"Good Lord, look at that, boys!" exclaimed Frank, as they stood at the foot of the cairn.
There was a good reason for the boy's exclamation.
Distributed around the base of the pile were a dozen or, more human skulls.
"Are they those of white men?" asked Harry in an awed tone. Frank shook his head.
"No, they are those of negroes I believe," he replied after a careful examination, "and I imagine that Muley-Hassan killed them after they erected the cache so that they would not be able to spread the knowledge of its whereabouts to any of the marauding tribes who might even brave the ghostly voice when such a great treasure of ivory tempted."
A shout from Ben, who had been walking round the pile examining it from every view-point interrupted them. They looked up and saw the old adventurer pointing to the mountain summit where it cut the sky. Outlined against the deep azure was the object that had caused his exclamation. It was the figure of a man that had apparently been watching them intently.
But as they gazed the strange, crouched form suddenly vanished.