Please do not destroy or throw away this publication. If you have no furtlier use 

for it, write to the Geological Survey at Washington and ask for a frank t» return it

DEPARTMENT OF THE INTERIOR

Ray Lyman Wilbur, Secretary

XI. S. GEOLOGICAL SURVEY 

George Otis Smith, Director

Professional Paper 158—B

RECEIVED

UtC 1 0 192931 

L. C. DfcCIUS

THE CONTACT OF THE FOX HILLS AND LANCE FORMATIONS

BY

C. E. DOBBIN AND JOHN B. REESIDE, JR.

Shorter contributions to general geology, 1929

(Pages 9-25)

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1929
CONTENTS

Pagfr

Abstract. _______________________________________________________________________________________________ 9

Introduction. _______________________________________________________________________________________________ 9

Questions involved and general conclusions _______________________________________________________ _^_ _____________ 9

Criteria for separation of the Fox Hills and Lance formations__-_____-_-_-_-__---_--____-__________________________ 11

Fox Hills and Lance formations in different regions_-_____-_____--__---__-___--_______-_________________________ 11

Mouth of Cannonball Eiver, N. Dak______-_______-____________-___-_---___--_-_-_-_____-__-_______________ 11

Cannonball River to Fox Ridge, S. Dak____________________________________________________________________ 12

Fox Ridge to Little Missouri River, S. Dak__________________________________________________________________ 14

Marmarth, N. Dak________________________________________________________________________________________ 14

Marmarth, N. Dak., to Glendive, Mont____________________________-_____________________________________._ 15

Northeastern Montana.-____________________________________________________________________________'__'___ 17

Central Montana.__________»__________________________________________________________________________'_'__ 18

Southeastern Montana.___________________________________________________________________________________ 18

Ridge, Mont., to Lance Creek, Wyo_--_---____-_________---__-_----________-_-_--__-_ ______________________ 18

Central Wyoming___________________________•_____________________________________..______________________ 20

Southern Wyoming____________________________________________________________________________________ 21

Yampa Valley, Colo______________________________-_-__-__---_-___-_------___--_----_--_______ 23

Northeastern Colorado and the Denver Basin______-___________--______---__-_------------_---_-_----_______ 23

Western and southern margins of the Interior region. ________________________________________________________ 24

Constitution of the Colgate sandstone member of the Fox Hills sandstone. __________________________________________ 24

Summary of conclusions______________________________________--__-___--__---______--___-___-____________-_____ 25

ILLUSTRATIONS

Page

PLATE 4. A, Grayish-white sandstone at the top of the Fox Hills sandstone in the south bank of the Cannonball River 3K 

miles west of Solen, N. Dak.; B, Cross-bedding in the Fox Hills sandstone (?) in the SE. M sec. 15, T. 15 N., 

R. 8 E., near Govert, S. Dak.; C, Flutings in the weathered surface of the Colgate sandstone member of the Fox 

Hills sandstone in the railroad cut 3^ miles west of Marmarth, N. Dak—__,_.._-______..__-_-_--______._--_ 14

5. A, Local channeling in the Fox Hills sandstone on Little Beaver Creek in the S|E. M sec. 7, T. 102 N., R. 106 W., 

N. Dak.; B, Devil Creek, in T. 21 N., R. 32 E., Mont., showing the white Colgate sandstone and associated beds; 

C, Colgate sandstone 4 miles southwest of Glendive, Mont_________-_-_-_t--------_---------------_---- 14

FIGURE 1. Index map showing distribution of the Fox Hills sandstone._____________________________________________ 12

2. Diagram of faulting in the Lance formation on Worthless (Irish) Creek, in the SE. ^i sec. 23, T. 16 N., R; 20 E.,

S. Dak___-__--_-__-__--_------__-------_-----------------_---- 1 ----------------------------- 13

3. Details of bedding of outcrop of Fox Hills sandstone (?) near Govert, S. Dak_L_____-----.--- -_-___________, 14

4. Diagrammatic cross section across the Cedar Creek anticline at Iron Bluff, ne^r Glendive, Mont____————— 16 

ii '
THE CONTACT OF THE FOX HILLS AND LANCE FORMATIONS

By C. E. DOBBIN and JOHN B. REESIDE, Jr.

ABSTBACT

The presence or absence of an extensive unconforjmty at the 

contact between the Fox Hills and Lance fenactions ig an important element in the problem of the Cretaceous-Tertiary 

boundary in the Western Interior of the United States. Proponents of the theory that an unconformity exists have rested 

their case primarily on a correlation of the Arapahoe and Denver 

formations with the Lance and Fort Union formations, the 

supposed absence in the northern Great Plains of the Laramie 

formation, the relative thinness of the Fox Hills sandstone in 

the northern Great Plains as compared with that in the Denver 

Basin, and reported angular discordances between the Fox 

Hills and the Lance at several localities. The present writers 

describe, chiefly from personal observation, the contact of the 

Fox Hills and Lance formations over much of the area of their 

occurrence and of units equivalent to these formations in areas 

where other names are used, paying especial attention to localities in which there are reported discordances. They advocate 

the view that the Laramie, Arapahoe, and Denver formations 

of the Denver Basin are represented in the Lance formation; 

that the differing thicknesses of the Fox Hills are original 

and not due to varying amounts of pre-Lance erosion; that 

each supposed angular discordance is due to some other phenomenon, such as local small faulting or cross-bedding; and 

finally, as a general conclusion, that there is no unconformity 

between the Fox Hills and Lance other than such as is found 

along local minor erosion planes at many horizons within both 

formations. The suspicion that the peculiar lithology of the 

Colgate member of the Fox Hills sandstone might be due to a 

content of volcanic ash is disproved by petrographic examination.

INTRODUCTION

Many papers have been published on the problem 

of the Cretaceous-Tertiary boundary in the Western 

Interior of the United States, but many points nevertheless remain in dispute. The relation between the 

Fox Hills and Lance formations, a cause of particularly 

wide divergence of opinion, has been of especial interest to the writers because of intimate concern with 

it in the field, and they have ventured here to review 

the matter and to present certain observations and 

opinions regarding it.

The field work upon which the paper is based, carried 

out at different times during the years 1921 to 1926, 

covered most of the region where the Lance occurs. 

It included studies of the contact of the Fox Hills and 

Lance formations in areas that were mapped in detail; 

visits to localities cited by previous investigators as 

showing angular discordance or other marked evidence 

of unconformity between the formations; and examinations of the strata in areas where beds of Fox Hills

age are present in formations known by other

and are overlain by nonmarine beds that are variously

* For .historical details and references to the literature 

,of the subject the reader may consult recent p,ap°^ 

by Knowlton,1 Thorn and Dobbin,3 and War4.3

QUESTIONS INVOLVED AND GENEfiAL CONCLUSIONS

In ,the northern Qreat H&ms region the standard 

section of late Cretaceous and early Tertiary depo''i1js 

contains the following formations, in ascending orc1 ^: 

Pierce shale, Fox IJills sandstone, Lance formation,

-Fort Union formation, and Wasatch formation. Tlie 

Pierre shale contains a large marine fauna, including 

such characteristic ainxnonites as Plg^e^iceras, fcaphites of the group of 4c$ra6&p*(^j$^s? nqdogus, an$ 

;bfi.culites of the large species >5. ovatm, M. wmpressus, 

.and J3. grandis. The uppermost fierce includes .a 

group of scaphites of the genus IHscQ$caphites an4 

.certain .other fossils that Ire mo^e abundant in and 

more characteristic of the Fox Hills. Tsfete jFox Fife 

has a large marine fauna, of which ,the j&qst. distinctive 

fossils belong to the ammqni|e genus 

At some .places the uppermost Fox JJills 

brackish-water species which are foun$ also in the 

lower part of the overlying Lance. The Lance alsp 

contains a great variety of fresM-w.ater invertebrates, 

some reptiles, including especially the dinosaur an 

genus Triceratops, a few species .of mammals, and jt 

large flora. In a small area the upper part of the 

Lance contains a marine fauna similar to that of the 

Fox Hills but somewhat modified and without cephalopods. The Fort Union formation has yielded a 

small but characteristic fauna of fresh-water inveHebrates, a fairly large fauna of primitive mammals, 

and a large flora. The Wasatch formation has 

yielded a small fauna of fresh-water invertebrates, a 

large fauna of mammals of more modern type, and a 

flora like that of the Fort Union formation.

It has been generally agreed that the Pierre si «le 

and the Fox Hills sandstone are Cretaceous and that

1 Knowlton, P. H., The Laramie flora of the Denver Baaia: U. S. G6ol. Survey 

Prof. Paper 130, pp. 3-«2, 1922.

2 Thorn. W. T., jr., and Dobbin, O. E., Stratigraphy of the Cretaeeous^Eicene 

transition beds in eastern Montana and the Dakotas: Geol. Soc. America Bull., 

vol. 35, pp. 500-506, 1824.

3 Ward, Freeman, The Lance problem in South Dakota: Am. Jour. Sci., 5th ser., 

vol. 7, pp. 66-S8, 1024.

9
10 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1929

the Wasatch formation is Eocene. Concerning the 

intermediate formations—the Lance and the Fort 

Union—three views have been expressed. One view 

is that the base of the Wasatch formation is the proper 

plane of division between the Cretaceous and the 

Eocene because the Fort Union is apparently inseparable from the Lance, which contains dinosaurs, whereas 

the Wasatch contains modern types of mammals, and 

because a pronounced discordance at many places 

indicates pre-Wasatch orogeny. Another view is that 

the contact of the Fort Union and Lance formations 

indicates the boundary between the Cretaceous and the 

Eocene because the Lance formation contains the 

latest known dinosaurs, the Lance invertebrates are 

more like those of the Cretaceous, and the marine 

member of the Lance, which is the final marine deposit 

in the whole Western Interior region, is Cretaceous in 

aspect, though at most places the contact with the 

Fort Union appears transitional. A third view is 

that the Lance and Fox Hills are separated by a hiatus 

of great magnitude, which is the first after a great 

unbroken sequence of Cretaceous deposits and which 

therefore constitutes the proper plane of division between the Cretaceous and the Eocene.

The question whether the Lance and Fox Hills formations are or are not separated by a great unconformity ' therefore becomes an important element in the 

general problem, and the history of the view that such 

an unconformity exists will be of interest here. This 

view arose from a comparison of the stratigraphy in 

northeastern Wyoming, eastern Montana, and adjoining portions of North and South Dakota with the 

stratigraphy of the Denver Basin in Colorado, where 

the detailed studies of Emmons, Cross, and Eldridge 4 

were believed to have established the following propositions: The Cretaceous sea of the Western Interior 

invaded a region of low relief; there were no upward 

movements and no eroded areas of great size witMn 

the borders of this region until the end of Cretaceous 

time; there was, near the end of Cretaceous time, a 

passage into conditions of nonmarine sedimentation 

expressed by the Laramie formation; then followed an 

inception of mountain building over the present site 

of the Rocky Mountains and a period of active 

erosion, during which the sediments at places were 

stripped down to the pre-Cambrian; and a new set of 

deposits was then formed, resting in the Denver Basin 

itself on the eroded Laramie and beginning with the 

conglomerate of the Arapahoe formation.

The nonmarine Laramie formation was reported to 

contain a distinctive flora and a brackish and fresh 

water invertebrate fauna and to rest conformably upon 

the highest marine Upper Cretaceous beds in the basin, 

the Fox Hills sandstone. The conglomerate -of the 

Arapahoe formation was reported to contain pebbles

4 Emmons, S. F., Cross, Whitman, and Eldridge, G. H., Geology of the Denver 

Basin in Colorado: U. S. Geol. Survey Mon, 27, 1896.

derived from all the older rocks in the adjacent mountains, indicating the long period of mountain making 

and erosion that preceded. The succeeding Denver 

formation was reported to consist largely of andesitic 

debris not seen in the Arapahoe, a fa0t that implies, 

the elapse of the time necessary for the extrusion and 

erosion of the volcanic materials after the deposition 

of the Arapahoe. The Denver and Arawahoe formations were reported to contain a distirotive flora 

and a dinosaurian fauna that included the genusTriceratops.

In early discussions 5 the Arapahoe and E *mver were 

referred to the Tertiary, and the Laramie was left in 

the Cretaceous. In the monograph on the Denver 

Basin, in consideration of the dinosaurian fauna and 

despite the great hiatus believed to exist l^aeiatli the 

Arapahoe, both Arapahoe and Denver were placed in 

the Cretaceous. In later papers, chiefly because of the 

evidence of diastrophism between Laramie and Arapahoe time, the Laramie was considered by Cross 6 to 

be the uppermost Cretaceous and the Arnpahoe and 

Denver formations to be Tertiary. The Trieeratopsfauna in the post-Laramie beds was considered a relicof the Mesozoic fauna that lived on into Tertiary time.

