126 ON CORAL REEFS AND ISLANDS. 



could judge from the fossilized specimens. At the inner margin 

 of shore reefs, there is the same identity with existing genera. 

 We do not claim to have examined the basement of the coral 

 islands, and offer these facts as the only evidence on this point 

 that is within reach. We cannot know with absolute certainty 

 that the present races of zoophytes may not be the successors 

 of others of the secondary epoch : but we do know that we have 

 little reason in facts observed for even the suspicion. For a long 

 time volcanic action was too general and constant 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 evidence of subsidence from coral islands might be pur- 

 sued to other regions in other seas ; but we here only refer to 

 the facts on this point presented in our review of the geographi- 

 cal distribution of corals, since we cannot speak from personal 

 observation. 



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 which we shall 

 soon consider. In some of the Northern Carolines, the Pesca- 

 dores, and perhaps some of the Marshall Islands, the proportion 

 of dry land is so very small compared with the great extent of 

 the atoll, that there is reason to suspect a slow sinking even at 

 the present time : and it is a fact of special interest in connection 

 with it that this region is near the axial line of greatest depres- 

 sion, where, if in any part, the action should be longest continued. 



Among the Kingsmills and Paumotus there is no reason what- 

 ever for supposing that a general subsidence is still in progress; 

 the changes indicated are of a contrary character. 



The results to which we have here been led obviously differ 

 in many particulars from the deductions of Mr. Darwin. 



2. Elevations of Modern Eras in the Pacific. 



Since the period of subsidence, the history of which has occu- 

 pied us in the preceding pages, there has been no equally general 

 elevation. Yet various parts of the ocean bear evidence of chan- 

 ges confined to particular islands or groups of islands. While 

 the former exemplify one of the grander events in the earth's his- 

 tory, in which a large segment of the globe was concerned, the 

 latter exhibit its minor changes over limited areas. The instan- 

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

 that they convince us of a cessation in the previous general sub- 

 sidence. 



The most convenient mode of reviewing the subject is to state 

 in order, the facts relating to each group. 



