THE CORAL-REEF PROBLEM. 59 



bodily uplift rather than to organic and inorganic accumula- 

 tion, as we have most conclusive evidence of an uplift in the 

 peninsula of Florida in a period at least as late as the Plio- 

 cene. Nor are evidences of a more recent contrary movement 

 wanting in the same region. 



It will, however, naturally be urged against this assumption 

 of slow accumulation that the quantity of the salts of lime 

 already contained by the sea is vastly in excess of that which 

 is annually thrown in by the rivers, and that, therefore, the 

 amount of formative material on hand is amply sufficient to 

 meet all the exigencies of a rapid growth. The quantity' of 

 calcium actually contained in every cubic mile of sea-water is 

 estimated to be nearly 2,000,000 tons, while that held by an 

 equal volume of river-water is less than 150,000 tons. At the 

 rate of the present carrying capacity of rivers it is calculated 

 that it would require 680,000 years to pour into the ocean an 

 amount of calcium equal to that which is now held by it in 

 solution.* The question here naturally presents itself: To 

 what extent is this surplus quantity of lime drawn upon by the 

 oceanic organisms for the construction of their hard parts or 

 skeletons ? It is in the nature of things impossible to give a 

 direct answer to this question, but the following considerations 

 suggest themselves. As far as our knowledge permits us to 

 pass bej'ond the region of facts, we can but assume that the 

 salinity of the sea is progressive or cumulative, and not the 

 reverse, and that the saline constituents of ocean water are 

 primarily the products of destruction arising from the wear 

 and tear of the land-surface. There seems to be no good rea- 

 son for supposing that the quantity of salts in tlie sea, and of 

 lime especially, was ever much in excess of what it is to-day, 

 unless it was near the beginning of geological time ; on the con- 

 trary, there are some grounds for concluding that this quantity 

 may have been less, and even considerably less. If this con- 

 ception is true, it is manifest that, as far as organic consump- 



*Murray: " Structure, Origin, and Distribution of Coral Reefs and Islands." 

 Nature, Feb. 28, 1889, p. 426; 480,000 years according to Reade. 



