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	54	MINING IN CALIFORNIA AND NEVADA.

	Section II.—Mining Operations. According to a late return in 1877, during a period of seventeen years previous to the end of July in such year, rather more than twenty incorporated mining companies, holding ground of more or less extent each, for an aggregate length of about 20,000 feet, produced 237,000,000 dollars worth of bullion, from about 659,000 tons of ore raised. At the same time, there still remains a very large quantity of inferior ore in the " backs " that cannot profitably be treated until the general mining expenses—which are, in this desolate region, excessively large—have been considerably reduced. During the above-cited period, the average value of the bullion retorted stands, per ton of ore crushed and treated, at 39 dollars 10 cents, or about £7 3s. 6d., which is certainly very good. Nearly a score of distinct " bonanzas " have been discovered, of which nearly half commenced right from the surface ; but it is a significant fact, that bonanzas were also discovered in the deep ground at the 900, 1,100, and 1,300-foot levels. These deep bonanzas have no connection with nor possess any outlet at the surface, and some of these ore bodies have attained dimensions exceeding any known elsewhere. The deepest bonanza, at the 1,300 to 1,750-foot levels, measured 300 feet in length by 30 feet in width; others were limited to the same width by a length of 1,000 feet and a depth of 450 feet. The greatest quantity of ore from any one of these bonanzas, averaging 42 dollars per ton, was raised by the Crown Point and Belcher Company, of 1,374,528 tons, for a value of 58,110,240 dollars. The celebrated Consolidated Virginia and California United companies eclipsed that yield from a lesser quantity of ore, viz., 699,453 tons, which averaged 96 dollars per ton, or a value of 67,168,376 dollars. There are about thirty companies at work, which employ from 1,200 men down to a few each only, so that, if one shaft only is allotted to each company, ranging from say 800 to 2,200 feet in depth, it must be admitted that their mining operations have been carried out on a scale scarcely ever equalled, during their seventeen years, especially when the great difficulties are considered which hindered, and do now more than ever, the projected works. The winning of ore from so large a deposit, as long as the mines were not very deep, was not very difficult, but, with greater depth, another feature or drawback presented itself, which rendered it necessary that more than ordinary care and skill should be exercised, and which suggested itself mainly by the observance of the principles of mechanical science. In the lower levels, the rocks and ores are much impregnated with lime, and at the same time there are large quantities of iron pyrites existent, and through the decomposition of the latter a chemical reaction takes place with the former, causing the lime to be " slacked;" and thus it is explained why the temperature increases so rapidly with greater depth, exceeding that of the ordinary increase observed in deep mines. Another obstacle is presented by the impossibility to fill the large excavations with waste rock, as is usually done; the available waste being too costly to obtain, consequently these open spaces are secured by solid timber, of which more hereafter. The following remarks as to the principal shafts, plats (stations), and workings will perhaps deserve attention. The west shaft of the Virginia Consolidated and California United companies measures 20 feet in length by 5 feet 6 inches in width ; there are three compartments for winding, with double-storied cages, i.e., each cage raises two trucks every trip ; two of these are for ordinary work, and the third is worked specially for the