DEPARTMENT OF THE INTERIOR 

FRANKLIN K. LANE, Secretary . 

-UNITED STATES GEOLOGICAL SURVEY 

GEORGE OTIS SMITH, Director 

Professional Paper 108-J 

THE FLAXVILLE GRAVEL AND ·ITS RELATION TO 

OTHER TERRACE GRAVELS OF THE 

NORTHERN GREAT PLAINS 

BY 

ARTHUR J. COLLIER 

AND 

W. T. THOM, JR. 

Published January 26,1918 

Shorter contributions to general geology, 1917 

( Paates 179-184 ) 

WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1918 
CONTENTS. 

Introduction ............... ~ ... ~ ........... , ........... . .......... ~ ......................... ~ .... -.-----

Flaxville gravel ...................................................................... · .. . ............ · .... . 

Late Pliocene or early Pleistocene gravel. ..................................... . ..... . .. . .................• -

Late Pleistocene and Recent erosion and deposition ........................ . ..... . ..... .... ... ~ ............ . 

Oligocene beds in Cypress Hilla .................... .' ................. . ........................ . .......... . 

Summary ....•......................... ················· · ·· · ········· .············· ··" ···················· 

ILL USTRA 'fl ONS. 

PLATE LXII. Map of northeastern Montana and adjacent parts of Canada, showing the distribution of erosion 

Page. 

179 

179 

182 

182 

183 

183 

Page. 

levels and gravel horizons................................................................ 180 

J,XIII. A, Surface of the Flaxville plateau, northeastern Montana; B, Outcrop of cemented Flaxville 

gravel in escarpment ·of plateau northwest of Opheim, Mont.; C; Escarpment of the Flaxville 

plateau, northeastern Montana, showing outcrops of cemented sand and the thickness of the 

Flaxville gravel .................. ~ .......... ·.........•.................................. 182 

LXIV. A, Cemented gravel-interstratified with cemented sand 9 miles northeast of Scobey, Mont.; B, 

Cross-bedding of Flaxville gravel 5 miles west of West Fork post office, Mont................. 182 

LXV. A, Railway cut west of Flaxville, Mont.; B, Escarpment surrounding the late Pliocene or 

early Pleistocene bench in Milk River valley, Mont.; C, Vandalia dam, Mi.lk River, Mont., 

showing the escarpment surrounding the late Pliocene or-early Pleistocene bench............ 183 

FIGURE 27. Diagrammatic section showing the relative altitudes of the four erosion levels represented in northeastern Montana and the adjacent part of Canada.............................................. 184 

II 

i, 

'!· 
THE FLAXVILLE GRAVEL AND ITS RELATION TO OTHER TERRACE 

GRAVELS OF THE NORTHERN GREAT PLAINS. 

By ARTHUR J. CoLLIER and W. T. THoM, Jr. 

INTRODUCTION •

1 

In Nebraska and South Dakota there are 

widespread deposits of · gravel and other· 

material, largely surficial and generally unindurated, known as the White River, Arikaree, 

Ogalalla, and other formations, 2 which range 

in age from Oligocene to Pleistocene. West of 

these deposits, on the flanks of the Rocky 

Mountains, are several high piateaus covered 

with gravel, whose age, though not known, is 

generally regarded as Pleistocene. At some 

places the position of this gravel indicates its 

continuity with the Tertiary formations farther 

east, but their equivalency has not been proved. 

It is the purpose of this paper to outline the 

e'vidence obtained by. the writers in 1915 and 

1916 regarding the age of the gravel found on 

two high terraces in the northern part of the 

Great Plains ·and t.o show its relation to a 

still higher gravel, known to be of White 

River age, discovered by Canadian geologists 

some years ago. Messrs. R. F. Baker, E. T. 

Conant, and H. R. Bennett were enthusiastic 

coworkers in collecting this evidence, and to 

them much of the credit is due. 

The area described, as shown in Plate LXII, 

extends along the south side of the international boundary from Redstone, about 30 

miles west of the Montana-North Dakota line, 

w~stward to the west side of Boundary Plateau/ 

a distance of 175 miles. It continues northwestward from the plateau far enough to take 

in the whole of the Cypress Hills, where Canadian geologists have discovered deposits of 

·White River (Oligocene) age. 

1 An abstract of this paper has been published by the Washington 

Academy of Science. 

