STRUCTURE OF CORAL REEFS. 159 
Ix. A GOOD WORD FOR CORAL REEFS. 
All coral-bound coasts, and especially those of islands in mid 
ocean, derive great benefit from their reefs. The wide coral banks 
and the enclosed channels greatly enlarge the limits tributary 
to the lands they encircle. Besides being barriers against the 
ocean, they are dykes to detain the detritus of the hills. 
They stop the waters of the streams, and cause it to drop the 
silt they were bearing off, and thus secure its addition to the land. 
They prevent, therefore, the waste which is constantly going on 
about islands without such barriers ; for the ocean not only en- 
croaches upon the unprotected shores of small islands, but car- 
ries off much of whatever the streams empty into it. The del- 
ta of Rewa, on Viti Lebu, resulting from the detritus accumu- 
lations of a large river, covers nearly sixty square miles. This 
is an extreme case in the Pacific, as few islands are so large, 
and consequently rivers of such magnitude are not common. 
But there is rarely a coral-girt island which has not at least 
some narrow plains from this source; and upon them the vil- 
lages of the natives are usually situated. Around Tahiti these 
plains are from half a mile to two or three miles in width, and 
the cocoa-nut and bread fruit groves are mostly confined to 
them. 
The reefs also provide extensive fishing-grounds for the na- 
tives, and afford abundant fish, their main reliance in the way 
of animal food. They also supply large interior waters for 
practice in navigation and for safe communication between dis- 
tant 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. Communica- 
