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 through
geologic time, may feel compelled by what he knows of causation, and by
the general analogy of nature, to suppose that our solar system was once
a nebulous mass; that it gradually condensed, that it broke up into
that wonderful group of harmoniously rolling balls we call planets
and satellites, and that then each of these underwent its appointed
metamorphosis, until at last our own share of the cosmic vapour passed
into that condition in which we first meet with definite records of
its state, and in which it has since, with comparatively little change,
remained.

The doctrine of uniformity and the doctrine of progression are,
therefore, perfectly consistent; perhaps, indeed, they might be shown to
be necessarily connected with one another.

If, however, the condition of the world, which has obtained throughout
geologic time, is but the sequel to a vast series of changes which took
place in pre-geologic time, then it seems not unlikely that the duration
of this latter is to that of the former as the vast extent of geologic
time is to the length of the brief epoch we call the historical period;
and that even the oldest rocks are records of an epoch almost infinitely
remote from that which could have witnessed the first shaping of our
globe.

It is probable that no modern geologist would hesitate to admit the
general validity of these reasonings when applied to the physics of his
subject, whence it is the more remarkable that the moment the question
changes from one of physics and chemistry to one of natural history,
scientific opinions and the popular prejudices, which reflect them in
a distorted form, undergo a sudden metamorphosis. Geologists
and palaeontologists write about the "beginning of life" and the
"first-created forms of living beings," as if they were the most
familiar things in the world; and even cautious writers seem to be on
quit