2 Osborn, H. F., Cenozoic mamJl!,al horizons of western North America: 

U. S. Geol. Survey Bull. 361, p. 65, fig. 10, 1909. 

s The name Boundary Plateau was used by McConnell to designate 

the northern extension of what is called Cherry Ridge on the American 

side. It is retained in this paper for convenience. 

103977°-18 

FLAXVILLE GRAVEL. 

The Flaxville gravel, named from the town 

of Flaxville, on the Scobey branch of the Great 

Northern Railway, was deposited in Miocene 

or early · Pliocene time. The history of · its 

discovery is as follows: 

During the field seasons of 1915 and 1916, 

in the course of an investigation of the lignite 

resources. of northeastern Montana, the writers 

found some "extensive plateaus that are so 

deeply buried beneath a cap of gravel and 

kindred materials as to make the location of 

lignite outcrops impossible. This gravel has 

been described by several writers under the 

names ''glacial overwash, '' ''quartzite gravel,'' 

etc. Bauer 4 had recognized the possible significance of this terrane and had provisionally 

referred it to 'the Oligocene of the Cypress 

Hills.5 

On the third day in the field the senior 

writer inquired of Atle Taerum, the proprietor 

of the store at Avondale, whether in digging 

his well he had seen any signs of lignite. 

.Being answered in the negative, the writer 

made a personal examination of the well and 

found on the dump some fragments of bone 

said to have been found in sand at a depth of 

30 or 40 feet. From this beginning as close 

an inspection as the circumstances would 

permit was made of wells and other natural 

and artificial exposures of the gravel by members of the Geological Survey party. In many 

places fragments of fossil bones had been 

found but not preserved, as their significance 

was not appreciated. D. H. Linton, Hagen 

Hayenga (postmaster at West Fork), L. T. 

Greenup, Martin Presnell,. Warren Redfield, 

4 Bauer, c." M., Lignite in the vicinity of Plentywood and Scobey, 

Sheridan County, Mont.: U.S. Geol. Survey Bull. 541, p. 301, 1912. 

~ Cope, E. D., Species from the Oligocene or lower Miocene beds of the 

Cypress Hills: Canada Geol. Survey Contr. Canadian Paleontology, 1891. 

179 
180 SHORTER CONTRIBUTIONS T:O GENERAL GEOLOGY, 1917. 

J. A. Stewart, Herman Forbregd, and Prof. 

L. 0. Swenson contributed specin1ens . . 

As a result of · the search, fragments of 

foE?sil bones have been collected from 25 widely 

distributed localities. · These fragments were 

submitted to Dr. J. W. Gidley, of the United 

States National Museum, who identified them 

as representing various forms of the three-toed 

horse (protohippid, Protohippus; Neohipparion, 

and Merychippus), horned gopher (mylagaulid), rabbit (Lepus), rhinoceros (Teleoceras), 

oreodont (Merycodus), camel (ProcameZ.us, 

camelid, and Gamelops), saber-tooth tiger . 

(machaerodont), doglike animal (amphicyonid), 

and fish. His full report follows: 

F.l. SE. ! .sec. 26, T. 34 N., R. 42 E., Atle Taerum's 

well at Avondale: 

Protoh:i,ppid (astragalus). 

F. 2. Near north side of SW.! sec. 27, T. 34 N., R. 42 E., 

excavation on land of D. H. Linton, Avondale: 

Protohi ppid (distal end ofradi us). 

?Mylagaulid (proximal half of humerus). 

Lagomorph cf. ?Lepus (fragment of maxillary and 

toe bone). 

F. 4. 300 feet southwest of northwest corner sec. 5, T. 35 

N., R. 45 E. 

Proto hi ppid (astragalus). 

? Procamel'us sp. (phalanx). 

F. 5. SW. l NW. l s.ec. 24, T. 34 N., R. 44 E., Hagen 

Hayenga's well: . 

Neohipparion sp. (part of upper cheek tooth). 

Procamelus sp. (distal end of meta podia!). 

F. 6. Near West Fork post office, T . 34 N., R. 44 E.: 

? Neohipparion sp. (upper cheek tooth of left side). 

F. 7. NW; t SW. t sec. 25, T. 34 N., R. 44 E.: 

Protohippid (fragments). 

F. 11. NE.l sec. 31, T. 36 N ., R. 45 E., "from gravel and 

sand resting on top of Fort Union bluff." 

Protohippid cf. Neohipparion ~p. (astragalus, portion 

of upper molar, and fragments). 

Camelid d. Procamelus sp. (astragalus, piece of toe 

bone, and fragments). 

