FORMATION OF CORAL REEFS AND ISLANDS. 949 
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 fresb- 
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 
