EXISTENCE AND DISTRIBUTION OF MARINE ORGANISMS. 401 



In the terrigenous deposits now being laid down in the shallow and 

 deep waters of the continental areas, we have in the organic remains 

 quartz, glauconite, phosphatic nodules, an assemblage of materials 

 resembling in all important respects the stratified layers making up 

 the larger part of the continental masses. 



When we turn to the deposits in the abysmal regions far removed 

 from continental land we rind that deposits are being formed which do 

 not resemble so closely the continental rocks. In depths of less than 2 

 miles the deposits are principally made up of the dead shells of carbon- 

 ate of lime secreting organisms, which had lived at the surface of the 

 sea, such as calcareous alga?, foraminifera, pteropods, and other pelagic 

 mollusks, forming globigerina and pteropod oozes. In the colder parts 

 of the extratropical regions the siliceous frustules of diatoms which 

 had lived on the surface predominate in the deposit, and thus produce 

 a diatom ooze. In the still greater depths of the ocean, i. e., over _J 

 miles, the carbonate of lime organisms are partially or wholly removed, 

 either while falling to the bottom or shortly after reaching the bottom, 

 through the solvent action of the sea water. Where they are wholly 

 removed, the deposit may, as, for instance, in the western parts of the 

 Pacific, contain a considerable percentage of radiolarian skeletons, 

 which had lived in the surface and intermediate waters, and the deposit 

 is then called a radiolarian ooze, but usually the deposit is what has 

 been called a red (or chocolate-colored) clay, and this covers a larger 

 proportion of the sea bed than any other kind of deposit. 



The red clay has evidently accumulated at an extremely slow rate. 

 It consists principally of hydrated silicate of alumina and the perox- 

 ides of iron and manganese, mixed with thousands of sharks' teeth, 

 represented by the dentine of Carcharodon, Lamna, and Oxyrhina, of 

 dense ear bones of various species of cetacea, and the dense mesoros- 

 tral bones of ziphioid whales. These red-clay deposits likewise con- 

 tain many magnetic spherules with crystalline or metallic nuclei, 

 which are believed to be the dust burnt off from the outer surfaces of 

 meteoric stones heated as they pass through our atmosphere. These 

 cosmic spherules probably fall all over the surface of the earth, but 

 their presence is here evident because the deposit may not accumulate 

 to the extent of more than an inch in several centuries. The manga- 

 nese and the iron are often deposited in concentric layers around the 

 sharks' teeth, ear bones, and volcanic lapilli, and in some places the 

 deposit contains many zeolitic minerals which have evidently been 

 formed in situ. 



When we turn to the observations on the pelagic fauna and flora it 

 will be found that there is a considerable difference between the organ- 

 isms observed near shore and those present in the open regions of the 

 ocean — a difference recognized in the terms neritic and oceanic plank- 

 ton. The coccospheres, rhabdospheres, pelagic foraminifera, hetero- 

 poda, pteropoda, and radiolaria, so abundant in tow-net gatherings in 

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