Contributions to 

Economic Geology 

1955

'.GEOLOGICAL SURVEY BULLETIN 1027

/: This bulletin was printed 

- as separate chapters A-P

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director
CONTENTS

[Letters in parentheses designate the separately published chapters of the volume] ,- ':' '. .'" " ' " -' ; ' ': ' , Page

(A) Physical stratigraphy of the Phosphoria formation in part of southwestern Montana, by Earle R. Cressman___,________--___________ 1

(B) Geology of the Crazy Woman Creek, Johnson County, Wyo., by

Richard K. Hose-.------------------------------------------ 33

(C) Dolomite deposit near Marble, Stevens County, Wash., by Charles

Deiss----'-------_---_--_--_---------->-------------------_-- 119

(D) Geology and mineral fuels of parts of Routt and Moffat Counties,

Colo., by N. Wood Bass, J. Brian Eby, and Marius R. Campbell._ _ _ 143. 

(E) Sugar Loaf and St. Kevin mining districts, Lake County, Colo., by

Quentin D. Singewald_______________________________________ 251

(F) Copper deposits of part of Helvetia mining district, Pima County,

Ariz., by S. C. Creasey and George L. Quick_____________________ 301

(G) Lithium resources of North America, by James J. Norton and Dorothy

McKenney Schlegel._______________..----__-__--__________..__ 325

(H) Geology of the .Christmas copper mine, Gila County, Ariz., by Nels P.

Petersonand Roger W. Swanson_______-_--__-_________________ 351

(I) Perlite resources of the United States, by Marion C. Jaster___ _ _______ 375.

(J) Geology of the Standford-Hobson area, central Montana, by James D.

Vine_____________________________________________________ 405.

(K) Exploratory drilling for evidence of zinc and lead ore in Dubuque

County, Iowa, by Arthur E. Flint and C. Ervin Brown.___________ 471

(L) Oil and gas wells drilled in southwestern Virginia before 1950, by J. W.

Huddle, EloiseT. Jacobsen, and A. D. Williamson______________ 501

(M) Reconnaissance geology of western Mineral County, Mont., by

Robert E. Wallace and John W. Hosterman.____________________ 575.

(N) Mineral resources of the San Carlos Indian Reservation, Ariz., by

by Calvin S. Bromfield and Andrew F. Shride__________________ 613

(O) Thorium and rare-earth minerals in the Powderhorn district, Gunnison

County, Colo., by Jerry C. Olson and Stewart R. Wallace________ 693.

(P) Geology of the Murray area, Shoshone County, Idaho, by John W.

Hosterman_________________________________________________ 725
Physical Stratigraphy 

of the Phosphoria 

y Formation in Part of 

Southwestern Montana

**.

By EARLE R. CRESSMAN .. - .' ' , Uv) i '.%

A CONTRIBUTION TO ECONOMIC GEOLOGY

GEOLOGICAL SURVEY BULLETIN 1027-A

Prepared as part of the program 

of the Department of the 

Interior for the Missouri River 

basin and of work done on behalf 

of the U. S. Atomic Energy Commission. 

The report is published with the 

permission of the Commission

\ UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1955
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

For aale by the Superintendent of Documents, U. S. Government Printing Office 

Washington 25, D. C. - Price 55 cents (paper cover)
CONTENTS

Abstract __ _._.____________.-____-__--_-.-.___-___-__----_--___. 1

Introduction. __-__-______--_-_-_____-----__----------_---- . 1

Purpose and scope of the report. _______-____-__--_- .__.. 1

Acknowledgments.. _ _________________--_-_-____-___--- .__. 2

Stratigraphy..... ____--___________--__-___._--_------_ _____ _ 3

Nomenclature and regional correlation ____ __.____-__.__-___-_-_ 3

Unit B... _ _____ __ _ _ _._ _ _ __ _ _ _._ _ _ __ -__-_._-__ 6

Unit C_. -_. ___-_---__---_--____-__-.__--_-_--..__-_-_---___ 9

Unit £>._._ -__--__.__-.-_-..___.-_..-..__- ___ ____ 13

Unit #.___-_--____-__---_----__----_--_----___--__- ---__-- 16

The Phosphoria-Dinwoody contact _ ___________ _ ... .. 20

Facies relationships. _______________________________________________ 22

Time zonation ___ ____.-_-___-_______._____..__-___--___.-___ 22

Source of detritus.. __ .__....__ ______ .-... ... . 22

Bedded chert facies__________-_______________________-_---____- 25

Carbonate rock facies _____ ___________________________________ 2ft

Phosphate rock facies _____ ________________-___-___--__---_-_ 26'>

Lateral sequences of rock types__._____________________-_______._ 26

Vertical sequence of rock types _ _______________________________ 27

Relationship of facies to'depth of water ____ _ ___________________ 27

Literature cited ____ _---_-_-___-_--________-__--__.-_----__--_--- 29

Index _ . _________________________ . ____________ 31

ILLUSTRATIONS

[All plates are in pocket]

PLATE 1. Stratigraphic sections showing relations of the Phosphoria 

formation from Big Sheep Canyon to Taylor Fork, Mont.

2. Stratigraphic sections showing relations of the Phosphoria 

formation from Cedar Creek to the Centennial Mountains, 

Mont.

3. Stratigraphic sections showing relations of the Phosphoria 

formation from Little Sheep Creek to Melrose, Mont.

4. Stratigraphic sections showing relations of the Phosphoria 

formation from Mountain Sheep Point to Three Forks, 

Mont.

5. Fence diagram showing a lithologic correlation of the Phosphoria formation in southwestern Montana.

FIGURE 1. Index map of southwestern Montana showing the location Pageof measured Stratigraphic sections._-_--______-_--__-__._ 2

2. Isopach.map of the combined units B, C, D, and E of the

Phosphoria formation _________________________________ 5

3. Isopleth maps of unit B of the Phosphoria formation _________ 7'

m
IV CONTENTS

Pag_ 

FIGURE 4. Map showing lithologic constitution of the uppermost bed of

unit A of the Phosphoriaformation______________________ 8

5. Isopleth maps of unit Cof the Phosphoria formation. _______ 10

6. Map showing lithologic constitution of the phosphatic bed in

the lower third of unit Cof the Phosphoria formation.______ 12

7. Isopleth maps of unit D of the Phosphoria formation _________ 13

8. Map showing lithologic constitution of the uppermost bed of

unit C of the Phosphoria formation ______________________ 14

9. Isopach map of unit B of the Phosphoria formation_______ 17

10. Maps showing the distribution of facies of unit E of the

Phosphoria formation.________________________________ 20

11. Direction of transport of sand and silt in the Phosphoria

formation___________________________________________ 23

12. Inferred relations between rock types in the Phosphoria

formation in Montana and the relative depth of water in

the depositional basin_________________________________ 28

TABLES

Page 

TABLE 1. East-west facies changes in the Phosphoria formation in

southwestern Montana________________________________ 24

2. North-south facies changes in the Phosphoria formation in

southwestern Montana________________________________ 24
A CONTRIBUTION TO ECONOMIC GEOLOGY

PHYSICAL STRATIGRAPHY OF THE PHOSPHORIA 

FORMATION IN PART OF SOUTHWESTERN MONTANA

By EARLE E. CHESSMAN

ABSTRACT

In much of southwestern Montana the Phosphoria formation of Permian age 

has been divided by previous workers into five units, tentatively designated 

as units A to E in ascending order.

Unit A consists of dolomite and quartz sandstone. It is underlain by the. 

Quadrant formation of Pennsylvanian age.

Unit B consists of phosphate rock and carbonaceous mudstone. . Immediately 

west of Lima, Mont., the unit is 30 feet thick, but 70 miles to the north and east 

it disappears.

A few miles east of Lima unit C is nearly 300 feet thick, but it thins to the 

east, north, and west. Near Lima bedded chert constitutes the lower third 

and dolomite the upper two-thirds of the unit. The dolomite grades westward 

into dolimitic sandstone, and both chert and dolomite thin eastward as sand 

becomes more prominent.

Unit D consists of phosphate rock and carbonaceous mudstone. Near Lima 

the unit thins from 80 feet to 5 feet or less in the Gravelly and Madison Ranges.

Unit E, which consists largely of standstone and bedded chert, is 100 to 130 

feet thick over much of the area. Facies changes between chert and sandstone are common and abrupt. The chert, in part, intertongues with or grades 

into mudstone on the extreme west and south parts of the region discussed.

Facies changes occur within units, but in most of the area there is little 

lateral gradation between units. Sand was derived from both east and west, 

and the silt and clay may have had a western source. Facies changes from 

sandstone to chert are thought to have resulted from the sorting of siliceous 

organic remains from detrital quartz sand.

INTRODUCTION

PURPOSE AND SCOPE OF THE REPORT

The Permian Phosphoria formation of the central and northern 

Rocky Mountains constitutes one of the world's largest reserves of 

phosphate. As part of a detailed investigation of the Phosphoria, 

members of the U. S. Geological Survey have measured 50 sections 

at 33 different localities in the part of southwestern Montana discussed in this report (fig. 1). The phosphatic units have been

. ' . ' . 1
CONTRIBUTIONS TO ECONOMIC GEOLOGY

FIODRB 1. Index map of southwestern Montana showing the location of measures stratigraphic sections and the lines of stratlgraphlc sections Illustrated In plates 1-4.

sampled at every locality and the samples analyzed for P2O0 and acid 

insoluble material, and all units have been sampled at several sections. Abstracts of the sections and the analytical data have been 

published (Swanson and others, 19530, &; Klepper and others, 1953; 

Cressman and others, 1953; Peterson and others, 1954). Field descriptions of closely spaced hand specimens from 10 of the localities have 

been checked by microscopic examination, and 240 thin sections from 

12 localities have been examined somewhat cursorily.

