AGENTS AT WORK IN THE OCEAN 237 
are active, either in eroding the shores, or in directly 
building up deposits; the motion is too slow for this. 
Indirectly, however, they do much work toward the for- 
mation of deposits in the ocean; for the warm currents, 
bearing as they do a great abundance and variety of mi- 
nute forms of life, carry quantities of food for the larger 
sea animals. Where these warm streams flow, corals 
grow in luxuri- 
ance (p. 251), and 
their life and 
growth depend in 
considerable  de- 
gree upon the 
presence of equa- 
torial currents. 
These interesting 
Fic. 133. 
little “creatures iis in shale, with beach at base, Lake Erie, N.Y. 
are building ex- 
tensive beds of limestone in thie sea, and it is to them 
that we owe the construction of the Bahamas, the Ber- 
mudas, and a part of the southern end of the Florida 
peninsula. §o in this indirect way, ocean currents have 
aided in the construction of certain coasts. | 
Erosion in Lakes. — While most lakes are eventually 
destroyed by filling, there are in progress during their 
existence, many changes due to erosion, which in most 
respects, resembles the action of erosion at the sea-shore. 
