rr senda 
—a 
On Coral Reefs and Islands. 367 
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 pringipally to shore material, the reefs have probably added 
mewhat to these accumulations; yet little coral sand can be 
detected in the mu eye, and the proportion is certainly 
very small. In many places where we anchored, having the reef 
hot 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 
_ Teference to the land. Sweeping on, they carry off 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 sucha case, the reef and 
the growing patches scattered over the lagoon, are the sources 
of nearly ail the material that is accumulated upon the bottom. 
Shore accumulations.—TVhe- 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 
ich enable them to practice and improve 
and communicate without danger be- 
Ee ‘ 
+ 
