CHAPTER II. 



BARRIER-REEFS. 



Closely resemble in general form and structure atoll-reefs. — Width and 

 depth of the lagoon-channels. — Breaches through the reef in front of 

 valleys, and generally on the leeward side. — Checks to the filling up 

 of the lagoon- channels. — Size and constitution of the encircled 

 islands. — Nzwiber of islands within the same reef — Barrier-reefs 

 of New Caledonia and Australia. — Position of the reef relative to 

 the slope of the adjoining land. — Probable great thickness of 

 barrier-reefs. 



The term 'barrier' has been generally applied to that 

 vast reef which fronts the N.E. shore of Australia, and by 

 most voyagers likewise to that on the western coast of 

 New Caledonia. At one time I thought it convenient 

 thus to restrict the term, but as these reefs are similar 

 in structure, and in position relatively to the land, to those, 

 which, like a wall with a deep moat within, encircle many 

 smaller islands, I have classed them together. The reef, 

 also, on the west coast of New Caledonia, circling round 

 the extremities of the island, is an intermediate form 

 between a small encircling reef and the Australian barrier, 

 which stretches for a thousand miles in nearly a straight 

 line. 



The geographer Balbi has in effect described those 

 barrier-reefs, which encircle moderately sized islands, by 

 calling them atolls with high land rising from within their 

 central expanse. The general resemblance between the 