F.. 13. SW. l sec. 13, T. 34 N ., R. 45 E., slope of TaylorGreen prospect: 

Camelid cf. Procamelus sp. (distal end of phalanx). 

F. 14. Near east -quarter corner of sec. 6, T. 34. N ., R. 

47 E., from well at depth of 28 fee.t: 

?Camelid (lumbar.vertebral centrum). 

F. 15. NE.l sec. 33, T. 35 N., R. 47 E.: 

Mylagaulid (lower molar). · 

F. 19. Sec. 20, T. 36 N. , R. 45 E.: 

· Protohippid (fragment of upper molar). 

. ?Procam~lus sp. (phalanx and astragalus). 

F. 20. Sec. 15, T. 37 N., R. 44 E.: . 

I . Protohippid (ge~us and species not determined). 

F .' 21. SW. t sec. 7, T. 36 N,, R. 44 E.:· 

Merycodus sp. (fragment of a left lower jaw containing four deciduous premolars). 

F. 22. Near center ofT. 35 N. , R. 41 E.: 

Neohipparion sp. 

F. 23. Sec. 12, T. 35 N. , R. 41 E., J. A. Stewart's well: 

Protohippid. 

F. 26. Sec. 32, T. 36 N., R. 49 E.: 

Protohippid (end of metapodial, ftagment of lower 

molar). 

F. 27. C.ut of Great Northern Railway a mile west of 

Flaxville station: 

?Teleoceras sp. or ?Aphelops (toe bone and fragments). 

?Procamelus sp. (tooth and toe-bone fragments). 

Protohippid, probably Neohipparion sp. (fragment 

of lower jaw containing teeth, three parts of teeth, 

astragalus, and fragments). 

F; 28. Just south of quarter corner between sees. 28 and 

29, T. 35 N., R. 50 E.: . 

· Protohippus sp. (fragments of teeth). 

Carnivore (?amphicyonid) (fragment of left maxillary containing fangs and alveoli). 

F. 29. T. 35 N., R. 50 E., first cut of Great Northern 

Railway west of Flaxville. 

Neohippar,ion ?affine or n. sp. (upper molar and lower 

molar possibly belonging to same speciei>). 

Neohipparion sp. (lower molar). 

Procamelus sp. (fragmentary foot bones and teeth). 

?Camelops sp. (large tooth, last right lower molar, 

wrapped in mud ball). Apparently Pleistocene 

species. 

Machaerodont, genus and species nqt determined 

(metapodial). 

Fish, not determined (lower jaw). 

F. 31. Sec. 33, T. 36 N., R. 50 E. , 2 miles north of Flaxville: · 

Camelid cf. Procamelus sp. (portion of posterior 

molar or left lower jaw). 

F. 33. In railroad cut a mile west of Flaxville: 

Protohippid (fragm.ents of jaw, toe, and limb bones). 

Artiodactyl, probably Merycodus (single phalanx). 

F. 34. Cut of Gre~t Northern Railway a mile west of Flaxville: 

Mylagaulid cf. Ceratagaulus sp. (large cheek tooth). 

Protohippid cf. Neohipparion niobrarensis (right 

upper molar). 

Protohippid ? Neohipparion sp. (fragments of three 

upper teeth). 

F. 35. Railroad cut a mile west of Flaxville: 

?Procamelus sp. (part ofulna, much broken). 

F. 36. Southeastern part ofT. 33 N ., R. 43 E., collected by 

W. C. Alden: · 

· Merychippus sp. (toe bone and fragment of jaw). 

Certainly one of the Miocene three-toed horses; 

probably upper Miocene. 

F. 37. Sec. 23, T. 36 N., R. 23 E., Prof. Swenson's well: 

?Protohippus, fragments of fossil mammals, one 

piece recognizable as fragment of upper molar 

of one of the Miocene h0rses. 

F. 38. Sec. 24, T. 36 N., R. 23 E., Louis Hoff's well: 

? Protohippus, fragments of manun:alian remains; 

among them portion of an upper molar of one of 

the Miocene horses. 
~ 

uJ 

~ IL 

co 

0 

-

~ 

ILl 

(L 

f:. 

...J 

< z 

0 

iii 

U') 

w 

I<. 

