where its outer parts were what
we term cold, and the whole of its mass approximately solid, it remained
as it does to-day, exceedingly hot in its central portions, and
therefore kept on slowly cooling. What we call the outer or crust part,
because it had already become cool, had little heat to lose. The greater
portion of the temperature, which crept away into the frigid places of
the heavens, where the thermometer is always some hundred degrees below
the freezing-point, came from the interior of the sphere. Because of
this cooling in the deeper parts of the earth the mass shrunk in its
interior portion, while the outer part, losing less heat, because it had
less to lose, did not contract to anything like the same extent. Thus it
came about that this crust portion which forms the surface, and that
which is below to the depth of many miles, were forced to wrinkle in
order to fit the diminished centre. The action may be compared, in a
way, to what takes place when in an apple or other similar fruit or
vegetable with a distinct skin the water dries out of the interior
parts. The skin wrinkles, because it has little water to lose. Let us
conceive that the heat which keeps the particles of matter apart in our
earth answers to the water which separates the solid portions of the
fruit, and the likeness becomes clear.

When the great wrinkles of the earth's crust were high enough to bring
their surfaces in part above the level of the ocean, another important
stage in the history of the sphere was begun. Before that time, the
water which the sun's heat had lifted into the air, and sent back to the
earth in the form of rain, had fallen into the ocean whence it came
without in any way affecting the solid parts of the crust. But now a
portion of it came down on what we call the dry land, making the
beginning of the rivers and the lakes, and in its course to the sea
wearing away the rocks over which it flowed, conveying the debris to the
oceans, where it served to build layers of rocks upon the bottom, which
with the further upward growth of the continent might in turn rise above
the sea. Thus we may fairly reckon the appearance of the land above the
seas as the third great event in the history of the earth.

After the earth had cooled down so that the waters had something like
their present temperature, and probably after the lands had appeared,
came the fourth and, on many accounts, the most interesting episode in
the history of