in the rocks, so, on the other side, the study of the marks left in the
ancient strata by past physical actions shows that these were similar
to those which now obtain. Ancient beaches are met with whose pebbles
are like those found on modern shores; the hardened sea-sands of the
oldest epochs show ripple-marks, such as may now be found on every
sandy coast; nay, more, the pits left by ancient rain-drops prove that
even in the very earliest ages, the "bow in the clouds" must have
adorned the palaeozoic firmament. So that if we could reverse the
legend of the Seven Sleepers,--if we could sleep back through the past,
and awake a million ages before our own epoch, in the midst of the
earliest geologic times,--there is no reason to believe that sea, or
sky, or the aspect of the land would warn us of the marvellous
retrospection.

Such are the beliefs which modern physical geologists hold, or, at any
rate, tend towards holding. But, in so doing, it is obvious that they
by no means prejudge the question, as to what the physical condition of
the globe may have been before our chapters of its history begin, in
what may be called (with that licence which is implied in the often-used
term "prehistoric epoch") "pre-geologic time." The views indicated, in
fact, are not only quite consistent with the hypothesis, that, in the
still earlier period referred to, the condition of our world was very
different; but they may be held by some to necessitate that hypothesis.
The physical philosopher who is accurately acquainted with the velocity
of a cannon-ball, and the precise character of the line which it
traverses for a yard of its course, is necessitated by what he knows of
the laws of nature to conclude that it came from a certain spot, whence
it was impelled by a certain force, and that it has followed a certain
trajectory. In like manner, the student of physical geology, who fully
believes in the uniformity of the general condition of the earth