Ch. V. OF CORAL-REEFS. 155 



reef, or even any barrier-reef, at least those encircling small islands, 

 would be preserved to a distant period. From this same cause, the 

 strata which were formed within the lagoons of atolls and the lagoon- 

 channels of barrier-reefs, and which must consist in a large part of 

 sedimentary matter, would more often be preserved to future ages, than 

 the exterior solid reef composed of massive corals in an upright posi- 

 tion ; although it is on this exterior part that the present existence and 

 further growth of atolls and barrier-reefs depend. 



