aks up and falls away, so that the sides
are always covered by angular shingle forming slopes corresponding to
the angle of friction of the rock in question. In the case of a volcanic
mountain, however, the same form is due either to accumulation of
fragmental material piled around the cup-shaped hollow, or crater, which
is usually placed at the apex of the cone, and owing to which it is
bluntly terminated, or else to the welling up from beneath of viscous
matter in the manner presently to be described.

_Views of Sir Humphrey Davy and L. von Buch._--The question how a
volcanic cone came to be formed was not settled without a long
controversy carried on by several naturalists of eminence. Some of the
earlier writers of modern times on the subject of vulcanicity--such as
Sir Humphrey Davy and Leopold von Buch--maintained that the conical form
was due to upheaval by a force acting from below at a central focus,
whereby the materials of which the mountain is formed were forced to
assume a _qua-qua versal_ position--that is, a position in which the
materials dip away from the central focus in every direction. But this
view, originally contested by Scrope and Lyell, has now been generally
abandoned. It will be seen on reflection that if a series of strata of
ashes, tuff, and lava, originally horizontal, or nearly so, were to be
forced upwards into a conical form by a central force, the result would
be the formation of a series of radiating fissures ever widening from
the circumference towards the focus. In the case of a large mountain
such fissures, whether filled with lava or otherwise, would be of great
breadth towards the focus, or central crater, and could not fail to make
manifest beyond dispute their mechanical origin. But no fissures of the
kind here referred to are, as a matter of fact, to be observed. Those
which do exist are too insignificant and too irregular in direction to
be ascribed to such an origin; so that the views of Von Buch and Davy
must be dismissed, as being unsupported by observation, and as untenable
on dynamical grounds. As a matter of fact, the "elevatory theory," or
the "elevation-crater theory," as it is called by Scrope, has been
almost universally abandoned by writers on vulcanicity.

_Principal Varieties of Volcanic Mountains as regards Form._--But whilst
rejecting the "elevatory theory," it is necessary to bear in mind that
volcanic cones and dome-shaped elevations have been formed in severa