THE ABYSS 229 



or erosion. In these cold and silent depths the deposits 

 vary according to the surface conditions ; where 

 organisms which secrete carbonate of lime abound at 

 the surface, we find Globigerina or Pteropod Oozes at 

 1 he bottom ; where, silica-secreting organisms abound 

 ;it the surface, we find Radiolarian or Diatom Oozes at 

 the bottom. In very great depths the calcareous 

 organisms are removed by solution, and in some places 

 the siliceous skeletons are also partly removed. From 

 1 he deep water of the South Pacific Ocean, at points the 

 farthest removed from continental land on the globe, 

 the trawl brings up over wide areas hundreds of sharks' 

 teeth and dozens of ear-bones of whales, some of them 

 belonging to extinct species, tons of manganese nodules, 

 and, mixed up in the 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 up or mask them, 

 as in other deposits. 



Throughout the abysmal area quartz fragments, 

 when present, are rare, when compared with their 

 abundance in the terrigenous deposits close to shore, 

 and it is very doubtful if any stratified rock has yet 

 been discovered which can be regarded as the equiva- 

 lent of any deposit now forming in the deep water far 

 from continental land. It is extremely difficult to 

 imagine how a continent, as we understand the term, 

 could ever have existed in the centre of any of the 

 great ocean basins, which appear to be the most stable 

 portions of the earth's crust, while the continental 



