters above 
the lake. The coast charts issued by the Corps of Engi- 
neers of the United States War Department figure a dune near 
Porter, Ind., which reaches an altitude of 57 meters above the 
lake. Of course, altitudes of individual dunes are subject to 
much change, although in the case of established dunes the 
figures need but slight revision. The highest series of dunes is 
along the Michigan shore between Michigan City and St. Joseph. 
A large number of dunes reach an altitude of more than 60 
meters; several are over go meters high; and one is figured on 
the coast chart which has an altitude of 117 meters above the 
level of the lake. An inspection of the map will show that these 
dunes must have been shaped primarily by northwest winds. 
The Michigan shore between St. Joseph and Frankfort, a 
distance of more than 250 kilometers, is fringed almost continu- 
ously with a narrow belt of dunes. Perhaps at no place within 
this region are there such extensive dunes in activity at the pres- 
ent time as at Dune Park, nor do the established dunes reach 
inland as a rule for more than a kilometer. At Dune Park there 
'S a gradation in the altitude of the dunes as one goes inland, 
until the low sand ridges pass all but insensibly into the prairies 
beyond. Along the Michigan shore, however, there is a narrow 
fringe of dunes close to the lake, commonly much higher than at 
Dune Park, and the transition between these dunes and the 
normal inland country is rapidly passed and plainly marked. : 
A very striking feature along the Michigan shore is the ten- 
cy of rivers to form small lakes near their mouths. These 
lakes determine the presence of cities, since they furnish the 
best of harbors. An inspection of the map (/ig.z)shows the pres- 
€nce of such natural harbors at the mouths of rivers at Holland 
(Ottawa Beach), Grand Haven, Muskegon, Whitehall, Pent- 
hai Ludington, and Manistee. A large amount of the silt 
Bice down by the rivers is deposited at the mouth, where the 
eet tS ate slackened by their opening out into the lake 
Ree action. The waves pile up this sand along the 
the winds pick it up and form extensive dunes at the 
den 
