224 CORALS AND CORAL LSLANDS. 



and although we have no soundings of the waters in and about 

 it, nor sketches of peaks, facts observed elsewhere authorize in 

 every essential point the transverse section here given, which 

 resembles closely, as is apparent, the preceding. The section 

 is made through the line bb, U b\ of the map. It is unnecessary 

 to add other illustrations. They may be made out from any of 

 the eastern groups of the Feejees, the Gambler Group of the 

 Paumotus, or Hogoleu in the Carolines. Wallis's Island is 

 another example of islets of rock in a large lagoon inclosed 

 by a distant barrier. 



It has been asked, why the interior channels do not become 

 filled by coral reef, as the island sinks, and thus a plane of coral 



MAP, AND IDEAL SECTION, OF AIVA ISLAND. 



result, instead of a narrow belt ; and this has been urged against 

 the theory. But it is a sufficient reply to such an argument to 

 state the fact that the subsidence admits of no doubt, and that 

 the islands referred to as exemplifications of it, present this 

 very peculiarity. It should be received therefore, as a conse- 

 quence of it, instead of an objection to the view, for it is the 

 most common feature with all islands that have broad reef- 

 grounds, or in other words, that show evidence of subsidence 

 during the growth of the reefs. Broad channels, and even 

 open seas within, as in Nanuku and the Exploring Isles, are 

 therefore to be received as results of the subsidence, for which 

 explanations should be sought. 



