pon it at the time, and were
then succeeded by long intervals of repose, when all things returned
to their accustomed order, ocean and river deposited fresh beds in
uninterrupted succession, the accumulation of materials went on as
before, a new set of animals and plants were introduced, and a time of
building up and renewing followed the time of destruction. These
periods of revolution are naturally more difficult to decipher than
the periods of rest; for they have so torn and shattered the beds they
uplifted, disturbing them from their natural relations to each other,
that it is not easy to reconstruct the parts and give them coherence
and completeness again. But within the last half-century this work has
been accomplished in many parts of the world with an amazing degree of
accuracy, considering the disconnected character of the phenomena to
be studied; and I think I shall be able to convince my readers that
the modern results of geological investigation are perfectly sound
logical inferences from well-established facts. In this, as in so many
other things, we are but "children of a larger growth." The world is
the geologist's great puzzle-box; he stands before it like the child
to whom the separate pieces of his puzzle remain a mystery till he
detects their relation and sees where they fit, and then his fragments
grow at once into a connected picture beneath his hand....

When geologists first turned their attention to the physical history
of the earth, they saw at once certain great features which they took
to be the skeleton and basis of the whole structure. They saw the
great masses of granite forming the mountains and mountain-chains,
with the stratified rocks resting against their slopes; and they
assumed that granite was the first primary agent, and that all
stratified rocks must be of a later formation. Although this involved
a partial error, as we shall see hereafter when we trace the upheavals
of granite even into comparatively modern periods, yet it held an
important geological truth also; for, though granite formations are by
no means limited to those early periods, they are nevertheless very
characteristic of them, and are indeed the foundation-stones on which
the physical history of the globe is built.

Starting from this landmark, the earlier geologists divided the
world's history into three periods. As the historian recognizes
Ancient History, the Middle Ages, and Modern History as distinct
phases i