Estelle smiled tenderly to herself as she remembered how Arthur had been the leading spirit in all the numberless enterprises in which the castaways had been forced to engage. He would come to her in a spare ten minutes, and tell her how everything was going. He seemed curiously boylike in those moments. Sometimes he would come straight from the fire-room--he insisted on taking part in all the more arduous duties--having hastily cleaned himself for her inspection, snatch a hurried kiss, and then go off, laughing, to help chop down trees for the long fishing-raft. He had told them how to make charcoal, had taken a leading part in establishing and maintaining friendly relations with the Indians, and was now down in the deepest sub-basement, working with a gang of volunteers to try to put the building back where it belonged. Estelle had said, after the collapse of the flooring in the board-room, that she heard a sound like the rushing of waters. Arthur, on examining the floor where the safe-deposit vault stood, found it had risen an inch. On these facts he had built up his theory. The building, like all modern sky-scrapers, rested on concrete piles extending down to bedrock. In the center of one of those piles there was a hollow tube originally intended to serve as an artesian well. The flow had been insufficient and the well had been stopped up. Arthur, of course, as an engineer, had studied the construction of the building with great care, and happened to remember that this partly hollow pile was the one nearest the safe-deposit vault. The collapse of the board-room floor had suggested that some change had happened in the building itself, and that was found when he saw that the deposit-vault had actually risen an inch. He at once connected the rise in the flooring above the hollow pile with the pipe in the pile. Estelle had heard liquid sounds. Evidently water had been forced into the hollow artesian pipe under an unthinkable pressure when the catastrophe occurred. From the rumbling and the suddenness of the whole catastrophe a volcanic or seismic disturbance was evident. The connection of volcanic or seismic action with a flow of water suggested a geyser or a hot spring of some sort, probably a spring which had broken through its normal confines some time before, but whose pressure had been sufficient to prevent the accident until the failure of its flow. When the flow ceased the building sank rapidly. For the fact that this "sinking" was in the fourth direction--the Fourth Dimension--Arthur had no explanation. He simply knew that in some mysterious way an outlet for the pressure had developed in that fashion, and that the tower had followed the spring in its fall through time.