latively minor effects. An
illustration of the general effect is afforded by a comparison of the
Cuban iron ores, which are soft and can be easily taken out, with the
Cle Elum iron ores of Washington, which seem to be of much the same
origin, but which have subsequently been buried by other rocks and
rendered hard and crystalline. In the first case the ores can be mined
easily and cheaply with steam shovels at the surface. In the second,
underground methods of mining are required, which cost too much for the
grade of ore recovered.

On the other hand, the same general kind of anamorphic processes, when
applied to coal, result in concentration and improvement of grade. The
same is true up to a certain point in the concentration of oil; but
where the process goes too far, the oil may be lost (pp. 140-141).

CONCLUSION

Mineral deposits are formed and modified by practically all known
geologic processes, but looked at broadly the main values are produced
in three principal ways:

(1) As after effects of igneous intrusion, through the agency of aqueous
and gaseous solutions given off from the cooling magma.

(2) Through the sorting processes of sedimentation,--the same processes
which form sandstone, shale, and limestone. Organic agencies are
important factors in these processes.

(3) Through weathering of the rock surface in place, which may develop
values either by dissolving out the valuable minerals and redepositing
them in concentrated form, or by dissolving out the non-valuable
minerals and leaving the valuable minerals concentrated in place. The
latter process is by far the more important.

The overwhelming preponderance of values of mineral deposits as a whole
is found in the second of the classes named.

Under all these conditions it appears that the maximum results are
obtained at and near the surface. On the scale of the earth even the
so-called deep veins may be regarded as deposits from solutions reaching
the more open and cooler outer portions of the earth. However, valuable
mineral deposits are found in the deepest rocks which have been exposed
by erosion, and the question of what would be found at still greater
depths, closer to the center of the earth, is a matter of pure
speculation.

Ultimately all minerals are derived from igneous sources within the
earth. The direct contributions from these sources are only in small
part of sufficient concentration to be of value; for the most part they
ne