126 CORAL FORMATIONS. 
leave only a single ridge and a few isolated summits peering above 
the waves. Would not its condition in this case be that of the Ex- 
ploring Isles? On such a supposition, reefs of large size encircling 
a mere point of rock might be explained in every feature. The sub- 
sidence of Goro, on the same principle, would produce an Angau, or, 
carried further, a Nanuku. 
It may be here remarked, that the fact that changes of level in the 
earth’s surface have taken place over vast areas, is fully proved, and 
accounts of some of them which are now in progress, as that of 
Sweden, are to be found in any geological treatise. 
But it admits of direct demonstration that such a subsidence has 
actually taken place. It has been stated that the depth of the reef at 
different distances from the shore it encircles may generally be estimated 
from the slope of the shore. On this principle it has been shown that 
the thickness of the distant barrier reef cannot be less in some instances 
than a thousand feet; and in many cases it is probably much greater. 
Now as reef corals do not grow below twenty fathoms, there is no 
way in which this thousand feet of reef could have been formed except 
by a gradual subsiding of the land upon which it stands. The large 
number of instances of distant barriers in the Pacific remove any 
doubt with regard to these conclusions. ‘The map of the Feejees 
abounds in them through its eastern part, and we may infer with 
reason that this has been a large area of subsidence, like that which 
is now going on in Greenland. 
Evidence of subsidence still more conclusive, if possible, is obtained 
by actual observation at Metia and some of the elevated coral islands. 
This island is 250 feet in height, full twice the coral-growing depth. 
At another island in the Hervey Group, Mangaia, the .coral rock is 
raised 300 feet out of water. 
The fact of subsidence having actually taken place during the for- 
mation of many reefs, is therefore put beyond doubt. It must form a 
part of any true theory of reefs, whether it be the crater hypothesis 
or the view here advocated. The latter has this advantage, that it 
explains all the facts, and requires no other element but this single one 
of subsidence. It rests on a simple fact and demands no hypothesis 
whatever. 
The manner in which subsidence would operate is shown in the 
following sketches, representing ideal transverse sections of an island 
and its reefs. In figure 1,if I be the water line, the island, like 
Goro, has a simple fringing reef, ff:—it is a narrow platform of rock 
