File:The world's opportunities and how to use them (1887) (14775257604).jpg

Identifier: worldsopportunit00guer (find matches)
Title: The world's opportunities and how to use them
Year: 1887 (1880s)
Authors: Guernsey, Alfred H. (Alfred Hudson), 1824-1902
Subjects: Industries
Publisher: New York, Harper & brothers
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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ial action as that by which tides and waves and currentsare now wasting away the rocks: pounding and crushing, andgrinding them into bowlders and pebbles, gravel and sand,clay and mud. The various substances, thus more or less dis-integrated, were carried along by the currents, and graduallydeposited, the larger and heavier portions first reaching thebottom. If these currents acted upon gold-bearing rocks, theparticles of the precious metal, being some seven times heavierthan the rest, were deposited sooner than fragments of quartzof similar size. But large pieces of rock and small piecesof gold would at first be deposited together. The continuedagitation by the currents would in the course of time causethe heavier metal to sink through the mass of bowlders, peb-bles, and sand, until they at last rested upon a bottom of rockor clay, impervious to water, and they could sink no farther.Below this rock or clay bed no gold is found. But very frequently the ancient beds of streams have be-
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THE PRECIOUS AXD NON - PRECIOUS METALS. come dried up, or the streams have found new channels; andplacer mines are often found in these dried-up beds, at a heightmuch above the present level of the surrounding country.Placer mining consists in a great part in directing a stream ofwater through or against these ancient river-beds, washing awaythe pebbles, sand, and mud, and collecting the gold by thevarious processes of washing, amalgamating, etc.; all involvingconsiderable outlay for furnishing the necessary water, and forother purposes. Practically, placer-mining is now carried onby a few large corporations, who have the means for conductingextensive and costly operations. Nearly two-thirds of the gold, and all but an inconsiderablefraction of the silver, of the United States are produced byudeep or vein mining. Here, man has to do that whichNature has done for him in placer-mining. He has to get thegold out of narrower veins diffused through the solid rock,which has not been broken

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