me we may suppose islands to be upheaved in mid-channel; and,
as the subterranean forces varied in intensity, and shifted their points
of greatest action, these islands would sometimes become connected with
the land on one side or other of the strait, and at other times again be
separated from it. Several islands would at one time be joined together,
at another would be broken up again, until at last, after many long ages
of such intermittent action, we might have an irregular archipelago
of islands filling up the ocean channel of the Atlantic, in whose
appearance and arrangement we could discover nothing to tell us which
had been connected with Africa and which with America. The animals and
plants inhabiting these islands would, however, certainly reveal this
portion of their former history. On those islands which had ever formed
a part of the South American continent, we should be sure to find such
common birds as chatterers and toucans and hummingbirds, and some of the
peculiar American quadrupeds; while on those which had been separated
from Africa, hornbills, orioles, and honeysuckers would as certainly be
found. Some portion of the upraised land might at different times have
had a temporary connection with both continents, and would then contain
a certain amount of mixture in its living inhabitants. Such seems to
have been the case with the islands of Celebes and the Philippines.
Other islands, again, though in such close proximity as Bali and
Lombock, might each exhibit an almost unmixed sample of the productions
of the continents of which they had directly or indirectly once formed a
part.

In the Malay Archipelago we have, I believe, a case exactly parallel
to that which I have here supposed. We have indications of a vast
continent, with a peculiar fauna and flora having been gradually and
irregularly broken up; the island of Celebes probably marking its
furthest westward extension, beyond which was a wide ocean. At the
same time Asia appears to have been extending its limits in a southeast
direction, first in an unbroken mass, then separated into islands as
we now see it, and almost coming into actual contact with the scattered
fragments of the great southern land.

From this outline of the subject, it will be evident how important an
adjunct Natural History is to Geology; not only in interpreting
the fragments of extinct animals found in the earth's crust, but in
determining past changes in the surface which