Stratigraphy and Petrology 

of the Permian Rocks of 

Southwestern Montana

GEOLOGICAL SURVEY PROFESSIONAL PAPER 313-C

Prepared on behalf of the

U.S. Atomic Energy Commission

Stratigraphy and Petrology 

of the Permian Rocks of 

Southwestern Montana

By EARLE R. CRESSMAN and ROGER W. SWANSON

GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

GEOLOGICAL SURVEY PROFESSIONAL PAPER 313-C

Prepared on behalf of the

U.S. Atomic Energy Commission

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1964
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

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

Washington, D.C. 20402
CONTENTS

Abstract _ ______________________________

Introduction. ____________________________

Purpose of investigation. ______________

Personnel and acknowledgments. _ ______

Geography _______________________

Geologic setting. _____________________

Methods of study _ __________________

Field procedures__________________

Laboratory procedures. ___________

Treatment of channel samples. _ 

Chemical analyses. ___________

P2 O5 _ ________... ________

Acid insoluble. ___________

Uranium ___ ____________

Carbonaceous matter __ __ 

Spectrographic analyses ___ 

Other analyses___________

Petrographic methods_____________

Examination of hand specimens 

Thin sections_________________

Size analyses_________________

Heavy-mineral separation _ ___

Terminology ___________________________________

Explanation of illustrations______________________

Stratigraphy and petrography. _______________________

Stratigraphic nomenclature ______________________

History of nomenclature.. _ __________________

Current nomenclature. ______________________

Park City Formation __ ________________________

General character and distribution. ___________

Lithology _______________________________

Carbonate rock _ ______________________

Sandstone _____________________________

Mudstone ___ _________________________

Chert. _____ _ _ __ _______ ___ _______

Stratigraphy. ____ _ _______________________

Grandeur Member.. ____________________

Franson Member.... ___________________

Phosphoria Formation __ _______________________

General character and distribution. ___________

Lithology _______________________________

Frequency of rock types. ________________

Occurrence of carbonaceous matter in the 

Retort Phosphatic Shale Member_______

Phosphorite. ___________________________

Mudstone ___ _ ________________________

Carbonate rock_________________________

Chert_ ----._____..____.___.__.___.____

Minor rock types_______________________

Trace elements_________________________

Contact metamorphism_.________________

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Stratigraphy and petrography Continued 

Phosphoria Formation Continued

Stratigraphy. _________-__-___---_--_--_----

Meade Peak Phosphatic Shale Member_ _ 

Lower phosphorite._________________

Rex Chert Member. ____________________

Retort Phosphatic Shale Member_________

Tosi Chert Member__________-----____-_

Cherty shale member__________-_________

Localization of exploitable phosphate deposits. _ 

Shedhorn Sandstone.____________________________

General character and distribution____________

Lithology-_ __________--_----_-_------------

Sandstone.________---_-__-------------

Chert._________-__------------_-------

Dolomite _______-___--_----------------

Stratigraphy ____________--._____--------_-_-

Lower member_________________----_---

Upper member____________-_-_---_----_

Age of Permian rocks in southwestern Montana. 

Relation of Permian strata to overlying beds.______

Facies relations.__________-___-__-___---_-_-----

Genetic interpretations__________-_-____-_-----------

Origin of the rock types__ _________-_--_---------

Well-sorted sandstone_____________----_----_

Lithologic character of source.___________

Location of source_-_--___----_---------

Environment of deposition_______________

Significance of glauconite________________

Silty sandstone and tan and red mudstone-____

Lithologic character of source ____________

Location of source____-___-___--_-----_-

Environment of deposition.. ______ _______

Chert. __________ - --- 

Source of silica.___________---------__--

Environment of deposition_______________

Diagenesis _____-__----_---_------------

Dark mudstone___________________________

Source of detritus-_-__-__----___--------

Source of carbonaceous matter. __________

Rate of production of carbonaceous matter. 

Environment of deposition.-.____________

Phosphatic mudstone-______________---__----

Solubility of apatite_-_-____---------_-_-

Source of phosphorus.___________________

Manner of deposition ___________________

Origin of pellets. _____________-------_-_

Bimodal frequency distribution of mudstone. _____________--___----_---__---

Summary. _______________-___--_-----__

Phosphorite-_________-__-----__--_---------

Carbonate rock_____________________±f_______

Park City Formation.___________________

in

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IV CONTENTS

Genetic interpretations Continued

Origin of the rock types Continued

Carbonate rock Continued Page 

Phosphoria formation ___________________ 378

Paleogeography _ ________________________________ 378

Tectonism _____________________________________ 380

Genetic interpretations Continued Page 

Summary of Permian events in southwestern

Montana ____________________________________ 381

Stratigraphic sections.-_____________________________ 383

Introduction ___________________________________ 383

References cited____________________________________ 562

Transgression and regression, ____________________ 380 Index__ ___________________________________________ 567

ILLUSTRATIONS

[Plates are in separate volume]

PLATE 14. Index map of southwestern Montana.

15. Map showing outcrops of Permian rocks in southwestern Montana and localities sampled for Phosphate. 

16-24. Stratigraphic sections showing relations of the:

16. Grandeur member of the Park City Formation from Hawley Creek, Idaho, to Indian Creek, Mont.

17. Grandeur Member of the Park City Formation from Crooked Creek to Big Hole Canyon, Mont.

18. Phosphoria and Shedhorn Formations and the Franson Tongue of the Park City Formation from 

Sheep Creek to Reas Peak, Mont.

19. Phosphoria, Shedhorn, and Park City Formations from Kelly Gulch to the Sixteen Mile Creek area, 

Mont.

20. Phosphoria and Shedhorn Formations and the Franson Member of the Park City Formation from 

Little Sheep Creek to the Melrose area, Mont.

21. Phosphoria and Shedhorn Formations and the Franson Member of the Park City Formation from 

Hawley Creek, Idaho, to Cinnabar Mountain, Mont.

22. Phosphoria, Shedhorn, and Park City Formations from North Boulder Creek, Mont, to Quadrant 

Mountain, Wyo.

23. Retort Phosphatic Shale Member of the Phosphoria Formation from Big Sheep Canyon to West 

Fo.k of Madison River, Mont.

24. Stratigraphic relations of the Retort Phosphatic Shale Member of the Phosphoria Formation from

Crooked Creek to La Marche Gulch, Mont. 

25. Maps showing Paleography in Southwestern Montana.

Page 

FIGURE 87. Bulldozer trench at Sheep Creek____________________________-_--_-_--___---------_-----------_- 278

88. Retort Phosphatic Shale Member of the Phosphoria Formation exposed in bulldozer trench at Greenstone

Gulch_____________ ______________________________________________________________ 278

89-90. Graphs comparing:

89. Original and rerun uranium analyses of 22 samples of phosphorite collected in 1949 ____________ 281

90. Sieve and thin-section size analyses__-_________________________________.____-_--------_--- 282

91. Diagram showing relation of class areas and D values to composition in a three-component system_____ 283

92. Isopach map of Permian rocks in southwestern Montana ___________________________________________ 284

93. Chart showing nomenclature of the Phosphoria, Park City, and Shedhorn Formations..._______________ 286

94-95. Maps showing:

94. Lithologic character of the Permian rocks in southwestern Montana.___________________________ 287

95. Constitution of the Permian of southwestern Montana by formations.__________________________ 288

96. Isopach map of the Park City Formation.._____________________----_-_-____________------_------- 289

97. Map showing lithologic character of the Park City Formation.._____________________________________ 290

98. Graph indicating thickness of bedding of dolomite in the Grandeur Member of the Park City Formation__ _ 291

99. Cumulative size distribution curves for six mudstones from the Grandeur Member of the Park City Formation____________________________________________________________________________________ 295

100. Isopach map of the Grandeur Member of the Park City Formation._________________________________ 298

101. Map showing lithologic character of the Grandeur Member of the Park City Formation________________ 299

102. Isopach map of the Franson Member of the Park City Formation.__________________________________ 301

103. Map showing lithologic character of the Franson Member of the Park City Formation.________________ 302

104. Isopach map of the Phosphoria Formation__---_-----___-----___---_--_-_-----_----------_-------- 304

105-106. Diagrams showing:

105. Mineral composition of rock types in the Retort Phosphatic Shale Member of the Phosphoria

Formation _________________________________________________________________________ 306

106. Relation of content of carbonaceous matter to rock composition in the Retort Phosphatic Shale

Member of the Phosphoria Formation.________________________________________________ 307
CONTENTS V

FIGTJBE 107-109. Graphs showing: Page

107. Frequency distribution of carbonaceous matter in the Retort Phosphatic Shale Member of the

Phosphoria Formation.______________________________________________________________ 308

108. Frequency distribution of value (darkness) for phosphorite of the Retort Phosphatic Shale Member

of the Phosphoria Formation_________________________________________________________ 308

109. Effect of weathering on value (darkness) of phosphorite___________-__--__--___-___-_-_-_--- 309

110. Photomicrograph of cherty phosphorite containing abundant foraminiferal tests as nuclei of pellets.______ 309

111. Diagram showing relative abundance of the three principal types of apatite grains in thin sections of phosphorite from the Phosphoria Formation. _____________________________________________________ 310

112. Photomicrographs of phosphorites_______________________________________________________________ 311

113-114. Graphs illustrating:

113. Size distribution of pellets in a muddy pelletal phosphorite___________________________________ 312

114. Value (darkness) of mudstone of the Retort Phosphatic Shale Member of the Phosphoria Formation, ________________________________________________________ 314

115. Photomicrographs of chert from the Tosi Chert Member of the Phosphoria Formation.________________ 318

116. Very sandy phosphorite from top of phosphatic sandstone bed underlying 4-foot andesite(?) porphyry sill

at Jack Canyon, Madison Range. ___________________________________________________________ 321

117. Isopach map of the Meade Peak Phosphatic Shale Member of the Phosphoria Formation_______________ 322

118-119. Maps showing:

118. Lithologic character of the Meade Peak Phosphatic Shale Member of the Phosphoria Formation. _ 324

119. Thickness of beds of carbonate rock in the Meade Peak Phosphatic Shale Member of the Phosphoria

Formation. _________________________________________-_--__--_---____-_------ 325

120. Isopach map of the basal phosphorite bed of the Meade Peak Phosphatic Shale Member of the Phosphoria

Formation. _____._________.__________________________________________ 326

121. Map showing character of apatite grains in the lower phosphorite of the Meade Peak Phosphatic Shale

Member of the Phosphoria Formation..______________________________________________________ 327

122. Isopach map of the Rex Chert Member of the Phosphoria Formation________________________________ 328

123-126. Maps showing:

123. Thickness and P2O5 content of the Retort Phosphatic Shale Member of the Phosphoria Formation, ________________________________________________________ 330

124. Lithologic character of the Retort Phosphatic Shale Member of the Phosphoria Formation_______ 331

125. Percent carbonate rock in the Retort Phosphatic Shale Member of the Phosphoria Formation.___ 332

126. Content of carbonaceous matter in the Retort Phosphatic Shale Member of the Phosphoria Formation _______________________________________________________________________________ 333

127. Diagram showing mineral composition of rocks in three facies of the Retort Phosphatic Shale Member of

the Phosphoria Formation___________________________________-_-_-___--------____-__-------- 334

128. Isopach map of the Tosi Chert Member of the Phosphoria Formation._______________________________ 337

129. Type locality of Shedhorn Sandstone__..____________________________________________ 339

130. Isopach map of the Shedhorn Sandstone_________________________________--__------_-_-___------ 340

131-132. Graphs showing:

131. Summary of size distribution data of Permian sandstone.______-_____-__-_____-_-_--__-----_- 341

132. Relation between coefficient of sorting (So) and phi median diameter (Md<£)____________________ 342

133. Photomicrograph of sandstone from the base of the upper member of the Shedhorn Sansdtone at Sheep

Creek____________________________________________________________________________________ 343

134. Graph comparing size distributions of zircon and tourmaline with that of total sample__________________ 343

135. Graph showing composition by weight of heavy accessory minerals in bed Us-124, lot 1234______________ 344

136. Diagram showing relative abundance of tourmaline color varieties.___________________________________ 345

137-138. Graphs showing:

137. Tourmaline of Shedhorn Sandstone classified by roundness and type of inclusions.______________ 346

138. Color of Shedhorn Sandstone-.--.---------.------___.._____________-__---_-_ ------ 348

139-140. Isopach maps of the:

139. Lower member of the Shedhorn Sandstone._________________-----_-_----------------------- 349

140. Upper member of the Shedhorn Sandstone._______---_-_--__------------------------------- 350

141. Columnar concretions of sandstone, cherty sandstone, and sandy chert from Permian rocks in Madison and

Gallatin Ranges, Montana.._______________________________---_----------------------------- 352

142-148. Maps showing distribution of facies in:

142. Late Grandeur time.______________________________-____-_---_--------------------------- 356

143. Rex time. _ ______ ____ _____-_-____--_-_-- -- -- - -- 358

144. Franson time._________________________________________--__--------_----_--------------- 359

145. Middle Franson time_______-____-__________---_-_--------------------------------------- 360

146. End of Franson time___--____-_---___________________-_-_______-___---_ _ __ 361

147. Early Tosi time___________________________________-__----_--_______________. 361

148. Late Tosi time____________________.____________-___-_____----------------------------- 363
VI CONTENTS

Page 

FIGURE 149. Diagram showing relation between phi median diameter (Md<£) and sorting (« <£) and skewness («<£) in

Permian sandstone__________________________-_____-_-_-_--_--_---------_-_--__----__-_--- 365

150-152. Graphs showing:

150. Size distribution curves of selected samples of Permian sandstone.____________________________ 366

151. Change in character of size^iistribution by removal of coarse fraction________________________ 366

152. Size distribution curves of sandstone and mudstone samples of the Grandeur Member of the Park

City Formation_____________________________-__-___------__----_-------------------_ 368

153. Isopach map of combined Rex and Tosi Chert Members of the Phosphoria Formation__________________ 370

154. Map showing thickness of apatite in the Retort Phosphatic Shale Member of the Phosphoria Formation____ 376

155. Diagram showing vertical movements of Permian tectonic elements._________________________________ 381

156. Isopach map of strata between the base of the Meade Peak Phosphatic Shale Member of the Phosphoria

Formation and the base of the Dinwoodv Formation.._________________________________________ 382

TABLES

Page 

TABLE 1. Climatic summary for southwestern Montana..__________________________________________________________ 277

2. Size parameters of sandstone from Shedhorn, Park City, Quadrant, and Phosphoria Formations of southwestern

Montana__.__._________._.____._______ _________________________________________________________ 293
GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

STRATIGRAPHY AND PETROLOGY OF THE PERMIAN ROCKS 

OF SOUTHWESTERN MONTANA

By EARLE E. CHESSMAN and EOGER W. SWANSON

ABSTRACT

The Permian rocks of southwestern Montana were studied as 

part of a broad investigation of the western phosphate field. 

In the southwestern part of the area studied, the Permian rocks 

are 600-850 feet thick and, from base to top, consist of successive 

layers of dolomite, phosphatic shale, chert, dolomite, phosphatic 

shale, and chert. The layers thin northeastward, the upper two 

extending the farthest. The chert and dolomite layers intertongue with sandstone to the northeast, and the chert layers 

in part grade into mudstone to the west. The phosphatic shale 

and chert layers are assigned to the Phosphoria Formation; the 

dolomite layers, to the Park City Formation; and the sandstone, 

to the Shedhorn Sandstone. Regionally, the three formations 

intertongue.

The Park City Formation is composed mostly of dolomite, 

but it includes some sandstone, mudstone, chert, and limestone. 

The dolomite is of three textural types: (1) aphanitic, composed of silt-size dolomite anhedra; (2) skeletal, composed of 

dolomitized bryozoan and brachiopod fragments; and (3) granular, composed of sand-size dolomite aggregates. The aphanitic 

variety is the most common. The sandstone consists of fine- and 

very fine grained quartz sand containing a few percent of chert 

and feldspar grains and is cemented by dolomite or calcite. It 

consists of two textural types: (1) well-sorted (So about 1.26) 

fine-grained sandstone, and (2) less well sorted (So=1.40-1.70) 

fine- and very fine grained silty sandstone. The silty sandstone 

grades into tan dolomitic mudstone. Chert nodules and lenses 

are common in the dolomite, and at least some were formed by 

replacement.

Rocks of the phosphatic shale members of the Phosphoria 

Formation consist of (1) carbonate fiuorapatite in apparently 

isotropic or microcrystalline pellets, oolites, skeletal fragments, 

and nodules, (2) calcite and dolomite, (3) clay minerals and 

detrital quartz, and (4) carbonaceous matter. Clay minerals 

and quartz silt are mixed with carbonate fluorapatite in all 

proportions, but weakly phosphatic mudstone, highly phosphatic 

mudstone, and relatively pure phosphorite are more common 

than intermediate mixtures. The carbonate rocks in the shale 

members are relatively pure, and mixtures of carbonates with 

significant amounts of the other constituents are not common. 

Carbonaceous matter makes up nearly 25 percent of some beds, 

but less than half the beds contain more than 4 percent; it is 

most abundant in the mudstone and phosphatic mudstone and 

least abundant in carbonate rock and phosphorite.

Phosphorites are divided into those that show evidence of 

current action and those that do not on the basis of the presence or absence of a matrix and the shape, orientation, and type 

of apatite grain.

The bedded chert in the Rex and Tosi Members of the Phosphoria Formation is composed of microcrystalline quartz and 

chalcedony mixed with clay and detrital quartz. Siliceous 

sponge spicules from the class Demospongia form a half to two 

thirds of the nondetrital silica. Spicule canals are generally 

enlarged and filled with apatite, glauconite, or chalcedony.

The Shedhorn Standstone is composed mostly of very well 

sorted (So=1.09-1.24) fine- and very fine grained quartz sandstone cemented with chert, quartz overgrowths, or carbonate. 

The detrital fraction contains about 10 percent of chert grains 

and 4-8 percent of apatite pellets and skeletal fragments. 

Glauconite is common near the western margin of the formation. The nonopaque accessory detrital minerals consist mostly 

of zircon but include considerable amounts of tourmaline and 

rutile and minor amounts of garnet and apatite. The tourmaline 

includes several shape and color varieties and both igneous and 

inetamorphic types.

Principal facies changes within the Permian rocks are (1) 

sandstone to mudstone to dolomite, (2) sandstone to chert, (3) 

sandstone to chert to mudstone, (4) sandstone to dolomite, (5) 

sandstone to chert to dolomite, (6) chert and skeletal-oolitic 

phosphorite to pelletal phosphorite and mudstone to mudstone, 

and (7) mudstone to interbedded pelletal phosphorite and mudstone to pelletal-nodular phosphorite and mudstone.

The immediate source of the Permian sandstone was a sedimentary terrane, as is indicated by the presence of only the most 

stable accessory minerals, the large number of tourmaline varieties, and the degree of rounding of the accessory minerals. 

The gross distribution of the sandstone indicates one source in 

central Montana and another northwest of the area, perhaps 

near the southern end of the Bitterroot Range. The well-sorted 

sandstone was deposited on a wide shallow shelf at depths of 

less than about 30 meters. The sand was reworked by waves and 

benthonic organisms. The silty sandstone and the tan mudstone 

accumulated in deeper water.

Chert was deposited as a spicule ooze, mostly at depths of 

less than 50 meters. The apparently inorganic silica was precipitated from interstital water but was derived probably from 

solution of siliceous tests within the sediment. Calculations indicate that organisms could have extracted sufficient silica from 

normal sea water to have formed the chert, and volcanism therefore, need not be considered as a source.

Dark mudstone of the phosphatic shale members of the Phosphoria was deposited below wave base in water containing little 

or no oxygen. The source of the carbonaceous matter was 

marine plankton. The surface water was well oxygenated, and 

surface circulation could not have been restricted; the bottom 

circulation need not have been restricted but may have been.

275
276 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

The source of phosphorus in the phosphatic mudstone and 

pelletal phosphorite was sea water, but it is not known whether 

the phosphate was extracted from sea water'by plankton or 

precipitated by inorganic processes. The current-washed oolitic 

apatite, however, was formed by inorganic precipitation around 

nuclei that were generally phosphatic; precipitation resulted 

from the increase in pH and the consequent decrease in apatite 

solubility when water of high P2O5 content moved upward into 

the zone of photosynthesis.

The facies distribution and thickness relations suggest that 

the main geographic elements in southwestern Montana during 

Permian time were a postive area in central and north-central 

Montana, an intermittently positive area to the west that was 

probably insular and perhaps in the southern Bitterroot Range, 

and a depositional basin that lay between the positive areas. 

Two cycles of transgression and regression produced the alternating sequence of rock types. When the western positive area 

was submerged, cold marine currents of relatively low salinity 

flowed southward through the area; either chert or phosphorite 

was deposited, depending partly on the depth of water in the 

depositional basin. When the western positive area was sufficiently high to divert the southward-flowing marine current, 

water in the depositional basin became warmer and more saline, 

and carbonates were deposited.

INTRODUCTION 

PURPOSE OF INVESTIGATION

Phosphorite was first discovered in the Permian rocks 

of Montana near Melrose by H. S. Gale, then of the U.S. 

Geological Survey, in the fall of 1910 (Gale, 1911). 

Phosphorite deposits were subsequently investigated in 

many other areas in Montana, particularly north of Melrose. The investigations included both geoglogic mapping and stratigraphic studies. Yet, at the beginning 

of World War II, the areal geology of large parts of 

western Montana was known only from broad reconnaissance, and only the gross outlines of the regional Permian stratigraphy had been determined.

In the early days of World War II, phosphatic shale 

beds near Melrose that had been sampled for vanadium 

were found to contain small amounts of uranium. A 

study of the Montana phosphate deposits was therefore 

undertaken in 1943 and 1944 by A. P. Butler and C. W. 

Chesterman of the U.S. Geological Survey on behalf of 

the Manhattan District. These investigations were 

greatly expanded after the war, partly because the 

search for uranium was intensified but also because the 

rapid post-war expansion of the phosphate industry 

greatly increased the need for geologic information on 

the western phosphate deposits.

Since the start of these new investigations in 1947, 

stratigraphic sections of the Permian rocks have been 

measured and samples of the phosphatic members have 

been collected over nearly the entire western phosphate 

field. (See McKelvey, 1949, and Swanson and others, 

1953, for preliminary reports on these investigations.) 

In addition, the geology of many hundreds of square

miles has been mapped in detail, chiefly in southwestern 

Montana and southeastern Idaho.

This report embodies the results of the stratigraphic 

and petrologic studies of the Permian rocks in that part 

of western Montana south of lat 46° N. Many results 

of the mapping program have already been released, 

mostly in preliminary form (Klepp'er, 1950; Swanson, 

1951; Kennedy, 1949; Myers, 1952; Lowell, 1949,1953; 

Honkala, 1953).

PERSONNEL AND ACKNOWLEDGMENTS

Twenty-two geologists participated in measuring 

and sampling the Permian rocks of southwestern Montana during the field studies on which this report is 

based, and their contributions are acknowledged in the 

descriptions of sections on pages 384-561. The field 

studies of M. R. Klepper, W. R. Lowell, F. S. Honkala, 

and J. A. Peterson are particularly noteworthy. We 

also gratefully acknowledge the many contributions 

that have been made to this report by our colleagues, 

particularly V. E. McKelvey, who organized and guided 

the program, and T. M. Cheney, R. P. Sheldon, R. A. 

Gulbrandsen, and L. D. Carswell. All these men have 

studied the Permian rocks in other parts of the western 

phosphate field.

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.

GEOGRAPHY

Southwestern Montana is characterized by mountain 

masses separated by wide intermontane basins (pi. 14). 

The Centennial Mountains, which extend westward 

from Yellowstone National Park along the Idaho-Montana State line, trend eastward, but most of the other 

ranges trend northward. A few peaks in the larger 

ranges exceed an altitude of 10,000 feet above sea level, 

and Koch Peak in the Madison Range, the highest 

point in the area, is 11,293 feet above sea level. The 

intermontane basins decrease in general altitude from 

south to north; Centennial Valley is nearly 7,000 feet 

above sea level, whereas Three Forks Basin ranges from 

4,000 to 5,000 feet in altitude.

Most of southwestern Montana is drained by headwaters of the Missouri River; the western two-thirds 

is drained by the Jefferson River and its tributaries 

the Big Hole, Beaverhead, and Ruby Rivers and the 

eastern third, by the Madison and Gallatin Rivers. The 

parts of Idaho included in the area discussed in this 

report drain to the Pacific by way of either the Salmon 

or the Snake Rivers.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 277

TABLE 1. Climatic summary for southwestern Montana 

[From U.S. Dept. of Agriculture Yearbook, 1941J

Station

Dillon Lima Hebgen 

Dam

Three Forks Ennis Virginia 

City

Temperature (°F)

Length of record (years)

January average.

July average. _ Maximum

Minimum

39

24.4

CC 1

98

-40

1Q

16.3

62.9

100

-43

35

11.7

59. 5

99

-60

14

21. 3

66.9

101

-49

21

21.7

64. 5

100

-43

29

20. 3

66. 1

103

-43

Average dates of killing frosts

Length of record (years) _

Last in spring

First in fall

Growing season (days)

39

May 22

Sept. 12

113

16

Sept. 6

87

35

Sept. 11

88

16

May 30

Sept. 19

112

21

June 2

Sept. 11

101

29

May 30

Sept. 18

111

Average monthly precipitation (inches)

Length of record (years)

January _

February

March__

April.

May

June

July._________________ ______

August

September _

October __ _ _

November __ _ _ _

December. _ _ __

Average annual

40

on

. 80

1.27

1.80

2.71

2.43

1 4Q

1. 30

1.37

QK

.82

.80

16.67

19

26

27

49

1 20

1 21

1 67

99

76

86

96

36

24

9.27

34

2.65

1.93

1.97

1. 57

2.09

2. 16

1.83

1. 40

1. 53

1. 78

1.81

2. 12

22. 84

19

.40

. 39

.42

1.03

1.73

2.09

1.40

.96

1.34

.92

.63

. 55

11.86

20

.53

.49

.67

.96

1. 43

1.71

1. 17

1.04

.95

.89

.44

.41

10. 69

28

.64

.46

.86

1. 18

1.90

1. 78

1.28

1.20

1.27

.99

.80

.62

12.98

Pertinent climatic data are listed in table 1. The 

winters are long and severe and the summers are short 

and mild. Precipitation is light, averaging 9-23 inches 

in the valleys and somewhat more in the mountains; 

nearly a third of it falls in May and June. The average annual snowfall for the period from 1899 to 1938 

ranged from 60 to more than 100 inches in different 

parts of the area, and the average duration of snow 

cover during the same period ranged from 120 to more 

than 160 days (U.S. Department of Agriculture, 1941, 

p. 727, 728); both the snowfall and the duration of 

snow cover are, of course, greater in the mountains.

The area is crossed by several paved highways, and 

in dry weather most of the back country is accessible by 

means of gravel and dirt roads. Most of the principal 

towns are connected by rail.

GEOLOGIC SETTING

The Paleozoic strata of southwestern Montana consist 

of shallow-water marine rocks that thicken from about 

3,000 feet near Yellowstone National Park to about 

7,000 feet near the 113th meridian. Most of the Paleozoic rocks are composed of limestone and dolomite 

but include several prominent units of quartz sandstone 

and shale; the thickest and most extensive sandstone is 

the Quadrant Formation of Pennsylvanian age, which 

directly underlies the Permian rocks. The Paleozoic 

beds were deposited on a slightly unstable cratonic 

shelf; the shelf was separated from the Rocky Mountain 

miogeosyncline to the west by a hinge zone that fluctuated between the present Lemhi Range and Tendoy 

Mountains (Scholten, 1957, p. 168). The hinge zone 

was uplifted sometime prior to the Middle Ordovician, 

in the Devonian, during the Early and Middle Mississippian, and probably during part of the Permian 

(Scholten, 1957, p. 169; 1960).

Lower Triassic rocks consist of marine shale, limestone, and sandstone. They are nearly 2,000 feet thick 

in the southern part of the area, but they thin abruptly 

northward and pinch out south of the Jefferson River. 

They may originally have extended as far north as 

lat 36° K (McKee and others, 1959, pi. 9).

Sometime between Early Triassic and Middle Jurassic time, central Montana was broadly uplifted and
278 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

eroded. Several hundred feet of marine and continental Middle and Upper Jurassic beds were then deposited 

across the truncated older rocks. As a result, Jurassic 

beds rest on the Mississippian in north-central Montana 

and on progressively younger beds to the west, south, 

and east (McKee and others, 1956, pi. 2). The Jurassic 

rests unconformably on the Permian in the Three Forks 

area, but elsewhere in the report area, it rests unconformably on the Lower Triassic.

The Cretaceous rocks consist of salt-and-pepper sandstone, siltstone, and shale and contain much volcanic 

debris. The section may in places exceed 9,000 feet in 

thickness (Reeside, 1944). The detritus was derived 

from a rising landmassto the west.

In Late Cretaceous and early Tertiary time, the preCenozoic rocks were deformed by the Laramide orogeny. 

West of the Beaverhead River the folds that resulted 

are tight, and the rocks have been thrust eastward along 

several low-angle faults; but east of the river the folds 

are generally open and are broken by high-angle reverse faults and local thrusts. The difference in the 

character of deformation in these two parts of the area 

is reflected in the outcrop pattern of the Permian rocks 

(fig. 6), which in the western third of the area is considerably more sinuous and complex than in the eastern 

two-thirds. The greater crustal shortening west of the 

Beaverhead River should be borne in mind when the 

isopach and facies maps of the Permian rocks are 

interpreted.

The present ranges and basins of southwestern Montana were formed by crustal movements that began as 

early as the Oligocene (Pardee, 1950, p. 366). The 

ranges result mostly from faultblock uplift, and Recent 

fault scarps may be seen along the front of several 

ranges. The intermontane basins contain thick accumulations of highly tuffaceous fine-grained water-laid 

sediments of Tertiary age that conceal the bedrock over 

large parts of the area.

METHODS OF STUDY 

Fimj> PROCEDURES

The Permian rocks in southwestern Montana are 

mostly relatively resistant sandstone, dolomite, and 

chert; the important phosphorite beds, however, occur 

in two nonresistant shale members that generally do not 

crop out. In the present investigation the shale 

members were exposed by trenching with bulldozers 

wherever possible (figs. 87 and 88) and by hand 

trenching where the members were too thin or too inaccessible to be reached by bulldozer. Sites for trenching 

were selected generally on steep slopes where float from 

the shale members was abundant and relatively unmixed with foreign material and where mapping and 

reconnaissance indicated no structural complications.

FIGURE 87. Bulldozer trench at Sheep Creek, locality 1234, where the 

entire Permian section was exposed by trenching. This is the type 

locality of the Retort Phosphatic Shale Member of the Phosphoria 

Formation. Beds dip 30°-40° toward the viewer.

Wherever possible, the entire Permian section was 

measured, but the shale members were described in more 

detail because of their economic importance. Within 

the shale members, distinct lithologic units thicker than 

0.1 foot were described separately unless they were a 

part of a uniformly interbedded sequence. Hand specimens were collected from every described unit, and 

channel samples were taken from every unit thicker 

than 0.5 foot. Beds less than 0.5 foot thick were 

grouped with adjacent beds to form sampling units of 

suitable thickness. The maximum thickness of sampled 

units in the shale member was 5.0 feet, and the average 

thickness was between 1 and 2 feet. The minimum 

weight of channel samples was 12 pounds, but where 

trenches were accessible to vehicles, samples as heavy 

as 80 pounds were collected.

Channel samples were collected from the nonphosphatic parts of the section at only a few localities, but

FIGURE 88. Retort Phosphatic Shale Member of the Phosphoria Formation exposed in bulldozer trench at Greenstone Gulch, locality 1250, 

Note depth of zone of creep.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 279

hand specimens were taken from every described bed 

in every section.

Each measured section was assigned a lot number; 

each measured bed, a unit number; and each channel 

sample, a sample number. The lot numbers and sample 

numbers used in this report are those originally assigned, but the units have been renumbered starting 

with 1 at the base of each section and continuing consecutively up section. The unit numbers are prefaced 

with letters that designate the stratigraphic member 

of which unit is a part.

In order to standardize the measurement and field description of the beds by the many geologists participating in the fieldwork, forms were used that contained 

spaces in which to record unit number, sample number, 

rock name, unit thickness, texture, grain size, hardness, 

thickness of bedding, color, jointing, nature of contact 

with the underlying unit, and the presence of fossils. 

An explanatory text by V. E. McKelvey described the 

use of the form and denned terms to be used. Colors 

were determined by comparison with the "Bock-color 

Chart" distributed by the National Eesearch Council 

(Goddard, 1948), supplemented by a specially prepared 

chart, in which the Munsell system was also used, that 

covered in detail the range of colors most common in 

the shale members.

Fossils were systematically collected from most of 

the sections that were measured.

LABORATORY PROCEDURES

TREATMENT Or CHANNEL SAMPLES

All channel samples were shipped to Montpelier, 

Idaho, where they were crushed to minus i/^-inch mesh 

and reduced to 10 pounds by use of a combination jaw 

crusher and Vezin-type splitter (Huleatt, 1950). The 

10-pound samples were sent to the U.S. Geological 

Survey laboratory at Denver, Colorado, where they were 

split into two parts, one of which was stored for future 

reference as needed. The other split was ground to 

minus 20 mesh, from which two 4-ounce splits were cut 

and ground to minus 80 mesh. One minus-80-mesh split 

was sent to the U.S. Bureau of Mines laboratory at 

Albany, Oreg., where it was analyzed for P2O5 and 

acid-insoluble content; the other was sent to the U.S. 

Geological Survey laboratory in Washington, D.C., 

where it was analyzed radiometrically for uranium. 

If a split showed a content of 0.005 percent equivalent 

uranium, it was analyzed chemically for uranium. 

Many of the samples were also analyzed for A12O3 , 

Fe2O3 , and loss on ignition, some by the Washington 

laboratory of the U.S. Geological Survey and some by 

the Albany, Oreg., laboratory of the U.S. Bureau of 

Mines. A few samples were analyzed chemically for

Fluorine and V2O5 , and some were analyzed spectrographically for a large number of elements by the U.S. 

Bureau of Mines laboratory, Albany, and the U.S. Geological Survey laboratory, Washington, D.C. Determinations of carbonaceous matter were made on several 

hundred samples of the black-shale units mostly by the 

Washington laboratory, but some were made by Bond 

Taber of the U.S. Geological Survey at Menlo Park, 

Calif.

CHEMICAL ANALYSES

P2<>5

A 0.3000-gram sample was treated with a mixture of 

5 milliliters concentrated HNO3 , 5 milliliters HC1, and 

8 milliliters concentrated HC1O4. After filtration, 

P2O5 was precipitated by (NH4 ) 2MoO4 at 65° C, and 

the precipitate was dissolved in an excess of standard 

NaOH; the excess NaOH was then titrated with standard HNO3 .

Two hundred samples of phosphatic rocks from all 

parts of the western phosphate field that had been analyzed by the U.S. Bureau of Mines laboratory at Albany, 

Oreg., were subsequently analyzed by the U.S. Geological Survey laboratory at Washington, D.C. Eighty 

percent of the duplicate analyses differed from the original by less than 1.3 percentage points; 90 percent, by 

less than 2.0 percentage points; and 95 percent, by less 

than 2.5 percentage points. Although comparison of 

these analyses does not afford a statistically correct 

measure of either accuracy or precision, it does demonstrate that the analyses are sufficiently reliable for the 

purposes for which they have been used in this report.

Gross errors were detected by comparing the analyses 

with the mineralogic composition of the hand specimens 

and the powder splits, and the samples were reanalyzed 

as necessary. The errors were not necessarily analytical 

but may have originated in the labeling of samples, in 

bookkeeping, or in copying of results.

The phosphorus in the Permian rocks of Montana, as 

in most marine apatites, is in the mineral carbonatefluorapatite (Altschuler and Cisney, 1952), which in 

these rocks probably has a composition of (Ca, Na, 

Sr, U)io(P, Si, S) 6_X (0,F) 24_3X (C03 ) XF2 (Gulbrandsen, 

1960) -1 The extent of substitution, and thus the exact 

composition, is not known. It is assumed in this report 

that carbonate-fluorapatite contains approximately 39 

percent P2O5 and that the P2O5 content can be converted to apatite content by multiplying by 2.56. Because of the large number of substitutions possible in

1 Gulbrandsen (1960a) discussed the applicability of the terms "cellophane" and "francolite" to the apatite variety present in the Phosphoria 

Formation and concluded that their use is not justified. The usage in 

this paper follows Gulbrandsen's recommendation in calling the phosphate mineral carbonate-fluorapatite or simply apatite where it is the 

only phosphate mineral of reference.
280 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

the apatite lattice, the conversion factor 2.56 is only an 

approximation.

ACID INSOLUBLE

The part of the 0.3000-gram sample that was insoluble in the mixture of HNO8 , HC1, and HC1O4 was 

washed with water, ignited at 1,000° C for 1 hour, 

cooled, and weighed.

Ninety-nine samples that had originally been analyzed at the Albany laboratory of the U.S. Bureau of 

Mines were reanalyzed at the same laboratory. The 

acid-insoluble analyses of 49 of the samples differed 

by less than 1 percentage point and of 84, by less than 

2 percentage points. The mean value of the reanalyses, 

however, differed by about 1 percentage point from the 

mean of the original analyses. The results cannot be 

applied to the acid-insoluble analyses as a whole, but 

they indicate that any lack of precision in the determinations is unimportant for most purposes.

The acid-insoluble analyses are an approximation of 

the total quartz and silicates. They are minimum values, for silicates soluble under the conditions of the 

analyses may constitute several percent of the total 

quartz and silicates of the more argillaceous samples.

UBANIUM

All samples were analyzed radiometrically for uranium, and those that contained more than 0.005 percent 

equivalent uranium were then analyzed fluorimetrically.

Fluorimetric uranium values determined prior to 1949 

are consistently low, and the radiometric determinations for those years are a more reliable indication of 

the actual uranium content (Z. S. Altschuler and F. S. 

Grimaldi, written communication, 1951).

Some measure of the precision of uranium analyses 

of samples collected in 1949 and subsequent years is 

given in figure 89, in which the original analyses of 22 

samples collected in 1949 are compared with repeat 

analyses of the same samples made 5 years later. The 

samples were chosen at random from among all phosphatic samples collected in 1949 in the western phosphate field.

CARBONACEOUS MATTER

The sample was heated to constant weight at 230° C 

and again to constant weight at 450° C. The percent 

carbonaceous matter equals the difference in weights at 

the two temperatures divided by the weight of the sample and multiplied by 100 (Grimaldi in Thompson, 

1953).

No rigorous test of the reliability of the carbonaceousmatter determinations has been made, but nine samples 

were analyzed at different times by two different analysts. Five of the nine samples differed by less than 1

percentage point; seven, by less than 2 percentage 

points; and eight, by less than 3 percentage points.

SPECTBOGRAPHIC ANALYSES

Kesults of the semiquantitative spectrographic analyses are based on comparisons with a standard plate 

representing known quantities of the elements tested for 

and made at the same exposures. The standard sensitivities for the elements noted in this report are as 

follows:

Element Percent 

Al ______________ 0. 005

Sb

As

Ba

Be

Bi

B _

Cd

Oa

Or

Co

Ou

Ga

Ge

Au

Fe

Pb

,05

1

,08

,001

,002

,001

,1

,01

,02

,01

,001

,05

,01

,01

,005

,1

,2

Element

Mg_

Mn _ 

Mo_

Ni

Nb _ _

P

Pt

Si

Ag _____ 

Na

Sr

Ta

Sn __ - 

Ti

W - 

V __ - -

Zn _ 

Zr _ -

Percent

_ _ 0.001

.004

_ _ __ .004

_ _ _ .01

___ __ .01

__ _ _ .8

__ _ .01

.002

_ __ . 001

_ _ _ .05

.1

_ _ 1.0

.01

_ _ .002

_ _ _ .1

_ _ .01

____ __ . 05

_ __ .003

OTHER ANALYSES

Loss on ignition was determined by igniting the sample at 1,000°C. The mineralogical significance of the 

value obtained is uncertain, but the loss on ignition includes chiefly carbonate CO2 , carbonaceous matter, 

water, and sulfur.

Total iron is reported as Fe2O3 . Most of the iron 

occurs in limonite, pyrite, or glauconite.

Aluminum was precipitated and weighed as aluminum phosphate but reported as A12O3 . Nearly all the 

aluminum occurs in the clay minerals, but some is present in glauconite and feldspars.

Most of the fluorine reported occurs in carbonatefluorapatite, but fluorite has been noted in some beds.

PETROGRAPHIC METHODS

EXAMINATION OF HAND SPECIMENS

Nearly all hand specimens collected in the field were 

examined in the laboratory under the binocular microscope ; approximately half of these specimens were also 

powdered and examined in oils under the petrographic 

microscope, generally in order to determine the amount 

and type of carbonate minerals.

THIN SECTIONS

More than 400 thin sections were studied. The quantities of constituents were generally estimated, but esti-
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 281

25

o 20 

X

ID 

H 

LU

O

LU 15

10

Chemical

r =0.906 

S.,* =1.84

Radiometric 

r= 0.937 

S, x =1.27

10 15 25 25 0 5 

= RERUN ANALYSIS, IN PERCENT U X 10 3

10 15 20 25

FIGURE 89. Comparison of original and rerun uranium analyses of 22 samples of phosphorite collected in 1949; r is correlation coefficient,

Sy.x is standard error of the mean.

mates of about 20 of the specimens were checked by 

point counts.

SIZE ANALYSES

Sieve analyses produced poor results. Much, of the 

sandstone is only moderately well cemented and was 

disaggregated with little difficulty to pass 60 mesh, but 

enough small groups of grains were so tightly cemented 

that most of the material retained on the 60-, 70-, and 

80-mesh screens consisted of aggregates. Furthermore, 

apatite and glauconite grains were crushed during disaggregation and concentrated in the finer sizes, and 

chert cement broke into angular fragments that were 

present in all size fractions. We therefore resorted to 

thin-section size analyses.

The thin-section size analyses were made by means 

of a micrometer ocular and a point counter; the short 

axis of the grain at each point was measured and tallied 

in the appropriate ^-phi class. Only detrital grains 

were counted. This procedure yielded a volume-percent distribution which, because of the similar specific 

gravities of nearly all the grains counted, closely approximated a weight-percent distribution.

The values for several of the thin-section size distributions were corrected for the effect of sectioning by the 

method of Packham (1955). In general, correcting the 

distribution value increased the median-diameter value 

by ^-phi unit or less and decreased the sorting coefficient (/So) by less than 0.1 and generally by less than 

0.05. Unfortunately, the corrected size-distribution 

curves of several of the specimens exceeded 100 percent. For pictorial representation and for comparison 

between samples, therefore, the uncorrected thin-section 

data have been used, but values for the corrected distributions have been used for comparison with pipetteanalyses data and with sieve data of other investigations. 

We do not know how close the corrected distribution 

would match the distribution of the unconsolidated 

sand, but the Packham correction method at least 

changes the value for the distribution in the proper 

direction. Size-distribution curves constructed from 

the sieve data and the uncorrected and corrected thinsection data for one sample are compared in figure 90. 

Pipette analyses were made of several mudstone 

samples. The samples were ground to minus 80 mesh 

and soaked for several months in distilled water to 

which a few milliliters of ammonium hydroxide had 

been added. The samples were shaken intermittently.

HEAVY-MINERAL SEPARATION

Heavy minerals were separated by centrifuging in 

bromof orm having a specific gravity of 2.58. Limonite 

stains were removed before centrifuging by heating the 

sample in 2-percent hydrochloric acid for half an hour. 

Separations were made into the following size fractions: 

0.044-0.062 mm, 0.062-0.088 mm, 0.088-0.125 mm, and 

0.125-0.177 mm.

X-RAY

X-ray diffraction patterns of 30 bulk samples from 

the shale members were made by Bond Taber of the 

U.S. Geological Survey in order to identify the carbon-
282

120

100

CUMULATIVE PERCENT

J> r>o o <r>o o

0

GEOLOGY OF PERMIAN ROCKS I

)

 1 

I 

1

/r

il1 1

' ! 1 

I?/ 

/// ~^J/

/*\

/ V'

» \ / \

/ ' /

,' >

,' /

? //-' 

' r

I /I '<

/I 1 /Thir // r

x/ /

' ' X

/ < x 

"; I'// F "i

' / Sieve 

' / Thin sectic 

/ Thinsectio

/

^Corrected thin s

^

Sieve

t^x-^ '

i section

Md^ 

3.05 

n 3.38 

n, corrected 3.22

ection

<

A^<y So 

0.120 1.24 

0.096 1.22 

0.107 1.15

DIAMETER, IN PHI

FIGURE 90. Comparison of sieve and thin-section size analyses ; sample 

Us-124, lot 1234. Md<t>, phi-median diameter; Md, median diameter 

(mm) ; So, Trask sorting coefficient.

ate minerals, determine the gross mineralogy of the clay 

fraction, and detect feldspar and gypsum.

TERMINOLOGY

Color. The color names and numerical designations 

are those of the Munsell color system.

Hardness. If a rock did not break under a single 

sharp blow of the hammer it was termed "hard"; if it 

did break, it was termed "medium hard"; but if it 

crumbled or retained an imprint of the hammer head, 

it was termed "soft." The terms "crumbly," "plastic," 

and "brittle" were used if appropriate.

Thickness of bedding. Thickness of bedding as used 

in this report might more appropriately have been 

called thickness of splitting on weathering; it refers to 

the thickness of layers between visible cracks parallel 

to stratification. The quantitative terms are defined as

follows: Feet 

Very thick bedded_______________ >1. 0 

Thick-bedded _________________ 0. 2-1. 0 

Thin-bedded __________________0. 02-0. 2 

Fissile ______________________ <0.02

Rock terms. Definition of the rock terms are as follows (the adjective forms are in parentheses) :

Phosphorite (phosphatic): A rock composed dominantly of 

carbonate-fluorapatite; rocks containing more than 19.5 percent 

P2Os are phosphorites, and rocks containing more than 7.8 

percent P2O5 are phosphatic.

Limestone (calcareous): A rock composed dominantly of 

calcite.

Dolomite (dolomitic): A rock composed dominantly of the 

mineral dolomite.

Carbonate rock (carbonatic): A rock composed, dominantly 

of a mixture of calcite and dolomite, or one composed dominantly of carbonate minerals, the identity of which is not 

known.

Sandstone (sandy): A rock composed dominantly of detrital 

quartz and silicates having a modal grain size between 0.062 

and 2.0 mm. Nearly all the detrital grains in the sandstone 

discussed in this report consist of quartz and chert, and all 

the sandstone belongs to the quartzite series of Krynine (1948, 

p. 149).

Mudstone (muddy): A rock composed dominantly of detrital 

quartz and silicate having a modal grain size of less than 0.062 

mm. If the modal grain size is between 0.004 and 0.062 mm, 

the rock is a siltstone (silty) ; if the modal size is less than 

0.004 mm, it is a claystone (clayey). In practice, the difficulty 

in determining grain size in the finer grained rocks has resulted 

in classifying most of them as mudstone.

Chert (cherty): A rock composed dominantly of nondetrital 

quartz and chalcedony. The adjective "cherty" is used only if 

the authigenic quartz and chalcedony are evenly distributed 

through a rock; it is not applied to a rock containing chert 

nodules.

Oolite (oolitic) : A constructional particle 0.062-0.2 mm in 

diameter having a concentric structure.

Pellet (pelletal) : A constructional particle 0.062-0.2 mm in 

diameter having no regular internal structure.

Nodule (nodular) : A constructional particle larger than 2 mm 

in diameter.

Skeletal fragment (skeletal): A particle consisting of the 

hard part of an organism; where used as part of a rock name, 

it refers only to particles between 0.062 and 2 mm in diameter.

Grain (granular): Where used as part of a rock name, a 

particle between 0.062 and 2 mm in diameter.

The grade scale used is that of Wentworth (1922), 

and the size terms "very coarse," "coarse," "medium 

fine," and "very fine" have the same grade limits when 

applied to phosphorite and carbonate rock as they do 

when applied to sandstone. For example, a finely pelletal phosphorite consists of apatite pellets having a 

modal diameter between 0.125 and 0.250 mm. Phosphorite and carbonate rock in which the constituent 

grains are of silt or clay size are described as aphanitic.

EXPLANATION OF ILLUSTRATIONS

The outcrops of Permian rocks and the exact location 

of each measured section and partial section are shown 

in relation to the land net in plate 15. The relations 

of the localities of measured sections to major geographic features are shown in plate 14, in which the 

locations of the sections are identical with those given ~
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 283

in plate 15, except for several where the complete 

section has been pieced from several lots or where one 

of several closely spaced sections has been chosen to 

represent the area. The locations, lot numbers, and 

locality names in plate 14 are those used throughout 

the text of the report.

The lithology and correlation of the Grandeur 

Member of the Park City Formation are shown in plates 

16 and 17, and similar information on the rest of the 

Permian section is shown in plates 18-22. Correlations within the Retort Phosphatic Shale Member of the 

Phosphoria Formation are shown in more detail in 

plates 23 and 24.

Maps showing the areal variations of lithologic character have been constructed by a method devised by 

Pelto (1954, p. 503-505), in which the variation of 

any number of components is mapped as a single function. In constructing the maps, the rocks are divided 

into classes, each of which contains a unique end member consisting of either a single component (such as 

sand or carbonate) or a mixture of simple type (such 

as equal amounts of sand and carbonate). These classes 

are designated class I if the end member is a single 

component, class II if the end member is a mixture of 

two components, class III if the end member is a mixture of three components, and so on. A variable quantity D expresses variations in composition within each 

class; the minimum value of D is that of the end member, and the maximum value, 100, is that at the class 

boundary. In the maps in this paper, the component is 

generally a single constituent rather than a rock type;

for example, all the sand in the mapped unit constitutes 

the component rather than all the sandstone.

To calculate the D function, the proportions of the 

components are arranged in order of increasing magnitude from left to right, and zero is added to the left of 

the smallest component. Positive differences are taken 

between adjacent components and are labeled from right 

to left as (Ap)i, (Ap) n, and so on. The class number 

is denoted by the subscript of the largest (A^>). The 

largest (A^>) is then denoted as (A^?) TO and the next 

largest as (Ap) vm. The D function is then defined as:

Z>=100 (l-[Ap) m -(Ap) cm ]).

For example, consider a rock unit containing 42 percent 

quartz sand, 40 percent dolomite, 15 percent clay, and 

3 percent apatite. The calculation is as follows:

Apatite 

0.03

Clay 

0.15

Dolomite 

0.40

Sand 

0.42

Subtracting adjacent numbers and labeling the differences from right to left, we obtain:

(Ap)iv 

0.03

(Ap)m 

0.12

(Ap)n 

0.25 0.02

The class number is II; that is, the rock is a nearly 

equal mixture of two components. Continuing,

EXPLANATION

D=100 (1-(0.25-0.12)) =87

The D function is contoured in only a few of the 

maps, as the density of control in the remaining maps 

was insufficient.

Figure 91 illustrates the relation of the class areas and 

the D value to composition in a three-component system.

Chert

Class I area Class II area Class in area

Sand Sand and carbonate Sand, chert,

and carbonate

Carbonate Chert and carbonate

 80 

Contour of £> value

Contour interval 2O units

Sand

-

:-:-:-:-x-:^-^:-:-:£-:-:-:-:-:*:-:^

Carbonate

FIGURE 91. Relation of class areas and D values to composition in a three-component system. Modified from Pelto (1954, fig. 2).
284 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

STRATIGRAPHY AND PETROGRAPHY

STBATIGBAPHIC NOMENCLATURE

HISTORY OF NOMENCLATURE

The Permian section of southwestern Montana is composed of four major rock types chert, dolomite, sandstone, and interbedded phosphorite and dark mudstone. 

Just east of Lima, Mont., where the interval is about 

600 feet thick (fig. 92), a three-member sequence of 

dolomite, phosphatic shale, and chert is repeated twice 

from bottom to top. The layers thin toward the northeast, and the upper two layers extend farther eastward 

than the rest of the sequence; the chert and dolomite 

layers intertongue with sandstone to the northeast, and 

the chert layers in part grade into mudstone to the

west. These changes in both character and thickness 

of the individual layers cause the gross aspect of the 

Permian to differ in various parts of southwestern Montana. West and south of Dillon the Permian is composed dominantly of chert and mudstone; near Melrose 

it is composed dominantly of dolomite; and near Yellowstone National Park it is composed dominantly of 

sandstone.

Before 1910, when phosphate-bearing beds were first 

recognized ~ in Montana, ' the more resistant beds of the

sequence were grouped either with the underlying beds 

in the Quadrant Formation (Peale, 1893, p. 41-43, and 

1896; Iddings and Weed, 1894) or with the overlying 

beds as the Teton Formation (Hague and others, 1896,

112° 111°

MONTANA 

"/^WYOMING

FIGURE 92. Isopach map of Permian rocks in southwestern Montana. X. control point; figure shows measured thickness, in feet.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 285

and 1899, p. 34). In reporting the first discovery of 

phosphorite in the Permian of Montana, Gale (1911) 

did not assign a formational name to the phosphatic 

interval and the related rocks but referred to them as 

"beds of Pennsylvanian age which overlie the Quadrant 

formation." In 1913, Emmons and Calkins in discussing the stratigraphy of the Philipsburg quadrangle, 

included the phosphate-bearing beds and the overlying 

chert and quartzite in the Quadrant, but they quoted 

Gale on the probable correlation of these beds with 

the Park City Formation of Utah and southeastern 

Idaho (Emmons and Calkins, 1913, p. 72-74). Pardee 

(1913) followed the same usage in reporting his discovery of phosphorite in 1911 in the Garnet Range.

The name Phosphoria, the type area of which is in 

southeastern Idaho, was first applied to Permian rocks 

in Montana by Stone and Bonine (1914, p. 375), who 

applied it to the thin Permian section of phosphorite, 

chert, and sandstone in the Elliston region, about 20 

miles west of Helena, From 1911 to 1956, with the exception of the Philipsburg area (Calkins and Emmons, 

1915, p. 8), the mapping of which had already been 

completed, the Permian rocks of western Montana were 

assigned to the Phosphoria.

During most of the investigation for this report, the 

name Phosphoria was retained for all the rocks between 

the massive Quadrant Quartzite and the Mesozoic formations. The Phosphoria itself was divided into five 

units, from oldest to youngest, the A, B, C, D, and E 

members. The B and D members are the two phosphatic 

shale units; the A member, the basal dolomite unit; the 

C member, a chert, dolomite, and sandstone unit; and 

the E member, the uppermost chert and sandstone unit. 

This terminology was first used in 1945 by A. P. Butler 

and C. W. Chesterman and first published in summary 

by McKelvey (1949). Klepper (1950) first described 

these members in detail. The terminology has been followed in all preliminary reports published during the 

present investigation. (For example, see Cressman, 

1955.)

CURRENT NOMENCLATURE

In the nomenclature recently adopted by the U.S. 

Geological Survey for the western phosphate field (McKelvey and others, 1956 and 1959), an attempt has been 

made to give some lithologic significance to the formational names by (1) restricting the name Phosphoria to 

the phosphorite, dark-mudstone, and chert facies, (2) 

restricting Park City to the limestone and dolomite 

facies, and (3) introducing a new name, Shedhorn 

Sandstone, for the sandstone facies in Yellowstone National Park and adjacent areas. Relations between 

facies are expressed in terms of intertonguing; thus, the 

Park City Formation in the Wasatch Mountains of

709-931 O 63 2

Utah consists of two members separated by a tongue of 

the Phosphoria Formation, and the Phosphoria in extreme western Wyoming consists of two parts separated 

by a tongue of the Park City Formation. The formations are subdivided into members, and the member 

names are extended as far as the units retain their lithologic character. Thus, the Meade Peak Phosphatic 

Shale Member of the Phosphoria Formation of southeastern Idaho extends into the Wasatch and Uinta 

Mountains of Utah and into the Yellowstone National 

Park area of Wyoming as the Meade Peak Phosphatic 

Shale Tongue of the Phosphoria Formation. Figure 

93 illustrates the resulting formational and member 

nomenclature. Locality 4 shown on figure 93 is near 

the type section of the Shedhorn Sandstone; locality 6 

is near that of the Phosphoria Formation; and locality 

7 is near that of the Park City Formation.

The stratigraphic nomenclature of the Permian in 

southwestern Montana is shown in detail in plates 16-22. 

The units present are as follows: (1) The Park City 

Formation, consisting of the Grandeur and Franson 

Members; (2) the Phosphoria Formation, consisting of 

the Meade Peak and Retort Phosphatic Shale Members, 

the Rex and Tosi Chert Members, and the cherty shale 

member; and (3) the Shedhorn Sandstone, consisting 

of an upper and a lower member.

The success of the nomenclature in reflecting the lithologic character of the interval may be judged by comparing figure 94, which shows the lithologic character 

of the Permian rocks, with figure 95, which shows the 

constitution of the Permian section by formations. Although the agreement between the two figures is good, 

better agreement is prevented by the lithologic variation 

within the Park City Formation. Both the Grandeur 

and Franson Members contain terrigenous material in 

the western part of the area that locally makes up most 

of the formation. To separate these beds from the Park 

City and raise them to formational rank would be consistent with the nomenclature adopted for the Permian 

rocks, but the area in which they are known to crop out 

is too small to justify such action now.

Although the stratigraphic nomenclature adopted for 

these rocks reflects more closely their lithologic character and conforms more closely to the recommendations 

of the American Commission on Stratigraphic Nomenclature (1961) than did the earlier nomenclature, its 

application does present some difficulties. First, in areas 

where intertongumg is complex, the nomenclature is 

correspondingly complex. Complex nomenclature in 

such an area is very meaningful to a geologist studying 

regional stratigraphy, but it is a nuisance to the geologist mapping a restricted area. Second, the tongues 

cannot be traced continuously in outcrop but must be
286 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

EXPLANATION

Hiatus

t HELENA

MONTANA

IDAHO | -Jacksoli

6|WYOMING

Montpelier^

RADO 

UTAH

100 200 MILES

FIGURE 93. Nomenclature of the Phosphoria, Park City, and Shedhorn Formations. 'Modified from McKelvey and others (1956, fig. 4).

correlated from section to section across areas of no 

exposure; therefore, the nomenclature reflects in part 

our confidence or in part lack of confidence in the 

correlation.

The second point is illustrated by differences of opinion between the authors. Swanson would, in general, 

prefer to extend formation and member names farther 

than Cressman. For example, at Big Sheep Canyon and 

Dalys Spur, Swanson would assign sandstone that is 

herein included in the Franson Member of the Park 

City Formation (p. 288) to the Shedhorn Sandstone, 

and at Indian Creek he would formally recognize chert 

beds that are herein included in the lower member of the 

Shedhorn Sandstone as tongues of the Rex Chert Member of the Phosphoria Formation.

PARK CITY FORMATION 

GENERAL, CHARACTER AND DISTRIBUTION

The type area of the Park City Formation is Big 

Cottonwood Canyon near Salt Lake City, Utah, where 

the formation consists of a lower and an upper member, each composed of limestone and dolomite containing some interbedded sandstone; the members are separated by the Meade Peak Phosphatic Shale Tongue of 

the Phosphoria Formation. Cheney (in McKelvey and 

others, 1956, p. 2840, 2842-2843) named the upper unit 

the Franson Member and the lower unit the Grandeur 

Member (Cheney in McKelvey and others, 1959, p. 36) ; 

he applied the names to beds that extend northward 

through western Wyoming and into Montana. In 

southwestern Montana the-Park City Formation com-
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 287

113°

Permian rocks disconformably overlain 

by Ellis Group (Jurassic) north of line

ONTANA 

WTOMING

Permian rocks disconformably overlain 

Dinwoody Formation (Triassic) east of line

EXPLANATION

Sand Chert Mud Carbonate Conglomerate

Pattern used singly where one constituent is dominant (class 

I areas); combined where 2 or 3 constituents are dominant 

(class I and Mareas)

FIGURE 94. Lithologic character of the Permian rocks in southwestern Montana. 'X, control point; A, control point, data approximate.

prises the strata, dominantly dolomite but in a few localities mostly sandstone and siltstone, that are underlain by the massive well-sorted quartz sandstone of the 

Quadrant Formation of Pemisylvanian age and that 

are overlain by the phosphorite and dark mudstone of 

the Eetort Phosphatic Shale Member of the Phosphoria Formation. In the southwestern part of the report area, the Grandeur and Franson Members of the

Park City Formation are separated by the Meade Peak 

and fvex Tongues of the Phosphoria Formation. These 

tongues of the Phosphoria pinch out to the northeast, 

and where they are absent, the Grandeur and Franson 

Members cannot be readily distinguished from each 

other. Carbonate rock of the Park City Formation 

intertongues in part with sandstone both to the east 

and west. The sandstone to the east is assigned to the
288 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

ill 0

Permian rocks disconformably overlain 

by Ellis Group (Jurassic) north of line

Permian rocks disconformably overlain by

Dinwoody Formation (Triassic) east of line

EXPLANATION

Patterns used singly where one formation is dominant (class I 

areas); combined where 2 or 3 formations are dominant 

(class U and HI areas)

FIGURE 95. Constitution of the Permian of southwestern Montana, by formations. X, control point; A, control point, data approximate.

Shedhorn Sandstone, but that to the west, as well as 

the associated dolomitic mudstone, is included in the 

Park City because it cannot be demonstrated to be continuous with the Shedhorn of the type area.

The distribution and thickness of the Park City Formation in southwestern Montana are illustrated in figure 96, and the lithologic character of the information

is indicated in figure 97. In both illustrations, tongues 

of other formations have been excluded. The eastern 

edge of the Park City Formation is in the vicinity of 

the Gallatin River; the formation thickens southwestward and reaches a maximum of about 600 feet at Hawley Creek on the western side of the Beaverhead Range. 

The general thickening trend is interrupted by thinning
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

113° 112° 111°

289

FIGURE 96. Isopach map of the Park City Formation. X, control point showing measured thickness in feet; A, control point data 

approximate.

along a line northwestward through Wadhams Spring. 

The dominance of carbonate rock in the Park City is 

well indicated in figure 97. Sandstone makes up most 

of the formation in a relatively small area west of 

Dillon.

LITHOLOGY

CARBONATE ROCK

The typical carbonate rock of the Park City Formation in Montana is a hard light-colored aphanitic dolomite of low chroma. Dolomite greatly predominates 

over limestone and constitutes more than 95 percent of 

the total carbonate rock at most localities.

Most of the carbonate rock in the Park City Formation ranges in color from medium and light gray to 

yellowish gray and pale brown. The hues range from 

5Y to 10 TR (with the exception of a very few red-hued 

beds), but in rocks of such low chroma the recorded differences in hue are not very significant. In general, 

the color of all the carbonate rocks within a member 

at a given locality is rather consistent. At Big Sheep 

Canyon, for example, 27 of 28 dolomite beds in the 

Grandeur Member have values of 5 and 6, and 10 of 13 

beds in the Franson Member have values of 7 or greater.

The dolomite of the Grandeur Member of the Park 

City is thin bedded in the southwest part of the area but
290 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

EXPLANATION

Sand Chert Carb 

Patterns used singly in class I areas; combined in 

class H and HI areas

 50 

Isopleth of D values

Contour interval 25 units

FIGURE 97. Llthologic character of the Park City Formation. X, control point (numeral is value of D function) ; A, control point, data

approximate.

is thick bedded in the eastern and northern parts. The 

histograms of bed thickness given in figure 98 are arranged in geographic sequence from southwest to northeast and show the general increase in thickness in that 

direction. Most of the carbonate rock in the Franson 

Member is thick bedded, the only suggestion of a regional variation of bedding characteristics being afforded by the fact that more of the section is very thick 

bedded at Hawley Creek and Big Sheep Canyon and 

in the Big Hole Canyon-Melrose area than elsewhere. 

Carbonate rock of the Park City Formation can be 

divided into three major textural types: aphanitic, gran-
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 291

100

 50

1224 1249 1301 

Big Sheep Hogback Sliderock 

Canyon Mountain Mountain 

LOCALITY

EXPLANATION

1307 

Alpine 

Creek

Very thick bedded 

(greater than 1 ft)

Thin-bedded 

(0.02 to 0.2 ft)

Fissile 

(less than 0.02 ft)

FIGURE 98. Thickness of bedding of dolomite in the Grandeur Member 

iof the Park City Formation.

ular, and skeletal. A fourth type, which is quantitatively insignificant, consists of discrete carbonate crystals of sand size. Both limestone and dolomite exhibit 

the three major textures, but a much larger proportion 

of the limestone is skeletal. No aphanitic or granular 

limestone was studied in thin section; so, the more detailed discussion of these types will refer to dolomite 

only.

The asphanitic dolomite consists of an equigranular 

mosaic of dolomite anhedra. The average grain diameter in most samples is between 15 and 30 microns but 

in some samples is as small as 5 microns and in a few 

is as large as 62 microns. The sorting of the dolomite 

grains is excellent; in a sample in which the average 

grain size is 20 microns, only a few grains are as large 

as 50 microns. Sparse euhedral rhombs of dolomite 

are present in most thin sections, but in only one sample do they total more than a few percent. The rhombs 

are generally either the same size as the anhedra or only 

slightly larger.

Detrital quartz-silt grains are rather evenly scattered 

through most of the dolomite. The silt constitutes generally less than 15 percent of the rock and in some 

places less than 5 percent, but a few silty dolomites contain nearly 50 percent silt. The quartz grains are almost invariably corroded and are replaced around the 

perimeter by dolomite. The dolomite and detrital 

quartz grains in most samples of the Grandeur Member are similar in size, but this generalization does not 

hold for grains in the Fraiison Member. Several aphanitic dolomites from the Franson Member as seen under a binocular microscope and in thin section contained abundant quartz sand; this evidence suggests 

that much of the dolomite may have originally had a

granular texture that has since been destroyed. Several samples contain a few doubly terminated hexagonal prisms of authigenic quartz that are generally 

0.1-0.2 mm in diameter.

Most of the dolomite examined contains about 1 percent brown and reddish-brown iron oxide as scattered 

small equant grains having a maximum diameter of 15 

microns, as irregular aggregates as much as 50 microns 

in diameter, or as streaks. Many of the smaller grains 

are polygonal in outline and are probably pseudomorphs 

after pyrite. The larger grains may originally have 

been aggregates of pyrite crystals.

Most of the dolomite beds described as granular in 

the section descriptions and on the correlation diagrams 

have been so identified by examination of hand specimens with a binocular microscope. Although the nature of the dolomite grains could not be determined, 

most of them seem to be skeletal fragments, probably 

of bryozoans; however, in the few thin sections of granular dolomites examined, most of the grains are not 

obviously organic. Bed F-40 from Canyon Camp is 

composed of 10 percent fine quartz sand and 90 percent 

dolomite; nearly two-thirds of the dolomite consists of 

well-sorted and rounded fine-grained pellets that are 

composed of an aggregate of anhedral dolomite crystals 

averageing less than 5 microns in diameter. The dolomite pellets, quartz grains, and a few recognizable fossil 

fragments are in a clear matrix of dolomite anhedra that 

average about 20 microns in diameter. The sorting, 

rounding, size, and packing of the dolomite pellets suggest that the pellets were transported and deposited 

by the same current and under the same conditions as 

the associated quartz sand. Several beds of the lower 

member of the Park City Formation at Alpine Creek 

consist of sandy dolomite that contains pebbles of aphanitic dolomite similar in lithology to adjacent beds. 

These pebbles were evidently derived intraformationally. The sandy dolomite matrix in which the pebbles 

are set consists of very fine quartz sand and fine-grained 

subangular dolomite fragments composed of extremely 

fine grained anhedra. Like the dolomite pebbles, the 

dolomite grains are probably intraformationally derived.

The most prominent occurrences of skeletal carbonate 

rock are in the Franson Member of Little Sheep Creek 

and at Wadhams Spring. At the first locality the skeletal carbonate is mostly limestone, and at the second it 

is mostly dolomite; but, megascopically at least, the 

textures in the two sections are remarkably similar. 

Both the limestone and the dolomite consist mostly of 

medium to very coarse sand-size fragments of brachiopod and pelecypod shells and of bryozoans. Well-preserved brachiopod shells are present at several horizons
292 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

in both sections and are locally so abundant that the rock 

is coquinoid.

SANDSTONE

The sandstone of the Park City Formation may be 

divided into two groups on the basis of size and sorting 

of the detrital grains: (1) well-sorted very fine and 

fine-grained quartz sandstone and (2) somewhat less 

well sorted very fine grained silty quartz sandstone. 

The first group corresponds to the dolomitic and siliceous orthoquartzites of Weaver and the second to his 

illitic orthoquartzite (Weaver, 1955, p. 186). The wellsorted sandstone group can in turn be subdivided on 

the basis of the presence or absence of dolomite, calcite, 

and chert and on the abundance of apatite and clastic 

chert grains; on the other hand, the silty sandstones 

form a rather homogeneous group. In figure 131, the 

grain-size distribution of a well-sorted sandstone is 

compared with that of two silty sandstones. As can be 

seen from the figure, the differences in both grain size 

and sorting between the two groups are small, and even 

the silty sandstones are rather well sorted. Nevertheless, the differences are significant and can be detected 

with little difficulty in hand specimens. Furthermore, 

the groups differ, although less sharply, in color and 

bedding characteristics; generally, well-sorted sandstone is thick bedded and has a high color value and 

little or no chroma, whereas .the silty sandstone is thin 

bedded and has lower color value and moderate chroma; 

in other words, the silty sandstone is thinner bedded, 

darker, and more colorful, apparently because it contains more clay and limonite than the well-sorted 

sandstone.

The well-sorted sandstone ranges in modal diameter 

from about 0.12 to 0.2 mm. Quartz grains as large as 

0.6 mm have been seen, but they are scarce. A grainsize analysis has been made for only one sample of this 

group (lot 1299, G-35), but visual comparison of the 

thin section of the analyzed sample with other thin 

sections of the group suggests that the sorting coefficient of the sample, $0=1.26 corrected for sectioning, 

is representative of the group as a whole. The quartz 

grains are mostly subangular and subroimded; the 

larger grains are better rounded. Well-rounded 

grains are scarce and are limited to the largest sizes. 

Most of the quartz grains are nearly equidimeiisional 

in thin section; less than one-fourth are noticeably 

elongate, and in most specimens considerably less than 

one-tenth are markedly so. Three-fourths to ninetenths of the quartz grains exhibit only slight strain 

shadows; most of the rest are highly strained, and a 

very few are compound. Both potassium feldspar and 

plagioclase (probably oligoclase) in amounts not exceeding several percent have been seen in specimens

from the Grandeur Member at Alpine Creek and at 

Hawley Creek; most of the feldspar is unaltered. 

Chert grains compose not more than about 2 percent of 

the total clastic grains of the well-sorted sandstone of 

the Grandeur Member, but in the sandstone of the 

Franson Member, the ratio of quartz grains to chert 

grains is quite variable and ranges as low as 3:1. Apatite pellets and skeletal fragments are absent in the 

sandstone of the Grandeur Member but are present in 

the sandstone of the Franson Member in amounts 

averaging 5 or 6 percent but reaching as much as 15 

percent.

Dolomite is the most common cement, although calcite cement is more common than one would expect 

from the low ratio of limestone to dolomite in the more 

carbonatic parts of the formation. The carbonate 

cement commonly composes 10-25 percent of the rock, 

but in many beds in the Franson Member at Big Sheep 

Canyon, it nearly equals the amount of the quartz sand. 

Texturally the dolomite cement is a mosaic of anhedra 

similar in size and character to the anhedra of the 

aphanitic dolomites. The dolomite in many samples 

lias irregularly replaced the periphery of the quartz 

grains.

Quartz overgrowths on the sand grains are common 

in many samples of the carbonatic sandstone, but they 

rarely constitute more than a few percent of the rock. 

A few samples contain small amounts of quartz cement, 

and a mosaic texture has resulted from pressure solution 

of the quartz grains and minor redeposition of quartz 

as overgrowths; the resulting rock is a compact quartz - 

ite having very low porosity. (See also Weaver, 1955, 

p. 186.) Microcrystalline quartz cements a few sandstone beds, most of which are adjacent to members of 

the Phosphoria Formation.

Relatively unweathered beds of the well-sorted sandstone are generally hard, very thick bedded, and of 

neutral hue and high color value (7 or greater). The 

more weathered beds are generally thin or medium 

bedded and soft or medium hard; they are colored 

shades of brown, yellowish brown, and orange (YR 

hues) having moderate color values (5 and 6) and 

moderate chromas (4 and greater). Some sandstone 

in the Grandeur Member at Little Sheep Creek is 

crossbedded.

Silty sandstone is found only in the Grandeur Member 

of the Park City Formation. Characterizing parameters of the size distributions of four samples of this 

rock type (lot 1299, G-54 and G-8; lot 1249, K-4a and 

K-8) are summarized in table 2. In spite of indicated 

differences in median diameter, three of the four samples 

are more poorly sorted than any analyzed sample in 

either the Quadrant or Shedhorn Formations. The
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 293

estimated modal grain size of all samples of the silty 

sandstone that were examined in thin section ranges 

from about 0.2 mm to the lower limits of the sand size, 

but all are more poorly sorted than the other Permian 

sandstones and the sandstone of the underlying QuadTABLE 2. Size parameters of sandstone from Shedhorn, Park City 

Quadrant, and Phosphoria Formations of southwestern Montana

Lot and sample

Size parameter

Uncorrected for 

sectioning

Md Md, So

Corrected for sectioning

Md Md<t> So tr<j> a<t>

Upper member of Shedhorn Sandstone and equivalents

11399 

Us-183.. ...................

181. . ..... ... .

171..... .............

162.......... __ . . .

1234 

Us-124.. ...... .

117... ...............

1214 

Us-74b ............. ..

64c... __ .... _ .. . .

57a ___ ..

To-54b _ ....

1358

Us-65b ____ ... ... 

65a__._ __ . __ . __ ..

1307

Us-46..... ________ .. 

44... ___ .. ____ . _

1302

Us-87... __ ... __ . __ ..

1218

RWS 103e__ __ . .. 

lOlc.. . ............

0.181

.182

.100 

.092

.096

.083 

.086

.125

.088

.081

.092 

.092

.159 

.088

.088

.130 

.118

2.47

9 dfi

3.33 

3.45

3.38

3.59 

3.53

3.00

3.50

3.36

3.45 

3.45

2.65 

3.50

3.50

2.94 

3.08

1.31

1.14

1.23 

1.24

1 99

1.20 

1.21

1.25

1.18

1.14

1.19 

1.32

1.25 

1.21

1.21

1.31 

1.34

0.207

.107

090

------ -

.......

2 97

3 99

......

1 09

 

11^

1 to

0.41

o-i

.30

 

+0.51

 -

Lower member of Shedhorn Sandstone and equivalents

1SOO

Ls-15.... ___ _. .

1214

R-29a_..__ ___ .

Ls-28a_ _____________

28b ... _ ......

1302

Ls-44.... _ _____

1299

Ls-83.... ___ ..

R-74_. __________

73... _. .. ..

1307

Ls-28______-.___.__________

11318

RWS 85a__.._.__

me

RWS 51c _

1SB4 

F-12 ___ ... __ ..........

0.106

128

140

.141

.128

.103

.120

.068

.109

.138

.130

.120

3.24

9 Q7

2.84

9 R3

2.97

3.28

3.06

3.88

3.20

2.86

2.94

3.05

1 10

1.25

1 29

1.24

1.23

1.23

1.26

1.14

1.27

1.37

1.36

1.24

0.120

1 Kf\

164

 

3.05

9 7*

2 CO

2 fi1

 

1.14

1 90

1.24

1.17

 

O OQ

.43

ds

DO

 

0

+ f!9

-.05

M

TABLE 2. Size parameters of sandstone from Shedhorn, Park City, 

Quadrant, and Phosphoria Formations of southwestern Montana Continued

Lot and sample

Size parameter

Uncorrected for 

sectioning

Md Mdo So

Corrected for sectioning

Md Mdo So W w

Grandeur Member of Park City Formation

1299 

Q-54.. _____ - _

35. 

8_ 

1S4» 1

E Q

0.068

.103

.043

3.87

3.28

4.55

1.52

1.31

1.50

0.082

.118

.053

.114

.116

3.60

3.08

4.27

3.13

3.10

1.49

1.26

1.42

1.60

1.70

0.80

.49

.82

+0.06

0

+.17

Quadrant Formation

1218

S 1133a_ .-_ . _ 

11346 1 

W-l 

QQ

6a._... __ __ 

9 . . . .

12d_._-._ 

12341

0.106 3.24 1.38

0.189

.112

.139

.129

.159

.151

2.40

3.15

2.85

2.95

2.65

2.73

1.26

1.29

1.31

1.49

1.33

1.34

 -

Retort Phosphatic Shale Member of Phosphoria Formation

1369

"R f 14. TiAllofc

11399

0.241

.176

160

2.05

2.51

2.64

1.37

1.32

1.32

i Sieve analyses from Weaver (1955, p. 179). Sample numbers are those of Weaver.

rant Formation. Poorly defined graded laminae are 

common in the silty sandstone but are extremely scarce 

in the well-sorted variety.

The detrital grains of the silty sandstone are very 

similar in character to those in the well-sorted sandstone. In most samples, more than 95 percent of the 

detrital grains are composed of quartz; most grains are 

subangular, but in the coarsest fraction they are subrounded and even rounded. Chert grains compose as 

much as 10 percent of the detrital fraction of a very 

few samples, but they are not at all conspicuous in hand 

specimens. The quartz grains are mostly equant, and 

most display only slightly undulant extinction.

Weaver (1955, p. 168) reported that several of his 

samples contained lath-shaped quartz crystals similar 

to the quartz paramorphs after tridymite described by 

Wager and others (1953). Similar lath-shaped quartz 

occurs in silty sandstone from near the base of the 

Park City Formation at Hogback Mountains. These 

laths average 25 microns in diameter and 150 microns
294 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

in length and are both unicrystalline and polycrystalline; all show inclined extinction. In one thin section 

similar-appearing laths radiate from a common center 

and seem to be fossil replacements or fillings; so, the 

igneous origin of the laths is by no means certain. 

About 1 percent of potassium feldspar and plagioclase 

was seen in several samples.

Dolomite makes up 40^t5 percent of many beds of 

the silty sandstone, and few beds contain less than 10- 

15 percent dolomite. Several samples contain large 

equant unicrystalline anhedral dolomite grains that 

are similar in size to the associated quartz grains and 

that constitute as much as half the total dolomite, and 

several samples contain numerous composite grains, also 

similar in size to the quartz, that are composed of microcrystalline dolomite anhedra. The dolomite grains 

bear the same relationship to other grains and to the 

matrix and cement as do the detrital quartz grains: 

this evidence indicates that both the large unicrystalline 

grains and the aggregates were deposited with the 

quartz by currents. The remainder of the dolomite is 

intergranular and consists of small anhedra.

Weaver (1955, p. 186) described quartzite from the 

Grandeur Member at Kelley Gulch that contains 10-15 

percent illite. We have not examined thin sections of 

these rocks from Kelley Gulch, but few similar-appearing rocks from the same stratigraphic interval at other 

localities contain more than a few percent clay minerals 

and mica.

Weaver (1955, p. 180-185) studied the heavy minerals of five samples of silty sandstone of the Park City 

Formation three from Kelley Gulch and two from 

Sheep Creek. The most abundant nonopaque detrital 

heavy mineral in Weaver's samples is zircon. Tourmaline is also common, and figure 136 (reproduced 

from Weaver's figure 11) indicates the relative 

abundances of the color varieties of that mineral. 

Weaver also observed small amounts of rutile, apatite, 

and garnet. Of the opaque minerals, leucoxene is by 

far the most common, constituting 15-30 percent of the 

total heavy minerals. Anatase is present as outgrowths 

on many leucoxene grains. Most of the heavy-mineral 

grains are subrounded to well rounded, and Weaver 

(1955, p. 180-181) concluded that most were derived 

from older sediments.

Most of the silty sandstone is thin bedded and hard. 

The sandstone is colored generally brown to yellowish 

orange (TR hues) having values of 5 and 6 and chromas of 4 and greater. One exception is sandstone from 

Dalys Spur, where the sandstone of the lower part of 

the Park City is hard, thick bedded, and light gray.

MUDSTONE

Mudstone occurs in both the Franson and Grandeur 

Members of the Park City Formation, but in the Franson Member it is restricted for the most part to a zone in 

the middle of the member that is present at only two 

sections, those at Little Sheep Creek and Wadhams 

Spring. The mudstone at these two localities is thick 

bedded and highly dolomitic and ranges in color from 

pale brown where fresh to pale yellowish orange where 

weathered. The detrital fraction seems to consist almost exclusively of silt-size quartz.

Mudstone forms a large part of the Grandeur Member of the Park City in the western part of the area. 

The mudstone consists of two types that differ apparently only in color. The first type is a pale-reddishbrown (10.ff5/4) dolomitic mudstone that is mostly thin 

bedded and medium hard to hard; the second type is a 

medium-hard to hard dolomitic mudstone that ranges in 

color from yellowish gray to dusky yellow and in thickness of bedding from thin to very thick. These are 

referred to as red mudstone and tan mudstone respectively, in the following discussion.

Size-distribution curves of the acid-insoluble fractions of three red mudstones and three tan mudstones 

from the upper part of the Grandeur at Big Sheep 

Canyon are shown in figure 99. The median diameter 

of five of the samples falls within the medium-silt class, 

and that of the sixth sample is in the coarse-silt class. 

The average median diameter of the three red mudstone 

samples is 5.07 phi (30 microns), which is slightly 

coarser than the average median diameter of 5.47 phi 

(23 microns) of the tan mudstone. The content of claysize particles (finer than 8 phi) ranges from 8 to 25 

percent; the average content of clay-size particles in 

the red mudstone is 11 percent, and that in the tan mudstone is 19 percent. The red mudstone is also somewhat 

better sorted than the tan mudstone, as is indicated by 

the sorting coefficient, tfo. The differences in size and 

sorting between the two groups, indicated by size curves, 

are not significant when tested by Student's t* but additional analyses might show the differences to be significant. Facies changes from sandstone to mudstone 

within the member indicate that the median diameters 

range probably from at least 17 microns to 62 microns. 

The median size probably does not range much below 

17 microns, for neither claystone nor any highly argillaceous siltstone has been seen.

The composition of the detrital fraction of the mudstone is similar to that of the silty sandstone of the 

Grandeur Member. The mudstone commonly contains 

about one percent of rather fresh-looking feldspar, a
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 295

100

DIAMETER, IN PHI 

7 8

7 8 

DIAMETER, IN PHI

FIGURE 99. Cumulative size distribution curves for six mudstones from the Grandeur Member of the Park City 

Formation at Big Sheep Canyon (lot 1224). Md<f>, phi-median diameter; So, Trask sorting coefficient.
296 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

trace of mica, and some clay, but most of the detritus 

consists of angular and subangular quartz silt. In thin 

section, mica and clay seem to constitute 15-30 percent 

of the rock (see also Weaver, 1955, p. 187), but the size 

analyses and the weak mica and kaolinite peaks on the 

X-ray patterns suggest that the amount of clay minerals 

is rather small and that much of the clay-size material 

is quartz. Weaver (1955, p. 174-175) showed that the 

clay mineral at Kelley Gulch is mostly illite, whereas 

that at Sheep Creek and Wadhams Spring is mostly 

kaolinite. X-rays of samples from Big Sheep Canyon 

show small amounts of muscovite or illite and possibly 

kaolinite. Red iron oxide evenly stains the finer grained 

matrix of the red mudstone.

With the exception of some highly weathered beds 

at Sheep Creek, all the mudstone of the Grandeur Member of the Park City is dolomitic. The dolomite is present in two forms. It consists most commonly of anhedra 

about 5 microns in diameter that occur as a rather evenly 

distributed intergranular matrix, but it also occurs as 

larger anhedra and as equant aggregates of smaller 

anhedra; both the larger anhedra and the aggregates 

are similar in size to the quartz silt and are grains 

rather than cement.

Thin sections show that some of the mudstone has a 

lamination not seen in hand specimen. The alternating 

laminae consist of medium- and fine-grained silt, range 

from 0.2 to 2 mm in thickness, and are irregular and 

discontinuous. Some possible microchanneling has been 

noted.

CHERT

Chert, both bedded and nodular, is present throughout 

the Park City Formation, but it is a prominent constituent only locally and only in the Franson Member. In 

outcrop, the nodular chert ranges from well-formed, 

round, equant bodies to lenses and extremely irregular 

masses. The well-formed nodules are commonly 0.4- 

0.5 foot in diameter, but they range in diameter from 

less than an inch to a little more than a foot. Chert 

nodules generally constitute only a few percent of a 

bed, but locally they may constitute one-half or onethird. They are most common in the dolomite but are 

present in some sandstone and dolomitic-mudstone beds.

Weaver (1955, p. 168-171) described the nodular chert 

of the Grandeur Member in considerable detail, and 

this paragraph is based on his discussion. Microscopically, the chert appears to be composed of tightly 

packed grains of quartz ranging in diameter from 1 to 

60 microns and averaging 5-10 microns. The smaller 

grains have irregular penetrating boundaries, and all 

grains show undulose extinction. Bubble inclusions are 

abundant, and sericite and illite shreds are common. 

Lenses and veins of coarse-grained vein quartz and fibrous chalcedony are present in some nodules. Electron 

micrographs of samples of two chert nodules are published in Weaver's paper; one shows the sample to consist of indistinct, tightly packed xenomorphic patches of 

quartz, and the other shows the sample to consist of 

distinct, tightly packed equant to prismatic, apparently 

polygonal particles, most of which are 1-3 microns in 

diameter. Weaver concludes that the grain size as 

measured in thin section is a "pseudo feature" and that 

the apparent interpenetrating boundaries and undulant 

extinction result from the superposition in the thin 

section of several individual crystals having diameters 

only one-tenth the thickness of the section.

Chert occurs as interbeds in dolomite in both members 

of the Park City Formation. Although locally a few 

chert interbeds may exceed 5 feet in thickness, most 

interbeds are less than half a foot thick. Some zones 

of interbedded chert and dolomite, but not individual 

beds, may be correlated from section to section.

Both the chert nodules and the thin chert interbeds 

show unequivocal evidence of replacement origin at several localities. At Wadhams Spring textures in thin 

lenses and discontinuous beds of chert in the Franson 

Member closely reproduce those of bryozoan limestone; 

at Hawley Creek a chert bed in the lower member consists largely of silicified corals, and at Alpine Creek a 

small chert nodule retains the texture of the intraformational dolomite breccia in which it occurs.

In addition to the chert nodules and the thin chert 

interbeds, thicker sections of bedded chert are present 

in the Park City Formation at several localities. The 

most prominent of these is at Sheep Creek, where 40 

feet of bedded chert occurs near the top of the Franson 

Member. It consists of alternating beds 1.0-1.5 feet 

thick of hard yellowish-orange chert. The entire 40 

feet is similar in gross lithology to beds that are elsewhere placed in the Tosi and Eex Chert Members of 

the Phosphoria Formation and would also be included 

in one or the other of those members if its continuity 

with either of them could be demonstrated.

STRATIGRAPHY

GRANDEUR MEMBER

The Grandeur Member of the Park City Formation 

consists of the interbedded carbonate rock, carbonatic 

sandstone, and carbonatic siltstone that underlie the 

Meade Peak Phosphatic Shale Member of the Phosphoria Formation and overlie the Quadrant Formation 

(Cheney and others, in McKelvey and others, 1956, p. 

2841). At most localities the contact between the dolomite or the silty sandstone and mudstone of the Park 

City and the massive light-colored well-sorted sandstone 

of the Quadrant is sharp and can be located without
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 297

difficulty. Locally, however, well-sorted sandstone and 

dolomite are interbedded and the contact seems gradational as in parts of the Melrose area,2 at Lazyman Hill 

in the Gravelly Range, and at Indian Creek and Shell 

Canyon in the Madison Range. The -contact with the 

overlying Meade Peak Member of the Phosphoria is also 

sharp and distinct, but the Grandeur Member is distinguished with some difficulty from the similar-appearing 

Franson Member of the Park City in the eastern and 

northern parts of the areas where the Meade Peak and 

Rex Members of the Phosphoria Formation are not 

present. Although there is always some doubt in placing the contact in such areas, the Grandeur and Franson 

Members can generally be separated in the Madison 

Range by the character of the associated sandstone; 

sandstone associated with the Franson Member commonly contains conspicuous amounts of chert grains 

and apatite pellets and fossil fragments, whereas sandstone associated with the Grandeur Member does not. 

Although the division can also be made by the same 

criteria in several sections in the Three Forks region, 

the two members there must be combined in most places.

At Hawley Creek, where the westernmost section was 

measured, the Meade Peak Tongue of the Phosphoria 

is absent, and the correlation shown in plates 16 and 

21 is not the only one possible; an alternative correlation is that the Franson Member of the Park City Formation may pinch out east of Hawley Creek and, so, all 

the Park City at Hawley Creek may belong to the 

Grandeur Member. However, the correlation shown 

seems to be a likely one and has been followed in constructing the isopach and lithof acies maps.

The Grandeur Member has not been studied in as 

much detail as have the overlying strata. Fewer complete sections of the member were measured than of the 

other members, and where sections were measured, the 

Grandeur Member was generally described in less detail 

than the rest of the Permian rocks. Partly for these 

reasons and partly because of the lack of distinctive 

beds or sequences of beds within the member, only the 

broad outline of its stratigraphy is known.

The areal variation in thickness of the Grandeur 

Member is shown in figure 100, and the areal variation 

in lithologic character, in figure 101. In general, the 

member thickens southwestward from a few tens of 

feet in the Madison Range area to a maximum of nearly 

600 feet at Hawley Creek. The trend is not continuous 

but is interrupted by an abrupt thickening to a maximum of more than 380 feet in the eastern Snowcrest 

Range and a complementary thinning along an axis

B Pierce,- H. W., 1952, Geologic studies of the Phosphoria formation 

in restricted areas, faelrose Phosphate Field, Montana: Indiana Univ., 

Master's thesis, p. 9.

running northward from Wadhams Spring to near 

Dillon. The thickening in the eastern Snowcrest Range 

is abrupt more than 300 feet in 12 or 13 miles and 

perhaps as much as 280 feet in only 4 miles. Westward 

from the low at Wadhams Spring, the member thickens 

at an average rate of a little more than 12 feet per mile.

The Grandeur Member may be divided into two 

parts the upper terrigenous beds and the lower dolomite. Westward along the line of sections shown in 

plate 16, the upper terrigenous beds are present at 

Hogback Mountain, where they consist of 75 feet of 

silty dolomitic sandstone. The average grain size of 

the terrigenous material is finer westward from Hogback Mountain, and at Wadhams Spring the interval 

consists of about 70 feet of dolomitic mudstone and 

dolomite. Farther west at Big Sheep Canyon most of 

the mudstone is red, but at Hawley Creek there is no 

conspicuous zone of either sandstone or mudstone, unless the beds assigned to the Franson Member are actually part of the Grandeur, and the part of the section 

that is most probably equivalent to the upper terrigenous beds consists chiefly of dolomite. East of Hogback Mountain the upper terrigenous beds have probably been removed by erosion that preceded deposition 

of the Meade Peak Phosphatic Shale Member.

The entire Grandeur Member of the Park City Formation in the Gravelly and Madison Ranges consists of 

the lower dolomite. West of the Ruby River the lower 

dolomite thickens to 310 feet at Hogback Mountain, 

thins to 50 feet at Wadhams Spring, and thickens again 

to 235 feet at Big Sheep Canyon. The lower dolomite 

beds west of the Ruby River are nearly all aphanitic. 

Chert, both as nodules and as thin beds, is more common 

from Wadhams Spring westward, and sandstone, of 

both the well-sorted and silty types, is present as sparse 

interbeds. Other than for the granular dolomite and 

dolomite-pebble breccia at Alpine Creek, the changes in 

thickness of the lower dolomite do not seem to be reflected in the composition or texture of the rock.

Correlation of the two units northward is uncertain, 

inasmuch as in the 28-mile stretch from Big Sheep 

Canyon to Sheep Creek, in which there is no intermediate control, the Grandeur Member thins from 347 

feet to on-ly 40 feet; most of the Grandeur Member at 

Sheep Creek, Dalys Spur, and in sections north and 

northwest of Dillon, however, correlates probably with 

the upper terrigenous beds (pi. 17). The Grandeur 

Member at Dalys Spur is composed about half of sandstone and half of dolomite; the sandstone grades southeastward into mudstone at Sheep Creek and northward 

into mudstone at Kelley Gulch, into dolomite and chert 

at Big Hole Canyon, and into dolomite at Melrose.
298 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

113° 112° ' lll c

Franson and Grandeur Members not differentiated 

north of lat 45°40'

MONTANA 

WYOMING

o

FIGURE 100. Isopach map of the Grandeur Member of the Park City Formation. Contour interval, 100 feet where member is more than 100 

feet thick; 50 feet where it is less than 100 feet thick. X, control point showing measured thickness in feet; A, control point, data 

approximate.

In the Three Forks area, the probable equivalent of 

the Grandeur Member of the Park City Formation 

consists of aphanitic dolomite and some interbedded 

dolomite and chert. The dolomite may grade northward into interbedded silty and well-sorted sandstone 

at North Boulder Creek. The Grandeur member in the 

Three Forks area can be correlated only in a gross 

manner with the presumed equivalent member to the 

south and southwest. It has not been determined 

whether these strata are equivalent to the entire member at localities such as Hogback Mountain or to only 

part.

The nature of the contact between the Grandeur Member and the Quadrant Formation is not well known. 

The greater amount of sandstone, similar in character 

to sandstone in the Quadrant, in the Grandeur Member 

at Indian Creek than in the sections at Shell Canyon 

and Mountain Sheep Point suggests that the Grandeur 

Member at Indian Creek in part interfingers with and 

grades into the uppermost part of the Quadrant; interfingering is also suggested by relations between the sections at Three Forks and at Logan (pi. 19). In neither 

comparison, though, is such a f acies change well documented, and the possibility that the Grandeur Member
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

113° 112° 111°

299

Franson and Grandeur Members not differentiated 

north of lat 45°40'

MONTANA 

WYOMING

EXPLANATION

Sand Mud Carbonate

Patterns used singly in class I areas; combined in 

class H and HL areas

FIGURE 101. Lithologlc character of the Grandeur Member of the Park City Formation. X, control point; A, control point, data approximate.

actually pinches out to the east cannot be rejected. To 

the southwest, the comparison of the Grandeur Member at Alpine Creek with that at Lazyman Hill (pi. 16) 

also suggests that the basal part of the Grandeur Member grades into sandstone to the east.

The available f aunal evidence indicates, on the other 

hand, that the Quadrant and Grandeur are separated 

by a hiatus that at least in the eastern part of the area

represents most or all of Upper Pennsylvanian time and 

perhaps part of Wolf campian time as well. Fusulinids 

of Des Moines age have been reported from about 30 

feet below the top of the Quadrant at Mountain Sheep 

Point (Henbest, 1956, p. 59), and fusulinids reported 

by Henbest to be "middle or upper Wolfcamp (or possibly early Leonard)" in age have been found near the 

base of the Park City Formation at Three Forks (Wil-
300 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

liams, in McKelvey and others, 1956, p. 2857). Thus, 

any interfingering between the two formations must be 

minor and would involve only the very uppermost part 

of the Quadrant.

Disconformable relations between the Park City Formation and the Quadrant Formation have been reported 

by Theodosis 3 on the basis of thickness variations of the 

Quadrant and the presence of "weathered friable sandstone in the uppermost part" that was thought to mark 

an old erosion surface. The Park City Formation in 

the same area ranges from 34 to 187 feet in thickness 

according to measurements made by Peterson and others 

(1954), Theodosis, Fowler,4 and Rooney.5 Although 

these relations suggest disconformity in the Melrose 

area, they by no means prove it and may instead represent facies changes.

.The relation of the Grandeur Member of the Park 

City Formation to other formations of different lithology to the west and south is highly conjectural. Blackstone (1954) reported a limestone sequence in the southern Lemhi Range of Idaho that contains Wolfcamp 

fusulinids and therefore may be a westward continuation of the Grandeur. Farther west, the dolomite may 

grade into sandstone of the Wood River Formation, 

for Bostwick (1955, p. 944) assigned a Wolfcamp age 

to the upper tw^o-thirds of the Wood River near Hailey 

in central Idaho. The larger amount of sandstone in 

the Grandeur at Crooked Creek than at Little Sheep 

Creek (p. 17) suggests a southeasterly source of sand; 

this in turn suggests that at least the lower part of this 

lower member of the Park City Formation in southwestern Montana may be the equivalent of part of the 

sandy member of the Wells formation, much of which, 

according to J. Stewart Williams (1953, p. 39), may be 

of Permian age.

FRANSON MEMBER

The type area of the Franson Member of the Park 

City Formation is Franson Canyon, Utah, where Cheney 

(in McKelvey and others, 1956, p. 2842) applied the 

name to a sequence of light-gray and grayish-brown 

dolomite and limestone that overlies the Meade Peak 

Phosphatic Shale Tongue of the Phosphoria Formation 

and underlies the Woodside Formation. Carbonate 

rock of the Franson Member can be traced from the 

type area in Utah through western Wyoming and eastern Idaho into Montana (McKelvey and others, 1956, 

fig. 2). In Montana the Franson Member consists of 

the carbonate rock, largely dolomite, that lies between 

the Rex Chert Member and the Retort Phosphatic Shale

8 Theodosis, S. D., 1955, Geology of the Melrose area, Beaverhead and 

Silver Bow Counties, Montana : Indiana Univ., Ph. D. thesis.

4 Fowler, W. E., 1955, Geology of the Trusty Lake-Quartz Hill Gulch 

area, Beaverhead County, Montana: Indiana Univ., Ph. D. thesis.

6 Rooney, L. F., 1956, A stratlgraphlc study of the Permian formations 

of part of southwestern Montana: Indiana Univ., Ph. D. thesis.

Member of the Phosphoria Formation. It intertongues 

eastward with the lower member of the Shedhorn Sandstone. A western sandstone and chert facies near Dillon 

is included in the Franson because of the small area in 

which it crops out and because it does not seem to be 

continuous with the lowrer member of the Shedhorn 

Sandstone.

The contact of the Franson with the underlying and 

overlying units is sharp almost everywhere. Near Lima 

the Franson directly overlies chert of the Rex Member 

of the Phosphoria and directly underlies phosphorite 

of the Retort Member of the Phosphoria, but to the east 

and northeast it is separated from these two units by 

tongues of the Shedhorn Sandstone. In the Madison 

Range, where the Meade Peak Tongue of the Phosphoria 

is absent, the Franson Member can be distinguished 

from the Grandeur Member of the Park City Formation 

by the character of the associated sandstone, as noted 

in the description of the Grandeur.

The thickness and distribution of the Franson Member are shown in figure 102. The greatest measured 

thickness of the Franson is at Wadhams Spring, where 

it is approximately 210 feet thick. From Wadhams 

Spring it thins to the north, west, and southwest. The 

member thins eastward and intertongues with the lower 

member of the Shedhorn Sandstone; at Logan and 

North Boulder Creek in the northern part of the area, 

no beds can be assigned with assurance to the Park City. 

At Hawley Creek the beds assigned to the Franson 

Member are only 40 feet thick, indicating that it may 

have originally pinched out a few tens of miles farther 

west; however, it is possible that this part of the section 

is actually the upper part of the Grandeur Member and 

that the Franson pinches out between Big Sheep Canyon and Hawley Creek.

The areal variation of the gross lithic composition 

of the Franson Member is shown in figure 103. The 

illustration shows the general uniformity of composition of the member, which is, of course, a reflection of 

the definition of the member, and clearly shows the 

western terrigenous facies. The dolomite of the Franson in the Snowcrest Range is relatively low in contaminants, as is shown by the low D values on the map, 

but the amount of minor constituents (mostly sand and 

nodular chert) increases both eastward and westward. 

The area of cherty dolomite shown in the northern Madison Range may extend northward, for the Park City 

Formation at Three Forks contains a large proportion 

of chert as interbeds, lenses, and nodules.

The transition of the member from the western terrigenous facies into the predominant dolomite facies 

may be followed in some detail in plate 20. At Balys 

Spur, the Franson contains no dolomite but consists
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

113° 112° 111°

301

Franson and Grandeur members not differentiated 

north of lat 45°40'

MONTANA 

V~~ WYOMING

V

CONTOUR INTERVAL 50 FEET

FIGURE 102. Isopach map of the Franson Member of the Park City Formation. X, control point showing measured thickness in feet;

A, control point, data approximate.

of sandstone and subordinate chert and minor mudstone. Twenty-five miles to the south at Little Water 

Canyon, the upper part of the member is composed 

mostly of dolomite rather than sandstone, and much of 

the sandstone in the lower part of the member is carbonatic. Four miles farther south at Big Sheep Canyon, the upper half of the Franson is composed mostly of 

carbonate rock, cherty carbonate rock, and bedded chert, 

and the lower half is composed of interbedded granular carbonate rock, sandy carbonate rock, and dolomitic 

sandstone; several thin tan dolomitic mudstone beds are 

present in the middle of the member. Nine miles farther southeast, at Little Sheep Creek, the Franson is 

composed mostly of carbonate rock, half of which is

709-931 O 63 3

granular or skeletal, but about a quarter of the member is composed of tan dolomitic mudstone that occurs 

in the middle of the section. Thus, as one traces the 

member southward, carbonate rock makes up a progressively greater proportion of the section, the sandstone is progressively more carbonatic, and mudstone 

forms a progressively greater proportion of the terrigenous material. The change in gross aspect of the 

member from Dalys Spur to Little Water Canyon, a 

distance of 25 miles, seems no greater than the change 

from Little Water to Big Sheep Canyons, a distance of 

only 4 miles, or from Big Sheep Canyon to Little Sheep 

Creek, a distance of only 9 miles. One minor difference 

in the facies distribution, shown in plate 20, is that glau-
302 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

113° 112°

Franson and Grandeur Members not differentiated 

north of lat 45°40'

MONTANA 

WYOMING

EXPLANATION

Sand Chert Carbonate

Patterns used singly in class I areas; combined in 

c/ass I and 1R'areas

Isopleth of D values

Contour interval 25 units

 -25 -

Isopleth of ratio 

calcite

total carbonate X'100 

FIGURE 103. Lithologic character of the Franson Member of the Park City Formation. X, control point (numeral is value of D function).

conite occurs in the sandy carbonate-carbonatic sandstone sections but not in the sandstone section at Dalys 

Spur or the limestone section at Little Sheep Creek. 

A similar change in facies from sandstone to dolomite takes place north of Dalys Spur (pi. 20) and

northeast of Kelley Gulch (pi. 19), but the nature of 

the change is not shown by the sequence of sections as 

well as it is in the sections south of Dalys Spur. The 

sandstone does not grade into mudstone northward and 

northeastward, but it either grades directly into dolo-
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 303

mite or else from sand to bedded chert and thence to 

dolomite.

From the mixed sand and carbonate section at Big 

Sheep Canyon, the sandy beds in the upper and lower 

parts of the Franson member grade eastward into dolomite at Wadhams Spring, whereas the sandy beds in 

the center part grade into dolomitic mudstone (fig. 12). 

The mudstone zone may be represented by silty dolomite at Sawtooth and Hogback Mountains, but no trace 

of it is found at Sliderock Mountain or in the sections 

east of the Ruby River. Nearly half of the carbonate 

rock is granular or bioclastic in all sections from Big 

Sheep Canyon to Sawtooth Mountain, but from Hogback Mountain east it is nearly all aphanitic, even 

though the dolomite is sandy in the Gravelly and 

Madison Ranges. In the western section, the granular 

dolomite does not seem to be restricted to any part of 

the member but occurs throughout the section. Perhaps the only generalization that can be made is that 

at most localities the basal carbonate of the member is 

aphanitic.

Two zones of thin chert layers, lenses, and nodules 

are the only beds within the Franson Member that can 

be traced widely. The two zones are most conspicuous 

at Wadhams Spring (p. 21), where the upper consists 

of nodules near the top of the dolomitic mudstone and 

the lower consists of discontinuous beds, lenses, and 

nodules near the base of the dolomitic mudstone. The 

lower cherts in particular preserve the textures of skeletal carbonate rock. The westward correlatives of the 

upper zone are not known with any certainty, but the 

lower zone can be traced with confidence to the sections 

in the Tendoy Mountains west of Lima. The two chert 

zones converge to the northeast. They are distinguishable as separate zones at Sawtooth Mountain, but at 

Hogback Mountain they form a single zone of nodules 

and interbeds. The chert zones cross major lithologic 

boundaries and pass eastward from the sandstone-carbonate rock facies into dolomitic mudstone and finally 

into dolomite.

Neither the upper nor the lower contact of the Franson Member can be considered a time plane. Evidence 

that the lower contact crosses time horizons may be 

seen in plate 20, where in the sections from Little Water 

Canyon to Sheep Creek, the contact between the Rex 

Chert and Franson Members crosses a phosphatic bed. 

If the phosphatic bed was deposited nearly synchronously over the area, as is suggested by its uniqueness in 

this part of the section, the contact between the Franson and Rex is older at Dalys Spur than it is1 either at 

Sheep Creek or near Lima.

The upper contact of the Franson may nearly coincide 

with a time plane in the western part of the area, where

the member is directly overlain by the Retort Phosphatic Shale Member of the Phosphoria Formation; but 

to the east, where a tongue of the Shedhorn Sandstone, 

is equivalent to the upper part of the Franson of the 

Lima area, the upper contact of the Franson is older 

than it is in the Lima area.

As with the Grandeur Member, the exact manner in 

which the Franson Member terminates to the east is not 

clear. Certainly the interval is in part represented by 

sandstone of the lower member of the Shedhorn, and 

the dolomite itself undoubtedly thins eastward. Individual beds probably pinch out eastward and hiatuses 

there are probably more numerous and of greater time 

significance.

PHOSPHORIA FORMATION 

GENERAL CHARACTER AN1> DISTRIBUTION

The type locality of the Phosphoria Formation is 

Phosphoria Gulch, Bear Lake County, Idaho, where the 

formation was named by Richards and Mansfield in 

1912 (p. 684). Two members were recognized: the 

phosphatic shale member, about 200 feet thick, and the 

overlying Rex Chert Member, consisting of 150 feet of 

bedded chert overlain by 100 feet of mudstone and 

cherty mudstone.

In 1956 (McKelvey and others, 1956, p. 2844-2850), 

applied the name Meade Peak Phosphatic Shale member 

to the phosphatic shale of the type section, restricted 

the term Rex Chert Member to the 150 feet of bedded 

chert, and applied the name cherty shale member to the 

upper mudstone. The member names Meade Peak and 

Rex were extended to beds in western Wyoming and 

from there to beds in southwestern Montana on the basis 

of work by Sheldon (McKelvey and others, 1953).

Three members of the Phosphoria Formation are not 

found at the type locality of the formation; these are 

the Retort Phosphatic Shale Member, named in Montana and extending southward to western Wyoming 

(Swanson in McKelvey and others, 1956, p. 2850), the 

Tosi Chert Member, named in western Wyoming and 

extending into Montana (Sheldon, in McKelvey and 

others, 1956, p. 2841), and the lower chert member, 

present only in western Wyoming (Sheldon, in McKelvey and others, 1956, p. 2845).

In most of southwestern Montana, four of the six 

members of the Phosphoria Formation are present. 

These are, in ascending order, the Meade Peak Phosphatic Shale, the Rex Chert, the Retort Phosphatic 

Shale, and the Tosi Chert Members. In addition, beds 

betweeen the Retort and Tosi Members at Big Sheep 

Canyon are tentatively assigned to the cherty mudstone 

member. The Rex chert and Meade Peak Phosphatic 

Shale Members pinch out east of the Gravelly Range
304 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

113° 112° 111°

EXPLANATION

-IOOIsopach

Contour interval 50 feet

 30 

Isopleth of percent of the 

formation composed of the 

phosphatic shale members

Contoured at 10, 30, and 

50 percent

FIGURE 104. Isopach map of the Phosphoria Formation. X, control point showing measured thickness in feet:

approximate.

k, control point, data

and north of Big Hole Canyon, but where present they 

are separated from the Retort Phosphatic Shale Member by the Franson Tongue of the Park City Formation. 

The thickness and distribution of the Phosphoria 

Formation are shown in figure 104. The location of the 

featheredge of the formation northeast of Three Forks

is based on work by Klemme." McMannis (1955, p. 

1404) described 0-26 feet of chert breccia in a sandstone 

matrix that crops out along the east flank of the Bridger 

Range north and northeast of Bozeman. McMannis

6 Klemme, H. D., 1949, The geology of Sixteen Mile Creek area, Montana : Princeton Univ., Ph. D. thesis.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 305

questionably assigned the unit to the Jurassic, but the 

similarity of these beds to the conglomerate of Permian 

age described by Klemme suggests that the conglomerate 

of the Bridger Range may also be Permian.

Near the mouth of Rocky Creek Canyon, southeast 

of Bozeman, the following sequence is exposed on top of 

typical Quadrant Formation: 5 feet of conglomeratic 

sandstone grading up into cherty carbonate rock and 

calcareous shale; 11 feet of nodular- to medium-bedded 

chert and limestone and shale interbeds; 6 feet of massive sandy carbonate rock; 3 feet of fine-grained calcareous sandstone containing angular chert fragments 

at the top; 3 feet'of fine-grained thick-bedded carbonate 

rock; 5 feet of chert; 2 feet covered; and 1 foot of finegrained white sandstone. The overlying interval is 

covered for a distance from its base to the Jurassic beds 

overlying it. The strata described above resemble units 

of the Permian interval to the west, in that they contain phosphate pellets and spicular chert. Cobban, 

Imlay, and Reeside (1945) redescribed the type section 

of the Ellis Formation (Jurassic) at this locality as 

including, on top of the Quadrant Quartzite, 5 feet of 

conglomerate, 3 feet of limestone, and 84 feet of interbedded gray shale, calcareous shale, and limestone, the 

lowermost 23 feet of which is shale. It is difficult to 

reconcile the two sections overlying the Quadrant unless 

it is assumed that the rocks called Quadrant by them are 

part of the quartzite at the top of the section. No fossils were found in the section, which was measured near 

the highway and in less detail than most other sections 

described in this report. However, specimens were 

collected of each bed measured, and in thin sections of 

these, the sponge spicules, phosphate pellets, and spicule 

canal fillings typical of the Phosphoria were noted, 

particularly in samples from the top bed of the 

sequence.

The Phosphoria thickens south westward from Bozeman, and the maximum thickness of 330 feet occurs at 

Big Sheep Canyon.

The Rex and Tosi Chert Members constitute most of 

the Phosphoria, and in only a few places do the two 

phosphatic shale members constitute more than half of 

the formation.

L.ITHOL.OGY

FREQUENCY OF ROCK TYPES

Rocks of the Phosphoria Formation consist of mixtures of five major constituents: (1) authigenic microcrystalline quartz in the form of chert; (2) carbonate 

fluorapatite in the form of isotropic or microcrystalline 

pellets, oolites, and skeletal fragments; (3) calcite and 

dolomite; (4) clay minerals and detrital quartz; and 

(5) carbonaceous matter. All the constituents except 

carbonaceous matter occur in sufficient amounts to

form the major part of many beds. Most rocks of the 

two chert members are rather simple mixtures of authigenic microcrystalline quartz and minor clay and detrital quartz, but combinations of three or more of the 

major constituents are common within the two phosphatic shale members. This lithologic character is best 

seen in rocks of the Retort Phosphatic Shale Member, 

for which more data are available than for other 

members.

Figure 105, illustrating the gross mineral composition of the Retort Phosphatic Shale Member, was constructed from analyses of rocks at eight localities. The 

number of samples at each locality is roughly proportional to the thickness of the member at that point, and 

the localities are relatively evenly spaced over the area; 

so the diagram is probably representative of the member 

as a whole in southwestern Montana. In plotting the 

samples the amount of carbonaceous matter was subtracted and the amount of the remainder of the constituents recalculated to 100 percent. The points were 

plotted on the triangular diagram and then contoured 

in a manner similar to that used in contouring petrof abric diagrams.

Perhaps the most striking feature shown by figure 

105 is the near absence of mixtures of significant 

amounts of the carbonates with either the detrital silicates or apatite. On the other hand, apatite is mixed 

in nearly all proportions with the quartz and clay end 

member. Even so, two conspicuous modes in the apatite-silicate mixtures are apparent; the two most common rock types are (1) mudstone and (2) highly 

phosphatic mudstone and argillaceous phosphorite. 

The barren zone between the quartz and clay-apatite 

join, and the band representing the silicate-apatite mixtures results from the presence in most of these rocks of 

gypsum, iron oxides, pyrite, and soluble silicates.

OCCURRENCE OF CARBONACEOUS MATTER IN THE RETORT 

PHOSPHATE SHALE MEMBER

Carbonaceous matter is a universal and characteristic 

component of the shale members, although it is nowhere 

a dominant constituent. The relations of carbonaceous 

content to the other constituents of the Retort member 

are shown in figure 106. The carbonaceous content for 

each sample was noted at the proper position in the triangle, a 1-percent-area triangle was moved systematically over the area of the larger triangle, and the average of all values within the 1-percent area was noted at 

each stop. The resulting average values were then 

contoured.

There are two bands of high carbonaceous rocks. 

The most conspicuous coincides approximately with the 

highly phosphatic mudstone mode shown in figure 106; 

the second very roughly coincides with the mudstone
306 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

EXPLANATION APATITE 

Sample density, in percent

QUARTZ 

CLAY 

Feldspar 

Mica

CALCITE

DOLOMITE

Gypsum

Pyrite

Limonite

Soluble silicates

FIGURE 105. Mineral composition of rocks in the Eetort Phosphatic Shale Member of the Phosphoria Formation. Analyses of 97 samples 

representing every third bed at localities 1224. 1234, 1249, 1253, 1299, 1319, 1362, and 1363 were plotted on the compositional triangle 

and contoured by use of a triangle having an area 1 percent that of the compositional triangle. Major constituents in upper-case letters; 

minor constituents in lower-case letters.

mode. Both the high-grade phosphorites and the carbonate rocks contain little carbonaceous matter.

Figure 106 shows only average values; therefore, a 

frequency diagram of the organic content of the same 

samples is shown in figure 107. More than half the 

samples contain less than 4 percent carbonaceous matter and more than 90 percent of the samples contain less 

than 10 percent. The highest value reported is 23 percent for bed Rt-193 at Big Sheep Canyon, which contains 5.7 percent P2O5 and 36.7 percent acid insoluble 

material.

The relation of carbonaceous matter to other constituents can be studied in more detail in the Retort Member at Sheep Creek (lot 1234), where 16 of the samples 

that have been analyzed for acid insoluble, A12O3 , and 

Fe2O3 have also been analyzed for carbonaceous matter.

Fe O

A12 03

1 0. 789

r.,o,

2 0. 526

2. 733

Carbonaceous matter

0.354

2. 525

2. 615

The correlation coefficients between constituents in these 

samples are listed in the following table:

1 Coefficient significant at the 1-percent level.

2 C oefficient significant at the 5-percent level.

The correlation of carbonaceous matter with acid 

insoluble is not significant, but the correlation of carbonaceous matter with A12O3 is significant and probably 

reflects the commonly observed tendency of carbonaceous matter to be concentrated in finer grained 

sediments (Trask, 1939, p. 433). The correlation of
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

APATITE 

EXPLANATION 

Carbonaceous content, in percent

307

10-20

QUARTZ 

CLAY 

Feldspar 

Mica

CALCITE

DOLOMITE

Gypsum

Pyrite

Limonite

Soluble silicates

FIGURE 106. Relation of content of carbonaceous matter to rock composition in the Retort Phosphatic Shale Member of the Phosphoria

Formation. Based on the same samples as used in figure 105.

carbonaceous matter with. Fe2O3 is also statistically significant and probably reflects a direct relation between 

carbonaceous matter and reducing conditions in the 

original sediment.

PHOSPHORITE

Phosphorites are rocks in which apatite is the dominant constituent.

There is little uniformity in color among the phosphorites as seen in outcrop or in trenches. Perhaps the 

only generalization that can be made is that the phosphorites are nearly all low in chroma. The frequency 

distribution of value (the measure of darkness) for 

phosphorites of the Retort Member is shown for several 

localities in figure 108. The lack of any regional trend 

in the value suggests that the differences in color as seen

at the surface may in large part be a function of the 

degree of weathering. The frequency distribution of 

the value for hard phosphorite is compared with that 

for medium and soft phosphorite in figure 109; this 

particular comparison is made because the harder beds 

are assumed to be generally less weathered. The differences between the two distributions were tested by x2 

and were found to be highly significant (P<1 percent) ; therefore, the medium and soft phosphorites are 

lighter in color. The most highly weathered section is 

at Wadhams Spring, where the rocks were weathered 

deeply prior to deposition of a Tertiary conglomerate. 

Here 75 percent of the phosphorites have color values 

of 7 or more.

In relatively fresh surface exposures, oolitic and 

skeletal phosphorites are commonly lighter in color
308 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

50-|

H 4(H

z

Ul

O tr

UJ

Q- 30H

O

Z 20-

O

UJ

tr 10-

0 2 4 6 8 10 12 14 16 18 20 22 24 

CARBONACEOUS MATTER, IN PERCENT

FIGURE 107. Frequency distribution of carbonaceous matter in the 

Retort Phosphatic Shale Member of the Phosphoria Formation. 

Based on the same samples as used in figure 105.

than pelletal phosphorite, partly because the oolitic and 

skeletal beds originally contained less carbonaceous 

matter than the pelletal phosphorites and partly because many of the skeletal and oolitic beds are more 

pervious and weather more rapidly. Inasmuch as the 

Meade Peak Member contains generally more oolitic 

and skeletal phosphorite than the Retort Member, it is

distinctly lighter in color than the Retort over much 

of the area.

The phosphorites are somewhat more uniform in 

thickness of bedding than in color. About 50 percent 

are thin bedded, and about 40 percent are thick bedded; 

the rest are equally divided between fissile and very 

thick bedded types.

The phosphate-bearing mineral in the Phosphoria, 

as in most marine phosphorites, is carbonate-fluorapatite 

(Altschuler and Cisney, 1952). The apatite crystals 

in many grains are either obscured by inclusions or are 

too small to be resolved, but anisotropism is much more 

common than one would expect from descriptions in 

the literature. Many of the grains are composed of 

minute weakly biref ringent crystals having an apparent 

crystal size of 1 or 2 microns; the resulting pin-point 

extinction closely resembles that of chert. This type 

is termed "microcrystalline apatite" in this report. Anisotropic apatite also occurs as concentric laminae within or as exterior rings about apatite grains. Individual 

crystals cannot be distinguished, but their mass orientation with the C axes arranged radially (the slow ray 

vibrates tangentially) results in weakly biref ringent, 

somewhat fibrous-appearing rings that exhibit the 

spherulitic cross. This type is termed "microfibrous 

apatite.'"1 Most skeletal fragments also show a weak, 

streaky birefringence that probably also results from

H 60fZ

40

20

Cedar Creek 

1256

Dalys Spur 

1222

EXPLANATION 

Value

Melrose area 

1359, 1366

7-9 

(Very light)

5 and 6 

(Light)

60

40

20

3 and 4 

(Dark)

Big Sheep Canyon 

1224

Blacktail Creek 

1302

Hogback Mountain 

1299

Gravelly Range 

1300,1307

Madison Range 

1214,1362

1 and 2 

(Very dark)

FIGURE 108. Frequency distribution of value (darkness) for phosphorite of the Retort Phosphatic SLale Member of the Phosphoria Formation.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 309

o

2] 60

- 40 

O

=> 20 

O

58 samples 64 samples

J

| |

Wadhams Sprinf

EXPLANATION 

Value

D7-9 

(Very light)

5 and 6 

(Light)

3 and 4 

I (Dark)

^^

u

1 and 2 

(Very dark)

Hard phosphorite Medium-hard and soft 

phosphorite

Data from following lots: 

1222, 1224, 1234, 1247, 

1256, 1257, 1299, 1302

FIGURE 109. Effect of weathering on value (darkness) of phosphorite.

mass orientation of minute crystals. In general, the 

anisotropic grains occur in the lighter colored rocks. 

Yet, patches of anisotropic material have been observed 

in some of the darkest colored phosphorite, and many 

very light colored apatite grains, particularly in phosphatic sandstone, are isotropic.

Crystallite sizes have not been determined by means 

of X-ray techniques for any of the Phosphoria apatite, 

but Arrhenius and others (1957) report marine inorganic apatite having crystallite sizes greater than 

20,000 angstroms (2 microns).

The apatite grains consist of three major morphologic 

types: pellets, skeletal fragments, and oolites. Pellets 

are grains having no regular internal structure. Most 

pellets are of fine- and medium-sand size, although some 

may be as large as 1 or 2 mm in diameter; few are of 

silt size. Many pellets are elongate in section; the long 

diameter is as much as 3 times as long as the short diameter, but most pellets are equant or only slightly elliptical in section. The pellets may be well formed and 

regular in shape and have distinct borders or may be 

somewhat irregular in form and have indistinct borders. 

The color as seen in thin section ranges from moderate 

brown (YR 4/4) in the more argillaceous rocks to light 

brown (10T7? 5/6) or lighter in the less argillaceous 

rocks. Most pellets contain numerous very fine quartzsilt particles and mica shreds that are randomly oriented, and most are clouded by carbonaceous matter. 

Some pellets, mostly dark-colored ones, contain foraminiferal tests as nuclei (fig. 110), and a few contain 

silt inclusions arranged in loops and swirls that may be 

tests of arenaceous Foraminifera. Although most pellets are structureless, some contain several indefinite, 

poorly defined round areas f ormed by finer crystal size 

or by darker color. The several round areas within a 

pellet are about the same size and are closely packed, 

having tangential contacts.

The term ''oolite" is restricted to apatite grains having a conspicuous concentric structure. The structure 

may be defined by color rings or by rings of apatite of

FIGURE 110. Photomicrograph of cherty phosphorite containing 

abundant foramlniferal tests that form the nuclei of pellets (bed 

Rt-8, lot 1215, Madison Range). Pellets are generally oval to 

elliptical and have smooth outer rims that are free of silty inclusions. Some are shattered. Chert fills interstices between pellets, 

cracks in pellets, and cells of fossils. Oolitic rings have formed 

around the exterior of some pellets.

different crystal habit, which is the more common type. 

The rings consist of either alternating microfibrous and 

microcrystalline apatite or alternating microfibrous and 

apparently isotropic apatite, but in both types the microfibrous rings are the thinner. Most of the oolites have 

formed about nuclei of quartz or chert grains, skeletal 

fragments, or, commonly, apatite pellets. Complete 

gradation can be found from pellets surrounded by a 

single ring of microfibrous apatite to oolites containing 

no observable pellet nucleus. Several pellets may be 

surrounded by a sheath of rings, or several oolites may 

together form the nucleus of a compound oolite. In 

contrast, oolites in a few beds are surrounded by a thick 

ring of microcrystalline or aphanitic apatite similar to 

that forming pellets. Most oolites are of medium-sand 

size, and the extremes of silt size and very coarse sand 

size are uncommon. The oolites are generally somewhat elliptical in section, and nearly all are well 

rounded.

The phosphatic skeletal fragments consist of bones, 

scales, teeth, and linguloid-brachiopod shell fragments, 

which were all originally highly phosphatic; however, 

only a few fragments can be classified as one or the 

other of the skeletal types. Fish teeth and bones and 

cosmoid fish scales have been identified, but many fragments consist of either dense enamellike material or 

spongy bonelike material that is probably skeletal but
310 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

that cannot be more closely identified. A few fragments are composed of alternate layers of closely spaced 

diagonal striations and are probably linguloid shell 

fragments. All types of skeletal fragments may be 

seen in a single specimen, but scale, bone, and teeth 

fragments seem to be more common than shell fragments. Most skeletal fragments are light colored and 

lath shaped in thin section but show great variety in 

both size and shape. The fragments may be angular, 

or, as in sandy rocks, well rounded.

Nodules constitute a fourth type of grain that is conspicuous where present but is quantitatively unimportant in southwestern Montana. Most nodules occur 

in pelletal beds, where they constitute a minor part of 

the total apatite. They are composed of pellets cemented 

by apatite, which are identical to those in the matrix, 

and have resulted probably from local cementation in 

place. The nodules range generally from 15 to 30 mm 

in diameter. Nodules that occur in sandy and oolitic 

phosphorite beds are probably of clastic origin.

Pellets are by far the most common type of apatite 

grain and are present in all phosphorites examined. 

They may constitute all the apatite or may be mixed 

with skeletal fragments, oolites, or both. These relations are illustrated in figure 111, which is based on 

estimates of amounts of the types seen in thin sections. 

The pelletal end member is the only modal occurrence.

The phosphorites may be divided into two broad 

types: (1) those that were sorted and winnowed by 

currents and (2) those that were not, The phosphorites 

that show evidence of sorting and winnowing may consist entirely of pellets or of mixtures of pellets, oolites 

(fig. 110), and skeletal fragments (fig. 112,4). They 

are characterized by well-formed grains having distinct

Skeletal 

fragments

Pellets Oolites

FIGURE 111. Relative abundance of the three principal types of apatite 

grains in thin sections of phosphorite from the Phosphoria Formation. 

Each small circle represents one sample.

boundaries and by the absence of a fine-grained detrital 

matrix. The apatite grains are mostly light colored 

in thin section; grain contacts are mostly tangential, 

and elongate grains are imperfectly oriented subparallel 

to the bedding. Quartz-sand grains are common, both 

as oolite nuclei and as separate grains. The rock may 

be cemented by clear microcrystalline apatite, by microcrystalline quartz (fig. 1125), or by poikiloblastic calcite. The evidences of strong current action are as follows : (1) Many of the rocks contain a variety of apatite 

grain types that had different histories; (2) many pellets contain fine-grained quartz-silt and mica inclusions 

similar to those found in muddy phosphorites, whereas 

the only matrix material present is quartz sand, which 

suggests that the grains formed in a more tranquil environment than that in which they finally accumulated; 

(3) the imperfect orientation of elongate grains suggests deposition of the grains by currents, as orientation produced by post-depositional processes such as 

compaction would be more uniform; and (4) the 

tangential contacts between apatite grains indicate that 

the grains were deposited as solid particles and that 

they did not form in place.

The phosphorites that do not show evidence of appreciable sorting and winnowing by currents are dark, 

pelletal, and commonly argillaceous. The pellets themselves are dark brown in thin sections and contain many 

quartz-silt grains and mica shreds as inclusions. Where 

the pellets are in contact with each other, the boundaries 

are distinct and are commonly mutually accommodating, but where surrounded by silt and clay, the pellets 

are generally poorly formed and have indistinct boundaries. Many muddy phosphorites consist of laminae, 

0.1 to about 2 mm thick, of phosphorite and muddy 

phosphorite or phosphatic mudstone. Within the 

muddy layers the pellets may be isolated in the argillaceous matrix or they may be concentrated in small clusters 

and lenses. Markedly elongate pellets are well oriented 

parallel to the bedding (fig. 112*7). The features that 

suggest the absence of strong currents are as follows: 

(1) Inclusions within pellets are similar in size and 

character to the matrix material, suggesting that the 

pellets formed in a muddy environment; (2) the finegrained silt and clay matrix would have been removed 

by any current strong enough to transport the apatite 

pellets; and (3) the presence of carbonaceous matter 

indicates a lack of oxygenated (and thus strongly agitated) water.

