CHAPTER 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.
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