382 



PROFESSOR J. W. JUDD. 



Depths in fathoms. 



Mean 



percentage of 



carbonates. 



Number of 

 analyses. 



Under 500 



86-04 



14 



From 500 to 1000 . 







66-86 



7 



„ 1000 „ 1500 . 







70-87 



24 



„ 1500 „ 2000 . 







69-55 



42 



„ 2000 „ 2500 . 







46-73 



68 



„ 2500 „ 3000 . 







17-36 



65 



„ 3000 „ 3500 . 







0-88 



8 



„ 3500 „ 4000 . 







0-00 



2 



Over 4000 .... 







trace 



1 



HoGBOM has shown conclusively by a discussion of these same " Challenger " 

 analyses* that, under the action of the carbon dioxide in sea-water, the calcium 

 carbonate passes into solution much more rapidly than the magnesium carbonate. 

 This fact appears most strikingly apparent from the following table, which is taken 

 from Hogbom's suggestive Memoir : — 



Limits of carbonates. 



Mean calcium 

 carbonate. 



Mean magnesium 

 carbonate. 



Percentage of 



magnesium 



carbonates to 



calcium carbonate. 



Nuijiber of 

 analyses. 



80 to 100 per cent. . . 



60 „ 80 



40 „ 60 



20 „ 40 „ 



10 „ 20 



5 „ 10 



3 „ 5 



1 „ 3 „ 



86-7 



68-3 



52-0 



32-0 



16-2 



6-1 



3-7 



2-0 



0-7 

 1-4 

 1-2 

 0-9 

 1-6 

 0-7 

 1-6 

 2-1 



0-8 



2-0 



2-4 



3-0 



10-0 



11-5 



430 



105-0 



8 

 8 

 8 

 3 

 4 

 1 

 7 

 9 



It is evident from a comparison of the two tables given above that, under the 

 conditions which exist in the open sea, the carbonates are being gradually dissolved out 

 of materials as they slowly descend to the floor of the deep ocean, and also that the 

 calcium carbonate is being more rapidly removed in solution than the magnesium 

 carbonate. 



The experiments and observations which have been described point to the conclusion 

 that the relative solubilities of the calcium and magnesium carbonates in water 

 containing carbon dioxide may vary greatly under different conditions of temperature, 

 pressure, and the presence of other salts in the solution. That, in many parts of the 

 ocean, conditions prevail which tends to the leaching out calcium carbonate, and the 



* ' Neues Jahrb. fiir Min.,' &c., 1894, vol. 1, p. 262. 