In the 20 years that followed the publication of the= 

Denver Basin monograph the Fox Hills sandstone and 

overlying strata at many places in northeastern Wyoming, eastern Montana, and western North and South 

Dakota were examined in detail by geologists of the. 

United States Geological Survey, who did not find a 

thick Fox Hills formation, a typical Laramie flora, nor 

a conglomerate similar to the Arapahoe of the Denver 

Basin. On the contrary, a Trieeratops fsuna and a. 

flora identified as like that of the Fort Unioi] formation, 

which, is widely accepted as Tertiary, were found in 

the Lance formation, directly above the relatively 

thin Fox Hills sandstone, and in the sandstone was 

found the same distinctive Cretaceous {aura as in the 

Denver Basin. For some geologists the only answerto the query thus raised seemed to be that the "Trieeratops beds" (the Lance formation) aro separated 

from the underlying marine Fox Hills sandstone by 

the same great unconformity as that supposed to be 

marked by the conglomerate of the Arapaho^ formation 

in the Denver Basin; that erosion was greater in the 

north than in the Denver Basin; and that in the north 

there are no strata equivalent in time to the Laramie 

formation and part of the Fox Hills fomation. In 

the north, however, no suitable plane of ur^onfoEmity 

was at first observed, owing to the absence of a conglomerate similar to that of the Arapahoe. Further 

search revealed local details that were interpreted by 

some geologists as proof of a widespread and at some

6 See, for example, Cross, Whitman, The Denver Tertiary fonx ation: Am. Jour. 

Sci., 3d ser., vol. 37, pp. 261-282, 1889.

6 Cross, Whitman, The Laramie formation and the Shoshone gr">up: Washington 

Acad. Sci. Proc., vol. 11, pp. 27-45,1909; Are the Lance and Fort Union formations, 

of Mesozoic time?: Science, new ser., vol. 53, pp. 304-308, 1921.
CONTACT OF FOX HILLS AND LANCE FORMATIONS

places angular unconformity between the Fox Hills 

and Lance formations.

The interpretation of geologic history given above, 

the assignment of a great time value to the unconformity in the Denver Basin, and the evidence of the 

presence of a corresponding unconformity farther 

north have been vigorously disputed, and a list of 

papers contributed to the discussion is long. The 

strongest support for the theory of a large hiatus 

beneath the Lance formation lies hi the supposed 

existence of an angular unconformity due to deformation and erosion, and no other specific explanation of

•some of this important physical evidence has yet been 

published.

In brief, then, the specific question to be considered 

liere is whether the Lance formation rests conformably 

on the Fox Hills sandstone, or whether there is immediately beneath the Lance a great hiatus that represents the time required for the deposition of a considerable thickness of beds and for the occurrence of 

notable events in the geologic history of the Western 

Interior region. The writers' answer to this question 

is that there is nowhere hi the areas considered a 

great unconformity between the Fox Hills and Lance 

formations and at most localities not even a minor one.

CRITERIA FOR SEPARATION OP THE FOX HILLS AND 

LANCE FORMATIONS

In a consideration of the nature of the boundary 

between the Lance and Fox Hills formations one must 

first determine what criteria shall be used for identifying the two formations and thus settle upon a means 

of locating the boundary between them. In general, 

minor individual lithologic units are not persistent in

•either the Fox Hills or the Lance. On the other hand, 

larger lithologic units, aggregations of these smaller, 

variable units, persist over large areas and are trustworthy features for identification. In some places, 

however, there is little lithologic distinction between 

beds that contain characteristic Lance species and 

others that contain characteristic Fox Hills species, 

and in these places the fossils must be made the chief 

reliance for separating the formations.

In eastern Montana, western North and South 

Dakota, and northeastern Wyoming the Fox Hills 

formation usually consists of an upper white sandstone (in eastern Montana called the Colgate sandstone member), beneath which occur alternating beds 

of gray, yellow, and buff sandstone and sandy shale. 

As noted on page 9, this formation contains a marine 

fauna, in part characteristic but in part similar to 

that found in the upper part of the underlying Pierre 

shale. Locally a brackish-water fauna that contains 

an admixture of marine forms occurs at the top of the 

formation. At and west of Glendive, Mont., the 

Colgate member contains only fossil plants, though 

the lower member of the formation contains a few

marinfe invertebrates. Here both the lithology and 

the marine fauna are of assistance in identification.

In central and southern Wyoming and northwestern 

Colorado marine forms characteristic of the $ox Hills 

occur in sandstones that have been interpreted at 

some places as part of the Lewis shale and at others as 

part of the overlying beds, variously named, but.th^re 

is no definite, separable Fox Hills formation. TH 

beds immediately below the horizon of these Fox 

Hills fossils are in part nonmarine, and the beds above 

are all nonmarine. Here the marine fossils alone are 

characteristic.

With the exception of the Cannonball marine mem-* 

ber hi a small area in North and Sjeuth Dakota, the 

Lance formation of Montana, tnV Dakotas, and 

eastern Wyoming is of nonmarine origin. The lov^er 

part is made up of somber-colored sandy shale alternating with lenticular beds of buff or brown sandstone 

and thin beds of coal. The contained fossils include 

plants, reptiles, especially dinosaurs of the genus 

Triceratops, and a few mammals. The fact that 

vertebrate remains are especially abundant near the 

base of the Lance provides an excellent criterion for 

separating it from the underlying Fox Hills formation hi areas where the lithology is similar, but at 

many places the lithology also is of great service. 

The upper 75 to 350 feet of the Lance usually consists of soft buff and cream-colored calcareous sandstone and shale with numerous beds of coal.

In central Wyoming the Lance formation consists 

of interbedded fine-grained tan sandstone, light-gr<*y 

shale, and thin layers of carbonaceous shale and oal 

and is not conveniently divisible into members. It 

contains, however, the same nonmarine fossils as the 

Lance of the areas to the east and north.

In southern Wyoming and northwestern Colorado 

beds believed by the writers to be the equivalent of 

the Lance formation, though known by several lon<al 

names, have the same lithology as the Lance of central 

Wyoming.

FOX HILLS AND LANCE FORMATIONS IN 

DIFFERENT REGIONS

In setting forth the local features on which is founded 

the general conclusion that there is nowhere an important unconformity between the Lance and the 

Fox Hills the data are presented by convenient geographic units, recognizable on Figure 1.

MOUTH OF CATOTONBALL BITER, N. DAK.

In the area near the mouth of the Cannonball Rr^er 

the gray-white sandstone at the top of the Fox Hills 

forms a variable upper part of an upper member of 

the formation. The remainder of the member consists 

of light-gray clayey sandstone and olive-colored sandy 

shale; the two parts together attain a thickness of 100 

feet. Above the white sandstone and to all appear-
12 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1929

alnces conformable with it are thick beds of impure 

lignite and carbonaceous shale of the Lance formation. 

(See pi. 4, A.) The lower member of the Fox Hills 

in this area is a thick-bedded yellowish-brown sandstone about 100 feet thick. Further details regarding 

the character &{ the Fox Hifls in this area are given by

o Rawlins JWalcott 

Rock Springs

Outcrop of. Fox 

Mills sandstone

Section of parts of Fox HiUs and Lante formati&t^ on south

bank of Cannonball River 3% miles voest of Solen, N. Dak. 

Lance formation (basal part): Feet 

Irregular assemblage of purple and gray shale and gray 

sandstone______ ___________________________ 6O

Lignite-- ———— ———— ___________________ 1

Purple carbonaceous shale._______________________ 2

Fox Hills formation:

Sandstone, white, more r^st&tant 

than inclosing bedsj , contains • many casts of roots ______'__-__ 3

Sandstone, grayish white, soft; 

weathers into fluted cbannels; 

contains many layers and concretions of ferruginous brown 

sandstone and Halymenites major 

throughout (see pi. 4)__.._____ 60

Large concretions of cinnamonbrown sandstone________--_-_- 2

Shale, olive-colored, sandy _______ 50

Sa'ndsferie, brown, thick bedded,, 

several feet; top of lowe* member. 

Level of the Cannonball River.

Both members of the Fos* HiUs contain throughout HalylhemUs intiydr, d 

fossil believed to be a usable criterion 

of marine origin. The lower member 

at the west end of the railroad cut 

one-third of a mile west of Solen, N. 

Dak., yielded, at a horizci 30 feet 

below the top, Pterw nebrascdna 

Evans and Shumard, P. linfmae/ormi^ 

Evans and Shumard, Tettina scitida Meek and Hayden, and Mactra 

jormosa Meek and Hayden, all of 

which afre Jfong-ranging sj^seies tfeat 

^6rve" ol^y 60 confirm tit& it-dicatiO-t 

6f B^yrhenites that the beds are

marine.

The fox Sills near t£ie mouth of 

Cs&tfoAttfi Riv^, therefore, 

two riteitffeM fed fe 

fcftnttrfMe bfeneath tl_e 

Sbm'6 nut*dreds of fe^t hig^^r in the 

^6^6ir the CstortfoHb^lI marine menifeer of te La&ce appfeftrs ^itb A 

fte& ^b i^rm1_tr to that* of 

f tfx ifitfs a^ to i§irgge3t thf ,t no 

p^rio$ coitldf Mte intervened in 

dition to tha*t (luring vMcn

the

tfee

FIGCKE 1.—Index map showing distribution of the Fox Hills sandstone. Certain outcrops hi central 

South Dakota and eastern Colorado and beds of Fox Hflls age included in other formations in 

central Wyoming and western Colorado are not shown

lower Ltoce 

laid down.

sediments were being

Leonard.7 A fairly representative section of the beds 

exposed on the Cannonball River is as follows:

? Leonard, A. Q., The Cretaceous and Tertiary formations of western North 

~ * * ^BiaiiAfoBfeum: Jxmr. Geology, vol. 19, pp. 511-514, 1911.

cAirtf o]!rBli,i fto teas, s.

Observations made by the writers between the 

Cannonball River and Fox Ridge, the type locality of 

the Fox Hills formation, are in complete accord with the
CONTACT OF FOX HILLS AND LANCE FORMATIONS IS

W.

findings of Stanton,8 who reports that the Fox Hills 

exhibits much evidence of irregular deposition, channeling between beds, and variability in thickness, but 

that it nowhere shows evidence of a major break at its 

top. The occurrence at isolated localities in this area 

at or near the top of the Fox Hills of beds that have an 

irregular base and contain a fauna of chiefly brackishwater species has led to the assumption of a widespread 

unconformity beneath these beds and the selection of 

this unconformity as the "pre-Tertiary" break.9 The 

beds immediately above the "hiatus," however, contain a number of significant species of the Fox Hills 

fauna and preclude an interruption greater than that 

represented by any one of the admittedly minor erosion 

planes present in both Fox Hills and Lance formations. 

The fossils are delicate shells that would show any 

reworking very distinctly. Although the white sandstone of the upper Fox Hills was largely concealed 

along the route followed by the writers 

through this area, its presence locally is 

attested by Calvert, who says: 10 "In 

some areas the lignite-bearing beds of the 

Lance abruptly change to the white marine sandstone of the Fox Hills, but in 

others the rocks of the two formations 

are very similar and no hard and fast 

line can be drawn between them."

Particular attention was paid to the locality on Worthless Creek (locally known 

as Irish Creek), in the SE. % sec. 23, T. 16 

N., R. 20 E., where Calvert n observed 

what he regarded as an angular unconformity between 

the Fox Hills and the Lance that is cited a number 

of times in the literature. 12 Calvert's description is as 

follows:

On Worthless Creek, in T. 16 N., R. 20 E., where exposures 

are especially good, the most striking example of unconformity 

between the Fox Hills and Lance formations was observed. 

On the west side of the Worthless Creek Valley, near the line 

between sees. 25 and 26, the "somber beds" of the Lance formation transgress across the Fox Hills sandstone, and the upper 

part of the Fox Hills down to the banded shale is absent. The 

unconformity at this locality is angular as well as erosional, for 

the banded shale dips 4° N., whereas the Lance is horizontal. 

A section of the strata 500 feet long reveals the Lance filling a 

channel eroded in the banded shale of the Fox Hills to a depth 

of 40 feet, so that the vertical amount of combined transgression and erosion is at least that amount. On the opposite side 

of the valley the undoubted Fox Hills is believed to be absent

s Stanton, T. W., Fox Hills sandstone and Lance formation ("Geratops beds") 

in South Dakota, North Dakota, and eastern Wyoming: Am. Jour. Sci., 4th ser., 

vol. 30, pp. 173-182, 1910.

» Knowlton, F. H., Further data on the stratjgraphie position of the Lance formation (" Ceratops beds"): Jour. Geology, vol. 19, pp. 362-360,1911.

w Calvert, W. R., and others, Geology of the Standing Rock and Cheyenne River 

Indian Reservations, N. and S. Dak.: IT. S. Qeol. Survey Bull. 575, p. 18,1914.

