Quick as a flash the stone dropped and Buckden went out of sight like a meteor. Down into a black void went the young New Yorker. He was swallowed up as literally as if engulfed in the sea. For an instant Frank Reade, Jr., was so overcome with horror that he did not know what to do. Then a wailing cry broke from his lips: ‪“Oh, my God!” he cried. ‪“Tony has gone to his death.” Of course Frank had no idea as to the depth of the abyss or where it went to. Buckden, for aught he knew, had fallen to the center of the earth. The young inventor was overcome with horror and agony. ‪“Something must be done!” he cried, wildly. ‪“He must be saved!” But what was to be done? It was an awful question. For a moment Frank knew not what answer to make. He stood like one in a trance. Then he made sudden and swift action. He threw himself flat upon his stomach and shouted down into the abyss of darkness. ‪“Tony!” he cried, at the top of his voice. ‪“Where are you? If you can hear me, give me an answer!” But no sound came back. All was the stillness of the grave. It seemed as if Tony Buckden’s fate was sealed. Certainly, if alive and uninjured, he would answer. Frank shouted again and again. But no answer came back from the awful stillness below. It was like the silence of the grave. A queer sensation came over Frank. He felt as if likely to faint. A cold perspiration broke out upon him, and he seemed dizzy and sick. Then a strange and awful thing happened. Suddenly and without warning, the stone beneath him began to slide. He felt himself going, and made a spasmodic effort to save himself. In vain was this. Just as he was about to recoil from the verge of the awful pit, there was a grinding sound as of mortar giving way, and then, wholly unable to save himself, Frank went headlong into the abyss. Down, down he felt himself going. He clutched at the air wildly, experienced a sense of suffocation, then he felt a sudden shock and knew that he was in water. It seemed as if his breath must leave his body before he came up out of this water. Coming to the surface, he drew in a deep breath, and then struck out to swim. The water was icy cold, and he knew that its depth must be great. Also, he believed its extent to be considerable, as the reverberations coming to his ears were far-reaching and loud. Frank had no means of knowing into what sort of place he had fallen, or what was to be the outcome of this adventure. CHAPTER X. THE SEALED CHAMBER. But he did know that he was in the embrace of some underground lake or reservoir of water. That it was not a river he was assured as there was no current whatever. Involuntarily he looked about for light. There was a faint square far above his head. This he knew must be from the aperture through which he had fallen. Certainly that must have been a fearful distance to have fallen. To have survived that fall seemed a miracle.