Although the evidence indicates that the pellets were 

not transported but were formed at the site of accumulation, no evidence has been found to determine whether 

the pellets formed at the surface of the sediment or 

within the sediment during diagenesis.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 311

FIGURE 112. iPhotomicrograplis of phosphorites. A, Phosphorite containing quartz-sand grains (g) and apatite oolites (o), pellets (p), and 

skeletal fragments (s). Note oolite nuclei consisting of quartz-sand grains (gn) and apatite pellets (pi). Ordinary light. B, Pelletal, 

oolitic phosphorite cemented by microcrystalline quartz. Most oolites contain a pellet nucleus. Ordinary light. C, Pelletal argillaceous 

phosphorite showing poorly defined laminae, silt and clay matrix, and elongate, poorly defined pellets. Ordinary light. \D, Pelletal phosphorite showing mosaic tecture.
312 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Figure 113 is the size-distribution curve of a phosphorite having several of the features that indicate that 

the pellets were not transported; yet, the pellets are well 

sorted, and the distribution is log normal, except for 

finer sizes. Thus, in spite of evidence in thin sections 

that the pellets were not transported, the size distribution differs little from that of a well-sorted sandstone.

Some pelletal phosphorites cannot be classed in either 

group. Grain borders are distinct, grain contacts are 

tangential, elongate grains are imperfectly oriented, and 

inclusions in the pellets are much smaller than the grains 

of the detrital matrix. The pellets, however, are all of 

one type, and the matrix grains, although much larger 

than inclusions in the pellets, are too small to be hydraulic equivalents of the pellets. These phosphorites may 

originally have contained much clay and silt that was 

winnowed by currents not strong enough to transport 

the pellets any significant distance.

A few relatively pure phosphorites consist of moderate-brown pellets that are tightly packed and have a 

mosaic texture (fig. 112Z>). Silt and clay inclusions,

100

80

Q- 60

40

20

M/<6=2.64 

So = 1.32

are present but are less abundant than in more argillaceous phophorites. The mosaic texture suggests that 

pellets were soft at the time of deposition and thus 

could not be transported. Presumably the current was 

sufficient to prevent silt from being deposited but was 

insufficient to move the pellets.

Many features of the phosphorites described in the 

foregoing discussion are similar to those described by 

Lowell (1952) in his excellent study of the phosphatic 

rocks near the type area of the Phosphoria Formation 

in southeastern Idaho. Lowell (1952, p. 38-39) also 

found evidence that some beds have been reworked by 

currents or waves, whereas other beds have not. Although his terminology differs from that used herein, 

his descriptions of the phosphorites could be substituted 

in this report with little change.

The similarities of the textures of the Phosphoria 

phosphorites to those of the Bahaman calcareous sands 

described by Illing (1954) are striking. Pelletal phosphorites of the Phosphoria are similar to Bahaman calcareous sands; phosphatic nodules, to calcareous grape98

95

90

85

80

70

60

50

40

30

20

15

10

7

1 2 3 4 5123. 45

DIAMETER, IN PHI

FIGURE 113. Size distribution of pellets in a muddy pelletal phosphorite. Thin-section size analysis of bed Rt-96, lot 1299 ; not corrected for

sectioning. Curve on right plotted on logarithmic probability paper.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 313

stone aggregates; and phosphatic oolites, to calcareous 

oolites. The photographs in Tiling's paper could well 

illustrate Phosphoria phosphorites except for differences in composition. There are, of course, some differences in texture the calcareous silt of the Bahamas has 

no phosphatic counterpart in southwestern Montana, 

and the detrital quartz and silicates of the Phosphoria 

do not exist in the Bahamas. Nevertheless, the very 

great similarities in texture must indicate corresponding 

similarities in the mode of origin.

MTTDSTONE

The mudstone and the phosphatic-mudstone modes 

shown in figure 105 are so distinct that one might expect 

accompanying differences in texture and structure, but 

for the most part, these differences do not seem to exist. 

Frequency distributions of thickness of bedding, hue, 

chroma, and vane have been compared for the two types 

of mudstone, but the x2 test indicates that the differences 

are not significant. A more subtle difference, however, 

can be shown to exist in at least one locality. In the 

Ketort Member at Sheep Creek, the acid insoluble/A!2O3 

ratio averages 5.27 for phosphatic mudstone but averages 6.32 for weakly phosphatic mudstone. The difference is highly significant (P<1 percent), according to 

Student's t test that is, the detrital fraction of the 

weakly phosphatic mudstone contains a significantly 

smaller proportion of A12O3 , and thus of clay, than does 

the detrital fraction of phosphatic mudstone. It should 

be emphasized again that the assumption that the acidinsoluble content is the detrital fraction is only approximately correct inasmuch as at least several percent of 

the silicates in mudstone may dissolve in the procedure 

used.

Most of the mudstone of the Phosphoria is thin 

bedded; but about 20 percent of the mudstone in the 

measured units is fissile, and less than 5 percent is very 

thick bedded. The thin-bedded mudstone is darker in 

color than the thick-bedded mudstone (fig. 114); this 

relation is possibly explained by Ingram's observation 

(1953, p. 877) that carbonaceous matter increases the 

tendency toward parallel arrangement of the clay particles. Ingram (1953, p. 871) also stated that in the 

suite of rocks he examined the mudstones having a 

flaggy structure (splits into fragments with two flat 

parallel sides and with the width and length much 

greater than the thickness) are predominantly black 

or dark gray, whereas those having a flaky structure 

(splits into uneven flakes, thin chips, and wedgelike 

fragments) are predominantly gray or gray black. In 

the Phosphoria, however, the opposite relation exists. 

The best example is at Big Sheep Canyon, where the 

black and olive-black highly carbonaceous mudstone of

the Retort is flaky, whereas the olive-gray carbon-poor 

mudstone of the cherty shale member is platy.

About one-third of the mudstone beds of the Phosphoria are neutral in hue; most of the rest have YR 

hues and low chromas. The value is variable over the 

region but may be rather consistent in any one exposure 

(fig. 114). The variability in value seems to be related more to conditions of exposure rather than to any 

regional trend and contrasts with the strong regional 

trend in the content of carbonaceous matter. To test 

the effect of weathering on color, the frequency distributions of hue, chroma, and value of soft mudstone were 

compared with those of hard mudstone by means of the 

X2 test. Differences in hue and chroma are not significant, but differences in value are highly so, as the 

soft mudstone is lighter in color (fig. 114). No significant differences in the thickness of bedding were 

found between hard and soft mudstone. Relatively 

unweathered mudstone is thus generally hard, thin 

bedded, and dark gray and brownish gray to black and 

brownish black. Weathering lightens the color and reduces the hardness but does not greatly affect the chroma 

or thickness of bedding.

The mudstone consists of mixtures of quartz silt, clay, 

apatite, and carbonaceous matter. The quartz silt is 

angular and contains a large proportion of elongate 

grains, but it is otherwise similar to the detrital quartz 

in sandstone of the Park City and Shedhorn Formations. Small amounts of both plagioclase and potassium feldspar have been noted in X-ray patterns of 

some, but not all, of the mudstone, but they have not 

been observed in thin section.

Clay minerals have been identified from X-ray patterns of bulk samples from several beds at Big Sheep 

Canyon, Sheep Creek, Hogback Mountain, and the 

Centennial Mountains. Illite and kaolinite are present in nearly all the samples, but illite is dominant; 

montmorillonite has been detected. Herr 7 studied 

the fraction containing particles less than 2 microns in 

size of several samples from Big Sheep Canyon and 

concluded that the dominant clay mineral is a mixedlayer illite-montmorillonite. Rooney,8 also working 

with fine-grained separates, found that illite is the most 

abundant clay mineral in the sections near Three Forks 

and that kaolinite, chlorite, and mixed-layer illitemontmorillonite are minor accessories. In the Melrose 

area, however, Rooney found that montmorillonite is 

very abundant and in places dominant, and that kaolinite is common. He believed that the montmorillo7 Herr, G. A., 1955, Clay minerals in the Phosphoria formation in 

Beaverhead County, Montana : Indiana Univ., M.A. thesis.

8 Rooney, L. F., 1956, A stratigraphic study of the Permian formations of part of southwestern Montana: Indiana Univ., Ph. D. thesis, 

p. 54-61.
314 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Soft mudstone 

(80 beds)

Hard mudstone 

(84 beds)

Thin-bedded 

mudstone 

(131 beds)

Thick-bedded 

mudstone 

(49 beds)

80n

Big Sheep Canyon Dalys Spur Cave Creek

EXPLANATION

Value

Hogback Mountain

1 and 2 3 and 4 5 and 6 7 and over

FIGUEH 114. Value (darkness) of mudstone of the Retort Phosphatic Shale Member of the Phosphoria

Formation.

nite and kaolinite of the Melrose area most probably resulted from hydrothermal alteration.

Apatite pellets in the mudstone are dark colored, commonly elongate, of fine- and medium-sand size, and differ only in abundance from those in dark argillaceous 

phosphorite. Sparse bone, scale, or tooth fragments 

are present in many samples.

Carbonaceous matter is seen in thin section as black 

and brown pigment that is generally concentrated in 

the more argillaceous parts of the specimen. The carbonaceous matter in some samples is so abundant that 

the thin sections are opaque. Rooney (1956) found 

the C13/C12 ratio of organic carbon in the Phosphoria 

of Montana to range from 89.80 to 91.25, values similar 

to those of modern stagnant water plants as determined by Wickman (1952, p. 252). According to Craig

(1953) these values are also typical of the organic carbon of both petroleum and marine shales.

Iron oxide is ubiquitous in the mudstone and stains 

the argillaceous material yellow and brown. Pseudomorphs of iron oxide after pyrite are scattered through 

most thin sections as minute grains; in other samples 

aggregates of the pseudomorphs form clusters and 

streaks. The Fe2O3 content rarely exceeds 5 percent 

and averages about 2 or 3 percent. (See analyses for 

Sheep Creek, lot 1234.)

The relative proportion of the various constituents 

composing the matrix are difficult to determine in thin 

section because of the extremely small grain size; the 

size distribution was not determined by sedimentation 

techniques because of the difficulty in dispersing the 

grains in rocks saturated with carbonaceous matter.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 315

However, estimates of the relative amounts of quartz 

and clay in the mudstone can be made by means of the 

ALO3 analyses. If all the A12O3 of the mudstone in 

the Retort Member at Sheep Creek is in illite (an assumption at least partially justified by X-ray data) having an A12 O,, content of 26 percent (Grim, 1953, p. 372), 

then the acid insoluble/ALO., ratios indicate that about 

75 percent of the detrital fraction of the phosphatic 

mudstone and 60 percent of the detrital fraction of the 

weakly phosphatic mudstone are clay. Inasmuch as 

some of the detrital silicates are soluble, these percentages are a little too large, but the A12O3 content assumed 

for illite is probably near the maximum. If the illite 

is similar in composition to those analyzed by Kerr and 

others (1950) and contains only about 18 percent A12O3 , 

then all the detrital fraction of the phosphatic mudstone is clay. Whatever the composition of the illite, 

much of the mudstone in the Retort Member, and probably also in the Meade Peak Member, is actually claystone or silty claystone. Some mudstone beds within 

the shale members, however, are properly classed as 

siltstone; for example, the detrital fraction of the basal 

bed of the Retort at Sheep Creek contains only about 

30 percent clay (from analyses, assuming 26 percent 

A12O3 in illite), the basal bed at Hogback Mountain 

contains about 15 percent (from measurements on a 

thin section), and the entire lower half of the Retort 

at Sawtooth Mountain consists of siltstone that is not 

particularly argillaceous.

The silt in many silty claystones is concentrated in 

lenses and poorly defined and discontinuous laminae, 

and the clay in many clayey siltstones is concentrated 

in streaks; such uneven distribution is more the rule 

than the exception. Apatite pellets are also generally 

concentrated in laminae, lenses, and small groups, although many pellets are isolated in the matrix.

CARBONATE ROCK

Most of the carbonate rock of the Phosphoria consists 

of thin interbeds of aphanitic dolomite. In relatively 

unweathered sections the colors are mostly grayish 

brown and pale brown colors having low chroma and 

values ranging from 3 to 6. The rocks are darker than 

dolomite of the Park City Formation but lighter in 

color than the shale and chert with which they are 

interbedded. Few of the dolomite beds are fissile, but 

otherwise there is little uniformity in thickness of bedding. A larger proportion of the dolomite than of the 

mudstone is thick and very thick bedded.

Texturally, the dolomite of the Phosphoria resembles 

the aphanitic dolomite of the Park City Formation. 

Most of the beds are composed largely of a mosaic of 

dolomite anhedra that average about 20 microns in 

diameter. Dolomite rhombs about the same size as the

anhedra are scattered through several samples, and in 

a few samples, half the total dolomite consists of 

rhombs. One sample contains poorly defined circular 

areas of aggregates similar to those noted in some 

dolomite of the Park City. Carbonate fossil fragments 

make up 10 or 15 percent of several samples; at least 

some are replaced siliceous sponge spicules, which occur 

with siliceous spicules that are corroded and only partly 

replaced.

Either apatite or quartz silt may constitute more than 

20 percent of the dolomite, but silty dolomite is more 

common than phosphatic dolomite. The apatite pellets 

are dark in color and have extremely irregular borders; 

they are generally evenly distributed throughout the 

dolomite. The quartz silt in most samples is also evenly 

distributed. The borders of nearly all the quartz grains 

are deeply corroded and invaded by dolomite. Little 

clay has been identified in thin sections of the dolomite.

The dolomite beds of the Phosphoria, especially those 

of the shale members, are particularly susceptible to 

weathering. They become soft and crumbly and somewhat lighter in value and stronger in chroma. The resulting colors are light brown, yellowish gray, and weak 

yellowish orange. If the degree of weathering is extreme, most of the dolomite is removed, and the insoluble residue forms a thin soft mudstone bed.

None of the few limestone beds of the Phosphoria has 

been studied microscopically, but in hand specimen they 

differ little in appearance from the aphanitic dolomite.

CHERT

Chert is both the most common and the most conspicuous rock type of the Phosphoria Formation. 

Throughout much of the area the more massive beds 

of the chert members crop out in cliffs and combs that 

contrast with the soil-covered swales formed on the 

phosphatic shale members.

As seen in outcrop, the chert ranges in color from 

nearly black to white, in thickness of bedding from less 

than 0.02 foot to nearly 10 feet, and in character of bedding from planar to very irregular and massive. The 

chert may consist almost entirely of microcrystalline 

quartz or it may contain considerable amounts of silt 

and clay, quartz sand, or much less commonly 

apatite, calcite, and dolomite, In unweathered sections 

the more argillaceous chert is generally dark colored 

and thin and even bedded, whereas the purer chert is 

lighter colored and more irregularly bedded.

The argillaceous chert is particularly susceptible to 

weathering. Where fresh, it is olive gray and lightbrownish gray to grayish black, opaque, and dull or 

slightly resinous and has a splintery fracture; but on 

weathering it becomes weak yellowish orange and dusky 

yellow to white, porcelaneous or earthy, and much less
316 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

brittle and splintery in fracture. It may retain chertyappearing streaks on the interior of beds, but otherwise 

the weathered chert, as seen megascopically, closely resembles siltstone and has often been so described in the 

field. In thin section the only difference noted between 

specimens of weathered and unweatliered chert collected" 

from the same bed was a pervasive limonite stain in 

the weathered samples.

The purer chert ranges in color on fresh surfaces from 

brownish gray and medium gray to white. The luster 

is subvitreous and the fracture subconchoiclal. The 

thickness of bedding ranges from thin to very thick; 

where thin bedded, the individual beds, although continuous for long distances, commonly thicken and thin 

so that the bedding surfaces are midulant. Weathered 

surfaces range in color from light gray to weak yellowish orange or pale brown, probably depending on the 

original content of pyrite and carbonaceous matter; 

but, in marked contrast to the argillaceous chert, even 

extreme weathering has little other effect.

The predominant constituent of the chert is microcrytalline quartz. The average apparent grain diameter 

may be less than § microns or as large as 50 microns, 

but it is generally about 10 microns. The grain contacts are sinuous and, in many instances, apparently 

gradational, and the extinction is markedly undulant. 

Both the nature of the contacts and the undulant extinction may be an aggregate effect (Folk and Weaver, 

1952, p. 500). Although the grain size is generally 

rather uniform, many samples contain many poorly defined roughly circular areas about 20 microns in diameter, in which the grain size is less than 1 to 2 microns 

and within which are many inclusions. In addition to 

microcrystalline quartz, chalcedony is present in some 

thin sections as fibrous-appearing ribbons and festoons,, 

as spherulites, and as veins, but it rarely forms more 

than a small part of the total authigenic silica.

Clay commonly forms streaks, patches, and poorly 

defined laminae in the chert. The amount of clay, both 

in hand specimen and thin section, is difficult to determine, but comparison with the few A12O3 analyses of 

these cherts indicates that the clay content has generally 

been underestimated, in some beds by amounts of 10 or 

15 percent of the total rock. Small quantities of angular quartz silt are scattered through much of the chert, 

and the detrital grains in sandy chert may be either 

evenly disseminated in the microcrystalline quartz or 

concentrated into sandy laminae. Scattered dolomite 

rhombs 10-20 microns in diameter are common, but they 

rarely constitute more than a few percent of the rock. 

Quartz pseudomorphs of dolomite are scattered through 

some thin sections. Calcite is rare, but where present it 

has generally replaced the microcrystalline quartz.

Iron oxide grains, 5-10 microns in diameter and pseudomorphic after pyrite, are scattered through nearly 

all thin sections of chert that have been examined. Most 

individual grains are cubes, many of which are combined with octahedrons, but some are suggestive of 

pyritohedrons. The iron content of the chert beds that 

have been analyzed is remarkably high; total iron reported as Fe2 O3 in the Rex Chert Member at Big Sheep 

Canyon averages about 4 percent, and most beds of the 

Tosi Chert Member at Sheep Creek contain about 3 percent.

The amount of carbonaceous matter in the chert is 

small compared with that in the mudstone. Most beds 

that have been analyzed contain considerably less than 

1 percent, and only one contains as much as 2 percent; 

yet those containing only a percent or so of carbonaceous matter are generally colored black or nearly black.

Apatite occurs as rounded grains of probable organic 

origin, as pellets, and as canal fillings and replacements 

of siliceous sponge spicules. The total amount of apatite exceeds 4 or 5 percent in only a few chert beds that 

are either in or immediately adjacent to the phosphatic 

shale members.

The most striking feature of the chert as observed in 

thin section is the abundance of siliceous sponge spicules. 

The spicules in some thin sections are apparent in planepolarized light; others are inconspicuous in transmitted 

light but may be seen readily in reflected light or by 

dark-field illumination; in other thin sections the spicules are seen under crossed nicols as laths, ovals, and 

circles of quartz more coarsely crystalline than that 

of the matrix; in still others, only phosphatic axialcanal fillings can be seen. Nearly all the spicules are 

simple rods (oxea) that range from 0.01 to 0.8 millimeters in diameter. A few small diaxial and triaxial 

spicules have been noted; the rays are 10-20 microns in 

diameter and consist of isotropic apatite. The axial 

canals of the oxea are generally enlarged and have 

diameters as large as two-thirds the total diameter of 

the spicule. The enlarged canals may be filled with 

microcrystalline quartz, isotropic apatite, or, more 

rarely, glauconite. Carbonaceous matter is present in 

some canals (fig. 1157?), but clay fillings have not been 

identified. The fact that spicules having very different 

amounts of canal enlargement, spicules having quartzfilled canals, and spicules having apatite-filled canals 

may be seen in the same one field of view indicates that 

much of the solution of the spicules and filling of the 

canals took place before final accumulation of the 

sediment.

The apatite interiors of a few spicules seem to have 

formed by both the filling of enlarged canals and the 

replacement of silica in the canal walls. The apatite
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 317

interiors of the spicules consist of two distinct parts 

a central rod that is presumably the canal filling and 

a surrounding envelope that may have resulted from the 

replacement of silica adjacent to the central canal. However, most apatite spicule fillings and all glauconite fillings that have been seen in thin sections are structureless and exhibit no evidence of actual replacement.

The oxea are oriented subparallel to the bedding and 

may also be crudely oriented linearly within the bedding ; therefore, in some thin sections most of the spicules are seen in cross section, in others they are seen in 

longitudinal section, and in a few they are seen in alternating laminae of cross sections and longitudinal 

sections.

Nearly all the siliceous spicules consist of microcrystalline quartz, as described previously, but in at 

least one thin section they consist of chalcedony that in 

most spicules radiates from the central canal, although 

the chalcedony radiates from several centers within the 

body of several of the spicules. In cross section most 

spicules consist of microcrystalline quartz that is either 

unoriented or oriented with the C axis tangential to the 

spicule. Many, however, are spherulitic in cross section.

Figure 115^4 shows a relatively pure chert from the 

Tosi Member in which the spicules are extremely well 

preserved. The spicules are simple oxea, exceptionally 

large, some of which still retain the original concentric 

structure; some axial canals are moderately enlarged 

and filled with microcrystalline quartz. Some solution 

has occurred at spicule contacts, which is a feature uncommon in other samples. Figure 115# shows a slightly 

argillaceous and carbonaceovis chert from a bed that directly overlies the Retort Phosphatic Shale Member. 

Spicules are very abundant, but internal structure is not 

preserved. Figure 11561' shows an argillaceous chert, 

also from the Tosi Chert Member. The long, slender 

rods having high relief are apatite canal fillings, some 

of which are surrounded by a siliceous exterior. Figure 

115Z> shows a relatively pure chert of the Tosi Member. 

No siliceous spicules can be seen, but the abundant oriented apatite rods suggest that the rock was originally 

composed mostly of siliceous spicules.

The sequence of photographs illustrates why it is difficult to estimate the number of spicules. Spicules are 

apparent in the thin section shown in figure 115A because of the well-preserved internal structure, in figure 

115# because of the carbonaceous matter in the matrix, 

in figure 115(7 because of the matrix material and the 

canal fillings, and in figure 115Z> because of the canal 

fillings. If no carbonaceous or argillaceous matter 

were present in the thin section shown by figure 115#, 

the spicules would be extremely difficult to detect, as 

suggested by the parts of the specimen that contain little

709-931 O 63 4

matrix material. The presence of spicules in the specimen shown on figure 115Z> could not be deduced at all 

if the canals had not been filled with apatite. The absence of observable spicules, therefore, does not mean 

that they were not present originally. If one takes these 

factors into consideration, then the most reasonable estimate is that most of the silica in most of the chert was 

once in the form of spicules. Nevertheless, much matrix 

silica must be accounted for in some other manner.

M. W. de Laubenf els examined a number of thin sections of chert of the Phosphoria and stated (oral communication, 1957) that the general aspect of the fauna 

is that of the class Demospongia. Many families and 

species are represented, but no more than could be found 

in a modern Demospongia assemblage. The few diaxial 

and triaxial spicules may be of the class Hyalospongia 

but could also belong to Demospongia. De Laubenfels 

found no microseres and no lithistid types.

MINOR ROCK TYPES

Rocks consisting of mixtures of clay, quartz sand and 

silt, apatite pellets, and sponge spicules occur in the 

middle of the Retort Phosphatic Shale Member at Hogback Mountain. The relative amounts of the constituents differ, forming rocks such as phosphatic cherty 

mudstone and sandy and muddy chert, but the general 

aspects of the rocks are much more similar than the 

range of names suggests. The finer grained constituents are generally concentrated in mudstone laminae, 

but some of the pellets, quartz sand, and spicules are 

distributed throughout. The coarse laminae may 

thicken, thin, or pinch out. Many of the siliceous spicules have been partly or wholly replaced by isotropic 

apatite, and some of the mudstone has been silicified. 

The content of carbonaceous matter is low, generally 

only 1 percent or less, but it is sufficient to color the 

rocks medium and dark gray.

A rock type that occurs at the top of the Tosi Chert 

Member at several localities consists of mixtures of 

quartz silt, carbonate grains of silt size, and sponge 

spicules. Muscovite shreds and glauconite may also be 

present in small amounts. The carbonate, which is most 

commonly dolomite but in some beds is largely calcite, 

replaces partially or completely many of the siliceous 

spicules. The relative amount of the constituents is 

variable, the gross composition ranging from carbonatic 

chert to carbonatic mudstone to cherty carbonate rock. 

The rocks are generally thin bedded, and the color 

ranges from light gray to pale brown. One unusual 

variety of this rock type is found near the top of the 

Tosi at Lazyman Hill; the center of each bed of the 

thinbedded siltstone is cherty, whereas the upper and 

lower thirds are dolomitic, much of the dolomite clearly 

having replaced spicules.
318 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

7f -t ,^ .-*' ...!YJ - \-^^f»+ 4^<

jr.-" f -'i _ » £9 ? '-. m-r T ,._i i^gv^m^-

w'UMuS^ ->.f.i--

FIGURE 115. Photomicrographs of chert from the Tosi Chert Member of the Phosphoria Formation. A, Relatively pure spicular chert from 

Hawley Creek, Idaho. Axial canals of spicules are enlarged and filled with microcrystalline quartz clouded by minute unidentified 

inclusions. Ordinary light. B, Spicular chert from Sliderock Mountain, Mont. Carbonaceous matter stains the argillaceous matrix 

black Ordinary light. C, Argillaceous chert from Sheep Creek, Mont. Slim dark rods are apatite canal fillings. Note the triaxial 

apatite spicules (h) and the faintly visible siliceous spicules (s) surrounding some rods. Ordinary light. D, Chert from Wadhams 

bprmg, Mont., showing apatite rods and dolomite rhombs. Ordinary light.

TRACE ELEMENTS

The trace-element content of black shale and phosphorite has been studied by Krauskopf (1955), and the 

trace-element content of phosphorite in the Phosphoria 

Formation, by Gulbrandsen (1960b and written communication). Gulbrandsen's results confirm those of 

Krauskopf. Gulbrandsen (written communication, 

1961) found that the following elements are concentrated in the phosphorites of the Phosphoria by a factor 

of two or more over their crustal abundance: Silver,
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 319

zinc, vanadium, chromium, molybdenum, arsenic, antimony, selenium, strontium, uranium, and rare earths. 

According to Gulbrandsen, strontium, uranium, and 

rare earths are probably in the apatite mineral; the 

other elements are those commonly concentrated in black 

shale (Krauskopf, 1955, p. 422), and they probably owe 

their concentration in the phosphorites to the carbonaceous matter that is also present.

Gulbrandsen (1960b) listed the abundance of these 

elements, in weight percent, in phosphorite of the 

Phosphoria from all parts of the western phosphate 

field as follows:

Element

Ae AT __:_:_::_:::::::_______

Cr

Mo____ 

Nd

Sb _ - _ - _____ - _ __

Se

Sr _ ______

U _____________ ___ ______________

V

Yb_____-_--_______________________-

Zn

Mode

0 0003

004

1

003

03

0007

001

1

009

03

001

03

Maximum

0 003

02

3

03

03

004

007

1

021

1

003

03

The semiquantitative spectrographic analyses on page 

439 of samples from Sheep Creek are in accord with 

Gulbrandsen's results.

The occurrence of uranium in phosphorites of the 

western phosphate field has been summarized by McKelvey and Carswell (1956). The distribution of uranium in phosphorites of the Meade Peak Member in 

southeastern Idaho has been studied by Thompson 

(1953, 1954), and the distribution of uranium in the 

Phosphoria of western Wyoming has been analyzed 

by Sheldon (1959). An excellent study of the geochemistry of uranium in phosphorites has been published by Altschuler and others (1958) . It suffices here 

to note that in Montana, as in Wyoming (Sheldon, 1959, 

p. 100), there is a direct relation between uranium and 

phosphate. The correlation coefficient of radiometrically determined uranium to P2O5, based on 40 samples 

selected at random from analyses of samples from the 

Retort Member in lots 1234, 1239, 1240, and 1299, is 0.668 

(P<1 percent). The regression equation calculated 

from the same data is

wThere y is the weight percent uranium X 1,000, and x 

is the weight percent P2O5 .

CONTACT METAMORPHISM

Lowell (1955), described contact effects at several 

localities where igneous rocks have injected into or near 

Phosphoria strata. Most of the intrusives are andesitic

sills, but one is an apophysis from a quartz monzonite 

stock. In addition, he described Phosphoria strata in 

roof pendants or near the borders of large intrusive 

bodies, where metamorphic effects might be anticipated.

Near Mount Fleecer, nearly 4 miles northwest of Divide, Mont., a one-half-mile wide prong of quartz monzonite extends northward nearly 2 miles from a stock 

and occupies the axial part of an anticline. The prong 

is probably in conformable contact with the base of the 

Quadrant Formation and has replaced most of the underlying carbonate rock of the Carboniferous and probably also of the older formations.9 At the land surface 

the base of the Phosphoria Formation on the east limb 

of the anticline is 300-900 feet from the intrusive contact (Lowell, 1955, p. 723). If the contact between the 

quartz monzonite and the Quadrant is conformable, as 

appears likely, the stratigraphic distance from the 

Phosphoria to the intrusive is only 200-500 feet. Near 

the base of the prong, where an apophysis of quartz 

monzonite cuts across the Phosphoria and into the overlying Triassic strata, a series of thin lamprophyre sills 

described by Lowell (1955) occur within the Eetort 

Phosphatic Shale Member. Lowell (1955, p. 728) 

found that the light-gray phosphate rock and phosphatic shale within a few feet of the andesite sill are nearly 

white in thin section; much of the pelletal structure was 

destroyed, and the phosphate was converted to small 

irregular grains of apatite. Microscopic veinlets of 

quartz and spherulitic apatite occur in the shale, and 

most of the carbonaceous matter has been removed. 

Strata farther away are dark colored and appear to be 

unaltered.

Lowell noted that analyses showing only moderate 

amounts of P2O5 in the quartz monzonite seemed to conflict with field evidence indicating that 4 linear miles of 

the Phosphoria Formation had been engulfed by the 

quartz moiizoiiite. Analyses of the quartz monzonite 

from the vicinity averaged 0.22 percent P2O5 ; four analyses from the apophysis averaged, 0.15 percent P2O5 ; 

and two analyses of the lamprophyre sills averaged 0.90 

percent P2O5 . Grout and Balk (1934, p. 884) considered 

the small stock exposed south of Mount Fleecer to be a 

branch or offshoot of the Boulder batholith. Thus the 

P2O5 gained by assimilation of phosphate rock might 

have been so diffused by dissemination through the magma as to be undetectable in chemical analyses. The 

Retort Member in this region is 20-30 feet thick and 

contains an average of 20 percent P2O5 - Addition of 

this phosphate to a column of magma 1 mile high would 

raise the P2O5 content of that magma only 0.08-0.11 

percent. A thicker column of magma and lateral disB Moore, G. T., 1956, Geology of the Mount Fleecer area, Montana: 

Indiana Univ.. Ph. D. thesis.
320 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

tribution by convection could easily combine to remove 

evidence of any contamination.

In the Highland Mountain area, where the Permian 

strata are located in the central part of a large roof 

pendant in quartz monzonite of the Boulder batholith, 

two andesite sills 4-9 feet thick intruded the Retort 

Member and a much thicker one intruded at the Quadrant-Phosphoria contact. The lack of contact metamorphism in the Eetort Member and sharp contacts with 

the andesite sills indicate that the sills were injected at 

a fairly low temperature and without assimilation of 

phosphatic material; but shale has been brecciated at 

one of the contacts, and much quartz has been introduced into some of the breccia fragments (Lowell, 1955, 

p. 725).

Lowell stated (1955, p. 725) : "Carbonaceous matter (?) may have been converted to fixed carbon by the 

heat of the intrusive to produce the black color of the 

phosphate rocks." This supposition coincides with our 

observations in sampling the beds of lot 1404 at a bulldozer trench cut below the zone of superficial weathering. There a 14-foot sequence of phosphorite and shale 

is underlain by a much altered porphyritic sill, presumably andesite, of undetermined thickness. The beds 

in the lower part of the section are grayish black to dark 

gray, those in the upper part are somewhat lighter, and 

the shaly layers at the top of the interval are medium to 

yellowish gray. All equipment used during the sampling became unusually dirty, much as they would from 

working in graphitic schists, and remained so thereafter. Although the dark color of these rocks, which appears in thin section to be a black matrix for quartz and 

collophane, suggests a fairly high content of carbonaceous material, the 14 samples averaged only 1.68 percent carbonaceous matter. It seems probable that much 

of the carbonaceous material occurs in the form of 

graphite, which would not be detected in the chemical 

analyses.

Lowell (1955, p. 730) described sills and dikes in the 

Maiden Rock mine, a few miles southeast of the Fleecer 

Mountain stock and southwest of the main mass of the 

Boulder batholith. The dikes and sills are much altered 

but had a composition apparently similar to the quartz 

monzonite of the large igneous bodies. Contacts with 

the phosphatic shales of the Retort Member are locally 

irregular, and small inclusions of the shale occur as 

much as 2 inches within the dike. Although Lowell 

found physical evidence of some assimilation, chemical 

analyses of two dike rocks showed only 0.18 and 0.22 

percent P2O5 , respectively.

A small andesitic sill occurs in the phosphatic shale 

at the South Boulder section (lot 1365), where, as 

Lowell (1955, p. 733) concluded, the induration of the

shale units next to the sill was the only metamorphic 

effect.

At Jack Canyon (lot 1218) in the Madison Range, 

a 4-foot andesite porphyry sill occurs near the base of 

the Retort Member. The sill is underlain by a thin 

layer of sandy phosphorite containing pellets and oolites 

in a darker matrix; the phosphorite in turn grades 

downward into fine-grained phosphatic sandstone containing abundant quartz overgrowths. In the sandstone within a few inches of the intrusive, much of the 

apatite in the matrix between quartz grains has been recrystallized to clusters of very fine grained (3-10 microns) clear apatite (fig. 116). The quartz overgrowths 

are characteristic of the Shedhorn Sandstone and apparently formed much earlier than recrystallization of 

the apatite. In the phosphorite layer some of the quartz 

grains appear to have been corroded and partly replaced by apatite. These features seem to be related 

directly to the heat from the sill.

At Kelley Gulch (lot 1249) a dike of probable dacitic 

composition has intruded the Retort Member. It appears to be about 30 feet thick but is exposed only in the 

hand trench and may be a very irregular body. The 

rock is strongly banded, chiefly dark gray to black having streaks of white, and shows a well defined flow structure. It contains very abundant angular inclusions of 

dark chert and mudstone of the Phosphoria Formation 

1-40 mm across, around which the flow bands are 

draped. In thin section many smaller inclusions are 

visible; they include quartz, sandy phosphatic chert 

containing abundant sponge spicules, phosphate pellets, 

and quartz-siltstone fragments. The groundmass is 

submicrocrystalline and contains euhedral phenocrysts 

of plagioclase and strongly corroded quartz. No contact effects with either the country rock or the inclusions 

have been noted, and the fine texture of the rock matrix 

and the well-defined flow structure indicate that the 

rock was forcefully injected at a low temperature and 

probably at shallow depth.

STRATIGRAPHY

MEADE PEAK PHOSPHATIC SHALE MEMBER

The Meade Peak Phosphatic Shale Member of the 

Phosphoria Formation was named by McKelvey (McKelvey and others, 1956, p. 2845) for Meade Peak in 

southeastern Idaho. In the type area the member consists of about 200 feet of phosphorite, carbonaceous 

mudstone, phosphatic mudstone, and dark dolomite and 

limestone. It is overlain by the Rex Chert Member of 

the Phosphoria and underlain by a tongue of the Grandeur Member of the Park City Formation. Most of the 

commercial phosphorite in the western phosphate field 

is produced from the Meade Peak. In southwestern
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 321

FIGURE 116. Very sandy phosphorite from top of phosphatic sandstone bed (Rt-10) underlying 4-foot andesitp(?) porphyry sill at Jack 

Canyon (lot 1218), Madison Range. A, ordinary light; B, crossed nicols. Note in B that much of the apatite is recrystallized, apparently by heat of intrusion, although apatite rims around quartz grains remain isotropic. Apatite farther from intrusive is not 

recrystallized. q, quartz grains; a, apatite.

Montana, as in southeastern Idaho, the Meade Peak 

Phosphatic Shale Member is characterized by phosphorite, black shale, and dark carbonate rock. In Montana 

the Meade Peak is thinner and less extensive and has 

been economically less important than the Retort Phosphatic Shale Member, which occurs higher in the section. Mining of the Meade Peak Member, however, was 

started in the Centennial Mountains in 1956, and the 

member is potentially more important economically than 

the Retort Member over much of the southern part of 

the area.

The Meade Peak Phosphatic Shale Member is underlain by the Grandeur Member of the Park City Formation throughout southwestern Montana, with the exception of that part in the vicinity of Quadrant Mountain, 

Yellowstone National Park. At Quadrant Mountain 

the underlying beds have been assigned to the Quadrant 

Formation, although the uppermost 40 feet are probably 

equivalent to beds included elsewhere in the Grandeur. 

The lower contact of the Meade Peak is normally sharp 

and planar, although at a few localities, such as Quadrant Mountain, phosphatic sandstone grades downward 

into nonphosphatic sandstone (Condit and others, 1928,

p. 188). Although the contact between the Grandeur 

Member of the Park City and the Meade Peak Member 

seems conformable where seen in outcrop, the regional 

stratigraphic relations show that the older rocks must 

have been eroded in the eastern half of the area prior 

to deposition of the Meade Peak. The strongest evidence of such erosion is the absence east of the Ruby 

River of the upper terrigenous beds of the lower member of the Park City or of any rock types that could 

be their shoreward equivalent. Thus the basal bed of 

the Meade Peak oversteps the upper part of the lower 

part of the Park City to the east. In the southwestern 

part of the area, there is little or no evidence of either 

overstepping or pre-Phosphoria erosion.

The contact of the Meade Peak with the overlying 

Rex Chert Member of the Pliosphoria is also sharp and 

distinct; the soft phosphorite and flaky mudstone of 

the Meade Peak contrast with the hard platy thinbedded chert of the basal part of the Rex. In much of 

the southern part of the area, the contact is marked by 

a thin phosphorite bed that is commonly skeletal and 

locally cherty. In the Gravelly Range where the Meade 

Peak is overlain by a tongue of the lower member of
322 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

the Shedhorn Sandstone, the highest phosphorite bed is 

separated from the relatively nonphosphatic Shedhorn 

by a bed of phosphatic sandstone that is included in 

the Meade Peak.

The distribution and thickness of the Meade Peak 

Member in southwestern Montana are shown in figure 

117. Very generally, the Meade Peak extends northnorthwestward into Montana as a tongue, thicker on 

the west than on the east, to Big Hole Canyon, the 

northernmost locality where the member has been found.

The eastern edge of the tongue roughly coincides with 

the Madison Valley, and the western edge is between 

Big Sheep Canyon, Mont., and Hawley Creek, Idaho. 

The thickest section of the member is at Big Sheep Canyon, where it is nearly 30 feet thick. Other thickness 

maxima are at Sawtooth Mountain, where the member 

is 16 feet thick, and in the Centennial Mountains, where 

it is as much as 18 feet thick. An area of thinning 

extends southeastward from the Sheep Creek-Dalys 

Spur region.

113°

45'

111°

EXPLANATION

 25 

Isopach

Contour interval 15 feet

Isopleth of percent P2Os in member

Contour interval 5 percent

FIGURE 117. Isopach map of the Meade Peak Phosphatic Shale Member of the Phosphoria Formation. X, control point showing measured

thickness ; A, control point, data approximate.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 323

In the Centennial Mountains where Honkala has 

mapped the Permian rocks in detail and measured a 

number of closely spaced sections, the Meade Peak 

Member changes radically in thickness within short 

distances and is absent in two areas (Honkala, 1953, 

pis. 2 and 4). One area in which the member is absent 

is between i/2 and 1 mile in diameter, which is too small 

to show on the thickness and facies maps; the other area 

is on the extreme west end of the area mapped by Honkala, and its extent, although not known, is assumed 

to be small.

The great distance of the Meade Peak Member at 

Quadrant Mountain from other exposures of the member and the necessitated sharp change in the trend of 

the zero isopach line in both Montana and Wyoming 

(Sheldon, 1957, fig. 13) indicate that the member at 

Quadrant Mountain may be part of an isolated lens. 

Evidence of such lensing is reported by Condit and 

others (1928, p. 189), who state that at the Quadrant 

Mountain section the beds now assigned to the Meade 

Peak Member consist of more than 3 feet of phosphorite, 

whereas at Bannock Peak 3 miles to the southeast, the 

same unit is an inconspicuous phosphatic sandstone.

The areal variation in lithologic character of the 

Meade Peak Member is shown in figure 118. The notable features are (1) the area of combined carbonate, 

apatite, and mud near Lima which coincides with the 

area of maximum thickness of the member, (2) the 

apatite-rich band around the edge of the area in which 

the member occurs, and (3) the change in character 

within short distances in the Gravelly Kange. Lithologic variation similar to that in the Gravelly Range 

would probably be found near the edge of the member 

in other areas if sections were as closely spaced. The 

distribution of carbonate rock in the Meade Peak Member is further shown in figure 119, which was constructed 

by totalling the thickness of all beds of carbonate rock 

in the member at each locality. The map shows a striking local concentration of carbonate rock west of Lima.

The Meade Peak Member can be divided into two 

parts in the Tendoy Mountains, the Snowcrest Range, 

and the Centennial Mountains. These are a lower 

phosphorite, which locally contains minor interbeds of 

mudstone and dolomite, and an upper phosphatic mudstone consisting of interbedded mudstone, phosphatic 

mudstone, phosphorite, and, locally, dolomite. The location of the boundary between the two units is uncertain in the Tendoy Mountains, and the units cannot be 

correlated northward to the Dillon area with any confidence. Nevertheless, the phosphorite in the northern 

sections is probably the continuation of the lower phosphorite, as is suggested by the occurrence of an upper

mudstone at Sheep Creek, Dalys Spur, and Big Hole 

Canyon.

LOWER PHOSPHORITE

The lower phosphorite of the Meade Peak ranges 

from 0 to 12 feet in thickness in the Centennial Mountains, is nearly 9 feet thick at Big Sheep Canyon, and 

is nearly 7 feet thick at Sawtooth Mountain (fig. 120).

The lithologic character of the lower phosphorite is 

somewhat variable (fig. 121), but everywhere, with the 

possible exception of Sheep Creek, it has either been 

deposited from or reworked by currents. The minor 

constituents of the bed range from conglomerate in the 

Gravelly Range to sand in the central part of the area 

and to mud in the Lima region.

Honkala (1953, p. 18) found that the lower phosphorite in the Centennial Range is split by lenses of 

sandy carbonate rock and carbonatic sandstone that 

pinch out within remarkably short distances. For example, a lens 4 feet thick may pinch out in less than 

10 feet along strike.

The upper phosphatic mudstone consists of relatively 

barren mudstone that contains thin interbeds of phosphorite and phosphatic mudstone. It is present 

throughout the Tendoy Mountains, where it is as much 

as 20 feet thick, the Snowcrest Range, where it ranges 

from 1 to 10 feet in thickness and the Centennial Mountains, where it is locally more than 7 feet thick. It 

disappears eastward by thinning of the mudstone and 

consolidation of the phosphatic layers and cannot be 

distinguished from the basal phosphorite east of the 

Ruby River. The upper phosphatic mudstone could not 

be traced with certainty northward from the Tendoy 

Mountains, but it may be represented by mudstone in 

the upper half of the Meade Peak at Dalys Spur, Sheep 

Creek, and Big Hole Canyon.

The character of both the mudstone and the apatite 

is the same wherever the upper phosphatic mudstone 

could be identified. The mudstone in the eastern Snowcrest Range may contain a smaller proportion of clay 

than the equivalent mudstone farther west, but the 

average grain size of the silt fraction is everywhere 

about 25-30 microns. The interbedded phosphorites are 

generally dark colored and pelletal and show little evidence of current action, with the exception of the thin 

phosphorite at the contact with the Rex chert. At 

several localities this phosphorite bed contains quartz 

sand, phosphatic skeletal fragments, and well-formed 

and rounded pellets that indicate current activity.

The Meade Peak Member in the Gravelly Range 

changes considerably in character within short distances, although the phosphorite itself is everywhere 

the current-deposited variety. At Canyon Camp more
324 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

112°

EXPLANATION

Apatite Carbonate (acid soluble 

other than apalite)

Patterns used singly in class I areas; combined in 

class n and in areas

FIGURE 118. Lithologic character of the Meade Peak Phosphatic Shale Member of the Phosphoria Formation. X, control point; A, control

point, data approximate.

than half the member consists of limestone, which is 

absent at Warm Springs Creek only 3 miles distant; 

most of the member at Lazyman Hill is composed of 

a chert bed 4 feet thick that is absent at Warm Springs 

Creek 6 miles northwest and at Alpine Creek 3 miles 

south; half the member at Alpine Creek consists of chert

and dolomite-pebble conglomerate that is not present in 

quantity in any of the neighboring sections.

Equivalents of the Meade Peak Member have not 

been identified with certainty in the Permian section 

in the Madison Eange; if any rock equivalents exist, 

they are probably insignificant in thickness, as is indi-
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 325

113° 112° 111°

MONTANA 

WYOMING

FIGURE 119. Thickness of beds of carbonate rock in the Meade Peak Phosphatic Shale Member of the Phosphoria Formation.

point showing measured thickness in feet; A, control point, data approximate.

X, control

cated by the marked thinning of the member in the 

Snowcrest and Gravelly Ranges. The manner in which 

the member terminates northward is not known, but 

there is no reason to believe that any significant part 

of the Permian section near Melrose or in the Three 

Forks area is equivalent to the Meade Peak farther 

south.

From the type area of the Meade Peak Phosphatic 

Shale Member in southeastern Idaho northward to Fall 

Creek in the Caribou Range of Idaho, the upper part 

of the Meade Peak passes into chert.and the lower part 

passes into dolomite containing minor chert (R. P. Sheldon, oral communication, 1957). The Meade Peak of

southwestern Montana is thus probably equivalent to 

only the central part of the member in southeastern 

Idaho.

REX CHERT MEMBER

The Rex Chert Member of the Phosphoria Formation 

was named by Gale for Rex Peak in the Crawford 

Mountains, Rich County, Utah (Richards and Mansfield, 1912, p. 684). McKelvey and others (1956, p. 

2847) pointed out that, although the strata near Rex 

Peak that were originally termed Rex consist largely 

of dolomite, subsequent usage has sanctioned the name 

as applying to the main chert unit of the Phosphoria. 

McKelvey therefore retained the name Rex but redesig-
326 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

113° 112° 111°

EXPLANATION

Isopach

Contour interval I foot; not contoured where unit is less than 

5 feet thick

- -25 

Isopleth of percent P2 O 5 in unit

Contour interval 5 percent

FIGURE 120. Isopach map of the lower phosphorite of the Meade Peak Phosphatic Shale Member of the Phosphoria Formation. X, control

point showing measures thickness in feet; A, control point, data approximate.

nated the type locality of the member as the Phosphoria 

Gulch area in southeastern Idaho and restricted the 

name to the dominantly cherty interval between the 

Meacle Peak Phosphatic Shale Member of the Phosphoria and the nonresistant mudstone and cherty mudstone at the top of the formation. As thus redefined, the 

Kex Chert Member at the type locality ''consists of a 

basal zone about 20 feet thick of nonresistant chert and

carbonate rock overlain by about 125 feet of resistant 

chert 1 ' (McKelvey and others, 1956, p. 2847).

The Kex Chert Member in southwestern Montana 

consists chiefly of bedded chert and locally contains 

minor amounts of cherty mudstone, phosphorite, and 

carbonate rock. It overlies the Meade Peak Phosphatic 

Shale Member of the-Phosphoria Formation, underlies 

the Fraiison Member of the Park City Formation, and
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

113° 112° 111°

327

MONTANA 

WYOMING

EXPLANATION

Nodules Oolites Skeletal fragments

Pellets are present at a/I localities

FIGURE 121. Character of apatite grains in the lower phosphorite of the Meade Peak Phosphatic Shale Member of the Phosphoria Formation.

intertongues eastward with the lower member of the 

Shedhorn Sandstone.

Both the upper and the lower contacts of the Rex 

Chert Member are generally sharp and conformable, 

but in some of the places where the Rex is directly overlain by sandstone, the upper contact is gradational. In 

parts of the Centennial Mountains and the Gravelly 

Range, the Rex Chert Member intertongues with the

Shedhorn Sandstone so that it is both overlain and 

underlain by sandstone.

The Rex Chert Member is approximately 80 feet thick 

in the central and western Snowcrest Range (fig. 122; 

from there it thins eastward, northward, and westward. 

The edge of the member could not be located accurately, 

but the Rex may extend as far eastward as the Gallatin 

River and as far northward as 10 or 20 miles south of
328 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

113° 112° 111°

MONTANA 

WYOMING

-20-

Isopach

Contour interval 20 feet

EXPLANATION

Isopleth of total thickness of 

mudstone beds in the Rex

Contour interval 5 feet

FIGURE 122. Isopach map of the Rex Chert Member of the Phosphoria Formation, x, control point showing measured thickness in feet;

A, control point, data approximate.

Butte. The Rex is only about a foot thick in the westernmost sections; so, it probably ends a few miles west 

of Kelley Gulch. It has not been identified at Hawley 

Creek.

A certain regularity exists in the vertical distribution 

of rock types within the member at several localities. 

A complete section consists of thin- and even-bedded 

dark-colored somewhat argillaceous chert at the base; 

the chert grades upward into lighter colored irregularly

bedded chert that in turn grades upward into lightcolored very thick bedded chert. The complete sequence 

is found at only a few localities; that at Hogback Mountain is the best example. The thin- and even-bedded 

chert is present at the base of the member in nearly all 

the thicker sections. The basal few feet are generally 

grayish black or dark gray, but higher in the member 

the color is lighter. The irregularly bedded chert overlies the evenly bedded chert at many Ipcalities, but at
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 329

a few localities, such as Wadhams Spring, very thick, 

bedded chert rests directly on the evenly bedded type. 

At other localities, Sliderock Mountain for example, irregularly bedded chert continues to the top of the member.

Variation of the proportions of the chert types at 

different localities results in regional differences in 

aspect of the Rex. Thus, most of the member at Little 

Sheep Creek and Wadhams Spring consists of thinand even-bedded chert, whereas most of the member in 

the eastern Snowcrest Range consists of irregularly 

bedded chert. Most of the Rex at Sheep Creek is thinand even-bedded, whereas at Big Hole Canyon it is very 

thick bedded. The sections near Lima that are composed 

dominantly of the thin- and even-bedded chert also contain interbedded cherty mudstone that makes up 10 or 

15 percent of the member. Cherty mudstone occurs in 

the Rex also at Canyon Camp, but it cannot be traced 

to any of the neighboring sections.

A phosphatic bed occurs in about the middle of the 

Rex Chert Member in the Tendoy Mountains and the 

western Snowcrest Range. It is more than a foot thick 

in places and ranges from phosphatic chert to phosphorite in lithologic character. The apatite grains show 

the effects of current action, and in most localities the 

bed consists of mixtures of well-formed and rounded 

pellets, oolites, and skeletal fragments.

The Rex Chert Member ends eastward by thinning 

and by intertonguing with the lower member of the 

Shedhorn Sandstone. The facies change from chert 

to Sandstone is most convincingly shown by comparing 

the section at Sliderock Mountain with that at Alpine 

Creek (fig. 12). The Rex probably ends to the north 

in part by pinching out, but the upper half of the Rex 

in the Tendoy Mountains may be the equivalent of the 

lower part of the Franson in the Dillon area.

The lower part of the Rex Member at Big Sheep Canyon in the Tendoy Mountains consists largely of mudstone and cherty mudstones that intertongue northward 

and eastward with chert more typical of the Rex.

The presence of the mudstone and cherty mudstone 

and also of a thin phosphorite bed in the Rex Member 

in the Tendoy Mountains suggests that at least the 

lower half of the Rex in that region may be the equivalent of part of the Meade Peak Phosphatic Shale Member of southeastern Idaho. Such a facies change would 

be in accord with the regional relationships, for R. P. 

Sheldon (oral communication, 1957) stated that the 

lowest part of the Rex is formed by progressively older 

rocks northward in Idaho.

RETORT PHOSPHATIC SHALE MEMBER

The Retort Phosphatic Shale Member of the Phosphoria Formation was named by Swanson (in

McKelvey and others, 1956, p. 2850) for Retort Mountain in the Blacktail Mountains about 10 miles south 

of Dillon, Mont. Although natural exposures exist in 

the type locality, in 1959'the member was best exposed 

in a bulldozer trench just east of the road crossing the 

divide between Small Horn Canyon and Sheep Creek 

drainages. This is the Sheep Creek locality, lot 1234, 

of this report. The Retort is the D member or unit of 

earlier reports.

The Retort Member at the type locality consists of 

60 feet of pelletal phosphorite, phosphatic mudstone, 

and mudstone mostly grayish and brownish black 

and contains 11.5 percent P2O5 (or nearly 30 percent 

apatite) and nearly 9 percent carbonaceous matter. It 

rests conformably on sandstone of the Franson Member 

of the Park City Formation, and at the top grades upward through a phosphatic sandstone bed 0.8 foot thick 

into the upper tongue of the Shedhorn Sandstone.

The Retort Member is underlain by sandstone and 

carbonate rock of the Park City Formation in the Melrose and Dillon areas and west of Lima, but elsewhere 

it is underlain by a tongue of the lower member of the 

Shedhorn Sandstone. Throughout much of southwestern Montana, the contact of the phosphorite and 

dark mudstone of the Retort with the underlying nonphosphatic light-colored rocks is gradational through 

a thickness of generally 2 feet or less, but at Cave Creek, 

it is gradational through as much as 6 feet. Elsewhere, 

as at the type section, the contact is sharp and 

conformable.

The Retort is overlain by a tongue of the Shedhorn 

Sandstone from West Fork of Blacktail Creek to Hogback Mountain in the Snowcrest Range, at Sheep Creek, 

and locally in the Melrose area. It is overlain by noncarbonaceous mudstone and cherty mudstone of the 

cherty shale member of the Phosphoria Formation west 

of Lima, but in nearly all other areas, it is overlain by 

the Tosi Chert Member. The upper contact is commonly gradational through an interval of a foot or less. 

Locally in the eastern part of the area, mudstone of 

the Retort grades upward into the Tosi Chert Member 

through an interval of interbedded chert and mudstone c5

as much as 20 feet thick, and where such gradation occurs, only the part that is dominantly mudstone is included in the Retort.

The Retort Member is about 85 feet thick along an 

axis trending northeast from Big Sheep Canyon to 

Hogback Mountain. From the axis the member thins 

to the east, north, and west (fig. 123). It pinches out 

between Sappington Canyon and the Three Forks section in the northeastern part of the area, and although 

the edge cannot be located elsewhere, it probably extends southeast from Three Forks to a short distance
330 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

113° 112° 111°

-20-

EXPLANATION

Isopach

Contour interval 20 feet

Isopleth of percent P2 O 5 in member

Contour interval 5 percent

FIGURE 123. Map showing thickness and P2O5 content of the Retort Phosphatic Shale Member of the Phosphoria Formation. X, control

point, showing measured thickness in feet; A, control point, data approximate.

east of Cinnabar Mountain. The member extends at 

least 45 miles north of Butte to the Elliston and the 

Garrison-Avon districts and perhaps as much as 60 

miles to the northwest in the Garnet Range near Drummond. The westward extent of the member is not 

known, but the rapid thinning; from Big Sheep Canyon 

to Hawley Creek and the oolitic nature of the phosphorite at Hawley Creek both suggest that the Retort 

was not deposited much farther west than the Beaverhead Range.

The lithologic character of the Retort- Member is 

shown in figure 124. Apatite is not anywhere dominant, 

but it is most abundant in two belts; one belt extends 

northward from Lima through Dillon and roughly coincides with the area of maximum thickness of the member, whereas the other is in the eastern part of the field, 

where the member is thin. This distribution is somewhat similar to that in the Meade Peak Member, in 

which apatite is abundant both in the area where the 

member is thickest and nearer the feather edge.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 331

The Ketort Phosphatic Shale Member can be divided 

into three facies on the basis of the character of the 

phosphorite. The facies are (1) The nodular-phosphorite facies, characterized by dark argillaceous pelletal phosphorite containing 10-20 percent of compound 

nodules; (2) the pelletal-phosphorite facies, containing 

dark pelletal phosphorite but no nodular, colitic, or

skeletal beds; and (3) the marginal facies, characterized 

by oolitic and skeletal phosphorite. The marginal 

facies is found generally east of the Euby Eiver, near 

the Jefferson Kiver, and in the Beaverhead Eange; the 

pelletal facies is found in the area between the Beaverhead and Ruby Eivers; and the nodular facies is found 

in the Tendoy and Pioneer Mountains. The member in

45

113° 112°

MONTANA 

WYOMING

EXPLANATION

Apatite

Patterns used singly in class I areas; combined i 

class H andffl areas

Carbonates and carbonaceous mattar (acid 

insoluble other than 

apatite)

FIGURE 124. Lithologic character of the Retort Phosphatic Shale Member of the Phosphoria Formation. X, control point.
332

part of the northern Madison Range consists of a local 

pelletal f acies located in the area of the marginal f acies. 

The overall f acies distribution, then, is as follows: The 

marginal f acies occurs in the eastern and westernmost 

parts of the area; it grades through the pelletal f acies 

into the nodular f acies, which occurs in the area where 

the member is the thickest.

The gradation between the pelletal and nodular f acies 

consists of an increase in the number of nodule-bearing 

beds and in the degree of induration of the nodules. 

In the Sheep Creek section, for example, few nodules 

were apparent in the freshly exposed rock, but weathering over a period of several years revealed compound 

nodules similar in size and distribution to those found 

in sections farther west, that consisted of pellets somewhat better cemented than those in the surrounding 

rock.

Although the coincidence is far from perfect, the carbonate rock (fig. 125), mostly dark aphanitic dolomite, 

is concentrated in the nodular phosphorite f acies of 

the Retort Member. The content of the carbonaceous 

matter (fig. 126) shows no obvious relation to f acies. 

The Big Sheep Canyon and Kelley Gulch sections of the 

Retort are both located in the nodular phosphorite 

facies, but the rocks at Big Sheep Canyon are highly 

carbonaceous and average 8.4 percent carbonaceous matter, whereas those at Kelley Gulch, although dark in 

color, average only 1.2 percent.

The three facies are further compared in figure 127, 

iu which frequency diagrams were constructed in the

MONTANA 

WYOMING

x°

10 0 10 20 30 MILES 

l , , , , l l i l

FIGURE 125. Percent carbonate rock in the Retort Phosphatic Shale Member of the Phosphoria Formation. X, A, control points.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

113° 112° 111°

333

FIGURE 126.- -Content of carbonaceous matter in the Retort Phosphatic Shale Member of the Phosphoria Formation. X, control point

showing percent carbonaceous matter in member.

same manner as those in figure 105. The nodular phosphorite facies consists mostly of phosphatic mudstone 

and contains some carbonate rock and carbonatic mudstone but little high-grade phosphorite. The pelletal 

phosphorite facies, as exemplified by the Sheep Creek 

and Hogback Mountain sections, also consists largely 

of phosphatic mudstone; it contains practically no calcareous and dolomitic beds but does include some highgrade phosphorite. In the Melrose district, however, 

pelletal phosphorite makes up a large part of the facies. 

The marginal facies does not have the well-formed 

phosphatic-mudstone mode present in the other two 

facies but contains a larger proportion of both carbonate rock and phosphorite. Details of the frequency

709-931 O 63 5

distributions differ, depending, of course, on which 

localities are selected to typify the different facies, but 

the general relations discussed above are probably common to the facies as a whole.

According to McKelvey (1949, p. 272), the beds composing the Meade Peak Phosphatic Shale Member of 

the Phosphoria Formation in southeastern Idaho are 

remarkable for their great lateral continuity. For example, the lower phosphate bed, the "cap" limestone, 

the "false cap" limestone, and many other beds can be 

traced from the Fort Hall region of Idaho southward 

to the Utah border, a distance of about 75 miles. In 

the Retort Member in Montana, however, detailed correlations can be made among only a few localities, andy
334 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

APATITE

Nodular Phosphorite Facies

(lot 1224)

Not contoured because of small 

number of analyses

APATITE

.CALCITE

AND 

DOLOMITE

Pelletal Phosphorite Facies 

(lots 1234 and 1299)

APATITE

DOLOMITE

Marginal Facies DOLOMITE 

(lots 1318, 1362, and 1365) UULUMI 11

EXPLANATION

Sample density, in percent

0-5 5-10 >10

FIGURE 127. Mineral composition of rocks in three facies of 

the Retort Phosphatic Shale Member of the Phosphoria 

Formation.

in general, individual beds of the Retort are undoubtedly less extensive than those of the Meade Peak Member in southeastern Idaho.

The Retort Phosphatic Shale Member in the type 

section at Sheep Creek, Mont., consists of three parts: 

the lower unit, 26 feet thick, consists mostly of interbedded phosphorite and phosphatic mudstone; the middle unit, a little more than 15 feet thick, consists of nonphosphatic carbonaceous mudstone; the upper unit, 19 

feet thick, consists of phosphorite and phosphatic mudstone similar to that in the basal unit. The upper phosphatic unit either pinches out OT grades into mudstone 

to the west, so that at Cedar Creek the Retort consists 

of only the lower two units (pi. 24).

The three units that compose the Retort Member at 

the type locality at Sheep Creek could not be traced 

with confidence either northward, eastward, or southward. The member at Kelley Gulch consists of three 

parts: The lower 30 feet is composed of interbedded 

phosphorite, phosphatic mudstone, mudstone, and dolomite ; the overlying 14 feet consists of barren mudstone; 

and the uppermost 10 feet is composed of mudstone that 

contains several interbeds of phosphorite. These threeunits are possibly the equivalents of the three units at 

the type section and at Dalys Spur, but this correlation 

is by no means certain, for the mudstone unit at Kelley 

Gulch is intruded by a dike that may have displaced 

some strata. Correlating the Retort at Kelley Gulch 

with that at Big Hole Canyon by way of the section at 

Cave Creek suggests that the upper phosphatic zone at 

Kelley Gulch is thicker and more phosphatic and that 

the middle mudstone thins eastward in a manner similar 

to the changes occurring from Dalys Spur to Sheep 

Creek. The Retort Member at Big Hole Canyon would 

thus consist of the upper and the lower phosphatic zone, 

as at Kelley Gulch, which are not separately recognizable in the absence of the middle mudstone. On the 

other hand, correlation by way of the Greenstone Gulch 

section rather than the Cave Creek section suggests that 

nearly all the Retort at Big Hole Canyon is the correlative of only the lower phosphatic zone at Kelley Gulch. 

The Cave Creek section, like that at Kelley Gulch, is 

cut by igneous intrusions, and much of the member at 

Greenstone Gulch is sheared and faulted; therefore, no 

clear choice can be made between the two possible correlations. The Retort Member at Big Hole Canyon is similar to that in the Melrose area, but it contains more 

dolomite and has phosphorite that is slightly lower in 

grade. The difficulty of correlating southward from 

the type area of the Retort is evident from plate 24.

The Retort Member in the Tendoy Mountains contains much carbonate rock in comparison with the member in the type locality, and much of the phosphorite is
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 335

nodular. The upper one-third or two-thirds of the 

member consists of black mudstone that contains little 

apatite. Most of the carbonate rock pinches out northeastward from the Tendoy Mountains into the Snowcrest Range; the phosphorite in the Snowcrest Range 

is not nodular but is almost entirely pelletal, and phosphorite beds occur at the top of the member (fig. 91). 

In the Snowcrest Range, the Retort changes abruptly 

in thickness and character within short distances; the 

lower half of the member is highly phosphatic at the 

West Fork of Blacktail Creek, barren at Sawtooth 

Mountain, phosphatic again at Hogback Mountain, and 

absent at Canyon Camp. These apparently erratic 

changes in the lower part of the section result probably 

from the fact that the line of sections crosses and recrosses facies strike; the interval actually passes from 

interbedded phosphorite and mudstone to barren mudstone and finally pinches out. The chert and sandstone 

in the middle of the Retort at Hogback Mountain seem 

to pinch out to the west rather than to grade into mudstone; but to the east in the Gravelly and Madison 

Ranges, they may be represented by chert and sandstone at the base of the Retort and at the top of the 

lower member of the Shedhorn Sandstone.

Whatever the details of the eastward change may be, 

the shale and phosphorite of the Retort in the Gravelly 

Range appear to be the equivalent of only the upper part 

of the member in the Snowcrest Range. The correlation of the member from Alpine Creek in the Grevelly 

Range to Indian Creek in the Madison Range is simple 

and direct; although the member at Indian Creek contains somewhat more phosphorite, it would not seem out 

of place if substituted in the section at Alpine Creek.

Farther south in the Gravelly Range and in the Centennial Mountains, the upper part of the Retort Member consists of nonphosphatic mudstone that is probably 

equivalent to the basal beds of the Tosi Chert Member 

in the northern Gravelly Range and may be a tongue 

of the cherty shale member of southeastern Idaho.

The member also includes progressively younger 

rocks from Indian Creek to Shell Canyon in the Madison Range (pi. 22) ; thus at Shell Canyon, the upper 

contact is probably higher in the section than it is in 

the northern Gravelly Range section and is probably 

also higher than in the Snowcrest Range section. Between Shell and Jack Canyons, the Retort intertongues 

with the lower part of the Tosi Chert Member, and the 

contact at Jack Canyon is therefore lower in the section than at Shell Canyon.

The correlation of the Retort from Big Hole Canyon 

to South Boulder Creek (pi. 19), a distance of 38 

miles across facies strike, has been made largely by 

analogy with the line of sections shown in plate 21,

where the lower half of the Retort pinches out to the 

east and the upper half passes only to a minor extent 

into chert. Thus the Retort at South Boulder Creek 

is probably equivalent to the upper part of the member at Big Hole Canyon, and the top of the member at 

South Boulder Creek is probably little if any lower in 

the section than it is at Big Hole Canyon. An alternate 

possibility that the upper part of the member in the 

Big Hole Canyon-Melrose area passes northeastward 

into chert and that the entire Tosi Member at South 

Boulder Creek is therefore the equivalent of the upper 

part of the Retort near Melrose has been advanced 

by Rooney (1956b) and is logical on the basis of the line 

of sections he presents. However, the correlation from 

the Snowcrest Range to the Madison Range and from 

there northward along the facies strike to Sappington 

Canyon supports the correlation presented herein.

Northward and eastward from South Boulder Creek, 

the mudstone of the Retort grades into chert so that at 

Three Forks the beds equivalent to the Retort consist of 

bedded chert containing thin phosphatic beds.

The changes in both the thickness and the lithologic 

character of the Retort from the Lima region westward 

can only be surmised inasmuch as at Hawley Creek 

most of the interval between the Tosi Chert Member 

of the Phosphoria and the Franson Member of the Park 

City is covered. The only phosphorite exposed at Hawley Creek consists of oolitic rock that rests directly on 

the Franson Member of the Park City Formation, but 

the covered interval is littered with muddy-chert and 

cherty-mudstone float. Thus, most of the Retort may 

pass westward into cherty mudstone, and the Retort itself at Hawley Creek is probably thin.

The stratigraphy of the Retort Member in southwestern Montana is summarized as follows: The lower half 

of the member pinches out east of the type section and 

is absent in the eastern half of the area. The upper 

half thins eastward and northeastward and passes into 

chert in the Three Forks area. Westward from the 

type area of the member, the upper half grades into 

mudstone and probably passes into cherty mudstone 

farther west. The lower half remains phosphatic farther to the west than the upper half.

Details of the relation of the Retort Phosphatic Shale 

Member in Montana to the Retort in western Wyoming 

and southwestern Wyoming are uncertain because of 

the distance 50 miles between exposures on the north 

and the south sides of the Snake River Plain and the 

Yellowstone Plateau. The upper part of the Permian 

section in the Gros Ventre Range of Wyoming and at 

Red Creek near the southern border of Yellowstone 

National Park consists of a thin Retort Phosphatic 

Shale Member overlain by about 50 feet of the Tosi
336 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Chert Member, which is in turn overlain by a tongue of 

the Sheclhorn Sandstone (Sheldon, 195T, pi. 13; McKelvey and others, 1956, fig. 2) ; the sequence is very 

similar to that found east of the Ruby River in Montana. The contact between the Retort and Tosi Members rises in the section west of the Gros Ventre Range, 

so that in the southern Teton Range of westernmost 

Wyoming, the upper tongue of the Shedhorn Sandstone 

rests directly on the Retort Member, the upper part of 

which is probably younger than any of the Retort in 

Montana. The same relation is suggested by the observation that the upper contact of the Retort rises 

somewhat in the section south in the Gravelly Range.

According to R. P. Sheldon (oral communication, 

1957) the Retort Member in the Big Hole Range of 

eastern Idaho is underlain by a highly phosphatic sandstone that can be traced eastward at least as far as the 

Gros Ventre Range of western Wyoming. In Montana, 

the beds underlying the Retort are generally not highly 

phosphatic, and the phosphatic sandstone of western 

Wyoming is possibly the equivalent of the sandstone 

in the middle of the Retort at Hogback Mountain. The 

lower half of the Retort in the Lima and Dillon areas 

would then be older than any beds included in the Retort 

in Wyoming or eastern Idaho. These inferred relationships are illustrated in figure 93.

TOSI CHERT MEMBER

The bedded chert that overlies the Retort Phosphatic 

Shale Member constitutes the Tosi Chert Member of 

the Phosphoria Formation. The member was named 

by Sheldon (in McKelvey and others, 1956, p. 2851) 

for Tosi Creek in the southern end of the Gros Ventre 

Range of western Wyoming, where it consists of 33 feet 

of bedded chert that overlies the Retort Member of 

the Phosphoria and underlies the upper tongue of the 

Shedhorn Sandstone.

In the westernmost exposures of Permian strata in 

southwestern Montana, the Tosi Chert Member consists 

of 90-150 feet of bedded chert that overlies mudstone 

of the cherty shale member or mudstone and phosphorite 

of the Retort Member and underlies calcareous mudstone of the basal part of the Dinwoody Formation. 

To the east, the Tosi passes into and intertongues with 

the upper member of the Shedhorn Sandstone. In the 

region from Big Hole Canyon southward to the central 

and eastern Snowcrest Range, the Tosi Chert Member 

and Shedhorn Sandstone are intertongued throughout 

the entire interval between the Retort and the Dinwoody Formation. East of the Ruby River most of the 

Tosi occurs as a distinct unit, 40-80 feet thick, between 

the underlying Retort and the overlying upper tongue 

of the Shedhorn Sandstone.

Figure 128 shows the regional variation in the thickness of beds assigned to the Tosi. The irregular thinning of the member to the east results in part from 

thinning of the interval but mostly from intertonguing 

with the Shedhorn Sandstone.

Vertical sequences of chert types that occur in the 

Tosi in parts of the area are similar to those in the Rex 

Member. In the Gravelly Range the basal few feet 

of the Tosi consists of argillaceous thin- and evenly 

bedded chert that is dark gray or brownish gray where 

unweathered. This chert passes gradually upward into 

thin and irregularly bedded chert that is less argillaceous and lighter colored. Still higher in the section, 

the thickness of bedding is about the same, but the undulant bedding surfaces are less distinct and the uppermost 10-30 feet of the chert has a massive appearance. 

In the Madison Range the chert is also argillaceous and 

thin- and even-bedded at the base of the member and 

contains many mudstone partings that are less evident 

upward. The chert is lighter colored, less well bedded, 

and variably sandy in the upper part of the section.

No such regularity in the vertical sequence of the 

chert is apparent in the rest of southwestern Montana. 

Most of the chert at both Sheep Creek and Wadhams 

Spring is argillaceous and thick- and even-bedded. At 

Big Sheep Canyon it is highly argillaceous and, for the 

most part, thin- and even-bedded. But at Hawley 

Creek, nearly all the chert is relatively pure and very 

thick bedded.

Although carbonate in amounts exceeding more than 

a few percent is uncommon in chert of the Tosi, both 

calcite and dolomite occur near the top of the section 

at several localities in carbonatic siltstone and chert. 

Discrete beds of dolomite, generally cherty, occur in the 

Three Forks area and in parts of the Centennial Mountains. Geodal vugs lined with calcite occur at Shell 

Canyon in the Madison Range.

A sequence of about 10 feet of sandy, dolomitic, and 

locally cherty siltstone beds that occur at the top of the 

Periman section in the Gravelly Range and the eastern 

Snowcrest Range has been included in the Tosi Chert 

Member, although it could nearly as logically have been 

placed in the Shedhorn Sandstone. It has not been 

placed in the basal part of the Dinwoody because the 

beds commonly contain both chert and glauconite, which 

are typical minerals of the Permian rocks.

CHERTY SHALE MEMBER

The Tosi Chert Member and the Retort Phosphatic 

Shale Member at Big Sheep Canyon are separated by 

nearly 60 feet of hard thin-bedded olive-gray mudstone 

that weathers into platy fragments. Similar mudstone, 

25 feet thick, occurs in the upper part of the Tosi Chert.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

113° 112° 111°

337

MONTANA 

WYOMING

FIGURE 128. Isopach map of the Tosi Chert Member of the Phosphoria Formation. X, control point showing measured thickness in feet;

A, control point, data approximate.

It contains very little apatite or carbonaceous matter. 

The contact of the cherty shale member with the underlying soft fissle and flaky grayish-black carbonaceous 

and slightly phosphatic mudstone of the Eetort is sharp, 

planar, and distinct. Although the hard platy mudstone does not seem to be cherty at Big Sheep Canyon, 

it closely resembles much of the rock of the cherty shale 

member of the Phosphoria Formation in the Fort Hall 

region in southeastern Idaho described by McKelvey 

and others (1956, p. 2849). Continuity with the cherty 

shale member of Idaho cannot be demonstrated, but the 

facies position of the mudstone of Big Sheep Canyon is 

such that continuity might be expected; that is, the general basimvard trend in the phosphate field is from

chert to cherty mudstone, and there is no reason to expect a reversal of the trend between the Lima region 

and the type area of the cherty shale member. For 

these reasons, the name cherty shale member is tentatively applied to the platy light-colored nonphosphatic 

and. noncarbonaceous mudstone at Big Sheep Canyon. 

Cherty mudstone is also present at Little Sheep Creek 

near Lima and may constitute most of the covered interval beneath the Tosi Chert Member at Hawley Creek; 

these rocks are also included in the member.

The cherty shale member at Big Sheep Canyon, 

passes eastward and probably northward and westward 

into chert of the Tosi Member. To the west, both the 

upper and lower contacts of the member may be lower
338 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

in the section, and if the covered interval at Hawley 

Creek is composed of cherty mudstone, it is probably 

the equivalent of the Retort Member at Big Sheep 

Canyon.

LOCALIZATION OF EXPLOITABLE PHOSPHATE 

DEPOSITS

Most phosphorite from the western field is treated 

either with sulfuric acid to produce fertilizer or in an 

electric furnace to produce elemental phosphorus. The 

sulfuric acid process requires rock having a minimum 

P2O5 content of 31 percent, whereas an electric furnace 

requires rock having a minimum of about 24 percent 

P2O5 . Acid-grade rock in beds as thin as 3 feet can be 

mined profitably if other factors are highly favorable, 

but rock of lower grade must occur in considerably 

thicker beds to be exploited successfully. The P2O5 

content of phosphatic rock can be increased by as much 

as 4 or 5 percent, to the required grade, if the greater 

thickness of the minable zone, favorable mining conditions, and favorable location offset the expense of beneficiation. The effects of rock type and of stratigraphic 

relations on the localization of deposits of minable 

thickness and grade are analyzed briefly here.

As discussed on page 310, the phosphorites can be 

grouped into two broad types: (1) those that were 

sorted and winnowed by currents, and (2) those that 

were not. Phosphorites of the first group contain little 

carbonaceous matter and little or no clastic matrix; cement, if present, is generally chert or apatite. Quartzsand grains may be admixed. In places, beds of current-washed phosphorite thicken and thin markedly, as 

the apatite sand had apparently been piled into banks 

and bars. At two localities in the western phosphate 

field in the Centennial Mountains and near Bear Creek 

in the Caribou Range of Idaho (Sheldon, 1957, p. 26) 

phosphorite of this type forms beds 12 feet thick, but at 

both places the beds thin markedly within short distances.

Phosphorites that do not show evidence of significant 

current activity are generally argillaceous and carbonaceous and are commonly interbedded and interlaminated 

with mudstone. The phosphorites and interbedded 

mudstones maintain their thickness and character over 

a considerable area.

Considering the characteristics of the two groups of 

phosphorites, one might expect to find acid-grade beds 

of minable thickness in units containing current-washed 

phosphorite, but because of thickness changes expectable in this type of rock, such deposits would be of relatively small extent. Beds of sandy phosphorite amenable to beneficiation might be found, but they would 

probably not be sufficiently thick or widespread to justify the expense. On the other hand, one would not

expect to find acid-grade beds of minable thickness in 

sections composed mostly of the phosphorite that shows 

little evidence of current activity, but furnace-grade 

beds of minable thickness might occur, depending on 

the abundance and thickness of mudstone and dolomite 

interbeds. Any such furnace-grade deposits would 

probably be of large extent.

In southwestern Montana, current-washed phosphorite is found principally in the lower part of the Meade 

Peak Member in the Centennial, Gravelly, and Snowcrest Ranges and in the marginal facies of the Retort 

Member. Acid-grade phosphorite of the currentwashed variety has been mined from the Meade Peak 

Member in the Centennial Mountains by J. R. Simplot 

Company; the high-grade bed there is as much as 11 or 

12 feet thick, thins to 4 or 5 feet within short distances, 

and is absent locally. Acid-grade rock of minable 

thickness has not been found elsewhere in the area discussed in this report, but it is at least possible that the 

basal bed of the Meade Peak Member may thicken sufficiently between measured sections in the Snowcrest 

and southern Gravelly Ranges to form small exploitable deposits. Approximately 12 feet of sandy current-washed phosphorite is present in the Retort Member at Cinnabar Mountain, but the rock would require 

beneficiation for furnace use. Its presence suggests 

that other small deposits might be found near the eastern margins of the Retort Member, but the available 

data are not encouraging.

In the area considered in this report, the phosphorite 

in the upper part of the Meade Peak Member and in 

the pelletal and nodular facies of the Retort Member 

is of the variety that shows little evidence of current 

activity. Furnace-grade rock has been mined from the 

Retort Member in the Melrose area; nearly the entire 

member is mined, but some beneficiation is required to 

raise the P2O5 content of the ore to the minimum grade 

required for the furnace charge. A minable thickness 

of furnace-grade rock has not been found in the member 

elsewhere in the area. South of Melrose mudstone interbeds become thicker and more abundant in the Retort. 

The upper part of the Meade Peak Member is both too 

thin and too low in P2O5 content to be an adequate source 

of furnace-grade rock.

SHEDHOBN SANDSTONE 

GENERAL CHARACTER AND DISTRIBUTION

The Shedhorn Sandstone has been defined as the 

dominantly sandy strata of Phosphoria age that occur 

within Yellowstone National Park and adjacent parts 

of southwestern Montana and northwestern Wyoming 

(Cressman and Swanson in McKelvey and others, 1956, 

p. 2852). The type section (locality 1362 of this report)
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 339

FIGURE 129. Type locality of Shedhorn Sandstone, northeast wall of 

Indian Creek Canyon, 0..3 mile below mouth of Shedhorn Creek, 

Madison Range, "fid Dinwoody Formation: psu, upper member of 

Shedhorn Sandstone ; Ppt and Pprt, Tosi Chert and Retort Phosphatic 

Shale Tongues of Phosphoria Formation ; ps|, lower member of Shedhorn Sandstone. Part of lower member of Shedhorn Sandstone, the 

Grandeur Tongue of Park City Formation, and top of Quadrant 

Formation hidden by trees.

is on the north side of Indian Creek in the Madison 

Range, Mont., one-quarter of a mile below the mouth 

of Shedhorn Creek (fig. 129).

At the type section the Shedhorn consists of an upper 

member ranging from 60 to 80 feet in thickness and a 

lower member 48 feet thick. The two members are 

separated by a tongue of the Phosphoria Formation that 

is nearly 50 feet thick, and the lower member is divided 

into two parts by a tongue of dolomite of the Franson 

member of the Park City Formation that is 7l/2 feet 

thick. Both members of the Shedhorn contain thin 

beds of chert that may be tongues of the Tosi and Rex 

Members of the Phosphoria, but, in the absence of clear

evidence for this correlation, they are included in the 

Shedhorn.

West of the type locality the upper member intertongues with the Tosi Chert Member, and the lower 

member intertongues with the Franson Member of the. 

Park City Formation and the Rex Chert Member of 

the Phosphoria. The sandstone tongues are identified 

with the name Shedhorn as far as they can be traced. 

The sandstone of the Shedhorn is distinguished from 

sandstone of the Quadrant Formation and of the Grandeur Member of the Park City Formation by the presence of apatite pellets and skeletal fragments and by 

the abundance of chert grains. Similar-appearing sandstone occurs in the Franson Member of the Park City 

Formation in the Tendoy Mountains and near Dillon, 

but the facies distribution (fig. 144) indicates that the<- 

sand came from a different source area and is not laterally continuous with the type Shedhorn.

The thickness and distribution of the Shedhorn Sandstone in southwestern Montana is shown in figure 130. 

Tongues of the upper member extend northward to the 

Garnet Range and southeastward to the Gros Ventre 

Range of Wyoming. The lower member has not been 

identified north of the area shown in figure 130, but in 

western Wyoming, tongues extend to the southern end 

of the Wyoming Range (R. P. Sheldon, oral communication).

LITHOLOGY

SANDSTONE

The Shedhorn Sandstone shows remarkable uniformity in grain size, sorting, composition of the detrital 

fraction, color, thickness of bedding, and hardness 

throughout the area; however, the amount and type of 

cementing material and the amount of glauconite differ 

widely from place to place.

The results of thin-section size analyses of samples 

of Shedhorn Sandstone are summarized in table 2 and 

in figure 131. The median diameter (uncorrected for 

sectioning) of 60 percent of the samples is in the very 

fine sand class, and the remainder is in the fine-sand 

class. The coarsest median diameter of any of the 

analyzed specimens is only 0.18 mm., and fine- and very 

fine grained sandstone undoubtedly constitutes most of 

the Shedhorn. Some medium-grained and finely pebbly 

sandstone has been seen, however, particularly in the 

lower part of the Shedhorn. The sandstone of the 

Shedhorn is extremely well sorted; the coefficient of 

sorting (So) of nearly 60 percent of the samples is less 

than 1.25, and that of the least well-sorted sample is 

only 1.37.

The sorting coefficients are plotted against the mean 

phi diameters in figure 132. The regression coeffcient,
340 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

112°

A 20

Permian rocks disconformably overlain by 

Ellis Group (Jurassic) north of line

WYOMING

X62 \

\ \ I Permian rocks disconformably overlain by > J

Dinwoody Formation (Triassic) east of line |

FIGURE 130. Isopach map of the Shedhorn Sandstone. X, control point showing measured thickness in feet; 

approximate.

control point, data

r, for the 28 pairs is 0.4316, which is significant (P< 

0.05 >0.01). The sorting coefficient /So varies inversely 

with Md$ ; that is, the sorting tends to improve as the 

grain size decreases.

The terrigenous fraction of the sandstone consists 

almost entirely of quartz and chert; feldspar grains 

are extremely scarce. The detrital quartz is very similar in character to that of sandstone of the Park City 

Formation, as the grains are mostly subangular and 

equant, although many of the coarser ones are subrounded and about 10 percent are elongate. Much less 

than one-fourth of the quartz grains show prominent 

strain shadows; these grains are generally crowded wTith 

bubble inclusions. The great majority of the grains

either have straight extinction or show slight straining; 

inclusions are not common, but wrhere present they 

consist of unoriented rutile needles, apatite, tourmaline, 

and planes of bubble inclusions.

Chert grains make up generally about 10 percent of 

the total sand-size fraction but may be present in 

amounts as much as 20 percent. This percentage is in 

marked contrast with those of sandstone of the Grandeur Member of the Park City and of the Quadrant 

which generally contain about 2 percent chert grains. 

The chert grains are similar in size to the associated 

quartz but are commonly somewhat better rounded. 

Most are shades of gray and brown, but a few are colorless or nearly so. In marked contrast with most sand-
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 341

DIAMETER, IN PHI 

234

DIAMETER, IN PHI 

234

100

Z 80

u 

O ir 

u Q.

u 60

40

20

All samples 3.21 

Lower half 3.45

Mean So 

All samples 1.23 

Lower half 1.24

Mean Md<f> 

Lined area 3.02

Mean So 

Lined area 1.26

0

Upper member of Shedhorn Sandstone. Curves for all 17 

samples fall within stippled area; all 7 samples from the 

lower half and 4 samples from the upper half fall within 

lined area

B. Lower member of Shedhorn Sandstone. 

Ten samples fall within lined area.

*"" on

U 

O

o:

u

Q.

u 60

_i

O 

> 40

u 

>

$

=1 ?o

s

Z>

o

n

Url*

1

Sn

L35 3.28 1.31

L54 3.87 1.52 

L8 4.55 1.50

I

I

T

A

J /

f

fi jf

299-L35

\J

f

4

T

4

1 ,

i f

* /

/ /

/ ti

i

_/

^1299-

L54 X

\^

7

/

/ /

' /

/

/

*

f

1299-L8

C. Grandeur Member of Park City Formation D. All samples

FIGURE 131. Summary of the size distribution data of Permian sandstone. Curves not corrected for sectioning. Md<i>, phi median diameter;

So, Trask sorting coefficient.

stone of the Shedhorn, sandstone of the upper tongue 

of the formation in the Melrose area contains almost 

no detrital chert.10

Apatite, generally constituting 4-8 percent of the 

rock, occurs as yellowish-brown isotropic sand-size 

pellets, as bone or shell fragments, and less commonly as large roughly oval grains of uncertain 

origin (fig. 133). The pellets are subrounded and 

well rounded and are about the same size or slightly 

larger than the associated detrital quartz grains. 

Many contain nuclei of quartz or chert grains, frag10 Rooney, L. F., 1956, A stratigraphic study of the Permian formations of part of southwestern Montana : Indiana Univ., Ph. D. thesis, 

p. 19.

ments of siliceous sponge spicules, or glauconite 

grains. Few oolites or micro-crystalline pellets have 

been seen in the sandstone, a surprising fact considering the abundance of both in sandy phosphorite. 

The large roughly oval grains of uncertain origin 

have a maximum length of several millimeters and 

range in shape from rather irregular grains to 

well-formed ovals. Some contain large quantities 

of silt and clay inclusions, others are crowded with 

sponge spicules replaced by apatite, and still others 

seem to be aggregates of indistinct pellets. The 

larger grains may represent both intraformational 

fragments and faecal pellets.
342 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

EXPLANATION

Upper part of Shedhorn Sandstone

Lower part of Shedhorn Sandstone

Grandeur Member of Park City Formation

1.0

FIGURE 132. Relation between coefficient of sorting (So) and phi median diameter (MdQ). Data from unconnected thin-section size

analyses. Lines of best fit based on Shedhorn samples only.

Apatite also occurs in some samples as yellowishgreen isotropic rims, about 5 microns thick, around 

quartz-sand grains. The boundary between the coating and the grain is generally somewhat irregular. 

Quartz overgrowths may surround the apatite rim.

Glaucoiiite grains are conspicuous in most of the 

sandstone in the western edge of the formation but are 

uncommon elsewhere. A few samples contain as much 

as 20 percent glauconite, but most glauconitic beds contain only 1 or 2 percent. The microcrystalline aggregates are green and yellowish green; weathered grains 

are light-brownish green. Morphologically the glauconite occurs as: (1) somewhat irregular grains and aggregates, whose form depends partly on the shape of 

the surrounding grain; (2) smooth, rounded, generally 

equant grains; and (3) fractured grains having one 

curved edge and one or two straight edges. All three 

types may be present in the same thin section. Hadcling (1932, p. 95, 99) considered the first type as having formed at the site of accumulation and the second 

type as having been transported. Many glauconite 

grains contain inclusions of pyrite or of iron oxides 

pseudomorphic after pyrite.

Heavy-mineral separations were made of five samples of the upper tongue of the Shedhorn from Sheep 

Creek and Wadhams Spring. The Shedhorn is so uni-
343

FIGURE 133. Photomicrograph of sandstone from the base of the upper 

member of 'the Shedhorn Sandstone at Sheep Creek showing apatite 

pellets having nuclei composed of quartz grains, an apatite skeletal 

fragment with apatite deposited about the exterior, and a large oval 

apatite grain of uncertain origin. Thin films of apatite surround 

many quartz grains, and the rock is cemented with microcrystalline 

quartz. Bed from which sample was taken contains 3.0 percent 

PaO5 (7% percent apatite). Ordinary light.

form in texture and composition of the light detrital 

material both areally and stratigraphically that there is 

no reason to expect any major differences in the assemblages of heavy accessory minerals; therefore, the values for these two localities are probably applicable in 

a general way to the formation as a whole.

The nonopaque accessory minerals consist almost entirely of the stable species-tourmaline, zircon, and rutile and very minor amounts of sphene, anatase, garnet, and apatite. Leucoxene is the only common opaque 

mineral. The heavy minerals that could be separated 

formed only 0.01 percent of the total sample, even 

though the efficient centrifuge method was used.

The samples were separated into size fractions before 

centrifuging. The separates coarser than 88 microns 

contained too few heavy mineral grains for a reliable 

count, so the relative amounts of the various species in 

the total heavy mineral assemblage could not be determined directly. The size distributions of zircon and 

tourmaline in one of the samples from Sheep Creek as 

determined from the counts and the sieve data were 

therefore plotted, and their relation to the total size 

distribution of the sample was compared with the theoretical relation developed by Rubey (1933) and the 

empirical relation found by Rittenhouse (1943) (fig. 

134).

According to Rubey, if quartz and zircon are deposited together, quartz having a diameter of 4 phi 

should have the same frequency as zircon having a 

diameter of 4.5 phi, and quartz having a diameter of 

2.5 phi should have the same frequency as zircon hav120

DIAMETER, IN PHI

FIGURE 134. Comparison of size distributions of zircon and tourmaline 

with that of total sample; bed Us-124, lot 1234.

ing a diameter of 3.3 phi. According to Rittenhouse, 

the zircon grains should be 0.9 phi unit smaller than 

the hydraulically equivalent quartz. The difference 

between the cumulative curves of quartz and zircon in 

figure 134 is thus smaller than one would expect, and 

nearly all the zircon is probably in the size fractions 

that were counted. Tourmaline should be 0.2 phi unit 

smaller than the hydraulically equivalent quartz (Rittenhouse, 1943), and the corresponding size distribution curve for tourmaline has been plotted in figure 134. 

If the corrected thin-section size analysis is correct, all 

but 10 percent of the tourmaline should be in the size 

fractions that were counted. The count data for leucoxene have not been plotted, but the curve would 

coincide approximately with that of tourmaline, the 

coincidence implying both a specific gravity and a total 

size distribution similar to those of tourmaline.

The weight frequencies of the species in the total 

heavy-mineral fraction of the sample were then calculated on the assumption that 10 percent by weight of 

both tourmaline and leucoxene was in the coarse frac-
344 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Rutile 

3 percent

FIGURE 135. Composition by weight of heavy accessory 

minerals in bed Us 124, lot 1234.

tions that had not been counted. The result plotted in 

figure 135 shows that leucoxene forms half of the total 

heavy minerals, and that tourmaline and zircon each 

constitute one-fourth. Rutile makes up only a few 

percent, and garnet, apatite, and anatase are present 

in negligible quantities.

The tourmaline was studied in some detail, because in 

orthoquartzites containing limited suites of accessory 

minerals, the comparison of varietal frequencies of the 

same mineral species offers the best means of detecting 

changes in provenance. Tourmaline has been studied 

successfully in this manner by Krynine (1946). In the 

Shedhorn Sandstone, however, the heavy mineral content is so small and the number of tourmaline varieties 

so large that the error for any one varietal frequency 

cannot be restricted to within a useful limit. Furthermore, the types are gradational, so that counts cannot 

be repeated with precision, and the varietal classification itself is so subjective that it is unlikely that any 

other person classify the tourmaline in exactly the same 

manner. The tourmaline data given in figures 136 and 

137 should therefore be considered semiquaiititative 

only.

The tourmaline consists of six major color varieties 

pink, green, brown, olive, blue, and multicolored of 

which the brown and olive varieties are by far the most 

common. Pink and green tourmaline are more abundant in the less than 44-microii fraction than in the 88- 

to 62-micron fraction, whereas brown tourmaline is 

more abundant in the coarser than in the finer size fractions. The frequencies of the color varieties in the 

Shedhorn samples are plotted in figure 136 and are compared with Weaver's data for samples from the Park

City and Shedhorn Formations (Weaver, 1955, p. 184). 

Cressman has seen Weaver's samples and believes that 

most of the differences shown 011 figure 136 result from 

subjectivity of the method rather than from actual differences between the assemblages. For example, the 

grains classified as colorless by Weaver would probably have been classified in this study as pink, pale olive, 

or pale blue.

Most of the tourmaline is subrounded (fig. 137 A). 

Rounded grains occur only in the sizes coarser than 44 

microns, and angular ones occur only in sizes finer than 

44 microns. Angular idiomorphic grains are present 

only in the fraction containing sizes finer than 44 microns, where they constitute about 20 percent of the 

tourmaline (fig. 137 B}. About half of the angular 

idiomorphic tourmaline contains inclusions similar to 

those called carbonaceous by Krynine, (1946, p. 69), 

but tourmaline containing few or no inclusions is most 

prevalent in the other roundness classes (fig. 137 C).

Most of the angular idiomorphic grains are pale pink 

and contain the so-called carbonaceous inclusions; these 

were probably derived ultimately (and perhaps directly) from a low-rank metamorphic source (Krynine, 

1946, p. 68). The rounded tourmaline grains in the 

two larger size fractions contain practically no.inclusions and are brown, green, or olive; these were probably derived ultimately from a plutonic source (Krynine, 1946, p. 68), although the rounding suggests that 

they have passed through several sedimentary cycles. 

The angular xenomorphic grains are mostly blue, olive, 

and green and contain few inclusions; they may have 

been derived in part from pegmatites (Krynine, 1946, 

p. 68). The subrounded type is the most prevalent in 

all size fractions, and although brown and olive grains 

having few inclusions are most common, the group includes grains of all colors and some grains having both 

bubble and carbonaceous inclusions. Both the rounding and the large number of varieties indicate that this 

group was derived from preexisting sediments.

Zircon, which constitutes about one-fourth of the 

heavy detrital minerals, consists of 80 percent colorless 

and 20 percent pale-pink grains. The surfaces of more 

than 90 percent are pitted, and about half of each color 

type are equant and half are elongate. More than 90 

percent of the zircon grains are appreciably abraded; 

half of these are rounded or subrounded. Weaver 

(1955, p. 184) found that in sandstone of the Quadrant, 

and of the Grandeur Member of the Park City 91 percent of the zircon grains are colorless and 40 percent 

are equant. Our observations are similar to his.

Rutile makes up about 3 percent of the heavy minerals; both reddish-brown and brown varieties were 

noted. All grains of garnet, which constitutes less
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 345

A, Grandeur Member of Park City Formation, 44 to 74 micron fraction; composite

of 5 sandstone samples from Kelly Gulch and Sheep Creek. 

B, Quadrant Formation, 44 to 74 micron fraction; composite of 4 sandstone

samples from Sheep Creek and Wadhams Spring. 

C, Dinwoody Formation, less than 44 micron fraction; composite of 3 calcareous

mudstone samples from Sheep Creek 

D, Upper member of Shedhorn Sandstone, 62 to 88 micron fraction; composite of

3 samples from Sheep Creek and Wadhams Spring. 

E, Same samples as in D, 44 to 62 micron fraction. 

F, Same samples as in D, less than 44 micron fraction.

Data for A and B from Weaver, 1955, p. 184 

FIGURE 136. Relative abundance of tourmaline color varieties.
00

FREQUENCY, IN WEIGHT PERCENT FREQUENCY, IN NUMBER PERCENT

**J ffs* 

s e.aMs ^ ^ i 51

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hb ® *.

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: ' ::vJy". :- ' .- :'-.-: '"'"'v :. . ' v. .-: ' *!' .:'-:':-:':i.: :' ': .;' ;;.:'.

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&« ^as & f IB-
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 347

than 1 percent of the heavy minerals, are deeply corroded. One euhedral diagenetic crystal of anatase was 

seen.

The sand is cemented with microcrystalline quartz 

(chert), quartz overgrowths, or, less commonly, cairbonate. The microcrystalline-quartz cement is similar 

in grain size and character to that in bedded chert. In 

places it forms nearly 50 percent of the rock but generally only 10 or 15 percent. Siliceous sponge spicules 

are present in many of the sandstone beds that contain 

large amounts of microcrystalline quartz, so the actual 

amount of interstitial chert cement is much less than 

first appears. Most chert cement contains grains of 

iron oxide pseudomorphic after pyrite, and pyrite itself 

lias been seen in several unweathered specimens. The 

detrital quartz grains in some thin sections of the sandstone are rimmed by chalcedony, which is in sharp 

contact with interstitial microcrystalline quartz; in 

other thin sections, the quartz grains are surrounded by 

irregular overgrowths of quartz in optical continuity 

with the grain that seem to grade outward into the 

microcrystalline quartz; in still other thin sections, 

contacts between microcrystalline quartz and the grains 

are sharp and distinct.

Unweathered specimens of chert-cemented sandstone 

fracture across the grains and are quartzitic in appearance, but weathering disaggregates the chert, and the 

rock becomes somewhat friable.

Nearly all sandstone seen in surface exposure is weathered the pyrite has been oxidized to iron oxides and 

the glauconite has turned olive brown and brown. The 

resulting rock has a low chroma with TR hues and a 

moderate to high value pale-brown, yellowish-brown, 

yellowish-gray, and very pale orange colors (fig. 138). 

Unweathered sandstone occurs in the interior of some 

beds, where pyrite and glauconite are unoxidized, the 

rock is extremely hard and somewhat vitreous appearing, and the color is grayish blue.

Nearly all the sandstone is thick- or very thick bedded 

and hard. More-weathered beds tend to be medium 

hard.

CHERT

Chert occurs as thin beds, lenses, and bodies of extremely irregular shape. Petrographically it differs 

little from the lighter colored chert in the Eex and Tosi 

Members of the Phosphoria Formation; many of the 

chert beds may be thin tongues of these members.

DOLOMITE

Dolomite forms a very minor part of the Shedhorn 

Sandstone. In the lower member, the dolomite is mostly 

aphanitic and very sandy, similar to dolomites of the 

Franson Member of the Park City Formation. Most

dolomite in the upper member of the Shedhorn is sandy 

and bioclastic, and several beds are microcoquinas 

formed of brachiopod fragments. The cementing material is anhedral dolomite having an average crystal 

size of 25-50 microns. The dolomite of the upper part 

of the Shedhorn is thick bedded and similar in color 

to the adjacent sandstone.

STRATIGRAPHY

LOWER MEMBER

At Indian Creek in the Madison Kange, the type 

locality of the Shedhorn, the lower member of the Shedhorn Sandstone is denned as the sandstone beds that 

underlie the Retort phosphatic shale tongue of the 

Phosphoria and overlie the Grandeur Member of the 

Park City Formation. The abundance of chert grains 

and the presence of small amounts of apatite pellets 

and skeletal fragments distinguish the sandstone from 

that of the Grandeur Member of the Park City Formation and from that of the Quadrant Formation.

The interval at the type section from the top of the 

lower member to the base is about 55 feet thick, but it 

includes a tongue of the Franson Member of the Park 

City 7y2 feet thick; so, beds actually assigned to the 

lowest member have a total thickness of about 47 feet. 

Several chert beds totaling nearly 10 feet in thickness 

are present in the lower member; they may be tongues 

of the Rex Chert Member, but they cannot be so identified with certainty. The original description of the 

lower member gave the thickness as 17 feet (Cressman 

and Swanson, in McKelvey and others, 1956, p. 2852), 

but the lower part of the type section has since been 

restudied.

The member is more than 25 feet thick in much of the 

eastern Centennial Mountains, the Snowcrest Range, 

and the northern Gravelly Range (fig. 139).

The lower member thins westward from the Gravelly 

Range by intertonguing with the Franson Member of 

the Park City Formation and the Rex Chert Member 

of the Phosphoria Formation (pi. 21), The most extensive tongue of the lower member lies directly beneath 

the Retort Phosphatic Shale Member of the Phosphoria 

and separates it from the Franson Member of the Park 

City. The tongue is present at the West Fork of Blacktail Creek and may extend as far west as Wadhams 

Spring. Another extensive tongue of the lower member 

occurs at the top of the Rex Chert Member and extends 

westward to Sawtooth Mountain.

The lower member abruptly thins eastward from 

the type area. The thinning probably takes place partly 

by eastward overlap at the base and partly by thinning
348 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

lOOr

75

50

25

Madison Range 

(lots 1214 and 1362)

100

75

50

I- 25

Z

UJ

O

cc

UJ

Q- 0

Gravelly Range 

(lots 1300 and 1307)

100 r

75

50

25

Hogback Mountain 

(lot 1299)

100r

75

50

25

0 L

3-4 5-6 7-9 

VALUE

Sheep Creek 

(lot 1234)

N Y YR 

HUE

0-3 4-8 

CHROMA

FIGURE 138. Color of Shedhorn Sandstone. Number and letter symbols are from National 

Research Council "Rock-Color Chart" (Goddard and others, 1948).
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

113° 112° 111°

349

MONTANA 

WYOMING

45

FIGURE 139. Isopach map of the lower member of the Shedhorn Sandstone. X, control point showing measured thickness in feet; A, control

point, data approximate.

of beds throughout the interval. Conglomeratic beds 

at the top of the member at Pulpit Rock may indicate 

removal of some beds at the top.

The lithologic character changes little, either areally 

or stratigraphically. Several sandstone beds in the 

Gravelly and Madison Ranges, the Centennial Mountains, and the Three Forks area contain scattered chert 

and dolomite pebbles, whereas the sandstone farther 

west does not; but the texture of the sand-size material 

remains remarkably constant. Other regional differences are (1) the prevalence of dolomite cement in the 

Gravelly Range but of siliceous cement, both as chert 

and as overgrowths, in the Madison Range and the

709-931

Centennial Mountains, and (2) the presence of at least 

a few glauconitic beds to the west of the Ruby River 

but not to the east.

The lower member of the Shedhorn is the equivalent 

of the Rex Chert Member and the Franson Member of 

the Lima region and thus of the Rex of southeastern 

Idaho. The lower member seems to be younger than 

any of the Meade Peak of Montana, but if the upper 

contact of the Meade Peak is lower in the section north 

of its type area, then the basal part of the lower part of 

the Shedhorn may well be the equivalent of the upper 

part of the Meade Peak of the Phosphoria Gulch section of southeastern Idaho.
350 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

UPPER MEMBER

At the type locality of the Shedhorn Sandstone, the 

upper member consists of the sandstone and chert interbeds, lenses, and nodules that lie between the Tosi Chert 

Member of the Phosphoria Formation and the Dinwoody Formation of Triassic age. Near the type section the thickness of the upper member varies from 64 

to 81 feet within a few hundred yards along the outcrop. 

Tongues of the upper member extend westward to Lima 

and the Pioneer Mountains, northwestward to the 

Garnet Range near Garrison, and southward to the 

Gros Ventre Range of Wyoming.

The upper member is overlain by the Dinwoody 

throughout the Madison and Gallatin Ranges, but in

much of the Gravelly Range it is separated from the 

basal part of the Dinwoody by about 10 feet of glauconitic, locally cherty, dolomitic mudstone that is con; 

sidered to be a tongue of the Tosi. From the Ruby 

River westward to Red Rock Valley and the Pioneer 

Mountains, the Tosi Chert Member and the upper 

member of the Shedhorn are intertongued throughout 

the interval between the Dinwoody Formation and the 

Retort Phosphatic Shale Member of the Phosphoria 

Formation.

The isopach map of the upper member of the Shedhorn (fig. 140) shows the total thickness of beds actually 

assigned to the member; it therefore shows the approximate total thickness of sandstone in the interval beMONTANA 

WYOMING

Permian rocks partly removed by preDinwoody erosion east of line

20 30 MILES

FIGURE 140. Isopach map of the upper member of the Shedhorn Sandstone. X, control point showing measured thickness in feet; A, control

point, data approximate.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 351

tween the Retort Member of the Phosphoria and the 

lowermost Mesozoic strata. Reentrants in the isopachs define a northward-trending zone through the 

Ruby Valley in which the upper member is thin and 

that divides the member into two parts. West of this 

zone, sandstone of the upper member extends fingerlike 

southward from Butte through most of the Snowcrest 

Range; it is interbedded with chert throughout the entire post-Retort and pre-Dinwoody interval. East of 

the Ruby River, the upper member of the Shedhorn 

generally overlies the Tosi Chert Member and occupies 

only the upper part of the post-Retort interval, 

although sandstone directly overlies the Retort at 

Quadrant and Cinnabar Mountains. The upper member extends as a wedge westward from the type area in 

the Madison Range to the Ruby River, where it 

apparently merges with the upper part of the southward-extending sandstone (pi. 20).

The upper member of the Shedhorn, like the lower 

member, is rather uniform in character. Nearly all the 

sandstone is well sorted in 17 analyzed samples So 

averages 1.23. The mean phi diameter of the 17 samples averages 3.21 (0.108 mm); it is thus somewhat finer 

grained than the lower member, for which the average 

mean phi diameter is 3.02 (0.123 mm) (fig. 131A). 

Some coarser grained beds having mean phi diameters 

ranging from 3 to nearly 2.5 (0.125 to 0.177 mm) 

characteristically occur in the uppermost 40 feet of the 

member. Brachiopod shells and shell fragments are 

present in the uppermost part of the member in several 

sections but are virtually absent elsewhere. Crossbedding has been noted only in the uppermost beds and 

only in the Gravelly Range.

The upper member differs laterally in the type of 

cement and in the glauconite content. Generally the 

sandstone is glauconite bearing and cemented by chert 

west of the Ruby River, is glauconite free and cemented 

by quartz overgrowth east of the Madison River, and 

is intermediate in character in the Gravelly Range. In 

the Three Forks area the member is mostly nonglauconitic, and much of the sandstone is cemented by dolomite. Although chert-cemented sandstone is not as 

common in the Madison and Gallatin Ranges as to the 

west, chert lenses, nodules, and beds are more common.

A striking feature of the Permian rocks in the area 

dominated by the Shedhorn Sandstone is the presence 

of abundant columnar bodies of sandstone, cherty sandstone, sandy chert, and chert (fig. 141) that are oriented 

nearly perpendicular to the bedding. These columns 

range from V2 to more than 5 inches in diameter, although they are mostly between 1 and 3 inches in diameter ; some are several feet in length. In some areas, 

fragments of columns are common in the soil or talus,

but complete columns are rarely found except in cliff 

exposures.

Many of the sandstone columns have irregular outlines (fig. 141, A and B) ; but others, particularly those 

that are more cherty, tend to be plane sided, and the 

columns of chert are generally rather smooth sided. A 

few seem to branch or to have small satellitic columns 

on the side (fig. 14L4). Bedding planes in the host 

rock are interrupted by the columns, which may cross 

contacts betwen different rock types, but most columns 

occur within one host type. In a few places they cross 

the complete bed and are so closely spaced that they are 

more abundant than the host rock. The host rock may 

be of the same composition as the column or it may be 

different.

Some columns show concentric structure in cross section resembling the annular rings of woody plants (fig. 

141 D and F). The rings may be composed of alternating chert and sand or of alternating light- and darkcolored chert. The dark variety of chert is generally 

typical of Phosphoria types; it is microcrystalline and 

contains abundant spicules, grains of apatite, and sand. 

The light variety is chalcedonic and has flamboyant extinction and banding; it appears to be secondary in 

origin and may represent filling of shrinkage cracks. 

The rings seem to be restricted to cherty parts of the 

columns.

The sand in the sandstone columns is about the same 

as that in adjoining sandstone beds, but it generally 

contains more apatite. The apatite occurs chiefly as 

pellets, organic fragments and rims about quartz grains.

At Cinnabar Mountain (lot 1363) columns of phosphorite composed almost entirely of the skeletal-fragment variety cross skeletal phosphorite beds and a bed 

of carbonatic mudstone. The columns average nearly 

2 inches in diameter, tend to be elliptical in cross section, and are separated by 1-3 inches of host rock. 

Overlying beds of mudstone, carbonate rock, chert, and 

sandstone also contain abundant columns composed 

chiefly of cherty sandstone and sandy chert that are 

as much as 4 feet in length and may constitute more 

than 50 percent of the total rock.

In the eastern part of the area, columns occur in almost all parts of the section. Inasmuch as the upper 

member of the Shedhorn Sandstone dominates the section in this area, it contains the most columns; but 

columns are found also in the lower member of the 

Shedhorn, particularly in the Centennial Mountains, 

and also in the Retort and Tosi Tongues.

The origin of these columnar bodies is not clear. The 

explanation that appears to us to be most satisfactory, 

from the standpoint of both distribution and morphology, is that the columns represent the burrows of
352 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

FIGURE 141. COLUMNAR CONCRETIONS OF SANDSTONE, CHERTY SANDSTONE, AND SANDY

A. Typical sandstone column showing layer structure (parallel to bedding) and irregular outline. Some cherty siltstone of transected bed

(light colored) clings to column.

B. Sandstone column having unusually lobate outline, oriented as above.

O. Smooth-sided column having rounded terminus. Found in float, so orientation uncertain. See D below. 

D. Broken end of column in C showing sandstone exterior around concentrically ringed chert center.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 353

ENGINFFR

CHERT FROM PERMIAN ROCKS IN MADISON AND GALLATIN RANGES, MONTANA.

E. Segment of sandstone column crossing bed of laminated chert (horizontal and preserved at base). 

F. Cross section of column showing sandstone center surrounded by concentrically ringed chert.

G. and H. Bottom (left) and top of %-inch bed of cherty mudstone containing sandstone casts of many burrows (?) and some crosscutting 

columns. Many of the worm-like casts turn down at one end and cross through the bed.
354 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

bottom-dwelling animals. The fact that the columns 

are confined to the platform sediments indicates that 

any such burrowing animals were of shallow-water 

habitat. However, Ellis Yochelson (written communication, 1961), who has examined the columns in the 

field, stated that "they exhibit none of the characteristics 

that I would associate with burrows"; their origin 

therefore remains enigmatic.

In the Madison Range about 4 miles west-northwest 

of the mouth of the west Fork Gallatin River and at 

the top of the principal tongue of Tosi Chert Member 

is found a fissile to thin-bedded cherty mudstone that 

contains many small (^4-% inch in diameter) sandstone bodies lying in the plane of the bedding and a few 

larger ones iyz inches in diameter crossing the bedding 

(fig. 141, G and H). Xhe larger ones are like others 

described above, and many of the smaller ones display 

the same external characteristics but lie in the plane of 

the bedding instead of perpendicular to it. A few, 

however, have longitudinal ridges but are otherwise 

rather smoothsided. A great many of the small ones 

turn down at one end and cross the bedding, and others 

that cross the bedding have no bedding-plane counterpart. These seem to be fillings of burrows made by 

animals that crawled through the muds and, in so doing, passed the sediment through their digestive tracts. 

The relatively high content of phosphate characteristic 

of these bodies suggests that the phosphate may have 

been faecal in origin.

The upper part of the Permian sequence in the 

eastern part of the area the thin Retort Phosphatic 

Shale Member overlain by the Tosi Chert Member, 

which is in turn overlain by the upper member of the 

Shedhorn so closely resembles the sequence in the 

northern Teton Range of Wyoming, at Red Creek near 

the south boundary of Yellowstone Park, and in the 

Gros Ventre Range (Sheldon, 1957, pi. 13) that a direct 

correlation seems justified. The part of the Permian 

section from the base of the Retort to the Dinwoody, as 

formed in these parts of western Wyoming, passes 

westward into the upper part of the Retort Member of 

the Phosphoria and eastward into the Ervay Tongue 

of the Park City Formation (R. P. Sheldon, oral communication, 1957) ; thus both the Tosi and the upper 

part of the Shedhorn of Montana are also at least partly 

equivalent to the upper part of the Retort of westernmost Wyoming and southeastern Idaho and the Ervay 

Tongue of central Wyoming.

AGE OF PERMIAN ROCKS IN SOUTHWESTERN 

MONTANA

Knowledge of the age of the Park City Formation 

and its correlatives in the western phosphate field and 

their correlation with the Permian of other areas has

been summarized by Williams (in McKelvey and others, 

1956, p. 2856-2861). Fusulinids were collected from 

near the base of the Park City Formation at Three 

Forks (locality 1356) by Frenzel and Mundorff (1942), 

who believed them to be of Wolf camp age; Henbest concluded that fusulinids from the same bed are middle or 

late Wolf camp or possibly early Leonard in age (quoted 

by Williams in McKelvey and others, 1956, p. 2857). 

Henbest (1956, p. 60) restudied fusulinids collected by 

Condit, Finch, and Pardee (1928, p. 192-193) at the 

Cabin Creek locality in the Madison Range from a 

horizon about 30 feet below the top of the Quadrant as 

defined in this paper and concluded that they are of 

Des Moines age. Therefore, if the lithologic correlation 

from Three Forks to the Madison Range is correct, the 

contact between the Quadrant and Park City Formations in the eastern part of the area must approximate 

the contact between the Pennsylvanian and the Permian Systems. To the west, the Grandeur Member of 

the Park City includes younger beds at the top and may 

include older beds at the base; therefore, the lower 

part of the Park City near Lima and at Hawley Creek 

may include beds of Leonard as well as Wolfcamp age. 

Duncan (1961, p. B-236), reported that corals collected 

66 feet and 185 feet above the base of the Park City 

Formation at Hawley Creek are probably pre-Kaibab 

in age and that these beds are therefore somewhat older 

than the Grandeur Member of the type area in Utah.

The Meade Peak Member of the Phosphoria and the 

overlying Permian strata are generally considered to 

be Word and possibly post-Word in age (Williams, in 

McKelvey and others, 1956, p. 2857), but in Montana 

the beds above the Grandeur Member of the Park City 

can be dated only by tracing them into the better known 

sections of Idaho, Wyoming, and Utah. Although dating by such a procedure compounds the uncertainties, 

the most reasonable conclusion is that the beds above the 

base of the Meade Park in Montana are also largely 

post-Leonard in age. How much of post-Leonard 

Permian time they may represent is not known.

RELATION OF PERMIAN STRATA TO OVERLYING 

BEDS

Jurassic beds of the Ellis Group rest disconf ormably 

on Permian beds in all sections along the Jefferson River 

and in the Three Forks and Sixteen Mile Creek areas. 

In the Three Forks area 50 or 60 feet of Permian beds 

must have been eroded away prior to Jurassic deposition. At all other localities examined in the area discussed in this report, the Permian is overlain by Lower 

Triassic beds.

In the Tendoy Mountains, cherty, calcareous mudstone of the uppermost Phosphoria is overlain conform-
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 355

ably by calcareous mudstone of the Dinwoody Formation. The Dinwoody and Phosphoria are also conformable in the western Snowcrest Range, where mudstone beds similar to those of the basal Dinwoody alternate with chert beds having a typical Phosphoria 

aspect for 20 or 30 feet below the contact. In the eastern 

Snowcrest Range and that part of the Gravelly Range 

from Warm Springs Creek south, beds of the basal 

part of the Dinwoody rest conformably on a thin tongue 

of the Tosi Chert Member that contains chert, glauconite, and sand typical of the Tosi and Shedhorn but 

that also contains silt, clay, and carbonate typical of the 

basal part of the Dinwoody. Although the contact is 

apparently conformable at all these localities, siliceous 

sponge spicules, chert, glauconite grains, and apatite 

pellets all characteristic of the Permian beds are not 

present above the Dinwoody contact.

The Dinwoody Formation may rest disconformably 

on Permian strata in the northern Gravelly Range, for 

the Tosi Chert Member and the upper member of the 

Shedhorn have a total thickness of only 31 feet at Wigwam Creek; this evidence suggests that some beds were 

eroded prior to deposition of the Dinwoody Formation.

Diseonf ormity between the Dinwoody and Shedhorn 

Formations in the Madison Range is suggested by several lines of evidence. At Shell Canyon, stringers of 

the basal limestone of the Dinwoody that contain coarse 

grains of Shedhorn-like quartzite extend downward into 

cracks in the uppermost bed of the Shedhorn, and at 

Indian Creek the thickness of the upper member of the 

Shedhorn changes from 64 to 80 feet within a quarter 

of a mile, suggesting pre-Dinwoody erosion. Furthermore, the uppermost beds of the Shedhorn, particularly 

where cherty, seem more weathered than the underlying 

beds in several eastern sections.

The Tosi Chert Member at Reas Peak in the Centennial Mountains is overlain by nearly 40 feet of sandstone of the upper member of the Shedhorn, but only 9 

miles to the west a thinner section of Tosi is overlain 

by calcareous mudstone similar to the basal part of the 

Dinwoody elsewhere. An abrupt lateral change from 

sandstone to mudstone, particularly without an intervening chert f acies, is unknown in this part of the section in Montana; so, the upper part of the Shedhorn 

west of Reas Peak was probably eroded prior to deposition of the Dinwoody. Furthermore, the thickness of 

the Tosi Member varies considerably in the area where 

the Shedhorn is absent. A thin phosphorite bed that 

contains fish teeth and large abraded bone fragments at 

the contact between the Tosi and Dinwoody at locality 

1254 also indicates a disconf ormity.

The time interval represented by the break between 

the Permian and Triassic rocks is not known. Kummel (1954, p. 168) found lower Cythian ammonites and 

Claraia within 5 feet of the base of the Dinwoody, but 

the age of the uppermost beds of the Permian sequence 

is not known. Whatever the time interval represented, 

it certainly increases to the east, for the contact becomes more distinct in that direction, and northeast of 

the area, the Triassic progressively oversteps the Quadrant, Amsden, Heath, Otter, and upper part of the 

Madison Formations (McKee and others, 1956, pi. 2).

FACIES RELATIONS

Facies changes are implied by the iiomenclatural 

scheme adopted for rocks of the Park City interval and 

have been alluded to in the preceding discussion of 

stratigraphy. They are examined in more detail in 

the following pages.

Recognition of time horizons is, of course, essential 

to facies analysis. The more accurately defined and 

the more closely spaced the time horizons, the more sensitive is both the delineation of environments and the 

analysis of their migration in time. As faunal zones 

have not been recognized in the Permian strata of Montana, time relations have been deduced from lithologic 

criteria, the principal one of which is the assumption 

that thin beds or thin distinctive sequences of beds of 

wide extent were deposited nearly synchronously. Examples are the uppermost phosphorite of the Retort 

Prosphatic Shale Member in the Snowcrest Range, the 

thin phosphorite bed in the Rex Chert Member in the 

Tendoy Mountains and adjacent areas, and the sequence 

of beds in the Meade Peak Phosphatic Shale Member in 

the Tendoy Mountains and the Snowcrest Range. A 

second criterion is presence or absence of intertonguing 

or intergradation, for if two adjacent lithologic units 

are time equivalents they should interfinger or intergrade. In the post-Retort beds, for example, the interbedding and intergrading of chert and sandstone in 

many sections indicate that the Tosi Chert Member and 

the upper member of the Shedhorn Sandstone are equivalent. But in the same area, the lack of interbedding 

of shale and phosphorite with sandstone or chert indicates that the upper part of the Retort is not equivalent 

to any large part of either the Tosi or the upper part 

of the Shedhorn. A third and far less satisfactory 

lithologic criterion is relative thickness. For example, 

about two-thirds of the post-Retort interval at Alpine 

Creek consists of chert which is overlain by sandstone; 

but at Indian Creek, the next section to the east, the fact 

that chert constitutes the lower third of the interval and 

sandstone mostly constitutes the upper two-thirds suggests that the chert-sandstone contact is younger toward 

the west.

In the following discussion, each time-rock unit is
356 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

identified by the name of the member or part of member 

that constitutes the bulk of the unit in the Lima region 

even though elsewhere the time-rock unit may be composed partly or wholly of other members. The datum 

planes delineating the time-rock units are indicated on 

the correlation charts.

Lower Grandeur interval. We are unable to construct a valid facies map of the lower dolomite beds of

the Grandeur Member of the Park City Formation inasmuch as the nature of the contact with the underlying 

Quadrant Formation is not known in sufficient detail. 

Nevertheless, any facies map constructed would show 

that rocks of early Grandeur age in most of the area 

west of Ruby Valley consist mainly of aphanitic dolomite, that much of the dolomite in the Gravelly Range 

is granular, and that sandstone forms an increasingly

113° 111°

Rocks of Grandeur Member of Park City Formation 

probably eroded east of line before deposition of 

Meade Peak Phosphatic Shale Member of Phosphoria Formation

EXPLANATION

(Tan) -_"^_ _ _ - (Red)

 Patterns used singly in class I areas; combined in 

class H and II areas

FIGUEE 142. Distribution of facies in late Grandeur time. X, control point; A, control point, data approximate.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 357

greater proportion of the interval eastward from Ruby 

Valley.

Upper Grandeur interval (-fig. 142). Rocks deposited 

in late Grandeur time consist of the upper terrigenous 

beds of the Grandeur Member and their probable equivalents.

Sand is the most abundant constituent in the western 

part of the area at Dalys Spur and in the eastern part 

at Hogback Mountain. Both sand bodies grade into 

mud in the intervening area. Some of the mud apparently related to the western sand area, is red, but 

otherwise the eastern and western terrigenous materials 

are indistinguishable in texture and compositions. 

Sandstone of this interval is more poorly sorted and 

more feldspathic than younger Permian sandstone. 

The terrigenous material passes northward, southward, 

and southwestward into dolomite.

Meade Peak interval (-fig. 118) . The salient features 

of the f acies distribution in the Meade Peak interval are 

the belt of high apatite content near the feather edge 

of the member and the area of prominent carbonate in 

the Lima region.

Rex interval (-fig. 143). Sand is present on both 

eastern and western margins in the Rex interval, but 

the intervening area is composed almost entirely of 

chert that increases in purity toward a central area in 

the Snowcrest Range. Mud is not sufficiently abundant 

to show on the f acies map, but it is more common near 

Lima than elsewhere. Glauconite occurs in small 

amounts in both chert and sandstone on the margins of 

the chert field; it is not present either in the class I 

sand areas or in the central part of the chert facies.

Franson interval (fig. 144). The distribution of 

sand in the Franson interval is very similar to that in 

the Rex interval, but in the central area the interval is 

made up of dolomite rather than chert, which is conspicuous only in a small area near Dillon. Skeletal 

carbonate rock is interbedded with aphanitic carbonate 

rock throughout the interval in the southwestern part 

of the carbonate facies; but it is not common elsewhere, 

and limestone makes up a significant proportion of the 

carbonate only in the sections west of Lima.

The Franson interval is so thick that extremes of the 

facies distribution are averaged out and cannot be 

shown in the map of the entire interval. Facies maps 

of two horizons within the interval illustrate two extreme distributions. The first map (fig. 145) is of a 

zone in the middel of the interval, and the second (fig. 

146) is of the horizon that is directly below the Retort 

Member in the Lima and Dillon regions. The presence

of two bodies of sand in both maps, the mud facies derived from the west in middle Franson time, and the 

much greater extent of the eastern sand facies in late 

Franson time should be noted.

Retort interval. The lower half of the Retort Phosphatic Shale Member of the Phosphoria pinches out to 

the east; so, the lithologie map, unlike that of the 

Meade Peak Member, is not a facies map. Unfortunately, horizons within the member cannot be traced 

widely, and accurate maps cannot be constructed of 

intervals within the member.

Lower Tosi interval (fig. 14?)- Chert constitutes 

most of the lower Tosi interval. Some sand is present 

in the easternmost section, but the largest sand body 

extends fingerlike southward through the center of the 

area. Glauconite occurs only along the westernmost 

boundary between the chert and the mixed chert and 

sand facies. The muddy facies that enters the area 

from the south is, apparently, everywhere separated 

from the sand facies by a chert facies.

Upper Tosi interval (fig. 148) Because of difficulty 

in correlating an upper boundary horizon, the facies 

map of the upper Tosi interval has been constructed 

directly on the basis of field evidence rather than by 

calculating the D function.

A body of sand extends southward from Butte nearly 

to Lima, but the eastern sand extends much farther 

west than that in the lower Tosi interval and coalesces 

with the southward-extending body to form a single 

sheet. A muddy facies extends northward into the 

area, but it is less extensive than that in the lower Tosi 

interval.

Summary. The facies changes illustrated by the 

maps are listed as follows:

1. Sand to mud to carbonate.

2. Sand to chert.

3. Sand to chert to mud.

4. Sand to carbonate.

5. Sand to chert to carbonate.

6. Chert and skeletal-oolitic apatite to skeletal-oolitic 

apatite and mud to pelletal apatite and mud to mud 

to cherty mud.

7. Mud to pelletal apatite and mud to pelletal, nodular 

apatite and mud.

GENETIC INTERPRETATIONS

In the following discussion, the stratigraphic and 

lithologie data are analyzed to determine the origin of 

the Permian rocks in southwestern Montana. The 

Permian paleogeography is then reconstructed, and
358 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

13° 112° lll c

EXPLANATION

Chert Carbonate

Patterns used singly in class I areas; combined in class LI and 

HI areas, except that where glauconite is present the glauconite pattern is superimposed

-40-

Isopeth of D vaules

Contour interval 20 units

FIGURE 143. Distribution of facies in Rex time. X , control point; A, control point, data approximate.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

113° 112° 111°

359

MONTANA

WYOMING

EXPLANATION

Glauconite

Glauconite pattern superimposed wherever glauconite is present; 

other patterns used singly in class I areas, combined in class 

I and Mareas

FIGURE 144. Distribution of facies in Franson time. X, control point; A, control point, data approximate.

the tectonic significance of the rock types and their 

facies and thickness relationships are discussed.

ORIGIN OF THE BOCK TYPES 

WSJL1>SORTED SANDSTONE

LITHOLOGIC CHARACTER OF SOURCE

The small number of heavy-mineral species, the large 

number of tourmaline varieties, and the great predominance of rounded and subrounded grains of both tourmaline and zircon indicate that the sand was derived 

largely f ro>m older sediments. The conclusion that the 

sand has been reworked is not disproved by the fact 

that the quartz grains are angular, for Tanner (1956) 

stated that grains finer than about 0.1 mm do not, in 

general, have rounded shapes, probably because of the 

effect of buoyancy on abrasion. A large part of the
360 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

113° 112° 111"

45'

EXPLANATION

Patterns used singly in class I areas; combined in 

class II and HI areas,

FIGURE 145. Distribution of facies in middle Franson time. X, control point; A, control point, data approximate.

sand grains of the Shedhorn are therefore too fine to 

have been rounded, even though they may have passed 

through several sedimentary cycles.

