ubic feet ofair a minute for underground ventilation. Some of the older copper mines in the United States rank among the deepest holes in the world. The Red Jacket shaft district, for instance, an opening about five feet in size, has been sunk j to a depth of nearly five tJwusatici^^ T is claimed… … Coal Miners 6o THE MARVEL OF NATIONS shaft are innumerable cross-cut channels, through which the copper ore iscarried to the main artery of communication, and hoisted to the surface in ten-ton cages, each ofwhich makes half adozen round trips inan hour, enabling thehoisting of more thanfive…
Prophecies
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