illustrations of
the arguments and results as occur to him in a place far removed from
all means of reference and exact information.

_A Law deduced from well-known Geographical and Geological Facts._

The following propositions in Organic Geography and Geology give the
main facts on which the hypothesis 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.

6. Most of the larger and some small groups extend through several
geological periods.

7. In each period, however, there are peculiar groups, found nowhere
else, and extending through one or several formations.

8. Species of one genus, or genera of one family occurring in the same
geological time are more closely allied than those separated in time.

9. As generally in geography no species or genus occurs in two very
distant localities without being also found in intermediate places, so
in geology the life of a species or genus has not been interrupted. In
other words, no group or species has come into existence twice.

10. The following law may be deduced from these facts:--_Every species
has come into existence coincident both in space and time with a
pre-existing closely allied species._

This law agrees with, explains and illustrates all the facts connected
with the following branches of the subject:--1st. The system of natural
affinities. 2nd. The distribution of animals and plants in space. 3rd.
The same in time, including all the phaenomena of representative