VITI ISLANDS. 351 
and four feet in diameter, worn out of the solid tufaceous rock. Its 
sides are smooth and even, leaving no doubt that it was excavated by 
the action of water. This natural well is connected below with a hori- 
zontal chamber, which opens on the face of the rocky bluff. Another 
horizontal cavern near by, extended several rods into the hill; but it 
was too low for exploration. ‘The character of the caverns, and the 
nature of the place—at the head of a deep valley which opens on the 
sea—tell us of some former age when the ocean washed these shores. 
The place reminded us of the blow-holes which are still common 
among these Pacific islands. The horizontal caverns are gradually 
enlarging, by a kind of exfoliation usual in soft granular sedimentary 
rocks ; the sand above peels off slowly, in consequence of the erystal- 
lization of common salt, or some of the saline minerals which are 
formed in caverns. This process raises the floor more than the in- 
crease in height: so that this enlarging process actually diminishes 
the passage. ‘The walls of the well are firm, and are not undergoing 
this kind of enlargement. 
The evidence afforded by the coral reefs with respect to an extensive 
subsidence in the Feejce Group during the progress of these reefs, is 
presented in another part of this volume. Since this subsidence 
ceased, there has been an elevation of several feet, as is indicated by 
the height of the same coral reefs along the shores. ‘The rise referred 
to, can be proved to equal four or five feet in several parts of the 
larger islands, and possibly may exceed twice this amount. 
On the north-northwestern side of Viti Lebu, the highest part of 
the shore reef is three feet out of water at low tide. This reef con- 
sists of the large massive Astreas, ten or twelve feet or more in dia- 
meter, lying in the position of growth, and it bas not been increased in 
height by the accumulation of a coral conglomerate, or limestone. 
An extensive series of observations have proved that a foot above low 
tide is the extreme height to which the large corals can grow; and 
with respect to Astraas, the instances were so few, and on so small a 
scale, that it is a safe conclusion that a solid reef of Astras never 
rises above ordinary low tide. 
In addition, we may remark, that this reef lies just at the foot of a 
declivity of five or six hundred feet, which, in the rainy season, would 
carry a large amount of fresh water into the sea, proving destructive to 
the coral, if it were not at some distance below the surface. We may 
hence conclude that the rise, here indicated, amounts not merely to 
two aud a half or three feet, but probably to twice this height. The 
