ijo DEPTHS OF THE OCEAN chap. 



Mr. Lucas on board the S.S. "Scotia," and on portions of the 

 cable recovered in 1903 being submitted to Mr. Lucas, he was 

 quite convinced that no deterioration had taken place during the 

 interval of fifteen years. This is ascribed to the fact that the 

 cable when lifted in 1888 was covered by Globigerina ooze, 

 which is believed to act as a preservative upon cables in 

 contact with it. As in 1888 the cable had been submerged 

 for thirteen years, this implies a rate of deposition of one 

 inch of the deposit in some period less than thirteen years ; 

 but as the deterioration noted in the cable, especially in the 

 hemp serving, had probably taken some years to effect, it is 

 perhaps fair to assume a period of ten years for the accumula- 

 tion of a layer of the deposit one inch in thickness, in the 

 position referred to. Another cable lifted from the bed of the 

 equatorial Atlantic (lat. 2' 47' N., long. 30^ 24' W.) from a 

 depth of 1900 fathoms in 1883, after having been submerged 

 for nine years, was found to be in much better condition than 

 the North Atlantic cables examined after having been laid for 

 a similar period, and this is supposed to be due to the more 

 rapid deposition of the Globigerina ooze in the warmer waters 

 of the equatorial Atlantic than in the colder waters of the 

 North Atlantic, so that the cable became more rapidly covered 

 over by the Globigerina ooze.^ 



While, therefore, it may be assumed that the Globigerina 

 ooze accumulates at the rate of about one inch in ten years in 

 the central part of the North Atlantic in lat. 50° N., and at a 

 still more rapid rate in the central part of the equatorial Atlantic, 

 it would appear from the recent observations of the " Michael 

 Sars " Expedition that the rate of deposition of sediment may 

 be almost nil even at depths of 1000 fathoms in certain parts 

 of the North Atlantic, where glaciated stones have been dredged 

 in considerable quantities. Possibly, however, these glaciated 

 stones may have been deeply covered by the ooze since the 

 close of the glacial period, and may have been subsequently 

 exposed by the action of deep tidal currents sweeping away the 

 Globigerina shells from the top of a low ridge perhaps recently 

 elevated by earth-crust displacements in the deep sea. We 

 now know that tidal currents prevent the formation of muddy 

 deposits on the top of the Wyville Thomson Ridge in depths 

 of 250 to 300 fathoms, while just below the summit of the ridge 

 on both sides mud is deposited. 



1 See Murray and Peake, On Recent Con/rihutions to our A'nozvledge of the Floor of the 

 North Atlantic Ocean, extra publication of the Royal Geographical Society, London, 1904, 

 pp. 21 and 22. 



