Cockatoos similarly restricted? Insects
furnish a countless number of analogous examples;--the Goliathi of
Africa, the Ornithopterae of the Indian Islands, the Heliconidae of South
America, the Danaidae of the East, and in all, the most closely allied
species found in geographical proximity. 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 test 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 to disprove it, not _a priori_ arguments against its
probability.

_Geological Distribution of the Forms of Life._

The phaenomena of geological distribution are exactly analogous to those
of geography. Closely allied species are found associated in the same
beds, and the change from species to species appears to have been as
gradual in time as in space. Geology, however, furnishes us with
positive proof of the extinction and production of species, though it
does not inform us how either has taken place. The extinction of
species, however, offers but little difficulty, and the _modus operandi_
has been well illustrated by Sir C. Lyell in his admirable
"Principles." Geological changes, however gradual, must occasionally
have modified external conditions to such an extent as to have rendered
the existence of certain species impossible. The extinction would in
most cases be effected by a gradual dying-out, but in some instances
there might have been a sudden destruction of a species of limited
range. To discover how the extinct species have from time to time been
replaced by new ones down to the very latest geological period, is the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 give