The much greater abundance of chert-grains in the 

Shedhorn Sandstone than in sandstone of the Grandeur 

Member and the Quadrant Formation suggests that 

most of the chert grains were derived from the reworking of the post-Grandeur Permian rocks rather than

from older rocks that may have been exposed in the 

source areas. Such reworking of the Permian sediments probably occurred near the margins of the depositional basin, where intermittent uplift of the adjoining 

land areas and changes in sea level would have exposed 

the sediments to erosion. Similarly, the apatite pellets 

in the Shedhorn were probably derived in large part by 

reworking of phosphorite, for none are present in the
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

113° 112° 111°

361

 ONTANA 

WYOMING

EXPLANATION

Glauconite pattern superimposed wherever glauconite is present; 

other patterns used singly in class I areas, combined in class 

IIand HI areas

FIGURE 146. Distribution of f acies at the end of Pranson time. X, control point showing phi median diameter of analyzed thin section;

A* control point, data approximate.

Grandeur Sandstone and oolites (which might be expected to form if phosphate were being deposited in 

such an environment) are scarce.

LOCATION OF SOURCE

Facies maps of the upper Grandeur, Franson, and 

Bex intervals indicate that sand was derived from two

sources. A possible location of the source of the eastern 

sand may be inferred in part from the present distribution of Permian sedimentary rocks. The eastern 

feather edge of the Permian deposits is in the northeastern corner of the area and probably extends southeastward to near Bozeman. Permian redbeds, evaporites, and limestone are present in the Williston Basin
362 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

.3° 112° 111"

EXPLANATION

Sandstone Chert Mudstone Glauconite

Patterns used singly in class I areas; combined in class I and 

Hareas; where glauconite is present the glauconite pattern 

is superimposed

FIGURE 147. Distribution of fades in early Tosi time. X, control point; A, control point, data approximate.

and in the northern Bighorn Basin; so, the possible 

location within Montana of the source area is limited 

to the Central Montana Platform, as defined by Sonnenberg (1956, p. 28), and to the Sweetgrass Arch. The 

eastward thinning of the Permian sediments and the 

presence of conglomerates and pebbly beds in several 

of the eastern sections suggest that at least the southern

part of this source area was intermittently positive 

throughout much of Permian time. How much of the 

sand of the Shedhorn may have been derived from this 

area is problematical; the positive area may have extended into Canada, and much of the sediment may 

have been transported southward by longshore currents. 

Facies maps of the upper Grandeur interval and
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

113° 112° 111"

363

Rocks of Tosi interval north 

of patterned area removed 

by pre-EMis erosion

EXPLANATION

Sandstone Cherty mudstone

FIGURE 148. Distribution of fades in late Tosi time. X, control point.

middle Franson time suggest that the western sand and 

the associ at ed finer detritus were derived from a source 

northwest of the Lima area. In the absence of strata 

known to be of post-Wolfcamp Permian age in central 

and northern Idaho and northwestern Montana, the 

actual location of the western source area can only be 

surmised; Ross (1934, p. 999) believed that the region 

now occupied by the Idaho batholith was positive during Phosphoria time as well as during much of the rest

of the Paleozoic, and that the terrigenous material in 

the Permian near Dillon and Lima could well have been 

derived from the northern part of such a landmass. On 

the other hand, if the Casto Volcanics of central Idaho, 

which are more than 3,000 feet thick, are Permian in 

age as is suggested by their similarity to the Seven 

Devils Volcanics of westernmost Idaho that contain 

a Phosphoria fauna, at least part of the area of the 

batholith may have subsided during the Permian.
364 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

According to Scholten (1957), the area between the 

Lemhi Range and the Tendoy Mountains was one of 

recurrent uplift during the Paleozoic. The isopach 

and facies maps of the Permian rocks from the base of 

the Meade Peak Member to the top of the Retort indicate that although the general area of the Beaverhead 

Range was submerged during that part of the Permian, 

the water in the area was shallower and the subsidence 

was less than in most of southwestern Montana and 

the range was thus a relative high. The source area 

may have been located northward along the trend of the 

relative high in the general area of the southern part 

of Bitterroot Range. Such a positive area and its 

southward extension as a submarine high might have 

separated the nonvolcanic southwestern Montana basin 

from the Casto area in central Idaho, the Seven Devils 

region of western Idaho, and the Baker quadrangle of 

eastern Oregon, where volcanics were being deposited 

(Ross, 1934, p. 994; Anderson, 1930, p. 13; GiUuly, 

1937, p.21).

The facies maps of the lower and upper Tosi intervals indicate that during Tosi time a considerable quantity of sand entered the area near Butte and was transported southward nearly to the Idaho State line. The 

source areas of this sand cannot be specified. The 

source may have been on the west side of the basin somewhere northwest of the area, or the sand may have come 

from a northwestern extension of the eastern source.. 

Wherever the source may have been located, the areal 

distribution of this sand is much different from that of 

the western-derived sand of the Grandeur and Franson 

Members of the Park City and thus implies a different 

paleogeography. This implication is supported not 

only by the facies distribution but also by the fact that 

the interval from the base of the Meade Peak to the base 

of the Retort thins markedly from Lima to Hawlay 

Creek, whereas the Tosi interval does not.

ENVIRONMENT OF DEPOSITION

One of the most informative works relating grainsize distribution to environments is that of Inman and 

Chamberlain (1955), who studied Recent near-shore 

marine sediments near La Jolla, Calif., and near the 

Rockport, Tex., and the east Mississippi delta area of the 

Gulf of Mexico. Inman and Chamberlain used the following parameters in describing their data: (1) The phi 

median diameter, Md<f> ; (2) the phi deviation measure, 

<*£=% (4>84-<£l6), where <j>84 and <£l6 are the 84th and 

16th percentiles, respectively; (3) the phi skewness 

measure, a.$=M<t> Md<t>, where M$=y± (016+084). 

These parameters have been calculated from the reconstructed size analyses made on thin sections of several 

representative Permian samples; the relation between 

a<£ and Md(f) and between <r<£ and Md^> are plotted in

figure 149 so that they may be compared with similar 

diagrams by Inman and Chamberlain. With the exception of one sample having a relatively high positive 

skewness, the well-sorted sandstone field shown in figure 

149 corresponds with that of the off-shore sands and 

near-shore shelf sands (class II) of Inman and Chamberlain.

Although turbidity currents, major ocean currents, 

and tidal currents all attain velocities sufficient to transport fine sand, Eaton (1950, p. 142) stated that ordinarily on an open seacoast only wave-induced currents have 

sufficient bottom velocity to set the bed material in 

motion. If the well-sorted Permian sand was transported by wave-induced currents, the inverse relation 

between the sorting coefficient So and the phi median 

diameter Md<}> (fig. 132) may be explained by reasoning 

similar to that employed by Humphreys (1956). As 

each wave passes, the horizontal current velocity varies 

from zero to a maximum that depends largely on the 

the wave characteristics and the depth of water. The 

sand remaining at a locality will be a lag deposit of 

material, brought in under very high velocities, that 

has a threshold velocity greater than the maximum 

horizontal velocity occurring during normal wave conditions. Sand about 0.2 mm in diameter has the lowest 

threshold velocity (Inman, 1949). If most of the sediment is of fine-sand size and smaller, the grains having 

diameters of 0.2 mm will be removed first, and, progressively smaller and larger grains will then move as the 

velocity increases. Thus the remaining sand becomes 

better sorted, and the mediam diameter becomes smaller 

through loss of the coarser fractions.

If the well-sorted sands are lag depoists, the commonly observed departure of the size distribution from 

log normality, as illustrated by curves 1302-Ls 44 and 

1358-F 12 in figure 150, can readily be explained. For 

example, curve A in figure 151 represents a sand having 

a log normal distribution. Curve B has been derived 

from curve A by assuming a maximum current velocity 

sufficient to initiate movement of grains coarser than 

0.15 mm and then by plotting the values for the distribution of the remaining fraction. The shape of the 

curve closely resembles that for the two Permian 

samples. The deviation of curves 1234 Us 117 and 

1299-R 73 from log normality cannot entirely be explained in this manner, but it may have resulted from 

mixing of several log normal sands, possibly by burrowing organisms.

The depth at which wave-generated currents will 

move sand of a given size depends mostly on the wavelength and wave height which are functions of velocity, 

duration, and fetch of the wind. During strong gales 

on exposed coasts, sand might be moved at depths as
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 365

+ .5

-Tan and red 

mudstone

Silty sandstone

-.5

Tan and red 

mudstone

Silty sandstone

PHI MEDIAN DIAMETER, (Md<f>)

FIGURE 149. Relation between phi median diameter (Md<p) and sorting (<r<f>) and skewness (a<p) in Permian sandstone. Dots from

reconstructed thin-section analyses; crosses from pipette analyses.

709-931 0 63-
366 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

98

95

90

80

70

60

50

40

30

20

10

.±£L

/ /

rr

7 i

DIAMETER, IN PHI

FIGURE 150. Size-distribution curves of selected samples of Permian 

sandstones plotted on logarithmic probability paper.

great as 200 meters, but according to Eaton (1950, p. 

142), under normal conditions, the limiting depth of 

movement is of the order of 200 feet (about 60 meters). 

The class II sand in the east Mississippi delta area is, 

for the most part, restricted to depths of less than 60 

feet (18 meters) (S'hepard, 1956, p. 2555). Similar 

sand in the Rockport area extends locally to depths of 

50 feet (15 meters) but is found mostly above the 35- 

foot (11-meter) depth; at La Jolla, however, the sand 

extends to depths of 100 feet (30-meters).

The variables of wave height and period are, of course, 

not known for Permian time in southwestern Montana; 

so, the depth of deposition cannot be determined directly from the grain size. However, the facies position of much of the sand shoreward from the bedded 

chert is strong evidence that the sand accumulated at 

depths of less than about 50 meters (p. 371). The extreme seaward edge of the upper Shedhorn sand must 

have been at least 100 miles from the shore (fig. 148); 

so, the average gradient of the sea floor was not more 

than 1.6 feet per mile, much less than the average gradient of nearly 5.8 feet per mile of the present-day graded 

slope off the southern shore of Martha's Vineyard (Stetson, 1939, p. 239). Using theoretical considerations,

DIAMETER, IN PHI

FIGURE 151. Change in character of size distribution by removal of 

coarse fraction. Curve A, hypothetical log normal distribution. 

Curve B, derived from curve A by removal of values for all grains 

larger than 0.15 mm (2.740).

Keulegan and Kmmbein (1949) derived an equation 

for the stable profile of the bottom slope in a shallow 

sea, according to which the sea would be 9 meters (30 

feet) deep. 100 miles from the shore; the average gradient would be 0.3 foot per mile. Keulegan and Krumbein derived the equation on the assumption that no 

energy was being expended transporting sediment; so,
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 367

the average gradient of the Shedhorn sea was undoubtedly somewhat greater.

The near absence of laminations, ripple marks, and 

crossbedding suggests that the sand was thoroughly reworked by burrowing benthonic organisms that could 

be expected to inhabit the sandy bottom in the inner 

sublittoral environment. The sandstone and chert 

columns are perhaps direct evidence of such a fauna.

SIGNIFICANCE OF GLAUCONITE

Glauconitic sandstone is found only near the basinward margins of the sandstone sheets. The definite 

facies position and the conformation of many grains to 

the shape of the surrounding quartz grains indicate 

effectively that the glauconite was in large part formed 

where it is now found.

According to Burst (1958, p. 315 and 318), the factors required for the formation of glauconite are (1) a 

parent material having a layered silicate lattice, (2) a 

plentiful supply of iron and potassium, (3) a favorable 

oxidation potential, and (4) a process by which the 

parent argillaceous material is deposited or aggregated 

into pelletal form. The favorable oxidation potential 

is one intermediate between strongly oxidizing and 

strongly reducing the oxygen is sufficient to oxidize all 

the organic matter but is insufficient to convert all the 

iron to the ferric state (Smulikowski, 1954, p. 96).

As emphasized by Burst (1958), the presence of glauconite indicates only the prerequisite conditions and 

not any specific environment. Nevertheless, surveys of 

glauconite occurrences show that some environments 

are more favorable for glauconite genesis than others, 

Glauconite forms generally in sea water of normal salinity (Smulikowski, 1954, p. 95), although Shepard 

(1956) reported grains of glauconite-like material in 

distributary channels of the Mississippi delta. In 

modern marine deposits, glauconite occurs most commonly between depths of 10 and 400 fathoms, but in the 

warmer waters of Indonesia, it is found only below 30 

fathoms and in abundance only below 130 fathoms 

(Cloud, 1955, p. 488). According to Hadding (1932), 

glauconite forms most, commonly in cold water or in 

regions where warm and cold currents meet.

Glauconite in the Permian sandstone of Montana 

formed in marine water of normal salinity and at depths 

not exceeding about 50 meters, as shown by the abundant associated Demospongia spicules. The water 

was sufficiently agitated to move sand and sufficiently aerated to support the sponges, indicating that 

the Eh required for glauconitization was restricted to 

the immediate vicinity of the pellets. The glauconite 

pellets do not appear to be internal casts of organisms, 

and they may well have been faecal pellets in which the

oxidation of organic matter would have lowered the Eh 

sufficiently to allow glauconitization of included clays. 

The distribution of the glauconite pellets may thus reflect the distribution of the pellet-producing organism. 

Glauconite occurs in the Permian rocks as canal fillings of sponge spicules as well as pellets. The favorable local environment may have resulted from the oxidation of organic matter in the spicules, but it is difficult 

to imagine the infiltration of parent clay into the narrow canals. Perhaps glauconite can form from a parent silica-alumina gel as well as from a pre-existing 

layered silicate lattice.

SH/TY SANDSTONE AND TAN AND RED MUDSTONE

These rock types are discussed together because they 

are laterally gradational and similar in both texture 

and composition.

LITHOLOGIC CHARACTER OF SOURCE

The character of the heavy-mineral assemblage of 

the silty sandstone is very similar to that of the wellsorted sandstone, and it, too, indicates that the material 

was largely derived from a sedimentary terrain 

(Weaver, 1955, p. 181). The silty sandstone and the 

mudstone differ in composition from the well-sorted 

sandstone, as they contain abundant mica shreds and 

clay and traces of feldspar. The presence of mica 

shreds and clay may indicate a, different enviroment 

of deposition rather than a different source, but the 

presence of feldspar is more difficult to explain. Its 

presence in silty sandstone derived from two different 

source areas, both of which subsequently supplied the 

nonfeldspathic well-sorted sand, suggests that its 

absence in the well-sorted sand resulted either from 

more severe weathering at the source during Shedhorn 

time or from mechanical sorting during transportation 

and at the site of deposition, rather than from any 

differences in the source rocks.

LOCATION OF SOURCE

The f acies distribution (fig. 142) clearly indicates 

that the silty sandstone and the tan mudstone were derived from the same two source areas as the well-sorted 

sandstone. The red mudstone was derived from the 

northwestern source.

ENVIRONMENT OF DEPOSITION

The parameters of size distribution of the tan and 

red mudstone (fig. 149) resemble most closely those of 

the delta silt type Ila of Inman and Chamberlain 

(1955, p. 122, 124), which is found in shallow distributaries and marshes of the Mississippi delta. This seems 

an unlikely environment for the Permian sediments. 

The good sorting of the red and tan mudstone may 

result in part from incomplete disaggregation, and
368 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

the actual sorting may be somewhat poorer. If so, the 

samples would more closely resemble the "muds" of 

Inman and Chamberlain. These sediments border the 

near-shore sands in the Rockport area, but in the east 

Mississippi delta are found along the delta front. The 

silty sandstone seems most closely related to the transition sand class Ilia of the La Jolla area, which 

occurs just seaward of the type II sand. Fine material 

settles out because of reduced wave intensity, and sand 

is added to the deposit by gravity movement down the 

slope; the transition sand occurs only where bottom 

slopes are greater than 1:15 (Inman and Chamberlain, 

1955, p. 114). However, in the absence of other evidence of steep slopes, such as slumping, a gradient of 

1:15 seems too great to postulate for the Permian sea 

floor.

The size distribution curves for two mudstones, two 

silty sandstones, and one well-sorted sandstone are 

plotted on logarithmic probability paper in figure 152.

The curves for the two mudstones and for the finer 

grained silty sandstone may be interpreted as indicating that the rocks formed from the simultaneous deposition of a traction load and of a suspended load, both of 

which had a log normal distribution (Groot, 1955, p. 

95). Nearly all the coarser grained silty sandstone 

probably represents a traction load. Although the 

coarse end of the curve is irregular, it does not exhibit 

the marked convexity typical of well-sorted sandstone; 

this fact indicates that the rock had not been subjected 

to reworking after deposition. The lamination commonly present in both the silty sandstone and the mudstone also indicates the absence of effective wave-generated currents at the depositional interface.

Both the silty sandstone and the tan and red mudstone 

were deposited in water below effective wave base. No 

evidence is available to indicate the origin of the color 

of the red mudstone. Probably, however, the red color 

originated in the source area by weathering or by the

20

10

5 6

DIAMETER, IN PH|

FIGURE 152. Size distribution curves of sandstone and mudstone samples of the Grandeur Member of the Park City Formation plotted on 

logarithmic probability paper. Curves for 1224-G-41 and 1224-G-50 from pipette analyses; others from corrected thin-section analyses.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 369

reworking of pre-existing red beds and was preserved 

where the Eh was insufficient to reduce the ferric iron.

CHERT

SOURCE OF SILICA

The immediate source of most of the silica in the chert 

was siliceous sponge spicules. Spicules that can be 

observed or whose presence may reasonably be inferred 

by the presence of canal fillings comprise at least half 

and perhaps as much as two-thirds of the silica in the 

chert of the Phosphoria. The problem is thereby narrowed to determining the source of the remaining onethird to one-half of the silica that is present as cement 

in spicular chert and in chert in which no spicules can 

be seen. The marked enlargement of the axial canals 

of nearly all spicules in chert of the Phosphoria, part of 

which apparently took place before final burial (p. 

316), indicates that the Permian sea was undersaturated 

with respect to opaline silica; therefore, the matrix 

silica could not have been precipitated directly from sea 

water.

Bien and others (1958) found that much of the dissolved silica in Mississippi River water is precipitated 

by inorganic processes when the river water mixes with 

water of the Gulf of Mexico; precipitation occurs 

largely by adsorption of soluble silica on suspended 

matter as the silica comes in contact with electrolytes of 

the gulf water. Silica precipitated in such a manner 

might be available for redistribution during diagenesis, 

but most would be concentrated in a deltaic or esturine 

environment rather than in one of normal marine salinity, which characterized the Phosphoria sea. Inasmuch as inorganic precipitation either directly by supersaturation or by adsorption seems unlikely to have occurred in the Phosphoria sea, the matrix silica was 

probably originally incorporated in the sediment in the 

form of siliceous skeletal remains. The remains may 

have been microscleres and small megacleres of sponges, 

now conspicuously absent in the chert (M. W. de Laubenfels, oral communication, 1957), or the delicate siliceous remains of planktonic organisms such as diatoms, 

silicoflagellates, and radiolaria.

Although the immediate source of nearly all the silica 

was thus probably siliceous organisms, the nature of the 

ultimate source is not known. The common association 

of deposits of siliceous organisms with volcanic ash has 

led some authors to suggest that much of the silica 

utilized by the organisms may have been released by 

weathering of volcanic ash (Taliaferro, 1933, p. 54; 

Bramlette, 1946, p. 41). There is no evidence in the 

Permian rocks of Montana of more than a trace of volcanic ash from which silica could have been extracted, 

but Permian volcanics are common and extensive in

northern California, Oregon, Washington, and western 

Idaho and Nevada, and silica derived from these volcanics may have enriched the waters from which the 

chert was deposited. However, the calculations discussed in the following paragraphs indicate that normal 

sea water itself could have been an adequate source, and 

so extraordinary enrichment need be postulated.

The efficacy of sponges in extracting silica from sea 

water is not known, but the ability to planktonic organisms to extract it can be estimated from (1) the rate 

of accumulation of biogenic silica in pelagic sediments, 

(2) the rate of depletion of silica in sea water in areas 

of high organic productivity, and (3) the rate of production of organic matter measured in areas of high 

productivity.

Arrhenius (1952, p. 31) found the maximum rate of 

accumulation of biogenic silica in sediment cores from 

the east Pacific to have been 860 milligrams per square 

centimeter per 1,000 years. The maximum thickness of 

bedded chert in the Phosphoria of Montana is about 200 

feet (60 meters) (see figure 153). Assuming the chert 

to contain an average of 70 percent by volume of nondetrital quartz having a density of 2.65, a column 1 centimeter square and 60 meters high contains 1.113 XlO4 

grams of nondetrital silica. At the maximum rate of 

accumulation of biogenic silica determined by Arrhenius 

in the east Pacific, 13 million years would have been 

required to deposit the silica in the thickest sections of 

the chert of the Phosphoria. This is about 30 percent 

of Permian time (Holmes, 1960). Present knowledge 

of the age of the Phosphoria Formation and its equivalents indicates that this much time may have been available for deposition of the chert members.

The rate of depletion of silica in sea water in an area 

of upwelling can be estimated from oceanographic data. 

In the north equatorial divergence in the Pacific Ocean, 

the average silicate-silicon content of the upwelling 

water below the zone of photosynthesis is about 15 microgram atoms per liter; surface water moving away from 

the divergence contains less than 5 microgram atoms of 

silicate-silicon per liter (Sverdrup and others, 1942, p. 

710), more than 10 microgram atoms per liter having 

been extracted by planktonic organisms. If 10 microgram atoms of silicate-silicon per liter (0.6 part per 

million SiO2 ) is the amount of depletion and if the 

rate of upwelling is 20 meters a month 240 meters a 

year (the rate of upwelling in the California current; 

Sverdrup and others, 1942, p. 725) the amount of 

silica extracted annually for each square meter of surface is:

(240) (10s ) (0.6 XlO-8 ) =144 grams per year.

Sverdrup's data (1938) suggest that upwelling in the 

California current occurs across a zone about 40 kilo-
370 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

113° 112° lll c

FIGURE 153. Isopach map of combined Rex and Tosi Chert Members of Phosphoria Formation. Dashed line encloses area for which volume

calculations are made ; X, control point showing measured thickness in feet.

meters wide. If a current of this character had flowed 

south-southeastward across the area delineated by the 

dashed line in figure 153, a distance of 134 kilometers, 

the amount of silica extracted from the sea water yearly 

would have been:

144X (40X10?) (134X103 ) XlO-6=7.7XHf metric tons.

The volume of chert in the area enclosed by the dashed 

line in figure 153 is 6.0 X1011 cubic meters. If the 

chert contains 70 percent by volume of nondetrital 

quartz having a density of 2.65, the chert weighs:

(6.0X1011 ) X 0.7 X2.65=10.8X1011 metric tons.

It would have taken (10.8X1011 )/(7.7X105 ) =1.4X106 

years for the chert to have been formed by a current

of the character postulated. This period is well within 

the limit of time available. Silica would undoubtely 

be extracted elsewhere than in the zone of up welling; 

so, the time required would be even less. If the belt 

of upwelling were wider, the time required would be 

reduced correspondingly.

The third method of estimating the organic production of silica is to calculate the amount of silica extracted from the measured rates of production of organic carbon in the modern sea. The annual production 

of organic carbon on the continental shelf off New York 

is 160 grams per square meter per year (Ryther and 

Yentsch, 1958). At that rate, 4.38 X106 metric tons 

of organic carbon would have been produced annually
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 371

in the 27,400 square kilometers outlined by the dashed 

line in figure 153. Fedosov (1959) listed the relative 

content of the principal biogenic elements in marine 

phytoplankton as N, 5.5-10; P, 0.14-0.5; Si, 1-22. Redfield (1958) gave 1:106 as the ratio of phosphorus to 

carbon in plankton. Given the median values for silicon and phosphorus in Fedosov's table, the annual production of silicon in the area outlined in figure 153 

would have been:

4.38X10"X11.5=1.5X106 metric tons. 

106 0.32

This amount is equivalent to 3.2 XlO6 metric tons of 

SiO2 . At this rate of production, it would take only 

(10.8XlO11 )/(3.2XlO6 ) =340,000 years to extract the 

amount of silica in the Permian chert. The time required would be less if higher rates of organic productivity are assumed. For example, Riley and others 

(1949, p. 114) found the production of organic carbon 

in the Florida Straits to be 1.3 grams per square meter 

per day, or 475 grams per square meter per year. At 

this rate, only 115,000 years would be required to extract the silica in the chert of the Phosphoria.

In summary, although the time required by the first 

method of calculation is near the maximum amount of 

time available and although the second and third 

methods ignore solution and recycling of silica extracted 

by organisms, all three methods indicate that organisms could extract sufficient silica from normal sea 

water to form the bedded chert of the Phosphoria.

Silica, like other nutrients, is rapidly depleted in the 

zone of photosynthesis, and a continual renewal of silica 

in the surface waters is necessary to support to a dense 

population over any considerable length of time. This 

renewal may be accomplished by (1) the up welling of 

water from beneath the zone of photosynthesis, (2) 

the mixing of waters by turbulence where currents flow 

over shoal areas, and (3) the supplying of nutrients by 

river waters (Prokopovich, 1952, p. 878). The facies 

realtions of the Permian rocks do not indicate the influx of any major system of land drainage; so, the 

silica may have been renewed by deeper water rising 

along the shelf or by turbulence in a current flowing 

parallel to the coast.

ENVIRONMENT OF DEPOSITION

Most of the information in the following paragraph 

was supplied by M. W. de Laubenfels (oral communication, 1957), who kindly examined several thin sections 

of the chert.

The assemblage of spicules in the chert of the Phosphoria is typical of that produced by the class Demospongia. These sponges are shallow-water forms that 

do not thrive below the photic layer (approximately the

upper 50 meters, although it varies with latitude and 

water turbidity; see Holmes, 1957, p. 123). Demospongia can thrive on a rock, coarse-grained sand, or 

ooze substrate but not in large numbers on a fine-grained 

sand bottom, for the fine-grained sand particles clog the 

oscules. Both stagnant water and rapid currents are 

unfavorable; the optimum current velocity is probably 

about 2 or 3 kilometers an hour. A few genera live in 

brakish water, but de Laubenfels believed that the 

sponge fauna of the Phosphoria required full oceanic 

salinity.

The large and uniform size of the Phosphoria spicules 

as compared with those in modern Demospongia assemblages suggested to de Laubenfels that the spicules 

had been sorted. The apparent sorting of the spicules 

had been previously noted, and it had been suggested 

that the facies relations between sandstone and chert 

resulted in part from winnowing of spicules from the 

sand and their subsequent accumulation on the basinward side of the sand (Cressman, 1955, p. 26). However, the inability of Demospongia to thrive on a fine 

sand substrate indicates that no large proportion of 

the spicules could have originated in the area of the 

sand facies; the rather abrupt facies change from 

sandstone to chert resulted more from environmental 

requirements of the sponges than from sorting. Although smaller spicules may have been transported 

basinward, thus extending the chert facies into deeper 

water, the conditions indicated by the ecological requirements of the Demospongia must have prevailed throughout at least the landward portions of the chert facies; 

that is, the water was less than 50 meters deep and of 

normal marine salinity, and the current velocity was 

moderate.

DIAGENESIS

The principal diagenetic changes within the siliceous 

sediments were solution of spicules and enlargement of 

axial canals, cementation by silica, and alteration of 

opal to quartz and chalcedony.

After sedimentation, the silica content of the interstitial water may be expected to increase and, if the 

sediment contains sufficient amounts of opaline silica, 

to eventually reach saturation. This process is illustrated by Emery and Rittenberg's core 5 (1952, p. 746) 

from the Santa Cruz Basin, where the silica concentration increases to nearly 70 parts per million approximately the solubility of amorphous silica at the prevailing temperature of 4°C (Krauskopf, 1956, p. 23) at 

a depth of 190 centimeters below the sediment surface. 

The process is also substantiated by the observations of 

Arrhenius (1952, p. 88) and Revelle (1953, p. 34), who 

found that siliceous tests in pelagic sediments of the 

Pacific had been corroded or removed after burial.
372 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Tests of planktonic organisms and of small and delicate 

microscleres would probably be dissolved first, as suggested by the survival of spicules in the more altered 

rocks of the Monterey Formation (Bramlette, 1946, p. 

48). The amount of silica that must be dissolved from 

an opaline sediment to raise the silica content of the 

interstitial water to saturation with respect to amorphous silica is negligible. If the original sediment consists of 70 percent of sponge spicules having a density of 

2.02 (the density of opal with a water content of 8 percent) and 30 percent quartz and if the porosity is 80 

percent, only 6.4 X 10~5 grams of silica per cubic centimeter need be dissolved to raise the silica content of the 

interstitial water from 0 to 80 parts per million. This 

amount is only about 0.025 percent of the spicular silica. 

Therefore, large amounts of silica can be dissolved from 

an opaline sediment only if there is large-scale circulation of undersaturated interstitial water or if there 

is simultaneous precipitation.

The mechanism by which silica was precipitated from 

the saturated interstitial water is not known, but several 

possibilities can be suggested. First, as proposed by 

Arrhenius (1952, p. 85) to account for silica-cemented 

laminae in sediments of the East Pacific Ridge, silica 

might have been deposited from rising interstitial water 

heated at depth. In the Permian sediments, however, 

there was apparently no way for the entrapped water 

to have been significantly heated. Second, according 

to Baas Becking and others (1960, p. 276), the pH of 

connate water in strongly reducing sediments might 

be raised well above 9 by reduction of sulfate and precipitation of the calcium, magnesium, and carbonate or 

bicarbonate. The solubility of amorphous silica increases rapidly as the pH rises above 9 but is little affected by pH changes below 9 (Krauskopf, 1956, p. 23). 

Interstitial water having a high pH and a high silica 

content might have evolved in the mudstone facies. 

Silica might have then been precipitated as the water 

moved either up the dip or section into the less alkaline 

environment of the spicule ooze.

In both cementing mechanisms suggested above, the 

matrix silica would have been derived largely from 

outside the chert facies. An alternative mechanism is 

that the cementing silica was derived from within the 

chert facies itself by simultaneous solution and deposition of opal, as proposed by Bramlette (1946, p. 52) 

for the Monterey Formation. At least three mechanisms can be suggested. First, differences in solubility between the spicular opal and the precipitated 

opal might have resulted from differences in particle 

size. Acording to Her (1955, p. 11), the solubility of 

amorphous silica decreases with decreasing grain size 

below 50 millimicrons but does not change appreciably

above 50 millimicrons. The efficacy of such a process 

cannot be evaluated until the primary particle size 

in sponge spicules and opaline cement is determined. 

Second, Weyl (1953, p. 156) has observed that the 

solubility of silica is decreased by the chemisorption 

of polarizable foreign molecules, dipoles, or charged 

particles. The solubility of the cementing opal might 

have been less than that of the spicular opal because 

of such chemisorption. Third, the opal cement might 

have been precipitated as one of the polymorphs of 

cristobalite or tridymite that would be less soluble than 

the amorphous silica of the spicules. This process is 

suggested by the work of Swineford and Franks 

(1959), who found that massive opal, opal cement, and 

opalized wood in the Ogallala Formation (Pliocene) of 

Kansas gave X-ray patterns interpreted as those of 

low cristobalite-tridymite, whereas diatomite in the 

same formation was composed of amorphous opal.

Much of, and perhaps all, the chert was cemented 

during Permian time, as indicated by the large number 

of chert grains throughout the Shedhorn Sandstone 

and by the occurrence of chert pebbles of Phosphoria 

aspect in conglomeratic beds of Phosphoria age.

The siliceous spicules were originally opal, and by 

analogy with more recent sediments, so was the siliceous 

cement; but the chert is now composed of microcrystalline quartz and minor amounts of chalcedony. In 

general, spicules are not observed in areas composed 

largely of chalcedony; so, the preservation of the bioclastic texture in most areas of microcrystalline quartz 

suggests that the original opal was transformed directly to quartz without passing through an intermediate chalcedony stage. In opaline chert of the Monterey Formation, chalcedony occurs generally as vein 

fillings or fills the large pore spaces such as chambers 

of Forarninifera (Bramlette, 1946, p. 18). Occurrences of chalcedony in the chert of the Phosphoria 

may be analogous; chalcedony veins are common, and 

chalcedonic spicules might be casts of spicules rather 

than composed of the original spicular silica. If comparison with the Monterey is valid, much of the chalcedony crystallized relatively early and probably directly from solution, whereas the microcrystalline quartz 

formed later from previously deposited opal. It 

should be noted, although, that under some conditions 

opal can be converted directly into chalcedony (White, 

and others, 1956, p. 54)

The undulant bedding surfaces characteristic of 

much of the chert are very likely a diagenetic feature, 

for they do not resemble any known primary structure. 

Although the formation of the undulant bedding cannot be explained in detail, it probably resulted from 

the solution, migration, and redeposition of the silica;
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 373

the character of the bedding depended, at least in part, 

on the original permeability of the bed. The bedding 

surfaces of the argillaceous chert may have remained 

planar because the clay content reduced permeability; 

in contrast, the undulantly bedded chert contains less 

clay and was probably originally more permeable, enabling silica in solution to migrate greater distances 

before precipitation.

DARK MUDSTONB

SOURCE OF DETRITUS

Cressman (1955, p. 23-25) expressed the opinion that 

most of the silt and clay was derived from the northwesterly source area. This conclusion was based partly on the observation that post-Meade Peak sandstone 

derived from the east does not grade directly into 

mudstone whereas sandstone derived from the northwest does and partly on the much greater thickness 

of argillaceous rocks in the Paleozoic section of Idaho 

than in that of central Montana. However, the f acies 

relations of the upper terrigenous beds of the Grandeur 

Member of the Park City Formation (fig. 142) indicate 

that fine detritus was supplied from both areas during 

at least part of Permian time.

SOURCE OF CARBONACEOUS MATTER

The source of carbonaceous matter in most marine 

sediments is marine phytoplankton (Trask, 1939, p. 

436-437), and considering the wide extent of carbonaceous beds in the Phosphoria, no other source seems 

possible.

Rooney (1956) published 10 analyses of the C12/C13 

ratio of organic carbon from the Phosphoria of Montana; the value of the ratio ranges from 89.90 to 91.26, 

and six values fall between 91.02 and 91.26. By comparing these values with those for Recent plants published by Wickman (1952, p, 252), Rooney concluded 

that the carbonaceous matter of the Phosphoria was 

most probably derived from plants that grew in stagnant Water, as the value of the ratio in the Phosphoria 

samples was considerably higher than that in presentday marine plants. (The stagnant-water plants analyzed by Wickman are lacustrine types.) However, 

Craig (1953) found that in most sedimentary rocks, 

even in those containing marine fossils, the OyG1'3 

ratio is about the same as in terrestrial plants. 

Furthermore, although C12/C13 ratio in most petroleum 

is higher than in the Phosphoria, most of the values 

for Phosphoria specimens are within the lower limit 

of petroleum values (Rankama, 1954, p. 198). 

Rooney's data, although from widely scattered localities and different stratigraphic levels, suggest a southeasterly increase in the C12 /C13 ratio. Rooney interpreted the trend as reflecting a southeasterly increase 

in the stagnancy of the Phosphoria sea ; however, the 

carbon isotope ratio is determined not only by the 

original isotopic composition of the carbonaceous 

matter but also by diagenetic and metamorphic processes (Forsman and Hunt, 1958, p. 773). In the absence of more detailed studies of the composition of 

the carbonaceous matter, Rooney's data can be interpreted as indicating only that the isotopic composition 

of organic carbon in the Phosphoria Formation is similar to that of organic carbon in other marine formations.

RATE OF PRODUCTION OF CARBONACEOUS MATTER

The amount of carbonaceous matter in the Retort 

Member within the area of 20,300 square kilometers 

denned by the dashed line in figure 154 has been determined from an isopach map of the total carbonaceous 

matter to be 2.03 X106 metric tons. An approximate 

minimum length of time required to produce this much 

carbonaceous matter may be calculated by assuming 

that the entire area was one of high organic productivity. If 475 grams of carbon were produced for each 

square meter of surface area, a rate that has been measured in the highly productive waters of the Florida 

straits (Riley and others, 1949, p. 114), the amout of 

carbon produced yearly in the area outlined by the 

dashed line in figure 154 would have been 9.64X106 

metric tons. According to Emery and Rittenberg 

(1952, p. 776), less than a sixteenth of the carbonaceous 

matter produced off the coast of southern California 

reaches the bottom; and according to Trask (1939, p. 

441), the organic content is reduced an additional 40 

percent during burial and lithification. Given these 

values and Trask's factor (1939, p. 30) of 1.8 for the 

conversion of carbon to carbonaceous matter (intermediate between the ratios in plankton and in sedimentary 

rock), the amount of carbonaceous matter finally incorporated in the rock would be

9.64X106 ) (1.8) (0.60) ^ 

 '\ a /v - = 6.50 X 10 

lo

L . L metric tons.

At this rate, only (2.03 X1010 )/(6.50X105 ) =31,200 

years would be required to deposit the amount of carbonaceous matter in the Retort Member.

The water over the entire area was probably not as 

highly productive as assumed in the foregoing calculation. A more reasonable estimate of the time required 

to deposit the carbonaceous matter may be made by 

assuming that an upwelling current similar to that off 

the coast of California flowed southward through the 

area. ( Evidence that such a current existed in Permian 

time is discussed on pages 379-380). Sverdrup and 

others (1942, p. 938) estimated the annual production 

of organic carbon in the area of upwelling off the coast
374 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

of southern California to be 215-430 grams per square 

meter. Given an intermediate value of 320 grams carbon per square meter per year and an upwelling that 

occurred across a belt 40 kilometers wide (p. 369), the 

amount of organic carbon produced yearly by the current flowing a distance of 134 kilometers south-southeastward across the area enclosed by the dashed line in 

figure 154 would have been 1.72 X106 metric tons. The 

amount of carbonaceous matter finally incorporated in 

the rock would have been

(1.72X108 )( 1.8) (0.60) 11aw1A5 . . . 

 - - -=1.16Xl05 metric tons per year.

At this rate, (2.03X1010 )/(1.16X105 ) =175,000 years 

would have been required to produce the amount of 

carbonaceous matter incorporated in the rock.

ENVIRONMENT OF DEPOSITION

Under conditions of slow deposition, carbonaceous 

mudstone such as that in the shale member of the Phosphoria could accumulate and be preserved only below 

wave base in water containing little or no oxygen. Such 

conditions can exist on an open shelf having no topographic barrier to circulation if the supply of carbonaceous matter is great and the waters impinging on 

the bottom are oxygen deficient (Richards and Redfield, 

1954, p. 281). For example, shelf sediments off the 

coast of Angola and Southwest Africa are highly organic; upwelling supports luxuriant plankton growth, 

and a large part of the carbonaceous matter that reaches 

the sea floor is preserved because the bottom water is 

drawn from the oxygen-minimum layer of the open Atlantic (Currie, 1953). The presence or absence of barriers to bottom circulation must therefore be deduced 

from other evidence. Similarly, the presence of carbonnaceous matter and the formation of pyrite is not certain evidence that the bottom water contained H2S and 

had a negative redox potential. For example, Emery 

and Rittenberg (1952, p. 738, 781) found that surface 

sediments in basins off the California coast contain as 

much as 11 percent carbonaceous matter, even though 

the Eh of the bottom water is positive; their cores show 

that negative Eh values and pyrite apparently form 

during diagenesis. Even so, highly carbonaceous sediments most commonly accumulate where bottom circulation is impeded, and in some such areas, reducing 

conditions prevail in the bottom waters.

PHOSPHATIC MUDSTONE

Phosphatic mudstone, though a modal type, differs 

from weakly phosphatic mudstone only by having a 

much higher phosphate content and, if the data from 

Sheep Creek may be extrapolated to other areas, by 

having a slightly greater ratio of clay minerals to 

quartz. The origin of the detrital and carbonaceous

fractions was probably much the same as for those of 

the mudstone; so, only the origin of the apatite is 

discussed.

SOLUBILITY OF APATITE

The most pertinent data on the solubility of apatite 

are those of Kazakov (1950), who studied phase relations at room temperature in the system P2O5 -CaO-FH2O. In his experiments that were conducted in the 

pH range found in the oceans, the CaO concentrations 

were well below that of sea water; so, his solubility data 

cannot be applied directly to natural conditions. The 

general relationships however, are informative. Very 

generally, Kazakov found that in acid or near neutral 

solutions Ca3P2O8 'H2O is precipitated, but in those 

having a pH more than about 7.1, the apatite Ca5 (PO4 )s 

(F,OH) is the stable phase. The solubility of the 

apatite increases slowly as the pH decreases from 10.5 

to about 7.9 and then increases rapidly as the pH decreases further.

SOURCE OF PHOSPHORUS

It has generally been accepted that marine waters 

were the source of phosphorus in the Phosphoria. McKelvey and others (1953, p. 56-57) calculated that the 

Phosphoria Formation in all the western field contains 

1.7 X1012 metric tons of P2O5 , which is more than five 

times the amount in the ocean, and that over a period 

of 15 million years, about half of Permian time, between 

15X1012 and 68X1012 metric tons of P2O5 would be 

added to the sea. They conclude that the ocean would 

have been an adequate source for phosphate of the Phosphoria but that oceanic circulation through the area 

would have been necessary.

MANNER OF DEPOSITION

Various hypotheses on the origin of marine phosphorites have been summarized by Mansfield (1927, p. 362) 

and by Kazakov (1937, p. 95). In general, the hypotheses may be divided into two groups the chemogenic 

and the biogenic.

The most comprehensive and persuasive hypothesis of 

the chemogenic origin of marine phosphorites has been 

advanced by Kazakov (1937). Briefly, Kazakov believed that phosphate is precipitated where deep waters 

of the sea basins, rich in phosphorus, ascend a shelving 

bottom. Precipitation results from decreasing partial 

pressure of CO2 , and thus increasing pH, as the water 

rises. Kazakov stated that precipitation cannot occur 

either in the zone of photosynthesis, where phosphorus 

is extracted by organisms, or in the deep regions of the 

sea, where the CO2 content is too great; the most favorable depth is stated to be between 50 and 200 meters. 

The necessary conditions for precipitation are a direct 

connection of the zone of precipitation with the part 

of the ocean that lies from 200 to 500 meters below the
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 375

surface and the existence of cold phosphate-rich, bottom 

currents that ascend the shelf into,the zone of precipitation. A more detailed summary of the work of 

Kazakov and a discussion of its application to the 

Phosphoria Formation is found in a paper by McKelvey 

and others (1953). Van Vloten (1954, p. 140) pointed 

out that, contrary to the assumptions of Kazakov, upwelling currents are not warmed very much below the 

photic zone, and oceanographic data (Sverdrup and 

others, 1942, fig. 198) indicate that below the photic 

zone, temperatures, salinity, and oxygen content all 

remain relatively constant in the up welling mass. 

As discussed on page 377, oolitic phosphorite 

resulted directly from precipitation of apatite from sea 

water, but these beds, formed at depths of less than 

60 meters, contain only a small amount of the total 

apatite in the Phosphoria.

The biogenic hypotheses postulate that the phosphorus is extracted from sea water by organisms. 

After death of the organisms, the phosphorus then dissolves and is then precipitated inorganically. A variant on the hypothesis proposed by Breger (1911) is 

that the phosphorus is extracted from sea water by 

microorganisms and deposited directly as the phosphate 

mineral.

The adequacy of the hypothesis indicating extraction 

by planktonic organisms may be tested by computing 

the amount of time necessary for organisms in an area 

of high organic productivity to extract an amount of 

phosphorus equivalent to that in the Retort Member. 

If 475 grams of organic carbon were produced each 

year for each square meter of area, 9.64 X106 metric 

tons of carbon would be produced yearly in an area 

equivalent to that outlined by the dashed line in figure 

154. If 1:106 is the ratio of phosphorus to carbon in 

plankton (Redfield, 1958), 9.1 X104 metric tons of 

organic phosphorus would be produced. This amount 

should be reduced by one-fourth, or to 6.8 X104 metric 

tons, to account for recycling within the photic zone 

(Sverdrup and others, 1942, p. 40). The Retort Member shown within the dashed line in figure 154 contains 

9.4 X1010 metric tons of apatite, or 1.6 XlO10 metric 

tons of phosphorus. At the assumed rate of organic 

production, (1.6X1010 )/(6.8X104 )=235,000 years 

would be required for the plankton to extract the 

amount of phosphorus in the Retort. If the more 

reasonable assumption is made that high organic productivity was restricted to a zone of upwelling similar 

to that off the coast of California (p. 369), the time 

required to extract the phosphorus in the Retort would 

have been 1,300,000 years.

In the ocean, inorganic phosphorus is rapidly liberated from sinking, decaying plankton (Barnes, 1957, p.

304), and most of the phosphorus is apparently released 

within the upper few hundred meters of the water 

column (ZoBell, C. E., 1946, p. 167-169). Therefore, 

in order for any large amount of the phosphorus extracted by the plankton to have been incorporated in 

sediment, it seems necessary to assume that most of 

the Phosphoria sea below the zone of photosynthesis 

was saturated with phosphorus. The release of phosphorus from decaying plankton would thus have resulted in supersaturation and precipitation.

With our present knowledge, we are not able to 

determine whether most of the apatite pellets resulted 

from biogenic or strictly chemogenic processes. More 

information is needed on the character of marine water 

in areas of upwelling and in other highly productive 

areas before it can be known whether any large amount 

of apatite can be precipitated by rising waters below 

the zone of photosynthesis or whether any conditions 

exist under which a large proportion of phosphorus extracted by planktonic organisms can be incorporated 

into the bottom sediment.

ORIGIN OF PELLETS

The pellets in the phosphatic mudstone do not appear 

to have been transported but were probably formed 

either at the surface of or within the unconsolidated 

sediment. Neither do they appear to have resulted 

from replacement of calcite pellets or oolites; for not 

only have we seen no evidence of any such replacement 

features, but we do not know of any calcareous sediment that even remotely resembles the phosphatic mudstone in texture.

The phosphatic mudstone is similar in texture to mud 

of the Clyde Sea area that consists largely of faecal 

pellets (Moore, 1931, p. 337). Nearly all the phytoplankton is eaten by animals (Harvey, 1955, p. 40), 

but Moore found that the pellets of planktonic organisms are friable and break down and that most of the 

pellets in the sediment are those of burrowing benthonic 

organisms. The apatite pellets of the Phosphoria may 

indeed be faecal pellets that have been infiltrated by 

phosphate, but the fine alternate lamination of pellets 

and mudstone and of silt and clay that is common in 

many specimens indicates that the sediments were undisturbed after deposition and suggests that bottomdwelling and burrowing organisms were not common.

As pointed out by McKelvey and others (1953, p. 61), 

both natural phenomena and industrial pelletizing 

processes demonstrate that fine-grained particles may 

be aggregated in many ways, and a faecal origin is 

not proved merely by the presence of pellets. Rather, 

the pellets may have formed directly by precipitation 

from sea water, or they may have resulted from in-
376 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

113° 112° 111°

MONTANA 

WYOMING

FIGURE 154. Thickness of apatite in the Retort Phosphatic Shale Member of the Phosphoria Formation. Dashed line encloses area for

P&rcent apatite X bed thickness which, volume calculations are made. Constructed by summing

X, control point showing calculated thickness in feet; A, control point, data approximate.

&f &u bedg . Q the member at each locality.

organic accretion of phosphatic material disseminated 

through the freshly deposited sediment.

BIMODAL FREQUENCY DISTRIBUTION OF MUDSTONE

The occurrence of distinct mudstone and phosphaticmudstone modes in the frequency distribution of rock 

types in the Ketort Member could have resulted either 

from a preferred rate of apatite deposition or from a 

preferred locus of deposition. Analysis of data from 

the Sheep Creek section has shown that the acid insoluble/A12O3 ratio in phosphatic mudstone is higher than 

that in weakly phosphatic mudstone, which suggests 

that the bimodality resulted from a preferred locus of

deposition. That is, phosphatic mudstone was, in 

general, deposited in quiter and probably deeper water 

than was the weakly phosphatic mudstone.

SUMMARY

Most phosphatic mudstone was deposited in quiet 

water below wave base. Although the surface water 

was sufficiently aerated to support large quantities of 

plankton, the bottom water contained little or no 

oxygen. Apatite may have been precipitated inorganically by an increase in the pH of upwelling water; but 

much, and perhaps most, of the phosphate was probably 

derived from planktonic organisms that extracted it
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 377

in the euphotic zone but settled into deeper phosphorus^ 

saturated water after death. The pellets may be replaced or infiltrated faecal pellets or may have resulted 

from inorganic accretion of disseminated phosphate 

within or at the surface of the sediment. Phosphatic 

mudstone was deposited in probably less agitated water 

than was weakly phosphatic mudstone.

PHOSPHORITE

Much of the preceding discussion applies to those 

phosphorites that do not seem to have been reworked 

as well as to phosphatic mudstone. However, the ratio 

of organic carbon to phosphorus in these phosphorites 

is much lower than in phosphatic mudstone. Several 

explanations are possible: (1) the apatite may have 

been precipitated inorganically from the sea water; 

(2) phosphorus may have migrated from adjacent 

beds; (3) currents may have removed carbonaceous 

matter without disturbing either the pellets or fine 

clastic material; (4) the oxygen content of the bottom 

water may have been sufficient to oxidize most of the 

carbon that reached the sea floor; or (5) part of the 

carbonaceous matter may have been converted to hydrocarbons that subsequently escaped. Whichever explanation is correct, it need apply to only a minor 

amount of the total apatite, for this type of phosphorite 

is not abundant in Montana.

A large proportion of all phosphorites and most 

high-grade phosphorites have been subjected to current 

activity and are, to some extent, mechanical concentrates. The following discussion refers to this type.

The immediate source of the phosphorus was threefold: (1) apatite pellets were reworked from phosphatic muds; (2,') phosphatic skeletal fragments were 

supplied by organisms; and (3) apatite was precipitated from sea water in layers surrounding nuclei of 

skeletal fragments, apatite pellets, or quartz and 

chert grains. That the apatite oolites common in these 

phosphorites resulted from direct precipitation of the 

phosphatic material, and not from replacement of calcareous oolites, is indicated by the fact that most nuclei 

are skeletal fragments and pellets that were themselves 

originally phosphatic.

Many phosphorite beds contain fine and medium 

quartz sand; so, they must have been deposited at about 

the same depth as were sands of the Shedhorn that 

is, in water less than 60 meters and probably less than 

30 meters deep. On the Bahama Bank, calcareous 

oolites occur in areas of particularly strong tidal currents and on beaches where warm wave-generated currents wash back and forth over them; they do not 

begin to form until the water is sufficiently warmed

to become supersaturated with calcium carbonate 

(Illing, 1954, p. 43). Much of the Bahaman oolitic 

sand has been heaped up by currents into great submarine ridges or "dunes" (Newell and Rigby, 1957, 

p. 56). The oolitic phosphorites of the Phosphoria are 

so similar in texture to the Bahaman oolitic sands that 

they, too, probably formed in extremely shallow water 

where they were continually moved back and forth 

by waves. The irregular distribution of the basal 

phosphorite of the Meade Peak Member in the Centennial Mountains and in Yellowstone National Park 

suggests comparison with the submarine "dunes" of 

the Bahamas.

Reworked pelletal phosphorites were formed probably in somewhat deeper water, where the current 

velocity was sufficient to remove the fine detritus but 

not necessarily strong enough to move the pellets any 

significant distance. Similar-appearing calcareous 

sand on the Bahama Bank forms by aggregation of 

calcareous silt where the current is sufficiently strong 

to remove matrix silt and to prevent the formation 

of multiple aggregates (Illing, 1954).

The apatite oolites have obviously formed in water 

that was saturated with phosphorus, and inasmuch as 

the water was both shallow and agitated, the pH was 

certainly above 7.8, probably above 8.0, and perhaps 

as high as 8.2 (Sverdrup and others, 1942, p. 209; 

Bruneau and others, 19!53, table 1). The absence of 

significant calcite or dolomite in the shallow-water 

phosphorites suggests that either the salinity or the 

temperature, or both, were lower than in areas of 

carbonate deposition of the present day. Trask (1937) 

showed that in positive correlation exists between 

salinity of surface water and the calcium-carbonate 

content of modern marine sediments and noted that 

where the surface salinities are less than 34 parts per 

thousand the carbonate content of the sediment is generally less than 5 percent. The oolitic apatite rings, 

therefore, were probably deposited where water 

saturated or nearly saturated with phosphorus but 

having a salinity of 34 parts per thousand or less 

entered a shallow area where the pH was increased 

by contact with the atmosphere and by biologic 

processes.

After burial, many of .the current-deposited phosphorite beds were cemented by clear apatite. The 

phosphorus in the apatite cement must have migrated 

a significant distance, for neither the entrapped water 

nor the small amount of carbonaceous matter that could 

survive in an agitated shallow water environment 

would have been an adequate source, although solution 

at grain contacts might have supplied small amounts.
378 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

CARBONATE BOCK

PARK CITY FORMATION

By far the greater part of the carbonate rock in the 

Park City Formation of Montana is dolomite. The 

skeletal dolomite was formed from the replacement of a 

calcareous sediment, but the much more common 

aphanitic dolomite bears no direct evidence of either 

primary or secondary origin; however, inasmuch as 

there is no clear evidence that dolomite has ever been 

directly precipitated in a marine environment (Fairbridge, 1957, p. 130), we assume that the aphanitic 

dolomite has also resulted from replacement.

The source of the calcium carbonate in the skeletal 

rocks is obvious, but the aphanitic carbonate rocks may 

have formed either as a primary precipitate or as an, 

accumulation of comminuted shell debris. Whether 

the sediment was of organic or inorganic origin, the 

water must have been nearly saturated with calcium carbonate, at least in the surface layers; for unlike silica, 

calcium carbonate can be extracted in quantity by 

organisms only when the salinity is high and the water 

is nearly saturated (Trask, 1937, pi. 71; Sverdrup and 

others, 1942, p. 999). During deposition of the carbonate of the Park City Formation, the surface 

salinity was therefore probably greater than 34 parts 

per thousand.

The carbonates were deposited under a wide range of 

current conditions. Much of the aphanitic dolomite in 

the Grandeur Member of the Park City was deposited 

in tranquil water, which, in the absence of any physiographic barriers, must mean depths below 30 or 40 

meters. On the other hand, skeletal rocks of the 

Franson Member must have accumulated above wave 

base.

Sheldon (1963) showed that in the Permian of 

western Wyoming, dolomite occurs shoreward from 

limestone of equivalent age; the distribution of rock 

types in the Franson Member of Montana (fig. 103) 

suggests a similar relationship. These facies positions 

of limestone and dolomite indicate that dolomitization 

took place soon after deposition. The grain size of the 

calcite (or aragonite) lutites was preserved during the 

dolomitization, but the presence of sandy aphanitic 

dolomite indicates that aggregate structures such as 

pellets and fossil fragments were destroyed in some 

beds.

FHOSFHORIA FORMATION

Carbonate rock in the shale members of the Phosphoria Formation is interbedded with mudstone and 

phosphorite that accumulated below wave base in 

tranquil oxygen-deficient water, which are conditions 

unfavorable for the growth of a benthonic fauna. The

carbonate beds must have been deposited under similar 

conditions; so, it seems unlikely that they could represent accumulations of comminuted or altered shells of 

bottom-dwelling organisms. Inasmuch as pelagic Foraminifera did not exist until the late Mesozoic, 

the Phosphoria carbonate was probably precipitated 

inorganically.

The paucity of rocks intermediate in composition 

between carbonate rock and mudstone or between carbonate rock and phosphorite (fig. 105) indicates that 

carbonate was deposited much more rapidly than either 

the fine detritus or the apatite. This accords with the 

statement of Krumbein and Garrels (1952, p. 9) that 

when calcite and phosphorite coprecipitate because of 

pH increase, the ratio is very high in favor of calcite; 

so, the resulting sediment is composed of calcite and 

only a trace of phosphorite. The carbonate beds of 

the shale members, therefore, may have been precipitated by a slight increase in pH, but an increase in 

salinity might also have resulted in precipitation.

In isolated basins in which the renewal of bottom 

water is slow, the deeper water tends to become saturated with calcium carbonate (Fleming and Kevelle, 

1939, p. 101). It is not surprising, then, that interbedded carbonate rock in both shale members of the 

Phosphoria of Montana is most commonly found in 

the nodular phosphorite facies which accumulated in 

the deepest part of the sea.

PALEOGEOGRAPHY

Permian paleogeography has been reconstructed 

from the distribution of facies and from conclusions 

on the origin of rock types and is thus more tenuous 

than either. Use of alternate correlations and alternate hypotheses of origin could alter the paleogeographic maps considerably, but the reconstruction 

presented here is that which is best supported by the 

available evidence and is probably consistent and 

plausible.

The inferences on which the paleogeographic maps 

(p. 25) are based are as follows:

1. Well-sorted sandstone accumulated at depths of less 

than 30 meters.

2. Silty sandstone accumulated below wave base on 

slopes steeper than those on which well-sorted 

sand was deposited.

3. Chert accumulated as a spicule ooze at depths generally less than 50 meters.

4. Oolitic phosphorite accumulated in agitated water 

at depths not greater than a few tens of meters.

5. Sand was derived from a source area in central 

Montana and from a source area near the Bitterroot Range.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 379

6. The land areas are assumed to have been emergent 

only during those times in which their presence is 

clearly indicated by facies distribution. 

The depths of water indicated for deeper parts of the 

basin during deposition of the Meade Peak and Eetort 

Phosphatic Shale Members of the Phosphoria Formation are only rude estimates.

The evidence for the existence of two source areas 

has been discussed previously, but it should be emphasized that neither the configuration nor the size of 

either source is known and that although the general 

location of the source of the eastern detritus can be 

deduced with some confidence, only the general direction in which the source of the western detritus lay is 

known. In the following discussion the source of the 

western terrigenous material is termed the "western 

source," and that of the eastern terrigenous material, 

the "eastern source."

Although the rocks can be divided with little difficulty into those deposited above and those deposited 

below wave base, only relative depths of accumulation 

can be determined within the deeper water group. 

For example, the nodular phosphorite facies of the 

Eetort Member was deposited in the deepest part of 

the basin, but this may have been as shallow as 100 

meters or as deep as 1,000 meters. In the Pacific Ocean 

of the present day, the oxygen-minimum layer is at 

depths of 300-400 meters, and if the bottom water of 

the Retort and Meade Peak seas was drawn from this 

layer, the deeper parts of the basin must have been 

under at least 300 meters of water. Eichards and 

Vaccaro (1956) found that in the Cariaco Trench off 

the Venezuelan coast, anaerobic conditions are found 

only below depths of about 375 meters, although the 

maximum depth of the sill seperating the basin from 

the rest of the Caribbean is only 150 meters. If the 

bottom circulation in the Meade Peak and Eetort seas 

was restricted by topographic barriers, we might infer 

from comparison with the Cariaco Trench that the 

highly carbonaceous rocks of the shale mmbers were 

deposited under at least several hundred meters of 

water.

Several interesting relationships are suggested by 

the paleogeographic maps. Neither the eastern nor the 

western source supplied much sand while phosphorite 

and carbonaceous mudstone were being deposited, and 

there is no conclusive evidence that either source was 

emergent during most of Meade Peak and Eetort times; 

large amounts of bedded chert were formed when the 

western source supplied only small amounts of sand 

(Eex time) or no sand at all (Tosi time). These were 

the times during which the surface water was less than 

34 parts per thousand in salinity but, as shown by the

sponge fauna, was still sufficiently saline to be considered normal marine in character. They were also 

times of high organic productivity. On the other hand, 

when the western source was supplying large quantities 

of sand, the salinity of the surface water was greater 

than 34 parts per thousand, and carbonatic sediments 

were deposited. Exceptions to these relationships 

would seem to have occurred during Early Grandeur 

time, but if the Grandeur Member of the Park City 

is equivalent to the upper part of the Wood Eiver 

Formation, a western land existed, but west of the 

area of this report.

Whenever the distribution of detritus indicates that 

a strong and persistent current existed, the current 

flowed southward and southeastward. The first evidences of the current are seen in the upper part of the 

Grandeur Member of the Park City Formation. The 

current influenced the distribution of shallow-water 

sediments in both Franson and Tosi time, and it presumably persisted through Meade Peak and Eetort 

time. When the western source was supplying sand, 

the current apparently flowed through the extreme 

southwestern part of the area; but when the western 

source was not supplying sand, as during Tosi time, the 

current flowed south through the central part of the 

area. During such times, the salinity and probably 

the temperature were low. The current was thus similar in both direction of flow and in the character of the 

water to the southward-flowing California current of 

the present Pacific, which consists of cool (10°-15°C) 

subarctic water having surface salinities of 33 to 34 

parts per thousand (Sverdrup and others, 1942, charts 

2, 3, and 4). The Permian current, like the California 

current, was probably part of the major northern 

Pacific circulatory system.

Permian geography west of the area of this report 

is not well known, for the nearest rocks known to be of 

post-Wolfcamp Permian age are in the Seven Devils 

region of western Idaho, about 150 miles west of the 

feeaverhead Eange (Anderson, 1930). These rocks are 

marine volcanics. The Casto Volcanics, which occur 

about halfway between the Seven Devils region and the 

Beaverhead Eange, are somewhat similar to the Seven 

Devils Volcanics and may be Permian (Eoss, 1927), 

but neither their age nor their environment of deposition is known. Land areas, perhaps large ones, may 

have existed west of Montana, as suggested by Eoss 

(1934, p. 999), even during those times in which their 

existence is not reflected in the distribution of detritus, 

but the evidence of a persistent southward-flowing 

current of North Pacific character strongly suggests 

that any such land areas were insular.
380 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

At the present time, intermittent upwelling occurs in 

the California current at least as far north as the latitude of southwestern Montana. The prerequisite for 

upwelling along a western coast in the Northern Hemisphere is a prevailing wind having a southward component parallel to the coast (Sverdrup and others, 1942, 

p. 501) ; the driving force for upwelling in the California current is the northeasterly trade winds and the 

westerlies that in the summer actually blow over the 

coast from the northwest. Poole (1957) concluded 

from the analyses of the direction of eolian crossbedding on the Colorado plateau that during Paleozoic 

and early Mesozoic time the Northern Hemisphere 

trade-wind belt was 10° to 20° farther north than at 

present. If so, Montana was well within the zone of 

northeast trade winds.

Even though the western source may not have been 

subaerially exposed in Meade Peak and Retort times, 

the general area of the Beaverhead Range was shallower than the basin to the east and may have served 

to restrict the circulation of bottom water in the southwestern Montana basin.

TECTONISM

During most of Paleozoic time southwestern Montana 

was a semistable cratonic shelf separated from the 

Rocky Mountain geosyncline of central Idaho by a 

recurrently positive hinge that migrated between the 

Tendoy Mountains of Montana and the Lemhi Range 

of Idaho (Scholten, 1957, p. 168). The relations of 

the Permian of southwestern Montana extend this concept of the Paleozoic tectonic framework into Permian 

time.

The general area of the Beaverhead Range subsided 

less rapidly than did the Tendoy-Snowcrest area in 

Permian time, and by analogy with the earlier Paleozoic it may be considered to be part of the hinge separating the semistable cratonic shelf of southwestern 

Montana from a geosyncline to the west. The width 

of the hinge area is not known, but thick eugeosynclinal 

deposits were being formed in westernmost Idaho.

The area now occupied by the Snowcrest Range and 

the Tendoy, Blacktail, and Pioneer Mountains was submerged throughout Permian time. Although the area 

was mainly one of subsidence, intermittent uplift 

periodically brought deeper water sediments to above 

wave base, resulting in the winnowing and reworking 

of the sediments and in the superposition of shallowwater sediments on deep-water sediments.

The area east of Ruby Valley may be considered to be 

part of the craton proper. The part of the area from 

the Gravelly Range to the Gallatin Range was submerged most of the time, but the water was shallow

and the accumulated sediments were relatively thin. 

During at least part of Retort time, the area of the 

Madison Range appears to have subsided more than 

the areas of either the Gravelly or Gallatin Ranges. 

The Sweetgrass Arch and the Central Montana Platform were low positive .areas much of the time, but 

movements of small amplitude resulted in expansion 

and contraction of the land area and in intermittent 

reworking of sediments about its margin.

The vertical movements of the three major tectonic 

elements the eastern source area, the southwestern 

Montana basin, and the northwestern source area are 

illustrated in figure 155. The sequence of uplift and 

subsidence in the Beaverhead Range was probably 

similar to that of the western source area, but the 

range was entirely below sea level. The three tectonic 

elements moved in concert from the beginning of 

Meade Peake time through Retort time, but not in 

Grandeur or Tosi times.

The uplift and subsidence from the beginning of 

Meade Peak time through Retort time when the three 

elements seem to have moved together may have resulted from eustatic changes in sea level, but differential 

vertical movements, perhaps basement-controlled, seem 

to have occurred during Grandeur and Tosi times.

Both the basal bed of the Meade Peak Member and 

the uppermost bed of the Permian sequence are shallowwater deposits over most of the area; so, the thickness 

of beds from the base of the Meade Peak to the base of 

the Dinwoody is a close estimate of the net amount of 

subsidence in post-Grandeur time (fig. 156). Maximum net subsidence was about 500 feet in the vicinity 

of Lima. The Beaverhead Range subsided nearly 300 

feet; half of the subsidence took place in Tosi time. 

Subsidence in the northern and eastern parts of the 

area can only be estimated because of post-Permian 

erosion, but it probably amounted to less than 200 feet.

TRANSGRESSION AND REGRESSION

The sequence of Permian strata in western Wyoming, 

which is very similar in character to that in southwestern Montana, was explained by Sheldon (1957, p. 

152) as having resulted from two transgressions and 

regressions of areally zoned environments. The major 

features of the Permian sequence in southwestern Montana may be explained in a similar manner. The phosphatic shale members represent two transgressions, 

whereas the two members of the Shedhorn Sandstone 

and their equivalents represent two regressions. The 

record in Montana, however, is not as clear as that in 

Wyoming. Transgressive and regressive relationships 

are obscured by sand from two source areas that were
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 381

NORTHWESTERN 

SOURCE AREA BASIN

EASTERN 

SOURCE AREA

Tosi time

Retort time

Franson time

Rex time

Meade Peak time

Grandeur time

Quadrant time

HIATUS

m

EXPLANATION

Subsidence

Uplift

Below sea level

FIGURE 155. Vertide movements of Permian tectonic elements.

not always rising or subsiding simultaneously, and intermittent uplift of the source areas destroyed parts of 

the record in the marginal parts of the basin.

SUMMARY OF PERMIAN EVENTS IN 

SOUTHWESTERN MONTANA

During Quadrant time, sand was spread westward 

across southwestern Montana. Deposition kept pace 

with subsidence and the sea remained shallow over the 

entire area, but in Early Permian time either increasing subsidence or a decreasing supply of sand resulted 

in a lowering of the sea floor in the areas west of the 

Ruby River and in the deposition below wave base 

of carbonate lutite of the Grandeur Member. The carbonate facies may have transgressed eastward. In 

central Idaho a land area probably existed that to some 

extent restricted oceanic circulation in the southwestern 

Montana sea. The Grandeur sea was relatively warm 

and saline and lacked strong currents.

Toward the end of Grandeur time subsidence in the 

center of the basin was accompanied by a complement70&-931 O 63 8

ary uplift in the eastern source area located in central 

Montana and by uplift of a source area to the northwest, perhaps near the site of the Bitterroot Range. 

Both sources were composed of older sediments. A 

Current flowed souther istward through the southwestern corner of the area and distributed detritus from 

the northwestern source area. Carbonate continued to 

be deposited.

The record of earliest Meade Peak time is not preserved in Montana, for whatever sediments may have 

been deposited were removed on subsequent uplift. 

The first Meade Peak sediments preserved in the area 

were deposited in a siallow sea that in most places 

could not have been more than a few tens of meters 

deep. Neither source area supplied sand, and both may 

have been submerged. Water rich in phosphorus 

moved upward onto the shallow shelf and became supersaturated by an increase of pH that resulted from 

photosynthesis and from contact with the atmosphere. 

Apatite was then deposited in the shallow agitated water as oolitic rings aroind nuclei consisting of skeletal
382 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

113° 112° 111°

Strata partly stripped by pre-Ellis (Jurassic) 

erosion

a partly stripped by pre-Dmwoody 

(Triassic) erosion

FIGURE 156. Isopach map of strata between the base of the Meade Peak Phosphatic Shale Member of the Phosphorla Formation and the 

base of the Dinwoody Formation. X, control point showing measured thickness in feet; A, control point, data approximate.

fragments, reworked pellets, and quartz grains. The 

oolites were continually washed back and forth and in 

places were piled up in banks. The water was cool 

and, although still normal marine in character, of relatively low salinity.

The rate of subsidence increased in late Meade Peak 

time, and the sea floor in much of the area was lowered 

well below wave base. A submarine ridge near the 

Beaverhead Kange may have restricted bottom circulation!. A current, probably upwelling, that flowed 

southward through the area and consisted of cool subarctic marine water having relatively low salinity supported a rich growth of plankton. After death, the

planktonic organisms settled into deeper water, either 

directly or as faecal pellets of grazing zoo-plankton, 

and supplied both carbon and phosphorus to the bottom 

sediments. Water below the photic zone was deficient 

in oxygen and saturated with phosphorus. Water in 

the deepest part of the basin periodically became supersaturated with calcium carbonate, which was then 

rapidly precipitated.

At the beginning of Hex time, the sea floor was raised 

to within the photic zone over most of the area, probably by uplift rather than by sedimentary filling. The 

eastern source area again supplied sand. The southward-flowing current supported a dense Demospongia
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 383

population, and spicules accumulated to form a siliceous ooze. Currents winnowed out some of the smaller 

spicules and deposited them with silt and clay in those 

parts of the basin that were below wave base. The 

growth of calcareous organisms was inhibited by the 

low temperature and salinity of the inflowing subarctic 

water. The northwestern source area locally supplied 

some sand in Rex time.

Sand and silt were supplied by the northwestern 

source area during all of Franson time. Much sand 

was also derived from central Montana during early 

and late Franson times, but carbonate sediments transgressed as far east as the Madison Eange during the 

middle of the interval. Emergence of the northwestern source area deflected the major southward-flowing 

current west of the area, and the sea in southwestern 

Montana became warmer and more saline. The sea 

continued to be shallow, probably no deeper than 30 or 

40 meters in most places, and skeletal carbonate sands 

were deposited. Subsidence was slow and was approximately compensated by sedimentation.

Sharp subsidence marked the beginning of Eetort 

time. Neither source area supplied sand, and both 

may have been submerged. A submarine ridge extended southward approximately along the present 

Montana-Idaho State line. Submergence of the northwestern source area again permitted the southwardflowing current to move through the area. Plankton 

bloomed and supplied carbon and phosphorus to the 

bottom sediments, as in late Meade Peak time. These 

conditions were interrupted briefly in middle Retort 

time by uplift in the eastern part of the area that resulted in the deposition of sand and chert now exposed 

in the Snowcrest Range and possibly in the destruction 

of lower Retort sediments that may have been deposited 

east of Ruby Valley. Events in late Retort time were 

similar to those in early Retort time; but the basin was 

not as deep, and phosphatic mud deposited in the Snowcrest and Dillon areas was intermittently reworked. 

Late Retort subsidence in the Madison Range resulted 

in the deposition of deeper water sediments there than 

to the west in the Gravelly Range. Some of the deeper 

water, rich in phosphorus, moved eastward onto the 

shallow shelf, where apatite was deposited as oolites by 

an increase in pH.

In Tosi time, most of the basin was again under less 

than 50 meters of water, probably largely as the result 

of uplift. Sand was again derived from central Montana, but the northwestern source area was either of 

small extent or remained submerged. The southwardflowing current continued to sweep through the area

and distributed sand from an unknown source as a long 

tongue extending southward. The area not covered, 

by sand supported a dense sponge population, and its 

floor was covered by a spicule ooze. Sand gradually 

spread westward from the central Montana source area 

and eventually filled the study area from the shore to 

the southward-extending tongue. Toward the end of 

Tosi time, the salinity increased to a concentration 

where some carbonate was deposited. Tosi time was 

probably succeeded in much of the area by a period of 

noiideposition that possibly resulted from base-leveling 

of central Montana and the attainment of a profile of 

equilibrium in southwestern Montana, but sedimentation may have continued into Triassic time in the. Lima 

region.

STRATIGRAPHIC SECTIONS

INTRODUCTION

The stratigraphic sections measured in southwestern 

Montana as part of the U.S. Geological Survey's investigation of the western phosphate field and the chemical analyses of the sampled beds are presented in the 

following pages. Specific credit for each measured 

section is given in the heading for the section. The 

rock names assigned in the field have been revised where 

necessitated by the chemical analyses or by the study 

of hand specimens and thin sections. Swanson is responsible for the revision and final preparation of the 

stratigraphic sections in the Madison and Gallatin 

Ranges and the Centennial Mountains; Cressman is 

responsible for the others. Brief descriptions of thin 

sections have been added to several of the stratigraphic 

sections in the Madison and Gallatin Ranges where relatively close-spaced samples have been studied.

The rock names in the bed descriptions consist of (1) 

a noun denoting the dominant constituent, (2) adjectives denoting other constituents present in amounts 

greater than 20 percent that are arranged from left to 

right in order of increasing abundance, and (3) adjectives also arranged from left to right in order of increasing abundance that describe the size and type of grains 

comprising the dominant constituent. The rock name 

is combined with terms describing hardness, thickness 

of bedding, and color; additional information, such as 

the presence of an unusual or distinctive mineral occurring in amounts of less than 20 percent or the grain size 

of a subordinate constituent, is denoted by phrases such 

as "contains glauconite" or "quartz sand is fine." The 

terms used have been defined on page 282.

The sections are arranged in order according to the 

lot number; so, sections in a particular area must be 

located by first referring to plates 14 or 15.
384 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Shell Canyon, Mont., lot

[Permian rocks measured, and Retort Phosphatic Shale Member of Phosphoria Formation sampled from cliff exposures and hand trench on north side of Shell Creek Canyon 

about 600 ft above canyon floor, SEJ4NEJ4 sec. 33, T. 6 S., R. 1 E., Madison County, Mont., near crest of small denial structure at west side of Madison Range synclme, 

in August 1947. Beds strike about N. 5° W. and dip 10-15° W. Measured by R. W. Swanson and sampled by 3. A. Mann and 3. Q. Evans. Analyzed for PsO5 and 

acid insoluble by U.S. Bur. of Mines, and for uranium by U.S. Qeol. Survey]

Chemical analyses (percent)

Bed

D-76.

Us-75.

74.

73.

72. 

71.

70.

Description

Din woody Formation, basal bed:

Limestone: dolomitic, hard, very finely 

crystalline, medium- to thick-bedded, 

light-brownish-gray (5YR 6/1). 

Stringers penetrate underlying bed. 

Contains many Lingula shells in lower 

part. 

Upper member of Shedhorn Sandstone:

Sandstone: locally carbonatic and 

cherty, very fine grained, hard, 

light-brownish-gray (5YR 5/1). 

Maximum overgrowths on dustyrimmed subrounded quartz grains. 

Light-brown apatite pellets, 10 percent, including some rims on quartz 

grains; chert grains, 5-10 percent. 

Stringers of limestone projecting 

from overlying bed into cracks in 

the quartzite contain coarse grains 

of similar quartzite having minor carbonate matrix, and carbonate penetrates very little beyond walls of 

cracks in quartzite, suggesting early 

silicification (overgrowths) and subsequent unconformable deposition 

of limestone of the Dinwoody.

Sandstone: very fine grained, hard, 

thick-bedded to massive, lightbrownish-gray (5YR 6/1). Small 

chert concretions and lenses in upper 

2 ft and laminated chert common 

near base. Somewhat calcareous in 

lower part. Basal contact irregular.

Chert and sandstone: thin-bedded hard 

light-brownish-gray (5YR 6/1) chert 

mottled with dark gray and crossed 

by closely spaced 1- to 3-in.-diameter 

columns of hard very fine grained 

light-brownish-gray (5YR 6/1) to 

brownish-gray (5YR 4/1) sandstone 

containing small dark apatite pellets. 

Bed is 2 ft thicker 300 ft to east.

Sandstone: hard, thick-bedded, 

medium-grained (coarser near top), 

light-brownish-gray (5YR 6/1).

Carbonate rock and sandstone, interlaminated: cherty, sandy microcrystalline carbonate rock interlaminated with cherty, calcareous 

very fine grained sandstone; both 

are hard and light-brownish-gray 

(5YR 6/1). Carbonate generally 

more finely crystalline in carbonaterock layers and commonly rhombic 

in sandy layers and in cherty areas; 

quartz grains subangular having 

common but incomplete overgrowths; 

chalcedonic chert is disseminated 

through carbonate rock and locally 

constitutes the principal cement of 

sandstone layers and irregular 

patches in carbonate-rock layers; 

chert grains and clear to dusty lightbrown apatite pellets common in the 

sandstone. Layers thicker and carbonate content greater near top.

Sandstone: fine-grained, hard, lightbrownish-gray (5YR 6/1); contains 

numerous apatite pellets.

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Uranium

PaOs

Acid insolubleRadio- Chemical 

metric eU U

0. 75 0. 75

6. 0 6. 75

3. 4 10. 15

12.95

1. 45 14. 4

15. 1
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 385

Shell Canyon, Mont., lot 1214 Continued

Chemical analyses (percent)

Us-69.

68.

67.

66. 

65.

64.

63. 

62.

61. 

60.

Description

Upper member of Shedhorn Sandstone 

Continued

Chert and sandstone, interbedded: 

hard sandy grayish-brown to lightbrownish-gray (WYR 4/3 to SYR 

6/1) chert interbedded with finegrained light-brownish-gray cherty 

sandstone. Quartz grains moderately well rounded and dusty rimmed 

by overgrowths; overgrowths are 

euhedral in contact with phosphate 

but are corroded in chert layers; 

chert grains common in sandstone, 

chert layers rich in sponge spicules; 

beds contain about 5 percent colorless to brown apatite pellets and 

numerous phosphatic shell fragments 

and sponge-spicule canal fillings. 

Contacts between layers very sharp.

Chert: sandy, hard, grayish-brown 

(10 YR 4/3) to light-brownish-gray 

(SYR 6/1). Contains thin interbeds 

of fine-grained sandstone at base and 

irregular patches of sand elsewhere.

Sandstone: hard, fine-grained, thickbedded to massive, light-brownishgray (SYR 5/1). Contains chert 2.5 

ft above base. Quartz grains moderately well rounded and dusty 

rimmed by extensive overgrowths; 

in places, patches of chert containing indistinct sponge spicules; chert 

grains common in sandstone; bed 

contains 5 percent clear to dusty 

light brown apatite pellets and 

sponge-spicule canal fillings; rounded 

carbonate grains fairly common; 

rhombic carbonate grains in chert. 

Calcareous chert lenses are found 

along strike.

Chert: hard, thick-bedded, brownishgray (SYR 4/1); locally sandy.

Sandstone: cherty, hard, fine-grained, 

thick-bedded, medium to lightbrownish-gray. Chert lenses and 

nodules common in basal half and 

scattered in upper 1 ft. Irregular 

basal contact.

Chert and sandstone: very irregularly 

bedded hard light-gray (N 8) chert 

(75 percent) and hard fine-grained 

light-brownish-gray (SYR 6/1) sandstone. Irregular basal contact.

Sandstone: hard-fine-grained, thickbedded, light-brownish-gray (SYR 

5/1). Irregular basal contact.

Sandstone and chert, interbedded: 

thick-bedded hard very fine grained 

brownish-gray (5YR 4/1) quartzitic 

sandstone (60 percent) interbedded 

with hard light-gray (N 8) sandy 

chert (40 percent). Irregular basal 

contact.

Sandstone: hard, fine-grained, thickbedded, light-brownish-gray (5 YR 6/1). 

Irregular basal contact.

Chert: locally sandy, hard, poorly bedded, light-brownish-gray (SYR 6/1).

Uranium

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Acid in- Radio- Chemical 

soluble metric ell U

2. 1 17. 2

1. 5 18. 7

3. 4 22. 1

1. 0 23. 1

3. 0 26. 1

5. 8 31. 9

2. 9 34. 8

11. 3 46. 1

5. 2 51. 3

1. 7 53. 0
386 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Shell Canyon, Mont., lot 1214 Continued

Bed

Us-59-

58-

57-

56-

To-55-

54.

53.

52-

Description

Upper member of Shedhorn Sandstone 

Continued

Sandstone: hard, fine-grained, massive, 

brownish-gray (5YR 4/1). Quartz 

grains moderately rounded by much 

secondary growth; dusty orphosphatic rims on original grains very common; contains 5-10 percent brown 

and, in places, clear apatite pellets 

and sponge-spicule canal fillings; bed 

contains 5 percent carbonate grains 

generally rounded, some rimmed by 

phosphate and some by well-formed 

overgrowths. Irregular basal contact.

Chert: hard, thin-bedded, mediumgray (N 5) to brownish-gray (5F.R 

4/1); contains about 10 percent of 

lenses of hard fine-grained lightbrownish-gray sandstone. Irregular 

basal contact.

Sandstone: hard, fine-grained, thickbedded to massive, brownish-gray 

(5YR 4/1). Basal contact gradational over narrow zone.

Sandstone: cherty, hard, fine-grained, 

not bedded, light-brownish-gray (5 YR 

5/1); cherty patches irregularly distributed. 

Tosi Chert Tongue of Phosphoria Formation:

Chert: hard, thin- to thick- and rather 

poorly bedded, medium-dark-gray (N 

4); locally sandy; contains persistent 

sandstone parting at base, and in 

lower 1 ft, contains a few irregular 

lenses of hard, very fine grained to 

coarsely silty grayish- to dusky-brown 

(5YR 3/2- 2/2) sandstone; sandstone 

contains nearly 15 percent phosphate, 

and has chert cement (20 percent). 

Quartz mostly subangular to angular; 

many grains show overgrowths, 

some on top of phosphate rims; apatite as clear to dusty pellets, and 

light- to dusky-brown sponge-spicule 

canal fillings and rims on quartz 

grains; chert grains common; some 

sponge spicules evident; carbonate 

(5 percent) chiefly as rounded grains, 

some with phosphate rims and overgrowths.

Sandstone and chert: top 0.2 ft and 

basal 0.1 ft composed of sandy hard 

black (N 2) chert; rest composed of 

har,d cherty fine-grained dusky-brown 

(5YR 2/2) sandstone; irregular contacts between layers. Basal contact 

irregular.

Chert: hard, thin-bedded, brownishblack (5YR 2/1); contains very thin 

mudstone partings. Basal contact 

gradational.

Chert: hard, thin-bedded, brownishblack (5YR 2/1); thickness of beds 

increases upward; contains thin 

fissile mudstone partings. Basal 

contact gradational.

Chemical analyses (percent)

Uranium

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Acid in- Radio- Chemical 

soluble metric e~U U

1. 6 54. 6

3. 0

5. 3

1. 7

4. 6

57. 6

62. 9

64. 6

69. 2

69. 9 RWS-24-47 1. 6 90. 2 0. 0005

3. 2 73. 1

4. 15 77. 25

23-47

22-47

.6 86.7 .0005 __-_.__

.8 84. 7 . 0005 0. 000
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 387

Shell Canyon, Mont., lot 1214- Continued

Bed Description

Tosi Chert Tongue of Phosphoria Formation Continued

To-51____--_- Chert: hard, thin-bedded, dark-gray 

(N 3) banded in part by medium 

gray (N 5); contains fissile brownishgray (5YR 4/1) mudstone partings. 

At 0.6 ft above base is a vuggy 

lenticular calcareous concretion 

about 0.3 ft across and 0.15 ft thick 

lined with calcite crystals; chert 

layers are warped around the concretion and are thinner above and 

below central part. Basal contact 

gradational.

50 ________ Chert and mudstone, interbedded:

hard thin-bedded gravish-blac^ (N 

2) chert (80 percent) interbedded 

with hard fissile dusky brown (5YR 

2/2) mudstone (20 percent), uontains vuggy concretion similar to 

that in bed To-51 at 0.8 ft above 

base and others in cliff nearby at 

similar horizon. Basal contact gradational.

49__ ______ Chert and mudstone, interbedded:

hard thin-bedded grayish-black (N 

2) chert (75 percent) interbedded 

with hard fissile brownish-black 

(5YR 2/1) mudstone (25 percent); 

thin section reveals distinct lamination that is due chiefly to distribution of quartz grains, organic matter (?), and calcite but also that 

reflects the texture of chert; contain 

numerous sponge spicules; grains 

angular to moderately rounded; 

quarfz grains of silt to very fine sand 

size; carbonate tends to be rhombic. 

Crosscutting stylolite. Sharp basal 

contact.

Retort Phosphatic Shale Tongue of Phosphoria Formation:

Rt-48_-_--__- Mudstone: silty, hard, alternating fissile to thin-bedded, brownish-black 

(5YR 2/1). Basal contact irregular.

47________ Phosphorite: cherty, muddy, hard,

poorly bedded, grayish-ulack ( N2), 

coarsely oolitic, coarsely nudular 

in upper part; apatite partly pelletal 

but mostly oolitic; fossil nuclei 

common; pellets commonly rich in 

sponge spicules and dusty with 

carbonaceous material; chert erratically distributed, locally comprising 

all cement and in places oolite nuclei ; 

laminated carbonate at top is probably algal.

46________ Mudstone: carbonatic, hard, thin- to

thick-bedded, laminated in part, 

grayish-brown (5YR 3/2) to darkgray (A 3); carbon micro crystalline; 

quartz mostly silt size and angular, 

larger grains rounded. Basal contact 

gradational.

45________ Mudstone: cherty, hard, fissile to

thin-bedded, brownish-black (5YR 

2/1); lower part calcareous. Basal 

contact gradational.

44________ Mudstone: cherty, hard, thin-bedded,

locally fissile to laminated, duskybrown (5YR 2/2).

Chemical analyses (percent)

Thick- Cumulative

ness thickness

(feet) (feet) Sample

5. 0 82. 25 RWS-21-47

Uranium

P205

Acid insoluble

Radiometric e~U

Chemical 

V

0. 5 85. 0 0. 0005

5. 2 87. 45 20-47 .6 82. 1 . 0005 0.000

5. 1 92. 55 19-47 .9 82. 3 . 0005 .000

1. 2 93.75

55 94. 3

18-47

17-47

1. 1 73. 7 . 001

19. 2 43. 9 006

.000

.003

1. 15 95. 45

3. 7 99. 15

. 75 99. 9

16-47

15-47

14-47

. 9

.6

50.0

74.9

72.0

.001

.001

.0005 .000
388 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Shell Canyon, Mont., lot 1214 Continued

Bed Description

Retort Phosphatic Shale Tongue of Phosphoria Formation Continued 

Rt-43________ Mudstone: hard, fissile to thin-bedded,

dusky-brown (5YR 2/2). Thin section shows strong lamination; quartz 

fine-silt size, elongate grains parallel 

to bedding, muscovite rods common, carbonate (15 percent) microcrystalline to cryptocrystalline.

42________ Phosphorite: cherty, friable to hard,

medium- to coarsely pelletal, thickbedded, grayish-black (A 2). Apatite mostly pelletal, partly oolitic; 

many pellets contain fossils (Foraminifera?) that comprise much of 

pellet; much of matrix also phosphatic; chert constitutes much of 

the cement and the centers and 

cracks of many phosphate pellets and 

corrodes perimeters of some pellets. 

Basal'contact irregular.

41__-_-__- Phosphorite: medium- to coarsely pelletal (finely pelletal at base), friable, 

brownish-black (5YR 2/1). Apatite 

fairly similar to that in bed Rt-42 

except that it is not cherty and there 

is not much matrix between the 

pellets; pellets fit together closely; 

fossils within pellets are very numerous; finer grained layers contain considerable amounts of carbonaceous 

material.

40_ _______ Phosphorite: medium coarsely pelletal,

friable to medium-hard, thin and 

irregularly bedded, brownish-black 

(5YR 2/1). Characteristics in thin 

section, similar to bed Rt-41, but 

oolites common in some layers and 

fossils much less abundant.

39________ Mudstone: silty, medium-hard, thinbedded, dark-gray (N 3); contains 

about 25 percent angular, elongate 

quartz grains and 10-15 percent mica 

plates in a dark-brown to black 

matrix that includes some apatite 

pellets.

38________ Dolomite: silty, microcrystalline, medium-hard, massive, brownish-gray 

(5YR 4/1); contains considerable 

amounts of fine black carbonaceous 

matter.

dqlomitic, soft, dusky2/2); unit highly37.

36. 

35.

34_

Mudstone

brown (5YR

sheared. 

Mudstone

Rt-37.

unit sheared and much like 

Irregular basal contact.

Mudstone and phosphorite: thin layers 

of phosphorite at base and top and 

mudstone in middle; phosphorite 

medium coarsely pelletal, mediumhard, grayish-black (N 2); mudstone 

probably carbonatic, soft, duskybrown (5YR 2/2); mudstone and 

upper phosphorite sheared.

Sandstone and chert: hard duskybrown (5YR 2/2) mudstone parting 

at base overlain by 0.2 ft hard 

brownish-black (5YR 2/1) chert and 

0.8 ft hard medium-bedded finegrained weak-brown to brownishblack (5YR 3/2-2/1) phosphatic 

sandstone that is darker and more 

phosphatic upward. Irregular basal 

contact.

Chemical analyses (percent)

Thick- Cumulative

ness thickness

(feet) (feet) Sample

2. 05 101. 95 RWS-13-47

Uranium

Acid in- Radio- Chemical 

soluble metric eV U

0. 1

. 75 102. 7 12-47 23. 6

80. 5 0. 001

30. 2 . 008

0. 000

.006

. 5 103. 2 11-47 32. 4 8. 1 . Oil . 013

1. 5 104. 7

. 5 105. 2

1. 2 106. 4

. 8 107. 2

. 45 107. 65

. 65 108. 3

10-47

9-47

32. 5 8. 4 . Oil . 009

3. 7 70. 6 . 004 .001

8-47

7-47

6-47 

5-47

.5 20. 0 . 0005

3. 6 55. 2 003

6. 0 47. 3 . 005 . 003

14. 9 40. 4 . 009 . 004

1. 0 109. 3 4-47 ). 5 70. 5 . 003 . 002
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 389

Shell Canyon, Mont., lot 1214 Continued

Chemical analyses (percent)

Bed Description

Lower member of Shedhorn Sandstone:

Ls-33._______ Sandstone: hard, thick-bedded, finegrained, light-brownish-gray to medium-gray (5YR 5/1-AT" 5) quartzitic. 

Irregular basal contact.

32_ _______ Sandstone: cherty, hard, thick-bedded,

fine- to medium-grained, mediumdark-gray (N 4); quartz is subangular and has minor overgrowths; 

chert abundant as cement; abundant 

sponge spicules. Basal contact irregular.

31_-______ Sandstone: cherty, hard, mediumgrained, light-brownish-gray (5 YR 

5/1), quartzitic; quartz subangular 

to subrounded with some overgrowths; abundant cherty matrix 

contains many sponge spicules, some 

having overgrowths; contains scattered apatite pellets and somewhat 

similar appearing but less well 

rounded grains of chert.

30________ Sandstone: hard, medium - grained,

thick - bedded to massive, light - 

brownish-gray (5YR 5/1); mediumgray (N 5) at base.

29________ Chert: hard, thin- to thick-bedded,

medium-dark-gray (AT 4) to grayishblack (N 2); calcareous near top; 

contains irregular lenses of fine 

brownish-gray (5YR 4/1) sandstone. 

Irregular basal contact.

28_ _______ Sandstone and chert: 0.3-0.4 ft bed of

sandy hard medium-gray (A 5) sandstone grading upward to brownish-gray 

(5YR 4/1) sandstone containing scattered chert nodules. Quartz is mostly 

subangular to subrounded and has extensive overgrowths; about 5 percent 

apatite, chiefly well-rounded, clear to 

moderately dusty light-brown pellets; 

also contain shell fragments and 

angular coarse-grained fragments of 

probable apatite nodules; also contain rounded chert, carbonate grains, 

and some interstitial carbonate. 

Irregular basal contact.

27_ _______ Dolmite: sandy, hard, thick-bedded,

light-brownish-gray (5YR 6/1), finegrained; pebbles of chert, carbonate 

rock, quartzite, and phosphorite as 

much as \% in. diameter at top, middle, and base of bed. Pebbles of 

carbonate rock, generally cherty, and 

of spicular chert and phosphorite; 

quartz grains are as much as J^mm 

but mostly less than }4mm in diameter and are subrounded by common but not very obvious overgrowths; apatite occurs as pellets, 

spicule canal fillings, and pebbles or 

grains of spicular nodules; carbonate 

in sandstone and chert is generally 

very fine grained, but some is coarse 

and probably secondary; much of 

carbonate in chert is rhombic. 

Franson Tongue of Park City Formation: 

F-26._______ Dolmite and sandstone: irregularly

distributed hard fine-grained thickbedded to massive light-brownishgray (5 YR 6/1) sandy dolomite and 

dolomitic sandstone.

Uranium

Thick- Cumulative

ness thickness

(feet) (feet)

1.9 111.2

85 112. 05

112. 75

Sample

RWS-3-47

2-47

Acid in- Radio- Chemical 

P2O5 soluble metric ell U

1. 1 90. 1 0. 0005 0. 002

1. 0

1-47

93. 3 . 0005

92. 2 . 0005

.000

.000

5. 55 118. 30

3. 75 122. 05

2. 5 124. 55

1. 1 125. 65

2. 0 127. 65
390 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Shell Canyon, Mont., lot 1214 Continued

Chemical analyses (percent)

F-25. 

24.

23. 

Ls-22.

F-21. 

Ls-20.

F-19.

18-

17.

16.

15.

Description

Fransan Tongue of Park City Formation 

Continued

Dolomite: sandy, hard, fine-grained, 

medium-gray (N 5).

Chert: very sandy, hard, spicular, yellowish-gray (10 YR 8/1); quartz sand 

is very fine; contains streaks and 

lenses of fine-grained pale-brown 

(10 YR 5/2) dolomitic sandstone.

Dolomite: sandy, hard, very fine 

grained, massive, light-brownishgray (5YR 6/1). Gradational basal 

contact.

Sandstone: dolomitic, cherty, hard, 

massive, fine-grained, pale-brown 

(WYR 6/2) to light-gray (N 7). 

Thin section reveals numerous grains 

of dense carbonate rock as much as 

5 mm long having finely crystalline 

carbonate in matrix; cherty zones 

are spicular and contain shell fragments and pellets of apatite and 

rhombic abraded carbonate. Undulating basal contact.

Dolomite: sandy, locally pebbly, hard, 

very fine grained, thick-bedded, 

pale-brown (WYR 5/2).

Sandstone and chert: hard very fine 

grained locally pebbly thick-bedded 

yellowish-gray (WYR 7/1) sandstone 

and sandy chert.

Dolomite: hard, aphanitic, thick-bedded, light-brownish-gray to palebrown (10YR 5/1-5/2); contains 

chert pebbles as much as 20 mm 

diameter in lower third and numerous small bits of black carbonaceous?) material, some showing 

organic markings.

Dolomite: sandy, local cherty, hard, 

very fine grained, massive, lightbrownish-gray to medium-gray 

(WYR Q/l-N 5); locally pebbly and 

more cherty in lower half and notably 

at base. Chert at base is very finely 

sandy and very spicular and contains 

rhombic carbonate and apatite as 

spicule canal fillings and pellets.

Chert and dolomite: locally sandy hard 

poorly bedded to laminated 

yellowixh-gray (WYR 7/1) chert 

containing irregularly distributed 

lenses and patches of dolomite.

Dolomite: locally cherty and sandy, 

hard, fine-grained to aphanitic, 

massive, light-brownish-gray to 

grayish-green (10 YR 6/1 to WGY 

5/2). Very irregular basal contact.

Sandstone: cherty, hard, fine-grained, 

pale-brown (WYR 5/2); chert very 

finely sandy, irregularly distributed, 

brownish-gray (10YR 4/1); sand at 

base has much phosphatic material 

in matrix, abundant apatite pellets, 

some apatite shell fragments, and 

numerous small pebbles of sandy and 

spicular chert; contains numerous 

tiny black globules (M30 microns), 

generally clustered, that appear 

amber under an oil immersion lens 

and may be petroliferous matter. 

Irregular basal contact.

Uranium

Thick- Cumulative

ness thickness

(feet) (feet) Sample

0. 9 128. 55

. 6 129. 15

Acid insoluble

Radiometric eU

Chemical 

U

3. 5 132. 65

2. 5 135. 15

1. 4 136. 55

1. 3 137. 85

1. 2 139. 05

9. 7 148. 75

4. 0 152. 75

2. 8 155. 55

. 8 156. 35
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 391

Shell Canyon, Mont., lot 1214 Continued

Chemical analyses (percent)

Bed Description

G-14_-_-____- Grandeur Member of Park City Formation:

Dolomite: hard, aphanitic, massive, 

light-brownish-gray (10 YR 6/1) to 

yellowish-gray (10 YR 7/1); contains 

irregular streaks of fine sand. 

Angular to subrounded sand at top 

includes chert grains, including those 

of the peculiar variety of chert found 

in bed G-12, and numerous small 

apatite shell fragments, pellets, and 

spicule canal fillings; matrix consists 

of dolomite rhombs and corroded 

quartz and apatite grains; some 

pebbles of carbonate are present. 

13-__------ Sandstone and dolomite: irregularly

intermixed dolomitic hard finegrained sandstone and sandy 

aphanitic dolomite; light-yellowishbrown (10 YR 6/4) to very pale 

orange (10 YR 8/2).

12-___--_,_ Chert: dolomitic, hard, pale-yellowishbrown (IOYR 6/2). Thin section 

reveals numerous quartz grains and 

much chert as grains, pebbles, or replacements in a fine dolomite matrix. 

Chert is characterized by coarse 

texture and considerable dust that is 

concentrated chiefly in lines or bands, 

many of which clearly show crystal 

forms of quartz; clastic quartz grains 

not common to chert areas. Undulating basal contact. 

11_________ Dolomite: hard, aphanitic, massive,

light-brownish-gray (IOYR 6/1). Irregular basal contact. 

10___._____ Sandstone and dolomite: interlayered

and intermixed hard fine-grained 

sandstone and very sandy dense 

dolomite; poorly bedded, pale-brown 

(7.5 YR 6/2). Strongly undulating 

basal contact.

9_________ Dolomite: hard, aphanitic, massive,

light-brownish-gray (10 YR 6/1).

8-------._ Dolomite: hard, aphanitic, lightbrownish-gray (5YR 6/1); basal 0.8 

ft, softer and shaly, forms undercut 

in cliff, and contains pencillike flat 

limonite concretions. Gradational 

basal contact.

7_ ________ Dolomite: hard, aphanitic, massive to

thick-bedded, light-brownish-gray 

(5YR 6/1); contains 0.3 ft very fine 

sandy zone near top.

6_-_-__.__ Dolomite: hard, aphanitic, poorly bedded to massive, light-brownish-gray 

(10YR 6/1); contains some crosscutting sandstone stringers and a fine 

dolomitic sandstone zone at the top.

5_________ Dolomite: hard, aphanitic, massive,

yellowish-gray (10 YR 7/1); contains 

several thin (0.1-0.2 ft) layers and 

some crosscutting stringers of clean 

fine-grained yellowish-gray (10 YR 

7/1) sandstone having abundant 

quartz overgrowths; numerous small 

grains of zircon and tourmaline, and 

some clastic carbonate. Irregular 

basal contact.

4.________ Dolomite: hard, aphanitic, massive,

yellowish-gray (IOYR 7/1); hackly 

weathering in middle. Irregular 

basal contact.

Thickness

Cumulative 

thickness 

(feet) Sample

Uranium

Acid insoluble

Radiometric eTJ

Chemical 

U

6. 5 162. 85

2. 5 165. 35

1. 0 166. 35

2. 0 168. 35

1. 8 170. 15

4. 0 174. 15

1. 8 175. 95

4. 0 179. 95

4. 5 184. 45

8. 0 192. 45

5. 5 197. 95
392 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Shell Canyon, Mont., lot 1214~~Continued

Bed

G-3.

Q-lDescription

Grandeur Member of Park City Formation Continued

Sandstone: hard, quartzitic, fine- to 

medium-grained, massive, mediumlight-gray (N 6). A very clean 

quartz sandstone having almost complete destruction of porosity by overgrowths; grains fairly well rounded; 

small zircon grains common; contains little tourmaline, leucoxene, 

and chert (as grains). Irregular 

basal contact.

Dolomite: hard, aphanitic; upper half 

massive; lower half thin-bedded, possibly argillaceous, and in cliff, weathers to form undercut; very pale 

brown (IOYR 7/2); finely sandy at 

base and locally cherty.

Quadrant Formation, top bed only:

Sandstone: hard, fine-grained, massive, locally crossbedded, pale-brown 

(SYR 5/2). Grains mostly quartz 

having dominant overgrowths; locally dolomite cement rather than 

quartz overgrowths; clear coarser 

dolomite disseminated through rock. 

Irregular basal contact.

Chemical analyses (percent)

Thick- Cumulative

ness thickness

(feet) (feet) Sample

3. 5 201. 45

Uranium

Acid insolubleRadio- Chemical 

metric eV U

3. 5 204. 95

8.0 8. 0

Aspen Valley, Mont., lot 1215

[Retort and Tosi Members of Phosphoria Formation sampled in hand trench near top of ridge on west side of Aspen Valley, SEJ4SEJ4 sec. 11, T. 6 S., R. 1 E., Madison 

County, Mont., on overturned limb of Madison Range syncline, in August 1947. Beds strike N. 45° E. and dip 55° NW. Measured by R. W. Swanson and sampled by 

J. A. Mann and J. O. Evans. Analyzed for PaOs and acid insoluble by U.S. Bur. of Mines and for uranium by U.S. Oeol. Survey]

Bed

Us-20.

19.

To-18.

Description

Upper member of Shedhorn Sandstone; top 

not exposed:

Sandstone: carbonatic, fine-grained, 

medium-hard, light-brownish, gray 

(5Y726/1) to light-gray (N 7); has 

indistinct bedding. Contains patches 

of dusky-brown (5 YR 2/2) quartzite 

similar to that constituting underlying bed. Gradational basal contact. Overlying beds are covered.

Sandstone: cherty, hard, fine- to very 

fine grained, brownish-gray (5YR 

4/1) to dusky-brown (5YR 2/2). 

Quartz angular to well rounded, 

not well sorted; chert, about 40 

percent of rock, forms matrix for 

sand; spicules common, some large 

(l/2-}i mm wide); some rounded 

grains of chert; apatite about 5 percent, mostly light- to dark-grayishbrown pellets, some clear shell fragments and brown sponge-spicule 

canal fillings. Irregular basal contact.

Tosi Chert Tongue of Phosphoria Formation; contains thin tongue of Retort Phosphatic Shale Member:

Chert: hard, thin-bedded, dark-gray 

(W3) to brownish-black (5YR 2/1); 

contains several thin layers (0.06 ft) 

of fissile moderate-brown (5YR 4/4) 

mudstone in lower half and 10 to 12 

mudstone partings in upper half; 

contains vuggy carbonatic concretion lined with calcite crystals in top 

foot. Gradational basal contact.

Chemical analyses (percent)

Thickness 

(feet)

2. 1

Cumulative 

thickness 

(feet) Sample

Uranium

Acid insolubleRadio- Chemical 

metric eV U

2. 1

75 2. 85 RWS-43-47 1. 3 90. 1 0. 0005

4. 2 7. 05 42-47 . 9 81. 8 . 0005
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 393

Aspen Valley, Mont., lot 1215 Continued

Bed Description

Tosi Chert Tongue of Phosphoria Formation; contains thin tongue of Retort Phosphatic Shale Member Continued

To-17________ Chert: dark-gray (N3), thin-bedded,

hard, brittle; 0.7-ft-thick layer of 

chert at base, thin-bedded and contains 10 partings of soft fissile grayish-brown (5YR 3/2) mudstone in 

upper part. 

16-------- Chert and mudstone: hard fissile to

thin-bedded dark-gray (N 3) chert 

(75-80 percent) and 15 interbedded 

layers of soft fissile to thin-bedded 

grayish-brown (5YR 3/2) mudstone; 

3-in. mudstone layers at middle and 

top; chert thicker bedded in lower 

third.

Rt-15-------- Mudstone: soft, fissile to thin-bedded,

brownish-gray (5YR 4/1) to grayishbrown (5YR 3/2); more fissile in 

lower third.

14-------- Phosphorite: cherty, hard, thin-bedded, medium coarsely oolitic and 

coarsely nodular, medium-dark-gray 

(N 4). Oolites light brown, commonly cherty; several have fossil 

nuclei; nodules light to medium 

brown, mostly structureless but rich 

in cherty sponge spicules; fine quartz 

grains common. Irregular basal 

contact. 

13_------- Carbonate rock: cherty, hard, thin- to

thick-bedded, brownish-gray (5RY 4/ 

1); thin dark-gray (N 3) chert lenses. 

Carbonate laminated, mostly microcrystalline, rhombic in cavity fillings 

and in cherty spots; chert microcrystalline, disseminated throughout 

but more abundant in some layers; 

quartz silt fairly common, angular.

To-12__ ______ Chert and mudstone, interbedded:

fissile to thin-bedded hard brownishblack (5YR 2/1) chert (85 percent) 

and 17 interbedded layers of hard 

fissile dusky-brown (SYR 2/2) mudstone. Two-in. shear zone about 1 

ft above base strikes N. 5° W. and 

dips steeply west. Gradational basal 

contact. 

11 ________ Chert and mudstone, interbedded:

dark-gray to brownish-black (N 3 

to SYR 2/1) hard fissile to thinbedded chert (75 percent of unit) 

and 17 interbedded layers of duskybrown (5YR 2/2) to grayish-brown 

(5YR 3/2) hard fissile mudstone. 

Gradational basal contact. 

10________ Chert and mudstone, interbedded:

hard fissile to thin-bedded dark-gray 

(N 3) to brownish-black (5YR 2/1) 

chert (80 percent) and 13 interbedded layers of hard fissile duskyto grayish-brown (5YR 2/2- 3/2) 

mudstone. Thinner bedded in bottom foot and at 2.3-4.0 ft above 

base. Gradational basal contact.

9--_--___ Chert: hard, fissile to thin-bedded 

(thicker in upper half), dark-gray to 

brownish-black, and eight hard 

fissile brownish-gray mudstone partings and a 3-in. mudstone layer at 

0.8 ft above base.

Chemical analyses (percent)

Thickness 

(feet)

2. 5

Cumulative

thickness

(feet)

Uranium

Sample

9. 55 RWS-41-47

PaOs

0. 6

Acid insoluble

Radiometric eU

Chemical 

U

4. 45 14. 0 40-47

84. 0 0. 0005

78. 0 . 0005

55 14. 55

25 14. 8

39-47

38-47

1. 3

23.5

75. 4 001

31. 4 . 007 0. 006

1.0 37-47 . 5 37. 6 . 0005

4. 55 20. 35 36-47 . 5 50. 6 . 001 . 000

4. 45 24. 80 35-47 .7 82. 1 . 0005

4. 5 29.30 34-47 . 7 82. 4 . 0005

2. 25 31. 55 33-47 .5 84. 9 .0005
394 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Aspen Valley, Mont., lot 1215 Continued

Bed

Ls-1.

Description

Retort Phosphatic Shale Tongue of Phosphoria Formation:

Phosphorite: medium hard to friable, 

very finely to very coarsely pelletal, 

medium-dark-gray (2V 4) to duskybrown (5YR 2/2) (very light brown 

in thin section). Contains very 

abundant fossil nuclei in both pellets 

and oolites; oolites common but not 

abundant; microcrystalline chert 

common in matrix of pellets, which 

are not closely packed, and as fossil 

filling. Gradational basal contact.

Phosphorite: medium-grained, soft to 

friable, laminated, grayish-black (N 

2); contains considerable amounts 

of grayish-brown (5YR 3/2) mud 

near base and top.

Mudstone: grayish-brown (5YR 3/2), 

thin-bedded, medium-soft. Fairly 

sharp basal contact.

Carbonate rock: hard, thin- to thickbedded, brownish-gray (5YR 5/1), 

microcrystalline, basal 0.2 ft soft, 

silty and clayey; basal contact somewhat gradational.

Mudstone: carbonatic, soft, clayey, not 

bedded, grayish-brown (5YR 3/2) to 

brownish-black (5YR 3/1).

Phosphorite and mudstone: soft, friable 

medium-grained thin-bedded darkgray (N 3) phosphorite 0.4 ft thick 

overlying 0.2 ft soft thin-bedded 

brownish-gray (5YR 4/1) to brownishblack (5YR 2/1) clayey mudstone; 

some mudstone partings in phosphorite.

Phosphorite and sandstone: mediumhard medium-pelletal light-gray 

(N 7) sandy phosphorite 0.25ft thick 

overlying 0.3-ft hard fine- to medium-grained light-brownish-gray quartzitic phosphatic sandstone. Phosphorite about one-half pelletal; pellets and quartz grains in somewhat 

darker phosphatic groundmass and 

concentrated in layers; overgrowths 

on most quartz in the sandstone; 

phosphate chiefly pelletal but also 

as matrix between quartz grains. 

Lower member of Shedhorn Sandstone, 

basal bed:

Sandstone: carbonatic, light-brownishgray (5YR 6/1), medium-hard, fineto medium-grained. Underlying beds 

not exposed.

Chemical analyses (percent)

Thickness 

(feet)

Cumulative

thickness

(feet)

Uranium

Sample

1. 6 33. 15 RWS-32-47 31.0

Acid in- Radiosoluble metric eU

11. 8 0. 009

Chemical 

U

0. 008

33. 45

45 33. 9

83 34. 73

35. 43

36.03

31-47

30-47

29-47

28-47

27-47

26.9

1. 4

3. 7

14. 6

18. 0 . 015

72. 3 . 003

15. 4 . 0005

56. 7 . 005

37. 0 . 010

. 014

.003

.004

55 36. 58 26-47 21. 3 38. 9 . 007 . 006

37. 38 25-47 1.6 92. 9 . 0005

West Fork of Gallatin River, Mont., lot 1216

[Part of Phosphoria and Shedhorn Formations sampled and described from natural exposure and hand trench on mountain slope about 300 ft above north bank of West Fork 

of Gallatin River in NWJ.4SEH sec. 32, T. 6 S., R. 4 E., Gallatin County, Mont., from upturned strata south of Gardiner thrust fault, in September 1947. Beds strike 

N. 35° W., and dip 45-50° SW. Measured by R. W. Swanson and sampled by J. A. Mann and J. G. Evans. Analyzed for P2 Os and acid insoluble by U.S. Bur. of Mines 

and for uranium by U.S. Geol. Survey]

Chemical analyses (percent)

Bed

Us-32.

Description

Upper member of Shedhorn Sandstone; top 

not exposed:

Sandstone and chert: poorly exposed, 

not logged in detail. Quartzite containing interbedded chert and many 

crosscutting sandstone columns as 

much as 3 in. in diameter and 1-3 

ft long.

Thick- Cumulative

ness thickness

(feet) (feet)

Uranium

Sample P2 05

Acid insoluble

Radiometric eV

Chemical 

U

4.0 4. 0
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 395

West Fork of Gallatin River, Mont., lot 1216 Continued

Chemical analyses (percent)

Bed Description

Upper member of Shedhorn Sandstone; top

not exposed Continued 

Us-3!________ Chert: poorly exposed, not logged in

detail; contains crosscutting quartzite columns similar to those in bed 

Us-32.

30________ Sandstone: hard, fine-grained, thin- to

thick- but irregularly bedded, lightbrownish-gray (5YR 5/1); contains 

lenses of very finely sandy chert and 

columns gf brownish-gray (5YR 4/1) 

cherty quartzite.

29________ Sandstone: hard, fine- to mediumgrained, poorly bedded, lightbrownish-gray (5YR 5/1); contains chert nodules and lenses and 

columns like those in bed Us-31. 

Irregular basal contact.

28________ Limestone: medium-hard, thin- and

poorly bedded, light-brownish-gray 

(5 YR 6/1); contains columns of cherty 

quartzite, some of which cross entire 

bed. Iregular basal contact. Limestone microcrystalline; sandstone 

medium- to fine-grained, angular to 

subrounded, cherty, phosphatic, and 

moderately calcareous; quartz shows 

some overgrowths and some corrosion by chert and calcite of matrix; 

chert grains common and comprise 

most of matrix; some sponge spicules evident; phosphate occurs as 

apatite pellets and nodules, shell 

and bone fragments (some anisotropic), sponge-spicule fillings, and 

clear grains of uncertain origin; 

calcite locally abundant and coarsely 

crystalline but most is finely crystalline and irregularly disseminated; 

some veinlets in sharp contact with 

adjoining limestone.

Tosi Chert Tongue of Phosphoria Formation:

To-27_-----__ Chert: thin-bedded, hard, brittle, medium-light-gray (N 6); contains 

many crosscutting quartzite columns, 

some 3 ft long, and some lenses of 

fine-grained quartzite. Basal contact not exposed.

26_--_--__ Covered; thickness approximate. 

Overlying beds measured about 50 ft 

lower on hillside than beds described 

below.

25__-____^ Chert: brittle thin-bedded mediumgray (N 5) chert; contains some 

quartzite in basal 0.15 ft which is 

overlain by 0.2-ft fissile lightbrownish-gray (5YR 5/1) mudstone; 

top 3.0 ft contains crosscutting finegrained sandstone columns as much 

as 5 in. in diameter and 4 in. or more 

apart. Lenticular vuggy carbonate 

concretions as much as 3 in. thick and 

6-8 in. across occur 1.5, 4.0, and 7.5 ft 

above base.

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Uranium

Acid in- Radio- Chemical 

soluble metric eU U

2. 0

10. 5

2. 0

6.0

16. 5

18. 5

19. 2

5. 5 24. 7

25. 2

8. 85 34. 05 RWS-63-47 0.8 90. 1 0. 0005
396 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

West Fork of Gallatin River, Mont., lot 1216 Continued

Bed

To-24_.

23.

22.

21.

Rt-20.

19.

18.

Description

Tosi Chert Tongue of Phosphoria Formation Continued

Sandstone: cherty, hard, fine- to medium-grained, grayish- to duskybrown (5YR 3/2); very cherty at base. 

Quartz moderately rounded to 

angular; overgrowths common although matrix is composed mostly of 

chert; chert is brown and dusty and 

contains numerous siliceous sponge 

spicules; clear to dusty and lightbrown to black apatite pellets, clear 

to medium-brown shell fragments, 

and brown spicule fillings of apatite 

are common.

Chert: hard, brittle, fissile to thinbedded, brownish-black (5YR 2/1); 

contains 1.0 ft of soft fissile to thinbedded pale-brown (5YR 5/2) mudstone that forms 27 rather uniformly 

spaced layers.

Chert and mudstone, interbedded: 

hard, brittle fissile to thin-bedded 

dark-brownish-gray (5YR 3/1) chert 

(75 percent) containing 15 layers 

totaling 0.9 ft of soft fissile palebrown (5YR 5/2) mudstone. Thicker 

layers of mudstone occur 0.7, 2.3, and 

2.9 ft above base and commonly 

contain thin (0.01 ft) lenses of chert.

Chert and mudstone, interbedded: 

hard- brittle fissile to thin-bedded 

dark-brownish-gray (5YR 3/1) chert 

(75 percent) containing 23 layers 

totaling 1.2 ft of soft fissile brownish gray (5YR 4/1) mudstone, mudstone layers thicker and more closely 

spaced at 1.2-2.8 ft above base. 

Slightly irregular basal contact. 

Retort Phosphatic Shale Tongue of Phosphoria Formation:

Phosphorite: cherty, sandy, hard, finely 

pelletal to finely nodular, darkgray (N 3). Chiefly apatite pellets 

and nodules (40 percent) and fine 

sand (25 percent) in a cherty matrix 

(35 percent). Apatite nodules are 

very silty and generally rich in siliceous sponge spicules; pellets are 

mostly dusty but some are clear; 

apatite shell fragments and spicule 

fillings are common; quartz grains 

are mostly subangular to rounded; 

chert grains are common; chert cement is mostly dusty brown and rich 

in sponge spicules and corrodes both 

quartz and apatite. Irregular basal 

contact.

Mudstone: medium-hard, thin-bedded 

(upper third fissile), grayish-brown 

(5YR 3/2) to moderate-brown (5YR 

4/4),

Chert (?): medium-hard to soft, thinbedded, locally fissile, weak-yellowish-orange (10 YR 7/6) to moderateyellowish-brown (1QYR 5/4); 0.4 ft 

dark-brownish-gray (WYR3/2) layer 

near middle. Appears to be composed chiefly of cryptocrystalline 

chert groundmass containing angular 

quartz silt and lesser amounts of carbonate, muscovite, and carbonaceous material.

Chemical analyses (percent)

Thick- Cumulative

ness thickness

(feet) (feet)

Uranium

Sample

0. 65 34. 7 RWS-62-47

Acid in- Radio- Chemical 

soluble metric eTJ II

2. 0 89. 2 0. 0005

5. 75 40. 45

3. 4 43. 85

61-47

60-47

.7 84. 8 . 0005

.6 90. 7 . 0005

4. 45 48. 3 59-47 .7 91. 0 . 0005

48.6 58-47 14. 9 56. 3 .006 0.005

1. 35

1. 8

49.95

51.75

57-47

56-47

9 81. 1 . 001

3. 1 . 001
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 397

West Fork of Gallatin River, Mont., lot 1216 Continued

Bed

Rt-17.

14.

Ls-13.

12.

11.

Description

Retort Phosphatic Shale Tongue of Phosphoria Formation Continued

Chert (?): soft to medium-hard, fissile 

to thin-bedded, moderate-yellowishbrown (10 YR 5/4) to brownish-black 

(10 YR 2/1). Chiefly cryptocrystalline 

chert containing quartz silt and carbonaceous material, as does bed Rt18. Contains very fine phosphate 

pellets.

Mudstone: medium-hard to soft, fissile 

to thin-bedded, brownish-gray (5YR 

4/1) to grayish-brown (5YR 3/2). 

Phosphorite: cherty, medium-hard, 

medium- to very coarsely oolitic (60 

percent) to pelletal, medium-gray 

(N 5) to brownish-gray (5YR 4/1). 

Oolites and pellets pale brown, some 

have quartz or fossil nuclei; matrix 

composed of pale-brown cryptocrystalline chert near oolites and clear 

fine to medium-coarse comb- and 

flamboyant-structure quartz in central areas between loosely packed 

oolites.

Phosphorite: medium-hard to friable, 

poorly bedded, fine to coarsely 

oolitic-pellatel, brownish-black (5YR 

2/1) to grayish-black (N 2). Basal 

0.2 ft sandy (medium-grained quartz) 

and moderately pelletal to nodular; 

contains numerous shell fragments, 

all in a phosphatic matrix much like 

that of pellets; remainder composed of fairly closely packed apatite oolites and pellets, containing 

numerous subrounded quartz grains 

cemented by cryptocrystalline chert. 

Gradational basal contact. Contains 

L/ingula.

Lower member of Shedhorn Sandstone: 

Sandstone: phosphatic, medium-hard 

(locally soft), thick-bedded, fine to 

medium-grained, moderate-yellowishbrown (IOYR 5/4) to brownish-gray 

(IOYR 4/1). Overgrowths on quartz 

very common; apatite (20 percent) 

occurs as medium to coarse pellets 

but also commonly as shell fragments; 

rounded grains of chert are common; 

some secondary chert occurs. " Gradational basal contact. 

Sandstone: medium-hard, poorly bedded, 

medium-grained, pale-brown (5 YR 

5/2); contains pebbles of mudstone 

and chert at base. Quartz has dominant overgrowths; chert grains are 

very common; apatite is common, 

chiefly as shell fragments but also as 

pellets and rims on quartz grains. 

Irregular basal contact. 

Mudstone and sandstone: soft fissile 

grayish-brown (10 YR 4/2) mudstone 

containing many crosscutting 0.1- to 

0.2-ft diameter hard fine-grained sandstone concretions. Quartz in sandstone has abundant overgrowths; 

apatite (10 percent) occurs as pellets, 

shell fragments, rims on quartz grains, 

sponge spicule fillings, and matrix; 

some is probably secondary; chert 

grains are very common (5-1- percent); 

some dusty-brown chert cement; many 

grains coarsely chalcedonic. Irregular 

basal contact.

Chemical analyses (percent)

Thick- Cumulative

ness thickness

(feet) (feet) Sample

85 52. 6 RWS-55-47

Uranium

Acid insoluble

Radiometric eU

Chemical 

U

0.8 81. 1 0. 002

2.5 55. 1 54-47 1. 1

45 55. 55 53-47 22. 2

84. 2

39.4

. 001

.008

0. 000

.008

56.25 52-47 26.2 27.0 .009 .007

1. 5 57. 75 51-47 70.2 .003 .001

1. 6 59. 35 50-47 .6 .0005 .000

1.3 60. 65 49-47 1. 1 81.3 .001 .000

709-931 O 63-
398 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

West Fork of Gallatin River, Mont., lot 1216 Continued

Bed Description

Lower member of Shedhorn Sandstone 

Continued 

Ls-10-- ______ Chert, sandstone, and mudstone: 0.3 ft

hard, brittle sandy dusky-brown 

(SYR 2/2) to brownish-black (SYR 

2/1) chert at base, overlain by a 0.4 ft 

medium-hard to soft brownish-gray 

(SYR 4/1) mudstone, a 0.2 ft chert 

like that at base, and a 0.45 ft finegrained hard dark-gray (N 3) sandstone at top. Unit contains many 

crosscutting chert and sandstone 

columns that render bedding inconspicuous. Irregular basal contact.

9_--_--_- Sandstone: cherty, hard, mediumgrained, poorly bedded, lightbrownish-gray (SYR 5/1). Chert 

occurs in irregular masses and nodules, more abundant toward top. 

Unit contains many crosscutting columnar bodies of sandstone containing quartz having abundant overgrowths, several percent apatite 

occurring as shell fragments, pellets, 

and matrix, 10 ± percent chert grains, 

and chert and very fine calcite cement. Irregular basal contact apparently crossed by some columnar 

bodies.

8_--_--_- Mudstone and sandstone: soft fissile to 

thin-bedded moderate-yellowishbrown (10 YR 5/6) carbonatic sandy 

mudstone containing abundant crosscutting quartzitic sandstone columns; 

columns are 0.05-0.2 ft in diameter, 

irregular sided, and closely spaced.

7-_______ Mudstone and sandstone, interbedded:

medium-hard to soft fissile to thinbedded weak-yellowish-orange (10 YR 

8/4) to light-brownish-gray (10 YR 

5/1) carbonatic mudstone, interbedded with hard fine-grained thinbedded brownish-black (SYR 2/1) 

sandstone; beds are lenticular. Top 

part locally conglomeratic; basal 

contact irregular.

6________ Sandstone: hard, medium-grained,

thick-bedded, brownish-gray (5 YR 

4/1); 2-in. zone containing chert 

pebbles near middle. Quartz, moderately well rounded; has abundant 

overgrowths; chert grains and apatite pellets and shell fragments common. Gradational basal contact.

5________ Sandstone: hard, thin- to thick- but

poorly bedded, fine-grained, medium-gray (N 5); contains worm(?) 

borings. Thickness 3.2 ft a few 

feet below the trench.

R-4________ Chert: hard, brittle, thin-bedded, locally sandy, brownish- to lightbrownish-gray (SYR 4/1- 5/1); locally shattered.

Chemical analyses (percent)

Uranium

Thick- Cumulative

ness thickness

(feet) (feet) Sample

1. 35 62. 0 RWS-48-47

Acid in- Radio- Chemical 

PjOs soluble metric eV U

1. 5 55. 0 0. 0005 0.000

2.2 64.2 47-47 1.4 91. 9 . 001 .000

1. 15

1. 05

65.35

66. 4

46-47

45-47

2.2 87. 2 005 .000

.9 77. 1 . 0005

1. 2 67. 6 44-47 .8 95. 2 . 0005 . 000

4.3 71.9

73. 7
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 399

West Fork of Gattatin River, Mont., lot 1216 Continued

Bed

R-3.

Q-i

Description

Lower member of Shedhorn Sandstone 

Continued

Chert: hard, brittle, thin-bedded, locally sandy, brownish-gray (5YR 

4/1); contains four layers totaling 

0.55 ft of medium-hard fine-grained 

light-brownish-gray sandstone. Basal contact not exposed. Sandy 

chert near base contains 40 percent 

moderately rounded fine-grained 

quartz in a cryptocrystalline chert 

cement; quartz grains are commonly 

corroded; siliceous sponge spicules 

are abundant, particularly in less 

sandy parts; apatite pellets common, 

and some broken pellets and a few 

clusters suggest reworking of a 

phosphorite bed; some pellets have 

quartz nuclei.

Covered. Includes the contact between the Quadrant Formation and 

the strata of the Shedhorn Sandstone. 

Quadrant Formation, top bed:

Sandstone: medium-hard to friable, 

locally hard, white (N 9), thickbedded to massive. Not described 

in detail.

Chemical analyses (percent)

Thick- Cumulative

ness thickness

(feet) (feet) Sample

6. 3 80. 0

Uranium

Acid in- Radio- Chemical 

soluble metric eU U

10. 0 90. 0

10. 0 100. 0

Porcupine Creek, Mont., lot 1217

[Phosphoria Formation and part of Shedhorn Sandstone and Retort and Tosi Tongues of Phosphoria Formation sampled from natural exposures and hand trench on upper 

part of mountain slope H*j miles north of Porcupine Creek in NEHSE54 sec. 10, T. 78., R. 4 E., Qallatin County, Mont., from upturned strata south of Oardiner thrust 

fault. Beds strike N. 40° W. and dip 75° SW. Measured by R. W. Swanson and sampled by J. A. Mann and J. Q. Evans, in September 1947. Analyzed for P2O and 

acid insoluble by U.S. Bur. of Mines and for uranium by U.S. Oeol. Survey]

Chemical analyses (percent)

Bed

Us-23.

22.

21.

20.

Description

Upper member of Shedhorn Sandstone; 

uppermost beds not exposed:

Sandstone: hard, massive, fine- to 

medium-grained, light-brownish-gray 

(SYR 6/1); contains dark phosphate 

or chert grains, or both. Irregular 

basal contact. Overlying strata not 

exposed.

Chert: hard, brittle, thin- to thickbedded, light-gray (N 7); contains 

lenses of fine- to medium-grained 

sandstone and many crosscutting of 

sandstone columns.

Sandstone: hard, fine-grained, thickbedded, yellowish-gray (SYR 7/2) 

to light-brownish-gray (5YR 6/1). 

Some layers weather gray. Not 

very well exposed. Basal contact 

irregular.

Sandstone: hard, fine- to mediumgrained, light-brownish-gray (5 YR 

6/1); cherty and finer-grained near 

top. Quartz grains angular to moderately rounded and have abundant 

overgrowths; chert grains common; 

apatite (4 percent) chiefly as shell 

fragments.

Cumulative 

Thickness thickness 

(feet) (feet)

Uranium

Sample Ps06

Acid 

insoluble

Radiometric Chemical 

eU U

6. 0

2.6

4.8

6. 0

13. 4

14. 0 RWS-79-47 1. 6 93. 1 0. 0005
400 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Porcupine Creek, Mont., lot 1217 Continued

Bed Description

Tosi Chert Tongue of Phosphoria Formation: 

To-19________ Chert: hard, brittle, thin-bedded, lightbrown (5YR 6/4); contains 12 interbeds of soft fissile mudstone totalling 

0.3 ft thick.

