"Back!"
"What's up?"
"Nothing's up, but we'll be down if we don't take care!"
"What do you mean?"
Before Dave could reply, Bob saw what had caused the young diver to become alarmed.
They were walking over some moss and brushwood, and the mass under their feet was shaking like so much jelly.
Both started to retreat, but it was too late! Down went the mass of brushwood, at first slowly and then swifter and swifter.
They tried to clutch at the sides of the opening, but in vain. Everything they grasped gave way—sticks, moss, stones, bushes, vines. Nothing could stop that downward course.
The moss was dry and the dust filled their eyes, almost blinding them.
"We are lost!" gasped Bob, and then the dust got into his throat and he began to cough as though choking.