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and their density, according to the more or less bad qual-
ity of the sub-soil. Sometimes a fontis was three or four feet
deep, sometimes eight or ten; sometimes the bottom was
unfathomable. Here the mire was almost solid, there almost
liquid. In the Luniere fontis, it would have taken a man a
day to disappear, while he would have been devoured in five
minutes by the Philippeaux slough. The mire bears up more
or less, according to its density. A child can escape where
a man will perish. The first law of safety is to get rid of ev-
ery sort of load. Every sewerman who felt the ground giving
way beneath him began by flinging away his sack of tools, or
his back-basket, or his hod.
The fontis were due to different causes: the friability of
the soil; some landslip at a depth beyond the reach of man;
the violent summer rains; the incessant flooding of winter;
long, drizzling showers. Sometimes the weight of the sur-
rounding houses on a marly or sandy soil forced out the
vaults of the subterranean galleries and caused them to
bend aside, or it chanced that a flooring vault burst and split
under this crushing thrust. In this manner, the heaping up
of the Parthenon, obliterated, a century ago, a portion of the
vaults of Saint-Genevieve hill. When a sewer was broken in
under the pressure of the houses, the mischief was some-
times betrayed in the street above by a sort of space, like
the teeth of a saw, between the paving-stones; this crevice
was developed in an undulating line throughout the entire
length of the cracked vault, and then, the evil being visible,
the remedy could be promptly applied. It also frequently
happened, that the interior ravages were not revealed by any