reversal of the pressure, the force of the explosive tending to drive
the oil back for an instant.

The large shots now used (up to 200 quarts, or say 660 pounds of
nitroglycerine) must exert some influence of this kind, especially
when held down by 500± feet of liquid tamping. In the course of these
tests, it was noticed that fresh water has a more energetic
disintegrating action on the shales and clay than on salt water.

This may furnish a reason for the fact, noticed by the oil men, that
fresh water has a much more injurious effect than salt in clogging a
well. No oil-bearing sand rock is free from laminæ of shale, and when
fresh water gets down into the sand, the water must, as the
experiments show, rapidly break up the shale, setting free fine
particles, which soon are driven along into the minute interstices of
the sand rock, plastering it up and injuring the well.--_Engineering
and Mining Journal._

* * * * *




THE GROTTO OF GARGAS.


The grotto of Gargas is located in Mount Tibiran about three hundred
yards above the level of the valley, and about two miles southeast of
the village of Aventignan. Access to it is easy, since a road made by
Mr. Borderes in 1884 allows carriages to reach its entrance.