In addition to the stratigrapnic sections described as part of tne 

present program, several measured sections published by Condit,

Finch, and Pardee (1928) have been utilized.

ACKNOWLEDGMENTS

Although the author took part in the measurement or examination 

of sections at 18 of the 33 localities discussed in this report, many 

other geologists have participated in gathering the data, particularly 

R. W. Swanson, W. K. Lowell, F. S. Honkala, M. E. Klepper, and
STRATIGRAPHY, PHOSPHORIA FORMATION, MONTANA 3

J. A. Peterson. Swanson is especially familiar with the Phosphoria 

formation in Montana and his many suggestions are gratefully 

acknowledged. Discussions with T. M. Cheney, R. P. Sheldon, R. A. 

Gulbrahdsen, and L. D. Carswell, all members of the Geological 

Survey who are studying other parts of the western phosphate field, 

have helped clarify many of the concepts presented. V. E. McKelvey 

organized the program of which this work is a part and has critically 

reviewed the manuscript.

The investigation has been conducted as part of the Department 

of the Interior program for the Missouri River basin and has been 

supported partly by the Division of Raw Materials of the U. S. Atomic 

Energy Commission.

STRATIGRAPHY

NOMENCLATURE AND REGIONAL CORRELATION

The type locality of the Phosphoria formation is at Phosphoria 

Gulch, near Georgetown in southeastern Idaho (Richards and Mansfield 1912, p. 684^689). The formation in that region is divided into 

two members: a lower phosphatic shale member, which consists of 

about 180 feet of phosphatic mudstone, mudstone, and phosphate rock; 

and an upper member, the Rex chert, which consists of about 240 feet 

of bedded chert. Cherty mudstone that contains some thin phosphatic 

beds occurs at the top of the formation and locally is distinct enough 

to be considered a third member (McKelvey, 1949, p. 272). The 

Phosphoria formation at the type locality is underlain by the Wells 

formation, largely of Pennsylvanian age but possibly in part of Permian age (Williams, 1953, p. 39), and is overlain by the Dinwoody 

formation of early Triassic age (Newell and Kummel, 1942).

Recent work by Sheldon (McKelvey and others, 1953a) has shown 

that northeastward from the type locality the phosphatic shale member thins, the Rex chert member becomes largely carbonate rock and 

sandstone, .and the uppermost phosphatic, cherty mudstone thickens 

to a distinct upper phosphatic shale member. In much of western 

Wyoming the upper phosphatic shale member is overlain by a chert, 

carbonate rock, and sandstone member that has not been recognized 

in southeastern Idaho. Beds of carbonate rock between the Tensleep 

sandstone and the lower phosphatic shale member are included in the 

Phosphoria formation in western Wyoming, where the formation 

consists of five members, two phosphatic and three nonphosphatic. 

In central Wyoming the Phosphoria intertongues with red beds and 

evaporites (see particularly Thomas, 1934).

The name Phosphoria was first extended to Montana by Stone and 

Bonine (1914, p. 375), who applied it in the Elliston region to an 

interval of sandstone and shale, 80 feet thick, which contains a thin 

bed of phosphate rock at the base. Equivalent strata in Montana
previously had been either included as part of the Quadrant quartzite 

of Pennsylvanian age (Peale, 1893, p. 39-43; Iddings and Weed, 1894; 

Emmons and Calkins, 1913, p. 71-74) or grouped with overlying 

Triassic rocks as the Teton formation (Hague and others, 1899, p. 34).

In most of southwestern Montana the Phosphoria formation is 

underlain by the Quadrant quartzite of Pennsylvanian age and overlain by the Dinwoody formation of Early Triassic age. In the northern end of the Tobacco Boot Mountains and the southern end of the 

Elkhorn Mountains, the Phosphoria was truncated by post-Permian 

erosion and is unconformably overlain by Jurassic rocks of the Ellis 

group.

In much of southwestern Montana the Phosphoria has been divided 

into five members (Butler and Chesterman; l Klepper and others; 2 

Klepper, 1950, p. 61). These are, in ascending order, a basal quartz 

sandstone-dolomite member (unit A), a thin lower phosphatic shale 

member (unit Z?), a middle sandstone-dolomite-chert member (unit 

0), an upper phosphatic shale member (unit Z>), and a chert-quartz 

sandstone member (unit E). The lower sandstone, limestone, and 

chert member of Sloss and Moritz (1951, p. 2167) includes units A, B, 

and C of this paper.

The lowest horizon in the Phosphoria formation that can now be 

correlated over southwestern Montana is the base of unit B ; therefore, 

strata below unit B have not been considered in this report.

The Phosphoria formation exclusive of unit A is nearly 500 feet 

thick near Lima. It thins northward and eastward; in the vicinity 

of Butte, Bozeman, and the west boundary of Yellowstone Park, the 

formation is only about 100 feet thick (fig. 2).

On the basis of physical data, Sheldon 3 has been able to correlate 

major units of the Phosphoria in northwestern Wyoming with the 

Phosphoria of southeastern Idaho. Similarities between some of the

Montana sections and sections in Wyoming described by Sheldon 

strongly suggest that unit B in Montana is the equivalent of the phosphatic shale member in southeastern Idaho and that unit C is the 

partial equivalent of the Eex chert. On the same basis, unit D is 

equivalent at least in part to the upper cherty mudstone that has been 

recognized at the top of the Rex chert member in southeastern Idaho.

Beds equivalent to unit E either are not present in southeastern Idaho 

or are represented by part of the upper cherty mudstone.

i Butler, A. P., Jr., and Chesterman, C. W., Investigation of trace elements in the

PhOSphOria formation in Southwestern Montana, preliminary report (unpublished).

3 Klepper, M. R,, and others, Distribution and stratigraphy of the Phospboria formation

In southwestern Montana: Paper read at North-west Science meeting, Spokane, Wash.,

December 1948.

a gheidon, R. P., Physical stratigraphy of the Phosphoria formation in northwestern

Wyoming: U. S. Geol. Survey Bull, 1027-(in press).
STRATIGRAPHY, PHOSPHORIA FORMATION, MONTANA

Control point

Numeral indicates thickness 

of measured sections

25 50 Miles

Contour interval. 50 feet 

FIGURE 2. Isopach map of the combined units B, 0, D, and E of the Phosphorla formation.

Baker and Williams (1940, p. 624^625) have found in north-central 

Utah that the fauna of the Phosphoria formation is generally younger 

than that of the Kaibab limestone. If the lithologic correlation, suggested in this paper, between the Phosphoria in Montana and the type 

Phosphoria in Idaho is correct, and if the correlative lithologic units 

are also approximate time equivalents, then the Phosphoria in Montana, exclusive of unit J., is also probably post-Kaibab in age. 

Fusulinids of Wolf camp age have been described from the Phosphoria 

near Three Forks, Mont., by Frenzel and Mundorff (1942), but were 

collected from beds in the lower part of the formation that are possibly equivalent to unit A.

The lithology and correlation of units #, (7, #, and E are presented 

separately below. Some of the relationships discussed are illustrated 

by columnar sections (pis. 1-4) and in a fence diagram (pi. 5). The 

sedimentary rocks in the region have been extensively folded and

327853 55 2
6 , . CONTRIBUTIONS TO ECONOMIC GEOLOGY

faulted (Klepper, 1950; Lowell; 45 Myers; 6 Swanson 7 ), and there 

has been much crustal shortening, particularly in the Tendoy and 

Pioneer Mountains near the west side of the area. No attempt has 

been made in the illustrations to restore the sections to their relative 

preorogenic locations.

UNIT B

Thickness and distribution. Unit B of the Phosphoria formation 

is more than 25 feet thick just west of Lima (pis. 1, 5; fig. 3J.). It 

thins progressively northward and eastward and is not identifiable 

beyond a radius of 70 miles north and east of Lima. The unit is absent 

at two places near the west end of Phosphoria exposures in the Centennial Mountain; 8 one area, of known extent, is too small to represent in figure 3, and the other, although of unknown extent, is thought 

to be small and is likewise not shown. These small areas may have

been local topographic highs during the time in which unit B was 

deposited.9

Sheldon 10 has shown that jthe variability in thickness of the phosphate rock increases toward the edge of the shale units of the Phosphoria in Wyoming. Similarly, in a few places in the eastern and 

northern parts of the Montana area, there are large local variations 

in the thickness of unit B, although the information on the nature 

and extent of the variations is not sufficient to represent them in 

figure 3. In the Centennial Mountains the change in thickness of the 

unit from nearly 20 feet to complete disappearance within 1 or 2 miles

is extreme,11 but at the canyon of the Big Hole Eiver (fig. 1, section 31)

it thickens from 2.5 feet on the north side of the canyon to 6.5 feet 

at a locality 2 miles to the south. Although unit B is absent in the 

Madison Kange, there is a 3-foot bed of phosphate rock at Quadrant 

Mountain, Wyo. (fig. 1, section 29), that is probably correlative 

with it.

The lithologic character of the bed that immediately underlies unit

B is illustrated in figure 4. The sandstone in the southwest corner of 

the area that is separated from other units by a solid line is believed 

to be stratigraphically higher than the other rocks represented. East

'Lowell, W. R., 1949, Geology of tbe Small Horn Canyon, Dalys Spur, cedar creek,

and Dell areas, Montana : U. S. Geol. Survey Open File Report.

5 Lowell, W. R., 1953, Geologic map and structure sections of the south-west quarter 

Willls quadrangle, Beaverhead County, Mont.: U. S. Geol. Survey Open File Report.

aMyers, W. B., 1952, Geology and mineral deposits of the northwest quarter WHIIB

quadrangle and adjacent Brown's Lake area, Beaverhead County, Mont.: U. S. Oeol. 