0 

a:: 

(L 

> w 

> 

~ 

~ 

~ 

...J 

~ § 

0 

~ ~ 

"' 2 

~ 

~~ 

~§ 

~~ ~~(/) o H 

~~~ ~~ (/)~ 

~u 

~~ ~ 

~~ z 

;;~O:!lj;"g Lri 

~ 'g s. ~--g ... ~ 

B 'C E :E .8 .!: i- c 8. c: ~ 2: o~:S.g~5~ Ec:~,g~-

lS"'~~Eg a :~a:~;s::~ g ~~ ~-;;.!if(!; go.~;~«J 

rn ~:=o ~ 

$~~~~~ a:~ t:ge-., c: E .., a ..,6-£; "' .. 8. ..... c: ., >. -,.... 1 :O .c.o f,) "Q..&:..o 

r- E=» -=:;-:s'2 .xi~oea.~ ~GJ -.,.4)1'Q= o..ee"'.c:e ..c t: >- ,g ~ >- .!.! 5. 0 . . ..c _: 

~j:~ li-g E~ ;: ~ 2: ~ ~8 

o~ ~~s~ € ~~ ~8 -g t:i 

goo .2 !co cr ... ~~ 2:E ,._ c: ~., (.!l c._ ..c 

'8: ::> .§ 11 ~ § E~ ~£5tCQ ~ ... :~ .,'9o5 l:S 60~ :a J!l "' -

c~~~ ... ~-f:i:Z~!S:o C) ..= .5: £i i .11 «1 .e 

.... 

(/) 

!~ ; 

~ 

l!)~ ;... ...J 

oz 

:z;S 

0~ ~0r ;J~ e . ~ 8. ~ gJ ~ 'B o ~ r.fJ 

0 

~ £ 

l!)~ 9 

~ ~ ffi 

~] 

8~ 

t£t a:: ·g 

t~ ~..<: 

l;j 

oo 

c:u 

~~ ~ i~ Iii 

g 

i )(= ·;;; 

~~ ~ ~ 

"0 u 0 c: c: IJ... 

LJ~i nl, ~·~ L>-

u 

n: g ~ ~ g " t ·- to :I _J+-' ....... 

... r--... 

o I r/ 4 /1.· .· v ·· t < /( , r ~ ~ / ·/<' • 

I// 

. ~ 

%/1<-( , 3 / / / / ~f/5r a\' . . 2. 

:.-· . 

> / ~ / 

7 > / ;:(-A~L ::t[1 • f 7 7 I 

~ ~ 

.. ~ >- t:~ ...c tf 

!~t-~ cCf,.. c 

~~ ~ '15'5 8 u a.O. ..<: eet:: 

,..u 8..o t).,ECO 

~a.~"O 

:d~ co u 1/l-(11)'0..<:. 

- &. c: ~"' ~Qm ... :::~ ..... _s..o-

]-gil g_~ ~~ :> _-t 

ui'- ~ 'i) ::> ::l~ cl/l Og~

~!~ui C)'C .; -2 .. c:i': \!) ~ ~ .. z til!) 
. THE FLAXVILLE GRAVEL OF THE NORTHERN GREAT PLAINS. 181 

Mr. Gidley further remarks: 

None of the material is sufficiently good or complete to 

make positive specific determinations, and it is therefore 

of no value as indicating horizon, except in a broad way. 

With the exception of the specimen reported as Pleistocene 

all the material appears to belong to the upper Mipcene. 

It can be stated positively, I think, that with the exception noted, the beds from which these fragments were collected can not be older than Miocene or younger than 

lower Pliocene. 

The formation from which these fossils were 

collected caps a series of even-topped plateaus 

ranging in altitude from about 2,600 feet at its 

east end, a few miles south of Redstone, to . 

3,200 feet in the west _front of the Boundary 

Plateau in the Cherry Creek quadrangle. It is 

from a few feet to 100 feet thick and rests upon 

the eroded surfaces of the Fort Union, Lance, 

and Bearpaw formations. A characteristic 

view of the plateau surface is given in Plate 

LXIII, A. In the opinion of the writers this 

plateau represents an erosional level developed 

during a period . subsequent to the Oligocene 

as represented in the Cypress Hills, and the 

fossil-bearing formation must have been deposited in Miocene or early Pliocene time. It 

seems hardly possible that these fossils could 

have been eroded and redeposited over so wide 

an area in -the Pleistocene epoch, especially 

as no source from which they could have come 

has been recognized. Moreover, there seems 

to be no intermingling of Pleistocene fossils 

with the ·Miocene. 

The distribution of the Flaxville gravel is 

shown on the accompanying map (Pl. LXII). 

It is generally composed of yellowish to ashgray gravel, clay, and sand, but in some places 

it contains beds of white marl and volcanic ash. 

The gravel consists of well-rounded pebbles 

from less than an inch to a foot or more in diameter, of quartzite and argillite derived from 

the Rocky Mountains. Limestone pebbles 

from the same source may have been dissolved 

and the lime redeposited as cementing material 

and beds of marl. The materials composing 

the Flaxville gravel are mostly noncoherent and 

are excavated easily by well diggers, though 

beds of hard sandstone and conglomerate cemented with calcite from 1 foot to several feet 

thick are encountered in most of the wells. In 

places the formation is very thoroughly cemented with calcite and forms prominently 

outcropping ledges of sandstone and conglomerate, as shown in Plate LXIII, B and C. 

Many such outcrops present a great deal of 

