Hall immediately broke out laughing, and, slapping me good-naturedly on the shoulder, exclaimed: "Come, come now! If you go to kicking back at a fellow like that, I shall be sorry I ever undertook this adventure." VII A MYSTERY INDEED! When President Boon had heard our story he promptly approved Hall's dismissal of the men. He expressed great surprise that Dr. Syx should have resorted to a deception which had been so disastrous to innocent people, and at first he talked of legal proceedings. But, after thinking the matter over, he concluded that Syx was too powerful to be attacked with success, especially when the only evidence against him was that he had claimed to find artemisium in his mine at a time when, as everybody knew, artemisium actually was found outside the mine. There was no apparent motive for the deception, and no proof of malicious intent. In short, Mr. Boon decided that the best thing for him and his stockholders to do was to keep silent about their losses and await events. And, at Hall's suggestion, he also determined to say nothing to anybody about the discovery we had made. "It could do no good," said Hall, in making the suggestion, "and it might spoil a plan I have in mind." "What plan?" asked the president. "I prefer not to tell just yet," was the reply. I observed that, in our interview with Mr. Boon, Hall made no reference to the side tunnel to which he had appeared to attach so much importance, and I concluded that he now regarded it as lacking significance. In this I was mistaken. A few days afterwards I received an invitation from Hall to accompany him once more into the abandoned tunnel. "I have found out what that sidetrack means," he said, "and it has plunged me into another mystery so dark and profound that I cannot see my way through it. I must beg you to say no word to any one concerning the things I am about to show you." I gave the required promise, and we entered the tunnel, which nobody had visited since our former adventure. Having extinguished our lamp, my companion opened the peep-hole, and a thin ray of light streamed through from the tunnel on the opposite side of the wall. He applied his eye to the hole. "Yes," he said, quickly stepping back and pushing me into his place, "they are still at it. Look, and tell me what you see." "I see," I replied, after placing my eye at the aperture, "a gang of men unloading a car which has just come out of the side tunnel, and putting its contents upon another car standing on the track of the main tunnel." "Yes, and what are they handling?" "Why, ore, of course." "And do you see nothing significant in that?" "To be sure!" I exclaimed. "Why, that ore--" "Hush! hush!" admonished Hall, putting his hand over my mouth; "don't talk so loud. Now go on, in a whisper." "The ore," I resumed, "may have come back from the furnace-room, because the side tunnel turns off so as to run parallel with the other."