»Idem, p. 18.

is Knowlton, F. H., Further data on the stratigraphic position of the Lance formation ("Ceratops beds"): Jour. Geology, vol. 19, p. 346,1911; Cretaceous-Tertiary 

boundary in the Rocky Mountain region: Geol. Soc. America Bull., vol. 25, p. 327, 

1914.

and the lignitic zone, of $&''%&&$& rests on a brown 

shale, which may rejweseut'the ifij> of the Kerre or 

part. of the Fox Hills. la any event, there is surely less IJ 

25 feet of Fox HiUs present at this place. In view of the' 

that the Fox Hills sandstone i& normally at least 160 feet t 

it seems that the time during wMch erosion took place 

considerable duration.

The writers visited thtk loemEty early in May, 

the outcrops were not hidden by vegetation and i^ 

possible to study the structural relations in detail.; 

most casual inspection under such conditions 

that the "unconformity" is doe to a small fault 

has displaced a carbonaceous shale bed about 

the downthrown bed dipping into the fault at aa 

of about 4°. (See fig. 2.) Dinosaur bones at' 

base of the bluffs indicate that the beds in the exp®r 

are Lance rather than Fox Hills, and tbis fact 

why Calvert failed to find Foot Hills beds on the 

posite side of the valley. There is probably a §©ec**€l

FIGURE 2.—Diagram of faulting in Lance formation on Worthless <Irisb)-Creek, in the 

23, T. 16 N., R. 20 E., 8. Dak. The throw is about 20 feet

small fault a few hundred feet away, thought its 

presence is not very clearly shown.

Wilson and Ward i3 report that the contact of the 

Fox Hills and Lance is transitional in the Worthless 

Creek district and that the lowest bed of coal or eaibonaceous shale in the Lance occurs just above an oyster 

bed that marks the top of the Fox Hills over a rather 

broad area. That small faulting is common in the 

whole area is also evident from their work and fr>m 

that of Russell. 14 A small fault of the same type as 

the one at Worthless Creek is clearly shown on the 

north bank of the Moreau River about 11 miles e*st 

of Bixby, in «ec. 15, T. 14 N., R, 14 E., where a throw 

of 35 feet introduces a local dip of 4° in bade that 

probably constitute the upper part of the FoX HiUs, 

An example of irregularities of deposition is well shown 

on the bank of the Moreau River at Bixby. The ujir>er 

part of the exposure may be Lance, but even BO tne 

relations between the irregular beds are so intricate 

that it is unreasonable to pick out any plane in the 

sequence as more significant than the rest.

w Wilson, R. A., and Ward, Freeman, Tbe possibilities of oil ia northern fJ-^aeh 

County: South Dakota Oeol. and Nat. Hist. Survey Ote:. 13, pp. 8-7, iB23.

i' Russell, W. L., Tbe possibilities of oil in western Ziebach Gouaty: South 

. Dakota Geol. and Nat. Hist. Surrey Giro. 20, pp. 12-23,1926.
14 SHORTEB CONTRIBUTIONS TO GENERAL GEOLOGY, 1929

FOX BIDG1 TO LITTIE MISSOTTBI BIVER, S. DAK.

From Fox Ridge westward to the Little Missouri 

River the contact of the Fox Hills and Lance is, as a 

rule, exposed only .in the more or less isolated bluffs 

along stream valleys. Practically all outcrops of 

both formations near their contact show local channeling, cross-bedding, faulting, and slumping on a 

small scale. The Fox Hills is about 125 feet thick 

and consists of light-colored marine sandstone which 

is overlain by the basal coal-bearing beds of the 

Lance. No distinct or persistent division into a 

lower yellow sandstone and an upper white sandstone 

could be recognized, though it must be admitted that 

the outcrops are scarcely adequate.

One locality that received particular attention in the 

area west of Fox Ridge was that in the SE. 3^ sec. 15, 

T. 15 N., R. 8 E., South Dakota, 1 mile south of 

Go vert post office, which has been reported by several 

writers as showing an angular unconformity between

The sandstone and conglomerate capping some of 

the high buttes on the divide between the Belle 

Fourche and Owl Rivers, northeast of Belle F6urche, 

S. Dak., which have been doubtfully called the Fox 

Hills sandstone,16 are of White River (Olig->cene) age, 

according to Rubey,17 who has examined them in detail.

As a brief summary, it may be said that all data 

obtained by the writers regarding the contact of the 

Fox Hills and Lance in South Dakota aro in accord 

with the findings of Ward,18 who says: "It seems 

plain that the evidence points consistently and convincingly to the fact that there is no sharp or welldefined break between the Fox Hills and Lance— 

certainly no break which would warrant a division 

between the Mesozoic and Cenozoic."

MAEMARTH, H. DAK.

At the south end of the Cedar Creek anticline, in 

the vicinity of Marmarth, N. Dak., the cor tact of the

^I.T.VJ??.'.!.... . ....'...•-. • •'•..........•'.;.••:•.:•..•.'• V:':^:;;:7---: :. :.'": potent.hi»HaiBd''iia'nfi^.'..:i;.'.-.';.-"."v.'-"""'--.'•'•'.•: •:.•.'.•.'.•..'.•;.;'.v.".'^

——-__ Gray clay shale— — — Z_ ———— — 

Brown carbonaceous shale - '— ~ _r— —^r—__ /Gray-white sandstone_

so Feet

FIGURE 3.—Details of bedding of outcrop of Fox Hills sandstone (?) in the SE. H sec. 15, T. is N., E. 8 E., near 

Govert, 8. Dak. Length of section shown, 125 feet, drawn to scale. Part of this outcrop is shown in Plate 4, B

the Fox Hills and the Lance.15 The exposure at this 

locality is shown in Plate 4, B, and exhibits the 

following section:

Section on bank of Moreau River near Govert, S. Dak.

Feet 

Dark-colored wash and soil_________________________ 10

Recent sand_______________________________________ 6

Clay, gray. ————— _--.______.________________ 5

Sandstone and sandy shale with topset and foreset bedding. 18 

Talus.

A detailed examination of this exposure shows that 

the inclined bedding planes represent merely foreset 

bedding and are not a result of folding and erosion. 

The sketch in Figure 3, made to scale, gives the 

details of bedding not clearly visible in the photograph. No evidence could be obtained to indicate 

the age of the individual beds in this outcrop, and it is 

not possible to assign them definitely to either the 

Lance formation or the Fox Hills sandstone.

is Knowlton, F., H., Further data on the stratlgraphic position of the Lance 

formation (" Ceratvps beds"): Jour. Geology, vol. 19, p. 367, 1911; Cretaceous- 

. Tertiary boundary in the Rocky Mountain region: Geol. Soc. America Bull., 

vol. 25, p. 327,1914. Catvert, W. B., and others, op. dt., p. 19.

Fox Hills and Lance exhibits all the characteristics 

observed farther east. On little Beaver Creek in 

the SE. y± sec. 7, T. 132 N., R. 106 W., the transition 

zone between the typical Pierre shale and the .basal 

Fox Hills sandstone is about 40 feet thick. Through 

this zone the rock grades upward into a soft yellowish 

massive sandstone about 50 feet thick,, which is 

overlain by the grayish-white sandstone tjia-t is seen 

farther east and is now known in eastern Montana 

as the Colgate sandstone member of the Fox Hills 

formation. The top of the Colgate sandstone shows 

local channels (see pi. 5, A), which have been interpreted to indicate an unconformity. 19 The section at 

this locality is as follows:

w Darton, N: H., TJ. 8. Geol. Surrey Geol. Atlas, Belle Fourct« foUo (No. 164), 

p. 5,1909.

w Eubey, W. W., personal communication.

w Ward, Freeman, The Lance problem in South Dakota: Am. Jiur. Sci., 5th ser., 

vol. 7, p. 67,1924.

M Leonard, A. G., The geology of southwestern North Dakota with special 

reference to coal: North Dakota Oeol. Survey Fifth Blenn. Bept., pp. 43-44, 1908. 

Knowlton, F. H., The stratigraphic relations and paleontology of the "Hell Creek 

beds," "Ceratops beds," and equivalents and their reference te the Fort Union 

formation: Washington Acad. Sci. Prop., vol. 11, pp. 201-202,1908.
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 158 PLATE 4

A. GRAYISH-WHITE SANDSTONE AT THE TOP OF THE FOX HILLS SANDSTONE IN THE SOUTH BANK OF 

THE CANNONBALL RIVER 3^ MILES WEST OF SOLEN, N. DAK.

£. CROSS-BEDDING IN THE FOX HILLS SANDSTONE (?) IN THE SE. % SEC. 15, T. 15 N., R. 8 E., NEAR

COVERT, S. DAK.

C. FLUTINGS IN THE WEATHERED SURFACE OF THE COLGATE SANDSTONE MEMBER OF THE FOX 

HILLS SANDSTONE IN THE RAILROAD CUT 3J^ MILES WEST OF MARMARTH, N. DAK.
TJ. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 158 PLATE 5

A LOCAL CHANNELING IN THE FOX HILLS SANDSTONE ON LITTLE BEAVER CREEK IN THE SE. 

SEC. 7, T. 102 N., R. 106 W., NORTH DAKOTA

B. DEVIL CREEK, IN T, 21 N., K. 32 E., MONTANA, SHOWING THE WHITE COLGATE SANDSTONE AND

ASSOCIATED BEDS

C. COLGATE SANDSTONE 4 MILES SOUTHWEST OF GLENDIVE, MONT.
OF FOX HILLS AND LANCE FOi

Section in the Fox Hills and Lance formations on JWflfo Beaver 

Creek in the SE. H sec. 7, T. IS® N., fi. 106 W., N. Dak.

[See pi. 5, A]

Lance formation (lower part) : " Feet 

Sandstone, light yellowish brown, eoarse grained;

contains scattered fragments of carbonized wood__ 1 

Sandstone, yellowish brown, soft, cross-bedded, 

medium grained; contains large copper-colored 

concretionary masses that are hard and weather 

out unbroken______-____________»»_,__--.__--_- 15

Sandstone, shaly, and sandy shale, light gray to drab, 

soft; contains thin crusts of limonitic material and 

small limonitic concretions; cross-bedded. ________ 22

Sandstone, rust-colored, eoarse grained, much crossbedded; contains many siderite concretions; at 

some places hard, at others,soft_________________ 11

Sandstone, soft, light gray; contains rust-colored, 

iron-stained masses that are hard and contain many 

plant impressions__________________-____-_--___ 3

Shale, sandy, and shaly sandstone, brown, carbonaceous. ______________________________________ 5

Shale, black, carbonaceous________________________ 4

Shale, brown, carbonaceous. ______________________ 6

Sandstone, gray white, shaly, coarse grained, crossbedded locally but otherwise massive. ____,.___.___ 7

Shale, brown, carbonaceous, irregular. _____________ 1

Shale, drab to light gray____ __ __________________ 7

Fox Hills formation:

Colgate sandstone member (part) —

Sandstone, Mght gray, soft; «ontaizi«! aaaany fossil 

roots of plants_-__________-________________ 5

Shale, drab to light gray, with very irregular 

base_____ ______ — __!______________ ________ 2

Sandstone, gray-white, and gray shale, very much

cross-bedded and irregular __ _„ _ __„_ _ .__ 8 

Sandstone, gray- white, massive .to jrather indistinctly bedded, shaly in places; lower 10 feet 

streaked with iron stains; locally contains irregular thin lenses of carbonaceous shale. Halymenites major throughout. Forms the smooth 

wall above creek level shown in Plate 5, j4____ 40

Shale, carbonaceous-.. _______________________ 6

Creek level.

In the railroad cut 3^ miles west of Marmarth the 

Colgate sandstone is about 30 feet thick, massive, 

locally cross-bedded, and overlain by a carbonaceous 

shale bed 1 foot thick. (See pi. 4, C.} About 5 miles 

sputh of Marmarth, in the NE. ^ sec. 32, T. 132 N., 

B. 106 W., the Colgate is again well exposed and 

contains abundant remains of Halymenites major. 

Other details regarding the Fox Hills and Lance 

formations in the Marmarth area are given by Stanton,20 with whose conclusions the writers concur — that 

"it is most probable that the abrupt change from 

marine to fresh-water and land conditions seen near 

Marmarth is purely local and that the eroded surf ace

26 Stanton, T. W., Fox Hills sandstone and Lance formation {"Ceratops beds") 

in South Dakota, North Dakota, and eastern Wyoming; Am. Jour. Sci., 4th ser., 

vol. 30, pp. 182-184, 1910.

33225°— 29 —— 2

at the top of

15

not represent a time 

interval of any importance."

MAHMARTH, V. DAK,. TO GLENDIVE, MONT.

