s below our feet, that at every
release of pressure the solid rock bursts into molten lava? Is the steam
from the contact of underground rivers and deep-lying fires the origin
of the terrible rending powers of the volcano's depths? Truly we can
answer none of these questions with assurance, and can only guess
and conjecture from the few facts open to us what lies concealed far
beneath.

RARITY OF ANCIENT ACCOUNTS

In the history of earthquakes nothing is more remarkable than the
extreme fewness of those recorded before the beginning of the Christian
era, in comparison with those that have been registered since that time.
It is to be borne in mind, however, that before the birth of Christ only
a small portion of the globe was inhabited by those likely to make a
record of natural events. The vast apparent increase in the number
of earthquakes in recent times is owing to a greater knowledge of
the earth's surface and to the spread of civilization over lands once
inhabited by savages. The same is to be said of volcanic eruptions,
which also have apparently increased greatly since the beginning of the
Christian era. There may possibly have been a natural increase in these
phenomena, but this is hardly probable, the change being more likely due
to the increase in the number of observers.

The structure of a volcano is very different from that of other
mountains, really consisting of layers of lava and volcanic ashes,
alternating with each other and all sloping away from the center. These
elevations, in fact, are formed in a different manner from ordinary
mountains. The latter have been uplifted by the influence of pressure in
the interior of the earth, but the volcano is an immediate result of the
explosive force of which we have spoken, the mountain being gradually
built up by the lava and other materials which it has flung up from
below. In this way mountains of immense height and remarkable regularity
have been formed. Mount Orizabo, near the City of Mexico, for instance,
is a remarkably regular cone, undoubtedly formed in this way, and the
same may be said of Mount Mayon, on the Island of Luzon.

In many cases the irregularity of the volcano is due to subsequent
action of its forces, which may blow the mountain itself to pieces.
In the case of Krakatoa, in the East Indies, for instance, the whole
mountain was rent into fragments, which were flung as dust miles high
into the air. The main point we wish to indicate