SUBMARINE DEPOSITS 193 



seas and the great Southern Ocean, where it forms a belt 

 round the globe extending, on the average, from about 

 50° to 65° S. latitude. There is also a broad belt extending 

 across the North Pacific from the north of Japan to the 

 terrigenous deposits of North America south of Alaska and 

 the Aleutian Isles. At its edges in both north and south 

 circumpolar areas it becomes mixed with and passes into 

 terrigenous deposits, and is reaUy present irrespective of 

 depths being dependent more upon the absence of other 

 deposits and the presence of enormous quantities of Diatoms 

 in the water above, the frustules of which make up from 

 50 to'80 per cent, of the material. This is the only pelagic 

 deposit which is formed of the remains of plants (with the 

 exception of the minute CoccoHths in Globigerina ooze), 

 and many of the animals in Antarctic seas are found to 

 have their stomachs filled with it. But aU submarine 

 deposits contain organic matter, and many of the deep- 

 sea animals graze upon the bottom and nourish themselves 

 by passing the ooze through their alimentary canal. 



Looking at the submarine deposits as a whole, the terri- 

 genous form a broad belt along the shores of continental 

 land and around islands. Red Clay occupies the greater 

 part of the deep Pacific and lesser areas in the Atlantic 

 and Indian Ocean, Globigerina ooze is characteristic of the 

 Atlantic and parts of the Indian Ocean and South Pacific, 

 the deep-water siliceous Radiolarian ooze and the shallow- 

 water calcareous Pteropod ooze occupy restricted areas in 

 tropical waters, and the siHceous Diatom ooze forms circum- 

 polar belts in the cold waters of the Southern Ocean and the 

 North Pacific. 



I may conclude this subject with the following summary, 

 adapted from the writings of Sir John Murray, on the distri- 

 bution of carbonate of lime over the floor of the ocean : — 



By far the larger part of the carbonate of lime which 

 is found in the marine deposits now covering the floor of 

 the ocean has been derived from sea-water by the action 



o 



