eces.

[Illustration: FIG. 12.]

Though the new system is especially adapted to the removal of heavy
masses of rock, yet it has been applied with success in cases where
several light beds overlie each other. In one such instance 10 sheets,
measuring in all only 6 ft., were broken by a blast, but in cases of
this kind the plug and feather process applies very well, and the new
system, when used, must be in the hands of an expert, or the loss will
be serious.

Referring again to our stone step, let us imagine a case where this
stairway runs between two walls. We have here each step fixed at each
end and free only on the top, the bottom, and one face. Let us assume
that there is a back seam, that is, that the step is not fixed at the
back. In a quarry, this seam, unless a natural one, should be made by
a channeling machine. In order to throw this step put of place it must
be cut off at both ends, and for this purpose the V-shaped holes are
put in at right angles to the face. It is well, however, to put the
first two holes next the back seam in a position where the grooves
will converge at the back so as to form a sort of key, which serves a
useful purpose in removing the block after the blast. In quarries
where there are no horizontal beds a channeling machine should be used
to free the block on all sides and to a suitable depth, and then the
ledge may be "lofted" by holes placed horizontally.

Where "pressure" exists in quarries, the new system has certain
limitations. After determining the line of "pressure" it is only
practicable to use the system directly on the line of thrust, or at
right angles to it. It is much better, however, to release the
"pressure" from the ledge by channeling, after which a single end may
be detached by a Knox blast. It is well to bear in mind that the holes
should invariably be of small diameter. In no case should the diameter
of a hole be over 11/2 in. in any kind of rock. This being the case, the
blocks of stone are delivered to the market with but little loss in
measurement. It is a noticeable fact that stone quarried by the new
system shows very little evidence of drill marks, for the faces are
frequently as true as though cut with a machine.

A further gain is the safety of the system. The blasting is light and
is confined entirely within the holes. No spalls or fragments are
thrown from the bast.

The popular idea that the system is antagonistic to the channeling
process is a mi