In the SW. M we. 34, T. 7 N., E. 61 W., Mont., 

about 1 mile west of the Morth 0akota line, the Colgate 

sandstone displays a dewa-eot contact with the overlying horizontal La-ice beds. The sandstone is cr^ssbedded and channeled on a small scale, but the significance of the iiaeonformity is minimized by the 

fact" that at short distances away the contact is noj 

sharp nor discordant. xf

Other unconformities between the Fox Hills

Lance formations^ reported by Knowlton 21 on . 

authority of Calvert to occur in sec. 22, T. 6 

R. 60 E., and sec. 32, T. 7 N., R. 61 &, Montana, 

not found ia these sections. The writers examined 

every outcrop* along-4het contact in T. 7 N. but could 

find no evidence of unooafojmity other than crossbedding and purely local channeling of a kind present 

at many levels in both Fex Hills and Lanee, ' As 

Knowlton was quoting Calvert, who supervised the 

mapping of the area by Bowen,22 it is possible that a 

mistake was mad© somewhere in the process of handing 

on the references and that it was intended to cite the 

localities as ia seca 27 and 32, .T. 6 N., B. 60 E,, as 

said elsewhere by Carver*,8* though Bowetfs" 1m ap 

shows no Colgate in sec. S2} T, 6 N., R. 60 E. Sec. 32, 

T. 7 N., R. 61 E., is on the east side of the Cedar Creek 

anticline and not on :tihe west side, as said by Knowlton* 

Published photogmpla® 24 of one of these unconformities 

show local ehanneliftl afrtt cro$s-bed^ag, sti«li «s characterize the upper part of the Fox Hills thwughow* its 

extent.

It has been stated tijat the Fox Hilte and Iianee are 

unconf ormable along the Cedar Creek antidi»« beemse 

in the Baker field the Colgate sandstone, which at the 

time the statement was made was eoflsidered a merrber 

of the Lance, " appears to rest directly on Pierre sMle 

without the intervention of the lower strata so notice-' 

able at Iron Bluff" (near Qlendive)/6 The .writers* 

examinations along the whole length of the anticline 

have convinced them tjiat the basal brown 

of the Fox Hills is preseat femgfto 

the anticline, though it is replfwsed by gray sftady s^lde 

in a few localities, aad feat the upper white «ands*one 

contains Halymeniies &t many places and is marine

» Knowlton, F. H., Further data m th« stratigraphic position of tbe Lan-^ fwrmation ("Cerataps beds"): Jour. Geotogy, jol. 19, p. 3«6, flgs, & 3, 1SBL

s* Bowea, C. f., The Baker ligpite Md, CtBte O^aty, MOB*.: U. a CteoL 

Survey Bull. 471, pp. SOS^Sft, »lk :

% Calvert, W. E., Cteofcigy « ^cartato Ugalle ftuMs in eastern Montaaa: 17, S. 

Qeol. Surroy Butt. -

25 Calvert, W. R., Geology at eertaia 

Oeol. Purvey Bal£ ^,"
16 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1920

The rocks near Glendive were first studied by 

Leonard,26 who says:

In the Glendive region there are no beds above the marine 

Pierre that correspond to the supposed Fox Hills clay and 

sandstone of Hell Creek. In fact, the line of contact between 

the Pierre and the overlying dinosaur-bearing beds, while not 

discordant so far as structure is concerned, may possibly represent a time break in which most of the upper fresh and brackish 

water beds of the Cretaceous are wanting.

It may be seen from this statement that all the rocks 

above the Pierre shale were included by Leonard in the 

dinosaur-bearing beds, the Lance formation. Leonard's section is as follows:

35 feet thick is 150 feet stmtigraphieally above F'erre shale. 

In the Baker field, however, this white sandstone, which 

Leonard states constitutes the most prominent stir tuna, in the 

region, appears to rest directly on Rerre shale rdthout the 

intervention of the lower strata so notieeaMe at Iron Bluff.

Observations made by the writers at Iron Bluff and 

vicinity show that the section published by Leonard 

and quoted by Calvert is in error. It was assumed by 

Leonard that the sandstone (No. 3 of Leorard's section) capping Iron Bluff (see fig. 4) dips eastward 

beneath the Colgate sandstone in the bluffs east of 

Sand Creek. It is clear, however, that the Colgate is 

present in Iron Bluff beneath the top of Leonard's No.

W.

Iron 

Bluff

4.—Diagrammatic cross section across the Cedar Creek anticline at Iron Bluff, near Glendive, Mont.

Section of rocks at Iron Bluff and vicinity

8. Coal bed, burned but probably 6 feet thick. Feet 

7. Shale with a few thin beds of sandstone; abundant collection of fossil plants in sandstone bed 20 feet from 

base——___________________________ 150 

6. Sandstone, massive, gray._________________________ 40

5. Shale and sandstone; a few fossil plants at base-______ 160

4. Sandstone, white, massive; most prominent stratum in

the region____________-_____________________ 35

3. Sandstone, brown; fossil leaves in bottom part; forms

summit of Iron Bluff__________________________ 75

2. Shale and sandstone; fossil leaves in upper 20 feet_____ 75

1. Shale, dark, Pierre, with limestone concretions containing abundant marine fossils; exposed to river level-_ 100

635

Calvert a later grouped Nos. 2, 3, and 4 of Leonard's 

section into the Colgate sandstone member of the 

Lance formation and wrote:

Although there is in the Iron Bluff section an appearance of 

transition from the Pierre shale into the overlying arenaceous 

strata, which suggests that the sandstone occupies "the stratigraphic position of the Fox Hills, the evidence of fossil leaves 

indicates that much if not all of it is of later age.

Referring to the finding in units 2 and 3 of fossil 

plants that were identified by Knowlton as Tertiary 

species, he says:

It is certain that if the Fox Hills sandstone is present in 

this section it is restricted to the 70-foot interval between the 

location of the fossil plants and the top of the Pierre shale. 

* .* * Southward from Iron Bluff the stratigraphy suggests 

6ven more strongly that the Fox Hills is not present. In the 

section near Iron Bluff, as given by Leonard, a white sandstone

» Leonard, A. G., The coal fields of parts of Dawson, Rosebud, and Ouster 

Counties, Mont.: U. S. Geol. Survey Bull. 316, pp. 197-198,1907.

» Calvert, W. R., Geology of certain lignite fields in eastern Montana: U. S. Geol. 

Survey Bull, 471, pp. 194-196,1910.

3, as shown in the section on the east face of Iron 

Bluff given below. (See also fig. 4.) On the north 

face of Iron Bluff the Colgate is much discolored by 

brown ferruginous stain leached from the overlying 

rust-brown sandstone, a lens in the basal Lance which 

does not seem to extend eastward across Send Creek. 

On Sand Creek the upper part of the lower member of 

the Fox Hills yielded marine fossils.

In summary, it may be said that near Glendive the 

Fox Hills sandstone maintains all the characteristics 

observed farther east, except that the Colgate member 

contains well-preserved fossil plants, which have been 

identified by Knowlton as Fort Union (Tertiary) 

species.28

As shown in Plate 5, B, beds of lignite also occur in 

the Colgate member and in the Hell Creel: member, 

immediately above. Sections at Iron Bluff and Sand 

Creek are as follows:

Section of the Fox Hills and Lance formations at Iron Bluff, southwest of Glendive, Mont.

Feet 

Lance formation (part of Hell Creek member or "somber

beds"):

Sandstone, brown, platy; makes top of Iron Bluff__ 4 

Concealed, probably like unit above-______________ 20

Sandstone, light gray with rusty stain locally, fairly 

cross-bedded-__________________________ 6

Concealed, probably sandstone.--—____-__—__ 11

Fox Hills sandstone:

Colgate sandstone member—Sandstone, white, fine 

grained, massive; deeply stained at places by material leached from the overlying ferruginous sandstone. _ ______•_________________,-_-_-_________ 44

28 Calvert, w. R., Geology of certain lignite fields in eastern Montana: II. S. 

Geol. Survey Bull. 471, p. 195,1912.
CONTACT OF FOX HILLS AND LANCE FOKKAWOSB 17

Fox Hills sandstone—Continued. i

Lower member— Feet 

Sandstone, brown, containing many ferruginous

nodules___________________________________ 11

Sandstone, soft, yellow, containing discontinuous

layers of dark-brown platy sandstone-..-______ 25

Sandstone, soft, yellow.______________________ 9

Sandstone, light gray, fine grained, concretionary. 1 

Sandstone, soft, yellow____-____-_________-___ 10

Sandstone, dark brown, platy and concretionary. 1 

Sandstone, dark colored, soft; weathers yellow.__ 10 

Sandstone, soft, shaly, light gray; weathers

yellow__ — _ — _________________________ 16

Shale, sandy, gray, stained with limonite-______ 5

Shale, brown and gray, sandy___________ 13

Total lower member______._____________ 101

Pierre shale: Shale, gray, sandy, with many large fossiliferous concretions in upper 20 feet.

Section of the Fox HiUs sandstone on east side of Sand Creek, 

4 miles southwest of Glendive, Mont.

Lance formation (Hell Creek member or "somber beds")- 

Fox Hills sandstone:

Colgate sandstone member— Feet 

Sandstone, white, fine grained, massive, sugary; 

crops out in a prominent white bluff and contains many well-preserved fossil plants identified 

as Fort Union (Tertiary) species_____________ 7

Coal, impure_______________________________ 2

Sandstone, like that above._________________ 45

Total Colgate member..__________________ 54

Lower member—

Sandstone, concretionary, lenticular__^_________ 5

Sandstone, brown, limonitic, slabby, grading upward into soft yellow shaly sandstone and sandy 

shale; contains Vanikoro ambigua, Fusus dakotensis, and Anomiaf sp. 15 feet below top___ 70

Pierre shale.

Total lower member__________________ 75

NORTHEASTEBN MONTANA

In western and northwestern Garfield County, 

Mont., the lower member of the Fox Hills consists of a 

massive yellow-brown coarse-grained sandstone that 

averages about 75 feet in thickness and makes a prominent wall along the tributaries to the Musselshell and 

Missouri Rivers. The white Colgate member overlies 

the lower member and can be seen for miles as its outcrop meanders in and out of numerous coulees. (See 

pi. 5, C.) The lower member is marine in this region, 

but no fossils were found in the Colgate member. 

Eas|i of Hell Creek the white Colgate member is replaced by friable yellow to brownish sandstone and 

sandy shale.

Channeling and cross-bedding are common in the 

Colgate member in this region, but during detailed 

mapping by Mr. Dobbin, extending over two field 

seasons, no evidence was found to indicate a major 

break at the top of the Fox Hills. This conclusion is 

in accord with the findings of Brown,29 who says:

» Browa, Barnum, Cretaceous-Eocene correlation in New Mexico, Wyoming, 

Montana, Alberta: Oeol. Soc. America Bull., vol. 25, pp. 357-358.- 1914.

On the east fork of Crooked Greek near the old Cook ranch, 

on the west fork of Crooked Greek near the Gus Colin clr'm, 

and on the east fork of Hell Greek near the EE cattle camp, 

these marine beds (Pox Hills) have been eroded in places, soT**etimes to a depth of 10 feet, before the succeeding massive sandstones of the fresh-wafer "Lane©" were deposited. The strata 

are, however, in all eases parallel to the bedding plane of the 

succeeding sandstones, and the break is evidently of local erosional character. * * * No g%a of an angular unconformity has been noted between the Fox Hills and the "Lame," 

and I have never yet seen any geologic evidence of the " 

diastrophic break" which is alleged to occur

The following section is typical of the Fox E"*Ub 

sandstone along the Musselshell and Missouri Rir%s 

in Garfield County:

Section of Fox Hitts sandstone on Dm? Creek, in the *ee.

10, T. 21 N., R. &£ E., Mont. •

Lance formation (Hell Creek member or "somber bfeds)." 

Fox Hills sandstone:.

Colgate sandstone member: Sandstone, white, fine

grained, massive-. ———————————————— --- : — <J0 

Lower member:

Shale, yellow, sandy, with thin beds of sandstone. _ II 

Sandstone, concretionary. __---_---_----_----- 1

Sandstone, brown, hard; makes a ledge; contains

Lingida ntiida. Meek and Haydea in abundance _ 2 

Shale, yellow, sandy _ _„_________->._.. ——— 1__ 5

Sandstone, yellow, fairly hard; makes a wall- _ , _ 15 

Sandstone, brownish yellow. _____ — _ — ____ — __ 15

Shale, gray, sandy--.---.---- —— — - —— — - 4

Sandstone, yellow, soft, shaly at base— ____ — ___ 20

Total Fox Hflte sandstone 103

Bearpaw shale (== upper Pierre).

