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Show 16 BASIS OP AMERICAN HISTORY [ 1500 about one- third of the entire coal supply of the world, with an estimated value of $ 367,000,000.* Iron is also of great importance and widely distributed, and in recent years the value of the output in the United States has exceeded that of coal. In 1902 seventy- six per cent, of the ore came from the Lake Superior district, while Alabama followed with ten per cent, of the product. Other metals of which the annual yield in the United States exceeds a value of $ 1,000,000 are, with their approximate values in millions, gold ( 80), copper ( 77), silver ( 29), lead ( 22), zinc ( 14), aluminum ( 2), and quicksilver ( i£). Numerous other metals are produced in smaller quantities. Gold is found in considerable abundance in several of the western states and in Canada, Alaska, and Mexico. Silver is also a metal of wide distribution, and Mexico leads all countries of the world in its production. In the output of copper Montana is in the lead, with the Lake Superior region second. Lead is produced mainly in the West; Kansas leads in the production of zinc; and California is first in quicksilver. Among the non- metallic mineral products are many of great significance and value, such as petroleum, natural gas, clay, borax, gypsum, salt, etc. Nearly all the mineral materials needed in the industrial life of the United States are found within its borders and in sufficient quantities. Those 1 See for these and following figures, U. S. Geol. Survey, Report on Mineral Resources of U. S. for 1903. |