While Jack lay back and indulged in daydreams, the others watched the
professor as he tested the black sand over a portable assaying furnace
and made all sorts of experiments to determine its value and the
proportion of the different precious metals contained in it.

There was a slight rustling in the bushes behind him. Jack, whose
nerves had been rather on edge since the occurrences of the preceding
night and that morning, faced round quickly.

The next instant he uttered a loud shout.

Peering out of the bushes was a hideous, hairy face, more like an
ape's than a human being's. From it glowed two wild, piercing eyes,
like those of a beast of prey.

As Jack shouted and the others started toward him, the face vanished
like a flash.

CHAPTER XXXIV.

THE INTERLOPERS.

"Well, we'll git ter ther bottom uv this afore we leave ther island,"
declared Zeb vehemently, "but right now, pussonally, I'm more
interested in gitting those lead carboys filled up with Z. 2. X. and
gitting away from here."

"So are we," said Jack, thinking of his father.

They all donned their asbestos gloves and foot coverings under the
professor's directions and put on the huge black goggles that had been
brought along at the scientist's directions.

"I guess we'd scare that wild man into conniption fits if he could see
us now," chuckled Tom, surveying his mates as they started out for the
black barren.

"Yes, we look like a lot of men from Mars," agreed Dick.

Armed with shovels they attacked the dark, soft earth at a place the
professor indicated. For an hour or more they worked and filled three
of the lead carboys. Then Jack spoke.

"It's queer," he said, "but I begin to feel terribly tired, and I
haven't worked long, either."

"So do I," said Tom. "I don't feel as if I could lift another
shovelful."

"I'm all in," added Dick, throwing down his spade.

"Same here. Jes' 'bout tuckered out," chimed in Zeb.

"It's the effect of the stuff we are working in," said the professor.
"Anyhow, we've done enough for to-day. We'll load the lead carboys on
the Wondership and then knock off. I don't want you boys to get sick."

They took the loaded carboys to the grounded craft and the professor
sealed and soldered a cover on each of them. Then they went back to
the camp. Curiously, as soon as they reached it, the lassitude they
had felt while working on the black barren left them. Jack proposed a
hunting trip to Tom. Dick said he