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
_Globigerinae_ than that of analogy is forthcoming. It so happens that
calcareous skeletons, exactly similar to the _Globigerinae_ 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 _Globigerinae_, and of the
part which they play in rock-building, is singular enough. It is a
discovery which, like others of no less scientific importance, has
arisen, incidentally, out of work devoted to very different and
exceedingly practical interests.

When men first took to the sea, they speedily learned to look out for
shoals and rocks; and the more the burthen of their ships increased, the
more imperatively necessary it became for sailors to ascertain with
precision the depth of the waters they traversed. Out of this necessity
grew the use of the lead and sounding-line; and, ultimately,
marine-surveying, which is the recording of the form of coasts and of
the depth of the sea, as ascertained by the sounding-lead, upon charts.

At the same time, it became desirable to ascertain and to indicate the
nature of the sea-bottom, since t