On Coral Reefs and Islands. v7 
ume,*) will show how large a portion of the reef increases from 
these fine accumulations. The exterior of a coral island, for a 
few hundred yards, excepting some islets within, is the only part 
which is the proper growth of the living reef. Within the ex- 
terior reef the coral structure may consist almost wholly of the 
compact homogeneous white limestone we have described. The 
elevated island of Metia was for a long time after elevation ex- 
posed to the ravages of the sea, before the present shore-reefs ac- 
cumulated to give it protection. Proofs of degradation along the 
coast have been referred to. ‘There is much reason, therefore, 
for believing that the Metia now existing, exposes on its eastern 
and southern sides at least (where particularly examined by us) 
of a few degrees, not exceeding eight, towards the water. 
tock of the drift-hills or accumulations is more finely laminated, 
ss firmly cemented, and dips whichever way the a 
sandhill sloped, the layers being the successive sheets of 
Which wert drifted over it. 
pr by passages mostly 20 to 200 feet deep, and often of great 
Min he substratum, however, is continuous coral-rock ; 
“sé more elevated parts were removed by a 3 r 
oe as the whole reef-grounds. This is at once seen from 
figures of the Kingsmill chart and others on a preceding 
Page. In an island like Deans’s, one of the Paumotus, these reef- 
at the we 1000 square miles in’extent. It is true that the reefs 
‘ the surface gradually widen if the land is undergoing no sub- 
dence. t when situated on a sloping bank, as usual, this 
ia the wool 
in the fullest sect. 
2 a. 
thitis chart presents to the eye a map of oue of the most remarkable reef grounds 
, MARE whole theory femal ry 7 
