80 Couthouy on Coral Formations 



Such we may consider the Tahiiian, Samoan and other 

 groups of elevated volcanic islands in Southern Polynesia, in- 

 terspersed among which are occasionally found lagoon islands 

 also. The rocks of the former class, from New Zealand to 

 Tahiti, (and I might include most of the Hawaiian islands, 

 two thousand four hundred miles farther north,) are so near- 

 ly alike in all respects, that on seeing a series of specimens 

 from each group placed together, any mineralogist ignorant 

 of the fact would in all probability decide that the whole 

 were collected within a short distance of each other. Indeed, 

 it was necessary in packing specimens collected by myself of 

 the deeper seated rocks of South New Zealand, Tahiti and 

 Kauai, for me to use great precaution in keeping them sepa- 

 rate : as if once mingled it would have been impossible from 

 any difference of character to identify their several localities 

 again.* May we not be justified then, in assuming this com- 

 mon character to be some proof of a common age as well as 

 origin for those islands, and an indication at least, that though 

 now so widely separated, there was a period when they were 

 connected together in a grand whole ? 



It may perhaps be asked, if this theory of subsidence be 

 well founded ; why is it that the original shore reef does not, 

 instead of forming a lagoon, present aflat surface, on the total 

 submergence of the land, extending over the whole area once 

 occupied by this latter ? But this could not possibly occur 

 unless the submerged island had been of very small extent, 

 and rose almost perpendicularly from the sea. In all the 

 shore reefs that I have seen, there is a narrow interval of 

 shallow water between them and the shore, which the wash 

 of the beach renders too impure and turbid for the growth of 

 the coral in any quantity. This space would be continually 

 widening during the subsidence, (even were the lateral in- 

 crease of the coral equal to that upwards, which is doubtful,) 

 by reason of the recession of the mountain side from the reef 

 being greater than its perpendicular descent. Thus if we 



* These specimens are now deposited in the new Patent Office at Washington, 

 and, as I learn, are open to public inspection ; so that any one maj there easily 

 convince himself of the truth of these remarks. 



