Although Pythagoras (500 B. C.) believed that sea and land must often
have changed places, and a few other observers at different epochs came
to the same conclusion, yet, till quite recent times, the earth was
generally supposed to have been always very much as it is now; people
spoke of “the eternal hills”; and the great mountain ranges, the mighty
ravines and precipices, as well as the deep seas and oceans, were
believed to be the direct work of the Creator.
It was only in the latter half of the eighteenth century that a few
observers began to see the importance of studying the nature of the
earth’s crust, so far as it could be reached in ravines, quarries, and
mines; and one of the most earnest of these students, Dr. Hutton, of
Edinburgh, after more than thirty years of travel and study, published
his great work, _The Theory of the Earth_, which must be considered to
be the starting-point of modern geology. He maintained that it was only
by observing causes now in action that we can explain the phenomena
presented by the stratified and igneous rocks; he showed that the
former must have been laid down by water, and that the larger part of
them, containing as they do marine shells and other fossils, must have
been deposited on the sea-bottom. He showed how rain and rivers, frost
and snow, wind and heat disintegrated the hardest rocks and would in
time excavate the deepest valleys; while earthquakes, however small
an elevation any one of them might produce, would in time raise the
sea-bottom sufficiently high to form, when denuded, mountain ranges,
plains, and valleys like those we now see everywhere upon the earth’s
surface. He also showed that the most ancient stratified rocks, those
that lie at the very base of the series, presented every indication of
having been formed in exactly the same way as the most recent ones.
Hence he stated a conclusion which excited a storm of opposition, in
these words: “In the economy of the world I can find no traces of a
beginning, no prospect of an end.” This was thought to imply a denial
of creation, and was quite sufficient at that period to prevent the
work of any man of science from being judged impartially.
But although Playfair and a few others upheld Hutton’s views, they
were too novel to receive much support by his contemporaries, and this
was especially the case as regards the slow and continuous action
of existing causes being sufficient to account for all the known
phenomena presented by the crust of the earth. Hence the belief in
catastrophes and cataclysms—in great convulsions tearing mountains
asunder, and vast floods sweeping over whole continents—continued to
prevail, till finally banished by the genius and perseverance of one
man, Sir Charles Lyell. His _Principles of Geology_ was first published
in 1830, and successive editions, revised and often greatly extended,
continued to appear till the author’s death, forty-five years later. As
this work affords a fine example of the application of the principles
of evolution to the later phases of the earth’s history, and as it not
only revolutionized scientific opinion in its own domain, but prepared
the way for the acceptance of the still more novel and startling
application of the same principles to the entire organic world, it
will be necessary to show what opinions prevailed at the time it first
appeared in order that we may understand how great was the change it
effected.
In the earlier years of the nineteenth century the standard geological
work, both in Great Britain and on the Continent, was Cuvier’s _Essay
on the Theory of the Earth_. In 1827 a fifth edition of the English
translation appeared, and there was a German translation so late as
1830—sufficient proofs of its wide popularity. Yet this work abounds
in statements which are positively ludicrous to any one conversant
with modern geology. It never appeals to known causes, but again and
again assumes forces to be at work for which no evidence is adduced and
which are totally at variance with what we see in the world to-day. A
few examples justifying these statements must be here given. Cuvier
shows that he was acquainted with the theory of modern causes, but he
altogether rejects it, saying that “the march of nature is changed,
and none of the agents she now employs would have been sufficient
for the production of her ancient works.” He adduces “the primitive
mountains” whose “sharp and bristling ridges and peaks are indications
of the violent manner in which they have been elevated.” He allows
that atmospheric agencies may form sea-cliffs, alluvial deposits, and
taluses of loose matter at the foot of the precipices, but he adds:
“These are but limited effects to which vegetation in general puts
a stop, and which, besides, presuppose the existence of mountains,
valleys, and plains—in short, all the inequalities of the globe—and
which, therefore, cannot have given rise to those inequalities.” He
contrasts the calm and peaceful aspect of the surface of the earth
with the appearances discovered when we examine its interior. Here, in
the raised beds of shells, the fractured rocks, the inclined or even
vertical stratification, he finds abundant proofs “that the surface of
the globe has been broken up by revolutions and catastrophes.”
