CORAL BUILDERS. 241 



their skeleton. It is calculated that the water of the 

 ocean contains, in solution, from one twenty-fourth to ' 

 one thirty-sixth of all its soluble ingredients in salts 

 of lime, chiefly in the condition of sulphate of lime ; 

 and, according to Bischof, there are about sixteen 

 parts of sulphate of lime in 10,000 of sea water. 

 This proportion may at first appear to be small, but 

 by rapid infiltration, and deposit, by myriads of 

 animals, it has been considered ample to account for 

 the results. After all, no one can estimate the enor- 

 mous period of time throughout which the coral has 

 been deposited to form existing reefs. This leads us 

 to an interesting subject, suggested by Professor 

 Dana, in his work already so often quoted, and this 

 is, death and life in progress together in the coral 

 structure. No one must suppose that a mass of 

 coral, which may be dredged up from the sea-bottom, 

 is necessarily living from end to end. Whatever the 

 species may be, and in whatever direction its growth 

 may proceed, there will be found to be an old and 

 dead portion, with a new and vigorous one, death 

 and life side by side, and both going on together. 

 The animal portion decays and vanishes, but the 

 corallum, or coral stock, remains imperishable fot 

 ages. It is by means of this process that masses of 

 coral, which would otherwise be very small, attain to 

 a very large size. The animals at the top, as they 

 deposit their coral, keep ascending, whilst the older 



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