18________ Chert: Like that of To-19; bed contains

21 layers of interbedded mudstone 

totalling 0.5 ft thick.

17________ Chert and mudstone, interbedded: hard

brittle thin-bedded chert (65 percent) 

and soft fissile mudstone (20 layers 

totalling 1.3 ft); both chert and mudstone are light-brown (5 YR 6/4) ; 

two 0.2-ft mudstone layers in middle.

16_ _______ Chert and mudstone, interbedded:

chert (70 percent) and mudstone 

(five layers) like that of bed To-17; 

1-ft layer of chert near top and 

mostly mudstone below. Chert contains considerable amounts of .coarse 

angular quartz silt and nearly 10

E

ercent apatite as sponge-spicule 

llings and small pellets and in 

matrix.

15_ _______ Chert and mudstone, interbedded:

chert (75 percent) and mudstone 

(five layers) like that of bed To-17.

14_ _______ Chert and mudstone, interbedded:

chert (70 percent) and mudstone 

(four layers) like that of bed To-17.

13_____-__ Chert and mudstone, interbedded: 

chert (65 percent) and mudstone 

(four layers) like that of bed To-17. 

Re.tort Phosphatic Shale Tongue of Phosphoria Formation:

Rt-12_ _ ______ Sandstone: hard, medium-grained, thinto thick-bedded, medium-gray (N 5); 

contains nearly 18 percent apatite as 

oolites, pellets, shell fragments, 

sponge-spicule fillings, and rims on 

quartz grains. Chert is common as 

grains and as matrix. Mudstone 

partings occur near base. Basal 

contract irregular.

!!________ Mudstone: carbonatic. medium-hard to

soft, thin-bedded to fissile, lightbrown (SYR 6/4) to dusky-yellow 

(5Y 6/4); softer and thinner bedded 

higher in bed; locally it is a muddy 

carbonate rock containing 25 percent 

coarse angular quartz silt, mica 

flakes, and dark carbonaceous to 

phosphatic matrix. Many small 

almond-shaped phosphatic concretions (}£ in. long) occur in lower half.

10________ Mudstone: carbonatic, medium-hard,

thin-to thick-bedded, light-brownishgray (5YR 6/1). 

9________ Mudstone: soft, fissile to thin-bedded,

dusky-yellow (5F6/4) to light-brown 

(SYR 6/4). 

8_ _______ Phosphorite: pherty, medium-hard,

medium to coarsely oolitic, pinkishgray (SYR 7/1). Contains thin 

(0.05 ft) fissile mudstone layer at 

base. Oolites (commonly having 

quartz nuclei) and pellets of apatite 

are immersed in dusty cherty cement 

that is coarser and clearer near centers of interstitial areas. Basal contact irregular.

Chemical analyses (percent)

Cumulative 

Thickness thickness 

(feet) (feet) Sample

4. 6 18. 6 RSW-78-47

3. 9 22. 5 77-47 

3. 6 26. 1 76-47

Uranium

Acid JRadiometric Chemical 

insoluble eV U

0. 8 82. 1 0. 0005

1. 55 27. 65 75-47

.4 86. 0 . 0005

.9 84. 8 . 0005

3. 3 87. 0 . 0005

1. 0 28. 65 74-47

. 95 29. 6 73-47

1. 65 31. 25 72-47

. 6 31. 85 71-47

.8 87. 4 . 0005

.6 86. 0 .0005

1. 1 87. 4 0005

6. 9 76. 6 . 001

. 8 32. 65 70-47 1. 4 60. 8 . 001

. 7 33. 35 69-47

2. 9 36. 25 68-47

1. 0 37. 25 67-47

.4 45.5 .0005 ____-

1.6 81.8 .002 ..____.

22. 9 35. 0 . 009 0. 007
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 401

Porcupine Creek, Mont., lot 1217 Continued

Chemical analyses (percent)

Bed Description

Retort Phosphatic Shale Tongue of Phosphoria Formation Continued

Rt-7________ Carbonate rock and sandstone: medium-hard massive microcrystalline 

pale-brown (5YR 5/2) cherty carbonate rock containing many crosscutting hard fine- to medium-grained 

light-brownish-gray (5F.R6/1) cherty sandstone columns that average 

0.05-0.2 ft in diameter and 0.3 ft apart. 

Sandstone poorly sorted, grains angular to moderately rounded; chert 

matrix mostly microcrystalline; apatite common as pellets (clear to dark 

brown and dusty), fossil fragments, 

rims on quartz grains, and spongespiculefillings; chert grains common; 

carbonate fairly common as rounded 

grains and small secondary rhombs.

6________ Mudstone: soft, fissile, dusky-yellow

(5 Y 6/4); contains many crosscutting 

columns of fine-grained p'ale-brown 

(10 YR 6/2) sandstone about 0.1 ft 

in diameter that appear to project 

into overlying bed Rt-7 and are 

lithologically similar to those of bed 

Ls-5.

Lower member of Shedhorn Sandstone: 

Ls-5-----_-_ Sandstone: hard, cherty, fine- to

medium-grained, brownish-gray 

(5YR 4/1), locally calcareous; contains many crosscutting chert columns averaging 0.1 ft in diameter 

and 0.5 ft apart and scattered fossils 

(Lingula?) near top. Quartz grains 

(50 percent) immersed in dusty 

crypto- to microcrystalline chert (35 

percent) and commonly corroded by 

chert; contains 5-10 percent chert (?) 

grains and apatite as pellets, shell 

fragments, rims on quartz grains, 

and sponge-spicule fillings; siliceous 

sponge spicules common in chert. 

Irregular basal contact.

4-------- Sandstone: carbonatic, hard, mediumgrained, poorly bedded, mediumgray (N 5) to light-brownish-gray 

(5YR 6/1); locally conglomeratic at 

5.7 ft above base and in top foot.

3________ Sandstone: 1.0 ft fine- to mediumgrained hard yellowish-gray (5YR 

7/2) quartzitic sandstone overlain by 

0.5 ft medium-grained hard lightbrownish-gray (5YR 5/1) calcareous 

sandstone containing many gastropods and chert pebbles at top that 

are as much as 1 in. across. Quartz 

has abundant overgrowths on dustyrimmed grains, and calcite dust and 

very small crystals are abundant at 

old grains boundries and in matrix 

between grains. Chert grains and 

pellets and shell fragments common.

Cumulative 

Thickness thickness 

(feet) (feet)

Uranium

Sample

1. 25 38. 5 RWS-66-47

Acid Eadiometric Chemical 

PsO6 insoluble eU U

0. 8 59. 3 . 0005

39. 1 65-47 1. 8 78. 5 . 0005

64-47 2. 6 86. 7 . 0005

9. 5

1. 5

49. 3

50. 8
402 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Porcupine Creek, Mont., lot 1217 Continued

Bed

Ls-2.

Q-l.

Description

Lower member of Shedhorn Sandstone 

Continued

Sandstone and chert: top and bottom 

thirds composed of cherty sandstone; 

middle third, sandy chert; all are 

hard, thin- to thick-bedded; sandstone (65 percent) fine- to very fine 

grained, yellowish-gray (5Y 7/2) 

(darker upward), having chert cement, apatite pellets and spongespicule fillings, and siliceous sponge 

spicules; carbonate occurs as rounded 

grains and very fine matrix; chert 

irregularly bedded to concretionary, 

light-gray (N 7). Basal contact 

somewhat sheared.

Quadrant Formation, top bed:

Sandstone: mostly medium-hard (locally 

hard) or friable, massive, fine-grained 

yellowish-gray (2.5 Y 8/1) to white 

(N 9); irregularly cherty near top. 

Quartzite near top nearly all quartz 

and also minor tourmaline, titanite, 

magnetite (?), and chert; quartz 

subangular to well rounded and has 

extensive overgrowths; one thin 

layer has fine silty matrix. Chert 

near top is both microcrystalline and 

fairly coarse «>£ mm), and is partly 

chalcedonic and coarsely flamboyant; 

dust lines, more or less concentric to 

nuclei of crystallization, outline 

euhedral forms.

Chemical analyses (percent)

Thickness 

(feet)

11. 4

Cumulative

thickness

(feet)

62. 2

Uranium

Sample

Acid 

insoluble

Radiometric Chemical 

eU U

10. 0 10. 0

Jack Canyon, Mont., lot 1218

[Part of Phosphoria, Shedhorn, and Park City Formations sampled and described from cliff exposures and small hand trench about 900 ft above Creek on north side of Jack 

Creek Canyon in SEJ4NEJ4 sec. 35, T. 5 S., R. 1 E., Madison County, Mont., on overturned and faulted west limb of Madison Range syncline. Beds strike N. 60° E. 

and dip 45 N W. Measured by R. W. Swanson and sampled by J. G. Evans in September 1947. Analyzed for uranium by U.S. Geol. Survey, and for other constituents by U.S. Bur. of Mines. LOI, Loss on ignition]

Bed Description

Dinwoody Formation, basal

beds:

D-41____ Mudstone: soft, weak-yellowish-orange (2.5Y 7/4) 

to pale-brown (2.5Y 5/2), 

thin- to thick-bedded; 

contains thin layers of 

fine-grained ripple-marked 

sandstone and of aphanitic g'-ay limestone.

40_. __ Sandstone: carbonatic, 

muddy, soft to mediumhard, very fine grained, 

light-brownish-gray (5 YR 

6/1); weathers yellowishgray; contains 0.1 ft chertpebble conglomerate at 

base and a few thin mudstone partings.

Chemical analyses (percent)

Cumulative 

Thickness thickness 

(feet) (feet)

Uranium

Sample

Acid 

insoluble AljOs LOI

Radio- Chemical 

metric eU U

6. 0 6. 0

1. 6 7. 6
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 403

Jack Canyon, Mont., lot 1218 Continued

Chemical analyses (percent)

Cumulative 

Thickness thickness 

Bed Description (feet) (feet)

Upper member of Shedhorn

Sandstone:

Us-39___ Sandstone: calcareous, con- 5. 2 5. 2 

glomeratic, hard, thickbedded to massive, fineto medium-grained, lightbrownish-gray (5 YR 6/1); 

pebbles are composed of 

chert.

38_ Sandstone: irregularly 3. 0 8. 2 

bedded, medium-grained, 

light-brownish-gray (5 YR 

6/1); contains very light 

gray (N 8) chert nodules; 

irregular basal contact.

37.__ Sandstone: hard, medium- 18. 1 26. 3 

grained, massive, lightbrownish-gray (5 YR 5/1); 

locally cherty; contains 2 

in. of flat-pebble limestone conglomerate at 7.0 

and 13.3 ft above base; 

contains sandstone colums in top 2 ft; irregular 

basal contact.

36_ __ Sandstone: medium-hard to 12.8 39. 1 

hard, thin-bedded to massive (thinner-bedded toward top), mediumgrained, light-gray (N 7) 

to light-brownish-gray 

(5YR 6/1); contains flatpebble limestone conglomerate at base and 

thin-bedded chert at top. 

Irregular basal contact. 

Overgrowths on quartz 

grains include considerable amounts of microcrystalline rhombic carbonate at margins of old 

grains or between present 

grains; laminae of microcrystalline carbonate and 

of chert present; chert 

and carbonate do not 

penetrate areas of quartz 

overgrowths; numerous 

apatite pellets present.

35___ Chert and sandstone: 1.8 8.4 47.5 

ft sandstone and chert at 

top, underlain by 0.5 ft 

limestone and chert, 4 ft 

chert, and 2 ft moderately 

well-bedded cherty quartzite. Chert is hard, generally poorly bedded and 

shattered, dark-gray 

(N 3); sandstone is fine 

grained, calcareous, medium hard, brownish gray 

(5 YR 4/1); contains some 

columnar sandstone concretions (1-2 in. in diameter) in the chert below 

the limestone. Irregular 

basal contact.

Uranium

Sample

Acid 

insoluble A12O3 LOT

Radio- Chemical 

metric eV U

RWS-107-47 0. 8 68. 4 1. 6 2. 6 12. 2 0. 0005

106-47 1. 5 74. 0 1. 3 9.7 0005

105-47 1. 5 81. 3 1. 9 6.5 0005

104-47 8 85.0 9 2.6 4. 7 0005
404 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Jack Canyon, Mont., lot 1218 Continued

Chemical analyses (percent)

Cumulative 

Thickness thickness 

Bed Description (feet) (feet)

Upper member of Shedhorn

Sandstone Continued

Us-34___ Sandstone: hard, medium- 0. 9 48. 4 

grained, light-brownishgray (5YR 5/1).

33___ Sandstone: phosphatic, .5 48. 9 

hard, thin-bedded, medium-grained, pale-brown 

(5YR 5/2); apatite chiefly 

pelletal, but much in 

matrix of some thin 

layers; apatite shell fragments and secondary 

apatite present; overgrowths on most quartz 

grains; apatite constitutes about 20 percent of 

bed.

32. __ Chert; sandy, hard, thin- 1.35 50.25 

bedded to nodular, medium-gray (N 5) to darkgray (N 3); top 3 in. 

contains thin layers of 

calcareous mudstone.

31___ Sandstone: hard, medium- 1. 2 51. 45 

grained, pale-brown (SYR 

5/2); cherty at base.

30___ Sandstone: hard, medium- 2.15 53.6 

grained, light-brownishgray (5YR 5/1).

29. __ Chert: sandy, hard, thin- 2.5 56.1 

bedded to nodular, medium-gray (N 5) to darkgray (N 3); sand is fine.

28. __ Sandstone: hard, thick- 10. 5 66. 6 

bedded, fine-grained, 

pale-brown (5YR 5/2); 

somewhat cherty at top.

27-.- Sandstone: hard, fine- to 9.65 76.25 

very fine grained, mostly 

thick- but poorly, bedded, 

light-brownish-gray (5 YR 

5/1); irregular basal contact. Six ft above base 

most quartz has overgrowths; apatite (5-10 

percent) occurs mostly as 

pellets.

Tosi Chert Tongue of Phosphoria Formation; contains two 

thin tongues of Retort Phosphatic Shale Member of 

Phosphoria Formation in 

lower part:

To-26___ Chert: variably sandy, 2.5 78.75 

hard, poorly bedded, 

dark-gray (N 3); contains 

irregular lenses of sandstone.

25. __ Sandstone: cherty, hard, 2.5 81.25 

poorly bedded, fine- to 

medium-grained, palebrown (5YR 5/2); contains apatite pellets.

24. __ Chert: hard, thin-bedded, .9 82.15 

dark-gray (N 3).

23_ _ _ Sandstone: cherty, hard, . 3 82. 45 

fine-grained, pale- brown 

(SYR 5/2).

Uranium

Sample PjOs

Acid 

insoluble Al2 Oa LOT

Radio- Chemical 

metric eU U

RWS-103-47 1. 8 0. 8 2. 1 2. 1 0. 0005

102-47 1. 4 75. 3

101-47 2. 1 89. 3

1. 1

9 1. 3

9. 0

1. 8

0005

0005

100-47 1. 3 9 3. 5 2. 0 0005
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 405

Jack Canyon, Mont., lot 1218 Continued

Chemical analyses (percent)

Uranium

Cumulative 

Thickness thickness 

Bed Description (feet) (feet)

Tosi Chert Tongue of Phosphoria Formation; contains two

thin tongues of Retort Phosphatic Shale Member of

Phosphoria Formation in

lower part Continued

To-22__. Chert: fissile to thin-bed- 3.9 

ded, hard, dark-gray (2V 

3); contains 17 fissile 

brownish-gray (5YR 4/1) 

mudstone partings and 

0.3 ft of thin-bedded 

mudstone at base.

21__. Chert: hard, thin-to thick- 5.25 91.6 

bedded, dark-gray (N 3); 

contains a few 0.1-ft 

layers of fissile to thinbedded brownish-gray 

(SYR 4/1) mudstone. 

Contains considerable 

amounts of very fine 

sand and silt and many 

siliceous and phosphatic 

sponge spicules.

20_ __ Chert: hard, thin-bedded, 6.9 98.5 

dark-gray (N 3); contains 

27 layers totaling 0.6 ft 

of fissile to thin-bedded 

dusky-brown mudstone.

19___ 'Phosphorite: sandy, cherty, . 17 98. 67 

coarsely pelletal, hard, 

medium-dark-gray (N 4). 

Apatite pellets in cherty 

phosphate cement; qaurtz 

nuclei common in pellets; 

siliceous sponge spicules 

common; chert has locally 

replaced much apatite.

18. __ Chert and mudstone, inter- 2.4 101.07 

bedded: fissile to thinbedded hard grayish-black - 

chert (75 percent)interbedded with soft to medium-hard dusky-brown 

(SYR 2/2) mudstone.

Rt-17. _ _ Phosphorite: cherty, hard, . 5 101. 57 

coarsely oolitic and pelletal to coarsely nodular, 

grayish-black (TV 2). Apatite mostly oolitic but 

forms numerous pellets 

and nodules, in a cherty 

phosphate cement; pellets 

form nuclei of many oolitic grains; chert has irregularly replaced much 

of the matrix and the 

oolites; contains siliceous 

sponge spicules. Irregular basal contact.

16_ __ Mudstone: carbonatic, me- . 9 

dium-hard, thin-to thick- (3.25) 

bedded, laminated, brownish-gray (SYR 4/1). This 

bed and 1.6 ft of underlying chert repeated by 

near-bedding-plane fault. 

Original sampled bed 3.25 

ft thick; fault interpretation worked out after 

sampling. Probable composition: P2Os, 1.0; acid 

insoluble, 49.0 ±; A12O3 , 

2.5; Fe2O3, 3.5; loss on 

ignition, 21.5.

Sample

Acid 

insoluble Ala Os LOI

Radio- Chemical 

metric eU U

86. 35 RWS-99-47 6 85. 0 3. 1 5. 1 3. 0 0. 0005

98-47 1. 3 83. 1 1. 8 4. 3 4. 1 0005

97-47 9 84. 5 3. 2 5. 5 2. 9

96-47 18. 9 44. 0 1. 3 2. 9 2. 2

001

004

95-47 1. 2 81. 3 6. 0 5. 2

94-47 22. 9 37. 4 1. 4 2. 6

4. 2 001

1.8 006 0. 005

102. 47

93-47

(1.0?) (49.0?) 

67. 8

(2.5?) 

3. 6

(3.5?) 

4. 1

(21.5?) 

11. 9 0005
406 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Jack Canyon, Mont., lot 1218 Continued

Bed Description

Tosi Chert Tongue of Phosphoria Formation; contains two 

thin tongues of Retort Phosphatic Shale Member of 

Phosphoria Formation in 

lower part Continued

To-15--_ Chert: fissile to thin-bedded, 

brittle, brownish-black 

(5YR 2/1); contains 15 

layers totaling 0.4 ft of 

fissile brownish-black 

mudstone; somewhat 

thicker-bedded and less 

mudstone upward. Gradational basal contact. 

14___ Chert: fissile to thin-bedded, 

brittle, medium-dark-gray 

(N 4), contains 15 layers 

totaling 0.5 ft of fissile 

dusky-brown mudstone 

and 0.1 ft mudstone bed 

2.4 ft above base. Gradational basal contact. 

13___ Chert: fissile to thin-bedded, 

brittle, dark-gray (N 3); 

contains 0.3 ft -(15 layers) 

of fissile dusky-brown 

(5YR 2/2) mudstone. 

Retort Phosphatic Shale Tongue

of Phosphoria Formation: 

Rt-12.__ Phosphorite: soft, friable, 

poorly bedded, coarsely 

oolitic, dusky-brown 

(5YR 2/2).

11___ Carbonate rock: muddy, 

soft, grayish-brown (5 YR 

3/2). Underlain by 4-ft 

andesite porphyry sill 

having a plane, transecting contact.

10._ . Sandstone and phosphorite: 

0.4 ft sandy medium- to 

coarsely oolitic and pelletal dark-gray (N 3) 

phosphorite gradationally 

underlain by a 0.4 ft 

hard, fine-grained brownish-gray (5YR 4/1) sandstone. Apatite oolites 

and pellets occur in and 

are dominated by darker 

brown phosphatic matrix ; subangular quartz 

particularly common in 

some layers; some replacement of quartz by 

apatite. Subrounded 

quartz grains of the sandstone have abundant 

overgrowths; apatite (12 

percent) occurs chiefly as 

pellets and as matrix, 

much of which is recrystallized and colorless; 

chert grains common. 

Irregular basal contact.

Chemical analyses (percent)

Uranium

Thickness 

(feet)

Cumulative

thickness

(feet) Sample P2 05

Acid 

insoluble Fe2 Os LOI

Radio- Chemical 

metric e~U U

4. 05 106. 52 RWS-92-47 0. 6 87. 3 4. 7 4. 7 2. 4 0. 001

4. 6 111. 12 91-47 86. 9 4. 5 4. 9 2. 4 0005

4. 4 115. 52 90-47 6 87. 5 4. 3 4. 1 2.5 001

1. 15 116. 67

117. 07

0. 8 117. 87

89-47 28. 8 19. 0 1. 4 1. 9 4. 5

24. 9 4. 7 2. 3 32. 6

85-47 12. 7 61. 3 1. 9 3. 0 1. 7

010

001

004

009

004
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 407

Jack Canyon, Mont., lot 1218 Continued

Chemical analyses (percent)

Uranium

Bed Description

Lower member of Shedhorn

Sandstone:

Ls-9_-__ Sandstone: hard, finegrained, thin-bedded to 

massive, light-brownishgray, irregular basal contact.

8-_-_ Sandstone: hard, thin- to 

thick-bedded, fine- to medium-grained, lightbrownish-gray (5 YR 5/ 

1); top 0.7 ft thin-bedded 

and cherty.

7_ ___ Sandstone and chert: 1.9 ft, 

hard fine-grained thickbedded light-brownishgray (5YR 5/1) sandstone 

having 0.3 ft thick layers 

of hard brittle fissile to 

thin-bedded chert 0.8 ft 

above base and at top of 

bed.

6____ Conglomerate: 0.5 ft hard 

medium-gray (N 5) to 

light-brownish-gray (5 YR 

5/1) chert-pebble conglomerate overlain by %- 

in. layers of mudstone 

and chert. Sandstone in 

conglomerate bed mostly 

medium grained; pebbles 

as much as 40 mm across. 

Irregular basal contact.

5____ Mudstone and sandstone: 

0.3 ft muddy, calcareous 

medium-hard finegrained medium-gray (N 

5) sandstone overlain by 

1.0 ft of soft calcareous, 

sandy light-brown (5YR 

6/4) to dusky-yellow (5 Y 

6/4) mudstone. Abundant but incomplete 

quartz overgrowths on 

grains in sandstone; some 

are oscillatory, having 

good crystal outlines; secondary calcite fills remaining interstices. 

Contains chert grains and 

some apatite pellets. 

Gradational basal contact.

4____ Sandstone: hard, finegrained, poorly bedded, 

locally cherty or calcareous, medium-gray (N 5) 

to light-brownish-gray 

(5FE5/1). Quartz grains 

have abundant overgrowths that have good 

crystal outlines; secondary calcite in interstices; 

contains nearly 20 percent chert grains and 

numerous dusty apatite 

pellets; overgrowths on 

some carbonate grains.

Cumulative 

Thickness thickness 

(feet) (feet) Sample Ps06

Acid 

insoluble AhOa LOI

Radio- Chemical 

metric «U U

4. 6 122. 47 RWS-84-47 1. 3 90. 7 2. 4 0. 0005

3. 95 126. 42

2. 5 128. 92

83-47

82-47

8 92. 1 1. 4 1. 9

94. 2 1. 0 1. 9

0005

0005

6 129. 52 81-47 2. 4 2. 8 3. 1 7.3 001

1. 3 130. 82 80-47 70. 4 6. 5 3. 2 9. 6 001

2. 2 133. 02
408 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Jack Canyon, Mont., lot 1218 Continued

Chemical analyses (percent)

Bed Description

Lower member of Shedhorn 

Sandstone Continued

LS-3---_ Chert and sandstone: medium to poorly bedded 

hard light-gray sandy 

chert containing interbeds and lenses of very 

fine grained calcareous 

sandstone and a few small 

lenses of sandy carbonate 

rock. Chert and carbonate are microcrystalline 

and contain considerable 

amounts of fine-grained 

quartz sand and about 5 

percent apatite as pellets 

and sponge-spicule canal 

fillings; chert contains 

abundant siliceous sponge 

spicules. Unit much 

shattered and not well 

exposed.

Franson Tongue of Park City 

Formation:

F-2_____ Carbonate rock and chert: 

thin- to medium-bedded 

hard medium-light-gray 

carbonate rock containing numerous thin interbeds, lenses, and some 

nodules of chert; some 

cherty, quartzitic sandstone layers up to 0.4 ft 

thick.

!-____ Dolomite: sandy, cherty, 

poorly bedded to massive, 

hackly weathering, lightbrownish-gray (5YR 6/1). 

Dolomite microcrystalline; sand is very fine 

angular quartz; contains 

numerous apatite pellets 

and sponge-spicule fillings.

Cumulative 

Thickness thickness 

(feet) (feet)

11. 5 144. 52

Uranium

Sample

Acid 

PaOj insoluble A12 03 LOI

Radio- Chemical 

metric eU U

11. 0 155. 52

8. 0 163. 52

Dalys Spur, Mont., lots 1222 and 1223

[Permian rocks measured and sampled near Dalys Spur, west side of Beaverhead River, T. 8 8., R. 10 W., Beaverhead County, Mont. Retort Phosphatic Shale Member 

of Phosphoria Formation (lot 1222) measured in hand trench, NWJ-4SW!4 sec. 36; rest of section (lot 1223) measured in hand trench and natural exposures, SWJ4SWH 

sec. 36, T. 8 8., R. 10 W. Beds strike north to N. 30° E. and dip 30°-40° W. Section measured by W. R. Lowell and sampled by D. A. .Bostwick, R. L. Parker, and

E. T. Rupple, in July 1947. Analyzed for PjOs, F, and acid insoluble by U.S. Bur. of Mines and for uranium by U.S. Geol. Survey]

Chemical analyses (percent)

Bed

Us-97_

To-96. 

Us-95_

To-94_. 

Us-93_.

Description

Dinwoody-Shedhorn contact concealed by 

basalt flow; approximately 20 ft of Permian rocks are covered. 

Upper tongue of Shedhorn Sandstone; contains several thin tongues of Tosi Chert 

Member of Phosphoria Formation: 

Sandstone: hard, medium-gray (N 5), 

thick-bedded, fine-grained; contains 

scattered chert lenses that occur between sandstone beds; contains glauconite.

Chert: hard, brittle, medium-gray 

(N 5), thick-bedded; contains glauconite.

Sandstone: hard, medium-gray (N 5), 

thick-bedded, fine-grained; contains 

glauconite.

Chert: hard, gray (N 5), thick-beddedSandstone: cherty, hard, medium-gray

(N 5), thick-bedded, fine-grained.

Thick- Cumulaness tive Mck-

(feet) ness (feet)

Uranium

Sample

Acid insoluble F

Radio- Chem.kal 

metric eU U

23. 7

12. 5

4.0

3.8 

2.0

43. 7 WRL-286-47 2. 2 4 __ 0.001 0.000

56.2

60. 2

64.0

66.0

285-47 1. 5 91. 0

284-47 2. 2

. 001 . 000

. 001 . 000
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 

Dalys Spur, Mont., lots 1222 and 1228 Continued

409

Chemical analyses (percent)

Acid insoluble

WRL-283-47 1.5 90.1 ____

282-47 1.6 89.6 ___.

281-47 2.5 87.3 ____

89. 1 _._.

78.3 __..

278-47 2.6 86.3 ....

277-47 16. 6 50. 6

45-47 3.5 80.0 __

44-47 3. 2 78. 5

Thick- Cumulaness tive thickBed Description (feet) ness (feet) Sample

Tosi Chert Member of Phosphoria Formation: 

To-92.______ Chert: hard, light-olive-gray (5 Y 6/1), 20.4 86.4

thick-bedded; contains glauconite; 

grades from bed below.

91______. Chert: hard, light-gray (N 7), thick- 22.3 108.7

bedded; contains glauconite; grades 

from bed below.

90_______ Chert: sandy, hard, light-gray (N 7), 7.4 116.1

thick-bedded; contains glauconite; 

sand is very fine.

89 -___- Chert: silty, hard, light-gray (N 7), 14.7 130.8 280-47 1.7 

thick-bedded; contains glauconite.

88-_____- Mudstone: gypsiferous, soft and me- .5 131.3 279-47 2.2 

dium-hard, medium-gray (N 5), 

fissile.

87____-__ Chert: hard, medium-gray (N 5), thick- 3.6 134.9 

bedded; contains glauconite; contains skeletal apatite in lower part; 

contains gypsum in fractures; grades 

from bed below.

86_ ______ Chert: phosphatic, hard, medium- 1.2 136.1

gray (N 5), thick-bedded; apatite 

is skeletal and finely pelletal; contains flauconite. Fossil-collection 

numbers 9797, 9799.

Retort Phosphatic Shale Member of Phosphoria Formation: 

Rt-85_ ______ Mudstone: medium-hard, light-gray 1.0 137.1

(N 7) and medium-gray (N 5); 

grades from bed below.

84_ ______ Mudstone: hard, medium-light-gray 1.3 138.4

(N 7) and light-brownish-gray (SYR 

6/1), thin-bedded; grades from bed 

below.

83-_-_-_- Mudstone: medium-hard, grayish- 1.4 139.8 43-47 1.8 

black (A 2), fissile.

82 _______ Phosphorite: muddy, medium-hard, .8 140.6 42-47 25.3

weak-orange-pink (SYR 8/2), thickbedded, medium pelletal.

81------- Mudstone: phosphatic, black (N 1), -7 141.3 41-47 13.7

thin-bedded.

80-_---__ Phosphorite: muddy, medium-hard, .3 141.6 40-47 28.6 

light-brown (5YR 6/4) and moderatebrown (5YR 4/4), thick bedded, 

finely pelletal.

79-----__ Mudstone: phosphatic, medium-hard, 1.2 142.8 

moderate-brown (SYR 4/4), very 

finely pelletal; bed is brecciated; 

grades from bed below.

78---___- Phosphorite and mudstone, inter- 1.5 144.3 

bedded: medium-hard moderatebrown (SYR 4/4) thin-bedded phosphorite inter bedded with mediumhard moderate-brown (5YR 4/4) 

thin-bedded phosphatic mudstone; 

apatite is finely to coarsely pelletal.

77----___ Mudstone: medium-hard, black (N 1), . 9 145. 2 

fissile; gypsum coats fracture and 

bedding surfaces.

76--__-__ Phosporite: muddy, medium-hard, .6 145.8 

light-brown (SYR 6/4), thin-bedded, 

very finely pelletal; grades from bed 

below.

75_--_-_- Mudstone: phosphatic, medium-hard, .5 146.3 35-47 10.1 53.8 

light-brown (SYR 6/4) to moderatebrown (SYR 4/4), thin-bedded.

74_ ______ Mudstone: medium-hard, moderate- .4 146.7 34-47 4.8 71.5

brown (SYR 4/4), very thick bedded.

Uranium

66. 7

30. 1

51. l 

22. 2

39-47 17.0 45. 1

38-47 22. 1 32. 8

37-47 6. 1 45. 5

36-47 22. 2 32. 0

Radiometric e\J

0.001

.0005

. 001

.0005

.001

.001

.003

Chemical 

U

0. 000

.000

.000

.000

.000

.000

.001

2.44

1. 17

.003

.002

.002

.007

.004

.008

.016

.007

004

010

006

. 41 . 004

.000

. 000

. 001

.009

.002

.007

.005

. 007

. 010

.004
410 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Dalys Spur, Mont., lots 1222 and 1223 Continued

Chemical analyses (percent)

Bed

Rt-73_

72

70. 

69-

68. 

67_ 

66_ 

65_

64 _ 

63- 

62_

61- 

60- 

59-

58.

57-

56. 

55.

54.

Description

Retort Phosphatic Shale Member of Phosphoria Formation Continued

Phosphorite: muddy, medium-hard,

black (N 1), thick-bedded, very finely

to coarsely pelletal; contains 0.01 ft

thick seam of gypsum in middle. 

Mudstone: medium-hard, black (N 1),

thin-bedded; contains 0.1 ft thick

seam of gypsum at top; grades from

bed below. 

Phosphorite: crumbly, light-brown

(5YR 6/4) to moderate-brown (SYR

4/4), thin-bedded, very finely pelletal; grades vertically and laterally

into mudstone lenses; gypsum coats

fractured surfaces. 

Mudstone: medium-hard, black (N 1),

thin-bedded; gypsum coats fractures;

grades from bed below. Fossil-colln.

No. 9796. 

Mudstone: medium-hard, black {N 1),

fissile and thin-bedded; contains gypsum in fractures; grades from bed

below. 

Mudstone: medium-hard, black (N 1),

thin-bedded; grades from bed below.

Fossil-colln. No. 9795. 

Mudstone: medium-hard, black (N 1),

fissile; grades from bed below. Fossil-colln. No. 9794. 

Mudstone: hard, black (N 1), fissile and

thin-bedded; grades from bed below.

Fossil-colln. No. 9793. 

Mudstone: medium-hard, black (N 1),

fissile; grades from bed below. Fossil-colln. No. 9792. 

Mudstone : hard, dark-gray (N 3) , thinbedded; grades from bed below. 

Mudstone : hard, dark-gray (N 3) , thinbedded; grades from bed below. 

Mudstone: hard, black (N 1), thinbedded ; grades from bed below. Fossil-colln. No. 9791. 

Mudstone: medium-hard, moderatebrown (5 YR 4/4) , thin-bedded ; grades

from bed kelow. 

Mudstone : medium-hard, grayish- black

(N 2), thin-bedded; grades from bed

below. Fossil-colln. No. 9790. 

Mudstone : medium-hard, grayish-black

(N 2) , thin-bedded ; irregular contact

with bed below. Fossil-colln. No.

9789. 

Phosphorite: hard, dark-gray (A 3),

thick-bedded; finely pelletal and

nodular; irregular contact with bed

below. 

Mudstone: hard, black (N 1), thinbedded; contains gypsum on fractured surfaces. 

Phosphorite: hard, dark-gray (N 3),

very thick bedded; medium pelletal. 

Mudstone: medium- hard, dark-gray

(N 3), fissile and thick-bedded; contains seams and lenses of gypsum in

fractures and on bedding surfaces;

grades from bed below. Fossil colln.

No. 9787. 

Phosphorite: muddy, medium-hard,

dark-gray (N 3), thin-bedded, very

finely pelletal; contains gypsum

seams in fractures.

Thick- Cumvlaness tive thick-

(Jeef) ness (feet)

Uranium

Acid in- Radio- Chemical 

Sample PzOs soluble F metric eV U

0. 4 147. 1 WRL-33-47 22. 4 23. 5

. 3 147. 4

. 3 147. 7

4. 0 151. 7

5. 0 156. 7

. 8 157. 5

2. 1 159. 6

1. 6 161. 2

2. 7 163. 9

1. 2 165. 1

1. 2 166. 3

1. 6 167. 9

. 8 168. 7

1. 7 170. 4

1. 2 171. 6

. 3 171. 9

. 8 172. 7

1. 2 173. 9

1. 4 175. 3

1. 7 177. 0

32-47 2. 9 55. 8

31-47 19. 0 33. 0

30-47 4. 2 42. 6

29-47 2. 9 49. 9

28-47 2. 7 61. 3

27-47 .6 65. 9

26-47 1. 6 67. 9

25-47 2. 0 63. 3

24-47 1. 6 65. 5

23-47 0. 6 63. 6

22-47 1.1 35. 0

21-47 1. 2 69. 4

20-47 1. 8 71. 5

19-47 2. 9 50. 2

0. 010 0. 008

. 003

.009 . 007

.003

.004

.003

. 002

. 003

.003

.002

. 002

. 002

.002

.002

.004

18-47 27. 4 19. 3 3. 8 . 007

17-47 4. 4 60. 6 .003

16-47 33. 1 6. 7 4. 1 . 007 

15-47 6.8 52.3 ____ .005

14-47 22. fi 24. 62 __ .007

. 002

.005

.002

.007

.003

.005
Bed

STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS 

Dalys Spur, Mont., lots 1222 and

Description

OF SOUTHWESTERN MONTANA 

' Continued

411

Thick- Cumulaness live thick-

(feet) ness (feet)

Retort Phosphatic Shale Member of Phosphoria Formation Continued 

Rt-53.______ Dolomite: hard, olive-gray (5Y 4/1), .9 177.9

thick-bedded.

52_______ Mudstone: phosphatic, medium-hard, .8 178.7

grayish-black (N 2), thin-bedded; 

apatite is finely pelletal.

51__.___- Phosphorite: medium-hard, brownish- .3 179.0 

black (10 YR 2/1), thick-bedded, very 

finely pelletal and nodular.

50. _ _ _ _ Mudstone: soft, light-brown (5 YR 6/4), . 2 179. 2 

thin-bedded.

49______- Phosphorite: hard, light-brownish-gray .3 179.5

(5YR 6/1), thin-bedded, very finely 

pelletal; grades from bed below.

48--__--_ Mudstone: hard, brownish-gray (5 YR .6 180.1 

4/1), thin-bedded; grades from bed 

below.

47_-__-_- Phosphorite: hard, light-brownish-gray .4 180.5 

(5YR 6/1), thin-bedded; very finely 

pelletal.

46. _-_-.- Phosphorite: muddy, medium-hard, 1.3 181.8 

light-gray (N 7), thick-bedded, very 

finely pelletal; upper 0.3 ft is 

crumbly.

45.______ Mudstone: medium-hard, light-gray . 5 182. 3

(N 7), thick-bedded; contains a few 

phosphorite nodules at center and at 

top.

44_______ Phosphorite: hard, medium-gray (N 5), . 2 182. 5"\

thick-bedded, very finely pelletal.

43_____._ Mudstone: hard, light-olive-gray (5Y .3 182.8 

5/2), thick-bedded.

42_______ Phosphorite: hard, medium-gray (N 5), . 6 183. 4

thick-bedded, very finely pelletal.

41_._____ Mudstone: hard, light-olive-gray (5Y .4 183.8 

5/2), thick-bedded.

40.______ Mudstone: medium-hard, light-olive- 1. 0 184. 8

gray (5Y 6/1), thick-bedded; contains a few phosphorite nodules 0.3 

ft below top of bed.

39-______ Phosphorite: muddy, medium-hard, 1. 6 186. 4

medium-gray (N 5), thin-bedded, 

very finely pelletal; contains thin 

gypsum seam 0.6 ft below top; 

grades from bed below.

38_______ Phosphorite: muddy, medium-hard, 1. 4 187. 8

light-gray (N 6), finely pelletal; contains several thin seams of gypsum.

37_______ Mudstone: medium-hard, light-brownish- .9 188.7

gray (SYR 6/1), thin-bedded; contains gypsum.

36_______ Mudstone: phosphatic, medium-hard, .8 189.5

very light gray (N 8), thick-bedded.

35_._____ Mudstone: phosphatic, hard, medium- 1. 2 190. 7 

light-gray (N 7), thin-bedded; may 

be sandy.

34_______ Phosphorite: sandy, hard, medium- 1. 1 191. S\

gray (N 5), very thick bedded; contains glauconite and skeletal apatite 

fragments; grades from bed below. 

Franson Tongue of Park City Formation: 

F-33_______ Sandstone: phosphatic, hard, medium- 1. 1 192. 9

gray (N 5), fine-grained; contains 

glauconite and phosphatic skeletal 

fragments.

32_______ Sandstone: cherty, hard, light-gray (N 1. 6 194. 5"

7), very thick bedded, fine-grained.

31_______ Chert: hard, light-gray (N 7), thick- 1.1 195.6

bedded.

Chemkal analyses (percent)

Uranium

Sample

Acid in- Radio- Chemical 

soluble F metric e~U U

WRL-13-47 3.9 18.6 ____ 0.001 

12-47 10.0 49.1 _.-- .004

11-47 22. 8 21. 3 . 005 . 003

10-47 11.0 48. 3 .004

9-47 24. 4 24. 7 2. 48 .005 . 005

8-47 .2 68.3 __ .001 .000

7-47 14. 7 48. 2 1. 28 . 005 . 003

6-47 5. 3 71. 2 .68 . 002 . 003

5-47 17.2 36.9 _-__

4-47 20.3 27.5 _-__

3-47 8.8 62.1 _.__

2-47 3.3 75.8 ..__

1-47 13. 8 45. 9 1. 33

. 005 . 003

.005

. 004

. 003

. 005

. 003

. 003

. 007

.003

276-47 15. 1 56. 1 1. 39 . 003 . 003

275-47 3. 9 77. 2 . 001 . 001
412 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Dalys Spur, Mont., lots 1222 and 1223 Continued

Bed - Description

Franson Tongue of Park City Formation Continued 

F-30-------- Sandstone: calcareous, hard, light-gray

(N 7), very thick bedded, finegrained. 

29---.---- Sandstone: hard, light-gray (AT 7),

thick-bedded, fine-grained; grades 

from bed below.

28-___---_ Chert: hard, light-gray (N 7), thickbedded. 

27__------ Siltstone: cherty(?), light-gray (N 7),

thick-bedded; grades from bed below. 

26____--__ Sandstone: cherty(?), light-gray (N 7),

thick-bedded, fine-grained; grades 

from bed below. 

25________ Chert:sandy, hard, medium-gray (N5),

very thick bedded. 

24________ Sandstone: hard, light-gray (N 7), very

thick bedded, fine-grained; grades 

from bed below. 

23 ________ Sandstone: medium-hard, light-gray

(N 7), very thick bedded, finegrained; contains chert nodules in 

upper 6.7 ft.

Rex Chert Member of Phosphoria Formation: 

R-22________ Chert: sandy, medium-hard, very light

gray (AT 8), thick-bedded. 

21________ Sandstone: medium-hard, light-gray

(N 7),thick-bedded, very fineg-ained; 

contains glauconite and phosphatic 

skeletal fragments. 

20________ Chert: hard; contains glauconite-_____

19________ Sandstone: hard, medium-gray (N 6),

thick-bedded, fine-grained; contains 

glauconite. 

Meade Peak Phosphatic Shale Member of

Phosphoria Formation:

M-18__-___- Siltstone: sandy(?), hard, light-gray 

(N 7), thin-bedded; uppermost 1.0 ft 

contains some very fine apatite pellets. 

17_ ______ Mudstone: hard, light-brownish-gray

(5YR 6/1), thin-bedded. 

16_______ Phosphorite: soft and crumbly, very

light gray (AT 8), thick-bedded, finely 

to coarsely pelletal.

l5-_____- Mudstone: medium-hard, light-olivegray (5Y 6/1), thin-bedded. Fossilcolln. No. 9798.

14_______ Phosphorite: soft and crumbly, lightgray (N 7) and reddish-gray, thinbedded; finely oolitic and pelletal; 

contains phosphatic skeletal fragments.

Thick- Cumulaness five thick-

(feet) ness (feet) Sample

8. 7 204. 3 WRL-274-47 

11.0 215.3 273-47

9. 2 258. 2

10. 0 268. 2

1. 0 269. 2

6. 0 275. 2

6. 1 281. 3

3. 1 284. 4

Chemical analyses (percent)

Uranium

Acid in- Radio- Chemical 

soluble F metric eV U

0. 8 

1. 3

9.0

7. 2

7.3

2.8

7.4

224. 3

231. 5^1

238. 8 1

241. 6

249. 0

272-47

271-47

270-47

269-47

. 2

. 5

1. 3

2. 5

46.9 -___ 0.001 0.000

90.8 _--_ ------ _-----.

95.1 --__ .0005 .000

92.8 --__ ------ -------

91.3 .-_- ------ -------

78.2 _--_ .001 .000

268-47 5. 4 80. 0 0. 71 . 001 . 000

267-47 1. 9 87. 6

266-47 1. 1 92. 5

. 001 . 000

.001

265-47 6. 7 67. 0 .68 . 005

. 000

. 003

. 8

. 4

. 3

. 7

285.

285.

285.

286.

2

6

9

6

264-47

263-47

262-47

261-47

6.

35.

4.

36.

0

7

5

4

69.

6.

76.

5.

6 _.._

4 3.56

5 -_--

2 3. 57

. 003

.011

.003

. 009

.001

. 010

.001

. 008
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

Dalys Spur, Mont., lots 1222 and 1228 Continued

413

Bed Description

Grandeur Tongue of Park City Formation: 

Gr-13_._____ Sandstone: medium-hard, yellowishgray (5Y 7/2), thick-bedded, finegrained. 

12_ ______ Clay: soft, very light gray (N 8)

11______- Sandstone: medium-hard, ligh

(N 7), thick-bedded, fine-gr 

grades from bed below. 

10_______ Sandstone: cherty, medium-hard, very

light gray (N 8), thick-bedded; unit 

is brecciated.

9_---___ Siltstone: cherty, sandy, soft

dium-hard, grayish-yellow (5Y 8/4), 

thick-bedded.

8_______ Siltstone: soft to medium-hard, grayish-yellow (5Y 8/4), thick-bedded.

7___-___ Siltstone: calcareous, sandy, sc 

medium-hard, grayish-yellow 

8/4), thick-bedded; grades from bed 

below.

6_______ Sandstone: calcareous, silty, mediumhard, light-gray (N7), thick-bedded, 

very fine grained.

5__.____ Dolomite: medium-hard, very

gray (N 8), aphanitic; contains numerous black medium-gri 

lets (manganese-oxide?); grades from 

bed below.

4_______ Siltstone: sandy, medium-hard,

lowish-gray (5Y 7/2), thin-bedded.

3_______ Dolomite: medium-hard,

gray (5Y 7/2), very thick bedded; 

contains pellets similar to 

found in bed G-5.

2_______ Mudstone: soft, pinkish-gray,

bedded.

!_______ Dolomite: hard, yellowish-gray

7/2), very thick bedded. Underlain 

by sandstone of Quadrant Formation.

Chemical analyses (percent)

Thick- Cumulaness tive thick-

(feet) ness (feet) Sample

Uranium

Acid in- Radio- Chemical 

soluble F metric eU U

2. 4 289. 0 WRL-260-4 4. 4 84. 4 0. 001 0. 001

t-gray 

ained ;

, very 

; unit

o me7 8/4),

grayled.

Dft to

(5Y

m bed

2.

1.

2.

1. 

1.

8 

5

4

0

0 

2

dium- 3. 0

3dded,

light 

as nud pelsfrom

yelded.

owishidded; 

those

thin-

(5Y

2.

3.

1.

6.

8

7

5

5

7

289. 

292.

293.

295.

296. 

297.

300.

303.

304.

8] 

3

259-47

7 258-47

r

7 

9

257-47

9 256-47

7 255-47

4 254-47

307. 9 253-47

309.

316.

4 252-47

1 251-47

. 5 82.

.8 90.

. 6 80.

. 1 76.

. 2 18.

. 5 79.

. 0 2.

. 4 80.

.3 1.

0 ____

5 ____

0 ___.

6 ____

9 ---_

3 ___.

6 ____

6 ___.

9 ____

. 002

. 001

.002

.001

.0005

.002

.0005

. 002

.0005

. 000

. 000

. 000

. 000

.000

.000

.000

.000

.000

709-931
Big Sheep Canyon, Mont., lots 1224, 1225, 1226, and 1227

[Permian rocks measured and sampled in hand trenches and natural exposures on east limb of Dixon Mountain syncline; lot 1224 measured in NEJ<S WJ£ sec. 26; lot 1225, in SE^S

sec. 35, T. 13 S., R. 10 W.; lot 1227, in N WMN WJ4 sec. 11, T. 14 S., R. 10 W., Beaverhead County, Mont. Beds strike northwest and dip 30-40° SW. Measured by W. R. Lo

E. T. Rupple, and R. L. Parker in August 1917. Samples analyzed for uranium and organic matter by U.S. Geol. Survey, and for other constituents by U.S. Bur. of Mines. 

Chemical analyses (per

Bed 

To-232

231_____

230_-__-

229-.---

228-.-.-

227_.___

226_--_-

225--__-

224 _ _

223--.--

222_--_-

221_-__-

220_----

219-.---

218--__-

217--.-.

216____.

215__ _

214____.

213.-__.

Cs-212____.

211.___.

210__-_.

209___..

208____.

Description

Tosi Chert Member of Phosphoria Formation: 

Chert: calcareous, silty, hard, olivegray (5Y 4/1). Overlying beds are 

probably the basal part of the Dinwoody Formation.

Mudstone: cherty, carbonatic, hard,

olive-gray (5Y 4/1), thin-bedded.

Similar to bed To-231__ ____________

Similar to bed To-231____ _ _

Similar to bed To-231__ _-___ _._ _

Similar to bed To-231. __________ _

Mudstone: carbonatic, moderate-yellowish-brown (10YR 5/4), thinbedded.

Mudstone: carbonatic, medium-hard,

brownish-gray (5YR 4/1), thinbedded.

Chert: muddy, dolomitic, hard, medium-dark-gray (N 4), thin-bedded.

Chert: muddy, dolomitic, hard, medium-gray (N 5), thick-bedded.

Chert: carbonatic, hard, mediumdark-gray (N 4), thick-bedded.

Chert: muddy, hard, olive- gray (5Y

4/1), thick-bedded.

Chert: hard, olive-gray (5Y 4/1),

thick-bedded; grades from underlying chert.

Similar to bed To-220_ _____________

Chert: hard, olive-gray (5Y 4/1), thinbedded.

Dolomite: muddy, hard, moderateyellowish-brown (IOYR 5/4), thickbedded, aphanitic.

Chert: hard, olive-gray (5Y 3/2), thinbedded.

Similar to bed To-216__ ____________

. _ Chert: hard, olive-gray (5 Y 4/1), thinbedded.

Carbonate rock: hard, moderate-yellowish-brown (1QYR 5/4), very thick

bedded, aphanitic.

Cherty shale member of Phosphoria Formation:

Mudstone: hard, olive-gray (5Y 4/1),

thin-bedded.

Similar to bed Cs-212_____ __ ______

Similar to bed Cs-212__-_ __ _ ___

Similar to bed Cs-2 12 _ _ _ ___

Similar to bed Cs-2 12 _ _.__ __ __

Thick- Cumulative 

ness thickness 

(feet) (feet)

25. 0 25. 0

3.

4.

5.

4.

4

1.

4.

5.

5.

4.

5.

1.

4

4.

4.

1.

1.

5

0

0

2

2

8

3

6

0

0

7

0

7

4

8

9

5

9

0

2. 2

5.

2.

2.

2.

0

2

5

7

28.5

32.5

37.5

41. 7

45.9

46.7

48. 0

52.6

57.6

62. 6

67.3

72. 3

74. 0

78.4

79.2

84. 1

88. 6

90.5

91.5

93.7

98.7

100.9

103.4

106. 1

Sample 

Lot 1224

WRL-222-47

221-47

220-47

219-47

218-47

217-47

216-47

215-47

214-47

213-47

212-47

211-47

210-47

209-47

208-47

207-47

206-47

205-47

204-47

203-47

202-47

201-47

200-47

199-47

P2 05

1.

1.

1.

1.

1.

1.

1.

1.

1.

1.

1.

2.

1.

1.

1.

1.

1.

1.

1.

5

3

3

8

2

9

9

2

6

0

2

5

4

2

5

3

6

3

5

5

4

5

9

4

Acid 

insoluble AljOa FejOa

78.

71.

74.

74.

75.

66.

75.

76.

80.

80.

80.

78.

85.

77.

3.

74.

75.

85.

1.

76.

78.

76.

75.

80.

9 ____ _____

7 __._ _____

6 ____ _____

6 ____ _____

5 ____ _____

6 -_-_ _____

3 ___- _____

1 ____ ---__

9 ____ _____

3 __ __

3 _-_- _-_--

9 -__- _____

0 --_- _____

8 _.__ _____

0 ___- _____

3 ---_ _____

5 __._ _____

7 ._-- _____

4 ____ _____

4 ___ __ -

7 ____ _____

7 _-- -----

5 .___ _____

4 _-__ _ __

VsOs LOI 

_____ 

_____ ____ 

__ _ __ 

____- ____ 

_ __ __._ 

_____ ____ 

--_-_ ---_ 

_-___ _.__ 

_____ ____ 

_____ ____ 

_____ ____ 

_____ __-_ 

_____ ____ 

_____ ___- 

_____ ____ 

_____ ____ 

_____ ____ 

_____ ____ 

_____ ___. 

_____ ___- 

_____ ____ 
207.

206. 

205- 

204. 

203.

202.

201.

200.

199.

Rt-198.

197.

196.

195.

194. 

193. 

192-

191.

190.

189.

188.

187.

186.

185.

184.

183.

182.

181. 

180- 

179.

178.

177.

176.

Mudstone: medium-hard,

(574/1), thin-bedded. 

Similar to bed Cs-207_____________

Similar to bed Cs-207_____________

Similar to bed Cs-207_____________

Similar to bed Cs-207; grades from

bed below. 

Mudstone: medium-hard, olive-gray

(574/1), thin-bedded. 

Similar to bed Cs-202_____________

Similar to bed Cs-202___________

Similar to bed Cs-202; grades from bed 

below. Fossil-colln. No. 9913 from 

beds Cs-199 through Cs-202. 

Retort Phosphatic Shale Member of Phosphoria Formation:

Mudstone: soft, grayish-black (N 2) to

dark-gray (AT 3), fissile. 

Similar to bed Rt-198_____________

Similar to bed Rt-198 _____________

Mudstone: phosphatic carbonatic, 

medium-hard, medium-gray (N 5), 

very thick bedded.

Carbonate rock: muddy, soft, darkgray (AT 3). 

Mudstone: soft, dark-gray (N 3),

fissile.

Mudstone: medium-hard, dark-gray 

(N 3) and brownish-black (10YR 

2/1).

Phosphorite: medium-hard, dark-gray 

(N 3), thin-bedded; nodular in basal 

0.3 ft and in upper 0.3 ft. 

Mudstone: medium-hard, grayishblack (N 2), thin-bedded. 

Phosphorite medium-hard grayishblack (N 2), thin-bedded, finely 

pelletal. 

Similar to bed Rt-190_____________

Phosphorite: muddy, soft, brownishgray (5YR 4/1), fissile, nodular and 

finely pelletal.

Mudstone: carbonatic, medium-hard, 

olive-gray (57 3/2), thin-bedded; 

grades from bed below. 

Mudstone: phosphatic, medium-hard, 

brownish-black (WYR 2/1), thickbedded apatite is finely pelletal; grades 

from bed below. 

Similar to bed Rt-186 ____________

Similar to bed Rt-185_____________

Similar to bed Rt-168; grades from bed

below.

Phosphorite: medium-hard, olive-gray

(5 73/2), thick-bedded; finely pelletal.

Mudstone: medium-hard, olive-gray

(573/2), thick-bedded. 

Phosphorite: medium-hard, olive-black 

(5 72/1), thick-bedded, finely pelletal. 

Mudstone: soft, olive-black (5 72/1), fissile. 

Similar to bed Rt-179_____________

Mudstone: phosphatic, medium-hard, 

pale-olive (5 75/2); basal 0.4 ft, thickbedded; upper 0.2 ft fissile.

olive-gray 5. 0 111. 1 107-47 1. 2 78. 

4

5. 0 

5. 0 

5. 0 

5.0

4. 2

5. 0 

3.3

5. 0 

5. 0 

1.3

116. 1

121. 1

126. 1

131. 1

5. 0 136. 1

140. 3

145. 3

148.6

5. 0 153. 6

158. 6

163.6

164.9

4. 1 169. 0

5. 0 174. 0

1. 2 175. 2

2. 5 177. 7

. 3 178. 0

. 2 178. 2

. 2 178. 4

1. 5 179. 9

106-47 

105-47 

104-47 

103-47

1.6 

1.6

97-47 

96-47 

95-47

8.9

80.2

1. 3 77. 4

1. 3 80. 3

102-47 1. 3 79. 4

101-47 1. 4 82. 6

100-47 1. 3 81. 1

99-47 3. 5 66. 1

98-47 5. 8 50. 3

5. 6 50. 5

7. 8 46. 3

6. 8 40. 8

94-47 1. 8 19. 2

93-47 5. 7 36. 7

92-47 6. 8 38. 1

91-47 26. 8 12. 3

90-47 8. 8 49. 4

89-47 22.5 41. 7

88-47 6. 9 56. 9

87-47 16. 7 23. 7

86-47 21. 7 13. 5

85-47 12. 9 32. 3
Big Sheep Canyon, Mont., lots 1224, 1225, 1226, and 1227 Continued

Chemical analyses (perc

Bed 

Rt-175- ----- -

174-------

173-------

i 79

17l---____

170-.-----

169-----.-

168

165

164 _-___.

163--.. __.

1 ^Q

1 ^fi

Retort Phosph 

phoria Form 

Dolomite: 

olive-bla 

aphaniti 

Dolomite: 

5/2) thic 

Similar to 

Phosphori 

brownis 

bedded, 

Dolomite: 

gray (N 

2/1), thii 

Mudstone: 

brownis] 

bedded; 

phospho 

Dolomite: 

brownis] 

bedded, 

Dolomite: i 

ish-gray 

aphaniti 

phospho 

Mudstone 

medium 

very thi 

Carbonate 

light-gra 

Mudstone 

medium 

bedded. 

Carbonate 

gray (5 

nitic. 

Mudstone 

medium 

4), thii 

nodules. 

Carbonate 

gray (5 

nitic. 

Mudstone 

medium 

bedded;

ish-gray 

Mudstone

dark-gn 

Phosphori 

grayishvery fin

Description

atic Shale Member of Phosation Continued 

phosphatic, medium-hard, 

ck (57 2/1), thick-bedded, 

c. 

medium-hard, pale-olive (5 Y 

k-bedded, aphanitic. 

bed Rt-175 ------------

,e: muddy, medium-hard, 

i gray (5 Y 7,4/1), very thick 

finely pelletal. 

muddy, medium-hard, dark3) and brownish-black (10 YR 

i-bedded. 

calcareous, medium-hard, 

i-gray (57 4/1), very thick 

contains some finely pelletal 

rite lenses, 

muddy, medium-hard, 

i-gray (5YR 4/1), very thick 

aphanitic. 

nuddy, medium-hard, brown- 

(5 YR 4/ 1) , very thick bedded, 

c ; contains some finely pelletal 

rite lenses, 

carbonatic, phosphatic, 

-hard, grayish-black (N 2), 

ck bedded, 

rock: argillaceous, hard, 

y (AT 7), thick-bedded, 

dolomitic, phosphatic, 

-hard, dark-gray (N 3) , thinrock: hard, light-brownishYR 6/1), thin-bedded, aphadolomitic, phosphatic, 

-hard, medium-dark-gray (N 

i-bedded; contains apatite

rock: hard, light-brownishYR 6/1), thick bedded, aphacarbonatic, phosphatic, 

-hard, dark-gray (N 3), thincontains apatite nodules. 

: muddy, hard, light-brown- 

(5YR 6/1), thick-bedded. 

: dolomitic, medium-hard, 

ly (Ar 3), thin-bedded, 

te: calcareous, medium-hard, 

black (N 2), thin-bedded, 

ely pelletal and nodular.

Thick- Cumulativ 

ness thickness 

(feet) (feet)

Lo

0. 3 187. 2

. 2 187. 4

. 2 187. 6 

1. 7 189. 3

. 5 189. 8 

1. 3 191. r

1. 6 192. 7 

2. 9 195. 6

1. 3 196. 9

1. 8 198. 7 

1. 2 199. 9

1. 6 201. 5 

. 6 202. 1

. 7 202. 8 

1. 4 204. 2

1. 2 205. 4 

. 6 206. 0 

1. 5 207. 5

9

Sample 

t 1224 Continued

WRL-84-47

83-47 

82-47

> 81-47 

80-47

79-47

78-47 

77-47

76-47 

75-47

74-47 

73-47

72-47 

71-47 

70-47

P.Os

5. 4

13.8 

5. 1

14.9 

4.9

8.5

5. 3 

9. 1

6.6 

10.0

3.8 

9.2

4.0

7. 1 

18.0

Add 

insoluble AlzOa FesOs

341 _.-- -----

33.2 .-__ _--__

39.9 ____ -----

33.7 _--_ -----

26.3 _--- -----

41 Q

15.2 _--- -----

46.0 --._ -----

18.3 _-_- --_-

42.6 --__ -----

15.2 __-_ -----

46.1 _--- -----

22.6 ---- -----

50.6 .--- -----

26.5 _-_- -----

V.Os LOI 

__.-_ ____ 

_____ __-- 

_____ _.__ 

_____ ____ 

____ _--. 

_. _ 

_ _ _.__ 

___. ___- 

_____ ___. 

_____ ____ 

_____ ____ 

_____ _--. 

_____ ____ 

_____ ____ 

-.___ _ _ 
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 417

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T T 00 t-

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00

tM*

i I 

tM

(H 0)

HX!

S^ ^3

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-, , ' -I, S3 T3

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|5 'lS.-o

a^s'sg .a"s N 2Sft-°2 % 2^? 

S^^o^^l^ i

6 ..o ..i-a'S ro

"Iril^i"""
Bed Description

Retort Phosphatic Shale Member of Phosphoria Formation Continued

Rt-139_-_--__ Phosphorite: muddy, carbonatic, medium-hard, brownish-black (1QYR 

2/1), thick-bedded, finely pelletal 

and nodular; grades from bed below.

138_______ Phosphorite: muddy, carbonatic, medium-hard, brownish-black (1QYR 

2/1), thin-bedded, finely pelletal 

and nodular; grades from bed below.

137_ ______ Phosphorite: muddy, medium-hard,

brownish-black (1QYR 2/1), thinbedded, finely pelletal and nodular; 

grades from b.ed below.

136 _____-- Phosphorite: muddy, medium-hard, 

brownish-black (10YR 2/1), thinbedded, finely pelletal and nodular.

135. ______ Mudstone: phosphatic, carbonatic, medium-hard, dark-gray (N 3), thinbedded; apatite is finely pelletal.

134_______ Carbonate rock: hard, medium-darkgray (N 4), thick-bedded, aphanitic.

133_ ____-- Mudstone: phosphatic, carbonatic, medium-hard, brownish-black (10YR 

2/1), thick-bedded; apatite is finely 

pelletal; bed is crumpled. 

Franson Tongue of Park City Formation: 

F-132. ______ Sandstone: calcareous, phosphatic,

hard, brownish-gray (5YR 4/1), 

very thick bedded, fine-grained; 

apatite is skeletal; contains glauconite; grades to sandy skeletal phosphorite at top. Fossil-colln. No. 

18582.

131 _______ Limestone: medium-hard, light-gray

(N 7), very thick bedded; upper 2.3 

ft skeletal, lower 8.0 ft aphanitic. 

Fossil-colln. No. 9914 and 9915.

130. ______ Sandstone: calcareous, medium-hard

very light gray (N 8), and olive-gray 

(5F 4/1), very thick bedded, very 

fine grained; contains glauconite.

129 _______ Chert': sandy, hard, medium-light-gray

(N 7), thick-bedded.

128_-__--_ Chert: sandy, hard, light-gray (N 7) 

and light-olive-gray (5Y 6/1), thinbedded.

127_______ Dolomite: cherty, hard, brownish-gray

(5YR 4/1), thick-bedded, aphanitic.

126.______ Dolomite: cherty, hard, brownish-gray

(5YR 4/1), thick bedded, aphanitic.

125_ ______ Mudstone: dolomitic, medium-hard

pale-brown (5YR 5/2), thin-bedded. 

Fossil-colln. No. 9916 and 18581.

Thick- Cumulative

ness thickness

(feet) (feet) Sample

?, and 1227 Continued 

Chemical analyses (perc

P.Os uble AljOs Fe_O3 V2 05LOT 

Lot 1224 Continued

1. 3 226. 8 WRL-52-47 14. 6 32. 7

4 227. 2

. 5 227. 7

. 6 228. 3

. 6 228. 9

. 8 229. 7

1. 8 231. 5

1. 7 233. 2

51-47 15. 9 29. 1 

50-47 11. 2 43. 9

49-47 .8 19. 5

48-47 8. 8 42. 7

47-47 13. 3 55. 4

Lot 1225

10. 3 243. 5 198-47 1.0 32. 6 .5 1. 1 01 26. 5

8. 3 251. 8

7. 4 259. 2

9. 9 269. 1

11. 0 280. 1

7. 2 287. 3

5. 0 292. 3

197-47 1. 0 73. 1 3. 5 2.2

196-47 . 7 73. 1 3. 5 2. 5

195-47 . 5 75. 1 4. 3 3. 7

194-47 . 5 63.2 1. 3 5. 1

193-47 . 3 62. 3 3.2 2.6

192-47 1. 1 59. 0 6. 2 2. 4

.01

01

01

8.4

9.8 

8.0

01 12. 1

01 13. 8

01 14. 1
124.

123.

122.

121.

120.

118.

117.

116-

115.

114.

113.

112.

111.

110-

109.

108-

107.

106. 

105-

Carbonate rock: cherty, hard, mediumgray (N 5), very thick bedded, 

granular; grades from bed below. 

Fossil-colln. No. 9917.

Limestone: sandy, hard, lightbrownish-gray (5YR 6/1), very thick 

bedded, skeletal; contains glauconite. 

Fossil-colln. No. 9918.

Mudstone: calcareous, hard, mediumgray (N 5), thin-bedded; contains 

glauconite. Fossil-colln. N. 9918.

Sandstone: dolomitic, very fine grained; 

contains glauconite.

Dolomite: hard, yellowish-gray (5F 

7/2), very thick bedded, aphanitic; 

grades from bed below.

Dolomite: sandy, hard, yellowish-gray 

(5F 7/2), very thick bedded, 

aphanitic.

Sandstone: hard, yellowish-gray (5F 

7/2), very thick bedded, fine-grained; 

grades from bed below.

Dolomite: sandy, hard, light-gray (AT" 

7), thick-bedded, aphanitic; sand 

grains are unevenly distributed.

Dolomite: sandy, hard, medium-gray 

(N 5), very thick bedded, aphanitic; 

sand is unevenly distributed.

Sandstone: dolomitic, hard, mediumlight-gray (N 7), very thick bedded, 

fine-grained; dolomite nodules are irregularly distributed through bed.

Sandstone: dolomitic, hard, mediumlight-gray (N 7), very thick bedded.

Dolomite: sandy, hard, medium-lightgray (N 7), very thick bedded.

Limestone: hard, medium-gray (N 7), 

very thick bedded, granular; chert 

nodules irregularly distributed in 

bed. Fossil-colln. No. 9919.

Carbonate rock: cherty, hard, lightbrownish-gray (5YR 6/1), very thick 

bedded; geodes as much as 0.2 ft in 

diameter lined by calcite and quartz 

crystals are irregularly distributed in 

bed. Fossil-colln. No. 9919.

Sandstone: dolomitic, hard, lightbrownish-gray (5YR 6/1), very thick 

bedded, fine-grained; contains glauconite; calcite geodes as much as 

0.15 ft in diameter are irregularly 

distributed in bed.

Carbonate rock: sandy, hard, mediumgray (N 5), thick-bedded, aphanitic; 

contains glauconite.

Sandstone: dolomitic, hard, mediumlight-gray (N 7), very thick bedded, 

fine-grained.

Dolomite: sandy, hard, medium-gray 

(N 7), very thick bedded, aphanitic.

Similar to bed F-108_______________

Dolomite: sandy, hard, medium-lightgray (N 7), thick-bedded, aphanitic; 

sand irregularly distributed in bed.

4. 4 296. 7

4. 3 301. 0

3. 1 304. 1

1. 0 305. 1

2. 2 307. 3

4. 0 311. 3

3. 8 315. 1

2. 5 317. 6

2. 7 320. 3

5. 8 326. 1

2. 0 328. 11

5.3 333.41

7. 8 341. 2

3. 7 344. 9

1. 4 346. 3

4. 5 350. 8

8. 5 359.

2. 0 361. 31

1. 8 363. ij

2. 4 365. 5

191-47 . 5 52. 9 .3 3. 5 .01 17. 6

190-47 . 4 43.2 4. 1 1. 7 .01 22. 8

189-47 . 6 62. 7 1. 1 2.7 .01 14. 5

188-47 . 7 36. 0 .5 1. 1 .01 27.4

187-47 .6 51. 3 .6 1. 6 .01 10. 9

186-47 . 8 44. 6 .6 1. 7 .01 23. 2

185-47 . 6 20. 5 .8 1. 2 .01 35. 0

184-47 1. 8 58. 6 .2 1. 3 .01 16. 1

183-47 . 8 37. 0 .7 1. 6 .01 26. 3

182-47 . 3 43. 1 .5 2. 6 .01 22. 2

181-47 . 3 63. 8 1. 3 3.2 .02 13. 5

180-47 . 8 47.4 .6 2.04 .02 21. 5

179-47 . 7 40. 6 .6 1. 6 .02 25. 4

178-47 . 7 55. 4 .2 1. 9 .02 18. 5

177-47 .6 21. 3 .9 1. 2 .01 34. 
Big Sheep Canyon, Mont., lots 1224, 1225, 1226, and 1227 Continued

Bed Description

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Chemical analyses (per

Acid 

insolPaOs uble AUO3 FezOs V2 05

LOT 

Lot. 1225 Continued

F-104______

10^

1O9

101------

R-100-- _ .

QQ

no

97

QC

Q4

Q3

GO

91

QO

CO

87-.--..

86---__-

85

84_-____

Franson Tongue of Park City Formation Continued 

Sandstone: dolomitic, hard, mediumlight-gray (N 7), very thick bedded, 

fine-grained. 

Dolomite: cherty, sandy, hard, mediumlight-gray (N 7), very thick bedded. 

Dolomite: hard, medium-light-gray

(N 7), very thick bedded, granular. 

Fossil-colln. No. 9920. 

Sandstone: hard, medium-light-grav

(N 7), very thick bedded; dolomitie in upper 3.0 ft. 

Rex Chert Member of Phosphoria Formation: 

Chert: sandv, hard, medium-gray

(N 5), very thick bedded; grades 

from bed below. 

Chert: hard, medium-light-grav (N 7),

thick-bedded; grades from bed below.

gravish -black (N 2), thin -bedded. 

Similar to bed R-98--- ___ ____

Similar to bed R-98- __.________--__

Similar to bed R-98- ________

Similar to bed R-98__-_____--___-_-

Similar to bed R-98__ __________ _.._

grayish-black (N 2), thin-bedded; 

grades from bed below; mudstone 

partings 0.05 ft thick occur 1.0, 1.5, 

and 3.0 ft above base. 

Mudstone: medium-hard, grayishblack (N 2), fissile.

Chert: brittle, grayish-black (N 2),

thin-bedded. 

Mudstone: brittle, gravish-black (N2),

thin-bedded.

medium-gray (N 5), thick-bedded; 

grades from bed below. 

Dolomite: olive-grav (5T 3/2), thickbedded, aphanitic; phosphatic near 

top.

thick -bedded.

gray (N 3), thick-bedded; contains 

apatite nodules and skeletal fragments in basal 0.25 ft. Fossil-colln. 

No. 9921

5.4

1.3

6. 2

9. 5

4. 2

2. 0

3.2

5.0

5. 0

5. 0

5. 0

5. 0

5. 0

4. 0

.5

. 9

1. 5

. 6

1 S

2.3

370. 9

372. 2

378.4

387. 9

392. 1

394. 1

397.3

402. 3

407.3

412. 3

417. 3

422. 3

427.3

431. 3

431. 81

432. 7

434. 2

434. 8

435. 6

437. 4

439 7

WRL-176-47

175-47

174-47

173-47

172-47

171-47

170-47

169-47

168-47

167-47

166-47

165-47

164-47

163-47

162-47

161-47

160-47

159-47

158-47

157-47

1. 5

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3.4

5. 7

6. 9

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24.9

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11.4
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 421

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422 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

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Similar to bed G-47________________

Similar to bed G-47__ ______________

Similar to bed G-47. _______________

Similar to bed G-47 ________________

Mudstone: dolomitic, hard, pale-reddish-brown (10R 5/4), thin-bedded.

Mudstone: dolomitic, medium-hard, 

pale-reddish-brown (10R 5/4), thinbedded.

Similar to bed G-41 ________________

Similar to bed G-41 ________________

Similar to bed G-41_ _______________

Similar to bed G-41 ___.-___--._____

Similar to bed G-41 ________________

Similar to bed G-41; grades from bed 

below.

Mudstone: dolomitic, moderate- reddish-brown (10R 4/6), very thick 

bedded; contains poorly formed 

cross-bedding.

Mudstone: dolomitic, medium-hard, 

dusky-yellow (5Y 6/4), thin-bedded.

Mudstone: dolomitic, medium-hard, 

moderate-yellowish-brown (10 KB 

5/4), thick-bedded.

Sandstone: dolomitic, medium-hard, 

moderate-yellowish-brown (10 KB 

5/4), thin-bedded.

Similar to bed G-31-_______________

Dolomite: cherty, sandy, hard, yellowish-gray (5F7/2), thin-bedded, aphanitic; sand is very fine.

Dolomite: sandy, hard, weak-yellowish-orange (10F.fi 8/4), thick-bedded.

Chert: brittle, medium-gray (N 5), 

thick-bedded.

Dolomite: cherty, brittle, pale-olive 

(5F 5/2), thick-bedded, aphanitic.

Dolomite and chert, interbedded: hard 

light-brownish-gray (5 KB 6/1) thickbedded aphanitic dolomite interbedded with hard pale-olive (5F 

5/2) and dusky-green (5G 3/2) thickbedded chert; irregular contact with 

bed below.

Dolomite: hard, olive-gray (5Y 4/1), 

thick-bedded, aphanitic.

Sandstone: dolomitic, hard, very light 

gray (N 8) and light-gray (N 7); 

grades from bed below.

Sandstone: hard, light-gray (N 7), very 

thick bedded; grades from bed below.

Dolomite: hard, light-gray (N 7), very 

thick bedded; grades from bed below.

Dolomite: hard, weak-yellowish-orange 

(2.5F 8/4), thick-bedded, aphanitic; 

sandy in middle part.

Dolomite: hard, pinkish-gray (5R 8/1), 

thick-bedded; grades from bed below.

Dolomite: hard, very light gray (N 8) 

and medium-light-gray (N 7), thickbedded, aphanitic; contains chert 

nodules; grades from bed below.

5.0 

5. 0 

5.0 

5. 0 

2. 5

3.7

5. 0 

5. 0 

5.0 

5.0 

5. 0 

5.0

4. 5

2. 8

1. 8

1. 8

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1. 9

2. 4

1. 0

2. 6

3. 5

534. 7 

539. 7 

544.7 

549. 7 

552. 2

555. 9

560. 9 

565. 9 

570. 9 

575. 9 

580. 9 

585. 9

590.4

593. 2

595. G\

596. 8f

597. 2\ 

599. 1J

601. 5

602. 5

605. 1

608.6

1. 8

11. 2 

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7. 7

25. 6 

5.8

122-47 

121-47 

120-47 

119-47 

118-47

117-47

116-47 

115-47 

114-47 

113-47 

112-47 

111-47

1. 3 72. 1

1. 3 71. 4

70. 9 . 1 

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9

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1.3 

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. 1

1.4 

1. 2

109-47

108-47

250-47

5. 6 616. 0

627. 2

635. 2

642. 9

668. 5

674. 3

68.9

65. 5

65.4

65. 6

65. 0

58. 6

110-47 1. 2 69. 3

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.3 70. 2

.5 48. 1

249-47 .3 48. 4

248-47 31. 4 12. 0

247-47 .5 34. 1

246-47 .3 29. 1

610. 4 245-47 . 1 

Lot 1227

244-47 .0 48. 4

243-47 .1 68. 3

242-47 .1 28. 0

241-47 1. 3 19. 9

240-47 .4 55. 1
424 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

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STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 425

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426 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Sheep Creek, Mont., lot 1234

insoluble by U.S. Bur. of Mines and for all other constituents by U.S. Geol. Survey. LOI, Loss on ignition]

Bed Description

Dinwoody Formation, basal 

bed:

D-137___ Mudstone: dolomitic,

soft, grayish-yellow

(5Y 8/4), thin-bedded.

Intertonguing upper member

of Shedhorn Sandstone and

Tosi Chert Member of

Phosphoria Formation:

Us-136__-_ Sandstone: medium-hard, 

weak-yellowish-orange 

(10 YR 7/4), thickbedded, fine-grained; 

contains glauconite; 

grades from bed below. 

Fossil-colln. Nos. 10823 

and 18575.

To-135____ Mudstone and chert, interbedded: mediumhard very pale orange 

(10 YR 8/2) thick-bedded cherty mudstone 

containing interbeds 

and lenses ranging from 

0.05 to 0.9 ft in thickness of hard light-gray 

(N 7) thick-bedded 

muddy chert; contains 

glauconite.

Us-134-___ Sandstone- hard, cherty, 

very pale orange (10F.R 

8/1), thick - bedded, 

fine-grained; contains 

glauconite.

To-133_-__ Chert: Brittle, light-gray 

(N 7), thick-bedded; 

contains glauconite.

Us-132____ Sandstone: cherty, medium-hard, brownishgray (5YR 4/1), thickbedded; fine-grained; 

contains glauconite.

131____ Sandstone: cherty, medium-hard, brownishgray (5YR 4/1), very 

thick bedded, finegrained; contains glauconite; grades from bed 

below.

130____ Sandstone: medium-hard, 

brownish - gray (5 YR 

4/1), thick-bedded, 

fine-grained; contains 

glauconite and irregular discontinuous lenses 

and laminae of medium-gray sandstone. 

129____ Sandstone: medium-hard, 

brdwnish-gray (5YR 

4/1), thick-bedded,finegrained; contains many 

lenses and interbeds of 

hard medium gray 

(N 7), thick-bedded 

cherty sandstone; contains glauconite; grades 

from bed below. Fossil-colln. No. 10822. 

See footnotes at end of table.

Chemical analyses (percent)

Uranium

Thick- Cumulative

ness thickness

(feet) (feet)

5.4

Sample

Add insoluble Al»Oj FesOs LOI

Organic 

matter

Radiometric 

eU

Chemical 

U

DAB-80 1.0 71.4 8.1 4.0 10.0 _____ 0.0005 0.001

79 1. 7 87. 9 2. 5 4. 6 1. 5 . 0005 . 000

22. 2 28. 0 LAT-78 1. 6 87. 3 5. 1 3. 0 2. 3 . 0005 . 000

1. 1

1.0

1. 6

28. 6)

29. 7

30. 7

32. 3

5. 1 37. 4

45. 5

2 77 2. 1 8. 9 4. 4 3. 4 1. 8 . 0005 . 001

76 1.7 88.6 2.3 3.5 1.5 _____ .0005 .001
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 427

Bed Description

Intertonguing upper member 

of Shedhorn Sandstone and 

Tosi Chert Member of 

Phosphoria Formation 

Continued

Us-128____ Sandstone: hard, gray 

ish-brown (WYR 4/2), 

very thick bedded, 

fine-grained; contains 

glauconite.

To-127____ Chert: medium-hard 

grayish-brown (WYR 

4/2) thin-bedded chert 

interbedded with brittle medium-light-gray 

(N 7), thick-bedded 

chert; bedding surfaces 

are undulant.

Us-126____ Sandstone: hard grayishbrown (WYR 4/2), 

thick-bedded, very fine 

grained; contains (20 

percent) lenses ranging 

from 0.2 to 0.5 ft in 

thickness of hard moderate-brown cherty 

sandstone; contains 

glauconite.

To-125_ _ _ _ Chert: medium-hard very 

pale brown (WYR 7/2) 

thick-bedded chert interbedded with hard 

light-gray (N 8) thinbedded chert; grades 

from bed below.

Us-124 _ _ _ _ Sandstone: medium-hard, 

moderate-yellowishbrown (WYR 5/4), 

thin-bedded, very fine 

grained; contains (20 

percent) lenses of hard 

brownish-gray (WYR 

4/2) cherty sandstone; 

contains glauconite; 

grades from bed below. 

123____ Sandstone: cherty, hard, 

brownish-gray (WYR 

4/2), thick-bedded, 

very fine grained; contains glauconite.

122_ ___ Sandstone: medium-hard, 

grayish-yellow (5F 8/4) 

to d a r k-y e 11 o w i s horange (WYR 6/6), 

thick-bedded, very fine 

grained; contains (30 

percent) lenses of brittle moderate-brown 

(5F#3/4) cherty sandstone; contains glauconite.

121._._ Similar to bed Us-123.._ 

120_... Similar to bed Us-122-.

Sheep Creek Mont., lot 1234 Continued

Chemical analyses (percent)

Uranium

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Acid inPsO5 soluble AlsOa

Organic 

LOI matter

Radiometric Chemical 

eU U

1. 2

5.9

46.7

52. 6

7.9 60. 5

ERC-75 2.4 86.9 2.1 3.9 1.0 .-_-. 0.0005 0.001

18.7 79. 2 74 2. 6 88. 1 2. 9 2. 8 1. 3 . 0005 . 000

11.8 91.0

1. 0 92.0

6. 5 98. 5

. 5 

2. 9

99.0

101. 9

73 2. 7 87. 0 1. 0 4. 0 1. 0 0005 . 001

DAB-72 3. 3 2. 2 3. 2 1. 2 0005 . 001
428 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Sheep Creek, Mont., lot 1234- Continued

Bed Description

Intertonguing upper member 

of Shedhorn Sandstone and 

Tosi Chert Member of 

Phosphoria Formation 

Continued

To-119____ Chert: muddy, mottled 

light-gray (N 8) and 

moderate-yellowishbrown (WYR 5/4), 

thin-bedded.

118____ Chert: muddy, mediumhard, mottled lightgray (N 8) and strongyello wish-brown 

(IOYR 5/8), thickbedded.

Us-117____ Sandstone: cherty, medium-hard, moderateyellow (5Y 7/6), thickbedded, very fine 

grained; contains glauconite; nearly half of 

the bed consists of irregular lenses of hard, 

medium-light-gray (N 

7), cherty sandstone. 

116____ Sandstone: phosphatic, 

medium-hard, yellowish-brown (1QYR 5/4), 

thick-bedded; apatite 

is medium pelletal. 

Retort Phosphatic Shale 

Member of Phosphoria Formation :

Rt-115____ Mudstone: phosphatic, 

soft, laminated grayish-brown (10 YR 4/2) 

and brownish-gray 

(SYR 4/1), thinbedded; apatite is very 

finely pelletal.

114____ Mudstone: soft, laminated brownish-black 

(5YR 2/1) and moderate-brown (5YR 4/4), 

thin-bedded. Fossilcolln. Nos. 10909 and 

10820.

113____ Mudstone: phosphatic, 

soft, laminated brownish-black (5YR 2/1) 

and moderate-brown 

(SYR 4/4), thin-bedded; apatite occurs as 

fine-grained pellets 

concentrated in the 

brownish-black laminae. Fossil-colln. Nos. 

10908 and 10819.

H2____ Mudstone: soft, brownish-black (IQYR 2/2), 

thin-bedded; contains 

(10 percent) moderatebrown (5YR 4/4) mudstone laminae. Fossilcolln. Nos. 10907 and 

10818.

111____ Mudstone: soft, brownish-black (5YR 2/1), 

thin-bedded. Fossilcolln. No. 10906.

Chemical analyses (percent)

Uranium

Thick- Cumulative

ness thickness

(feet) (feet) Sample P2 06

Acid insoluble AhOa FejO3 LOI

Organic 

matter

Radiometric 

eU

Chemical 

U

1. 8 103. 7

9. 5 113. 2

3. 4 116. 6

DAB-71 1.6 88.3 4.8 2.3 2.8 _____ 0.0005 0.001

70 3. 0 87. 9 1. 0 3. 2 . 0005 . 001

8 117. 4 69 17. 2 51. 1 2. 2 1. 5 . 006 . 003

9 118. 3 VEM-1 16. 2 43. 6 7. 4 3. 6 8. 0 .007

1. 3 119. 6

2. 3 121. 9

7. 4 64. 6 9. 2 2. 4 9. 7 . 004

.004

. 001

3 12. 5 51. 9 8. 7 2. 3 10. 0 3. 30 004 . 004

1. 3 123. 2 1. 7 79. 0 11. 2 1. 9 9. 3 . 003 .001

2. 2 125. 4 JES-5 3. 2 70. 4 9. 9 4. 3 13. 4 .002 .002
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

Sheep Creek, Mont., lot 1234 Continued

Chemical analyses (percent)

429

Bed Description

Retort Phosphatic Shale 

Member of Phpsphoria Formation Continued

Rt-110_- Mudstone: soft, laminated brownish-black 

(IOYR 2/2) and moderate-brown (5YRB/4), 

thin-bedded; grades 

from bed below. Fos- 

.sil-colln. No. 10905.

109.--- Mudstone: phosphatic, 

soft, laminated moderate-yellowish-brown 

(10 YR 5/4) and duskyyellowish-brown (10F.R 

2/2), thin-bedded; apatite is finely pelletal; 

grades from bed below. 

Fossil-colln. No. 10904.

108.--- Mudstone: phosphatic, 

medium-hard, grayishblack (N 2), thin-bedded; contains a few 

lenses averaging 1 mm 

thick of moderate-yellowish-brown (ioy.R 

5/4) pelletal phosphorite.

107.--- Phosphorite: muddy, 

crumbly, erayishbrown (IOYR 4/2), 

thick-bedded, medium 

pelletal and nodular; 

nodules are approximately 10 mm in diameter; irregular contact with bed below.

106 _ _ _ _ Mudstone: medium-hard, 

grayish-black (N 2), 

fissile.

105_ ___ Phosphorite: muddy, 

crumbly, brownishblack (5YR 2/1), thinbedded, medium-pelletal; irregular contact 

with bed below.

104_ ___ Mudstone: soft, palebrown (10 YR 5/2), 

thin-bedded.

103_-__ Phosphorite: muddy, soft, 

brownish-black (5YR 

2/1), thin-bedded.

102 _ . _ _ Phosphorite: muddy, soft, 

dusky-yellowish-brown 

(10 YR 2/2), fissile, 

medium-pelletal.

101___- Phosphorite: soft, grayish-brown (SYR 3/2), 

thin-bedded, mediumpelletal and nodular; 

nodules average 7 mm 

in diameter.

100-_-_ Mudstone: phosphatic, 

soft, dusVy-yellowishbrown (10 YR2/2), thinbedded; apatite is medium pelletal.

99-__. Phosphorite: soft, moderate-brown (5F.R4/4), 

medium-pelletal.

0. 5 125. 9

1. 6 127. 5

1. 4 128. 9

129.4

129. 8

130. 1

130. 4

1. 9 132. 3

133. 4

133. 6

Uranium

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Acid in- Organic 

soluble AhOa FezOa £07 matter

Radiometric Chemical 

eU U

JES-6 1. 6 76. 3 8. 8 2. 0 11. 8 5.. 36 0. 002 0. 002

7 15. 6 45. 9 6. 7 2. 8 11. 1

9. 2 54. 4 9. 0 3. 3 14. 2

10 3. 8 67. 0 12. 2 3. 1 16. 8

11 18. 3 34. 4 7. 0 2. 4 14. 0

12 6. 7 60. 7 10. 3 3. 6 12. 8 4. 60

13 17. 6 36. 3 6. 5 2. 1 13. 2

132. 8 LAT-14 25. 8 28. 1 2. 9 1. 9

133. 1

. 008 . 007

. 005 . 005

OAP-9 22. 1 34. 5 4. 7 2. 3 7. 5 2. 03 . 005 . 001

0003 . 001

007 . 002

004 . 001

007 . 005

006 . 002

FSH-15 20. 2 37. 7 4. 8 1. 6 9. 0 3. 54 . 006 .002

709-931 -11
430

Bed

Rt-98

97

96_

95

94

93_

92 _

91

90_

89_

87

86-

85_

GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Sheep Creek, Mont., lot 1234 Continued

Chemical analyses (percent)

Description

Thick- Cumulative

ness thickness

(feet) (feet)

Retort Phosphatic Shale 

Member of Phosphoria Formation Continued

Mudstone: phpsphatic, 0. 3 133.9 

soft, brownish-black 

(5 YR 2/1), thin-bedded; 

apatite is medium pelletal.

Phosphorite: soft, mod- . 4 134. 3 

erate-brown (5YR 3/4), 

thin-bedded, mediumpelletal.

Mudstone: soft, dusky- .2 134. 5 

yellowish-brown (IOYR 

2/2), thin-bedded.

Phosphorite: soft, dark- . 1 134. 6 

gray (N 3), thinbedded, medium pelletal; irregular contact 

with bed below.

Mudstone: soft, very . 8 135. 4 

dusky red (IOR 2/2) 

to dusky-reddish-brown 

(IOYR 3/4), thinbedded.

Phosphorite: muddy, . 8 136. 2 

soft, moderate-yellowish-brown (IOYR 

5/4), thick-bedded, 

medium-pell etal.

Mudstone: soft, brownish- 2. 7 138. 9 

black (5 YR 2/1), thinbedded; contains some 

black (N 1) mudstone 

laminae. Fossil-colln. 

No. 10903.

Mudstone: medium-hard, . 4 139. 3 

grayish-black (N 2), 

thin-bedded.

Mudstone: soft, brownish- . 2 139. 5 

black (SYR 2/1), thinbedded.

Mudstone: hard, grayish- . 4 139. 9 

black (N 2), thickbedded; grades from 

below.

Mudstone: soft, brownish- 2. 2 142. 1 

black (5YR 2/1), thinbedded; irregular contact with bed below. 

Fossil-colln. No. 10902.

Mudstone: medium-hard, 1. 5 143. 6 

grayish-black (AT2), fissile. Fossil colln. Nos. 

10902 and 10817.

Mudstone: medium-hard, . 9 144. 5 

black (N 1), fissile; 

irregular contact with 

bed below. Fossil-colln. 

No. 10902.

Mudstone: medium-hard, 2. 3 147. 3 

black (N 1), fissile. 

Fossil-colln. No. 10902.

Uranium

Sample PsOs

Acid insoluble AhO3 FeaOa LOI

Organic 

matter

Radiometric Chemical 

eV U

FSH-16 20.2 35.6 5.8 2.1 10.5 _____ 0. 008 0.004

17 6. 4 60. 9 2. 5 14. 1 _______ . 005 . 003

18 26. 0 25. 5 3. 9 1. 5 3. 48 . 008 . 004

19 5.2 60.5 10.2 3.2 18. 4 _______ .005 .002

ERG-20 1.4 72.7 10.7 2.9 20. 8 ____ _ .002 .001

LAT-21 3. 5 64. 2 10. 0 3. 4 16. 4 8. 41 . 002 . 003

22 2.4 53.3 9.2 3.7 30. 1 _______ .003 .002

23 1. 6 54. 2 4. 1 30. 5 _______ . 002 . 001

24 1.4 63.2 10:9 3.7 21.1 17.45 .0005 .001
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

Sheep Creek, Mont., lot 1234 Continued

Chemical analyses (percent)

431

Uranium

Bed Description

Retort Phosphatic Shale 

Member of Phosphoria Formation Continued

Rt-84 _____ Mudstone: soft, brownishblack (5YR 2/1), thinbedded.

83. _ _ _ _ Mudstone: medium-hard, 

dark-gray (N 3), thinbedded.

82. _ _ _ _ Mudstone: medium-hard, 

laminated, dark-gray 

(A/"3) and brownish-black 

(5 YR 2/1), thin-bedded 

irregular contact with 

bed below.

81--__- Mudstone: medium-hard, 

dark-gray (A? 3), fissile; 

grades from bed below. 

Fossil-colln. No. 10901.

80_-___ Mudstone: medium-hard 

dark-gray (A7" 3), fissile; 

grades from bed below, 

Fossil-colln. No. 10900.

79_ _ _ _ _ Mudstone: medium-hard, 

dark-gray (A7 3), thinbedded; grades from 

bed below. Fossil-colln. 

No. 10899.

78_ _ _ _ _ Phosphorite: muddy, medium-hard, black (N 1) 

fissile; irregular contact with bed below. 

Fossil-colln. Nos. 10898 

and 10816.

77_____ Phosphorite: soft, grayishbrown (5 YR 3/2), fissile 

coarsely pelletal; irregular contact with bed 

below.

76_____ Mudstone: phosphatic, 

soft, pale-yellowishbrown (WYR 6/2), 

thick-bedded.

75_____ Phosphorite: soft, palebrown (5YR 5/2), thickbedded, medium pelletal; 

irregular contact with 

bed below.

74_ _ _ _ _ Mudstone: medium-hard, 

dark-gray (N 3), thinbedded. Fossil-colln. 

No. 10897.

73_ _ _ _ _ Phosphorite: soft, brownish-gray (10 YR 3/2), 

thick-bedded, mediumpelletal. Fossil colln. 

No. 10897.

72_ _ _ _ _ Mudstone: medium-hard, 

dark-gray (N 3), thinbedded.

71_____ Phosphorite: soft, paleolive (57 5/2), thickbedded, medium-pelletal.

70_-___ Phosphorite and mudstone, interbedded: 

medium-hard mediumlight-gray (N 7) thinbedded medium-pelletal 

phosphorite interbedded 

with soft medium-gray 

(N 5) thick-bedded 

mudstone.

Thick- Cumulative

ness thickness

(feet) (feet)

0.4 147.7

148.0

148. 2

1.9 150.1

8 150. 9

8 151,7

Sample

Acid insoluble AhOs FezOs LOT

Organic 

matter

Radiometric Chemical 

eU U

ERC-25

26

4. 5 64. 3 11. 1 4. 7 20. 9

1. 6 56. 7 10. 6 4. 1 30. 6

0. 004 0. 002

. 003 . 001

27 2. 2 63. 6 9. 0 2. 8 26. 2 14. 69 . 003 . 003

28 3.8 58.0 10.0 1.9 30.0 _____ .002 .003

1. 1 152. 8 LAT-29 26. 2 24. 0 5. 6 2. 9 14. 3 . 004 . 003

153.5

153.9

1. 2 155. 1

155.2

155.4

155.6

155.9

1.3 157.2

30 31. 9 13. 8 3.9 1.9 8. 1 2. 44 . 007 . 006

31 24. 0 21. 2 5. 6 1. 5 16. 8 . 007 . 004

DAB-32 21. 3 23. 7 6. 8 1. 7 20. 0 . 006 . 004

33 16. 4 35. 0 6. 7 3. 7 19. 6 15. 10 . 004 . 004
432 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Sheep Creek, Mont., lot 1234 Continued

Bed

Rt-69.

68.

67.

66.

65.

64.

63.

62.

Retort Phosphatic Shale 

Member of Phpsphoria Formation Continued

Phosphorite: muddy; uppermost 0.4 ft mediumhard, medium-dark-gray 

(N 4), thick-bedded; 

middle 0.6 ft, mediumhard, brownish-black 

(SYR 2/1), fissile; lowermost 0.2 ft, soft, 

medium-gray (N 6), 

thin-bedded. Fossilcolln. No. 10815.

Mudstone: phosphatic, 

medium-hard, laminated light-gray (N 7) 

and dark-gray (N 3), 

thick-bedded; mediumgrained apatite; pellets 

are concentrated in 

light-gray laminae.

Mudstone: phosphatic, 

medium-hard, laminated dark-gray (N 3) 

and light-gray (N 7), 

fissile; medium-grained 

apatite pellets are concentrated in light-gray 

(N 7) laminae.

Mudstone: medium-hard, 

dark-gray (AT 3), thinbedded; contains a few 

laminae of mediumgrained apatite pellets.

Phosphorite: mediumhard, light-brownishgray (SYR 6/1), thinbedded, medium-pelletal.

Mudstone: phosphatic, 

medium-hard, laminated dark-gray (N 3) 

and light-brownish-gray 

(SYR 6/1), fissile; apatite pellets are medium 

grained and are concentrated in the palebrown laminae.

Mudstone: phosphatic, 

medium-hard, laminated dark-gray (N 3) 

and light-brownish-grav 

(SYR 6/1), thick-bedded; apatite pellets are 

medium grained and 

are concentrated in the 

pale-brown laminae.

Phosphorite: soft, lightbrownish-gray (SYR 

6/1), thick-bedded, 

finely pelletal; grades 

from bed below.

Chemical analyses (percent)

Uranium

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Acid insoluble LOI

Organic 

matter

Radiometric Chemical 

eU U

1.2 158.4 DAB-34 14.6 39.0 7.9 2.6 19.0 _____ 0.005 0.004

158. 7

159. 4

159. 7

159. S

160.4

160. 8

160. 9

ERC-35 14. 0 39. 1 8. 8 2. 5 22. 5 .005 . 004

36 14. 7 39. 8 8. 3 2. 2 19. 8 13. 72 . 005 . 005
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 433

Sheep Creek, Mont., lot 1234 Continued

Bed Description

Retort Phosphatic Shale 

Member of Phosphoria Formation Continued 

Rt-61______ Mudstone: phosphatic,

medium-hard, laminated grayish-black (A 

2) and medium-lightgray (N 7), thin-bedded; apatite is finely 

pelletal.

60______ Mudstone: soft, brownish-black (SYR 2/1), 

thin-bedded.

59______ Mudstone: phosphatic,

medium-hard, laminated grayish-black (N 

2) and medium-lightgray (N 7), thin-bedded; apatite is finely 

pelletal.

58-_-___ Phosphorite: soft, medium-light-gray (A7 7), 

fissile, medium-pelletal.

57______ Mudstone: phosphatic,

medium-hard, laminated grayish-black (N 

2) and medium-lightgray (N 7), fissile, finely 

pelletal; grades from 

bed below. Fossil-colln. 

No. 70814.

56______ Phosphorite: mediumhard, medium-lightgray (N 7), thick-bedded; apatite is medium 

pelletal. Fossil-colln. 

Nos. 10895 and 10896.

55_-_.__ Phosphorite and mudstone, interlaminated: 

medium-hard mediumgray (N 6) phosphorite 

interlaminated with 

medium-hard darkgray (N 3) mudstone; 

apatite is medium pelletal. Fossil-colln. Nos. 

10813, 10894 and 

18574.

54______ Mudstone: soft, grayishbrown (10 YR 4/2), thinbedded. Fossil-colln. 

No. 10893.

53______ Phosphorite and mudstone, interlaminated: 

medium-hard lightolive-gray (57 6/1) 

phosphorite interlaminated with mediumhard dark-gray (A7 3) 

mudstone; apatite is 

medium pelletal; grades 

from unit below. Fossil-colln. No. 10893.

52_ _____ Mudstone: medium-hard,

dark-gray (N 3), thinbedded; contains a few 

laminae of light-olivegray (57 6/1) finely 

pelletal phosphorite. 

Fossil-colln. No. 10893.

Chemicas analyses (percent)

Uranium

Thick- Cumulative

ness thickness

(feet) (feet)

0. 5 161. 4

Sample

Acid insoluble FesOs 107

Organic 

matter

Radiometric Chemical 

eU U

1 161. 5

162.0

162. 2

162.6

ERC-37 18.8 23.7 6.0 2.0 25.5 ___ 0.006 0.005

5 163. 1 DAB-38 32. 3 11. 9 2. 6 1.0 7. 1

2. 2 165. 3 39 15. 5 40. 2 7. 3 2. 9 17. 0 10. 10

006

004

005

003

165.8

1. 6 167. 4

40 6. 5 72. 8 10. 2 3. 6 8. 0 003 002

8 168. 2

41 12. 3 50. 7 9. 5 2. 6 14. 2 004 004
434 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Sheep Creek, Mont., lot 1234 Continued

Bed Description

Retort Phosphatic Shale 

Member of Phosphoria Formation Continued

Rt-51 _ _ _ _ _ Phosphorite: muddy, soft, 

light-brownish-grav (10- 

YR 6/2), thick-bedded, 

coarsely pelletal. Fossilcolln. No. 10893.

50_--_- Mudstone: medium-hard, 

grayish-black (N 2), 

thin-bedded. Fossilcolln. No. 10893.

49-__-_ Phosphorite: soft, paleolive (5F 5/2), thickbedded, medium-pelletal. Fossil-colln. No. 

10893.

48 _____ Mudstone: phosphatic, 

soft, brownish-gray 

(10 YR 4/2) to brownish-black (10 YR 2/2), 

fissile; apatite is medium pelletal; grades 

from bed below. Fossil-colln. No. 10893.

47_____ Mudstone: medium-hard, 

laminated light-brownish-gray (10 YR 6/2), 

and grayish-brown 

(5YR 3/2), fissile; irregular contact with 

unit below. Fossilcolln. No. 10892.

46_____ Mudstone: soft, brownish-gray (10 YR 4/2), 

fissile; contains a few 

light - brownish - gray 

(10 YR 6/2) laminae of 

phosphatic mudstone; 

apatite in laminae is 

finely pelletal.

45_-___ Mudstone: medium-hard, 

light-brownish-gray 

(WYR 6/2), thickbedded.

44_ _ _ _ _ Mudstone: medium-hard, 

light-brown (SYR 5/5), 

thick-bedded.

43_ _ _ _ _ Phosphorite: mediumhard, light-brown (5YR 

5/2), thick-bedded, 

medium-pelletal.

42_____ Phosphorite: muddy, 

medium-hard, duskyyellowish-orange (10- 

YR 6/6), medium pelletal; irregular contact 

with bed below. Fossil-colln. No. 10812. 

Franson Tongue of Park City

Formation:

F-4!__.._ Sandstone: soft, duskyyellowish-orange (10F.R 

6/6) thick-bedded; uppermost 0.4 ft grayishyellow (5F8/4).

Chemical analyses (percent)

Uranium

Thick- Cumulative

ness thickness

(feet) (feet)

170. 0

1. 3 171. 3

2. 4 175. 2

6 175. 8

176.0

176.4

8 177. 2

177.7

Sample PaO8

Acid \nsoluble FejOjOrganic 

LOI matter

Radiometric Chemical 

«U U

1. 3 169. 5 DAB-42 15. 9 37. 4 10. 5 2. 7 17. 6 6. 39 0. 006 0. 006

43 21. 7 32. 6 6. 3 2. 5 10. 5 006 . 007

1. 5 172. 8 ERC-44 10. 4 56. 8 9. 7 3. 8 14. 5 005 006

45 6. 0 65. 7 11. 1 3. 5 16. 0 6. 50 . 005 . 004

46 6. 6 69. 5 11. 9 4. 4 10. 4 003 . 001

DAB-47 15. 0 46. 2 8. 0 7. 1 5. 6

48 27. 0 28. 7 2. 0 1. 7 2. 4 0. 10

005 . 004

012 . 010

2. 9 180. 6 49 3.4 85. 9 3. 7 2. 9 2. 5 005 . 003
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

Sheep Creek, Mont., lot 1234 Continued

Chemical analyses (percent)

435

Bed Description

Franson Tongue of Park City

Formation Continued 

F-40_____ Sandstone: soft, duskyyellowish-orange (10- 

YR 6/6), thin-bedded; 

contains irregular 

roughly spherical concretions, 0.08 ft in 

diameter composed of 

black (N 2) sandstone, 

that comprise 15 to 20 

percent of unit; irregular contact with bed 

below.

39_____- Sandstone: soft, duskyyellowish-orange (10 YR 

6/6), thin-bedded.

38_____- Sandstone: medium-hard, 

dusky-yellowish-orange 

(1QYR 6/6); contains 

irregular chert nodules 

3 mm in diameter comprising 5 percent of 

rock; grades from bed 

below. Fossil-colln. 

No. 10811.

37______ Chert: medium-hard

dusky, yellowish-orange 

(10 YH 6/6) chert interbedded with mediumhard light-gray (N 8) 

to medium-gray (N 6) 

chert; bedding is obscure and probably disturbed by slumping; 

grades from bed below.

36______ Chert: hard light-olivegray (5Y 6/1) very 

thick bedded chert interbedded with medium-hard yellowishgray (5Y 7/2) very 

thick bedded chert.

35--_-_- Similar to bed F-36____

34-_____ Dolomite: medium-hard, 

white, aphanitic; contains a few chert nodules in lower 1.0ft.

33______ Sandstone: dolomitichard, medium-gray (N 

6); contains a few chert 

stringers.

32______ Chert: hard, brownishgray (10Y# 4/2) and 

medium-gray (N 6), 

thick-bedded.

31______ Dolomite: medium-hard,

light-gray (N 8), thinbedded; contains numerous chert nodules and 

many lenses averaging 

1.5 ft in diameter.

30______ Dolomite: medium-hard,

brownish-gray (10Y.R 

4/2) and medium-gray 

(N 5); contains numerous chert nodules, some 

of which are elongated 

perpendicular to bedding; thickness of bedding obscured by slump 

and weathering; grades 

from bed below.

Uranium

Thickness 

(feet)

Cumulative

thickness

(feet) Sample

Acid insoluble FejOa

Organic 

LOI matter

2. 3 182. 9 ERC-50 3. 6 68. 6 3. 1 1. 7 9. 4

Radiometric Chemical 

e\J U

0. 001 0. 002

3. 4 186. 3

3. 8 190. 1

5. 5 195. 6

51 3.2 3. 0 2. 5 1. 6

52 2. 7 89. 2 2. 2 2. 4 1. 3

001 . 001

002 . 003

15. 0 210. 6 LAT-53 6 94. 1 2. 1 2. 4 1. 4 0005 . 001

20. 5 

6. 2

231. 1

237.3

54 9 91. 3 4. 1 2. 9 2. 3

2. 2 239. 5

8 240. 3

3. 8 244. 9

4. 6 248. 7

55 1. 2 32. 2 2. 0 1. 9 29. 7

0005 . 001

002 . 001

ERC-56 5 58. 8 1. 3 3. 4 16. 0 002 . 002
436 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Sheep Creek, Mont., lot 1234 Continued

F-29.

28.

27. 

26.

25.

24.

R-23.

22.

21. 

20.

19.

Description

Franson Tongue of Park City 

Formation Continued

Dolomite: medium-hard, 

white, aphanitic.

Dolomite: medium-hard, 

light-gray (N 8), aphanitic ; irregular contact 

with bed below. Fossilcolln. No. 10891.

Dolomite: medium-hard, 

moderate-brown (5YR 

3/4) to dark-yellowishorange (10 YR 5/8), 

thin-bedded, aphanitic.

Sandstone: dolomitic, 

medium-hard, grayishyellow (57 8/4), finegrained ; contains numerous chert nodules 

averaging 0.2 ft in diameter.

Dolomite: sandy, crumbly, light-gray (N 8), 

aphanitic, contains 

glauconite-; irregular 

contact with bed below. Fossil-colln. No. 

11715.

Sandstone: medium-hard, 

dusky-yellow (57 6/7), 

thin-bedded; contains 

glauconite; contains 

some chert lenses near 

top.

Rex Chert Member of Phosphoria Formation:

Chert: sandy, soft to 

hard, brownish-gray 

(5YR 4/1), thin-bedded; sand is very fine; 

contains glauconite. 

Fossil-colln. No. 18573.

Chert: light-yellowishbrown (10 YR 6/4) thinbedded chert interbedded with hard mediumgray (N 5) thickbedded chert. Fossilcolln. No. 10810.

Sandstone: hard, palebrown (107/2 6/3), 

thick-bedded.

Chert: hard, strongyellOwish-brown (107/2 

5/8) to medium-gray 

(N 5), thick-bedded; 

contains some irregular 

beds and lenses of sandstone; grades from bed 

below.

Sandstone: medium-hard, 

light-brown (5 YR 6/4), 

thick-bedded. Fossilcolln. No. 11714.

Uranium

Thick- Cumulative

ness thickness

(feet) (feet)

16. 5 265. 2

4. 5 269. 7

270.0

3. 3 278. 3

Sample P2O6

Acid insoluble AZ2 Os Fe2 O3 LOTOrganic 

matter

Radiometric 

eV

Chemica 

U

3. 2 276. 5

1. 6 278. 9

3. 3 281. 4

290. 1

ERC-57 0. 6 23. 3 1.1 1. 1 34 3 0. 0005 0. 003

58 3. 1 35. 6 3. 0 1. 8 26. 0 .001 .001

DAB-59 5. 9 78. 3 1.1 3. 7 1. 3 002 002

60 90. 7 2. 5 4. 2 1. 3 006 001

290.5

7. 0 297. 5

2. 2 299. 7

61 2. 1 3. 9 1. 3 0005 .001
Bed

R-18. 

17.

M-16.

15.

13.

12.

G-ll.

10-

Uranium

Thickness 

(feet)

7.5

9.5

Cumulative 

thickness 

(feet)

307. 2 \

316. 7

.Rad/oAeid in- Organic metric 

Sample PzOs soluble A^Os Fe2Os 107 matter eV

 LAT-62 2. 2 89. 1 2. 4 2. 9 1. 6 0. 002

Chemical 

U

0. 001

2.0 318.7 RLP-393 2.2 85.0 9.5 3.3 4.1 ___ 0.002 0.002

STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

Sheep Creek, Mont., lot 1234 Continued

Chemical analyses (percent)

Description

Rex Chert Member of Phosphoria Formation Con.

Chert: hard, light-gray 

(N 8), thin-bedded.

Chert: hard, black (N 

1), thick-bedded; contains some inter beds of 

medium-hard mediumgray (N 6) thick-bedded chert. Fossilcolln. No. 11713. 

Meade Peak Phosphatic Shale 

Member of Phosphoria Formation:

Mudstone: medium-hard, 

dark-yellowish orange 

(10 Yti 6/6), thinbedded; a lens of pelletal phosphorite 0.1- 

0.2 ft thick lies 0.7 ft 

above base of unit.

Mudstone: phosphatic, 

soft, pale-yellowishbrown (10 YR 6/2), to 

moderate-yellowishbrown (10 YR 4/5), 

thin-bedded.

Phosphorite: soft, palebrown (5FjB 4/1), thinbedded; apatite is medium pelletal.

Mudstone: soft, pale-yellow ish-brown (10 YR 

6/2), fissile.

Phosphorite: soft, brownish-gray (5YR 4/1), 

thin-bedded, mediumpelletal.

Grandeur Tongue of Park City 

Formation:

Mudstone: soft, pale-yellowish-brown (10F.K 

6/2), fissile.

Mudstone: medium-hard, 

dark - yellowish - orange 

(1QYR 5/8), thinbedded.

Mudstone: dolomitic, 

soft, very pale orange 

(10 YR 8/2).

Mudstone: medium-hard, 

dark - yellowish - orange 

(IQYR 5/8), thinbedded.

Mudstone: friable, white, 

thick-bedded.

Mudstone: medium-hard, 

dark - yellowish - orange 

(IQYR 6/6), thinbedded.

Mudstone: dolomitic, 

soft, light-gray (N 8), 

thin - bedded; grades 

from bed below.

Dolomite: silty, medium- 10. 5 

hard, grayish - orange 

(IQYR 7/4), duskyyellowish-orange (10 YR 

6/6) near base, thinbedded. Fossil colln. 

Nos. 10807, 10808 and 

10809 and 48-KPM29.

437

319. 3

1 319. 4

319. 6

319.8

320. 2

5. 9 326. 1

. 7 326. 8

6. 9 333. 7

63 14.5 51.2 7.2 3.2 4.3 _____ .005 .004

. 5

6. 5

334. 2

340. 7

395

394

64

LAT-65

7 90.7 8.6 2.9 3.6 _____ .001 .002

58.9 4.2 3.9 17.2 _____ .0005 .002

3 93. 0 2. 8 2. 6 1. 5

4 89. 0 2. 1 2. 5 1. 3

. 0005 . 001

. 001 . 001

6.7 347.4 DAB-66 . 3 60. 7 4.6 2.3 17.9 _-___ .0005 .001

357. 9 67 3 47.5 3.1 2.3 24.9 ----- 0.0005 0.001
438 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Sheep Creek, Mont., lot 1284 Continued

Chemical analyses (percent)

Uranium

Bed

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Add insoluble AZzOa LOI

Organic 

matter

Radiometric Chemica 

Description U

Quadrant Formation, uppermost part:

Sandstone: medium-hard, ____ ______ _________ ____ ____ ____ ____ ____ _____ ______ _____

light-gray (AT 8), thickbedded, fine-grained.

Mudstone: soft, dusky- ____ ______ _________ ____ ____ ____ ____ ____ _____ ______ _____

yellowish-orange (10 YR 

6/6).

Sandstone: medium-hard, ____ ______ _________ ____ ____ ____ ____ ____ _____ ______ _____

light-gray (AT 8).

1 Sample LAT-78 represents the upper 10-2 ft of bed To-135.

2 Sample LAT-77 represents beds To-133, Us-134, and the lower 10.2 ft of To-135.

Oil-shale analyses Sheep Creek, Mont., lot 1234

[Oil shale analyses of samples of the Eetort Phosphatic Shale Member of the Phosphoria Formation, Sheep Creek, Mont. (See immediately preceding pages for location 

of section, thickness and description of strata, and chemical analyses of samples.) Analyses made by U.S. Bur. of Mines Petroleum and Oil-Shale Expt. Sta., Laramie, 

Wyo, by the modified Fischer-Retort method. None of the samples showed a tendency to coke. LOI, loss on ignition]

Q-3. 

2. 

1.

Yield of products

Weight (percent)

Sample 

VEM-1_ _____________________

JES-5 ___ -

7

8

OAP-9. _____________________

385_ - -

10 _ 

11

12 

13 _-__ 

LAT-14_-._ _________________

386

FSH-15--- ___--_-

16

17

18 _ __ _ _ _ _

19

20

ERC-21__-____ ______________

LAT-22___ -___-___ __ __

23_ _ __ _ ._ _

24 . -__ _ _ _

ERC-25_

387_. _

26

27 _ 

28

LAT-29 _ _

30 _ __ ___

31

DAB-32 -__

33__

34 _ __ _____

ERC-35. _______ ___

36_ _ _____ _ _ ____

37___ __________________

Oil

.___-__._______ 0.

_ ____ 1

2

------________ 8.

--_---________ 7.

----__________ 5.

--__-__.______ 1.

------______._ 2.

---___________ 9.

-------___.___ 3.

---___________ 7.

1

----__________ 3.

---.-__.______ 3.

----_.________ 3.

------._______ 4.

-------__.____ 3.

------._______ 5.

Water Spent Shale

3. 8 95. 1 

4. 2 94. 0 

4. 6 93. 2 

4. 0 94. 4 

6. 5 91. 3

4. 8 93. 3

5

0

7

4

9

2

8

3

9

6

7

2

8

9

2

3

7

3

7

5

5.4

5.8

3. 5

3.2

6.4

5.0

6. 2

5.2

3. 1

3.4

3.8

4. 5

5. 5

3.4

7.5

5. 6

7.0

5. 2

6. 0

4. 4

7.7

6. 5

4. 3

7. 2

5.6

7. 5

4. 2

5. 3

5.0

5.0

4.8

5. 6

5. 2

5.0

92.9

91. 6

95.7

95. 7

90. 1

91. 7

91.9

92. 5

96. 1

94. 8

94. 1

93.9

92. 1

95. 1

89. 4

88.9

89.6

82. 7

82. 9

87.8

87. 3

85.7

82. 7

85. 8

81. 3

91. 1

94. 4

89. 8

89. 0

88. 8

88.8

87. 0

87. 7

86. 6

Gas+loss

1. 1 

1. 8 

2.2 

1. 6 

2. 2

1.9

1.7

2. 1

. 8

1. 1

2. 5

2.6

1.9

2.3

. 8

1.4

2. 1

1. 6

2. 4

1. 5

3. 1

2.6

3. 4

3.9

3.3

2. 5

3. 1

5. 2

3. 3

3. 8

5.3

1. 4

1. 4

3. 0

2.8

2.9

2.7

3. 1

3.4

2.9

Gallons per ton

Oil

1 1.

'2.

>1.

'0.

7

20.

18.

12. '4.

'6.

23

7.

18.

i 4.

7.

'8.

8.

10.

8.

13.

3

6

8

9

0

0

8

8

7

6

6

8

9

8

6

4

9

4

9

4

Water

9. 1 

10. 1 

11.0 

9.6 

15. 6

11. 5

12. 9

13. 9

8.4

7.7

15. 3

12. 0

14. 9

12. 5

7.4

8. 1

9. 1

10.8

13. 2

8. 1

18.0

13.4

16. 8

12. 5

14. 4

10. 5

18. 6

15.6

10.3

17. 3

13.4

18.0

10. 2

12. 7

12. 0

12.0

11. 5

13. 4

12. 5

12.0

Specific 

gravity of Properties of spent shale 

oil at (percent of original

0. 986

. 989

.990

. 990

.989

.990

. 991

1. 002

.994

. 990

.986

.990

LOI

3.6 

4.3 

4.2 

4. 9 

5.3

5. 5

5.0

6.8

3. 5

3.5

7.3

6.4

6. 2

6.3

4. 8

4.7

4. 3

4. 1

6.4

4. 2

7.9

9.9

7.8

12. 5

14.8

10. 1

10.4

10.7

14. 2

11.9

13.0

6. 1

6. 0

8.0

7.8

9. 2

9.0

9.4

9.8

9.0

Ash

91. 5

89. 7 

89. 0 

89. 5 

86. 0

87. 8

87.9

84. 8

92. 2

92. 2

82. 8

85.3

85. 7

86. 2

91. 3

90. 1

89.8

89. 8

85. 7

90. 9

81. 5

79.0

81.8

70.2

68. 1

77.7

76. 9

75. 0

68. 5

73. 9

68.3

85.0

88. 4

81.8

81. 2

79.6

79. 8

77.6

77.9

77.6

i Estimated.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 439

Oil-shale analyses Sheep Creek, Mont., lot 1234 Continued

Yield of products

WeigH (percent)

Sample 

DAB-38___---___-___________.

40

41

42

43

ERC-44

45

46

DAB-47____.__ _ ____________

i Estimated.

Oil Water i 

______________ __ ___ 3.0

______________ 2.5 5.4

.__---_-_-.-__ 0.8 5.7

.______.___.__ ______ 4.8

.----____-___. __ _. 8.5

.-.- ____ __ ____ 5. 5

7 ^

______________ ______ 8.0

.-.-_-_______. ______ 5.5

________ _ ___ ______ 3.2

. _ ____ _ -. __ 1. 5

3pent Shale (

96. 7 

89.9 

92. 6 

94. 8 

91. 1

93. 1 

89. 7 

88.8 

94. 2 

96.5 

98. 5

Has+loss

.3 .

2.2 

0.9 

.4 

.4

1.4 

2. 8 

3.2 . 

.3 .

.0 .

Oallons per ton

Oil Water 

7 2

1 6. 4 12. 9 

1 1. 9 13. 7 

. __ _ 11.4

. ___ 20.4

..____ 13.2

______ 18.0

. ___ 19.2

______ 13.2

7 7

______ 3.6

Properties of spent shale 

Specific (percent of original 

gravity of shale) 

oil at

F LOl

3.4

8.0

3.4

6.4

7.2

5. 1

8. 0

7.6

3.8

2.2

1.6

Ash

93.3

81.9

89. 2

88.4

83.9

88.0

81. 7

81.2

90.4

94.3

96.9

Spectrographic analyses Sheep Creek, Mont., lot 1284

[Semiquantitative analyses of samples of the Phosphoria, Park City, and Shedhorn Formations, Sheep Creek, Mont. (See immediately preceding pages for location of 

section, thickness and description of strata, and chemical analyses of samples.) Analyses made by U.S. Bur. of Mines laboratory, Albany, Oreg. In addtion to the 

elements listed in the table below, Sb, As, Ba, Be, Bi, Cd, Ga, Ge, Au, In, Li, Hg, Pt, Ta, Sn, and W were looked for in all samples but were not detected. Explanation 

of symbols: A, > 10 percent; B, 5-10 percent; C, 1-5 percent; D, 0.1-1 percent; E, 0.01 -0.1 percent; F, 0.001-0.01 percent; G, < 0.001 percent; ND, not detected]

Sample 

DAB-80.. .._...

79__.____.

LAT-78___ _ _.

77_ __ ...

76. ___.__.

ERC-75- __-._.

74. _.____.

73__.._._.

DAB-72_. __.__.

71__.._._.

70_. ......

69

VEM-1.. ______

2__ ______

3________

4________.

JES-5_-___-..

6... _.___.

7

8-____.__

OAP-9____._...

385_---_-

10. ______

!!_______

12. ______

13__.____.

LAT-14.. ______

386_____-

FSH-15_______.

16_______.

17._.-__.

18__.-___.

19____-__.

ERC-20__..__.

LAT-21_______.

22_______.

23_______.

24

ERC-25____.__.

387______.

26_______.

27

28_______.

LAT-29. _______

30_. ._.._.

Al

._ C

._ c

._ c

._ c

._ D

.. C

-_ C

._ C

._ C

._ C

._ C

.. C

._ c

-. C

__ c

.- C

._ c

__ B

._ B

._ C

__ c

.. B

__ C

__ c

._ c

._ c

.. c

._ c

._ c

-_ C

._ c

._ c

._ B

._ C

.. c

.. c

.. c

._ c

._ c

._ c

.. c

B

F

F

E

E

E

F

F

F

F

F

F

F

F

F

F

F

F

F

E

F

F

F

F

F

F

F

F

F

F

F

F

E

E

E

F

F

F

F

F

F

F

Ca 

A

C

C

C

C

C

C

C

C

C

C

A

D

D

A

B

A

A

C

A

C

A

A

A

A

A

C

A

D

D

D

D

D

E

D

D

r>

D

C

A

A

Cr 

ND

ND

F

F

F

E

E

E

E

E

E

E

D

D

D

D

E

E

E

E

E

D

D

E

D

D

D

D

D

E

D

D

D

D

E

D

E

E

E

D

E

Co 

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Cb 

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

E

E

E

ND

ND

ND

ND

ND

E

E

Cu 

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

C

G

G

G

G

G

G

G

G

G

G

G

G

Fe

C

B

B

B

C

C

C

C

C

C

C

C

f!

C

C

C

B

C

0

C

C

C

C

C

C

C

C

0

r,

B

B

B

C

C

c

c

c

c

c

Pb 

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Mg

D

D

D

D

D

D

D

D

D

D

D

D

D

D

D

D

D

C

D

D

D

D

D

D

D

D

D

D

C

D

D

D

D

D

C

D

D

D

D

D

Mn 

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

F

F

E

F

F

F

E

F

E

E

E

E

E

F

E

E

F

E

F

E

F

F

F

F

F

Mo 

F

F

F

F

F

F

F

F

F

F

F

F

E

E

E

E

E

E

E

E

E

E

E

F

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

Ni 

F

F

F

F

F

E

E

E

F

F

F

F

E

E

E

E

E

E

E

E

E

E

E

F

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

Si

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

B

Ag

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

F

F

F

F

G

G

G

G

G

F

F

F

G

G

F

F

F

F

F

F

F

F

G

G

G

G

G

F

F

Na 

E

E

E

E

F

F

E

F

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

F

E

E

E

n

D

Sr 

ND

ND

F

F

F

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

E

E

F

F

F

E

ND

F

ND

ND

ND

ND

ND

ND

ND

F

F

F

ND

ND

ND

ND

ND

E

E

Ti 

E

E

E

E

E

E

E

E

E

E

E

E

E

D

E

D

D

D

D

D

D

D

E

E

E

E

D

E

D

E

D

D

D

D

E

D

E

E

E

E

E

V

E

E

E

E

E

E

E

E

E

E

E

E

D

D

D

D

E

E

E

E

E

E

D

E

D

D

D

D

D

D

D

D

D

D

D

n

D

D

D

D

D

Zn 

E

E

ND

ND

ND

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

Zr

F

E

E

F

F

F

F

F

F

F

F

F

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E
440 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Spectrographic analyses Sheep Creek, Mont., lot 1234 Continued

Sample 

31_______.

DAB-32___ _ _.

33_______.

34_______.

ERC-35.______.

36_______.

37_______.

DAB-38_______.

39_______.

40_______.

41_______.

42_______.

43_______.

ERC-44.. ______

45_______.

46_______.

DAB-47_._____.

48-__-_-_.

49____ _ .

ERC-50_______.

388 _ ___.

51-__ __ .

52_______.

LAT-53-______.

54_______.

391______.

390______.

389______.

55___ _ _.

ERC-56_______.

57-.. ... ..

58_______.

DAB-59 _______

392______.

60_______.

61_______.

LAT-62_______

RLP-393_ ______

63_______.

395______.

394______.

64__..___.

LAT-65._. __ .

396______.

DAB-66 _____

67. _ ___.

68,______.

Al

._ C

._ c

.. c

._ c

._ c

._ c

._ c

._ c

._ c

._ c

.. c

._ c

._ c

._ c

.. c

._ c

._ c

.- C

- C

.. c

.. c

._ c

.. c

. c

- C

._ B

.. B

._ B

._ C

.- C

._ C

._ c

._ c

._ c

._ c

._ c

._ c

._ B

.. C

_ C

_ c

_ c

.. B

._ B

.. C

._ C

._ C

B 

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

E

F

F

F

F

Ca 

A

A

A

A

A

A

A

A

A

0

A

A

A

A

0

C

A

A

A

B

0

0

C

D

D

0

C

C

A

B

A

A

B

C

C

0

C

0

A

D

0

D

D

0

A

A

C

Cr 

D

E

E

E

E

E

E

E

E

E

D

D

E

E

D

D

E

E

E

E

E

E

E

F

F

E

E

E

F

E

E

E

E

ND

E

E

F

E

E

F

E

F

F

F

E

E

E

Co 

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

E

ND

ND

ND

ND

F

F

E

ND

ND

ND

ND

ND

ND

ND

ND

ND

F

ND

F

F

ND

F

F

ND

ND

ND

Cb 

E

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

E

E

E

ND

ND

ND

ND

ND

ND

ND

ND

ND

E

ND

ND

ND

ND

ND

E

ND

ND

ND

Cu 

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

Fe

C

c

c

c

c

c

c

c

c

c

c

o

c

c

c

c

c

c

c

c

c

c

B

B

B

A

A

C

0

c

o

c

c

c

c

B

B

0

B

B

B

B

A

0

C

C!

