herwise have held.

It remains that I should put before you what I understand to be the
third phase of geological speculation--namely, EVOLUTIONISM.

I shall not make what I have to say on this head clear, unless I
diverge, or seem to diverge, for a while, from the direct path of my
discourse, so far as to explain what I take to be the scope of geology
itself. I conceive geology to be the history of the earth, in precisely
the same sense as biology is the history of living beings; and I trust
you will not think that I am overpowered by the influence of a dominant
pursuit if I say that I trace a close analogy between these two
histories.

If I study a living being, under what heads does the knowledge I obtain
fall? I can learn its structure, or what we call its ANATOMY;
and its DEVELOPMENT, or the series of changes which it passes
through to acquire its complete structure. Then I find that the living
being has certain powers resulting from its own activities, and the
interaction of these with the activities of other things--the knowledge
of which is PHYSIOLOGY. Beyond this the living being has a
position in space and time, which is its DISTRIBUTION. All
these form the body of ascertainable facts which constitute the _status
quo_ of the living creature. But these facts have their causes; and the
ascertainment of these causes is the doctrine of AETIOLOGY.

If we consider what is knowable about the earth, we shall find that such
earth-knowledge--if I may so translate the word geology--falls into the
same categories.

What is termed stratigraphical geology is neither more nor less than the
anatomy of the earth; and the history of the succession of the
formations is the history of a succession of such anatomies, or
corresponds with development, as distinct from generation.

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 phaenomena 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 organization of a
plant and the solar light and heat. And, as the study of the activities
of the living being is called its ph