thrown back far down out of sight; but the noise it made
was loud enough, and as Bart listened he heard it strike heavily six
times, then there was a dead silence for quite a minute, and it seemed
that the last stroke was when it reached the bottom.

Bart was just about turning to speak to the Doctor when there came
hissing up a horrible echoing, weird sound, like a magnified splash, and
they knew that far down at an immense depth the great stone had fallen
into water.

"Ugh!" ejaculated Bart, involuntarily imitating the Indians. "What a
hole! Why, it must be ten times as deep as this place is high. I
shouldn't care about going down."

"Horrible indeed, Bart; but what should you think? Is this place
natural or dug out?"

"Natural, I should say, sir," replied Bart. "Nobody could dig down to
such a depth as that."

"Yes, natural," said the Doctor, carefully scanning the sides of the
place with a small glass. "Originally natural, but this place has been
worked."

"Worked? What, dug out?" said Bart. "Why, what for--to get water?"

"No," said the Doctor, quietly; "to get silver. This has been a great
mine."

"But who would have dug it?" said Bart, eagerly. "The Indians would
not."

"The people who roughly made the zigzag way up to the top here, my boy."

"But what people would they be, sir? The Spaniards?"

"No, Bart. I should say this was dug by people who lived long before
the Spaniards, perhaps thousands of years. It might have been done by
the ancient peoples of Mexico or those who built the great temples of
Central America and Yucatan--those places so old that there is no
tradition of the time when they were made. One thing is evident, that
we have come upon a silver region that was known to the ancients."

"Well, I am disappointed," cried Bart. "I thought, sir, that we had
made quite a new find."

"So did I at first, Bart," replied the Doctor; "but at any rate, save to
obtain a few scraps, the place has not been touched, I should say, for
centuries; and even if this mine has been pretty nearly exhausted, there
is ample down below there in the canyon, while this mount must be our
fortress and our place for furnaces and stores."

They descended cautiously for about a couple of hundred feet,
sufficiently far for the Doctor to chip a little at the walls, and find
in one or two places veins that ran right into the solid mountain, and
quite sufficient to give ample employment to all the men w