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Ch. 1: Gold, Silver, Platinum in 1892

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PRECIOUS METAL INDUSTRY IN THE UNITED STATES.         71
of whose value is in silver. Besides the base metal mines which contain silver as well as gold, argentiferous galena ores are also found in the Potsdam sandstone, but the main silver product has been derived from contact deposits in the Carboniferous limestones in association with eruptive rocks, and it is to variations in the productiveness of these mines probably that the fluctuating character of the silver product as a whole is mainly due.
The gold product, which showed a steady decrease during the first part of the decade, increased as steadily during the latter part and had already reached its former level. Whether it continues this increase as a whole is mainly dependent on the gold belt mines, but a fair increase in the product of outside mines may be looked for. The product of silver will probably continue to be small and uncertain.
IDAHO.
The State of Idaho in different portions partakes of the physical and geological'characteristics of adjoining States. North of the great lava flows of the Snake Plains it is a mountainous region with high, well-watered valleys, similar physically and geologically to the adjoining region of western Montana. South and southwest of the Snake River valley it incloses part of the great basin region of Utah and Nevada.
In the larger valleys of the northern portion are considerable accumulations of gold-bearing gravels, many of which are so situated that they could not have been deposited by present streams, and bear considerable resemblance to the older placer deposits of California. The immediate valley of the Snake river also contains gravel bars rich in placer gold brought down from its headwaters in the Rocky mountains. It is, however, in so flue a state of division that great difficulty is found in saving it by the ordinary processes. The mountains of the northern portion contain both silver-lead and gold ores, which occur both in granites and sedimentary rocks of Paleozoic age. The former class of ores has received the most attention on account of the demand by large smelters for ore of this character, which it has consequently been possible to mine at a profit in spite of the fall in the price of silver. The most important new development during the decade has
Ch. 1: Gold, Silver, Platinum in 1892 Page of 76 Ch. 1: Gold, Silver, Platinum in 1892
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US Geol. Surv. 1892. Gemstones, Metals.
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