the same way. If it were examined
microscopically, it would show itself to be a more or less distinctly
laminated mineral substance and nothing more.

But the slice of chalk presents a totally different appearance when
placed under the microscope. The general mass of it is made up of very
minute granules; but, imbedded in this matrix, are innumerable bodies,
some smaller and some larger, but, on a rough average, not more than
a hundredth of an inch in diameter, having a well-defined shape and
structure. A cubic inch of some specimens of chalk may contain hundreds
of thousands of these bodies, compacted together with incalculable
millions of the granules.

The examination of a transparent slice gives a good notion of the manner
in which the components of the chalk are arranged, and of their relative
proportions. But, by rubbing up some chalk with a brush in water and
then pouring off the milky fluid, so as to obtain sediments of different
degrees of fineness, the granules and the minute rounded bodies may be
pretty well separated from one another, and submitted to microscopic
examination, either as opaque or as transparent objects. By combining
the views obtained in these various methods, 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
Globigerina 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 rai