Time is long, and nature never hurries. She builds for infinite
years, and recks not the time of building. The human mind is far
too feeble to comprehend the duration of time that sped away and
was gone ere the slowly falling temperature of the Earth
admitted the formation of a crust over her surface. When that
came, the first great scene was closed. The star had expired,
the planet rolled in her annual course around the still glowing
central sun. Now came the formative age of the world, when the
great continents were outlined.

The atmosphere gradually freed itself from its weight of water-
vapor, the rains descended, and the ocean took form and contour.
We are concerned only with the outlines of Geology, not with its
details. It is full of the most interesting facts, but is
foreign to our present purpose. We will only say, there is a
marked progression in the scale and importance of life forms.

The lower forms of animals appear first to be followed in time
by the higher. It is true that some forms have survived through
all the changes of Geological time to the present: yet, speaking
generally, some forms of life are peculiar to each age, and the
general phase of animal life is different with each period.
They thus form epochs in the history of the world as read from
the rocks, and though the beginning and ending of each age may
blend by insensible gradations with that of the preceding and
following, yet, taken as a whole, we observe in each such
singularities of form and structure as to give name to each
particular age.

In the fullness of time man appears; and it is our pleasant task