Survey Open File Report.

7 Swanson, R. W., 1O5O, Geology of a part of the Virginia City and Eldrldge quadrangles'.

Montana: U. S. Geol, Survey Open File Report.

s Honkaia, p. s., 1953, Preliminary report on geology of Centennial Range, Mont-Idaho,

phosphate deposits; U. S. Geol. Survey Open Pile Report, pL IL

8 Honkaia, P. S., idem, p. 14.

30 Sheldon, R. P., op. cit.

^ Honkaia, P. S., op. cit., p. 10, pis. II and VI. ....
Butte0

ISOPACH MAP 

Contour interval 5 feet

TOTAL THICKNESS OF CARBONATE FLUORAPATITE 

Contour interval 2 feet

EXPLANATION

Control point

Numeral indicates thickness 

of measured sections

TOTAL THICKNESS OF SILT AND'CLAY 

Contour interval 2 feet

50 Miles

 FIGURE 3. Isopleth maps of unit B of the Phosphorla formation.

of the Kuby River unit A thins rapidly. The presence of conglomerate at the base of unit B in parts of the Gravelly Range (Swanson 

and others, 1953&, p. 17; Condit, 1918, p. 113) indicates that the 

contact of units A and B is disconf ormable east of the Ruby River 

where the rocks immediately underlying unit B are probably older 

than those to the west. Regionally, the meager evidence suggests that 

the basal bed of unit B oversteps the uppermost beds of unit A to a 

small degree and that unit A incorporates stratigraphically higher 

beds toward the southwest. It is not known whether the postulated 

overstep at the contact of units A and B is unique within the formation or whether similar relations might exist at other horizons in the 

Phosphoria.

Lithologic character. Unit B consists mostly of dark-colored phosphate rock and mudstone. The phosphate rock is composed of cryptocrystalline carbonate-fluorapatite (Altschuler and Cisney, 1*952),
CONTRIBUTIONS TO ECONOMIC GEOLOGY

Dashed lines separate lithologic units that are 

stratigraphically correlative; solid lines separatelithologic units that are not stratigraphically correlative

\

25 50 Miles

:ap snowing uthoiogic constitution of the uppermost bed of unit A of the 

Phosphoria formation.

which occurs chiefly as structureless pellets that average %6 to *4 millimeter in diameter. The color of the phosphate rock ranges from black 

and brownish black to medium gray and light brown, largely depending on the degr.ee > of weathering. The .pellets in the basal phosphate 

bed, averaging from ^ to 1 millimeter, are larger than those in the

other phosphate beds. At several localities the basal bed contains

small phosphatic nodules, and in most sections it contains abundant

fish scales, bone fragments, phosphatic shell fragments, and Oolites 

with well-defined concentric structure. 

The mudstone is a mixture of unidentified clay minerals and very

fine grained silt composed of quartz and muscovite. The color ranges 

from brownish black to weak yellowish orange, depending on the 

degree of weathering.

Mixtures of argillaceous and phosphatic material are common, forming argillaceous phosphate rock and phosphatic mudstone. Carbonaceous matter is present in most rocks of the unit in roughly estimated amounts of 5 or 10 percent.
STRATIGRAPHY, PHOSPHORIA FORMATION, MONTANA 9

In the north end of the Gravelly Kange (fig. 1, sections 16 and 18), 

where unit B is thin, it contains phosphatic quartz sandstone and 

sandy phosphate rock. At Alpine Creek (fig. 1, section 18) the unit 

contains several thin beds of chert- and limestone-pebble conglomerate, in which the pebbles average about 20 millimeters in diameter.

Regional relations. At Little Sheep Creek (fig. 1, section 1; pi. 3, 

section 1) at the south end of the Tendoy Mountains, unit B consists 

of a basal phosphate bed that constitutes about one-third of the member, an overlying mudstone that contains several thin beds of phosphate 

rock, and a thin (0.8 foot) uppermost bed of cherty phosphate rock. 

These features are of necessity somewhat generalized on the stratigraphic diagrams. The sequence can be followed 30 miles northeastward to the Snowcrest Kange and 40 miles eastward to the. 

Centennial Mountains (pis. 2, 3). The basal bed of the unit is continuous northeastward to the Gravelly Range. The correlation of 

the thick basal bed of phosphate rock in the Tendoy Mountains with 

the thin bed of phosphate rock that composes the B member in the 

sections just south of Dillon is tentative, but it is assumed that the 

thick basal phosphate bed is more likely to be continuous than the; 

thinner beds of phosphate rock higher in the unit (pi. 3).

There are f acies changes within unit B in the Gravelly Range and 

Centennial Mountains where the member is sandy and conglomeratic, 

but elsewhere the gross lithologic character of the unit is relatively 

constant.

The distribution of the total equivalent carbonate-fluorapatite 

(calculated as percent P2 05 X2.6) and the total silt and clay (total 

acid insoluble minus estimated sand and chert) .is shown in figure 3. 

There are two maxima in the apatite distribution. The eastern 

maximum is caused largely by thickening of the basal phosphate bed; 

the western maximum is caused largely by the presence of thin beds 

of phosphate rock in the upper part of the unit. Comparison with a 

similar map of unit B in northwestern Wyoming 12 indicates that 

these two maxima are local irregularities and that the broad relation 

is one of apatite content increasing to the southwest, The map 

showing distribution of silt aiTd clay has -one maximum that overlaps 

in large part the two apatite maxima and bridges the low area between 

them.

UNIT C

Thickness and distribution. Unit C thins to the east, north, and 

west from a maximum thickness of about 300 feet just east of Lima 

(fig. 5A). The unit is about 50 feet thick at the easternmost and 

northernmost exposures of unit B. Where unit B is absent, the baseof unit C probably can be located at the contact between gray phos12 Sheldon, R. P., op. cit.
10 CONTRIBUTIONS TO ECONOMIC GEOLOGY

ISOPACH'MAP . Contour interval 50 feet

TOTAL THICKNESS OF SANDSTONE 

Contour interval 10 feet

Butte

Bozeman 

MONTANA

-~-ol 

9X ./

^

A !

\JWYO

I O A H O

113' H2'1 HI'

TOTAL THICKNESS OF CARBONATE ROCK

Contour interval 4O feet EXPLANATION

113' 112' itr 

TOTAL THICKNESS OF CHERT

Contour interval 20 feet

Control point

Numeral indicates thickness 

of measured sections

2,5 9 , SOMiles 

FIGURE 5. Isopleth. maps of unit O of the Phosphorla formation.

Sandstone and the underlying lighter nonphosphatic sandstone

(Condit, 1018, p. 113).

Where unit C is more than 1OO feet thick, it is composed dominantly

of carbonate rock and bedded chert; where it is less than 100 feet 

thick, it is composed largely of quartz sandstone.

Lithologic character. The carbonate rock of unit C is nearly all 

dolomite. The most notable exception is at Little Sheep Creek (fig.

i; pi. 3, section 1) where most of the carbonate rock in the upper half 

of the unit is limestone, Rocks equivalent to this limestone are

dolomite in the Gravelly Hange.

The dolomite ranges in color from medium and light g¥Siy to Jfillowish gray and pale brown. The dolomite beds mostly range from 

0.3 to 0.8 foot in thickness, although there are some thicker beds.
STRATIGRAPHY, PHOSPHORIA FORMATION, 'MONTANA 11

Coquinoid limestone occurs in the middle of the unit at Little Sheep 

Creek (pi. 3, section 1), but most of the carbonate rock is dense and 

shows little evidence of clastic origin. Microscopically, most of the 

carbonate rock is composed of an extremely fine grained mosaic of 

anhedral dolomite grains that range from 5 to 25 microns in diameter.

Bedded chert composes the lower third of unit C over much of the 

area. It consists largely of microcrystalline quartz, which in most 

localities contains only a small admixture of .detrital silicates. Siliceous sponge spicules are present at all localities and in all or nearly all 

chert beds, and some beds are composed almost entirely of these 

spicules. In the lower third of the unit most of the chert is in beds 

from 0.1 to 0.4 foot thick, but in several sections the chert beds are 

somewhat thicker near the contact between the bedded chert and the 

overlying dolomite. Unweathered chert is black to medium gray 

immediately overlying unit B, but in several sections it is lighter 

higher in the section. Weathered chert is mostly in shades of yellowish 

brown and yellowish orange.

The quartz sandstone of unit G contains small but conspicuous 

amounts of chert grains, carbonate-flu orapatite grains and bone fragments, and glauconite grains. No feldspar has been detected. The 

sand is mostly very fine and fine grained and is more poorly sorted 

than is sand in unit E. The sandstone ranges in color from browinish gray to light gray and in thickness of bedding from 0.2 foot ;to

several feet. ;

i

Dolomitic quartz siltstone and silty dolomite occurs in the middle 

of unit C at Little Sheep Creek and Wadhams Spring (pi. 1, section 

10; pi. 3, section 1). The silt is believed to be the finer grained 

equivalent of the sandstone at Big Sheep Canyon (pi. 1, section 2).

Regional relations. Immediately east of Lima, where unit C is 300 

feet thick, the lower third of the unit is bedded chert and the upper 

two-thirds is dolomite. From this point the unit thins to the north 

and east but retains about the same character as far as the 100-foot 

isopach (fig. 5A) . East of the 100-foot isopach the unit is dominantly 

sandstone; the chert grades and interfingers eastward into sandstone, 

and the dolomite thins to a few small beds (pi. 1). North of the 100- 

foot isopach the chert apparently grades into dolomite (pis. 3, 5). 

