I find three, more or less contradictory, systems of geological thought,
each of which might fairly enough claim these appellations, standing
side by side in Britain. I shall call one of them Catastrophisim another
Uniformitarianism, the third Evolutionism; and I shall try briefly
to sketch the characters of each, that you may say whether the
classification is, or is not, exhaustive.
By Catastrophism I mean any form of geological speculation which, in
order to account for the phenomena of geology supposes the operation of
forces different in their nature, or immeasurably different in power,
from those which we at present see in action in the universe.
The Mosaic cosmogony is, in this sense, catastrophic, because it assumes
the operation of extra-natural power. The doctrine of violent upheavals,
_debacles_ and cataclysms in general, is catastrophic, so far as it
assumes that these were brought about by causes which have now no
parallel. There was a time when catastrophism might, pre-eminently, have
claimed the title of "British popular geology"; and assuredly it has
yet many adherents, and reckons among its supporters some of the most
honoured members of this Society.
By Uniformitarianism I mean especially the teaching of Hutton and of
Lyell.
That great though incomplete work, "The Theory of the Earth", seems to
me to be one of the most remarkable contributions to geology which is
recorded in the annals of the science. So far as the not-living world
is concerned, uniformitarianism lies there, not only in germ, but in
blossom and fruit.
If one asks how it is that Hutton was led to entertain views so far
in advance of those prevalent in his time, in some respects; while, in
others, they seem almost curiously limited, the answer appears to me to
be plain.
Hutton was in advance of the geological speculation of his time,
because, in the first place, he had amassed a vast store of knowledge
of the facts of geology, gathered by personal observation in travels of
considerable extent; and because, in the second place, he was thoroughly
trained in the physical and chemical science of his day, and thus
possessed, as much as any one in his time could possess it, the
knowledge which is requisite for the just interpretation of geological
phenomena, and the habit of thought which fits a man for scientific
inquiry.
It is to this thorough scientific training that I ascribe Hutton's
steady and persistent refusal to look to other causes than those now in
operation for the explanation of geological phenomena.
The internal heat of the earth, the elevation and depression of
its crust, its belchings forth of vapours, ashes, and lava, are its
activities, in as strict a sense as are warmth and the movements and
products of respiration the activities of an animal. The phenomena of
the seasons, of the trade winds, of the Gulf-stream, are as much the
results of the reaction between these inner activities and outward
forces as are the budding of the leaves in spring and their falling
in autumn the effects of the interaction between the organisation of a
plant and the solar light and heat. And, as the study of the activities
of the living being is called its physiology, so are these phenomena
the subject-matter of an analogous telluric physiology, to which we
sometimes give the name of meteorology, sometimes that of physical
geography, sometimes that of geology. Again, the earth has a place in
space and in time, and relations to other bodies in both these respects,
which constitute its distribution. This subject is usually left to the
astronomer; but a knowledge of its broad outlines seems to me to be an
essential constituent of the stock of geological ideas.