The wonders of modern mechanismA résumé of recent progress in mechanical, physical, and engineering science . ng is necessary to get up the miners below drill the rock with compressed air drills,the air being forced down through three-quarters of a mileof tubing by means of compressors. When a sufficientnumber of holes are drilled a blast is made, and, as soonas the gases dissipate, men are set to work gathering theore into the cars, while another gang goes on No. 3 was sunk first through fifteen feet of drift,then a hundred feet or more of trap-rock, then throughseveral
The wonders of modern mechanismA résumé of recent progress in mechanical, physical, and engineering science . ng is necessary to get up the miners below drill the rock with compressed air drills,the air being forced down through three-quarters of a mileof tubing by means of compressors. When a sufficientnumber of holes are drilled a blast is made, and, as soonas the gases dissipate, men are set to work gathering theore into the cars, while another gang goes on No. 3 was sunk first through fifteen feet of drift,then a hundred feet or more of trap-rock, then throughseveral seams of amygdaloid rock, which is full of smallcavities. In many mines these cavities are more or lessfilled with pure metal, but here there is no copper untilthe conglomerate vein, composed of fragments of pre-existing rocks, is struck. The ore hoisted from the 262 WO^^DERS OF MODERN MECHANISM. shafts is carried seventy-five feet above the surface, tocouceutration works, wiiere it passes through a series ofcrushers, etc. For a description of these see the chapteron ore-crushing machinery. Fi<;. EOCK-DRILLING. The timbering of mines constitutes an important partof mine-engineering. It is especially difficult in swell-ing ground, as the miners term it, that tends to bulgeinto the shafts, or in loose, watery ground, or in quick-sand. There are cases where mines have been abandonedas unprofitable because of these annoyances. The shafts MINING AND MINING-MACHINERY. 263 on the Comstock, and in Calaveras and Amador Counties,California, also at Leadville, Colorado, were difficult inthe extreme, and reflect great credit on the size of timbering in shafts varies all the way fromeight by eight to twenty by twenty-four, or even shafts require heavier timbers than vertical shafts,as they have to support a part of the weight as well as thethrust of the ground. Very stout wall-plates are used,and joints are made by mortising. Pumping and man-way comp
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