In T. 16 N., R. 3S E., Montana, about 

north of Forsyth, Bauer 38 found quartzite ad pnrphyry pebbles at a horizon considered by Mm the I ise 

of the Lance formation. The. pebbles are hall an r*<sh 

to 3 inches or more in diameter and are embedded in 

impure limonite, which ranges in thickness from 3 to 8 

inches. A detailed examination of this locality by Mr. 

Dobbin has shown that the conglomerate is conformable with the underlying beds in most of the exposu'-es, 

though locally there are indications of ehanneliftg snch 

as characterize the upper part of the Fox Hifls tJ|rcm^hout its extent. As tile conglomerate occurs only in 

this small area, its presence affords little proof of the 

existence of a major imconfomaty at the contact of 

the Fox Hills and the Lance.

The relations between the Fox HiDs and Lauce 

formations in the region between tibe Missouii River 

and the Canadian boundary can not be satisfactorily determined, owing to the covering of laite Tertiary and Pleistocene deposits. Studies by

M Bauer, C. M.,Qiua'tzit« pebbles at t^ ba^ of tfae Lanee £«matto 14 Mon*^n«: 

Am. Assoe. Petroleum Geologists Bull., vol. 9, pp. 344-346, 1925, ;

31 Smith, c: Z>_ The Fort Peek Indian Keservatton lignite Md, J^ait.: D. a 

Geol. Survey Bull. 381, p. 42, 1910. !
18 SHOBTBB CONTRIBUTIONS TO GENERAL GEOLOGY, 1029

Beekly,32 and Collier 3S indicate that the beds tentatively called Fox Hills in this region are probably of 

continental origin, as shown by the lack of marine 

fossils and by the finding of remains of a trachodont 

dinosaur in a sandstone "which surely lies only a 

short distance above the Bearpaw" ( = upper Pierre).34 

These remains were identified as belonging to the 

species Trachodon annectens Marsh, a form which 

also occurs in the Lance of the Hell Creek area. This 

occurrence is noteworthy in view of the fact that the 

Fox Hills contains marine fossils on the south bank of 

the Missouri River and also in Canada, only a few 

miles from the locality where the dinosaur remains 

were found.38 Studies by McConnell 36 indicate that 

the Fox Hills and "Laramie" (Lance) are conformable 

also in the Cypress Hills, which lie but a short distance 

northwest of the Wood Mountain Plateau.

CENTRAL MONTANA

West and southwest of Forsyth, Mont., the Bearpaw shale ( = upper Pierre) is conformably overlain 

by nonmarine sandy shale and sandstone, locally 

indistinguishable from the rest of the Lance formation. These beds are indubitably of fluviatile origin, 

yield characteristic Lance fresh-water invertebrates, 

and probably represent the purely continental phase 

of the marine Fox Hills of the Dakotas.

SOUTHEASTERN MONTANA

The Fox Hills formation in the southeast corner of 

Montana is similar to the outcrops near Marmarth, 

N. Dak., except that locally the white Colgate member is replaced by brown sandstone. Near Ridge 

tjie Colgate member is more resistant than in areas 

to the north and east and makes bluffs 60 feet high. 

Excellent exposures at certain localities in this area 

fail to show any evidence of an unconformity between 

the Fox Hills and Lance.

RIDGE, MONT., TO LANCE CREEK, WTO.

Between the Montana-Wyoming State line and 

Moorcroft, Wyo., the contact of the Fox Hills and 

Lance could not be studied in detail, because of the 

lack of exposures in areas of low relief. The lower 

part of the Fox Hills in this area consists of brown 

slabby marine sandstone and sandy shale, which -crop 

out in a pronounced escarpment that stands well

M Beekly, A. L., The Culbertson lignite field, Valley County, Mont.: U. S. Oeol. 

Survey Bull. 471, pp. 329-330,' 1912.

33 Collier, A. J., Geology of northeastern Montana: U. S. Geol. Survey Prof. 

Paper 120, pp. 30-31,1919.

« Collier, A. J., op. cit., p. 31.

>« Rose, Brace, Wood Mountain coal area, Saskatchewan: Canada Geol. Survey 

Summary Kept, for 1914, p. 66, 1916.

w McConnell, B. G., Report on the Cypress Hills, Wood Mountain, and adjacent 

country: Canada Geol. Survey Ann. Rept., new ser., vol. 1, pt. C, p. 26 c, 1886.

above the Pierre lowlands to tfea east. Rubey 37 has 

mapped this area in detail and repotts thafc the Colgate 

sandstone member of the Fox Hills is eitiaeV afesent or 

present as some other lithologie fftpi^-^fojr .example, 

a brown unconsolidated sandstone that owvrs loeally 

between the marine Fox Hills and the Tfweratopsbearing Lance beds may be equivalent to tVe Colgate 

sandstone member.

On Good Lad Creek, less than a quarter of a mile 

below Oshoto post office, in the SW,J£ sec, 7, T. 53 N., 

R. 67 W., Wyoming, sandy beds that are possibly ol 

Fox Hills age stand vertical in a cut bank, and 400 feet 

upstream, directly opposite Oshoto post office, beds of 

brown and gray sandstone containing pronr\nent concretions, such as characterize the Lance, dip about 

5° SW. The great decrease in dip within so short a 

horizontal distance has been throught by some to indicate a structural unconformity between the Lance and 

Fox Hills. An examination of the locality by the 

writers showed that the exposures are tco poor to 

reveal the structure with certainty. It is believed, 

however, that the abrupt change in dip is due either to 

sharp unsymmetrical folding or to folding and faulting 

on a prominent monocline, which has been mapped by 

Rubey 37 for a distance of 30 miles.

In the same area as that described in the preceding 

paragraph Darton and O'Harra M reported the Fox 

Hills to be apparently 400 to 450 feet thick and to 

contain vertebrate bones, fossil wood, and species of 

Inoceramus. That the record of Inoceramus was due 

to a misidentification of Unio couesi which cr.used these 

writers to include a portion of the Lance containing 

this fossil in the Fox Hills sandstone has been proved 

by a subsequent examination of the precise locality 

described. The true thickness is much less than that 

reported.

At 4 miles southeast of Moorcroft the Fox Hills 

sandstone is well exposed in a conspicuous ridge but 

affords no evidence of an unconformity with the Lance. 

The Fox Hills is about 200 feet thicfc at tHs

The Fox HiHs is also well exposecl in 

7 miles northwest of Upton, Wyo. Its top is a white 

sugary sandstone overlain by a bed of purple carbonaceous shale. The white sandstone contains Halymenites. major and is possibly a correlative of the Colgate sandstone of southeastern Montana, though this 

can not be proved. Dinosaur bones were cof <acte<l from 

the Lance beds less than 50 feet above the purple 

carbonaceous shale, and marine fossjls wer^ obtained 

in the lower member of the Fox Hills.

About 13 miles west of Newcastle the Fox Hills and 

Lance exhibit the following section:

» Rubey, W. W., personal communication.

M Darton, N. H., and O'Harra, C. C., U. S. Geol. Survey Ge^. Atias, Devils 

Tower folio (No. 150), p. 5, 1907.
CONTACT OF FOX HILLS AND LANCE FORMATIONS,

Section 18 miles west of Newcastle, Wyo.

Lance formation (part): Feet 

Sandstone, yellow-brown, containing flat hard brown 

sandstone concretions; unit weathers into "toadstools "___________________________________-. 30

"Somber shale," composed of dark-gray sandy clay 

with small botryoidal masses of Mmonitic sand, 

brown concretions, and a little hard sandstone in 

thin layers; turtle and dinosaur bones at top____ 50

Slope probably underlain by gray sandy clay shale_ 70 

Sandstone, soft, light gray, and shale, dark gray, 

alternating in thin layers; contains a little hard 

brown platy sandstone; no fossils noted, assignment 

arbitrary-___________________________________ 30

Pox Hills sandstone:

Sandstone, hard, platy, dark brown; forms cap rock

of many small buttes. _______ _________________ 3

Sandstone, rather soft, yellow to light gray; weathers 

to a slope___________________________________ 62

Sandstone, argillaceous, very soft,. slope forming; 

contains a few somewhat harder layers, some thin 

layers, and a few concretions of siderite. At 44 

feet above base (U. S. G. S. locality 12833) contains Crenetta elegantula Meek and Hayden, Venietta humilis Meek and Hayden, Pyrifusus newberryi Meek and Hayden, Haminea sp.; at 5 feet 

above base (U. S. G. S. locality 12832), Serpulaf 

sp., Nucula sp., Yoldia evansi Meek and Hayden, 

Pecten nebrascensis Meek and Hayden, Anomia 

gryphorhynchus Meek and Hayden, Modiola 

meeki Meek .and Hayden, Crenetta elegantula 

Meek and Hayden, Crassatellites subquadratus 

Whitfield?, Lunatia concinna Hall and Meek, 

Anchura americana Evans and Shumard. Pyrifusus newberryi Meek and Hayden, Fasdolaria culbertsoni Hall and Meek, Cinulia concinna HaJl and 

Meek, Baculites ovatus Say, and undetermined 

fish scales.. —— ____________________ 60

Total Fox Hills sandstone__ _______ 125 

Pierre shale:

Limestone concretions, gray, 3 to 4 feet in diameter, 

most of them septarian and without fossils; B&culites ovatus Say, B. compressus Say, Yoldia evansi 

Meek and Hayden seen_______________________ 3

Shale, greenish gray, sandy, with a few small calcareous concretions____________________________ 20

Concealed under a grassy flat, probably in part large 

sandy gray shale; extends eastward from Fox 

Hills escarpment____________________________ ±150

Concretions brown, calcareous, with many fossils. 

About a mile east of the Fox Hills escarpment 

(U. S. G. S. locality 12757) contains Nucula sp., 

Yoldia evansi Meek and Hayden, CucuUaea shumardi Meek and Hayden, GerviUia subtortuosa 

Meek and Hayden, Inoceramus fibrosus (Meek), 

Inoceramus sagensis Owen, Pteria nebrascana 

Evans and Shumard, Ostrea sp., Pecten nebrascensis Meek and Hayden, Syncyclonema halli Gabb, 

Anomia gryphorhynchus Meek and Hayden, Modiola meeki Evans and Shumard, Crenetta elegantula 

Meek and Hayden, Cuspidaria sp., Lucina sp., 

Protocardia subquadrata Evans and Shumard, P. 

borealis Whiteaves, Corbula cf. C. crassimarginata 

Meek and Hayden, Dentalium gracile Meek and 

Hayden, Lunatia occidentalis Meek and Hayden, 

Anchura sp., Haminea subcylindrica Meek and 

Hayden, Baculites ovatus Say, B. grandis Hall 

and Meek, Discoscaphites nicotteti Morton, D. 

abyssinus Morton, and D. conradi Morton var.

The Fox Hills sandstone has been reported,48 en tike 

authority of D. E. Windfctester and V. H. Bamfctt, to. 

be 1,040 feet thick on J^k&li Creek, on, the game.^nej 

of outcrop as the much thinner sections reported, n^ar 

Newcastle and Moorcroft. This greater thickness lias 

been interpreted as normal for the formation aad the 

smaller thicknesses found elsewhere as representing 

only a remnant left by pre-Lance erosion.41 Tfye gTMt 

thickness reported is, however, incorrect, as shown by 

the detailed section measured by the writers and gi^en 

below. The Fox Hills on Alkali Creek is thicker, it is 

true, than at the more northerly localities, but it 

reaches only the moderate thickness of 357 feet and is 

transitional into the overlying Lance, AS described by 

Brown.42 Stanton's section at the mouth of Lance 

Creek,43 some miles south of Alkali Creek, agrees T^ell 

with that measured by the writers, though it is somewhat thicker—about 400 feet.

Section measured in sec. 18, T. 40 N., R. 61 W., and sees. It -and 

IS, T. 40 N., R. 6$ W., Wyo., between Alkali Creek and 

Robbers Roost Creek

Lance formation (part): Feet 

Shale, somber colored; contains abundant remains of

turtles and dinosaurs_-___-..-_--_--__----_-_--.-_ 50 , Shale, carbonaceous, and coal-_______________________ 3

Fox Hills formation:

Sandstone, brown, concretionary; contains abundant 

remains of dinosaurs, crocodiles, .and turtles near 

top. V. H. Barnett and D. E. Winchester" reported marine fossils at a horizon 35 feet below top 

of this unit. The present writers did not succeed 

in verifying their report. This unit may bekmg ia 

the Lance-_-____-___----_-.-_-._--.'------_— ____- 60

Sandstone, gray, filled with shells of Corbiffula ef. €. 

subdliptica Meek and Hayden; a brackish-water deposit that may belong to the Lance._____________ 23

Sandstone, gray, and soft sandy shale, inseparable in 

grass-covered slopes___ — _______________________ 74

Sandstone, yellowish, hard, capped by ripple-marked 

fissile concretions; contains Yoldia evansi Meek and 

Hayden, CreneUa? sp., and Haminea m^nor Meek in 

basal part (U. S. G. S. locality 12586)________ 4

Shale, dark gray, and sandstone, soft, light gray, interlaminated; contains botryoidal masses of limonite 

and concretions ,of platy brown sandstone; mass 

weathers into slopes like the Lance "somber beds"; 

contains Nucula sp. indet., Modiola attenuata Meek 

and Hayden, Cardium spedosum Meek and Hayden, 

Tettina sp. indet.,* 25 feet below top (U. S. G. S. 

locality 12585)_______________--___— 70

Sandstone, platy, hard, brown___ — ____ —— _______ 1

Clay, somber-colored_________-___-_-_-_-_---__-_- 10 °

Concealed; probably interlaminated gray and brown 

sandy shale and sandstone much like third unit above- 80

« Oalvert, W. R., and others, Geology of the Standing Rock and Cheyenne r.lver 

Indian Reservations, North and South Dakota: U. S. Qeol. Survey Bull. 675, 

p. 12,1914.

