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 very similar
to its present distribution in space.
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