Northeast of the 100-foot isopach the chert grades into sandstone.and 

the dolomite either pinches out or grades abruptly into sandstone 

(pi. 2). West of Lima, the dolomite in the upper two-thirds of unit G 

grades into dolomitic sandstone and sandy dolomite, and the chert 

in part grades into or interfingers with mudstone (pi. 1).

A thin phosphatic bed in the lower third of unit G can be .traced 

from the Tendoy Mountains north to Dillon (pi. 3, sections 1,,2,-and 

5), northeastward into the Snowcrest Range (pi. 1, sections 2,10, and
12 CONTRIBUTIONS TO ECONOMIC GEOLOGY

_ lia- 1 I

Butte0

MONTANA

 -.: . .: : Dillon? ' .

1 : -1 5 ':":;J9*fe. . "*$$$ '$$?

_.'. f; ,,.' r ' ,] ; , .;_ " .'W'S'

*'' ' ' x,. - ' Sandstone ^___^

EXPLANATION

Cherty, phosphatic sandstone

'

Phosphatic sandstone

Phosphate rock

Sandy phosphate rock

Argillaceous phosphate rock

^^

Phosphate mudstone

Phosphate chert

X

Control point

\ t%*%'~^\ M:2$fy\ Cnert \ Sandstone f 1 I 

^mudstone^|g, J|^ ^ \--" ^-^^' yjW . Y O

1 D A H O

i i 1 <

45'

FIGURE 6. Map Showing lithologlc constitution of the phosphatic bed In the lower third

of unit 0 of the Phosphoria formation.

s.

11), and east into the Centennial Mountains (pi. 2, section 20). , The 

carbonate-flu orapatite content of the bed ranges from 15 percent (pi. 

2, section 9) to more than 50 percent (fig. 1, section 3), and the rocks

range from argillaceous, sandy, and cherty phosphate rock to slightly

phosphatic chert and sandstone (fig. 6). Xhe bed is 1 to 2 feet tloiok

in most sections in the vicinity of Lima and in the Centennial Mountains, but at Big Sheep Canyon (pi. 1, section 2) it is 5 feet thick.

Immediately south of Dillon the teJ is more than 5 feet thick. In

Spite of the range in thickness, phosphate content, and gross uthoiogic 

character, tke bed is, in all localities where it has been .identified, a

relatively thin Unit that iS Considerably more phosphatic than the

adjacent beds.

TWO zones Of dolomite containing nodules and interbeds of chert 

are present from Little Sheep Creek in the Tendoy Mountains (pi; S? 

section 1) to Hogback Mountain in the Snowcrest Eange (pi. 2, section 

13). A sandstone bed occurs at the top of unit G over most of the area.
STRATIGRAPHY, PHOSPHORIA FORMATION,, MONTANA 13

The distributions of total sand, carbonate rock, and chert in unit C 

are illustrated in figure 5. The similarity of the maps showing the 

thickness of carbonate rock and chert to the isopach map suggests 

that the accumulation of carbonate and chert was governed by the 

amount of subsidence of the depositional basin. The increase of 

sandstone to the west indicates that sand was derived in large part 

from that direction. Small amounts of sand must have been derived 

from the east as indicated by the eastern sand maximum and by the 

line of stratigraphic sections in plate 1.

UNIT D

Thickness and distribution. Unit D thins northward and eastward 

from a maximum of at least 80 feet just west of Lima (fig. 7A ). Unit 

D in the Gravelly Kange is only 5 or 10 feet thick. In the sections

M .\CM, N T A N A

ISOPACH MAP 

Contour interval 20 feet

TOTAL THICKNESS OF CARBONATE FLUORAPATITE 

Contour interval 5 feet

EXPLANATION

. Control point

Numeral indicates thickness

of measured, sections

TOTAL THICKNESS OF SILT AND CLAY

Contour interval 10 feot 

25 0 SO Miles

FIGDRE 7. Isopleth maps of unit D of the Phosplioria formation. 

"327853 55 3
14 CONTRIBUTIONS TO ECONOMIC GEOLOGY

112°

EXPLANATION

Sandstone Carbonate rock

25 0

Chert Chert-pebble 

conglomerate

Control point

50 Miles

FIGUBB 8. Map showing lithologic constitution of the uppermost bed of unit O of the

Phosphoria formation.

along the Jefferson River it is 3 feet thick or less. The unit thins most

rapidly in the vicinity of the Ruby Valley. Eastward from the Snowcrest Kange to the Euby Eange, the lower half of the unit lenses out 

and the upper half thins abruptly by loss of both carbonatefluorapatite and fine detritus (pi. 1, sections 12 and 17).

The lithologic character of the bed immediately underlying unit D 

is illustrated in figure 8. A minor disconformity on the east and 

northeast margins Of the area is suggested by chert-pebble conglomerate at several localities, but elsewhere there is little evidence for an 

Unconformity at this horizon. Sandstone underlies the D member

over most of the region and grades into carbonate rock to the southwest and probably to the northwest. . The bedded chert that overlies 

the sandstone in two areas may have resulted from local postsandstone
15

deposition, the incomplete stripping of a continuous bed of chert, or 

local facies change from the sand. The passing of conformable con^ 

tacts at the center of the basin into unconf ormable contacts near the 

margins is to be expected and probably occurs throughout the 

formation.

Lithologic character. Unit' D is fairly similar to unit R. Many 

phosphate beds throughout the unit in the westernmost sections (fig. 

1, section's 3, 4, and 6) contain 10 or 20 percent of carbonate-fluorapatite nodules in a matrix of structureless apatite pellets. The nodules 

range from 2 to 25 millimeters in diameter and are themselves composed of pellets. In sections just to the east (fig. 1, sections 5, 7, 8, 9, 

and 31), nodules are neither as common nor as distinct. Phosphate 

rock in the sections in the south-central part of the area (fig. 1, sections 

10,11,12,13,14, and 38) are composed almost entirely of structureless 

apatite pellets that are about 1/16 to 1/4 millimeter in diameter. 

Phosphate rock composed of oolites and fossil fragments occurs at 

the base of unit D in the Gravelly Range, and most of the phosphate 

rock in the sections along the Jefferson River are oolitic and nodular. 

In summary, the phosphate rock in the western edge of the field is 

composed of compound nodules in a matrix of pellets, in the central 

area of structureless: pellets, and in the eastern part of the area of 

oolitic, organic, and nodular phosphate rock! The phosphate nodules 

in the eastern part of the area are in a different matrix and are associated with different rocks than the nodules in the west; they are probably of a different origin. Other than in the Gravelly Range, where 

the basal phosphate bed is oolitic but higher beds are pellety, there 

is little stratigraphic difference in the type of phosphate rock in any 

one section, the variation being geographic rather than stratigraphic.

The mudstone of unit D is much like that of unit B. The organic 

matter may constitute as much as 20 or 25 percent of some beds, and 

some of the mudstone contains as much as 10 percent by weight of 

distillable oil (Swanson and others, 1953a, p. 23; Bowen, C. F., 1918). 

There is little obvious lateral variation in the character of the 

mudstone.

Dolomite, in beds averaging 0.4 to 1.0 foot thick, is present in unit 

D in many sections. The dolomite is brownish black and brownish 

gray; texturally it is a very fine grained anhedral mosaic. Fossils are 

rare in most of the dolomite beds. The dark color and small grain size o

of the dolomite makes its field identification difficult. Unit D has been 

sampled at most localities discussed in this report and analyzed for 

P2 05 and acid-insoluble content (acid-insoluble content represents 

that part of the sample not soluble in aqua regia and not ignitable at 

about 1000° C; see McKelvey and others, 1953c, p. 3). The part of 

the rock that is not in the carbonate-fluorapatite or acid-insoluble 

portions contains a great variety of elements, but in rocks that contain
16 ;* !.' 'CONTRIBUTIONS TO , ECONOMIC GEOLOGY, , .,

'a-negligible amount of organic matter, gypsum, and iron sulfides, 

oxides, and sulfates it consists mostly of carbonates. Unit Z>, howeverj 

contains so much carbonaceous material that the carbonate content 

cannot be deduced from the. analyses.

There is some phosphatic sandstone in the upper part of unit D at 

Hogback Mountain (pi, 2, section 13), but it has not been identified 

at' any other locality and its stratigraphic relations are not known. 

- In unit Z>, as in unit B, carbonate-fluorapatite, silt and clay, and 

dolomite combine to form intermediate rock types.

Regional relations. The uppermost phosphate bed of unit D is 

continuous from just-east of Lima to the eastern edge of the field, but 

it is not known whether or not it extends northward to the Dillon 

region and ;the Pioneer Mountains. The position of this bed, and thus 

of the contact of units D and E, at Big Sheep Canyon (pi. 1, section 

2) is not certain, but there the contact between members has been 

placed at the contact between phosphatic and noiiphosphatic mudstone. Other than the uppermost bed, individual beds in unit D 

cannot be correlated over the region. A bed-for-bed correlation of 

the unit has been made from the West Fork of Blacktail Creek to 

Hogback Mountain (fig. 1, sections 11 and 13), a distance of about 

25 miles; and correlation in considerable detail is possible from Wadhams Spring (pi. 1, section 10) to Hogback Mountain, a distance of 

35 miles. Several zones in unit D can be carried from the sections 

just south of Dillon to .those in the Pioneer Mountains, a distance of 

about 30 miles, j Unit D is very similar in the sections in the Gravelly 

and .Madison Ranges, consisting 'of' a thin lower phosphate bed, an 

overlying mudstone, and. an uppermost bed of phosphate rock.

"Figure 7 includes maps that show the total thickness of apatite and

of silt and clay in unit D. Melrose (fig. 1, section 8), the only place 

in the area where phosphate rock is currently being mined from unit 

Z?, is located where the apatite content is only moderately high but the 

content of silt and clay is relatively low.

