seem to be directly descended from, the Fauna of the early tertiaries.

"I think the latter result might almost have been anticipated; and,
probably, further investigation will largely add to this class of data,
and will give us an opportunity of testing our determinations of the
zoological position of some fossil types by an examination of the soft
parts of their recent representatives. The main cause of the destruction,
the migration, and the extreme modification of animal types, appear to be
change of climate, chiefly depending upon oscillations of the earth's
crust. These oscillations do not appear to have ranged, in the Northern
portion of the Northern Hemisphere, much beyond 1,000 feet since the
commencement of the Tertiary Epoch. The temperature of deep waters seems
to be constant for all latitudes at 39°; so that an immense area of the
North Atlantic must have had its conditions unaffected by tertiary or
post-tertiary oscillations."[8]

[Footnote 8: The Depths of the Sea, pp. 51-52.]

As we shall see, the assumption that the temperature of the deep sea is
everywhere 39° F. (4° Cent.) is an error, which Dr. Wyville Thomson
adopted from eminent physical writers; but the general justice of the
reasoning is not affected by this circumstance, and Dr. Thomson's
expectation has been, to some extent, already verified.

Thus besides _Globigerina_, there are eighteen species of deep-sea
_Foraminifera_ identical with species found in the chalk. Imbedded in the
chalky mud of the deep sea, in many localities, are innumerable cup-
shaped sponges, provided with six-rayed silicious spicula, so disposed
that the wall of the cup is formed of a lacework of flinty thread. Not
less abundant, in some parts of the chalk formation, are the fossils