s, each of the
rounded bodies may be proved to be a beautifully constructed
calcareous fabric, made up of a number of chambers communicating
freely with one another. The chambered bodies are of various forms.
One of the 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 Globigerinae and granules. Let us fix
our attention upon the Globigerina. It is the spore 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.

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 the shoals and rocks; and the more
the burden 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 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 the object by "arming" the bottom of the lead with a
lump of grease, to which more or less of the sand or mud or broken
shells, as the case might be, adhered, and was brought to the surface.
But however well adapted such an apparatus might be for rough nautical
purposes, scientific accuracy could not be expected from the armed
lead; and to remedy its defects (especially when applied to sounding
in great depths), Lieutenant Brooke of the American Navy some years
ago invented a most ingenious machine, by which a considerable portion
of the superficial layer of the sea bottom can be scooped out and
brought up from any depth to which the lead descends. In 1853
Lieutenant Br