number of questions to her regarding the mysterious sound in the
cavern.

"It must have been the wind," said Nan. "Though it didn't sound
like it."

"What did it sound like?" asked her friend.

"I don't know that I can tell you, Walter. It seemed so
strange--shrill, and sort of stifled. Why! it was as uncanny as the
neigh of that big horse we saw calling to the herd the other
morning."

"The outlaw?" asked Walter.

"Yes."

"Maybe it was another horse," he said doubtfully.

"How could that be? In that cave? Why didn't it come nearer, then?
Oh, it couldn't have been another horse."

"I don't know," ruminated Walter. "You saw that Mexican, too. There
may have been some connection between him and that sound."

"How could that be possible?" asked Nan, in wonder.

"Well, if he had a horse, say? And he had hidden it deeper in the
cave? And had hitched it so it could not run away? How does that
sound?"