Falconer, E. Forbes, etc., and all our greatest geologists, as Lyell,
Murchison, Sedgwick, etc., have unanimously, often vehemently,
maintained the immutability of species. But I have reason to believe
that one great authority, Sir Charles Lyell, from further reflexion
entertains grave doubts on this subject. I feel how rash it is to
differ from these great authorities, to whom, with others, we owe all
our knowledge. Those who think the natural geological record in any
degree perfect, and who do not attach much weight to the facts and
arguments 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.
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
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