While they stood on the edge of the chasm considering the situation, a bright blaze leaped up some distance to the north.
"Some one's burning green boughs!" exclaimed Tommy.
"How do you know that?" asked Sam.
"Look at the white smoke!" answered Tommy. "I guess if you had made and answered as many Boy Scout smoke signals as I have, you'd know how to make a smudge."
"It's so bloomin' dark I couldn't tell whether the smoke is while or black!" declared Sam. "I can see only the bulk of it."
"If it was good and black," Tommy answered, "we couldn't see it so plainly. And, come to think about it," he added, laying a hand excitedly on Frank's shoulder, "there are two columns of smoke."
"I see the two now," Frank answered. "One column has just begon to show. You know what that means, of course!"
"It means a Boy Scout signal for assistance," replied Tommy.
Doctor Pelton turned to the boys with an anxious face.
"Do you really mean that?" he asked.