1872.] 



' Shearwater ' Scientific Researches. 



585 



" The other portions still live unaffected by the injury thus sustained. Even 

 " the Fungice, which are broad simple species, are occasionally destroyed 

 " over a part of the disk through the same cause, and yet the rest remains 

 "alive. It is natural, therefore, that wherever streams or currents are 

 " moving or transporting sediment, there no Corals grow ; and for the same 

 " reason we find few living Zoophytes upon sandy or muddy shores" (p. 121). 

 — I venture, therefore, still to maintain that the doctrine I propounded in 

 my former Report has not been set aside by Dr. M c Intosh's facts and 

 arguments. 



76. Gases of the Bottom-water. — I am now disposed, however, to attri- 

 bute more influence to the other condition which I suggested in my Report 

 for 1870 (§ 103) as likely to operate prejudicially to Animal life; namely, 

 the stagnation produced by the almost entire absence of Vertical Circula- 

 tion. In the great Oceanic system, if the doctrine previously advocated 

 be correct, every drop of water is in its turn brought to the surface, and 

 exposed to the purifying influence of prolonged exposure to Atmospheric 

 air ; whereby a large proportion of its Carbonic acid and other products of 

 the decomposition of Organic matter will be removed, and Oxygen will be 

 absorbed in their place. But from this movement, the water of the Me- 

 diterranean may be said to be virtually excluded. The effect of the 

 Gibraltar Currents is limited to a stratum of which the depth is very 

 small in comparison with that of the principal area of each basin ; and to 

 whatever extent they may produce a change in the water of the deeper part 

 of the Western basin in the neighbourhood of the Strait, it is obvious that 

 the amount of such change must diminish as the distance increases, and 

 that it cannot in any degree affect the water of the Eastern basin. Now, 

 as the Nile is constantly bringing down a very large quantity of Organic 

 matter, the finer particles of which seem to be diffused through the whole 

 mass of the water in the basin and to be slowly gravitating to its bottom, it 

 might be anticipated that in their gradual decomposition they would gene- 

 rate Carbonic acid at the expense of the Oxygen dissolved in the water ; so 

 that the abyssal water, being separated from the atmosphere by an inter- 

 vening stratum of many hundred fathoms, and being never brought to the 

 surface, would come to be unfit for the maintenance of Animal life. 



77- It will be recollected that in the * Porcupine ' Expedition of 1869*, it 

 was found that the presence of a very large proportion of Carbonic acid in 

 the bottom-water was not incompatible with the existence of Animal life in 

 great abundance. In fact there was reason to believe that there was a 

 general relation of conformity between the proportion of Carbonic acid and 

 the quantity of Animal life on the bottom as indicated by the dredge- 

 results ; the effect of the respiratory and other changes produced by the 

 latter being to increase the proportion of Carbonic acid at the expense of the 

 Oxygen. Thus whilst the percentage of Oxygen in surface-water averaged 

 about 2;3 per cent., and that of Carbonic acid averaged something less than 

 * See " Keport," pp. 483-486. 



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