. The Vermilion iron-bearing district of Minnesota : with an atlas . Fig. 14.—Horizontal section through the fifth level of No. 8 shaft, Soudan. arrangement of the drifts and their connection with the crosscut in thefoot wall connecting them with main shaft. On the main level the ladderways and chutes or mills, 6 feet square, requiring timbers 7 feet long andaveraging 12 inches in diameter, with a minimum of 9 inches in diameter,are timbered up a few feet above the drift sets. The space from which theore has been removed is then filled and the drift sets covered with severalfeet of rock. Fig.
. The Vermilion iron-bearing district of Minnesota : with an atlas . Fig. 14.—Horizontal section through the fifth level of No. 8 shaft, Soudan. arrangement of the drifts and their connection with the crosscut in thefoot wall connecting them with main shaft. On the main level the ladderways and chutes or mills, 6 feet square, requiring timbers 7 feet long andaveraging 12 inches in diameter, with a minimum of 9 inches in diameter,are timbered up a few feet above the drift sets. The space from which theore has been removed is then filled and the drift sets covered with severalfeet of rock. Fig. 15 illustrates the way in which these fills are made, andshows how connection is maintained, by means of chutes and ladder ways,with the inain drifts at the bottom of the level. PI. IX, B shows the top of one of the fills in the MinnesotaCompanys mine. In the background is seen the cribbed jiortion of the U. S. GEOLOGrCAL SURVEY MONOGRAPH XLV PL. IX. .1. MAIN-LEVEL TIMBERING, MINNESOTA MINE.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectgeology, bookyear1903