Pb 

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

E

E

ND

ND

ND

ND

E

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

E

E

D

ND

ND

ND

ND

ND

ND

ND

ND

Mg

D

D

D

D

D

D

D

D

D

D

D

n

D

D

D

D

D

D

D

C

D

E

E

E

D

0

C

C

C

B

B

D

D

D

D

E

D

D

D

C

D

D

0

C

C

D

Mn 

F

E

E

E

F

F

F

F,

E

F,

E

E

E

F

F

F

E

E

E

D

C

E

E

E

E

E

D

D

E

E

E

E

E

E

E

E

E

F

E

E

D

E

E

D

E

E

E

Mo 

E

E

E

E

E

E

E

F

E

E

F,

E

E

P,

E

E

E

F

F

F

E

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

F

Ni 

E

E

E

E

E

E

E

E

E

F

E

E

F

E

E

E

E

F

F

D

D

E

E

E

E

D

n

E

E

E

E

E

F

E

F

F

E

E

E

F,

E

E

E

E

F

F

F

Si

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

Ag

F

G

G

G

G

G

G

G

G

G

G

F

F

G

G

G

F

G

G

ND

G

ND

ND

G

G

G

G

G

G

ND

ND

ND

G

ND

G

G

G

F

F

G

G

G

G

G

ND

ND

ND

Na 

D

E

E

E

E

E

E

E

E

E

E

E

E

E

F

F

E

E

E

F

E

F

F

E

E

E

E

E

E

F

F

F

E

E

E

E

E

E

n

F

E

E

E

F,

E

E

F,

Sr 

E

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

F

F

F

F

F

F

ND

ND

ND

ND

ND

ND

ND

F

F

F

F

F

F

F

F

ND

ND

ND

Ti 

E

E

E

F,

E

E

E

E

E

E

E

E

E

E

D

D

E

E

E

E

F,

E

E

E

E

D

D

D

E

E

E

E

E

E

E

E

E

D

E

E

E

E

D

F,

F,

E

F,

V

D

n

D

E

n

n

n

E

E

E

D

D

E

D

D

D

D

E

E

E

D

E

E

E

E

E

E

E

E

E

E

F,

E

E

E

E

E

E

E

E

F,

E

F,

E

E

F,

E

Zn 

E

E

E

E

E

E

E

ND

E

E

E

E

E

E

E

E

E

E

E

E

D

E

E

E

E

D

D

E

E

E

E

E

E

E

E

E

E

E

E

E

E

D

E

D

E

E

E

Zr 

E

F

F,

E

E

E

F,

F

E

E

F,

E

F

E

E

E

F

F

F

F

E

F

F

E

E

E

E

E

E

F

F

F

F

F

F

F

E

E

F,

E

E

E

F,

E

F

F

F
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 441

Canyon Creek No. 1, Mont., lot 1237

[Part of Retort Phosphatic Shale Member of Phosphoria Formation measured in hand trench near Canyon Creek, SE}4 sec. 12, T. 2 S., R. 10 W., 

on west limb of an overturned anticline. Beds strike N. 60° W .and dip 50° SW. Measured by M. R. Klepper and sampled by E. T. Ruppel, 

pies analyzed for PjOs and acid insoluble by U.S. Bur. of Mines and for other constitutents by U.S. Geol. Survey. LOI, loss on ignition ]

Beaverhead County, Mont, 

in September 1948. SamChemical analyse* (percent)

Thicknets 

(jeet)

1.0

Cumulative 

thickness 

(jeet)

1.0

Uranium

Sample

MRK-270

Pa06

7. 2

Acid 

insoluble Ala 1

77. 0 __

Padiometric 

08 GejOs LOI eV

__ _.__ ____ 0.002

Chemical 

U

0.002

Rt-5.

Bed Description

Tosi Chert Member of Phosphoria

Formation, basal bed: 

To-6_ ____ Chert: hard, brownish-black

(10 YR 2/1), thick-bedded. 

Retort Phosphatic Shale Member ot 

Phosphoria Formation; base not exposed:

Phosphorite: hard, dark-gray 1.0 2.0 

(A7 3), medium-pelletal; most 

of rock is aphanitic and only a 

few pellets are apparent. 

4_______ Mudstone: Phosphatic, carbon- 1. 4 3. 4

atic(?), hard, brownish-black 

(10YR 2/1), thin-bedded; apatite is medium pelletal.

3_--___- Phosphorite: hard, medium-dark- 1. 8 5. 2 

gray (N 4), thick-bedded; 

coarsely pelletal. 

2_______ Mudstone and phosphorite, inter- 1.0 6.2

laminated: sheared fissile mudstone interlaminated with phosphorite. 

!_______ Mudstone: phoshatic, soft, light- 6.0 12.2

brownish-gray (WYR 5/1) to 

black (N 1), thin-bedded: apatite is medium pelletal. Underlying beds not exposed.

Canyon Creek Number 2, Mont, lot 1238

[Part of Retort Phosphatic Shale Member of Phosphoia Formation measured in hand trench near Canyon Creek, EJiSEJI sec. 6, T. 2 S., R. 9 W., Beaverhead County, 

Mont., on overturned east limb of an anticline. Beds strike N. 5°-10° W. and dip 70° W. Measured by M. R. Klepper and sampled by E. T. Ruppel in September 

1948. Samples analyzed for P2O 5 and acid insoluble by U.S. Bur. of Mines and for other consitituents by U.S. Geol. Survey. LOI, loss on ignition]

Chemical analyses (percent)

269 34. 7 7. 2 1. 3 2. 57 1. 64 . 007 . 007

268 10. 1 47. 8 9. 7 8. 74 6. 72 . 005 . 003

267 34. 6 6. 1 2. 6 2. 40 3. 60 . 009 . 010

266 16. 3 39. 3 8. 5 5. 38 7. 74 . 006 . 006

265 19. 6 38. 7 7. 9 2. 34 7. 06 . 007 . 007

Bed

Us-5.

Rt-4_ 

3.

Description

Upper Tongue of Shedhorn Sandstone, 

basal bed:

Sandstone: cherty, fine-grained; 

contains chert and quartzite 

pebbles in basal 0.1 to 0.3 ft; 

irregular contact \vith bed below.

Retort Phosphatic Shale Member of 

Phosphoria Formation; base not exposed :

Clay: gougy, red; grades from bed

below.

Mudstone and phosphorite, interlaminated: bed is crumbly and 

weathered; so, no detailed subdivision or description is possible.

Mudstone and phosphorite, interlaminated: too weathered to describe in detail.

Phosphorite: hard, black (N 1), 

thick-bedded, coarsely pelletal; 

underlying beds not exposed.

Thick- lative

ness thickness

(feet) (feet) Sample

Uranium

Radio

Acid metric Chemical

PnOi insoluble AhOs FeaOs LOI eU U

0. 2 

3.0

0.2 

3. 2 MRK-273 19.1 43.2 ____ ____ ____ 0.005 0.003

3. 8 7. 0

3. 0 10. 0

272 19. 1 35. 0 . 005 . 005

271 30. 8 7. 1 1. 1 0. 90 7. 08 . 007 . 007
442 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Melrose Adit No. 2, Mont., lot 1289

[Part of Retort Phosphatic Shale Member of Phosphoria Formation sampled in an adit of the Anderson Phosphate Mines, Inc., of Butte, Mont., known as Melrose Property, 

in NWH sec. 5, T. 2 S., R. 9 W., Silver Bow County, Mont., in the normal limb of a northwest-trending overturned syncline. Beds Rt-7 through Rt-15 sampled at 

heading of a south-southeast drift, approximately 1,400 ft from portal; beds D-1 through D-5 sampled 36 ft from heading. Beds strike northwest and dip 45° SW. Measured by M. R. Klepper and O. A. Payne and sampled by Payne, in September 1948. Analyzed for uranium by U.S. Geol. Survey Laboratory and for other constituents 

by U.S. Bur. of Mines. LOI, loss on ignition]

Chemical analyses (percent)

Uranium

Bed Description

Retort Phosphatic Shale member 

of Phosphoria Formation; base 

not exposed:

Rt-15____ Mudstone: soft, light-brownish-gray (IQYR 5/1), thinbedded; overlain by conglomeratic-chert hanging wall 

that is either the basal bed 

of Tosi Chert Member or 

uppermost bed of Retort 

Phosphatic Shale Member. 

14____ Phosphorite: muddy, hard, 

dark-gray (A7 3), thick-bedded; very finely pelletal; 

contains thin mudstone 

lenses in lower 0.5 ft; grades 

from bed below.

13-___ Phosphorite: soft, lightbrownish-gray (IQYR 6/1), 

thin-bedded; finely pelletal; 

contains a few apatite nodules as much as 10 mm in 

diameter.

12_ _ _ _ Phosphorite: medium-hard, 

dark-gray (N 3), nodular 

and finely pelletal; nodules 

as much as 20 mm in diameter.

11____ Mudstone: hard, dark-gray 

(N 3); irregular contact 

with bad below.

10_.__ Phosphorite: soft, very light 

gray (N 8), thin-bedded, 

med ium-pelletal.

9____ Phosphorite: medium-hard, 

dark-gray (N 3), thin-bedded; medium-pelletal; irregular contact with bed below.

8____ Mudstone: hard, black (N 2), 

thin-bedded.

7____ Phosphorite: medium-hard, 

thick-bedded, coarsely pelletal; grades from very dark 

gray (A7 3) at bottom to 

dark-gray (A7 4) at top; irregular contact with bed 

below.

6____ Mudstone: carbonatic, soft, 

pale-brown (IQYR 6/3), 

thin-bedded; irregular contact with bed.

5____ Phosphorite: medium-hard, 

black (A7 2), thin-bedded, 

medium-pelletal; contains 

apatite nodules in uppermost 0.1 ft; irregular contact with bed below.

4____ Mudstone and phosphorite, 

interlaminated.

3____ Phosphorite: soft, dark-gray 

(N 3), thin-bedded, finely 

pelletal; may be sheared; irregular contact with bed 

below.

Thick- Cumuness lative 

(feet) thickness 

(feet)

0. 2 0. 2

Acid

Sample PzOs insolu- AhOs 

ble

LOI

Radio- Chemical 

metric U 

eV

1. 3 1. 5 MRK-293 23. 9 32. 6 2. 2 2. 6 2. 14 1. 5 0. 004 0. 003

1.8

2. Q}

1 2. 1

3.0

1. 4 4. 4 

1. 9 6. 3

6.7

6 7. 3

292 27. 5 16. 0 6. 3 2. 5 2. 75 006 . 003

291 33. 3 10. 1 1. 9 1. 4 3. 05 1. 8 . 007 . 006

290 3. 8 61. 7 13. 0 5. 6 .71 4. 3 . 003 . 002

289 36. 4 4. 8 1. 1 1. 1 3. 28 1. 6 . 006 . 005

228 4. 4 39. 9 10. 4 10. 0 2. 4 6. 2 . 005 . 003

287 31. 2 15. 3 3. 2 2. 0 2. 78 2. 2 . 005 . 002

8. 5

286 26.2 24. 5 4. 9 2. 1 2. 3 2. 7 .007 .003
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 443

Melrose Adit No. 2, Mont., lot 1239 Continued

Chemical analyses (percent)

CumuThick- lative 

ness thickness 

(}eef) (J'eet) Sample

Uranium

Acid insoluPsOs ble LOIPadiometric Chemical 

eU II

3.4 MRK-285 35. 2 .... 1.8 1. 3 3. 16 2.2 0.005 0.004

Bed Description

Retort Phosphatie Shale member 

of Phosphoria Formation; base 

not exposed Continued

Rt-2.____ Phosphorite: soft, brownishblack (10 YR 2/1), thin-bedded; medium-pelletal; in 

fault contact with bed 

below.

!_____ Phosphorite: muddy, soft, 

dark-gray (N 4); finely pelletal; pellets are indistinct 

in hand specimen but are 

apparent in thin section.

Melrose Adit No. 1, Mont., lot 1240

[Retort Phosphatic Shale Member of Phosphoria Formation measured in southwest crosscut 269 ft from portal of Anderson Phosphate Mines, Inc., of Butte, Mont., known 

as the Melrose P_roperty, NW14 sec.Ji, T. 2 S., 9 W., Silver Bow County, Mont., on normal limb of overturned syncline. Beds strike northwest and dip 45° SW. Meas- 

_ . . _ . Analyzed for P2O5 and acid insoluble by U.S. Bur. of Mines, and for other con3. 0 12. 4 284 5. 9 2. 5 2. 1 4. 6 .005 . 004

ured by M. R. Klepper and O. A. Payne and sampled by Payne, in September 1948. 

stituents by U.S. Geol. Survey. LOI, loss on ignition]

Chemical analyses (percent)

Bed

To-17.

Rt-16.

15. 

14.

13. 

12.

11. 

10.

Description

Tosi Chert Member of Phosphoria 

formation, basal bed:

Chert: hard, dark-gray (N 3);

grades from bed below. 

Retort Phosphatic Shale Member of

Phosphoria Formation:

Phosphorite: cherty, brownishblack (10YR 2/1), thin-bedded; 

contains pebbles of pelletal 

phosphorite from 15-45 mm in 

diameter cemented by chert; 

bed ranges in thickness from 

0.3 ft to 0.7 ft; irregular contact with bed below.

Mudstone: soft, moderate-yellowish-brown (IOYR 4/4), thinbedded; sheared.

Phosphorite: nodular and medium-pelletal, medium-hard, darkgray (N 3), thick-bedded; nodules are as much as 20 mm in 

diameter.

Phosphorite: medium-hard, darkgray (N 4), thin-bedded, finely 

pelletal.

Phosphorite: medium-hard, darkgray (N 3), thick-bedded, finely 

pelletal; contains a few apatite 

nodules as much as 15 mm in 

diameter.

Clay: bluish-white-___ _________

Phosphorite: muddy, mediumhard, dark-gray (N 3), thinbedded, finely pelletal.

Mudstone: medium-hard, darkgray (N 3), thin-bedded.

Phosphorite: hard, dark-gray (N 

3), thick-bedded, medium pelletal; irregular contact with bed 

below.

Thick- Cumulative

ness th ickness

(feet) (feet) Sample

Uranium

Acid insoluble AlsOs FesOs LOI

Radio- Chemical 

metric eU U

0. 5 0. 5 MRK-283 27. 4 25. 0 1. 6 2. 09 2. 04 0. 005 0. 003

282 5. 4 66. 6 9. 5 7. 05 4. 26 003 002

1.6

1.9

2.3

2.5 

3.3

1. 2 4. 5

2. 1 6. 6

281 29. 1 18. 6 2. 7 2. 37 2. 16 . 006 001

280 24. 1 29. 4 5. 4 2. 96 2. 56 005 003

279 1. 1 76. 6 13. 0 6. 29 4. 68 . 002 . 001

278 28. 4 6. 4 1. 5 1. 55 1. 68 007 003
444 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Melrose Adit No. 1, Mont., lot 1240 Continued

Bed

Thickness 

(feet)

Cumulative 

thickness 

(feet)

Rt-7. 

6.

5.

4.

Pc-1.

Description

Retort Phosphatic Shale Member of 

Phosphoria Formation Continued 

Fault gouge___ .-_-_-_-_-______ 0.1 6.7

Phosphorite: hard, dark-gray (N .7 7. 4

3), thin-bedded, finely pelletal. 

Fault gouge_________________ .2 7.6

Phosphorite: soft, medium-gray 3. 9 11. 5

(N 5), thin-bedded, mediumpelletal; base of bed is gougy

fault zone, several strands of

which cut dark mudstono and

phosphorite. 

Phosphorite: muddy, medium- 9. 0 20. 5

hard, black (N 2), aphanitic;

very few pellets are visible in

hand specimen; irregular contact with bed below. 

Chert: hard, black (N 1), thin- .8 21. 3

bedded. 

Park City Formation; top bed:

Dolomite: creamy-white.------- ____ ____

Chemical analyses (percent)

Uranium

Sample PsOs

Acid insoluble AlaOs FezOs LOI

Radio- Chemkal 

metric ell U

MRK-277 27. 6 19. 5 4. 9 2. 51 3. 50 . 005 . 003

276 32. 0 14. 3 1. 4 1. 39 2. 70 . 006 002

275 15.8 33.7 _._. ____ ____ .005 .003

Sawtooth Mountain, Mont., lot 1241

[Permian rocks measured on Sawtooth Mountain, NE >4S W}4 sec. 10, T. 12 S., R. 5 W., Beaverhead County, Mont., on overturned east limb of Snowcrest anticline. Meade Peak 

and Retort Phosphatic Shale Members of Phosphoria Formation measured in hand trenches, rest of section measured from natural exposures. Beds at top of section 

strike N. 5° W. and dip 75° W.; beds at base of section strike N. 40° E. and dip 64° SW. Measured by F. S. Honkala, O. A. Payne and sampled by Payne, in August 

1948. Analyzed for PiOs and acid insoluble by U.S. Bur. of Mines and for uranium by U.S. Geol. Survey Laboratory]

Chemical analyses (percent)

Bed Description

Tosi Chert Member of Phosphoria Formation: 1

To-132__ ______ Mudstone: cherty, hard, brownishgray (IOYR 3/1), thin-bedded. Fossil-colln. No. 10857. 

Upper tongue of Shedhorn Sandstone:

Us-131________ Sandstone: cherty, hard, light-brownish-gray (IOYR 5/1), thin-bedded, 

very fine grained; contains glauconite.

130________ Sandstone: hard, pale-brown (2.5F

6/2), very thick bedded, fine-grained; 

contains glauconite.

129-_--____ Sandstone: hard, yellowish-gray (IOYR 

7/1), very thick bedded, fine-grained; 

contains glauconite; grades from bed 

below.

128________ Sandstone: cherty, hard, light-brownish-gray (IOYR 6/1), very thick 

bedded, fine-grained; grades from 

bed below.

127._______ Sandstone: hard, yellowish-gray (2.5F

7/2), very thick bedded, fine-grained.

126________ Sandstone: hard, yellowish-gray (IOYR

7/2), very thick bedded, fine-grained; 

grades from bed below.

125_ _______ Sandstone: hard, pale-brown (2.5F

5/2), very thick bedded, fine-grained; 

grades from bed below.

124________ Sandstone: cherty, hard, medium-gray

(N 5), thick-bedded, fine-grained.

123________ Chert: sandy, hard, medium-gray (N

5), thick-bedded; grades from bed 

below.

122________ Chert: sandy, medium-gray (N 5),

thick-bedded; sand is very fine; 

grades from bed below.

121________ Sandstone: hard, pale-brown (2.5F

5/2), very thick bedded, fine-grained; 

grades from bed below. 

See footnote at end of table.

Thickness 

(feet)

5.0

2. 4

4. 3

5. 0

5. 0

Cumulative

thickness

(feet)

5.0

7. 4

11. 7

16. 7

21. 7

Uranium

2. 8 24. 5

5. 0

5. 0

3. 4 

5. 0

5. 0

5. 0

29. 5

34. 5

37. 9

42. 9

47. 9

52. 9

Sample P.05

Acid insoluble

Radio- Chemical 

metric eV U
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 445

Sawtooth Mountain, Mont., lot 1241 Continued

Chemical analyses (percent)

Bed

Us-120.

118.

116.

99.

Description

Upper tongue of Shedhorn Sandstone 

Continued

Sandstone: hard, light-brownish-gray 

(IQYR 5/1), very thick bedded, finegrained.

Sandstone: hard, pale-brown (2.5Y 

5/2), very thick bedded, fine-grained; 

grades from bed below.

Sandstone: hard, pale-brown (2.5Y 

5/2), very thick bedded, fine-grained; 

grades from bed below.

Sandstone: cherty, hard, medium-gray 

(N 6), thick-bedded, fine-grained.

Sandstone: cherty, hard, light-brown 

(5YR 5/6), thick-bedded; grades 

from bed below.

Retort Phbsphatic Shale Member of Phosphoria Formation:

Phosphorite: sandy, hard, mediumgray (N 5), thick-bedded, very 

coarsely pelletal.

Phosphorite: muddy, hard, dark-gray 

(N 3), thick-bedded, very coarsely 

pelletal.

Mudstone: hard to soft, black (N 1), 

thin-bedded.

Similar to bed Rt-113____________

Phosphorite: muddy, medium-hard, 

black (N 1), thick-bedded, very 

coarsely pelletal.

Mudstone: soft, brownish-black (IQYR 

2/1), thin-bedded.

Phosphorite: muddy, medium-hard, 

black (N 1), thick-bedded, very 

coarsely pelletal.

Mudstone: soft, brownish-black (IQYR 

2/2), thin-bedded.

Mudstone: soft, black (N 1), fissile...

Phosphorite: muddy, medium-hard, 

dark-gray (N 3), thick-bedded, very 

coarsely pelletal.

Similar to bed Rt-107_____________

Similar to bed Rt-106_____________

Similar to bed Rt-107_____________

Phosphorite: muddy, medium-hard, 

dark-gray (N 3), thick-bedded, 

coarsely pelletal.

Mudstone: medium-hard-black (AM), 

thin-bedded.

Phosphorite: medium-hard, dark-gray 

(N 3). thick-bedded, coarsely pelletal.

Dolomite: medium-hard, lightbrownish-gray (IQYR 6/2), thinbedded, aphanitic.

Chert: muddy, phosphatic, hard, black 

(N 1), thin-bedded. Fossil-colln. 

No. 10856.

Chert: medium-hard, dusky-brown 

(IQYR 2/2), thin-bedded.

Mudstone: medium-hard, dusky-brown 

(iQYR 2/2), thin-bedded.

Similar to bed Rt-96______________

Mudstone: medium-hard, dusky-brown

(IQYR 2/2), thin-bedded. 

Mudstone: medium-hard, dusky-brown 

(IQYR 2/2), thin-bedded.

Mudstone: medium-hard, brownishgray (5YR 4/1), thin-bedded.

Chert: hard, dark-gray (N 3), thinbedded.

ick- ' ?ss 

set)

3. 8

5.0

5. 0

5.0

2. 5

1. 0

1. 8

1. 0

4. 6 

. 5

. 5

1. 5

5.0

. 8 

. 3

. 4 

1. 3 

2. 2

. 8

1. 2

. 3

2.0

.9

3.2

5. 0

5.0 

5.0

5.0

5. 0

2. 3

-/umulQ&ive

thickness 

(feet)

56. 7

61. 7

66. 7

71.7

74. 2 '

75. 2

77. 0 ;

78.0

82. 6 

83. 1 '

83. 6

85. 1

90. 1

90. 9 } 

91. 2

91. 6 

92.9 

95. 1 J 

95. 9 '

97. 1

97. 4

99. 4 ;

100.3

103. 5

108. 5

113. 5 

118. 5

123. 5

128. 5 

130. 8

Acid inSample PzOs soluble

FSH-438 7. 4 77. 7

437 14. 7 51. 7

436 4. 7 63. 1

435 20. 9 27. 5

434 7. 9 50. 7

433 16. 3 33. 8

432 16. 9 35. 4

431 6. 9 18. 7

430 .2 85. 7

429 .3 84. 9

428 .4 83. 7 

427 .3 87. 3

426 .4 83. 3

425 .2 86. 3

Uranium

Radio- Chemical 

metric ell U

0. 002 0. 001

. 003 . 003

. 004 . 002

. 007 . 006

. 005 . 003

. 007 . 005

. 007 . 005

. 003 . 002

. 002 . 001

. 002 . 001

. 002 . 001 

. 002 . 001

. 002 . 001

. 002 . 001

709-931 O 63- -12
446 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Sawtooth Mountain, Mont., lot 1241 Continued

Chemical analyses (percent)

Bed Description

Lower tongue of Shedhorn Sandstone:

Ls-90 _ _____ Sandstone: medium-hard, grayishbrown (2.5YR 4/2), very thick 

bedded, fine-grained: contains glauconite.

89 _ _ _ Sandstone: medium-hard, pale-brown 

(2.5F 5/2), very thick bedded, finegrained. 

88--__----- Sandstone: hard,pale-brown (2.5 Y 5/2),

very thick bedded, fine-grained. 

87 _____ Sandstone: medium-hard, pale-brown

(2.5F 5/2), very thick bedded, finegrained. 

86____---_- Sandstone: hard, dark-gray (N 3),

thin-bedded, fine-grained. 

85_________ Sandstone: cherty, hard, medium-gray

(N 5), thin-bedded, fine-grained. 

Franson Tongue of Park City Formation; 

contains tongue of lower member of 

Shedhorn Sandstone near top: 

F-84__ _______ Mudstone and chert, interbedded:

hard medium-gray (N 5) thin-bedded 

sandy chert interbedded with hard 

medium-gray (N 5) cherty mudstone.

83_________ Conglomerate: hard, dark gray (N 4),

thick-bedded; pebbles are composed 

of chert and average 2 mm by 10 mm; 

contains phosphatic skeletal fragments; irregular contact with bed 

below. Fossil colln. No. 10855.

82_______ Chert: hard, yellowish-white (10 YR

9/1), thin-bedded.

81 _________ Covered-: light-gray dolomite float____

80_ _ _______ Dolomite: hard, yellowish-gray (10 YR

8/1), very thick bedded, granular; 

grades from bed below.

79_________ Dolomite: sandy, hard, yello'nish-gray

(10 YR 8/1), very thick bedded, granular; grades from bed below.

78_________ Dolomite: hard, yellowish-gray 1(10YR

8/1), thin-bedded, granular; grades 

from bed below.

Ls-77_ ________ Sandstone: dolomitic, hard, weakyellowish-orange (2.5 YR 8/4-), thickbedded, very fine grained; grades 

from bed below.

76_________ Sandstone: dolomitic, hard, weak-yellow ish-orange (2.5YR 8/4), thickbedded, very fine grained; grades 

from bed below.

F-75_________ Siltstone:dolomitic, hard, weak-yellowishorange (10 YR 7/6), very thick 

bedded; grades from bed below.

74_________ Dolomite: bard, yellosvish-gray (2.5 Y

7/2), \ ery thick bedded, aphanitic.

73_________ Dolomite: nard, yellowish-gray (2.5F

7/2), very thick bedded, aphanitic; 

grades from bed below.

72_________ Dolomite: hard, yellowish-gray (2.5 Y

7/2), thick-bedded, aphanitic; contains phosphatic skeletal fragments; 

grades from bed below.

71_________ Dolomite: sandy, hard, yellowish-gray

(2.5 Y 7/2), thick-bedded, granular; 

grades from bed below.

70_________ Dolomite: sandy, hard, yellowishwhite (2.5 Y 9/2), thick-bedded, 

granular.

69_________ Dolomite: silty, hard, pale-brown (2.5F

6/2), thick-bedded, aphanitic.

68---_--_._ Dolomite: hard, pale-brown (2.5F6/2), 

thick-bedded, aphanitic.

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Uranium

4. 3 135. 1

5. 0 140. 1

3. 3 147. 2

3. 2 150. 4

2. 7 153. 1

. 6 153. 7

4. 0 157. 7

11.0 168.7

5. 0 173. 7

5. 0 178. 7

5. 0 183. 7

5. 0 188. 7

2. 5 191. 2

5. 0 196. 2

2. 6 198. 8

5. 0 203. 8

5. 0 208. 8

5. 0 213. 8

5. 0 218. 8

2. 0 220. 8

3. 0 223. 8

Acid in- Radio- Chemical 

soluble metric eU U

2.0 142.1 __________

1. 8 143. 9 FSH-424 3. 6 86. 7 0. 0005 0.001
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 447

Sawtooth Mountain, Mont., lot 1241 Continued

Chemical analyses (percent)

Bed Description

Franson Tongue of Park City Formation;

contains tongue of lower member of

Shedhorn Sandstone near top Continued

F-67--.--.___ Chert: hard, pale-brown (2.5Y 6/2),

thick-bedded.

66..__.._ Chert: hard, pale-brown (2.5F 6/2), 

thick-bedded; grades from bed below.

65--------- Chert: hard, pale-brown (2.5 Y 5/2),

thick-bedded; grades from bed below.

64_________ Dolomite: silty, hard, pale-brown (2.5 Y

5/2), thin-bedded, aphanitic.

63.---__-__ Dolomite: hard, pale-brown (2.5 Y 5/2), 

thick-bedded, aphanitic.

62_________ Carbonate rock: hard, yellowish-gray

(5Y 7/2), thick-bedded, granular. 

Fossil- colln. No. 10854.

61_________ Dolomite and chert, interbedded: hard

yellowish-gray (5Y 7/2) thick-bedded 

dolomite interbedded with hard 

grayish-orange (IQYR 7/4) thickbedded chert; approximately half of 

unit is composed of chert.

60__-______ Similar to bed F-61, but chert comprises 75 percent of unit.

59_._______ Similar to bed F-61_______________

58-________ Dolomite: hard, yellowish-gray (5Y

7/2), thick-bedded, granular; grades 

from bed below.

57_________ Dolomite:medium-hard, yellowish-gray

(577/2), thick-bedded, granular.

56---______ Dolomite: hard, yellowish-gray (5Y

7/2), thick-bedded, granular; grades 

from bed below.

55_________ Carbonate rock: hard, yellowish-gray

(5Y 7/2), thick-bedded, granular; 

contains some bryozoan fragments; 

grades from bed below.

54-________ Dolomite: hard, yellowish-gray (5Y

7/2), thick-bedded, granular; contains a few phosphatic skeletal fragments; grades from bed below.

53_________ Dolomite: hard, yellowish-gray (5Y

7/2), thick-bedded, aphanitic; grades 

from bed below.

52_________ Dolomite: hard, yellowish-gray (5Y

7/2), thick-bedded, aphanitic; irregular contact with bed below.

51 _________ Dolomite: medium-hard, grayish-

 orange (10 YR 7/4), thin-bedded, 

aphanitic.

50_________ Dolomite: hard, light-gray (N 8),

thick-bedded, aphanitic. 

Rex Chert Member of Phosphoria Formation; contains several thin tongues of 

lower member of Shedhorn Sandstone: 

R-49-________ Chert: hard, moderate-brown (5YR

4/4), thick-bedded. 

Ls-48_ ________ Sandstone: soft, yellowish-gray (5Y

7/2), very thick beaded, mediumgrained.

R-47-._______ Chert: hard, light-gray (N 7), thickbedded.

46_ ________ Chert: hard, very light gray (N 8),

thick-bedded.

45___._____ Similar to bed R-46_ _______________

44.__ _ Chert: hard, light-gray (N 8), thickbedded.

43__ _ Similar to bed R-44_.____________

42_________ Similar to bed R-44______---__-___-

41_. _______ Similar to bed R-44_ _______________

40_________ Similar to bed R-44____.____-_.____

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Uranium

PsOs

Acid insolubleRadio- Chemical 

metric eU U

1. 1 224. 9

3. 5 228. 4

5. 0 233. 4

5. 0 238. 4

1. 6 240. 0

4. 2 244. 2

5. 0 249. 2

5. 0 254. 2

5. 0 259. 2

3. 0 262. 2

5. 0 267. 2

5. 0 272. 2

5. 0 277. 2

5. 0 282. 2

5. 0 287. 2

5. 0 292. 2

3. 4 295. 6

3. 7 299. 3

3. 5 302. 8

1. 4 304. 2

1. 8 306. 0

4. 4 310. 4

5. 0 315. 4

5. 0 320. 4

5. 0 325. 4

5. 0 330. 4

5. 0 335. 4

5. 0 340. 4
448 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Sawtooth Mountain, Mont., lot 1241 Continued

Bed

Chemical analyses (percent)

Description

Thick- Cumulative

ness thickness

(.feet) (feet) Sample

Uranium

P2 08

Acid insoluble

Radiometric eV

Chemical 

U

Rex Chert Member of Phosphoria Formation; contains several thin tongues of 

lower member of Shedhorn Sandstone 

Continued 

R-39__________ Chert: hard, medium-dark-gray (AT 4), 5.0 345.4

thick-bedded. 

38 _______ Chert: hard, medium-gray (N 5), thin- 5. 0 350. 4

bedded. 

37__________ Similar to bed R-38________________ 4.8 355.2

Ls-36__ _______ Sandstone: hard, brownish-gray (5 YR 3.0 358.2

4/1), thin-bedded, very fine grained. 

R-35 _______ Chert: hard, light-olive-gray (5 Y 6/1), 1.0 359.2

thin-bedded. 

34_.______ Chert: hard, light-olive-gray (5 Y 6/1), 3.8 363.0

thin-bedded. 

33 _____ Similar to bed R-34________________ 5.0 368.0

32 _______ Chert: hard, medium-gray (N 6), thin- 5. 0 373. 0

bedded. 

31 _______ Similar to bed R-32________________ 5.0 378.0

30 _______ Similar to bed R-32_ _____________ 5.0 383.0

29 .____ Chert: hard, dark-gray (N 3), thin- 5.0 388.0

bedded. 

Meade Peak Phosphatic Shale Member of

Phosphoria Formation: 

M-28_________ Phosphorite: medium-hard, dark-gray .3 388.3

(AT 3), thin-bedded, coarsely pelletal;

contains phosphatic skeletal fragments. ^ FSH-423 4. 0 80. 8 0. 003 0. 002 

27_________ Mudstone:soft, light-brown (5 YR 5/6), 2.8 391.1

very thick bedded. 

26_________ Phosphorite: soft, brownish-black .6 391.7

(1QYR 2/2), thin-bedded, mediumpelletal. \ 422 5. 2 73. 6 . 004 . 002 

25_ ________ Mudstone: soft, moderate-brown (5 YR 3. 0 394. 7

3/4), thick-bedded. 

24_________ Mudstone: soft, moderate-brown (5 YR 1.5 396.2

3/4), thick-bedded. 

23_________ Mudstone: soft, brownish-black (5YR .6 396.8 ,, 01 ~ n Rn i nn ,i

2/1), fissile. 42i ' U bU' ' U 

22_ ________ Mudstone: soft, moderate-brown (5 YR .7 397.5

3/4), thick-bedded. 

21_________ Phosphorite: medium-hard, dusky- 2.7 400.2' 420 27.6 12.7 .009 .007

brown (10YR 2/2), thick-bedded,

very coarsely pelletal; contains phosphatic skeletal fragments. 

20_________ Dolomite: phosphatic, soft, grayish- 1.2 401.4 419 10.2 24.0 .003 .001

orange (IOYR 7/4), thin-bedded;

apatite is very coarsely pelletal;

contains phosphatic skeletal fragments. Fossil-colln. No. 10853. 

19_________ Phosphorite: medium-hard, black 2.8 404.2 418 23.5 30.3 .007 .006

(N 1), thin-bedded; very coarsely

pelletal; contains phosphorite pebbles

and phosphatic skeletal fragments.

Fossil-colln. No. 10852.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 449

Sawtooth Mountain, Mont., lot 1241 Continued

Chemical analyses (percent)

Bed Description

Grandeur Tongue of Park City Formation,

upper part: 

G-18-________ Chert: hard, grayish-orange-pink (5 YR

7/2), thin-bedded. Fossil-colln. No. 

10851. 

17______-___ Dolomite: medium-hard, pinkish-gray

(5YR 8/1), thin-bedded, aphanitic; 

contains chert layer 0.2 ft thick 

approximately 2.0 ft above base of 

unit.

16_________ Dolomite: muddy, medium-hard, darkyellowish-orange (10 YR 6/6), thinbedded, aphanitic. 

15 _________ Mudstone: soft, greenish-black (5G

2/1), thin-bedded.

14_ ________ Dolomite: muddy, soft, dark-yellowish-orange (IOYR 6/6), thick-bedded, 

aphanitic. 

13 _________ Mudstone: dolomitic, medium-hard,

light-brown (5YR 6/4), thin-bedded. 

12 _________ Mudstone: dolomitic, medium-hard,

light-brown (5YR 6/4), thin-bedded. 

11_________ Sandstone: dolomitic, medium-hard,

light-brown (5YR 6/4), thin-bedded. 

10_________ Mudstone: dolomitic, medium-hard,

light-brown (5YR 6/4), thin-bedded. 

9_ ________ Sandstone: dolomitic, medium-hard,

light-brown (5 YR 6/4), thin-bedded, 

very fine grained. 

8_________ Sandstone: dolomitic, medium-hard,

light-brown (5YR 6/4), thin-bedded, 

very fine grained. 

?_________ Sandstone: dolomitic, medium-hard,

light-brown (5YR 6/4), thick-bedded, 

very fine grained.

6_________ Dolomite: muddy, medium-hard, grayish-yellow (5Y8/4), thin-bedded, 

aphanitic. 

5_ ________ Mudstone: dolomitic, medium-hard,

grayish-yellow (5 Y 8/4), thin-bedded. 

4_ ________ Mudstone: dolomitic, medium-hard,

grayish-yellow (5Y 8/4), thin-bedded. 

3_________ Mudstone: dolomitic, medium-hard,

grayish-yellow (5Y 8/4), thin-bedded. 

2__ ___ Similar to bed G-3______.__________

!_________ Mudstone: dolomitic, medium-hard,

grayish yellow (5T8/4), thin-bedded; 

underlying beds are covered. 

1 Overlying beds not measured, and distance to Dinwoody contact not known.

Thick- Cumulative

ness thickness

(feet) (feet)

1. 8 406. 0

4. 2 410. 2

1. 0 411. 2

. 6 411. 8

3. 0 414. 8

2. 6 417. 4

5. 0 422. 4

5. 0 427. 4

5. 0 432. 4

5. 0 437. 4

5. 0 442. 4

3. 7 446. 1

5. 0 451. 1

5.0 

5.0 

5.0

5. 0 

5.0

456. 1

461. 1

466. 1

471. 1

476. 1

Uranium

Sample

Acid insolubleRadio- Chemical 

metric eTJ U
450 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Wadhams Spring, Mont., lots 1246 and 1247

[Permian rocks sampled at bulldozer trenches near Wadhams Spring, sees. 22 and 28, T. 13 S., R. 7 W., Beaverhead County, Mont., on southeast limb of anticline. Beds 

R-47 to D-138 (lot No. 1246), sampled in north trench, SEHS WH sec. 22: rest of section (lot No. 1247) in south trench, SWKNEM sec. 28. Section is deeply weathered. 

Beds strike N. 30° E. and dip 70-80° SE. Measured by D. A. Bostwick, E. R. Cressman, and L. A. Thomas and sampled by Bostwick, Cressman, Thomas, and W. H. 

Wilson, in August 1948. Samples analyzed for PzOs and acid insoluble by U.S. Bur. of Mines and for uranium by U.S. Qeol. Survey]

Bed Description

Din woody Formation, lower part: 

D-138_______ Mudstone: medium-hard, dusky-yellow

(5Y 6/7), weathers pale brown 

(5YR 5/2), thin-bedded; breaks into 

platy fragments; grades from bed 

below.

137_______ Mudstone: medium-hard, dusky-yellow

(5F 6/7), weathers dusky-yellow 

(5F 6/7), thin-bedded; breaks into 

platy fragments; grades from bed 

below.

136_______ Mudstone: medium-hard, dusky-yellow

(5F 6/7), weathers grayish-orange 

(WYR 7/4), thin-bedded; breaks into

E

laty fragments, 

ert Member of Phosphoria Formation; contains several thin tongues of 

Shedhorn Sandstone in upper part:

To-135_____.__ Mudstone: sandy, cherty, mediumhard, dark-yellowish-orange (10 YR 

6/6); sand is fine; contains glauconite.

134________ Chert: dolomitic, medium-hard, moderate-yellowish-brown (10F.R 5/4), 

thick-bedded; contains glauconite; 

bedding is poorly formed; grades 

from bed below.

133________ Dolomite: silty, cherty, medium-hard,

dark-yellowish-orange (10 YR 6/6), 

thick-bedded, aphanitic; contains 

glauconite.

132________ Chert: brittle, brownish-gray (SYR

4/1), thick-bedded; bedding surfaces 

are irregular.

131________ Mudstone: dolomitic, sandy, mediumhard, grayish-yellow (5F 8/4), thinbedded; very fine sand concentrated 

in irregular laminae; contains glauconite.

Us-130-___-___ Sandstone: hard, light-gray (N 7), 

thick-bedded, fine-grained; contains 

glauconite.

To-129________ Mudstone: medium, hard, light-olivegray (5F5/2), thin-bedded; contains 

numerous irregular laminae and 

lenses of grayish-orange (WYR 7/4) 

mudstone.

128_ _______ Chert: hard, moderate-yellowish-brown

(WYR 5/4), thick-bedded.

127________ Mudstone: soft, grayish-orange (WYR

7/4), thick-bedded.

126_ _______ Chert: medium-hard grayish-orange

(WYR 7/4) thin-bedded chert interbedded with hard brittle moderateyellowish-brown (WYR 5/4) thickbedded chert.

125________ Chert: medium-hard, grayish-orange

(WYR 7/4), thick-bedded; contains 

numerous lenses of hard brownishgray (5YR 4/1) chert; grades from 

bed.

124__ .__ Chert: medium-hard, yellowish-gray 

(5F 7/2), thin-bedded; contains a 

few lenses of hard, light-gray (N 7) 

chert; grades from bed below. 

See footnotes at end of table.

Chemical analyses (percent)

Uranium

Thick- Cumulative

ness thickness

(feet) (feet) Sample Pa05

Acid insoluble

Radio- Chemical 

metric eU U

5.4

4.5

1.4

.3 0.3

1. 0 1. 3

.4 1.7

.5 2.2

2. 3 4. 5

.8 5.3

2. 9 8. 2

3. 9 12. 1

.8 12. 9

5. 2 18. 1

5. 1 23. 2 ^

4. 5 27. 7

ERG-156 1. 4 78. 5 0. 0005

155 1. 3 78. 2 .001

DAB-154 1. 4 3. 1 . 0005

153 1. 4 89. 1 0005
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 451

Wadhams Spring, Mont., lots 1246 and 1247 Continued

Chemical analyses (percent)

Bed Description

Tosi Chert Member of Phosphoria Formation; contains several thin tongues of 

Shedhorn Sandstone in upper part Con. 

To-123________ Chert: medium-hard variegated white

(AT 9) and grayish-orange (10 YR 7/4) 

thin-bedded chert interbedded with 

hard laminated medium-gray (N 6) 

and pale-brown (5YR 6/2) thinbedded chert.

122________ Chert: medium-hard, dusky-yellow

(5Y 6/7), thin-bedded; grades from 

bed below. 

US-121________ Sandstone: hard, grayish-orange (IOYR

7/4), thick-bedded, fine-grained; contains glauconite.

120______ Covered_________--__--_---____--

119__._____ Similar to bed US-121_ _____________

To-118________ Chert: medium-hard light-gray (N 8)

thin-bedded chert interbedded with 

brittle light-brownish-gray (5 YR 6/1) 

thick-bedded chert.

117__-_-__- Chert: medium-hard, light-gray (N 8), 

thin-bedded; contains a few lenses 

of fine-grained sandstone.

116_ _______ Chert: brittle, light-brownish-gray

(5YR 6/1), thick-bedded.

115__ ______ Chert: medium-hard pinkish-gray

(5YR 8/1) to light-gray (_V 8) thickbedded chert interbedded with brittle light-brownish-gray (5YR 6/1) 

to medium-light-gray (N 7) thickbedded chert; some beds of the 

brittle chert lense out within outcrop.

114_____.__ Similar to bed To-115-___-________

113______ Similar to bed To-115--___________

112________ Similar to bed To-115. Fossil-colln.

No. 10849.

Ill-------- Chert: phosphatic, hard, medium-gray

(N 6), thick-bedded; apatite is 

coarsely pelletal. 

Retort Phosphatic Shale Member of

Phosphoria Formation: 

Rt-110________ Mudstone: phosphatic, medium-hard,

yellowish-gray (2.5 Y 7/2), thinbedded; apatite is medium pelletal; 

beds are highly contorted and 

weathered; grades from bed below.

109________ Phosphorite: muddy, medium-hard,

yellowish-gray (10 YR 7/1), thinbedded, medium-pelletal; beds are 

contorted and deeply weathered; 

grades from bed below.

108_________ Phosphorite: muddy, medium-hard,

dark-yellowish-orange (10F.R 6/6), 

thin-bedded, medium pelletal; grades 

from bed below; beds are contorted 

and deeply weathered.

107...______ Mudstone: phosphatic, soft, very pale

brown (10 YR 7/2), thick-bedded, 

finely pelletal.

106.________ Mudstone: soft, grayish-brown (7.5 YR

7/2), thin-bedded. Fossil-colln. No. 

10848.

Thick- Cumulative

ness thickness

(feet) (feet)

.7 35. 1

.4 35. 5

6. 9 42. 4

2. 2 44. 6

6. 5 51. 1

14. 1 65. 2

11. 3 76. 5

19. 5 96. 0

16. 6 112. 6

.8 113.4

1. 5 114. 9

2. 0 116. 9

Uranium

Sample

. 41 31. 8 DAB-152

2. 2 34. 0 

.4 34. 4

ERG-151 1. 4

150

149

DAB-148 

147 

146

ERG-145

144

143

Acid in- Radio- Chemical 

soluble metric eU U

1. 3 86. 3 0. 0005

3. 7 . 0005

1. 7 90. 5 . 0005

1. 1 89. 9 . 0005

1.4 92.0 .0005 _.___--

1.0 92.5 .0005 ____--.

1.1 93.1 .0005 __.-.

16. 9 53. 2 . 005 0. 005

17. 0 51. 2 . 003

28. 5 20. 2 . 009 . 007

.5 117. 4 DAB-142 21. 6 31. 7 . 006 . 006

.8 118.2 141 9.9 59.6 .005 .004

3.3 121.5 140 3.9 75.9 .003 -------
452 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Wadhams Spring, Mont., lots 1246 and 1247 Continued

Chemical analyses (percent)

Uranium

Bed

Rt-105. 

104-

103-

102.

101.

100.

99.. 

98..

97.. 

96..

95_ 

94. 

93. 

92. 

91. 

90.

89. 

88.

87.

86.

85.

84. 

83.

Description

Retort Phosphatic Shale Member of

Phosphoria Formation Continued

Mudstone: soft, grayish-brown (7.5YR 

3/2), fissile.

Phosphorite: medium-hard, very pale 

brown (IQYR 7/2), thin-bedded, 

finely pelletal.

Mudstone: phosphatic, soft, laminated 

very pale brown (10F.R 7/2) and 

grayish-brown (7.5 YR 3/2), fissile; 

apatite is finely pelletal and is concentrated in very pale brown laminae.

Mudstone: crumbly, pale-yellowishorange (2.5F9/4), thin-bedded.

Mudstone: soft, very pale brown 

(10 YR 7/2), fissile.

Phosphorite: muddy, soft, laminated 

very pale brown (10 YR 7/2) and 

pale-brown (10F.R 5/3), fissile, medium pelletal.

Mudstone: soft, dusky-yellow (5F6/7), 

thin-bedded.

Mudstone: phosphatic, soft, moderateyellowish-brown (10 FR 4/4), thinbedded.

Phosphorite: muddy, crumbly, yellowish-gray (2.5F8/2), thin-bedded, medium-pelletal.

Mudstone and phosphorite, interlaminated: medium-hard, brownish-gray 

(10 YR 3/2) fissile medium pelletal 

phosphorite interlaminated with 

medium-hard brownish-gray (10F.R 

3/2) fissile mudstone.

Mudstone: phosphatic, soft, duskybrown (10 F^ 2/2), thin-bedded.

Mudstone: soft, brownish-gray (10F.R 

3/2), thin-bedded.

Phosphorite- crumbly, very pale brown 

(10 F^ 7/2), finely pelletal.

Mudstone: soft, brownish-gray '(IOYR 

3/2).

Mudstone: medium-hard, weak-yellowish-green (5 GY 6/2), fissile.

Mudstone: soft, pale-brown (10F.R 

6/2), thin-bedded; grades from bed 

below.

Mudstone: soft, weak-yellowish-orange 

(2.5 F 7/4), very thick bedded.

Mudstone: phosphatic, soft, brownishgray (IQYR 3/2), thin-bedded, very 

finely pelletal.

Mudstone: phosphatic, crumbly, laminated very pale brown (10 YR 7/2) 

and grayish-brown (7.5YR 3/2), thinbedded; apatite is finely pelletal and 

is concentrated in very pale brown 

laminae; grades from bed below.

Mudstone: soft, very pale brown 

(10 YR 7/2), thin-bedded.

Mudstone: phosphatic, soft, very pale 

brown (10YR 7/2), fissile; apatite is 

finely pelletal.

Phosphorite: soft, very pale brown 

(IQYR 7/2), thin-bedded, finely pelletal.

Mudstone: phosphatic, soft, laminated pale-brown (IQYR 6/2) and 

moderate yellowish-brown (10 FR 

4/4), fissile; apatite is very finely 

pelletal; contains hard dark-gray 

(N 4) chert lens 0.1 ft by 0.4 ft at 

base of unit.

Thick- Cumulative

ness thickness

(feet) (feet)

1. 1 122. 6

. 2 122. 8

2. 2 125. 0

1. 2 126. 2

. 2 126. 4

. 5 126. 9

1. 8 128. 7

1. 5 130. 2

. 3 130. 5

. 3 130. 8

1. 0 131. 8

. 2 132. 0

. 3 132. 3

. 3 132. 6

1. 0 133. 6

. 3 133. 9

1. 6 135. 5

. 5 136. 0

. 6 136. 6

. 7 137. 3

. 5 137. 8

. 3 138. 1

3. 4 141. 5

Sample

ERC-139

138

137

DAB-136 

135

134

133

132

131

ERC-130

129

128

127

Acid in- Radio- Chemical 

soluble metric eU U

14. 2 48. 0 0. 006 0. 006

3. 6 72. 9 . 002

10. 5 52. 0 . 005 . 004

4.4 71.3 .003 _______

11. 4 53. 3 . 005 . 005

17. 9 44. 3 . 006 . 006

9. 7 55. 8 . 005 . 005

14. 3 46. 1 .007 . 007

6. 2 66. 0 . 003

6. 4 65. 8 . 002

3. 5 52. 5 . 005 . 003

6. 3 63. 0 . 004

17. 1 40. 3 . 005 . 005
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 453

Wadhams Spring, Mont., lots 12^6 and 1247 Continue^

Bed

Rt-82. 

81.

80.

79.

78.

77.

76.

75.

74. 

73.

72.

F-71. 

70.

69.

68. 

67.

66. 

65.

64.

Description

Retort Phosphatic Shale Member of

Phosphoria Formation Continued

Mudstone: crumbly, very pale brown 

(IOYR 7/2), thick-bedded; grades 

from bed below.

Mudstone: phosphatic, soft, laminated pale-brown (IOYR 6/2) and 

light-brown (7.5YR 5/6), fissile; 

apatite is finely pelletal; grades from 

bed below.

Phosphorite: muddy, medium-hard, 

very pale brown (IOYR 7/2), thickbedded.

Mudstone: soft, yellowish-gray (IOYR 

8/1), fissile.

Phosphorite: soft, very pale brown 

(IOYR 7/2), thin-bedded, mediumpelletal.

Mudstone and phosphorite, interlaminated: soft moderate-brown 

(7.SYR 4/4) thin-bedded mudstone 

interlaminated with soft pale-brown 

(7.5 YR 5/2), thin-bedded finely pelletal phosphorite.

Mudstone: soft, moderate-brown 

(7.SYR 4/4).

Phosphorite: medium-hard, very pale 

brown (IOYR 7/2), thin-bedded, 

medium-pelletal.

Mudstone: soft, pale-brown (10 YR 

5/3), fissile.

Phosphorite: medium-hard, very pale 

brown (IOYR 7/2), thin-bedded, 

finely pelletal.

Covered. Nearly entire interval is 

probably underlain by the lower half 

of the Retort Member. 

Franson Tongue of Park City Formation:

Sandstone: dolomitic, medium-hard, 

yellowish-gray (10 YR 7/1), very fine 

grained; grades from bed below.

Dolomite: medium-hard, yellowishgray (10 YR 7/1), aphanitic; contains 

a few chert nodules 0.4 ft in diameter.

Dolomite: medium-hard, yellowishwhite (10 YR 9/1), aphanitic; contains approximately 15 percent bivalve fragments. Fossil-colln. No. 

10847.

Dolomite: medium-hard, light-brownish-gray (10Y7i! 6/1), granular, grades 

from bed below.

Dolomite: medium-hard, yellowishgray (IOYR 8/1), granular; contains 

pelecypod fragments. Fossil-colln. 

No. 10846.

Dolomite: medium-hard, yellowishgray (10 YR 8/1), thick-bedded, aphanitic; contains some sand in upper 

part. Fossil-colln. No. 10845.

Dolomite: medium-hard, weak-yellowish-orange (IOYR 8/4), thick-bedded, 

aphanitic; contains a few pelecypod 

and brachiopod shell fragments. 

Fossil-colln. No. 10844.

Dolomite: medium-hard, yellowishgray (25 Y 8/2), granular; grades 

from bed below.

Chemical analyses (percent)

Thickness 

(feet)

2.3

Cumulative 

thickness 

(feet) Sample

Uranium

3.0 

. 2

.7 

. 2

1.2 

.2

1.0 

6. 5

148.4

148.6

. 4 149. 0

149. 7 ^ 

149. 9

151. 1

151. 3

29. 0 180. 3

181.3

187.8

13. 3 201. 1

Acid in- Radio- Chemical 

soluble metric eU U

142.3 ERG-126 5.3 75.7 0.002 _______

144. 6 125 14. 3 45. 1 . 006 0. 006

. 8 145. 4 DAB-124 16. 2 41. 3 . 003

123 ). 7 59. 0 . 005 .005

122 7.2 61. 7 . 005 005

ERG-121 0. 7 11. 3 .008 002

2. 0 203. 1

22. 5 225. 6 DAB-120 1. 2 16. 5 . 001

15. 0 240. 6

2. 8 243. 4

15. 6 259. 0

119 .8 11.3 .001

118 .6 16.0 .0005
454 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Bed

Wadhams Spring, Mont., lots 1246 and 1247 Continued

Description

Chemical analyses (percent)

F-63. 

62_ 

61.

60. 

59_

58_

57_ 

56.

55.

54. 

53. 

52-

51. 

50.

49.

48.

R-47. 

46.

Franson Tongue of Park City Formation 

Continued

Mudstone : dolomitic, medium-hard,

pale-yellowish-orange (25 Y 9/4),

thin-bedded. 

Mudstone: dolomitic, medium-hard,

yellowish-gray (25 Y 7/2), thin-bedded. 

Mudstone : dolomitic, medium-hard,

very pale brown (10 YR 7/3), thinbedded ; contains a few chert nodules

0.4 ft in diameter. 

Mudstone: dolomitic, medium-hard,

pale-brown (10 YR 5/3), thick-bedded. 

Mudstone: dolomitic, medium-hard,

pale-brown (10YR 5/3), thin-bedded. 

Mudstone: dolomitic, medium-hard,

very pale brown (1QYR 7/2), thickbedded; contains a few chert nodules

0.4 ft in diameter. 

Limestone : hard, pale-grayish-brown

(7.5YR 6/1), thick-bedded, granular;

contains a few chert nodules that

have replaced the limestone. 

Dolomite: white (N 9), very thick

bedded, aphanitic; approximately

one-fourth of the uppermost 2 ft of

bed is composed of brachiopod and

bryozoan skeletal fragments. Fossilcolln. No. 10843. 

Dolomite: medium-hard, yellowishgray (10 YR 8/1), granular; approximately 20 percent of bed consists of

brachiopod and pelecypod shell fragments. Fossil-colln. No. 10842. 

Dolomite: medium-hard, grayishorange (10 YR 7/4), thin-bedded,

aphanitic. 

Dolomite: medium-hard, yellowishwhite (10 YR 9/1), thick-bedded,

aphanitic. 

Dolomite: medium-hard, yellowishwhite (2.5 Y 9/2), thick-bedded,

aphanitic; contains several thin chert

lenses 0.2 ft in diameter, 9.0 ft above

base of bed. 

Dolomite: medium-hard, yellowishwhite (2.5 Y 9/2), very thick bedded,

aphanitic. 

Dolomite: medium-hard, yellowishgray (2.5 Y 8/2), thick-bedded, aphanitic. 

Dolomite: soft, yellowish-gray (2.5Y

8/2), aphanitic. 

Sandstone: dolomitic, medium-hard,

light-gray (N 7), very thick bedded,

fine-grained.

Rex Chert Member of Phosphoria Formation:

Chert: hard, light-gray (N 7), very

thick bedded. 

Chert: hard black (N 2), thick-bedded

chert interbedded with medium-hard

light-gray (N 8) thin-bedded chert.

ness 

(feet)

4.5 

3.4

9. 8 

19. 4

. 9

199

6. \j

1*7. O

1Q Q

thickness 

(feet)

263. 5 > 

266. 9

276. 7 

296. 1 '

297.0 

qno 9

Oil Q

1A.A- Q

Uranium

Acid in- Radio- Chemical 

Sample PtOs soluble metric «U U

ERG 117 .6 053.3 0.001 ___ --

116 .4 73.4 .001 _-- __

115 .7 57.0 .001 --._.__

DAB 114 .3 18.9 .0005 __..

113 .3 6. 8 . 0005 _ _____

119 .3 5.8 .0005 . -..-

12. 1 357. 0

2. 8 359. 8

9. 6 369. 4

4. 0 373. 4

7. 3 380. 7

8. 2 388. 9

1. 2 390. 1

14. 8 404. 9

17. 7 422. 6

111 .3 12. 6 . 0005

110 .2 12. 5 . 0005

109 .2 5. 9 . 0005

108 .3 21. 3 . 0005

107 1. 3 56. 5 . 001

106 .2 87. 7 . 0005

LAT-105 .7 93.9 .0005
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 455

Wadhams Spring, Mont., Lots 1246 and 1247 Continued

Bed Description

Rex Chert Member of Phosphoria Formation Continued

R-45 ________ Chert: hard medium-gray (N 5) thickbedded chert interbedded with 

medium-hard white thick-bedded 

chert. 

44__________ Chert: hard dark-yellowish-orange

(10YR 6/6) thin-bedded chert interbedded with medium-hard dark yellowish orange (10YR 6/6) thin-bedded 

chert.

43__ _ _______ Chert: medium-hard, white (Af9), thinbedded.

42__________ Sandstone: phosphatic, hard, lightgray (N 8), thick-bedded; contains 

phosphatic pellets and skeletal gragments. Fossil-colln. No. 10841. 

41 __________ Mudstone: cherty, medium-hard,

white (N 9) to grayish-orange (10YR 

7/4), thick-bedded. Fossil-colln. 

No. 10840. 

40________ Chert: hard, pale-brown (5YR 5/2),

thick-bedded; contains some interbedded soft grayish-yellow (57 8/4) 

chert. 

39_.________ Chert: brittle, medium-dark-gray (N

4) to light-gray (N 8), very thickbedded. 

38._________ Chert: brittle grayish-brown (5 YR 3/2)

thick-bedded chert interbedded with 

medium-hard light-gray (N 8) thickbedded chert. 

37__________ Chert: medium-hard, pale-brown (57R

5/2), thin-bedded grades from bed 

below.

36__________ Chert: medium-hard, laminated grayish-yellow (57 8/4) and mediumgray (N 5), thick-bedded.

35__________ Chert: hard medium-gray (N 5) thickbedded chert interbedded with medium-hard grayish-yellow (5 78/4) 

to white (N 9) thick-bedded chert; 

grades from bed below. 

Meade Peak Phosphatic Shale Member of

Phosphoria Formation: 

M-34_ ________ Phosphorite: sandy, medium-hard,

pale-brown (10YR 6/2), thin-bedded, 

medium-pelletal; contains phosphatic skeletal fragments; sand is very 

fine; grades from bed below. Fossilcolln. No. 10838. 

33_ ________ Mudstone: soft, light-brown (5YR

5/6), thick-bedded. Fossil-colln. No. 

10839. 

32_________ Phosphorite: muddy, soft, light-gray

(N 7), coarsely pelletal.

31_________ Carbonate rock: medium-hard, lightgray (N 8), thick-bedded, aphanitic. 

30_________ Phosphorite: soft, light-gray (N 7),

thick-bedded, coarsely pelletal and 

oolitic; contains phosphatic skeletal 

fragments.

Grandeur Tongue of Park City Formation: 

G-29__________ Mudstone: dolomitic, soft, grayishorange (10 KB 7/4), thick-bedded.

28__________ Mudstone: dolomitic, soft, dark-yellowish-orange (WYR 6/6), thinbedded.

27__________ Carbonate rock: medium-hard, darkyellowish-orange (10772 6/6), thinbedded, aphanitic. 

See footnotes at end of table.

Chemical analyses (percent)

Thick- Cumulative

ness thickness

(feet) (feet) Sample

1. 4 424. 0

Uranium

Acid in- Radio- Chemical 

PsOs soluble metric eU U

4. 0 428. 0

DAB-104

8. 2 436. 2

1. 3 437. 5 LAT-264

11. 9 449. 4 3 DAB-103

0. 7 93. 3 0. 001

10. 7 70. 0 . 002

2. 2 87. 2 . 002

1. 4 450. 8^

3. 2 454. 0

4. 6 458. 61

1. 1 459. 7

10. 6 470. 3^|

3. 7 474. 0

102

ERG-101

. 35 95. 3 . 0005

.6 93. 3 . 001

100 .3 94. 0 .0005

. 9 474. 9 99 26. 1 29. 5 . 009 . 007

3. 2 483. 1 LAT-98

. 8 483. 9 263

. 6 484. 5 (No

sample) 

4. 3 488. 8 LAT-262

3. 8 492. 6' 

2. 8 495. 4

4.6 74.0 .004 _--_ 

26.3 22.4 .011 .013

23. 2 23. 6 . 013 . 013

. 2 495. 6

96 .6 76. 0 .001
456 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Wadhams Spring, Mont., lots 1246 and 1247 Continued

Chemical analyses (percent)

Bed

G-26.

25. 

24_ 

23.

22. 

21.

20. 

19.

18. 

17. 

16.

15. 

14. 

13.

12.

11. 

10.

Thick- Cumulative

ness thickness

Description (feet) (feet)

Grandeur Tongue of Park City Formation 

Continued

Mudstone: dolomitic, medium-hard, 3. 5 499. 1 

grayish-orange (WYR 7/4), thickbedded.

Mudstone: dolomitic, medium-hard, . 3 499. 4 

light-brown (5YR 6/4), fissile.

Dolomite: medium-hard, light-gray 2. 0 501. 4 

(N 8), thin-bedded.

Mudstone: dolomitic, medium-hard, 3. 2 504. 6 

grayish-orange (IQYR 7/4), thinbedded; contains a few nodules of 

medium-gray (N 6) chert that are 

0.15 ft in diameter.

Dolomite: hard, weak-yellow (5YR 3.3 507.9 

8/4), thick-bedded, aphanitic.

Mudstone: dolomitic, medium-hard, 1. 9 509. 8 

white (N 9) to grayish-yellow (5Y 

8/4), thin-bedded.

Mudstone: dolomitic, hard, light-gray 4. 6 514. 4 

(N 8), thick-bedded. Fossil-colln. No. 

10837.

Dolomite: medium-hard, light-gray .8 515. 2 

(N8), thin-bedded, aphanitic; grades 

from bed.

Mudstone: dolomitic, soft, dusky- 3. 4 518. 6 

yellow (5Y 6/4), thin-bedded.

Mudstone: dolomitic, hard-grayish- 5. 3 523.9 

orange (IQYR 7/4), thick-bedded.

Dolomite: hard, mottled medium-gray 1. 4 525. 3 

(N 5) and pale-red (5R 6/2), very 

thick bedded, aphanitic.

Mudstone: dolomitic, soft, light-gray 2. 6 527. 9 

(NS), thick-bedded.

Mudstone: dolomitic, soft, light-gray 12. 7 540. 6 

(NS), thick-bedded.

Mudstone: dolomitic, soft, laminated 11. 6 552. 2 

light-gray (N 8) and dark-yellowishorange (IQYR 6/6), thick-bedded.

Mudstone: dolomitic, hard, light-gray 9. 4 561. 6 

(N 8); contains lenses and nodules 

of dark-gray (N 4) chert 0.4 ft in 

diameter constituting about 20 percent of bed.

Dolomite: medium-hard, grayish- 1.1 562.7 

orange (IQYR 7/4), light-gray (N 8), 

very thick bedded; contains chert 

nodules and lenses, 0.1 ft in diameter.

Dolomite: muddy, medium-hard, mod- 2. 5 565. 2 

erate-red (5R 5/4), aphanitic; contains a few chert nodules.

Dolomite: moderate-yellowish-orange 4. 5 569. 7 

(IQYR 7/4), aphanitic; contains chert 

lenses 0.1 ft in diameter.

Dolomite: muddy, soft, grayish-yellow 5. 7 575. 4 

(57 8/4) to white (N 9), thin-bedded, 

aphanitic; contains medium-darkgray chert nodules 0.15 ft in diameter.

Dolomite and chert, interbedded: 5. 3 580. 7 

crumbly grayish-yellow (5Y 8/4) 

thick-bedded aphanitic muddy dolomite interbedded with brittle lightolive-gray (5 Y 5/2) to medium-darkgray (N 4) thick-bedded chert.

Dolomite: muddy, hard, grayish-orange . 6 581. 3 

(IQYR 7/4), thick-bedded, aphanitic.

Dolomite: soft, white (N 9) to grayish- 3. 2 584. 5 

yellow (5Y 8/4), thin-bedded, aphanitic.

Dolomite: soft, white (N 9) to weak- 15. 0 599. 5 

yellowish-orange (57 7/5), aphanitic.

Uranium

Sample

ERC-95

94

93

DAB-92 

91

90

Acid in- Radio- Chemical 

PjOs soluble metric eU U

0. 6 51. 6 0. 002

.2 6.5 ______

.4 67. 6 . 001

.2 10. 2 . 0005

. 25 70. 1 . 002

.3 6. 7 . 0005

LAT-S

87 

ERC-86

1 50. 0 . 001

1 57. 0 . 001

25 66. 6 . 002

4 72. 8 . 001

85 .4 32. 4 . 0005

ERC-84 56. 6 . 0005

DAB-83 4. 6 . 0005
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 457

Wadhams Spring, Mont., lots 1246 and 1247 Continued

Chemical analyses (percent)

Bed

G-3. 

2.

Q-lDescription

Grandeur Tongue of Park City Formation 

Continued

Sandstone: hard, light-gray (N 8), 

very thick bedded, fine-grained.

Siltstone: soft, white (N 9) to duskyred (5R 3/4) and light-yellowishbrown (10 YR 6/4); contains small 

irregular chert nodules.

Quadrant Formation:

Sandstone: medium-hard, light-gray 

(N8) to dark-yellowish-orange (10F.fi 

6/6), fine-grained.

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Uranium

2. 2 601. 7

10. 2 611. 9

18. 0 629. 9

DAB-82

81

P2 05

0.5

Acid insoluble

Radio- Chemical 

metric eU U

85. 5 0. 001

.2 97. 6 . 000

1 Sample ERG-156 includes beds To 4132 to To 4135 and upper half of bed To-131.

2 Sample ERC-155 includes beds To 4129 and To 4130 and lower half ol bed To-131.

3 Sample DAB-103 represents beds R-41 and R-42.

Kelley Gulch, Mont., lot 1249

[Phosphoria and Park City Formations measured near Kelley Gulch, sec. 2, T. 6 8., R. 11W., Beaverhead County, Mont. Franson Tongue of Park City Formation measured 

from outcrop; rest of section measured in bulldozer trenches. A dacitic sill 2.7 ft thick occurs 2.1 ft above base of Tosi Chert Member of Phosphoria Formation; a dacitic 

dike 35 ft thick transects beds in upper part of Retort Phosphatic Shale Member of Phosphoria Formation. Beds strike N. 25° E. and dip 25° NW.; measured by R. L. 

Parker and D. A. Bostwick and sampled by R. L. Konizeski, J. E. Joyce, D. A. Bostwick, J. A. Kelleher, and E. T. Ruppel, in August 1948. Samples analyzed for PzOs 

and acid insoluble by U.S. Bur. of Mines, and for uranium and organic matter by the U.S. Geol. Survey]

Chemical analyses (percent)

Uranium

Bed

To-89-

88_ 

87_ 

86_

85_ 

84_ 

83_ 

82_

81_ 

80-

Rt-79-

78- 

77. 

76.

75. 

74.

73.

72.

71.

Cumulative 

Thickness thickness 

Description (feet) (feet)

Tosi Chert Member of Phosphoria Formation; contact with overlying Dinwoody 

Formation approximately located:

Chert: sandy, hard, light-brownish- 27. 0 27. 0

gray (10YR 5/1) to dark-gray (N 3). 

Similar to bed To-89-__-____________ 25. 0

Similar to bed To-89______________ 25. 0

Chert: hard, dark-gray, (N 3), thick- 25. 0

bedded. 

Chert: hard, dark-gray (N 3), thick- 29. 0

bedded. 

Mudstone: medium-hard, mottled 4. 5

gray and brown. 

Chert: hard, dark-gray (N 3), thick- 2. 6

bedded. 

Chert: hard, black (N 2), thin-bedded; 7. 4

separated from bed To-81 by dacitic

sill 2.7 ft thick. 

Chert: hard, dark-gray (N 3), thin- 2. 1

bedded. 

Chert: hard, dark-gray (N 4), thin- 1. 2

bedded.

Retort Phosphatic Shale Member of Phosphoria Formation:

Chert: phosphatic, hard, dark-gray 2. 2

(N 4), thick-bedded; apatite is 10831

coarsely pelletal. Fossil-colln. No. 

Mudstone: plastic, grayish-brown . 2

(10F/2 4/2). 

Phosphorite: medium-hard, dark-gray . 5

(N 3), thin-bedded, medium-pelletal. 

Mudstone: plastic, grayish-brown . 2

(IOYR 4/2).

Mudstone: plastic, dark-gray (N 2)__ 3. 0 

Mudstone: plastic, grayish-brown . 4

(2.5 Y 3/2), thin-bedded. 

Mudstone: soft, brownish-black (IQYR . 4

2/1), fissile. 

Mudstone: soft, brownish-black (10 YR . 2

2/1), thin-bedded, grades from bed

below. 

Mudstone: plastic, grayish-brown . 3

(2.5 Y 4/2).

Sample

Acid Organic Radioinsoluble matter metric e~U

Chemical 

U

52.0

77. 0

102.0

131.0

1 QK C

1 ^8 1

1 4.^ ^

147.6

148. 8 '

151. 0

151. 2 ' 

151. 7

151.9

155. 3 ' 

155. 7

1 KK Q

156. 2

"n A "R 99Q n ^ &^ 7 n 009

228 1. 2 91. 4 __ .0005 _._ __

227 1.4 90.7 ____ .0005 _______

99 C 1 Q QQ Q OOQ

> 224 5.6 69.3 ___ .003 _______

L T>T p 990 91 Q o« 4. n fin nod

222 2.1 74.2 __ .003 __-_---

221 4.4 76.5 ____ .003 _______
458 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Kelley Gulch, Mont., lot 1249 Continued

Chemical analyses (percent)

Bed Description

Retort Phosphatic Shale Member of Phosphoria Formation Continued 

Rt-70-________ Phosphorite: muddy, hard, dark-gray

(Af 3), thin-bedded, medium-pelletal; 

cut by several small faults of unknown 

displacement; irregular contact with 

bed below.

69 _______ Mudstone: medium-hard, grayishbrown (10 YR 4/2), thin-bedded.

68__-----_- Phosphorite: crumbly, medium-pelletal, 

variegated red, brown, and yellow; 

bed is sheared and slickensided.

67 _________ Mudstone: soft, light-brownish-gray

(IQYR 5/1).

66_________ Mudstone: medium-hard, moderateolive-brown (5 Y 4/4).

65______-_- Mudstone: hard, laminated mediumgray (N 5) and dark-gray (N 3), 

thick-bedded; separated from bed 

Rt-64 by dacitic dike 35 ft thick.

64_________ Phosphorite: medium-hard, finely pelletal.

63_____---_ Mudstone: light-brownish-gray (10 YR 

6/1).

62 __ __ _ _ _ Mudstone: soft, brown (10 YR 3/2). _ _

61_________ Dolomite: hard, dark-gray (N 4), thickbedded, aphanitic.

60__------- Dolomite: phosphatic, hard, dark-gray

(N 4), thick-bedded, aphanitic; apatite is medium pelletal.

59-________ Dolomite: hard, dark-gray (AT4), thickbedded, aphanitic.

58_________ Phosphorite: hard, dark-gray (N 4),

medium-pelletal.

57__---_-_- Dolomite: hard, dark-gray (AT4), thickbedded, aphanitic.

56_________ Dolomite and phosphorite, interbedded:

medium-hard dark-gray (N 3) thinbedded aphanitic dolomite interbedded with medium-hard light-brownish 

gray (10 YR 6/1) thin-bedded finely 

pelletal phosphorite.

55_________ Mudstone: hard, medium-gray (N 5),

thick-bedded.

54_________ Mudstone: phosphatic, medium-hard,

yellowish-gray (10 YR 7/1), thin- bedded; apatite is medium pelletal; contains a few apatite nodules as much 

as 26 mm in diameter.

53__________ Phosphorite: muddy, soft, mediumgray (N 6), fissile, medium-pelletal.

52__________ Phosphorite: medium-hard, mediumgray (N 6), thin-bedded, finely pelletal; contains a few apatite nodules as 

much as 30 mm in diameter. Fossilcolln. No. 10830.

51__________ M udstone: phosphatic, hard, dark-gray

(A7" 3), thin-bedded; contains apatite 

nodules as much as 20 mm in diameter.

50__________ Mudstone: phosphatic, hard, lightbrownish-gray (IQYR 5/1), thinbedded; apatite is finely pelletal; 

contains a few apatite nodules as 

much as 30 mm in diameter.

49__________ Phosphorite: muddy, hard, black (AT 1),

thin-bedded, medium pelletal; contains apatite nodules as much as 30 

mm in diameter.

48--________ Phosphorite: muddy, medium-hard,

grayish-brown (2.5 Y 3/2), thin-bedded, finely pelletal; contains apatite 

nodules as much as 12 mm in diameter in lower 0.7 ft.

Cumulative 

Thickness thickness 

(jeet) (feet)

Uranium

Acid Organic Radio- Chemical 

insoluble matter metric e\J U

1. 1 157. 3 220 RLP-22. 9 34.6 1. 02 0. 007 0.005

1. 3 

7.0

1. 3

157. 6 '

157.7

158. 1

159. 4

219

218

166. 4 DAB-217

.4

1. 8

3.6 

1. 1

.9

. 8

.6

1. 1

.7

166. 8

168.6

172. 2 

173. 3 '

174. 2

075.0

209

208

207

175. 6 206

176. 7 205

177. 4 204

178. 7

179. 6

180. 0

180. 5

181. 0

181. 4

203

202

6. 3 62. 5 . 006 . 003

2.3 72.7 __ .004 

1. 8 82. 9 1. 04 . 002

9.8 58.0 __ .004 

4. 5 65. 5 1. 63 . 004

11. 0 6. 8 .002

24.3 9.3 __ .003

6. 7 11. 6 .62 . 001

9.7 19.2 ____ .003

2. 6 6. 1 --_- . 0005 

11. 9 39. 2 1. 00 . 003

201 22. 5 30. 5 __._ . 006 . 004

200 8. 9 62. 5 .003

.7 182. 1 RLP-199 19. 4 36. 5 1. 03 . 003 

1. 7 183. 8 198 18. 0 38. 8 . 004
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 459

Kelley Gulch, Mont., lot 1249 Continued

Chemical analyses (percent)

Cumulative 

Thickness thickness 

Bed Description (feet) (feet)

Retort Phosphatic Shale Member of Phosphoria Formation Continued

Rt-47__-_---___ Mudstone: phosphatic, medium-hard, 1. 2 185. 0 

pale-brown (5YR 5/2), thin-bedded; 

apatite is finely pelletal and nodular; 

nodules have a maximum diameter 

of 18 mm.

46-_-_--__-_ Mudstone: phosphatic, hard, light- .6 185. 6 

brownish-gray (10 YR 6/1), thin-bedded; apatite is medium pelletal.

45__________ Mudstone: medium-hard, brownishgray (10 YR 4/1), thin bedded.

44__________ Mudstone: phosphatic, medium-hard,

brownish-gray (IQYR 4/1), fissile; 

apatite is finely pelletal.

43._________ Mudstone: hard, olive-gray (5F 4/1),

thin-bedded.

42._________ Mudstone: phosphatic, medium-hard,

olive-gray (5F3/2), fissile; apatite is 

finely pelletal.

41__________ Mudstone: medium-hard, dark-gray

(N 3), thin-bedded.

40_________ Mudstone: phosphatic, soft, brownishgray (10 YR 4/1), thin-bedded; apatite is finely pelletal.

39 _________ Mudstone: phosphatic, soft, lightbrown (7.5YR 5/6), fissile; apatite 

is finely pelletal.

38.________ Dolomite: muddy, hard, dark-gray (N 1. 7 191. 2

3), thick-bedded, aphanitic.

37.________ Mudstone: medium-hard, grayish- . 9 192. 1

brown (2.5 Y 3/2), fissile.

36_________ Mudstone: medium-hard, light-brown- 3. 0 195. 1

ish-gray (10 YR 6/1), fissile; contains 

a few apatite nodules as much as 30 

mm in diameter.

35_________ Mudstone: phosphatic, medium-hard, . 5 195. 6

yellowish-gray (10F.R 7/1), finely 

pelletal.

34_________ Mudstone: phosphatic, medium-hard, 1. 2 196. 8

light-brownish-gray (10F.R 6/1), 

thin-bedded; apatite is finely pelletal.

33--_______ Mudstone: medium-hard, brownish- . 6 197. 4

gray (5F.R 5/1).

32.________ Mudstone: phosphatic, medium-hard, . 8 198. 2

brownish-gray (IQYR 4/1), thinbedded; apatite is finely pelletal.

31_________ Mudstone: medium-hard, brownish- 1. 5 199. 7 ^

black (IQYR 2/2), thin-bedded.

30_________ Mudstone: phosphatic, hard, brownish- .6 200.3

black (5YR 2/1); apatite is finely 

pelletal; contains a few apatite nodules as much as 20 mm in diameter.

29_________ Mudstone: soft grayish-brown (10 YR .6 200.9

4/2).

28_________ Mudstone: hard, dark-gray (N 3), 1.0 201.9

thick-bedded.

27.________ Mudstone: phosphatic, medium-hard, . 4 202. 3

thin-bedded; apatite is finely pelletal and nodular; nodules as much 

as 10 mm in diameter. 

Franson Tongue of Park City Formation: 

F-26.________ Dolomite: cherty, hard, black (N 2), 5.0 207.3

thick-bedded, aphanitic.

25-________ Sandstone: hard, light-brownish-gray 32. 2 239. 5

(10 YR 5/1), thick-bedded, finegrained; contains many irregular 

masses of cherty sandstone.

24.________ Dolomite: sandy, hard, light-gray (N 24. 0 263.5

7), thick-bedded, aphanitic; sand is 

fine; contains many irregular chert 

nodules and masses.

Uranium

Sample 

RLP-197

Acid Organic Radio- Chemical 

PzOs insoluble matter metric eU U

16. 6 42. 9 0. 004

. 7

.2

. 6

.4

. 4

1. 1

. 5

186.3

186.5

187. 1

87. 5 >

187. 9

189. 0 ;

189. 5

196 9. 5 57. 8 1. 69 . 004 ____

195 5. 2 70. 6 __._ . 005 . 001

1

1 Q4 104 ^O 0 004

193 1. 8 20. 7 .52 . 0005

192 7.2 58.8 __ .003

191 6.4 62.9 -_.- .003

190 13. 2 49. 9 1. 73 . 003

189 9.3 59.6 ___. .003

188 7.2 61.8 __ .003

DAB-187 13. 8 52. 7 .69 . 006 . 005

(?) (?) (?)
460 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Kelley Gulch, Mont., lot 1249 Continued

Chemical analyses (percent)

F-23-. 

R-22.. 

M-21.

20.

19. 

18.

G-17_

13

10

Q-l.

Bed Description

Franson Tongue of Park City Formation 

Continued

________ Sandstone: hard, brownish-gray(5 YR

4/1), medium-grained.

Rex Chert Member of Phosphoria Formation?:

________ Chert: hard dark-gray (N 4), thinbedded.

Meade Peak Phosphatic Shale Member of 

Phosphoria Formation:

Phosphorite: cherty, hard, pale-brown 

(10YR 5/3) to dark-gray (_V 3), 

thick-bedded, medium-pelletal and 

oolitic.

________ Mudstone: phosphatic, hard, dark-gray

(N 4), thin-bedded; apatite is medium pelletal.

________ Phosphorite: cherty, hard, dark-gray

(A/' 4), medium-pelletal and oolitic.

________ Phosphorite: sandy, hard, dark-gray

(N 3), thin-bedded; contains a few 

apatite nodules. 

Grandeur Tongue of Park City Formation:

_________ Sandstone: cherty, hard, dark-gray

(_V 3), thick-bedded.

________ Mudstone: soft, weak-yellowish-orange

(}QYR 7/6).

________ Mudstone: dolomitic, hard, weakyellowish-orange (10 YR 8/4), thickbedded; irregular contact with beti 

below.

________ Mudstone: dolomitic, hard, mediumgray (N 5), thick-bedded.

________ Sandstone: dolomitic, hard, mediumgray (N 5), thick-bedded.

________ Mudstone: dolomitic, hard, very pale

brown (10 YR 7/3), thin-bedded.

________ Sandstone: dolomitic, hard, reddishpurple, thin-bedded, very fine 

grained.

________ Mudstone: dolomitic, hard, weakyellowish-orange (2.5 Y 7/4), thickbedded.

________ Mudstone: dolomitic, medium-hard,

very pale brown (10 YR 7/3) to 

moderate-brownish-orange (10 YR 

6/6), thin-bedded.

--_-____ Mudstone: dolomitic, medium-hard, 

very pale brown (10 YR 7/3) to 

moderate-brownish-orange (10 YR 

6/6), thin-bedded.

.--_-____ Mudstone: dolomitic, hard, weakorange (7.5 YR 7/4), thick-bedded.

________ Mudstone: dolomitic, hard, pale-brown

(10 YR 7/4), thick-bedded.

_________ Sandstone: hard, moderate-brownishorange (10 YR 6/6), thick-bedded.

.-_______ Sandstone: medium-hard, weak-yellowish-orange (10 YR 7/6), thickbedded; contains lenses 'of cherty 

sandstone.

_________ Sandstone: medium-hard, light-yellowish-brown (10 YR 6/5) to moderate-yellowish-brown (10 YR 5/6), 

thick-bedded.

_________ Sandstone: hard, grayish-orange (10 YR

7/4). 

Quadrant Formation:

._-_-____ Sandstone: hard grayish-orange (10 YR 

7/4), thick-bedded.

Thickness 

(feet)

.3

.7

1.0

. 2

.4

. 2

Q 7

4.2

1 /~k c

Q 1

Q Q

2.8

1. 5

2.8

10. 4

17. 7 

13. 9

9.8 

2. 6

3. 7

17. 3

1.8 

K. n

thickness 

(feet)

263.8 '

264. 5

265. 5

265. 7 '

266. 1

266. 3 

07/1 n

974. 9

9SA S

OQ7 Q

9Q1 9

294.0

295. 5

298.3

308.7 

326.4

340. 3

350. 1 

352.7 ^

356. 4

373. 7

375. 5 

Q«n K

^4dd 

Sample PjOs insoluble

DAB-186 2. 9 82. 3

RLP-185 27. 9 21. 9

184 22. 4 31. 9

1 QQ 9 A ftf» 7

T» A T> 1 OO 1 fl Q7 ^

181 .6 73. 4

1 Qfl Q 7Q f»

 1 TO 1 T£l 1

"RT P 1 7S 1 7*^ fi

m i 79 «

1

1 7R ^l 7^ R

|> DAB-175 .3 94. 9 

174 .2 85.6

175 2 Q7 2

frawmro

Organic Radio- Chemical 

matter metric eV U

___. 0.002 _______

____ .010 0.008

____ .007 .006

____ .0005 __--__.

____ .002 ._._.__

____ .002 ___-...

____ .001 -------

____ .002 .-_-_-.

.002 ----- _

____ .002 _____..

.002 __ _

____ .0005 ----- .

.0005 .

.000 ___ .-
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 461

Spring Creek, Mont., lot 1251

[Part of the Meade Peak Phosphatie Shale Member of the Phosphoria Formation sampled by F. S. Honkalaand O. A. Payne, in August 1948, and measured by Honkalaand 

R. W. Swanson, in September 1953, from the south bank of the east fork of Odell Creek, NWJiSEli sec. 5, T. 15 S., R. 1 W., Beaverhead County, Mont. Beds strike 

about N. 85 W. and dip 12° S. Analyzed for PzOs and acid insoluble by U.S. Bur. of Mines and for other constituents by U.S. Qeol. Survey. LOI, loss on ignition]

Bed

M-12.

11.

10.

G-3. 

2. 

1.

Description

Meade Peak Phosphatie Shale Member 

of Phosphoria Formation; top not 

exposed:

Limestone: medium-hard, thickbedded, finely crystalline, yellowish-gray (2.5F 8/2); contains 

quartz sand; weathers soft and 

spongy.

Phosphorite: medium-hard, thinbedded, coarsely oolitic to nodular, pale-brown (2.5 Y 5/2); contains Lingula.

Mudstone: soft, fssile, weak-yellowish-orange (2.5F 8/4); contains grit-sized quartz; in middle is thin bed of hard mediumpelletal pale-brown (2.5F 6/2) 

phosphorite.

Limestone: medium-hard, thinbedded, medium coarsely crystalline, pale-brown (2.5 F 6/2); 

contains quartz sand.

Mudstone: soft, fssile, light-yellowish-brown (WYR 6/4).

Phosphorite: medium-hard, thinbedded, coarsely oolitic and pelletal to nodular, pale-brown 

(2.5F 6/2) to light-brownishgray (WYR 6/1); thin muddy 

zone near middle.

Phosphorite: medium-hard, thickbedded, coarsely oolitic, lightbrownish-gray (10 YR 6/1); soft 

friable zone at base.

Mudstone and phosphortie: upper 

half sandy hard fine to medium 

coarsely pelletal phosphorite 

overlying hard mudstone, both 

pale-brown (2.5 F 6/2); lower 

half soft thin-bedded pale-brown 

(2.5 F 5/2) mudstone, containing 

small phosphate nodules; clayey 

at base.

Phosphorite: hard, thick-bedded, 

coarsely oolitic, pale-brown 

(2.5F 6/2) to yellowish-gray 

(2.5F 7/2); contains abundant 

shell fragments (fish scales?); 

chert pebbles common in lower 

0.3 ft; basal contact irregular. 

Grandeur Tongue of Park City Formation, upper part:

Limestone: hard, dense, yellowishgray (WYR 8/1), locally silty.

Limestone: hard, massive, dense, 

light-gray (N7).

Sandstone: calcareous, mediumhard, very fine grained, very pale 

orange (WYR 9/2).

Chemical analyses (percent)

CumuThick- lative 

ness thickness 

(feet) (feet) Sample

Uranium

Acid 

insoluble AhOa LOI

Radiometric Chemical 

eU U

0. 9 0. 9

1. 2

1.6

2.0

.2 2. 2 

1. 6 3. 8

1. 8 5. 6

60.

1.0 7. 0

FSH-261 31.3 10.9 0.97 0. 81 3.90 0. 012 0. 010

.4 7.4

1. 6 9. 0

.5 9.5

709-931 O 63- -13
462 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Odell Creek, Mont., lot

[Uppermost part of Phosphoria Formation sampled and lower part of Dinwoody Formation measured in hand trench on west side of Odell Creek, SEJ4 sec. 1, T. 15 S., R. 

2 W. Beaverhead County, Mont., on southward tilted Centennial Mountains fault block. Beds strike N. 82° E. and dip 30° S. Measured by F. S. Honkala and O. A. 

Payne and sampled by Payne and J. A. Kelleher in July 1948. Descriptions based entirely on field notes and analytical data. Analyzed for PjOs and acid insoluble by 

U.S. Bur. of Mines, and for uranium by U.S. Qeol. Survey]

Chemical analyses (percent)

Bed

D-51_ 

50. 

49.

48. 

47.

46. 

45.

44.

43.

42.

41.

40.

39.

38.

37.

36. 

35. 

34.

33.

32. 

31. 

30. 

29.

Cumulative 

Thickness thickness 

(feet) (feet)

2.1

4.9

7.5

10.4

13.0

Description

Dinwoody Formation, lower part:

Limestone: medium-hard, thin- to thick-bedded, 2. 1

dusky-yellow (5F6/4). 

Limestone: medium-hard, thick-bedded, dusky- 2. 8

yellow (5F6/4). 

Mudstone: plastic to crumbly, thin-bedded, 2. 6

light-olive-gray (5F5/2). 

Limestone: medium-hard, thick-bedded, dusky- 2. 9

yellow (5 Y 6/4); contains shel fragments. 

Limestone: medium-hard, thin- to thick-bedded, 2. 6

finely crystalline, light-olive-gray (5F 6/1);

contains shell fragments. 

Dolomite: hard, thick-bedded, finely crystalline, 1. 0 14. 0

medium-gray (N 6). 

Limestone: hard (some soft layers at middle), 5. 0 19. 0

thin- to thick-bedded, yellowish-gray (5 Y 7/2);

contains Lingula sp. 

Mudstone: calcareous, plastic to medium-hard, 4. 9 23. 9

thin-bedded, moderate-yellowish-brown (WYR

5/4) to grayish-brown (10 YR 4/2). 

Limestone: sandy, medium-hard, thick-bedded, 2. 2 26. 1

medium coarsely crystalline, yellowish-gray

(5F 7/2); sand, medium to coarse; contains

Lingula. 

Mudstone: calcareous, somewhat sandy, soft, .5 26. 6

fissile to thin-bedded, light-olive-gray (5YR

5/2). 

Dolomite: silty, hard, thin- to thick-bedded, 4. 5 31. 1

dense to finely crystalline, grayish-orange

(10 YR 7/4) to light-brownish-gray (10 YR

6/1); contains pelecypod casts. 

Dolomite: hard, thin- to thick-bedded, aphani- 5. 0 36. 1

tic, very light gray (N S) to medium-lightgray (N 6); weathers dark reddish brown (IOR

3/4); contains 0.3 ft calcareous medium-hard

fissile to thin-bedded mudstone, 2.8 ft above

base; contains shell fragments. 

Dolomite: hard, thin- to thick-bedded, aphani- 3. 3 39. 4

tic, yellowish-gray (5 F 7/2); weathers moderate brown; middle 0.7 ft, medium-light-gray

(N 6), weathers light brown (5YR 6/4); contains Lingula. 

Dolomite: hard, thin to thick-bedded, aphanitic, 5. 0 44. 4

light-gray (N 8); weathers pale reddish brown

(10R 5/4); contains shell fragments. 

Dolomite: hard, thin-to thick-bedded, aphanitic, 2. 2 46. 6

medium-light-gray (N 7); weathers pale

reddish brown (IOR 5/4); contains Lingula. 

Mudstone: calcareous, soft, fissile to thin- .5 47. 1

bedded, grayish-brown (10 YR 4/2). 

Dolomite: hard, thin-bedded, finely crystalline, 1. 8 48. 9

light-olive-gray (5 F 6/1); contains Lingula. 

Dolomite: hard, thin- to thick bedded, finely 3. 3 52. 2

crystalline, light-brownish-gray (SYR 6/1);

contains abundant Lingula. 

Limestone: medium-hard, thin-bedded and 1.8 54.0

flaggy, light-brownish-gray (IOYR 6/1); contains shell fragments. 

Dolomite: hard, finely crystalline, light-olive- 1. 0 55. 0

gray (5F6/1). 

Limestone: silty, medium-hard, thin-bedded and 1. 0 56. 0

flaggy, light-olive-gray (5F 5/2). 

Dolomite: hard, thick-bedded, finely crystalline, 1. 4 57. 4

light-olive-gray (5F5/2). 

Mudstone: upper 1.3 ft hard, fissile to thin- 3. 2 60. 6

bedded, medium-gray (N 5); lower 1.9 ft

dolomitic, soft, fissile to thin-bedded,

brownish-gray (SYR 4/1); contains shell

fragments.

Sample

Acid 

insoluble

Uranium

Radiometric eU
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 463

Odell Creek, Mont., lot 1252 Continued

Bed Description

Dinwoody Formation, lower part Continued

D-28________ Dolomite and mudstone: upper 0.4 ft thinbedded hard finely crystalline medium-darkgray (AT 4) dolomite, underlain by 0.1 ft plastic 

to fissile medium-gray (N 5) mudstone; contains shell fragments.

27________ Dolomite: hard, thick-bedded, finely crystalline,

medium-dark-gray (N 4), weathers to darkreddish-brown (10.R 3/4); soft mudstone 

parting below middle; contains shell fragments.

26 _______ Dolomite: hard, thick-bedded, finely crystalline,

medium-gray (N 5); contains shell fragments 

and calcite veinlets.

25 _______ Dolomite: hard, thick-bedded, finely crystalline,

medium-gray (N 5); contains Lingula in upper 

part and calcite veinlets.

24__________ Dolomite and mudstone, interbedded; hard

thin- to thick-bedded medium-gray (N 5) 

dolomite (60 percent) and soft fissile to thinbedded brownish-black (SYR 2/1) mudstone.

23__________ Dolomite: hard, thick-bedded, finely crystalline,

dark-gray (N 3).

22. ______ Dolomite: hard, dense, fine-grained, thick-bedded, medium-dark-gray (N 4); contains 1 mm 

to 1 cm fractures filled with calcite.

21 _______ Dolomite and mudstone: 0.2 ft of medium-hard

fine-grained medium-dark-gray (N 4) mudstone overlying 1.4 ft of hard aphanitic thinto thick-bedded dark-gray (N 3) dolomite.

20__________ Mudstone: carbonatic, thick-bedded, hard,

medium-gray (N 5).

19 ______ Mudstone: medium-hard, thin- to thick-bedded,

grayish-brown (10 YR 4/2).

18 ______ Mudstone: upper 0.9 ft, medium-hard, thinbedded, dark-gray (N 3); lower 1.3 ft, soft, 

thin-bedded, moderate-yellowish-brown (10 

FB 5/4).

17 ______ Carbonate rock and mudstone: 0.7 ft of hard

thin-bedded moderate-yellowish-brown (10 YR 

5/4) carbonatic mudstone underlain by 1.7 ft 

of medium-hard dense thin-bedded grayish-red 

(5R 4/2) carbonate rock. Contains Lingula, 

Monotis, and Aviculopectin.

16 ______ Mudstone: carbonatic, plastic, thin- to thickbedded, grayish-brown (10 YR 4/2); top 0.5 ft 

brecciated(?) and may be fault zone. Basal 

contact may be fault zone.

15__________ Mudstone and limestone: 1.6 ft of plastic poorly

bedded moderate-brown (SYR 4/4) finely 

oolitic calcareous mudstone underlain by 0.2 

ft of hard pale-brown (5 YR 5/2) aphanitic 

muddy limestone.

14 ______ Carbonate rock: muddy, plastic, thin-bedded,

grayish-brown (10 YR 4/2) to grayish,red 

(10R 4/2), finely oolitic.

13__________ Limestone: medium-hard, thin-bedded, laminated, grayish-red (10.R 4/2), coarsely oolitic.

12 ______ Mudstone: calcareous, plastic, light-olive-gray

(5F 5/2).

11 ______ Limestone: medium-hard, thick-bedded, locally

laminated, moderate-brown (5YR 3/4), oolitic; 

contains unidentified shell fragments; emits 

strong petroliferous odor on striking with 

hammer.

10 _ _ _____ Limestone: muddy, soft, fissile, moderate-yellowish-brown (10 YR 5/4); contains unidentified 

shell fragments.

Cumulative 

Thickness thickness 

(feet)

0.5

2. 0

1.7

1. 4 

3. 1

1. 6

2. 1

2. 2

2.4

2. 6

1.5

.2 

1. 0

61. 1

1. 3 62. 4

64.4

66. 1

3. 0 69. 1

85.3

1. 8 87. 1

3. 6

89.4

89.6

90.6

90.9

Chemical analyses (percent)

Uranium

Sample PsOs

Acid 

insoluble

Radiometric e~U

70.5

73.6

75.2

77.3

78. 1

80. 3

82. 7 FSH-417 0. 6 17. 6 0. 0005

416

415

414

413

412

411

410

.4 57. 1

.3 49. 2

.4 45. 0

.7 15. 6

.5 50. 6

.7 11.6

. 75 29. 6

002

002

002

0005

002

005

001
464 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Odell Creek, Mont., lot 1252 Continued

Bed Description

Cumulative 

Thickness thickness 

(feet) (feet)

Chemical analyses (percent)

Uranium

D 9__

To-6. 

5.

Dinwoody Formation, lower part Continued

Limestone: medium-hard, muddy, laminated to 1. 3 92. 2

thick-bedded, moderate-brown (5YR 3/4)

very coarsely oolitic; contains shell fragments;

lower 0.3 ft, soft, pale-yellowish-green (IOGY

7/2) to moderate-yellowish-brown (10 FK

5/4). 

Mudstone: calcareous, soft, fissile to thin-bedded, . 6+ 92. 8 +

dusky-yellow (5F 6/4). Small diagonal fault

at base; so, true thickness is unknown. 

Mudstone: calcareous, soft, moderate-yellowish- 1. 6+ 94. 4 +

brown (10FR 5/4); irregular basal contact.

contact. Total thickness unknown due to

fault contact with overlying bed. 

Tosi Chert Member of Phosphoria Formation, top 

part:

Chert: hard, brittle, fissile to thin-bedded, 1.4 1.4

moderate-brown (5FK 4/4). 

Mudstone: medium-hard, fissile to thin-bedded, 4. 5 5. 9

cherty, light-olive-gray (5F 5/2); basal 0.5 ft,

soft to hard, medium-dark-gray (N 4) to

moderate-brown (5YR 3/4); basal contact

gradational.

Chert: hard, dark-gray (N 3), thin-bedded___ 1. 5 7. 4 

Sandstone and mudstone: .25 ft soft light-olive- .7 8. 1

gray (5F 6/1) mudstone underlain by 0.25 ft

medium-hard fine-grained light-brownish-gray

sandstone. 

Sandstone?: soft, crumbly, not bedded, grayish- .7 8. 8

black (N2) to strong-brown (5F4/8); contains

shell fragments. 

Chert: hard, thick-bedded, medium-dark-gray 2. 6 11.4

(AT 4).

Acid RadioSample PiOs insoluble metric e\5

FSH-409 0.4 38. 5 0. 0005

408 .2 70. 0 . C02

407 .9 78. 9 .001

406 1. 8 86. 7 . 0005 

OAP-405 1. 5 84. 0 . 001

404 1. 05 90. 6 . 0005

403 1. 3 89. 3 . 0005

402 4. 6 82. 9 . 0005

401 .4 94. 8 . 0005

Centennial No. 1, Mont., lot 1253

[Phosphoria, Shedhorn, and part of Park City Formation measured and sampled in hand trench near crest of Centennial Mountains, NW cor. sec. 33, T. 14 S., R. 1 W., 

Beaverhead County, Mont. Beds strike east and dip 20° S. on Centennial Mountains fault block. Measured by P. S. Honkala and O. A. Payne and sampled by J. A. 

Kelleher, in July 1948. Descriptions based entirely on field notes and analytical data. Analyzed for PzOs and acid insoluble by U.S. Bur. of Mines, and for uranium by 

U.S. Geol. Survey]

Chemical analyses (percent)

Uranium

Bed

D-59. 

58.

57. 

56.

55.

To-54. 

53- 

52, 

51.

Description

Dinwoody Formation, lower part:

Limestone: hard, thick-bedded, medium-gray (N 5); weathers darkyellowish orange (IOYR 6/6).

Mudstone: calcareous, medium-hard, 

fissile to thin-bedded, medium-gray 

(N 5); contains laminae of strongyellowish-brown (WYR 5/8) siltstone.

Mudstone: medium-hard, thin-bedded, 

silty, medium-light-gray (N 6).

Mudstone: calcareous, medium-hard, 

fissile to thin-bedded, silty, mediumgray (N 5).

Mudstone: calcareous, medium-hard, 

fissile to thin-bedded, medium-gray 

(N 5) to medium-light-gray (N 6). 

Sharp plane contact at base. 

Tosi Chert Member of Phosphoria Formation:

Chert: hard, thick-bedded, mediumgray (N 5); arbitrary basal contact.

Chert: hard, thick-bedded, dark-gray 

(N 3); gradational basal contact.

Chert: hard, thin-bedded, olive-gray 

(5F 4/1); arbitrary basal contact.

Chert: hard, thin- to thick-bedded, 

olive-gray (5F 4/1); arbitrary basal 

contact.

Thickness 

(feet)

0.7

2. 8

2. 5

3. 4

2.0

Cumulative

thickness

(feet) Sample

Acid insoluble

Radiometric eU

Chemical 

U

0. 7 OAP-496

3. 5

6.0 

9.4

11. 4

495

494

493

492

0.8

1.3

1. 4 

1. 3

1.3

79. 7 0. 0005 0. 0005

75. 7

74.6

75.0

001

001

001

001

0005

0005

0005

0005

1. 5

3. 5

4. 1

3. 2

1.5

5.0

9. 1

12.4

491

490

489

488

1.0

. 3

. 5

.7

77. 7

95. 3

83. 3

90. 2

.0005

.0005

.0005

.0005

.0005

.0005

.0005

.0005
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 

Centennial No. 1, Mont., lot 1253 Continued

465

Chemical analyses (percent)

Bed Description

Tosi Chert Member of Phosphoria Formation Continued 

To-50_________ Chert: hard, massive, olive-gray (5F

4/1); arbitrary basal contact.

49_________ Chert: hard, massive, brownish-gray

(5YR 4/1); contains chalcedonic 

veinlets; arbitrary basal contact.

48_________ Chert: hard, thin- to thick-bedded, medium-dark-gray (N 4); locally laminated; arbitrary basal contact.

47.________ Chert: like bed To-48; contains laminated mudstone parting above middle.

46_________ Chert: like bed To-48; contains laminated mudstone partings.

45______ Chert: like bed To-48_______---___-

44_________ Mudstone: calcareous, hard, fissile to

thin-bedded, silty, medium-light- 

'gray (N 6).

43_________ Dolomite: silty, hard, thick-bedded,

aphanitic, medium-gray (N 5).

42_________ Chert: hard, thin- to thick-bedded,

medium-dark-gray (N 4); arbitrary 

basal contact.

41_________ Chert: hard, thin-bedded, mediumdark-gray (N 4).

40_________ Carbonate rock: hard, thin-bedded,

coarsely crystalline, medium-lightgray (N 6).

39-____.___. Chert: like bed To-41-_._____________

38_________ Carbonate rock: like bed To-40___

37_________ Chert: like bed To-41; arbitrary basal

contact.

36_________ Chert: hard, thin- to thick-bedded,

medium-dark-gray (N 4); contains 

calcareous mudstone partings; arbitrary basal contact.

Retort Phosphatic Shale Tongue of Phosphoria Formation:

Rt-35_________ Mudstone: cherty, hard, thin- to thickbedded, dark-gray (N 3).

34.________ Limestone: muddy, hard, thick-bedded,

coarsely crystalline, dark-gray (N 3).

33_________ Chert: hard, thin-bedded, mediumdark-gray (N 4).

32_________ Limestone: muddy, hard, thin-to thickbedded, coarsely crystalline, grayishblack (N 2).

31_________ Mudstone: hard, fissile to thin-bedded,

grayish-black (N 2); arbitrary basal 

contact.

30_________ Mudstone: cherty, hard, fissile to thinbedded, dark-gray (N 3); arbitrary 

basal contact.

29_________ Mudstone: medium-hard, thin-bedded,

dark-gray (N 3); arbitrary basal 

contact.

28 _________ Mudstone: medium-hard, fissile to

thin-bedded, silty, grayish-black 

(N 2); gradational basal contact.

27_________ Mudstone: medium-hard, fissile to

thin-bedded, dark-gray (N 3); 

contains thin grayish-black (N 2) 

bands; arbitrary basal contact. 

Mudstone lens: hard, massive, mediumgray (N 5); about 3 ft long.

26_________ Mudstone: hard, fissile to thin-bedded,

medium-dark-gray (N 4); arbitrary 

basal contact.

25_ ________ Mudstone: hard, thin-bedded, mediumdark-gray (N 4); gradational basal 

contact.

24__.______ Mudstone: medium-hard, fissile, grayish-black (N 2).

Thickness 

(feet)

2.9 

5.0

Cumulative

thickness

(feet)

15.3

20.3

Uranium

5. 0 25. 3

5.0 

5. 0

5.0 

1.0

2. 2 

4. 2

.7 

.3

2. 5

1. 0

. 5

5.0

30.3

35.3

40. 3

41.3

43. 5

47.7

48.4

48. 7

51. 2

52. 2

52. 7

57. 7

SampZe

GAP-487 

FSH-486

485

484

483

482

481

480

P.Os

0.5 

.6

.6

.5 

.5 

. 5

Acid insoluble

Radiometric eU

093. 5 0. 0005

93. 3 . 0005

88.0

86. 7

86.7

85.2

50. 7

84.3

0005

0005

0005

0005

0005

0005

Chemical 

U

0. 0005

.0005

.0005

.0005

.0005

.0005

.0005

.0005

479

478

82. 3

77.0

0005 .0005

0005 .0005

2. 1

1. 4

1.0

1. 5

2. 5

5.0

3.3

2. 2

1. 2

(0-1. 0)

4.6

2.0

1.7

59. 8 '

61. 2

62. 2 <

63.7

66.2

71.2

74.5

76.7

77.9

82. 5

84. 5

86.2

477

476

475

OAP-474

473

472

471

470

469

. 5

. 6

. 8

1.0

.9

1. 5

. 6

2.2

3.3

76.2

81.7

77.3

76.0

77. 5

74.7

69.0

71.7

67.9

.0005

.0005

.001

.001

.002

.003

.002

.003

.003

.0005

.0005

.0005

.001

.001

.001

.001

. 201

.002
466 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Centennial No. 1, Mont., lot 1253 Continued

Bed Description

Retort Phosphatic Shale Tongue of Phosphoria Formation Continued 

Rt-23-_------- Mudstone: medium-hard to crumbly,

fissile, dark-gray (N 3).

22 _________ Phosphorite: soft, thin- to thickbedded, medium coarsely pelletal, 

medium-gray (N 5). 

21_-__-____ Mudstone: carbonatic?, medium-hard,

thick-bedded, silty, brownish-black 

(WYR 2/2). 

20-_------- Mudstone: phosphatic, medium-hard,

thick-bedded, dark-gray (N 3); phosphate, finely pelletal.

19--------- Phosphorite: medium-hard, thin-bedded, coarsely pelletal, medium-gray 

(JV5).

18--_----__ Mudstone: medium-hard, thick-bedded, silty, mo derate-yellowish-brown 

(10 YR 5/4).

Lower tongue of Shedhorn Sandstone: 

Ls-17_ -------- Sandstone: medium-hard, thick

bedded, medium-grained, moderatebrown (SYR 4/4); arbitrary basal 

contact.

16_ _-_-__-_ Sandstone: medium-hard, thickbedded, medium-grained, lightbrown (5YR 5/6); arbitrary basal 

contact; contains abundant columns of medium-light-gray (N 6) 

quartizite, 0.1-0.3 ft in diameter and 

as much as 5 ft or more long; columns 

more phosphatic than matrix. 

15___-_-___ Sandstone: like bed Ls-16-_-______--

14__-__-_-_ Sandstone: like bed Ls 16___________

13-_------- Sandstone: like bed Ls-16______-__-_

12_-____-_- Sandstone: like bed Ls-16.______-__-

ll___--____ Sandstone: like bed Ls-16, but medium- to coarse-grained and lightbrownish-gray (5YR 6/2). 

10- ________ Sandstone: soft, massive, medium-to

very coarse-grained, moderate-brown 

(5 YR 4/4); contains shell fragments 

and considerable amount of medium 

to coarsely oolitic phosphate; arbitrary basal contact. 

9_________ Sandstone: soft, massive, medium- to

very coarse grained, pale-red (10.R 

6/2); contains shell fragments and 

nodular masses of medium-grained 

light-brownish-gray (SYR 6/1) 

quartzite. Irregular basal contact; 

scattered small pebbles near base. 

8_ ________ Chert and sandstone: sandy, hard,

thin- to thick-bedded light-brownishgray (5YR 5/1) chert containing 

numerous streaks and lenses of medium-hard medium-grained darkyellowish-orange (10 YR 6/6) sandstone as much as 0.6 ft long and 0.3 

ft thick.

7-__--__-_ Sandstone: hard, thick-bedded, fine-to 

medium-grained pale- to light-brown 

(SYR 5/2- 5/6); contains small 

pebbles in lower part; contains 

elongated chert nodules that are as 

much as 0.6 ft long but are mostly 

small; irregular basal contact. 

Franson Tongue of Park City Formation: 

F-6--_______ Limestone: sandy, dolomitic, hard,

thin- to thick-bedded, aphanitic, 

light-brownish-gray (5YR 6/1); 

sand, fine; finely oolitic phosphatic 

nodules in upper part.

Chemical analyses (percent)

Thickness 

(feet)

. 4

. 8

. 9

1. 1

1. 1

1. 0

Cumulative 

thickness 

(feet)

86. 6

87. 4

88. 3

89. 4

90. 5

91. 5

Uranium

Sample

OAP-468

467

466

465

464

OAP-463

P205

7. 6

33. 6

7. 5

8.0

29. 3

6. 6

Acid insoluble

53. 5

6. 4

45. 7

51. 5

15. 2

66. 0

Radiometric ell

0. 003

. 010

. 005

.007

.008

.004

Chemical 

U

0. 002

. 008

.002

.003

.006

. 002

2. 8 94. 3

5. 0 99. 3

4. 2 103. 5

5. 0 108. 5

5. 0 113. 5

2. 6 116. 1

5. 0 121. 1

1. 1 122. 2

3. 9 126. 1

4. 0 130. 1

1. 2 131. 3

3. 0 134. 3

FSH-462 2. 8 90. 7 .001 .001

461 2. 1 92. 9 001 . 001

460

459

458

457

456

455

1. 7

1. 7

1.7

2. 1

2. 2

7. 6

92. 6

91. 8

92. 7

91. 0

90. 7

74. 2

. 001

.0005

.001

. 001

.0005

. 002

. 0005

.0005

. 0005

.001

. 001

. 0005

454

453

452

451

2. 4

1. 6

83. 8 . 0005

80. 3 . 0005

001

001

2.0 89. 0 . 0005 001

1. 7 36. 0 . 0005 0005
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 467

Centennial No. 1, Mont., lot 1253 Continued

F-5_ 

4_

Ls-2.

Description

Franson Tongue of Park City Formation 

Continued

Limestone: muddy, hard, thin- to 

thick-bedded, finely to very coarsely 

crystalline, very light gray (N 8).

Limestone: sandy, medium-hard, thinto thick-bedded, dark-yellowishorange (10 YR 6/6); sand, fine to 

coarse.

Limestone: medium-hard, thin-bedded 

to massive, medium to very coarsely 

crystalline, pinkish-gray (SYR 8/1); 

locally sandy, locally porous.

Sandstone: hard, fissile to thin-bedded, 

fine- to coarse-grained.

Limestone: sandy, hard, fissile to thickbedded, dense, grayish-orange (10 

YR 7/4); sand very fine. Underlying rocks covered by snow at time 

section was measured.

Chemical analyses (percent)

Thick- Cumulative

ness thickness

(feet) (feet) Sample

2. 5 136. 8 >

Uranium

Acid in- Radlometric e~U

Chemical 

U

1. 0 137. 8

5. 0 142. 8

2. 8 145. 6 ^

2. 0 147. 6

FSH-450 0. 2

449 . 0

32. 2 0. 0005 0. 001

16. 3 . 0005 . 0005

448 . 1 62. 5 .001 . 0005

Centennial No. 3, Mont., lot 1254

[Grandeur Tongue of Park City Formation and lower part of Meade Peak Phosphatic Shale Member of Phosphoria Formation measured from hand trench at crest of Centennial Mountains in SE. cor. sec. 1, T. 15 S., R. 1 W., Beaverhead County, Mont., by F. S. Honkala and O. A. Payne and sampled by J. A. Kelleher and R. L. Konizeski, in July 1948. Beds strike N. 80° W. and dip 10° SW. Descriptions based entirely on field notes and analytical data. Analyzed for P2Os and acid insoluble by 

U.S. Bur. of Mines, and for uranium by U.S. Qeol. Survey]

Chemical analyses (percent)

Thick- Cumulative

ness thickness

Bed Description (feet) (feet) Sample

Meade Peak Phosphatic Shale Member of

Phosphoria Formation, lower part: 

M-15_ __.--___ Chert: hard, thick-bedded, mottled 1.0 1.0 OAP-541

white and medium-light-gray (N 6).

The bed is on crest of ridge; upper

half of Meade Peak member eroded. 

14_________ Phosphorite: muddy, soft to medium- 1.7 2.7 506

hard, thin-bedded, coarsely oolitic

to pisolitic, medium-gray (N 5);

lower part softer. 

13_ ________ Phosphorite: hard, thin- to thick- 4.6 7.3 505

bedded, coarsely oolitic to pisolitic,

medium-gray (N 5); contains shell

fragments. 

12_________ Conglomerate: calcareous, hard, very .2 7.5

light gray (N 8); probably phosphatic. 504 

Grandeur Tongue of Park City Formation: 

G-ll__________ Limestone: sandy, hard, thick-bedded, 2.5 10.0

very light gray (N 8); contains small

limonitic stains; arbitrary basal

contact. 

10__________ Limestone: very sandy, hard, thin- 4.8 14.8 503

bedded to massive, finely crystalline,

very light gray (N 8); contains small

limonitic concretions; arbitrary basal

contact. 

9__________ Limestone: sandy, medium-hard, thick- 1. 6 16. 4

bedded, finely crystalline, very pale

orange (lOYfl 8/2); contains" much FSH-502

fine to coarse sand. 

8__________ Sandstone: calcareous, medium-hard, 3.4

thin-bedded, fine- to medium-grained,

weak-yellowish-orange (10 YR 7/6);

arbitrary basal contact.

Uranium

P2 05

0.4

Acid insoluble

Radiometric e~U

Chemical 

U

93. 2 0. 0005 0. 0005

32.4

2. 7

1. 5

34. 1

8.4

47. 2

60. 3

005

013

001

001

001

008

Oil

002

000

0005
468 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Centennial No. 3, Mont., lot 1254 Continued

Bed

G-7_.

6..

Q-iDescription

Grandeur Tongue of Park City Formation 

Continued

Sandstone: calcareous, soft, thinbedded, fine- to coarse-grained, lightyellowish-brown (2.5F6/4).

Sandstone: calcareous, medium-hard, 

thin-bedded, fine- to medium-grained, 

very pale brown (IOYR 7/3); arbitrary basal contact.

Sandstone: calcareous, soft, fissile, fineto medium-grained, weak-yellowishorange (IOYR 7/6).

Limestone: sandy, medium-hard, thickbedded, dense, very pale brown 

(IOYR 7/3); sand, fine to medium.

Sandstone: calcareous, medium-hard, 

thin-bedded, fine- to very coarsegrained, moderate-yellowish-brown 

(1QYR5/G).

Conglomerate: calcareous, hard, thickbedded, light-brownish-gray (10 YR 

6/1); grain size ranges from mediumsand size to 0.2 ft; pebbles, composed 

chiefly of chert but also of limestone 

and sandstone, are poorly rounded 

and sorted; stringers penetrate 0.2- 

0.6 ft into cracks in underlying bed, 

contact generally irregular. 

Quadrant Formation, top bed:

Sandstone: calcareous, medium-hard, 

fissile to massive, medium- to very 

coarse-grained, very pale brown 

(IOYR 7/3).

Chemical analyses (percent)

Thickness 

(feet)

Cumulativi

thickness

(feet)

Uranium

3. 4 23. 2

1. 6 24. 8

2. 1 36. 5

Sample

FSH-501

500

499

498

Acid in- Radio- Chemical 

P2OS soluble metric eV U

0. 1 68. 6 0. 001 0. 0005

4 68. 7 . 001 . 0005

0 64. 5 . 002 . 0005

2 56. 0 . 005 . 0005

4. 4 4. 4 497 .3 61. 0 . 0005 . 000

Centennial No. 2, Idaho, lot 1255

[Shedhorn Sandstone and Tosi Chert and Retort Phosphatic Shale Members of Phosphoria Formation measured from hand trench near crest of Centennial Mountains N W. 

of center of sec. 12, T. 14 N., R. 40 E., Clark County, Idaho, by F. S. Honkala and O. A. Payne and sampled by J. A. Kelleher and R. L. Konizeski, in July 1948. Beds 

strike N. 65 W. and dip 14° S W. Descriptions based entirely on field notes and analytical data. Analyzed for P2O5 and acid insoluble by U.S. Bur. of Mines and for 

uranium by U.S. Geol. Survey]

Chemical analyses (percerd)

Bed

Cumulative

thickness

(feet)

Uranium

Sample

Acid Radiometric e

D-41.

40_

39.

38. 

37_ 

36. 

35. 

34.

33_

Thickness 

Description (feet)

Dinwoody Formation, lower part:

Mudstone: medium-hard, thin-bedded, strong- 0.5 0.5 __________ ______ ______ _______

yellowish-brown (10 YR 5/8); contains fine- to

medium-grained sand. 

Mudstone and limestone: 0.2 ft muddy hard .8 1. 3 FSH-540 0. 65 77. 5 0. 001

dense light-gray (N 7) limestone underlain by

0.6 ft of medium-hard thin-bedded grayishbrown (10 YR 4/2) mudstone. 

Mudstone: medium-hard, hssile to thin-bedded, 5.0 6.3 539 1.0 81. .001

light-olive-gray (5Y 5/2); arbitrary basal

contact. 

Mudstone: medium-hard, fissile to thin-bedded, 1. 3 7. 6

grayish-brown (10 YR 4/2). 

Limestone: bard, thin-bedded, finely crystal- .3 7. 9

line, light-brownish-gray (SYR 6/1). 

Mudstone: medium-hard, fissile to thin-bedded, .7 8. 6

grayish brown (10 YR 4/2). } 538 1.1 81.5 .001 

Mudstone: carbonatic, medium hard, strong- .5 9. 1

yellowish-brown (10 YR 5/8). 

Mudstone: medium-hard, fissile to thin-bedded, 2. 2 11. 3

grayish-brown (IOYR 4/2); arbitrary basal

contact. 

Mudstone: medium-hard, fissile to thin-bedded, 5. 0 16. 3 537 1. 2 74. 4 . 001

grayish-brown (10 YR 4/2).
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 469

Centennial No. 2, Idaho, lot 1255 Continued

Bed Description

Dinwoody Formation, lower part Continued 

D-32 ________ Conglomerate: hard, medium-gray (N 5) to

light-brown (5YR 5/6); pebbles, as much as 

2 cm in diameter; contains apatite pellets and 

numerous fossils (shark teeth, pelecypods, 

and others).

Tosi Chert Member of Phosphoria Formation:

To-31_-______- Chert: hard, moderate-brown (5YR 3/4); arbitrary basal contact.

30___--__-- Chert: hard, thin-bedded, brownish-gray (10 YR 

4/1); arbitrary basal contact.

29__--_____ Chert: hard, thin- to thick-bedded, dark-gray 

(N 3); contains some finely sandy mudstone 

stringers; arbitrary basal contact.

28-_-___--- Chert: hard, fissile to thin-bedded, dark-gray 

(N 3); contains a few mudstone partings; 

arbitrary basal contact.

27__------- Chert: like bed To-28; arbitrary basal contact.

26_________ Chert: like bed To-28; arbitrary basal contact25____-___- Chert and mudstone, interbedded: alternating

hard fissile to thin-bedded pale-brown (\OYR 

6/2) chert (75 percent) and medium-hard 

fissile brownish-gray (IOYR 4/1) mudstone. 

Retort Phosphatic Shale Member of Phosphoria

Formation: 

Rt-24_________ Mudstone and chert: hard fissile to thin-bedded

brownish-gray (IOYR 4/1) mudstone constitutes most of unit and grades upward into 

chert; arbitrary basal contact.

23___--__-_ Mudstone: hard, fissile to thin-bedded, brownishgray (IOYR 4/1) to light-brownish-gray (10 YR 

5/1).

22_________ Mudstone: medium-hard, thin-bedded, alternating brownish-gray bands (IOYR 3/1 and 

4/1); contains medium sand.

21 _________ Mudstone: medium-hard laminated to thinbedded, brownish-black (IOYR 2/1), contains 

very thin medium- to light-gray layers; contains medium sand; arbitrary basal contact.

20__------- Mudstone: medium-hard, thin-bedded, brownish-gray (IOYR 3/1); contains medium sand; 

small offset and drag along cross-cutting 

shear.

19_-_-----_ Mudstone: hard, fissile to thin-bedded, brownish-gray (IOYR 3/1); top 0.5 ft soft and brecciated, pale-brown (IOYR 5/3).

18----_--_- Mudstone: hard, thin- to thick-bedded, darkgray (N 3)

17---__-__- Mudstone: hard, fissile to thick-bedded, grayish-black (N 2).

16_--_---_- Phosphorite: medium-hard, thin-bedded, 

coarsely pelletal, medium-gray (N 5).

15---__---- Mudstone: medium-hard, fissile to thin-bedded, 

dark-gray (AT" 3).

14_________ Mudstone: soft, thick-bedded, pale-brown

(10 YR 5/2); basal 0.2 ft fissile, medium-darkgray (N 4).

13_________ Phosphorite and mudstone, interlaminated: alternating bands of muddy medium-hard thinto thick-bedded medium coarsely pelletal 

medium-dark-gray (N 4) phosphorite (80 

percent (and phosphatie brownish-gray (IOYR 

3/1) mudstone.

12_ ________ Phosphorite: medium-hard, thin- to thickbedded, medium coarsely pelletal, mediumdark-gray (N 4).

!!_________ Mudstone: medium-hard, thick-bedded, grayish-brown (lOl^R 4/2) to moderate-yellowishbrown (IOYR 4/4).

10.________ Phosphorite: muddy, medium-hard, thin- to

thick-bedded, coarsely pelletal, medium-lightgray 

See footnote at end of table.

Chemical analyses (percent)

Cumulative 

Thickness thickness 

(feet) (feet)

1. 3

3.8 

2. 7 

4. 0

4. 4

8. 2

10.9

14.9

1. 8 16. 7

1. 7 18. 4

.9 __---_

1. 6 20. 9

3. 0 23. 9

3. 2 27. 1

Sample

Uranium

Acid Radioinsoluble metric e~U

. D

.3

. 6

2. 2

ID. y

.3

FSN-536

.9 535

3. 1 534

1.3

. 4

. 4

89.0

93. 0

92. 5

0. 0005

.0005

.0005

533

532

531

530

529

87.4

89. 5

90. 2

90. 1

525

524 80. 3

. 0005

. 0005

.0005

. 0005

. 65 81. 6 . 001

528 . 80 82. 4 . 001

OAP-527 .8 86. 5 . 001

526 1. 0 81. 5 . 002

1. 05 80. 7 . 002

. 002

2. 2

5.0

1. 5

. 7

. 7

.7

. 7

1. 7

. 9

29. 3 523

34. 3 522

35. 8 521

36. 5 520

37. 2 <

37.9

38. 6

519

518

40. 3 517

41. 2 516

1. 1

1. 7

31.4

5.4

9. 65

34. 5

2. 8

19. 8

77. 1

70. 6

10. 0

66. 0

52. 3

4. 3

74. 4

35. 2

.002

. 003

1 . Oil

. 005

. 006

. 008

. 003

. 009
470 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Centennial No. 2, Idaho, lot 1255 Continued

Bed

Ls-9.

8. 

7. 

6-

Description

Lower tongue of Shedhorn Sandstone; base not 

exposed:

Sandstone: hard, thick-bedded, light-gray (N 

7); contains shell fragments.

Sandstone: hard, thick-bedded to massive, palebrown (10FR 6/2); contains shell fragments.

Sandstone: hard, massive, light-gray (N 7); 

contains considerable amounts of calcite.

Sandstone: hard, massive, light-olive-gray (5F 

6/1); contains sandstone columns 0.1-0.3 ft 

across and as much as 5 ft long, nearly normal 

to bedding; arbitrary basal contact.

Sandstone: like bed Ls-6; locally gritty. ______

Sandstone: hard, massive, yellowish-gray (5F 

7/2); contains considerable amounts of phosphate and contains fossils in lower 0.5 ft.

Sandstone: hard, massive, medium-grained, 

light-gray (N 7); contains shell fragments and 

sandstone columns 0.1-0.3 ft diameter and as 

much as 5 ft long, nearly normal to bedding.

Sandstone: phosphatic, hard, thick-bedded, 

medium-grained, pale-brown (10 FR 6/2); 

apatite medium coarsely oolitic; contains 

shell fragments; gradational basal contact.

Sandstone: calcareous, hard, massive, coarsegrained, light-gray (N 7); contains considerable amounts of phosphate and shell fragments. Underlying beds covered.

Thickness 

(feet)

Cumulative

thickness

(feet) Sample

1. 6 42. 8 FSH-5I5

3. 0 45. 8 514

2. 6 48. 4 513

5. 0 53.4 512

5. 0 58. 4

2. 1 60. 5

5. 0 65. 5

1. 1 66. 6

4. 3 70. 9

511

510

509

508

507

Chemical analyses (percent)

Uranium

Acid RadioPsOj insoluble metric eU

3. 2 87. 1 0. 001

1. 7 92. 9 0005

1. 3 76. 2 . 0005

1. 7 85. 7 . 0005

2. 8 85. 3 . 001

5. 0 80. 2 . 002

3. 7 77. 0 . 001

12. 8 52. 6 . 007

7. 5 45. 2 . 004

Chemical II, 0.009 percent.

Cedar Creek, Mont., lot 1256

[Retort Phosphatic Shale Member of Phosphoria Formation measured in bulldozer trench near Cedar Creek, sec. 26, T. 9 S., R. 11 W., Beaverhead County, Mont., on east 

limb of syncline. Beds strike north and dip 61° W. Measured by E. T. Ruppel and sampled by J. A. Kelleher, in August 1948. Analyzed for PzOs and acid insoluble by U.S. Bur. of Mines, and for uranium by U.S. Geol. Survey]

Chemical analyses (percent)

Bed

To-59-

Rt-58-

57- 

56_ 

55_

54. 

53.

52_ 

51. 

50.

49.

Description

Tosi Chert Member of Phosphoria Formation, basal bed:

Chert: hard, grayish-brown (7. 5 KB

4/2), thick-bedded.

Retort Phosphatic Shale Member of Phosphoria Formation:

Mudstone: medium-hard, very pale

brown (10 YR 7/3), thin-bedded.

Fossil-colln. No. 10829. 

Mudstone: medium-hard, very pale

brown (WYR 7/3), thick-bedded. 

Phosphorite: cherty(?),hard, dark-gray

(N 3), thick-bedded. 

Limestone: sandy, phosphatic, soft,

weak - yellowish - orange, thickbedded; sand is very fine; apatite is

very finely pelletal. 

Mudstone: soft, light- yellowish-brown

(10 YR 6/4), very thick bedded. 

Mudstone: calcareous, phosphatic,

soft, very pale brown (10 YR 7/3),

thick-bedded; apatite is finely pelletal. 

Mudstone: soft, pale-orange (7.5YR

8/4), very thick bedded. 

Mudstone: soft, dark-yellowish-orange

(10FR 6/8), thick-bedded. 

Phosphorite: muddy, soft, pale-brown

(7.5YR 6/2), thin-bedded, coarsely

pelletal. 

Mudstone: soft, weak-yellowish-orange

(10 YR 7/6), thick-bedded.

Thickness 

(feet)

5. 0

11. 5

10. 0

. 8 

. 3

1. 5 

. 3

3. 0 

. 3 

. 1

. 6

Cumulative 

thickness 

(feet)

5.0

16. 5

26. 5

27.3

27. 6

29. 1

29. 4

32. 4

32. 7

32. 8

33. 4

Uranium

Sample 

ETR-585

584

583

582

581

580 

579

K78

P2 05 

2. 3

1.0

1. 1 

15. 4

11.4

4. 6 

9.2

2. 0

Acid 

insoluble

78. 5

74.0

82. 3 

34. 2

22. 7

62. 6 

42. 2

77. 6

Radiometric 

eU

0. 0005

.001

. 001 

.007

. 005

.004 

. 005

. 004

Chemical 

U

.005

. 005

. 004

577 9. 6 51.0 006 .004
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

Cedar Creek, Mont., lot 1256 Continued

471

Rt-48_ 

47. 

46_

45_ 

44.

43.

42_

41-

40- 

39-

38. 

37.

36_ 

35_

34_

33-

32- 

31-

30. 

29-

28.

27.

Chemical analyses (percent)

Description

Retort Phosphatic Shale Member of Phosphoria Formation Continued

Mudstone: medium-hard, pale-brown 

(7.5YR 6/2), thick-bedded.

