eatly agitated all around. Then followed volcanic smoke, and
quantities of stones, ashes, and pumice; the two latter being scattered
over the surface of the sea to a great distance. Loud thundering reports
accompanied this eruption, and all the ships in the neighborhood felt
concussions like those produced by an earthquake. These phenomena seem
to have ended in the formation of some great submarine chasm, into which
the waters rushed with extreme violence and a terrific roar.

Occurrences similar to this last have been several times observed in
a tract of open sea in the Atlantic, about half a degree south of the
equator, and between 20 and 22 degrees of west longitude. Although
quantities of volcanic dross have been from time to time thrown up to
the surface in this region, no island has yet made its appearance above
water.

The events here described repeat on a far smaller scale similar ones
which have occurred in remote ages in many parts of the ocean and left
great island masses as the permanent effects of their work. 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 impr