ined problems
relative to the activities of the earth; or, it may be
distributional speculation, if it deals with modifications of the
earth's place in space; or, finally, it will be aetiological
speculation if it attempts to deduce the history of the world, as
a whole, from the known properties of the matter of the earth, in
the conditions in which the earth has been placed."

Huxley then proceeded to shew that uniformitarianism and catastrophism
had neglected this last and most important branch of geology, the
attempt to trace the interaction of causes which had brought the world
into its present condition. He gave a striking display of the wide
knowledge of his reading by going back to the foundation of this branch
of modern science, and giving a masterly account of the then
little-known treatise of Immanuel Kant, who in 1775 had written _An
Attempt to Account for the Constitutional and Mechanical Origin of the
Universe upon Newtonian Principles_. Next he declared that evolution
embraced all that was sound in both catastrophism and uniformitarianism
while rejecting the arbitrary limits and assumptions of both.

Finally he came to the great question to which these observations upon
the existing schools of geology had led. The most distinguished
physicist of the age, then Sir William Thomson, now Lord Kelvin, and
Huxley's immediate successor in the Presidential Chair of the Royal
Society, had stated that the English school of geology had assumed an
impossible age for the earth. By physical reasonings, Thomson stated
that he was able to prove "That the existing state of things on the
earth--all geological history showing continuity of life--must be
limited within some such period of time as one hundred million years."
This pronouncement had been received with acclamation by those who
feared the geological and biological sciences, as a sign of internal
dissensions within the house of science. Huxley, then, as all through
the latter part of his life, at once constituted himself the champion
of science, and, taking Thomson's arguments one by one, shewed by a
series of masterly deductions from known facts that there was a great
deal to be said for the other side, and that physicists were as little
certain as geologists could be of the exact duration of time that had
elapsed since the dawn of life. His plea for more time since the
cooling of the globe than physicists were willing to allow remai