which many readers are
more familiar. He begins:

Every naturalist who has directed his attention to the subject of
the geographical distribution of animals and plants must have been
interested in the singular facts which it presents. Many of these
facts are quite different from what would have been anticipated,
and have hitherto been considered as highly curious but quite
inexplicable. None of the explanations attempted from the time of
Linnaeus are now considered at all satisfactory; none of them have
given a cause sufficient to account for the facts known at the
time, or comprehensive enough to include all the new facts which
have since been and are daily being added. Of late years, however,
a great light has been thrown upon the subject by geological
investigations, which have shown that the present state of the
earth, and the organisms now inhabiting it, are but the last stage
of a long and uninterrupted series of changes which it has
undergone, and consequently, that to endeavour to explain and
account for its present condition without any reference to those
changes (as has frequently been done) must lead to very imperfect
and erroneous conclusions.... The following propositions in
Organic Geography and Geology give the main facts on which the
hypothesis [_see_ p. 96] is founded.

GEOGRAPHY

(1) Large groups, such as classes and orders, are generally spread
over the whole earth, while smaller ones, such as families and
genera, are frequently confined to one portion, often to a very
limited district.

(2) In widely distributed families the genera are often limited in
range; in widely distributed genera, well-marked groups of species
are peculiar to each geographical district.

(3) When a group is confined to one district and is rich in
species, it is almost invariably the case that the most closely
allied species are found in the same locality or in closely
adjoining localities, and that therefore the natural sequence of
the species by affinity is also geographical.

(4) In countries of a similar climate, but separated by a wide sea
or lofty mountains, the families, genera and species of the one
are often represented by closely allied families, genera and
species peculiar to the other.

GEOLOGY

(5) The distribution of the organic world in time is ver