"Better take a hitch around your waist in case you should slip," advised
Butler.

Ned did so, and by bracing his feet against the side of the rock he was
able to aid them not a little in their efforts to haul him to the
surface. Ned fixed Stacy with stern eye.

"Were you bluffing all the time?" he demanded.

"Was I bluffing? Think a fellow would need to bluff when a big chump
like you fell in on him? I thought the mountain had caved in on me, but
it was something softer than a mountain, I guess," added Stacy
maliciously.

"What did happen?" demanded Ned, gazing at the hole wonderingly.

"It's one of those thin crusts," announced the guide, examining the
broken place in the lava with critical eyes, in which occupation the
Professor joined.

"Yes, it was pretty crusty," muttered Chunky.

"You see, sir, this occurs occasionally," nodded the guide, looking up
at the grizzled face of Professor Zepplin. "One never knows in this
country when the crust is going to give way and let him down. I guess
the rain must have weakened the ground."

"And I fell in again," growled Stacy.

"You were bound to fall in sooner or later," answered Tad. "Perhaps it