Missouri, but it was not until a century later that operations assumed much importance. About 1825 mining began in the region which includes the adjacent corners of the three States of Wisconsin, Illinois, and Iowa, and later in southwestern Missouri and the adjacent corner of Kansas. For a number of years the mining of lead was, after iron, the most important metal-mining industry in the United States. It was mined in Utah in 1858. About 1875 work began on the Leadville Mine, Colorado. The Leadville ores are argentiferous, and the silver obtained in the early days of mining was of greater value than the lead itself. A little later argentiferous lead mines were developed in Idaho (Cœur d'Alêne) and other Cordilleran States. The total product of the country increased from 8000 short tons in 1830 to 30,000 in 1845, then decreased to 14,700 in 1865, since which time it increased almost steadily to 97,825 short tons in 1880, 178,554 in 1891, and 270,700 short tons in 1901, valued in the latter year at $23,280,200. Of the total only 57,898 short tons were soft lead, the remainder being desilverized lead. Idaho, Colorado, and Utah in the order named led in importance, the Mississippi Valley mines producing the greater part of the rest.
Zinc. Zinc-mining in the United States is limited chiefly to the lead-mining region of the Mississippi Valley above described. Its development began about 1850. Northern New Jersey at one time yielded considerable quantities of spelter, but its output has declined in recent years. The total product of zinc increased from 7343 short tons in 1873 to 63,683 in 1890 and 140,822 in 1901, giving the United States second rank among the countries of the world. The principal contributing States were Kansas, 74,240 short tons; Illinois, 44,896; Missouri, 13,083; and all other States, 8603. The value of the product was $11,265,760.
Clay. The various kinds of clay suitable for brick, tile, pottery, and other purposes are widely distributed and largely exploited. The total value of the different products made in 1901 was $110,211,587. Ohio is the largest producer, followed by Pennsylvania, New Jersey, Illinois, and New York, in the order mentioned.
Quicksilver. The mining of quicksilver began about 1845 in California, and its production has been confined almost wholly to that State. The output in 1900 was 29,727 flasks (76½ pounds per flask), valued at $1,382,305. The United States rivals Spain for first rank.
Aluminum. The production of aluminum began in 1883, and developed rapidly, the product in 1901 amounting to 7,150,000 pounds, valued at $1,920,000, this being over one-half of the total product of the world.
Stone. Stone suitable for building and other industrial purposes is abundant in almost every State. Because of its bulk and the consequent shipping expenses, its production is largely limited to a comparatively local market. Hence in many of the States which have the most valuable resources of stone the quarrying industry has scarcely more than begun. The utilization of stone varies with the economic condition of the country, the total value having fallen from $53,035,620 in 1889 to $31,346,171 in 1896, and advanced steadily to $55,615,926 in 1901. Limestone is in most common use, only a few States failing to report its production in the latter year, when its aggregate value was $21,747,061. This figure does not include limestone to the value of $4,659,836 used for flux. About $8,204,054 worth of limestone was burned into lime, the bulk of the remainder being used for building purposes, or crushed for road-making. Indiana leads in the quarrying of limestone for building purposes. Granite is second in importance, the value of the product in 1900 being $14,266,104. While its production is also widely distributed. New England yields the largest quantities. Maine leads in its production for building purposes, and Vermont in its production for monumental purposes. The value of sandstone in 1901 was $8,844,974, including bluestone, grindstones, and whetstones. Pennsylvania, Ohio, and New York are the largest producers of these varieties. New York and Vermont produce most of the slate and Vermont and Georgia the bulk of the marble, the value of these two products in 1901 being respectively $4,787,525 and $4,965,699. The value of trap-rock was $1,710,857, about one-half of which was contributed by New Jersey.
Salt. Salt is somewhat broadly distributed as between the East and the West. In 1901 the United States produced 20,566,661 barrels, valued at $6,617,449. Michigan leads and New York follows closely. Kansas is third and Ohio fourth in rank. Nearly 90 per cent. of the total domestic product in 1901 came from these four States. California, Louisiana, and Utah are important producers. The deposits are of various ages. Thus the deposits of New York are of Silurian age, being interstratified with the sedimentary rocks of that time. The salt of Kansas and Louisiana is of Mesozoic or Tertiary age, and that of the Great Salt Lake region is recent.
Cement. The production of Portland cement has a very recent development in the United States. From 335,500 barrels in 1890 the output increased steadily to 12,711,225 barrels in 1901, valued at $12,532,360. Of the total, 67.7 per cent. was reported from Lehigh and Northampton counties, Pa., and Warren County, N. J. The output of natural hydraulic cement in 1901 amounted to 7,084,823 barrels, valued at $3,056,278.
Gypsum. The production of gypsum increased from 256,259 short tons in 1892 to 659,659 short tons in 1901, valued in the latter year at $1,577,493. Michigan is the largest producer, followed by Kansas, Iowa, New York, and Ohio.
Phosphate Rock. The United States is the world's largest producer of phosphate rock. The production of this mineral began in South Carolina in 1867, and reached a maximum output there of 541,645 long tons in 1889, having decreased to 321,181 long tons in 1901. Its production in Florida began in 1888, and has increased almost steadily to 751,996 long tons in 1901. Tennessee, the only other State producing large quantities, began to yield in 1894, and in 1901 it produced 409,653 long tons. The total value in 1901 for all the States was $5,316,403.
Mineral Waters. Almost every State has mineral-water springs from which water is sold annually. The production of the United States increased from 2,000,000 gallons in 1880 to 18,392,732 in 1891, and 55,771,188 gallons in 1901, valued in the last year at $7,586,962. New York,
