ns one
of the classics of geological literature. But he carried the question
much farther. The inference which was widely drawn by the enemies of
evolution from the arguments of Sir William Thomson was that if
geologists had overestimated the age of the cooled earth there was not
time for the evolution of animals and plants to have taken place.
Huxley pointed out a fact which should be quite obvious, but which
even yet is frequently neglected. The evidence for the gradual
appearance of life in the past history of the earth depends simply on
the fact that the successive forms of life appear in successive
strata, and the length of time taken for these changes simply depends
upon the length of time which was taken up by the formation of the
strata. Our only reason for supposing the evolution of life, made
plain by fossil records, to have taken place very slowly is that
geologists have stated that the deposition of the strata took place
very slowly. Whether these strata were deposited slowly or less
slowly, we know that the forms of life changed at the same rate.

"Biology takes her time from geology. The only reason we have for
believing in the slow rate of change in living forms is the fact
that they persist through a series of deposits which, geology
informs us, have taken a long while to make. If the geological
clock is wrong, all the naturalist will have to do is to modify
his notion of the rapidity of change accordingly; and I venture
to point out that, when we are told that the limitation of the
period during which living beings have inhabited this planet to
one, two, or three hundred million years requires a complete
revolution in geological speculation, the _onus probandi_ rests
on the maker of the assertion, who brings forward not a shadow of
evidence in its support."

Perhaps, although this is now an old controversy, it is worth while
to recall that the keenness of Huxley's language was not directed
against Sir William Thomson, between whom and Huxley there was no more
than the desire to argue out an interesting scientific question upon
which their conclusions differed, but between Huxley and those
outsiders who were always ready to turn any dubious question in
science into an argument discrediting the general conclusions of
science.

The last time that Huxley occupied the Presidential Chair of the
Geological Society was in 1870, and he occupied his