As the banks became poorer, the miners turned their attention to the river beds. In New Zealand, in the early days, they worked the banks as far down into the river as they could reach with a spoon dredge. Then a dredge was made resembling a ladder of buckets, continually revolving, and operated by wheels driven by the current. When the river got low the current became too weak, and a steam engine was substituted. Then a revolving screen was put on to separate the large rocks from the fine sand, and gradually the modern dipper dredge has been evolved, with its pumps, screen, distributors, and tables and sluices, handling 2000 yards of gravel a day at a cost of three cents a yard.
In 1859 the Comstock lode in Nevada was discovered, and it is to this district that we owe the “square set” method of timbering, so largely in vogue in wide veins to-day. Some of the “bonanzas,” that is, pockets of rich ore, were of enormous size. For example, one found in the “Gould and Curry” was 400 feet long, 80 feet wide, and 400 feet deep. As the walls were not sufficiently solid to stand unsupported, and a single stick of timber was too short to reach across, splicing was tried. It was soon found that this weakened the timber too much, and the method of square “setting” was invented. This consists in framing timbers together in rectangular sets, having a square base of four pieces, usually six feet long, placed horizontally as sills. Into these are framed posts, surmounted by a cap of four additional timbers which become the base for the next set. The timbers are usually twelve inches square, and cost on the Comstock about $10 a set. From 1870 to 1891 there is said to have been used up on the Comstock 200,000 acres of forest, valued at $45,000,000.
The amount of timber which is consumed under ground in a single year must be enormous. Mr. C. W. Goodale estimates that in Butte alone, in 1895, 37,500,000 feet, equal to 3750 carloads, were used in the mines. As the timber decays in from five to fifteen years, and has to be replaced, efforts are constantly directed toward decreasing the large expense which is thus continually recurring. In shafts and levels for permanent use iron is an economical substitute. Wherever possible, new methods of mining are being introduced. Thus in the Lake Superior iron regions, the mine development is planned along lines almost unheard of ten years ago. In the first place the gravel which overlies the ore is stripped off, even if it is fifty feet thick. This is done with steam shovels, which load the gravel upon cars. These are then pulled away by one locomotive while a second places new “empties” in position to be filled. One shovel will load from 150 to 175 cars a day; that is, will take from 3500 to 4500 tons of dirt from the sides of the pit and put it upon the cars. This method obviates the use of timber for holding up the surface.
After the overlying gravel is removed, should the conditions be favorable, the ore is taken out with a shovel. If this cannot be done, some method depending on rock-filling is adopted. At the Auburn mine, after stripping and driving the levels, raises are made to the surface at intervals of about fifty feet, the ore broken down around them, starting at the surface, and dropped down through them. This leaves openings in the shape of inverted cones, having their bases at the surface. Additional raises are then made halfway between the others, and the remaining material extracted.
GOLD DREDGING ON SWAN RIVER, COLORADO.
At the Fayal mine they take out rooms twenty-four feet wide by three hundred feet long, with a twenty-four-foot pillar between them. These rooms are carried up from the first level to the surface, and filled with gravel which is run in from above. Then the pillars are mined by “slicing and caving;” that is, by running drifts along the sides of the pillar and caving the ore down from the roof. After removing this ore another drift is run, the roof caved, and another slice taken off. It is claimed the saving in timber by using this method amounts to ten cents on each ton of ore mined.
All of these, and many other inventions, have constantly tended to decrease mining costs. Yet the industry is carried on to-day in so many out-of-the-way places, and under such varying conditions, that the cost per ton of the ore mined vacillates between wide extremes. As an example of what can be accomplished, working on a large scale, and where supplies are easily and quickly obtained, the Atlantic mine, in Michigan, may be mentioned. This mine produced, in 1898, 370,000 tons of ore, at a cost of sixty-six cents per ton.
With all these wonderful advances in mine mechanics, engineering, ventilation, and lighting, have come the foundation and development of mining schools, the rise of technical societies, and a general governmental recognition of the importance of the industry. It is not so very far back in the preceding century that we find among the statutes of England the following: “Stealing ore out of mines is no larceny, except only those of black lead, the stealing ore out of which is felony without benefit of clergy.” It would be interesting to know the name of the gentleman who owned the black-lead mine, for, in modern parlance, he certainly “had a pull.” By 1833 mining legislation had so far progressed in England that laws were enacted regulating the employment of children under ground. In this country, in 1830, a state geological survey was inaugurated by Massachusetts, and this institution has since been copied by many States. The majority of the States where mining is carried on have passed laws tending to increase the safety of men working under ground.
Abroad, carefully prepared codes describe the method of lease or sale of mining rights, and define the rights of owners of ground. In this country the first legislation of this character was in 1807, when the government mineral bearing lands were withdrawn from sale and ordered leased. In 1834 the miners refused to pay the royalty, owing to the large number of illegal entries, and in 1847 the lands were opened to sale. It was not until 1866, after fifteen years of self-government among the miners of the West, that Congress earnestly undertook to regulate the acquisition of mining titles on the public domain. Leagues beyond the towns, miles from the nearest roads, hurrying from the scene of one excitement to another, pushed by the crowd of constantly arriving adventurers, with surveyors unobtainable and courts not accessible, almost without time to measure, and in a region absolutely unlocatable, it had been impossible for the miner of the West to secure a legal title to his land as contemplated by the act of 1847. Accordingly, there had grown up the custom which gave to the discoverer of a lode the right to a certain length of it, and it was this right which was recognized by Congress, and became the basis of the law of 1866.