here must
have been when these stones came tumbling down!"

"More likely that water had been coming down in a regular stream for
hundreds and hundreds of years till all the earth and small stones had
been washed away and made a great hollow underneath which held up the
cliff as long as it could, and then gave way all at once."

"You're talking as if a torrent ran down from the top of the cliff
yonder."

"Jusso," said Griggs.

"Then where did it go to?" said Chris.

"That's what we've got to find out. Got a hole of its own underground,
perhaps, and dives down, to come up again miles away, perhaps, and--
Water it is!"

"Where?" cried Chris excitedly, and he threw up his head, his nostrils
expanded, and he sniffed loudly.

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."

"Would it be?"

"To be sure, my lad. Sound's just like light in that. It strikes
a