, 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, "I cannot
tell."

If the further question be put, whether physical geology is in
possession of any method by which the actual synchrony (or the reverse)
of any two distant deposits can be ascertained, no such method can be
heard of; it being admitted by all the best authorities that neither
similarity of mineral composition, nor of physical character, nor even
direct continuity of stratum, are 'absolute' proofs of the synchronism
of even approximated sedimentary strata: while, for distant deposits,
there seems to be no kind of physical evidence attainable of a nature
competent to decide whether such deposits were formed simultaneously, or
whether they possess any given difference of antiquity. To return to an
example already given: All competent authorities will probably assent to
the proposition that physical geology does not enable us in any way to
reply to this question--Were the British Cretaceous rocks deposited at
the same time as those of India, or are they a million of years younger
or a million of years older?

Is paleontology able to succeed where physical geolog