The previously mentioned difficulty of identifying carbonate rock 

in unit D makes it impossible on the basis of data available to determine any regional relationships in the areal distribution of carbonate 

rock. However, the small amount of acid-soluble material other than

carbonate-fluorapatite at Sheep Creek, Sawtooth Peak, and Hogback

Mountain (fig. 1, sections 9,12, and 13) suggests that carbonate rock

is least common where the phosphate content is highest.

UNIT E

Thickness and distribution. Over much of the area unit E is 100 

to 130 feet thick; it is more nearly uniform in thickness than are the 

other units, although west of Lima it is 140 feet thick and it thins to 

60 feet within 100 miles eastward. In the northern end of the Tobacco
STRATIGRAPHY, PHOSPHORIA FORMATION, MONTANA 17

113° 111"

46' .Butte

MONTANA

Bozeman

45'

/ Truncated by > 

Dinwoody formation EXPLANATION

I DA H O Control point

Numeral indicates thickness 

of measured sections

46"

45"

113° 112"

25 0

I .... I

111°

50 Miles 

I

Contour interval 20 feet 

FIGURE 9. Isopach-map of unit E of the Phosphoria formation.

Root Mountains and the southern end of the Elkhorn Mountains unit 

E has been truncated by erosion and is unconformably overlain by 

Jurassic rocks of the Ellis group (pis. 4, 5; fig. 9). At Sawtelle Mountain in the Centennial Mountains (fig. 1, section 21) the unit is 90 

feet thick; but 9 miles west of Sawtelle Mountain the beds are only 50 

feet thick and are overlain by mudstone similar to that of the basal 

Dinwoody formation (pi. 2, section 20). The change in thickness of 

the.rocks of unit E in the Centennial Mountains may be due to a westward facies change from sandstone at Sawtelle Mountain to mudstone similar to that in the Dinwoody to the west, but no such abrupt 

change from sandstone to mudstone is evident elsewhere in the unit. 

It is possible that the thinness of the westernmost Centennial section 

may have resulted from stripping of the upper 50 feet of unit E during a pre-Dinwoody erosion interval.
18

Lithologic character. Unit E is composed mostly of bedded chert 

and sandstone. Unweathered chert is dark and medium gray to grayish brown. Where the chert has been subjected to intensive weathering, many of the beds are dull and in lighter shades of yellowish brown 

and orange so that they megascopically resemble siltstone. Weathered 

chert is interbedded with unweathered chert in some sections (fig. 1, 

sections 9 and 11), suggesting some primary difference in composition 

that has not been detected in thin sections.

The thickness of bedding of the chert ranges from less than 0.01 foot 

to several feet. In the Gravelly Range, chert in the basal part of unit 

E is in beds about 0.1 foot thick. Higher in the sections the beds are 

also about 0.1 foot thick, but the bedding planes become less distinct; 

about 30 feet above the base of the member the chert IS massive. 

Similar relations are evident in the Madison Range, but elsewhere no 

consistent stratigraphic variation in thickness of bedding is evident.

The chert is composed of microcrystalline quartz with small admixtures of silt and clay. Siliceous sponge spicules are present in every 

thin section of unit E chert that has been examined. Many spicules 

are nearly indistinguishable from the surrounding siliceous cement so 

that it is difficult to estimate the amount of spicules in a thin section, 

but a conservative estimate is that they make up at least 25 percent of 

the nondetrital quartz in nearly every specimen examined. A few 

samples of the chert are composed almost entirely of spicules. All 

samples of the chert that have been examined in thin section contain 

many small spicules of carbonate-fluorapatite. Many of these apatite 

spicules are hexactinal in form and thus represent either replacements 

of siliceous spicules or canal fillings of spicules, the siliceous part of

which has been dissolved or rearranged. It is possible that much of 

the apparently inorganic microcrystalline quartz in the chert may have 

resulted from solution and redeposition of silica from spicules that are 

now represented by the apatite replacements or canal fillings. The 

solution and redeposition of silica from spicules is also suggested by

the observation that enlarged axial canals of many siliceous spicules

are filled with inorganic microcrystalline quartz.

The sandstone ranges in color from grayish brown to light brownish 

gray and very pale orange. The thickness of bedding is,extremely 

variable. Sandstone near the top of unit E in the Gravelly Kange is 

crossbedded, but no current bedding has been observed farther west. 

There are no ripple marks.

The Sandstone is composed largely of subangular quartz grains averaging 0.08 to 0.18 millimeter in diameter. About 10 percent of the

detrital grains are chert. Glauconite grains are present in HlOSt Of

the sandstone west of the Kllby Eiver, and sandstone in the upper part 

of unit E in the Gravelly Range is glauconitic. The glauconite rarely 

forms more than about 5 percent of the rocK.
STRATIGRAPHY, PHOSPHORIA FORMATION, MONTANA 19

The heavy detrital minerals make up only about 0.01 percent of unit 

E sandstone. They consist almost exclusively of zircon, tourmaline, 

and rutile, all of which are highly resistant to weathering. There are 

very minor amounts of garnet and apatite. The varietal complexity 

of the tourmaline, and to a lesser extent of the zircon, suggests an 

ultimate source that included sedimentary, metamorphic, and igneous 

rocks. However, the immediate source of most of the heavy minerals, 

and thus of the quartz sand, was probably older sedimentary formations, as is indicated by the predominance of subrounded tourmaline 

and zircon and the extreme varietal complexity of the subrounded 

tourmaline as compared to the relative varietal simplicity of the 

angular tourmaline.

Pyrite has been observed in a few unweathered specimens of sandstone. Pseudomorphs of limonite after pyrite have been observed in 

many thin sections, and the yellowish brown and orange color of the 

weathered sandstone is probably caused by iron oxides produced by 

the weathering of pyrite. Most of the sandstone is cemented by 

microcrystalline quartz, and there are siliceous sponge spicules in 

many beds. The sorting of the sandstone is excellent, contrasting 

with the rather poor sorting of much of the sandstone in unit 0.

In the Gravelly Range, sandstone in the middle of unit E is light 

gray, contains little glauconite or pyrite, and is cemented largely by 

overgrowths on the quartz sand grains.

The upper and lower thirds of unit E at Big Sheep Canyon (pi. 1, 

section 2) are mudstone. There are a few beds of thin-bedded brownish gray mudstone in the lower part of unit E at the south end of the 

Gravelly Kange, and much of the lower half of unit E in the Centennial Mountains is thin-bedded brown and brownish gray mudstone. 

The mudstone contains very fine grained quartz and muscovite silt in 

a clay matrix and differs from mudstone in'unit D largely in being 

lighter in color. Part of unit E in the Tendoy Mountains consists of 

mixtures of silt and clay and microcrystalline quartz, which form 

cherty mudstone and argillaceous chert.

Some carbonate rock occurs near the top of unit E in the Gravelly 

Range and throughout the lower half of the member near Three Forks 

(fig. 1, section 36). Most of the carbonate rock in the Gravelly Range 

is a mixture of extremely fine grained calcite and dolomite, but a few 

beds, contain large amounts of shell fragments.

A few thin beds of phosphate rock in the lower half of unit E in 

the northern Madison Range, the Gallatin Range, and near the Jefferson River may have resulted from the reworking of older phosphate 

beds of unit D.

Fossils other than sponge spicules are extremely rare in most of 

unit E; but the uppermost beds, in a number of sections at Alpine 

Creek, Hogback Mountain, West Fork of Blacktail Creek, and Sheep
20 CONTRIBUTIONS TO ECONOMIC GEOLOGY

EXPLANATION

Mudstone and Interbedded chert 

cherty mudstone and carbonate rock

0 50 Miles

Control point

FIGURE 10. Maps showing the distribution ot fades of unit E of the Phosphoria formation. 

A, lower half of the unit. B, upper half of the unit.

Creek (fig. 1, sections 18, 13, 11, and 9), contain many brachiopod 

shells and fragments. A limestone composed, largely of crinoid stem 

plates occurs at the top of unit E in Small Horn Canyon approximately a mile north of the Sheep Creek section (fig. 1, section 9).

Regional relations. Unit E may be divided roughly into a lower 

and m upper half, each of which has a distinctive pattern of facies 

distribution. These are summarized in figure 10. Sand in the upper 

half of the unit was evidently derived from the northeast; the source 

of sand in the lower half of the unit appears to.have been derived from 

the north, according to regional relations in this area, but its character

is so similar to sand in the upper half of the unit that it may have been

derived from the same source.

THE PHOSPHORIA-DINWOODY CONTACT

In the northeastern part of the area,'rocks of the Ellis group overlie 

truncated beds of unit E ; in the Centennial Mountains, the upper half

of unit E may have been stripped off before deposition of the Dinwoody formation; and at Shell Creek in the Madison Range the Dinwoody rests disconformably on the Phosphoria (Swanson, R. W., 

written communication, 1954). In most other localities, however, the 

Dinwoody formation overlies the Phosphoria with apparent conformity. . ' .

Over mo^t Of the region the lithologic change from Phosphoria to 

Dinwoody is abrupt; chert, carbonate-fluorapatite pellets, sponge spicul'es, and quartz sand all disappear at the top of unit ff, ana clay,

which is present in only small amounts in unit E, forms a large part 

of the basal mudstone of the Dinwoody. However, in the sections near
21

Lima, which are nearer to the center of the basin of deposition, the 

transition from unit E to Dinwoody is more gradual. At Wadhams 

Spring (fig. 1, section 38) beds of unit E and the Dinwoody alternate 

near the top of unit E, and irregular quartz sandstone laminae in the 

basal beds of the Dinwoody formation are very similar to sandstone 

in the Phosphoria. Clay does not appear abruptly at the contact as 

it does in most of the region, but is present in the upper third of unit 

E and increases in amount toward the contact. In the Tendoy Mountains (fig. 1, section 2) the Phosphoria-Dinwoody contact is apparently within a sequence of mudstone. Although in most localities the 

grain size of the detrital quartz in the basal mudstone of the Dinwoody is considerably smaller than that of the detrital quartz in 

unit E, there is no obvious difference either in the varieties of quartz 

or in the species and varieties of heavy minerals between the two 

formations.

