The Stone Quarrying Industry.

Progress, Volume VI, Issue 9, 1 July 1911, Page 726

The Stone Quarrying Industry.

(By Theodore Arnold, M.E.E.)

The enactment of “The Stone Quarries Act 1910” directs attention to the importance of this industry in this Dominion. The Anderson’s

Bay quarries at Dunedin are claimed to possess the most up-to-date appliances, as well as the best stone for general purposes. In the Dominion no granite is found, the best rock found being of the Trap species. The term “Trap" is derived from “Trappa,’’ the Swedish name for stair, and is applied to this rock because rocks of this class frequently occur in large tabular masses, rising one above another like steps or stairs. Basalt is one of the best varieties, and an excellent deposit of this nature is found at Anderson Bay. It is a dark green stone, composed of both augiste and felspar, very compact in texture, and of considerable hardness. Basalt itself is an Etheopian word, for iron, hence its application to this particular class of stone. Trap rock is a large group of igneous rocks allied to granite, and is composed of felspar, augite and hornblende. Felspar is opaque, yellowish in colour, composed of silicuous and aluminous matter, with a small proportion of potash. The principal uses of these rocks are for paving and macadamising. They are vastly superior to flinty stone, which, though hard, is brittle, and easily reduced to dust by the attrition of traffic. It may always be recognised that granite, and granity stone is the best road metal procurable, and flint and flinty stone the very ' worst. At the Anderson’s Bay quarries, the boring of the rock for blasting purposes is performed by the Giant rock drills, made by the Ingersol Band Company, which are driven by compressed air. Hammer and drill work, the dull and dreary old method, is here a thing of the past, and six holes can be driven by a Giant drill in the time formerly occupied in drilling one. The method of blasting, too, is an advanced one. Time fuses are discarded, and electric detonators used. The result is total immunity from danger from blasting to the workmen, and a considerable saving of time. When the holes are charged and ready for shooting, it is only necessary to remove the men from the danger zone for half a minute while an electric spark is transmitted to the charge, and the blast has taken effect, and work is resumed. The stone is conveyed from the quarry to the quaratory stone-cutters by tramlines, the cutters being machines by Jacques (for screenand by Austin (for metal). For power, electricity is used, the works being supplied with three electric motors of 50, 30 and 15 b.h.p. respectively. The Dunedin Corporation possesses a quarry of excellent stone, which is, however, difficult to work, on account of the excessive amount of overburthen, or stripping, necessary to be removed before the stone is accessible.

Queries. What is the difference between an object moving through still air at the rate of 10 miles an hour, and a breeze blowing at the rate of 10 miles an hour against the same object stationary? Answer: Whether the pressure against the object is obtained by the object moving or the wind moving is immaterial. The pressure would be exactly the same in either case.