In perhaps another hour the boat appeared. It came from down the river, propelled close inshore by two members of their own party who had gone to fetch it. At first the travelers thought it a long, oblong raft. Then as it came closer they could see it was constructed of three canoes, each about thirty feet long, hollowed out of tree-trunks. Over these was laid a platform of small trees hewn roughly into boards. The boat was propelled by long, slender poles in the hands of the two men, who, one on each side, dug them into the bed of the river and walked with them the length of the platform. On to this boat the entire party crowded and they were soon well out on the shallow river, headed for its opposite bank. The Very Young Man, seated at the front end of the platform with his legs dangling over and his feet only a few inches above the silver phosphorescence of the rippling water underneath, sighed luxuriously. "This beats anything we've done yet," he murmured. "Gee, it's nice here!" When they landed on the farther bank another group of natives was waiting for them. The party, thus strengthened to nearly forty, started off immediately into the forest, which on this side of the river appeared equally dense and trackless. They appeared now to be paralleling the course of the river a few hundred yards back from its bank. After half an hour of this traveling they came abruptly to what at first appeared to be the mouth of a large cave, but which afterwards proved to be a tunnel-like passageway. Into this opening the party unhesitatingly plunged. Within this tunnel, which sloped downward at a considerable angle, they made even more rapid progress than in the forest above. The tunnel walls here were perhaps twenty feet apart--walls of a glistening, radiant, crystalline rock. The roof of the passageway was fully twice as high as its width; its rocky floor was smooth and even. After a time this tunnel was crossed by another somewhat broader and higher, but in general of similar aspect. It, too, sloped downward, more abruptly from the intersection. Into this latter passageway the party turned, still taking the downward course. As they progressed, many other passageways were crossed, the intersections of which were wide at the open spaces. Occasionally the travelers encountered other natives, all of them men, most of whom turned and followed them. The Big Business Man, after over an hour of this rapid walking downward, was again near the limit of his endurance, when the party, after crossing a broad, open square, came upon a sort of sleigh, with two animals harnessed to it. It was standing at the intersection of a still broader, evidently more traveled passageway, and in it was an attendant, apparently fast asleep.