“PI. IX, A, shows these mainlevel timbers being put in on the floor of the stope. After the timbering is completed, filling is begun. These drift-set timbers are apparently fully strong enough, as 80 feet of rock which is present over some of the drifts has not broken them.” 

“PI. IX, B shows the top of one of the fills in the Minnesota Company's mine. In the background is seen the cribbed portion of the raise, which passes through the level and from which rock for the filling is obtained, with a loaded tram car below its mouth. This raise extends upward through the foot wall, with ore forming the front side of the raise, to the level above, through which it passes in a cribbed way, and so on to the surface.”

Minnesota's first iron ore mine—the Soudan Mine—opened in 1882. Operations went underground by 1892 since the ore body continued deep into the ground. The mine's value was in the special kind of ore it produced. The ore's high oxygen content was used to make high-quality steel in open-hearth furnaces. When technology changed, the ore from the mine was no longer needed. Low-cost ores of the Mesabi Range took over, and Soudan Mine closed in 1962.

Size of sheet is overall length 9” X 11 1/2” wide.