d to, it appears that
there are between sixty and seventy northern genera in Fuegia and Southern
Chile, while about forty of the species are absolutely identical with those
of Europe and the Arctic regions. Considering how comparatively little the
mountains of South Temperate America are yet known, this is a very
remarkable result, and it proves that the transmission of species must have
gone on up to comparatively recent times. Yet, as only a few of these
species are now found along the line of migration, we see that they only
occupied such stations temporarily; and we may connect their disappearance
with the passing away of the last glacial period which, by raising the
snow-line, reduced the area on which alone they could exist, and exposed
them to the competition of indigenous plants from the belt of country
immediately below them.

Now, just as these numerous species and genera have undoubtedly passed
along the great American range of mountains, although only now found at its
two extremes, so others have doubtless passed on further; and have found
more suitable stations or less severe competition in the Antarctic
continent and islands, in New Zealand, in Tasmania, and even in Australia
itself. The route by which they may have reached these countries is easily
marked out. Immediately south of Cape Horn, at a distance of only 500
miles, are the South Shetland Islands and Graham's Land, whence the
Antarctic continent or a {522} group of large islands probably extends
across or around the south polar area to Victoria Land and thence to Adelie
Land. The outlying Young Island, 12,000 feet high, is about 750 miles south
of the Macquarie Islands, which may be considered a southern outlier of the
New Zealand group; and the Macquarie Islands are about the same distance
from the 1,000-fathom line at a point marking the probable southern
extension of Tasmania. Other islands may have existed at intermediate
points; but, even as it is, these distances are not greater than we know
are traversed by plants both by flotation and by aerial currents,
especially in such a stormy atmosphere as that of the Antarctic regions.
Now, we may further assume, that what we know occurred within the Arctic
circle also took place in the Antarctic--that is, that there have been
alternations of climate during which some portion of what are now ice-clad
lands became able to support a considerable amount of vegetation.[142]
During such periods there woul