Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1939-10-14
CHESTER AREA
CONTINUED from Page one)

I fCOulnueu from rage Out3
facilitate departmental administra-
ton OF oil and gas provisions OF
/ federal mineral leasing laws. A
few copies of this map are avail
able for free distribution at the
offices of the geological survey in
Washington, Denver and Great
Falls.
Finds Few Exposures
, The Dunkirk y Chester region,
known locally as '-the flats" Is a
sparsely inhabited, southward-slop-
ing plain OF low relief and of little
utility except for grazing. Its sur
face is occupied by a thick cover
OF glacial drift and alluvium, and
identifiable exposures of the under
lying rocks we're found at only two
places in the area mapped. Infor-
nation concerning the identity and
structure of the underlying rocks
was obtained chiefly from SO wells
drilled in the area for oil and gas.
Rocks Dip Eastward
As inferred from the meager ev-
idence, rocks on which the surface
cover directly rests are all of Up
per Cretaceous age and consist, in
eastward progression across the
area, of the uppermost third of the
Colorado shale, succeeded through
a sandy transition zone by the
Eagle sandstone, including the Vir-
gel1e sandstone member at its
base, the C1aggett shale and the
basal part of the Colorado shale,
.-..,-,.a - .-da~ Fraun xtnuuCar "a
older, are the Blackleaf sandy menu
Der of the Colorado shale. of Up
per Cretaceous age; the Kootenaii
formation, of Lower Cretaceous
age; the Ellis formation. of Up,
per Jurassic age, and the Madison
limestone, of lower Mississippian
age. The general features of these
stratigraphic units have been de-
scrfbed in earlier geological survey
publications relating to this and
adjoining areas, particularly bulle-
tins 641-C, S1z-B and 847-F and
professional paper COG. Their
characteristics in the Dunkirk-
Chester region are indicated in
co1umnar section on the recently
published map.
Is Big Monociine
Structura1ly, the Dunkfrk-C hes-
ter region is primarily monocline,
with low inclination to the east a.
way from the crest OF the Sweet
grass arch, which is a few miles
to the west. Near the northeast
corner OF the area the rocks have
a distinct southwark warp resulting
from the uplift OF the Sweetgrass
hills to the north. The primary
structure is further diversified by
two transverse up-warps-one in |
the northern part of the area. a |
fairly definite eastward plunging |
fold of considerable linear extent, |
known as the Utopia nose, and the |
other, in the southern part, an in
distinct southeastward plunging |
fold OF uncertain form and extent, |
known as the Galata nose. Struc- /
tural closure was not detected a.
long the crest of either nose.
Describes Devon
The Devon gas field, near the
west end of the Utopia nose, com
Drises an area of about Fix square
niles in which natural gas has
been obtained in commercial guam
titles at relatively shallow depths
rom lenticular sandstones in the /
3lackleaf sandy member of the
Colorado shale. Oil in small guam
tiles has been found in this field
n the same sands. Showings of
10Th gas and oil have been obtained
rom sandstones in the Kootenai
The discovery well No.
f, McDonough, In the SWH sWA
lection II, Township SO North,
tango 2 East, Montana principal
meridian, was completed by the
Tashti Petroleum Co. in August, {
929, at a depth of 1913 feet and
ad an initial open flow capacity
{ 100000 cubic feet of gas a
ay.
Ten Wells Drilled
Ten wells have been drilled in In
he field to date. OF these 2 were ]
ry, 8 others were abandoned be-
ause of small productivity and s {
re gas wells, shut In, with an ag-
regate open flow capacity Of a. {
out 100000 cubic feet a day.
he Devon field is without present +