Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1940-12-28
DEVONIAN EXPOSURES


CONTINUED from Pass onel
down the westerly dipping flank of
this broad fold and into the trough
OF the geosyncline. we have a well
defined Eastward gradient
The Pondera, Cut Bank and
| Ksvin-Sunburs oil fields are all
located on the basinward flank dos
cribed. They produce from the
strata above the MadiSon-Ellis I'M
conformity. II the photographic
character and composition OF the
beds in any given area are known
] to be suitable, few biologists are
inclined to doubt the success OF
deeper drilling of the Madison and
Devonian formations where located
on favorable structure.
POrosity and saturation are the
general partners of structure com
prising geologicaHy the oil field
trio.
bureau OF Mines Points Way
Important and little published
work of DR.. Charles f. Deiss Of he
+ geological department OF the Uni
versity of Montana done under the
auspices of the Montana Bureau Of
Mines and Geology is. as stated by
him the first known atteu : 20
make carefully measured e&trati-
graphic sections or to determine
the character and composition of the
Paleozoic rocks in Northwestern
Montana The area chosen for in
vestigauon lies in the Lewis ana
Clark and Flathead National Forests
and extends along and easterly from
the continental divide. 1t Is mostly
at the west edge of Pondera and
Teton Counties. The results of this
intensive and significant work were
published in three papers. One by
the Bureau in 1888 as Memoir No.
6, entitled "Paleozoic Formations
of Northwestern Montana. Another
published by the Geological Society
of America, in 1888. entitled
"Cambrian Formations and Sections
in part of Cordilleran Trough" and
the third, published by the Society
in 1889 entitled ''Cambrian Strait
graphy and Trilobites Of North
western Montana" COPIES of the
Memoir are unobtainable except in
some public Ebraries) Quoting very
briefly from Memoir No. s, the fol-
lowing facts are of interest to the
geOlogist:
The rocks are relatively
undisturbed in the area and
it contains the largest and best
exposed PaleOZOic basin in
Northwestern Montana.
Ten sections (stratigraphic)
The quadrant formation was
either never deposited In the
area or more probably was
completely removed by erosion,
prior to Jurassic time. -.
The PaseOzoic rocks belonging
to three systems are the Cam
brian, Devonian and MISSISSIPPI
plan and only portions of each
are represented. The
Three Forks shale, upper De-
vOnian, has no lithOlogic equi-
valent within the area.
So far as known the difference
in thickness of the IimestOnes
upon which the basal Madison
beds rest. and therefore the
amount of disconfomity (be-
tween the Madison and Devon
lam is 425 feet. The
Jefferson HmestOnes within the
area are tentatively considered
to be only Middle DevOnian in
age. The Mississippdan
(MadisOn) rocks average 74O
feet In thickness. :"
Typical of the several widely
Devonian sections ex-
lmined in detail by Deiss, from
oentagon Mountain at the North
o the Dearborn River at the North
ire the following:
LONE BUTTE (tOp) MEM
BIER OF DEVONLAN Measured
in Secs. 23, 25, %, T. 23N.,
r. IS, w.
Limestone, massive, brown to
steel-gray and extremely petrO-
liferOus, magnetism (dOlomite.)
Beds thinner i'm lower part;
wcathers brown, 40 feet.
Limestone, massive. chOcO-
late to chocolate gray, fine
grained and magnesian; wealth.
crs white-buff and TO irregular
surfaces, 20 feet.
Limestone, massive, steel =
gray, yitreOus, sandy, fine :
grained, 141 feet.
Limestone, tan to steel-gray, /
vitreous, extremely sandy, pet
trOliferOus; weathers drab-
brown, "a feet.
Total thickness Of Lone Rutfe -