cross-bedding and 'are not continuous over · 

large areas. 

In ~he railway cuts west of Flaxville (see 

Pl. LXV, A), where the best collection of fossils was made, about half the material exposed 

is gravel _and the remainder clay and sand; 

about 1 foot of marl or concretionary calcite is 

also present. The bedding is very irregular, as 

might be expected of deposits on the flood 

plain of a river. North of Flaxville the road 

to Whitetail crosses a considerable thickness of 

gravel. Ten miles southeast of Flaxville, in · 

the escarpment at the edge of a plateau, the focmation consists of about 35 feet of cemented 

sand and gravel overlain by uncemented sand. 

Northeast of Scobey about 55 feet of more 

or less cemented sand and gravel is overlain 

by· 25 feet of uncemented gravel and soil. 

Plate LXIV, A, shows a bed of gravel interstratified with sand. The following section of 

a well southwest of Scobey was given by Martm 

Presnell, the owner: 

Section of a well southwest of Scobey, Mont., in sec. 33, T. 35 

N. , R. 47 E. 

Ft. in. 

GraveL .......... ... --. . . . . . . . . . . . . . . . . . . . . . . . . . . 6 0 

Clay ... .. ......... -............................... 52 0 

Lignite slack.... . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . 6 

Clay ........................................... ·. 2· 0 

Lignite slack..... . ........... . .. .. ............... 1 0 

Gravel and bones; water. 

61 6 

In a well 2 miles southwest of the Presnell 

well 28 feet of coarse gravel, carrying bones, 

was found. About 20 miles west of Scobey 

there are several good exposures of the lower 20 

feet of the formation, together with the underlying Fort Union. The gravel is uncemented _ 

and in"terstratified with cemented sand, and the 

surface is strewn with loose gravel containing 

bone fragments. A very striking exposure of 

the fo~mation occurs 5 miles west of West Fork 

post office, south of Hell Coulee, in sec. 30, T. 

34 N., R. 44 E., where ltbout 30 feet of hard 

sandstone showing very marked cross-bedding 

caps the edge of the plateau. This feature is 

shown in Plate LXIV, B. The sandstone probably rests on gravel, for an exposure of uncemented gravel was found near the bottom of 

the coulee. In sees. 19, 20, and 29, T. 35 N., 

R. 43 E., 8 miles nor~heast of Avondale, south 
182 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, l917. 

of Dawson Coulee, a slightly different phase is 

presented, as shown by the following generalized section: 

Generalized section of Flaxville gravel in sees. 19, 20, and 29, 

T. 35 N., R. 43 E. 

[Thicknesses approximate.] 

Feet. 

Marl, containing a few scattered quartzite pebbles.... 15 

Sandstone cemented with calcite ......... __ .___ __ . . _ 30 

Volcanic ash, white to yellow, very pure but mixed 

with the underlying gravel at the base. _ . ___ ... _ . 15 

Gravel, more or less cemented._ ......... _._. ___ .. _._ 20 

Fort Union formation. 

80 

The marl (an impure soft white limestone) 

was either deposited by water flowing over the 

surface into a shaJlow pond or gathered from_ 

the underlying beds and brought to its present 

position by percolating waters. Similar occurrences are indicated by fragments of marl in 

the soil of the townships to the west and nor.th. 

This is the only locality where pure volcanic 

ash has been recognized, though similar material mixed with sand has been noted about 12 

miles to the northeast. The gravel is very 

coarse, and well-rounded pebbles at least a 

foot in diameter, which must have been derived from it, were noted on the surface a short 

distance away in Daw$on Coulee. 

On Boundary Plateau in the vicinity of 

Cherry Ridge 74 feet of sandy gravel overlies 

8feet of cemented sandstone in a well in sec. 10, 

T. 36 N., R. 23 E., south of which two other 

wells of somewhat less depth have yielded 

fragments of fossil bone. The eastern . edge 

of the formation is exposed in Tps. 35 and 36 

N., R. 27 E.~ where it is dissected by Woody 

