commonest is something like a
badly-grown raspberry, being formed of a number of nearly globular
chambers of different sizes congregated together. It is called
_Globigerina_, and some specimens of chalk consist of little else than
_Globigerinoe_ and granules. Let us fix our attention upon the
_Globigerina_. It is the spoor of the game we are tracking. If we can
learn what it is and what are the conditions of its existence, we shall
see our way to the origin and past history of the chalk.

A suggestion which may naturally enough present itself is, that these
curious bodies are the result of some process of aggregation which has
taken place in the carbonate of lime; that, just as in winter, the rime
on our windows simulates the most delicate and elegantly arborescent
foliage--proving that the mere mineral water may, under certain
conditions, assume the outward form of organic bodies--so this mineral
substance, carbonate of lime, hidden away in the bowels of the earth, has
taken the shape of these chambered bodies. I am not raising a merely
fanciful and unreal objection. Very learned men, in former days, have
even entertained the notion that all the formed things found in rocks are
of this nature; and if no such conception is at present held to be
admissible, it is because long and varied experience has now shown that
mineral matter never does assume the form and structure we find in
fossils. If any one were to try to persuade you that an oyster-shell
(which is also chiefly composed of carbonate of lime) had crystallized
out of sea-water, I suppose you would laugh at the absurdity. Your
laughter would be justified by the fact that all experience tends to show
that oyster-shells are formed by the agency of oysters, and in no other
way. And if there were no better reasons, we should be justified, on like
grounds, in believing that _Globigerina_ is not the product of anything
but vital activity.

Happily, however, better evidence in proof of the organic nature of the
_Globigerinoe_ than that of analogy is forthcoming. It so happens that
calcareous skeletons, exactly similar to the _Globigerinoe_ of the chalk,
are being formed, at the present moment, by minute living creatures,
which flourish in multitudes, literally more numerous than the sands of
the sea-shore, over a large extent of that part of the earth's surface
which is covered by the ocean.

The history of the discovery of these living _Globigerinoe_, and of the
par