jar provided a groove has been filed in its surface. Numerous other
instances might be cited to prove the value of the groove. Elasticity
in rock is a pronounced feature, which varies to a greater or less
extent; but it is always more or less present. A sandstone has
recently been found which possesses the property of elasticity to such
an extent that it may be bent like a thin piece of steel. When a blast
is made in the new form of hole the stone is under high tension, and
being elastic it will naturally pull apart on such lines of weakness
as grooves, especially when they are made, as is usually the case in
this system, in a direction at right angles with the lines of least
resistance.

Horizontal holes are frequently put in and artificial beds made by
"lofting." In such cases where the rock has a "rift" parallel with the
bed, one hole about half way through is sufficient for a block about
15 ft. square, but in "liver" rock the holes must be drilled nearly
through the block and the size of the block first reduced.

A more difficult application of the system, and one requiring greater
care in its successful use, is where the block of stone is so situated
that both ends are not free, one of them being solidly fixed in the
quarry wall. A simple illustration of a case of this kind is a stone
step on a stairway which leads up and along a wall, Fig. 11. Each step
has one end fixed to the wall and the other free. Each step is also
free on top, on the bottom and on the face, but fixed at the back. We
now put one of the new form of holes in the corner at the junction of
the step and the wall. The shape of the hole is as shown in Fig. 12.

[Illustration: FIG. 11.]