There was ample warrant for Una's enthusiasm. From the stifling atmosphere of the tunnel the explorers had entered a great rock chamber that widened as they advanced, opening up vistas of majestic spaciousness that contrasted strangely with the straitened path they had first followed. Overhead the outlines of a vast arching roof could be dimly made out by the flickering light from the lamps. At either side the dusky walls, with their flanking pinnacles and fantastic gargoyles, suggested the ornate escarpment of some Gothic cathedral. More noticeable even than these architectural features, was the delightful atmosphere, mild, fragrant, invigorating, pervading the great silent spaces. Usually the air in the famous caves familiar to tourists, although pure enough, is chilly and damp, so much so that the explorer is forced to exercise in order to keep warm. Here, on the contrary, one enjoyed the temperature of a perfect day in early summer--a fact that had called forth Una's praise, and was silently noted by Harold Leighton as one of the novel features of the Guatavita cave. "Of course we must go on," Leighton decided impatiently. "If Mrs. Quayle is nervous, she had better wait for us outside." "Perhaps I will be only in the way here," said that lady contritely. "But what will you do without me, Una?" "I will take her," interposed Miranda in a chivalric outburst. "Come!" he added, turning unceremoniously to retrace his steps to the opening of the tunnel, a point that could not be far away, although not near enough to be revealed by the light thrown from their lamps. In spite of the extended area of the subterranean chamber in which they were standing, it was easy to return to the tunnel by simply retracing the path they were on. This path was marked by a depression in the uneven rocky floor across which it was laid. It was fairly smooth and overspread by a fine sand that bore the impress of many sandaled feet. There was no danger of losing one's way, and the energetic doctor, hurried along so as to spend the least possible time on his self-appointed mission. He did not notice that the terrified Mrs. Quayle, convinced that his invitation concealed a plot to rob her of her jewels, failed to accompany him. The others, amused at his abrupt departure, patiently awaited his return, watching the speck of light made by his lamp bobbing about in the distance. Presently the light disappeared, and they concluded that Miranda had entered the tunnel. But in this they were mistaken. In a few minutes they were startled by an explosive "Caramba!" followed shortly by the apparition of the doctor running towards them, breathless from his exertions, and exploding with mingled wrath and consternation. "It has gone--lost! I cannot find him!" he shouted in an incoherent torrent of Spanish and English. "What has gone?" demanded Leighton. "We are lost! We are lost! The tunnel has gone!" "Nonsense!"