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THE JOURNAL OF GEOLOGY.

surfaces to solution, and 2800 for globigerina, smaller shells, relatively more massive. Commenting on this, Dittmar says:[1]

"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 another 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 equilibrium. If the land yields more carbonates 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 evaporation which balances the inflow.

Since the amount of lime in the ocean is thus balanced between that contributed by the land, and that precipitated by organic or chemical means, it is worth while to review the con-

  1. ↑ Op. cit., p. 221.
  2. ↑ Op. cit., p. 206.
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