ENGINEERING. 



289 



air only, 2,250 feet from the entrance and 211 

 feet in depth, was begun in May, 1872, and 

 finished in a few weeks. In the beginning of 

 1871 the bore had been completed for 1,750 

 feet ; in that year 915 feet additional was 

 penetrated, making 2,665 feet in all ; in 1872, 

 815 feet was made, giving a total length at 

 the end of the year of 3,480. In 1873 there 

 was 1,919 feet bored, including the bore which 

 was made in each direction from the bottom 

 of the first shaft, which amounted to 655 

 feat ; the total length at the end of this year 

 was 5,399 feet. In the course of 1874 six 

 Burleigh drills were put in action, the boring 

 before having been entirely by hand. These 

 were provided with compressed air by a pow- 

 erful steam compressor of the make of the 

 Societ6 John Co.ckrill in Belgium, which was 

 placed at Shaft No. 1. The progress made in 

 1874 with these aids was 2,680 feet, an aver- 

 age of 223 feet per month, carrying the 

 header 8,079 feet from the entrance. In 1875 

 the bore penetrated 3,728 feet farther, or 

 11,807 feet from the mouth ; the average 

 progress per month was 310 feet. When 

 during this year the great body of water, 

 which filled the second shaft and the drifts at 

 its bottom, was encountered, the delicate and 

 dangerous task was undertaken of tapping it 

 with a drill-hole and allowing the water to 

 discharge itself through the tunnel. The col- 

 umn of water in the shaft was over a thou- 

 sand feet high ; and when a hole was made 

 100 feet through the rock with a diamond 

 drill, it burst forth with terrific force, but 

 was closed up again with fragments of rock 

 and timber which were forced into it. Bored 

 a second time, the water forced the drill like 

 a shot into the tunnel. In a week's time the 

 vast volume of water had discharged itself. 

 Another compressor, built by the Humboldt 

 Company of Kalk, on the Rhine, was put into 

 operation at Shaft No. 2. In the year 1876 

 the progress made was 3,670 feet, or 305f 

 feet per month ; the total length of the tunnel 

 at its close was 15,477 feet. In 1877 the prog- 

 ress was 3,130 feet, or 260| per month, the 

 length of the tunnel being extended to 18,607 

 feet. Less headway was made this latter year 

 on account of the troublesome and dangerous 

 nature of the rock encountered, a soft, slippery 

 clay, which often swelled after exposure to 

 the air to such an extent as to displace the rail- 

 road track and sometimes to break the tim- 

 bering. Here the tunnel was timbered up to 

 the face of the drift, and often lagging driven 

 in ahead of the drift. Only light charges of 

 gunpowder, and sometimes none at all, could 

 be used, for fear of displacing the timbers. In 

 1878 the average progress was still smaller, 

 being, up to September, only 235J feet. The 

 same soft, treacherous rock continued, and the 

 heat and bad air became more and more op- 

 pressive as the bore advanced. The total 

 length of the tunnel up to the 1st of Septem- 

 ber, 1878, was 20,489 feet. The tunnel pene- 

 VOL. xvin. 19 A 



trated to the Savage mine, forming the first 

 connection with the Comstock lode, on July 

 8th. The junction with the Savage mine was 

 at the 1, 650-foot level, at a point distant 20,- 

 018 feet from the mouth of the tunnel. A 

 strong current of air immediately started up 

 the shaft of the mine, and a draught entered 

 the mouth of the tunnel. The air in the head- 

 er and in the lower drifts of the mine, which 

 was extremely noxious, was purified in a few 

 days by the circulation, and the heat at the 

 2,000-foot level of the Savage mine was re- 

 duced from 120 to 90 Fahr. 



The drainage of the Sutro Tunnel will be 

 effected by a covered drain extended through 

 its whole length and issuing at the mouth. 

 It is necessary to cover the drain to protect 

 life from the hot vapors of the waters, which 

 in some of the mines stand at a temperature 

 of 150 to 160 Fahr. The drain is to be 

 built in sections simultaneously, and made of 

 a strong and lasting character. 



A branch is being built extending from a 

 point 19,716 feet from the mouth to the Julia 

 mine. The length of this bore is 1,400 feet. 

 It is of the same dimensions as the main tun- 

 nel 8 feet in height by 10 in width. This 

 branch was commenced September 1, 1878, 

 and is expected to be completed by February 

 1st. It will then be extended southward beyond 

 the Julia to Gold Hill and Gold Cation, while 

 near the Belcher mine another branch will 

 fork off toward American Flat. 



A still more important extension of the tun- 

 nel will be its continuation into Mount David- 

 son. The point at which it enters the moun- 

 tain, under Virginia City, is nearly 2,000 feet 

 below the streets of the town. At a distance 

 of 3,000 feet farther into the mountain the per- 

 pendicular distance from the summit to the 

 level of the tunnel will be 3,600 feet. It is 

 thought that rich veins of gold may be en- 

 countered in the syenite of which the moun- 

 tain is composed. 



The average temperature of the air at the 

 header during the progress of the main tunnel 

 was, in the year 1875, 82, of the water 81; 

 in 1876 the average temperature in the air was 

 85, in the water 86 ; in 1877 the thermome- 

 ter averaged 92 in the air, 93 in the water ; 

 in 1878, in the air 95, and in the water 105. 

 In 1878, up to September 1st, the average 

 flow of water per day was about 1,285,000 gal- 

 lons. 



A report made to the shareholders of the 

 St. Gothard Railway in June, 1878, states that 

 the length of bore pierced on the north side 

 of the mountain was 3,316 metres, of which 

 1,018 metres was completed. On the south 

 side 1,317 metres had been pierced. The prog- 

 ress has been considerably slower than was 

 expected, on account of the hardness of the 

 rock. The directors hope that the bore will 

 be completed by the close of the year 1881. 

 The estimated cost of the line of 801,000 

 francs per kilometre, it is hoped, may be re- 



