[I-10]

The limits allotted to this article are nearly reached, yet only four of
the fourteen chapters of the volume have been touched. These, however,
contain the fundamental principles of the theory, and most of those
applications of it which are capable of something like verification,
relating as they do to the phenomena now occurring. Some of our extracts
also show how these principles are thought to have operated through the
long lapse of the ages. The chapters from the sixth to the ninth inclusive
are designed to obviate difficulties and objections, "some of them so grave
that to this day," the author frankly says, he "can never reflect on them
without being staggered." We do not wonder at it. After drawing what
comfort he can from "the imperfection of the geological record" (Chapter
IX), which we suspect is scarcely exaggerated, the author considers the
geological succession of organic beings (Chapter X), to see whether they
better accord with the common view of the immutability of species, or with
that of their slow and gradual modification. Geologists must settle that
question. Then follow two most interesting and able chapters on the
geographical distribution of plants and animals, the summary of which we
should be glad to cite; then a fitting chapter upon classification,
morphology, embryology, etc., as viewed in the light of this theory, closes
the argument; the fourteenth chapter being a recapitulation.

The interest for the general reader heightens as the author advances on his
perilous way and grapples manfully with the most formidable difficulties.

To account, upon these principles, for the gradual elimination and
segregation of nearly allied forms--such as varieties, sub-species, and
closely-related or representative species--also in a general way for their
geographical association and present range, is comparatively easy, is