332 CORALS AND CORAL ISLANDS. 



In the island of Metia, elevated two hundred and fifty feet, 

 the corals below were the same as those now existing, as far 

 as we could judge from the fossilized specimens. At the in- 

 ner margin of shore reefs, there is the same identity with ex- 

 isting genera. We do not claim to have examined the base- 

 ment of the coral islands, and offer these facts as the only ev- 

 idence on this point that is within reach. We cannot know 

 with absolute certainty that the present race's of zoophytes 

 may not be the successors of others that nourished, on the same 

 sites, even before the Tertiary era in Cretaceous and Jurassic 

 times ; but as yet have little reason in facts observed, for such 

 a conclusion. For a long time volcanic action may have been 

 too general and constant over the Pacific, for the growth of 

 corals ; and this may have continued to interfere till a com- 

 paratively late period, if we may judge from the appearance 

 of the rocks, even on Tahiti. The subsidence has probably for 

 a considerable period ceased in most, if not all, parts of the 

 ocean, and subsequent elevations of many islands and groups 

 have taken place. 



V. ELEVATIONS OF MODERN ERAS IN THE PACIFIC. 



Since the period of subsidence discussed in the preceding 

 pages, there has been no equally general elevation. Yet va- 

 rious parts of the ocean bear evidence of changes confined to 

 particular islands, or groups of islands. While the former 

 exemplify one of the grander events in the earth's history, in 

 which a large segment of the globe was concerned, the latter 

 exhibit its minor changes over limited areas. The instances 

 of these changes are so numerous and so widely scattered, that 

 they afford convincing evidence of a cessation in the previous 

 general subsidence. 



