es us with too much force of one kind, namely, that of
subterranean movement, while it deprives us of another kind of
mechanical force, namely, that exerted by the waves and currents of the
ocean, which the geologist requires for the denudation of land during
its slow upheaval or depression. It may be safely affirmed that the
quantity of igneous and aqueous action,--of volcanic eruption and
denudation,--of subterranean movement and sedimentary deposition,--not
only of past ages, but of one geological epoch, or even the fraction of
an epoch, has exceeded immeasurably all the fluctuations of the
inorganic world which have been witnessed by man. But we have still to
inquire whether the time to which each chapter or page or paragraph of
the earth's autobiography relates, was not equally immense when
contrasted with a brief era of 3000 or 5000 years. The real point on
which the whole controversy turns, is the relative amount of work done
by mechanical force in given quantities of time, past and present.
Before we can determine the relative intensity of the force employed, we
must have some fixed standard by which to measure the time expended in
its development at two distinct periods. It is not the magnitude of the
effects, however gigantic their proportions, which can inform us in the
slightest degree whether the operation was sudden or gradual, insensible
or paroxysmal. It must be shown that a slow process could never in any
series of ages give rise to the same results.

The advocate of paroxysmal energy might assume a uniform and fixed rate
of variation in times past and present for the animate world, that is to
say, for the dying-out and coming-in of species, and then endeavor to
prove that the changes of the inanimate world have not gone on in a
corresponding ratio. But the adoption of such a standard of comparison
would lead, I suspect, to a theory by no means favorable to the pristine
intensity of natural causes. That the present state of the organic world
is not stationary, can be fairly inferred from the fact, that some
species are known to have become extinct in the course even of the last
three centuries, and that the exterminating causes always in activity,
both on the land and in the waters, are very numerous; also, because man
himself is an extremely modern creation; and we may therefore reasonably
suppose that some of the mammalia now contemporary with man, as well as
a variety of species of inferior classes, m