« Knowlton, F. H., Cretaceous-Tertiary boundary In the Rocky Mountain 

region: Qeol. Soc. America Bull., vol. 25, pp, 326-327,1914.

42 Brown, Barnum, Cretaceous-Eocene correlation in New Mexico, Wyotttag, 

Montana, Alberta: Geol. Soc. America Bull., vol. 25, p. 358,1914.

« Stanton, T. W., Fox Hills sandstone and Lance formation ("Cervtops bets)" 

in $outh Dakota, North Dakota, and eastern Wyoming: Am. Joor. Sei., 4th ser., 

voli 30, pp. 184-186,1910.

«' Unpublished data.
20 CONTRIBUTIONS TO GENERAL GEOLOGY, 1929

Fox Hills formation—Continued. Feet 

Sandstone, gray, platy; makes bench.______________ 10

Sandstone, brown, limonitic, hard and platy; makes

the cap rock on the lowest Fox Hills escarpment. __ 12 

Sandstone, yellow, massive, soft; contains large hard 

brown calcareous concretions, which yielded (U. S. 

G. S. locality 12584) Metnbranipora n. sp., Gervillia 

svfotortuosa Meek and Hay den, Inoceramus (Aetinoeeramus) ftbrosus Meek and Hayden, Venietta 

humilis Meek and Hayden, Protocardia subquadrata 

Evans and Shumard, Tellina equilaferalis Meek and 

fiayden, DentaHium gratile Meek and Hayden, 

Faseiolaria cheyennensis Meek and fiayden?, Pasciolaria ffalpinianum Meek and Hayden, Cinulia 

concinna Hall and Meek, Discoscaphites nicolleti 

(Morton), Sphenodiscus lenticidaris (Owen), Hypsodon sp., and Centrarchites? sp__________________ 40

Sandstone, gsay, shaly but hard enough to make a 

prominent bench____________________________ 23

Total Fox Hills. 

Pierre shale.

357

In the upper Lance Creek area the Fox Hills is about 

500 feet thick and is transitional into the Lance. 

Winchester 45 reports a thickness of 748 feet, but examination by others has not substantiated so great a 

thickness as this. An increase in thickness toward the 

southwest has been established for all the marine 

formations of the Montana group and for the overlying 

Lance and Fort Union formations and is possibly due 

to the fact that the chief source of the sediments lay 

toward the southwest. Practically all sections of the 

Fox Hills in this particular area contain several beds of 

massive white sandstone, some of which are associated 

with beds of coal and impure shale. The following 

section, given by Stanton,** is typical of the Fox Hills 

in this area:

Section on Johnson Bros.' ranch near Buck Creek

Feet 

Lance formation: Sandy shale with thin beds of coal_____ 25

Fox Hills sandstone: = 

Massive white sandstone with Halymenites major.... 60

Yellowish massive sandstone with brown concretions. 20 

More thinly bedded brown sandstone with Heclymenites 25 

Massive white sandstone___,____________, 75

Soft, somewhat sandy shales with thin sandstone 

bands containing marine Fox Hills shells._________ 30

Brown shaly ssndstone_-___-____-________________ 5

Massive white sandstone____--_____-_________-____ 60

Thin-bedded brown and gray sandstone___________ 130

Yellowish massive sandstone with concretions containing Fox Hills fauna-___-_---_.______.__________ 100

Total Fox Hifl&_____________________ 505 

Plerre shale.

CENTRAI WYOMING

In the district near the Salt Creek oil field the freshwater Lance formation is 3,200 feet thick and is

« Winchester, D. E., The Lost Spring coal field, Converse County, Wyo.: U. S. 

Q&A. Survey Bull. 471, p. 478, 1912.

« Stanton, T. W., Fox Hills sandstone and LaAee formation (" Cferafcip* beds") 

in Sonth Dakota, North Dakota, and eastern Wyoming: Am. Jour. Sci., 4tb ser., 

vol. 30, p. 186, IWO.

underlain conformably by a series of beds designated 

the Lewis shale. The uppermost part ef the L«wk 

is a pure-white sandstone 100 to-150 feet tP^k wnich 

bears Halymenites and is possibly a correlative of the 

Colgate sandstone of eastern Montana. Shale associated with the white sandstone contains Fox Hills 

fossils,47 and the sandstone itself contains or*e or more 

coal beds, generally only a few inches tircfc but in 

some places as much as 5 feet thick. The beis through 

an interval of 600 feet below the white saM%tene are 

predominantly sandy, though in at least b%_f ol this 

interval they contain distinctive Pierre fosses and are 

equivalent to the uppermost part of the Pierre shale 

of eastern Wyoming. Deposition of sandy beds, 

therefore, began earlier here thait it did farther east. 

There are only arbitrary boundaries between representatives of the Pierre, Fox Hilfe, aisd Lan^e.

At Glenrock, east of Casper, the uppermost piart of 

the Lewis shale, just under the Glenrock coal bed of 

the Lance, is a massive pure-white sandstone about 

75 feet thick that contains Halymenites throaghout. 

Under it lies perhaps 125 feet of yeBow-bro^iL massive 

sandstone containing many concretions of red-brown 

hard calcareous sandstone. Beneath tHs yellowbrown sandstone lies about 125 feet of ahale, thinbedded sandstone, and coal, beneath which in turn 

is a second yellow sandstone 70 feet thick. Bamett ffi 

reports the beds above the coal-bearing zone as 100 

feet thick, but this figure is not quite large enough. 

Beneath the rocks above described, which are very 

likely of Fox Hills age, lie some 600 feet of interbedded 

sandstone and shale and, still lower, less s^.ndy beds. 

These all contain a Pierre fauna and aro therefore 

older than the Fox HiUs.

In the Poison Spider district, 35 miles wesf. of Casper, 

the Lewis s&aie is about 800 feet thick artf consists 

of alternating beda of sandstone, shale,, carbonaceous 

shale, and coal; the upper beds contain a distinctive 

Fox ffilte fauna with Sphenodiscus, etc., and the 

lower beds an upper Hetre fauna. There are alternations of marine and nonmarine beds,- and tke entire 

section can be interpreted only ss showing a gradual 

change from marine to continental conditions. JL 

section illustrative of this district follows:

Section at the center of T. 88 N.f R. 88 W., Wyo,, S iHte» stntlhwesfr

of the Poison Spider oil field FeetLance formation (b&gal part): Shale, s&ndy, grry, with 

carbonaceous shale, thlft doal beds, aiid concretionary 

sandstone; forms a prominent scarp. This unH is the 

lower part of the eeal-bearmg zone of the Lane? fornaa.- 

tion__-_ ____________ — ^_ ___________________________ 154-

« Weeemaoa, C. fiU Ttts Soss^s coal field, Johnson, Natror<v and Converse* 

Counties, Wyo.: U. 8. O«ri. Samy BuH- *71, P. **5, M2; The Salt Creek oil field,. 

Wyo.: U. S. Geol. Survey Bull. 670, p. 23,1818.

<s Barnett, V. H., Possibilities of oil in the Big Muddy dome, Converse and. 

Natrona Counties, Wyo.: U. S. Qeol. Survey Bull. 581, p. 114, 19:5,
or FOX Hn-Ls AND LANCE

Lewis shale:

• Sandstone, yellow, calcareous,

into irregular pieces and conta 

Sandstone, gray-white, soft. _. 

Shale, gray to brown, sandy._ 

Sandstone, brown, concretionary 

plants in upper part (U. S. G

eluding Taxodium occidentals

erelli Knowlton?, Rhamnus saUtifolius Lesquereux?,

and Ficws sp.; also Ostrea glob) a Meek and Hayden

in lower 6 inches (U. S. G. S. >cality 10708) ______ 5

Shale, sandy, gray; c6ntaiiw thin lenses" of papery 

sandstone- _______________

Shale, brown, sandy, grading upxSa'rd into ar prominent

ontains a Fox Hills 

chneris vrgomingensis 

vans and Shumard, 

Plena nebrddcana Evens and S luniard, Ostrm cf. 0.

concretionary sandstone that 

fauna, including Nucula sp., Gl 

(Meek), Pteria lingy&eformis

glabra Meek and Hayden, 3 

Meek and Hayden, CardtutA 

Hayden, Cattista, nebrdscensis 

Tellina scitula Meek and Hayi 

described, Pyrifusus newberryi 

Sphenodiscus lenticulare (Owen 

10707). _____________

Shale, gray, sandy____-_______

Lignite and brown carbonaceous 

Sandstone, gray, fairly hard; c< ntains

naceous debris. . 

Shale, gray, sandy 

Coal..._____. 

Shale, sandy, grayish white; GO 

yellow concretionary sandstont

incretionftry'; breaks

Feet

1

80

65

limy; contains fossil 

S. locality 7508), inewberry, ficus cock75

ancredia avtiericana? 

, Mfeek and 

Meek and Hayden, 

Tnrritetta sp. unand Hayden, 

(U. S. G. S. locality

shale.

much carbothffl lenses of

25

40

3

5

10

1

90 

Sandstone, gray, platy, concretionary _ ____________ 1

Shale, sandy, gray and brown, sc 't _ _______________ 80

Shale, gray, and carbonaceous shale, sandy shale, and

concretionary sandstone; app^eaT^ to be nonmarine. 70 

Sandstone, brown, hard; makes a Small rfdge_______ 3

Shale, gray, carbonaceous. ______ _ _______________ 25

Sandstone, soft, carbonaceous; contains several hard 

layers_ _________________ ___ _________________ 6

Shale, sandy, gray and brown_ ____________________ 30

Shale, some sandy and some carbonaceous __________ 1

Sandstone, gray, carbonaceous ____________________ 8

Sandstone, white; contains many gray cannon-ball concretions as much as 3 feet in diameter ____________ 62

Shale, sandy, brown; occupies alow valley. __ _ _.___ 66

Sandstone, gray and brown, with many large darkbrown concretions; contains in upper p&rt st large 

Pierre fauna including BaculiteA c&mprtssus Say, 

B. ovatus var. baculus Meek, and Scaphites nodosits 

Owen (IT. S. G. S. localities 10705, 10706) __ ______ 100

Shale, gray, marine, sandy, grading upward into overlying brown sandstone; Baculites compressus Say 

(U. S. G. S. locality 10709) _ _ ____________ 200 

Mesaverde formation: Teapot sandstonfe hogback.

In southern Wyoming the marine Lewis shale is 

succeeded by beds formerly called the Laramie formation but now designated "Laramie" of Medicine 

Bow formation. There is complete transition from 

marine to nonmarine deposits, and the transition beds 

are generally assigned to the succeeding formation 

because they are sandy and hence more like it in 

lithology than the underlying Lewis shale.

About 10 miles w^st of Kftwlins, just north of 

station on the Union Pacific Railroad, good 

of Lewis and overlying beds show the transition 

marine to nonmarine beds through strata that are 

undoubtedly of Fox HMfe age but here, as if* the 

Casper region, are not separable except arbitrarily 

from the beds above and below. Tne following section illustrates the sequence:

Section 10 miles w&tft of Rawlins, Wyo.

