ments of other kinds given in this volume, will undoubtedly at once
reject my theory. For my part, following out Lyell's metaphor, I look at
the natural geological 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.

* * * * *

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CHAPTER X.

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