GEOLOGICAL SURVEY BULLETIN 1026 PLATE 2

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Formation . oo
23
System| Series | Group and eee a° Description
member Cia ga
&
Hell Creek formation poise Sandstone, massive, soft;and greenish-gray sandy shale
850 to| Shale, dark-gray, concretionary; upper unit
Bearpaw shale 1,100 | Shale, dark-gray, with many bentonite beds; middle unit
Shale, dark-gray, concretionary; lower unit
Eee 50 | Sandstone, massive, brown, with hard nodular limonitic coneretions; upper unit
Shale, dark-gray sandy and silty; lower unit
g Shale, dark-gray with bright orange- and brown-weathering fossiliferous
£ Claggett shale member 350 concretions; upper unit. Shale, dark-gray, concretionary; middle unit
ie Shale, dark-gray, with many bentonite beds; lower unit
2
Shale member equivalent
8 Paaers ee ees SNe Shale, sandy, gray, with many beds of thin hard rusty-weathering ironstones;
Ss 8 thin bed of ledge-forming sandstone about 170 ft above base; thick
@ bentonite zone about 280 ft above base
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5
a 2 $
a & s oad ts Shale, sandy, gray; weathers to yellowish sandy soil
8
3) 2
a
& 4
3 Es Shale, dark-gray, with numerous gray septarian concretions and thin
6 *s bentonite beds; a thin calcareous shale zone about 80 ft above base
O° | Niobrara shale member forms light-colored band of soil
5 Shale, dark-gray, sandy in middle; a 25-ft zone of thin hard ironstones 100 ft.
3 Carlile shale member 275 above base; a 10- to 20- ft zone of large concretions 180 ft above base
ie
§ =
3 Greenhorn calcareous === 60 to | Shale, dark-gray, white-weathering, calcareous; limonitic bentonite at base
member —
Shale, dark-gray, concretionary; thick bentonite bed 60 ft above base
Lower member
ea Shale, dark-gray, sandy, with sandstone lenses; thick Soap Creek bentonite bed at top
‘rontier formation
=) 345 to| Shale, gray, siltstone, and sandstone, partly siliceous; weathers silvery gray to
g aS Be 400 bluish gray; Clay Spur bentonite bed at top
2 P
3
3 ; Shale, dark-gray, with several beds of bentonite; zone of sandstone
8 Thermopelie hats aay dikes about 250 ft below top
be
S
g
3 Sandstones, thin at top underlain by shale, siltstone, "rusty beds",
225 to| variegated shales, and the lenticular Pryor conglomerate member
Le 1;
reece sd Neat eee 650 of the Cloverly formation, Mostly variegated shale and greenish
6 e siltstone and sandstone below Pryor conglomerate member
eg | £8
5 90 to | Sandstone and siltstone, fossiliferous, glauconitic; and calcareous
3 P= Swift formation 170 shale; has ledge-forming very fine grained calcareous sandstone at base
e
5 2
2g 2
°c | 8@ FA Rierdon formation 178 to] Shale, light-brown, fossiliferous, calcareous
ua
£
ar 2 3 Piper formation 150 to| Siltstone, red, and shale; upper unit. Limestone, gray;
3 a8 180 middle unit. Shale, red, above gypsum; lower unit
iB :
Ras Chugwater formation 375 to| Siltstone, red, and sandstone; thin limestone 40 to 100 ft below top may be Alcova
Te 675 limestone member; basal gypsiferous and limestone unit is equivalent to Embar
Py UNCONFORMITY ae yea
e Ra Tensleep sandstone 115 | Sandstone, gray to yellowish-gray; few chert and dolomite beds
a
Bit Amsden formation 230 to| Shale, red, siltstone, and sandstone and thin beds of dolomite and limestone.
te i GnTaaeraise 280 Chert predominates near middle; red siltstone and shale at base
a Brecciated zones and channels filled with limestone fragments and redbeds;
ae ; eee 150 ft. Limestone, light-gray, and limestone, dolomitic; 315 ft. Limestone,
g a Madison. Mmestane tao. |  f08siliferous, purplish-gray; 85 ft. Limestone, light-gray, with chert beds
a from 40 to 80 ft above base; 155 ft
7a | ba : ’ ;
$ ‘i , rownish- and greenish-gray, shaly and sandy; upper :
>< | 30g ‘Three Forks shale and Limestone, light br h- and Sh. haly and sandy; upper 200 ft
Bz | Bae Gane ee ae Pe 300 Dolomite, very light-gray, and dolomitic limestone; lower 100 ft
ae undifferentiated | =
Qe B38 ; = Dolomite, light-gray to white, and dolomitic limestone; upper unit, Limestone,
85 | kes Bignesntcoioe te S277 285 to| — dolomitic, massive, cliff-forming, light-brown is 180 ft thick in Bighorn
is! 5 aie ‘anyon lower uni
io} Ex) | I | 480 Canyon 1 it
A
at. 8 Soe ; non ;
= lgos2 Galiatlimestondlend Sseees Limestone, with thin siltstone and shale partings; upper part. Limestones,
a |S5a¢4 Gros Ventre formation, = ==F11.000: | thin-bedded, flat-pebble, and green shale; lower part. About 700 ft
2 |e°o4 undifferentiated | exposed in Bighorn Canyon but largely concealed by talus
a 8 =| al y' e y
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Geology by G. E. Prichard
GENERALIZED COLUMNAR SECTION OF ROCKS EXPOSED BETWEEN THE BIGHORN MOUNTAINS AND HARDIN. MONT.

334328 O ~ 55 (In pocket) No. 1