"That we'd better be skedaddling as quick as possible," shot out Pete, brusquely.
The professor, who had wandered away from the group and was down inside the hollow altar, was hastily summoned and apprised of the strange approach of the mysterious cavalcade.
"Why, bless me, boys, what can it mean?" he cried, nimbly attempting a flying leap over the edge of the altar in his haste to ascertain for himself the nature of the approaching party.
Suddenly, however, as his feet touched the top, and he was scrambling over, he gave a sharp cry and fell back within the altar with a gasp of pain.
"Are you hurt?" asked Jack, running to the side of the ancient place of sacrifice.
The professor lay prostrate within. His face was white and set and beads of sweat stood out on his forehead.
"My—my ankle," he groaned. "I broke it some time ago, and in hurrying to clamber over the top of the altar I fear I have snapped it again. Oh!"
He gave a heartrending groan of pain. The boys stood stricken with consternation. It was going to be a long and difficult task to get the professor out of his present predicament, and there seemed need for haste.
"Here, put this under your head," said Jack, stripping off his jacket hastily, and throwing it within, "I'll tell Coyote Pete about your accident, and we can get remedies from the packs."
But when Jack turned, only Ralph and Walt stood beside him. The sturdy cow-puncher had vanished.