238 ELEMENTARY GEOLOGY 
The great majority of lakes are small; and here the 
likeness is rather to enclosed bays, harbors, and 
estuaries than to the exposed coast; but erosion in 
some of the larger lakes bears a close resemblance 
to the ocean. 
In the large lakes there are great waves and wind- 
formed currents, but rarely tides. The action of the 
Fie. 134. 
A spit built by waves in Lake Michigan. 
waves and currents is nearly the same ‘as in the ocean ; 
cliffs are cut (Fig. 135), beaches and bars formed (Fig. 
134), and sediment deposited in the water. Therefore 
what is said of marine erosion and ocean sedimentary 
rocks, holds in the main for lakes. Of course, the ani- 
mals that live in lake water are unlike those of the sea; 
and if any of these are preserved as fossils, they serve 
to tell us whether they lived in lake or ocean water. 
