The advocates of continuity possess one immense advantage over
those who believe in violent and revolutionary convulsions, that
they call into play only agencies of which we have actual knowledge.
We _know_ that certain forces are now at work, producing certain
modifications in the present condition of the globe; and we _know_
that these forces are capable of producing the vastest of the
changes which geology brings under our consideration, provided
we assign a time proportionately vast for their operation. On
the other hand, the advocates of catastrophism, to make good
their views, are compelled to invoke forces and actions, both
destructive and restorative, of which we have, and can have, no
direct knowledge. They endow the whirlwind and the earthquake,
the central fire and the rain from heaven, with powers as mighty
as ever imagined in fable, and they build up the fragments of a
repeatedly shattered world by the intervention of an intermittently
active creative power.

It should not be forgotten, however, that from one point of view
there is a truth in catastrophism which is sometimes overlooked
by the advocates of continuity and uniformity. Catastrophism
has, as its essential feature, the proposition that the known
and existing forces of the earth at one time acted with much
greater intensity and violence than they do at present, and they
carry down the period of this excessive action to the commencement
of the present terrestrial order. The Uniformitarians, in effect,
deny this proposition, at any rate as regards any period of the
earth's history of which we have actual cognisance. If, however,
the "nebular hypothesis" of the origin of the universe be well
founded--as is generally admitted--then, beyond question, the
earth is a gradually cooling body, which has at one time been