he work
are then applied to explain the phenomena presented by the floras and
faunas of the chief islands of the globe, which are classified, in
accordance with their physical origin, in three groups or classes, each
{533} of which are shown to exhibit certain well-marked biological
features.

Having thus shown that the work is a connected whole, founded on the
principle of tracing out the more recondite causes of the distribution of
organisms, we will briefly indicate the scope and object of the several
chapters, by means of which this general conception has been carried out.

Beginning with simple and familiar facts relating to British and European
quadrupeds and birds, I have defined and shown the exact character of
"areas of distribution," as applied to species, genera, and families, and
have illustrated the subject by maps showing the peculiarities of
distribution of some well-known groups of birds. Taking then our British
mammals and land-birds, I follow them over the whole area they inhabit, and
thus obtain a foundation for the establishment of "zoological regions," and
a clear insight into their character as distinct from the usual
geographical divisions of the globe.

The facts thus far established are then shown to be necessary results of
the "law of evolution." The nature and amount of "variation" is exhibited
by a number of curious examples; the origin, growth, and decay of species
and genera are traced, and all the interesting phenomena of isolated groups
and discontinuous generic and specific areas are shown to follow as logical
consequences.

The next subject investigated is the means by which the various groups of
animals are enabled to overcome the natural barriers which often seem to
limit them to very restricted areas, how far those barriers are themselves
liable to be altered or abolished, and what is the exact nature and amount
of the changes of sea and land which our earth has undergone in past times.
This latter part of the inquiry is shown to be the most important as it is
the most fundamental; and as it is still a subject of controversy, and many
erroneous views prevail in regard to it, it is discussed at some length.
Several distinct classes of evidence are adduced to prove that the grand
features of our globe--the position of the great oceans {534} and the chief
land-areas--have remained, on the whole, unchanged throughout geological
time. Our continents are shown to be built up mainly of "