. The Vermilion iron-bearing district of Minnesota : with an atlas . n run out into the trams. Rock to fill the topmost level,or any other level being worked atthe same time with it, is taken fromthe accumulations of loose materialat the bottom of the open pit, de-rived from the caving in of its sidesand from the drift at its surface, orelse from material which has beenblasted down from the walls of thepit. After the topmost level isworked out filling may be run downinto the level below that, and so ondown as the development requires 16 is a cross section through theMinnesota mine show
. The Vermilion iron-bearing district of Minnesota : with an atlas . n run out into the trams. Rock to fill the topmost level,or any other level being worked atthe same time with it, is taken fromthe accumulations of loose materialat the bottom of the open pit, de-rived from the caving in of its sidesand from the drift at its surface, orelse from material which has beenblasted down from the walls of thepit. After the topmost level isworked out filling may be run downinto the level below that, and so ondown as the development requires 16 is a cross section through theMinnesota mine showing how theraise in the foot wall connects withthe surface, and how connection ismaintained with the levels at variousheights as the filling proceeds. Upon this filling the workmenstand, and here the (frills are placed, mounted on braced cribbing, or inany other way that will give them ;i sufiiciently firm foundation. Thiskeeps the workmen near the roof, which is one of the advantages of oA-er-hand stoping, in that the roof can be easiy examined and accidents from. Ifi.—Cross section of Soudan mine show-ins raise. U. S. GEOLOGICAL SURVEY MONOGRAPH XLV PL.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectgeology, bookyear1903
