birds in so effectually stocking these Alpine heights is
equally out of the question. The difficulty was so great,
that some naturalists were driven to believe that these
species were all separately created twice over on these
distant peaks. The determination of a recent glacial epoch,
however, soon offered a much more satisfactory solution,
and one that is now universally accepted by men of science.
At this period, when the mountains of Wales were full
of glaciers, and the mountainous parts of Central Europe,
and much of America north of the great lakes, were
covered with snow and ice, and had a climate resembling
that of Labrador and Greenland at the present day, an
Arctic flora covered all these regions. As this epoch of
cold passed away, and the snowy mantle of the country,
with the glaciers that descended from every mountain
summit, receded up their slopes and towards the north
pole, the plants receded also, always clinging as nowT to
the margins of the perpetual snow line. Thus it is that
the same species are now found on. the summits of the
mountains of temperate Europe and America, and in the
barren north-polar regions.
But there is another set of facts, which help us on
another step towards the case of the Javanese mountain
flora. On the higher slopes of the Himalaya, on the tops
of the mountains of Central India and of Abyssinia, a
number of plants occur which, though not identical with
those of European mountains, belong to the same genera,
and are said by botanists to represent them; and most
of these could not exist in the warm intervening plains.
Mr. Darwin believes that this class of facts can be
explained in the same way; for, during the greatest severity
of the glacial epoch, temperate forms of plants will have
extended to the confines of the tropics, and on its departure,
will have retreated up these southern mountains,
as well as northward to the plains and hills of Europe.
But in this case, the time elapsed, and the great change
of conditions, have allowed many of these plants to become
so modified that we now consider them to be. distinct
species. A variety of other facts of a similar nature, have
led him to believe that the depression of temperature was
at one time sufficient to allow a few north-temperate
plants to cross the Equator (by the most elevated routes)
and to reach the Antarctic regions, where they are now
found. The evidence on which this belief rests, will be
found in the latter part of Chapter II. of the “ Origin
of Species;’" and, accepting it for the present as an
hypothesis, it enables us to account for the presence of
a flora of European type on the volcanoes of Java.
It will, however, naturally be objected that there is
a wide expanse of sea between Java and the continent,
which would have effectually prevented the immigration
of temperate forms of plants during the glacial epoch.