The change in gross lithologic constitution between unit E and the 

Dinwoody is apparently no more abrupt than the break between units 

within the Phosphoria formation. Nevertheless, the absence in the 

Dinwoody of sponge spicules, chert, glauconite, and phosphate pellets, 

constituents that occur throughout the Phosphoria, suggests that the 

change from unit E to Dinwoody was accompanied by a greater 

change in total environment than was any lithologic change within 

the phosphoria. Crossbedding at the top of unit E in the Gravelly 

Range, larger grain size of the uppermost sandstone of unit E in 

several sections, and the appearance of brachiopod shells in the uppermost beds of unit E all suggest shoaling of the Phosphoria sea toward 

the end of unit E deposition.

The abrupt lithologic break between the Phosphoria and Dinwoody 

formations and the indications of shoaling toward the end of unit E 

deposition suggest a hiatus between deposition of unit E and of the 

lower part of the Dinwoody formation. The length of any such interval of nondeposition and whether or not it was any longer than 

intervals of nondeposition within the Phosphoria must be evaluated 

by the paleontologist.

It frequently has been stated that the faunal break between the 

Phosphoria and Dinwoody formations is so great that it suggests a 

stratigraphic break of considerable magnitude (Mansfield, 1927, p. 

188; Newell and Kummel, 1941, p. 205, and 1942, p. 938). Kummel 

has found lower Scythian ammonites and Olarcda within 5 feet of the 

base of the Dinwoody formation in southwestern Montana (Kummel, 

1954, p. 168), but the Phosphoria formation in Montana, and the 

upper two units in particular, can at present be dated as post-Kaibab 

only by means of a long-range lithologic correlation with beds in 

Utah, Idaho, and Wyoming (Baker and Williams, 1940, p. 624-625).
22 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Therefore, the length of time represented by the break between the 

two formations remains unknown.

FACIES RELATIONSHIPS

TIME ZONATION

The recognition of time horizons is prerequisite to detailed analysis 

of lithologic facies and their paragenesis. Unfortunately, the study 

of the faunas collected by the Geological Survey from most of the 

sections mentioned in this report has not been completed. It is possible, moreover, that a faunal zonation of a thin formation of such 

contrasting lithologic facies will not result in a satisfactory time 

zonation.

If two adjacent lithologic facies are time equivalents, interfingering 

or intergradation of the facies should be expected. Other than in 

the Tendoy and Centennial Mountains there is no prominent interbedding or integradation in the Phosphoria between the phosphate 

rock-mudstone assemblage and the chert-sandstone-dolomite as-i 

semblage. Furthermore, the continuity of the same sequence of mudstone and phosphate rock in units B and D over a wide region suggests 

near contemporaneity of the individual zones. Finally, the uniform character of the phosphate rock within any one section of unit 

D indicates the persistence of uniform conditions at any one locality 

throughout the time in which unit D was deposited. All of these 

lines of evidence suggest that there has been no major transgression 

or regression in time by correlative rock units and thus that the 

unit contacts are approximate time horizons.

| Evidence indicative of the migration of facies in time is the presence 

of mudstone and cherty mudstone in unit E and the base of unit 0 

in the Tendoy Mountains and mudstone in unit E in the Centennial 

Mountains. Both of these localities are near the margins of the area.

Assuming, then, that the unit contacts are nearly time horizons over

most of the region, a number of facies changes can be detected in the 

Phosphoria. These facies changes are listed in tables 1 and 2.

SOURCE OP DETRITUS

The direction of transport of the sand and silt is summarized in 

figure 11. The source has been deduced mostly from the gross areai

distribution of rock types t>ut partly dProrn. cRange of grain size.

Sand was derived from the east, west, and northwest, and probably

from the north. Silt -was derived from the west and northwest.

The source of the mudstone is not evident, and no direct evidence 

has been detected in units E or D. The fWQ'gr&lmd. detritus ID 

unit E (fig. 10) may have been derived from the west or it may have
STRATIGRAPHY, PHOSPHORIA FORMATION, MONTANA 2& 

ii3° i»2« nr

46'

Well-sorted sand 

Lower unit E

. Bozeman

Well-sorted sand 

Upper unit E

FIGURE 11. Direction of transport of sand and silt in the Phosphoria formation.

been winnowed from sand on the east and deposited to the west afterbypassing the area of chert deposition.

Sand that has been derived from the west grades eastward intodolomite (table 1, sequence III), siltstone (table 1, sequence IV), or 

mudstone (table 1, sequence VIII). Sand that has been derived from 

the north or northwest grades southward into chert (table 2, sequences 

IX and X), siltstone (table 2, sequence XI), or mudstone (table 2,. 

sequence XII). Sand that has been derived from the east grades 

westward into chert (table 1, sequences I, V, VI, VII, and VIII) 

or dolomite (table 1, sequence III), but never directly into mudstone 

or siltstone, thus suggesting that silt and clay were derived from the 

west, northwest, and possibly the north, but not from the east. If 

the fine-grained detritus was derived from the west, the relations 

further suggest that little fine-grained silt and clay were available 

in the eastern source area but the western or northwestern sourcesupplied detritus with a considerable range of grain size.
24 CONTRIBUTIONS TO ECONOMIC GEOLOGY

e

thwestern Monta

g

brmation ins< 

and sand] of silt;

 ' -» £

 o O

*? I

O o3

o. S 03 0

2 d

 J? ®

 ft, s

to £

'« 

s S **> S

S -2 

c» 3

S ^

 1 1

*8 <» SP

-S. -

"oo 

to 

§

«}

e

:&q .

I

 1 i

H

K5

«

«!

rlj .T^

jj *o | 05 ""!

^ O ft V ^ «

^ -B -<

 ~ S ~

PH H PH

a

o

1

 2 KJ o'

° *» .12

1 * § 

^ & ^ §3 

a .15 & ft fl 0,

D t> &

0 I 0) 0)

! -II !

 S «f8" 1

8:1 -2 2 S e8 -p ^H w 

« * ft OQ

1* ° n

tH~0

11*

-art o O m t-> 'TJT

&

\

I

«0 M

8, 1 e» o

* » »i

'S S

-* -43^

s ft ^ S '

§

r^ .

o, _g

s ! >> *1

* -P -P M

« fe ® o

* "« o 

O PL, p

1 0) "2 "S

13 e8

S

rO

ft

03 

bx, °

-iS1 ^ 1 & ^3 C

0 >> o

* ^ ^

^ T) ® ^

fi 75 0

2 ft* 15 

°< i

O> ' 0

S f-T P 0 v c8 "2 |sl^ i ^ 3T3 0 ^

P co o H 0

S ^ P

3c«

& h-l

* 1 1 H- 1 H-l t 1 I I

«O

T)r*4

a

rH

CO S

d

£

d

3 

1)

^ 

T)

§

CD

.____Dolomit

CD

£3

o

IM P 

fl

CO

o

-i-3

Dolorai

i

Sandstone

> I i

CO

b

S

O

-to 'p

3

.a

TJ CD 

X5 

«;

1 

^3 

P

O3

0

J=l 

PH

CD

< 

Sandston

4- 

^ 

a

rd

c

a,

p 

y

T: 

^

>

i-H

) 

PH

d

ti 

a

H S3 ^

o

^

CD

< 

.___Sandston

Chert..

!

1

I

1

1

1

cu

0

-p

tc

T3S

£

1

o3 

 g 

g

HH 

>

 *

bb

s

d t-i

0<-< rM 

 p

O

02

^f«

a

 3« 

§^

stft? ftf 

P

o

< !

-Sandston.__ 

-* 

.p

CD

6

0)fi

0

TD

i

1

11

Dolomite.

HH

HH

>

^

bi

S

d 

§3

^ -P

M 

O

c

! "<

!13 t-> i *

0

^ D 

&

^ e^~

N 

(11

C 

0

-p

03

T

la ^.

N 

P

a

6

a.

C

_0

" ~a.

T: 

s

&

C 

P 

9] "ti

§ 

X

tt 

>

)

tiCD

Pi c8 

<M 

o

1

c

?

_c "?

K

'

0

« 

*i

<

s

S *c

s

'<"c

i

_c

I <:

r<

1

<

r£

Q

«

ri

5 '*

C

«

t

i

*c

<

<: '?

4 

^

i

c

r-C

1

»<

<

Cf:

P

«

t

3

»

3

> 

i

3

A

3d

0

i

1

»

3

i

0

sand]ilt andof

3 £

* 0

5 8

1! 2 

; o

rt * s

0 2

i 0 3 -g £ TS

" <BH o it t> ~"

? |

S 5

 > .a

& t- 3 1

3 B

? - 

S

5

I

S

5>H

i"

q

a 

q

D

H

s

IV

«?

8

' §o

Position inse

1

«

1*=»

"Si

1fsi &

ff

S

I

«

S

£

1ex

*

^

.-I

r- 1

bb

£

RJ

-P PH

a 

s

!-, 

CD

^ 

O 

^

<u

-Sandstoni.__ 

-p M 0)

6

*-< o>,-<

rM 

O

^3

§

Mudstone

Xh- 1

IO

-a

o

w

<N

CO

s

d

4J '3

?

