298 Packard—Occurrence of Copper in Western Idaho. 
Art. XXXI.—On an Occurrence of Copper in Western 
Idaho; by R. L. Packarp. 
THE Seven Devils is the name (of rough frontier origin) 
given to a range or group of mountains on the extreme western 
border of Idaho where that state is separated from Oregon by 
the Snake River on its northerly course to empty into the 
Columbia. The river runs through a deep gorge as it passes 
the. mountains, the east side of which is formed by members 
of the Seven Devils group, while the western side or wall, 
which is very precipitous, is formed by a range on the Oregon 
side called the Eagle Mountains. The few sharply pointed, 
precipitous peaks which are the Seven Devils proper and have 
given their name to the whole group have an altitude of over 
seven thousand feet. They are of igneous origin and attracted 
the attention of prospectors many years ago, who found gold 
in the streams issuing from their domain and copper in the 
mountains adjoining them. 
The only occurrence of copper of importance which has so 
far been exploited is found in the southern part of the range 
and is confined to the neighborhood of a body of whitish 
granitic rock of very considerable but not yet determined 
extent. The copper occurs as bornite and the principal mine 
of the locality is named the Peacock, from the nature of the 
ore. ‘The igneous rock, which evidently has a genetic relation 
to the copper deposits, has the general appearance of a granite 
and has always been so called. It is grayish white in color, 
and in hand specimens does resemble a biotite granite without 
muscovite. It weathers into rounded blocks which are some- 
times met with in isolated groups, and at one point on the 
wagon road leading up from the Snake River to the copper 
mines, and about a mile from the latter, the head of a small 
ravine is filled with bowlders of this rock several feet in 
diameter which give the appearance of having been purposely 
rolled into the place. Water runs down among these rocks at 
some distance out of sight. . | 
The whitish rock, where exposed, and in the bowlders, is 
seen to contain areas of a darker color which vary in size from 
two or three inches to as many feet in diameter and impress 
one at first as being inclusions of some other rock. 
This igneous rock, one would say, was evidently the cause, 
if not the source, of the copper deposits found on its contact 
aud in veins in its substance, and it became a matter of curi- 
osity to examine its mineralogical and chemical character. 
Specimens were, accordingly, procured from points about a 
