unusual and gigantic displays of force had caused them.  On the other hand, Hutton and Lyell attempted to find adequate explanation of the greatest changes in the slow forces which may be seen in operation at the present time.  Slow movements of upheaval and depression, amounting at most to an inch or two in a century, may be shown to be actually in existence now, and such slow changes acting for very many centuries would account for the raising of continents above the sea, so that old sea-bottoms became the surface of the land, and for the depression of land areas so that new sedimentary rocks might be deposited upon them.  They shewed how air and water slowly crumbled away the hardest rocks, and how rivers deepened their beds steadily but excessively slowly; and they held that while great catastrophic changes might occasionally have occurred, there was ample evidence of the present operation of forces which, granted sufficient time for their operation, would have made the crust of the earth such as it is.  This doctrine of Uniformitarianism, of the action of similar forces in the past and present history of the earth, had almost completely triumphed over the older catastrophic views.  As Huxley put it, the school of catastrophe put no limit to the violence of forces which had operated; the uniformitarians put no limit to the length of time during which forces had operated.

“Catastrophism has insisted upon the existence of a practically unlimited bank of force, on which the theorist might draw; and it has cherished the idea of development of the earth from a state in which its form, and the forces which it exerted, were very different from those which we now know.

      “Uniformitarianism, on the other hand, has with equal justice
     insisted upon a practically unlimited bank of time, ready to
     discount any quantity of hypothetical paper.  It has kept before
     our eyes the power of the infinitely little, time being granted,
     and has compelled us to exhaust known causes before flying to the
     unknown.”

But there was a third influence at work in geology, an influence which may best be described in Huxley’s own words: 

“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 it passes