FORMATION OF CORAL REEFS AND ISLANDS. 245 



The instances brought forward are a fair example of what 

 is to be found throughout coral seas ; and they establish, be- 

 yond dispute, that while much in harbor-making should be at- 

 tributed to the transported sand or earth of marine and fresh- 

 water currents, in preventing the growth of coral, but little 

 is due to the freshening influence of the streams of islands. 



But while observing that currents have so decided an in- 

 fluence on the condition of harbors, we should remember an- 

 other prevalent cause already remarked upon, which is perhaps 

 more wide in its effects than those just considered. I refer to 

 the features of the supporting land, or the character of sound- 

 ings off a coast. We need not repeat here the facts, showing 

 that many of the interruptions of reefs have thus arisen. 

 The wide break off Matavai may be of this kind. The widen- 

 ing of the inner channel at Papieti, forming a space for a har- 

 bor, may be another example of it; for the reef here extends 

 to a greater distance from the shores, as if because the waters 

 shallowed outward more gradually off this part of the coast. 



The same cause — the depth of soundings, on the principle that 

 corals do not grow where the depth much exceeds a hundred 

 feet — has more or less influence about all reefs in determining 

 their configuration and the outlines of harbors. A remark- 

 able instance of the latter is exemplified in the annexed chart 

 of Whippey harbor, Viti Levu, reduced from the chart of the 

 Wilkes Expedition to the scale of half an inch to the mile. 



The existence of harbors should therefore be attributed, to 

 a great extent, to the configuration of the submarine land ; 

 while currents give aid in preventing the closing of channels, 

 and keeping open grounds for anchorage. This subject will be 

 further illustrated in the following pages. 



The permanency of coral harbors follows directly from the 

 facts above presented They are secure against any immediate 



