In other words, the old Portland system was to drill a large, round hole, put in a canister, and then fill up a good part of the hole.  Were it possible to drill the hole in the shape of the canister, it would obviously save a good deal of work which had to be undone.  The Portland system was, therefore, an extravagant one, but the results accomplished were such as to fully warrant its use.  Straight and true breaks were made, following the line of the longer axis of the canister section, as in Fig. 2.

[Illustration:  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 far less expense.  It can best be described by illustrations.

[Illustrations:  Figs. 3, 4, 5, 6]