" Laramie " formation- (|»art): Feet 

Shale, sandy, brown, with tain cafbOBaeeotas- efiale 

beds and concretionary santtetone; eonfcaias 

prisons Meek and Harden-, Cfempdoma 

Meek and Hsbydsn, ftdoioma, tk&mpsam White, and 

Goniobasis tenuicarin&ta Meek and Hayden-14# feet 

.below top (U. S. G. S. locality 12607); Unfa prisevs 

Meek and Hayden 165 feet befow top (U. S. G. S. 

locality 12507); and Unio hol-mesianus White 40 

feet above base (U. S. G. S. locality 12505-)---__ 280 

Sandstone, brown______________________-___---__- 6

Shale, sandy, brown, with a few concretionary sandstone lenses. Fragment of undeterminable dinosaur bone 85 feet below top; ceratopsiftnr reaastinfr 

300 feet below top_ j__________________. 385 

Sandstone, brown, concretionary; contains many 

Halymenites; higJiest marine horizon noted _______ &

Shale, brown, sandy, with thin piaty sandstone.—__- 21 

Coal____________1__________________ 3

Sandstone, brown, concretiofeary; ^ay mn&y shale; 

and several carbonaceous shale beds 2 to 4 feet 

thick____________________________. 40

Sandstone, brown, concretionary; gray sandy shal^; 

an^f caTbonaeeou* bVowfi 0isS^,'. 'At 

middle of this unit tod half a 

of the section (U. S. G. S. IcxsaMty 10722) were 

found Nticula sp., Yoidia eoansi Meek and Hayden, - 

Barbatia? sp. undescribed, Ostrea sp., Cardiwn 

(EthmotarSiuiti) sp. undescribed, Mactm nitiduM 

Meek and Hayden, &n$ptdaria aff. C. m&reanensiti 

Meek and Harden, tiMei^rinined c#ab, and Behidnocephaltt&f sp,________,__-___-.__-_-^ — ______-„ 110

Shale, brown, sandy_-_-__>_______-^___- — ________ 38

Shale, carbonaceous_______________________-______ 3

Sandstone and gray ^hale_______--_----_--_--_ — - 3$

Coal______________-_-_____--_______-___-_-__--_ 2f

Sandstone and gray shale-___--___-_-_----__--.---_ W

Shale, carbonaceous; contains st the middle (U. S.

G. S. localities 10720, 12503) Ostrea glabra Meek___ & 

Shale, gray, sandy, with brown concretionary saiyi+ 

stone and beds of carbonaceous shale, ftom a soft 

sandstone 20 feet below the top $««I£Q sp., Anotitia 

gryphaeiformfe Siaiiton, Umo subsjUMnlatnsf Meeft 

afid Hayden^ Uwio dttn&ef Meek and Hayden, Uni& 

sp., Campeloma muMilineat&f Meek and Hayden, 

and Viviparus sp. (U. S. G. S. localities 102504, 

10721); and fth&mnm wittiardi Knowlton, Querem 

sp., Viburnnm sp., aiwj Ore@d&fittt»f sp. <tt. S. G. $. 

locality 7510)___.— -_-___----__----- — -.--- 14»

Sandstone, brown, concretionary, marine; HMymemte» 

abundant and fragiaeiats of shells.____—_________ &

Shale, gray, san<.y______—________________________ 28

Shale, carbonaceous___-___________-__-________--_ 1

Shale, gray, and eoflcretiohtfry ea*tdst««Mj- __________ fo

Shale, carbonae6oUs__-_______-_-____-____-_-____- .4
22 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1929

" Laramie " formation (part)—Continued. Feet 

Shale, gray, and concretionary sandstone ___________ 96

Coal. __________________________________________ 2

Shale, gray___________________________________ 40

Coal-...____________________________ 3 

Shale, gray_-____________ —— — ___________— 8

Coal. ___ — ._.________.________________ 2

Shale, sandy, gray, and thin platy sandstone. _______ 70

Shale, carbonaceous; contains Ostrea glabra Meek and

Hayden (U. S. G. S. locality 12502).___._____ 6 

Shale, gray, sandy, with numerous discontinuous ferruginous concretionary beds_____________________ 140

Sandstone, dark brown; massive to platy; contains 

Ostrea sp., Cardium speciosum Meek and Hayden, 

Baculites sp. (U. S. G. S. locality 12501) _______ 6 

Shale, sandy, dark brown_________________________ 82

Shale, sandy, gray, with a few sandstone lenses._____ 71

Sandstone, brown, concretionary, contains macerated 

plant remains_________________________________ 10

Shale, dark gray; weathers light colored ________ __ 28

Sandstone, platy, calcareous______________________ 4

Shale, gray, sandy__________-__________________ 112

Sandstone, brown, concretionary; contains Ostrea sp., 

Cardium speciosum Meek and Hayden, and Corbula 

undifera Meek (U. S. G. S. locality 12500) ______ 4 

Sandstone, gray, platy_______________________ 53

Shale, sandy, dark gray; weathers light colored.____ 55

Sandstone, grayish brown, concretionary.___________ 2

Lewis shale: Shale, gray, with minor thin beds of sandstone and calcareous concretions; contains Pierre fossils. 

Thickness not measured.

E. E. Smith and M. W. Ball 49 collected at other 

localities in this area distinctive Fox Hills fossils from 

strata comparable to the uppermost marine beds of 

this section, and there is no doubt that the higher 

marine beds are of Fox Hills age. The lower beds are 

definitely of upper Pierre age. Plants collected from 

the nonmarine beds above the highest marine beds 

have been ascribed to the Laramie flora and given an 

age assignment older than that of the Lance beds, but 

an abundant invertebrate fauna is identical with that 

of the Lance of northeastern and central Wyoming. 

At no place in the sequence, either in the part described here or in considerable thicknesses above and 

below it, is there a plane suggesting an important 

interruption.

In the Hanna Basin 60 the change from marine to 

nonmarine beds—from Lewis shale to Medicine Bow 

formation—is exactly parallel to the change near 

Rawlins from Lewis to "Laramie." A typical example is the section 5 miles .north of Walcott, Wyo. 

Here massive light-gray to brown sandstone 270 feet 

thick rests on several thousand feet of marine Lewis 

shale. Upon the sandstone lies about 300 feet more 

of shale, poorly exposed but probably marine and 

included in the Lewis by Bowen; then 550 feet of 

shale, soft gray to brown sandstone, and some hard 

dark-brown sandstone, which is not very fossiliferous

« Unpublished data.

w For a general description see Bowen, C. F., Stratigraphy of the Hanna Basin, 

Wyo.: U. S. Geol. Survey Prof. Paper 103, pp. 227-235, 1913.

but yields a few oysters and scattered plant remains 

and forms the basal part of the Medicine Bow formation. Next above is a thin zone of hard brown concretionary sandstone with Fox Hills fossil1*, including 

Yoldia evansi Meek and Hayden, Yoldiaf sp., Ostrea 

sp., Anomia sp., Modiola sp. undescribed, Anatina 

aff. A. doddsi Henderson, Phdadomya subwntne&sa 

Meek and Hayden, Thrada subgratiKs? WMtfield, 

Cardium speciosum Meek and Hayden, TeMna sctiula 

Meek and Hayden, Legumen planulatum Conrad, 

Mactra cf. M. warrenana Meek and Hayden, Dentalium sp., Jjwnatia conciumja, Hall and Meelr, Haminea 

sp., Anisomyonf sp., and Sphenodiscus lenticulare 

(Owen) (U. S. G. S. locality 10723). At a horizon 

15 feet higher (U. S. G. S. locality 10724) occur Ostrea 

glabra Meek and Hayden, Anomia gryphorkynchus 

Meek, and Corbicula sp.—a brackish-water fauna— 

and at 15 feet higher still (U. S. G. S. locality 10725) 

Ostrea glabra Meek and Hayden and Corbwda sp. 

Above these only plant remains were found in a hasty 

search, though fresh-water invertebrates are abundant 

at many places in the formation in adjacent sections. 

The flora of the Medicine Bow formatkn has been 

identified with that of the Laramie of the E -jnver Basin 

and has been considered pre-Lance in age. The same^ 

zone of marine beds as that noted at Wrlcott, or at 

least a very similar one, well above the base of the 

Medicine Bow formation, was noted by Stanton 51 at 

several other places in the Hanna Basin, and there 

seems to be little doubt that a fairly thick transition 

zone of alternating marine and nonmarine deposits is 

widespread. A misinterpretation of the stratigraphy 

of this area 52 by some of the earlier studeE ts led to the 

concept of the presence here of a very g-^ftfc unconformity comparable to the supposed pre-Lance and 

pre-Arapahoe unconformities, but the earful restudy 

of the region by Bowen and others has shown that 

the only great unconformity in the section is at a 

much higher stratigrapMc plane, the 1 *se of the 

Wasatch. **

In this same general a-rea the writers, with. J. B. 

Eby, examined and measured the section on Muddy 

Creek near Dad, Wyo. Here is found essentially the 

same unbroken sequence from Lewis up into "Laramie."

For southern Wyomiag as a whole the beds called 

"Laramie" or Medicine Bow are identical in Ethology 

with those a short distance to the north, beyond the 

Sweetwater Mountains, which are accepted as Lance 

by everyone who has examined them; the same large 

nonmarine fauna occurs in both sets of beds and also 

the same Trweratops fauna; both succeed conformably

M Stanton, T. W., personal communication.

® Veatca, A. C., Coal fl»M» «$east-central Carbon County, Wyo.: IT. 8. Qeol. 

Survey Bull. 316, p. 250,1907. ftnowlton, F. H., Further data on the stratigraphie 

position of the Lance formation (" Ceratops beds"): Jour. Geolory, vol. 19, pp. 359- 

362,1911; Cretaceous-Tertiary boundary in the Eoeky Mountain region: Qeol. Soc. 

America Bull., vol. 25, p. 328,1914.
CONTACT OF K»X HILLS ANB LANCE FOBMATI$8?8 '

a zone containing the Sphenodiseus fauna of Fox Hills 

age. The only discordant note is that the flora of the 

Lance beds is said to be a Fort Union flora, whereas the 

flora of the "Laramie" or Medicine Bow formation is 

said to be a Laramie flora and older than Lance. 

Hares 53 some years ago expressed the opinion that 

the Lance of the Casper region and much of the Medicine Bow ("Lower Laramie") of southern Wyoming 

are equivalent, an opinion which the writers believe to 

be substantially correct.

YAMPA VALLEY, COLO.

An area of especial interest as being the farthest west 

in Colorado at which a typical Fox Hills fauna is 

known is in the Yampa Valley in the vicinity of Craig 

The section here includes a shale formation designated 

the Lewis shale, overlain by a formation still known, 

as are the similar beds in parts of southern Wyoming, 

by its old name "Laramie," originally applied because 

the upper part of it contains Laramie plants.64 The 

"Laramie" in Yampa Valley begins with a massive sandstone, above which lie thin beds of shale and 

sandstone that include a coal bed and zones of marine 

and brackish-water fossils. These fossils, including 

Sphenodiseus,M belong to the Fox Hills fauna and range 

as high as 350 feet above the base of the "Laramie," 

as the formation was originally identified and as the 

name is applied now for convenience in mapping. 

Above the marine beds are shale, sandstone, and thin 

beds of coal, an assemblage much Kke that which in 

Wyoming is called Medicine Bow and Lance, though it 

is much thinner. The upper boundary of the "Laramie" has been drawn beneath a conglomerate that 

marks the beginning of the "post-Laramie" formation—a unit that has a flora of Fort Union aspect and 

a lithology somewhat different from that of the "Laramie." There is no evidence of unconformity in the 

section except the presence of the conglomerate— 

evidence of somewhat doubtful value.

NORTHEASTERN COLORADO AND THE DENVER BASIN

The Fox Hills sandstone has been interpreted in this 

general region as including a series of sandstones and 

sandy shales with a conspicuous sandstone at the top, 

the whole assigned a thickness stated by some geologists 

to be as much as 2,000 feet, though by others only 800 

to 1,000 feet, the difference being due in part, perhaps, 

to difference in choice of basal boundary, in part to 

differences in calculation of thickness. The sandstone 

at the top was designated by Henderson K the Milliken

83 Hares, C. J., Correlation of some of the Cretaceous and Eocene formations of 

central Wyoming [abstract]: Washington Acad. Sci. Jour., vol. 5, pp. 328-330,1915. 

"« Gale, H. S., Coal fields of northwestern Colorado and northeastern Utah: 

U. S. Geol. Survey Bull. 415, pp. 72-74f 1910.

" Hancock, E. T., Geology and coal resources of the Axial and Monument Butte 

quadrangles, Moffat County, Colo.: IT. S. Geol. Survey Bull. 757, p. 22, 1925.

«• Henderson, Juntas, The Cretaceous formations of northeastern Colorado: 

Colorado Geol. Survey Bull. 19, p. 22,1920.

sandstone; and the miggeitaon was made that its fc

would have beett chosea as the logical plane

division of the Montana group had the group been f *»t 

studied in Colorado. Tije lower Fox Hills, taken 1& 

the usual sense as iaehjiding beds well below 

Milliken sandstone member, contains neither 

most characteristic of thje Fox Hills nor those 

characteristic of the Herrp, but it does contain & 

of species that occur in boih Fox Hills and upper H^rre"; 

the Milliken sandstone itself contains the distinctive 

ammonite Spkenodiscus . ! It seems to the writers that 

only the Milliken and possibly any marine beds above 

it should be considered strictly as of Fox fiills age p.nd 

comparable to the typical iFox Hills, though the grounds 

for this opinion are chiefly negative and therefore we«<k. 

