98 BOTANICAL GAZETTE [ FEBRUARY 
Denmark have helped greatly to make clear the true content of 
ecology, and they have been a constant incentive to more care- 
ful and thorough work. Most of the photographs were taken 
especially for this paper by Mr. E. W. Martyn, a Chicago pho- 
tographer. Some of the views were taken by Messrs. S. M. 
Coulter and H. F. Roberts, students in the Hull Botanical Lab- 
oratory. The map was prepared by Mr. S. M. Coulter. 
II. General features of the coast of Lake Michigan. 
Along the eastern shore of Lake Michigan there are hills of 
wind-blown sand almost continuously fringing the border of the 
lake. This line of sand hills also continues around the southem 
end of the lake and along the western shore as far as Chicago. 
These sand hills or sand dunes form striking topographic features 
in the landscape, and in this respect present a strong contrast to 
the level prairies or fields beyond. ti | 
Geologically speaking, the sand dunes belong to the most | 
recent formations, as they are entirely post-glacial. In mot) 
cases the origin of the existing topographic forms is to be 
referred to the most recent phases of post-glacial history, and 
in many instances the topographic forms are either being made 
or unmade at the present time. Asa rule the dunes are directly 
superposed upon the beach. On the northeastern shores of 
lake, however, the dunes are commonly superposed upon blufis 
of clay or gravel, sometimes 120 meters above the present beach. 
In the lake region there is a decided prevalence of westet!) 
winds, chiefly from the southwest or northwest. As 4 conse: 
quence, the dunes are found along the entire eastern and souther? 
shores of the lake, whereas the dunes on the western shore, 
to easterly winds are merely small hillocks of sand. Such i. 
dunes have been seen at Waukegan, IIl., and on North Manito! 
and Beaver islands. The dunes toward the southern portion” 1 
suis 
ze 
almost entirely by the northwest winds. In order to secu” | 
extensive formation of sand dunes, it is necessary for the oe q 
to gather force by sweeping over the lake and to strike the # ft 
