" We shall see
that it is probable that an even higher type of animal, the
mammal, was born in the throes of the Permian revolution. But
enough has been said in vindication of the phrase which stands at
the head of this chapter; and to show how the great Primary age
of terrestrial life came to a close. With its new inhabitants the
earth enters upon a fresh phase, and thousands of its earlier
animals and plants are sealed in their primordial tombs, to await
the day when man will break the seals and put flesh once more on
the petrified bones.
CHAPTER XI. THE MIDDLE AGES OF THE EARTH
The story of the earth from the beginning of the Cambrian period
to the present day was long ago divided by geologists into four
great eras. The periods we have already covered--the Cambrian,
Ordovician, Silurian, Devonian, Carboniferous, and Permian--form
the Primary or Palaeozoic Era, to which the earlier Archaean
rocks were prefixed as a barren and less interesting
introduction. The stretch of time on which we now enter, at the
close of the Permian, is the Secondary or Mesozoic Era. It will
be closed by a fresh upheaval of the earth and disturbance of
life-conditions in the Chalk period, and followed by a Tertiary
Era, in which the earth will approach its modern aspect.
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