136 T. C. CHAMBERLIN 



regarded rather as adaptations to existing temperatures, salinities, 

 and gas-contents which happen to vary with depth, than as adapta- 

 tions to pressure simply. The present distributions of abysmal 

 deposits are therefore probably the products of a complex of 

 variables of which temperature, saUnity, and gas-content are not 

 unlikely more potent than pressure. 



Deep-sea deposition is at present singularly conditioned by the 

 action of the sea-water. If the surface life were essentially uniform, 

 and if some appreciable amount of life occupied all lower depths, 

 as seems to be the case, the deposits of any period, if unmodified, 

 should increase in thickness with increase of sea depth; but almost 

 the reverse seems to be the real fact. This reversal is assigned 

 to the solvent action of the sea-water. The larger portion of all 

 the life relics assignable to the upper levels is wanting at the 

 greatest depths. It is nearly absent over a large fraction of the 

 abysmal area. The calcareous element is more largely removed 

 than the silicious, but the latter seems to suft'er also. This selec- 

 tive action gives to the residue of the extreme abysmal deposits 

 their striking character more largely perhaps than any abundance 

 of life rehcs that are known to be confined to great sea depths. 

 This solvent action is most plausibly assignable at present to the 

 exceptional absorption of oxygen and carbon dioxide in the polar 

 seas whence it is carried to all the abysmal depths, giving them at 

 once their low temperature and their high content of these active 

 gases. The sections of Brennecke showing the distribution of 

 oxygen in the North Atlantic between latitude 60° N. and 50° S. 

 are very instructive in this respect.^ The oxygen acting on organic 

 matter gives rise to carbon dioxide and this, added to the original 

 content, gives competency to dissolve the calcareous shells that 

 fall from above. The loss of the silicious relics is not so well deter- 

 mined nor so well explained so far as it may be a fact. 



In interpreting oceanic deposits of other ages than the present, 

 the possibility, if not the probabihty, that different groups of 

 organisms and different solvent results marked the various bathy- 

 metrical horizons, because the gas-contents, the sahnities, and the 

 temperatures were probably different, is not to be overlooked. 



'Murray and Hjort, The Depths of the Ocean (191 2), pp. 255, 256. 



