TUNNELS THKorcil IIAKH HOCK 121 



drilled. The first set of eight holes were driven in two rows 

 from top to bottom, the holes being about 2 ft. ajuirt on the 

 surface, and converging toward the center of the tunnel. 

 These holes were 12 ft. deep, and the action of the blast was 

 to blow out a wedge-shaped cavity in the face. The holes of 

 the second set were drilled at the sides of the front and 

 parallel to the sides of the section, and the blast blew out the 

 remainder of the rock into the wedge-shaped center cavity. 

 The method of excavating the bench was nearly the same as 

 that of excavating the heading. 



Mi-i-fnini'-'it Iiintiiffufittn. The following machinery was 

 employed in connection with the construction of the tunnel: 

 at the Ivanhoe end, three 100 H. I*, boilers; two 20 x 24 in. 

 Ingersoll compressors, and one 20 x 24 in. Norwalk compres- 

 sor; a 10 II. 1'. engine driving an electric-light dynamo, and a 

 20 H. P. engine driving a No. 6 Baker blower, forcing fresh 

 air into the tunnel through a 14-in. pipe. In the tunnel one 

 No. 7 and one No. 9 Cameron pump, and a Deane duplex 

 pump with a 10-in. stroke, were employed to keep the excava- 

 tion clear of water, since tli3 grade descended uniformly from 

 the Ivanhoe end, and the water followed the workings. At the 

 Husk end the plant consisted of three 80 II. P. boiler*. t\v.. 

 20 X 24-in. Ingersoll compressors, 10 H. P. and 20 H. P. en- 

 gines respectively, for the electric light dynamo and the blm\-r. 

 Four 3 in. Ingersoll eclipse drills were used in each heading, 

 and two on each bench, making six drills at each end of the 

 tunnel. 



Strnttiiii/ and Lining. For about 78% of its length the 

 tunnel is lined with timlier. The timbering consist* <f a five- 

 segment arch for the roof, resting on a wall plate which is car- 

 ried by vertical side jiosts. The segments of the arch, the wall 

 plates, and the posts, are 12 X 12-inch timbers. The roof arches 

 and tin- |>',-ts supporting the wall plates are spaced 4 ft. apart, 

 center to center. Alx>ve the arches is laid a lagging of 2-inch 

 longitudinal planks. The arches were set up as fast as the 



