"Why Joy and I found something just as interesting as that," laughed
Enid. "Under the trees here, the wall of that small cliff has the most
peculiar weather markings. Take a look at it, Professor Gillette.
It's interesting."

The professor bent away some of the branches of the trees so as to get
a good view of the rock. The girls standing near, heard him give a
gasp of astonishment.

"What's the matter now?" asked Bet Baxter.

"Those markings were never made by the weather. They were carved by
human hands. And our arrow is pointing straight toward it. I don't
understand why we didn't see it before."

"It's the treasure!" exclaimed Bet. "Let's see what's there!"

CHAPTER XV

_A SPY_

The professor's hand trembled with excitement as he scratched the
surface of the rock, tapped the face of the wall for a possible hollow
sound, then called on Bet to bring him a pick.

He dug at the base of the wall, but soon came to solid rock.

"There's nothing there!" he exclaimed. "But this is interesting." The
desert weeds had grown over all the crevices in the rock, and when the
professor had carefully scraped them away, he found what he had hoped
for; a small opening. Behind that wall there was a tunnel. As he
looked into the darkness, a rattlesnake glided through the hole, and
the old man sprang back just in time to save himself.

"That was a close shave!" Wiping his forehead with his handkerchief,
Professor Gillette sat down on the rock to decide what the next step
would be.

"Guess we'd better call it a day. We are all tired out. We can just
get back in time for dinner," said Enid. "And Dad said you were to
come home with us, Professor."

"I'd like to consult with the judge," said the old man. "He can give
us valuable advice I'm sure." He wouldn't for the world acknowledge
that the hot dinner, already prepared, tempted him to accept the
invitation.

The girls turned away from the wall, unwillingly. They now felt sure
that they were leaving a treasure behind them. And tomorrow seemed so
far away!

Bet and Enid helped Joy to hobble along to the edge of the cliff, and
Kit hastened down the incline to where they had left the horses near
the stream.

"I'll bring Dolly up, that is if she'll climb, the lazy thing!" called
Kit as she disappeared. By this time Joy's foot was badly swollen and
was giving her acute pain.

Before leaving the wall, the professor had concealed the opening that
he