82 ON CORAL REEFS AND ISLANDS. 



knowing that none of these so-called rivers are over three feet in 

 depth; and the most that they can do is to produce a thin layer of 

 brackish water over the sea within the channels. 



e. The annexed figure of the harbor of 

 Falifa, Upolu, represents another coral harbor, 

 as surveyed by Lieutenant Emmons. At its 

 head there is a fine stream twenty-five or 

 thirty yards wide, and three feet deep. Not- 

 withstanding the unusual size of the river, 

 the coral reef lies near its mouth, and projects ^^9^4 

 some distance in front of it. Its surface is dead, 'W* 

 but corals are growing upon its outer slope. harbor of falifa. 



f. The harbor of Rewa, in the Feejees, may be again alluded 

 to. The waters received by the bay amount to at least 500,000 

 cubic feet a minute. Yet there is an extensive reef enclosing 

 the bay, lying but three miles from the shores, and with only 

 two narrow openings for ships. The case is so remarkable that 

 we can hardly account for the facts without supposing the river's 

 mouth to have neared the reef by depositions of detritus since 

 the inner parts of the reef were formed ; and there is some evi- 

 dence that this was the case, though to what distance, we can- 

 not definitely state. With this admission, the facts may still sur- 

 prise us; yet they are explained on the principle that fresh water 

 does not sink in the ocean, but is superficial, and runs on in a 

 distinct channel; its effect is almost wholly through hydrostatic 

 pressure, and detritus depositions. Besides these instances, there 

 are many others in the Feejees, as will be observed on the Ex- 

 pedition charts. Mokungai has a large harbor, without a stream 

 of fresh water ; — so also Vakea, and Direction Island. 



The instances brought forward are a fair example of what is 

 to be found throughout coral seas; and they establish, beyond 

 dispute, that while much in harbor-making should be attributed 

 to the transported sand or earth of marine and freshwater cur- 

 rents, in preventing the growth of coral, but little is due to the 

 freshening influence of the streams of the islands. 



But while observing that currents have so decided an influence 

 on the condition of harbors, we should remember another preva- 

 lent cause, already remarked upon, and perhaps more wide in its 

 effects than those just considered. I refer to the features of the 

 supporting land, or the character of soundings off a coast. We 

 need not repeat here what has already been dwelt upon, showing 

 that many of the interruptions of reefs have thus arisen. The 

 wide break off" Matavai may be of this kind. The widening 

 of the inner channel at Papieti, forming a space for a harbor, 

 may be another example of it ; for the reef here extends to a 

 greater distance from the shores, as if because the waters shal- 

 lowed more gradually outward off this part of the coast. The 



