ological record,
as a history of the world imperfectly kept, and written in a changing
dialect; of this history we possess the last volume alone, relating only
to two or three countries. Of this volume, only here and there a short
chapter has been preserved; and of each page, only here and there a few
lines. Each word of the slowly-changing language, in which the
history is supposed to be written, being more or less different in
the interrupted succession of chapters, may represent the apparently
abruptly changed forms of life, entombed in our consecutive, but widely
separated formations. On this view, the difficulties above discussed are
greatly diminished, or even disappear.

10. ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS.

On the slow and successive appearance of new species. On their different
rates of change. Species once lost do not reappear. Groups of species
follow the same general rules in their appearance and disappearance as
do single species. On Extinction. On simultaneous changes in the forms
of life throughout the world. On the affinities of extinct species to
each other and to living species. On the state of development of ancient
forms. On the succession of the same types within the same areas.
Summary of preceding and present chapters.

Let us now see whether the several facts and rules relating to the
geological succession of organic beings, better accord with the common
view of the immutability of species, or with that of their slow and
gradual modification, through descent and natural selection.

New species have appeared very slowly, one after another, both on the
land and in the waters. Lyell has shown that it is hardly possible to
resist the evidence on this head in the case of the several tertiary
stages; and every year tends to fill up the blanks between them, and to
make the percentage system of lost and new forms more gradual. In
some of the most recent beds, though undoubtedly of high antiquity if
measured by years, only one or two species are lost forms, and only one
or two are new forms, having here appeared for the first time, either
locally, or, as far as we know, on the face of the earth. If we may
trust the observations of Philippi in Sicily, the successive changes in
the marine inhabitants of that island have been many and most gradual.
The secondary formations are more broken; but, as Bronn has remarked,
neither the appearance nor disappearance of their many now extinct