ot 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 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.

Al