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272 the republic became settled by the accession of President Diaz to power, the mining industry immediately began to revive, and to-day its output of the white metal exceeds that of any other nation.

Previous to 1859, when silver was first discovered in the United States (in Nevada), silver mining was not an organized industry in any sense of the word, but an occupation dependent largely for success upon the accidental discovery of bonanzas of very rich ore, and the ability to secure labor upon a basis of practical slavery. The Mexican and South American mines were worked by natives who were clothed, fed and sheltered merely to a sufficient extent to keep them alive during the prime of their physical powers. Only one step on the road of progress had been taken in the metallurgy of the metal, namely, the invention of what is known as the "patio process," which depended for its success largely on the element of unlimited time for its operation, coupled with nearly costless animal power. But when it became evident that the Comstock Lode in Nevada contained vast quantities of silver, the natural ingenuity and aptitude of the American transformed mining into a commercial industry, and the metal began to pour in such torrents into the money centers of the world that financiers became alarmed, and between 1870 and 1873 full coinage rights were finally denied by the principal nations. Meantime, a remarkable industry had come into existence in the mountain regions of our west. Thousands of silver mines had been discovered, scores of processes invented and put into practise for the treatment of their ores, and a vast number of metalliferous deposits developed that have since been yielding copper, lead, zinc, iron and manganese in addition to the white metal.

Silver occurs in veins or deposits in the rocky crust of the earth, and is never found in the gravel of stream beds as is gold. In a small number of cases the gangue, or material with which the metal is associated, is quartz alone, but generally one or more of the base metals is present, predominating vastly in quantity, and often in value. This is especially true after a little depth is gained on the veins, so that in due time mines that were opened as straight silver deposits became rather deposits of the other metals, the silver being practically a by-product. A good example of this change is to be found in the lodes of Butte, Montana. The veins at Parral, Pachuca and Guanajuato in Mexico are samples of straight silver mines, yet all of them are showing more or less associated iron or copper as depth is gained. On the other hand, wherever lead is found, silver is always present in some quantity, and, at the Comstock as well as at the Mexican districts just mentioned, there is invariably a proportion of gold. In the Comstock bullion it amounted to 40 per cent, of the total values. Thus the metallurgy of silver ores is not a simple matter, and in the days between 1860 and