OCEANOGRAPHIC INFORMATION FOR SUBMARINE CABLES 



1073 



and red clay make up the approximately 300 fathoms of sediment. A 

 photograph (Fig. 14) .shows the bottom at a depth of 3,000 fathoms in 

 the abyssal hills. This remarkable shot .shows ball-shaped objects that 

 have been identified as mangane.se nodules. The most interesting feature 

 of this photo is the scour marks around the objects, implying an ap- 

 preciable current at a depth of 3,000 fathoms. 



Seamounts present extremely varied conditions. Rocks, from crystal- 

 line basalt through hardened limestone to soft marl, are encountered. 

 Sediments, including sticky ancient formations, deep sea oozes, and shell 

 sand are found. Photographs show all types from tranquil mud bottom 

 through wave-rippled silt and sand to craggy rock. Some of these types 

 are illustrated in Fig. 15. 



The flanks of the Mid-Atlantic Ridge are areas of irregular topog- 

 raphy. The steeper .slopes are probably bare rock and the sediment 

 removed from these .slopes probably is deposited in the intermountain 

 basins. Cores are usually of globigerina ooze, but the different rates of 

 sedimentation on steep slopes and on basin floors cause changes in thick- 

 ness of sediment and relatively great changes in physical properties over 

 short distances. The deeper flanks of the ridge are covered by red clay. 

 A very similar bottom is found on the Bermuda Rise. 



Fig. 14 

 57°22'W. 



Abyssal-liills photograph taken at 3,190-fatliom depth at 29°17'X, 



