eptionally rich and solid masses, showing no evidence of having
replaced earlier sulphides. It is regarded as a product of primary
deposition, under the influence of hot solutions related in some way to
the igneous flows; but whether the solutions were magmatic, originating
in the lavas or below, or whether they were meteoric waters rendered hot
by contact with the extrusives, and thereby made effective in leaching
copper from them, is not clear. The oxidation of the Kennecott copper
ores is not extensive. It presents an interesting feature, in that since
glacial time the ground has been frozen and the moisture is now present
in the form of ice. The oxidation clearly took place before glacial
time. Abundant fragments of both the oxide and the sulphide ores are
mined from the lateral moraine of a nearby glacier. This is a good
illustration of the cyclic nature of secondary concentration which is
coming to be recognized in so many camps.

The Boleo copper deposits of Lower California occur in volcanic tuffs
and associated conglomerates of Tertiary age. They have certain peculiar
mineralogic associations--the ores containing large quantities of all
the common copper oxide minerals, and a number of rare oxide minerals of
copper, lead, silver, and cobalt, together with gypsum, sulphur, and
much iron and manganese oxide. The copper oxides and carbonates are in
places gathered into rounded concretions called "boleos" (balls).
Sulphides are present in the lowest beds and may represent the form in
which the copper was originally deposited. The copper-bearing beds have
been much silicified, and it has been suggested that mineralization was
accomplished by hot-spring waters, probably of igneous origin. These
deposits have a few marked similarities to the Lake Superior copper
ores.

=Copper veins in igneous rocks.= A second group of copper ores in
igneous rocks is made up of deposits in distinct fissure veins and as
replacements along such veins. The chief deposits of this type are at
Butte, Montana--which is, from the standpoint of both past and present
production, the greatest single copper district in the world. Here a
large batholith of Tertiary granite was intruded by porphyry dikes; and
faulting, accompanying and following the intrusions of the dikes,
developed numerous fissures. The fissures were mineralized with copper
sulphides and arsenides, iron sulphides, and locally with zinc sulphide
and manganese carbonate,--all in