162 THE DEPTH AND MARINE DEPOSITS OF THE PACIFIC OCEAN. 



accumulate on the continental areas, rendering these rocks specifically 

 lighter than the deposits on the oceanic areas. 



In the abysmal regions, beyond the depth of the mean sphere level, cover- 

 ing about one-half of the earth's surface, the physical conditions are uniform 

 and widespread ; the temperature everywhere approaches zero centigrade ; 

 the darkness is reheved only by phosphorescent light ; motion of all kinds 

 must be extremely slow, and there is no evidence of transport or erosion, 

 although where the abysmal area passes into the continental slope a creep 

 of large masses of deposits is sometimes indicated. In these cold and silent 

 depths, which are undoubtedly affected at times by volcanic outbursts, the 

 deposits generally vary according to the surface conditions : where carbon- 

 ate of lime secreting organisms abound at the surface Globigerina Ooze or 

 Pteropod Ooze is found at the bottom ; where silica-secreting organisms 

 abound at the surface, Radiolarian Ooze or Diatom Ooze is found at the 

 bottom. In very great depths, however, the carbonate of lime remains are 

 removed by solution, and in some places the siliceous skeletons are also 

 partly or wholly removed. In the deep water of the South Pacific Ocean, 

 at points the furthest removed from continental land on the globe, the trawl 

 brings up, in a single haul, over wide areas, hundreds of sharks' teeth and 

 dozens of ear-bones of whales, belonging to extinct species, tons of man- 

 ganese nodules, and mixed up in the Red Clay magnetic spherules of 

 metallic iron and nickel and chondres, which are only found in meteorites. 

 All the indications go to show that the rate of accumulation of the deposit 

 is extremely slow, possibly not more than a foot since tertiary times. The 

 reason why these teeth and bones and extra-terrestrial spherules are found 

 here more abundantly than elsewhere is because few other materials reach 

 these remote and deep areas to cover them up or mask them as in other 

 deposits. 



The above is the explanation which has hitherto been advanced to account 

 for the phenomena presented by the deep-sea deposits situated far from con- 

 tinental land towards the central regions of the great ocean basins. Gener- 

 ally speaking it seems to be a sufficient explanation. The large number of 

 deposits which have now been procured and examined from the central re- 

 gions of the Pacific present, however, in some cases, difficulties ; for instance, 

 at Stations 4719 and 4544, where the depths are respectively 2285 and 1955 

 fathoms, we have deposits of Red Clay without any calcium carbonate. Thus 

 at these relatively shallow depths a pure Red Clay is found where we should 



