et CORALS AND CORAL ISLANDS 
the Kingsmills, soundings continue for three miles from the 
north extremity, along a bank stretching off from this point 
to the north-northwest. 
Ill. STRUCTURE OF CORAL ISLANDS. 
The descriptions of reefs and their islets already given apply © 
with equal force to coral islands. By transferring here the 
statements respecting the former, we should have a nearly 
complete account of the latter. ‘The same causes, with scarcely 
an exception, are at work :—the growing of coral zodphytes, and 
the action of the waves, of oceanic currents, and of the winds. 
This resemblance will be rendered more apparent by a review 
of their characters. The description will be found to be a sim- 
ple recapitulation of a former paragraph. 
The reef of the coral atoll, as it lies at the surface still 
uncovered with vegetation, is a platform of coral rock, usually 
two to four hundred yards wide, and situated so low as to be 
swept by the waves at high tide. The outer edge, directly 
exposed to the surf, is generally broken into points and 
jagged indentations, along which the waters of the resurging 
wave drive with great force. Though in the midst of the 
breakers, the edge stands a few inches, and sometimes a foot, 
above other parts of the platform; the incrusting Nullipores 
cover it with varied tints, and afford protection from the 
abrading action of the waves, There are usually three to five 
fathoms water near the “margin ; and below, over the bottom, 
which gradually degnans outward, beds of corals are growing 
profusely among extensive patches of coral sand and frag- 
ments. Generally the barren areas much exceed those flour- 
ishing with zoéphytes, and not unfrequently the clusters are 
scattered like tufts of vegetation in a sandy plain. The grow- 
ing corals extend up the sloping edge of the reef, nearly to 
