maintain, the sun gave out perceptibly more heat in past ages
than now, this alone would cause an increase in almost all the forces that
have brought about geological phenomena. With greater heat there would be a
more extensive aqueous atmosphere, and, perhaps, a greater difference
between equatorial and polar temperatures; hence more violent winds,
heavier rains and snows, {113} and more powerful oceanic currents, all
producing more rapid denudation. At the same time, the internal heat of the
earth being greater, it would be cooling more rapidly, and thus the forces
of contraction--which cause the upheaving of mountains, the eruption of
volcanoes, and the subsidence of extensive areas--would be more powerful
and would still further aid the process of denudation. Yet again, the
earth's rotation was certainly more rapid in very remote times, and this
would cause more impetuous tides and still further add to the denuding
power of the ocean. It thus appears that, as we go back into the past,
_all_ the forces tending to the continued destruction and renewal of the
earth's surface would be in more powerful action, and must therefore tend
to reduce the time required for the deposition and upheaval of the various
geological formations. It may be true, as many geologists assert, that the
changes here indicated are so slow that they would produce comparatively
little effect within the time occupied by the known sedimentary rocks, yet,
whatever effect they did produce would certainly be in the direction here
indicated, and as several causes are acting together, their combined
effects may have been by no means unimportant. It must also be remembered
that such an increase of the primary forces on which all geologic change
depends would act with great effect in still further intensifying those
alternations of cold and warm periods in each hemisphere, or, more
frequently, of excessive and equable seasons, which have been shown to be
the result of astronomical, combined with geographical, revolutions; and
this would again increase the rapidity of denudation and deposition, and
thus still further reduce the time required for the production of the known
sedimentary rocks. It is evident therefore that these various
considerations all combine to prove that, in supposing that the rate of
denudation has been on the average only what it is now, we are almost
certainly over-estimating the _time_ required to have produced the whole
series of form