on 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 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