71 



moval of the dead rock from the interior portions by currents, 

 or by the action of carbonic acid dissolved in sea-water ;" fur- 

 ther, that " barrier reefs have built out from the shore on a 

 foundation of volcanic debris or on a talus of coral blocks, coral 

 sediments, and pelagic shells, and the lagoon channel is formed 

 in the same way as a lagoon." 