He also refers to the numerous large blocks of the primitive rocks
scattered over the surface of secondary formations, and separated by
deep valleys or even by arms of the sea from the peaks or ridges from
which they must have been derived, as further proofs of catastrophes;
for, it is argued, they must have been either ejected by volcanic
eruptions or carried by waters, which, in either case, “must have
exceeded in violence anything we can imagine at the present day,” and
he therefore concludes that “it is in vain we search among the powers
which now act upon the surface of the earth for causes sufficient to
produce the revolutions and catastrophes, the traces of which are
exhibited in its crust.” He is quite confident that all these changes
go on rapidly, periods of catastrophe alternating with periods of
repose. The present surface of the earth he holds to be quite recent,
and he maintains “that, if anything in geology be established, it
is that the surface of our globe has undergone a great and sudden
revolution, the date of which cannot be referred to a much earlier
period than five or six thousand years ago; that this revolution
overwhelmed and caused to disappear the countries which were previously
inhabited by man, and the species of animals now best known; that, on
the other hand, it laid dry the bottom of the last sea, and formed
of it the countries which are at the present day inhabited.” And he
further declares that “this event has been sudden, instantaneous,
without any gradation; and what is so clearly demonstrated with respect
to this last catastrophe is not less so with reference to those which
preceded it.”
The method followed by Lyell was the very reverse of that of Cuvier.
Instead of assuming hastily that modern causes were totally inadequate,
and appealing constantly to purely imaginary and often inconceivable
catastrophes, Lyell investigated these causes with painstaking
accuracy, applying the tests of survey and time measurement, so as in
many cases to prove that, given moderately long periods of time—not
a few thousands only, but hundreds of thousands of years—they were
fully adequate to explain the phenomena. He also showed that the
imaginary causes of Cuvier would not explain the facts, for that
everywhere in the crust of the earth we found conclusive proofs of very
slow continuous changes exactly analogous to what now occur, never
of great convulsions, except quite locally, as we have them now. He
showed that modern volcanoes had poured out vast masses of melted rock
during a single eruption, covering areas as extensive as those which
any ancient volcano could be proved to have ejected in an equally
short period; that strata were now in process of formation comparable
in extent and thickness with any ancient strata; that organic remains
are being preserved in them just as in the older rocks; that the land
is almost everywhere rising or sinking as of old; that valleys are
being excavated and plateaus or mountains upheaved; that earthquake
shocks are producing faults beneath the surface; that vegetation is
still preparing future coal beds; that limestones, clays, sandstones,
metamorphic and igneous rocks are all still being formed; and that,
given time, and the intermittent or continuous action of the causes we
can now trace in operation, and all the varied features of the earth’s
surface, as well as all the contortions and fractures which we discover
in its crust, and every other phenomenon supposed to necessitate
catastrophes and cataclysms will be again produced.
In the massive volumes of the later editions of the _Principles of
Geology_ all these points are discussed and illustrated with such a
wealth of facts and such cogent yet cautious reasoning as have carried
conviction to all modern students. It affords us perhaps the very best
proof yet given of evolution in one department of the universe—that of
the surface and the crust of the earth we inhabit. Not only have all
the chief modifications during an almost unimaginable period of time
been clearly depicted, but they have in almost every case been shown to
be the inevitable results of real and comparatively well-known causes,
such as we now see at work around us.
The grand generalizations of Lyell have been strengthened since his
death by more complete investigations of certain phenomena and their
causes than were possible in his day; while the only objections to them
seem to be founded, to some extent, upon a misconception. He has been
termed a “Uniformitarian,” and it is alleged that it is unphilosophical
to take the limited range of causes we now see in action, as a measure
of those which have acted during all past geological time. But neither
Lyell nor his followers make any such assumption. They merely say, we
do not find any proof of greater or more violent causes in action in
past times, and we do find many indications that the great natural
forces then in action—seas and rivers, sun and cloud, rain and
hail, frost and snow, as well as the very texture and constituents
of the older rocks, and the mode in which the organisms of each age
are preserved in them, must have been in their general nature and
magnitude very much as they are now. Other objections, such as that
the internal forces were greater when the earth was hotter, and that
tidal effects must have been more powerful when the moon was nearer
the earth, are altogether beside the question until we can obtain
more definite measures of past time than we now possess in reference
to both geological and cosmical phenomena. It may well be that the
physical changes above referred to have been so slow that they would
have produced no perceptibly increased effect at the epoch of the
early stratified rocks. Lyell’s doctrine is simply that of real
against imaginary causes, and he only denies catastrophes and more
violent agencies in early times, because there is no clear evidence
of their actual existence, and also because known causes are quite
competent to explain all geological phenomena. It must be remembered,
too, that uniformitarians have never limited the natural forces of
past geological periods to the precise limits of which we have had
experience during the historical period. What they maintain is, that
forces of the same _nature_ and of the same _order of magnitude_ are
adequate to have brought about the evolution of the crust of the earth
as we now find it.