les and tied them
up after analysis in little white cardboard boxes, he marked each one
very carefully and neatly with the words, PYRITES: WORTHLESS.

Beside the professor worked a young demonstrator of last year's
graduation class. It was he, in fact, who had written the polite notice
on the card.

"What is the stuff, anyway?" he asked.

"A sulphuret of iron," said the professor, "or iron pyrites. In colour
and appearance it is practically identical with gold. Indeed, in all
ages," he went on, dropping at once into the classroom tone and
adopting the professional habit of jumping backwards twenty centuries
in order to explain anything properly, "it has been readily mistaken
for the precious metal. The ancients called it 'fool's gold.' Martin
Frobisher brought back four shiploads of it from Baffin Land thinking
that he had discovered an Eldorado. There are large deposits of it in
the mines of Cornwall, and it is just possible," here the professor
measured his words as if speaking of something that he wouldn't
promise, "that the Cassiterides of the Phoenicians contained deposits
of the same sulphuret. Indeed, I defy anyone," he continued, for he was
piqued in his scientific pride, "to distinguish it from gold without a
laboratory-test. In large quantities, I concede, its lack of weight
would betray it to a trained hand, but without testing its solubility
in nitric acid, or the fact of its burning with a blue flame under the
blow-pipe, it cannot be detected. In short, when crystallized in
dodecahedrons--"

"Is it any good?" broke in the demonstrator.

"Good?" said the professor. "Oh, you mean commercially? Not in the
slightest. Much less valuable than, let us say, ordinary mud or clay.
In fact, it is absolutely good for nothing."

They were silent for a moment, watching the blue flames above the
brazier.

Then Gildas spoke again. "Oddly enough," he said, "the first set of
samples were undoubtedly pure gold--not the faintest doubt of that.
That is the really interesting part of the matter. These gentlemen
concerned in the enterprise will, of course, lose their money, and I
shall therefore decline to accept the very handsome fee which they had
offered me for my services. But the main feature, the real point of
interest in this matter remains. Here we have undoubtedly a sporadic
deposit--what miners call a pocket--of pure gold in a Devonian
formation of the post-tertiary period. This once established, we must
revis