FRINGING AND BARRIER REEFS. 43 
enclosed 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 accumulating 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 practise and improve their 
skill in navigation, and communicate without danger between distant 
settlements: and the effect is evident in the spirit of maritime 
enterprise which has characterized the Polynesians; for these cir- 
cumstances have favoured 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, 
harbourless and thinly habitable, like most extratropical islands, the 
shores are blooming to the very edge, and wide plains are spread out 
with breadfruit and other tropical productions. Ports, safe for scores 
of vessels, are also opened by the same means, and some islands 
number a dozen, when the unprotected shores would have hardly 
offered a single good anchorage. Coral reefs are sometimes viewed 
as only traps to surprise and wreck the unwary mariner. But one 
who has visited the dreary prison-house, St. Helena, can have some 
appreciation of the benefits derived from the growth of the zoophyte. 
The area of level shores, alluded to as added to many of the high 
islands by this means, is one of the most striking of these benefits. 
These plains are sometimes of large extent. The reefs stop the 
detritus from the hills, and are thus the means of its being added 
again to the land: they prevent, therefore, that waste which is con- 
stantly going on about islands without such barriers; for the 
ocean not only encroaches upon the unguarded shores of the smaller 
islands, but carries off whatever the streams may empty into it. The 
delta of Rewa, on Viti Lebu, resulting from the detritus accumulations 
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 an island 
which has not at least some narrow plains from this source ; and upon 
them the villages of the natives are usually situated. Around Tahiti 
these plains are from half a mile to two or three miles in width, and 
the cocoanut and breadfruit groves are mostly confined to them. 
Beach sandrock.—Besides the accumulations from a shore source, 
