It seemed to fill the air. To come from every quarter of the
compass at once.




CHAPTER X

THE ARAB'S CACHE


The mysterious cries were not repeated that night although the boys
laid awake till daylight listening for any repetition. No theory
they could advance, although these ranged all the way from cannibals
and gorillas to ghosts, had any effect on the solution of the
mystery. They finally agreed to trust to solving it in some chance
way, and like sensible boys did not continue to worry themselves
over the unsolvable.

Frank's first action was to send out a wireless to the river camp
and to his great relief he found that events there were still
proceeding with the same regularity as before. Nothing had occurred
to mar the even life of the young adventurers left behind. This was
the tenor of the message, but there was something about it that
worried Frank. Lathrop, he knew, was an expert wireless operator,
but the sending that he performed that morning was so jerky and
irregular that the rankest amateur might have done better.

"What is the matter?" asked Frank sharply after the sending had