ation: Fig. 2.]

It was found that with the old Portland canister two breaks might be
made at right angles by a single blast, when using a canister shaped
like a square prism. In some of the larger blasts, where blocks
weighing in the neighborhood of 2,000 tons were sheared on the bed,
two holes as deep as 20 ft. were drilled close together. The core
between the holes was then clipped out and large canisters measuring 2
ft. across from edge to edge were used.

In regard to another of the older systems of blasting, known as
Lewising, Mr. Saunders says:

A Lewis hole is made by drilling two or three holes close
together and parallel with each other, the partitions between
the holes being broken down by using what is known as a
broach. Thus a wide hole or groove is formed in which powder
is inserted, either by ramming it directly in the hole, or by
puling it in a canister, shaped somewhat like the Lewis hole
trench. A complex Lewis hole is the combination of 3 drill
holes, while a compound Lewis hole contains 4 holes. Lewising
is confined almost entirely to granite. In some cases a series
of Lewis holes is put in along the bench at distances of 10
and 25 ft. apart, or even greater, each Lewis hole being
situated equidistant from the face of the bench. The holes are
blasted simultaneously by the electric battery.

After noting another system used to a limited extent, and not to be
commended, viz., the use of inverted plugs and feathers (the plugs and
feathers being inserted as a sort of tamping which the blast drives
upward to split the rock), Mr. Saunders continues in substance as
follows:

It is thus seen that the "state of the art" has been
progressive, though it was imperfect. Mr. Sperr, in his
reference to this subject, made in the report of the tenth
census, says: "The influence of the shape of the drill hole
upon the effects of the blast does not seem to be generally
known, and a great waste of material necessarily follows."
This was written but a few years before the introduction of
the new system, and it is doubtless true that attention was
thus widely directed to the conspicuous waste, due to a lack
of knowledge of the influence of the shape of a drill hole on
the effect of a blast. The system developed by Mr. Knox
practically does all and more than was done by the old
Portland system, and it does it at