Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1946-02-09

amount Of red shale may be near
the base.
Beneath the Jurassic strata occur
about $50 feet of white to pinkish
derise doiomitic limestone inter
padded with some red and gray
sfale, all of which make up the
Anaszen formation of Upper Missis-
sippisn age. Oil La the recently dis
covered Gage oil field near Round
up OCCURS in this formation in a
dolUnuitic limestone which in that
locality Is porous.
Underlying the Amsden is the
Big Snowy group of formations, con-
sisfing of Heath, Otter, Kibbey, and
Charles.
The Heath, which Is essen
TALLY a shaie formation, Is re-
cognized by the presence of
beds of black fissile oil shaIe,
womae of which win burn I'm the
flame OF u match.
At places 20 feet or more of this
coaIblack shale may be present,
and IL may cave In to the hole badly
In the drilling operations Some
fine grained sandstone and dense
The Otter, underlying the Heath,
Is also mainly shale, but the colors
are lighter, and some beds are vivid
green, a characteristic which aids
In Identification. Dense limestone
and fine grained sandstone mem
beers are also present In the Otter.
The Kibbey formation is char
acteristEcally reddish Iirny or
sfaaly sandstone, but in places a
relatively pure white sandstone
may be present In addition to the
sandy beds occur shales, varigated
In color or gray; and bed of anhy-
drite may be found. Red celebrations
generally aid in identification of
the Kibbey gandgtOnes.
The Charles formation (probably
more closely related to the Madison
than TO. the Big Snowy group is
mainly crystalline dol0mite or dolo-
mite limestone, but thick beds of
anhydrite are present, and these
serve TO distinguish the formation.
Some dark gray sf1ale Is inter
bedded with the liIny and gypsi-
ferrous strata.
The division between the
Charles and the Madison fOrma-
lions Is difficult TO make, be-
C&MSG E361sE#WN HEIRESS-LOVE EEEakr
~ resembles Charles limestone.
The Madison has been divided in
to an upper portion, about TOO feet
member, which is massive crystal.
line pure limestone, and a lower
portion, about $50 feet thick, called
Isodgepole member, which is finer
grained, darker, and cherry, and
the limestone beds are separated
by shay partings
Devonian strata have not
been identified beneath the
Madison In the Cat Greek area,
and are believed TO be absent.
Bem@a9h the dark cherry lime
stones of the Lodgepole member
occurs about 100 feet of cream to
buff coIored dolomite, rather dense
but showing a little pOrosity This
has been identified by l. L. Sloss
as OF 0rdavician age, and is cor
felatad with the Big Horn fOrna
ton. Beneath this dolonaite occurs
about 80 feet of sandy and shay
sediments interbedded with dolo
mite WHICH are buff 60 brown ir
color. TflRy naay be equivalent Il
the Ord0gieaan Whitewood forma
ton of the Black Hills region.
Underlying these strata is thicl
series (more than 700 feet) O
dense gray dolornites interrupted
by gray or green nicaceous shalt
bodies believed to be of CambriaH
age. Some of this material is
limestone conglomerata
The AFRO Oil and Refining Co
California Co.'S Charles NO. 4 wei
on sec. I'll, r. Ism, r. 3OE., bottom
ed at a total depth of SOS feet
after penetrating about TOO feet o
what has been identified as Cam
brian strata.