Copper.— Copper ores are found in Michi gan and most of the western States with Ari zona, Montana, Utah, Nevada and New Mexico as especially prominent producers. Michigan came into prominence about 1840; its ores carry native copper and are found on Keweenaw Peninsula that projects into Lake Superior. The western deposits began to attract attention in the last quarter of the 19th century and have lately come under intensive development that has caused the production to double in a few years.
The total output in 1918 was 1,908,533,595 pounds.
Lead and The principal lead deposits are in Missouri, Idaho, Utah and Colorado. The output is now above 500,000 tons a year. Zinc ores are extensively mined in Missouri, New Jersey, Montana, Colorado and Idaho and the product of metallic zinc is about the same as that of lead.
Salt.— Rock salt is mined in New York, Michigan, Kansas and Louisiana, while natural brines are utilized for salt manufacture in many States. The total yield of salt in 1918 was 7,238,744 short tons, valued at $26,940,361. Much of the product is utilized for chemical purposes, particularly for making other sodium salts like the carbonate and bicarbonate, salt cake (sodium sulphate) and caustic soda.
Quarry Stone for building and engineering works is extensively quarried in nearly all States. New England supplies the larger part of the granite for building and mon umental purposes from quarries situated in Vermont, Maine, Massachusetts, New Hamp shire and Connecticut. New York and Wiscon
sin have granites suitable for almost all uses. Marbles are quarried in many of the Appala chian States, notably Vermont, Tennessee and Georgia, and sandstone and limestone over much of the country. Limestone serves a vari ety of uses besides for constructional work, it being employed as flux in metallurgical opera tions, as a chemical reagent and for Portland cement manufacture, an industry that has made rapid progress in the last two decades.
Clay The manufacture of clay wares and building materials constitutes one of the more important and widely represented branches of the mineral industry, the total value of the output in 1917 amounting to $248,023,364. Practically every kind of pottery is now made, although the demand for porcelains and art wares is scarcely met by the domestic products and considerable quantities are im ported. The ceramic industry is chiefly cen tred in New Jersey and Ohio, but the white clays used in the best wares come from the South. Clay building materials are made in most of the States, with New Jersey, New York, Pennsylvania, Ohio and Illinois as the larger producers.