nly affirmed that its velocity would be immeasurably short of the
observed or theoretic velocity of the great earth-wave, or true shock in
earthquakes."[784]

_Liquid gases._--The rending and upheaving of continental masses are
operations which are not difficult to explain, when we are once
convinced that heat, of sufficient power, not only to melt but to reduce
to a gaseous form a great variety of substances, is accumulated in
certain parts of the interior. We see that elastic fluids are capable of
projecting solid masses to immense heights in the air; and the volcano
of Cotopaxi has been known to throw out, to the distance of eight or
nine miles, a mass of rock about one hundred cubic yards in volume. When
we observe these aeriform fluids rushing out from particular vents for
months, or even years, continuously, what power may we not expect them
to exert in other places, where they happen to be confined under an
enormous weight of rock?

The experiments of Faraday and others have shown, within the last twelve
years, that many of the gases, including all those which are most
copiously disengaged from volcanic vents, as the carbonic, sulphurous,
and muriatic acids, may be condensed into liquids by pressure. At
temperatures of from 30 degrees to 50 degrees F., the pressure required
for this purpose varies from fifteen to fifty atmospheres; and this
amount of pressure we may regard as very insignificant in the operations
of nature. A column of Vesuvian lava that would reach from the lip of
the crater to the level of the sea, must be equal to about three hundred
atmospheres; so that, at depths which may be termed moderate in the
interior of the crust of the earth, the gases may be condensed into
liquids, even at very high temperatures. The method employed to reduce
some of these gases to a liquid state is, to confine the materials, from
the mutual action of which they are evolved, in tubes hermetically
sealed, so that the accumulated pressure of the vapor, as it rises and
expands, may force some part of it to assume the liquid state. A similar
process may, and indeed must, frequently take place in subterranean
caverns and fissures, or even in the pores and cells of many rocks; by
which means, a much greater store of expansive power may be _packed_
into a small space than could happen if these vapors had not the
property of becoming liquid. For, although the gas occupies much less
room in a liquid state, yet it exerts exac