§3 ft ft 

D

CD

< 

-Sandston.__ 

Chert _

i i

Dolomite.

M

0

CO

. . bC

S S

fc

£

^0 .

_g

Middle C_. unit Phosphatic bed 

C. unit 

0) O

-Doloniit.___ 

' 4 

sandston atic 

^ft

COO

M 

PH

1. 1 0

o

-p

CO

T3

a02

i

i

I

I

1 1

1 1

i o

i 1 s §

03 5

-p cS

^ H 

"03 ,, Dolomitie Phosphatil

i i

I-H » I X M
STRATIGRAPHY, PHOSPHORIA FORMATION, MONTANA 25

The western source area was probably in north-central Idaho. The 

region now occupied by the Idaho batholith was a positive area during much of the Paleozoic era (Ross, 1934, p. 996-1000). Central 

Idaho supplied sediment to the east during Carboniferous time, and 

Ross (1934, p. 999) believes that the region remained positive during 

at least part of the Permian. The Paleozoic section in south-central 

Idaho contains thick argillaceous formations that in places have a 

total thickness of more than 5,000 feet (Ross, 1934, fig. 2). These 

are the Garden Creek phyllite of possible Cambrian age, the Lower 

Ordovician Ramshorn slate, and the Milligen formation of Mississippian age. These fine-grained sediments together with pre-Cambrian argillites of the same region would have been a more than adequate source for the mudstone in the Phosphoria formation.

Klemme,13 working in an area approximately 30 miles north-northwest of Bozeman, has concluded from the study of pebbles from conglomerate in the Phosphoria that the shoreline of the eastern positive 

area was actively eroding the Madison limestone (Mississippian age),, 

the Amsden formation (Pennsylvanian and Mississippian age), and 

the Quadrant formation (Pennsylvanian age), and it is probable that 

most of the sand in the Phosphoria was derived directly from the 

Quadrant. Eardley's paleogeologic map of the western United States 

at the close of the Permian (Eardley, 1949, p. 672) indicates that the 

eastern source area consisted largely of Mississippian and Pennsyl^ 

vanian rocks with smaller more distant outcrop belts of lower Paleozoic and pre-Cambrian rocks. Although the Paleozoic sequence to 

the east includes some argillaceous units, particularly in the BigSnowy group of late Mississippian and Pennsylvanian (?) age, they 

are much thinner than the argillaceous Paleozoic rocks of south-central 

Idaho, and their belt of outcrop during Permian time was probably 

more distant from the site of Permian deposition than was the central 

Idaho positive area. Thus a western source for the Phosphoria mudstone is suggested by the f acies relations and the paleogeography, but. 

the evidence is not conclusive.

BEDDED CHEBT F ACIES

Bedded chert is adjacent to sandstone in seven of the f acies sequences, 

in tables 1 and 2 (sequences I, V, VI, VII, VIII, IX, and X). In each 

sequence the chert is basinward from the sandstone. Although much 

of the sandstone contains chert cement, sandy chert is not common 

and the f acies change from cherty sandstone to chert is abrupt at 

many places. The chert appears to have resulted in large part f romt 

the accumulation and partial diagenetic reorganization of sponge

u Klemme, D. H., The Geology of Sixteen Mile Creek Area, Montana: unpublished' Ph. D.. 

thesis, Princeton University:
26 CONTRIBUTIONS TO ECONOMIC GEOLOGY

spicules and other siliceous organic remains, and the facies relations 

between sandstone and chert probably resulted from the sorting of 

the siliceous organic remains from the quartz sand and the subsequent 

accumulation of the organic silica on the basinward side of the sand. 

The abruptness of the facies change probably reflects both the efficiency 

of the sorting and the uniform size of quartz sand that was supplied 

to the depositional basin.

CARBONATE ROCK FACIES

Carbonate rock is interbedded to some extent with all other rocktypes and is probably polygenetic. Dolomite that occurs as a geographically distinct facies is either immediately adjacent to sandstone 

(table 1, sequence III) or is separated from the sandstone by a bedded 

chert facies (table 2, sequence X). These facies relations indicate 

that most of the carbonate accumulated in deeper, less turbulent water 

than did sand and chert and that the original grain size was finer 

than sand size.

PHOSPHATE ROCK FACIES

Most of the phosphate rock is intimately interbedded with carbonaceous mudstone and, as with the mudstone, probably accumulated in 

fairly deep, relatively quiet water poor in oxygen. The areal distribution of the types of phosphate rock in unit D fossiliferous, nodular, 

oolitic phosphate rock on the east, pellety phosphate rock in the central 

part of the region, and nodular, pellety phosphate rock on the west 

suggests that the fossiliferous, nodular, oolitic phosphate rock was 

deposited in shallower, more turbulent water than was the pellety rock. 

The sequence from east to west in unit D of fossiliferous, oolitic, nodular phosphate rock pellety phosphate rock nodular, pellety phosphate rock suggests that the nodular, pellety phosphate rock was deposited in deeper water than were the two more eastern facies, but

 deposition in deeper water in the western part of the area as difficult 

to reconcile with a western source for the mudstone.

LATERAL SEQUENCE OF BOCK TYPES

Assuming that mudstone in unit E in the Tendoy and Centennial

Mountains was deposited under about the same conditions as mud-

 stone in units B and Z), the sequence of facies in the Phosphoria forma-

 tion from shoreward to seaward is as follows: Sandstone, chert, mudstone, interbedded pellety phosphate rock and mudstone, and interbedded nodular, pellety phosphate rock and mudstone. Carbonate

rock is interbedded to some extent with all other lithologic types but

for the most part occurs basinward from the sandstone. Fossiliferous, 

nodular, oolitic phosphate rock is associated with all other rock types
STRATIGRAPHY, PHOSPHORIA FORMATION, MONTANA 27

with the exception of nodular, pellety phosphate rock. Nonglauconitic sandstone in unit E occurs for the most part on the eastern 

or shoreward margin of the area, but in several sections it is overlain 

by crossbedded fossiliferous, glauconitic sandstone that was apparently deposited in shallower water.

McKelvey (oral communication; and McKelvey and others, 1953&, 

table 1) has deduced the following shoreward to seaward sequence of 

iacies in the Phosphoria formation from the gross lithologic constitution of sections in southeastern Idaho and western Wyoming: 

redbeds, sandstone, glauconitic sandstone, carbonate rock, chert, 

organic phosphorite, pisolitic phosphorite, pellety phosphorite, and 

mudstone. The sequence in Montana is generally similar to that in 

Idaho and Wyoming, but carbonate rock, fossiliferous phosphate rock, 

mudstone, and nonglauconitic sandstone do not seem to occupy definite 

positions in the Montana sequence.

VERTICAL SEQUENCE OF BOCK TYPES

According to Sheldon," the Phosphoria formation in northwestern 

Wyoming consists vertically of two cyclical rock sequences. Each 

cycle consists of an upward sequence of carbonate rock, tubular chert, 

nodular and concretionary chert, organic phosphorite, oolitic and 

nodular phosphorite, pellety phosphorite, oolitic and nodular phosphorite, bedded chert, nodular and concretionary chert, tubular chert, 

and carbonate rock. The cycles are incomplete, and generally one or 

more of the phases are not present, especially the phases from the 

lower carbonate rock to the lower organic phosphorite. Analogously 

in Montana, there is a similar twofold vertical repetition of rock types 

in the Phosphoria formation. The phosphatic mudstone-bedded 

chert-carbonate rock sequence that comprises units B and 0 is repeated 

in the phosphatic mudstone of unit D and the chert of unit E. The 

uppermost silty and sandy carbonate beds that are near the top of 

unit E at some localities complete the upper sequence.

RELATIONSHIP OF FACIES TO DEPTH OF WATER

The rock types and their distribution have resulted from a number 

of complexly interrelated factors, such as the location, altitude, topography, climate, and drainage of each of the two source areas; the 

lithologic character of the rocks exposed in the source areas; the depth 

and submarine topography of the depositional basin; the nature of 

currents in the depositional basin; and the concentration of elements 

in the basin waters and in the inflowing marine and river water. It is 

difficult to determine what factors were the most important in the

Sheldon, R. P., op. clt.
28 CONTRIBUTIONS TO ECONOMIC GEOLOGY 

ROCK TYPE

Sandstone Chert Mudstone

Phosphate rock

Organicooliticnodular

Pellety Nodularpellety

FIGURE 12. Inferred relations between rock types in the Phosphoria formation in Montana 

and the relative depth of water in the deDOgitional basin.

deposition of any one fades, and it is not known what changes in

environment resulted in the vertical sequences of rock types. However, assuming that depth, of water was the most important factor

influencing turbulence, the relations illustrated in figure 12 between 

rock types and relative depth of water have been deduced from associations of gross lithologic units and the lateral sequence of f acies. 

If the relations in figure 12 are correct, then the standstone and chert 

of units C and E probably were deposited in shallower water than were

the mudstone and phosphate rock of units B and D. This, together

with the absence over most of the region of clear evidence of the transgression of time horizons by unit contacts, suggests that the vertical 

sequences of rock types resulted from vertical tectonic movements that 

affected most of the region nearly simultaneously.
STRATIGRAPHY, PHOSPHORIA FORMATION, MONTANA 29

Sheldon 15 believes that the two vertical cycles of rock types in the 

Phosphoria of western Wyoming resulted from tectonic movements 

and thus presumably from changing depth of water.. The tectonic

 changes led to transgression and regression of environments that were 

recorded there by trarisgressive and regressive f acies.