Dolomite: phosphatic(?), soft, light-yellowish-brown (10 YR 6/4), fissile.

Mudstone: medium-hard, pale-brown 

(7.5YR 6/2), thin-bedded; grades 

from bed below.

Limestone: muddy, medium-hard, yellowish-gray (10 YR 8/1), thin-bedded.

Mudstone: soft, laminated yellowishwhite (2.5Y 9/2) and grayish-brown 

(7.5YR 4/2), fissile.

Phosphorite: carbonatic, medium-hard, 

very pale brown (10 YR 7/3), thinbedded, medium-pelletal.

Carbonate rock: phosphatic, mediumhard, very pale orange (10 YR 8/2), 

thick-bedded; apatite is medium 

pelletal.

Phosphorite: dolomitic, hard, mediumgray (N 6), thick-bedded, nodular 

and coarsely pelletal; nodules are as 

much as 50 mm in diameter.

Mudstone: medium-hard, weak-yellowish-orange (10 YR 7/6), thickbedded.

Phosphorite: muddy, soft, very pale 

brown (10 YR 7/3), thin-bedded, 

nodular; nodules are as much as 70 

mm in diameter.

Phosphorite: hard, medium-gray (N 

5), thick-bedded, medium-pelletal; 

contains many phosphatic brachiopod shells. (Analysis in error.)

Phosphorite: muddy, medium-hard, 

light-brown (7.5 YR 6/4), thickbedded, finely pelletal. Fossil-colln. 

No. 10828.

Mudstone: soft, light-brown (7.5YR 

5/6), fissile.

Phosphorite: medium-hard, light-yellowish-brown (10 YR 6/4), thin-bedded, finely pelletal.

Phosphorite: muddy, soft, light-brown 

(7.5YR 6/4), thick-bedded, nodular; 

nodules are as much as 60 mm in 

diameter.

Phosphorite: argillaceous, hard, palebrown (IQYR 6/2), thick-bedded, 

finely pelletal.

Mudstone: soft, weak-yellowish-orange 

(IQYR 8/4), thick-bedded.

Mudstone: phosphatic, soft, very pale 

brown (10 YR 7/3), thick-bedded; 

apatite is finely pelletal; grades from 

bed below.

Mudstone: phosphatic, soft, weakyellowish-orange (10 YR 7/6), fissile; 

apatite is nodular.

Phosphorite: muddy, medium-hard, 

light-gray (N 7), thin-bedded, finely 

pelletal.

Mudstone: phosphatic, carbonatic, 

soft, light-brown (7.5 YR 6/4), fissile; apatite is finely pelletal.

Phosphorite: hard, yellowish-gray 

(IQYR 7/1), thin-bedded, finely 

pelletal.

Cumulative 

Thickness thickness

(feet) (feet) Sample Pz05

Acid 

insoluble

Uranium 

ffadiometric Chemical

eTJ U

0.2

. 4

. 2

1.2

1. 2

.4

. 6

33. 6 >

04 OTC. n\J

34. 2

OC A DO. Tt

36. 6

37.0 '

37. 6

ETR-576 6.3 42.8 0.004 _______

575 1.8 48.3 .001 _______

574 7. 6 12. 7 005 0. 003

573 17. 4 19. 6 . 005 . 004

0. 2

. 1

. 2

38.4

39. 3

39. 5

40. 2

40. 5

41. 2

41.3

42. 0

42.5 

 43.0

43.4

43. 6

43.7

43.9

572

571

570

569

568

567

566

565

564

563

562

561

560

21. 0

1. 4 

18.9

32.6

23. 5

5.7 

20.9

17.5

22. 1 

3.5

2.6

72. 0

33. 5

25. 0

64.7

33. 0

24. 3

39. 1

41. 4

58.3

20.3

004

, 003

004

006

006

, 004

. 006

.005

007

.003

, 004

. 004

. 0006

. 006

. 004

. 005

. 005

. 006

0. 005
472 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Cedar Creek, Mont., lot 1256 Continued

Chemical analyses (percent)

Bed Descriptirn

Retort Phosphatic Shale Member of Phosphoria Formation Continued

Rt-26-________ Phosphorite: argillaceous, mediumhard, light-gray (N 7), fissile, 

medium-pelletal. Fossile-colln. No. 

10827.

25_________ Phosphorite: hard, medium-gray (N

6), thick-bedded, nodular and 

medium-pelletal; nodules are as much 

as 160 mm in diameter.

24_________ Mudstone: medium-hard, light-brown

(7.5 YR 6/4), fissile.

23_________ Phosphorite: calcareous, hard, medium-gray (N 6), thick-bedded, 

nodular and finely pelletal; nodules 

are as much as 150 mm in diameter.

22_________ Mudstone: phosphatic, soft, weakorange (7.SYR 7/6), thick-bedded; 

apatite is nodular.

21_________ Dolomite: muddy, medium-hard, weakyellowish-orange (WYR 7/6), thickbedded, aphanitic.

20_________ Dolomite: muddy, phosphatic, medium-hard, light-brown (7.SYR 6/4), 

thick-bedded, aphanitic; apatite is 

finely pelletal.

19_________ Phosphorite: hard, very pale brown

(10 YR 7/2), thick-bedded, nodular 

and medium-pelletal; nodules are as 

much as 50 mm in diameter; grades 

from bed below.

18_________ Mudstone: phosphatic, soft, lightbrown (7.SYR 6/4), fissile; apatite is 

nodular and pelletal; grades from 

bed below. Fossil-colln. No. 10826.

17_________ Mudstone: phosphatic, soft, lightbrown (7.SYR 6/4), fissile; apatite is 

finely pelletal; grades from bed 

below.

16_________ Phosphorite: dolomite, soft, very pale

brown (10 YR 7/2), thin-bedded, 

medium-pelletal.

15_________ Mudstone: soft, light-brown (7.5 YR

5/6), thin-bedded.

14__ _______ Mudstone: phosphatic, soft, lightyellowish-brown (10 YR 6/4), thinbedded; apatite is medium pelletal.

13_________ Phosphorite: carbonatic, medium-hard,

light-brownish-gray (10 YR 5/1), 

thick-bedded, nodular and mediumpelletal; nodules are as much as 80 

mm in diameter.

12_________ Mudstone: phosphatic, soft, very pale

brown (10 YR 7/3), thin-bedded; 

apatite is finely pelletal; grades 

from bed below.

!!_________ Mudstone: soft, very pale brown (10 YR

7/3), thin-bedded. Fossil-colln. No. 

10825.

10-________ Phosphorite: medium-hard, light-gray

(N 7), thin-bedded, finely pelletal; 

contains a few apatite nodules as 

much as 20 mm in diameter. 

9_________ Phosphorite: hard, light-brownish-gray

(10 YR 6/1), thin-bedded, mediumpelletal.

8_________ Phosphorite: argillaceous, mediumhard, very pale brown (10 YR 7/2), 

thin-bedded, finely pelletal. 

7_-_______ Mudstone: carbonatic, medium-hard,

weak-yellowish-orange (10 YR 8/4), 

thin-bedded.

Cumulative 

Thickness thickness 

(feet) (feet)

0. 6 44. 5

.4 44. 9

.2 45. 1

.3 45. 4

.3 45. 7

.6 46. 3

.3 46. 6

.3 46. 9

.3 47. 2

6 48.4

1 48. 5

2 48. 7

4 49. 1

,3 49. 4

1 49. 5

,1 49. 6

,1 49. 7

.2 49. 9

.6 50. 5

Sample 

ETR-559

Uranium

Acid Padiometric Chemical 

ivsoluble eU TJ

22. 8 27. 0 0. 007 0. 006

558

557

556

555

554

553

20. 3 26. 6 005 . 004

10. 1 55. 0 . 004

2.9 58. 9 002

25. 1 17. 6 . 006 . 005

9.9 56. 1 005 . 003

12. 4 52. 1 005 . 003

-552

551

550

16. 8 3. 8 . 006 . 004

20. 8 17. 7 005 . 005

14. 1 46. 5 . 006 . 004

549

548

547

19. 7 30. 2 . 005 . 004

21. 5 30. 6 006 . 004

6. 6 49. 8 003 ____---
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 473

Cedar Creek, Mont., lot 1256 Continued

Chemical analyses (percent)

Uranium

Bed

Rt-6. 

5-

4_ 

3.

2. 

1.

Description

Retort Phosphatic Shale Member of Phosphoria Formation Continued

Mudstone: soft, weak-yellowish-orange 

(10 YR 7/6), thick-bedded; grades 

from bed below.

Mudstone: soft, laminated light-gray 

(N 8) and weak-yellowish-orange 

(10KR 7/6), fissile.

Phosphorite: muddy, soft, light-gray 

(N 7), thin-bedded, finely pelletal.

Phosphorite: muddy, soft, laminated 

weak-yellowish-orange (10 YR 7/6) 

and light-gray (AT 8), fissile, mediumpelletal.

Mudstone: phosphatic, soft, weakyellowish-orange, fissile; apatie is 

nodular.

Phosphorite: sandy, hard, grayishbrown (10F.K 4/2), very finely 

pelletal; underlying bed not described. Fossil-colln. No. 10824.

Cumulative 

Thickness thickness 

(feet) (fee) Sample

0. 5 51. 0 ETR-546 

.6 51. 6 545

Acid Radio metric Chemical 

insoluble e\J U

1.7 79.4 0.003 _______

6. 7 62. 0 . 005 0. 003

.1 51. 7

1. 0 52. 7

.4 53. 1

3. 0 56. 1

544

543

542

16. 5 40. 3 005 . 004

8.2 51.1 .002 --_-___ 

26. 3 28. 6 . 007 . 006

Cave Creek, Mont., lot 1257

[Parts of Phosphoria and Shedhorn Formations measured on south side of Cave Creek, NWHNWW sec. 10, T. 6 S., R. 10 W., Beaverhead County, Mont., about 2,000 ft 

west of axis of northeastward-plunging Cave Creek syncline. Beds strike N. 25° W. and dip 40° NE. Beds To-48 to Us-54 are poorly exposed, and descriptions are 

based largely on float; beds Rt-4 to Rt-45 were described in bulldo'er trench. Measured by E. T. Ruppel and sampled by J. A. Kelleher, in August 1948. Analyzed 

for P2Os and acid insoluble by U.S. Bur. of Mines and for other constituents by U.S. Geol. Survey]

Chemical analyses (percent)

Bed Description

Upper tongue of Shedhorn Sandstone;

contains beds of intertonguing Tosi

Chert Member of Phosphoria Formation:

Us-54_________ Quartzite: gray_-__-______-_---___.

53_________ Chert and quartzite_________________ 16.0

52_________ Do-__--_-__-_-_-____-__-____.

50_________ Do-_--___-_-----____---__III_

Tosi Chert Tongue of Phosphoria Formation :

48_____-___ Chert: black to ~tan-----__I__-_IIIIL 32.5

47_________ Chert: hard, dark-gray (N 3), thickbedded. 

(46)_________ Rhyolite(?) sill ranging from 4.5 to 6 (5. 25)?

ft in thickness separates beds Rt-45 

and To-47.

Retort Phosphatic Shale Member of Phosphoria Formation:

Rt-45-___--___ Phosphorite: hard, dark-gray (N 3), 

thick-bedded, medium-pelletal.

44_________ Phosphorite: argillaceous, hard, darkgray (N 4), thick-bedded. 1

(43)-_---__- Rhyoiite(?) sill, 1.2 ft thick, separates (1. 2)? 

beds Rt-42 and Rt-44.

42_________ Mudstone: phosphatic, medium-hard,

weak-yellowish-orange (10 YR 7/6), 

thin-bedded; apatite is finely pelletal. 2

41 _________ Mudstone: medium-hard, light-brown

(7.SYR 6/4), thick-bedded.

40_________ Mudstone: soft, light-gray (A 7), thinbedded.

39_________ Chert: phosphatic, soft, medium-gray

(N 6), thick-bedded; apatite is finely 

pelletal.

38_________ Mudstone: soft, yellowish-gray (2.5F

7/2), thick-bedded.

See footnotes at end of table.

Uranium

Thick- C 

ness 

(jeet)

11.0 

16.0 

11.0 

20.0 

22. 0

28. 0 

32. 5 

3. 5

(5. 25)?

. 6 

. 8 

(1. 2)? 

1. 4

1. 1 

3.0 

1. 3

thickness 

(feet)

11. 0 

27.0 

38.0

58.0 

80.0

108.0 

140. 5 

144. 0

145. 6

147. 4

148. 8

149. 9 

152. 9 

154. 2 1

Labora- Acid metric 

Field tory P.Os insoluble e~U

TTTTJ ftOn QOTC Q 1 CQ C (\ (\C\~\

619 2977 . 9 92. 4 . 003

618 2976 30. 4 18. 9 . 006 

617 ---_ 29.4 21.5 .005 

616 ---_ 3.7 71.5 .003 

615 ____ 9. 7 58. 7 .005

614 ____ 1.4 76.8 .004 

613 ____ 5.6 64.4 .005

Chemical 

U

0. 005 

.005

. 005

. 003

612 8. 5 62. 2 005 .003

6
474 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Cave Creek, Mont., lot 1257 Continued

Bed Description

Retort Phosphatic Shale Member of Phosphoria Formation Continued 

Rt-(37) _______ Lens like bodies of rhyolite(?) as much

as 2.3 ft thick have been intruded 

between beds Rt-35 and Rt-38.

36_________ Mudstone: soft, light-gray (NT).....

35_ ________ Phosphorite: soft, yellowish-gray (2.5 Y

7/2), thick-bedded, medium-pelletal; 

contains a few apatite nodules as 

much as 60 mm in diameter.

34________- Mudstone: phosphatic, soft, yellowishgray (10 YR 7/1), thin-bedded; apatite is finely pelletal; contains a few 

apatite nodules as much as 30 mm in 

diameter.

33 _______ Phosphorite: argillaceous, mediumhard, yellowish-gray (2.5F7/2), thinbedded, medium-pelletal.

32_________ Mudstone: phosphatic, medium-hard,

yellowish-gray (2.5 Y 7/2), thinbedded; apatite is finely pelletal and 

is concentrated into poorly defined 

laminae.

31--------- Mudstone: phosphatic, medium-hard,

light-gray (N 8), thick-bedded; apatite is medium pelletal.

30_------__ Phosphorite: soft, weak-yellowishorange (2.5 Y 8/4), thick-bedded; 

medium-pelletal. Possil-colln. No. 

10836.

29___------ Mudstone: soft,weak-yellowish-orange

(2.5 Y 7/4), thin-bedded.

28__---_-__ Mudstone: phosphatic, soft, light-gray 

(N 7), thick-bedded; apatite is finely 

pelletal.

27-------_- Mudstone: soft,light-gray (N7), thickbedded. (Analysis may be in error.)

26_-__ --_- Phosphorite: argillaceous, soft, yellowish-gray (10Y72 8/1), thin-bedded, 

medium-pelletal.

25__---_-__ Phosphorite: medium-hard, yellowishgray (2.5 Y 7/2), thick-bedded, finely 

pelletal; contains a few apatite nodules as much as 60 mm in diameter.

24.________ Mudstone: phosphatic,soft.pale-brown

(10YR 6/2), fissile; fine-grained apatite pellets are concentrated in laminae.

23 _________ Phosphorite: argillaceous, mediumhard, light-gray (N7), thick-bedded, 

finally pelletal; grades from bed below.

22_--__--__ Mudstone: phosphatic, medium-hard, 

light-yellowish-brown (WYR 6/4), 

thick-bedded; apatite is very finely 

pelletal; contains a few apatite 

nodules as much as 45 mm in 

diameter.

21_________ Mudstone: soft, weak-yellowish-orange

(10 YR 7/6), thin-bedded.

20_--_____- Mudstone: phosphatic, soft, very pale 

orange (IOYR 8/2); apatite is finely 

pelletal.

Thick- Cumulative 

ness thickness

(feet) (feet)

(2. 3)?

4. 6 59. 4

. 8 160. 2

. 5 160. 7

. 5 161. 2

. 8 162. 0

. 4 162. 4

. 4 162. 8

. 3 163. 1

. 4 163. 5

. 4 163. 9

. 9 164. 8

. 8 165. 6

. 2 165. 8

. 4 166. 2

. 7 166. 9

. 5 167. 4

. 3 167. 7

Sample number

Chemical analyses (percent) 

Uranium

RadioLabora- Add metric Chemical 

Field tory P2O5 insoluble e~U U

ETR-611

610

1.8 76. 8 0.012 0.002

. 5 79. 5 . 003

609 ____ 32. 85 9.6 .007 .007

608 _-__ 15.85 43.5 .006 .003

607 _ _ _ _ 22. 1 33. 0 . 006 . 004

606 _ _ _ - 6. 7 66. 3 . 005 . 002

605 _ _ _ _ 23. 6 29. 0 . 007 . 005

604 __-_ 14.4 49.8 .005 .004

603 ---- 24. 6 25. 6 .007 .005

602 -___ 30. 7 15.0 .006 .004

601 2959 21. 1 34. 3 . 005 . 004

600 2958 11. 8 57. 0 . 005 . 003

599 2957 9. 4 71. 0 . 003
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 475

Cave Creek, Mont., lot 1257 Continued

Bed Description

Thick- Cumulative -

ness thickness

(feet) (feet)

Sample number

Chemical analysis (percent) 

Uranium

LaboraField tarry

PadicAeid metric Chemical 

P2Os insoluble eU U

Retort Phosphatic Shale Member of Phospharia Formation Continued 

Rt-19_________ Mudstone: phosphatic, medium-hard, 0.6 168.3

light-brownish-gray (10 YR 6/1), 

thin-bedded; apatite is medium 

pelletal; contains a few apatite 

nodules as much as 50 mm in 

diameter. (Analysis may be in 

error.) 

18__---____ Phosphorite: muddy, hard, light-gray .4 168.7

(N 7), thin-bedded, medium-pelletal. 

Fossil-colln. No. 10835.

17-__-_---_ Mudstone: phosphatic, medium-hard, .4 169.1 

pale-brown (2.5 Y 5/2), thin-bedded; 

apatite is finely pelletal; contains a 

few apatite nodules as much as 60 

mm in diameter. 

16-_-_-____ Mudstone: phosphatic, medium-hard, . 4 169. 5

very pale brown (10 YR 7/2), thickbedded ; apatite is finely pelletal.

15__-_--___ Phosphorite: muddy, soft, light-gray . 2 169. 7 

(N 8), thin-bedded, finely pelletal. 

Fossil-colln. No. 10834. 

14_________ Mudstone: phosphatic, medium-hard, .4 170.1

very pale brown (10F.R 7/2), thinbedded; apatite is finely pelletal. 

13_____-__- Mudstone: phosphatic, soft, light-gray . 9 171. 0

(N 8); apatite is finely pelletal. 

Fossil-colln. No. 10833. 

12___-----_ Phosphorite: muddy, medium-hard, 1.6 172. 6

light-gray (N 8), thin-bedded, finely 

pelletal. 

!!___--____ Phosphorite: muddy, soft, moderate- . 1 172. 7

yellowish-brown (10 YR 5/6), fissile, 

finely pelletal. 

10_________ Mudstone: phosphatic, soft, yellowish- . 6 173. 3

gray (2.5 Y 7/2),) thin-bedded; apatite is finely pelletal. Fossil-colln. 

No. 10832. 

9_--______ Mudstone: soft, yellowish-gray (2.5F 1.4 174.7

7/2, thick-bedded. 

8___-_-___ Mudstone: soft, light-brown (7.5YR .2 174.9

5/6, thin-bedded. 

7_________ Mudstone: phosphatic, soft, yellowish- 1.3 176.2

gray (2.5 Y 7/2), thin-bedded; apatite 

is finely pelletal. 

6_________ Mudstone: soft, yellowish-gray (2.5F

7/2), thin-bedded; contains a few 

apatite nodules as much as 130 mm 

in diameter. 

5_ ________ Phosphorite: muddy, medium-hard, .3 177.2

dark-gray (./V4), thin-bedded, nodular and finely pelletal; nodules are as 

much as 50 mm in diameter. 

4_________ Phosphorite: sandy, soft, yellowish- .9 178.1

gray (2.5F/72), thin-bedded; grades 

from bed below. 

3_________ Sandstone: phosphatic, yellowish-gray 2.2 180.3

(10 YR 7/1), thick-bedded, mediumgrained; irregular contact with bed 

below. 

_________ Similar to bed Rt-3-------_--------- .4 180.7

Franson Tongue of Park City Formation,

uppermost bed: 

-------__ Sandstone: cherty(?)-_-----_------__- .9 181.6

3, 1.6 percent; Fe2Os, 1.24 percent; loss on ignition, 2.25 percent. 

3, 1.8 percent; Fe2Os, 1.00 percent; loss on ignition, 2.18 percent.

ETR-598 2956 2. 0 59. 5 0. 005 0. 003

597 2955 24. 5 25. 7 . 007 . 006

596 2954 10. 5 57. 8 . 006 . 004

595 2953 18. 7 38. 4 . 008 . 006

594 2952 14. 7 45. 1 . 008 . 005

593 2951 14. 9 44. 4 . 006 . 004

592 2950 18. 4 39. 7 . 007 . 005

591 2949 13. 8 51. 3 . 007 . 005

590 2948 4.8 61.4 .004 ____

589 2947 13. 6 44. 6 . 005 . 003

5882946 6.4 62.3 .004 ____

587 2945 29.4 21.6 .004 _______

586 2944 20. 2 45. 4 . 004
476 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Little Sheep Creek, Mont., lots 1294 and 1295

[Permianrocks measured at Little Sheep Creek, Beaverhead County, Mont, on south end of major anticlinal structure. Beds Q-l to R-65 (lot 1294) measured from bulldozer 

trench, and beds R-66 to F-79 from natural exposure near Middle Fork of Little Sheep Creek, SWJ-i sec. 34, T. 14 S., R. 9 W. Beds strike N. 50° W. and dip 25° SE. 

Beds F-80 to To-119 (lot 1295) measured from bulldo-er trench near West Fork of Little Sheep Creek, S J-i sec. 33, T. 14 S., R. 9 W. Beds strike N. 80° E. and dip 10° S. 

Measured by E. R. Cressman, W. H. Wilson, and C. W. Tandy, and sampled by W. J. Garmoe, B. K. Replogle, R. F. Gosman, and J. L. Elliott, in July 1949. Samples 

analyzed for PzOs and acid insoluble by U.S. Bur. of Mines and for uranium by U.S. Geol. Survey]

Chemical analyses (percent)

Bed

To-119_.

117.

116.

112.

111.

110.

Cs-109_

Rt-108_

107-

(106).

105_

104. 

103 _

102_ 

101.

100. 

99..

98. 

97.

Description

Tosi Chert Member of Phosphoria Formation; upper part not exposed:

Chert: muddy, medium-hard, grayishbrown (2.5F 4/2), thin-bedded.

Chert: muddy, medium-hard, palebrown (2.5F 5/2), thin-bedded.

Chert: muddy, dolomitic, mediumhard, grayish-brown (2.5F 4/2), 

thick-bedded.

Chert: silty, medium-hard, grayishbrown (2.5F3/2), thin-bedded.

Dolomite: medium-hard, grayishbrown (10 YR 4/2), very thick-beded, aphanitic; pinches out along 

strike.

Chert: muddy, medium-hard, grayishbrown (2.5F 3/2), thin-bedded; in 

fault contact with unit below.

Chert: muddy, medium-hard, brownish-gray (10 YR 3/1), thin-bedded.

Chert: muddy, medium-hard, palebrown (10 YR 6/2), thin-bedded. 

Fossil-colln. No. 11663.

Chert: muddy, medium-hard, grayishbrown (2.5 F 3/2), thin-bedded. 

Fossil-colln. No. 11662.

Chert: muddy, medium-hard, brownish-gray (10 YR 4/1), thin-bedded. 

Fossil-colln. No. 11661. 

Cherty shale member (?) of Phosphoria Formation:

Mudstone: cherty, medium-hard, palebrown (2.5 F 4/2), thin-bedded. Fossil-colln. No. 11660.

Retort Phosphatic Shale Member of Phosphoria Formation:

Mudstone: medium-hard, black (AT 2), 

thin-bedded; basal 0.1 ft of bed is 

crumbly and may be a shear zone. 

Fossil-colln. No. il659.

Mudstone: medium-hard, black (AT 2), 

thin-bedded. Fossil-colln. No. 11658.

Covered: (Beds Rt-105 and Rt-107 

are separated by a covered interval 

and by at least one fault of unknown 

displacement.)

Mudstone: medium-hard, brownishgray (10 YR 4/1), thin-bedded.

Mudstone: crumbly, black (N 2)_-___

Mudstone: soft, dusky-brown (10F.R 

2/2), thick-bedded.

Mudstone: crumbly, black (N 2)_--__

Mudstone: medium-hard, black (N 2), 

thin-bedded.

Mudstone: crumbly, black (A7 2)_--_-

Mudstone and phosphatic mudstone, 

inter bedded: soft dusky-brown 

(WYR 2/2) thin-bedded phosphatic 

mudstone interbedded with mediumhard black (N 2) thin-bedded mudstone; apatite is finely pelletal; 

grades from bed below.

Carbonate rock: phosphatic, muddy, 

crumbly, brownish-gray (10 YR 3/1); 

apatite is finely pelletal.

Mudstone and phosphorite: bed is 

faulted and weathered; so, that 

detailed logging is not possible.

Cumulative 

Thickness thickness 

(feet) (feet)

Uranium

Sample

Acid Radiometric Chemical 

insoluble eU U

7. 1 

3. 9 

3. 5

4.0 

1. 3

14.0

8.0

5. 5

10. 4

15.0

2. 3

5. 3

3.7 

1. 1

. 4 

. 2

1. 7

2. 0

7. 1 

11.0

14. 5

18. 5

19. 8

38. 6

46. 6

52. 1

62. 5

77. 5

79. 8 ERG-358

85. 1 357

2. 0 53. 6 0. 002

5. 5 46.0 002

2. 0

89. 9

90.0

90. 4

90. 6

92. 3

94. 3

95. 0

97. 0

356 1. 0 84. 5 001

355 1. 3 59. 2 003

354 3. 8 54. 2 004

353 6. 7 41. 9 004

352 11.5 20.9 .004

351 10. 7 41. 1 004
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 477

Little Sheep Creek, Mont., lots 1294 and 1295 Continued

Chemical analyses (percent)

Bed

Rt-96. 

95_

94- 

93-

92. 

91.

90-

87. 

86_ 

85-

84_ 

83- 

82- 

81.

F-80- 

79.

78.

77. 

76. 

75.

98. 5

99. 9

Cumulative 

Thickness thickness 

Description (feet) (feet)

Mudstone: carbonatic, soft, weak-yel- 0. 8 97. 8 ^ 

lowish-orange (10 F^ 7/6), thickbedded.

Limestone: phosphatic, medium-hard, .2 98. 0 

yellowish-gray (10F.K 7/1), thinbedded; apatite is very finely pelletal ; bed is locally brecciated and is 

in fault contact with unit below.

Limestone: muddy, soft, weak-yellow- . 5 

ish-orange (10 F^ 7/6), thick-bedded.

Mudstone: phosphatic, calcareous, 1. 4 

crumbly, light-brownish-gray (10F.B 

7/1); apatite is finely pelletal. Fossilcolln. No. 11657.

Mudstone: crumbly, light-brown . 4 100. 3 

(7.5F^ 5/4), fissile.

Phosphorite: silty, crumbly, very pale . 2 100. 5 

brown (10F^ 7/2), nodular and 

finely pelletal.

Mudstone: plastic, moderate-reddish- . 1 100. 6 

brown; grades from bed below.

Phosphorite and mudstone, inter- 1. 7 102. 3 

bedded: crumbly yellowish-gray 

(10 F^ 7/1) thick-bedded finely pelletal muddy phosphorite interbedded 

with crumbly grayish-brown (7.5 YR 

3/2) finely pelletal phosphatic mudstone; grades from bed below.

Mudstone: plastic, moderate-yellow- .5 102. 8 

ish-brown (10F.K 5/6), fissile; bed is 

sheared.

Mudstone: soft, grayish-brown (10F.B 

4/2).

Phosphorite: soft, brownish-gray 

(10F.K 3/2), finely pelletal.

Mudstone: phospbatic, soft, moderatebrown (7.5YR 4/4); apatite if finely 

pelletal.

Phosphorite: soft, brownish-gray 

(10F^ 3/2), finely pelletal; grades 

from bed below.

Mudstone: soft, light-brown (7.5YR 

5/4), thin-bedded; grades from bed 

below.

Mudstone: phosphatic, soft, grayishbrown (7.5F.K 3/2), fissile; apatite 

is finely pelletal.

Phosphorite: sandy, medium-hard, 

dark-gray (V 3), thick-bedded; most 

of apatite is apparently aphanitic; 

sand is fine; contains glauconite and 

phosphorite nodules as much as 15 

mm in diameter. Fossil-colln. No. 

11656. 

Franson Tongue of Park City Formation:

Limestone: medium-hard, light-brownish-gray (10F^ 6/1), thick-bedded, 

granular.

Limestone: hard, very pale orange 

(7.5F.R 8/2), very thick bedded; contains up to 20 percent of recognizable 

bryozoan fragments. Fossil-colln. 

No. 11653.

Limestone: hard, very pale orange 9. 0 123. 7 

(7.5F^ 8/2), very thick bedded, 

skeletal; contains a few interbeds of 

chert.

Limestone: hard, light-brownish-gray 4. 6 128. 3 

(10 F^ 5/1), very thick bedded, 

skeletal. Fossil-colln. No. 11652.

Limestone: cherty, silty, hard, light- 31. 0 159. 3 

brown (7.5F^ 6/4), thick-bedded, 

aphanitic.

Siltstone: carbonatic, hard, pale-brown 25. 0 184. 3 

(10F^ 6/2), thick-bedded. Fossilcolln. No. 11651.

Sample

345

Uranium

Acid Radiometric Chemical 

insoluble eTT U

ERG-350 14. 3 26. 9 0. 002

349 2.

348 10.

5 20. 3 . 001

6 45. 1 . 007

. 2

. 2

. 1

. 4

. 5

. 6

1. 1

103. 0 '

103. 2

103. 3

103.7

104. 2

344 23.

343 6.

104. 8 342 8.

105. 9 341 16.

1. 8 107. 7 340 

7.0 114.7 ___.___.__

347 8. 6 54. 9 . 004

346 17. 0 37. 1 006

1. 5 72. 9 . 003

7 23. 7 007

7 63. 2 003

5 56. 3 . 005

9 25. 4 . 009

5. 0 .001

709-931 O 63- -14
478 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Little Sheep Creek, Mont., lots 1294 and 1295 Continued

Chemical analyses (percent)

Bed Description

Franson Tongue of Park City Formation 

Continued 

F-73_ _________ Limestone and chert, interbedded:

very pale orange (7.5 YR 8/2) thickbedded skeletal limestone interbedded with very pale orange (10 YR 

8/2) thick-bedded chert. Fossilcolln. No. 11650. 

74__________ Limestone: hard, light-brownish-gray

(IOYR 5/1), very thick bedded, 

finely skeletal; contains approximately 30 percent recognizable 

brachiopod valves and fragments. 

Fossil-colln. No. 11649.

72__________ Limestone: medium-hard, yellowishgray (2.5 YR 8/2), thick-bedded, 

skeletal. 

?!__________ Dolomite: hard, yellowish-white (2.5F

9/2), very thick bedded, skeletal.

70__________ Dolomite: medium-hard, yellowishwhite (2.5 Y 9/2), very thick bedded, 

skeletal. 

69_ _________ Dolomite: hard, pale-brown (2.5 Y 6/2),

thick-bedded, aphanitic. 

68__________ Dolomite: hard, yellowish-gray (2.5 Y

8/2), very thick bedded, aphanitic. 

67__________ Sandstone: medium-hard, pale-brown

(IOYR 5/2), thick-bedded, finegrained. Fossil-colln. No. 11648. 

Rex Chert Member of Phosphoria Formation: 

(66).-____--_ Covered.._________________________

R-65__ ________ Chert: medium-hard, pale-orange

(7.5 YR 8/4), thin-bedded. 

64__________ Phosphorite: muddy, medium-hard,

light-gray (N 7), thick-bedded, finely 

pelletal. Fossil-colln. No. 11647. 

63__________ Phosphorite: sandy, medium-hard,

light-gray (N 7) to brownish-gray 

(IOYR 4/1), thin-bedded, nodular, 

skeletal, finely pelletal; nodules are 

as much as 5 mm in diameter; contains glauconite; irregular contact 

with bed below. 

62__________ Chert: hard grayish-brown (7.5F.B

4/2) thick-bedded chert interbedded 

with hard light-yellowish-brown 

(IOYR 6/4), thick-bedded chert. 

61__________ Mudstone: cherty, medium-hard,

brownish-gray (10F.R 4/1), thickbedded. 

60__________ Chert: hard dusky-brown (IOYR 2/2)

thin-bedded chert interbedded with 

hard light-brown (7.5YR 5/6) thinbedded chert. 

Meade Peak Phosphatic Shale Member of

Phosphoria Formation:

M-59_________ Phosphorite: muddy, crumbly, brownish-black (IOYR 2/1), thin-bedded, 

very finely pelletal. 

58_ ________ Mudstone: soft, pale-brown (IOYR

6/2) to moderate-yellowish-brown 

(IOYR 4/4), thin-bedded.

57_________ Mudstone: soft, moderate-yellowishbrown (IOYR 5/6), thin bedded. 

56_ ________ Mudstone: phosphatic, crumbly,

dusky-brown (IOYR 2/2), thin-bedded, very finely pelletal. 

55_ ________ Mudstone: soft, dark-yellowish-orange

(IOYR 6/8), thin-bedded.

54_ ________ Mudstone: phosphatic, soft, duskybrown (IOYR 2/2), thin-bedded. 

53_________ Mudstone: soft, dark-yellowish-orange

(IOYR 6/8), thin-bedded.

Cumulative 

Thickness thickness 

(feet) (feet)

11. 0 195. 3

6. 0 201. 3

4. 7 206. 0

7. 0 213. 0

4. 0 217. 0

12. 0 229. 0

12. 0 241. 0

4. 5 245. 5

30. 0 

6. 0

275. 5

281. 5

1. 1 282.

282. 8

13. 3 296. 1

9. 3 305. 4

8 306. 2

8 307. 0

307. 7}

1. 8 309. 5 

. 3 309. 8\

1.4 311.2

. 5 311. 71

.2 311.91

Uranium

Sample

Acid 

insoluble

Radiometric Chemical 

eU U

CWT-339

338

337

336

335

334

333

332

331

0.6

25.3

88. 7 0. 001

2.9

16. 5

8. 3

9. 2

17. 8

92. 5

87.2

83. 8

39. 5

79. 7

62. 3

51. 8

008

001

002

002

Oil

003

006

007

0. 008

Oil

006

006
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 479

Little Sheep Creek, Mont., lots 1294 and 1295 Continued

Chemical analyses (percent)

Uranium

Bed Description

Meade Peak Phosphatic Shale Member of

Phosphoria Formation Continued

M-52- ________ Mudstone: phosphatic, soft, duskybrown (10 YR 2/2), thin-bedded.

51_________ Phosphorite: crumbly, dusky-brown

(10 YR 2/2), thin-bedded, mediumpelletal. Fossil-colln. No. 11646.

50_________ Mudstone: soft, moderate-yellowishbrown (10 YR 5/6), thin-bedded.

49_________ Phosphorite: siltv, soft, dusky-brown

(IQYR 2/2), thin-bedded, finely pelletal. Fossil-colln. No. 11645.

48--__-_.__ Phosphorite: crumbly, brownish-gray 

(IQYR 3/1), thick-bedded, skeletal, 

and coarsely pelletal and oolitic.

47_________ Phosphorite and mudstone, interbedded: soft medium-gray (N 5) thinbedded nodular and finely pelletal 

phosphorite interbedded with soft 

grayish-brown (7.5YR 3/2) to weakyellowish-orange (IQYR 7/6) thinbedded phosphatic mudstone; nodules are as much as 3 mm in diameter.

46 _________ Phosphorite: crumbly, medi um-gray

(N 5), thick-bedded, coarsely pelletal.

45_-------- Phosphorite: medium-hard, mediumgray (N 5), thick-bedded, skeletal, 

finely pelletal and oolitic. 

Grandeur Tongue of Park City Formation;

basal part not exposed: 

G-44__________ Sandstone: medium-hard, very pale

brown (IQYR 7/2), thin-bedded, 

very fine grained; contains phosphatic skeletal fragments; grades 

from bed below.

43__________ Sandstone: dolomitic, hard, yellowish,

gray (10 YR 8/1), very fine grained; 

beds G-42 and G-43 are separated 

by a block of dolomite 3 ft thick that 

is bounded by faults and is probably 

equivalent to part of bed G-42. 

Scattered phosphatic skeletal fragments in the upper part of bed G-42 

indicate that little or no thickness is 

missing.

42__________ Dolomite: hard, pale-brown (2.5Y 6/2),

very thick bedded, aphanitic.

41__________ Mudstone: dolomitic, crumbly, yellowish- gray (2.5 YR 7/2), thin-bedded.

40___-______ Carbonate rock: hard, light-brownishgray (IQYR 6/1), thick-bedded, aphanitic.

39_--------- Mudstone: medium-hard, light-pinkish-gray, thin-bedded.

38______-___ Mudstone: dolomitic, medium-hard,

yellowish-gray (IQYR 7/1), thickbedded.

37_----_____ Mudstone: dolomitic, medium-hard, 

dusky-pink, thick-bedded.

36_ _________ Mudstone: dolomitic, medium-hard,

weak-yellowish-orange (2.5Y 7/4), 

thin-bedded.

35____-____- Mudstone: dolomitic, medium-hard, 

moderate-reddish-brown (10 YR 5/4), 

thin-bedded.

34__________ Similar to bed G-35- _______________

33____ ______ Mudstone: dolomitic, medium-hard,

moderate-reddish-brown (IQYR 5/4), 

thin-bedded.

32__________ Similar to bed G-33_ ______-__-___-_

31-.___-_-__ Mudstone: dolomitic, soft, weak-yellowish-orange (2.5 Y 7/4), thin-bedded.

Cumulative 

Thickness thickness 

(feet) (feet)

0. 6 312. 5

1. 3 313. 8

1. 4 315. 2

1. 5 316. 7

1. 2 317. 9

. 8 318. 7

Sample

CWT-330 

329

328

327

ERG-326 

325

Acid Radiometric Chemical 

P.Os insoluble «U U

9. 4 44. 8 0. 008

26. 5 16. 0 . 018

6. 4 65. 3 . 006

20. 3 24 3 . 007

33. 0 1. 7 . 008

21. 2 28. 5 . 008

0. 006

. 017

. 004

. 006

. Oil 

. 008

. 3 319. 0

1. 2 320. 2

. 2 320. 4

6. 0 326. 4

324 32. 4 5. 0 . 008 .008

10. 6

Q o

4. 7

. 1

. 9

. 3 

ft 9

4. 8

1 1 9

1 Q 4.

10.0

. 2

QQ.7 f)

340.0

0.4.4. 7

344. 81 

345. 7

346.0

QCO 9

o r 17 f\

QftO O

001 /?

391. 6

391. 8

CWT-323

 pp-pf* 099

 391

090

CWT 319

01 O

QI 7

T?~D f~* Q1 K

QI C

. 3

9

. 1

. 1

9

. 1

.0

.0

. 1

1

cc

3

9c

PL7

63.

70.

79

64.

5

7

7

1

1

7

Q

0

.001 _______

.002 _______

.0005 -------

.002 __--__.

.002 _______

.002 _______

.004 _______

.001 ___----

.002 _____--
480 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Little Sheep Creek, Mont., lots 1294 and 1295 Continued

Chemical analyses (percent)

Cumulative 

Thickness thickness 

Bed Description (feet) (feet)

Grandeur Tongue of Park City Formation;

basal part not exposed Continued 

G-30-_________ Dolomite: medium-hard, yellowish- 1.3 393. 1

white (WYR 9/1), thick-bedded, aphanitic.

29__________ Mudstone: calcareous, medium-hard, 1. 2 394. 3

weak-yellowish-orange (2.5F 8/4), 

thick-bedded.

28_-_--_____ Mudstone: calcareous, hard, light-gray .7 395.0 

(N 8), thick-bedded; contains a few 

irregular nodules of chert; irregular 

contact with bed below.

27_---______ Dolomite: hard, very pale orange 6.3 401.3

(WYR 8/2), thick-bedded, aphanitic; 

contains many chert nodules averaging 0.3 ft in diameter.

26 ------- Dolomite: hard, yellovish-gray (2.5 Y 2.1 403.4

8/2), very thick bedded, aphanitic.

25__________ Dolomite: muddy, medium-hard, weak .8 404.2

yellowish-orange (2.5F 8/4), thinbedded, aphanitic.

24__-_______ Dolomite: muddy, very pale orange 1. 6 405. 8

(WYR 8/2), thick-bedded.

23__-------- Dolomite: hard, very pale orange 3.5 409.3

(WYR 8/2), thick-bedded, aphanitic. 

Fossil-colln. No. 11644.

22._________ Dolomite: medium-hard, yellowish- 7.1 416.4

gray (2.5 Y 8/2), thick-bedded, aphanitic; contains chert nodules averaging about 0.1 ft in diameter.

21__________ Limestone: dolomitic, medium-hard, yel- 5.6 422.0

lowish-gray (WYR 8/1), thin-bedded; 

in fault contact with unit below.

20__________ Limestone: medium-hard, yellowish- 3. 8 425. 8

gray (WYR 8/1), thin-bedded, aphanitic; in fault contact with unit below.

19___ ______ Dolomite: medium-hard, yellowish- 1. 8 427. 6

gray (2.5 Y 7/2), thick-bedded, aphanitic; contains numerous chert nodules averaging 0.2 ft in diameter.

18__________ Dolomite: medium-hard, very thick 14.4 442.0

bedded, aphanitic; color ranges from 

pale-brown (2.5F 5/2) at base to 

light-gray (N 7) at top. Fossilcolln. No. 11643.

17__________ Limestone: hard, pale-brown (WYR 2.0 444.0

6/2), thick-bedded. Fossil-colln. No. 

11642.

16_________ Limestone: cherty, hard, light-brown- 2. 1 446. 1

ish-gray (WYR 6/1), very thick 

bedded.

15__________ Limestone: muddy, hard, grayish-brown 1.4 447.5

(2.5F3/2), very thick bedded, aphanitic; in fault contact with unit 

below.

14__________ Dolomite: medium-hard, yellowish- 2.4 449.9

gray (2.SYR 8/2), very thick bedded.

13_-----____ Dolomite: muddy, medium-hard, yel- 1.8 451.7 

lowish-gray (2'.5YR 8/2), very thick 

bedded, aphanitic.

12__________ Mudstone: calcareous, soft, weak-yel- .2 451.9

low ish-orange (2.5F 7/4), thinbedded.

!!__________ Dolomite: calcareous, muddy, medium- 1.7 453.6

hard, very pale orange (1QYR 9/2), 

thin-bedded, aphanitic.

10_-----___- Sandstone: calcareors, hard, yellowish- 7.4 461.0 

white (WYR 9/1), thick-bedded, 

cross-bedded, fine-grained; in fault 

contact M ith unit below .

9__----_____ Sandstone: calcareous, hard, very pale 2.3 463.3 

orange (WYR 8/2), thin-bedded, finegrained.

Uranium

Sample P.05

Acid 

insoluble

Radiometric Chemical 

eTJ U
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 481

Little Sheep Creek, Mont., lots 1294 and 1295 Continued

Bed

Cumulative 

Thickness thickness 

Description (feet) (feet)

Grandeur Tongue of Park City Formation; 

basal part not exposed Continued

Sandstone: soft, pale-yellovrish-orange 7. 5 470 8 

(2.5 Y 9/4), thick-bedded, finegrained.

Sandstone: soft, pale-yellovrish-orange 7. 8 478. 6 

(2.5 Y 9/4), thick-bedded, finegrained.

Limestone: sandy, hard, yellowish-gray 3. 0 481. 6 

(IOYR 7/1), thin-bedded; sand is 

fine; irregular contact with bed 

below.

Dolomite: silty, hard, yellowish-gray 2. 5 484. 1 

(10 YR 7/1), very thick bedded, 

aphanitic.

Siltstone: crumbly, light-yellowish- . 3 484.4 

brown (2.5 Y6/4).

Dolomite: hard, light-brownish-gray . 5 484.9 

(10 YR 6/1), thick-bedded, aphanitic.

Dolomite: silty, hard, pale-brown(2.5 Y . 2 485. 1 

6/2), fissile, aphanitic.

Dolomite: hard, yellowish-gray 2. 1 487. 2 

(10YR 7/1), thick-bedded, aphanitic; 

contains a few chert nodules as much 

as 0.1 ft in diameter; underlying beds 

are covered.

Chemical analyses (percent)

Uranium

Acid Radio-metric Chemical 

insoluble eU U

Crooked Creek, Mont., lots 1296 and 1297

[Grandeur Tongue of Park City Formation and parts of Phosphoria Formation measured in two bulldozer trenches near the head of Crooked Creek SWH sec. 1, T. 15 S., 

R. 8 W., Beaverhead County, Mont., from southeastward-dipping strata near the south end of a large anticlinal structure. Beds Q-l through F-69 (lot 1296) measured 

at upper trench from beds striking N. 60° E. and dipping 65° SE; beds Rt-71 through To-107 (lot 1297) described at the lower trench (350 feet east of upper trench) from 

overturned beds striking N. 50° E. and dipping 70° NE. Retort Phosphatic Shale Member of the Phosphoria Formation is so strongly sheared that the thickness and 

stratigraphic sequence may be incorrect. Section measured by E. R. Cressman and W. H. Wilson and sampled by J. L. Elliott, B. K. Replogle, and W. J. Garmoe, 

in July 1949. Samples analyzed for P2 O5 and acid insoluble by U.S. Bur. of Mines and tor uranium by U.S. Geol. Survey]

To-107.

106.

Rt-105---

102_ 

101- 

100.

99_- 

98_. 

97.-

Description

Tosi Chert Member of Phosphoria Formation, lower part:

Chert: muddy, hard, grayish-brown 

(10YR 4/2), thick-bedded; grades 

from bed below; overlying beds are 

covered.

Chert: argillaceous, hard, grayishbrown (IOYR 4/2), thick-bedded. 

Retort Phosphatic Shale Member of Phosphoria Formation:

Mudstone: phosphatic, crumbly, 

dusky-brown (10 YR 3/2), thin-bedded; apatite is very finely pelletal.

Mudstone: plastic, moderate-yellowish-brown (10 YR 5/6).

Mudstone: dusky-brown (10 YR 3/2), 

fissile; contains a few irregular laminae of very fine grained apatite 

pellets.

Mudstone: soft, duskv-brown (IOYR 

3/2).

Mudstone: plastic, moderate-yellowish-brown (10 YR 5/6).

Mudstone: phosphatic, soft, duskybrown (10 YR 3/2); grades from bed 

below.

Mudstone: soft, moderate-yellowishbrown (10 YR 5/6).

Mudstone: soft, dusky-brown (IOYR 

3/2); grades from bed below.

Mudstone: soft, mottled brownishgray (IOYR 3/1) and pale-brown 

(IOYR 5/3); bedding is contorted 

and sheared.

Thickness 

(feet)

11.7

. 2

1.7

4. 1

.2

4.3

1.8 

1.7

4.8

Chemical analyses (percent)

Cumulative

thickness

(feet)

11.7

Uranium

Sample PsOs

Acid 

insoluble

Radiometric e~U

Chemical 

U

15. 2 26. 9 WHW-636 1.3

27.3

ERG-635

634

633

632

631

4.4

7.4 

13.7

7. 5 

6. 5

82.0

65. 5 0. 003

56. 1

45.8

53.9

48.0

004

004

004

004
482 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Crooked Creek, Mont., lots 1296 and 1297 Continued

Thickness 

Bed Description (feet)

Retort Phosphatic Shale Member of Phosphoria Formation Continued 

Rt-96 ________ Similar to bed Rt-97---------_---_- 3.8

95____---_- Similar to bed Rt-97_-__------------ 4.3

94____-___- Similar to bed Rt-97--------------_ 4.0

93.___-____ Mudstone: soft, mottled brownish- 3. 3 

gray (WYR 3/1) and pale-brown 

(10 YR 5/3), thick-bedded.

92__ _______ Mudstone: soft, mottled brownish- .9

gray (WYR 3/1), and pale-brown 

(10 YR 5/3); bedding is contorted 

and sheared, and nearly every 

surface is slickensided.

91__-_-___- Mudstone: soft, mottled brownish- 4. 4 

gray (IQYR 3/1) and pale-brown 

(WYR 5/3); bedding is contorted 

and sheared, and nearly every surface is slickensided; contains several 

lenses averaging 0.2 ft thick and 1.0 

ft long of yello\\ish-gray (WYR 7/1) 

mudstone.

90___----_- Similar to bed Rt-91_- _----------- 4.5

89-_-_---__ Phosphorite: muddy, medium-hard 3. 5 

moderate yello\\ ish-brown (WYR 

5/6).

88----____- Mudstone: soft, black (N 2), thin- 5.0 

bedded; grades from bed below.

87____---__ Carbonate rock: muddy, phosphatic, 1.7 

soft, black (N 1), thick-bedded, 

aphanitic; apatite is medium pelletal.

86 _________ Mudstone: medium-hard, ff ray ish-brown 3. 7

(7.5 YR 4/2), thick-bedded; grades 

from bed below.

85_____---_ Phosphorite: muddy, medium-hard, . 3 

brownish-gray (WYR 3/1), thinbedded.

84.________ Phosphorite: muddy, soft, moderate- .5

yellowish-brown (WYR 5/6), thinbedded.

83_-------- Dolomite: muddy, soft, pale-brown 1.2

(WYR 5/3), thick-bedded, aphanitic.

82_________ Phosphorite: muddy, soft, weak-yellow- 1. 3

ish-orange (WYR 7/6), thick-bedded.

81_________ Mudstone: phosphatic, carbonatic, soft, 1. 2

moderate-yellowish-brown (WYR 

5/6).

80___-_---- Phosphorite: crumbly, brownish-gray . 2 

(WYR 4/1), thick-bedded, mediumpell etal.

79____---_- Mudstone: soft, moderate-brown 1.0 

(7.5 YR 4/4).

78_____-___ Phosphorite: medium-hard, light- .5 

brownish-gray (WYR 5/1), thickbedded, medium-pelletal.

77_________ Mudstone: soft, moderate-yellowish- . 2

brown (WYR 5/6), thin-bedded

76_________ Phosphorite: medium-hard, brownish- . 1

gray (WYR 3/1), thin-bedded, medium-pelletal.

75_________ Mudstone: phosphatic, soft, moderate- . 6

yellowish-brown (WYR 5/6), medium-pelletal.

74. -------- Phosphorite: soft, light-brown (7.5 YR . 8

5/4^, finely pelletal.

73--_------ Phosphorite: medium-hard, light- .8

brov nish-gray (WYR 6/1), thickbedded, medium-pelletal.

72_____-_-_ Mudstone: soft, light-yellowish-brown 1. 6 

(WYR 6/4).

Chemical analyses

Cumulative

thickness

(feet)

62. 4

79.8

81. 5

85. 2

85. 5

86.0

90.9

91. 4

91. 6

91.7

92.3

Sample

49.9 ERG-630

54. 2 629 

58. 2 628 

61. 5\

627

626

71.3 625 

74. 8 WHW-624

623

622

621

384

383

87. 2

88. 5

89. 7 ERG-382

381

95. 5

380

379

378

Uranium

Acid Radio- Chemical 

insoluble metric e\J II

7. 1 48. 3 0. 004

6. 4 47. 3 . 004

5. 5 48. 3 . 004

3. 6 53. 1 . 003

7. 5 36. 0 . 005 0. 0005

7. 6 37. 4

14. 5 32. 9

7. 4 40. 7

8. 6 18. 7

5. 2 59. 6

.005

.004

.004

.004

.003

.005

18.3 31.3 .005 __---_-

8.1 48.0 .003 __-.--.

8.7 45.3 .004 ___--_.

18. 3 35. 3 . 006 . 005

13. 7 47. 0 . 006 .005

27. 9 14. 3 . 007 . 006

4.7 68.5 .004 _______
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 483

Crooked Creek, Mont., lots 1296 and 1297 Continued

Chemical analyses (percent)

Bed Description

Franson Tongue of Park City Formation,

basal beds:

F-71. ____-__- Sandstone: phosphatic, hard, lightbrown (7.5YR 5/4), very fine grained; 

contains glauconite.

(70)_________ Unknown stratigraphic interval between beds F-69 and F-71.

69-_____-__- Sandstone: dolomitic(?), hard, lightgray (N 7), thick-bedded, very fine 

grained. Fossil-colln. No. 11694.

68___------- Dolomite: hard, light-gray (JV7), thinbedded, aphanitic.

Rex Chert Member of Phosphoria Formation: 

R-67___ _______ Chert: brittle, light-brownish-gray

(1QYR 6/1), thin-bedded.

66__________ Dolomite: cherty, medium-hard, yellowish-gray (1QYR 7/1), thin-bedded; 

contains a few stringers and laminae 

of chert averaging 1 mm thick.

65_--_---__- Dolomite: hard, pale-brown (10 YR 

6/2), thick-bedded, aphanitic.

64__________ Mudstone: soft, pale-brown (7.5YR

5/2), thin-bedded.

63________ Chert: brittle, brownish-gray (10 YR

4/1), thick-bedded.

62__________ Mudstone: soft, pale-orange (7.5YR

8/4), thin-bedded; contains a few laminae of fine-grained apatite pellets.

61 __________ Phosphorite: soft, moderate-yellowishbrown (10 YR 4/4), thin-bedded, 

medium-pelletal.

60___ _______ Phosphorite: sandy, medium-hard,

dark-gray (N 4), thin-bedded, medium-pclletal; contains phosphatic 

skeletal fragments and a few angular 

chert fragments that average 7 mm 

in diameter.

59-_------__ Mudstone: soft, grayish-brown (7.5YR

4/2), fissile.

58__________ Chert: sandy, medium-hard, brownishgray (10KR 3/1), thin-bedded; sand 

is very fine.

57__________ Chert: soft, moderate-yellowish-brown

(10 YR 5/6), thick-bedded; bed is 

composed of a felted mass of siliceous 

sponge spicules.

56__________ Mudstone: soft, grayish-brown (2.5KB

3/2), thin-bedded; irregular contact 

with bed below.

55__________ Chert: hard, pale-brown (10YR 5/2),

thick-bedded.

54__________ Similar to bed R-55_ ________-_-_-_-

53__________ Similar to bed R-55; grades from bed

below. 

Meade Peak Phosphatic Shale Member of

Phosphoria Formation: 

M-52__________ Phosphorite: cherty(?), medium-hard,

medium-gray (N 5), thick-bedded, 

medium-pellet al.

51_ _________ Phosphorite: crumbly, pale-brown

(7.5 YR 6/2), thin-bedded; finely 

pelletal.

50__________ Mudstone: plastic, light-yellowishbrown (10 KB 6/4); grades from bed 

below.

(feet) 

5.9

11.4

. 5

3. 6

q Q

1. 2

. 7

.6

4. 3

1.0 

.05

.05 

. 1

.8 

. 2

5 A

o n

K K

. 4

. 2

thickness 

(feet)

101.4

112.8

113. 2

116.9

126.8

128.0

128. 7

129. 3

133. 6

134. 6 

134. 65

134. 7 

134. 8 '

135. 6

135. 8 

141. 2 '

144. 9

150.4

150. 8

151.0

Uranium

Acid Radio- Chemical 

Sample PsOs insoluble metric «TJ U

ERG-377 13. 6 35. 3 0. 009 0. 009

376 1.2 84.8 .003 _______

375 24.5 26.0 .002 _______

374 10. 9 58. 8 .007 . 005 

373 .3 89.0 .001 _______

372 .3 89.8 .001 _______

371 1.0 87.5 .002 _______

370 23.1 28.0 .001 _______

1. 9 152. 9 369 80. 8 .003 .002
484 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Crooked Creek, Mont., lots 1296 and 1297 Continued

Bed

M-49.

48- 

47.

46. 

45.

44_ 

43 _

42.

40. 

39- 

38. 

37.

36. 

35.

34.

33__. 

32--

31__ 

30__

29.

28.

Chemical analyses (percent)

Description

Meade Peak Phosphatic Shale Member of 

Phosphoria Formation Continued

Dolomite: muddy, medium-hard, lightyellowish-brown (10 YR 6/4), very 

thick bedded, aphanitic.

Phosphorite: soft, pale-brown (10 YR 

5/3), thin-bedded, finely pelletal.

Mudstone: dolomitic(?), soft, moderate-yellowish-brown (10 YR 5/6), 

thin-bedded.

Phosphorite: soft, pale-brown (10 YR 

5/3), thin-bedded, finely pelletal.

Mudstone: dolomitic(?), soft, moderate-yellowish-brown (1QYR 5/6), 

thin-bedded.

Phosphorite: crumbly, light-brownishgray (10 YR 5/1), finely pelletal.

Mudstone: dolomitic, soft, light-yellowish-brown (10 YR 6/4), thickbedded; grades from bed below.

Phosphorite: crumbly, yellowish-gray 

(10KB 7/1), medium-pelletal.

Mudstone: dolomitic, soft, light-yellowish-brown (10 YR 6/4), thinbedded.

Phosphorite: soft, pale-brown (1QYR 

6/2), thin-bedded, finely pelletal.

Mudstone: carbonatic, soft, weak-yellowish-orange (10 YR 7/6), thick-bedded.

Mudstone: plastic, grayish-brown 

(7.5 YR 3/2), thin-bedded.

Phosphorite: soft, yellowish-gray 

(IQYR 7/1), thin-bedded, mediumpelletal.

Mudstone: dolomitic, soft, light-brown 

(7.5YR 5/6), thin-bedded.

Mudstone: carbonatic, medium-hard, 

pale-brown (IQYR 6/2), very thick 

bedded.

Mudstone: carbonatic, soft, moderateyellowish-brown (10 YR 5/6), thickbedded.

Mudstone: plastic, grayish-brown 

(7.5 YR 3/2), thin-bedded.

Phosphorite: medium-hard, brownishgray (10 YR 3/1), thin-bedded, finely 

pelletal.

Mudstone: soft, light-brown (7.5YR 

5/6).

Phosphorite: medium-hard, brownishgray (10 YR 3/1), thin-bedded, finely 

pelletal. Fossil-colln. No. 11693.

Mudstone: soft, light-brown (7.5F.R 

5/6).

Phosphorite: medium-hard, lightbrownish-gray (IQYR 5/1), thinbedded, finely pelletal; contains phosphatic skeletal fragments and very 

fine quartz sand. Fossil-colln. No. 

11692.

Uranium

Sample

ERG-368

P2 05

0.0

Acid Radiometric Chemical

insoluble

36. 5 0. 001

U

. 1

. 4

. 1

. 3

. 2

0 Q

£t. O

. 2

. 9

. 2

. 6

. 2

. 1

1. 1

. 4

. 2

. 8

. 1 

. 5

. 1

. 5

154.3

154. 7

154. 8 

155. 1

155. 3 

157. 6

157. 8 '

158. 7

158.9

159. 5

159. 7

1 1DU. fifl 9£t

160. 3 >

161. 4

161. 8 '

162.0

162. 8 '

162. 9 

163.4

163.5

164.0

367 5. 9 59. 7 . 005 0. 004

366 2.1 64.5 .002 _______

365 5.8 49.7 .004 _______

364 7.9 46.5 .004 _______

363 27.1 11.6 .020 _______

362 6. 4 38. 0 . 005 . 004

361 3.9 58.0 .004 _______

360 31.2 6.2 .016 .016

359 27. 3 17. 2 . 007 . 007
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 485

Crooked Creek, Mont., lots 1296 and 1297 Continued

Chemical analyses (percent)

Bed 

G-27-_.___

26_______

25_______

24______.

23__-_-._

22_______

21______

20_ __ _

19. 

18------

17______

16__ __

15______

14_. ___

13__.__.

12.__.__

11____ 

10_____.

9

8-.___._

7

6-_-___ _

(5).._-__

4______.

3__ _

(2)

Q-l.._ .

1 

Description

Grandeur Tongue of Park City Formation:

pale orange (7.5 YR 8/2), thickbedded, very fine grained.

aphanitic.

ffiay (IOYR 6/1), thick-bedded, 

aphanitic.

8/2), very thick bedded, aphanitic.

brown (IOYR 7/2), thick-bedded, 

aphanitic.

gray (IOYR 6/1), thick-bedded.

thick-bedded. Fossil-colln. No. 11691.

(10 YR 8/2), very thick bedded, aphanitic.

7/2), thick-bedded, aphanitic.

(2.5 F 5/4), thin-bedded.

7/1), very thick bedded, aphanitic.

lowish-orange (2.5F 7/4), thinbedded.

7/1), thick-bedded, aphanitic. Fossil-colln. No. 11690.

orange (IOYR 8/2), thin-bedded.

orange (10 F^ 8/2), thin-bedded.

pale brown (IOYR 7/2), thickbedded, very fine grained.

pale orange (10 YR 8/2), very thick 

bedded, fine-grained.

bedded, aphanitic.

8/1), thick-bedded, aphanitic.

gray (2.5 F 8/2), very thick bedded, 

very fine grained.

gray (2.5 YR 8/2), thick-bedded, 

very fine grained.

lowish-gray (2.5F 8/2), very thick 

bedded, very fine grained.

8/2), thick-bedded, aphanitic.

gray (2.5F 8/2), very thick bedded, 

very fine grained.

Quadrant Formation: 

Sandstone: not measured. _ _

C

"hickness i 

(feet)

3.3

. 5 

. 6

2.0 

1. 3

8.9 

10. 0 

6.3

1. 6 

. 9 

3. 3 

4. 5

5.0

5.8 

6. 3 

8. 0

10. 6

7. 2 

7. 4 

14. 1

7. 5 

6. 0

10. 0 

12. 5

13. 2 

10. 0

Uranium

thickness Acid Radiometric Chemical 

(feet) Sample PtOs insoluble e\J U

167.3 __________ _---__ ______ ______ -._-_--

167.8 ___---_--. ______ ______ ______ _--_--_

168.4 __________ ______ ______ .__ __ _______

170.4 __________ --_-_. ______ ______ __-_--_

m 7

180.6 __________ ______ ______ ______ _______

190.6 __________ ______ ______ ______ __.--_-

IQfi Q

198.5 __________ ______ ______ ______ _______

1QQ 4

202.7 __________ ______ ______ ______ _______

207.2 __________ ______ ______ ______ _______

212.2 __________ ______ ______ ______ _______

218.0 ___-___--_ _---__ ______ ______ __.-_--

224.3 __________ ______ ______ ______ _______

232.3 __.__-___- ______ ______ ______ -___---

242. 9 _

250.1 __________ ------ ------ ------ -------

oc7 c

271.6 -_--_-_--_ ______ ______ ______ _______

279 1

285.1 ____------ __---- ______ ------ -------

295.1 ---------- ------ __---- ------ -------

307.6 -_-__-__-_ -_--_- --.__- ______ _______

320.8 _--_------ ------ ------ ------ -------

330.8 --__ _ _-_ ------ ------ ------ -------
486 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Hogback Mountain, Mont., lot 1299

[Permian rocks measured on Hogback Mountain, S^NW^ sec. 8, T. 11 S., R. 4 W., Madison County, Mont., on overturned west, limb of Ruby Valley syncline. Retort 

and Meade Peak Phosphatic Shale Members of Phosphoria Formation measured and sampled in hand trenches on east scarp of mountain; rest of section measured from 

natural exposure. Beds strike N. 40° E. and dip 50° W. Measured by W. II. Wilson, R. S. Jones, W. J. Garmoe, and B. K. Replogle and sampled by Replogle, J. L. 

Elliott, and R. F. Gosman, in August 1949. Petrographic descriptions by use of binocular microscope by E. R. Cressman. Analyzed for PzOs and acid insoluble by U.S. 

Bur. of Mines and for other constituents by U.S. Geol. Survey]

Chemical analyses (percent)

Bed

To-190_

Us-189-

To-188- 

187_ 

186- 

185- 

184_

Us-183- 

182-

To-180-

Us-179_

178_

177_ 

176_

175_

Description

Tosi Chert Tongue of Phosphoria Formation; includes two thin tongues of Shedhorn Sandstone:

Siltstone: carbonatic, sandy, mediumhard, pale-brown (2.5F 5/2), thinbedded; contains glauconite. Fossilcollection number 11680. Overlying 

beds covered; top of bed To-190 may 

be Dinwoody contact.

Sandstone; cherty, carbonatic, medium 

hard, light-yellowish-brown (2.5F 

6/4), thin-bedded, very fine grained; 

contains glauconite.

Chert: sandy, medium-hard, brownishgray (10 YR 4/1), thin-bedded; contains glauconite; sand is very fine.

Mudstone: medium-hard, pale-brown 

(2.5F 5/2), thin-bedded; contains 

glauconite.

Chert: carbonatic, hard, brownish-gray 

(10 YR 3/1), thin-bedded to fissile; 

contains glauconite.

Chert: calcareous, medium-hard, lightbrownish-gray (10 YR 5/1), fissile; 

contains glauconite.

Chert: carbonatic, hard, grayish-brown 

(10 YR 4/2), thin-bedded; contains 

glacuconite.

Sandstone: hard, pale-brown (7.5YR 

6/2), thick>bedded, medium-grained; 

contains glauconite.

Sandstone: cherty, carbonatic, hard, 

grayish-brown (10 YR 4/2), thinbedded, fine-grained; contains glauconite.

Sandstone: hard, light-olive-gray (5F 

5/2), thin-bedded, fine-grained; contains glauconite and phosphatic 

skeletal fragments.

Chert: carbonatic, brittle, grayishbrown (10 YR 4/2), thin-bedded; contains glauconite.

Upper tongue of Shedhorn Sandstone; contains several beds of Tosi Chert Member 

of Phosphoria Formation.

Sandstone: hard, light-olive-brown 

(2.5F 5/4), very thick bedded, very 

fine grained; contains glauconite; 

grades from bed below.

Sandstone: medium-hard, light-yellowish-brown (2.5F 6/4), very thick 

bedded, fine-grained; contains glauconite; contains columnar bodies of 

sandstone(?) 10 mm in diameter and 

1.0 ft long, some of which branch 

outward at base of column.

Sandstone: hard, pale-brown (2.5F 6/2), 

thick-bedded; irregular contact with 

bed below.

Dolomite: sandy, hard, pale-brown 

(10 YR 6/2), very thick bedded, finegrained; sand is very fine.

Sandstone: medium-hard, pale-brown 

(2.5F 5/2), very thick bedded, finegrained; contains lenses of finegrained yellowish-gray (2.5F 7/2) 

sandstone; irregular contact with bed 

below. Fossil-collection number 

11679.

Thick- Cumulative

ness thiclcness

(feet) (feet)

7. 3

. 8

2.9

. 5

1. 0

1. 6

1. 5

. 5

1. 9

. 5 

3. 4

7. 3

8. 1

11. 0

11. 5

12. 5

14. 1

15.6

16. 1

18. 0

18. 5

21. 9

5. 9 27.

15. 5 43. 3

1. 5 44. 8

3. 3 48. 1

7. 5 55. 6

Uranium

ftample P2 05 f

Acid Organic Radiometric Chemical 

nsoluble matter eV TT
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 487

Hogback Mountain, Mont., lot 1299 Continued

Chemical analyses (percent)

Tied Description

Upper tongue of Shedhorn Sandstone; contains several beds of Tosi Chert Member 

of Phosphoria Formation Continued 

To-174.______ Chert: sandy, hard, pale-brown (2.5F

5/2), thick-bedded.

173_----__ Chert: sandy, ^ hard, yellowish-gray 

(IOYR 7/1), thick-bedded.

172-_____- Chert: sandy, hard, light-brownishgray (IOYR 6/1), thick-bedded; 

irregular contact with bed below.

Us-171____-__ Sandstone: hard, pale-brown (IOYR 

5/3), very thick bedded, fine-grained; 

grades from bed below.

170_------ Sandstone: hard, weak-yellowishorange (2.51" 7/4), very thick bedded, 

fine-grained; contains a few chertnodules 0.3 ft in diameter.

160_______ Sandstone: hard, weak-yellowishorange (2.5}" 7/4), very thick bedded, 

fine-grained; contains a few chert 

nodules elongated parallel to bedding.

168_______ Chert: sandy, hard, thick-bedded; sand

is very fine.

167___-___ Sandstone: hard, very pale brown 

(IOYR 7/2), fine-grained; contains a 

few chert nodules 0.2 ft in diameter.

166__---_- Sandstone: hard, light-yellowishbrown (IQYR 6/2), thick-bedded, 

fine-grained; irregular contact with 

bed below.

165_------ Sandstone: cherty, hard, light-gray

(N 7), thick-bedded, fine-grained; 

irregular contact with bed below.

164__--_-_ Sandstone: cherty, hard, pale-brown 

(IOYR <ol2), thick-bedded, very fine 

grained; contains irregular bodies of 

sandy chert; irregular contact with 

bed below.

163 _______ Chert: sandy, hard, brownish-gray

(IOYR 4/1), thin-bedded; contains a 

few columnar bodies of chert 0.25 ft 

diameter and 0.3 ft long; irregular 

contact with bed below.

162__-____ Sandstone: hard, pale-brown (IOYR 

6/2), thick-bedded, very fine grained; 

contains glauconite; irregular concontact with bed below. Fossilcollection number 11678. 

Retort Phosphatic Shale Tongue of the

Phosphoria Formation:

Rt-161_____-_ Phosphorite: muddy, soft, grayishbrown (7.SYR 4/2), fissile, finely 

pelletal.

160_----_- Phosphorite: medium-hard, grayishbrown (IOYR 4/2), thin-bedded, 

finely pelletal.

159______- Phosphorite: hard, light-brownishgray (IOYR 6/1), thin-bedded, finely 

pelletal.

158-______ Mudstone: soft, very pale brown

(IOYR 7/3), thin-bedded.

157_------ Mudstone: Phosphatic, medium-hard

dark-gray (N 3;, thin-bedded; apatite is medium-oolitic and pelletal.

156_----__ Mudstone: phosphatic, soft, palebrown (IOYR 5/3), thick-bedded; 

apatite is medium-pelletal.

155__-____ Dolomite: hard, light-brownish-gray 

(IOYR 6/1), thick-bedded, aphanitic.

154_______ Mudstone: phosphatic, medium-hard,

dusky-browu (IOYR 2/2), thin-bedded 

apatite is finely pelletal.

Thickness

1. 3 

3. 6

3. 6

11. 9

10. 7

Cumulative

thickness

(feet}

Uranium

56. 9

60. 5

64. 1

76. 0

86. 7

13. 3 100. 0

2. 1 102. 1

3. 8 105. 9

2. 8 108. 7

4. 4 113. 1

4. 8 117. 9

118. 7

3. 6 122. 3

1. 0 123. 3

1. 0 124. 3

. 7 125. 5

4. 7 130. 2

8 131.

3.0 134.0

. 7 134. 7

Sample

Acid Organic Radiometric Chemical 

insoluble matter eV U

RSJ-3553 26.7 22.9 ____ 0.009 0.006

3552 31. 2 14. 7 1. 2 . 007 . 010

WJG-3551 13.6 42.0 ____ .004 .005

3550 13.7 42.5 __._ .006 .006

3549 6. 95 41. 9 2. 00 . 003 . 003

3548 8.9 52.3 _._. .004 .002
488 GEOLOGY OF PERMIAN ROCKS

Hogback Mountain,

Bed Description

Retort Phosphatic Shale Tongue of the

Phosphoria Formation Continued

Rt-153_______ Mudstone: medium-hard, grayishbrown (10 YR 4/2), thin-bedded.

152_______ Mudstone: phosphatic, hard, darkgray (N 3), thick-bedded; apatite is 

finely pelletal.

151---____ Mudstone: medium-hard, brownishblack (10 YR 2/1), fissile.

150__-_--_ Phosphorite: hard, dark-gray (N 4), 

thin-bedded, finely pelletal.

149--___-- Mudstone: hard, brownish-gray (10 YR 

3/1), thin-bedded.

148--_-___ Chert: carbonatic, hard, medium-gray 

(N 6), thick-bedded; contains some 

very fine quartz sand.

147________ Mudstone: phosphatic, medium-hard,

brownish-black (IOYR 2/1), thinbedded; apatite is medium-pelletal; 

grades from bed below.

146 _______ Mudstone: phosphatic, hard, darkgray (N 4), thin-bedded; apatite is 

finely pelletal.

145_______ Sandstone: phosphatic, medium-hard,

dark-gray (N 4), thin-bedded, very fine 

grained; apatite is finely pelletal; 

grades from bed below.

144_-_____ Phosphorite: muddy, sandy, mediumhard, light-brownish-gray (IOYR 

5/1), thin-bedded, medium-pelletal; 

sand is fine.

143-_-_--- Chert: dolomitic, hard, medium-gray 

(N 5), very thick bedded; contains 

some very fine quartz sand; grades 

from bed below.

142 _______ Mudstone: phosphatic, hard, brownishgray (IOYR 4/1), thin-bedded; apatite is finely pelletal; contains some 

fine quartz sand.

141_______ Mudstone: phosphatic, hard, dark-gray

(N 3), thin-bedded; apatite is medium-pelletal.

140_______ Chert: carbonatic, hard, dark-gray

(N 4), thick-bedded.

139_______ Mudstone: carbonatic, hard, black (TV 2),

thin-bedded; irregular contact with 

bed below.

138 _______ Chert: sandy, hard, grayish-brown

(7.5 YR 3/2), thick-bedded; sand is 

fine; irregular contact with bed 

below.

137_______ Mudstone: hard, dusky-brown (1077?

2/2), thin-bedded; irregular contact 

with bed below.

136_______ Chert: hard, dark-gray (N 4), thickbedded.

135__.____ Chert: hard, dark-gray (N 4), thinbedded; contains some very fine 

quartz sand; irregular contact with 

bed below.

134____-__ Chert: argillaceous, hard, dark-gray 

(N 3), thin-bedded; irregular contact 

with bed below.

133-______ Chert: argillaceous, sandy, hard, lightbrownish-gray (IOYR 5/1), thinbedded; sand is very fine; grades 

from bed below.

132____--_ Chert: argillaceous, hard, very pale 

brown (10 YR 7/2), thin-bedded.

131__-____ Chert: sandy, muddy, hard, darkyellowish-brown (IOYR 4/2), thinbedded; sand is very fine.

IN THE WESTERN PHOSPHATE FIELD

Mont., lot 1299 Continued

Chemical analyses (percent)

Uranium

Thick- Cumulative

ness thickness

(feet} (feet} Sample

Acid Organic Radiometric Chemical 

insoluble matter eIT IT

0.9 135.6 WJG-3547 5.7 63.9 ____ 0.004 

. 9 136. 5 3546 16. 8 43. 3 3. 81 . 006

1.4 140.3

1. 3 141. 6

2. 4 144. 0

. 8 144. 8

1. 5 146. 3

1. 6 147. 9

1. 1 149. 0

1. 0 150. (T)

. 7 150. 7

2. 0 152. 1

1. 1 153. 8

. 3 154. 1

. 5 154. 6

2. 6 157. 2

2. 3 159. 5

2. 3 161. 8

2. 6 164. 4

3545 8. 3 54. 7

3544 3. 7 62. 4

3542 8. 8 63. 1

3541 11. 6 57. 6

3539 1. 8 55. 5

3538 12. 7 57. 3

3536 4. 3 55. 3

3535 2. 7 87. 2

3534 6. 1 71. 7

3533 1. 7 88. 1

. 005

. 002

3543 11. 3 49. 8 6. 41 . 005

0.004

.005

.007

. 002

. 007

. 004 . 005

. 004 . 005

3540 14. 2 53. 0 1. 46 . 005 . 005

. 000 . 001

. 003 . 004

3537 8. 1 66. 7 3. 71 . 003 . 004

. 002 . 003

. 001 . 002

. 004 . 004

. 002 . 002

3532 1.1 92. 8 ____ .000 . 002 

3531 1. 7 88. 9 1. 11 . 002 . 003

3530 2. 8 85. 7

3529 3. 4 81. 4

. 002 . 002

. 002 . 002
Bed

Rt-130.

129.

128.

127.

126.

125.

124.

123.

122. 

121. 

120_ 

119. 

118.

117.

116.

115.

114.

113.

112.

111.

110.

109.

108.

107_

106.. 

105-

STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA

Hogback Mountain, Mont., lot 1299 Continued

489

Chemical analyses (percent)

Description

Retort Phosphatic Shale Tongue of the

Phosphoria Formation Continued

Mudstone: phosphatic, medium-hard, 

grayish-brown (10 YR 4/2), thinbedded; apatite is medium-pelletal.

Mudstone: phosphatic, medium-hard, 

dusky-brown (10 YR 2/2), thinbedded; apatite is finely pelletal.

Dolomite: silty, hard, light-brown 

(7.5YR 5/4), thin-bedded, aphanitic.

Mudstone: phosphatic, plastic, darkgrayish-brown (IOYR 3/2), thinbedded; apatite is medium-pelletal; 

grades from bed below.

Mudstone: phosphatic, hard, dark-gray 

(N 3), thin-bedded; apatite is medium pelletal; grades from bed below.

Mudstone: phosphatic, medium-hard, 

brownish-gray (IOYR 4/1), thinbedded; apatite is medium pelletal.

Mudstone: medium-hard, black (N 2), 

thick-bedded.

Phosphorite: hard, dark-gray (N 4), 

thin-bedded, coarsely pelletal; grades 

from bed below.

Mudstone: medium-hard, light-brown 

(7.5 YR 5/4), thin-bedded.

Phosphorite: muddy, hard, dark-gray 

(./V3), medium-pelletal.

Mudstone: medium-hard, brownishgray (IOYR 3/1), thin-bedded.

Phosphorite: muddy, hard, dark-gray 

(./V4), thin-bedded, medium-pelletal.

Mudstone: medium-hard, brownishblack (IOYR 2/1), thin-bedded; 

grades from bed below.

Mudstone: hard, grayish-brown (2.5FR 

3/2), thin-bedded.

Mudstone: plastic, moderate-orange 

(7.5 YR 6/8), thick-bedded.

Mudstone: hard, brownish-gray (10F.R 

3/1), thin-bedded.

Phosphorite: muddy, medium-hard, 

pale-brown (10 YR 5/2), thin-bedded, 

finely pelletal.

Phosphorite: hard, light-brownish-gray 

(10 FR 6/1), thin-bedded, mediumpelletal and oolitic; grades from bed 

below.

Mudstone: crumbly, weak-yellowishorange (10 YR 7/6), thick-bedded.

Mudstone: phosphatic, soft, grayishbrown (10 YR 4/2), thin-bedded; 

apatite is finely pelletal.

Mudstone: phosphatic, medium-hard, 

pale-brown (IOYR 5/3), thin-bedded; 

apatite is finely pelletal. 

Mudstone: phosphatic, plastic, grayish-brown (7.5 YR 3/2), thin-bedded; 

apatite is finely pelletal.

Phosphorite: hard, medium-gray (-/V6) 

thin-bedded, medium-pelletal; grades 

from bed below.

Phosphorite: muddy, hard, pale-brown 

(IOYR 5/2), thin-bedded, finely 

pelletal.

Phosphorite: muddy, hard, black (N 2),

thin-bedded, finely pelletal. 

Mudstone: medium-hard, light-gray 

(N 7), fissile.

Thick- Cumulative 

ness thickness 

(feet) (feet)

0. 5

. 5

1. 7

3. 0

. 8

. 7

.3

. 3

. 8 

. 4

.8

. 4

2. 5

. 3

. 5

1. 0

1. 5

. 9

. 4

2. 6

1. 3

.7

1. 0

1. 7

1. 0

. 9

164. 9^1

165. 4r

167. 1

170. 1

170. 9

171. fr

171. 9

172. 2

173. 0] 

173. 4

174. 2:

174. 6

177. 1

177. 4'

177. 9

178. 9'

180. 4 >

181. 3

181. ?1

184. 3 1

185. 6 N

186. 3

187. 3

189. 0

190. 0

190. 9

Uranium

Sample

Acid Organic Radiometric Chemical 

insoluble matter e~U U

WJG-3528 11. 2 54. 1 3. 80 0. 005

3527 5. 7 35. 4

3526 15. 6 43. 7

. 003

.007

0.007

.003

. 008

3525 12. 0 44. 4 10. 40 . 006 . 006

3524 12. 3 37. 5

3523 11. 0 47. 1

. 006 . 006

. 006 . 007

3522 11. 9 43. 4 10. 50 . 005 . 007 

3521 6.3 51.3 ____ .006 .006

3520 2. 3 71. 0 . 004 . 002

3519 13. 1 48. 7 1. 81 . 006 . 006 

3518 34.5 4.5 ____ .011 .013

3517 8. 1 55. 7

3516 10. 7 37. 3

. 005 . 004

. 006 . 007

3515 29. 3 10. 7 1. 69 . 013 . 015

3514 17.3 32.7 ____ .008 .011

3513 13.9 33.3 8.89 .009 .011
490 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Hogback Mountain, Mont., lot 1299 Continued

Chemical analyses (percent)

Bed

Rt-104. 

103_ 

102. 

101. 

100-

99_. 

98..

95. 

94.

92. 

91. 

90.

Ls-84_ 

83_

82.

81-

Description

Retort Phosphatic Shale Tongue of the 

Phosphoria Formation Continued

Mudstone: hard, grayish-brown 

10 YR 3/2), thick-bedded.

Mudstone: plastic, brownish-black 

(lOFfl 2/1), thick-bedded.

Mudstone: soft, grayish-brown 

(7.5Ffl 3/2), thin-bedded.

Mudstone: dolomitic, soft, black (N 1), 

thin-bedded; grades from bed below.

Mudstone: phosphatic, mediumhard, dark-gray (N 3), thin-bedded; 

apatite is finely pelletal.

Mudstone: plastic, moderate-brown 

(7.5 YR 4/4), thin bedded.

Phosphorite: muddy, medium-hard, 

black (A7 2), thin-bedded, mediuinpelletal; pellets are concentrated 

in laminae and lenses.

Phosphorite: soft, yellowish-gray 

(10F.R 7/1), thin-bedded, mediumpelletal; grades from bed below.

Phosphorite: muddy, medium-hard, 

weak-orange (7.SYR 7/6), thickbedded, medium-pelletal.

Mudstone: medium-hard, weak-yellowish-orange (IOYR 7/6), thick-bedded.

Phosphorite: crumbly, medium-gray 

(N 6), thin-bedded, medium-pelletal; 

grades from bed below.

Phosphorite: muddv, medium-hard, 

dusky-brown (IOYR 2/2), thickbedded, finely pelletal.

Mudstone: medium-hard, pale-brown 

(lOFfl 5/3), thick-bedded.

Mudstone: earthy, light-brown (7.5- 

YR 5/6), thick bedded.

Mudstone: hard, moderate-yellowishbrown (IOYR 4/4), thick-bedded; 

grades from bei below.

Mudstone: phosphatic, medium-hard, 

black (N 1), thick-bedded; apatite is 

finely pelletal.

Mudstone: earthy, light-brown (7.SYR 

5/6), thin-bedded.

Phosphorite: hard, black (A7 2), thickbedded, coarsely pelletai; contains 

some very fine quartz sand; grades 

from bed below.

Siltstone: hard, dark-gray (A7 3), thickbedded.

Chert: brittle, brownish-gray (WYR 

3/1), thin-bedded; contains glauconite and phosphatic skeletal fragments; grades from bed below. 

Lower tongue of Shedhorn Sandstone:

Sandstone: hard, very pale brown 

(WYR 7/2), very thick bedded, finegrained; grades from bed below.

Sandstone: hard, very pale brown 

(IOYR 7/2), very thick bedded, finegrained; grades from bed below.

Sandstone: hard, light-brownish-gray 

(IOYR 6/1), very thick bedded, finegrained; contains chert lenses 0.3 ft in 

diameter in layers at base and 4.0 ft 

above base; contains phosphatic 

skeletal fragments.

Dolomite: hard, yellowish-gray (WYR 

7/1), thick-bedded, aphanitic; grades 

from bed below.

Thick- Cumulative

ness thickness

(feet) (feet)

Uranium

. 8 196. 9

. 7 197.

.9 198.51

. 8 199. 3

. 3 199.

. 2 199.

. 9 200.

.6 201.3

1. 2 202. 5'

. 1 202. 6

. 3 202. 9

. 7 203. 6

1. 5 205. 1

1. 3 206. 4

5.4 211.8

5. 0 216. 8

3. 7 220. 5

Acid Organic Radiometric Chemical 

.^Sample PzOs insoluble matter eU U

WJG-3512 5. 3 59. 0

3511 5.7 37.5

0. 004 0. 005

. 005 . 006

3510 9. 7 43. 3 7. 63 . 007 . 008 

3509 16.6 30.7 __._ .009 .008

3508 32. 1 5. 2 . 008 . 010

3507 10. 1 57. 5 1. 23 . 003 . 003 

3506 29.7 18.5 _.__ .008 .010

3505 12. 3 32. 7 . 003 . 004

3504 6. 0 64. 5 1. 35 . 004 . 003 

3503 9. 8 46. 2 _ _ _ _ .006 . 006

3502 22. 8 ^23. 6 . 009 . 010

3501 3. 1 80. 5 1. 98 . 003 . 002
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 491

Hogback Mountain, Mont., lot 1299 Continued

Chemical analyses (percent)

Bed Description

Lower tongue of Shedhorn Sandstone Con. 

Ls-80_------- Sandstone: hard, very pale brown

(1QYR 7/2), very thick bedded, finegrained; contains irregular chert 

nodules 0.5 ft in diameter near top; 

contains phosphatic skeletal fragments.

Franson Member of Park City Formation; 

contains some thin tongues of Shedhorn 

Sandstone: 

F-79.________ Dolomite: cherty, hard, yellowish-gray

(WYR 7/1), very thick bedded, 

aphanitic. 

Ls-78- _______ Sandstone: dolomitic, medium-hard,

pale-orange (7.5 YR 8/4), thinbedded, fine-grained. 

F-77-________ Dolomite: hard, yellowish-gray (10 YR

7/1), thick-bedded, aphanitic; sandy 

in lower 5 ft; irregular contact with 

bed below. 

76_________ Dolomite and chert, interbedded: hard

light-brownish-gray (10 YR 6/1), 

thick-bedded aphanitic dolomite 

interbedded with thick-bedded chert; 

dolomite contains some chert nodules 

and is muddy in lower 15 ft. 

75_-------- Dolomite: hard, yellowish-gray (10 YR

7/1), very thick bedded, aphanitic. 

Fossil collection number 11677. 

Ls-74 ________ Sandstone: hard, yellowish-gray (10 Y R

7/1), thick-bedded, fine-grained; 

grades from bed below. 

Rex Chert Tongue of Phosphoria Formation; contains thin tongue of Shedhorn 

Sandstone near top:

R-73- _______ Dolomite: sandy, cherty, hard, yellowish-gray (10 YR 7/1), very thick 

bedded, aphanitic; sand is very fine; 

contains phosphatic skeletal fragments and glauconite.

Ls-72_ _______ Sandstone: cherty, hard, yellowishgray (10 YR 7/1), very fine grained. 

R-71_________ Chert: brittle, yellowish-gray (WYR

7/1), poorly bedded. 

70_ ________ Chert: hard, light-brownish-gray

(10 YR 5/1) thick-bedded. 

69.________ Chert: hard, brownish-gray (-IQYR

3/1), thin-bedded. 

68. ________ Chert: brittle, light-brownish-gray

(WYR 6/1), thick-bedded; grades 

from bed below.

67.. ________ Chert: brittle, dark-gray (N 3), thickbedded. 

Meade Peak Phosphatic Shale Tongue of

the Phosphoria Formation: 

M-66_ _______ Phosphorite: sandy, medium-hard,

pale-brown (WYR 6/2), thin-bedded, 

finely pelletal; contains phosphatic 

skeletal fragments.

65. _______ Mudstone: medium-hard, light-yellowish-brown (WYR 6/4), thin-bedded; 

grades from bed below.

64________ Siltstone: soft, moderate-yellowishbrown (10 YR 4/4), thin-bedded.

63 ________ Phosphorite: muddy, soft, duskybrown (WYR 2/2), thin-bedded, 

very finely pelletal.

62 ________ Siltstone: soft, moderate-yellowishbrown (10 YR 4/4), thin-bedded. 

61________ Phosphorite: crumbly, dusky-brown

(10 YR 2/2), thin-bedded, coarsely 

pelletal and oolitic.

Thickness

Cumulative

thickness

(feet)

Uranium

Sample P2 05

Acid Organic Radiometric Chemical 

insoluble matter eV U

4. 1 224. 6

10. 1 234. 7

8. 5 243. 2

24. 0 267. 2

22. 5 289. 7

46. 0 335. 7

10. 0 345. 7

10. 0 355. 7

2. 0 357. 7

14. 5 372. 2

5. 4 377. 6

1. 6 379. 2

30. 2 409. 4

2. 8 412. 2 WHW-3374 0. 4 64. 0 0. 002

1. 0 413. 2

2. 0 415. 2

1. 1 416. 3

. 1 416. 4

. 9 417. 3

4. 0 421. 3

3373 6. 0 67. 7

3372 8. 8 66. 5

3371 28. 8 16. 0

. 003

. 005 0. 004

.013 .013
492 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Hogback Mountain, Mont., lot 1299 Continued

Chemical analyses (percent)

Bed Description

Meade Peak Phosphatic Shale Tongue of

the Phosphoria Formation Continued

M-60 ________ Phosphorite: medium-hard, lightbrownish-gray (IOYR 5/1), thickbedded, coarsely oolitic and pelletal; 

contains phosphatic skeletal fragments. Fossil-colln. No. 11676. 

59_ _______ Siltstone: hard, pale-brown (10FE6/2),

thin-bedded. Fossil-colln. No. 71676. 

Grandeur Member of Park City Formation: 

G-58_ _---___ Dolomite: hard, pale-orange (7.5 YR 

8/4), very thick bedded, aphanitic.

57- ------ Dolomite: silty, hard, pale-orange

(7.5 YR 8/4), very thick bedded, 

aphanitic.

56_________ Sandstone: muddy, dolomitic, mediumhard, very pale brown (IOYR 7/3), 

thin-bedded, very fine grained.

55----_--__ Similar to bed G-56_____-_--______-

54 _______ Similar to bed G-56______---______-

53_________ Similar to bed G-56___-_-__-___--__

52--------- Similar to bed G-56_____----____ 

51_________ Similar to bed G 56; grades from bed

below.

50_ ________ Mudstone: dolomitic, medium-hard,

yellowish-gray (2.5 Y 7/2), thinbedded.

49__-______ Similar to bed G 50; grades from bed

below

48_________ Sandstone: silty, medium-hard, very

pale brown (WYR 7/3), thin-bedded, 

very fine grained.

47 ------- Similar to bed G-48______________

46_-----___ Dolomite: hard, light-gray (N 7), 

thick-bedded, aphanitic.

45_ ________ Dolomite: hard, very pale brown (10 YR

7/2), thin-bedded, aphanitic; contains scattered chert nodules.

44_________ Dolomite: hard, yellowish-gray (IOYR

7/1), very thick bedded; aphanitic.

43_________ Dolomite: hard, yellowish-gray (IOYR

8/a), thick-bedded, aphanitic. Fossil 

collection number 11675.

42_________ Sandstone: muddy, hard, yellowishgray (IOYR 8/1), very thick bedded, 

very fine grained.

41 _________ Dolomite: hard, yellowish-gray (IOYR

7/1), thick-bedded, aphanitic.

40_________ Dolomite: hard, very pale orange (10 YR

8/2), thin-bedded, aphanitic. Fossilcollection number 11674.

39_________ Dolomite: medium-hard, very pale

orange (IOYR 8/2), thin-bedded, 

aphanitic.

38_________ Dolomite: hard, yellowish-white (IOYR

9/1), very thick bedded, aphanitic.

37_________ Similar to bed G-38______-_--____-_

36---______ Dolomite: hard, yellowish-gray (IOYR

8/1), thick-bedded, aphanitic.

35_________ Sandstone: brittle, weak-yellowishorange (IOYR 7/6), very thick 

bedded, fine-grained.

34_________ Dolomite: brittle, light-brownish-gray

(IOYR 6/1), thick-bedded, aphanitic.

33_________ Similartobed G-34___ _____________

32_________ Similartobed G-34__-_-__ _______

31_________ Dolomite: sandy, brittle, light-gray

(N 8), thin-bedded, aphanitic.

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Uranium

6. 2 

6.0 

5.4

5. 5

6. 0

10. 8

33. 4

7. 8 

6.0

13. 0

15.0

2. 5

Acid Organic Radiometric Chemical 

PaOs insoluble matter eV IT

0. 7 422. 0 WHW-3370b 23. 4 34. 1 0. 006 0. 006

1. 1 423. 1

3. 5 426. 6

3. 4 430. 0

7. 5 437. 5

443.7

449. 7

455. 1

460. 6

466. 6

4. 8 471. 4

4. 9 476. 3

11. 2 487. 5

498. 3

531. 7

26. 4 558. 1

3. 0 561. 1

27. 2 588. 3

7. 3 595. 6

15. 0 610. 6

10. 8 621. 4

2. 6 624. 0

15. 0 639. 0

646.8

652.8

6. 5 659. 3

12. 8 672. 1

685. 1

700. 1

702.6

3370a 8 91. 8 000 . 001

3369

3368

3367

3366

3365

3364

3363

qoco

3361

3360

 3QKQ

K

g

. ?,

9

. 1

9

. i

. i

. i

11.5 ____

28.0 ____

70.3 ____

cc 9

n

o

n 9

67.8 -___

63.7 --_-

64.6 ____

7n ^

71.0 ___-

.001 -------

.001 -------

.002 __-__--

.001 -------

.001 -------

. 002 _-- ---

.002 - _-_

.002 -------

.002 -------

.001

.001 -__ _ _
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 493

Hogback Mountain, Mont., lot 1299 Continued

Red

G-30_

29__.

28_

27. 

26.

25.

23_ 

22_

20..

19.

18.

17.

16.

15. 

14.

13

12.

11- 

10.

Description

Grandeur Member of Park City Formation Continued

Sandstone: silty, dolomitic, brittle, 

light-yellowish-brown (2.5 Y 6/4), 

thin-bedded, very fine grained.

Dolomite: brittle, light-yellowishbrown (2.5 Y 6/4), thin-bedded, aphanitic; contains scattered black chert 

lenses 0.05 by 1 ft; grades from bed 

below.

Dolomite: hard, yellowish-gray (IOYR 

7/1), thick-bedded, aphanitic; contains numerous chert nodules 0.1 ft 

to 0.5 ft in diameter.

Similar to bed G-28____--_--------_

Carbonaterock: hard, dark-gray (N3), 

thick-bedded, aphanitic.

Carbonate rock: hard, light-brownishgray (10 YR 5/1), thin-bedded, aphanitic. Fossil-colln. No. 11673.

Similar to bed G-25______----__--_-

Carbonate rock: hard, pale-brown 

(2.5 Y 6/2), thin-bedded, aphanitic.

Sandstone: hard, yellowish-gray (IOYR 

7/1), thick-bedded, fine-grained.

Dolomite: hard, pale-brown (IOYR 

6/2), thin-bedded, aphanitic.

Sandstone: muddy, dolomitic, brittle, 

light-yellowish-brown (10 YR 6/4), 

very thick bedded, fine-grained.

Chert: calcareous, brittle, white (N 9), 

very thick bedded.

Dolomite: brittle, light-brownish-gray 

(IOYR 6/ ), very thick bedded, 

aphanitic.

Sandstone: silty, dolomitic, brittle, 

weak-yellowish-orange (2.5 F 7/4), 

very thick bedded, fine-grained.

Dolomite: brittle, light-brownish-gray 

(IOYR 6/1), thick-bedded, aphanitic; 

grades from bed below.

Dolomite: brittle, very pale brown 

(IOYR 7/3), thick-bedded, aphanitic.

Sandstone: silty, hard, pale-brown 

(IOYR 6/2), thick-bedded, fine 

grained.

Dolomite: brittle, yellowish-gray 

(10FT? 7/1), thick-bedded, aphanitic.

Sandstone: silty, dolomitic, crumbly, 

weak-yellowish-orange (2.5F 8/4), 

fissile, very fine grained.

Dolomite: brittle, light-gray (N 7), 

thick-bedded, aphanitic.

Sandstone: brittle, weak-yellowishorange (2.5F 8/4), thin-bedded, finegrained.

Dolomite: hard, yellowish-gray (IOYR 

7/1), thick-bedded, aphanitic.

Sandstone: dolomitic, hard, very pale 

orange (7.5YR 8/2), thin-bedded, 

very fine grained.

Dolomite: brittle, yellowish-gray (IOYR 

7/1), very thick bedded, aphanitic.

Sandstone: brittle, moderate-yellowishbrown (10 FT? 4/4), thick-bedded, 

very fine grained.

Dolomite: brittle, very pale brown 

(10 YR 7/2), thin-bedded, aphanitic; 

grades from bed below.

Dolomite: brittle, light-gray (N 7), 

fissile, aphanitic; grades from bed 

below.

2. 4 

9. 4

15.0

5. 7

8. 5 

2.6

3. 5

2.0

3. 0 

5. 2

4. 0

2. 6

6. 5 

1. 0

705. 0

714.4

9. 0 723. 4

738.4

744. 1

4. 8 748. 9

757.4

760.0

763. 5

772. 3

774.3

777.3

782. 5

786. 5

789. 1

. 3

.3

.3

. 1

1. 6

. 4

. 6

.3

3.0

.3

789. 4

789. 7

790.0

790. 1

791. 7

792. 1

792. 7

793. 0

796.0

796. 3

802. 8

803.8

Chemical analyses (percent)

Uranium

Thick- Cumulative

ness thickness

(feet) (feet) Sample PsOs

Acid Organic Radiometric 

insoluble matter ell

Chemical

U

709-931 O 63- -15
494 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Hogback Mountain, Mont., lot 1299 Continued

Chemical analyses (percent)

Bed

Thick- Cumulative 

ness thickness 

(feet)

Uranium

(feet) Sample PzOs

Acid Organic Rad,iometric 

insoluble matter eU

Chemical

U

G-3_ 2. 7 806. 5

806. 8

Description

Grandeur Member of Park City Formation Continued

Dolomite: medium hard, yellowish 

white (2.5 Y 9/2), thick-bedded, 

aphanitic.

Dolomite: silty, medium-hard, weakyellowish-orange (2.5F 8/4), thinbedded; dolomite is aphanitic. 

Quadrant Formation:

Sandstone: hard, yellowish-white (2.57 ____ ______ ___________ ____ ____ ____ ______ _______

9/2, thick-bedded, fine-grained.

Warm Springs Creek, Mont., lot 1300

[ Pennian rocks measured near Warm Springs Creek, N WH sec. 22, T. 9 S., R. 3 W., Madison County, Mont., near crest of small anticline. Retort Phosphatic Shale Tongue 

of Phosphoria Formation measured and sampled in hand trench; rest of section measured from natural exposures. Beds strike N. 30° E. and dip 2° N.W. Measured by 

W. H. Wilson, B. K. Replogle, and J. L. Elliott and sampled by Elliott, Replogle, and R. F. Gosman, in August 1949. Analyzed for P2 O5 and acid insoluble by U.S. 

Bur. of Mines and for uranium by U.S. Geol. Survey]

Chemical analyses (percent)

Q-i.

Bed

(42). 

Us-41_

40_ 

39.

38. 

37-

36. 

35_

34-

To-33. 

32- 

31. 

30. 

29.

Cumulative 

Thickness thickness 

Description (feet) (feet)

Upper member of Shedhorn Sandstone:

Covered; contact between Dinwoody 4. 5 4. 5

and Shedhorn formations located

approximately by change in float. 

Sandstone: medium-hard, yellowish- 4. 4 8. 9

gray (107728/1), thick-bedded; finegrained; contains glauconite; grades

from bed below. 

Chert: hard, light-brownish-gray 1. 4 10. 3

(WYR 6/1), thin-bedded; contains

glauconite; grades from bed below. 

Sandstone: hard, pale-brown (WYR 5. 0 15. 3

5/3), medium-light-gray (N 7) on

unweathered interiors of some fragments, thick-bedded, fine-grained;

contains glauconite; grades from

bed below. 

Sandstone: medium-hard, light-brown- 3. 0 18. 3

ish-gray (WYR 5/1), thick-bedded,

cross-bedded; fine-grained: contains

glauconite. 

Sandstone: medium-hard, light-brown- 17. 3 35. 6

ish-gray (WYR 5/1), thick-bedded;

fine-grained; contains glauconite;

grades from bed below. 

Similar to bed US-37 but does not 20. 0 55. 6

contain glauconite; irregular contact

with bed below. 

Sandstone: cherty, brownish-gray . 5 56. 1

(1077? 4/1), thick-bedded, very fine

grained; contains columns of finegrained sandstone that are perpendicular to bedding. 

Sandstone: hard, light-brownish-gray 2. 3 58. 4

(WYR 5/1), thick-bedded; very fine

grained; grades from bed below. 

Tosi Chert Tongue of Phosphoria Formation:

Chert: brittle, pale-brown (1077? 6/2), 6. 8 65. 2

thick-bedded; grades from bed below. 

Chert: hard, light-brownish-gray 32. 1 97. 3

(WYR 6/1), thick-bedded.

dark-gray (N 3), thick- 21. 5 118. 8

Uranium

Acid Radiometric Chemical 

insoluble eU U

Chert: hard, 

bedded.

Chert: hard, 

bedded.

Chert: hard, 

bedded.

dark-gray (N 3), thin- 5. 0 123. 8

dark-gray (N 3), thin- 1. 9 125. 7 WHW-3385 0. 5 92. 8 0. 001
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 495

Warm Springs Creek, Mont., lot 1300 Continued

Chemical analyses (percent)

Uranium

Bed

To-28_ 

27.

Rt-26_ 

25_ 

24_

23. 

22_

21. 

20-

Ls-16. 

15

Ls-11

10

R-9

Tosi Chert Tongue of Phosphoria Formation Continued

Chert: hard, dark-gray (N 3), thinbedded; grades from bed below.

Chert: hard, dark-gray (N 3), thinbedded; contains thin mudstone 

partings between chert beds. 

Retort Phosphatic Shale Tongue of Phosphoria Formation:

Phosphorite: muddy, medium-hard, 

grayish-brown (WYR 3/2), fissile; 

pelletal.

Phosphorite: muddy, crumbly, darkgray (N 4), thin-bedded; very finely 

pelletal.

Phosphorite: muddy, crumbly, laminated grayish-brown (7.5YR 4/2) 

and dark-gray (A'" 4), thin-bedded; 

argillaceous material is concentrated 

in grayish-brown laminae.

Phosphorite: medium-hard, dark-gray 

(N 4), thin-bedded, finely pelletal.

Mudstone: phosphatic, crumbly, duskybrown (10 YR 2/2), thin-bedded; 

grades from bed below.

Mudstone: soft, brownish-gray (1QYR 

4/1), thin-bedded.

Phosphorite: crumbly, dark-gray (Af 4), 

thin-bedded; finely pelletal.

Chert and mudstone, interbedded: 

hard, dark-gray (N 3), thin-bedded, 

chert interbedded with medium-hard 

light-brown (7.5YR5/&) thin-bedded 

cherty mudstone.

Chert: hard, dark-gray (N 3), thinbedded.

Chert: hard, dark-gray (N 3), thickbedded; contains glauconite. 

Lower member of Shedhorn Sandstone:

Sandstone: hard, light-brownish-gray 

(10YR 5/1), very thick bedded; finegrained.

Sandstone: hard, pale-brown (IOYR 

6/2), very thick bedded, fine-grained.

Sandstone: dolomitic, medium-hard, 

very pale brown (WYR 7/3), thickbedded, fine-grained. 

Franson Tongue of Park City Formation:

Dolomite: hard, very pale orange 

(10 YR 8/2), thick-bedded; aphanitic; 

contains some nodules and interbeds 

of dolomitic chert.

Limestone: hard, very pale brown 

(10 YR 7/2), very thick bedded; finely 

granular; irregular contact with bed 

below. 

Lower member of Shedhorn Sandstone:

Sandstone: hard, pale-brown (2.5F 

5/2), very thick bedded; fine-grained; 

contains irregular lenses of sandy 

chert; contains phosphatic skeletal 

fragments.

Sandstone: hard, light-brownish-gray 

(WYR 6/1), very thick bedded; finegrained.

Rex Chert Tongue of Phosphoria Formation:

Chert: hard, pale-brown (10 YR 6/2), 

thick-bedded, contains a few interbeds of light-brownish-gray (10 YR 

6/1), fine-grained sandstone.

Cumulative 

Thickness thickness

(feet) (feet) Sample

Acid Radiometric Chemical 

P2O 5 insoluble «U U

2.5 128.2 WHW-3384 0.4 93.2 0.001 _.____- 

2. 0 130. 2 3383 .7 93. 6 . 0005 0. 001

1. 7 131. 9

. 9 132. 8

. 7 133. 5

1. 7 135. 2

1. 1 136. 3

2. 5 149. 3

5. 0 154. 3

10. 0 164. 3

3. 8 168. 1

3. 4 171. 5

18. 7 190. 2

3. 1 193. 3

3. 2 196. 5

3382 18.5 41.3 .001 ____.-_

3381 27. 3 23. 0 . 008 . 008

3380 26. 7 20. 2 . 010 . 010

3379 31. 2 10. 5 009 . 009

3378 10. 4 43. 7 . 007 . 007

1. U^

. 2

1. 6

1 -L. 9£j

6. 0

m o

. o

138. 0>

139. 6

140. 8

146. 8

3377 1. 8 75. 5 003 .___ __

3376 3.3 80.5 .003 _______

IIT^ 4. Q9 O 001
496 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Warm Springs Creek, Mont., lot 1300 Continued

Bed

7.

M-6.

G-3_ 

2.

1.

Description

Lower member of Shedhorn Sandstone:

Sandstone: hard, light-gray (N 7), 

thick-bedded, medium-grained; contains glauconite and phosphatic 

skeletal fragments; contains small 

black chert pebbles.

Dolomite: hard, light-brownish-gray 

(10 YR 6/1), thick-bedded; very fine 

grained; contains chert nodules 0.1 

ft in diameter.

Meade Peak Phosphatic Shale Tongue of 

Phosphoria Formation:

Phosphorite: sandy, carbonatic, medium-hard, medium-gray (.V 6), thinbedded; nodular and medium-pelletal 

and oolitic; nodules average 0.05 ft 

in diameter.

Sandstone: phosphatic, hard, mediumgray (N 6), thick-bedded; fine-grained; apatite pellets are concentrated in 

laminae that constitute 20 percent of 

bed.

Phosphorite: sandy, hard, mediumgray (N 5), thick-bedded, apatite is medium grained, oolitic; contains phosphatic fossil fragments. 

Grandeur Member of Park City Formation, 

upper part:

Sandstone: hard, medium-gray (N 5), 

very thick bedded; very fine grained.

Sandstone: medium-hard, weak-yellowish-orange (IOYR 8/4), thick-bedded, 

very fine grained.

Dolomite: hard, very pale brown (IQYR 

7/2), thick-bedded; aphanitic; underlying rocks are covered. Fossilcolln. No. 11681.

Chemical analyses (percent)

Thickness 

(feet)

Cumulative

thickness

(feet)

Uranium

0. 8 197.

Sample

WHW-750

Pa05

Acid 

insoluble

Radiometric Chemical 

eU U

3. 3 78. 3 0. 001 0. 001

197.

8 198. 7

1. 2 199. 9

2. 5 202. 4

9. 8 212. 2

15. 0 227. 2

744

743

19. 4

21.9

45. 4

39.3

004

004

005

004

Sliderock Mountain, Mont., lot 1301

[Permian rocks measured on Sliderock Mountain, N^i sec. 25, T. 10 S., R. 4 W., Madison County, Mont., on overturned west limb of Ruby Valley syncline. Thrust faulting was recognized in older formations exposed up slope from outcrop of Permian rocks. Average strike is about north and the dip is about 40° W. Park City Formation 

and tongues of lower member of Shedhorn Sandstone measured from natural exposure and phosphatic shale members of Phosphoria Formation from hand trenches on 

spur between heads of South and Middle Forks of Fawn Creek. Tosi Chert Member of Phosphoria Formation measured from natural exposure in gully at head of Middle 

Fork of Fawn Creek. Measured by C. W. Tandy and E. R. Cressman and sampled by R. F. Gosman and W. J. Garmoe, in August 1949. Petrographic descriptions 

with binocular microscope by E. R. Cressman. Analyzed for PaOs and acid insoluble by U.S. Bur. of Mines and for uranium by U.S. Geol. Survey]

Bed

To-76.

Us-75, 

To-74.

73. 

72.

Description

Tosi Chert Member of Phosphoria Formation; contains several thin tongues of 

Shedhorn Sandstone:

Mudstone: dolomitic, medium-hard, 

grayish-brown (10 YR 4/2), thinbedded; contains glauconite. Overlying beds covered; top of bed To-76 

may be Dinwoody contact.

Sandstone: glauconitic, medium-hard, 

light-brownish-gray (10 YR 5/1), 

thin-bedded, fine-grained; irregular 

contact with bed below.

Chert: brittle, light-brownish-gray 

(10 YR 5/1), thin-bedded; contains 

glauconite and scattered laminae 

and lenses of cherty siltstone; bedding is undulant.

Chert: silty, brittle, brownish-gray 

(IQYR 4/1), thin-bedded; contains 

glauconite.

Chert: brittle, light-brownish-gray 

(10F.R 6/1), fissile; contains glauconite; bedding is undulant; irregular 

contact with unit below.

Chemical analyses (percent)

Thickness 

(feet)

Cumulative

thickness

(feet)

Uranium

22. 0

1. 0

8. 6

22.0

2. 7 24. 7

20. 6 45. 3

46.3

54.

P»0j

Add Radiometric Chemical 

insoluble eU U
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 497

Sliderock Mountain, Mont., lot 1301 Continued

Bed Description

Tosi Chert Member of Phosphoria Formation; contains several thin tongues of 

Shedhorn Sandstone Continued 

Us-71._____--_ Sandstone: hard, light-brownish-gray

(1QYR 6/1), very thick bedded, finegrained; contains glauconite. 

To-70_________ Chert: sandy, brittle, Light-brownishgray (10YR 6/1), thin-bedded; contains glauconite; sand is very fine; 

irregular contact with unit below.

69________. Dolomite: brittle, light-brownish-gray

(10 YR 6/1), thick-bedded, aphanitic..

68.. _______ Chert: brittle, yellowish-gray (10 YR

111), thin-bedded; contains glauconite and irregular lenses and laminae 

of silty chert; contains several finegrained sandstone columns 0.2 to 

0.3 ft in diameter and 0.5 to 0.6 ft 

long. 

Us-67--_______ Sandstone: cherty, hard, pale-brown

(2.5 F 5/2), thick-bedded, finegrained; contains glauconite. 

To-66.-_------ Chert: hard, brownish-gray (10YR

4/1), thin-bedded; contains glauconite; irregular contact with unit 

below.

65-_--____- Chert: hard, medium-gray (N 6); 

contains approximately 25 percent 

of irregular lenses of hard, palebrown (10 YR 5/3), very fine grained 

sandstone; lenses in upper 0.3 ft are 

phosphatic, and uppermost bedding 

surface is coated with layer 0.01 to 

0.04 ft thick composed of phosphatic 

sandstone.

64. _._._.__ Chert: muddy, hard, black (N 2), thinbedded; in fault contact with unit 

below.

Retort Phosphatic Shale Member of Phosphoria Formation: 

Rt-63_________ Mudstone and phosphorite interbedded: soft brownish-black (10 YR 2/1) 

thin-bedded mudstone interbedded 

with medium-hard brownish-black 

(WYR 2/1) thin-bedded very finely 

pelletal phosphorite; irregular contact with unit below.

62_________ Phosphorite: dolomitic, muddy, medium-hard, brownish-black (107.fi 

2/1), thin-bedded, very finely pelletal; irregular contact with unit 

below.

61 _--_-____ Mudstone: soft, brownish-black (10YR 

2/1), thin-bedded; irregular contact 

with unit below.

60_________ Phosphorite: dolomitic, medium-hard,

brownish-biack (10YR 2/1), thinbedded, very finely pelletal.

59 _________ Dolomite: hard, light-brownish-gray

(1QYR 5/1), thick-bedded, aphanitic.

58 _________ Mudstone: crumbly, brownish-gray

(10YR 3/1); in fault contact with 

unit below.

57_________ Phosphorite: medium-hard, black (N 2),

very finely pelletal; in fault contact 

with unit below.

56_._______ Phosphorite: calcareous, medium-hard,

black (N 2), very finely pelletal; 

contains several small faults of unknown displacement.

Chemical analyses (percent)

Cumulative 

Thickness thickness 

(feet) (feet)

Uranium

Sample Ps06

Acid 

insoluble

Radiometric Chemical 

eU U

2. 9

5.9

57. 8

58.5

59. 1

65.0

3. 5

4. 8

68. 5

73.3

60. 0 133. 3

6. 0 139. 3 CWT-692

3. 8 143. 1 691

143.6

144.2

145. 1

145. 7

146.

690

689

687

686

2. 4

146. 71

149. 1 ERG-685

1.0 87.5 0.001 _______

7. 3 51. 7 005 0.004

12.0 22. 5 .005 .005

2.9 53.3 .004 _______

22. 6 18. 3 008 .008

4.8 8.3 .003

12. 2 37. 1 007 .006

23. 4 14. 5 .009 . 009
498 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Sliderock Mountain, Mont., lot 1301 Continued

Chemical analyses (percent)

Bed Description

Retort Phosphatic Shale Member of Phosphoria Formation Continued 

Rt-55___---_-_ Mudstone: medium-hard, brownishblack (WYR 2/1), fissile. 

54 __ ______ Phosphorite: medium-hard, brownishblack (WYR 2/1), thin-bedded, finely 

pelletal. 

53-_------- Dolomite: hard, pale-brown (2.576/2),

thick-bedded, aphanitic. Fossilcolln. No. 1 1672. 

52_ ___ Mudstone: phosphatic, medium-hard,

brownish-black (WYR 2/1), fissile; 

apatite is finely pelletal ; in fault contact with unit below. 

51--------- Phosphorite: soft, brownish-gray

(WYR 4/1), fissile, finely pelletal. 

50__ _______ Mudstone: soft, brownish-gray (WYR

3/1), thin-bedded. 

49 _----__-_ Mudstone: phosphatic, soft, brownishgray (10 YR 4/1), fissile; apatite is 

very finely pelletal.

(48) __---_-- Covered: thickness is approximate. 

Fault is probably present in covered 

interval.

Lower tongue of Shedhorn Sandstone: 

Ls-47 _________ Sandstone : dolomitic, medium- hard,

light-brownish-gray (WYR 6/1), 

thick-bedded, fine-grained; contains 

phosphatic skeletal fragments. 

46 _________ Sandstone: hard, yellowish-gray (10 YR

8/1), thick-bedded, fine-grained; 

grades from bed below. 

Franson Tongue of Park City Formation: 

F-45 ----_-____ Chert : hard, medium-gray (N 6) , thickbedded. 

44-_---_____ Dolomite: medium-hard, lightbrownish-gray (10 YR 6/1), very fine 

grained. 

43 __________ Dolomite: medium-hard, yellowishwhite (WYR 9/1), thick-bedded, 

aphanitic. 

42_ __ _______ Dolomite: medium-hard, yellowishgray (WYR 7/1), thick-bedded, 

aphanitic; contains a few very 

irregular nodules of white (N 9) chert 

0.1 to 0.8 ft in diameter. 

41__________ Dolomite: medium-hard, yellowishwhite (WYR 9/1), thick-bedded, 

aphanitic; contains a few very irregular nodules of white (N 9) chert 0.1 

to 0.8 ft in diameter. 

40-_________ Dolomite: medium-hard, yellowishgray (WYR 7/1), thick-bedded, 

aphanitic ; contains a few very irregular nodules of white (N 9) chert 0.1 

to 0.9 ft in diameter that are more 

numerous near base of unit; grades 

from unit below. 

39__________ Dolomite: hard, very pale brown

(WYR 7/2), thick-bedded, aphanitic; 

contains about 10 percent irregular 

chert nodules. 

(38) ---_-_

R-37_

Rex Chert Member of Phosphoria Formation; contains several thin tongues of 

Shedhorn Sandstone:

Chert: brittle, yellowish-white (WYR 

9/1), thin-bedded; contains much 

vuggy calcite; irregular contact with 

unit below.

Uranium

Cumulative 

Thickness thickness 

(feet) (feet) Sample

Acid Padiometric 

insoluble eV

0. 5 149. 

.2 149.8) ERG-684 21.6 20.4 0.010

2. 4 152. 2

1. 5 153. 7

6 154. 31

6 154. 9

4 155. 3

5. 0 160. 3

2. 6 162. 9

12. 5 175. 4

2. 2 177. 6

5. 0 182. 6

6. 0 188. 6

2. 4 191. 0

5. 8 196. 8

14. 2 211. 0

8. 7 219. 7

5. 5 225. 2

2. 7 227. 9

683

682 10. 2

12. 7

42. 0

681 13. 6 40. 7

001

006

007

Chemical

U

0.008

.006

. 006
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 499

Sliderock Mountain, Mont., lot 1301 Continued

Chemical analyses (percent)

Bed Description

Rex Chert Member of Phosphoria Formation; contains several thin tongues of 

Shedhorn Sandstone Continued

Ls-36_ __---.-_ Sandstone: hard, light-gray (N 7), 

thick-bedded, fine-grained; irregular 

contact with unit below. 

R-35____---..- Chert: brittle, yellowish-white (1QYR

9/1), thin-bedded; irregular contact 

with unit below. 

Ls-34_ ________ Sandstone: cherty, hard, yellowish-gray

(IQYR 8/1), very thick bedded, finegrained. 

R-33-_________ Chert: dolomitic, brittle, yellowish-gray

(10 YR 7/1), thick-bedded; bedding 

surfaces are undulant; irregular contact with unit below. 

Ls-32_ _______ Sandstone: hard, very pale brown (10 YR

7/2), thick-bedded, fine-grained; contains phosphatic skeletal fragments.

31________ Sandstone: medium-hard, light-brownish-gray (IQYR 6/1), thick-bedded, 

fine-grained; contains glauconite and 

phosphatic skeletal fragments. 

R-30--__------ Chert: sandy, brittle, very pale orange

(10 YR 8/2), thin-bedded; contains 

glauconite and a few apatite pellets; 

grades from unit below. 

29___------- Chert: brittle, yellowish-gray (IQYR

7/1), thick-bedded; bedding surfaces 

are undulent; grades from unit 

below. 

28-_-_------ Chert: brittle, medium-gray (N 5),

thin-bedded. 

Meade Peak Phosphatic Shale Member of

Phosphoria Formation: 

M-27- ________ Phosphorite: silty, medium-hard,

brownish-gray (10 YR 4/1), thinbedded, finely pelletal. 

26_-_----__ Siltstone: soft, light-yellowish-brown

(IQYR 6/4), thin-bedded; irregular 

contact with unit below. 

25 ___---___ Siltstone: medium-hard, pale-brown

(10 YR 5/3), thick-bedded. 

24_________ Sandstone: phosphatic, medium-hard,

pale-brown (IQYR 5/3), thin-bedded,

fine-grained; apatite is finely pelletal.

23___-_---- Sandstone: soft, dark-gray (N 3), very

fine grained. 

22_________ Phosphorite: sandy, soft, dusky-brown

(IQYR 2/2), medium-pelletal; sand 

is fine. 

21_________ Sandstone: soft, dark-gray (N 3), very

fine grained. 

20___-_---- Phosphorite: sandy, soft, dusky-brown

(IQYR 2/2), coarsely pelletal; sand is 

very fine; irregular contact with unit 

below. 

19_________ Sandstone: soft, dark-gray (N 3), very

fine grained. 

18-__------ Phosphorite: soft, grayish-brown

(IQYR 4/2), finely pelletal.

17 ____----_ Phosphorite: sandy, soft, grayishbrown (10 YR 4/2), corsely pelletal; 

sand is very fine; irregular contact 

with unit below. 

16_----_--_ Phosphorite: hard, medium-gray (N 6),

thin-bedded, coarsely pelletal.

Thickness 

(feet)

2.4

1. 5

1. 1

8.7

Q n

1.2

10. 6

1. 6

. 2 

. 5 

.3

.3 

. 5

.3 

1.3

. 5 

. 2 

. 5

thickness 

(feet)

230.3

231. 8

232. 9

241. 6

244. 6

244. 9

246. 1

256. 7

m Q

258. 5' 

259. 0 ' 

259. 3^

O K.C\ O V

260. r

260. 6

260. 8 

262. 2

262. 71 

262. 9 1 

263.4

Uranium

Acid ffadiometric Chemical 

Sample P.Os insoluble eU U

CWT-699 14. 3 53. 0 0. 005 0. 005 

698 5.7 72.7 .003 _______

697 18. 0 45. 5 . 006 . 007 

696 26. 7 20. 2 . 009 . 008

695 14. 2 60. 0 . 005 . 005 

694 26. 2 26. 0 . 008 . 008

1. 0 264. 4 693 34. 6 5. 0 Oil . 010
500 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Sliderock Mountain, Mont., lot 1301 Continued

Bed

14.

13. 

12.

11.

10.

Description

Grandeur Tongue of Park City Formation: 

Covered.._________________________

Dolomite: hard, yellowish-gray (2.5Y 

7/2), very thick bedded, aphanitic; 

unit is fractured and brecciated.

Dolomite: hard, dark-gray (N 4), 

thick-bedded, aphanitic.

Dolomite: hard, yellowish-gray (2.5Y 

7/2), very thick bedded, aphanitic.

Sandstone: dolomitic, calcareous, hard, 

yellowish-gray (2.5 Y 7/2), very 

thick bedded, very fine grained.

Dolomite: calcareous, hard, yellowishgray (10 YR 7/1), thick-bedded, 

aphanitic.

Limestone: hard, dark-gray (N 4), 

thin-bedded, aphanitic.

Dolomite: hard, very pale brown 

(10YR 7/2), thick-bedded, aphanitic. 

Fossil-colln. No. 11671.

Dolomite: hard, pale-brown (2.5Y 

6/2), very thick bedded, aphanitic.

Sandstone: calcareous, hard, yellowish-gray (2.5 Y 7/2), very thick 

bedded, very fine grained.

Dolomite: hard, pale-brown (2.5 Y 

6/2), very thick bedded, aphanitic; 

contains many calcite veinlets.

Dolomite: hard, pale-brown (2.5 Y 

6/2), very thick bedded, aphanitic.

Sandstone: dolomitic, hard, yellowishgray (2.5 Y 7/2), thick-bedded, finegrained.

Dolomite: medium-hard, yellowishgray (1QYR 8/1), thick-bedded, 

aphanitic.

Dolomite: medium-hard, medium-gray 

(N 6), thick-bedded, aphanitic. Underlain by sandstone of the Quadrant 

Formation.

Thickness 

(feet)

35.0

17. 0

Cumulative

thickness

(feet)

299.4

316.4

. 8 317. 2

2. 0 319. 2

1. 7 320. 9

4. 7 325. 6

1. 0 326. 6

12. 0 338. 6

4. 4 343. 0

5. 2 348. 2

1. 2 349. 4

1. 2 350. 6

5. 8 356. 4

6. 7 363. 1

6. 8 369. 9

Chemical analyses (percent)

Uranium

Sample PjOs

Acid 

insoluble

Padiometric

eV

Chemical 

U

West Fork of Blacktail Creek, Mont., lot 1302

[Permian rocks measured near West Fork of Blacktail Creek, SE}4 see. 26, T. 12 S.,R. 6 W., Beaverhead County, Mont., on southeast limb of an anticline. Beds G-l through 

F-42 measured in bulldozer trench near top of hill on northeast side of creek; beds Ls-44 through Us-87 measured in hand trench 1,500 ft farther south and about 250 ft up 

the slope from Blacktail road; rest of section measured from natural exposures near road. Beds strike N. 73° E. and dip 37° S. Section measured by E. R. Cressman 

C. W. Tandy, and W. H. Wilson and sampled by J. L. Elliott, B. K. Replogle, W. J. Garmore, and R. F. Gosman, in July 1949. Analyzed for PaOs and acid insoluble 

by U.S. Bur. of Mines and for other constituents by U.S. Geol. Survey]

Chemical analyses (percent)

Bed 

D-105...

104.

103.

102.

101.

To-100.

Description

Dinwoody Formation, lower part:

Mudstone: calcareous, crumbly, light- 1. 2

brown (7.5YR 6/4), fissile.' 

Covered_______________________ 8. 0

Limestone: clayey, crumbly, light- 1. 2 

brown (7.SYR 6/4), fissile.

Dolomite: hard, medium-gray (N&), .3 

thin-bedded; aphanitic.

Covered. Mudstone similar to that 7. 2 

of bed D-105 was exposed by digging and probably constitutes the 

entire interval.

Tosi Chert Member of Phosphoria Formation:

Limestone: sandy, brownish-gray 2. 7 

(1QYR 4/1), thick-bedded; contains 20 percent brachiopod shells, 

most of which are fragmental; 

sand is fine; grades from bed below. Fossil-colln. No. 18577.

Cumulative 

Thkk- thickness 

ness (feet) (feet)

Uranium

Sample

Acid 

insoluble Oil

Organic 

matter

Radiometric elT

Chemical 

U

2.7
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 501

West Fork of Blacktail Creek, Mont,, lot 1302 Continued

Bed Description

Tosi Chert Member of Phosphoria Formation Continued

To-99_____- Dolomite: silty, medium-hard, lightbrownish-gray (10 YR 6/1), thinbedded, aphanitic; contains glauconite.

98_____ Dolomite: silty, medium-hard, palebrown (2.5 Y 6/2), thin-bedded, 

aphanitic; contains glauconite. 

Fossil-colln. No. 11670.

97_____ Dolomite: cherty, silty, mediumhard, pale-brown (2.5 Y 5/2), thinbedded, aphanitic. Fossil-colln. 

No. 11670.

96_____ Chert: dolomitic, hard, light-brownish-gray (10 YR 5/1), thin-bedded.

95_---_ Chert: dolomitic, silty, medium-hard, 

pale-brown (2.5 Y 5/2), thin-bedded.

94__-__ Dolomite: cherty, hard, mediumgray (N 5), very thick bedded, 

aphanitic.

93_- - _ _ Chert: dolomitic, silty, medium-hard, 

pale-brown (2.5 y 5/2), thin-bedded.

92-__. Chert: hard, brownish-gray (10 YR 

4/1), thick-bedded; contains several indistinct laminae of very fine 

grained cherty sandstone; irregular 

contact with bed below. 

Intertonguing Tosi Chert Member of 

Phosphoria Formation and upper member of Shedhorn Sandstone:

Us-91 ______ Sandstone: cherty, hard, light-brownish-gray (10 YR 6/1), thick-bedded, 

fine-grained; contains glauconite.

To-90___--_ Chert: dolomitic, hard, brownishgray (10y«4/l), thin-bedded; irregular contact with bed below.

