But in the event his precaution turned out useless.  All day the men rolled logs into the current below the dam.  The click! clank! clank! of their peavies sounded like the valves of some great engine, so regular was the periodicity of their metallic recurrence.  They made quite a hole in the breast; and several times the jam shrugged, creaked and settled, but always to a more solid look.  Billy, the teamster, brought down his horses.  By means of long blocks and tackle they set to yanking out logs from certain places specified by Roaring Dick.  Still the jam proved obstinate.

“I hate to do it,” said Roaring Dick to Welton; “but it’s a case of powder.”

“Tie into it,” agreed Welton.  “What’s a few smashed logs compared to hanging the drive?”

Dick nodded.  He picked up a little canvas lunch bag from a stump where, earlier in the day, he had hung it, and from it extracted several sticks of giant powder, a length of fuse and several caps.  These he prepared.  Then he and Welton walked out over the jam, examining it carefully, and consulting together at length.  Finally Roaring Dick placed his charge far down in the interstices, lit the fuse and walked calmly ashore.  The men leisurely placed themselves out of harm’s way.  Welton joined Bob behind a big burned stub.

“Will that start her sure?” asked Bob.

“Depends on whether we guessed right on the key log,” said Welton.

A great roar shook the atmosphere.  Straight up into the air spurted the cloud of the explosion.  Through the white smoke Bob could see the flame and four or five big logs, like upleaping, dim giants.  Then he dodged back from the rain of bark and splinters.

The immediate effect on the jam was not apparent.  It fell forward into the opening made by the explosion, and a light but perceptible movement ran through the waiting timbers up the river.  But the men, running out immediately, soon made it evident that the desired result had been attained.  Their efforts now seemed to gain definite effects.  An uneasiness ran through the hitherto solid structure of the jam.  Timbers changed position.  Sometimes the whole river seemed to start forward a foot or so, but before the eye could catch the motion, it had again frozen to immobility.

“That fetched the key logs, all right,” said Welton, watching.

Then all at once about half the breast of the jam fell forward into the stream.  Bob uttered an involuntary cry.  But the practised rivermen must have foreseen this, for none were caught.  At once the other logs at the breast began to topple of their own accord into the stream.  The splashes threw the water high like the explosions of shells, and the thundering of the falling and grinding timbers resembled the roar of artillery.  The pattern of the river changed, at first almost imperceptibly, then more and more rapidly.  The logs in the centre thrust forward, those on the wings hung back.  Near the