132 The Bed of the Ocean. 



oceanic basins and to what we have termed the critical 

 latitudes. We may therefore expect the formation of deposits 

 composed mainly of organic particles in the centre of oceanic 

 basins and in the critical latitudes, where, as is the case 

 with atmospheric currents, we find areas of calms. This 

 conclusion is in harmony with observed facts. The central 

 plateaux of the North Atlantic and of the South Atlantic, the 

 wide plateaux between the latter, the Indian and the South 

 Pacific Ocean, and the Southern Ocean, are all found to be 

 covered with a stratum composed of the remains of the minute 

 organisms which live in the ocean. On the contrary, 

 the bottom of the areas of depression consists principally of 

 inorganic particles in the shape of extremely fine and very 

 tenacious clays, varying in colour from grey to yellow and red, 

 and occasionally deepening to a chocolate colour. 



Awaiting a more complete analysis of the specimens of 

 bottom brought up by the sounding-tube in the course of the 

 " Challenger " expedition, the marginal deposits have been des- 

 cribed as mud, sand, stones, rock, shells, &c., the deposits in the 

 areas of depression as red clay or grey ooze, and those in the areas 

 of elevation as globigerina ooze. The clays are composed of 

 very fine mineral particles mixed up with a small percentage 

 of organic remains. As the depth decreases, this percentage 

 is found to increase, until, at depths of less than 2000 fathoms, 

 the deposit is almost exclusively composed of the skeletons 

 and fraorments of skeletons of the minute forms of animal life 

 which inhabit the ocean. 



The previous arguments, which may be modified by future and 

 more detailed research, lead to several conclusions of some 

 importance to the geologist. As the discoveries made by the 

 expeditions on board H.M.S. "Lightning" and "Porcupine," 

 in the area between the Fit roe Islands and Scotland, have shown 

 that an Arctic and a southern fauna may exist side by side 



