economically valuable coal beds. Under these circumstances it can hardly expect to have the net work of railroads whose permanence is dependent upon a local population, and which do so much to reduce the cost of working ores in more favored regions; and for mining as an industry to nourish in such a region it is requisite that it should have either exceptionally rich ores ov remarkably large concentrations of ore in a limited district. Under such conditions even, the industry is necessarily liable to frequent fluctuations in its product, and such, as statistics show, has been the case with Nevada.
Placer deposits like those found in California, are necessarily wanting in Nevada owing to the absence of large running streams. Its surface is a series of broad valleys separated by narrow and isolated mountain ranges. These valleys have considerable accumulations of detrital material, which is spread out in long gentle slopes from the foothills of the mountains to the middle of the respective valleys. This material is the result of subaerial erosion, and, though metallic minerals are undoubtedly disseminated through the gravel, it would hardly be expected that they would be found to any great extent concentrated into workable deposits. Even if they were so concentrated, it is only under exceptional conditions, as for instance in the southeastern part of the State, that a sufficient supply of mining water could be obtained to work them.
Its mountains are made up of sedimentary rocks ranging in age from the J urassic back to Cambrian, and of a great abundance and variety of crystalline and eruptive rocks, whose geological conditions have been extremely favorable to the concentration of the precious metals into ore deposits. The greater part of the ores thus far developed have been, especially in the western part of the State, high grade silver minerals, relatively rich in gold, the amount of base metals associated with them seeming to be in larger proportion in the eastern part of the State.
As its development proceeded from west to east, and ores were naturally developed in proportion to their adaptability to amalgamation processes which were first perfected in the West, rather than to smelting, which alone is capable of treating profitably complicated base metal ores, the actual developments may represent rather the result of these conditions than of the relative proportions in which the metals exist in the rocks. Both classes of ore contain a relativelylarge proportion of gold, while of gold ores proper, that is, those which contain no appreciable values in other metals, the amount discovered has been very limited, and, so far as known, confined to the western borders of the State.
The production of the Comstock lode, which is a fault fissure in eruptive rocks, that has been worked on a length of nearly four miles and to a depth of 3,000 feet, has hitherto overshadowed that of all other mines in the State, having reached in 1892 a total of 8350,000,-
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