.. by the action of winds and currents," and
that the modified prototypes remaining are the "new species" which have
been "created in each on the plan of the pre-existing ones." This is
followed by a graphic sketch of the general effect of volcanic and
other action as affecting the distribution of species, and the exact
form in which they are found, even fishes giving "evidence of a similar
kind: each great river [having] its peculiar genera, and in more
extensive genera its groups of closely allied species."

After stating a number of practical examples he continues:

The question forces itself upon every thinking mind--Why are these
things so? They could not be as they are, had no law regulated
their creation and dispersion. The law here enunciated not merely
explains, but necessitates the facts we see to exist, while the
vast and long-continued geological changes of the earth readily
account for the exceptions and apparent discrepancies that here
and there occur. The writer's object in putting forward his views
in the present imperfect manner is to submit them to the tests of
other minds, and to be made aware of all the facts supposed to be
inconsistent with them. As his hypothesis is one which claims
acceptance solely as explaining and connecting facts which exist
in nature, he expects facts alone to be brought forward to
disprove it, not _a priori_ arguments against its probability.

He then refers to some of the geological "principles" expounded by Sir
Charles Lyell on the "extinction of species," and follows this up by
saying:

To discover how the extinct species have from time to time been
replaced by new ones down to the very latest geological period, is
the most difficult, and at the same time the most interesting,
problem in the natural history of the earth. The present inquiry,
which seeks to eliminate from known facts a law which has
determined, to a certain degree, what species could and did appear
at a given epoch, may, it is hoped, be considered as one step in
the right direction towards a complete solution of it.... Admitted
facts seem to show ... a general, but not a detailed
progression.... It is, however, by no means difficult to show
that a real progression in the scale of organisation is perfectly
consistent with all the appearances, and even with apparent
retrogression should such occur.