of sedimentary deposits, the bed
which lies lowest is the oldest. In many other vertical linear
sections of the same series, of course corresponding beds will
occur in a similar order."

It is of the utmost importance to determine whether or no the same
series occurring vertically in the same order in different parts of
the earth were deposited at the same time. To explain the problem,
Huxley took the following concrete example:

"The Lias of England and the Lias of Germany, the Cretaceous
rocks of Britain and the Cretaceous rocks of Southern India, are
termed by geologists 'Contemporaneous' formations; but whenever
any thoughtful geologist is asked whether he means to say that
they were deposited at the same time, he says, 'No, only within
the same great epoch.' And if, in pursuing the enquiry, he is
asked what may be the approximate value in time of a 'great
epoch'--whether it means a hundred years, or a thousand, or a
million, or ten million years--his reply is, 'I cannot tell.'"

Most of the standard writers on palaeontology had assumed that the
presence in two beds at different parts of the world of the same
fossils implied that the beds were contemporaneous, that they had been
formed at the same time. Huxley pointed out that the fact of identical
fossils being present was, on the whole, evidence against the beds
having been formed at the same time. Even some of the older writers
who believed in species having been created at definite places at
definite times had seen that time must have been required for sets of
animals to wander from the places in which they had come into
existence. The newer theory of evolution was equally opposed to the
notion of the appearance of similar animals at the same time on
far-distant parts of the earth. For such reasons he proposed to reject
the use of the word _Contemporaneous_ as applied to rockbeds in
different localities which contained the same fossils, and to replace
it by the word _Homotaxial_, which meant no more than that the beds
occupied corresponding places in the geological history of the earth.
Huxley did not pretend that these arguments were entirely original:
they represented the drift of the best geological opinion, and he
seized hold of them and set them down as permanent geological truths.

In 1869, in a Presidential Address to the Geological Society, Huxley
took up one of the burning questions of the