The Mining Industry 
115 
great furnaces to separate the pure metal or other mineral from the 
slag or waste material. . Often the slag rises to the top like froth, 
while the heavier liquid metal can be drained off below. Sometimes 
this work of smelting, as the melting is called, is done in mills near 
the head of the shaft; but usually it is cheaper to do it where there 
is an abundance of coal, and hence the ore is often carried great dis- 
tances from the mine. This is done with the Lake Superior iron 
ores, which are smelted in Pittsburgh, Cleveland, and elsewhere. 
Why some mines are open pits. Some deposits of minerals are so 
near the surface and cover areas so large that it is easier to reach 
them by removing all the overlying soil and rock than by digging 
shafts and tunnels. This is called the * open pit’ method of mining. 
The Mesaba range of Minnesota, near Lake Superior, containing the 
greatest iron deposit yet known, is mined by the open pit method. 
One can stand on the edge of one of the great pits and watch a train 
of empty ore cars take its way along the sides, down into the pit, 
and draw up beside a great steam shovel. The iron ore is here so 
easily pulverized that mild blasts with dynamite serve to loosen 
great quantities, and therefore it is readily handled by the steam 
shovel. 
IRON 
Iron, the most useful of metals, exists in great abundance. At 
present only the richest deposits are mined. That is why the iron- 
producing regions are not numerous. Iron can be procured so 
cheaply from the rich deposits that it does not pay to work the 
poorer ones. 
The consumption of iron. The time will come, however, when 
man will eagerly turn to the deposits he now passes by. In 1820, 
the iron goods made in the United States averaged only forty pounds 
for each individual. The amount rose to 175 pounds in 1870, to 400 
pounds in 1900, and is now about 700 pounds. During the World War 
the demand increased still further. It is fortunate that iron, unlike 
coal, can be used again and again. After iron has served its purpose 
in one form, as in a kitchen stove, it is collected as scrap iron and may 
be made into something else, like steel rails or nails. Hence, the iron 
deposits of the world will probably not be exhausted for thousands of 
years, whereas the coal deposits are likely to become seriously depleted 
within a few centuries. 
Where iron is mined in the United States. Each year nearly seventy 
million tons of iron ore are mined in the United States. This is about