Us-89--_--.- Sandstone: hard, brownish-gray 

(10 YR 4/1), thick-bedded, very 

fine grained; contains glauconite; 

contains several columnar bodies 

of black sandstone several millimeters in diameter and as much as 

a foot long that are nearly perpendicular to bedding; irregular 

contact with bed below.

To-88__--._ Chert: brittle, pale-brown (10 YR 

6/2), thick-bedded; bedding surfaces are irregular.

Us-87------ Sandstone: cherty, hard, brownishgray (10 YR 4/1), thick-bedded, 

very fine grained; contains glauconite; contains numerous very 

irregular patches of very pale 

brown (1QYR 7/2) cherty sandstone that is somewhat better cemented than rest of unit; contains 

several long columnar bodies 2 mm 

in diameter of black sandstone 

that are perpendicular to the bedding. 

Retort Phosphatic Shale Member of

Phosphoria Formation:

Rt-86_--__- Phosphorite: cherty, medium-hard, 

light-brownish-gray (10 YR 6/1), 

medium-pelletal; contains glauconite; grades from bed below.

85______ Phosphorite: muddy, soft, brownishgray (10 YR 3/1), thin-bedded, 

finely pelletal.

Chemical analyses (percent)

Cumulative 

Thick- thickness 

ness (feet) (feet)

Uranium

Sample

Acid 

PsOj insolubk Oil

Organic 

matter

Radio- Chemical 

metric eU U

1.0

2.4

12. 2

2.0

1.3

3.8

3.7

6.1

18.3

19.2

21.2

22.5

22.9

26. 7

2. 0 28. 7

5. 1 33.8

18. 0 51. 8

11.9 63.7

48. 0 111. 7

7 112.4 ERC-668 26.4 25.8 ___. _-.-_ 0.010 0.010

1. 0 113. 4 667 27.5 20.2 _.__ _____ .010 .010
502 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

West Fork of Blacktail Creek, Mont., lot 1302 Continued

Chemical analyses (percent)

Uranium

Bed Description

Retort Phosphatic Shale Member of

Phosphoria Formation Continued

Rt-84______ Phosphorite: muddy, soft, brownishgray (10 YR 3/1), finely pelletal; 

pellets are concentrated in laminae 

1 mm thick; grades from bed below. 

Fossil-colln. No. 11669.

83______ Mudstone: phosphatic, soft, brownish-gray (WYR 3/1), thin-bedded; 

apatite is very finely pelletal; 

grades from bed below.

82------ Mudstone: dolomitic, medium-hard,

light-brownish-gray (10 YR 6/1), 

thin-bedded.

81------ Mudstone: phosphatic, medium-hard,

brownish-gray (10 YR 3/1), thinbedded; apatite is very finely pelletal; grades from bed below.

80_ _ _ _- _ Mudstone: phosphatic, medium,hard, 

brownish-gray (10 YR 3/1), thinbedded; apatite is very finely pelletal.

79______ Dolomite: muddy, medium-hard,

light-yellowish-brown (10YR 6/4), 

aphanitic; grades from bed below. 

Fossil-colln. No. 11668.

78_ -____ Mudstone: dolomitic, soft, brownishgray (10 YR 3/2).

77---___ Phosphorite(?): muddy, soft, brownish-black (10 YR 2/1); bed is extensively sheared.

76_ _ - _ _ _ Mudstone: soft, brownish-gray (10 YR 

3/2), thin-bedded; grades from 

bed below.

75______ Phosphorite: muddy, soft, brownishgray (WYR 3/2), thin-bedded, 

very finely pelletal; grades from 

bed below.

74_-____ Mudstone: phosphatic(?), soft, palebrown (10 YR 5/2), thin-bedded.

73_--__- Dolomite: phosphatic(?), mediumhard, pale-brown (10 YR 6/2), 

aphanitic; grades from bed below.

72_----_ Mudstone: phosphatic, soft, brownish-gray (10YR 3/2), thin-bedded; 

grades from bed below.

71_-___- Mudstone: phosphatic, soft, brownish-gray (WYR 3/2), thin-bedded; 

grades from bed below.

70_-_-__ Mudstone: phosphatic, crumbly, 

brownish-gray (WYR 3/2), thinbedded; apatite is finely pelletal; 

grades from bed below.

69--____ Mudstone: phosphatic, soft, brownish-gray (WYR 3/1), thin-bedded; 

grades from bed below.

68--_-__ Dolomite: medium-hard, brownishgray (WYR 4/1), aphanitic.

67--__-_ Phosphorite: soft, brownish-gray 

(WYR 4/1), thin-bedded, mediumpelletal.

66_-_-__ Mudstone: medium-hard, brownishgray (WYR 3/1) to grayish-brown 

(WYR 4/2), thin-bedded; grades 

from bed below.

65______ Mudstone: medium-hard, brownishgray (WYR 3/1) to grayish-brown 

(WYR 4/2), thin-bedded; grades 

from bed below.

64___-__ Mudstone: soft, brownish-gray 

(WYR 3/1), thin-bedded; contains 

a few poorly defined laminae of 

fine grained apatite pellets.

Cumulative 

Thick- thickness 

ness (feet) (feet)

2. 4

3. 3

. 8 

1. 1

Sample

Acid Organic Radio- Chemical 

insoluble Oil matter metric eH U

2.7 116.1 ERG-666 16.3 37.8 ____ ----- 0.008 0.007

3. 8 119. 9 665 8.1 52.2 ____ ----- .006 .004

122. 3

125.6

664 5. 6 40. 8

663 8. 3 53. 7

. 002

. 004

3. 3 128. 9 662 10.6 49.3 ____ ----- .005 .005

2. 7 131. 6 CWT 661 3. 4 46. 7

660 8. 1 47. 2

659 4. 6 63. 4

658 16. 1 34. 6

. 5

.3

1.5

2.5

1. 9

1. 0

. 8

2.0

3. 0

132. 1}

132.4

133. 9

136.4

138. 3 X

139. 3

140. l'

142. 1

145. 1

2. 4 147. 5

148. 3

149. 4

2. 8 152. 2

3. 0 155. 2

1. 7 156. 9

ERG-669 1. 7 9. 8

652 26. 7 14. 2

651 4. 6 52. 7

650 2. 5 63. 2

649 4. 6 58. 0

. 001

.004 --_--

.003 -__-.

. 007 . 007

657 12.0 39.0 ____ -----

656 11.4 37.8 _.__ -----

655 8.1 52.2 __._ -----

654 7. 3 44. 8 1. 3 12. 01

653 10.2 46.6 ___- _____

. 005

. 004

. 004

.005

. 006

.002

. 009

.005

. 004

. 004

.005

. 005

. 005

. 010

. 006
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 503

West Fork of Blacktail Creek, Mont., lot 1302 Continued

Chemical analyses (percent)

Uranium

Thinness (feet)

1.

1.

Bed Description

Retort Phosphatic Shale Member of

Phosphoria Formation Continued

Rt-63__-__- Phosphorite and mudstone, inter 

bedded: medium-hard brownishgray (10 YR 3/1) thin-bedded finely 

pelletal phosphorite interbedded 

with medium-hard brownish-black 

(10 YR 2/1) phosphatic(?) mudstone.

62__-___ Phosphorite: medium-hard, brownish-gray (10 YR 4/1), thick-bedded, 

finely pelletal and oolitic. Fossilcollection number 11667.

61__-__- Mudstone: phosphatic, soft, brownish-black (WYR 2/1), thin-bedded; 

grades from bed below.

60____-_ Phosphorite: crumbly, light-brownish-gray (WYR 6/1), thin-bedded, 

finely pelletal.

59______ Mudstone: phosphatic, soft, brownish-black (WYR 2/1), thin-bedded; 

apatite is very finely pelletal.

58______ Dolomite: muddy, medium-hard,

grayish-brown (2.5F 4/2), aphanitic.

57------ Mudstone: phosphatic, crumbly,

brownish-gray (10 YR 3/1), thinbedded; apatite is very finely pelletal.

56-_____ Dolomite: muddy, medium-hard, 

grayish-brown (2.5 F 4/2), aphanitic.

55______ Phosphorite: muddy, crumbly,

brownish-gray (WYR 3/1), thinbedded; very finely pelletal.

54__-___ Dolomite: medium-hard, pale-brown 

(10[YR 5/2), thick-bedded, aphanitic.

53_-____ Phosphorite: muddy, crumbly, 

yellowish-gray (WYR 8/1), thinbedded, very finely pelletal. Fossil-colln. No. 11666.

52_____- Phosphorite: muddy, medium-hard, 

light-yellowish-brown (10FS6/4), 

thin-bedded, finely pelletal.

51_-____ Mudstone: medium-hard, yellowishbrown, thin-bedded.

50-_-___ Mudstone: soft, dark-brown, thinbedded.

49_____- Mudstone: phosphatic, soft, darkbrown, thin-bedded.

48_ _-___ Mudstone: medium-hard, brownishgray (10 YR 4/1). Fossil colln. 

No. 11665.

47-____- Mudstone: phosphatic, crumbly, 

grayish-brown (7.5YR 3/2), fissile; 

apatite is medium pelletal. Fossilcolln. No. 11665.

46______ Chert: brittle, brownish-gray (10 YR

4/1); grades from bed below.

45______ Chert: hard, light-gray (N 7)_ _._ 3.

Lower tongue of Shedhorn Sandstone: 

Ls-44 __-_-_ Sandstone: medium-hard, lightyellowish-brown (WYR 6/4), very 

thick-bedded, fine-grained.

(43)_____ Covered. Comparison with neighboring sections indicates that this 

interval is too thin. Either the 

thickness is in error or the concealed beds are faulted.

Cumulative

thickness

(feet)

2. 9

14. 0

Sample P.Os

Acid 

insoluble Oil

Organic 

matter

Radio- Chemical 

metric eV U

0.9 157.8 ERG-648 21.6 26.2 ____ -____ 0.008 0.007

159. 1 647 30.6 11.3 .008

2.7 161.8 CWT-677 8.4 44.8 1.4 11.15 .006

1. 5

162. 5'

162. 9

164. 4

8 165. 2

1. 0 166. 2

8 167. 0

1. 0 168. 1

170.

170. 6

170. 8

171. 2

172. 0

8 172. 8

178. 7

192. 7

47. 0 239. 7

676 18. 6 27. 9

675 3. 1 28. 1

007

. 003

674 10. 3 35. 1 1. 3 10. 79 . 007

. 010

.004

.006

. 005

R7Q 19 91 9

672 13.8 34.2 ____ .

R71 19 17°

670 14. 7 36. 0 - - - - .

ERG-680 26.7 20.5 ____ .

_____ .002

.__._ .007

.__._ .002

.____ .007

._-__ .007

. 005

.005

. 006

679 12.9 50.5 ____ ----- -007 006

678 5 94.3 __-- ----- .0005 .000
504 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

West Fork of Blacktail Creek, Mont., lot 1 SOS Continued

Chemical analyses (percent)

Bed Description

Franson Tongue of Park City Formation: 

F-42_______ Dolomite: silty, hard, very pale

brown (10 YR 7/2), aphanitic.

41_______ Dolomite: hard, light-brownish-gray

(IQYR 6/1), thick-bedded, aphanitic.

40__.____ Dolomite: muddy, hard, very pale 

brown (IQYR 7/2), thick-bedded, 

aphanitic.

39_______ Dolomite: sandy, medium-hard,

yellowish-gray (2.57 7/2), aphanitic.

38_ ______ Dolomite: hard, yellowish - gray

(IQYR 7/1), thick-bedded; irregular contact with bed below. 

Rex Chert Member of Phosphoria Formation:

R-37_______ Chert: dolomitic, hard, brownishgray (IQYR 3/1), thin-bedded, 

aphanitic; grades along bedding 

into hard very thick bedded 

brownish-gray (WYR 3/1) chert.

36_______ Dolomite: silty, medium-hard, lightbrownish-gray (IQYR 5/1), thinbedded, aphanitic; irregular contact with bed below.

35_______ Dolomite: silty, hard, light-brownish-gray (IQYR 5/1), thick,bedded.

34________ Dolomite: cherty, imiddy, brittle,

medium-gray (N 5), thick-bedded, 

aphanitic; grades from bed below.

33_ _ ____ Covered.________________________

32_______ Dolomite: muddy, hard, lightbrownish-gray (\.QYR 5/1), thickbedded, aphanitic.

31_______ Chert: dolomitic, hard, medium-gray

(N 5), thick-bedded.

(30)______ Covered_____ ____________________

29_______ Chert: hard, pale-brown (2.5F 5/2),

thin-bedded.

28 ____ Chert: silty, phosphatic(?), hard, 

pale-brown (IQYR 5/2), thinbedded.

27_______ Chert: hard, pale-brown (2.575/2),

thin-bedded; grades from bed below.

26_______ Chert: brittle, light-brownish-gray

(10 YR 5/1), thick-bedded.

25_______ Chert: silty, medium-hard, grayishbrown (7.5 YR 4/2), thin-bedded.

24 ____ Chert: brittle, light-brownish-gray 

(IQYR 5/1), thin-bedded; irregular 

contact with bed below; cut by 

several small faults of unknown 

displacement.

23_______ Chert: silty, crumbly, dusky-brown

(IQYR 2/2), thick-bedded; grades 

from bed below.

22_______ Chert: soft light-brown (7.5YR 5/6)

chert interbedded with mediumhard dark-gray (N 3) chert. 

Meade Peak Phosphatic Shale Member of

Phosphoria Formation: 

M-21______ Mudstone: soft, pale-brown (7.5 YR

6/2), thick-bedded; contains thin 

layer of phosphorite less than 0.1 

ft thick at top.

Thick- Cumulative

ness thickness

(feet) (feet)

4. 8 244. 5

1. 3 245. 8

2. 0 247. 8

9 248. 7

1. 7 250. 4

12. 7 263. 1

8 263.9

1. 2 265. 1

4. 2 269. 3

4. 5 

2. 1

9. 5 

13.0

273.8

275.9

1. 4 277. 3

286.8

299.8

1. 3 301. 1

1. 0 302. 1

6. 7 308. 8

1. 2 310. 0

17. 3 327. 3

327.8

Uranium

Sample

Acid 

insoluble OH

Organic 

matter

Radiometric eV

Chemical 

U

ERG-646 0.3 94.0 -___ ----- 0.001

1. 1 328. 9 WHW-645

1. 8 330. 7 644

2 95.2

6 87.0

0005

003 0. 001
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 

West Fork of Blacktail Creek, Mont., lot 1302 Continued

505

Chemical analyses (percent)

Bed Description

Meade Peak Phosphatic Shale Member of

Phosphoria Formation Continued 

M 20______ Mudstone: soft weak-orange (7.5 YR

7/6) thin-bedded mudstone interbedded with soft black (N 2) thinbedded phosphatic mudstone; apatite is very finely pelletal.

19______ Mudstone: soft, light-brown (7.5YR

5/6>, thick-bedded.

18______ Phosphorite: muddy, soft, black

(N 2), thin-bedded, medium-pelletal.

17______ Phosphorite: silty, soft, black (AT 2),

thick-bedded, finely pelletal.

16______ Mudstone: plastic, medium-yellowish-brown (10 YR 4/4), thick-bedded.

15______ Phosphorite: muddy, soft, black

(N 2), thin-bedded, mediumpelletal.

14______ Mudstone: crumbly, light-brown

(7.5 YR 5/6); grades from bed 

below (Analysis may be in error).

13______ Mudstone: muddv, phosphatic, clastic, brownish-black (10 YR 2/1); 

apatite is medium pelletal.

12______ Phosphorite: muddy, black (N 1),

crumbly, finely pelletal.

!]____-_ Phosphorite: sandy, cherty, medium-hard, brownish-gray (10 YR 

3/1), thin-bedded, finely pelletal; 

contains phosphatic skeletal fragments. Fossil-colln. No. 11664.

10____-_ Sandstone: phosphatic, mediumhard, dusky-brown (10 YR 2/2), 

thick-bedded, very fine grained; 

contains phosphatic skeletal fragments. Fossil-colln. No. 11664. 

Grandeur Tongue of Park City Formation, upper part:

G 9___-_-__ Mudstone: cherty, crumbly, weakyellowish-orange (WYR 7/6).

8__-____- Dolomite: crumbly, moderate-yellowish-brown (10 YR 5/6) thinbedded, aphanitic.

7________ Dolomite: silty, medium-hard, weakyellowish-orange (2.5 Y 7/4), thickbedded, aphanitic.

6________ Sandstone: dolomitic, medium-hard,

weak-yellowish-orange (2.5F 7/4), 

very fine grained.

5---____- Dolomite: soft, weak-yellowishorange (2.5F 8/4), aphanitic.

4._______ Dolomite: silty, medium-hard, weakyellowish-orange (2.5F 7/4), aphanitic.

3----_-_- Dolomite: silty, medium-hard, yellowish-gray (2.5y 7/2), thin-bedded, aphanitic.

2_ _______ Sandstone: crumbly, weak-yellowish-orange (10yR 7/6), finegrained.

l--_--___ Dolomite: silty, medium-hard, yellowish-gray (2.5 y 7/2), thin-bedded, aphanitic. Underlying beds 

are covered.

Thick- Cumulative

ness thickness

(feet) (feet)

Uranium

Sample P.O5

Acid 

insoluble

Organic Padio- Chemical 

Oil matter metric e~U U

1.5 332.2 WHW-643 6.5 69.5 ____

1. 9 334. 1

. 9 335.

4 335. 4

3 335. 7

336. 2

8 337.

. 7 338. 3 

1. 1 339. 4l

339. 7

3. 4 343. 1

2. 7 345. 8

6. 0 351. 8

5. 6 357. 4

2 2 359. 6

2. 9 362. 5

4. 5 367. 0

5. 0 372. 0

15. 0 387. 0

642 2. 3 81. 3

641 12. 0 52. 5

0.004

002

. 005 0. 004

640 20.3 26.3 1.3 10.79 .011

6 336. 8 ERG-639 3. 2 71. 5 005

Oil

003

638 19.8 28.8 ____ _____ .009 .008

637 19. 4 41. 0 . 008 .007
506 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Alpine Creek, Mont., lot 1807

[Permian rocks measured in southeast-facing slope at head of Alpine Creek, N}4 sec. 26, T. 10 S., K. 2 W., Madison County, Mont., on gently dipping east limb of Kuby 

Vallej syncline. Retort Phosphatic Shale Member of Phosphoria Formation measured and sampled in hand trench; all others from natural exposure. Beds strike N. 

5° E. and dip 8° W. Section measured by E. R. Cressman, W. H. Wilson, and R. L. Jones and sampled by W. J. Qarmoe and J. L. Elliott, in August 1949. Analyzed 

for PjOs and acid insoluble by U.S. Bur. of Mines and for uranium by U.S. Geol. Survey]

Chemical analyses (percent)

Bed

(50). 

Us-49-

48.

(47). 

46.

45. 

44.

To-43.

42.

41.

(40). 

39.

38_

Rt-37_ 

36_ 

35.

Description

Upper Tongue of Shedhorn Sandstone:

Beds overlying Us-49 are covered; 

thickness to contact with Dinwoody 

estimated.

Sandstone: dolomitic, medium-hard, 

very pale orange (7.5YR 8/2), thinbedded, cross-bedded, fine-grained; 

contains about 15 percent of dolomitic shell fragments; contains a few 

lenses 0.01 to 0.05 ft by 0.03 to 0.5 

ft of dolomite, some of which appear 

to be clastic. Fossil-colln. No. 

11689.

Dolomite: cherty, medium-hard, very 

pale orange (7.5YR 8/2), thickbedded; approximately half of bed 

is composed of silicified shell fragments. Fossil-colln. Nos. 11688 and 

18580.

Covered._ _________________________

Dolomite: sandy, medium-hard, very 

pale orange (7.5YR 8/2), thickbedded; dolomite consists largely of 

shell fragments; sand is fine. Fossilcolln. No. 11687.

Sandstone: medium-hard, light-gray 

(N 7), very fine grained.

Sandstone: medium-hard, light-gray 

(N 7), very fine grained; contains 

numerous roughly cylindrical columns 0.1 ft to 0.3 ft in diameter of 

hard pinkish-gray very fine grained 

cherty sandstone arranged perpendicular to bedding.

Tosi Chert Member of Phosphoria Formation:

Sandstone and chert: medium-hard 

light-gray (N 7) sandstone and hard 

light-brownish-gray (WYR 6/1) 

sandy chert; sand is very fine; grades 

from chert containing 25 percent 

irregular bodies of sandstone at base 

to sandstone containing 30 to 40 

percent irregular bodies of chert at 

top; grades from bed below.

Chert: hard, light-brownish-gray 

(WYR 6/1), very thick bedded; contains irregular bodies of very fine 

grained sandstone at top; grades 

from bed below.

Chert: brittle, light-brownish-gray 

(WYR 6/1), thin-bedded; bedding 

surfaces are undulant.

Covered._ _________________________

Chert: brittle, brownish-gray (10 YR 

3/1), thin-bedded.

Similar to bed To-39_______---_---_

Retort Phosphatic Shale Member of Phosphoria Formation:

Phosphorite: muddy, soft, light-brown 

(7.5 YR 5/4), thick-bedded, very 

finely pelletal.

Phosphorite: medium-hard, light-gray 

(N 7), thin-bedded, very finely 

pelletal.

Mudstone: plastic, pale-brown (WYR 

5/3).

Uranium

Cumulative 

Thickness thickness 

(feet) (feet)

10. 0

4. 9

4. 2

2.0 

3. 0

14. 0 

4. 8

8.0

36. 5

11. 5

9. 5 

5. 9

Sample

Acid 

insoluble

Radiometric Chemical 

U

10.0

14.9

19. 1

21. 1

24 1

38. 1

42. 9

50.9

87. 4

98.9

108.4

114. 3

2. 4 116. 7 WHW-3394 0. 9 90. 6 0. 001

117. 1

117.8

1. 8 119. 6

3393

3392

30. 5 13. 17

4.6 64. 6

. 009

.004

0. 001

. 009

.003
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 507

Alpine Creek, Mont., lot 1307 Continued

Bed Description

Retort Phosphatic Shale Member of Phosphoria Formation Continued 

Rt-34________ Dolomite: medium-hard, pale-brown

(10 YR 5/3), fissile, aphanitic.

33________ Phosphorite: calcareous, cherty, medium-hard, light-gray (N 7), thinbedded, very finely pelletal. 

32________ Mudstone: phosphatic, medium-hard,

moderate-yellowish-brown (IOYR 

5/6), thin-bedded. 

31________ Chert: brittle, brownish-gray (10 YR

3/1), thick-bedded; contains phosphatic skeletal fragments; grades 

from bed below. 

30________ Chert: hard, light-brownish-gray

(IOYR 6/1), very thick bedded; 

grades from bed below. 

Lower tongue of Shedhorn Sandstone: 

Ls-29_ _______ Sandstone: hard, light-gray (N 7),

thick-bedded, fine-grained; contains 

phosphatic skeletal fragments; 

grades from bed below.

28 ________ Sandstone: carbonatic, hard, lightgray (N 7) to pale-brown (7.5 YR 

6/2), thick-bedded, fine-grained; contains phosphatic skeletal fragments, 

fragments of pelletal phosphorites, 

dolomitic phosphorites, and bryozoan fragments replaced by apatite; 

contains dolomite pebbles, 3 mm in 

diameter at base.

Franson Tongue of Park City Formation: 

F-27_________ Dolomite: medium-hard, pale-brown

(IOYR 6/2), thick-bedded, aphanitic; 

grades from bed below.

26_________ Dolomite: sandy, hard, weak-yellowishorange (IOYR 8/4), thick-bedded, 

aphanitic; sand is very fine. 

25_________ Dolomite: hard, very pale brown

(10 YR 7/3), thick-bedded, aphanitic; 

grades from bed below. 

Lower tongue of Shedhorn Sandstone; contains thin bed of Rex Chert Member of 

Phosphoria Formation: 

Ls-24-_______ Sandstone: dolomitic, medium-hard,

weak-yellowish-orange (IOYR 8/4), 

thin-bedded, aphanitic; sand is fine. 

Fossil-colln. No. 18579. 

R-23_________ Chert: hard, very pale brown (IOYR

7/2), very thick bedded. 

Ls-22________ Sandstone: hard, yellowish-gray (IOYR

7/1), thick-bedded, fine-grained; contains apatite pellets and skeletal 

fragments and fragments of phosphorite; basal 0.2 ft contains chert 

nodules 0.15 ft in diameter. 

21------__ Dolomite: hard, light-brownish-gray

(IOYR 6/1), thick-bedded, aphanitic; 

penetrated by thin pencillike 

stringers of fine-grained to dolomitic 

sandstone of overlying bed; contains 

numerous chert nodules 0.1 to 0.2 

ft in diameter in basal 0.2 ft of bed. 

20________ Sandstone: hard, light-gray (N 7),

very thick bedded, fine-grained: contains apatite pellets and skeletal 

fragments; grades from bed below. 

19________ Sandstone: phosphatic, conglomeratic,

hard, light-gray (N 7), thick-bedded, 

fine-grained; apatite is both pelletal 

and skeletal; pebbles average about 

16 mm in diameter and are composed 

mostly of chert and dolomite. Fossilcolln. No. 11686.

Chemical analyses (percent)

Thickness 

(feet)

Cumulative

thickness

(feet)

Uranium

0. 8 120.

121.

1. 0 122. 1

3. 7 125. 8

6 126. 4

6. 7 133. 1

3. 0 136. 1

5. 2 141. 3

3. 6 144. 9

6. 8 151. 7

3. 2 154. 9

2. 2 157. 7

1. 7 158. 8

2. 3 161. 1

9 162. 0

Sample

Act, Radiometric Chemical 

eV U

120. 6} WHW-3391

3390

3389

2. 6

12. 1

5.6

29. 4 0. 002

52. 5

79.9

005

003

0. 002

004

003

3388

3387

2.3 90. 0

53. 7

000

002

002

002
508 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Alpine Creek, Mont., lot 1307 Continued

Chemical analyses (percent)

Bed Description

Meade Peak Phosphatic Shale Member of

Phosphoria Formation: 

M-18_________ Phosphate rock: conglomeratic, sandy,

hard, light-gray (N 7), thick-bedded, 

skeletal; pebbles average 3 mm in 

diameter, are composed mostly of 

chert and dolomite and are concentrated in layers. Fossil-colln. 

No. 11685.

Grandeur Tongue of Park City Formation: 

G-17__________ Dolomite: hard, yellowish-gray (10 YR

7/1), thick-bedded, aphanitic; contains a few chert nodules 5 mm in 

diameter.

16._________ Dolomite: hard, light-yellowish-brown

(IOYR 6/4), thick-bedded, aphanitic.

15__________ Dolomite: hard, yellowish-gray (2.5F

7/2), thick-bedded, cross-bedded, 

granular; irregular contact with bed 

below.

14__________ Dolomite: hard, very pale brown

(10 YR 7/2), thick-bedded, granular; 

grades from bed below.

13__________ Dolomite: hard, very pale brown

(10 YR 7/3), thick-bedded, crossbedded, very fine grained; contains 

a few chert nodules averaging 25 mm 

in diameter.

12._________ Dolomite: hard, yellowish-gray (IOYR

8/1), thick-bedded, granular.

11__________ Dolomite: silty, hard, yellowish-gray

(IOYR 8/1), thick-bedded, aphantic.

10-_ ---_____ Sandstone: dolomitic, hard, white 

(N 9), thick-bedded, fine-grained; 

grades from bed below.

9___________ Dolomite: sandy, hard, light-gray (N

8), thin-bedded, cross-bedded, aphanitic; sand is very fine; contains 

subangular fragments of sandy dolomite 1 mm in diameter and a few 

small chert nodules that replace 

both dolomite matrix and sandy 

dolomite fragments.

8___________ Dolomite: silty, hard, light-gray (N 8),

very thick bedded, very fine grained.

7___________ Sandstone: dolomitic, hard, light-gray

(N 8), very thick bedded, finegrained; 50 percent of bed at base 

grading to 20 percent of bed at top 

consists of pebbles averaging 20 mm 

in diameter of aphanitic dolomite; 

irregular contact with bed below.

6___ ________ Dolomite: medium-hard, light-gray

(N 8), massive; consists of subangular to subrounded pebbles of aphanitic dolomite averaging 8 to 10 mm 

in diameter, cemented by aphanitic 

dolomite; grades from bed below.

5. ________ Dolomite: medium-hard, light-gray

(N 8) to white (N 9), thick-bedded, 

aphanitic; grades from bed below.

4. __________ Dolomite: sandy, hard, light-gray

(N 8), very thick bedded; composed 

of subangular to subrounded pebbels 

of aphanitic dolomite (50 percent) in 

sandy dolomite matrix; sand is 

very fine.

Cumulative 

Thickness thickness 

(feet) (feet)

Uranium

Sample

Acid Radiometric Chemical 

insoluble eU U

1. 1 163. 1 WHW-3386 1. 1 19. 1 0. 007 0.006

2. 9 166. 0

2. 9 168. 9

3. 3 172. 2

3. 8 176. 0

. 8 176. 8

2. 2 179. 0

2. 8 181. 8

. 8 182. 6

. 9 183. 5

1. 7 185. 2

2. 4 187. 6

2. 0 189. 6

2. 8 192. 4

2. 6 195. 0
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 509

Alpine Creek, Mont., lot 1307 Continued

Chemical analyses (percent)

Bed

G-3.

Q-l.

Description

Grandeur Tongue of Park City Formation 

Continued

Dolomite; medium-hard, light-gray 

(N 8) to white (JV9), thick-bedded, 

aphanitic.

Dolomite: sandy, medium-hard, white 

(N 9), thick-bedded; sand is very 

very fine. 

Quadrant Formation, uppermost bed:

Sandstone: dolomitic, hard, white (N 

9), very thick bedded; sand is fine.

Cumulative 

Thickness thickness

Uranium

(feet) (feet) Sample

Acid Radiometric Chemical 

insoluble eU U

15. 5 210. 5

. 3 210. 8

5. 4 216. 2

Canyon Camp, Mont., lot 1811

[Permian rocks measured at Canyon Camp, Ruby River Canyon, NE}4 sec. 18, T. 9 S., R. 3 W., Madison County, Mont., on overturned west limb of Ruby Valley syncllne. 

Beds strike N. 10° W. and dip 50° W. Beds O-l through R-31 measured from natural exposures on north side of canyon 300 ft above ri^er; rest of section measured on 

south side of canyon, beds F-33 through Rt-48 and To-80 through D-99 from natural exposures, and beds Rt 49 through To-79 irom prospect trench. Measured by C. 

W. Tandy, R. S. Jones, E. R. Cressman, R. F. Oosman, and W. J. Garmoe and sampled by Gosman and Garmoe, in August 1949. Analyzed for PaOs and acid insoluble 

by U.S. Bur. of Mines and for uranium by U.S. Geol. Survey]

Chemical analyses (percent)

Bed

D-99. 

98.

To-97.

Us-96. 

95. 

94.

93. 

92_

To-9l_ 

90.

89.

Us-88.

Cumulative 

Thickness thickness 

Description (feet) (feet)

Din woody Formation, basal beds:

Limestone: hard, light-brownish-gray 1. 8 ______

(10YR 5/1), thin-bedded, skeletal.

Covered; probably underlain by cal- 15. 0 ______

careous mudstone.

Tosi Chert Member of Phosphoria Formation:

Mudstone: cherty, dolomitic, hard, 12. 3 

pale-brown (10 YR 5/2), thin-bedded; 

contains glauconite. 

Upper tongue of Shedhorn Sandstone:

Sandstone: cherty, hard, light-brown- . 2 

ish-gray (IOYR 5/1), thin-bedded, 

fine-grained; contains glauconite.

Chert: dolomitic(?), medium-hard, . 3 

grayish-brown (7.5YR 4/2), thinbedded; contains glauconite.

Sandstone: cherty, hard, light-brown- . 4 

ish-gray (WYR 5/1), thin-bedded, 

fine-grained; contains glauconite; irregular contact with bed below.

Chert: hard, light-brownish-gray 2. 7 

(WYR 5/1), thick-bedded; contains 

glauconite; irregular contact with 

bed below.

Sandstone: cherty, medium-hard, very 4. 2 

pale brown (10 YR 7/2), thick-bedded, very fine grained; contains 

glauconite.

Tosi Chert Member of Phosphoria Formation:

Chert: hard, medium-gray (N 5), 12. 8 32. 9 

thick-bedded; contains glauconite.

Chert: dolomitic, hard, light-brownish- 6. 0 

gray (IOYR 5/1), thick-bedded; contains glauconite and numerous lenses 

of very fine grained cherty sandstone; 

irregular contact with bed below.

Chert and dolomite, interbedded: dolo- 2. 1 

mitic hard medium-gray (N 5) 

chert interbedded with mediumhard light-brownish-gray (IOYR 6/1) 

dolomite; contains glauconite and 

phosphatic skeletal fragments; irregular contact with bed below. 

Upper tongue of Shedhorn Sandstone:

Sandstone: cherty, medium-hard, gray- 2. 0 

ish-brown (IOYR 4/2), thin-bedded, 

fine-grained; contains glauconite and 

phosphatic skeletal fragments; irregular contact with bed below.

Uranium

Sample

Acid 

insoluble

Radiometric Chemical 

eV U

12. 3

12. 5

12. 8

13. 2

15. 9

20. 1

38.9

41. 0

43. 0

709-931 O-64 16
510 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD 

Canyon Camp, Mont., lot 1811 Continued

Chemical analyses (percent)

Us-87

86

To-85_

84_

83

82

81. 

80-

79.

78_

77- 

76_ 

75_

74

Rt-73

72_

71-

70_

69-

68

67

66- 

65- 

64. 

63. 

62.

61- 

60.

Bed Description

Upper tongue of Shedhorn Sandstone Con.

Chert: hard, medium-gray (N 5), thinbedded; contains glauconite; irregular contact with bed below.

Sandstone: cherty, hard, light-brownish-gray (10YR 6/1), very thick 

bedded, very fine grained; contains 

glauconite; irregular contact with 

bed below.

Tosi Chert Member of Phosphoria Formation:

Chert: sandy, hard, light-gray (N 7), 

thick-bedded, very fine grained; separated from underlying bed by fault of 

unknown displacement.

Chert: hard, dark-gray (N 4), thinbedded; thickness is approximate; 

separated from underlying bed by 

fault of unknown displacement.

Chert: hard, dark-gray (N 4), thinbedded.

Chert: dolomitic, hard, dark-gray (N 

4), thin-bedded; separated from 

underlying bed by fault of unknown 

displacement.

Chert: dolomitic, hard, medium-gray 

(AT 5), thick-bedded.

Chert: dolomitic, hard, dark-gray (N 

4), thin-bedded.

Chert: hard, black (N2), thin-beddedChert: hard, dark-gray (N 3), thinbedded.

Chert: hard, dark-gray (N 3), thinbedded.

Chert: muddy, hard, dark-gray (N 3), 

thin-bedded.

Chert: dolomitic, hard, dark-gray (N3), 

thin-bedded.

Chert: dolomitic, muddy, hard, brownish-gray (10 YR 3/1), thin-bedded. 

Retort Phosphatic Shale Member of Phosphoria Formation:

Mudstone: cherty medium-hard, 

brownish-gray (10YR 3/1), thinbedded.

Mudstone: medium-hard, brownishblack (10 YR 2/1), thin-bedded.

Mudstone: soft, dark-brown (10 YR 

3/2), thin-bedded.

Mudstone: medium-hard, brownishblack (10 YR 2/1), thin-bedded.

Mudstone: medium-hard, brownishblack (10 YR 2/1), thin-bedded.

Mudstone: crumbly, brownish-black 

black (10 YR 2/1), thin-bedded. 9

Phosphorite: hard, brownish-black 

(10 YR 2/1), thick-bedded, mediumpell etal and oolitic.

Phosphorite: hard, black (AT 2), thickbedded, finely pelletal.

Dolmite: hard, brownish-black (10YR

2/1), thick-bedded, aphanitic. 

Mudstone: medium-hard, brownish- 

(10Ffl2/l), thin-bedded.

Phosphorite: hard, black (N 2), thinmedium- pelletal.

Phosphorite: muddy, medium-hard, 

black (N 2), thin-bedded, finely 

pelletal.

Mudstone: soft, black (N 1), thinbedded.

Mudstone: 

bedded.

soft, black (N 2), thinCumulative 

Thickness thickness 

(feet) (feet)

1. 6 44. 6 

23. 3 67. 9

14.0 81.9 

15. 0 96. 9

1. 7 98. 6 

3. 0 101. 6

1. 5 103. 1 

. 4 103. 5

.5 104. 0 

2. 0 106. 0

1.

1.

1.

2.

2.

1.

1.

1. 

1.

2.

1.

1.

5 106. 5

1 107. 6

4 109. 0

2 110. 2

3 112. 5

5 115. 0'

2 115. 2

5 115. 7

9 116. 6

8 117. 4

4 118. 8

1 119. 9^ 

9 120. 8

5 122. 3 

6 123. 9

6 126. 5

1 127. 6

6 129. 2

Sample

RSJ-725 

724

723

722

721

720

719

718

717

716

715

714

713

CWT-712

711

710

Uraniiim

Acid Radiometric Chemical 

PaOs insoluble eV U

0.

1.

3.

2.

6.

25.

17.

15.

15.

5.

7.

8 

8

6

3

8

5

0

8

3

9

5

6

5

2

8

4

80. 5 

81. 7

85. 1

84. 4

76. 8

57. 3

69- 3

60.6

70.0

50.8

11.3

5.8

33.6

27. 2

41.2

38.8

0. 001 

. 001

. 001

. 002

. 002

. 000

. 002

. 003

. 002

. 005

. 008

. 008

. 008

. 008

. 007

. 007

0. 001 

. 001

. 001

. 001

. 002

. 001

. 003

. 002

. 001

. 004

. 009

. 006

. 007

. 009

. 005

. 007
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 511

Canyon Camp, Mont., lot 1811 Continued

Chemical analyses (percent)

0. 6 129. 8 CWT-709

Cumulative 

Thickness thickness 

Bed Description (feet) (feet)

Retort Phosphatic Shale Member of Phosphoria Formation Continued 

Rt-59__.______ Mudstone: medium-hard, black (N 2),

thin-bedded; shear zone 0.1 ft thick

at top. 

58_________ Mudstone: medium-hard, black (A^ 2),

thin-bedded. 

57_________ Dolomite: hard, light-brownish-gray

(10 YR 5/1), thick-bedded, aphanitic. 

56_________ Mudstone: medium-hard, black (N 2),

thin-bedded. 

55 _________ Phosphorite: medium-hard, black

(N 2), thin-bedded, medium-pelletal.

Fossil-colln. No. 11684. 

54__ _______ Mudstone: dolomitic, hard, light- 3.0 138.5

brownish-gray (WYR 5/1), thinbedded. 

53_________ Mudstone: phosphatic, medium-hard, . 7 139. 2

brownish-gray (WYR 3/1), thinbedded. 

52_________ Phosphorite: calcareous, medium-hard, 1. 4 140. 6

black (N 2), thin-bedded, mediumpellatal and oolitic. 

51 _________ Mudstone: medium-hard, brownish- 1. 5 142. 1

gray (10 YR 3/1), thin-bedded. 

50_________ Mudstone: soft, dark-gray (AT 3), thin- . 9 143. 0

bedded. Fossil-colln. No. 11683. 

49_________ Chert: hard, brownish-gray (WYR .6 143.6

3/1), thin-bedded. 

48_________ Sandstone: carbonatic, hard, light- 1. 1 144. 7

brownish-gray (10 YR 5/1), very

thick bedded, fine-grained; irregular

contact with bed below. 

47_________ Chert: sandy, hard, medium-gray 2. 0 146. 7

(N 5), very thick bedded. 

46_________ Chert: sandy, hard, medium-gray 1. 2 147. 9

(N 5), very thick bedded; sand is

very fine. 

45_________ Chert: sandy, hard, dark-gray (N 3), 2. 2 150. 1

very thick bedded; sand is very fine. 

Franson Tongue of Park City Formation: 

F-44__________ Dolomite: sandy, hard, medium-gray 1. 8 151. 9

(N 6), very thick bedded, aphanitic;

contains a few small chert nodules. 

43__________ Dolomite: silty, hard, medium-gray 1. 3 153. 2

(N 6), very thick bedded, very finely

granular. 

42__________ Dolomite and chert, interbedded: hard 6.4 159.6

medium-gray (N 5) thick-bedded

aphanitic sandy dolomite interbedded with hard dark-gray (N 3)

thick-bedded chert. 

41__________ Dolomite: hard, yellowish-gray (10\YR 14.3 173.9

7/1), very thick bedded, aphanitic;

irregular contact with bed below. 

40_ _________ Dolomite: hard, light-brownish-gray 1. 7 175. 6

(WYR 5/1), very thick bedded,

finely granular. 

39__________ Chert: hard, mottled light-gray (N 8) .5 176.1

and dark-gray (N 3), thick-bedded. 

38._________ Dolomite: silty, hard, medium-gray 4.3 180.4

(N 5), very thick bedded, aphanitic;

irregular contact with bed below. 

37__________ Dolomite: hard, light-brownish-gray 2. 1 182. 5

(WYR 5/1), very thick bedded,

aphanitic. 

36. _________ Dolomite: sandy, medium-hard, light- 4.5 187.0

yellow (2.5F9/6), very thick bedded;

sand is fine. 

35_ _________ Dolomite: medium-hard, medium-gray 8.2 195.2

(N 6), very thick bedded, aphanitic;

irregular contact with bed below. 

34_ _________ Chert: hard, dark-gray (N 3), very 3.0 198.2

thick bedded.

Uranium

Sample

Acid Radiometric Chemical

insoluble e\J U

6. 1 44. 0 0. 007 0. 006

. 9

1. 6

1. 2

2. 0

130. 7

132. 3

133. 5

135. 5

708

707

706

705

6. 4

1.3

6. 8

23. 9

46. 0

8.7

40. 7

11. 8

. 007

. 001

. 005

. 008

. 005

. 001

. 005

. 009

704

703

702

701

700

1. 6

10. 0

22. 9

2.7

6. 5

43. 2

47. 0

11. 6

67. 8

71. 3

002 

005 

Oil

003

004

. 001

. 005

. 012

. 002

. 004
512 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Canyon Camp, Mont., lot 1311 Continued

Chemical analyses (percent)

Bed

F-33_

(32).

R-31. 

30.

29.

28.

27_.

26__ 

25 

24 

23 

22 

21 

M-20._

19_. 

18.. 

17..

16-. 

15.-

12. 

11.

10.

Description

Franson Tongue of Park City Formation 

Continued

Dolomite: hard, yellowish-gray (10YR 

7/1), very thick bedded, aphanitic.

Covered: an unknown thickness of beds 

intervenes between R-31 on north 

side and F-33 on south side of canyon.

Rex Chert Member of Phosphoria Formation:

Chert: hard, pale-brown (10 YR 6/2), 

thick-bedded.

Dolomite: hard, light-brownish-gray 

(10 YR 5/1), thick-bedded, aphanitic; 

grades from bed below.

Chert: sandy, hard, medium-gray 

(N 5), thick-bedded; irregular contact with bed below.

Sandstone: cherty, hard, dark-gray 

(N 4), thick-bedded, fine-grained; 

contains a few phosphorite pebbles 

or nodules as much as 3 mm in diameter; irregular contact with bed 

below.

Dolomite: cherty, sandy, hard, lightbrownish-gray (10 YR 6/1), thickbedded.

Mudstone: medium-hard, dusky-brown 

(10YR 2/2), fissile.

Chert: hard, brownish-gray (10 YR 

3/1), thin-bedded.

Siltstone: cherty, hard, grayish-brown 

(10 YR 2/3), thin-bedded; contains 

glauconite.

Chert: hard, brownish-gray (10 YR 

4/1), thin-bedded.

Chert: hard, brownish-gray (10 YR 

4/1), fissile.

Chert: hard, black (N 2), thin bedded. _ Meade Peak Phosphatic Shale Member of 

Phosphoria Formation:

Phosphorite: hard, brownish-black 

(IOYR 2/1), thin-bedded, mediumpelletal. Fossil-colln. No. 11682.

Limestone: medium-hard, white (N9), 

thick-bedded, aphanitic.

Chert: brittle, brownish-gray (1QYR 

3/1), thin-bedded.

Limestone: medium-hard, yellowishwhite (1QYR 9/1), thin-bedded, 

aphanitic.

Chert: brittle, brownish-gray (10 YR 

3/1), thin-bedded.

Phosphorite: sandy, hard, brownishgray (IOYR 3/1), .thick-bedded, 

medium-pelletal and oolitic; contains 

phosphatic skeletal fragments and 

chert and phosphorite pebbles as 

much as 0.1 ft in diameter. Analysis 

may be in error.

Grandeur Tongue of Park City Formation, 

upper part:

Dolomite: medium-hard, light-gray 

(N 8), very thick bedded, aphanitic.

Chert: dolomitic, hard, light-brownishgray (10 YR 6/1), thick-bedded.

Sandstone: hard, dark-gray (N 4), thinbedded, fine-grained.

Dolomite: hard, yellowish-gray (1QYR 

7/1), very thick bedded, aphanitic; 

contains a few chert nodules 5 to 20 

mm in diameter.

Chert: dolomitic, very pale brown 

(1QYR 7/2), thin-bedded.

Thickness 

(feet)

14. 3

1 9

. 6

1. 1

g

1. 4

. 6

. 8

4 7

5. 0 

. 3 

.4

.5

1. 0 

. 5 

. 1

. 2 

. 5

1. 7 

.3 

. 1 

1. 4

. 3

thickness 

(feet)

212. 5

213. 8

214 4

215. 5

216. 4

217. 8

m A

219. 2

OOQ Q

228. 9 

229. 21 

229. 6J

230. 1

231. 1 

231. & 

231. 7

231. 9 

232. 4

234. I 

234. 4 

234. 5

OQK Q

236. 2

Uranium

Acid Radiometric Chemical 

Sample PtOt insoluble ell II

ERG-732 0. 9 75. 4 0. 000 0. 001 

731 1. 1 85. 8 . 000 . 001

730 27. 0 18. 7 . 007 . 008 

729 3. 0 8. 8 . 000 . 002

728 2. 5 77. 7 . 001 . 002 

727 5. 6 15. 8 . 007 . 008

726 1. 2 28. 2 . 000 . 001
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 513

Canyon Camp, Mont., lot 1311 Continued

Chemical analyses (percent)

Bed

G-9.

Description

Grandeur Tongue of Park City Formation, 

upper part Continued

Dolomite: hard, light-brownish-gray 

(IOYR 6/1), thick-bedded, aphanitic; 

contains a few lenses and nodules of 

chert; irregular contact with bed 

below.

Chert: hard, medium-gray (N 5), thickbedded.

Dolomite: hard, medium gray (N 6), 

thick-bedded, aphanitic; irregular 

contact with bed below.

Chert: hard, brownish-gray (IOYR 

4/1), thin-bedded; pinches out along 

strike; irregular contact with bed 

below.

Dolomite: hard, light-brownish-gray 

(IOYR 5/1), very thick bedded, 

aphanitic; irregular contact with 

bed below.

Chert: dolomitic, hard, dark-gray (N 

4), thin-bedded; irregular contact 

with bed below.

Dolomite: hard, brownish-gray (iOYR 

4/1), thick-bedded, aphanitic.

Dolomite: hard, dark-gray (N 4), thickbedded, aphanitic; contains chert 

nodules averaging 30 mm in diameter.

Siltstone: calcareous, medium-hard, 

pale-brown (10 YR 5/3), thick-bedded; 

in fault contact with underlying bed.

Thickness 

(feet)

Cumulative

thickness

(feet)

Uranium

Sample P205

Acid 

insoluble

Radiometric Chemical 

eV U

0. 6 236. 8

. 3 237. 1

1. 3 238. 4

238. 6

1. 7 240. 3

240. 5

2. 4 242. 9

3. 5 246. 4

5. 6 252. 0

West Fork of Madison River, Mont., lot 1318

[Part of Permian rocks measured near West Fork of Madison River, SE % sec. 30. T. 12 S., R. 2 W., Beaverhead County, Mont., on northeast limb of small anticline. Phos' 

phoria Formation measured and sampled in bulldozer trench; Shedhorn Sandstone measured from natural exposure at northeast end of trench. Beds strike N. 30° Wand dip 30° NE. Measured by C. W. Tandy, J. L. Elliott, and E. R. Cressman and sampled by B. K. Replogle, in August 1949. Analyzed for PtOs and acid insoluble 

by U.S. Bur. of Mines and for uranium by U.S. Qeol. Survey]

Chemical analyses (percent)

Bed

Us-21.

20.

To-18-

16-

15.

14.

Cumulative 

Thickness thickness 

Description (feet) (feet)

Upper member of Shedhorn Sandstone, 

top not exposed:

Sandstone: hard, light-gray (N 7), 13. 5 13. 5

very thick bedded, fine-grained;

contains glauconite. Overlying beds

are covered; thickness to contact

with Dinwoody formation is not

known. 

Sandstone: hard, light-gray (N 7), 10. 1 23.6

very thick bedded, very fine grained;

contains glauconite. 

Sandstone: hard, medium-gray (N 6), 1. 9 25. 5

very thick bedded, very fine grained. 

Tosi Chert Tongue of Phosphoria Formation :

Chert: brittle, light-brownish-gray 16. 9 42. 4

(IOYR 5/1), thick-bedded. 

Chert: brittle, light-brownish-gray 10. 6 53. 0

(IOYR 5/1), thick-bedded. 

Chert: brittle, brownish-gray (IOYR 19. 0 72. 0

4/1), thick-bedded; contains a few

interbeds of medium-hard yellowishgray (IOYR 8/1) thin-bedded chert. 

Chert: brittle, light-brownish-gray 1. 3 73. 3

(IOYR 6/1), thin-bedded; contains

medium-hard weak-yellowish-orange

(2.5 Y 8/4) mudstone partings 0.03

ft thick, 0.8 ft above base of bed. 

Chert: argillaceous, brittle, light- 13.5 86. 8

brownish-gray (IOYR 6/1), thinbedded.

Uranium

Sample

Acid 

insoluble

Radiometric Chemical 

eU U
514 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

West Fork of Madison River, Mont., lot 1318 Continued

Bed

Rt-13.

12- 

11. 

10.

Chemical analyses (percent)

Cumulative 

Thickness thickness 

(feet) (feet) Sample

Uranium

Acid Radiometric Chemical 

PsOs insoluble eV U

13. 0 99. 8

2. 0 101. 8 JLE-3404

. 8 102. 6 3403

3. 1 105. 7 3402

1. 8 81. 3 0. 003

.8 82. 0 . 003

3. 3 74. 0 . 004

3401

3400

. 9 106. 6

. 5 107. 1

, 3 107. 4

4. 1 111. 5

. 7 112. 2

. 4 112. 6

.8 113. 4 CWT-3397

. 8 114. 2

1. 0 115. 2

17. 8 42. 6 .007

28. 4 20. 0 . 010

0. 002

.001

. 002

. 008

. 012

Description

Retort Phosphatic Shale Tongue of the 

Phosphoria Formation:

Mudstone: medium-hard, thin-bedded, 

yellowish-gray grades from (10 KK 

7/1) at base to (IOYR 8/1) at top.

Mudstone: brittle, light-brownishgray (WYR 6/1), thin-bedded.

Mudstone: medium-hard, pale-brown 

(WYR 5/2), thin-bedded.

Mudstone: brittle, pale-brown (7.SYR 

6/2), thin-bedded; grades from bed 

below.

Phosphorite: muddy, brittle, mediumgray (N 6), thin-bedded, mediumpelletal.

Phosphorite: brittle, medium-gray 

(AT 6), thick-bedded, medium-pelletal.

Phosphorite: muddy, plastic, palebrown (WYR 5/3), thick-bedded, 

medium-pelletal; grades from bed 

below.

Mudstone: brittle, pale-brown (WYR 

5/2).

Phosphorite: brittle, light-brownishgray (WYR 6/1), thick-bedded, 

finely pelletal.

Mudstone: phosphatic, plastic, palebrown (WYR 5/2), thick-bedded; 

apatite is finely pelletal.

Mudstone: phosphatic, brittle, lightbrown (7.5YR 5/6), thick-bedded; 

apatite is medium pelletal.

Phosphorite: crumbly, dark-gray 

(AT 3), thick-bedded, coarsely pelletal.

Mudstone: soft, phosphatic, yehowishgray (10F.R 7/1) to dark-yellowishorange (WYR 6/8); apatite is coarsely 

pelletal. Underlying beds are covered; approximate position of Meade 

Peak Phosphatic Shale Tongue of 

Phosphoria Formation marked by 

phosphorite float, 45 ft stratigraphically below bed Rt-1.

Lazyman Hill, Mont., lot 1319

[Permian rocks measured on Lazyman Hill, sec. 9, T. 10 S., R. 2 W., Madison County, Mont., on east limb of Ruby Valley syncline. Beds Rt-58 through To-74 exposed in 

hand trench on east face of hill; beds To-75 through Us-103 measured from natural exposure on east face of hill; rest of section measured from natural exposures on northeast 

face of hill. Beds strike N. 10° E. and dip 13° W. Measured by E. R. Cressman, B. K. Replogle, and W. J. Qarmoe and sampled by R. F. Qosman, in September 1949. 

Analyzed for P2Os and acid insoluble by U.S. Bur. of Mines and for other constituents by U.S. Qeol. Survey]

Chemical analyses (percent)

3399

3398b

3398a

-3397

3396

3395

5. 5

29.3

8. 5

12. 5

30. 7

11. 5

63. 3

14. 7

49. 9

49. 3

9.3

55. 0

. 005

. 010

. 006

.007

. 008

. 005

. 004

. 014

. 007

. 006

. 009

. 004

Bed 

(104).

To-103.

102.

101.

Description

Beds overlying To-103 are covered; 

thickness to contact with Dinwoody 

estimated. 

Tosi Chert Tongue of Phosphoria Formation:

Dolomite: sandy, medium-hard, very 

pale orange (7.5 YR 8/2), thin-bedded'; 

sand is very fine; contains glauconite 

and as much as 20 percent dolomitic 

shell fragments.

Dolomite: medium-hard, very pale 

brown (WYR 7/3), thin-bedded, 

aphanitic; contains glauconite.

Sandstone: dolomitic, hard, yellowishgray (WYR 8/1), thick-bedded, very 

fine grained; contains glauconite.

Cumulative 

Thickness thickness 

(feet) (feet)

10.0 _.___ .

Uranium

Sample P»05

Acid Organic Radiometric Chemical 

insoluble matter eU U

1. 0 1. 0

1. 5

2. 1
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 515

Laeyman Hill, Mont., lot 1319 Continued

Chemical analyses (percent)

Uranium 

Cumulative

Thickness thickness Acid Organic Radiometric Chemical 

Bed Description (feet) (feet) Sample PzOs insoluble matter eU TJ

Tosi Chert Tongue of Phosphoria Formation Continued 

To-100________ Siltstone: dolomitic, medium-hard, 3.3 5.4 __________ _.__ ____ ____ ______ _______

light-gray (N8), thin-bedded; center

one-quarter to one-half of nearly

every bed consists of cherty hard

medium-gray (N 6) siltstone; contains glauconite; bedding surfaces are

irregular. 

99_________ Siltstone: dolomitic, medium-hard, 3. 8 9. 2 __________ ____ ____ ____ ______ _______

 pale-orange (7.5YR 8/4), thin-bedded,

cross-bedded; contains lenses of crossbedded cherty siltstone averaging

0.05 ft by 0.2 ft that comprises 25

percent of rock; contains glauconite;

bedding surfaces are irregular. 

98_-__--_-_ Dolomite: silty, medium-hard, weak- 1. 0 10. 2 __________ ____ _-__ -___ _-___- _______

yellowish-orange (1QYR 8/4), fissile,

aphanitic. 

97_________ Siltstone: dolomitic, medium-hard, .8 11. 0 __________ ____ ____ ____ ______ ___----

weak-yellowish-orange (WYR 8/4),

thin-bedded. 

96_________ Dolomite: silty, medium-hard, weak- 2.4 13.4 __________ _.__ _-__ -__- _--_-_ _______

yellowish-orange (WYR 8/4), fissile,

aphanitic. 

95__.______ Mudstone: dolomitic, medium-hard, .9 14. 3 __________ ____ -___ __-- ------ ___-__.

weak-yellowish-orange (WYR 8/4),

thin-bedded. 

94_________ Dolomite: silty, medium-hard, weak- 2. 3 16. 6 __________ ____ ____ -___ ______ _______

yellowish-orange (WYR 8/4), fissile,

aphanitic. 

(93)______. Covered._________.______________-_ 5.3 21.9 __________ ____ __._ -___ ------ -------

Upper member of Shedhorn Sandstone: 

Us-92_-__--___ Sandstone: glauconitic, medium-hard, 1.0 22. 9 __________ ____ -___ ---- ------ _______

light-gray (N 8) to green, very thick

bedded, very fine grained; contains

phosphorite pebbles and phosphatic

fossil fragments; glauconite occurs

as matrix. 

91_______._ Chert: hard, light-gray (N 8), thin- .4 23.3 ___-.___-_ ____ ____ ---- ------ -------

bedded; irregular contact with bed

below. 

90.___-_-__ Sandstone: glauconitic, medium-hard, 2. 3 25. 6 __________ ____ ____ _-__ ------ -------

light-gray (N 8) to green, very thick

bedded, fine-grained; contains several thin irregular chert laminae. 

(89)_______ Covered_______________________ 2.9 28.5 ________ .___ _.._ ---- ------ -------

88_________ Sandstone: medium-hard, light-gray 4.1 32.6 __________ _-__ __-- ---- ------ -------

(N 8), thick-bedded, fine-grained;

grades from bed below. 

87--_-_-.-_ Sandstone: hard, light-gray (N 8), 8.5 41.1 __________ -___ _-__ ---- ------ -------

very thick bedded, fine-grained;

grades from bed below. 

86_ __--_-__ Sandstone: medium-hard, light-gray 4.3 45.4 __________ _-__ ____ __-_ ------ -_-___.

(N 8), very thick bedded, finegrained; contains irregular bodies

of fine-grained cherty sandstone

0.5 to 2.0 ft in diameter that constitute 10 percent of rock; grades

from bed below. 

85_________ Sandstone: hard,.yellowish-gray (WYR 15.2 60.6 __________ ____ __-_ ---- ------ -------

8/1), very thick bedded, very fine

grained; contains sandy chert masses

0.1 to 0.2 ft in daimeter and 0.7 to

1.0 ft long that constitute 20 percent

of rock; one-third of chert bodies are

elongated perpendicular to bedding;

grades from bed below.
516 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Lazyman Hill, Mont., lot 1319 Continued

Chemical analyses (percent)

Uranium 

Cumulative

Thickness thickness Acid Organic Radiometric Chemical 

Bed Description (feet) (feet) Sample PsOs insoluble matter eV U

Upper member of Shedhorn Sandstone 

Continued 

Us-84_________ Sandstone: hard,, yellowish-gray (10 YR 8.1 68.7 __________ ____ _.__ ___- ______ .____._

8/1), very thick bedded, very fine

grained; contains very irregular

bodies of sandy chert 0.05 to 1.0 ft

in diameter that constitute from 50

percent of rock at base of bed to 20

percent of rock at top; grades from

chert below.

Tosi Chert Tongue of Phosphoria Formation: 

To-83_-_____._ Chert: sandy, hard, white (N 9), very 9.0 77.7 ...____ _ -___ -_-- ------ --- -

thick bedded; sand is very fine; contains very irregular bodies of very

fine grained sandstone from 0.02 to

0.8 ft in diameter constituting several percent of rock at base of unit

to 50 percent at top; grades from

bed below. 

82_________ Chert: exposure is inaccessible.______ 7.9 85.6 __________ ____ ____ ___- ______ ____---

81-______-_ Chert: brittle, yellowish-gray (IOYR 8.2 93.8 ________ _.__ ____ ..__ ------ 

7/1), very thick bedded; irregular

contact with bed below. 

80__--_-___ Chert: brittle, light-brownish-gray .6 94.4 __________ .___ ____ ____ ------ _______

(10 YR 5/1), thick-bedded; irregular

contact with bed below. 

79__.______ Chert: brittle, light-brownish-gray 5.7 100.1 __________ ____ ____ ____ ------ -------

(IOYR 5/1), very thick bedded; 

78_--_-____ Chert: brittle, lMit-brownish-gray( 10 YR 2.8 102.9 _____-__-_ ____ ____ ____ ------ __. -

5/1), thin-bedded; bedding surfaces

are undulant; irregular contact with

bed below. 

77__-_-____ Chert: brittle, light-brownish-gray 8.5 111.4 __________ ____ ___- __-_ ____-- -------

(IOYR 5/1), thin-bedded; bedding

surfaces are undulant. 

76_--_-_-__ Chert: brittle, light-brownish-gray 3.7 115.1 ---------- ____ __._ ____ ------ -------

(IOYR 5/1), thin-bedded; bedding

surfaces are undulant; contains

roughly spherical concretions of

medium-crystalline calcite 1.0 to 2.0

ft in diameter; many of the concretions have weathered out. 

75____--__- Chert: brittle, light-brownish-gray 3.2 118.3 ___-_____- ___- ____ __-_ ------ _-_-._-

(IOYR 5/1), thin-bedded; bedding

surfaces are undulant. 

74__ _______ Chert: brittle, light-brownish-gray 3.5 121.8 ERG-742 0.7 93.8 0.00 0.000 0.000

(IOYR 5/1), thin-bedded; bedding

surfaces are undulant. 

73_________ Chert: medium-hard, yellowish-white .6 122.4")

(IOYR 9/1), fissile. 

72_________ Chert: hard, light-brownish-gray .7 123. lV 741 .8 90.4 ____ .002 .001

(IOYR 6/1), thin-bedded; grades

from bed below. / 

Retort Phosphatic Shale Tongue of Phosphoria Formation: 

Rt-71_________ Mudstone: medium-hard, yellowish- 1.0 124.1 740 . 5 87. 6 .70 .002 .001

gray (IOYR 8/1), thin-bedded. 

70_________ Mudstone: cherty, hard, yellowish-gray 1.3 125.4 739 1.2 86.3 .79 .001 .002

(IOYR 8/1), thin-bedded; grades

from bed below. 

69_________ Dolomite: medium-hard, light-yellow- .9 126.3 738 1.5 17.0 .85 .002 .003

ish-brown (2.5 Y 6/4), thin-bedded;

contains a few chert laminae 1 to 2

mm thick. 

68_________ Phosphorite: cherty, hard, light-gray . 8 127. 1^

(JV8), thick-bedded, medium-pelletal

and oolitic. > 737 28.0 19.2 .50 .008 .010 

67_--______ Phosphorite: crumbly, light-gray (N .4 127.5

8), thick-bedded, medium-pelletal. ) 

66___----__ Phosphorite: medium-hard, light-gray .9 128.4 736 33.7 7.6 .59 .008 .011

(N 8), thick-bedded, medium-pelletal.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 517

Lazyman Hill, Mont., lot 1319 Continued

Chemical analyses (percent)

Uranium

0.6

.9

. 1

. 2

. 7

. 1

. 4

. 2

129.0

129. 91

130.0

130.2

130. 9'

131.0

131.4

131.6

6. 1 137. 7 WJG-749

Cumulative 

Thickness thickness 

Bed Description (feet) (feef)

Retort Phosphatic Shale Tongue of Phosphoria Formation Continued 

Rt-65_________ Mudstone: phosphatic, soft, pale-brown

(2.5 Y 5/2); apatite is finely pelletal.

64_ ________ Mudstone: soft, pale-brown (2.5 Y 6/2),

fissile.

63__------- Phosphorite: muddy, soft, moderatereddish-brown, thin-bedded, mediumpelletal.

62_ ________ Mudstone: light olive-brown (2.5 Y 5/6),

fissile.

61_________ Mudstone: phosphatic, soft, darkgreenish-gray, thin-bedded; apatite 

is finely pelletal.

60________ Phosphorite: soft, reddish-brown, thinbedded, medium-pelletal.

59_________ Mudstone: phosphatic, medium-hard,

dark-greenish-gray, thin-bedded.

58 _________ Phosphorite: mediu m-hard, light-brown

(7.5YR 5/4), thin-bedded, coarsely 

oolitic; irregular contact with bed 

below.

57_______ Chert: hard, light-gray (N 7), thickbedded; irregular contact with bed 

below.

56_________ Chert: dolomitic, sandy, hard, pale- 2.0 139.7

brown (7. SYR 6/2), thin-bedded; 

sand is very fine.

Lower member of Shedhorn Sandstone: 

Ls-55- ________ Sandstone: cherty, hard, very pale 6.1 145.8

brown (10 YR 7/2), thick-bedded, 

very fine grained; contains chert 

nodules in lower 0.8 ft.

54. ______ Sandstone: hard, light-gray (N 8), 3.3 149.1

thick-bedded, fine-grained; contains 

a few chert and dolomite pebbles 

0.01 to 0.04 ft in diameter.

53_________ Dolomite: hard, pale-orange (7.5YB 1.2 150.3

8/4), very thick bedded, aphanitic.

52_________ Sandstone: dolomitic, hard, weak-yel- 8.5 158.8

lowish-orange (IQYR 7/6), thinbedded, very fine grained; poorly 

exposed.

51 _________ Sandstone: brittle, yellowish-gray 6.2 165.0

(2.5F 8/2), very thick bedded, finegrained; grades from bed below.

50_________ Sandstone: dolomitic, brittle, yellow- 7.7 172.7

ish-gray (2.5F 7/2), very thick bedded, fine-grained.

49_________ Sandstone: dolomitic, brittle, weak- 2.0 174.7

yellowish-orange (IQYR 8/4), very 

thick bedded, fine-grained.

48_________ Sandstone: hard, medium-gray (N 6), .7 175.4

thick-bedded fine-grained; contains 

phosphatic skeletal fragments; grades 

from bed below.

47-_--_____ Sandstone: hard, light-brownish-gray .3 175.7 

(10 YR 5/1), thick-bedded, finegrained.

46_________ Dolomite: sandy, brittle, pale-brown 2.5 178.2

(2.5 Y 5/2), very thick bedded, aphanitic.

45_________ Sandstone: hard, light-brownish-gray 2,0 180. 2

(IQYR 5/1), very thick bedded, finegrained.

44_ ________ Dolomite:brittle, yellowish-gray (IQYR 1. 2 181.4

7/1), thick-bedded, aphanitic.

43 _________ Sandstone: hard, light-gray (N 7), very 2. 3 183. 7

fine grained: irregular contact with 

bed below.

Sample

Acid Organic Radiometric Chemical 

insoluble matter eU U

ERG-735 10.4 49.4 1.47 0.006

734 6. 2 63. 4 1. 51 .005

0.006

.004

733 15. 6 42. 0 . 95

5 93.2

.006

.001

.007

.001
518 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Lazyman Hill, Mont., lot 1319 Continued

Chemical analyses (percent)

Bed Description

Rex Chert Tongue of Phosphoria Formation:

R-42.______. Chert: brittle, yellowish-gray (WYR 

7/1), thin-bedded; irregular contact 

with bed below.

Lower member of Shedhorn Sandstone:

Ls-41_ ________ Sandstone: cherty, hard, yellowishgray (10 YR 8/1), very thick bedded, 

fine-grained; irregular contact with 

bed below.

40_-------- Dolomite: brittle, light-brownish-gray

(10 YR 6/1), very thick bedded, 

aphanitic; contains chert nodules 0.1 

to 0.3 ft in diameter, some which 

have quartzite cores; nodules constitute 30 percent of bed.

39_._--_ __ Sandstone: hard, very pale brown 

(10 YR 7/2), very thick bedded, 

medium-grained; phosphatic fossil 

fragments.

38__-__-__- Dolomite: brittle, pale-brown (2.5F 

6/2), thick-bedded, aphanitic.

37_ ________ Sandstone: hard, light-brownish-gray

(10 YR 5/1), thick-bedded, finegrained.

36 _________ Sandstone: phosphatic, hard, lightbrownish-gray (WYR 5/1), very 

thick bedded, fine-grained; contains 

phosphatic skeletal fragments. 

Meade Peak Phosphatic Shale Tongue of

Phosphoria Formation:

M-35 _________ Phosphorite: brittle, light-brownishgray (10 YR 6/1), thick-bedded, medium-pelletal; contains phosphatic 

skeletal fragments.

34 ________ Chert: brittle, light-brownish-gray

(WYR 5/1), thin-bedded.

33 _________ Mudstone and chert, interbedded:

crumbly light-yellowish-brown (10 

YR 6/4) thin-bedded mudstone interbedded with brittle dark-gray (N 4) 

thin-bedded chert.

32 _________ Phosphorite: brittle, yellowish-gray

(10 YR 7/1), thin-bedded, coarsely 

pellet al.

31_________ Phosphorite: brittle, pale-brown (7.5

YR 5/2), thin-bedded, coarsely pelletal and oolitic; contains phosphatic 

skeletal fragments; contains cherty 

nodules or pebbles K to 1 in. in diameter near base.

Grandeur Tongue of Park City Formation: 

G-30-__-_-____ Dolomite: brittle, yellowish-gray (10

YR 7/1), thick-bedded, aphanitic.

29_ _________ Dolomite: sandy, brittle, yellowishgray (WYR 7/1), very thick bedded, 

aphanitic.

28__________ Dolomite: brittle, very pale orange

(7.5 YR 8/2), aphanitic.

27__________ Dolomite: brittle, yellowish-gray (10 YR

7/1), thin-bedded, aphanitic.

26 __________ Dolom ite: bristle, yellowish-gray

(10 YR 7/1), thick-bedded.

25__________ Dolomite: brittle, yellowish-gray (2.5Y

7/2), thick-bedded, aphanitic.

24__________ Dolomite: brittle, light-gray (N 7),

thick-bedded, aphanitic.

23__________ Sandstone: brittle, very pale brown

(10 YR 7/3), thick-bedded, finegrained.

22__________ Sandstone: brittle, yellowish-gray

(WYR 8/1), thin-bedded, finegrained.

Thickness 

(feet)

 3 Q

1 3

. 8

1 Q

O

.4

0 C

. 6

4. 2 

. 6

. 6

thickness 

(feet)

187. 6 .

188. 9 .

18Q 7

191. 0 .

m o

191. 6

1Q4. 1

194 7

198. 9 

199. 5^

200. 1

Uranium

Acid in- Organic Radiometric Chemical 

Sample PsO. soluble matter e\J U

BKR-748 0.6 91.0 ____ 0.000 0.001 

747 8.5 61.8 _ _ .004 .003

1. 5 201. 6

. 7 

6.5

4. 1 

4. 1 

3. 2 

8.6 

4.6 

5.6

202. 3

208.8

212. 9

217. 0

220. 2

228. 8

233.4

239. 0

746 27. 9 19.3

745 1. 7 20. 3

005 007

001 001

5. 6 244. 6
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 519

G-21. 

20.

19. 

18. 

17. 

16. 

15. 

14. 

13.

12.

Q-10.

(6).

(4).

(2).

Laxyman Hill, Mont., lot 1319 Continued

Thick- Cumulative

ness thickness

Bed Description (feet) (feet) Sample

Grandeur Tongue of Park City Formation 

Continued 

__--_--.. Carbonate rock: brittle, medium-gray 1.5 246.1 _________

(N 6), thick-bedded, aphanitic.

----_-_-. Dolomite: brittle, very pale brown 2. 5 248. 6 _________

(1QYR 7/2), thick-bedded, aphanitic;

grades from bed below. 

__-_____. Carbonate rock: brittle, medium-gray 3.7 252.3 _________

(N 6), very thick bedded, aphanitic.

-______._ Dolomite: brittle, light-gray (N 8), 1.8 254.1 _________

very thick bedded, aphanitic.

----_--_. Dolomite: brittle, pale-brown (7.SYR 2.9 257.0 _________

5/2), very thick bedded, aphanitic.

---______ Dolomite: hard, light-gray (N 7), 3.7 260. 7 _________

thick-bedded, aphanitic.

--____-._ Sandstone: hard, pale-orange (7.5 YR 2.6 263.3 _________

8/4), very thick bedded, fine-grained.

---__---. Dolomite: hard, pale-brown (10 YR 4.8 268.1 _________

6/2), thick-bedded, aphanitic.

---____-. Sandstone: calcareous, hard, weak- 7.0 275.1 _________

yellowish-orange (1QYR 8/4), very

thick bedded, fine-grained; lower 2.0

ft is dolomitic. 

_________ Dolomite: hard, weak-yellowish-orange 2. 5 277. 6 _ _______

(10 FT. 8/4), thick-bedded, aphanitic. 

_________ Dolomite: hard, white (N 9), thin- 3.3 2809 _________

bedded, aphanitic. 

Quadrant Formation, upper part:

--_______ Sandstone, calcareous, hard, white (N 12.0 292.9 _________

9), very thick bedded, fine-grained.

---_____. Sandstone: calcareous, hard, dark- 7.0 299.9 _________

yellowish-orange (10 FT. 6/8), very

thick bedded, fine-grained. 

_________ Sandstone: hard, light-gray (N 8), very 9. 1 209. 0 _________

thick bedded, fine-grained; upper

part is calcareous; lower part is

dolomitic; grades from bed below.

--_____-_ Dolomite: hard, brownish-gray (10FT. 1.0 310.0 _________

3/1), thin-bedded, aphanitic.

- ______ Covered___._______._______ 2.3 312.3 ______.

_ _____ Sandstone: calcareous, hard, very pale 3.7 316.0 _________

orange (7.5 YR 8/2), thick-bedded

fine-grained. 

_________ Covered_________________________ 4.5 320.5 ___.____.

----_____ Dolomite: hard, yellowish-gray (10Ftf 5.5 326.0 _________

7/1), thick-bedded, aphanitic.

- _______ Covered-_--___-___________________ 4.3 330.3 _________

_________ Sandstone: hard, yellowish-gray (10 YR 7.9 338.2 _______

8/1), very thick bedded, fine-grained.

Chemical analyses (percent)

Uranium

PsOe

Acid in- Organic Radiometric Chemical 

soluble matter ell U

Little Water Canyon, Mont., lot 1341

A_i<u_r£cu iui .raw auu awu msoiuDie oy u.s. tsur. oi mines ana lor uranium uy u.e. ueoi. survey, unemicai analyses lor i 

in accord with field descriptions or composition of hand specimens, suggesting that samples taken for analysis were mislabeled]

Bed Description

Tosi Chert Member of Phosphoria Formation, lower part: 

To-77._______ Chert: hard, medium-gray (_V 5),

thick-bedded; contains glauconite. 

76________ Mudstone: soft, dark-gray (N 4),

thick-bedded.

75__,_.___ Chert: hard, grayish-brown (7.SYR 

3/2), thick-bedded; contains glauconite. 

74_ _______ Mudstone: medium-hard, pale-brown

(7.5 F.R 5/2), thin-bedded; contains 

glauconite.

Cumulative 

Thickness thickness 

(feet)

Uranium

Sample P_05

Acid Radiometric Chemical 

eU U

1. 2

. 3

1.0

1. 2

1. 5

2. 5

2.7
520 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Little Water Canyon, Mont., lot 1341 Continued

Bed Description

Tosi Chert Member of Phosphoria Formation, lower part Continued

To-73.-..---- Chert: hard, light-gray (AT 8), thickbedded; contains glauconite; in fault 

contact with unit below. 

Cherty shale member (?) of Phosphoria

Formation: 

Cs-72________ Mudstone: hard, dark-gray (N 4),

thin-bedded; contains chert lenses; 

in fault contact with bed below. 

Retort Phosphatic Shale Member of Phosphoria Formation; upper part is faulted 

out: 

Rt-71 ________ Mudstone: soft, brownish-black (10 YR

2/1), thin-bedded; bed is sheared, 

and bedding is indistinct.

70________ Similar to bed Rt-71____-_----------

69________ Mudstone: soft, dusky-brown (WYR

3/2), thin-bedded.

68_-__--__ Mudstone: soft, dusky-brown (WYR 

2/2), thick-bedded.

67.._---__ Mudstone: soft, dusky-brown (WYR 

3/2), thin-bedded; grades from bed 

below.

66_-_---_- Mudstone: medium-hard, grayishbrown (WYR 4/2), thin-bedded.

65-__-____ Mudstone: soft, dusky-brown (WYR 

3/2), thick-bedded.

64________ Phosphorite: medium-hard, brownishgray (WYR 4/1), thin-bedded, 

coarsely pelletal and nodular; nodules are as much as 25 mm in 

diameter.

63________ Mudstone: soft, dusky-brown (WYR

3/2), fissile.

62--_--___ Limestone: medium-hard, pale-brown 

(2.5 Y 6/2), thin-bedded, aphanitic.

61-_______ Mudstone: soft, brownish-gray (WYR

3/1). Fossil-colln. No. 12307.

60_ _______ Phosphorite: medium-hard, duskybrown (WYR 3/2), thick-bedded, 

medium-pelletal; contains glauconite; contains many small gastropod 

shells replaced by apatite; unit is 

sheared. Fossil-colln. No. 12307.

59________ Mudstone: phosphatic, soft, brownish-gray (WYR 3/1), thick-bedded, 

finely pellatal and nodular; nodules 

are as much as 12 mm in diameter. 

Fossil-colln. No. 12307.

58________ Mudstone: phosphatic, soft, brownishgray (WYR 3/1), thin-bedded; 

apatite is finely pellatal; grades from 

bed below. Fossil-colln. No. 12307.

57 ________ Mudstone: medium-hard, duskybrown (WYR 3/2), thin-bedded; 

contains a few apatite nodules as 

much as 4 mm in diameter. Fossilcolln. No. 12307.

56________ Mudstone: phosphatic, medium-hard,

brownish-gray (WYR 3/1), thinbedded; apatite is nodular and finely 

pelletal; nodules are as much as 15 

mm in diameter.

55________ Mudstone: soft, dusky-brown (WYR

3/2), fissile. Fossil-colln. No. 12306.

54 ________ Phosphorite: soft, brownish-black

(WYR 2/1), nodular and finely 

pelletal; nodules are as much as 20 

mm in diameter. Fossil-colln. No. 

12306.

53._______ Mudstone: medium-hard, brownishgray (WYR 4/1),thin-bedded;grades 

from bed below.

Chemical analyses (percent)

Cumulative 

Thickness thickness 

(feet) (feet)

Uranium

4. 7

2. 6

2. 4

2. 4

. 9

2. 2

1. 2

1. 5

. 8

. 6

Sample

Acid Radiometric Chemical 

insoluble eU TI

7. 4

13. 8 21. 2

23. 8 TMC-5364 4. 1 53. 8 0. 005

26. 2

28. 6

29. 5

31.7

5363

5362

5361

5360

4.5 

5.5

8.3 

6. 1

5359

.9 32.

.6 33. 2

1. 1 34. 3 RGW-5358

35. 5

37.0

37.8

38. 4

5357

5356

5355

5354

21. 9

19. 5

31. 5

4. 1

. 3 38. 71

.3 39. 0

. 8 39. 8

1. 4 41. 2

. 2 41. 4^

1. 7 43. 1

1. 6 44. 7

5353

5325

5351

5350

5349

49. 2

47. 4

51.9

51. 7

.006

.005

.005

.005

0.003

. 004

.004

. 004

. 004

6. 1 52. 4 . 004

10. 4 39. 7 . 004

24.0

29.9

5.0

53.8

.005

.001

.004

.005

.004

.004

4. 5 49. 2 . 003

5. 5 47. 4 . 004

13. 3 40. 3 . 003

22. 7 19. 9 . 004

3. 8 68. 5 . 004
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 521

Little Water Canyon, Mont., lot 1341 Continued

Bed

Rt-52

50-

49 _

48_ 

47_ 

46-

45 _ 

44.

F-43_.

42.

41.

(40). 

39_ _

38.

37-

(36).

Description

Retort Phosphatic Shale Member of Phosphoria Formation; upper part is faulted 

out Continued

Mudstone: phosphatic, soft, brownishblack (WYR 2/1); apatite is nodular 

and finely pelletal; nodules are as 

much as 25 mm in diameter; grades 

from bed below.

Phosphorite: muddy, soft, brownishblack (10 YR 2/1), nodular and finely 

pelletal; nodules are as much as 30 

mm in diameter and are more numerous in lower 0.5 ft of bed. 

Mudstone: soft, moderate-yellowishbrown (10 YR 4/4); contains a few 

apatite nodules as much as 12 mm 

in diameter. Fossil-colln. No. 12305. 

Mudstone: phosphatic, medium-hard, 

grayish-brown (IOYR 4/2), thinbedded; apatite is finely pelletal. 

Fossil-colln. No. 12305. 

Mudstone: phosphatic, soft, grayishbrown (10 YR 4/2); apatite is finely 

pelletal.

Mudstone: phosphatic, soft, moderateyellowish-brown (10 YR 4/4); apatite 

is medium pelletal.

Mudstone: phosphatic, soft, brownishgray (IOYR 3/1); apatite is nodular 

and finely pelletal; nodules aie as 

much as 20 mm in diameter. 

Mudstone: soft, dusky-brown (10YR 

3/2); contains a few apatite nodules 

as much as 15 mm in diameter. 

Mudstone: phosphatic, soft, grayishgrown (7.5 YR 3/2); apatite is nodular and finely pelletal; nodules are 

as much as 4 mm in diameter. 

Fj/anson Tongue of Park City Formation: 

Sandstone: phosphatic, hard, mediumgray (N 5), very fine grained; contains apatite nodules as much as 20 

mm in diameter and phosphatic 

skeletal fragments; contains glauconite; grades from bed below. 

Fossil-collr. No. 12304. 

Sandstone: hard, light-yellowish-brown 

(10 YR 6/4), thick-bedded, fine-grained; 

contains glauconite and a few apatite 

nodules and skeletal fragments; 

rades from bed below. Fossil-colln. 

To. 12304.

Limestone: hard, medium-gray (N 5), 

very thick bedded, fine-grained. 

Fossil-colln. No. 12303. 

Covered,_______-___---_-________-_

Sandstone: calcareous, hard, palebrown (2.5 Y 6/2), thick-bedded, very 

fine grained: contains bryozoan fragments; grades from bed below. 

Limestone: hard, pale-brown (2.5F 

6/2), thick-bedded: contains chert 

nodules; grades from bed below. 

Fossil-colln. No. 12302 

Dolomite: silty, hard, pale-brown (2.5 Y 

6/2), thick-bedded, aphanitic, contains chert nodules and columnar 

bodies of chert 0.1 ft in diameter and 

0.4 ft long. 

Covered-.._____-_-___-_-__--__---_

grg

No

Chemical analyses (percent)

Cumulative 

Thickness thickness 

(feet) (feet)

Uranium

2.9

21.0 

3. 5

10.0

Sample PjOt

Acid 

insoluble

Radiometric Chemical 

eU U

1. 5 46. 2 RFG-5348 13.9 41. 3 0. 005 0. 003

1. 8 48. 0

1.8

1.3

48.31

49. 2

49.

50. 1

5347 21. 1 24. 6 006 .004

53. 2

54. 1

56.0

5346

RGW-5345

5344

5343

5342

5341

10. 2 52. 6 .005

10. 4 51. 8

13. 5

5.2

9. 2

11. 1

41.0

56. 1

55. 5

58. 2

56. 9

59.8

80.8

84. 3

94. 3

5340 6.4 64. 1

.004

.004

.002

.003

.005

.003

.002

.002

.004

10. 0 104. 3

10. 0 114. 3
522 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Little Water Canyon, Mont., lot 1341 Continued

Chemical analyses (percent)

Bed Description

Franson Tongue of Park City Formation 

Continued 

F-35-________ Sandstone: calcareous, hard, very pale

brown (10 YR 7/2), very thick bedded 

fine-grained; contains glauconite in 

uppermost 3.0 ft; grades from bed 

below. Fossil-colln. No. 12301.

34__.______ Dolomite: hard, very pale orange (10-

YR 8/2), very thick bedded, aphanitic; grades from bed below.

33_________ Sandstone: calcareous, medium-hard,

very pale orange (IOYR 8/2), very 

thick bedded, fine-grained; contains 

some glauconite in lower part of unit; 

bed is poorly exposed.

Rex Chert Member of Phosphoria Formation: 

R-32_________ Chert: hard, very pale brown (WYR

7/2), thick-bedded; contains glauconite; bed is poorly exposed; grades 

from bed below. Fossil-colln. No. 

12030.

31_________ Phosphorite: sandy, medium-hard,

weak-yellowish-orange (2.5 YR 8/4), 

thin-bedded, nodular and coarsely 

pelletal; nodules are as much as 10 

mm in diameter; contains glauconite 

and phosphatic skeletal fragments.

30_________ Chert: hard, light-brownish-gray (10-

YR 5/1), thick-bedded.

29___ ______ Dolomite: hard, pale-brown (IOYR

6/2), thick-bedded, aphanitic.

28_________ Chert: hard, light-brownish-gray (10-

YR 5/1), thick-bedded; grades from 

bed below.

27_________ Chert: hard, medium-gray (N5), thickbedded.

26_________ Chert: hard light-brownish-gray (10 YR

6/1) thick-bedded chert interbedded 

with medium-hard light-brownishgray (7.5 YR 5/4) thick-bedded chert.

25---______ Chert: muddy, very hard, pale-brown

(IOYR 6/3), thick-bedded.

24_________ Mudstone: cherty, hard, light-brownish-gray (IOYR 6/1), thin-bedded.

23_________ Chert: hard, light-brownish-gray (10

YR 6/1), thick-bedded.

22_______ Chert: muddy, hard, pale-brown (10 YR

5/2), thick-bedded. Fossil-colln. No 

12299.

21_________ Mudstone: cherty, medium-hard yellowish-gray (2.5 Y 7/2), thin-bedded.

20_________ Chert: hard, pale-brown (IOYR 6/2),

thin-bedded.

19_________ Mudstone: cherty, soft, light-brownishgray (IOYR 5/1), thin-bedded.

18__.______ Chert: muddy, hard, light-brownishgray (IOYR 5/1), thick-bedded.

17_________ Mudstone: cherty, soft, light-brownishgray (IOYR 5/1) 

Meade Peak Phosphatic Shale Member of

Phosphoria Formation: 

M-16_ _______ Dolomite: muddy, medium-hard, very

pale brown (19YR 7/2), thick-bedded, 

aphanitic. 

15________ Dolomite: muddy, medium-hard, very

pale brown (IOYR 7/2), thick-bedded 

aphanitic. 

14________ Phosphorite: soft, grayish-brown (10

YR 4/2), thin-bedded, coarsely pelletal.

13________ Mudstone: phosphatic, soft, light-yellowish-brown (IOYR 6/4). 

12__ ______ Phosphorite: soft, pale-brown (IOYR

5/3), medium-pelletal.

Uranium

Cumulative 

Thickness thickness 

(feet) (feet) Sample

Acid Radiometric Chemical 

insoluble eV U

14. 2 128. 5

2. 8 131. 3

24. 8 156. 1

20. 0 176. 1

. 3 176. 6

. 6 177. 2

1. 6 178. 8

9. 1 187. 9

5. 1 193. 0

3. 4 196. 4

1. 6 198. 0

. 4 198. 4

3. 8 202. 2

. 8 203. 0

1. 4 204. 4

. 6 205. 0

. 6 205. 6

2. 3 207. 9

1. 0 208. 9

1. 5 210. 4

210.

2. 0 212. 5

. 8 213. 3

2 176. 3 TMC-5373 18. 2 45. 6 0.009 0.008

RGW-5372 14. 2

5371 24. 2

43.0 007

Oil

005

Oil
523

Little Water Canyon, Mont., lot 1341 Continued

Chemical analyse? (percent)

Uranium

Bed

M-ll.

G-L

Description

Meade Peak Phosphatic Shale Member of 

Phosphoria Formation Continued

Mudstone: dolomitic, soft, pale-brown 

(IOYR 5f2).

Mudstone: phosphatic, soft, pale-brown 

(10 YR 5/2); apatite is medium pelletal; grades from bed below.

Dolomite: medium-hard, light-yellowish-brown (IOYR 6/4), thick-bedded, 

aphanitic; grades from bed below.

Mudstone: phosphatic, soft, pale-brown 

(2.5 Y 5/2).

Phosphorite: medium-hard, lightbrownish-gray (10 YR 5/1), thickbedded, very coarsely pelletal.

Mudstone: phosphatic, soft, yellowishgray (1QYR 7/1), thick-bedded; very 

coarsely pelletal; grades from bed 

below.

Phosphorite: soft, light-brownish-gray 

(10 YR 5/1), thick-bedded.

Mudstone: soft, weak-vellowish-orange 

(10 YR 7/6), thick-bedded

Phosphorite: soft, light-brownish-gray 

(10 YR 5/1), thick-bedded; very coarsely pelletal and nodular; nodules are 

as much as 6 mm in diameter.

Phosphorite: medium-hard, yellowishgray (10 YR 7/1), very thick-bedded; 

coarsely pelletal and oolitic; contains 

nodules as much as 8 mm in diameter; 

contains phosphatic skeletal fragments. Fossil-colln. No. 12298. 

Grandeur Member of Park City Formation, 

uppermost bed:

Dolomite: hard, very pale brown (IOYR 

7/3), very thick bedded, aphanitic; 

underlying beds are covered. Fossilcolln. No. 12297.

Cumulative 

Thickness thickness 

(feet) (feet) Sample

0. 6 213.

1.1 215.0V RGW-5370 17.0

2. 6 217. 6

2. 3 219. 9

. 4 220. 3^

. 4 220. 7

.3 221. 51

. 5 221. 8

. 3 223. 3

1. 5 223. 3

5369 7.0

5368 12. 7

5367 20. 2

Acid Radiometric Chemical 

insoluble eU U

28. 2 0. 010 0. 010

17. 3 .005 . 004

40. 2 .006 . 006

22. 2 .008 . 009

5366 19. 5 29. 9 . 008 . 007

5365 31.5 5.0 .011 .011

5. 6 228. 9

Taylor Creek Ridge, Idaho, lots 1342 and 

[LOI, loss on ignition] 

Lot 1342

[Lower part of Meade Peak Phosphatic Shale Member of Phosphoria Formation measured and sampled from wall of landslide crevasse in NE}4 sec. 19, T. 14 N., R. 41 E., 

Clark County, Idaho, by R. F. Gosman in September 1950. Beds strike N. 80° W. and dip 11° S. Analyzed for PjO6 and acid insoluble by U.S. Bur. of Mines and for 

other constituents by U.S. Geol. Survey]

Chemical analyses (percent)

Uranium

Bed

M-5 

4

G-2_

Description

Meade Peak Phosphatic Shale member of Phosphoria Formation:

Phosphorite: medium-hard, laminated to massive, oolitic; 

contains nodular chert.

Phosphorite: carbonatic, hard, 

coarsely oolitic to coarsely 

pisolitic; contains chert nodules; basal contact undulatory.

Phosphorite: medium-hard, thinto thick-bedded, coarsely 

oolitic; contains 0.1 ft laminated phosphatic shale layer 

near base and disseminated 

quartz sand.

Grandeur Tongue of Park City Formation:

Sandstone: medium-hard, massive, coarse-grained; contains 

coarse phosphorite oolites; 

grades from chert below.

Chert: not measured ---- _--_

Thickness 

(feet)

Cumulative thickness (feet) Sample

Acid 

Insoluble AljOs Fe 2O3 LOI

Radiometric

eV

Chemical

U

3. 5 3. 5 RFG-5562 30. 2 11. 4 0. 68 0. 77 5. 39 0. 013 0. 015

75 4 25 5563 17. 0 13. 6 . 62 1. 35 1. 97

1. 5 5. 75 5564 31.3 12.6 73 83 3.31

006

010

005

011

1. 6 7.35 5565 4.5 85.5 002
524 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Taylor Creek Ridge, Idaho, lots 134% and 1342-A Continued

[Section at same locality as lot 1342 but including some overlying strata. Measured by F. S. Honkala and R. W. Swanson, in September 1952 and August 1953]

Chemical analyses (percent)

Bed Description

Ls-28.

F-27. 

26.

Lower tongue of Shedhorn Sandstone; uppermost beds not measured:

Sandstone: hard, thin-bedded, 

medium-grained, very pale 

brown; dolomitic at base; 

grades from bed below. 

Franson Tongue of Park City Formation:

Dolomite: silty, hard, thinbedded, very pale brown. 

Dolomite: hard, thick-bedded to 

massive; grades from bed below.

Lower tongue of Shedhorn Sandstone; contains tongue of Rex 

Chert Member of Phosphoria Formation near base:

Sandstone: hard, massive, medium-grained, light-gray; cherty 

at base and contains some 

chert pebbles; carbonatic at 

top; irregular basal contact. 

Chert: hard, poorly bedded, 

white to light-gray; top and 

bottom locally contains chert 

pebbles; irregular basal contact.

Sandstone and chert: hard, 

poorly banded; irregular basal 

contact.

Sandstone and carbonate rock: 

0.3 ft carbonate rock, containing irregularly distributed 

chert nodules and fragments 

from bed below and sandstone 

stringers, that grades upward 

to 0.6 ft hard medium-grained 

sandstone. 

Chert: hard, irregularly banded,

white to light-gray. 

Sandstone: hard, medium-darkgray ; very irregular basal contact.

Carbonate rock: contains chert 

pebbles for nodules and irregularly distributed patches of 

sand.

Chert: hard and poorly banded 

in lower third; grades upward 

into concentrically banded 

nodules and irregularly distributed sandy carbonate 

rock; contains some patches 

of sand near top.

Ls-17_____ Sandstone: hard, massive medium-grained, medium-darkgray; contains chert fragments 

near top.

Ls-25-

24 _

23_ 

22.

21. 

20.

19. 

R-18..

Uranium

Thick- Cumulaness tive thick-

(feet) ness (feet) Sample

Lot 1342-A

PjOs

Acid 

Insoluble AljOa FejOa LOI

Radiometric 

eU

Chemical U

1. 1

1. 8 

1. 4

1. 5

1. 6

1. 1

2.9 

4.3

6. 2

6. 4

7. 3

7. 7

9. 7

2. 9 12. 6

1. 4 14. 0
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 

Taylor Creek Ridge, Idaho, lots 1342 and 134%-A Continued

Chemical analyses (percent)

525

Uranium

Bed

M-16

15

13- 

12.

11. 

10.

5. 

4_

3. 

2.

G-l.

Description

Meade Peak Member of Phosphoria 

Formation:

Siltstone: carbonatic, hard, thinbedded, light-brownish-gray; 

contains laminae and thin 

beds of chert.

Phosphorite: hard, mediumand very coarsely pelletal to 

oolitic, yellowish-gray (25 Y 

7/2); contains much brown 

apatite matrix; variably sandy 

upward; locally, contains 

quartzite pebbles.

Phosphorite: like bed M-15, but 

less sandy.

Siltstone and phosphorite: medium-hard thin-bedded very 

pale brown siltstone containing 0.1 ft pelletal phosphorite 

just about middle.

Limestone: hard, thick-bedded, 

aphanitic, light-yellowishbrown; contains considerable 

amounts of medium-grained 

quartz silt.

Mudstone: medium-hard, thinbedded; contains thin silt and 

chert lenses.

Chert: hard, poorly bedded, 

grayish-white; contains whiteweathering apatite pellets.

Siltstone: fissile and shaly at 

top, thin-bedded in lower part.

Phosphorite and chert: 0.2 ft 

hard phosphatic chert underlain by 0.3 ft sandy phosphorite; apatite chiefly medium to coarsely pelletal; 

quartz grains are fine.

Phosphorite and chert: hard 

massive medium-light-gray 

cherty phosphorite and phosphatic chert; irregularly distributed and locally quite variable ; contains considerable 

amounts of fine quartz sand; 

irregular basal contact.

Phosphorite: medium-hard, 

thick-bedded, coarsely oolitic 

to pelletal, light-gray (N 7); 

contains 3-in. hard aphanitic 

limestone lens.

Mudstone: medium-hard, fissile 

to thin-bedded.

Phosphorite: hard, massive, 

coarsely oolitic, medium-lightgray; contains abundant shell 

fragments; soft at base. 

Phosphorite: soft, coarsely 

oolitic, light-olive-gray (5 Y 

6/1).

Phosphorite: sandy, medium to 

coarsely oolitic, pale-brown 

(WYR 5/2); contains abundant shell fragments. 

Grandeur Tongue of Park City Formation, top bed:

Sandstone: calcareous, hard, 

massive, fine-grained, yellowish-gray (1QYR 7/1).

Thick- Cumulaness five thick-

(feef) ness (feet)

1. 0 15. 0

.7 15. 7

.6 16. 3

.2 16. 5

1. 0 17. 5

1. 1

1.5

18. 6

19. 2

20. 7

21. 2

1. 5 22. 7

1. 0 23. 7

.2 23. 9

1. 8 25. 7

.2 25. 9

.3 26. 2

2. 1 28. 3

Sample

Acid 

PjOs Insoluble FejOa

Radiometric ChemiLOI <U cal U

709-931 O-64 17
526 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Camp Frigid, Mont., lots 1843 and 1343-A 

[LOI, loss on ignition]

Chemical analyses (percent)

Uranium

Thick- Cumula- Radionest tive thick- Acid metric ChemiBed Description (feet) ness (feet) Sample PjO6 Insoluble A1SO3 Fe.Oj LOI «U cal IT

Lot 1343

[ Meade Peak Phosphatic Shale Member of Phosphoria formation measured and sampled from natural exposure near top of scarp slope of Centennial Mountains near 81/4 

corner sec. 34, T. 14 S., R. 1 W., Beawrbead County, Mont,, by B. K. Beplogle, in September 1950. Beds strike about N. 80° W. and dip 12° S. Analyzed for PjOj and 

acid insoluble by U.S. Bur. of Mines and for other constituents by U.S. Geol. Survey].

Lower tongue of Shedliorn Sandstone, basal bed: 

Ls-8______ Sandstone: hard, massive, yel- 1.0 1.0 BKR-5561 4.7 62.2 ____ ____ 0.002 

Ipwish-gray (WYR 8/1); 0.1 ft 

light-gray limestone at base. 

Meade Peak Phosphatic Shale Member of Phosphoria Formation: 

M-7______ Phosphorite: hard, pelletal to .75 1.7 5560 32.4 7.0 __ __ ___ .012 0.013

nodular, brownish-black (10 

YR2/1). 

(6).__ Covered..._____________ 9.0 10.7 _________ __ _- ---- - ----- 

5______ Phosphorite: hard, massive, 1.8 12.5 5559 33.9 2.8 0.24 0.28 4.30 .016 .018

coarsely oolitic, light-gray 

(N 7); arbitrary basal contact. 

4______ Phosphorite: like bed M-5; 2.2 14.7 5558 33.4 6.3 .83 .38 3.45 .015 .012

basal contact somewhat gradational. 

3______ Limestone: sandy, hard, mas- 1.8 16.5 5557 3.7 39.7 .10 .43 24.01 .002 

sive, yellowish-gray (10F.K 

8/1); contains apatite pellets 

and shell fragments; top 2 in. 

conglomeratic. 

2______ Phosphorite: hard, massive, 2.4 18.9 5556 31.0 9.3 .28 .43 5.68 .007 .009

medium coarsely pelletal, 

medium-gray (N 5); contains 

small chert pebbles near top 

and bottom; irregular basal 

contact.

Grandeur Tongue of Park City Formation, top bed: 

G-l______ Limestone: hard, massive, very 2.5 21.4 ___________ ____ ____ _-__ --_- ____- _-_-_ -____

light gray (AT 8).

Lot 1343-A

[A section across the entire Meade Peak Member about 140 feet west of locality of lot 1343 was measured by F. S. Honkala, in August 1952, and the section between the Meade 

Peak and Retort Members at this locality was measured in reconnaissance by R. W. Swanson, in August 1956]

Retort Phosphatic Shale Member of 

Phosphoria Formation, basal bed: 

Rt-37_____ Phosphorite: poorly exposed and ____ _____ ___________ _-__ ___- -___ ---- ----- ----- ___--

not described.

Lower tongue of Shedhorn Sandstone: 

Ls-36___-_ Sandstone: hard, massive, me- 19.5 19.5 ___________ ____ ____ -___ _--- _-__- __--_ _-___

dium-grained, light-brownish-gray; contains many columnar concretions as much 

as 5 ft or more long and 0.3 ft 

diameter, about normal to 

bedding, speckled with apatite 

grains and generally cherty; 

top 1/2 in. phosphatic. 

35_____ Sandstone: about 0.2 ft chert 4.4 23.9 ___________ ..__ ____ -___ _--- ----- ----- -----

pebble conglomerate at base 

overlain by sandstone; poorly 

exposed. 

34___._ Sandstone: cherty, hard, light- .6 24.5 ___________ ___- __-- ---- ---- ----- ----- -----

brownish-gray; contains considerable amounts of apatite; 

no parting at base but sandstone stuck fast like plaster to 

carbonate rock below. 

Franson Tongue of Park City Formation: 

F-33_____ Carbonate rock: hard, massive, 1.7 26.7 ___________ -_-_ --_- __-- ---- ----- ----- -----

aphanitic, light-gray; locally 

sandy and contains irregular 

streaks of sandstone.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 527

Camp Frigid, Mont., lots 1343 and 1343-A Continued 

[LOI, loss on ignition]

Chemical analyses (percent)

Bed Description

Franson Tongue of Park City Formation C ontinued

F-(32)-_-_ Carbonate rock: sandy, hard, 

massive, light-gray; contains 

numerous sandy chert nodules; top one-half in. is composed of cherty phosphorite 

that is stuck fast like plaster 

to underlying carbonate rock. 

(31) _ _ _ _. Covered: mostly carbonate rock 

float.

30_-_-_- Carbonate rock: sandy, hard, 

thin-bedded to massive, lightgray.

29_____- Carbonate rock: hard, massive, 

finely crystalline; locally 

sandy to silty, iron-stained; 

shaly parting at top.

28-_-__- Mudstone: soft, thin-bedded-__

27--____ Carbonate rock: medium-hard, 

thin-bedded to laminated; 

shaly zone below middle; top 

0.7 ft 30 percent fine sand in 

thin layers.

26______ Mudstone: silty to finely sandy,

soft, laminated.

25______ Carbonate rock: silty, hard,

massive, aphanitic, very pale 

brown.

24______ Mudstone: carbonatic, soft, fissile, light-brownish-gray; contains 0.15 ft dolomite in lower 

half.

23___-_- Carbonate rock: sandy, hard, 

massive, light-gray; grades 

from bed below.

22-_____ Sandstone: hard, massive, lightgray, speckled; grades from 

bed below.

21______ Carbonate rock: hard, massive,

light-gray, somewhat sandy.

20-_____ Chert and carbonate roek: 60 

percent chert grades upward 

into carbonate rock, pebbly.

19- _____ Chert and mudstone: hard nodular to wavy-bedded gray 

chert with matrix of soft mudstone; weathers to form undercut in cliff.

18_-_-_- Carbonate roek: hard, thickbedded, light-gray, locally 

gritty to pebbly.

17_---__ Sandstone: phosphatic, calcareous, hard, thick-bedded medium-grained; quartz grains 

angular. 

Meade Peak Member of Phosphoria

Formation: 

M-16_____ Chert________ _______________

15-__-_ Phosphorite: hard, coarsely pel

letal; contains chert.

14_____ Siltstone: soft, faintly laminated, mottled yellowishbrown and bluish- to greenishgray; includes 10-in. sandy 

carbonate rock lens near top. 

13 _____ Phosphorite: coaresly oolitic

12_ -___ Mudstone-__________________

11. - _ _ _ Phosphorite: coarsely oolitic

Thick- Cumulaness live thick-

(feet) ness (feet)

2. 5 28. 7

6. 0 34. 7

4. 1 38. 8

2. 8 41. 6

.3 41. 9

1. 7 43 6

.3 43. 9

2. 3 46. 2

.8 47. 0

1. 1 48. 1

1. 1 49. 2

1. 1 50. 3

.4 50. 7

.5 51. 2

.9 52. 1

.9 53. 0

.2 53. 2

.7 53. 9

1. 8 55. 7

. 25 55. 95

. 7 56. 65

. 2 56. 85

Uranium

Sample PsOs

Acid 

insoluble AhOj LOI

Radiometric ChemieU cal U
528 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Camp Frigid, Mont., lots 1343 and 1343-A Continued 

[LOI, loss on ignition]

Chemical analyses (percent)

Uranium

Bed

Thick- Camulaness tive thick- 

(feet) ness (feet)

Acid 

insoluble Fe2 0s

Radiometric ChemiLOI eU cal U

M-10. 

9.

Description (feet) ness (feet) Sample

Meade Peak Member of Phosphoria 

Formation Continued

Mudstone--_---------___-___ 1.8 58.65 ___________ __-_ -___ _-__ ---- ----- ----- -----

Phosphorite: soft, coarsely .7 59.35 ___-_---___ -___ ____ ____ --__ _____ _____ _____

oolitic. 

Mudstone--------___________ .25 59.6 ___-_-__-__ ____ ____ ____ -___ ----- _-___ _____

Chert--_-------------___-___ .4 60.0 ____--__-__ ____ ____ ____ -___ ----- ----- -----

Mudstone_-_-----______- __ .5 60.5 ___________ ____ ____ ____ ___- _____ _____ _____

Phosphorite: soft, thin-bedded, 1.0 61.5 ___________ -___ -___ -___ -___ _____ _____ _____

coarsely oolitic. 

Phosphorite: medium-hard, mas- 3.4 64.9 ______-__-- ____ ____ ____ -___ _____ _____ _____

sive, coarsely pelletal and 

oolitic, light-brownish-gray; 

basal part sandy and rich in 

shell fragments; basal contact 

very irregular, having 0.8 ft 

relief. 

Limestone: sandy, hard, mas- 3. 7 68. 6 ___________ ____ ____ ____ ____ _____ _____ _____

sive, yellowish-gray; locally 

gritty; contains chert nodules and apatite pellets and 

shell fragments; both contacts 

irregular and bed ranges in 

thickness from 3.3 to 4.1 ft. 

Phosphorite: sandy, hard, mas- 2.2 70.8 ___________ ___. ____ ____ ____ _____ _____ _____

sive, medium coarsely pelletal; 

contains abundant shell and 

tooth fragments; contains 

chert fragments; thickness 2.0 

to 2.4 ft; irregular basal contact.

Grandeur Tongue of Park City Formation, top bed:

Limestone: sandy, hard, mas- 4.4 75.2 ___________ ____ ____ ____ -___ _____ _____ _____

sive, aphanitic, light-brownish-gray; top part contains 

phosphate pellets and shell 

fragments and much finegrained quartz and probably 

belongs to Meade Peak interval although practicable contact remains at top of interval.

South Big Hole Canyon No. 1, Mont., lot 1354-A

[Park City Formation and Eetort Phosphatic Shale Tongue of Phosphoria Formation measured in natural exposure'and hand trench near top of ridge on south Fideof Big 

Hole Riverin SEJ4 sec. 3, T. 5 S., R. 8 W., Beaverhead County, Mont., on northwest limb of faulted anticline. Beds strike N. 60° E. and dip 20° N W. Measured 

by J. A. Peterson and sampled by R. F. Gosman, in June 1951. Analyzed for PzOs and acid insoluble by U.S. Bur. of Mines, and for uranium by U.S. Oeol. Survey]

G-l.

Chemical analyses (percent)

Bed

Rt-23.

22_

20.

19.

Description

Retort Phosphatic Shale Tongue of Phosphoria Formation, lower part:

Mudstone: phosphatic, medium-hard, 

black (N 1), thick-bedded; apatite 

is medium pelletal; grades from bed 

below.

Phosphorite: muddy, soft, brownishblack (WYR 2/1), medium-pelletal; 

grades from bed below.

Phosphorite: muddy, soft, dusky-brown 

(1QYR 3/2), medium-pelletal.

Dolomite: medium-hard, pale-brown 

(1QYR 6/2), very thick bedded, 

aphanitic.

Mudstone: phosphatic, soft, grayishbrown (IQYR 4/2); apatite is finely 

pelletal; grades from bed below.

Thickness 

(feet)

1.0

1. 6

3.0 

1.0

1.3

Cumulative

tfl lCK7lf!33

(feet)

Uranium

Sample P205

Acid insoluble

Radiometric eV

Chemical 

U

1. 0 JAP-5468 12. 6 49. 1 0. 006 0. 002

2.6

5. 6 

6.6

7.9

5467

5466

5465

5464

25.4

20. 3 

1. 1

16. 2

22. 4

29. 5 

4. 1

39. 1

008

008

. 001

. 006

.008

. 007

.006
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 529

South Big Hole Canyon No. 1, Mont., lot 1354-A Continued

Chemical analyses (percent)

Bed Description

Retort Phosphatic Shale Tongue of Phosphoria Formation, lower part Con. 

Rt-18_________ Dolomite: muddy, soft, black (N 1),

aphanitic; grades from bed below.

17__--_--_- Mudstone: phosphatic, soft, grayishbrown (1QYR 4/2), finely pelletal; 

grades from bed below. 

16__-______ Phosphorite: soft, variegated gray, red,

and brown, finely pelletal.

15-_-_-___- Fault breccia: fragments of phosphorite and carbonate rock in 

medium-crystalline carbonate matrix.

14_________ Carbonate rock; phosphatic, soft, variegated gray, red, and brown, aphanitic; apatite is finely pelletal. Bed 

is brecciated and recemented. 

Franson Member of Park City Formation: 

F-13-_____-_-_ Limestone: soft, moderate-reddishbrown (1QYR 4/6), very thick bedded, 

very coarsely crystalline. 

12__________ Dolomite: hard, light-gray (N 7), very

thick bedded, aphanitic; grades from 

bed below. 

ll-_-_______ Chert: sandy, hard, very pale brown

(10YR 7/2), very thick bedded; 

grades from bed below. 

10______-___ Dolomite: hard, pale-brown (IQYR

6/2), very thick bedded, aphanitic; 

grades from bed below.

9__________ Dolomite: medium-hard, light-brownish-gray (lOFfi 6/1), very thick 

bedded, aphanitic; contains chert 

nodules in uppermost 10 ft. 

Rex Chert Tongue of Phosphoria Formation (?) : 

R-8.--________ Chert: hard, pale-red (5R 6/2), very

thick bedded. 

(7) _________ Covered___--_----_-___---------__-

Grandeur Member of Park City Formation: 

G-6_ __ ________ Dolomite and chert, interbedded: hard

light-gray (N 7) very thick bedded 

aphanitic dolomite interbedded with 

hard light-gray (N 8) very thick 

bedded chert. 

5_--________ Dolomite and chert, interbedded: hard

yellowish-gray (1GYR 7/1) very thick 

bedded aphanitic dolomite interbedded with hard light-gray (N 8) 

very thick bedded chert; dolomite 

contains a few chert nodules. 

4_ __________ Dolomite: hard, light-brownish-gray

(IOYR 6/1), very thick bedded, aphanitic; unit is partly covered.

3___________ Limestone: sandy, medium-hard, thickbedded, pale-red (1GR 6/2), medium-crystalline; sand is very fine.

2__.________ Limestone: sandy, medium-hard, palereddish-brown (WR 5/4), very 

thick bedded, medium-crystalline.

!___________ Limestone: medium-hard, reddishbrown (10R 5/4), thick-bedded, 

medium-crystalline; underlain by 

very thick bedded sandstone of 

Quadrant Formation.

Thick- Cumulative

ness thickness

(feet) (feet) Sample

1. 4 9. 3 JAP-5463

1.8 11.1 5462

1.8 12.9 _---__----

.4 13.3 __________

Uranium

Acid insoluble

Radio- Chemical 

metric e~U U

1. 8 15. 1

3. 3 18. 4

7. 5 25. 9

5. 0 30. 9

20. 3 51. 2

29. 0 80. 2

6. 6 86. 8

12. 5 99. 3

19. 0 118. 3

39. 4 157. 7

14. 0 171. 7

6. 7 178. 4

5. 2 183. 6

4. 8 188. 4

1. 8 

17.3

40. 2 0. 005

42. 5 . 006

0. 004

.006
530 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

R-12_

M-ll.

10.

South Big Hole Canyon No. 2, Mont., lot 1354-B

[Meade Peak Shale Tongue of Phosphoria Formation measured in hand trench on ridge about 1 mile south of Big Hole River in SE//sec. 9, T. 5 S., R. 8 W., Beaverhead 

County, Mont. Measured by J. A. Peterson and sampled by R. F. Qosman, in June 1951. Analyzed for uranium by U.S. Qeol. Survey and for other constituents by 

U.S. Bur. of Mines. LOI, loss on ignition]

Chemical analyses (percent)

Bed Description

Rex Chert Tongue of Phosphoria 

Formation:

Chert: very thick bedde 

Meade Peak Phosphatic

Tongue of Phosphoria Formation: 

Mudstone: medium-hard, palebrown (7.5 YR 6/2), 

bedded; grades from 

below.

Mudstone: medium-hard, grayish-red (5R 4/2), thin-bedded. 

9 ______ Phosphorite: medium-hard, yellowish-gray (IOYR 7/1), thinbedded, medium-pelletal.

8---___ Mudstone: medium-hard, grayish-red (5fl 4/2), thin-bedded. 

7 ______ Phosphorite: medium -

brownish-gray (10Y.R 

bedded, coarsely pelletal. 

6 _ _ _ _ _ _ Phosphorite: me(

medium-gray (N 6), thickbedded, coarsely pelletal.

5 ------ Phosphorite: medium-hard, lightgray (N 8), thii 

coarsely pelletal and oolitic. 

4_-___- Phosphorite: sandy, 

hard, light-bro^ 

(10Y7. 6/1), thii 

medium-pelletal; sand is medium; contains apatite nodules 

as much as 50 mm in diameter; contains phos 

skeletal fragments. 

'Grandeur Member of Park

Formation: 

G-3__.--__ Mudstone: sandy, dole

medium-hard, variegated maroon, gray, and yellow; grades 

from bed below. 

2____-_- Mudstone: sandy,

medium-hard, lig 

ish-brown (WYR 6/4)", thinbedded. 

!_____.- Dolomite and chert

bedded.

phoria

Shale 

lation : 

palethini bed

grayedded. 

d, yeld. 

grayedded. 

hard, 

3/D, 

il. 

i-hard, 

thicktl. 

l.lightedded, 

litic. 

3diumh-gray 

edded, 

3 mediodules 

diamphatic

City

3d magrades

rellowthininterThickness 

(feet)

6.0

2. 7

. 5 

. 2

. 7 

.3

.5 

1. 0 

.5

1. 2

5. 2

17. 3

Cumuthickness 

(feet)

6. 0

8. 7

9. 2' 

9. 4

10. 1 

10. 4

10. 9 

11. 9 

12. 4

13. 6

18.8

36. 1

Uranium

Acid Radio- Chemin- metric ical 

Sample PjO5 soluble A1SO3 FejO3 LOI eU U

JAP-5399 1.7 79.7 __._ ____ ____ 0.002 _____

5398 6.7 68.0 ____ ____ ____ .003 _____

5397 33. 0 10. 7 3. 89 0. 68 2. 67 . 009 0. 010 

5396 34. 4 7. 3 1. 80 1. 99 2. 61 . Oil . 010 

5395 37. 6 2. 8 1. 16 . 64 2. 74 . 009 . 009 

5394 20. 5 39. 2 1. 19 2. 54 2. 25 . 006 . 006

3593 .4 69.9 ____ __.. _._. .001 _____

5392 .2 69.9 ____ ___. ____ .001 _____
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 531

Jefferson Canyon, Mont., lot 1355

[Permian rocks measured in natural exposure and hand trench about 200 feet above river on west side of Jefferson Canyon, SE}4 sec. 13, T. 1 N., R. 3 W., Madison County, 

Mont. Beds strike N. 45° E. and dip 45° N W. Measured by J. A. Peterson and sampled by R. F. Gosman, in June 1951. Analyzed for PsOs and acid insoluble by 

U.S. Bur. of Mines and for uranium by U.S. Geol. Survey]

Chemical analyses (percent)

Bed

E-36.

Us-35. 

34.

33 _

To-32. 

31. 

30.

29.

Us-28.

27. 

26. 

25. 

24.

To-23.

22. 

21.

20. 

19.

18.

Description

Ellis Group basal bed:

Sandstone: pebbly; contains oyster 

shells; irregular contact with bed 

below.

Upper tongue of Shedhorn Sandstone; contains tongue of Tosi Chert Member of 

Phosphoria Formation:

Chert: hard, pale-brown (2.5F 6/2), 

thin-bedded.

Sandstone: hard, yellowish-gray (10 YR 

7/1), thick-bedded, very fine grained; 

contains scattered elongate yellowishwhite (10FR 9/1) chert nodules at 

base; composition grades upward to 

about 60 percent chert nodules, beds, 

and stringers near center of unit to all 

sandstone in uppermost 2 ft.

Sandstone and chert interbedded: hard 

light-brownish-gray (10 YR 6/1) thinbedded fine-grained cherty sandstone 

interbedded with hard light-brownishgray (10 YR 6/1) chert.

Chert: hard, pale-brown (10 YR 5/3), 

thin-bedded.

Chert: hard, light-brownish-gray (10 FR 

5/1), thin-bedded.

Chert: sandy, hard, light-brownishgray (10 YR 5/1), thick-bedded; sand 

is fine; grades from bed below.

Chert: hard, light-brownish-gray (IOYR 

5/1), thick-bedded.

Sandstone: hard, light-gray (N 7), 

thick-bedded, fine-grained; upper 

half of unit contairs phosphatic 

skeletal fragments and scattered 

phosphorite nodules as much as 25 mm 

in diameter.

Chert: hard, light-brownish-gray (IQYR 

6/1), thin-bedded.

Sandstone: hard, yellowish-gray (10 FR 

7/1), very thick bedded, fine-grained.

Sandstone: hard, light-gray (N 7), very 

thick bedded, fine-grained.

Sandstone and chert, interbedded: 

hard light-gray (N 7) thick-bedded 

fine-grained sandstone interbedded 

with hard light-brownish-gray (10F.R 

5/1) thin-bedded chert. 

Tosi Chert Member of Phosphoria Formation:

Chert: phosphatic, medium-hard, medium-gray (N 5), thick-bedded; contains apatite nodules that average 

8 mm and are as much as 20 mm in 

diameter; slightly irregular contact 

with bed below.

Chert: hard, light-brownish-gray 

(IQYR 5/1), thick-bedded.

Phosphorite: cherty, hard, lightbrownish-gray (10F.R 5/1), contains 

a few apatite nodules as much as 30 

mm in diameter; thick-bedded, skeletal and coarsely pelletal; slightly 

irregular contact with bed below.

Chert: hard, pale-brown (IQYR 5/3), 

thin-bedded.

Chert: phosphatic, medium-hard, 

light-brownish-gray (IQYR 5/1), 

thick-bedded; apatite is skeletal and 

finely colitic and pelletal.

Chert: hard, black (N 1), thin-bedded_

Uranium

Thick- Cumulative

ness thickness

(feet) (feet)

5.0

1. 5 

10. 5

1.9

2.0 

3.6

Sample

Acid insoluble

Radio- Chemical 

metric eV U

1.5 

12.0

13.9

1. 7 15. 6

7. 8 23. 4

1. 0 24. 4

26. 4

30.0

.5 30. 5

2. 8 33. 3

1. 2 34. 5

5. 9 40. 4

.3 40. 7 JAP-5384 18. 6 48. 4 0. 003

2.9 43.6 _.__._-___ 

.5 44. 1 5383 18. 2 45. 0 003

1. 8 45. 9

.5 46. 4

.7 47. 1

5382 15. 5 53.6 002
532 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Jefferson Canyon, Mont., lot 1355 Continued

Chemical analyses (percent)

Bed

To-17.

16. 

15. 

14. 

13.

12.

Rt-11.

10. 

9_

To-7. 

6.

Description

Tosi Chert Member of Phosphoria Formation Continued

Chert: phosphatic, hard, medium-gray 

(N 5), thick-bedded; apatite is medium-pelletal and oolitic.

Chert: medium-hard, black (N 1), 

thick-bedded.

Dolomite: cherty, medium-hard, black 

(N 1), thick-bedded.

Chert: dolomitic, hard, brownish-gray 

(IOYR 3/1), thick-bedded.

Chert: phosphatic, medium-hard, 

dark-gray (N 3), thin-bedded; apatite is coarsely pelletal; grades from 

bed below.

Chert: muddy, medium-hard, brownish-gray (WYR 4/1), thin-bedded. 

Retort Phosphatic Shale Member of Phosphoria Formation:

Phosphorite: cherty, medium-hard, 

brownish-gray (IOYR 3/1), thickbedded, coarsely oolitic and pelletal.

Mudstone: cherty, medium-hard, darkgray (N 3), thick-bedded.

Phosphorite: cherty, medium-hard, 

pale-brown (IOYR 5/2), very coarsely 

pelletal and oolitic; contains phosphatic skeletal fragments and a few 

apatite nodules as much as 45 mm 

in diameter.

Mudstone: soft, pale-brown (2.5 Y 5/2),

fissile.

Tosi Chert Member of Phosphoria formation 

lower part:

Chert: hard, light-brownish-gray 

(IOYR 5/1), thick-bedded.

Phosphorite: hard, medium-gray (N 

5), thick-bedded, medium-pelletal 

and oolitic; contains some phosphatic 

skeletal fragments; grades from bed 

below. Fossil-colln. No. 12693.

Sandstone: cherty, hard, medium-gray 

(N 5), thick-bedded, fine-grained; 

contains phosphatic skeletal fragments; contains chert and quartzite 

pebbles in a zone about 0.5 ft above 

base of bed.

Chert: medium-hard, mottled lightgray, brown, and yellow, thickbedded. 

Lower tongue of Shedhorn Sandstone:

Sandstone: medium-hard, light-gray 

(N 7), thick-bedded, fine-grained; 

rounded chert and quartzite pebbles 

are as much as 20 mm in diameter.

Sandstone and chert, interbedded: 

medium-hard, yellowish-gray (IOYR 

7/1) thick-bedded fine-grained sandstone contains a few interbeds of 

chert; layer about 0.8 ft thick that 

contains chert and quartzite pebbles 

as much as 50 mm in diameter occurs 

approximately 5 ft above base of 

unit; grades from bed below.

Sandstone: pebbly, medium-hard yellowish-gray (IOYR 7/1), thickbedded, fine-grained; pebbles are 

composed of quartzite and chert; 

underlain by interbedded gray dolomite and chert of the Franson and 

lower tongues of the Park City Formation.

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Uranium

0.6

. 7

1.0

10. 4

. 5

3.6

.9

3.5

6.3

12. 5

1. 0

47. 2 JAP-5381

48.4

49.4

60.3

63.9

68. 3

69.2

69.6

75.9

76. 3

77. 2

77. 7

78.2

90. 7

91. 7

P2 05

17. 5

Acid insoluble

Radio- Chemical 

metric «U U

46. 8 0. 004

5380

5379

5378

5377

5376

5375

64. 3

2. 0 75. 0

22. 1

1. 1

24. 7

1. 7

31.9

64. 0

32. 4

72. 1

.003

. 002

.005

.002

.009

.003

0.006

.009

5374 7.3 77.9 . 003
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 533

Three Forks, Mont., lot 1356

[Permian rocks measured in natural exposure at north end of Milligan Canyon about 300 ft east of Willow Creek road, sec. 24, T. 2 N., R. 1 W., Jefferson County, Mont. 

Beds strike N. 80° E. and dip 25 ° N. Measured by ,T. A. Peterson and sampled by R. F. Gosman, in June 1951. Analyzed for P2Os and acid insoluble by U.S. Bur. of 

Mines and for uranium by U.S. Geol. Survey]

Chemical analyses (percent)

Bed

US-32.

To-31_

30.

29-

28.

27. 

26-

25.

24. 

23.

22.

20_ 

19- 

18. 

17. 

16.

15. 

14.

13. 

12.

11- 

10.

LS-9.

Description 

Upper tongue of Shedhorn Sandstone (?):

Sandstone: overlain by basal conglomerate of Ellis Group. 

Tosi Chert Tongue of Phosphoria Formation:

Mudstone: dolomitic, hard, lightyellowish-brown (WYR 6/4).

Phosphorite: cherty, hard, brownishgray (WYR 4/1), medium-pelletal; 

contains a few oolites and phosphatic skeletal fragments.

Chert: hard, brown___--___-____-___

Phosphorite: pebbly, sandy, soft, 

brownish-gray (WYR 3/1), nodular, 

medium-pelletal and colitic; sand 

is fine; pebbles are composed of chert.

Limestone: dark-gray_ ______________

Chert: brittle, light-brownish-gray 

(WYR 5/1).

Phosphorite: cherty, hard, brownishgray (WYR 4/1), nodular, finely 

pelletal; nodules are as much as 30 

mm in diameter.

Chert: muddy, hard, pale-brown 

(2.5 Y 6/2).

Chert: phosphatic, hard, medium-gray 

(N 5); apatite is finely pelletal; 

contains phosphatic skeletal fragments.

Chert: hard, pale-brown (WYR 6/2)__

Chert: phosphatic (?), hard grayishbrown (2.5F 4/2).

Chert: hard, light - brownish - gray 

(WYR 5/1).

Chert: hard, light - brownish - gray 

(WYR 5/1).

Dolomite: hard, light-brownish-gray 

(WYR 5/1), aphanitic.

Chert: muddy (?), hard, light-brownishgray (WYR 5/1).

Chert: phosphatic, hard, brownishgray (WYR 3/1); apatite is coarsely 

pelletal.

Phosphorite: cherty, hard, light-brownish-gray (WYR 6/1), coarsely oolitic.

Chert: dolomitic, hard, brownish-gray 

(WYR 3/1).

Chert: brittle, dusky-brown (10YR 3/2)_

Chert: phosphatic, hard, brownishgray (WYR 3/1); apatite is skeletal, 

nodular and medium pelletal; nodules 

are as much as 20 mm in diameter.

Dolomite: cherty, hard, brownish-gray 

(WYR 3/1), thin-bedded, aphanitic.

Dolomite: cherty, hard, grayish-brown

(2.5 Y 4/2), aphanitic. 

Lower tongue of Shedhorn Sandstone:

Sandstone: cherty, pebbly, hard, lightbrownish-gray (WYR 5/1), finegrained; chert, quartzite, and dolomite pebbles are as much as 25 mm 

in diameter.

Franson and Grandeur Members of Park 

City Formation, undifferentiated:

Dolomite and chert: hard yellowishgray (10YR 8/1) silty dolomite containing 25 to 35 percent of hard lightbrownish-gray (WYR 6/1) very irregular chert nodules and lenses.

Thick- C

ness . 

(feet)

1. 0

6. 2 

. 2

2. 3 

. 1

. 9 

.3

. 3

. 7 

. 3

7.0 

1. 0

1. 5 

1. 0 

. 5 

2. 0 

. 5

. 5 

2. 5

7.3 

1. 6

1. 5

. 6

Uranium

thickness Acid in- Radio- Chemical 

(feet) Sample FiOs soluble metric eU U

10

7.2 __-____-_. ------ -__-_- ___---

7. 4 JAP-5405 18. 8 44. 7 0. 005

9 7

9 8

10 7

11.0 ______-_-_ ______ ______ ______

11. 3 5404 20. 2 44. 7 . 005 

12.0 _-_-----_- ------ ------ _-_-_-

12. 3 5403 18. 9 43. 4 . 007 

19 3

on q

21.8 __--_-_-__ ______ ------ ------

22.8 _-_--__-_. __--_- ______ _'_-_--

23.3 __________ ______ ______ ------

25.3 __________ ------ ------ _-- --

25. 8 5402 10. 9 64. 0 . 003

26. 3 5401 23. 7 35. 7 . 009 

28.8 ______-__. ______ ------ ------

36. 1 __________ ------ ------ ------

37. 7 5400 16. 3 50. 0 . 005

 JQ 0

39. 8 ---------- ------ __-_-- ------

0. 004

. 006

.005

. 008

. 005

26. 3

42. 7

69. 0
534 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Three Forks, Mont., lot 1356 Continued

Chemical analyses (percent)

Bed

Thickness 

(feet)

Cumulative

thickness

(feet)

Uranium

Sample

Acid in- Radio- Chemical 

soluble metric eV U

PC-7. 

