THE DEPTH AND MARINE DEPOSITS OF THE PACIFIC OCEAN. 157 



PERCENTAGE OF CALCIUM CARBONATE IN THE DEPOSITS 

 COVERING THE FLOOR OF THE PACIFIC OCEAN. 



Map III. accompanying this paper represents the first attempt to show 

 the percentage of calcium carbonate in the deposits of the Pacific Ocean as 

 a whole. A similar map for the southwestern portion of the Pacific was 

 pubHshed in 1906 (Murray, op. cit, Map V.). 



As regards the source of the calcium carbonate found in marine deposits 

 it may be stated that by far the larger part has been derived from sea water 

 by the action of organisms, being made up of fragments of Fish bones, 

 Mollusc shells, Corals, spicules of Tunicates and Sponges, shells of Fora- 

 minifera, remains of calcareous Alg£e, and, indeed, remains of all the 

 calcareous structures secreted by marine organisms. 



A very important division maybe made of the calcareous remains into two 

 classes, viz., those which have been secreted by organisms living habitually 

 in the surface and subsurface waters of the ocean, such as pelagic Molluscs, 

 pelagic Foraminifera, and pelagic calcareous AlgEe (plankton organisms), 

 and those which have been secreted by organisms living on the bottom of the 

 ocean (benthos organisms). 



The remains of all the pelagic (plankton) organisms are especially abun- 

 dant in the deposits far from land and in moderate depths. Near the land 

 their presence is masked by detrital matters, while in great depths they dis- 

 appear, being dissolved by the action of sea water either while falling to the 

 bottom or soon after reaching the bottom. In depths of 1000 fathoms far 

 from land they may make up fully 95 per cent of the deposit. 



The remains of organisms which live at the bottom of the ocean (benthos), 

 such as Corals, Molluscs, Foraminifera, etc., are very poorly represented in 

 deep water, but in shallow water they may make up nearly the whole of the 

 deposit now in process of formation ; this is especially the case round coral 

 islands. 



On the accompanying map the percentage of calcium carbonate in the 

 deposits is shown by four shades of green color, the deeper the shade 

 the higher the percentage. Planimeter measurements give the following 



