first sight appear to be, that the Globigerinae of the
Atlantic sea-bottom do not live and die where they are found.

[Illustration: DIATOM OOZE DREDGED FROM A DEPTH OF 1950 FEET.

(Magnified nearly 300 diameters.)]

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, though they are not heavier
than the lightest dust, must have fallen, in some cases, through
fifteen thousand 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.

[Illustration: RADIOLARIA. (_a._ Natural size. _b._ One-third natural
size.)]

But if the Radiolaria and Diatoms are thus rained upon the bottom of
the sea, from the superficial layer of its waters in which they pass
their lives, it is obviously possible that the Globigerinae may be
similarly derived; and if they were so, it would be much more easy to
understand how they obtain their supply of food than it is at present.
Nevertheless, the positive and negative evidence all points the other
way. The skeletons of the full-grown, deep-sea Globigerinae are so
remarkably solid and heavy in proportion to their surface as to seem
little fitted for floating; and, as a matter of fact, they are not to
be found along with the Diatoms and Radiolaria, in the uppermost
stratum of the open ocean.

It has been observed, again, that the abundance of Globigerinae, in
proportion to other organisms of like kind, increases with the depth
of the sea; and that deep-water Globigerinae are larger than those
which live in the shallower parts of t