carrying the novice
beyond his depth, and appealing to facts and conclusions with which he
will be unacquainted, until he has studied some elementary work on
geology, but it may be useful to excite his curiosity, and lead him to
study such works by calling his attention at once to some of the
principal points of controversy.[125]

CHAPTER VI.

DOCTRINE OF THE DISCORDANCE OF THE ANCIENT AND MODERN CAUSES OF CHANGE
CONTROVERTED.

Climate of the Northern Hemisphere formerly different--Direct proofs
from the organic remains of the Italian strata--Proofs from analogy
derived from extinct quadrupeds--Imbedding of animals in
icebergs--Siberian mammoths--Evidence in regard to temperature, from
the fossils of tertiary and secondary rocks--From the plants of the
coal formation--Northern limit of these fossils--Whether such plants
could endure the long continuance of an arctic night.

_Climate of the Northern hemisphere formerly different._--Proofs of
former revolutions in climate, as deduced from fossil remains, have
afforded one of the most popular objections to the theory which
endeavors to explain all geological changes by reference to those now in
progress on the earth. The probable causes, therefore, of fluctuations
in climate, may first be treated of.

That the climate of the Northern hemisphere has undergone an important
change, and that its mean annual temperature must once have more nearly
resembled that now experienced within the tropics, was the opinion of
some of the first naturalists who investigated the contents of the
ancient strata. Their conjecture became more probable when the shells
and corals of the older tertiary and many secondary rocks were carefully
examined; for the organic remains of these formations were found to be
intimately connected by generic affinity with species now living in
warmer latitudes. At a later period, many reptiles, such as turtles,
tortoises, and large saurian animals, were discovered in European
formations in great abundance; and they supplied new and powerful
arguments, from analogy, in support of the doctrine, that the heat of
the climate had been great when our secondary strata were deposited.
Lastly, when the botanist turned his attention to the specific
determination of fossil plants, the evidence acquired still fuller
confirmation; for the flora of a country is peculiarly influenced by
temperature: and the ancient vegetation of the ear