"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 head of the jam the men worked like demons. Wherever the timbers caught or hesitated for a moment in their slow crushing forward, there a dozen men leaped savagely, to jerk, heave and pry with their heavy peavies. Continually under them the footing shifted; sullen logs menaced them with crushing or complete engulfment in their grinding mill. Seemingly they paid no attention to this, but gave all their energies to the work. In reality, whether from calculation or merely from the instinct that grows out of long experience, they must have pre-estimated every chance.

"What bully team work!" cried Bob, stirred to enthusiasm.

Now the motion quickened. The centre of the river rushed forward; the wings sucked in after from either side. A roar and battling of timbers, jets of spray, the smoke of waters filled the air. Quite coolly the rivermen made their way ashore, their peavies held like balancing poles across their bodies. Under their feet the logs heaved, sank, ground together, tossed above the hurrying under-mass, tumultuous as a close-packed drove of wild horses. The rivermen rode them easily. For an appreciable time one man perched on a stable timber watching keenly ahead. Then quite coolly he leaped, made a dozen rapid zigzag steps forward, and stopped. The log he had quitted dropped sullenly from sight, and two closed, grinding, where it had been. In twenty seconds every man was safely ashore.

The river caught its speed. Hurried on by the pressure of water long dammed back, the logs tumbled forward. Rank after rank they swept past, while the rivermen, leaning on the shafts of their peavies, passed them in review.

"That was luck," Welton's voice broke in on Bob's contemplation. "It's just getting dark. Couldn't have done it without the dynamite. It splinters up a little timber, but we save money, even at that."