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 NEVADA 265 forms in spring, which is gathered. Salt val- ley, 30 m. E. of Humboldt lake, is remarkable for its immense salt bed. In Lincoln co., in the S. E. part of the state, W. of the Rio Vir- gen, are the " salt bluffs," 500 ft. above the level of the valley, consisting of a mass of pure rock salt, nearly 2 m. long and 1 m. wide, of unknown depth, covered with a coating of sand and earth from a foot to several feet thick. The waters of the Eagle salt marsh, in Churchill co., 3 m. from Hot Springs on the Central Pacific railroad, contain 30 per cent, of salt, which is obtained by evaporation. There is also a salt marsh in Eureka co., 43 m. N. of the town of that name, where salt is made by evaporation. Borax is also an important product of the state. It is manufactured in Churchill co. near Hot Springs, and E. of the sink of the Carson, from boracic acid and the borates of lime and soda, which occur in the alkali flats. The richest and most exten- sive deposits of the salts of borax (containing 31 per cent, of that substance) are found near Columbus, in Esmeralda co., and large quanti- ties are here manufactured. The borates of lime and soda occur between two layers of salt, the lower one of which is itself underlaid by a bed of sulphate of soda (Glauber's salt). Soda is obtained from a small lake 25 m. from Wadsworth, on the Central Pacific railroad, in the central part of the state, forming on the shore in a nearly pure state as fast as removed. The general geological character of Nevada is volcanic. The mountain ranges are com- posed, first, of crumpled and uplifted strata, from the late Jurassic down to the azoic pe- riod; secondly, of ancient eruptive rocks, which accompany the Jurassic upheaval ; and thirdly, of modern eruptive rocks belonging to the volcanic family, and ranging in date prob- ably from as early as the late miocene up to the glacial period. The valleys are filled with quaternary detritus, the result of erosion from the early cretaceous period down to the pres- ent time. Syenite, granite, porphyry, slate, and quartzite prevail in some of the moun- tain ranges, while many of them are of lime- stone, mingled with calcareous spar ; this either rests upon or alternates with hard and compact grits and quartzite. In many of the cafions are found bowlders of serpentine, conglom- erate, talcose slate, fine gray granite, coarse red, crystalline white, and metamorphic sand- stone, gypsum, pebbles of alabaster, and vari- ous kinds of limestone. Marble of different textures is found in various localities. The volcanic action is indicated by the presence of lava, obsidian, scoria, and sulphur. In the mountains of the Colorado basin limestone predominates, besides which are found granite, syenite, serpentine, arenaceous and chloritic slates, all scored and marked by dikes and overflows of trachytic lavas and basaltic trap rock. Where granite and gneiss (which are the prevailing rock formations of the Sierra Nevada) occur here, they are for the most part hidden by porphyries, greenstone, amygdaloid, basalt, obsidian, and other rocks of igneous origin. Traces of coal of different varieties, but generally of inferior quality, have been found in various localities, but it has not been successfully mined, and is not known to exist in valuable quantities. Seams of coal of su- perior quality have recently been discovered in the Pancake mountains in White Pine co., 15 m. from Hamilton, but to what extent they can be made available is yet undetermined. Kaolin and other clays, useful in the manufac- ture of pottery and fire brick, mineral pig- ments, nitre, and alum are found. Copper oc- curs in Churchill co., E. of the lower Carson sink ; in Battle Mountain and Bolivia districts, Humboldt co., where several mines are in ope- ration ; and between the forks of Walker river. Rich lead and copper ores exist in Washoe co., and copper and iron are found in Robinson district, White Pine co., 45 m. E. of Hamilton. Veins of antimony are worked in Battle Moun- tain district. These metals, which are also found in other parts of the state, and cinna- bar, manganese, plumbago, magnesia, plati- num, zinc, tin, nickel, cobalt, and arsenic, gen- erally occur in connection with the precious metals. Gold and silver are commonly found associated with each other, gold predominating in the Antelope district, Churchill co. ; in Tus- carora district, on the head waters of the Owyhee river ; in Gold Mountain district, Es- meralda co. ; in Sacramento district, and in some of the mines of Sierra district, Humboldt co. ; and in some other places. But the great wealth of Nevada is in its silver mines, which exist in nearly every section. The richest deposit of silver in the state, if not in the world, is the Comstock lode, on the E. side of Mt. Davidson, in Storey co., and partly under the towns of Virginia and Gold Hill. Its ores contain about one third in value of gold and two thirds of silver. The lode has been traced on the surface 27,000 ft., and has been actually explored for 19,000 ft., within which space the principal mines are situated. It has been opened to a depth of 2,000 ft. New deposits were discovered toward the close of 1874, which are believed to be of incalculable value. A tunnel, known as the Sutro tunnel, is in progress, designed to drain the mines and oth- erwise facilitate operations on the lode. ^ It commences at a point 1^ m. from Carson river and 3 m. below Dayton, and runs N. W. to the Savage mine, a distance of 20,178 ft., where its depth will be 1,922 ft. At the close of 1874 it had reached a distance of 8,250 ft., and was pro- gressing at the rate of 7 ft. a day. Next to those of the Comstock lode, the most produc- tive silver mines are in the region near Eureka, in the E. central portion of the state, and in the Ely district, near Pioche, Lincoln co., in the S. E. The White Pine region in the E. part of the state, which after the discovery of the mines in 1868 was the scene of great excitement, now yields comparatively small