can live and flourish in the sea, at the vast
depths from which apparently living Globigerinae have been brought up,
does not agree very well with our usual conceptions respecting the
conditions of animal life; and it is not so absolutely impossible as
it might at first sight appear to be, that the Globigerinae of the
Atlantic sea bottom do not live and die where they are found.

As I have mentioned, the soundings from the great Atlantic plain are
almost entirely made up of Globigerinae, with the granules which have
been mentioned, and some few other calcareous shells; but a small
percentage of the chalky mud--perhaps at most some five per cent, of
it--is of a different nature, and consists of shells and skeletons
composed of silex or pure flint. These siliceous bodies belong partly
to the lowly vegetable organisms which are called Diatomaceae and
partly to the minute and extremely simple animals termed Radiolaria.
It is quite certain that these creatures do not live at the bottom of
the ocean, but at its surface, where they may be obtained in
prodigious numbers by the use of a properly constructed net. Hence it
follows that these siliceous organisms, tho they are not heavier than
the lightest dust, must have fallen in some cases through 15,000 feet
of water before they reached their final resting-place on the ocean
floor. And considering how large a surface these bodies expose in
proportion to their weight, it is probable that they occupy a great
length of time in making their burial journey from the surface of the
Atlantic to the bottom....

Thus not only is it certain that the chalk is the mud of an ancient
sea bottom, but it is no less certain that the chalk sea existed
during an extremely long period, tho we may not be prepared to give a
precise estimate of the length of that period in years. The relative
duration is clear, tho the absolute duration may not be definable. The
attempt to affix any precise date to the period at which the chalk sea
began or ended its existence is baffled by difficulties of the same
kind. But the relative age of the cretaceous epoch may be determined
with as great ease and certainty as the long duration of that epoch.

You will have heard of the interesting discoveries recently made in
various parts of western Europe, of flint implements, obviously worked
into shape by human hands, under circumstances which show conclusively
that man is a very ancient denizen of these regions. It has