the atmosphere in the former is far more
destructive to human life. In lead mines, the duration of life averages
scarcely more than thirty-two years, and in those containing arsenical
pyrites or quicksilver ores, the average is still lower. Before the use
of gunpowder in underground operations, the rocks containing the ore
were attacked with fire, indeed the practice is still retained in some
countries. Huge wood fires are made up against the face of the rock,
which becomes shattered and traversed by cracks, and when cooled, it is
easily detached with a pick or fork. Of late years, however, machines
have been devised for boring or breaking the rock. Some form a hole by
the continuous motion of a rotating drill, others by means of
intermittent blows. One of these rock-boring machines, manufactured by
Messrs. Turner, of Ipswich, performs its work by a combination of both
these operations. By the employment of these machines, the formation of
the tunnel under Mount Cenis was greatly facilitated. An example has
already been given of the way in which people have been saved from the
effects of inundations in mines, others have been dug out when buried by
the fall of roofs, but almost countless are the numbers who have
perished from other causes, for if the first have destroyed their
hundreds, the fire-damp in coal mines has proved the destruction of
thousands. It was at one time considered right every night to provoke
an explosion by lighting the fire-damp in order that the working stalls
should be accessible next morning. The man who performed this dangerous
operation wore a thick covering of wool or leather, his face was
protected, and his head was covered by a hood like a monk's cowl. He
crept along the ground, carrying in his hand a long pole with a light at
the end of it. He was known in the English mines as the fireman, but in
the French he was called either the cannonier, the monk, or the
penitent, the latter name being given him from his dress resembling that
of certain so-called religious orders in the Romish Church. Too
frequently the hapless penitent was destroyed by the explosion he had
provoked.

Our two friends, however, might have written several large volumes had
they given accounts of even a portion of the interesting matters
concerning mines which they gathered up during their long and varied
tour.

Mark did not fail to benefit largely by the information he obtained, and
he ultimately, with t