506 THE JOURNAL OF GEOLOGY. 



surfaces to solution, and 2800 for globigerina, smaller shells, 

 relatively more massive. Commenting on this, Dittmar says : x 



" At the greatest depths of the oceans all these calcareous 

 shells disappear from deposits in all latitudes. The cause of 

 this, in my opinion, is not that deep-sea water contains any 

 abnormal proportion of loose or free carbonic acid, but the fact 

 that even alkaline sea-water, if given sufficient time, will take up 

 carbonate of lime in addition to what it contains." 



The solvent action indicated by the disappearance of delicate 

 and microscopic shells, which enclose decaying organic matter, 

 yet sink through 9000 to 16,000 feet of water, is very moderate. 



Dittmar says: 2 "Sea-water is alkaline ; all the alkalinity 

 must be owing to carbonates, and of these carbonate of lime is 

 one." Now the very moderate solvent power of this alkaline 

 solution may be satisfied so far as carbonate of lime is concerned 

 by two sources — by organic tests in suspension, and by chemical 

 precipitate. The lime used by organisms is derived from the 

 solution to which it is partly returned by re-solution, but an- 

 other part is deposited, and the sea thus suffers constant loss. 

 This loss is supplied by the land. If this terrigenous supply is 

 less than the amount of organic deposit the sea will become less 

 alkaline, and will more efficiently dissolve calcareous tests until 

 the solvent is satisfied. If the land contribution is continuously 

 equal to the amount organically subtracted, there will be equili- 

 brium. If the land yields more carbonate of lime than that which 

 is being locked up in organic limestones, the alkalinity of the sea 

 will gradually increase until there is chemical precipitation. This 

 condition is favored by the entrance of lime-bearing fresh 

 water into a sea free from active currents and exposed to evapora- 

 tion which balances the inflow. 



Since the amount of lime in the ocean is thus balanced be- 

 tween that contributed by the land, and that precipitated by 

 organic or chemical means, it is worth while to review the con- 



J Op. cit., p. 221. 

 2 Op. cit., p. 206. 



