d since it finally passed away, while throughout the Miocene
epoch the snow-line would often be lowered during periods of high
excentricity, we are enabled to comprehend the nature of the causes which
may have led to the islands being stocked with those north tropical or
mountain types which are so characteristic a feature of that portion of the
Galapagos flora which consists of peculiar species.

On the whole, the flora agrees with the fauna in indicating a moderately
remote origin, great isolation, and changes of conditions affording
facilities for the introduction of organisms from various parts of the
American coast, and even from the West Indian Islands and Gulf of Mexico.
As in the case of the birds, the several islands differ considerably in
their native plants, many species being limited to one or two islands only,
while others extend to several. This is, of course, what might be expected
on any theory of their origin; because, even if the whole of the islands
had once been united and afterwards separated, long continued isolation
would often lead to the differentiation of species, while the varied
conditions to be found upon islands differing in size and altitude as well
as in luxuriance of vegetation, would often lead to the extinction of a
species on one island and its preservation on another. If the several
islands had been equally well {290} explored, it might be interesting to
see whether, as in the case of the Azores, the number of species diminished
in those more remote from the coast; but unfortunately our knowledge of the
productions of the various islands of the group is exceedingly unequal,
and, except in those cases in which representative species inhabit distinct
islands, we have no certainty on the subject. All the more interesting
problems in geographical distribution, however, arise from the relation of
the fauna and flora of the group as a whole to those of the surrounding
continents, and we shall therefore for the most part confine ourselves to
this aspect of the question in our discussion of the phenomena presented by
oceanic or continental islands.

_Concluding Remarks._--The Galapagos offer an instructive contrast with the
Azores, showing how a difference of conditions that might be thought
unimportant may yet produce very striking results in the forms of life.
Although the Galapagos are much nearer a continent than the Azores, the
number of species of plants common to the continent is much