GEOGRAPHICAL DISTRIBUTION. 109 



planting and increase of coral reefs is thus satisfactorily exhibited. 

 The existence of large reef-islands in open seas, where the neigh- 

 boring lands are mostly destitute of coral reefs, has farther sup- 

 ported our conclusions, as such islands are in general removed 

 from the deleterious influences just mentioned. 



The modifications of form and interruptions of reefs arising 

 from abrupt or sloping shores, and tidal or local currents, have 

 also been exemplified. The origin of the distant barrier has 

 been traced to a sinking of the land which it once simply fringed j 

 and the lagoon island to a continuation of this subsidence till the 

 original land had disappeared. 



This account of coral reefs and islands may be closed by a 

 statement or recapitulation of some deductions which have a 

 special bearing upon geology. 



