d, 600 miles away, in such
quantities as to destroy the crops. During the eruption of Tomboro, in
the East Indies, in 1815, so great was the quantity of dust thrown up
that it caused darkness at midday in Java 300 miles away and covered the
ground to a depth of several inches. Floating pumice formed a layer
on the ocean surface two and a half feet in thickness, through which
vessels had difficulty in forcing their way.

The steam which rises in large volumes into the air may become suddenly
condensed with the chill of the upper atmosphere and fall as rain,
torrents of which often follow an eruption. The rain, falling through
the clouds of volcanic dust, brings it to the earth as liquid mud, which
pours in thick streams down the sides of the mountain. The torrents of
flowing mud are sometimes on such a great scale that large towns, as in
the instance of the great city of Herculaneum, may be completely buried
beneath them. Over this city the mud accumulated to the depth of over 70
feet. In addition to these phenomena, molten lava often flows from the
lip of the crater, occasionally in vast quantities. In the Icelandic
eruption of 1783 the lava streams were so great in quantity as to fill
river gorges 600 ft. deep and 200 ft. wide, and to extend over an open
plain to a distance of 12 to 15 miles, forming lakes of lava 100 feet
deep. The volcanoes of Hawaii often send forth streams of lava which
cover an area of over 100 square miles to a great depth.

GREAT OUTFLOWS OF LAVA

In the course of ages lava outflows of this kind have built up in Hawaii
a volcanic mountain estimated to contain enough material to cover the
whole of the United States with a layer of rock 50 feet deep. These
great outflows of lava are not confined to mountains, but take place now
and then from openings in the ground, or from long cracks in the surface
rocks. Occasionally great eruptions have taken place beneath the
ocean's surface, throwing up material in sufficient quantity to form new
islands.

The formation of mud is not confined to the method given, but great
quantities of this plastic material flow at times from volcanic craters.
In the year 1691 Imbaburu, one of the peaks of the Andes, sent out
floods of mud which contained dead fish in such abundance that their
decay caused a fever in the vicinity. The volcanoes of Java have often
buried large tracts of fertile country under volcanic mud.

An observation of volcanoes shows us that th