see their explosions disturbing the surface of the waters is very
interesting, but not as yet clearly explicable. It is possible,
however, that a volcanic discharge taking place at the depth of
several thousand feet below the surface of the water would not be able
to blow the fluid aside so as to open a pipe to the surface, but would
expend its energy in a hidden manner near the ocean floor. The vapours
would have to expand gradually, as they do in passing up through the
rock pipe of a volcano, and in their slow upward passage might be
absorbed by the water. The solid materials thrown forth would in this
case necessarily fall close about the vent, and create a very steep
cone, such, indeed, as we find indicated by the soundings off certain
volcanic islands which appear only recently to have overtopped the
level of the waters.

As will be seen, though inadequately from the diagrams of Vesuvius,
volcanic cones have a regularity and symmetry of form far exceeding
that afforded by the outlines of any other of the earth's features.
Where, as is generally the case, the shape of the cone is determined
by the distribution of the falling cinders or divided lava which
constitutes the mass of most cones, the slope is in general that known
as a catenary curve--i.e., the line formed by a chain hanging between
two points at some distance from the vertical. It is interesting to
note that this graceful outline is a reflection or consequence of the
curve described by the uprushing vapour. The expansion in the
ascending column causes it to enlarge at a somewhat steadfast rate,
while the speed of the ascent is ever diminishing. Precisely the same
action can be seen in the like rush of steam and other gases and
vapours from the cannon's mouth; only in the case of the gun, even of
the greatest size, we can not trace the movement for more than a few
hundred feet. In this column of ejection the outward movement from the