Island Coulee; the western edge of the formation along the west escarpment of the Boundary Plateau has been mapped by Stebinger 

in Tps. 35, 36, and 37 N., ~. 21 E., where it 

consists of cemented sand, gravel, and marl. 

LATE PLIOCENE OR EARLY PLEISTOCENE 

GRAVEL. 

Below the Flaxville level there are extensive 

areas varying in altit1lde from 2,500 to 2,800 

feet on which the bedrock is exposed or can be 

found in wells at no :very great depth. The 

relative altitudes of this bedrock surface are 

indicated on _the maps prepared but not yet 

published by (he International ·Boundary 

Commission. In the ~ vicinity of Redstone it 

is a well-marked plateau or bench ranging in 

altitude from 2,400 to 2,500 feet. · This feature 

extends westward near the international boundary to Scobey (altitude 2,450 feet), at the 

forks of Poplar River. 

Between Opheim and the Boundary Plateau 

the same period of erosion is represented by a 

gn~at expanse of highly dissected country 

incl~ding level-topped areas, sloping grasscovered hills, and badlands on which the Bearpaw shale is exposed, ranging in altitude from 

2,500 feet nea~ Milk River to 3,000 feet at the 

international boundary near the crossing of 

Frenchman Creek. Small bodies of ~tratified 

gravel and silt have been noted in sec. 3, T. 36 

N., R. 52 E;·, east of Daleview; in several wells 

in the neighborho'od of Julian; west of Opheim, in sec. 13, T: 37 N., R. 39 E., and west 

of Baylor,. in sec. 25~ T. 35 N., R. 38 E. The 

best exposures seen are in sec. 23, T. 33 N., 

R. 30 E., north of Malta, a few miles from Milk 

River, where about 25 feet of interstratified 

gravel and yellowish silt caps the edge of the 

bench at an altitude of about 2,500 feet above 

the sea, . or 300 feet above· Milk River. The 

gravel is cemented, presumably with calcite, 

forming a conglomerate that crops out in the 

form of a small cliff. Fragments of bone and a 

single toothwere obtained from the face of the 

cliff. Dr. Gidley identified the tooth as that 

of a horse ·resembling the living species and 

states that it can not be so old as the Flaxville 

fauna. The formation here _ rests upon the 

Judith River formation, but about 5 miles east 

of this locality it rests upon the Claggett shale 

and consists of .about 25 feet of yellowish silt 

containing two beds of gravel, one at its hase 

and ·another 15 feet higher. The g~avel is comparatively fine, the pebbles being less than an 

inch in diameter. In the light of the evidence 

now at hand this formation i~ regarded as of 

late Pliocene or early Pleistocene age. The 

erosion of the very extensive areas below the 

Flaxville level must have been accomplished 

during middle Pli?cene time. 

LATE PLEISTOCENE AND RECENT EROSION AND 

. DEPOSITION. 

The streams of the · region have eroded' their 

valleys from 100 to 500 feet below· the level 

assigned to the late Pliocene or early Pleistocene. Milk River now occupies a valley 1 to 

5 miles wide eroded by Missouri River before 

the last great invasion of ice in the glacial 
Ua S, GEOLOGICAL SURVEY PROFESSIONAL PAPER 108 PLATE LXIII 

.A. SURFACE OF THE FLAXVILLE PLATEAU, NORTHEASTERN 

MONTANA. 

B. OUTCROP OF CEMENTED FLAXVILLE GRAVEL IN ESCARPMENT OF 

PLATEAU NORTHWEST OF OPHEIM, MONT. 

0 . ESCARPMENT :oF THE FLAXVILLE PLATEAU, NORTHEASTERN 

MONTANA, SHOWING OUTCROPS OF CEMENTED SAND AND THE 

THICKNESS OF THE FLAXVILLE GRAVEL. 

• 

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 108 PLATE LXIV 

A. CEMENTED GRAVEL INTERSTRATIFIED WITH CEMENTED SAND 9 

MILES NORTHEAST OF SCOBEY, MONT. 

B. CROSS-BEDDING OF FLAXVILLE GRAVEL 5 MILES WEST OF 

WEST FORK POST OFFICE, MONT. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 108 PLATE LXV 

A. RAILWAY CUT WEST OF FLAXVILLE, MONT 

B. ESCARPMENT SURROUNDING THE LATE PLIOCENE OR EARLY; 

PLEISTOCENE BENCH IN MILK RIVER VALLEY, MONT. 

0. VANDALIA DAM, MILK RIVER, MONT., SHOWING THE ESCARPMENT 

SURROUNDING THE LATE PLIOCENE OR EARLY PLEISTOCENE BENCH. 