Even if the Fox Hills is conceded to be very thick, the 

value of this thickness as proof of erosion in other areas 

is reduced by the fact that the underlying Pierre sh ale 

has in this area an astonishingly great thickness, in 

comparison with which even the greaf thickness of the 

Fox Hills would not be disproportionate.

According to Henderfeon 57 the Milliken sandstone 

consists of

massive, rather soft, usually greenish-yellow sandstone, from 

100 to 150 feet in thieknesis, almost entirely free from Shales 

except a few 1-inch bands in the lower part. The sandstone 

contains many large brown concretions and bands, more or less 

ferruginous and calcareous a fcd usually highly fossfiiferous. The 

more gentle slopes above ate occupied by alternating shalea and 

soft sandstones, containing marine fossils and not sharply 

separated from the overlying Laramie shales and sandstones. 

The Laramie is not well exposed In t&to region, ^W^'Jarr&ly 

to the absence or weakness of the .massive thick white sandstone, which is such a conspicuous and persistent feature of the 

lower Laramie in Boulder 0ounty.

In the Denver Basirtth© Milliken sandstone is overlain by two grayish-w|iite sandstones, each about 60 

feet thick, separated bjy about 4 feet of Hgnitic shale, 

which passes into coal in some places. A third and 

much whiter sandstone, about 10 feet thick, occurs 

60 feet higher in the Section and is a good marker in 

coal exploration because all workable beds in the lower 

part of the Laramie iformation of the Denver fi eld 

occur below it. 68

The rock sequence .as thus described might suggest 

that the Milliken sandstone is to be correlated with the 

basal brownish sandstone of the northern Fox HiDs; 

that the coal-bearing white sandstones of the brsal 

Laramie of the Denver Basin and northeastern Colorado are to be correlated with the Colgate sandstone 

member of the Fox ' Hills as developed in eastern 

Wyoming, eastern Montana, and the Dakotas; and 

that the Laramie clays are equivalent to the Hell 

Creek member of the Lance. Such long-range correlations on lithology alone are very uncertain, but it [ w Henderson, Junius, op. qlt., p. J!3. \

as Emmons, g. F., Gross, Whitman, and Bldridge, Q. H., Geology of the Denver 

Basin in Colorado: XT. 8. Geol. Survey Moa. 27, pp. 73-74, 1896.
SHOJRTE3J CONTRIBUTIONS TO GENERAL GEOLOGY, 1929

is on other ^grounds as nearly certain as such matters 

can be that the Millike,n is equivalent to some part of 

the typical Fox Hills. The view that the Laramie 

clays are of the same age as the Hell Creek member of 

t&e Lance is supported, as Stanton long ago pointed 

out, by the invertebrate fauna and by the recent 

finding in the Laramie beds.near Briggsdale, Colo.,59 of 

several horn cores identified as probably Triceraiops. 

The differences cited between the fossil floras of the 

Laramie and the Lance are no more impressive than 

those cited between the floras of the Denver and the 

Lance or Fort Union, both assigned to the Eocene by 

Knowlton.

No one has ever reported any evidence of unconformity between the Fox Hills and Laramie, and this fact, 

with the assignment of a great thickness to the Fox 

Hills, has been used as an argument that the Laramie 

and most of the Fox Hills were removed by pre-Lance 

erosion at places outside of the Denver Basin where 

no Laramie, as such, is recognized and the accepted 

Fox Hills is thin. If, however, the Laramie-Arapahoe 

unconformity represents a short interval, comparable 

to some of those represented by the admittedly minor 

unconformities within both Fox Hills and Lance 

formations, the Laramie, Arapahoe, and Denver with 

their Triceratops fauna become a logical equivalent 

for some part of the Lance,-and the sections in the 

Denver Basin and in the northern plains match. 

Hay 60- and Stanton 61 long ago expressed the opinion 

that the unconformity noted between the Laramie and 

Arapahoe formations is not of stratigraphic importance—an opinion with which the writers fully agree.

The emphasis that has been laid by some writers on 

the importance of the unconformity between the 

Laramie and the Arapahoe rests, as stated on page 10, 

upon the propositions (1) that in the Rocky Mountain 

region the Cretaceous sea was unbroken by any 

islands and undisturbed by any regressions from its 

entrance into the region in early Upper Cretaceous 

time until its withdrawal in jlate Upper Cretaceous 

time and (2) that the conglomerate of the Arapahoe 

contains pebbles derived from near-by exposures of 

practically all the pre-Arapahoe rocks—a necessary 

corollary being that between the deposition of the last 

Cretaceous beds and the beginning of the Arapahoe 

there must have occurred the elevation and erosion of 

the whole preceding section of some 12,000 feet. The 

first proposition would certainly not be accepted by 

students of the Interior Cretaceous to-day. The second appears to the writers highly debatable. Even if 

the identification of the pebbles as pre-Cambrian, 

"Red Beds," Dakota, Niobrara, Laramie, etc., is

® Toepellnan, W. C., Notes on the Laramie formation in central Weld County, 

Colo.: Jour. Geology, vol. 34, p. 834, 1926.

«° Hay, O. P., Where do the Lance Creek (" Ceratops") beds belong, in the Cretaceous or in the Tertiary?: Indiana Acad. Sci. Proc. for 1909, p. 284, 1910.

« Stanton, T. W., Boundary between Cretaceous and Tertiary in North America 

as indicated by stratigraphy and invertebrate faunas: Geol. Soc. America Bull., 

vol. 25, pp. 347-348, 1914.

granted—which appears not i»eyond some 4°wbt, considering the types of rocks concerned—-it is still p, 

gratuitous assump&osn that .they had to coaae from 

sources near .enough to .exclude .any possible areag .qf 

Cretaceous erosion. The demand for a :post-Laraj^|ie 

time interval long enough to permit ^elhvation and 

erosion of the whole thickness of pre-Ar/ip.aJiQe s<ediments is too great a strain on the known facts, pieh as 

the occurrence of very similar if not .identical 

sian dinosaurs in the Laramie and in 

Denver beds. The cited differences of the Laramie 

and post-Laramie in the floras are not ir^Dressive, in 

view of the differences in, time and in physical conditions supposed to exist—in fact, they ar^ no greater 

than those existing between the suppoF^d Tertiary 

Arapahoe-Denver flora on the one hand and the supposed Tertiary Lance-Forfc Union flora on,the other, the 

latter said by the paleobotanists to be essentially one 

flora, though occurring through a great thickness qf 

strata in which marked changes take place in the contained invertebrate and vertebrate -faunas.

WESTERN AND SOUTHERN MARGINS OF -TEE INTERIOR

In New Mexico, Arizona, Utah, ajod western Wyoming any beds of Fox Hills age that may be present 

are nonmarine and do not differ sufficiently in either 

lithologic constitution or fauna! content from associated 

beds older or younger jfchan $ie Fox Hills to permit any 

useful comparison to be made. In some rejdqnsj such a$ 

the San Juan Basin and the Raton coal field, New Mexico, unconformities are recognized within the series of 

nonmarine beds, but their relative importance can not 

now be determined. In the San Juan Basin dinosaur 

remains of very cjoady allied types occur .both bela^ 

and above , the ajost coiispicuous unconformity, suggesting that it is not very significant.

OF TJBE COLGATE SANDSTONE 

MEMBER QF-<*Bg SOS JULLS SANDSTONE

The record of volcanic ash in the Fox Hills sandstone 

east of the Missouri JRiver near Linton, N. Dak., by 

Stanton 62 led to the suspicion that the white color of 

the Colgate sandstone might be due to a content of 

volcanic ash, and to the hope that the ash might afford 

a basis for definite correlation.

The deposit n^ar liaton is described as. consisting of 

chalk-white strata .some 26 feet thick and 35 feet above 

the base of the Fox Hills sandstone. Spf oimens from 

this deposit were Bxaminecl by G. F. Lough&n, who reported them to contain 80 per cent of volcanic glass,

15 per cent of quartz and feldspar, 2 or 3 per cent of 

biotite, and scattered grains of other minerals. About

16 feet higher in the section is a greenalite bed that also 

contains volcanic glass. The nearest possible source

M Stanton, T. W., A Cretaceous volcanic ash bed on the Great Plains in North 

Dakota: Washington Acad. Sci. Jour., vol. 7, pp. 80-81, 1917.
CONTACT OF FOX HILLS AND LANCE FORMATIONS

of the glass now known is far to the west, in the Livingston region of Montana.

Clarence S. Ross examined specimens of white 

Colgate sandstone obtained in T. 21 N., R. 32 E., 

Mont., but found no evidence of volcanic material, 

as the following memorandum submitted by him 

indicates:

The specimens of Colgate sandstone examined are composed 

of a great variety of detrital materials. Sand grains form 

about one-third, and clayh'ke material the remainder of a 

typical specimen. Quartz is the most abundant single mineral 

element in the sand grains, but minor amounts of microcline, 

plagioclase, muscovite, biotite, chlorite, tourmaline, garnet, 

zircon, and apatite are present. The materials are not well 

sorted and range from 0.3 to 0.01 millimeter or less in diameter. 

Large grains are in direct contact with small ones, and there is 

no evidence of concentration of large or small grains along 

bedding planes. The sand grains are nearly all sharply angular.

Some specimens contain several per cent of calcite, and others 

contain almost none. Some of this is probably of detrital 

origin, but euhedral rhombs of calcite and'sparse grains of 

glauconite were probably formed during the deposition of the 

sediments.

The material between the quartz gtains is of the most heterogeneous nature. Most of it was not deposited as fine sediment 

but forms individual grains that have about the same diameter 

as the quartz. Much of it resembles the detrital material 

derived from more or less metamorphosed sediments, and the 

f erromagnesian minerals are those characteristic of metamorphic 

rocks. Some of the grains appear to be fine-grained quartzite, 

and others are chert or jasperlike quartz. Many grains are 

probably highly indurated shale; others resemble a sericitized 

rock, and some of the larger quartz grains appear to be partly 

sericitized. Qualitative chemical tests of the interstitial material show the presence of essential amounts of potash, and this 

indicates that this material is partly mica.

Clay minerals make up a considerable part of the interstitial 

material, and most of these appear to have formed in place by 

the alteration of detrital rock grains. At least two clay minerals 

are recognizable. The more abundant is a mineral of the kaolin 

group that is probably leverrierite or anauxite,63 and the other 

is beidellite. 64

The sandstone is nearly white, notwithstanding the fact that 

it contains grains of brown and other dark colors. Its light 

color is due to the white, chalklike appearance of the sericite 

and clay present as interstitial material between the grains 

of quartz—that is, the color of the sandstone is due to the tinting power of the large proportion of white interstitial material 

and not to freedom from impurities.

« Dittler, E., and Hibsch, J. E., Min. pet. Mitt., vol. 36, p. 85, 1923. 

« Koss, C. S., and Shannon, E. V., Washington Acad. Sei. Jour., vol. 15, p. 467, 

925.

SUMMARY OF CONCLUSIONS

The writers believe that the foregoing description 

of the contact of the Fox Hills and Lance formations 

and of units equivalent to these formations in areas 

where other names are used, together covering a large 

part of the Western Interior of the United States, 

supports the following statements:

The contact of the Lance and Fox Hills is everywhere 

essentially transitional.

All angular unconformities reported to exist between 

these formations are misinterpretations of faulting, 

cross-bedding, or slumping.

Erosion planes in the Fox Hills and Lance formations 

are unimportant chronologically, being merely evicSnce 

of local channeling of near-shore deposits by tidal 

currents and wave scour in the Fox Hills or of f '>odplain deposits by streams in the Lance—that is the 

result of contemporaneous erosion and redeposition.

The localities of certain collections of plants identified as belonging to the Fort Union flora and hitHrto 

considered to occur higher than the "unconfonrHy" 

above the Fox Hills are really in the upper part o* the 

Fox Hills sandstone.

The Fox Hills sandstone, from its type region at 

Fox Ridge, between the Cheyenne and Moreau Rivers, 

S. Dak., westward at least as far as the Musselshell 

River, Mont., and southward as far as Glenroek, 

Wyo., consists usually of a variable lower member of 

yellowish-brown marine sandstone and sandy shale and 

a variable upper member of white sandstone, whhh is 

locally of marine origin, though at some places it contains coal and plant remains; above the upper member 

at most localities occur beds of coal of variable purity, 

which belong to the Lance formation.

The Laramie and Arapahoe formations and at least 

part of the Denver formation of the Denver B««in, 

most of the Medicine Bow formation of southern 

Wyoming, and the "Laramie" formation of northwestern Colorado, conformable on beds of Fox Hills 

age, are equivalent to the Lance formation.

The white color of the Colgate member of the Fox 

Hills sandstone does not appear to be due to a cor tent 

of volcanic ash, and the formations therefore car not 

be correlated on this basis.

o
' «