76 ANIMAL LIFE AND SOCIAL GROWTH 



One of the best studies of these is in the Indiana 

 dune region at the south end of Lake Michigan. 

 Many of us have followed various stages of this 

 development during our lifetime but the whole 

 series of events there takes too long to be covered 

 by a single human life and our awareness of these 

 processes had not developed until nearly the end 

 of the last century, consequently the succession 

 has not been watched from beginning to end as 

 have those just described, but our certainty that 

 it has taken place in some such manner as will 

 now be sketched is almost as great as though we 

 had actually been present to observe the whole 

 process. 



The high bluffs on the western side of Lake 

 Michigan north of Chicago are eroded by wave 

 action and a shore drift results, particularly in 

 storms. The load of sand thus obtained is grad- 

 ually shifted southward to be piled up by the 

 waves at the south end. There as the sand dries, 

 it is picked up by the wind and carried back until 

 the force of the wind is broken and the load of sand 

 is deposited to form a dune. Many other things 

 besides the sand itself are cast up by these same 

 lake waves which have a part to play in the de- 

 velopment of the dune region. 



After an off-shore wind for a day or so, when the 

 wind changes, the waves deposit on the shore not 



