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valuable minerals of Oregon are: first, the precious metals, gold and silver; and second, copper, lead, iron, coal, marble, and salt. There are also various earths and stones useful for manufacturing purposes, and doubtless minerals of greater value concealed in the almost wholly unexplored mountain ranges, which the further development of the country will bring into notice.

Concerning the formation of the metals, more especially of gold, there are many theories. The age of the rocks associated with gold must serve as an indication of some value in pointing out its origin; the most probable theory of which seems to be, that, at a period when great changes were going on in the shape of the earth, the upheaval of mountains and overflow of volcanoes, certain vapors contained in the earth being forced by heat and pressure into the fissures of rock already hardened. Or even into the substance of rock not yet solidified, became precipitated in the form of gold upon the walls of the cavities which shut them in. Much of this gold was subsequently set free by the action of the water, and is found mixed with sand and gravel, or earthy matter, in old river-beds or valleys between high mountains. Much of it still remains in its original position, and has to be got out of the rock by blasting and crushing.