A dozen yards on his way he stopped and listened. A voice, sounding like that of a person in a deep well, reached his ears, and he turned back.
He gained the mouth of the cavern in half a minute and plunged inside. It was dark a dozen feet from the entrance, but he struck a match and moved on, finally coming to a smooth wall which appeared to shut off farther progress.
When he turned about and faced the opening every object between where he stood and the mouth stood revealed against the bright sunshine outside. There were a few loose rocks, a rude bench, a small goods box, and nothing else. Jack was nowhere in eight.
He examined the walls of the cavern but discovered no lateral passages. He called out to his chum, but received no response. Where was Jack? If he had left the cavern he would have been seen. It was a perplexing mystery, and the boy sat down on the box and listened for a repetition of the sounds he had heard.
For a moment no sounds came, then a voice, seemingly coming out of the solid wall behind him reached his ears. He could distinguish no words for a time, and then it seemed that he was being called by name.
He called to Jack again and again, but received no answer. Jack was evidently there somewhere, but where? The smooth walls gave no indication of any hidden openings, and there was in view no crevice through which a voice behind the walls might penetrate. It seemed either a silly joke or an impenetrable mystery.
[1] “Boy Scouts in Mexico; or, On Guard With Uncle Sam,” “Boy Scouts in the Canal Zone; or, The Plot Against Uncle Sam,” and “Boy Scouts in the Philippines; or, The Key to the Treaty Box.” Chicago: M. A. Donohue & Company, Publishers.
CHAPTER II.—THE SIGNAL IN THE SKY.
Frank left the cavern in a moment and walked along the beach toward the campfire. His thought was to gather embers and fresh fuel and build up a blaze at the end of the cave which would reveal every inch of the interior. He was certain that Jack had not left the place, and decided that he had fallen into some hidden opening which had escaped his own investigation.