ental thesis of the doctrine of Uniformity is, that,
in spite of all apparent violations of continuity, the sequence
of geological phenomena has in reality been a regular and
uninterrupted one; and that the vast changes which can be shown
to have passed over the earth in former periods have been the
result of the slow and ceaseless working of the ordinary physical
forces--acting with no greater intensity than they do now, but
acting through enormously prolonged periods. The essential element
in the theory of Continuity is to be found in the allotment of
indefinite time for the accomplishment of the known series of
geological changes. It is obviously the case, namely, that there
are two possible explanations of all phenomena which lie so far
concealed in "the dark backward and abysm of time," that we can
have no direct knowledge of the manner in which they were produced.
We may, on the one hand, suppose them to be the result of some
very powerful cause, acting through a short period of time. That
is Catastrophism. Or, we may suppose them to be caused by a much
weaker force operating through a proportionately prolonged period.
This is the view of the Uniformitarians. It is a question of
_energy_ versus _time_ and it is _time_ which is the true element
of the case. An earthquake may remove a mountain in the course
of a few seconds; but the dropping of the gentle rain will do
the same, if we extend its operations over a millennium. And
this is true of all agencies which are now at work, or ever have
been at work, upon our planet. The Catastrophists, believing
that the globe is but, as it were, the birth of yesterday, were
driven of necessity to the conclusion that its history had been
checkered by the intermittent action of paroxysmal and almost
inconceivably potent forces. The Uniformitarians, on the other
hand, maintaining the "adequacy of existing causes," and denying
that the known physical forces ever acted in past time with greater
intensity than they do at present, are, equally of necessity,
driven to the conclusion that the world is truly in its "hoary
eld," and that its present state is really the result of the
tranquil and regulated action of known forces through unnumbered
and innumerable centuries.

The most important point for us, in the present connection, is
the bearing of these opposing doctrines upon the question, as
to the origin of the existing terrestrial order. On any doctrine
of uniformity that orde