Ch. 1: Gold, Silver, Platinum in 1892

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	PRECIOUS METAL INDUSTRY IN THE UNITED STATES.	69

	The silver product of the three regions above named forms over 91 per cent, of the total product of the State, which therefore they practically regulate. In gold their proportion is smaller, being from 63 to 85 per cent, of the whole. Some of the balance is placer gold, but how much it is impossible to determine. There are many extensive and valuable placer deposits in Colorado, but relatively little attention 1ms been given to them. In 1880 their product was only 3.77 per cent, of the gold product of the State. While they are relatively less important than those of Montana or California, their product can doubtless be very considerably increased, with a profit to the owners. In considering the product of the entire State as given in the table below it will be seen that there has been an increase in the product of each of the precious metals during the decade, and that the rate of increase has been much higher since its close. For silver there was a decrease about the middle of the decade, due to the falling off in the Leadville product. This was replaced during the latter part of the decade by the rapid increase in Aspen's production, to which has been added since its close that of the new district of Creede, in either case, although primarily resulting from the discovery of large bodies of very rich ore, yet largely dependent upon the advent of railroads. The increase in the gold x>roduct in the last years is doubtless largely due to the product of the new Cripple Greet district, which the railroad has not yet reached. While the present decade may, therefore, see a considerable decrease in the silver product of the State, it is likely to be in a measure offset by an increase in its gold product. Production of gold and silver in Colorado since 1880.



	DAKOTA. The precious metal product of South Dakota is entirely derived from the isolated mountain group on its.western boundary, known as the Black Hills. This group, which is in the form of an ellipse about 100 by 50 miles in dimensions, is a most interesting and typical example of the structure known in geology as a quaquaversa! uplift, or one in which the strata dip away in every direction from a central nucleus. The central nucleus in this case consists of metamorphic slates,and granites of Huronian age. The sedimentary strata, which rest upon and wrap around its edges like the leaves of an onion, are successively Cambrian sandstones, Carboniferous limestones, and a series of sandstones and shales of

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