All
trees hitherto had been evergreen, and we need a specific and
adequate explanation why the earth is now covered, in the
northern region, with forests of trees which show naked boughs
and branches during a part of the year.
The majority of palaeontologists conclude at once, and quite
confidently, from this rise and spread of the deciduous trees,
that a winter season has at length set in on the earth, and that
this new type of vegetation appears in response to an appreciable
lowering of the climate. The facts, however, are somewhat
complex, and we must proceed with caution. It would seem that any
general lowering of the temperature of the earth ought to betray
itself first in Greenland, but the flora of Greenland remains far
"warmer," so to say, than the flora of Central Europe is to-day.
Even toward the close of the Cretaceous its plants are much the
same as those of America or of Central Europe. Its fossil remains
of that time include forty species of ferns, as well as cycads,
ginkgoes, figs, bamboos, and magnolias. Sir A. Geikie ventures to
say that it must then have enjoyed a climate like that of the
Cape or of Australia to-day.
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