250 James D. Dana, Esq., on 



the inner margin of shore reef's, 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 zoo- 

 phytes 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 comparatively 

 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 geo- 

 graphical distribution of corals (xiii. 338), 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 Pescadores, 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 depression, where, if in any part, 

 the action should be longest continued. 



Among the Kingsmills and Paumotus, there is no reason 

 whatever 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 

 occupied us in the preceding pages, there has been no equally 

 general elevation. Yet various parts of the ocean bear evi 



