6 THE WEALTH OF THE SEA 



contains Africa, Europe, Asia, North America, and 

 most of South America. The only land occurring in 

 the water hemisphere is the East Indies, Australia, 

 the South Sea Isles, the southern part of South 

 America, and that around the South Pole. 



Around the edges of the continents the oceans are 

 relatively shallow. These marginal portions down 

 to 600 feet in depth are really parts of the con- 

 tinental platforms and are called continental shelves. 

 In depths beyond 100 fathoms the bottom usually 

 drops off rapidly. Most of the ocean is very deep, its 

 average depth being 1916 fathoms; about three 

 fifths of it is between 2000 and 3000 fathoms. Little 

 of the floor of the ocean lies below this depth. There 

 are, however, fifty-seven known deeps, or valleys 

 in the ocean floor, which lie at depths of more than 

 3000 fathoms. Thirty-two of these deep places are 

 in the Pacific, the deepest of the oceans. The largest 

 and one of the deepest of them, the Tuscarora Deep, 

 is a depression running north and south in the North 

 Pacific to the east of Japan. Mount Everest, the 

 highest mountain on earth, could be dropped into 

 this deep, and its peak would be more than half a 

 mile below the surface. The Aldrich Deep, wKich 

 lies in the South Pacific, contains several places more 

 than 5000 fathoms in depth. 



For the most part, however, the floor of the ocean 

 far from land is a nearly flat plain which might be 

 compared to the level parts of the Mississippi Valley 

 in which the gradients are so slight as to be scarcely 

 noticeable. On approaching the continents, the slope 

 rises steeply up to the continental shelf. 



