The Anaconda standard. [volume] (Anaconda, Mont.) 1889-1970, 1898-07-14

L ABOUT II Ht WnOic tiaIks hh'N"
wide and 20 miles long. is underlain
by granite. in which are carved noun
tains. gorges and valleys. The gran
ite is traversed by varying, well de-
fined systems of joint planes, is extern
sively decomposed in some localities.
N weathers into rugged crags anu
monoliths and great boulder masses.
which form the picturesque scenery so
frequently typical OF granite areas.
Surrounding the granite area brok-
en- and holder ~sedimentary rocks form
higher peaks and ranges. These up-
turned s~edimentary beds, many thou
/ sand feet in thickness. are OF interest,"
in this connection only OF the
| evidences they present of the age n
| nature of the granite rocks. They
| consist of limestone, sandstone. shale
and slate. They contain fossils ana
| comprise strata of various ages from
| Oldest algonquin to late cretaceous. The
| contact between these rocks and the
granite shows unmistakable evidences
| of the eruptive nature of the granite.
The stratified rocks exhibit striking
effects of alteration at and near the
| contact. dark and dense limestone be-
ing altered to white, coarsely crystal
line marble. contact mineral, such as
garnet and epidote. occurring in album
dance, and otherwise soft shales being
1 Ddhtu W laiot ~
facts indicate that the granite. while
a molten rock, broke up through sedi-
mentary beds. The coarseness ana
| eveness of the granite mass as a whole
and it's undoubteds Unity show that the
| liquid rock cooled under a cover. 49,
THAT this great granite mass is not
archean but n more recent intrusion
of igneous rock is conclusively proved
by the exposure at several localities
Along the contact with the sedimentary
rocks. OF the rocks actually cut and
altered by the granite h youngest %
those containing recognizable fossils
are carboniferous but folded coal
bearing rocks of Laramie (~cretaceousD
| age occur near Anaconda. and the
| general mountain folding of the ad-
| jacent s~edimentary formations Is
| known to a occurred after the Lar
annie epoch. The GRANTEES are there
| fore younger than the carboniferous
rocks and are possibly of post-Laramie
date.
"A large part of the granite tract is
now covered by later volcanic rocks,
which have been cut through in the
canyons of the region. A LONG period
of erosion, however, must have inter-
vened between the time of the granite
intrusions and these later volcanic out
bursts, for the rocks above the gran
lite We're entirely removed and the
country was carved into a roughly hilly
surface before the succeeding period OF
volcanic activity began"
In regard to the rocks of the Butte
district, the atlas says:
The rocks of the Butte district are
all of igneous origin. are of few types
and are OF simple mineral composition.
They are mostly embers of the granite
family. whose essential characteristics
are alkali feldspar and quartz, with
varying. but smaller amounts of other
minerals. . Granite rocks cover
the greater part of the district, two va
rieties being distinguished. one is a
dark, grayish. coarse-grained granite,
the other a white or cream-colored rock,
variously called white" or "bluebird'
granite. These two rocks are intimately
associated and together constitute a part
of the great granite intrusion already
described. . They are the Oldest
rocks of the district and the great min
eral veins occur in them. The dark
colored granite of the district differs In
appearance and miners composition
from the rock commonly prevailing
throughout the surrounding region and
as IL is nearly constant in character and
is characteristic of the district IT has
been given the distinctive name of
Butte granite. . This, the COM
mon and characteristic rock, covers the
eastern half of the district. where the
great producing mines occur, and I'M
derlies the city"
Then is described the meteorological
composition of the Butte granite, the
inclusions of dioritic rock In the Butte
granite, the effect of heating, chilling
and wind on The granite, the chemical
alteration of the granite. and the fissure
systems. Apllte occurs in unusual
-
the western half of the district. 1t is a
granular. siliceous granite. The gran
lite forming Anaconda hill is cut by sew
eral bikes of quartz-porphyry, a rock
type not found in any other part of the
district. The freshest rock has a pale
green color and is thickly dotted with
small crystals of opaque white f~eldspar.
The intrusion of quartZ-por-
phyry can be traced on the surface
from the slopes Immediately above
Meaderville TO a point above the Modoc
mine. a vertical rise of 500 feet. :
No definite age can be given for the in
trusion of the quartz-porphyry. 1t APP
parently represents an independent pc
riod of rock fracturing and igneous in
trusion occurring before the ore deposl-
ton of the district. About one
fourth of the surface Of the Butte dis
trict is covered by rhyolite. 1t is the
49, 49, "a NV 'AEA y y
The rock usually weathers with
a reddish or rusty crust. 4" Or
exposed surfaces IL breaks up into small
fragments and no conspicuous outcrops
are seen within the limits of the dis.
trict, although n same rocks form
very striking and picturesque exposures
on the high hills Il the northwest and
in Silver Bow my and Browns
gulch. The rocks of the Butte ar,
grouped with the intrusive bikes of rhy,
olite. but the former really constitute {
complex Of both intrusive and e~xtrusiv,
rocks. The dixie rocks are massive rock
OF nearly uniform character.
The longest % these bikes Is seen neaI
the Nettie mine and is encountered II
the mine workings. The Ger
mania dixie trends nearly north an,
south just west of the mine of tina
anne. bikes Of rhvolitics ar
exposed by the placer workings west q