206 THE SEA FLOOR 



of our knowledge in this respect, for if the extent 

 of the ocean be great, it should be remembered that 

 the uniformity of the conditions is also great over 

 wide areas. Notwithstanding the great number of deep- 

 sea soundings recorded since 1895, when the depth- 

 hemispheres in the final volume of the " Challenger " 

 Reports were published, it is somewhat remarkable 

 that the contours shown on these have been com- 

 paratively little altered in their broad general outlines, 

 although many deeps and submarine elevations have 

 been discovered in recent years, and in some regions 

 the contour-lines now present a much more complicated 

 appearance. 



These depth-hemispheres have been kept up to 

 date by Sir John Murray and Mr. J. G. Bartholomew. 

 An inspection of the reduced chart given here will 

 show at a glance where deep soundings are most 

 abundant. 



The greatest depth yet recorded in the ocean is 

 5,269 fathoms (9,636 metres), or 66 feet less than 

 six English miles. This was a sounding taken by 

 the U.S.S. " Nero " in the Challenger Deep to the 

 south of the Ladrones, where the "Challenger" 

 recorded a depth of 4,575 fathoms. Depths greater 

 than 5,000 fathoms are also known in the Aldrich 

 Deep in the South Pacific. There are altogether ten 

 deeps in which depths exceeding 4,000 fathoms have 

 been recorded, two of these being in the Atlantic, and 

 the remainder in the Pacific. The term " deep " is 

 limited to those parts of the ocean in which soundings 

 of 3,000 fathoms or deeper have been taken. On the 

 depth-hemispheres above referred to, fifty-seven deeps 

 are now shown thirty-two in the Pacific, eighteen in 

 the Atlantic, five in the Indian Ocean, and two in the 

 Southern Ocean south of latitude 40 S. 