• 
THE FLAXVILLE GRAVEL OF THE NORTHERN GREAT PLAINS. 183 

epoch.~ This valley contains alluvium deposited by Missouri River, glacial drift, and th~ 

Recent alluvium of Milk River and is bounded 

on the north and south by steep escarpments 

rising 100 to 500 feet to the late Pliocene or early 

Pleistocene bench. Plate LXV, B and 0, shows 

views of these escarpments taken from the 

flood plain of Milk River. Big Muddy Creek 

flows in a valley cut 200 feet in the same bench. 

Similar benches are found along Poplar River 

and its branches. The canyon of Rock Creek 

where it crosses the bench is so precipitous as 

to have been considered unsurveyable by the 

United States Land Office. Frenchman Creek 

and Woody Island Coulee occ~py narrow val-

.leys, arid the latter was diverted from its old 

course westward into Whitewater Creek by 

the last glacial advance. 

OLIGOCENE BEDS IN CYPRESS HILLS. 

In 1883 and 1884 McConnell 2 and Weston, 

of the Canada · Geological Survey, examined 

the Cypress Hills and made a very good collection of fossil vertebrates at Bone Coulee, 

in the east end of the hills. This collection 

was submitted to Cope,3 who identified several 

species and pronounced them to be of Oligocene age and equivalent to the fauna of the 

White River formation of Nebraska. The 

locality was visited in 190~ by Lambe/ who 

made further collections of the fauna and 

reaffirmed the determination that the beds are 

of White River age. 

The formation exposed in the Cypress Hills 

is shown on McConnell's map as capping a 

series of plateaus ranging from 3, 700 feet in 

altitude at the east to 4,800 feet at the west. 

The gravel· on the Swift Current Creek plateau, 

which lies northeast of the Cypress Hills, is 

regarded by McConnell 5 as an eastern extension of the Oligocene gravel, though only . un1 Calhoun, F. H. H., The Montana lobe of the Keewatin ice sheet: 

U.S. Geol. Survey Prof. Paper 50, pp. 32-45, 1906. 

2McConnell, R. G., On the Cypress Hills, Wood Mountain, and adjacent country: Canada Geol. Survey Ann. Rept., vol. 1, new. ser., pp. 

1c-78c, 1886. 

a cope, E. D., The Vertebrata of the Swift Current Creek region of the 

Cypres11 Hills: Idem, pp. 79c-85c; The species from the Oligocene or 

lower Miocene. beds of the Cypress Hills: Canada Geol. Survey Contr. 

Canadian Paleontology, 1891. 

4 Lambe; L. M., A new species of H.vracodon (H. priscidens) from the 

Oligocene of the Cypress Hills, Assiniboia: Canada Roy. Soc. Proc. and 

Trans., 2d ser., vol. 11, sec. 4, pp. 37-42, 1906; Fossil horses of the Oligocene of the Cypress Hills; Idem, pp. 43-52; Vertebrata of the Oligocene 

of the Cypress Hills; Saskatchewan: Canada Geol. Survey Contr. Paleontology, vol. 3, pt. 4, 1908. 

6McConnell, R. G., op. cit., p . 34c. 

I 

I . 

identifiable bone fragments were found in it. 

As its altitude is about: 2,900 feet, or 200 feet 

below that of the nearest exposure of Flaxville 

gravel, it is suggested by the writers that a 

more thorough' search might result in the discovery of the Flaxville fauna. The Oligocene 

beds exposed near Bone Coulee, Cypress Hills, 

are described by McConnell 6 as follows: 

The Miocene [Oligocene] beds are characterized by the 

great quantity of waterwom pebbles, derived from the 

quartzite for~ations of the Rpcky Mountains, which are 

found in every part of the series. The pebbles are usually cemented together 1nto massive beds of hard conglomerate but also occur distributed irregularly through 

or ananged in layers and lenticular beds in the sands and 

sandstones. The more massive conglomerate beds are 

found toward the western part of the area or around its 

outskirts. * * * [The beds] are all very irregular and 

seldom remain constant in composition for · any distance 

along their strike. 

SUMMARY. 

The gravel that caps the Cypress Hills in . 

Canada is of Oligocene (White River) age. -It 

is made up of materials from the Rocky 

Mountains, to the west, . and rests upon a 

