We may
instance the Hawaiian group, which is wholly of volcanic origin, with
the exception of its minor coral additions, and represents a stupendous
activity of underground agencies beneath the domain of Father Neptune.
In part, as we have said elsewhere in this work, all oceanic islands,
remote from those in the shoal bordering waters of the continents, have
been of volcanic or coral formation, or more often a combination of the
two. No sooner does an island mass appear above or near the surface of
tropical waters than the minute coral animals--effective only by their
myriads--begin their labors, building fringes of coral rock around
the cindery heaps lifted from the ocean floor. The atolls of the
Pacific--circular or oval rings of coral with lagunes of sea-water
within--have long been thought to be built on the rims of submarine
volcanoes, rising to within a few hundred feet of the surface, much
as coral reefs around actual islands. If the volcanic mass should
subsequently subside, as it is likely to do, the minute ocean builders
will continue their work--unless the subsidence be too rapid for their
powers of production--and in this way ring-like islands of coral may
in time rise from great depths of sea, their basis being the volcanic
island which has sunk from near the surface far toward old ocean's
primal floor.
CHAPTER XXXI.
Mud Volcanoes, Geysers, and Hot Springs.
Our usual impression of a volcano is indicated in the title of "burning
mountain," so often employed, a great fire-spouting cone of volcanic
debris, from which steam, lava, rock-masses, cinder-like fragments, and
dust, often of extreme fineness, are flung high into the air or flow
in river-like torrents of molten rock.
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