He exerted all his strength. The rock was moving, and even with all the villainies the Indians had to their discredit Floyd's nerve almost failed him as he saw the great boulder sway as if for the plunge.
But to his chagrin he felt the rock move back toward him again. He tried to hold it away—to thrust it from him—but nature, in the guise of the attraction of gravitation—pulled the rock back into the socket-shaped bed where it had rested so long.
It rolled back with a grinding sound, and Floyd feared, for a moment that he had loosened it so that it would topple back and fall upon his feet.
But this did not happen. The great half-round stone oscillated to and fro and then came to rest. Floyd had only caused it to sway a little.
"Well, I moved it!" he said with a gasp. "I'll try again. If I can only get it started it will do the trick."
Again he pushed, with all his might, but again the same thing happened. He managed to make the rock sway outward, a little farther over the edge of the wall, but back it came again into its hollow resting place.
Then Floyd understood the nature of the matter.
"It's a balanced rock," he said to himself. "She's been resting here for ages, and you can move it just so far but no farther. It would take a team of army mules to dislodge it."
He looked over the wall again. The Indians were still in the same place, eagerly talking—a score or more of feet below the boy.
"It's too good a chance to miss!" whispered Floyd desperately. "I wonder if I can't find some sort of a lever and pry it loose."