e eastern side of the Atlantic, the cold was
moderated, and a milder climate ensued, such as we now enjoy in
Europe.[154]

_Proofs from fossils in secondary and still older strata._--A great
interval of time appears to have elapsed between the formation of the
secondary strata, which constitute the principal portion of the elevated
land in Europe, and the origin of the eocene deposits. If we examine the
rocks from the chalk to the new red sandstone inclusive, we find many
distinct assemblages of fossils entombed in them, all of unknown
species, and many of them referable to genera and families now most
abundant between the tropics. Among the most remarkable are reptiles of
gigantic size; some of them herbivorous, others carnivorous, and far
exceeding in size any now known even in the torrid zone. The genera are
for the most part extinct, but some of them, as the crocodile and
monitor, have still representatives in the warmer parts of the earth.
Coral reefs also were evidently numerous in the seas of the same
periods, composed of species often belonging to genera now
characteristic of a tropical climate. The number of large chambered
shells also, including the nautilus, leads us to infer an elevated
temperature; and the associated fossil plants, although imperfectly
known, tend to the same conclusion, the Cycadeae constituting the most
numerous family.

But it is from the more ancient coal-deposits that the most
extraordinary evidence has been supplied in proof of the former
existence of a very different climate--a climate which seems to have
been moist, warm, and extremely uniform, in those very latitudes which
are now the colder, and in regard to temperature, the most variable
regions of the globe. We learn from the researches of Adolphe
Brongniart, Goeppert, and other botanists, that in the flora of the
carboniferous era there was a great predominance of ferns, some of which
were arborescent; as, for example, Caulopteris, Protopteris, and
Psarronius; nor can this be accounted for, as some have supposed, by the
greater power which ferns possess of resisting maceration in water.[155]
This prevalence of ferns indicates a moist, equable, and temperate
climate, and the absence of any severe cold; for such are the conditions
which, at the present day, are found to be most favorable to that tribe
of plants. It is only in the islands of the tropical oceans, and of the
southern temperate zone, such as Norfolk Island, Otaheit