236 THE VERMILION IRON-BEARING DISTRICT. 



off at levels about 75 feet apart. From such a crosscut a slice of ore 

 extending- from the foot to the hanging wall, and from 15 to 20 feet thick, 

 is removed or stoped out. When this has been cleared out, drift sets 

 consisting of legs 9 feet long, and averaging 15 inches in minimum 

 diameter, with caps 11 feet long and averaging 16 inches as the minimum 

 diameter, with heavy lagging, are set up, running from the crosscut 

 through the stope, usually near its center. PL IX, A, shows these main- 

 level timbers being put in on the floor of the stope. After the timbering 

 is completed, filhng 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. Fig. 14, a horizontal section through the fifth 

 level of the Minnesota mine near its connection with the shaft, shows the 



Fig. 14.— Horizontal section through the fifth level of No. 8 shaft, Soudan. 



arrangement of the drifts and their connection with the crosscut in the 

 foot wall connecting them with main shaft. On the main level the ladder 

 ways and chutes or mills, 6 feet square, requiring timbers 7 feet long and 

 averaging 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 the 

 ore has been removed is then filled and the drift sets covered with several 

 feet of rock. Fig. 15 illustrates the way in which these fills are made, and 

 shows how connection is maintained, by means of chutes and ladder ways, 

 with the main drifts at the bottom of the level. 



PL 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 