6.

4. 3 

21. 3

73.3

94.6

7. 0 101. 6

Description

Franson and Grandeur Members of Park 

City Formation, undifferentiated Con. 

Sandstone: hard, very pale brown

(IOYR 7/3), very fine grained. 

Dolomite and chert: hard yellowishgray (IOYR 8/1) silty dolomite containing 25 to 35 percent of hard lightbrownish-gray (IOYR 6/1) chert in 

very irregular nodules and lenses.

5__________ Dolomite: silty, medium-hard, lightbrownish-gray (IOYR 6/1), aphanitic; contains numerous chert nodules and lenses.

4__________ Sandstone: hard, yellowish-gray (10

YR 7/1), thin-bedded, fine-grained.

3__________ Dolomite: hard, pale-brown (2.5 Y 6/2)

aphanitic.

2__________ Sandstone: hard, pale-brown (2.5F

6/2), fine-grained.

!__________ Dolomite: silty, medium-hard, very

pale brown (IOYR 7/2), aphanitic; 

underlain by very thick bedded sandstone of the Quadrant Formation.

Sappington Canyon, Mont., lot 1357

[Permian rocks measured in natural exposure along ridge on east side of Jefferson River in sec. 25, T. 1 N., R. 2 W., Gallatin County, Mont. Beds strike N. 80° W. and dip 

41° N. Measured by J. A. Peterson and sampled by R. F. Qosman in July 1951. Analyzed for PjOs and acid insoluble by U.S. Bur. of Mines and for uranium by U.S. 

Geol. Survey]

Chemical analyses (percent)

1. 5

2. 3

. 9

1.7

103. 1

105. 4

106. 3

108. 0

Uranium

Bed

E-46._

45_ 

Us-44.

43.

To-42. 

41_ 

40-

39_ 

38.

Description

Ellis Group, basal part:

Limestone: sandy, medium-hard, yellowish-gray (5Y 7/2), thin-bedded; 

contains many shell fragments and 

scattered crinoid stem fragments; 

grades from bed below.

Mudstone: calcareous, soft, thinbedded. 

Upper tongue of Shedhorn Sandstone:

Sandstone: hard, light-yellowish-brown 

(WYR 6/4), thick-bedded, mediumgrained; contains chert and quartzite 

pebbles as much as 30 mm in 

diameter; grades from bed below.

Sandstone: pebbly, hard, weak-yellowish-orange (10 YR 7/6), thick-bedded, 

fine-grained; angular and sub-angular 

chert and quartzite pebbles are as 

much as 40 mm in diameter, average 

3 to 10 mm in diameter; grades from 

bed below.

Tosi Chert Member of the Phosphoria 

Formation:

Chert: hard, medium-gray (Af 6), thinbedded; grades from bed below.

Sandstone: hard, light-olive-gray (5Y 

4/2), very thick bedded, fine-grained.

Chert: hard, pale-brown (IOYR 5/2), 

thin-bedded; contains thin lenses of 

sandstone in lower 2 ft; contains 

many columnar bodies of chert and 

sandstone.

Sandstone: hard, light-brownish-gray 

(10 YR 6/1), very thick bedded, finegrained; grades from bed below.

Chert: hard, grayish-brown (2.5F4/2), 

thin-bedded; contains many columnar bodies of sandstone constituting 

30 to 40 percent of bed.

Thickness 

(feet)

4. 2

1. 1

. 9

3.0

Cumulative

thickness

(feet)

4. 2

5.3

. 9

3.9

Sample

Acid insoluble

Radiometric eV

Chemical 

U

6.5 

1. 3 

6.9

1. 6

2. 4

10. 4

11.7

18. 6

20. 2

22. 6
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 535

Sappington Canyon, Mont., lot 1357 Continued

Bed Description

Upper tongue of Shedhorn Sandstone: 

Us-37_________ Sandstone: hard, light-brownish-gray

(IQYR 6/1), very thick bedded, medium-grained; contains columnar 

bodies and nodules of chert.

36__-_-_--_ Sandstone: calcareous, medium-hard, 

light-brownish-gray (10 YR 6/1), very 

thick bedded, medium-grained; contains abundant calcareous pelecypod 

and gastropod shell fragments, phosphatic skeletal fragments, and a few 

chert pebbles 3 mm in diameter. 

Fossil-colln. No. 12697.

35_ ________ Sandstone: calcareous, pebbly, mediumhard, weak-yellowish-orange (2.5 Y 

7/4), very thick bedded, fine-grained; 

basal foot of bed contains rounded 

flat pebbles composed of aphanitic 

dolomite; entire unit contains lenses 

and patches of chert and sandstone 

pebbles averaging 5 mm in diameter 

and that are as much as 50 mm in 

diameter; contains scattered patches 

or lenses of calcareous gastropod and 

pelecypod fragments and phosphatic 

skeletal fragments; unit is crossbedded throughout; irregular contact 

with bed below. Fossil-colln. Nos. 

18589 and 18588.

Tosi Chert Member of Phosphoria Formation: 

To-34_________ Chert: hard, pale-brown (10 YR 5/2),

thick-bedded.

33_________ Dolomite: cherty, medium-hard, lightyellowish-brown (WYR 6/4), thickbedded, asphanitic; grades from bed 

below.

32___ ______ Dolomite and chert, interbedded:

medium-hard pale-brown (10 YR 6/2) 

thin-bedded aphanitic cherty dolomite interbedded with medium-hard 

pale-brown (10 YR 6/2) thin-bedded 

dolomite chert. Fossil-colln. No. 

18587.

31_________ Chert: hard, light-brownish-gray (10-

YR 5/1), thick-bedded. 

Retort Phosphatic Shale Member of Phosphoria Formation: 

Rt-30-________ Phosphorite: cherty, medium-hard,

thin-bedded.

29_________ Chert and mudstone, interlaminated:

hard brownish-black (10 YR 2/1) 

thin-bedded dolomitic chert interbedded with medium-hard brownishblack (10 YR 2/1) thin-bedded dolomitic mudstone.

28. ________ Chert: phosphatic, medium-hard,

brownish-gray (10 YR 3/2), thinbedded; apatite is very coarsely 

pelletal; contains a few apatite 

nodules.

27__-__-_-_ Similar to bed Rt-29; grades from bed 

below.

26^________ Mudstone: dolomitic, medium-hard,

grayish-brown (IOYR 4/2), fissile.

25_ ________ Phosphorite: cherty, medium-hard,

brownish-gray (10 YR 4/1), thinbedded, coarsely pelletal and oolitic.

24_ ________ Dolomite: medium-hard, brownishgray (10 YR 4/1), thick-bedded, 

aphanitic.

Chemical analyses (percent)

Thick- Cumulative

ness thickness

(feet) (feet) Sample

Uranium

Acid in- Radiosoluble metric ell

Chemical 

U

3. 5

6.2

26. 1

32. 3

9.3 41. 6

16. 0 

1.3

6.9

57. 6

58.9

2. 7 68. 5

.2 68. 7 JAP-5483 23. 0 34. 9 0. 005 0. 007

3. 0

8. 0 

1. 8

1. 2

71. 7

71. 9

79. 9

81. 7

82. 2

83.4

5482 16. 1 47.3 . 004

5481

5480

5479

2. 0 

25.3

1. 2

73. 6

6.0

. 002

.007

. 000

.008
536 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Sappington Canyon, Mont., lot 1357 Continued

Chemical analyses (percent)

Bed Description

Retort Phosphatic Shale Member of Phosphoria Formation Continued 

Rt-23-________ Mudstone and phosphorite, interlaminated: soft light-yellowish-brown 

(WYR 6/4) mudstone interlaminated 

with soft brownish-gray (WYR 4/1) 

medium-pellet al argillaceous phosphorite.

22_ ________ Phosphorite: cherty, medium-hard,

dark-gray (N 4), thin-bedded, 

coarsely pelletal and oolitic; contains a few apatite nodules.

21 _________ Mudstone: phosphatic, dolomitic, soft,

pale-brown (WYR 5/3).

20_ ________ Phosphorite: cherty, medium-hard,

pale-brown (WYR 6/2), thick-bedded, coarsely pelletal and oolitic; 

contains a few apatite nodules in 

upper part as much as 4 mm in diameter.

19_ ________ Dolomite: sandy, phosphatic, soft,

thin-bedded, aphanitic; apatite is 

medium pelletal, sand is fine.

18--____-_. Sandstone: dolomitic, soft, light-yellowish-brown (WYR 6/4), fine-grained.

17_________ Mudstone: dolomitic, soft, grayishbrown (WYR 4/2), thick-bedded.

16_ ________ Phosphorite: cherty, medium-hard,

pale-brown (WYR 6/2), thin-bedded, 

coarsely oolitic and nodular; nodiiles 

are as much as 10 mm in diameter; 

contains phosphatic skeletal fragments.

15-________ Mudstone: dolomitic, medium-hard,

thin-bedded.

14_________ Phosphorite: cherty, sandy, hard,

brownish-gray (WYR 4/1), thickbedded, nodular and coarsely oolitic 

and pelletal; nodules are as much as 

20 mm in diameter; sand is fine; 

contains phosphatic skeletal fragments.

13_._______ Limestone: cherty, medium-hard, liehtyellowish-brown (WYR 6/4), thickbedded, aphanitic.

12_________ Chert: hard, light-brownish-gray

(10 YR 5/1) thick-bedded. May be a 

tongue of Tosi Chert Member of 

Phosphoric Formation. 

Lower tongue of Shedhorn Sandstone: 

Ls-ll_ ________ Sandstone: hard, very pale brown

(WYR 7/2), very thick bedded, 

medium-grained; lower 1.0 ft is 

dolomitic and contains subangular 

and subrounded quartzite and chert 

pebbles as much as 20 mm in diameter; grades from bed below. 

Franson and Grandeur Tongues of Park

City Formation, Undifferentiated: 

Pc-10_________ Chert and sandstone: hard pale-brown

(WYR 6/2) thick-bedded chert containing many lenses and stringers of 

fine-grained sandstone in lower 7 ft 

and interbeds of dolomite in upper 

2.5 ft.

9 _________ Limestone: medium-hard, weak-yellowish-orange (WYR 7/0), very thick 

bedded, finely crystalline; grades 

from bed below. 

8_---_____ Chert and sandstone, interbedded:

hard yellowish-gray (WYR 8/1) 

thick-bedded chert containing some 

interbeds of hard light-gray (N 7) 

thick-bedded chert.

Thick- Cumulative

ness thickness

(feet) (feet) Sample

0. 3 83. 7 JAP-5478

Uranium

.5

Acid in- Radio- Chemical 

PaOs soluble metric ell U

17.4 30. 7 0. 004

.2 83. 9

.3 84. 2

1. 1 85. 3

85. 8

.4 86. 2

.7 86. 9

.3 87. 2

2. 3 89. 5 

.5 90. 0

.9 90. 9

.7 91. 6

3. 0 94. 6

5477

5476

5475

5474

5473

5472

5471

5470

5469

29. 1 18. 8 . 007 0. 006

8.3 48.7 .004 _______

26. 8 18. 3 . 007 . 007

11. 4

6.8

4.6

18.3

30. 3

57.7

64.7

38.9

. 002

.004 _______

.002 _______

. 006 . 005

1. 5 72. 3 . 002

11. 5 59. 0 . 004

9. 5 104. 1

1. 3 105. 4

6. 5 111. 9
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 537

Sappington Canyon, Mont., lot 1357 Continued

Bed

Pc-7 

6_

Q-4.

Description

Franson and Grandeur Tongues of Park 

City Formation, Undifferentiated Con.

Dolomite: silty, medium-hard, lightyellowish-brown (WYR 6/4), thickbedded, aphanitic.

Sandstone: calcareous, pebbly, hard, 

very pale brown (WYR 7/2), thickbedded; contains many angular chert 

fragments as much as 15 mm in 

diameter.

Dolomite and chert, interbedded: 

medium-hard, very pale brown 

(10 YR 7/3), thick-bedded aphanitic 

dolomite interbedded with hard very 

pale orange (10 YR 8/2) thick-bedded 

chert; chert beds constitute 5 percent 

of unit at base and 60 percent of 

unit at top. 

Quadrant Formation, upper part:

Sandstone: dolomitic, medium-hard, 

weak-yellowish-orange (10 YR 7/6), 

thin-bedded, fine-grained; contains 

chert and quartzite pebbles in lower 

3.0 ft that are as much as 5 mm in 

diameter.

Sandstone: calcareous, medium-hard, 

weak-yellowish-orange (10 YR 7/6), 

very thick bedded, medium-grained; 

uppermost 1.0 ft contains chert and 

quartzite pebbles as much as 25 mm 

in diameter; grades from bed below.

Sandstone: calcareous, hard, verv pale 

brown (WYR 7/2), very "thick 

bedded, medium-grained; exhibits 

some small scale gentle crossbedding; 

grades from bed below.

Sandstone: calcareous, medium-hard, 

white (N 9), very thick bedded, 

medium-grained; contains some 

elongated light-gray (N 7) chert 

lenses; underlain by about 25 ft of 

interbedded sandstone and dolomite 

in beds 3 ft to 5 ft thick.

Chemical analyses (percent)

Thickness 

(feet)

Cumulative

Uranium

(feet) Sample

Acid in- Radiosoluble metric eUChemical

U

6. 9 118. 8

5 119. 3

11. 3 130. 6

16. 0 146. 6

6. 0 152. 6

14. 0 166. 6

5. 0 171. 6

North Big Hole Canyon, Mont., lot 1358

[Permian rocks measured in hand trenches and natural exposures on north side of Big Hole River in NE }4 sec. 3,T.5S.,R.8W., Madison County, Mont., on northwest limb 

of asymmetrical anticline. Beds G-8 through G-14 measured in lower trench, beds G-17 through M-23 in middle trench and beds Rt-26 through To-63 in upper trench. 

Remainder of beds measured in natural exposure. Exposures in upper trench are poor; so, although the sequence is probably correct, the measured thicknesses, especially 

in the lower half of the Retort Tongue, may be too small. Beds strike N. 70° E. and dip 20° N. Measured by J. A. Peterson and sampled by Peterson and R. P. Gosman, 

in June and July 1951. Analyzed for PaOs and acid insoluble by U.S. Bur. of Mines, and for uranium by U.S. Geol. Survey]

Bed

Us-72_

To-71. 

Us-70.

To-69.

Description

Upper member of Shedhorn Sandstone and 

Tosi Chert Member of Phosphoria Formation, intertongued:

Sandstone: hard, yellowish-gray (10 YR 

7/1), thick-bedded, fine-grained; contains glauconite. About 25 ft of 

strata are covered between top of 

bed Us-72 and the lowermost exposures of the Dinwoody formation.

Chert: hard, medium-gray (N 6), thickbedded.

Sandstone: hard, light-brownish-gray 

(WYR 6/1), thick-bedded, finegrained; contains chert nodules and 

glauconite.

Chert: silty, hard, medium-gray (N 6), 

thick-bedded; contains glauconite; 

crossbedded in part.

Chemical analyses (percent)

Thickness

Cumulative

thickness

(feet)

Uranium

Sample

Acid insoluble

Radiometric eU

Chemical 

U

4. 6 4. 6

9. 0 13. 6

2. 0 15. 6

8. 2 23. 8
538 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD 

North Big Hole Canyon, Mont., lot 1358 Continued

Chemical analyses (percent)

To-68.

Us-67- 

To-66.

Us-65.

To-64. 

63.

Rt-62. 

61.

58-

55.

52.

50_

49-

48.

47.

46.

45.

Bed Description

Upper member of Shedhorn Sandstone and 

Tosi Chert Member of Phosphoria Formation, intertongued Continued

______-- Chert: sandy, hard, grayish-brown

(WYR 4/2), very thick bedded; contains glauconite.

__--_--_ Sandstone: hard, pale-brown (10F.R 

5/3), very thick bedded, fine-grained.

____---_ Chert: hard, medium-gray (N 5), 

thick-bedded; contains glauconite; 

slightly sandy in upper few feet.

_____-_- Sandstone: cherty, hard, grayish-brown 

(WYR 3/2), very thick bedded, very 

fine grained; contains glauconite.

_____--_ Chert: dark-gray (N 4)______________

-__-__-- Chert: dark-gray (AM), thick-bedded; 

contains phosphatic skeletal fragments.

Retort Phosphatic Shale Tongue of Phosphoria Formation:

-------- Mudstone: soft, grayish-brown (10F.R

4/2), fissile.

-------- Mudstone: soft, brownish-gray (WYR

4/1).

-_-__-__ Mudstone: phosphatic, soft, duskybrown (10 YR 2/2); apatite is finely 

pelletal.

________ Phosphorite: carbonatic, medium-hard,

brownish-black (10 YR 2/1), coarsely 

pelletal.

_________ Mudstone: carbonatic, soft, duskybrown (WYR 3/2).

________ Mudstone: soft, dusky-brown (10F.R

3/2).

_________ Phosphorite: medium-hard, brownishgray (WYR 3/1), finely pelletal.

__-__--_ Phosphorite:muddy, soft, dusVy-brown 

(WYR 3/2), medium-pelletal.

______-- Mudstone: phosphatic, soft, duskybrown (WYR 2/2); apatite is very 

finely pelletal.

_____--- Phosphorite: medium-hard, black (N 

2), thin-bedded, finely pelletal.

________ Mudstone: soft, dusky-brown (10F.R

2/2).

________ Phosphorite: medium-hard, brownishblack (WYR 2/1), thin-bedded, 

medium-pelletal.

________ Dolomite: phosphatic, medium-hard,

dusky-brown (WYR 3/2), aphanitic, 

apatite is finely pelletal. 

Phosphorite: muddy, soft, brownishgray (WYR 4/1), thin-bedded, finely 

pelletal.

________ Phosphorite: soft, brownish-black

(WYR 2/1), medium-pelletal; grades 

from bed below.

. ______ Phosphorite: muddy, soft, brownishblack (WYR 2/1), medium-pelletal; 

grades from bed below.

.__--__-_ Phosphorite: muddy, soft, brownishblack (WYR 2/1), finely pelletal; 

grades from bed below. 

.____ Mudstone: soft, dusky-brown (10F.R

3/2); grades from beds below.

.____ Phosphorite: muddy, soft, brownishblack (WYR 2/1), finely pelletal.

Thick- Cumulative 

ness thickness 

(feet) (feet)

2. 0 25. 8

2. 0 27. 8 

21. 6 49. 4

26. 5 75. 9

4. 0 79. 9 

.6 80. 5

1. 0 81. 5 

1. 0 82. 5 

2. 2 84. 7

.6 85. 3

.5 85. 8 

.8 86. 6 

.6 87. 2

.7 87. 9

.6 88. 5

1. 3 89. 8

.5 90. 3

1. 8 92. 1 

.8 92. 9 

.6 93. 5

.8 94. 3

1. 7 96. 0

1. 7 97. 7

.4 98. 1

1. 4 99. 5

Uranium

Sample

JAP-5461

5460 

5459 

5458

5457

5456 

5455

5454

5453

5452

5451

5450

5449 

5448 

5447

5446

5445

5444

5443

5442

Acid in- RadioPzOj soluble metric eU

4. 5

2.4 

4.5 

13.3

15.9

4. 8 

4.7 

23.9

16. 4

11.7

23. 7

7.7

24. 3 

12. 0 

19. 4

21. 9

26.3

17.0

6. 3

16.3

82. 4

71. 3 

66. 4 

45. 4

12. 4

58. 6 

60. 7 

10. 9

31. 3

42. 3

9.9

49. 7

10.0 

8.0 

21. 3

20. 9

15.0

32. 6

59.5

31. 7

0. 002

. 003 

.002 

. 006

.005

.005 

. 004 

. 007

. 008

. 007

. 007

. 005

.006 

. 003 

. 007

. 007

. 008

.007

.005

.008

Chemical 

IT

0. 003

. 004

.005

. 007

. 006

. 005

. 006

. 003

. 005

. 006

. 007

. 009

. 005

. 002

. 006
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 

North Big Hole Canyon, Mont., lot 1358 Continued

539

Chemical analyses (percent)

Bed Description

Retort Phosphatic Shale Tongue of Phosphoria Formation Continued

Rt-43_-------- Phosphorite: muddy, soft, brownishblack (10 YR 2/1), medium-pelletal.

42_____---- Mudstone: phosphatic, soft, duskybrown (10 YR 2/2); apatite is medium 

pelletal; grades from beds below.

41_-------- Dolomite: medium-hard, brownishgray (10 YR 4/1), aphanitic; grades 

from beds below.

40--------- Dolomite: medium-hard, brownishgray (10 YR 4/1), thick-bedded, 

aphanitic.

39__------- Dolomite: medium-hard, dusky-brown

(10 YR 3/2), aphanitic.

38_-------- Phosphorite:muddy, soft, dusky-brown

(10 YR 2/2), medium-pelletal.

37__------- Dolomite: medium-hard, brownish-gray

(10 YR 4/1), aphanitic.

36___------ Mudstone: phosphatic, brownish-gray

(10yfl3/l).

35--------- Dolomite: medium-hard, brownishgray (10 YR 3/1), aphanitic.

34_._------ Mudstone: soft, dusky-brown (10 YR

3/2).

33_-------- Mudstone: phosphatic, soft, duskybrown (10 YR 2/2); apatite is medium 

pelletal.

32__-____-- Dolomite: medium-hard, brownishgray (10 YR 4/1), thick-bedded, 

aphanitic.

31-__-----_ Phosphorite: muddy, soft, brownishgray (10F# 3/1), medium-pelletal.

30--------- Dolomite: medium-hard, pale-brown

(10 YR 6/2), aphanitic

29_-------- Phosphorite: muddy, medium-hard,

grayish-brown (IOYR 3/2), finely 

pelletal.

28-_------- Mudstone: phosphatic, medium-hard,

grayish-brown (7.5YR 4/2); apatite 

is medium pelletal.

27__-_-_-_- Phosphorite: muddy, medium-hard, 

dark-gray (N 3), thick-bedded, 

medium-pelletal; contains phosphatic skeletal fragments.

26--------- Mudstone: hard, moderate-yellowishbrown (10 YR 5/6), thick-bedded; 

grades from bed below. 

Franson Member of Park City Formation,

uppermost bed: 

F-25---------- Sandstone: cherty, yellowish-brown.

Interval between beds R-24 and 

F-25 covered and not measured. 

Fossil-colln. No. 18584. 

Rex Chert Tongue of Phosphoria Formation: 

R-24-__-_._-_ Chert__-_____--------___-____-__-_

Meade Peak Phosphatic Shale Tongue of

Phosphoria Formation: 

M-23--------- Mudstone: medium-hard, pale-brown

(10 YR 5/3), thin-bedded-_________

22_--____-_ Mudstone: medium-hard, light-olivebrown (2.5 Y 5/4), thin-bedded.

21---_____- Phosphorite: hard, light-gray (N 7), 

thick-bedded, coarsely pelletal and 

oolitic; contains apatite nodules as 

much as 25 mm in diameter.

Thickness 

(feet)

1.4

2.3

. 4

.7

. 4 

. 5 

. 6 

1. 1 

1. 1 

. 7

. 4

.7

.5 

1. 4 

1.5

1. 5 

. 5

.5 

5.0

3.0

1.2

.8 

.6

Cumulative 

thickness 

(feet)

100. 9

103. 2 

103. 6 

104.3

104. 7 

105. 2 

105. 8 

106. 9 

108. 0 

108.7

109. 1 

109. 8

110.3 

111.7 

113.2

114.7 

115. 2

115. 7 

120. 7

123.7

124.9 

125.7 

126.3

Uranium

Sample

JAP-5441

5440 

5439 

5438

5437 

5436 

5435 

5434 

5433 

5432

5431 

5430

5429 

5428 

5427

5426 

5425

5411 

5410 

5409

PzOa

20. 6

14. 0 

2.3 

2. 5

3.4 

17. 6 

5. 1 

9. 8 

3.5 

7.9

11. 5 

3.3

14.7 

2.2 

19. 5

13. 8 

23.2

. 6 

.5 

34.0

Acid in- Radiosoluble metric e\J

22. 7

38. 5 

5. 0 

5. 8

7.7 

28. 5 

9. 9 

39. 3 

6. 1 

48.9

38. 4 

6. 1

27.2 

5.5 

27.5

38.5 

36.0

85. 3 

86. 3 

10. 0

0. 008

. 006 

.002 

. 001

. 002 

.008 

. 003 

. 005 

. 002 

. 006

. 008 

. 001

. 006 

.001 

.006

.004 

. Oil

.002 

.003 

. 007

Chemical 

U

0.008

.004

. 006

. 005

. 003

. 006

.005

.005

.007

.006
540 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

North Big Hole Canyon, Mont., lot 1358 Continued

Bed Description

Grandeur Member of Park City Formation: 

G-20-_-_______ Mudstone: carbonatic, soft, darkyellow (2.5 F 6/8), fissile. Fossilcolln. No. 12692.

19____------ Mudstone: dolomitic, medium-hard,

light-yellowish-brown (10 YR 6/4), 

very thick bedded.

18___------- Mudstone: dolomitic, medium-hard,

weak-yellowish-orange (10 YR 7/6), 

thin-bedded.

17___ ------- Mudstone: dolomitic, soft, light-yellowishbrown (IQYR 6/4), thin-bedded.

16--_------- Chert---__________________________

(15)-------- Not described-_-_-___--_----_-__-__

14_ ____-_-__ Limestone: muddy, soft, thin-bedded _

13____--_-_- Limestone: muddy, hard, very pale 

brown (10 YR 7/2), very thick bedded.

12--_-----_- Dolomite: muddy, hard, light-brownish gray (IQYR 6/1), very thick bedded, aphanitic.

11__________ Mudstone: dolomitic, medium-hard,

brownish-gray (IQYR 4/1), very 

thick bedded; grades from bed below.

10---------- Dolomite: muddy, medium-hard, black

(TV 1), very thick bedded, aphanitic; 

grades from bed below. Fossil-colln. 

No. 51-JAP-l.

9_____---_-_ Mudstone: dolomitic, medium-hard, 

grayish-brown (2.5 Y 4/2), very thick 

bedded; grades from bed below.

8._--__-_-_- Dolomite: muddy, soft, dusky-brown 

(IQYR 2/2), thin-bedded, aphanitic; 

grades from bed below.

7__-_-_-__ Dolomite:hard, pale-brown (10F.R6/2), 

very thick bedded, aphanitic.

6____------- Dolomite: hard, pale-reddish-brown

(IQR 5/4), thick-bedded, aphanitic.

5_---------- Dolomite: hard, light-brownish-gray

(IQYR 6/1), very thick bedded, 

aphanitic.

4__-_____- Chert: hard, light-gray (TV 8), thickbedded.

3_____--_--_ Limestone: medium-hard, pale-reddishbrown (IQR 5/4), very thick bedded, 

very coarse grained; contains some 

chert nodules.

2___________ Limestone: medium-hard, pale-reddishbrown (IQR 5/4), thin-bedded, very 

coarsely crystalline. 

Quadrant Formation, uppermost bed: 

Q-l__-__------ Sandstone: hard, light-brown (7.5YR

6/4), very thick bedded, fine-grained.

Chemical analyses (percent)

Uranium

1. 1 200. 8

. 8 201. 6

2. 8 204. 4

1. 0 205. 4

7. 6 213. 0

4. 3 217. 3

5407

Thick- Cumulative

ness thickness

(feet) (feet) Sample

0. 9 127. 2 JAP-,

2. 0 129. 2

3. 3 132. 5

4. 2 136. 7

1. 0 137. 7

50. 0 187. 7

1. 5 189. 2

1. 1 190. 3

1. 1 191. 4

3. 4 194. 8

1. 9 196. 7

1. 5 198. 2 5386

1.5 199.7 -_--_-_-__

Acid in- Radio- Chemical 

soluble metric eV U

0. 8 68. 3 0. 003

.3 69. 0 . 002

CQQA

5388

5387

.3

. 6

. 6

. 3

27. 3

 27 n

48.2

35. 3

.002 --___-_

.003 -------

.003 _-__---

.003 __--_--

.1 50. 2 . 004 

<. 1 19. 4 . 000
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 541

Canyon Creek No. 8, Mont., lot 1S59

[Permian rocks measured in hand trench and natural exposure about 1,500 ft northeast of Canyon Creek road on northeast limb of broad syncline in NWH sec. 13, T. 2 S., 

R. 10 W., Beaverhead County, Mont. Beds strike N. 25° W. and dip 38° SW. Measured by J. A. Peterson and sampled by R. F. Gosman, in July 1951. Samples

analyzed for PjOs and acid insoluble by U.S. Bur. of Mines and for uranium by U.S. Geol. Survey]

Chemical analyses (percent)

Bed

Us-36.

(35). 

34_

To-33_ 

32.

31_ 

30.

Rt-29.

28_

27_ 

26. 

25. 

24. 

23.

22. 

21.

20. 

19.

18.

Description

Upper tongue of Shedhorn Sandstone:

Sandstone: hard, light-brownish-gray 

(WYR 6/1), very thick bedded, finegrained; sand is slightly more coarse 

than underlying sands; so, this interval is probably the uppermost bed 

of the Shedhorn sandstone. Actual 

contact with the overlying Dinwoody 

formation is covered.

Covered: sandstone and chert float- __

Sandstone: hard, light-brownish-gray 

(10y.R 5/1), fine-grained; interval is 

partly covered: grades from bed 

below.

Tosi Chert Member of Phosphoria Formation:

Chert: sandy, medium-gray (N 5), 

hard; interval is partly covered; 

grades from bed below.

Sandstone and chert, interbedded: hard 

medium-gray (N 5) sandstone interbedded with hard medium-gray (N 5) 

chert; grades from bed below.

Chert: hard, brownish-gray (WYR 

3/1); interval is partly covered.

Chert: sandy, hard, dark-gray (N 4),

very thick bedded; sand is fine. 

Retort Phosphatic Shale Member of Phosphoria Formation:

Phosphorite: medium-hard, dark-gray 

(N 3), thick-bedded, coarsely pelletal.

Limestone: soft, light-brownish-gray 

(WYR 5/1), aphanitic; grades from 

bed below.

Mudstone: dolomitic, soft, pale-brown 

(7.5YR 6/2), fissile.

Phosphorite: hard, dark-gray (N 3), 

thick-bedded, very coarsely pelletal.

Mudstone: soft, pale-brown (IOYR 

6/2), fissile.

Phosphorite: medium-hard, dark-gray 

N 4, thick-bedded, medium-pelletal.

Mudstone: phosphatic, soft, light-olivebrown (2.SYR 5/4); apatite is finely 

pelletal.

Mudstone: phosphatic, soft, pale-brown 

(WYR 5/2); apatite is finely pelletal.

Phosphorite: muddy, soft, moderateyellowish-brown (10 YR 4/4), finely 

pelletal.

Mudstone: soft, vari-colored-________

Mudstone: phosphatic, soft, lightyellowish-brown (2.5F 6/4); very 

few pellets are apparent in hand 

specimen.

Mudstone: phsphatic, hard, mediumgray (N 5), thick-bedded; apatite 

is very finely pelletal; contains a 

few phosphatic skeletal fragments; 

grades from bed below.

Thick- Cumulative

ness thickness

(feet) (feet)

Uranium

1. 2

Sample

Acid in- Radio- Chemical 

soluble metric eU U

12. 0 20. 0

12. 0 32. 0

25. 0 57. 0

5.0

12. 0

2.0

.9 

q

. 4

. 9

Q

. 4

2. 2

1. 5

3. 0 

3. 5

2. 0

62. 0

74. 0

76.0

76.9

77 S

7R 9

79. 1 

7Q 4

79.8

82. 0

83. 5

86. 5 

90. 0

92. 0

JAP-5424 

5223

5422

5421 

5420

5419

5418

5417

5416 

5415

5414

31. 5 

1 9

.7

29. 0 

3. 6

27.3

20. 6

13. 6

23. 7 

4. 5

10. 5

15. 8 

16. 1

64 Q

4.9 

59. 3

5. 3

22. 9

47. 2

24. 5 

64. 5

54. 1

0. 006 

. 001

. 002

. 006 

. 004

. 007

.007

. 006

. 006 

. 004

. 005

0. 006

.005

. 007

. 004

. 004

.005

.002

93. 2 5413 13. 6 38. 3 . 005 . 003

709-931 O-64 18
542 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Canyon Creek No. 3, Mont., lot 1859 Continued

Chemical analyses (percent)

Bed Description

Franson and Grandeur Members of Park

City Formation, undifferentiated: 

Pc-17_________ Sandstone: phosphatic, medium-hard,

light-brownish-bray (10 YR 5/1), 

thick-bedded, fine-grained; apatite 

is finely pelletal; contains a few 

phosphatic skeletal fragments; grades 

from bed below.

16 _________ Limestone: sandy, medium-hard,

medium-gray (N 5), very thick 

bedded; sand is fine; contains some 

calcareous shell fragments; grades 

from bed below. Fossil colln. No. 

12694.

15_________ Sandstone: medium-hard, mediumgray (N 6) very thick bedded, finegrained.

14. ________ Dolomite: medium-hard, dark-gray

(N 4), very thick bedded, aphanitic; 

small chert nodules constitute about 

10 percent of bed.

13_ ________ Dolomite: medium-hard, dark-gray

(N 4), very thick bedded, aphanitic; 

light-brownish-gray (WYR 5/1), 

chert nodules and irregular masses 

constitute about half of unit.

12..________ Dolomite: silty, medium-hard, lightbrownish-gray (IQYR 5/1), thickbedded, aphanitic; small chert nodules constitute about 10 percent of 

unit; cross-bedded near base. 

(11) ------ Covered... ________________________

10_______ Dolomite: medium-hard, mediumgray (N 5), very thick bedded, 

aphanitic; 50 percent of unit consists 

of irregular masses of light-brown 

(7.5 YR 5/4 chert. 

9_________ Dolomite: medium-hard, medium-gray

(N 5), very thick bedded, aphanitic; 

contains some pale-brown (7.SYR 

6/2) chert nodules; grades from bed 

below. 

8_________ Dolomite: medium-hard, medium-gray

(N 6), very thick bedded, aphanitic.

(7) _________ Covered___________________________

6_________ Dolomite: medium-hard, medium-gray

(N 6) very thick bedded, aphanitic.

(5).______ Covered: medium-gray (2V 5) dolomite

float. 

4_________ Dolomite: hard, medium-gray (2V 6),

very thick bedded, aphanitic; about 

25 percent of unit consists of lightbrownish-gray (10 YR 5/1) chert 

nodules.

(3)_._______ Covered: moderate-yellow (2.5F 7/6)

mudstone float.

2________ Sandstone: cherty, hard, light-brownish-gray (10 YR 5/1), very thick 

bedded, very fine grained; contains 

some medium quartz sand. 

!_________ Dolomite: hard, medium-gray (N 5),

aphanitic; underlain by hard yellowish-gray sandstone of Quadrant 

Formation.

Thick- Cumulative

ness thickness

(feef) (feet) Sample

0. 7 93. 9 JAP-5412

Uranium

4. 5 98. 4

6. 0 104. 4

12. 7 117. 1

18. 0 135. 1

5. 0 140. 1

16. 5 156. 6

2. 0 158. 6

7. 4 166. 0

5. 7 171. 7

7. 0 178. 7

3. 0 181. 7

7. 0 188. 7

7. 0 195. 7

6. 3 202. 0

1. 5 203. 5

6. 0 209. 5

PtOt

15.9

Acid in- Radiosoluble metric eU

45. 3 0. 005

Chemical

U

0.003
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 543

London Ridge, Mont., lot 1361

[Meade Peak Pbosphatic Shale Tongue of Phosphoria Formation measured and sampled in bulldozer trench in SWJ4 sec. 27, T. 12 S., R. 2 W., Beaverhead County Mont 

Beds strike east-west and dip 25° S. Measured by J. A. Peterson and sampled by Peterson and R. F. Qosman, in August 1951. Samples analyzed for PsO5 and acid 

insoluble by U.S. Bur. of Mines, and for uranium by U.S. Qeol. Survey]

Chemical analyses (percent)

Bed

M-7.

G-l.

Description

Lower member of Shedhorn Sandstone, 

basal bed:

Sandstone: hard, light-brownish-gray 

(IOYR 6/1), thick-bedded, finegrained. Overlying beds are covered.

Meade Peak Phosphatic Shale Tongue of 

Phosphoria Formation:

Phosphorite: cherty, medium-hard, 

light-brownish-gray (IOYR 6/1), 

thin-bedded, coarsely pelletal.

Phosphorite: sandy, cherty, mediumhard, light-brownish-gray (IOYR 

6/1), thick-bedded, very coarsely 

pelletal.

Phosphorite: medium-hard, lightbrownish-gray (IOYR 6/1), thickbedded, very coarsely pelletal.

Phosphorite: sandy, medium-hard, 

light-brownish-gray (10 YR 6/1), 

thick-bedded, very coarsely pelletal.

Phosphorite: medium-hard, lightbrpwnish-gray (IOYR 6/1), very 

thick-bedded, very coarsely pelletal.

Phosphorite: medium-hard, lightbrownish-gray (IOYR 6/1), thickbedded, very coarsely pelletal. 

Grandeur Tongue of Park City Formation, 

uppermost bed:

Chert: hard, medium-gray (N 6), 

thick-bedded.

Cumulative 

Thickness thickness 

(feet) (feet)

3. 0

1. 1

1. 4

1. 1

1. 2

. 6

3. 0

3.6

4. 7

6. 1

7.2

*. 4

9.0

Uranium

Sample

Acid 

insoluble

Radiometric 

eU

Chemical 

U

3. 2 JAP-5489

5488

5487

5486

5485

5484

19. 3

18. 7

41. 5 0. 003

27.6

28. 7

26.3

46. 4

18.0

20.5

18.3

20. 6

004

005

004

005

005

0.005

.005

.006

Indian Creek, Mont., lot 1362

[Permian rocks measured from natural exposures on north side of Indian Creek Canyon in SWH sec. 21, T. 8 S., R. 2 E., Madison County, Mont., by R. F. Qosman and 

Retort Member sampled by J. A. Peterson, in August 1951. Section revised by R. W. Swanson in August 1955 and 1956. Beds strike N. 20°-25° W. and dip about 

25° NE. Analyzed for P2O5 and acid insoluble by U.S. Bur. of Mines, and for uranium by U.S. Qeol. Survey]

Chemical analyses (percent)

Bed

D-49.

Us-48.

47. 

46.

Description

Dinwoody Formation, basal bed:

Carbonate rock: hard, thick-bedded, 

aphanitic, pale-brown (IOYR 6/2), 

weathers to darker brown; basal 0.3 

ft muddy and thin-bedded to fissile; 

probably composed largely of dolomite; basal contact sharp. 

Upper member of Shedhorn Sandstone:

Sandstone: hard, thick-bedded to massive, fine-grained, pale-brown (IOYR 

5/2); contains numerous small chert 

nodules and thin streaks of very 

finely sandy to cherty carbonate 

rock; commonly, 0.2 ft mediumbluish-gray (5B 5/1) to light-bluishgray (5B 7/1) chert at top, and top 

foot generally lighter gray.

Chert: hard, wavy-bedded, white 

(AT 9).

Sandstone: hard, massive, fine- to medium-grained, light-brownish-gray 

(IOYR 6/1); contains 1-ft cherty zone 

in lower middle, numerous yellowishgray (IOYR 7/1) chert nodules, and 

cherty columnar concretions.

Thickness 

(feet)

40. 0

Curmtlative

thickness

(feet)

40. 0

Uranium

Sample

Acid insoluble

Radio- Chemical 

metric eU U

12.8 12.8

1.0 

5.6

13.8

19.4
544 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Indian Creek, Mont., lot 1362 Continued

Chemical analyses (-percent)

Bed Description

Upper member of Shedhorn Sandstone 

Continued 

Us-45_ ________ Chert and sandstone, interbedded:

chert dominant in middle; hard thinto thick-bedded; white (N 9) chert 

interbedded with fine-grained very 

pale brown (IQYR 7/2) sandstone 

that contains many dark grains; 

chert contains many spicules and 

apatite canal fillings, apatite rims on 

quartz and chert grains, apatite pellets, and small carbonate rhombs 

and limonite cubes after pyrite.

44_________ Sandstone: hard, massive, mediumgrained, light-brownish-gray (IQYR 

5/1- 6/1); contains shell fragments 

and many small lenses, flat pebbles, 

and irregular streaks of dense finely 

sandy carbonate rock.

43. _ _______ Sandstone: carbonatic,1 hard, massive,

fine- to coarse-grained, light-brownish-gray (IQYR 6/1) to pale-brown 

(IQYR 6/2); contains numerous lenticular zones of flat-pebble carbonate 

conglomerate and many dark apatite 

pellets; numerous silicified fossils 

project form cliff face.

42_________ Chert: hard, thin- to thick- and wavybedded, light-brownish-gray (10 YR 

6/1); contains concentrically banded 

columns; top \}i ft nodular with 

shaly matrix, and top one-half ft 

contains carbonate-rock lenses.

41 _________ Chert and sandstone: hard laminated

white chert capped by about half a 

foot of fine sandstone, with very 

irregular contact between; basal 

contact irregular.

40_________ Sandstone: hard, massive, fine- to medium-grained, pale-brown (IQYR 6/2); 

abundant but incomplete quartz 

overgrowths, coarsely crystalline carbonate matrix, and apatite pellets.

39_________ Sandstone: hard, massive, fine- to

medium-grained, pale-brown (7.5YR 

6/2); top half foot, chert; contains 

shell fragments.

38_________ Sandstone: hard, massive, fine-grained,

pale-brown (2.5 Y 5-6/2); contains 

much fine black material (solid hydrocarbon?) ; top foot contains whiteweathering cherty columnar concretions.

Tosi Chert Tongue of Phosphoria Formation: 

To-37_________ Chert: hard, thin- to thick-bedded,

dark-gray (N 3} grading upward to 

brownish gray (IQYR 4-5/1); top 

10 ft notably lighter and thicker 

bedded.

Retort Phosphatic Shale Tongue of Phosphoria Formation: 

Rt-36_________ Phosphorite and mudstone: one bed

having lateral gradations in lithology; hard, medium coarsely pelletal, brownish-gray (IQYR 3/1); 

contains phosphatic shell fragments.

35_________ Carbonate rock: medium-hard, thinbedded, dense, brownish-gray (IQYR 

4/1).

34_________ Phosphorite: soft, fissile to thin-bedded, finely to coarsely oolitic-pelletal, 

brownish-black (IQYR 2/1); contains 

considerable amounts of organic matter.

Thick- Cumulative

ness thickness

(feet) (feet)

1. 8 21. 2

Uranium

Sample P.Os

Acid insoluble

Radiometric eU

Chemical 

U

3. 8 25. 0

2. 7 27. 7

6. 4 34. 1

1. 0 35. 1

18. 7 53.

6. 5 60. 3

3. 2 63. 5

42. 0 105. 5

. 3 105. 8 RFG-5497 23. 9 32. 3 0. 008 0. 007

.4 106.2 5496 1.7 10.3 .001 _______

2. 0 108. 2 5495 23. 9 16. 3 . 008 . 007
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 545

Indian Creek, Mont., lot 1362 Continued

Chemical analyses (percent)

Bed 

Rt-33_.

32..

31..

30_.

29__

Ls-28.

27.

26. 

25.

24. 

F-23_.

22.

Description

Retort Phosphatic Shale Tongue of Phosphoria Formation Continued

Phosphorite: medium-hard, thick-bedded, finely to coarsely oolitic, brownish-black (10 YR 2/1); contains phosphatic shell fragments.

Mudstone: medium-hard, fissile to thinbedded, brownish-black (10 YR 2/1); 

contains a few shell fragments and 

considerable amounts of organic 

matter.

Dolomite: hard, very finely crystalline, dusky-brown (WYR 2/2).

Mudstone and phosphorite: 0.4 ft soft 

fissile grayish-brown (10 YR 4/2) 

mudstone overlain by 0.3 ft soft thinbedded medium coarsely oolitic black 

(N 2) sheared phosphorite; both 

contain much organic matter.

Mudstone: phosphatic, medium-hard, 

thin-bedded, grayish-brown (WYR 

4/2); contains much irregularly distributed fluorite, some purple, generally 

as replacement of siliceous sponge spicules or phosphate matrix, but some as 

replacement of quartz beneath earlier 

rim of apatite; apatite lighter colored 

near fluorite and commonly recrystallized near fluorite that is in contact with or has replaced silica; contains phosphatic shell fragments. 

Lower member of Shedhorn Sandstone; 

contains tongue of Franson Member of 

Park City Formation:

Sandstone: hard, thick-bedded to massive, fine- to medium-grained, lightbrownish-gray (10F.R 6/1); contains 

numerous cherty concretions and 

phosphatic shell fragments.

Sandstone and carbonate rock: carbonate rock at base grades upward 

into sandstone like that of bed Ls-28; 

numerous sandstone columns at base 

and irregular pebblelike sandstone 

masses above.

Chert: hard, thin-bedded, brownishgray (10 YR 4/1).

Sandstone: hard, massive, fine- to medium-grained, light-brownish-gray to 

pale-brown (10[YR 5/1 to 6/2); contains a prominent and persistent 

chert concretion and quartzite-pebble zone in lower third and numerous 

other chert concretions, some normal 

to bedding.

Mudstone: sandy, soft, fissile to thinbedded, pale-brown (7.5 YR 5/2); 

sand, fine to medium.

Carbonate rock: sandy, hard, massive, 

finely crystalline, yellowish-gray 

(1QYR 7/1); probably dolomite; 

apatite shell fragments in top 2 ft; 

very sandy in basal foot, which is 

overlain by half-foot zone containing small well-rounded chert, quartzite, and carbonate pebbles; pebbles 

also at top and 3 ft below top; some 

chert pebbles rich in sponge spicules.

Carbonate rock: very sandy, hard, yellowish-gray (10 YR 7/1); sand, fine to 

coarse; contains quartz, chert, and 

apatite grains and phosphatic shell 

fragments; thickness ranges from 

0-0.4 ft; irregular basal contact.

Uranium

Thick- Cumulative

ness thickness

(feet) (feet) Sample P20 5

Acid in- Radiosoluble metric ell

Chemical

U

1. 1 109. 3 RFG-5494 31. 9 3. 9 0. 010

1. 0 110. 3

. 4 110. 7

.7 111.4

.6 112. 0 5490

5493 3.8 63.3 .004 _______

5492 1.6 8.1 .001 _______

5491 19. 5 26. 5 . 009 0. 008

15. 0 47. 5 . 009 . 007

2. 8 114.

1. 3 116. 1

2. 4 118. 5

9. 3 127. 8

4. 0 131. 8

7. 2 139. 0

3 139. 3
546 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Indian Creek, Mont., lot 1362 Continued

Bed Description

Lower member of Shedhorn Sandstone; contains tongue of Franson Member of Park 

City Formation Continued 

Ls-21 _________ Sandstone: carbonatic, hard, massive,

fine-grained, yellowish-gray (10 YR 

8/1); locally very carbonatic and 

contains many clastic carbonate 

grains, some as much as 6 mm in 

diameter; contains apatite shellfragment pellets. 

20_________ Chert: hard, laminated to massive,

yellowish-white (10 YR 9/1); locally 

sandy. 

19__---____ Sandstone and chert, interbedded: hard

laminated yellowish-white (10 YR 

9/1) locally sandy chert, interbedded 

with fine- to medium-grained very 

pale brown (10 YR 7/2) sandstone 

containing phosphatic shell fragments.

18__-_-____ Sandstone: hard, thick-bedded, finegrained, yellowish-gray (IQYR 7/1); 

contains layers and streaks of laminated carbonate rock at 0.8 and 1.6 ft 

above base.

17_ _-_____- Chert: sandy, hard, laminated, yellowish-white (IQYR 9/1); contains laminae of cherty sandstone; sand is fine 

and contains apatite pellets, spicule 

canal fillings, and clear grains (probably water-worn shell fragments); 

chert generally spicular; zircon and 

tourmaline grains common in sandstone.

16.___--_-. Sandstone: hard, thick-bedded, finegrained, yellowish-gray (10 YR 7/1); 

contains thin carbonate layers near 

base and small chert and quartzite 

pebbles at middle; contains grains of 

spicular chert and light-brown apatite (lowest horizon at which phosphate and other Phosphoria indicators found).

Grandeur Tongue of Park City Formation: 

G-15__________ Carbonate rock: hard, massive, aphanitic, yellowish-gray (2.5 Y 8/2); contains considerable amounts of very 

fine sand; irregular basal contact.

14__________ Sandstone: hard, massive, cross-bedded in part, fine-grained, very pale 

orange (IQYR 8/2); locally, streaks 

of coarse gritty sand; extensive overgrowths on quartz. 

13____-_____ Dolomite: hard, thick-bedded, dense,

yellowish-gray (2.5 Y 8/1).

12._________ Dolomite: hard, massive, finely crystalline, yellowish-gray (IQYR 7/1); 

contains poorly preserved fossils at 

top and bottom. 

!!__________ Sandstone: hard, massive, fine- to very

fine-grained, yellowish-white (IQYR 

9/1); gritty at base, containing numerous round masses of chalcedonic 

chert in rhombic carbonate matrix 

and characterized by dust lines that 

commonly delineate crystal outlines, 

with angles usually nearly 90° as rr' 

of quartz, and suggesting zonal growth. 

10_-________ Dolomite: hard, thick-bedded, aphanitic, yellowish-gray (10 YR 8/1). 

9__________ Sandstone: hard, massive, fine-grained,

very pale orange (IQYR 8/2); locally 

crossbedded.

Chemical analyses (percent)

Uranium

Thick- Cumulative

ness thickness

(feet) (feet)

14. 2 153. 5

Sample PtOs,

Acid insoluble

Radiometric eU

Chemical 

U

3. 4 156. 9

2. 6 159. 5

2. 9 162. 4

3. 9 166. 3

1. 0 167. 3

2. 7 170. 0

4. 5 174. 5

2. 0 176. 5

1. 0 177. 5

5. 3 182. 8

3. 0 185. 8

3. 7 189. 5
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 547

Indian Creek, Mont., lot 1362 Continued

Chemical analyses (percent)

Uranium 

Thick- Cumulative

ness thickness Acid in- Radio- Chemical 

Bed Description (feet) (feet) Sample P_O5 soluble metric eV U

Grandeur Tongue of Park City Formation 

Continued 

G-8__________ Dolomite: silty, hard, massive, apha- 2.0 191.5 __________ ______ ______ ______

nitic, very pale orange (10 YR 8/2); 

basal part not well exposed. 

7__________ Sandstone: hard, massive, very fine 8.2 199.7 __________ ______ ______ ______ _______

to medium-grained, yellowish-gray 

(10YJ? 8/1); locally crossbedded; extensive overgrowths on quartz grains. 

6__________ Dolomite: hard, aphanitic, yellowish- .5 200.2 __________ ______ ______ ______ _______

gray (10F.R 8/1); crossed by calcite 

veinlets. 

5_-________ Sandstone: hard, very fine to fine- 1.0 201.2 __________ ______ ______ ______ _______

grained, yellowish-gray (10FR 8/1). 

4__________ Dolomite: silty, hard, aphanitic, yel- 1.0 202.2 __________ _ ____ ______ ______ _______

lowish-gray (10 YR 7/1). 

3__________ Sandstone: hard, massive, very fine 1.3 203.5 __________ ______ ______ ______ _______

to medium-grained, yellowish-gray 

(2.5F 7/2). 

(2)_________ Covered___________________________ 5.8 209.3 -_______._ ______ ______ ______ _______

Quadrant Formation, top part: 

Q-l------_-__- Sandstone and dolomite: sandstone, 7.0 ______ __________ ______ ______ ______ _______

hard, massive, fine-grained, paleyellowish-orange (2.5F 9/4), crossbedded, dominant overgrowths on 

quartz grains; hard dense yellowishgray (10 YR 8/1) dolomite in top foot.

Cinnabar Mountain, Mont., lot 1363

[Permian rocks measured from natural exposures on east side of Cinnabar Mountain, sec. 31, T. 8 S., R. 8 E., Park County, Mont., by J. A. Peterson, and Retort Member of 

Phosphoria Formation sampled by R. F. Gosman, in August 1951. Beds strike about N. 50° W. and dip 75° S W. Location of contact between Dinwoody and Shedhorn 

Formations is uncertain. Bed 21 is placed in the Shedhorn on the basis of the fossil collection. Analyzed for P.Os and acid insoluble by U.S. Bur. of Mines and for uranium 

by U.S. Geol. Survey]

Chemical analyses (percent)

Uranium 

Cumulative

Thickness thickness Acid RadioBed Description (feet) (feet) Sample PsO. insoluble metric eU

Dinwoody Formation, basal beds only: 

D-23__ _______ Dolomite: muddy, medium-hard, poorly to thin- 1.5 ______ __________ ______ ______ _______

bedded, light-gray (N 7); gradational basal 

contact. 

22__________ Limestone: hard, poorly bedded, aphanitic, 2.0 ______ __________ ______ ______ _______

medium-gray (N 5).

Upper member of Shedhorn Sandstone; contains two 

tongues of Tosi Chert Member of Phosphoria 

Formation: 

Us-21_________ Limestone: medium-hard, massive, aphanitic, 4.8 4.8 __________ ______ ______ _______

medium-gray (N 6), weathers pale-brown, 

10YR 6/2. Fossil-colln. Nos. 12695and 18844. 

20---______ Sandstone: eherty, hard, thin-bedded; dark- 6.5 11.3 __________ ______ ______ _______

gray (N 3) 

To-19_________ Chert: hard, poorly bedded to massive, medium- 11.8 23.1 __________ ______ ______ _______

gray (N 5); contains irregular masses and 

stringers of light-olive-gray (5Y 6/1) dolomite 

and some black crystalline calcite. 

US-18 ______ Sandstone: calcareous, hard, massive, fine- to 7.2 30.3 __________ ______ ______ _______

very fine grained, light-brownish-gray (10 YR 

6/1); locally eherty; contains 30 to 40 percent 

of finer grained sandstone columns. 

17_________ Dolomite: medium-hard, massive, aphanitic, 2. 5 32. 8 __________ ______ ______ _______

yellowish-gray (5Y 7/1); contains elongate 

nodules and columns of coarsely crystalline 

calcite containing small quartz grains and 

scattered glauconite grains. 

To-16_________ Chert and sandstone: hard massive very fine 8.0 40.8 __________ ______ ______ _______

grained pale-brown (10 YR 6/2) sandstone 

containing very abundant columnar concretions and elongate nodules of sandy chert 

(50 to 60 percent of rock).
548 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Cinnabar Mountain, Mont., lot 1863 Continued

Chemical analyses (percent)

Bed

Us-15-

Rt-14. 

13.

11.

10.

7. 

6.

5. 

4_

Ls-3_

Description

Upper member of Shedhorn Sandstone; contains two 

tongues of Tosi Chert Member of Phosphoria 

Formation Continued

Sandstone and chert: hard massive grayishbrown sandstone (10 YR 4/2) containing chert 

columns (constituting 50 percent of rock) up 

to 4 ft long and nodules similar to those in bed 

above; top foot contains angular fragments of 

chert but no concretions.

Retort Phosphatic Shale Tongue of Phosphoria 

formation:

Chert and mudstone, interbedded': hard finely 

sandy chert and soft calcareous mudstone, 

both brownish-gray (10 YR 3/1).

Limestone and chert: muddy hard dense medium- to dark-gray (N 4) limestone containing 

very abundant (50 percent) columnar concretions of sandy chert.

Mudstone: calcareous, soft, fissile, brownishgray (10y.R 3/1); contains annular-ringed 

columnar chert concretions and scattered 

small crystals of selenite.

Phosphorite: muddy, medium-hard, thickbedded to massive, brownish-black (10 YR 

2/1); contains fossil fragments and quartz 

sand.

Carbonate rock: phosphatic, hard, thin- to 

thick-bedded, medium-gray (N 5); contains 

abundant phosphatic shell fragments.

Phosphorite: muddy, soft, poorly bedded, 

brownish-gray (1QYR 3/1); contains abundant 

disseminated phosphatic shell fragments and 

columns composed of phosphatic shell fragments; concretions; arbitrary basal contact.

Phosphorite: like bed Rt-9_____________---_-

Phosphorite: like bed Rt-9, but less muddy; 

apatite resinous to bluish.

Mudstone: phosphatic, carbonatic, soft, fissile 

to thin-bedded, brownish-black (1QYR 2/1); 

phosphate chiefly as shell fragments in 

columnar concretions, which are also sandy.

Phosphorite: sandy, medium-hard, brownishgray (IQYR 3/1); phosphate as in bed Rt-6; 

gradational basal contact.

Conglomerate: phosphatic, hard, light-brownishgray (IQYR 5/1); chert and quartzite pebbles 

as much as 3 in. in diameter, average 3/4 in.; 

matrix is quartz sand and phosphatic shell 

fragments; gradational basal contact. 

Lower member of Shedhorn Sandstone:

Sandstone: calcareous, hard, thick-bedded to 

massive, fine- to medium-grained, very light 

gray (N 8); conglomeratic at top with pebbles 

as much as 1 in. in diameter; grains not well 

rounded, immersed in dusty carbonate matrix; 

contains apatite pellets and shell fragments 

and small orthoclase grains altered to calcite; 

basal contact sharp and fairly plane. 

Quadrant Formation, top beds:

Sandstone: calcareous, hard, massive, fine- to 

medium-grained, medium-gray (N 5); contains numerous very fine grains of orthoclase 

that are commonly altered to calcite around 

edges; somewhat irregular basal contact.

Sandstone: hard, massive, fine-grained, mediumgray (N 5); prominent overgrowths on quartz; 

scattered small orthoclase grains mostly 

altered to calcite; arbitrary basal contact.

Cumulative 

Thickness thickness 

(feet) (feet)

7. 0 47.

Sample

Uranium

Acid RadioPzOs insoluble metric eU

1.9

5. 0

1. 3 49. 1

2. 0 51. 1

.8 51.9

2. 3 54. 2

1. 0 55. 2

2. 2 57. 4

1. 7 59. 1

1. 5 60. 6

1. 4 62. 0

.7 62. 7

1. 0 63. 7

3. 0 66. 7

JAP-5530 

5529

5528

5527

5526

5519

5518

5517

5516

5499

5498

2. 1 72. 7 0. 000

3. 4 71. 9 . 001

4. 9 64. 5 . 001

19. 9 35. 8 . 002

8. 3 9. 3 . 001

21. 6 23. 03 . 004

21. 3 23. 7

23. 4 17. 5

12. 6 32. 5

16. 8 36. 3

12. 4 49. 6

. 003

. 002

. 004

. 003

. 003
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 549

North Boulder Creek, Mont., lot 1364

[Permian rocks measured in natural exposure on north side of road in NEJ4 sec. 4, T. 2 N., R. 2 W., Jefferson County, Mont. Beds strike N. 20° W. and dip 45° NE. Measured by R. F. Gosman and sampled by J. A. Peterson, in August 1951. Analyzed for PzOs and acid insoluble by U.S. Bur. of Mines and for uranium by U.S. Geol. 

Survey]

Chemical analyses (percent)

Bed

34. 

33.

Us-32_

To-3l_

30-

29-

28.

27_

Us-26_ 

To-25-

24.

23.

22-

21.

20. 

19.

18.

Ls-17.

16-

15- 

14.

Pc-13.

12-

Description

Ellis Group, lower part:

Sandstone: medium-hard, light-yellowish-brown 

(IOYR 6/4), fine-grained.

Conglomerate: sandy, hard, very thick bedded; 

consists of subrounded pebbles and cobbles 

as much as 0.5 ft in diameter composed of 

chert, quartzite, and phosphatic(?) chert in 

a salt and pepper sandstone matrix; irregular 

contact with bed below.

Tosi Chert Member of Phosphoria Formation; thin 

sandstone beds at top and middle may be tongues 

of Shedhorn Sandstone.

Sandstone: hard, pale-brown (IOYR 6/2), thickbedded, fine-grained; grades from bed below.

Chert: brittle, pale-brown (IOYR 5/3), thinbedded.

Chert: sandy, hard, brownish-gray (IOYR 4/1), 

thick-bedded; sand is very fine.

Chert: hard, brownish-gray (iOYR 4/1), thickbedded.

Chert: muddy, medium-hard, very pale orange 

(IOYR 9/2), thin-bedded; rock is light and 

porous and may have originally contained 

carbonate.

Chert: hard, brownish-gray (IOYR 4/1), thickbedded; grades from bed below.

Sandstone: hard, grayish-brown (2.5F 3/2), 

thick-bedded, fine-grained.

Chert: hard, yellowish-gray (5F 7/2), thinbedded.

Chert: hard moderate-yellowish-brown (IOYR 

5/6) thick-bedded chert interbedded with hard 

moderate-yellowish-brown (IOYR 5/6) thinbedded muddy chert; contains 0.2-ft zone of 

white phosphatic nodules 5.0 ft above base of 

unit.

Chert: phosphatic, hard, light-brownish-gray 

(IOYR 5/1), thick-bedded; apatite is skeletal, 

medium pelletal, and nodular; nodules are as 

much as 20 mm in diameter.

Mudstone: cherty, yellowish-gray (2.5F 7/2), 

thin-bedded; rock is light and porous and 

probably originally contained carbonate.

Chert: phosphatic, hard, brownish-gray (IOYR 

4/1), thin-bedded; apatite is skeletal, medium 

pelletal, and nodular; nodules are as much as 

10 mm in diameter.

Chert: hard, yellowish-gray (IOYR 8/1), thinbedded.

Chert: hard, grayish-brown (IOYR 4/2), thickbedded.

Chert: hard, light-yellowish-brown (IOYR 6/4). 

thin-bedded; lower 15 ft of unit is poorly 

exposed. 

Lower tongue of Shedhorn Sandstone:

Sandstone: hard, yellowish-gray (IOYR 7/1), 

thick-bedded, medium-grained.

Chert: sandy, hard, pale-brown (2.5F 6/2), 

thick-bedded.

Sandstone: cherty, hard, yellowish-gray (2.5F 

7/2), very thick bedded, very fine grained.

Chert: sandy, hard, yellowish-gray (2.5F 7/2),

thick-bedded; sand is medium.

Park City Formation; probably equivalent to 

Grandeur member:

Dolomite and sandstone: unit is mostly covered; 

float consists of dolomite and weathered 

dolomitic sandstone.

Dolomite: medium - hard, weak - yellowish - 

orange (2.5 Y 7/4), thick-bedded.

Cumulative 

Thickness thickness 

(feet) (feet)

15. 0 

1. 8

7. 2

1. 4

1. 2

2.0

19. 0

5.4

5. 6 

5. 0

20. 0

2. 7

15.0

22.5

22.9

24.9

25.2

44. 2

49. 6

6. 3 55. 9

61. 5

66. 5

86. 5

89. 2

Sample PaOs

Uranium

Acid Radiometrii 

insoluble «U

8.0

8. 8

9.0

10.4

13. 2

13. 9

15. 1

20. 9

21. 7 RFG-5533 16. 4 52. 5 0. 003

5532 14. 1 59.0 001

5531 4. 3 83. 4 001
550 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

North Boulder Creek, Mont., lot 1364 Continued

Chemical analyses (percent)

Bed

Pc-11.

Description

Park City Formation; probably equivalent to 

Grandeur member Continued

Mudstone: soft, moderate-yellow (2.5 Y 7/6), 

fissile.

Sandstone: medium - hard, weak - yellowish - 

orange (2.5Y 7/4), thick-bedded, fine-grained.

Sandstone: calcareous, soft, weak-yellowishorange (2.5F7/4), thin-bedded, fine-grained.

Sandstone: calcareous, pebbly, medium-hard, 

moderate-yellow (2.5F 7/6), medium-grained; 

chert pebbles are as much as 60 mm in diameter and average 15 mm in diameter.

Sandstone: silty soft weak-yellowish-orange 

(2.5F 7/4) very fine grained sandstone at base 

grades into medium-hard weak-yellowishorange (2.5F 7/4) fine-grained sandstone at 

top; unit is poorly exposed.

Sandstone: medium-hard, moderate-yellow 

(2.5F 7/6), thick-bedded, fine-grained.

Sandstone: hard, yellowish-gray (2.5F 8/2), 

very thick bedded, fine-grained.

Sandstone: silty, soft, moderate-yellow (2.5F 

7/6), very fine grained.

Sandstone: medium-hard, moderate-yellow 

(2.5F 7/6), thick-bedded, very fine grained.

Sandstone: hard, yellowish-white (2.5F 9/2), 

thick-bedded, medium-grained.

Sandstone: silty, calcareous, soft, weak-yellowish-orange (2.5F 7/4), very fine grained; unit 

is poorly exposed; underlain by hard yellowish-gray (10FR 7/1) fine-grained sandstone 

of Quadrant Formation.

Thickness 

(feet)

0.6

1. 6 

4.3

Cumulative

thickness

(feet)

89.8

90.2

91.8

96. 1

4. 7 100. 8

. 7 101. 5

2. 3 103. 8

3. 2 107. 0

1. 0 108. 0

1. 0 109. 0

6.3 115.3

Sample

Acid 

insoluble

Uranium

Radiometric eV

South Boulder Creek, Mont., lot 1365

[Permian rocks measured in hand trench and natural exposure about 200 ft above and west of Jack Creek in NW}4 sec. 10, T. 1 S., R. 3 W., Madison County, Mont. Beds 

strike east-west and dip 35° N. Measured by J. A. Peterson and sampled by R. F. Qosman, in August 1951. Analyzed for PjO? and acid insoluble by U.S. Bur. of Mines, 

and for uranium by U.S. Qeol. Survey]

Chemical analyses (percent)

Bed

E-47-

(46). 

45_.

(44). 

43.

(42).

To-41_ 

40_

39- 

38.

Description

Ellis Group, basal part: l

Limestone: medium-hard, light-brownishgray (10 YR 6/1); contains fragments 

of oyster shells.

Covered: oolitic-limestone and chert 

float.

Sandstone: hard, yellowish-gray (10 YR 

8/1), thick-bedded, fine-grained.

Covered--___-_-_______-_________--

Sandstone: hard, yellowish-gray (1QYR 

8/1), thick-bedded, medium-grained; 

contains some pebbles as much as 

30 mm in diameter.

Covered: yellowish-gray (WYR 7/1), 

fine-grained sandstone float. May 

be Shedhorn Sandstone. 

Tosi Chert Member of Phosphoria Formation:

Chert: hard, pale-brown (10 YR 5/2), 

thin-bedded.

Sandstone: phosphatic, hard, palebrown (10 YR 5/2), thick-bedded, 

fine-grained; contains a few phosphatic skeletal fragments.

Chert: hard, very pale brown (10 YR 

7/2), thin-bedded.

Chert: phosphatic, hard, light-browuish-gray (WYR 5/1), thick-bedded; 

apatite is medium pelletal; contains 

a few phosphatic skeletal fragments.

Cumulative 

Thickness thickness 

(feet) (feet)

Uranium

15.0 

1.0

3.0 

3.0

7.0

8.3 

1.0

11. 0

Sample P3 05

Acid 

insoluble

Radiometric Chemical 

eV U

8. 3 

9.3

20. 3

20. 7 JAP-5569 14. 4 59. 9 0. 001

See footnote at end of ta ble.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 551

South Boulder Creek, Mont., lot 1365 Continued

Bed

To-37_

36_

35_ 

34_

33_ 

32.

31

Rt-30_

29_

28-

Description

Tosi Chert Member of PhOsphoria Formation Continued

Chert: dolomitic, medium-hard, lightyellowish-brown (10 YR 6/4), thinbedded.

Chert: phosphatic, hard, brownishgray (WYR 4/1), thick-bedded; apatite is finely pelletal; contains a few 

phosphatic skeletal fragments.

Chert: hard, brownish-gray (10 YR 

4/1), thin-bedded.

Phosphorite: sandy, cherty, hard, 

light-brownish-gray (10 YR 5/1), 

thick-bedded, finely pelletal; contains phosphatic skeletal fragments 

and a few apatite nodules as much as 

20 mm in diameter.

Dolomite: cherty, hard, brownish-gray 

(10 YR 4/1), thick-bedded, aphanitic.

Phosphorite: cherty, hard, light-brownish-gray (WYR 5/1), thick-bedded, 

medium-pelletal and oolitic; contains 

phosphatic skeletal fragments and 

apatite nodules as much as 10 mm 

in diameter; grades from bed below.

Chert: hard, light-brownish-gray (10

YR 5/1), thin-bedded.

Retort Phosphatic Shale Member of Phosphoria Formation:

Mudstone: medium-hard, brownishblack (10 YR 2/1), thick-bedded.

Chemical analyses (percent)

Cumulative 

Thickness thickness 

(feet) (feet)

Uranium

____ Mudstone: medium-hard, brownishblack (10 YR 2/1), thick-bedded. 

27-_--_-___ Mudstone: medium-hard, brownishblack (10 YR 2/1), thin-bedded. 

26. ________ Phosphorite: cherty, medium-hard,

light-brownish-gray (10 YR 5/1),

thick-bedded, coarsely pelletal and

oolitic. 

25_ ________ Mudstone: soft, brownish-gray (10 YR

3/1), thin-bedded. Separated from

bed Rt-24 by andesite(?) sill 3.6 ft

thick. 

24- ________ Mudstone: medium-hard, grayishbrown (WYR 4/2), thin-bedded. 

23_ ________ Phosphorite : cherty, hard, light-brownish-gray (ioyfi'5/l), thick-bedded,

very coarsely oolitic. 

Tosi Chert Member of Phosphoria Formation, lower part: 

To-22___ ______ Chert: hard, brownish-black (10 YR

2/1), thick-bedded. 

21 _________ Phosphorite: medium-hard, brownishgray (10 YR 4/1), thick-bedded,

medium pelletal; contains phosphatic

skeletal fragments.

Lower Tongue of Shedhorn Sandstone: 

Ls-20_ _-_____- Sandstone: pebbly, hard, light-brownish-gray (10 YR 5/1), thick-bedded,

fine-grained; chert pebbles are as

much as 25 mm in diameter; contains

phosphatic skeletal fragments; grades

from bed below. 

19____-____ Sandstone : hard, light-brownish-gray

(10 YR 6/1), thick-bedded; contains

columnar bodies of sandstone that

cut across bedding. 

18_________ - Chert: hard, dark-gray (N 4), thickbedded. 

17 _________ Sandstone: hard, medium-gray (AT" 6),

thick-bedded, fine-grained. 

See footnote at end of table.

Sample

Acid Radiometric Chemical 

PsOs insoluble eV U

1.6 22.3 __________ ______ ______ ______

.4 22. 7 JAP-5568 16. 6 52. 5 0. 003

23. 4

23. 9

3. 0 26. 9 

.5 27. 4

7. 2 34. 6

2. 0 36. &\

.5 37. 1

3. 0 40. 11

5. 5 45. 6

.6 46. 2

1. 7 47. 9

.6 48. 5

.7 49. 2

7. 6 56. 8

.3 57. 1

.4 57. 5

4. 9 62. 4

1. 0 63. 4

.4 63. 8

5567 18. 3 47. 3 .003

5566 18. 6 45. 5 . 004

5540 1. 1 68. 06 . 001

5539 2.2 74.3 .002 _______

5538 25. 8 30. 26 . 006 0. 005

5537 1.8 71.06 .003 _______

5536 2. 2 70. 0 . 002

5535 26. 2 29. 5 . 007

5534 30. 5 11. 9 . 010 . 007
552 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

South Boulder Creek, Mont., lot 1365 Continued

Chemical analyses (percent)

Ls-16_ 

15. 

14. 

13.

12. 

11.

10.

Q-l.

Bed Description

Lower Tongue of Shedhorn Sandstone 

Continued

________ Chert: hard, brownish-gray (1QYR 3/

1), thick-bedded.

________ Sandstone: cherty, hard, medium-gray

(N 6), fine-grained.

________ Chert: hard, brownish-gray (10 YR 3/

1), thick-bedded. 

_______ Sandstone: medium-hard, pale-brown

(10 YR 5/3), thick-bedded, finegrained.

________ Chert: hard, brownish-gray (10 YR 3/

1), thick-bedded; grades from bed 

below.

________ Sandstone: pebbly, hard, light-yellowish-brown (10 YR 6/4), thick-bedded, 

fine-grained; chert and dolomite pebbles are as much as 75 mm in diameter; grades from bed below.

________ Sandstone: hard, very pale brown

(IOYR 7/2), thick-bedded, finegrained; crossbedded in part.

________ Sandstone: pebbly, medium-hard, palebrown (10 YR 6/2), thick-bedded, 

medium-grained; chert and dolomite 

pebbles are as much as 70 mm in 

diameter; irregular contact with bed 

below.

Park City Formation; Franson and Grandeur Members not differentiated:

________ Dolomite: Sandy, medium-hard, lightbrownish-gray (10F.R 5/1), very 

thick bedded.

________ Sandstone: pebbly, medium-hard,

weak-yellowish-orange (10F.R 7/6), 

very thick bedded, medium-grained; 

chert and dolomite pebbles are as 

much as 50 mm in diameter.

._ _ ____ Dolomite: medium-hard, yellowishgray (1QYR 7/1), thick-bedded, 

aphanitic; contains chert nodules. 

_______ Sandstone: dolomitic, pebbly, mediumhard, weak-yellowish-orange (10 YR 

7/6), very thick bedded, fine-grained; 

chert and dolomite pebbles are as 

much as 50 mm in diameter; grades 

from bed below.

________ Dolomite and sandstone, interbedded:

medium-hard yellowish-gray (10 YR 

8/1) thick-bedded aphanitic dolomite 

interbedded with medium-hand weakyellowish-orange (2.5F 7/4) finegrained sandstone; sandstone constitutes 50 to 75 percent of unit.

. -_____ Sandstone: hard, yellowish-white (2.5 Y 

9/2), very thick bedded, fine-grained.

________ Dolomite: silty, hard, light-brownishgray (10 YR 6/1), thick-bedded, 

aphanitic. 

Quadrant Formation:

________ Sandstone: hard, yellowish-white (2.5 Y

9/2), thick-bedded, fine-grained. 

Thickness unknown. 

1 Location of contact with underlying Permian beds not certain.

Cumulative 

Thickness thickness 

(feet) (feet)

0. 6 64. 4

.8 65. 2

2. 3 67. 5

.3 67. 8

.3 68. 1

1. 0 69. 1

Uranium

Sample

Acid 

insoluble

Radiometric Chemical 

eV IT

4. 0 73. 1

1. 0 74. 1

2. 0 76. 1

1. 3 77. 4

1. 6 79. 0

1. 6 80. 6

15. 0 95. 6

2. 0 97. 6

7. 0 104. 6
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 553

La Marche Gulch, Mont., lot 1366

[Phosphoria Formation exclusive of Tosi Chert Member and Park City Formation measured in hand trench and natural exposure near La Marche Gulch on west side of Big 

Hole River in sec. 32, T. 1 S., R. 9 W., Beaverhead County, Mont. Beds strike N. 40° W. and dip 45° SW. Measured by R. F. Gosman and sampled by J. A. Peterson, 

in August 1951. Analyzed for uranium by U.S. Geol. Survey and for other constituents by U.S. Bur. of Mines. LOI, loss on ignition]

Chemical analyses (percent)

Bed

Rt-49.

48. 

47.

46.

45. 

44.

43. 

42.

40- 

39_

38_

37_ 

36.

35. 

34.

33.

Description

Retort Phosphatic Shale Member of 

Phosphoria Formation:

Phosphorite: medium-hard, dark 

gray (-/V4), thick-bedded, 

nodular; chert y in places; 

apatite nodules or pebbles are 

as much as 30 mm in diameter; irregular contact with 

bed below. 

Mudstone: soft, medium-gray

(N 5), thin-bedded. 

Dolomite: medium-hard, lightbrownish-gray (10F.R 5/1), 

thick-bedded; contains some 

apatite nodules as much as 25 

mm in diameter and fine 

apatite pellets; PzO5 analysis 

may be too low.

Phosphorite: muddy, mediumhard, medium-gray (AT 5), 

thick-bedded, finely pelletal. 

Mudstone: soft, light-yellowishbrown (10 YR 6/4). 

Phosphorite: soft, dark-gray 

(-W3), thick-bedded, mediumpelletal; contains a few apatite 

nodules as much as 5 mm in 

diameter. 

Mudstone: carbonatic(?), soft,

light-gray (N 7). 

Phosphorite: medium-hard, 

black (N2), thick-bedded, 

medium-pelletal; zone in middle of bed contains considerable amounts of calcite 

cement.

Dolomite: muddy, medium-hard, 

dark-gray (A7 3), thick-bedded, 

very finely granular. 

Phosphorite: muddy, mediumhard, dark-gray (N 4), thickbedded, medium-pelletal; bed 

is sheared.

Phosphorite: muddy, light-gray 

(N 7), thin-bedded, mediumpelletal; contains a few apatite 

nodules as much as 18 mm in 

diameter; bed is sheared. 

Phosphorite: muddy, soft, lightgray (N 7), thin-bedded, 

finely pelletal.

Phosphorite: muddy, soft, thinbedded; bed may be faulted. 

Phosphorite: medium-hard, 

moderate-yellowish-brown 

(10 YR 5/6), thin-bedded, 

finely pelletal; contains a few 

apatite nodules.

Mudstone: medium-hard, moderate-yellowish-brown (10F.R 

4/4); grades from bed below. 

Phosphorite: muddy, mediumhard, moderate-yellowishbrown (10 YR 4/4), thickbedded finely pelletal. 

Dolomite: muddy, medium-hard, 

medium-gray (JV 6), very 

thick bedded, aphanitic.

Thickness 

ffeef)

0 K

. 4

1. 0

. 2 

1.3

1 9

1. 5

live 

thickness 

(feet)

n f»

q

1 Q

O K

2.7' 

4. 0

K 0

6. 7}

Uranium

RadioAcid metric Chemical 

Sample PsOs insoluble AhOa FezOs LOI eV U

RFG-5585 28.4 13.4 ____ ____ ----- 0.009 0.007

5584 3.9 68.3 ____ ____ ----- .002 _____

5583 4.3 17.7 ____ ____ ----- .004 _____

5582 22.4 12.1 1.49 2.19 14.02 .003 _____

5581 27. 0 22. 2 4. 24 2. 60 4. 18 . 006 . 005 

5580 .9 73.1 2.93 1.38 5.27 .003 _____

1. 2

4.0 

1.3

7.3

8. 5

3.0 11.5

2. 7 14. 2

18. 2

19. 5

6 20. 1

20. 3

1. 1 21. 4

5579 24. 0 2. 9 2. 26 1. 12 17. 63 . 006 . 004

5578 22. 8 27. 8 13. 6 2. 72 5. 44

5577 18. 7 37. 7 7. 02 3. 15 6. 94

5576 18. 7 37. 7 7. 02 3. 15 6. 94

5575 22. 7 31. 0 5. 72 2. 83 5. 7

5574 15. 4 44. 4

008

008

008

006

007

007

007 . 009

003

5573 .001
554 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

La Marche Gulch, Mont., lot 1366 Continued

Chemical analyses (percent)

Bed Description

Retort Phosphatic Shale Member of

Phosphoria Formation Con.

Rt-32. _____ M udstone: soft, light-yellowishbrown (10 YR 6/4), thinbedded.

31____- Mudstone: phosphatic, mediumhard, grayish-brown (10 YR 

4/2), thin-bedded; apatite is 

finely pelletal.

30____- Phosphorite: muddy, mediumhard, medium-gray (N 6), 

thin-bedded, finely pelletal. 

29--__- Phosphorite and mudstone, interbedded: soft light-gray (N 

7) thin-bedded finely pelletal 

muddy phosphorite interbedded with soft medium-gray 

(./V 6) thin-bedded phosphatic 

mudstone. 

28_-__- Mudstone: phosphatic(?), soft,

fissile.

27.---- Phosphorite: muddy(?), medium-hard, thin-bedded, pelletal.

26_ _ _ _ _ Mudstone: phosphatic, mediumhard, black (N 2), thinbedded; apatite is finely pelletal.

25---... Phosphorite: muddy, mediumhard, light-brownish-gray 

(10 YR 6/1), thick-bedded, 

medium-pelletal and skeletal. 

Park City Formation; Franson and 

Grandeur Members not differentiated :

Pc-24__-_-- Dolomite: medium-hard, lightgray (./V 7), thick-bedded, 

skeletal; contains a bed of 

chert 1.0 ft thick 4.0 ft above 

base of unit. Fossil-coll. No. 

12696.

23 ______ Sandstone: carbonatic, mediumhard, thick-bedded.

22______ Dolomite: medium-hard, darkgray (N 4), very thick bedded, aphanitic. 

21______ Siltstone: hard, light-brown

(7.5 YR 5,6), thin-bedded. 

20___-_- Dolomite: medium-hard, very

thick bedded.

19__---_ Dolomite: medium-hard, medium-gray (N6), thick-bedded, 

aphanitic; contains mudstone 

parting 0.2 ft thick at top.

18_---_- Dolomite: silty, medium-hard, 

medium-gray (Af 6), very thick 

bedded, aphanitic; contains 

light-brownish-gray (10 YR 5/1); 

mudstone partings 0.3 ft 

thick at top and base of unit. 

17_-___- Dolomite: medium-hard, medium-gray (./V 6), very thick 

bedded, aphanitic.

CumulaThick- five 

ness thickness 

(feet) (feet) Sample

0. 1 21. 51

Uranium

Acid 

insoluble Fe2 O3 LOT

Radiometric Chemical 

eU U

6 22. 1

22. 5

3. 3 25. 8

26.0

26. 2

26.4

26. 8

13. 0 39. 8

4. 1 44. 7

1. 0 45. 7

9. 3 55. 0

11. 0 66. 0

4. 2 70. 2

7. 5 77. 7

RFG-5572 15.8 44.7 ____ ____ ----- 0.004

5571 16. 7 43. 8 . 006 0. 004

5570 13. 4 50. 7 .004
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 555

La Marche Gulch, Mont., lot 1366 Continued

Chemical analyses (percent)

Bed

Pc-16.

15. 

14. 

13. 

12.

11. 

10.

Q-2. 

1.

Description

Park City Formation; Franson and 

Grandeur Members not differentiated Continued

Dolomite: medium-hard, lightbrownish-gray (WYR 6/1), 

very thich bedded: contains 

numerous lenses of sandstone 

as much as 0.3 ft thick and 

many dark-gray (N 4) chert 

nodules and lenses as much 

as 2.0 ft thick; becomes less 

cherty toward top of unit.

Siltstone: dolomitic, hard, lightyellowish-brown (WYR 6/4), 

very thick bedded.

Chert: hard, pale-brown (WYR 

5/2), very thick bedded; 

grades from bed below.

Sandstone: hard, light-yellowishbrown (WYR 6/4), very thick 

bedded, very fine grained.

Dolomite: cherty, medium-hard, 

light-brownish-gray (10 YR 

6/1), very thick bedded, aphanitic; much of chert occurs as 

sponge spicules.

Sandstone: dolomitic, hard, palebrown (2.5 Y 5/2), thickbedded, very fine grained.

Dolomite: cherty, medium-hard, 

aphanitic; bedding is indistinct; grades from bed below.

Dolomite: medium-hard, lightgray (N7), very thick bedded 

aphanitic: contains many 

round to eliptical nodules of 

light-yellowish-brown (10 YR 

6/4) chert; grades from bed 

below.

Sandstone: hard, pale-brown 

(WYR 6/2), very thick 

bedded, fine-grained; contains a few chert and dolomite pebbles as much as 45 

mm in diameter, most of 

which are concentrated near 

the base; grades from bed 

below.

Dolomite: medium-hard, medium-gray (N 5), thick-bedded, 

aphanitic; contains several 

lenses of very fine grained 

sandstone.

Siltstone: hard, light-yellowishbrown (WYR 6/4), thinbedded.

Dolomite: hard, medium-gray 

(N 5), thick-bedded, aphanitic.

Sandstone: hard, light-gray (N 

7), very thick bedded, finegrained.

Dolomite: sandy, muddy, hard, 

medium-gray (N 7), very 

thick bedded, aphanitic; sand 

is very fine. 

Quadrant Formation, upper part:

Sandstone: hard, light-brownish-gray (WYR 5/1), thickbedded, fine-grained.

Sandstone: hard, dark-gray (N 

4), very thick bedded, finegrained.

CumulaThick- tiae 

ness thickness 

(feet) (feet)

18. 0 95. 7

Uranium

Sample

Acid 

insoluble AljOs Fe2 03 LOI

Radiometric Chemical 

eU U

3. 0 98. 7

2. 2 100. 9

1. 0 101. 9

3. 0 104. 9

6. 5 111. 4

18. 0 129. 4

14. 6 144. 0

2. 0 146. 0

5. 5 151. 5

. 8 152. 3

7. 2 159. 5

4. 0 163. 5

7. 8 171. 3

5. 0 176. 3

3. 0 179. 3
556 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Logan, Mont., lot 1367

[Permian rocks measured along ridge on east side of road about 1 mile northwest of Logan, sec. 26, T. 2 N., R. 2 E., Gallatin County, Mont. Beds strike N. 70° E. and dip 

20° N. Measured by R. W. Swanson and J. A. Peterson and sampled by Swanson, in September 1951. Analyzed for PjOs and acid insoluble by U.S. Bur. of Mines, 

and for uranium by U.S. Qeol. Survey]

Chemical analyses (percent)

Bed

Us-34.

33-

32,

31.

To-30-

29.

28. 

27.

26.

25.

24-

23-

22.

21- 

20-

19-

Cumulative 

Thickness thickness 

Description (feet) (feet)

Upper tongue of Shedhorn Sandstone: 1

Sandstone: hard, very-pale-brown (10F.R 7/2), 17.0 17.0 

fine-grained; contains sandstone columns (?); 

thickness is approximate, and only about twothirds of unit is exposed in outcrop.

Sandstone: hard, fine-grained, yellowish-gray 4. 6 21. 6 

(WYR 7/1) to pale-brown (WYR 5/2), thickbedded; contains flat dolomite pebbles in lower 

1.5 ft; irregular contact with bed below.

Sandstone: hard, yellowish-gray (WYR 7/1), 13. 2 34. 8 

very thick bedded, fine-grained; contains black 

dolomite pebbles in beds 0.1 feet thick; crossbedded in part.

Sandstone: hard, very pale brown (WYR 7/2), 6. 0 40. 8 

fine-grained; crossbedded in 1-ft layers; irregular contact with bed below; contains scattered 

dolomite pebbles. 

Tosi Chert Member of Phosphoria Formation:

Chert: dolomitic, hard, light-brownish-gray 2. 0 42. 8 

(WYR 6/1); dolomite is irregularly distributed.

Sandstone: carbonatic, hard, very pale brown .5 43. 3 

(WYR 7/2), very fine grained; undulant contact with bed below.

Chert: hard, pale-brown (WYR 6/2), thin- 1. 7 45. 0 

bedded; contains some mudstone partings.

Dolomite: muddy, soft, very pale brown (WYR . 3 45. 3 

7/2), aphanitic; undulant contact with bed 

below.

Chert: sandy, hard, light-brownish-gray (WYR .4 45. 7 

6/1)., thin-bedded; contains phosphatic skeletal 

fragments.

Chert: hard, pale-brown (WYR 6/2), thin- .6 46. 3 

bedded; contains some sandy laminae.

Chert: dolomitic, hard, light-brownish-grav .9 47. 2 

(10 YR 5/1), thin-bedded.

Mudstone and chert, interbedd.ed: soft yellowishgray (2.5F 8/2) thin-bedded carbonatic 

mudstone interbedded with hard very pale 

brown (WYR 7/2) thin-bedded chert; chert 

constitutes 40 percent of unit.

Chert and limestone, interbedded: hard very 1. 9 

pale brown (10 YR 7/2) thin-bedded chert 

interbedded with soft yellowish-gray (2.5F 

7/2) thin-bedded muddy limestone.

Mudstone: soft, yellowish-gray (2.5 Y 7/2), . 7 

thin-bedded.

Chert: hard, very pale brown (WYR 7/2), thin- 1. 0 

bedded; irregular contact with bed below.

Chert: sandy, hard, pale-brown (WYR 6/2), 1.2 

very thick bedded; sand is fine; contains 

glauconite.

Sample

Uranium

Acid Radioinsoluble metric eU

1. 5 48. 7 RWS-5593

50. 6

51. 3

52. 3

53. 5"

5592

5591

1. 4 72. 7 0. 001

.9 68. 8 . 000

1. 3 62. 4 . 001

See footnote at end of table.
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 557

Logan, Mont., lot 1367 Continued

To-18-

17-

15-

13-

12- 

11.

10.

Bed Description

Tosi Chert Member of Phosphoria Formation Con. 

.___ Chert: hard, pale-brown (IOYR 6/2), thinbedded; contains columnar bodies 0.1 ft in 

diameter of fine-grained cherty sandstone in 

uppermost 2 ft. 

____ Sandstone: phosphatic, hard, pale-brown (IOYR

5/3), thick-bedded, fine-grained; apatite in 

skeletal and medium-pelletal; contains glauconite. 

____ Dolomite: sandy, hard, thick-bedded, aphanitic;

sand is very fine; contains glauconite; grades 

from bed below; contains scattered lenses and 

columnar bodies of dolomitic sandstone. 

____ Chert: hard, light-brownish-gray (IOYR 6/1),

thin-bedded; contains glauconite.

_ _. _ Chert: hard, thin-bedded; contains glauconite- _ _ 

____ Mudstone: sandy, carbonatic, soft, weakyellowish-orange (2.5F 8/4), thin-bedded; 

sand is fine.

____ Dolomite: muddy, medium-hard, weak-yellowish-orange (2.5F 8/4), thick-bedded, aphanitic. 

____ Dolomite: sandy, soft, weak-yellowish-orange

(2.5F 8/4), thin-bedded, aphanitic; sand is 

very fine.

____ Carbonate rock: muddy, medium-hard, weakyellowish-orange (2.5F 8/4), thin-bedded. 

9__________ Dolomite: sandy, hard, pale-brown (IOYR 5/2),

thick-bedded, aphanitic; sand is very fine; 

contains glauconite; grades from bed below.

8 __--_-_- Chert: sandy, hard, pale-brown (IOYR 6/2), 

thin-bedded; contains glauconite; composition of bed is variable, ranging from chert to 

cherty sandstone; grades from bed below. 

Fossil colln. No. 12699.

7__________ Chert: hard, pale-brown (IOYR 6/2), thinbedded; contains phosphatic skeletal fragments, glauconite, and a few scattered quartzite pebbles; irregular contact with bed below. 

Lower Tongue of Shedhorn Sandstone: 

Ls-6_ _________ Sandstone: dolomitic, hard, very pale brown

(IOYR 7/2), very thick bedded, very fine 

grained; irregular contact with bed below. 

Quadrant Formation, upper part: 

Q-5________.__ Sandstone: hard, yellowish-white (IOYR 9/1),

very thick bedded, fine-grained. 

4_ __________ Dolomite: medium-hard, light-brownish-gray

(10 YR 6/1), very thick bedded, aphanitic; 

contains stringers of fine-grained sandstone. 

3___________ Sandstone: hard, white (N 9), very thick bedded,

fine-grained, crossbedded in basal 1 ft. 

2___________ Dolomite: sandy, hard, light-yellowish-brown

(IOYR 6/4); sand is fine; contains a few dolomite pebbles. 

1_ __________ Sandstone: hard, white (N 9), very thick bedded,

fine grained.

1 Contact with overlying conglomerate of Ellis Group approximately located.

Cumulative 

Thickness thickness 

(feet) (feet)

5. 8 59. 3

Chemical analyses (percent)

Uranium

1. 1

1. 1

.7 

1. 0

60. 4

61. 5

1. 6 63. 1

.9 64. 0

1. 1 65. 1

65. 8

66. 9

1. 3 68. 1

1. 5 69. 6

1. 8 71. 4

.6 72. 0

2. 9 74. 9

9. 3 84. 2

2. 0 86. 2

4. 4 90. 6

2. 2 92. 8

6. 0 98. 8

Sample P.Os

Acid 

insoluble

Radiometric eU

709-931 O-64 19
558 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

Hawley Creek, Idaho, lot 1454

Phosphoria Formation and upper part of Park City Formation measured on north side of Hawley Creek, NE}4 sec. 36, and lower part of Park City Formation measured 

on divide west of Deer Creek, SEH sec. 25, T. 16 N., B. 27 E., Lemhi County, Idaho. Beds above unit Pc-29 strike N. 28° W. and dip 75° W.; beds below unit Pc-29 

strike N. 50°-75° W. and dip 15°-25° 8. Thickness of beds below unit Pc-29 is approximate because of poor exposures. Measured by E. K. Cressman in August, 1954]

Thickness Cumulative 

Bed Description (feet) thickness (feet)

Tosi Chert Tongue of Phosphoria Formation: 

To-43.------------------ Chert: hard, dark-gray, granular-appearing; weathers moderate yellow. 0. 5 0. 5

Overlain by dark-gray calcareous mudstone of Dinwoody(?) formation. 

42--.---------------- Chert: hard, dark-gray, granular-appearing._________________________ 1. 2 1. 7

41_____-__----_-__--- Mudstone: dark-gray to brownish-gray, thin-bedded to fissile__________ 4.0 5.7

40------------------- Chert: dark-gray, very thick bedded__..________--__-_-__-____-______ 112.0 117.7

39___________-_--__-- Chert: dark-gray, very thick bedded; contains irregular nodules of 2. 6 120. 3

medium-gray fine-grained carbonate rock. 

38 __ _--__--_----__ Chert: dark-gray, very thick bedded______________________________ 17.0 137.3

37_------------------ Chert: black, thin-bedded__-__-__-------_-------------_---------_- 7.8 145.1

36--_-_-__--_-------_ Dolomite: medium-gray to brownish-gray, fissile; contains a few apatite . 7 145. 8

pellets. 

-35------------------- Chert: black, thin-bedded; pitchy luster___-___---_-___-___________ 1.0 146.8

(34)__-_____________ Covered___________________________-----_______-__-____.__ 78. 0 224. 8

Retort Phosphatic Shale Tongue of Phosphoria Formation: 

Rt-33________-__-_-__-__ Phosphorite: dark-gray, finely to coarsely oolitic._-___-__-__-_-_.-___ .4 225. 2

Park City Formation: 

Pc-32.__________________ Dolomite and chert: sandy hard medium-gray very thick bedded dolomite 2. 5 227. 7

that contains black chert nodules and masses that constitute half of bed. 

31.________-___ ____ Dolomite: sandy, hard, medium-gray, very thick bedded._____________ 7.0 234.7

30______--___---_--._ Dolomite: sandy, weak-yellowish-orange, platy_____________________ 16. 0 250. 7

29._--_-----_------__ Sandstone: medium-gray, thick-bedded, very fine grained; slightly 3.0 253.7

dolomitic. 

(28)-_____--___-._ Covered..._______________________.___-_______-_______ 24. 4 278. 1

27.____..----_-__----_ Dolomite and chert: sandy dark-gray aphanitic dolomite passing laterally 4. 3 282. 4

and vertically into black chert. 

(26)-__ .-____-__-__ Covered..-___________________________________________ 8.0 290.4

25-____---__----- Similar to bed Pc-27__________________________________ 5. 5 295. 9

24_ _____-____-__-_-__ Dolomite: sandy (?), dark-gray, thick-bedded, aphanitic- ______________ 6. 6 302. 5

23-__ ___-____-__--___ Sandstone: Dolomitic, medium-light-gray, very fine grained-__________ 9.0 311.5

22___________-__--___ Dolomite: light-gray, thin-bedded, aphanitic___--____-_--_--_-__-_- 9.0 320.5

(21).________-___--__ Covered__________________-_-_.-______-_____-__._______.__ 18. 0 338. 5

20---___----_--_----- Chert: medium-gray, thick-bedded. ________________________________ 26.0 364.5

19___________________ Dolomite: medium-gray, thick-bedded, very fine grained to aphanitic; 25.0 389.5

contains a few medium-gray chert nodules. 

(18)-_._______________ Covered_____________________________________________________ 35. 0 424. 5

17. _____-__---___--__ Dolomite: light-gray, thin- to thick-bedded, very fine grained to aphanitic; 65. 0 489. 5

contains 25 percent medium-gray chert nodules. 

16__ _________--_--___ Sandstone: calcareous, yellowish-gray to light-gray, very fine grained; 16.0 505.5

laminated in part. 

(15)-_-__.-______- Covered-____________________________________________________ 133. 0 638. 5

14_______________.___ Chert: medium-gray____--___-_----__-_----_--_-------_--_----_-_- 5.0 643.5

(13)-________-_-___. Covered: dolomite float-____-____-_--_______-__-__-_-__-_-____--__ 18.0 661.5

(12)_._______________ Covered: dolomite and chert float---_--_-__-_-_--_-----_--___-_____ 6.0 667.5

11.__________________ Dolomite: light-gray, thin- to thick-bedded, very fine grained..________ 85. 0 752. 5

(10)________________ Covered: dolomite and chert float___--____-_--_______-_____________ 26.0 778.5

9,__________________ Dolomite: light-gray thin- to thick-bedded, very fine grained to aphanitic; 12. 0 790. 5

contains 10 percent medium-gray fossiliferous chert nodules. 

8_ __________________ Dolomite: light-gray, thin- to thick-bedded, very fine grained to aphanitic. 18. 0 808. 5

7-___._________-____ Chert: medium-gray____________________-_-_-__._______--_____ 6.0 814.5

6.__________________ Dolomite: light-gray, thin- to thick-bedded, very fine grained to aphanitic_ 15. 0 829. 5

5---__-___-________- Chert: light-gray, thick-bedded_-____-_--__-_-_-_-_---_--__-_______ 3.0 832.5

4.__________________ Dolomite: light-gray, thin- to thick-bedded, very fine grained to aphanitic_ 14. 0 846. 5

(3)_._______________ Covered: dolomite and chert float-__--___-_--______-__-__-_________ 7.0 853.5

2___________________ Chert: medium-gray-________--___---___-_____-_-_________-_______ 1.0 854.5

l-_-________________ Dolomite: light-gray, thin- to thick-bedded, very fine grained; underlain 2. 0 856. 5

by sandstone (Quadrant Formation?).
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 559

Pulpit Rock, Mont., lot 1479

[Shedhorn Sandstone and Phosphoria Formation measured in NEJ4NEH sec. 3, T. 9 S., R. 4 E., Gallatin County, Mont., on west side of Qallatin River about 

500 ft above Pulpit Rock by R. W. Swanson, assisted by W. B. Hall, in August 1956. Beds strike about N. 45° W. and dip 10° N W. Analyzed by U.S. Qeol. Survey]

Chemical Analyses 

(percent)

Acid 

Bed PzOs insoluble

D-36.

(35). 

Us-34..

33.

32- 

31.

30.

29.

28.

27.

26_. 

25..

(24). 

23_.

(22).

To-20. 

19.

Rt-18-

17.

16.

15.

14. 

13.

Description

Dinwoody Formation, basal part not measured:

Mostly covered: scattered small outcrops and much 

float of typical brown-weathering limestone of the 

Dinwoody. 

Upper member of Shedhorn Sandstone:

Covered: includes Shedhorn-Dinwoody contact

Sandstone: hard, massive, fine-grained, light-brownish-gray (10 YR 6/1); contains much nodular chert 

in top 0.3 ft.

Chert and sandstone, interbedded: hard fine-grained 

brownish-gray (10 YR 4/1) sandstone thinly interbedded with light-brownish-gray (10 YR 6/1) chert.

Chert: hard, thin- and somewhat wavy bedded, lightbrownish-gray (IQYR 6/1).

Sandstone: hard, massive, fine-grained, brownishgray (10 YR 4/1); contains thin beds of chert in 

upper and lower parts.

Chert: hard, thin- and wavy bedded, light-brownishgray (10Y.fi; 6/1); contains some interbedded sandstone in upper part.

Chert and sandstone: hard, thick-bedded to massive; 

sandstone and chert irregularly distributed.

Chert: hard, thin- and wavy bedded, light-brownishgray (10 YR 6/1); contains thin irregular layers of 

sandstone.

Sandstone: hard, massive, fine-grained, brownishgray (10 YR 4/1); contains lenses and irregular 

layers of chert in upper part.

Chert: hard, laminated to thin-bedded, light-brownish-gray (10 YR 6/1).

Sandstone: hard, fine-grained, light-brownish-gray 

(10F.R 6/1); contains numerous small chert nodules.

Covered.._ ____________-_-_-___-_-_-_---____-__

Sandstone: hard, massive, fine-grained, light-brownish-gray (10 YR 6/1); contains irregular masses of 

chert.

Covered._ _____________________________________

Sandstone: hard, thick-bedded to massive, finegrained, light-brownish-gray (10 FB 6/1). 

Tosi Chert Tongue of Phosphoria Formation:

Chert: hard, poorly bedded, brownish-gray (10F.R 

4/1); locally sandy.

Covered: probably chiefly thin-bedded chert _______

Retort Phosphatic Shale Tongue of Phosphoria Formation:

Mudstone: medium-hard, laminated to fissile, 

grayish-brown (WYR 4/2) to pale-brown (1QYR 

6/3).

Phosphorite: hard- to medium-hard, thick-bedded, 

finely to coarsely pelletal, grayish- to pale-brown 

(10FE 4/2 to 6/2); contains purple and white 

fluorite, quartz grains, and quartz veinlets.

Phosphorite: medium-hard, poorly bedded, mediumto coarsely pelletal, brownish-gray (10 YE 3/1); 

contains phosphatic shell fragements and purple 

and white fluorite.

Phosphorite: medium-hard, thick-bedded, finely to 

very coarsely pelletal, brownish-gray (10 YR 4/1); 

contains quartz sand.

Mudstone: soft, fissile, dusky-brown (IQYR 3/2); 

contains apatite pellets.

Sandstone: hard fine-grained pale-brown (lOFfi 6/2) 

sandstone containing locally many pebbles of chert 

to \% in. diameter and pellets, shell fragments, 

and sandy nodules.

Cumulative 

Thickness thickness 

(feet) (feet) Sample

1. 0

5.8

1.0 

6.8

3. 5 10. 3

2. 3 12. 6

5. 0 17. 6

4. 2 21. 8

9. 2 31. 0

2. 5 33. 5

7. 6 41. 1

.9 42. 0

1. 0 43. 0

2. 0 45. 0

10. 5 55. 5

8. 5 64. 0

5. 0 69. 0

12.5 81.5 __--__ -

14.5 96.0 -.____--_- ------

1.0 97.0 --__----_. ------

1. 0 98. 0 RWS-7544 25. 9

.8 98. 8

.5 99. 3

.2 99. 5

. 6 100. 1

7543 27. 2

7542 13. 5

27.5

20. 0

33.5
560 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD 

Pulpit Rock, Mont., lot 1479 Continued

Bed

(12). 

Ls-11-

(10).

(7).

(5)-

(2).

Q-l.

Description

Lower member of Shedhorn Sandstone:

Covered-______________________________________

Sandstone: medium-hard, poorly bedded, finegrained, light-brownish-gray (10 YR 6/1).

Covered.______________________________________

Sandstone: hard, medium- to thick-bedded, mediumgrained, pale-brown (10 YR 6/2); cherty 1 ft above 

base and chert nodules are found higher.

Sandstone and chert: hard thin- to medium-bedded 

medium-grained light-brownish-gray (10 YR 6/1) 

sandstone containing thin interbeds and some 

nodules of chert.

Covered-______________________________________

Sandstone: calcareous, hard, thin- to thick-bedded, 

coarse- to very coarse grained; locally contains 

pebbles of carbonate rock; very pale brown 

(10 YR 7/2); contains many dark grains and fossil 

fragments (bryozoa, gastropods, sponge spieules).

Covered.______________________________________

Sandstone: hard, thin- to thick-bedded, fine-grained, 

light-brownish-gray to pale-brown (10 YR 6/1 to 

2.5F 6/2); contains many drak grains and local 

carbonate lenses and flat pebbles.

Chert and sandstone, interbedded: hard fine-grained 

pale-brown (10 YR 6/2) sandstone containing 

numerous apatite grains interbedded with hard 

thin-bedded light-brownish-gray (10 YR 6/1) chert 

containing dolomite rhombs, sponge spieules, and 

locallv, much very fine quartz sand; at base, 

contains chert and carbonate pebbles as much as 

1 in. diameter.

Covered interval: dug out calcareous medium-hard 

fine- to very coarse-grained grayish-orange (10 YR 

7/4) sandstone 7 ft above base and silty to very 

finely sandy medium-hard weak-vellowish-orange 

(10 YR 7/6) to grayish-orange (10 YR 7/4) carbonate rock at 9}£, 18%, and 22 ft above base. 

Quadrant Formation, top bed:

Sandstone: hard massive, medium-grained- yellowishwhite (10 YR 9/1). Forms extensive bluffs.

Cumulative 

Thickness thickness 

(feet) (feet)

0. 9 

1. 6

3. 0 

3. 5

4. 3 

4. 8

10. 0

101. 0

102. 6

105. 6

109. 1

1. 7 110.

115. 1

119. 9

2. 2 122. 1

5. 5 127. 6

3. 5 131. 1

22. 0 153. 1

10. 0

Sample

Chemical Analyses 

(percent)

Acid 

PiOs insoluble
STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 561

Wigwam Creek, Mont., lot 1481

[Permian rocks measured in reconnaissance from natural exposures on north side of Wigwam Creek Canyon in SEJ4 sec. 33 and NWJ4 sec. 4, T. 7 and 8 S., K. 2 W., Madison

County, Mont., in July 1966, by R. W. Swanson. Beds strike NE and dip 10-15° NW]

Cumulative 

Thickness thickness 

Bed Description (feet) (feet)

Din woody Formation, basal bed: 

D-27__________________ Carbonate rock: medium-hard, thin-bedded, dense, pale-brown_____________ 3. 0 3. 0

Upper member of Shedhorn Sandstone: 

Us-26_______-___________ Sandstone: hard, thin-bedded, fine-grained, pale-brown (IQYR 5/2) to light- 8. 0 8. 0

brown (7.5YR 6/4); contains lenses of sandy chert. 

25___________________ Sandstone: calcareous, medium-hard, fine-grained, poorly bedded, yellowish- 9. 0 17. 0

gray (2.5F 7/2); not well exposed; contains shell fragments; basal contact 

irregular. 

24____---__-___-_-__- Sandstone: hard, thin- to thick-bedded, fine-grained, brownish-gray (IQYR 2. 0 19. 0

4/1).

Tosi Chert Tongue of Phosphoria Formation: 

To-23__...__._.__-____ Chert: hard, thin- to thick-bedded, pale-brown (IQYR 6/2) to light-yellowish- 12. 0 31. 0

brown (IQYR 6/4); locally sandy, lower part thinner bedded; fissile silty 

interbeds are common; contains columnar sandstone concretions. 

Lower tongue of Shedhorn Sandstone: 

Ls-22_____-_-_-_-_-_-___ Sandstone: phosphatic, hard, poorly bedded, fine-grained and locally gritty in 1. 8 32. 8

lower half, pale-brown (2.5F 6/2); cherty at top; contains shell fragments 

and teeth; basal contact coarsely irregular. 

21 _________-_-_-_-___ Sandstone: hard, very fine to medium-grained, pale-brown (10 YR 6/2); basal .8 33.6

contact irregular to undulating. 

20_ ___________________ Chert and sandstone: nodular to massive sandy pale-brown (IQYR 6/2) chert 5. 8 39. 4

(70 percent) containing irregular patches and lenses of fine-grained lightyellowish-brown sandstone; basal contact irregular. 

19._----------------_ Sandstone: cherty, hard, fine-grained, massive, pale-brown (7.5YR 6/2); very 6. 0 45. 4

cherty in top 1^_ ft; scattered chert found below; gradational basal contact. 

18____-------------__ Sandstone: cherty, hard, very fine to fine-grained, thick-bedded to massive, 40. 5 85.9

light-yellowish-brown (IQYR 6/4); light-brownish-gray (10F.R 6/1) chert very 

irregularly distributed throughout bed. 

(17)__________________ Covered__________________________-_-_-_--_--_-_-_-___-_-_-_---_--__- 26. 0 111. 9

16_ __________________ Sandstone: hard, fine-grained, somewhat cherty; contains apatite pellets. ___ 6.0 117.9

(15)---------_-------- Covered__-_-_-_-__-___-_-_-_----_____--__-_-----_---_----------_-_-_ 2. 0 119. 9

14__-_---_-_-_---___- Chert: sandy, thick-bedded, very pale orange (IQYR 9/2); contains sponge 3.0 122.9

spieules; sand very fine. 

(13)_________________ Covered: possibly carbonate rock____-___-___________-_-_-_-_.________ 13.0 135.9

12_ ___-_____-_-___-__ Chert: sandy, like bed Ls-14; contains abundant siliceous sponge spicules___ 2. 0 137. 9

11-_--____-_---_-_-_- Sandstone: calcareous, medium-hard, fine-grained, reddish-brown; contains .5 138.4

shell fragments and apatite pellets. 

10_ __________________ Carbonate rock: sandy, hard, aphanitic, light-gray; contains brachiopod 1.5 139.9

shells. 

(9).-._--._.-._.-.-.-. Covered ------_.-...-__._._._.---_-.-.----_-_._._.-.-.---.-_---._- . 5 140. 4

8---____-_-___--_--_- Sandstone: carbonatic, very fine to medium-grained, pale-brown (7.5 YR 6/2) __ .5 140.9

7--_-_-----_-_-_--__- Chert: sandy ____________________._._._._._.___._-_._._._._._._._._. 1.0 141.9

6_ ___________________ Sandstone: carbonatic to cherty, hard, fine-grained, light-brownish-gray 1.0 142.9

(10F.R 6/1); containa abundant siliceous sponge spieules and nvimerous 

apatite pellets. 

5_-__-_-____.________ Covered..._______________-________________--___-_-_-----______ 1. 0 143. 9

Grandeur Tongue of Park City Formation: 

G-4______-__-___________ Dolomite: hard, locally cherty, thick-bedded to massive, pale-brown (7.5Y.R 5. 2 149. 1

6/2); upper 4 ft weather hackly; forms low bluff. 

3---_----__-___-_-_-_- Dolomite: hard, aphanitic, thick-bedded, very pale brown to very pale orange 11. 5 160. 6

(IQYR 7/2-7.5YR 8/2); contains small round chert nodules. 

2_____________________ Covered: probably mostly dolomite- ___________________________________ 19.0 179.6

Quadrant Formation, top bed: 

Q-l______-_-_-____-_____ Sandstone: hard, fine-to medium-grained, white.________________________ 5.0 5.0
562 GEOLOGY OF PERMIAN ROCKS IN THE WESTERN PHOSPHATE FIELD

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 1950, The fluorapatite equilibrium system in the conditions of formation of sedimentary rocks: Akad. Nauk 

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 1948, The megascopic study and field classification of 

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 1952, Phosphatic rocks in the Deer Creek-Wells Canyon 

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 1934, Correlation and interpretation of Paleozoic stratigraphy in south-central Idaho: Geol. Soc. America Bull., v.

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 1959, Geochemistry of uranium in phosphorites and black 

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STRATIGRAPHY AND PETROLOGY, PERMIAN ROCKS OF SOUTHWESTERN MONTANA 565

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INDEX

Page

Acid insoluble, analyses of__________ 279,280 

Acknowledgments..... _ _ T ___________ 276

Alpine Creek- __ ._ 291,296, 299, 324, 335,355, 506 

Aluminum, analyses of.____________ 880 

Ammonites..___________________ 355 

Amsden Formation__. ____________ 355 

Anatase. ___________________ 294,344 

Angola._-------_-.______________ 374

Anticlines-_____________________ 319 

Apatite, general discussion. -_-________ 279, 

294, 308, 316, 330,342, 344,351 

solubility of _____________ 374 

trace minerals in________ ____ 319 

Aphanitic dolomite in the Park City Formation . _...--_ 291

Aspen Valley________. ___.._..__ 392

B

Bahama Bank. ..-_-___________ 377 

Bahaman calcareous sands, phosphorites

compared to____________ 312 

Bear Creek____________________ 338 

Beaverhead Range _______ 288, 364,379,380 

Bibliography__...... 297, 300,304,313, 319, 341,562

Big Cottonwood Canyon, Utah________ 286 

Big Hole Canyon-Melrose________ 290,297,334 

Big Hole Range------..-..__________ 336

Bighorn Basin-._________________ 362 

Big Sheep Canyon _____ 289,290,294,306,337 

Bitterroot Range. ________________ 364 

Blacktail Creek_--.._..___________ 347 

Blacktail Mountains...____________ 329 

Boulder batholith. _______________ 319,320 

Brachiopods_-__________________ 291 

Bryozoans_____________________ 291 

Burrowing organisms______________ 367

C

California current..._____________ 379 

Camp Frigid-.-._-______________ 5^6 

Canyon Camp_._______________ 335,509 

Canyon Creek No. 1_______________ 441 

Canyon Creek No. 2_____________ 441 

Canyon Creek No. 3.______________ 541 

Cap limestone_____ ____________ 333 

Carbonaceous matter, analyses of._____ 279,280 

clay-particle alinement affected by____ 313 

rate of production of ------- _.. ___ 373

Retort Phosphate Shale Member containing. .. ______ 305 

source of__________________ 373 

tourmaline containing..__________ 344 

Carbonate rock, defined. _________ __ 282 

general discussion.,..__________ 3/5,378 

Park City Formation containing.. ___ 280 

Carbonate-fluorapatite... __________ 308 

Cariaco Trench. _________________ 379 

Caribou Range, Idaho._____________ 338 

Casto area, Idaho__..........______ 364

Casto Volcanics..-______________ 363,379 

Cave Creek._________________ 334,473 

Cedar Creek___________________ 470 

Centennial Mountains...________ 323,338,347 

Centennial No. 1. _______________ 464

[Italic page numbers indicate major references]

Page

Centennial No. 2, Idaho___________ 468 

Centennial No. 3.______________ 467 

Central Montana Platform._._..._-.-_.... 362

Chalcedony.-.. . ..... . .._... 296,316,372

Chemical analyses, general discussion.____ 270

Chert, carbonaceous matter in_________ 316

defined.------- .. ___________ 282

diagenesis of--_________-_____ 371 

general discussion....__________ 3/5,351

Park City Formation containing.....__ 296

Shedhorn Sandstone containing...-___ 847 

source of . ___ 369 

total volume of______________ 360 

Cherty Shale Member of Phosphoria Formation, stratigraphy of._____ 336 

Cinnabar Mountain._________ 330,351,5^7 

Clay....________-___....___ 296,313,316

Climate..__-_____ _______ _ 277 

Clyde Sea._..._________________ 375 

Color, defined__________________ 282 

Commercial phosphorite, production of. - 320 

Continental shelf, production of organic carbon on_______________ 370 

Corals.______________________ 354 

Cratonicshelfs...________________ 380 

Crooked Creek-___...______ .._ 481 

Current action, evidence for__.. ._. 310 

Currents-- . _ 364,370,373,377,379

D

D function, calculation of____________ 283 

Dalys Spur .___-__________ 294,297,357 

Dark mudstone. See Mudstone. 

Demospongia_ _______ _. 371 

Depositional basins__________ __ 360 

Diatoms __.__-_._.________ 369 

Dikes.-.._____.______.___ 320 

Dillon-____.__________ 297,300,357 

Dinwoody Formation. __________ 336,350,355 

Dolomite, defined..________-______ 282 

Shedhorn Sandstone containing... _ 847 

Drainage._ _ #76

E

East Pacific Ridge. ______ _ 372 

Ellis Group _________________ 354 

Ervay Tongueof the Park City Formation.. 354 

Eugeosynclinal deposits..____ 380 

Evaporites.. __ _____ 361

F

Facies, general discussion_ ______ . 355,357

See also particular interval. 

False cap limestone._________-----_ 333

Fault scarps- - 278 

Faults-______________________ 278 

Faunal zones. ____________ _ 355 

Florida straits__________________ 373 

Folds . 278

Fort Hall, Idaho _.________-__ 333 

Fossils _ ____-_____ 315,347,351,354

See also particular formation.

Page

Franson Canyon, Utah___ 300 

Franson interval___-___ 357 

Franson Member of Park City Formation,

general discussion 285 

carbonate rock in_____ 289 

chert in .-______ __ _ 206 

mudstone in__ __ 294 

sandstone in_______ 292 

stratigraphy of--.-- 300 

thickness of - _-_ - 300 

Fusulinids _-____ 299,354

G

Gallatin River ___~_ __ . 288,394 

Garnet. 294, 844

Garnet Range. __ __ - 350 

Garrison.. 350 

Geodal vugs.__ __ 336 

Geography... 276 

Geology, general discussion 277 

Geosynclines 380 

Glauconite... _ -________ 341,842,351,357,367 

Grade scale, defined_____ _ 282 

Grain, defined- 282 

Grain-size distribution, relation to environments--_______ ... 364 

Grandeur Member of Park City Formation,

carbonate rock in. 289,297 

chert in _ - __ 297 

illustration of. 283

mudstone in.___________ 294,297

sandstone in.._______ 292,297

stratigraphy of. _ - - - 285,296

Gravelly Range.- ________ . 335,347,356

Greenstone Gulch-. . 334

Gros Ventre Range, Wyo - 335,350,354

Gulf of Mexico. __-___ ____- 364

H

Hardness, defined.-_____ 282 

Hawley Creek _____.. 288,290,297,335,336,558 

Heath Formation --.-.. .. 355 

Heavy minerals, in Shedhorn Sandstone 342 

Heavy-mineral separation. 28i 

Historical geology, summary of events 381 

Hogback Mountains....... 293,297,328,335,357, 486

Idaho batholith - 363 

Ulite ...____-_________-___ 294,296, 315 

Illustrations__ 282 

Indian Creek.__.__-__ 339,347,355, 543 

Indonesia, glauconite in 367 

Intrusives. 319 

Investigations, methods of field procedures.... 278 

purpose of 276 

Iron, analyses of. 280 

Ironoxides - 316,342

Jack Canyon. . - 320,335,^02 

Jefferson Canyon 531 

Jefferson River.. 354

567
568 INDEX

K Page

Kaolinlte._____________________ 296 

Kelly Gulch.._____________ 294,320,334,457

La Jolla, Calif.__.__...______ 364,366,368 

La Marche Gulch. _________________ 553 

Laboratory procedures_______-_____ 279 

Lag deposits._.._______________ 364 

Land areas, Permian...____________ 379 

Landon Ridge-__________________ 543 

Laramide orogeny________________ 278 

Lazyman Hill.____________ 299,317,324, 614 

Lemhi Range, Idaho.._________ 300,364,380 

Leucoxene__________________ 294,343,344 

Lima.____________________ 300,349,357 

Limestone, defined_______________ 882 

Lithologic classes, defined..._________ 883 

Little Sheep Creek....__________ 294,337,476 

Little Water Canyon______________ 519 

Logan_______________________ 556 

Loss on ignition, analyses of_________ 279,280 

Lower Grandeur interval____________ 356 

Lower Member of the Shedhorn Sandstone,

stratigraphy of___________ 347 

Lower phosphorite of the Meade Peak Member._________.______ 383 

Lower Tosi interval..______________ 357

M

Madison Formation.._____________ 355

Madison Range.._______________ 297,347

Maiden Rock mine_______________ 320

Martha's Vineyard______ _________ 366

Meade Peak interval. _____________ 357

Meade Peak Phosphatic Shale Member of

Phosphoria Formation, general

discussion______... 285,315,319,338

lithologic variations in___________ 323

phosphate in.._______________ 308

lower phosphorite..____________ 383

stratigraphy of...._____________ 230

Melrose Adit No. 1_______________ 443

Melrose Adit No. 2_______________ 448

Melrose district..._______________ 333

Metamorphism, contact____________ 319

Mica.______________________ 296

Microcrystalline apatite, defined..._____ 308

Mississippi delta area_____________ 366,367

Mississippi River, silica precipitated from.... 369

Monterey Formation______________ 372

Mount Fleecer__________________ 319

Mudstone, bimodal frequency distribution of. 376

defined.__________________._ 282

environment of deposition________ S67,374

general discussion...____________. 3/3

Park City Formation containing- ____ 294

source areas.-- _____ ________ 367,373

N

Nodule, defined______________ 282,310,332 

"North Big Hole Canyon.._._________ 537 

North Boulder Creek______________ 649

O

Ocean currents. See Currents. 

Odell Creek..____________.____ 402 

Ogallala Formation_______________ 372 

Oil-shale analyses, at Sheep Creek______ 438 

Oolite, defined. _______________ 282,309 

Oolitic sand__.________________. 377 

Organic carbon..............________ 370

Otter Formation... _______________ 355

P Page

Paleogeographic maps.____________ 378

Paleogeography... 378

Park City Formation, carbonate rock in___ 378

chert in____________________ 303

distribution_________________ 286

fossils in____________________ 299

general character.... ____.... 285,286

lithology of __ - __.__ 289

Pelecypods.____ ____ 291

Pellet, defined..______________ 282,309,314

Pellets, origin of-_ - 375

Permian rocks, age of__ __________ 354

origin of ___________________ 357, 459

relation to overlying beds __..___ 354

Permian Sea, transgression and regression _. 380

Phosphate, localization of minable deposits__ 338

Phosphatic mudstone. See Mudstone.

Phosphoria Formation, carbonate rock in__ 378

contact metamorphism in_________ 3/9

distribution .. .____________ 303

fossils in _________ _.._ 305,315

general character.-. 285,303

intrusives in.- __ _____ 320

lithology of - __- 305

minor rock types in ________ 3/7

stratigraphy 320

trace elements in _.... 3/8

See also particular member.

Phosphoria Gulch area, Idaho________ 326,349

Phosphorite, defined..... __ ...___ 282

general discussion . ._ 307,377

uranium in.. 319

Phosphorus, manner of deposition__.____ 374

source of... 374,377

Phosphorus pentoxide, analyses of ._. 279

Phytoplankton._ __. .... 373

Pioneer Mountains 350

Pipette analyses_ 28/

Planktonic organisms___.____ ____ 375

Porcupine Creek-. 399

Precipitation_____ _ __ __ 277

Pulpit Rock 349,559

Q

Quadrant Formation.____ 277,284,298,355 

Quadrant Mountain__ 351

R

Radiolaria . - 369

Reas Peak....__.. . 355

Red Creek __..._-_____. 354

Red Mudstone. See Mudstone.

Red Rock Valley 350

Red beds __-___-___ _... 361 

Retort interval- - 357 

Retort Mountain___ 329 

Retort Phosphatic Shale Member of the Phosphoria Formation, carbonaceous 

matter in... _____ . 305 

facies in______-____ 331 

Retort Phosphatic Shale Member, at Hogback Mountain__________ 317 

illustration of __._._ 283,285, 313,315 

phosphorite in________________ 308 

stratigraphy of. 329 

Rex Chert Member of Phosphoria Formation,

iron in. . 316

stratigraphy of... 325

Rex interval-.-__________ 357

Rock source areas, sandstone from 359 

Rock terms________ ___ 282 

Rockport, Tex_ _____________ 364,366,368 

Ruby River... 297

Page

Ruby Valley. _________________ 356 

Rutile.. .......__I______.. 294,343,344

Samples, methods of collecting_________ 278

treatment of_________________ 279

Sandstone columns_______________ 351

Sandstone, defined...______________ 282

environment of deposition________ 364,367

origins of ._ ____ __ 359

Park City Formation containing..____ 292

Shedhorn Sandstone containing-...___ 339

Sandstone source area, lithologic character.. 359, 367

location of_________________ 36/,367

Santa Cruz Basin. ________________ 371

Sappington Canyon.______________ 534

Sawtooth Mountain___________ 335,347,444

Seven Devils__________________ 364,379

Seven Devils Volcanics____________ 363

Shedhorn Sandstone_______________ 285

general distribution_____________ 338

heavy minerals in... ..__ . 342

lithology..... ______________ 339

stratigraphy of..... ____ .. .. 347

Sheep Creek...__ 306,329,332,334,336, 374,376,426

Shell Canyon _________.__ 335,336,355,384

Silica, mechanism of precipitation of _ .. 372

rate of deposition of______ _ 369

See also Chert.

Silicofiagellates.__ _.__ 369 

Sills.___. _________.__ __ 319,320 

Sixteen Mile Creek__________.____ 354 

Size analyses... -. 2&1 

Skeletal carbonate rock in the Park City Formation_ _____ ... 291 

Skeletal dolomite___________.____ 378 

Skeletal fragment, defined.. ___ . .. 283,309 

Sliderock Mountain._____________ 329,406 

Snowcrest Range.______ 297,323,335,347,355,357 

South Big Hole Canyon No. 1_________ 528 

South Big Hole Canyon No. 2.._.. . SSO 

South Boulder Creek____________ 335,550 

Southwest Africa__ ______ 374 

Spectrographic analyses.. _ .. 280 

Sheep Creek ____________ 439 

Sponges, ability to extract silica from sea

water._________ 369 

Sponge spicules-____ 315, 316, 341, 351, 367, 369,371 

Spring Creek___.__. ___ 46! 

Stocks.._______________ 319 

Stratigraphic nomenclature, current usage 285 

history of.__________________ 284 

Stratigraphic sections, general discussion. 383

See also particular locality.

Swales.___________ . 315 

Sweetgrass Arch..._________ 362

T

Tan Mudstone. See Mudstone. 

Taylor Creek Ridge, Idaho_ 523 

Tectonism-_______________ __ 380 

Tendoy Mountains...___ 323, 334, 354, 355, 364, 380 

Terminology used._____ 282 

Teton Formation..______ 284 

Teton Range, Wyo_________ 354 

Thickness of bedding, defined. __ 282 

Thin sections___________ 280 

Three Forks area...____ 294,298, 335,349, 354, 533 

Tidal currents. See Currents.
INDEX 569

Page Page Page

Time horizons. _________________ 355 Upper Member of the Shedhorn Sandstone, West Fork of Blacktail Creek. .. 335,500

Tosi Chert Member of Phosphoria Formation, stratigraphy of. __________ 360 West Fork of Madison River _ ____ 513

general discussion ______ 285,317 Upper Tosi interval. ________ ___ 367 Wigwam Creek 355,56;

stratigraphy of ... ____________ SS6 Uranium. _________________ 279,280,3^9 Williston Basin.. _ ___ 361

Tourmaline. . ______________ 294,343,344 Wood River Formation..-.. . 300,379

Transportation ____ . ____________ £77 v Woodside Formation. . 300 

Turbidity currents. See Currents. Volcanic ash.......... ______ .__ _ 369

w U X-ray analyses.... _ 281

Wadhams Spring... 289, 294, 296, 297, 329, 336, 347, 450 

United States Bureau of Mines.. - ... 279 Warm Springs Creek. ___ ___ ........ 365,494 z

Upper Grandeur interval __ - ________ S67 Wells formation. ________________ 300 Zircon ____________________ 294,343,344

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