all their parts; but the laws which direct those
changes, and the rules to which they are subject, have remained
invariably the same."--PLAYFAIR, _Illustrations of the Huttonian
Theory_, Section 374.

"The inhabitants of the globe, like all the other parts of it, are
subject to change. It is not only the individual that perishes, but
whole species.

"A change in the animal kingdom seems to be a part of the order of
Nature, and is visible in instances to which human power cannot have
extended."--PLAYFAIR, _Illustrations of the Huttonian Theory_, Section
413.

PREFACE TO THE NINTH EDITION.

The Principles of Geology in the first five editions embraced not only a
view of the _modern changes_ of the earth and its inhabitants, as set
forth in the present work, but also some account of those monuments of
analogous changes of _ancient_ date, both in the organic and inorganic
world, which it is the business of the geologist to interpret. The
subject last mentioned, or "geology proper," constituted originally a
fourth book, now omitted, the same having been enlarged into a separate
treatise, first published in 1838, in one volume 12mo., and called "The
Elements of Geology," afterwards recast in two volumes 12mo. in 1842,
and again re-edited under the title of "Manual of Elementary Geology,"
in one volume 8vo. in 1851. The "Principles" and "Manual" thus divided,
occupy, with one exception, to which I shall presently allude, very
different ground. The "Principles" treat of such portions of the economy
of existing nature, animate and inanimate, as are illustrative of
Geology, so as to comprise an investigation of the permanent effects of
causes now in action, which may serve as records to after ages of the
present condition of the globe and its inhabitants. Such effects are the
enduring monuments of the ever-varying state of the physical geography
of the globe, the lasting signs of its destruction and renovation, and
the memorials of the equally fluctuating condition of the organic world.
They may be regarded, in short, as a symbolical language, in which the
earth's autobiography is written.

In the "Manual of Elementary Geology," on the other hand, I have treated
briefly of the component materials of the earth's crust, their
arrangement and relative position, and their organic contents, which,
when deciphered by aid of the key supplied by the study of the modern
changes above alluded to, reveal to us the annals of a