st this, that there is someone else on it. Who or what it is I
don't know."

And Jack went on to explain all that he had seen.

CHAPTER XXXIII.

THE SECRET AT LAST.

Mysteries are always uncomfortable. As Jack proceeded with his
narrative, Dick and Tom looked nervously about them. Even the boys'
two elders looked grave. The presence of a man on the island was
almost inexplicable. But Jack's story was so circumstantial that there
was no room to suppose that he might be mistaken. Besides, he had the
bit of canvas to show, the scrap that he had taken from the thornbush.

After dinner Tom and Dick resumed their work of unloading necessaries
from the Wondership. Jack and the two elder members of the party
discussed plans.

"You haven't found any trace of mineral-bearing rock yet, have you,
professor?" asked Jack.

The professor shook his head.

"Not a speck of anything that even remotely corresponds with the
black sand that Zeb brought East with him," said the man of science,
dejectedly.

"It isn't possible that we have been fooled," said Zeb.

"Or landed on the wrong island," struck in Jack.

"It must be the right island," declared Zeb.

"How do you make that out?" asked Jack.

"Well, it's got every mark on it that the map gives, for one thing,"
said Zeb.

"That's so," agreed the professor, and then he added hopefully:
"However, I haven't covered half the ground yet."

Tom and Dick came tramping back at that juncture. They carried some
canned goods and Dick bore the rusty shovel that they had seen the day
before sticking up in the black barren.

"It was sticky and moist out there," he said, "but I figured we could
always use this shovel, so I went out and brought it along."

He flung himself down full length in the shade for it was hot and
there was not a breath of wind to fan the canyon. The professor, who
sat facing Dick, concentrated his attention for an instant on the
soles of the youngster's boots. Then he leaped up with a yell that
startled them.

"What is it? The wild man?" gasped Dick, looking round him in alarm.

"No, your boots, your boots; look at them!" cried the professor.

"Is there a snake on them?" cried Dick, preparing to jump up.

"Don't move! Don't move for your life!" fairly screamed the dumpy
little geologist, springing forward. He fell on his knees at Dick's
boots as if they had been sacred, and with trembling fingers flaked
off, into his left palm, some black mud wh