hey did not see him in such and such a place,
unless the witnesses are prepared to prove that they must have seen him
had he been there. But the evidence that animal life commenced with the
Lingula-flags, _e.g._, would seem to be exactly of this unsatisfactory
uncorroborated sort. The Cambrian witnesses simply swear they "haven't
seen anybody their way;" upon which the counsel for the other side
immediately puts in ten or twelve thousand feet of Devonian sandstones
to make oath they never saw a fish or a mollusk, though all the world
knows there were plenty in their time.

But then it is urged that, though the Devonian rocks in one part of the
world exhibit no fossils, in another they do, while the lower Cambrian
rocks nowhere exhibit fossils, and hence no living being could have
existed in their epoch.

To this there are two replies: the first, that the observational basis
of the assertion that the lowest rocks are nowhere fossiliferous is an
amazingly small one, seeing how very small an area, in comparison to
that of the whole world, has yet been fully searched; the second, that
the argument is good for nothing unless the unfossiliferous rocks in
question were not only _contemporaneous_ in the geological sense, but
_synchronous_ in the chronological sense. To use the _alibi_
illustration again. If a man wishes to prove he was in neither of two
places, A and B, on a given day, his witnesses for each place must be
prepared to answer for the whole day. If they can only prove that he was
not at A in the morning, and not at B in the afternoon, the evidence of
his absence from both is _nil_, because he might have been at B in the
morning and at A in the afternoon.

Thus everything depends upon the validity of the second assumption. And
we must proceed to inquire what is the real meaning of the word
"contemporaneous" as employed by geologists. To this end a concrete
example may be taken.

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
synchronously, he says, "No,--only within the same great epoch." And if,
in pursuing the inquiry, 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,