32 THE OCEAN 



continental slope and the continental shelf 

 has been called the continental edge, and 

 varies in depth and in distance from the shore 

 in different parts of the world, though on an 

 average it may be put at about 100 fathoms 

 and about 50 miles off coasts bordering the 

 great ocean basins (see Fig. 1, which is based 

 upon the percentages of the areas at definite 

 intervals of depth below sea-level and of 

 height above sea-level). 



The foregoing paragraphs, which apply to 

 general considerations concerning the depth 

 of the great ocean basins as a whole, may 

 be now supplemented by some information 

 concerning each ocean, the enclosed seas 

 connected therewith, and the submarine 

 barriers separating them from the main ocean- 

 basin. 



Depth of the Atlantic Ocean. — The dominant 

 feature of the relief of the North Atlantic Ocean 

 is a low submarine ridge, called the Dolphin 

 Rise, running from north to south almost 

 exactly in the central line of the basin, with 

 a series of deeps on either side. After a break 

 at the equator this central ridge, called the 

 Challenger Ridge, is continued through the 

 South Atlantic beyond lat. 50° S. The 

 entire ridge takes the form of an open S 

 in accordance with the trend of the coasts, 

 and is covered by an average depth of about 



