Page:Popular Science Monthly Volume 22.djvu/525

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brought to bear for obtaining it. Volcanic forces have brought gold as well as silver to the surface in the Rocky Mountains, but its exhaustion is approaching rapidly. Montana, in 1860, produced $18,000,000, while to-day its yield is $2,500,000; Idaho, from 1864 to 1871, yielded from $5,000,000 to $7,000,000, which in the year 1880 has decreased to $1,510,546; Oregon and Washington yielded, in the year 1868, $4,000,000; in 1879, not more than $1,275,000; Dakota has increased a little, and produced $2,420,000 in 1879; Colorado has an average yield of $3,000,000; California has passed through the several stages of a gold-producing country; the washing of the river-sands, after 1848, produced immense wealth, while at present only the Chinese are engaged in it, and earn a bare living. The gold on the surface is exhausted, and only the deep deposits and the veins remain to be worked.

It has been estimated that $1,200,000,000 of gold and silver have been mined in the West of the United States within the last thirty years; and that, in spite of the recklessness and extravagance which characterized the two decades from 1849 to 1869, a net profit of $30,000,000 per year was realized. Since 1850, the money invested and the labor expended in mining in the West for precious metals are estimated at $710,000,000. What may fairly be called the mining territory of the United States embraces an area of 1,190,000 square miles, with a population of barely 1,500,000.

The entire ridge of the Sierra Nevada consists of granite; but on the western slope limestone is found mixed with it. Where these two rocks come together, a belt from eight to nine miles wide, and running from north to south, is found, which contains all the gold leads of the district. The "Mother lode" commences at Mariposa, passes through the northern boundary of the State, and is covered by the lava of the large (not yet extinguished) volcanoes Pilot Peak and Lossan Peak farther north. This lava also covers an old alluvial bottom with overlying layers of basalt from fifty to two hundred feet thick, and these form the so-called "Table Mountains." We find the same formation south of the Sierra Nevada, near the "Big Trees," where the sedimentary deposits, lying upon granite, are covered with basalt. From here the auriferous sand was washed away by mountain-streams, and appeared on the surface. These deep deposits, in connection with the offshoots of the Mother lode, still sustain the gold production of California at from fifteen to seventeen million dollars.

In Nevada was discovered the Comstock lode, for a long time held to be inexhaustible, and this is also covered with later volcanic formation. The largest of these bonanzas is the Gold Hill mine, which lies 700 feet deep, and several companies have commenced to work this rich vein. The most important, the Virginia Consolidated, has sunk a shaft 1,600 feet deep, and driven a tunnel of 20,000 feet in length through the side of the mountain, projected by Engineer Sutro,