GEOLOGICAL SURVEY

BULLETIN 1023 PLATE 2

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Pas . 28 , a | §
. gS Bentonite :, A
Formation Character of rocks Be | Seas Section 3 < Character of rocks mete ot 3 q 4
34 § 6
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Sandstone, massive with green Hell Creek
sandy shale formation
As exposed in T. 9S., R. 36 E.,
(not shown on Plate 1), -- Bearpaw shale
200+ Shale, dark-gray, soft, contains =
marine fossils
As mapped from T. 3S., RS. 34
and 35 E. northward: Shale, eax
dark-gray with many bentonite Bed W
Bearpaw shale) beds and calcareous concretions | 885 S As mapped in T. 9S., R. 35 E., --
weathering gray or brown. Three Sandstone, brown and gray, argil-
thick bentonite beds near middle laceous, interbedded with green
of formation and gray sandy shales and dark- -
700 gray carbonaceous shale. Lower pper
Bed V part locally contains coal and unnamed | 6
clinker beds member) 5
Member interfingers with lower §
two-thirds of Bearpaw shale shown 8
on left side of column Ps
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x
Gi
3
3
5
As mapped in T. 9S., R. 35 E., --
Upper part: sandstone, massive,
As mapped in T. 3S., RS. 34 and soft, buff, brownish and olive-
35 E. and area to north: Equiva- green, containing harder brown- Parkman
Judith River | lent and lithologically si weathering sandstone concretions
pee arene ty eae a 255 350+ and rusty limonitic nodules. Pon
me member of Lower part: shale, silty to sandy, soemaper
Judith River formation buff-weathering, grades upward
into overlying sandstone; contains
silty calcareous concretions that
weather gray, yellowish-tan or
brown
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g
a
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Shale, dark-gray, with brown and onane
gray calcareous concretions and member
many bentonite beds
Bed U
Bed T
Bed S
Bed R 3
[Unnamed sandy 8
Shale, sandy, gray, with many fer- | Sha1¢ member| 8
ruginous and calcareous concre- Caen 2
tions. Thin resistant sandy zone | SU oN x
near middle of unit ao
a
a
5
a
Sandy shale, gray, much of which is Telegraph 2
interbedded with thin layers of soft Creek g
sandstone, weathers to buff soil member Q
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a
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Shale, dark-gray, calcareous in
lower part, with many calcareous Niobrara
concretions and several beds of shale
Bed Q bentonite. Bentonite beds P and member
Bed P Q occur near middle of formation
Shale, dark-gray with several beds ,
of bentonite and abundant concre- se
tions, many of them septarian. baa
. ‘ member
Sandy horizons in lower part 3
Bed O ¢
Bed N 8
3
is)
Shale, calcareous, containing lime- | Greenhorn
stone concretions; appears bright calcareous
moan gray on dry, weathered surfaces member
Bed L Part above Soap Creek bentonite
bed consists of dark-gray shale
Soap Creek and sandy shale with calcareous
béntonite concretions and bentonite bed L.
bed Part below Soap Creek bentonite Belle
bed consists of dark-gray shale Fourche
and sandy shale with a few obscure member
sandy beds and lenses and many
ferruginous concretions. Bentonite
eed beds I and J are in the lower third
of the member
Bed I
Clay Spur
bentonite
bed
Bed G
Shale, dark-gray, siliceous, sandy
Bed F in middle part, with many bentonite
beds. Forms ridges and scarps. an
Contains four thick bentonite beds, patil
most persistent of which is the
Clay Spur bentonite bed near top
of formation
2
3
3
3
Bed E 8
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j
Upper part largely dark-gray shale
Bed D containing bentonite beds A, B, C,
a and D and several thinner bentonite Thermopolis
beds. Lower part chiefly argilla- shale
ceous siltstone, which weathers
buff, and dark-gray sandstone
Bed B
Bed A

Based largely on field data obtained
by W. A. Cobban in 1947

COLUMNAR SECTION OF ROCKS EXPOSED IN HARDIN DISTRICT, MONTANA AND WYOMING
SHOWING STRATIGRAPHIC POSITIONS OF BENTONITE BEDS

347624 © - 55 (In pocket)