Suppose the huge block could swing on a pivot fixed at the corner next to the wall, at its eastern end--the end on the left hand, as one stood facing it. With a pivot at that point, a swinging outward of the giant cube would produce exactly the marks he had discovered. And why were they on that one flag, and no where else? Simply because that flag was an eighth of an inch higher than its mates. He stood back and looked. He felt that he had made an important discovery. Somewhere, out of sight, was mechanism by which the altar, ponderous as it was, could be moved out of place; and there, beneath it, would be found an entrance to regions below. He was as sure of it as he could be of anything which his eyes had not absolutely beheld. And further, there must be some very simple and ready way of setting the mass free, and moving it from the wall. Enormous weights with easily working pulleys operating beneath might do it. In fact, the explorer as he contemplated the scene could imagine several ways in which the end might be accomplished. But that did not help him. Where was the point of connection outside? That was the thing now, and the only thing. It must be very simple, wherever it was. The friar had accomplished the work of opening and closing the way very quickly, and with but little noise. Our adventurer looked around once more, and once more stood and reflected, with his head bent and his hands folded. Again he went down upon his knees, and with his probe went entirely around the altar a second time, closely examining the line of separation between the cube and the floor. And this time he noticed something which he had not noticed before. On the left-hand--easterly--end of the altar, the space between it and the pavement was marked. At the other end the huge block of stone sat firmly upon the flagging, there being places where even the thinnest probe he could fashion would not enter; but on that left-hand end it was different. There the stone of the altar came in direct contact with the pavement at no single point! And he found another thing: from the outer corner on that left-hand end to a point midway on the front side, that line of separation continued. It was very slight--not more than an eighth of an inch in width--and would never be detected by a person while standing erect. He would have to stoop to find it. Was there any meaning to this? Could the ponderous block possibly be tilted over toward that easterly end? Just half its bulk at bottom appeared to be free from resting upon the floor beneath, so there might be just that eighth of an inch play in case it could be moved. Percy looked the ground over once more, and then went around to the opposite--the westerly--end of the altar. That was where the spectral monk had last been seen.