t only crushed, but the crushed material is blown
out as dust, or expelled as liquid rock from between the walls of the
shell, which are thus enabled to approach each other; and thus, by
relief of the tangential thrusts, to permit the shell to descend, which
it is obvious that crushing alone, unless it extended to the whole mass
of the shell, could not accomplish.

It is a wonderful example of Nature's mechanism thus to see how simple
are the means by which this end is accomplished. The same inevitable
crush that dislocates the solid shell along certain lines, produces the
heat necessary to expel to the surface the material crushed.

When attempted to be made the basis for philosophic discovery, "final
causes" are no doubt barren, as Bacon has said; but when we have
independently and by strict methods arrived at a result, we may justly
appeal, as a test of its truth, to its showing itself as plainly
fulfilling a needful end, and, by a distinctly discernible mechanism,
preserving that harmony and conservation which are the obvious law of
the universe.

As has been said, if I mistake not by Daubeny, John Phillips, by
Herschell, and by myself, the function of the Earthquake and the
Volcano is not destructive but, preservative. But we now see that: that
the preservative scope of this function, as respects our earth, is far
wider than what has been previously attributed to it. The Volcano does
not merely throw up new fertile soil, and tend, in some small degree, to
restore to the dry land the waste for ever going on by rain and sea; it
fulfils a far weightier and more imperative task; it--by a mechanism the
power of which is exactly balanced to the variable calls demanded of it,
and which working almost imperceptibly, although in a manner however
terrible its surface-action may at times appear to us little
men[G]--prevents at longer intervals such sudden and unlooked-for
paroxysms in the mass of our subsiding earth's shell as would be
attended with wide-spread destruction to all that it inhabit.

To the popular mind, Volcanoes and Earthquakes are only isolated items
of curiosity amongst "the wonders of the world:" few geologists even
appear to realise how great and important are the relations of
Vulcanicity to their science, viewed as a whole. Yet of Vulcanicity it
is not too much to say, that in proportion as its nature and doctrines
come to be known and understood as parts of the Cosmos, the nearer will
it be seen to l