Page:The Overland Monthly Volume 5 Issue 3.djvu/14

 a fair guarantee that they will be finished.

The tunnels, aforesaid, have the same relative size, grade, and manner of construction; the work being done by contract, and by men employed by the Company. The average grade of all is not far from six inches to every twelve feet, and size about six feet in height by seven feet in width. They are built, mainly, through a solid bed of coarse slate, called by the miners "blue granite," and in which seams of gypsum are not unfrequent. The rock does not prove to be equally hard, and consequently the progress of the tunnel is irregular, varying from three and a half or four feet per week, in the hardest rock, to six or seven feet in rock of a soft material. In all cases of soft rock, the tunnel must be heavily timbered, or the work will prove fruitless, from the frequent caves that take place.

When the work on the tunnels is let by contract—a method very popular in the district—it is often customary to do it by the means of sealed proposals; the party bidding what he thinks will enable him to make a fair margin of profit, and the Company frequently giving a premium for the completion of a hundred feet or more within a stated period.

In cases of contracting for tunnel-work in the district, the price ranges from $34 to $37 per foot, in hard rock; and as, in miners' language, "the rock is very uncertain," the men sometimes make a fair profit, and frequently nothing at all. With fair rock, they average $5 per day, board excluded; while men employed by the Company are paid an average of $3 per day, with board.

Each tunnel works from six to nine nen, when there is but a single opening for work, who operate in alternate "shifts," sometimes two, but oftener three men to the "shift"—each party working eight hours to a "beat" —the former number prevailing when Giant Powder is used for blasting.

When shafts are sunk at different places on the line of the tunnel, men are worked according to the number of the same; each shaft affording two faces for working at the same time.

During the construction of a tunnel, the want of pure air for the workmen is often a most serious hindrance. Hour after hour, men are forced to breathe an atmosphere, never healthful, and frequently poisonous; and many a miner can point to-day to his work in the tunnel, as the reason of a disordered system, or, what is far worse, a ruined constitution. As a means of partially obviating this difficulty, when the tunnel is commenced from the bank, a shaft is sunk at a convenient distance from its mouth, and by means of communication with it brings about a circulation of pure air. The Companies also resort to different kinds of machinery, for forcing air into the tunnels; and among the most frequent, as well as the most efficient of any, is that called "the water-blast"—a very ingenious contrivance, in which a perpendicular fall of water is the motive-power, and the air is forced through a four-inch pipe up to the place of the miners' work.

During the existence of a mine, two tunnels, at least, may have to be built, in order to reach the lower level of the mine. Nor could this be obviated by running the first tunnel a given number of feet lower. In the first place, it would make the opening of the mine too difficult; and, in the second place, it would give a very high bank, which can be worked less profitably than one of a medium height.

Flaming, or sluicing, follows tunneling.

Each flume consists of a number of boxes, more or less, according to the length of the flume, each box being about twelve feet long.