of tranquil water.

[Illustration: Fig. 114.

View of Whitsunday Island. (Capt. Beechey.)[1116]]

The accompanying section will enable the reader to comprehend the usual
form of such islands. (Fig. 115.)

[Illustration: Fig. 115.

Section of a Coral Island.

_a_, _a_, Habitable part of the island, consisting of a strip
of coral, inclosing the lagoon.
_b_, _b_, The lagoon.

]

The subjoined cut (fig. 116.) exhibits a small part of the section of a
coral island on a larger scale.

[Illustration: Fig. 116.

Section of part of a Coral Island.

_a_, _b_, Habitable part of the island.

_b_, _c_, Slope of the side of the island, plunging at an angle of
forty-five to the depth of fifteen hundred feet.

_c_, _c_, Part of the lagoon.

_d_, _d_, Knolls of coral in the lagoon, with overhanging masses of
coral resembling the capitals of columns.]

Of thirty-two of these coral islands visited by Beechey in his voyage to
the Pacific, twenty-nine had lagoons in their centres. The largest was
30 miles in diameter, and the smallest less than a mile. All were
increasing their dimensions by the active operations of the lithophytes,
which appeared to be gradually extending and bringing the immersed parts
of their structure to the surface. The scene presented by these annular
reefs is equally striking for its singularity and beauty. A strip of
land a few hundred yards wide is covered by lofty cocoa-nut trees, above
which is the blue vault of heaven. This band of verdure is bounded by a
beach of glittering white sand, the outer margin of which is encircled
with a ring of snow-white breakers, beyond which are the dark heaving
waters of the ocean. The inner beach incloses the still clear water of
the lagoon, resting in its greater part on white sand, and when
illuminated by a vertical sun, of a most vivid green.[1117] Certain
species of zoophytes abound most in the lagoon, others on the exterior
margin, where there is a great surf. "The ocean," says Mr. Darwin,
"throwing its breakers on these outer shores, appears an invincible
enemy, yet we see it resisted and even conquered by means which at first
seem most weak and inefficient. No periods of repose are granted, and
the long swell caused by the steady action of the trade wind never
ceases. The breakers exceed in violence those of our temperate regions,
and it is impossible to behold them without feeling a conviction that
rocks of granite or quartz wou