Filling his lungs with air, he let out a most blood-curdling scream, followed by a series of wild and unearthly groans and a long hiss.
The savages were thunderstruck, and those on the bank of the stream took to their heels with all possible speed, while Chief Walru tumbled backward and then began to scramble over the rocks for dear life.
Again Dave let out a scream, and then groans which were more dreadful than the others.
In less than three minutes not a savage was to be seen.
"They have gone!" said Bob.
"If only they don't come back," returned Captain Broadbeam.
"I have an idea," said the young diver. "Why can't we pile up some stones in front of that opening? Then if the savages try to get through the waterfall they will get badly left."
"That's the talk!" came from Bob. "Are there stones handy, Stoodles?"
"Sure, plinty of thim."
And the Irishman showed the way to where lay a quantity of stones, large and small.