The New International Encyclopædia/Comstock Lode

COMSTOCK LODE. A remarkable compound fissure vein, rich in gold and silver, located in Storey County, Nev., on the eastern slope of Mount Davidson, a northeastern spur of the Sierras, at a point about 20 miles east of the California State line. Its discovery in 1859, when it received the name Washoe, created great excitement and led to the building up of Virginia City. The vein is about four miles in length, and varies in width from zero at the ends to 3000 feet at the middle point. It occupies a zone of displacement in igneous rocks, chiefly andesites of Tertiary age. The ore, which is of high grade, containing both silver and gold in proportion of three of the former to two of the latter, occurs in great pockets known as bonanzas, chiefly along the eastern portion of the vein. The excavations along this fissure vein have been carried to great depths, approximating 3500 feet, until operations became difficult through the inflow of hot water with a temperature of 170° F. The Sutro Tunnel, with a length of four miles, was driven with a view to draining this water, but with only partial success. The richness of the ore of this lode may be realized from the value of the product, the total value during the years 1860-90 having been $340,000,000; the greatest output for a single year was $38,000,000 in 1877. Since 1890 the production has declined.

Besides its economic value, the Comstock Lode is of great interest in other directions. One of the earliest classifications of igneous rocks (q.v.) was attempted in connection with the study of the geologic relations of the ore bodies by Von Richthofen in 1868; and Van Hise, Iddings, and Becker have at a later period perfected the modern classification of igneous rocks with aid of considerable information derived from the Comstock Lode and Sutro Tunnel. Also many important observations have been made on the relation between the size of grain and the rate of cooling, and upon the rate of development of crystallization in igneous rocks. Again, experiments have here been carried on by Carl Barus with the object of determining the temperature variations and electric manifestations in the deeper workings. For more precise information on the geologic features and methods of mining of the Comstock Lode, the reader is referred to the two following works: Becker, "Geology of the Comstock Lode and Washoe District," with folio atlas; being Monograph of the United States Geological Survey, vol. iii. (Washington, 1882); Lord, “Comstock Mining and Miners,” Monograph of the United States Geological Survey, vol. iv. (Washington, 1883).