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On Coral Reefs and Islands. 365 
impure or fresh waters and currents often operate to retard their 
growth 3 
Owing to the last mentioned cause, the inner reefs are not usu- 
ally joined close to the beach. They stand off a little, separated 
by an interval of shallow water. At Mathuata, in the Feejees, 
however, the reef extends quite up; and it is the more remarka- 
ble as the country is a plain, the site of a Feejee village, anda 
mile or two back stands a high bluff. On an island off, this part 
of Vanua, Lebu is another example of this fact, and many more 
might be cited. In such cases, however, there is evidence that 
the shores upon which the corals grew were bare rocks, instead 
of moving beach-sands. 
From these descriptions it appears that the main distinction 
between the inner and outer reefs consists in the less fragmentary 
character of the rock in the former case, the less frequent accumu- 
lations of debris on their upper surface, and the more varied fea- 
tures and slopes of the margin. Moreover, the Nullipores, which 
Seem to flourish best in the breakers, are of less extent, or but 
Sparingly met with elsewhere. 
The inner margin of a barrier reef, it should be observed, is 
entitled to rank with inner reefs, as its corals grow in the same 
quiet waters, and under like circumstances. The variety of coral 
_ Zoophytes is also greater in the stiller waters, and there are species 
peculiar to the different regions, as explained in another plaee. 
Channels among reefs.—To complete this review of the gen- 
eral appearance and constitution of reef formations, it remains to 
add some particulars respecting the channels which intervene be- 
tween coral patches, or separate them from the shores of an island, 
and also to describe the coral accumulations forming beaches. 
Within the inner reefs, a distance exceeding two hundred miles. 
The island of Tahiti on its northern side presents us, with a good 
illustration of a narrow channel, and at the same time exhib- 
its the usual broken or interrupted character of reefs, This is 
_ Seen in the following cut in which the reefs, both fringing and 
», are the parts enclosed by dotted lines. . The outer reef 
. 
igs i 
‘ee x Sip F alia: : 
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