CHAPTER XXI 



THE METHOD OF DEVELOPMENT OF THE REEF 

 BANK AND THE EEEF 



Sedimentation in the Open Ocean. — It is a statement which 

 will not be disputed that sediment is for ever dropping from 

 the surface of the ocean. When the real nature of the mate- 

 rial which composed the floor of the ocean was made known, 

 and the hard remains of a number of animal forms were 

 recognised, it was at once asked : do these forms live at the 

 depths at which their remains are found, or are they surface- 

 living creatures, whose heavier parts have dropped from the 

 surface waters after the death of the animal ? The tow-net 

 revealed the animals during life as surface-living forms; and 

 many investigations — especially the Challenger reports — have 

 made all the processes of deep-sea deposit quite clear. 



Not only are the troughs of all the oceans lined with ooze 

 of slightly varying nature, but the elevations which arise from 

 them are also clothed with the same deposit. There is then a 

 perpetual shower of sediment from the surface of the ocean. 

 Calcareous and siliceous remains of pelagic organisms, volcanic 

 dust, and other less considerable constituents form a never- 

 ceasing rain of particles from the surface-water to the ocean 

 depths. They drop, and line the ocean bed : they drop, and 

 cover ocean slopes and elevations, and come to rest wherever 

 the absence of wave action will let them settle. 



This certain knowledge prompts a very natural inquiry as 



to the extent to which this sedimentation building may take 



place. Supposing some elevation to be present on the ocean 



floor, or supposing more sediment to be deposited in any one 



particular spot, by reason of some ocean current ; how far 



below the waves would the rising mound come to a standstill ? 



237 



