COMPOSITION. The ores of iron always con tain more or less foreign matter, and only ap proximate the metallic content required by the chemical formula; the discrepancy commonly amounts to 10 per cent. or more. As the costs of handling and treatment per ton of iron are indirectly proportional to the purity of the ores, the higher grades are naturally in most demand. In the United States mining is confined practi eally to the hematite, limonite, and magnetite deposits, which on the average carry from 50 to 60 per cent. of iron, while elsewhere ores may be worked that run as low as 30 per cent. The nature of the impurities is of great importance in determining, the value of ores. The common impurities are those which enter largely into the composition of the rocks surrounding the de posits. They are silica (Si0,). alumina lime (Ca0), magnesia (MgO), water (11,0), and carbon dioxide (COO. Water and carbon dioxide are objectionable only as they replace the iron, while the others exert an influence upon the fluxing properties of the ore and the course of smelting operations. Of greater im portance, however, are the small quantities of phosphorus, sulphur, and titanium, these im purities being almost. wholly obnoxious in their effect. Phosphorus gives a fluid pig iron that can be converted into steel only by employing special methods of treatment. As a large part of the iron produced is now converted into steel by the acid Bessemer process, which does not eliminate phosphorus, ores adapted to this treat ment lied a ready market at, good prices. For such ores the outside limit of phosphorus relative to time iron is that is, an ore carry ing 60 per cent. of iron is not of Bessemer grade unless the phosphorous content falls below 0.06 per cent. In the United States common pi act ice fixes a still lower limit fur phosphorus.
hESOURCES OF' TOE UNI1ED STATES. The rela tive importance of the different iron ores mined in the United States is shown by the following percentages of the total output for 1901: Hema tite, 83.1; limonite, 10.4; magnetite, 6.3; si derite, 0.2 per cent. Hematite thus contributes more than four-fifths of the total production. A large part of this ore comes from the Lake Superior region, whore immense deposits have been found in metamorphosed Pre-Cambrian rocks. Five productive belts, or 'ranges,' as they are commonly called, are known. Tile Nla r (vette range. opened in 1856. is situated in Michigan, east of the Kett cenaw Peninsula. The Menominee Range, first develoix-d in 1877, lies on the border of Wiseonsin and the upper penin sula of Miehigan; it is succeeded farther west ward by the v:ogebie Range, which was opened in 1884. The Vermilion and Mesabi ranges are
situated northwest of Lake Superior, in Minne sota; they were first exploited in 1884. The de posits arc found near the surface, and operations are conducted on a large scale. In some cases the ore is excavated, after removing the over hurden, by steam shovels, which deposit it di reetiy in the ears. A single mine in Minnesota has produced 1.681.000 long tons of are ill a year, or more than the annual output of the en tire country prior to 1854. The total production of the Lake Superior mines up to and including 1901 was 192,008,000 long tons. The hulk of the ore is forwarded by rail to ports on Lakes Su perior and Michigan, and thence shipped by boat to Chicago and Lake Erie ports, a large proportion being destined for the manufacturing centres of western Pennsylvania. A great ship ping industry is engaged in the transport of Lake Superior ores, and it is largely owing to this fact that the tonnage of vessels passing through the Sault Sainte Marie Canal each year exceeds the annual commerce of the Suez Canal.
Hematite ores are also mined in many of the Appalachian and Pocky Mountain States. The Clinton formation of the Silurian, which out crops along the western slopes of the Appalaehi ans from New York to Alabama, contains valu able deposits interstratified with shales and limestones. Some ore is obtained at Clinton, N. Y., and near Chattanooga. Tenn.; but the most productive beds are in the Birmingham district of Alabama.
The limonite or bog ores are widely dis tributed. although. owing to their low iron con tent. they are worked extensively in only a few regions. Virginia, Alabama, Tennessee, and Colorado produce the largest quantities of limon ite. Magnetite occurs in the Adirondneks, the New Jersey Highlands. near Cornwall. Pa., and in many of the Western States. Siderite is asso dated with the coal measures of Ohio and Penn ayl•ania.
The total production of iron ores in the United States in 1901, according to the Mineral Re sources, was 28,887,479 long tons. This output was distributed among the leading States as fol lows: ...N1 innesota, 11,109,537 tons ; _Michigan, 9.654,037 tons; Alabama, 2,801,732 tons; and Pennsylvania, 1,040,684 tons. The imports for the same year were 966,950 tons, more than one half of which came from Cuba.