It is the one common fate that could
slay all classes. When we find that the surviving reptiles
retreat southward, only lingering in Europe during the renewed
warmth of the Eocene and Miocene periods, this interpretation is
sufficiently confirmed. And when we recollect that these things
coincide with the extinction of the Ammonites and Belemnites, and
the driving of their descendants further south, as well as the
rise and triumph of deciduous trees, it is difficult to see any
ground for hesitating.
But we need not, and must not, imagine a period of cold as
severe, prolonged, and general as that of the Permian period. The
warmth of the Jurassic period is generally attributed to the low
relief of the land, and the very large proportion of
water-surface. The effect of this would be to increase the
moisture in the atmosphere. Whether this was assisted by any
abnormal proportion of carbon-dioxide, as in the Carboniferous,
we cannot confidently say. Professor Chamberlin observes that,
since the absorbing rock-surface was greatly reduced in the
Jurassic, the carbon-dioxide would tend to accumulate in its
atmosphere, and help to explain the high temperature.
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