king extent, must be the figure
of the earth. To the protuberant mass is due the precession of the
equinoxes, which requires twenty-five thousand eight hundred and
sixty-eight years for its completion, and also the nutation of the
earth's axis, discovered by Bradley. We have already had occasion to
remark that the earth's equatorial diameter exceeds the polar by about
twenty-six miles.

Two facts are revealed by the oblateness of the earth: 1. That she has
formerly been in a yielding or plastic condition; 2. That she has been
modeled by a mechanical and therefore a secondary cause.

But this influence of mechanical causes is manifested not only in
the exterior configuration of the globe of the earth as a spheroid of
revolution, it also plainly appears on an examination of the arrangement
of her substance.

If we consider the aqueous rocks, their aggregate is many miles in
thickness; yet they undeniably have been of slow deposit. The material
of which they consist has been obtained by the disintegration of ancient
lands; it has found its way into the water-courses, and by them been
distributed anew. Effects of this kind, taking place before our eyes,
require a very considerable lapse of time to produce a well-marked
result--a water deposit may in this manner measure in thickness a few
inches in a century--what, then, shall we say as to the time consumed in
the formation of deposits of many thousand yards?

The position of the coast-line of Egypt has been known for much more
than two thousand years. In that time it has made, by reason of the
detritus brought down by the Nile, a distinctly-marked encroachment on
the Mediterranean. But all Lower Egypt has had a similar origin. The
coast-line near the mouth of the Mississippi has been well known
for three hundred years, and during that time has scarcely made a
perceptible advance on the Gulf of Mexico; but there was a time when the
delta of that river was at St. Louis, more than seven hundred miles
from its present position. In Egypt and in America--in fact, in all
countries--the rivers have been inch by inch prolonging the land into
the sea; the slowness of their work and the vastness of its extent
satisfy us that we must concede for the operation enormous periods of
time.

To the same conclusion we are brought if we consider the filling of
lakes, the deposit of travertines, the denudation of hills, the
cutting action of the sea on its shores, the undermining of cliff