we can't stop them," groaned Dick.

"Wait a minute," said the professor.

They continued to watch, and before many minutes had passed they saw
Sam Higgins lay down his shovel with a grunt.

"Go on and dig," ordered Masterson.

"Yes, hurry up, we haven't got all night," urged Eph.

Sam made a few more feeble movements and then quit.

'"I can't do any more," he said languidly.

"Ouch! my hands are burning," cried Eph suddenly, "and I feel as if
all my bones had turned to water. What's the matter with the place?"

After a few minutes more both Eph and Sam gave up, but Masterson stuck
doggedly to his task, although his hands were burning terribly, and
the radio-active stuff was eating through the sacking on his feet. At
last he, too, had to give in. They were too weak to carry the sacks
they had partially filled across the island, owing to the effects of
the black barren, and staggeringly they hid them to call for them at a
later time.

"I thought so," said the professor, as the hidden watchers saw
Masterson and the other two wearily clamber up the slope. "They'll
have bad sores to-morrow and may be crippled for some time."

"But they'll recover?" said Jack, whose conscience began to smite him.

"Oh, yes, but they will have quite a lesson first," rejoined the
professor.

"Let's see what they do next," suggested Jack, and he and Tom
carefully made their way to where the trio had left the boat.
Masterson ordered Sam to get on board; but just as the timorous youth
was about to obey another hideous laugh from near at hand startled him
so that he almost jumped out of his skin.

He leaped forward, but in his alarm missed the boat and gave it a
shove that sent it into the stream. Sam fell flat on his face, while
Masterson, with an exclamation of dismay, leaped for the boat. But the
swift current had it in its grasp and bore it rapidly away. Masterson
sprang on Sam and began beating him violently as the cause of all the
trouble. It was serious enough for them. The loss of the boat had
marooned them on the island.

The boat drifted past a rocky point further down the island shore. Had
they been there, they would have been able to seize it. They watched
it with alarmed eyes as it sailed down the current. All at once a dark
figure dashed from the trees and made a spring from a high rock,
hoping, seemingly, to land in the boat. Instead, there was the sound
of a heavy fall and then a piteous groan.

Whoever it was ha