felt himself lifted from the
ground by the force of the blast, and dashed down again.

Then he knew it was over, and staggered to his feet. The force of the
explosion had passed along the main road, and so up the shaft, and he
owed his life to the fact that he had been in the road off the course.
He returned into the main road, but near the bottom of the shaft he was
brought to a standstill. The roof had fallen, and the passage was
blocked with fragments of rock and broken waggons. He knew that the
bottom of the shaft must be partly filled up, that his comrades were
killed, and that there was no hope of escape in that direction. For a
moment he paused to consider; then, turning up the side road to the
left, he ran at full speed from the shaft. He knew that the danger now
was not so much from the fire-damp--the explosive gas--as from the even
more dreaded choke-damp, which surely follows after an explosion and
the cessation of ventilation.

Many more miners are killed by this choke-damp, as they hasten to the
bottom of the shaft after an explosion, than by the fire itself.
Choke-damp, which is carbonic acid gas, is heavier than ordinary air,
and thus the lowest parts of a colliery become first filled with it, as
they would with water. In all coal-mines there is a slight, sometimes a
considerable, inclination, or "dip" as it is called, of the otherwise
flat bed of coal. The shaft is almost always sunk at the lower end of
the area owned by the proprietors of the mine, as by this means the
whole pit naturally drains to the "sump," or well, at the bottom of the
shaft, whence it is pumped up by the engine above; the loaded waggons,
too, are run down from the workings to the bottom of the shaft with
comparative ease.

The explosion had, as Jack well knew, destroyed all the doors which
direct the currents of the air, and the ventilation had entirely ceased.
The lower part of the mine, where the explosion had been strongest,
would soon be filled with choke-damp, the product of the explosion, and
Jack was making for the old workings, near the upper boundary line of
the pit. There the air would remain pure long after it had been vitiated
elsewhere.

It was in this quarter of the mine that Bill Haden and some twenty other
colliers worked.

Presently Jack saw lights ahead, and heard a clattering of steps. It
was clear that, as he had hoped, the miners working there had escaped
the force of the explosion, which had, without do