Griggs threw up his head too, but he did not open his nostrils and sniff loudly. He only laughed.
“More ways of killing a cat than hanging it,” he cried merrily. “Other ways besides seeing and smelling. Hark!”
They had pushed their way in among the outer blocks that had bounded farthest, and their ponies had halted at the bottom of the slope because they could go no farther without attempting to climb.
“Hark? What to—what at? I can’t hear anything. Yes, I can,” cried the boy excitedly. “It’s a singing, gurgling noise. Why, Griggs, you’re right. There’s water running down below here.”
“Well done, hearing!” cried Griggs. “I’ll be bound to say there’s a big natural tunnel down below here. One minute. Let’s try a bit more to the right.”
They dismounted, and Griggs led the way, brushing the rocks about with his pole as he climbed up and up, listening the while, for about sixty or seventy yards, and then he stopped short, picked up a stone about as big as his head, and pitched it away forward.
There was silence for a few moments, and then, just as Chris climbed up alongside and found himself on the edge of a deep chasm going down into gloom, he heard a hollow, echoing splash.
“Sounds like water,” said Griggs coolly, “and plenty of it.”
“Yes,” cried Chris, as he listened. “Why, I heard that dull, rumbling sound before,” he continued, as he bent over, “but it seemed to come from high up in the cliffs, and I thought it was the wind.”
“So did I,” said Griggs. “I suppose the sound comes up and strikes against the rock-face, to be reflected off to where we could hear it down below.”