STRUCTURE OF CORAL REEFS. 15 



To the west of the larger Feejee islands, soundings commonly 

 indicated a bottom of basaltic mud, and this material was fre- 

 quently brought up with our dredges. On the north side of Va- 

 nua Lebu, a stream has so filled with its detritus the wide chan- 

 nel into which it empties, that for a mile our ship dragged its keel 

 in the mud, although elsewhere the water had been from twelve 

 to twenty fathoms deep ; and at least half a dozen square miles 

 of land had been added to the shores from this source. Though 

 due principally to shore material, the reefs have probably added 

 somewhat to these accumulations; yet little coral sand can be 

 detected in the mud by the eye, and the proportion is certainly 

 very small. In many places where we anchored, having the reef 

 not more than five hundred yards from the ship, we might have 

 judged, from the character of the bottom, that there were no cor- 

 als nor shells within many miles. When the materials from both 

 sources, the shore and the reef, are mingled, the proportion will 

 necessarily depend on the proximity to the mouths of streams, 

 the breadth of the inner waters or channels, and the direction and 

 force of the currents. These tidal currents often have great 

 strength, and are much modified and increased in force at certain 

 places, or diminished in others, by the position of the reef with 

 reference to the land. Sweeping on, they carry or! the coral de- 

 bris from some regions to others distant ; and again they bear 

 along only the shore detritus, and distribute it. It is thus seen 

 that the same region may differ widely in its adjacent parts, and 

 seemingly afford evidence in one place that there is no coral near, 

 and in another no basaltic land, although either is within a few 

 rods, or even close along side. The extent of the land in propor- 

 tion to the reef will have an obvious effect upon the character of 

 the channel or lagoon depositions. When the island stands like 

 Bacon's isles, (Feejees,) as a mere point of rock in a wide sea en- 

 closed by a distant barrier, the streams of the land are small and 

 their detritus quite limited in amount. In such a case, the reef and 

 the growing patches scattered over the lagoon, are the sources 

 of nearly all the material that is accumulated upon the bottom. 



Shore accumulations. — The wide coral banks and the enclosed 

 channels greatly enlarge the limits tributary to the islands they 

 encircle. They afford extensive fishing grounds for the natives 

 and internal waters which enable them to practice and improve 

 their skill in navigation, and communicate without danger be- 

 tween distant settlements ; and the effect is evident in the spirit 

 of maritime enterprise which characterizes the islanders: for 

 these circumstances have favored the construction of large sail- 

 canoes, in which they venture beyond their own land, and often 

 undertake voyages hundreds of miles in length. Instead of a 

 rock-bound coast, harborless and thinly habitable, like most extra- 

 tropical islands, the shores are blooming to the very edge, and 



