"There it is!" cried Dick, and he pointed to where, in the light of the lanterns, there could be seen, slowly ascending, a thin wisp of smoke.
"Look out!" yelled Old Billee as Dick dashed forward. "It may explode!"
Then, as Dick rushed up with his lantern, they saw trailing over the floor of the tunnel, and on the same side of the stream as themselves, a thin white fuse, like a sinister snake. It was this burning fuse which caused the smoke.
It was the work of but an instant for Dick to step on it, and extinguish the smouldering spark, while it yet had some distance to travel before the fuse lost itself in a mass of rocks.
"Whew! That was a close call!" exclaimed. Bud, when the fuse was entirely out.
"Let's see where it leads to," suggested Snake.
They followed it up, and discovered a hidden mine of explosives, tamped down into a hole that had been drilled in the rocky floor. Iron bars, hammers and other mining implements showed that the perpetrators of the dastardly deed had evidently fled in a hurry.
"They were going to blow up the tunnel!" cried Nort.
"And when that collapsed it would mean the end of Flume Valley," spoke Bud soberly.
"We never could have opened the tunnel again, with all these strange, branching streams playing around inside."