Atlantic, was the deep Atlantic (though merged in a vast easterly
extension) in the Cretaceous epoch, and that the _Globigerina_ mud has
been accumulating there from that time to this, seems to me to have a
great degree of probability. And I agree with Dr. Wyville Thomson against
Sir Charles Lyell (it takes two of us to have any chance against his
authority) in demurring to the assertion that "to talk of chalk having
been uninterruptedly formed in the Atlantic is as inadmissible in a
geographical as in a geological sense."

If the word "chalk" is to be used as a stratigraphical term and
restricted to _Globigerina_ mud deposited during the Cretaceous epoch, of
course it is improper to call the precisely similar mud of more recent
date, chalk. If, on the other hand, it is to be used as a mineralogical
term, I do not see how the modern and the ancient chalks are to be
separated--and, looking at the matter geographically, I see no reason to
doubt that a boring rod driven from the surface of the mud which forms
the floor of the mid-Atlantic would pass through one continuous mass of
_Globigerina_ mud, first of modern, then of tertiary, and then of
mesozoic date; the "chalks" of different depths and ages being
distinguished merely by the different forms of other organisms associated
with the _Globigerinoe_.

On the other hand, I think it must be admitted that a belief in the
continuity of the modern with the ancient chalk has nothing to do with
the proposition that we can, in any sense whatever, be said to be still
living in the Cretaceous epoch. When the _Challenger's_ trawl brings up
an _Ichthyosaurus_, along with a few living specimens of _Belemnites_ and
_Turrilites_, it may be admitted that she has come upon a cretaceous
"outlier." A geological period is characterized not only by the presence
of those creatures which lived in it, but by the absence of those which