It is evident, however, from the wide association of some rock types 

:such as carbonate rock and f ossilif erous phosphate rock and the interbedding of rock types that are usually deposited at different depths 

(for example, sandstone interbedded with mudstone and phosphate 

rock at Hogback Mountain) that relative depth of water was only one

 of a number of factors that determined the locus of deposition of the 

f acies.

LITERATURE CITED

Altschuler, Z. S., and Cisney, E. A., 1952, X-ray evidence of the nature of

carbonate-apatite: Geol. Soc. America Bull., v. 63, p. 1230-1231. 

Baker, A. A., and Williams, J. S., 1940, Permian in parts of Rocky Mountain

and Colorado Plateau regions: Am. Assoc. Petroleum Geologists Bull., v. 24,

p.617-635. 

Bowen, C. F., 1918, Phosphatic oil shales near Dell and Dillon, Beaverhead

County, Mont.: U. S. Geol. Survey Bull. 661-1.

 Condit, D. D., 1918, Relations of late Paleozoic and early Mesozoic formations 

of southwestern Montana and adjacent parts of Wyoming: U. S. Geol. 

Survey Prof. Paper 120-F.

 Condit, D. D., Finch, E. H., and Pardee, J. T., 1928, Phosphate rock in the Three 

Forks-Yellowstone Park region, Montana: U. S. Geol. Survey Bull. 795-G.

 Cressman, E. R., Wilson, W. H., Tandy, C. W., and Garmoe, W. J., 1953, 

Stratigraphic sections of the Phosphoria formation in Montana, 1949-50, 

part 1: U. S. Geol. Survey Circ. 302.

Eardley, A. J., 1949, Paleotectonic and paleogeologic maps of central and western 

North America: Am. Assoc. Petroleum Geologists Bull., v. 33, p. 655-682.

Emmons, W. H., and Calkins, F. C., 1913, Geology and ore deposits of the 

Philipsburg quadrangle, Montana: U. S. Geol. Survey Prof. Paper 78.

Frenzel, Hugh, and Mundbrff, M. J., 1942, Fusulinidae from the Phosphoria 

v formation of Montana: Jour. Paleontology, v. 16, p. 675-684.

Hague, Arnold, Iddings, J. P., and Weed, W. H., 1899, Geology of the Yellowstone 

Park, part II: U. S. Geol. Survey Mon. 32.

Iddings, J. P., and Weed, W. H., 1894, Description of the Livingston quadrangle, 

Mont.: U. S. Geol. Survey, Geol. Atlas, folio 1.

Klepper, M. R., 1950, A geologic reconnaissance of parts of Beaverhead and 

Madison.Counties, Mont.: U. S. Geol. Survey Bull. 969-C.

Klepper, M. R., Honkala, F. S., Payne, O. A., and Rupple, E. T., 1953, Stratigraphic sections of the Phosphoria formation in Montana, 1948: U. S. Geol. 

Survey Circ. 260.

Kummel, Bernhard, 1954, Triassic stratigraphy of southeastern Idaho and adjacent areas: U. S. Geol. Survey Prof. Paper 254-H.

McKelvey, V. E., 1949, Geological studies of the western phosphate field: Am. 

Inst. Min. Metal. Eng. Trans., v. 184, p. 270-279.

Sheldon, R. P., op. cit.
30 CONTRIBUTIONS TO ECONOMIC GEOLOGY

McKelvey, V. E., Swanson, R. W., and Sheldon, R. P., 1953a, Phosphoria formation in southeastern Idaho and western Wyoming in Intermountain Assoc. 

 Petroleum Geologists, Guidebook 4th Ann. Field Conf., p. 41-47.

 1953b, The Permian phosphorite deposits of western United States:

Internat. Geol. Cong., 19th sess., Comptes rendus, v. 11, p. 45-64. 

McKelvey, V. E., and others, 1953c, Stratigraphic sections of the Phosphoria

formation in Idaho, 1947-48, part I: U. S. Geol. Survey Circ. 208. 

Mansfield, G. R., 1927, Geography, geology, and mineral resources of part of

southeastern Idaho: U. S. Geol. Survey Prof. Paper 152. 

Newell, N. D., and Kummel, Bernhard, 1941, The Permo-Triassic boundary in

Idaho, Montana, and Wyoming: Am. Jour. Sci., v. 239, p. 204-208.

 1942, Lower Eo-Triassic stratigraphy, western Wyoming and southeastern

Idaho: Geol. Soc. America Bull., v. 53, p. 937-996. 

Peale, A. C., 1893, The Paleozoic section in the vicinity of Three Forks, Montana:

U. S, Geol. Survey Bull. 110. 

Peterson, J. A., Gosman, R. F., and Swanson, R. W., 1954, Stratigraphic Sections

of the Phosphoria formation in Montana, 1951: U. S. Geol. Survey Circ. 326. 

Richards, R. W., and Mansfield, G. R., 1912, The Bannock overthrust: Jour.

Geology, v. 20, p. 681-709. 

Ross, C. P., 1934, Correlation and interpretation of Paleozoic stratigraphy in

south-central Idaho: Geol. Soc. America Bull., v. 45, p. 937-1000. 

Sloss, L. L., and Moritz, C. A., 1951, Paleozoic stratigraphy of southwestern

Montana: Am. Assoc. Petroleum Geologists Bull., v. 35, p. 2135-2169. 

Stone, R. W., and Bonine, C. A., 1914, The Elliston phosphate field, Montana:

U. S. Geol. Survey Bull. 580-N. 

Swanson, R. W., Lowell, W. R., Cressman, E. R., and Bostwick, D. A., 1953a>

Stratigraphic sections of the Phosphoria formation in Montana, 1947-48:

U. S. Geol. Survey Circ. 209.

Swanson, R. W., Cressman, E. R. Jones, R. S., and Replogle, B. K., 1953b, Stratigraphic sections of the Phosphoria formation in Montana, part 2, 1949-1950:

U. S. Geol. Survey Circ. 303.

Thomas, H. D., 1934, Phosphoria and Dinwoody tongues in the lower Chugwater

of' central anQ southeastern Wyoming: Am. Assoc. Petroleum Geologists.

Bull., V. 18, p. 1655-1697. 

Williams, J. Stewart, 1953, Pennsylvanian and Permian rocks: Intermountain:

Assoc. Petroleum Geologists, Guidebook 4th Ann. Field Conf., p. 38-40.
Page

Acknowledgments...__... 2-3 

Amsden formation, Pennsylvanian and Misslsslpplan age._ 26

Bedded chert tocies 25-26

Bibliography. 29-30

Big Snowy group, Mlsslsslppian and Pennsylvanian age___ .- 26

Carbonate rock fades... 26 

Chert-quartz sandstone member, unit E... 4,16-20 

Claraia........__..._..... .......... 21

Correlation, regional... . ... ...... 3-6

Detritus, source of.. ...... ......... 22-25

Dlnwoody formation, contact with Phosphorla

formation......... .....__ 20-22

Triassicage..... .......-.... .-......-.- 3,4

Distribution of Phosphorla formation^.. 4,6-7, 

9-10,13-15,16-17

Bills group, Jurassic age.... . 4,17

Fades, bedded chert........... . ... 25-26

carbonate rock -_ ..... .. 26

lateral sequence... 26-27 

phosphate rock.... ... ......... 26

relationship to depth of water... 27-29 

vertical sequence... .--.......-___. 27

Fusulinids, Wolfcamp age... . 5

Garden Creek phylllte, Cambrian age. 25

Llthologlc character of Phosphorla formation. 7-9, 

10-11,15-16,18-20

Madison limestone, Misslssippian age... 25 

Milligen formation, Mississlppian age.... 25

Nomendature ___. 3-6

Phosphate rock fades_.... _____.. 26 

Phosphatic shale member, lower, unit B...... 4,6-9

upper, unit D. _____.______ 4,13-16 

Phosphoria,term flrst'used.. .. ____ 3-4 

Phosphoria formation, divisions.....____ 4

genera], thickness_.... .._...'.. 4

Quadrant quartzlte, Pennsylvanlan age......

Quartz sandstone-dolomite member, unit A..

Page 

4 

4

Ramshorn slate, Ordovlcian age_-_ __ 25 

Regional relations of Phosphorla formation..! 9,

11-13,16,20 

Rex chert member.. 4

Sandstone-dolomite-chert member, unit C_ 4,9-13 

Scope of report..__ _____._____ 1-2 

Scythian ammonites __.. __ 21 

Stratigraphic sections.. _. . pis. 1-4 

'Stratigraphy._________________ 3-22

Tensleep sandstone.- __ ...., 3 

Teton formation, Triasslc age..._______ 4 

Time zonation..._________._____ 22 

Thickness of Phosphoria formation_____ 4,6-7, 

9-10,13-15,16-17 

Type locality, Phosphoria formation_____ 3

Unit A, Phosphorla formation, definition, __ 4

Unit B, Phosphoria formation:

definition. ....__.....__........... 4

distribution...__._____._____ 6-7

lithologic character. ____________ 7-9

;- regional relations..______._____ 9

thickness..._ ....__________ 6

Unit C, Phosphoria formation:

definition......_.._..._____..... 4

distribution.... . 9-10

lithologic character._...________ 10-11 

regional relations. ___.__._._. 11-13 

thickness__________________ 9-10

Unit D, Phosphoria formation:

definition. . 4 

distribution.... .. ... ...... 13-15

lithologic character.___________ 15-16 

regional relations...___________ 16 

thickness______________.___ 13-15

Unit E, Phosphoria formation:

definition...__.___................_ 4

distribution...... .. .. 16-17

; lithologic: character.______'.____ 18-20 

 regional relations..____________ 20 

thickness. _ _ _.. 16-17

Quadrant formation, Pennsylvanian age__ 26 Wells formation, Pennsylvania age

o

3

31