it is said that as a
result of the great fall in the market value of the metal the mines can
now be operated only under the most favourable conditions and by exercise
of extreme economy. In Lake county, for example, very much of the
argentiferous ore that is too low for remunerative extraction (limit 1903
about $12.00 per ton) is used for fluxes.[1] The copper output was of
slight importance until 1889--$1,457,749 in 1905, and $1,544,918 in 1907;
and that of zinc was nil until 1902, when discoveries made it possible to
rework for this metal enormous dumps of waste material about the mines,
and in 1906 the zinc output was valued at $5,304,884. Lead products
declined with silver, but a large output of low ores has continued at
Leadville, and in 1905 the product was valued at $5,111,570, and in 1906
at $5,933,829. Up to 1895 the gold output was below ten million dollars
yearly; from 1898 to 1904 it ran from 21.6 to 28.7 millions. In 1897 the
product first exceeded that of California. In 1907 the value was
$20,826,194. Silver values ran, in the years 1880-1902, from 11.3 to 23.1
million dollars; and the quantities in the same years from 11.6 to 26.3
million ounces. In 1907 it was 11,229,776 oz., valued at $7,411,652.
Regarding again the total combined product of the above five metals, its
growth is shown by these figures for its value in the successive periods
indicated: 1858-1879, $77,380,140; 1879-1888, $220,815,709; 1889-1898,
$322,878,362; 1899-1904, $268,229,112. From 1900 to 1903 Colorado
produced almost exactly a third of the total gold and silver (market
value) product of the entire country.

In addition, iron ores (almost all brown hematite) occur abundantly, and
all material for making steel of excellent quality. But very little iron
is mined, in 1907 only 11,714 long tons, valued at $21,085. Of much more
importance are the manganiferous and the silver manganiferous ores,
which are much the richest of the country. Their product trebled from
1889 to 1903; and in 1907 the output of manganiferous ores amounted to
99,711 tons, valued at $251,207. A small amount is used for
spiegeleisen, and the rest as a flux.

The stratified rocks of the Great Plains, the Parks, and the Plateaus
contain enormous quantities of coal. The coal-bearing rocks are confined
to the Upper Cretaceous, and almost wholly to the Laramie formation. The
main areas are on the two flanks of the Rockies, with two smaller fields
in the Parks. The eas