d. "For years I have sought it. If I can find it I shall be
famous, for I shall have added to human knowledge."

"If the people of that city wrote on golden tablets, the yellow metal
must have been plentiful," commented Mr. Titus. "You might strike a
rich mine."

"I have no use for riches," said the professor.

"Well, I have," the contractor said, with a laugh. "That's why I'm
putting through this tunnel. And if my brother and I don't do it we'll
be in a bad way financially. We have struck traces of gold, but not in
paying quantities. I should like to see this lost city of yours,
Professor Bumper. It may contain gold."

"You may have all the gold, if I am allowed to keep the antiquities we
find," stipulated the scientist. "Then you will help me in my search?"

"As much as we can spare time for from the tunnel work," promised Mr.
Titus. "I'll instruct my men to keep their eyes open for any sign of
ancient writings on the rocks we blast out."

"Thank you," said the professor.

The night passed uneventfully enough, if one excepts the mosquitoes
which seemed to get through the nets, making life miserable for all.
And once Tom thought he heard gruntings in the bush back of the tent,
which noises might, he imagined, have been caused by a bear. Toward
morning he heard an unearthly screech in the woods, and one of the
Indians, tending the fire, grunted out a word which meant pumas.

"I can see it isn't going to be dull here," Tom mused, as he turned
over and tried to sleep.

Breakfast made them all feel better, and they set off on the final
stage of their journey.

"If all goes well we'll be at the tunnel entrance and camp to-night,"
said the contractor. "This second half of the trip is the roughest."

There was no need of saying that, for it was perfectly evident. The
trail was a most precarious one, and only a mule or llama could have
traveled it. The mules were most sure-footed, but, as it was, one
slipped, and came near falling over a cliff.

But no real accident occurred, and finally, about an hour before
sunset, the cavalcade turned down the slope and emerged on a level
plain, which ended against the face of a great cliff.

As Tom rode nearer the cliff he could make out around it groups of rude
buildings, covered with corrugated iron. There was quite a settlement
it seemed.

Then, in the face of the cliff there showed something black--like a
blot of ink, though more regular in outline.

"The mouth of