CHAPTER VII 

 OCEANS AND LAKES 



Oceans and ocean basins. : The oceans have an area 

 (143,000,000 square miles) nearly three times as great as 

 that of the lands (54,000,000 square miles). They cover 

 the low edges of the continents, so that their area is greater 

 (by some 10,000,000 square miles) than that of the ocean 

 basins. The ocean basins are a little more than twice as 

 extensive as the continental plateaus. The submerged edges 

 of the continental blocks are called the continental shelves 

 (Fig. 251). The shallow seas on the continental shelves 

 may be thought of as remnants of the vast, shallow seas 

 which at various times in the past covered large portions of 

 the continents. 



Continental 



Sea level 



FIG. 251. Diagram showing a continental shelf, and its relation to the 

 land on one side and to an ocean basin on the other. 



Soundings have shown that the bottoms of the ocean 

 basins are generally smooth. Mountain chains and plateau- 

 like swells are not altogether wanting, while great volcanic 

 cones are numerous in parts of the Pacific Ocean, many of 

 them rising as mountainous islands thousands of feet above 

 the level of the sea. There are also submarine fault scarps 

 and relatively small areas much lower than the surrounding 

 ocean floor, called deeps. Nevertheless, these features occupy 

 but a small fraction of the ocean bottom, nine tenths or 



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