Another pebble came rattling down from above, struck the ledge, and bounded down into the crater.
“There is something up there. Stones like that would not drop one at a time unless something started them,” Ted whispered. “I am going to watch the top while you keep your eyes on the bottom.”
But a short time elapsed. Stanley nudged his companion.
“Look!” he whispered. “The smooth, round stone is moving. It is creeping along as stealthily as the shadows themselves, and it is coming in our direction. It must be an animal of some kind.”
“There is one above, too,” Ted returned with bated breath. “They are stalking us from the top and the bottom.”
Stanley quickly looked upward. What he saw made him gasp. A massive head was clearly outlined against the dark rock of the wall, and a pair of eyes, blazing with a green fire, seemed to pierce him through.
“The guns, the guns; quick!” he panted, “before it springs. Don’t mind the one below——”
Ted was tugging at his weapon.
“I can’t. I can’t point it straight up. The angle is too great.”
“Kneel down. I will rest it on your shoulder.”