318 CONDITION OF THE FLOOK OF THE OCEAN. 



tion of all the data at present available; a consideration of the rate of 

 accumulation probably aifords a more correct interpretation. It 

 appears certain that the terrigenous deposits accumulate much more 

 rapidly than the pelagic deposits. Among the pelagic deposits the 

 pterapod and globigerina oozes of the tropical regions, being made up 

 of the calcareous shells of a much larger number of tropical species, 

 apparently accumulate at a greater rate than the globigerina oozes in 

 extratropical areas. Diatom ooze, being composed of both calcareous 

 and siliceous organisms, has again a more rapid rate of deposition than 

 radiolarian ooze. In red clay the minimum rate of accumulation takes 

 place. The number of sharks' teeth, of earbones and other bones of 

 Cetaceans, and of cosmic spherules in a deposit may indeed be taken as 

 a measure of the rate of deposition. These spherules, teeth, and bones 

 are probably more abundant in the red clays, because few other sub- 

 stances there fall to the bottom to cover them up, and they thus form 

 an appreciable part of the whole deposit. The volcanic materials in a 

 red clay having, because of the slow accumulation, been for a long time 

 exposed to the action of the sea water, have been profoundly altered. 

 The massive manganese-iron nodules and zeolitic crystals present in 

 the deposit are secondary products arising from the decomposition of 

 these volcanic materials, just as the formation of glauconite, phos- 

 phatic, and calcareous and barytic nodules accompanies the decomposi- 

 tion of terrigenous rocks and minerals in deposits nearer continental 

 shores. There is thus a striking difference between the average chem- 

 ical and mineralogical composition of terrigenous and pelagic deposits. 

 It would be extremely interesting to have a detailed examination of 

 one of those deep holes where a typical red clay is present, and even 

 to bore some depth into such a deposit, if possible, for in these positions 

 it is probable that not more than a few feet of deposit have accummu- 

 lated since the close of the Tertiary period. One such area lies to the 

 southwest of Australia, and its examination might possibly form part 

 of the programme of the approaching antarctic explorations. 



LIFE ON THE OCEAN FLOOR. 



It has already been stated that plant life is limited to the shallow 

 waters, but hshes and members of all the invertebrate groups are dis- 

 tributed over the floor of the ocean at all depths. The majority of 

 these deep-sea animals live by eating the mud, clay, or ooze, or by 

 catching the minute particles of organic matter which fall from the 

 surface. It is probably not far from the truth to say that three-fourths 

 of the deposits now covering the floor of the ocean have passed through 

 the alimentary canals of marine animals. These mud-eating species, 

 many of which are of gigantic size when compared with their allies 

 living in the shallow coastal waters, become in turn the prey of numer- 

 ous rapacious animals armed with peculiar i)rehensile and tactile organs. 



