Andrew, of course, still smarting from the experience of two days before, could not be expected to make so speedy a return to the scene of his adventure without some trepidation. But whatever sensations thrilled his susceptible heart, he put on a brave front and did not flinch from the part he was expected to take in the expedition. There was that dreadful lake, there the wall of rock he had described, and there the inconspicuous opening to the tunnel from whose hidden dangers he had been so mysteriously rescued--he faced it all and braced himself for the inevitable explanations. But his knowledge of the place was far less than Raoul's. "It was through this opening to Mr. Parmelee's tunnel that we entered upon the excavation by which we hoped to drain the lake three years ago," he remarked. From an engineering point of view the statement was mystifying because the opening of the tunnel was almost on a level with the surface of the lake. Thus, it was difficult to see what would have been gained had the waters of the latter been diverted into the tunnel. It was explained, however, that an intersecting tunnel at a very much lower level furnished the desired outlet, and the miners had planned to connect with this. As Leighton and the rest were not concerned in these bygone matters, the abortive attempts of the mining company to use this subterranean passage in the mountain was not traced out in detail. Time was urgent; there was no telling how long they might be in the tunnel. If they wanted to avoid making a night of it they would have to hurry. Unloading the mules, therefore, of their provisions, and leaving these melancholy animals in the care of two peons who had come with them from Bogota, the picnickers equipped themselves for their adventure--that is, they fastened the miners' lamps to their hats. In the case of the men this was not difficult. But Mrs. Quayle's extraordinary headgear, architecturally deceptive and insecure, proved so hopelessly difficult that its estimable owner was forced to do without the adornment of tin and kerosene provided for her. The more stable bit of millinery worn by Una was tractable enough, and with her lamp attached firmly to her gray felt hat she looked the part she expected to play.