is that volcanoes are
never formed by ordinary elevating forces and that they differ in this
way from all other mountains. On the contrary, they have been piled up
like rubbish heaps, resembling the small mountains of coal dust near the
mouths of anthracite mines.

It is to the burning heat of the earth's crust and the influence of
pressure, and more largely to the influx of water to the molten rocks
which lie miles below the surface, that these convulsions of nature are
due. Water, on reaching these overheated strata, explodes into volumes
of steam, and if there is no free vent to the surface, it is apt to rend
the very mountain asunder in its efforts to escape. Such is supposed
to have been the case in the eruption of Krakatoa, and was probably the
case also in the recent case of Mt. Pelee.

GENERAL DESCRIPTION OF ERUPTIONS

If we should seek to give a general description of volcanic eruptions,
it would be in some such words as follows: An eruption is usually
preceded by earthquakes which affect the whole surrounding country,
and associated with which are underground explosions that seem like
the sound of distant artillery. The mountain quivers with internal
convulsions, due to the efforts of its confined forces to find an
opening. The drying up of wells and disappearance of springs are apt to
take place, the water sinking downward through cracks newly made in the
rocks. Finally the fierce unchained energy rends an opening through the
crater and an eruption begins. It comes usually with a terrible burst
that shakes the mountain to its foundation; explosions following rapidly
and with increasing violence, while steam issues and mounts upward in
a lofty column. The steam and escaping gases in their fierce outbreaks
hurl up into the air great quantities of solid rock torn from the sides
of the opening. The huge blocks, meeting each other in their rise and
fall, are gradually broken and ground into minute fragments, forming
dust or so-called ashes, often of extreme fineness, and in such
quantities as frequently to blot out the light of the sun. There is
another way in which a great deal of volcanic dust is made; the lava is
full of steam, which in its expansion tears the molten rock into atoms,
often converting it into the finest dust.

The eruption of Mt. Skaptar, in Iceland, in 1783, sent up such volumes
of dust that the atmosphere was loaded with it for months, and it
was carried to the northern part of Scotlan