The Knox system is a recent invention; no mention was made of it in the tenth census, and no description has yet been given of it in any publications on quarrying.  The first work done by this method was in 1885, and at the close of that year 2 quarries had adopted it.  In 1886 it was used in 20 quarries; in 1887 in 44, in 1888 in upward of 100, and at the present time about 300 quarries have adopted it.  Its purpose is to release dimension stone from its place in the bed, by so directing an explosive force that it is made to cleave the rock in a prescribed line without injury.  The system is also used for breaking up detached blocks of stone into smaller sizes.

Quarrymen have, ever since the introduction of blasting, tried to direct the blast so as to save stock.  Holes drilled by hand are seldom round.  The shape of the bit and their regular rotation while drilling usually produce a hole of somewhat triangular section.  It was observed, many years ago, that when a blast was fired in a hand-drilled hole the rock usually broke in three directions, radiating from the points of the triangle in the hole.  This led quarrymen to look for a means by which the hole might be shaped in accordance with a prescribed direction of cleavage.

The oldest sandstone quarries in America are those at Portland, Conn.  It was from these quarries that great quantities of brownstone were shipped for buildings in New York.  The typical “brownstone front” is all built of Portland stone.  As the Portland quarries were carried to great depths the thickness of bed increased, as it usually does in quarries.  With beds from 10 to 20 ft. deep, all of solid and valuable brownstone, it became a matter of importance that some device should be applied which would shear the stone from its bed without loss of stock and without the necessity of making artificial beds at short distances.  A system was adopted and used successfully for a number of years which comprised the drilling of deep holes from 10 to 12 in. in diameter, and charging them with explosives placed in a canister of peculiar shape.  The drilling of this hole is so interesting as to warrant a passing notice.  The system was similar to that followed with the old fashioned drop drill.  The weight of the bit was the force which struck the blow, and this bit was simply raised or lowered by a crank turned by two men at the wheel.  The bit resembled a broad ax in shape, in that it was extremely broad, tapering to a sharp point, and convex along the edge.

[Illustration:  Fig. 1]

Fig. 1 illustrates in section one of the Portland drills, and a drill hole with the canister containing the explosive in place.  The canister was made of two curved pieces of sheet tin with soldered edges, cloth or paper being used at the ends.  It was surrounded with sand or earth, so that the effect of the blast was practically the same as though the hole were drilled in the shape of the canister.