t the attempt to solve such problems as these can lead to
no result, save that of entangling the inquirer in vague speculations,
incapable of refutation and of verification.

If such were really the case, I should have selected some other
subject than a "piece of chalk" for my discourse. But, in truth,
after much deliberation, I have been unable to think of any topic
which would so well enable me to lead you to see how solid is the
foundation upon which some of the most startling conclusions of
physical science rest.

A great chapter of the history of the world is written in the chalk.
Few passages in the history of man can be supported by such an
overwhelming mass of direct and indirect evidence as that which
testifies to the truth of the fragment of the history of the globe,
which I hope to enable you to read, with your own eyes, to-night.

[Illustration: MICROSCOPIC SECTION OF CHALK.

(Magnified nearly 300 times.)

1. Textularia. 2. Globigerina. 3. Rotalia. 4. Coccoliths.]

Let me add, that few chapters of human history have a more profound
significance for ourselves. I weigh my words well when I assert, that
the man who should know the true history of the bit of chalk which
every carpenter carries about in his breeches' pocket, though ignorant
of all other history, is likely, if he will think his knowledge out to
its ultimate results, to have a truer, and therefore a better,
conception of this wonderful universe, and of man's relation to it,
than the most learned student who is deep-read in the records of
humanity and ignorant of those of nature.

The language of the chalk is not hard to learn, not nearly so hard as
Latin, if you only want to get at the broad features of the story it
has to tell; and I propose that we now set to work to spell that story
out together.

We all know that if we "burn" chalk, the result is quicklime. Chalk,
in fact, is a compound of carbonic acid gas and lime; and when you
make it very hot, the carbonic acid flies away and the lime is left.

By this method of procedure we see the lime, but we do not see the
carbonic acid. If, on the other hand, you were to powder a little
chalk and drop it into a good deal of strong vinegar, there would be a
great bubbling and fizzing, and, finally, a clear liquid, in which no
sign of chalk would appear. Here you see the carbonic acid in the
bubbles; the lime, dissolved in the vinegar, vanishes from sight.
There are a great many other ways of