CHAPTER XIII 



THE STRUCTURE OF THE BARRIER 



Foe, tlie purposes of description alone, it is necessary to give 

 different names to different portions of the rock ledge that 

 forms the outskirts of the table-land of the summit of this 

 submarine ridge. 



In the giving of many names to portions of a whole, much 

 confusion may be caused, and a loss of the clear idea of the 

 whole may be suffered in searching for the origins of the 

 parts. 



By the term " Barrier " is generally understood the ledge 

 of the rock that stretches from the seaward margin of the 

 land to the edge of breaking surf; and it is certainly fittingly 

 named. But that ledge of rock is only a portion of a much 

 larger bed, which forms the basis of the islands and even the 

 rocks of the lagoon shore. In description some subdivision is 

 necessary, but it must be understood that the several parts 

 are in continuity, have been formed by the same agencies, 

 have fulfilled the same functions, and constitute one homo- 

 geneous whole. The ledge of rock from the surf-breaking 

 edge to the rising land of the island is conspicuous, its more or 

 less level surface becomes exposed in varying degrees with the 

 movements of the tides, and its continuity is unbroken to the 

 first rise of the land. Here, at the seaward beach, its structure 

 becomes more or less confused ; loose fragments of broken 

 coral boulders lie scattered on it, roughly strewn towards the 

 sea, piled by the waves towards the land, until the piling up 

 has become so considerable that the level which constitutes the 

 island dry land has been attained. But the barrier properly 

 speaking does not end here, for under the piled-up fragments 

 of its landward margin its solid level stratum can be readily 



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