logical and geological phenomena,
and one which is especially valuable for the light it throws on the
dispersal and existing distribution of organisms. The other important
theory, or rather corollary from the preceding theory--that of the
permanence of oceans and the general stability of continents throughout all
geological time, is as yet very imperfectly understood, and seems, in fact,
to many persons in the nature of a paradox. The evidence for it, however,
appears to me to be conclusive; and it is certainly the most fundamental
question in regard to the subject we have to deal with: since, if we once
admit that continents and oceans may have changed places over and over
again (as many writers maintain), we lose all power of reasoning on the
migrations of ancestral forms of life, and are at the mercy of every wild
theorist who chooses to imagine the former existence of a now-submerged
continent to explain the existing distribution of a group of frogs or a
genus of beetles.

As already shown by the illustrative examples adduced in this chapter, some
of the most remarkable and interesting facts in the distribution and
affinities of organic forms are presented by islands in relation to each
other and to the surrounding continents. The study of the productions of
the Galapagos--so peculiar, and yet so decidedly related to the American
continent--appears to have had a powerful influence in determining the
direction of Mr. Darwin's researches into the origin of species; and every
naturalist who studies them has always been struck by the unexpected
relations or singular anomalies which are so often found to characterize
the fauna and flora of islands. Yet their full importance in connection
with the history of the earth and its inhabitants has hardly yet {11} been
recognised; and it is in order to direct the attention of naturalists to
this most promising field of research, that I restrict myself in this
volume to an elucidation of some of the problems they present to us. By far
the larger part of the islands of the globe are but portions of continents
undergoing some of the various changes to which they are ever subject; and
the correlative proposition, that every portion of our continents has again
and again passed through insular conditions, has not been sufficiently
considered, but is, I believe, the statement of a great and most suggestive
truth, and one which lies at the foundation of all accurate conception of
the phy