sing 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 depths 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 this circumstance greatly affects its
goodness as holding ground for anchors. Some ingenious tar, whose name
deserves a better fate than the oblivion into which it has fallen,
attained this object by "arming" the bottom of the