SUMMARY- 291 



On the surface of the sea are waves varying in height 

 from a few inches to fifty feet. These stir up the water 

 and enable it to absorb more air, which is so necessary to 

 the living things in the sea. Not only is the surface of 

 the sea constantly in motion, but there are also great cur- 

 rents, such as the Gulf Stream, which carry the water from 

 one latitude to another. These currents are caused almost 

 entirely by the winds. 



The tides are due primarily to the action upon each 

 other of the earth, moon and sun. The range of tides 

 varies from two or three feet on oceanic islands to about 

 seventy feet at some .places in the Bay of Fundy. The 

 tides help drainage and assist vessels over bars that would 

 otherwise be impassable. 



QUESTIONS 



What portion of the earth's surface is sea? Into what divisions is 

 the sea usually divided V 



What is the continental shelf? Why is it of especial interest to 

 man ? 



Of what is the sea water composed ? How does its composition 

 affect animals ? 



If you were able to take a trip from the nearest beach over the 

 ocean bed to another continent, describe what you would probably 

 find along the way. 



What are waves ? What causes them ? 



What is the temperature of the ocean water in different parts of 

 its surface and at different depths? 



Describe the best known ocean currents. What is the cause of 

 these ? Why is a knowledge of ocean currents important to mariners 

 and also to those who would explain the climates of different places ? 



What are tides? What causes them? What are their effects? 



How are coral reefs formed ? What are atolls ? 



In what ways is the ocean useful to man ? 