series of plateaus cut on the Fort Union, Lance, 

and Bearpaw formations and ranging from 

4,800 feet in altitude at its west end to 3, 700 

feet ne~r its east end. 

The Flaxville gravel in Montana is from a 

few feet to 100 feet thick and is composed of 

well-rounded quartzite and argillite pebbles 

from the Rocky Mountains, sand, clay, marl, 

and volcanic ash. It rests upon a series of 

plateaus cut on the Fort Union, Lance, and 

Bearpaw formations, and ranging in altitude 

from 2,600 feet at the east to 3,200 feet at the 

west. Fragmentary fossils collected at 25 

well-distributed localities were not good enough 

for specific determination, but it can be stated 

positively that the formation can not be older 

than Miocene nor younger than early Pliocene. 

Below the Flaxville level there are extensive 

areas, eroded since its deposition, on which the 

covering is thin or absent. Stratified gravels 

and silts have been noted at several localities. 

A single fossil tooth collected from one of these 

exposures of gravel was identified as that of a 

horse resembling the living species. It certainly is not so old as the fauna of the Flaxville 

gravel. The formation is known to be older 

than the advance of the Wisconsin glacier. 

6 Idem, p. 69c. 
184 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1917. 

It must therefore be of late Pliocene or early 

Pleistocene age. 

Present drainage has eroded valleys from 100 

to 500 feet below the late Pliocene bench. 

¥ost of . this cutting was accomplished before 

the advance of the Wisconsin glacier, whose 

drift deposits lie alike on uplands and bench 

lands and. in the valleys. 

The relative altitudes of these four erosion 

levels and the gravel assigned to them are 

3 • 700 ....--0=1.,...i g-oc-en-e-----. 

3,.100 ----------------

2,500 

Flaxville 'gravel 

.(Miocene or early Pliocene) 

is suggested but must be regarded as not yet 

proved. These relations are at present under 

investigation. 

Terrace gravel found by Bowen 2 in the 

neighborhood of Musselshell River, south of the 

Missouri, is probably either Oligocene or 

Miocene; that around the Bearpaw,a Little 

Rocky, Highwood, Judith, Big Snowy, Little 

Belt, Crazy, and other mountain groups is 

probably of Tertiary age and represents one 

2,200 ----- ---·- ------------ ----------------------------------------------

FIGURE 27.-Diagrammatic section showing the relative altitudes of the four erosion levels represented in northeastern Montana and the 

· adjacent part of Canada. 

shown diagrammatically in figure 27. The 

Oligocene of the Cypress Hills is the highest, 

the Miocene or early Pliocene Flaxville gravel 

bench represents a second stage of erosion and 

deposition, the late Pliocene or early Pleistocene 

bench a third stage, .and the late Pleistocene 

and Recent level a fourth stage'.· 

The correlation of these erosio:J;l levels with 

the Blackfoot peneplain and the second and 

third lower benches in the Glacier National 

Park region, described by Alden and Stebinger, 1 

1 Alden, W. C., and Stebinger, Eugene, Pre-Wisconsin glacial drift in 

the region of Glacier National Park, Mont.: Geol. Soc. America Bull., 

vol. 24, p. 569, 1913. 

or more of the erosion levels described. The 

relation of these erosion epochS to the physiographic history of the Rocky Mountains, as 

presented by Atwood 4 and Blackwelder, 5 is 

very problematic and can not be solved until · 

all the factors are known. 

2 Bowen, C. F., The anticlines of the Musselshell Valley (in preparation). 

a Bowen, C. F., The Cleveland coal field, Blaine County, Mont.: U.S. 

GeoL Survey Bull. 5~1, p. 348, 1912. 

'Atwood, W. W., The physiographic conditions at Butte, Mont.; and 

Bingham Canyon, Utah, when the copper ores in these districts wera 

enriched: Econ. Geology, vol. 11, pp. 697-7-\.9, 1916. 

5 Blackwelder, Eliot, Post-Cretaceous history of the mountains of 

central western Wyoming: Jour: Geology, vol. 23, Nos. 2, 3, and 4, 

May-June, 1915. 

0