STRUCTURE OF CORAL ISLANDS. 193 
then to the bottom of what was once the lagoon, now for 
the most part forty to fifty fathoms under water, though hay- 
ing its shoals that are five to ten fathoms submerged. All 
points in the map that are shaded, have a depth of less than 
ten fathoms; the only emerged parts are three or four spots 
on the western margin, as indicated on the map above. The 
bottom over the interior is muddy; on the flat bordering it, 
15 to 20 fathoms deep, there is coral sand with ‘‘a very little 
live coral; the outer rim is coral rock with scarcely any live 
” while the shoals or knolls of the interior are ‘ cov- 
coral ; 
ered with luxuriantly-growing corals.” Darwin states also 
that the rim is steep on both sides, and outward slopes abruptly 
to unfathomable depths; at a distance of less than half a mile 
from one part no bottom was found with 190 fathoms; and 
off another point, at a somewhat greater distance, there was 
none with 210 fathoms. For other similar facts see page 
Metia and other elevated Coral Islands.—Metia, or Au- 
rora Island, is one of the western Paumotus. It is a small 
| island about four miles by two and a half in width, and two 
, hundred and fifty feet in height; and it consists throughout 

























































































METIA, OR AURORA ISLAND 
of coral limestone. Approached from the northeast, its high 
vertical cliffs looked as if basaltic, resembling somewhat the 
13 
