he oceanic islands which
are not coral-reefs are composed of volcanic rocks; and many of
these oceanic islands, as well as others lying near the shores of the
continents, contain active volcanoes.

Through the midst of the Atlantic Ocean runs a ridge, which, by the
soundings of the various exploring vessels sent out in recent years, has
been shown to divide the ocean longitudinally into two basins. Upon this
great ridge, and the spurs proceeding from it, rise numerous mountainous
masses, which constitute the well-known Atlantic islands and groups
of islands. All of these are of volcanic origin, and among them are
numerous active volcanoes. The Island of Jan Mayen contains an active
volcano, and Iceland contains thirteen, and not improbably more; the
Azores have six active volcanoes, the Canaries three; while about eight
volcanoes lie off the west coast of Africa. In the West Indies there are
six active volcanoes; and three submarine volcanoes have been recorded
within the limits of the Atlantic Ocean. Altogether, no less than forty
active volcanoes are situated upon the great submarine ridges which
traverse the Atlantic longitudinally.

But along the same line the number of extinct volcanoes is far greater,
and there are not wanting proofs that the volcanoes which are still
active are approaching the condition of extinction.

VOLCANOES OF THE PACIFIC

If the great medial chain of the Atlantic presents us with an example of
a chain of volcanic mountains verging on extinction, we have in the
line of islands separating the Pacific and Indian Oceans an example of a
similar range of volcanic vents which are in a condition of the
greatest activity. In the peninsula of Kamchatka there are twelve active
volcanoes, in the Aleutian Islands thirty-one, and in the peninsula
of Alaska three. The chain of the Kuriles contains at least ten active
volcanoes; the Japanese Islands and the islands to the south of Japan
twenty-five. The great group of islands lying to the south-east of the
Asiatic continent is at the present time the grandest focus of volcanic
activity upon the globe. No less than fifty active volcanoes occur here.

Farther south, the same chain is probably continued by the four active
volcanoes of New Guinea, one or more submarine volcanoes, and several
vents in New Britain, the Solomon Isles, and the New Hebrides, the three
active volcanoes of New Zealand, and possibly by Mount Erebus and Mount
Terror in the Ant