nd other
vessels, have shown that the bottom of the deepest portion of the ocean,
far away from the land, is covered with volcanic materials which have
been carried through the air or have floated on the surface of the
ocean.

Fragments of scoria or pumice may be thrown hundreds or thousands of
feet into the atmosphere, those that fall into the crater and are flung
up again being gradually reduced in size by friction. Thus it is related
by Mr. Poulett Scrope, who watched the Vesuvian eruption of 1822,
which lasted for nearly a month, that during the earlier stages of the
outburst fragments of enormous size were thrown out of the crater, but
by constant re-ejection these were gradually reduced in size, till
at last only the most impalpable dust issued from the vent. This dust
filled the atmosphere, producing in the city of Naples "a darkness that
might be felt." So excessively finely divided was it, that it penetrated
into all drawers, boxes, and the most closely fastened receptacles,
filling them completely. The fragmentary materials ejected from
volcanoes are often given the name of cinders or ashes. These, however,
are terms of convenience only, and do not properly describe the volcanic
material.

Sometimes the passages of steam through a mass of molten glass produces
large quantities of a material resembling spun glass. Small particles of
this glass are carried into the air and leave behind them thin, glassy
filaments like a tail. At the volcano of Kilauea in Hawaii, this
substance, as previously stated, is abundantly produced, and is known
as 'Pele's Hair'--Pele being the name of the goddess of the mountain.
Birds' nests are sometimes found composed of this beautiful material.
In recent years an artificial substance similar to this Pele's hair
has been extensively manufactured by passing jets of steam through the
molten slag of iron-furnaces; it resembles cotton-wool, but is made up
of fine threads of glass, and is employed for the packing of boilers and
other purposes.

The lava itself, as left in huge deposits upon the surface, assumes
various forms, some crystalline, others glassy. The latter is usually
found in the condition known as obsidian, ordinarily black in color,
and containing few or no crystals. It is brittle, and splits into
sharp-edged or pointed fragments, which were used by primitive peoples
for arrow-heads, knives and other cutting implements. The ancient
Mexicans used bits of it for shaving pu