Stratigraphy, Petrology, and 

Some Fossil Data of the 

Roberts Mountains Formation, 

North-Central Nevada
Stratigraphy, Petrology, and 

Some Fossil Data of the 

Roberts Mountains Formation, 

North-Central Nevada

By THOMAS E. MULLENS

GEOLOGICAL SURVEY PROFESSIONAL PAPER1063

A description of the regional stratigraphic 

relations, composition, and age of a silty 

laminated carbonate rock that is the host 

rock for the large gold ore deposits at 

the Carlin and Cortez mines, Nevada

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1980
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY

H. William Menard, Director

Library of Congress Cataloging in Publication Data

Mullens, Thomas Ellison, 1924-

Stratigraphy, petrology, and some fossil data of the Roberts Mountains Formation, North-Central Nevada.

(Geological Survey Professional Paper 1063)

Bibliography: p.58

Supt. of Docs, no.: I 19.16:1063

1. Geology, Stratigraphic Silurian. 2. Geology, Stratigraphic Devonian. 3. Petrology Nevada.

4. Paleontology Nevada. 5. Geology Nevada. I. Title. II. Series: United States Geological Survey

Professional Paper 1063. 

QE661.M9 551.7'3'0979332 77-608315

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

Washington, D.C. 20402 

Stock Number 024-001-03264-3
CONTENTS

Introduction————————————————————————————

Purpose ————————————————————————————

Acknowledgments ——————————————————————

Geologic setting of the Roberts Mountains Formation — ----- —

Methods of study —————————————————————— ------

Stratigraphy and petrology of the Roberts Mountains Formation ———————————————————————————

Basal cherty unit ———————————————————————

Distribution and composition ———————————————

Stratigraphic relations of the cherty unit —————————

Laminated limestone unit ----- - — — - — — -- —— — -- — - —— — — -

General character and composition ————————————

Distribution and thickness ———————————————

Petrography of the laminated limestone 

Jriesvy ininersis --------- ---- — - — -—««--—-—-—-—-

Page

j_ 

2 

2

2

3

4

5

7

7

8 

8 

8

10 

j^ ~j

14

Page

Stratigraphy and petrology of the Roberts Mountains Formation—Continued

Interbedded laminated limestone and coarse-grained limestone unit ————————————————————————— 22

Definition and distribution ———————————————— 22

Composition and petrography ——————————————— 23

Age of the Roberts Mountains Formation —————————— 25

Correlation of the Roberts Mountains Formation ——————— 29

Environment of deposition of the Roberts Mountains Formation ———————————————————————————— 31

Source of detrital material in the Roberts Mountains Formation -——--————————————————————---———- 40

Trace elements in the Roberts Mountains Formation —--——— 41 

Gold deposits in the Roberts Mountains Formation ————— 42

yVTyrjpTidiY* Fossil cists ~___—.—........________...........______.............._. 4*^

References cited"-""-"--------"""-"TM——-—""TM-——"TMTM"TM—-— 58

Index _———.——__...............__.............._..............._........... fiQ

ILLUSTRATIONS

Page

PLATE 1. Map showing outcrops of the Roberts Mountains Formation and fossil collection localities ———————————— In pocket

2. Columnar sections showing thickness, general composition, and relations of the Roberts Mountains Formation to adjacent formations ——————————————————————————————————————————— In pocket

3. Diagrams showing mineralogic composition of 228 samples of Roberts Mountains Formation and related formations ------------------------------------------------------------------------------------------------------------------------- In pocket

FIGURES 1-6. Photographs of the Roberts Mountains Formation:

1. Basal cherty unit ——------—-----—-------—----—-----—-------—----——------—-------—----—------——---—--—-—-------——-————— 7

2. Basal cherty unit ——~———-———————-——~——~———-———————-———-——-—--—-——-——-— 7

3. Laminated limestone unit——————.--------———————————-————————-——————-———--————— 9

4. Weathered laminated limestone unit —---——---——-—--—-————————--—-————————————————— 9

5. Slope formed in laminated limestone unit —————————————————————————————————————— 10

6. Samples of fresh and of weathered laminated limestone ~——-—-—~——~——-———-——-——-----—————- 10

7. Photomicrographs of laminated limestone of the Roberts Mountains Formation ———————————————————— 11

8. Diagrams showing composition of unaltered laminated limestone samples from Roberts Mountains Formation ——— 12 

9-13. Photomicrographs:

9. Laminated limestone from Rattlesnake Canyon ————————————————————————————————————— 15

10. Laminated limestone from 1.5 km west of the Carlin mine ———————————————————————————— 16

11. Laminated limestone from Mill Canyon ----------------———————————————————————————————— 16

12. Coarse-grained limestone interbedded with laminated limestone at Rattlesnake Canyon --——————————— 17

13. Secondary dolomite from Hot Creek Canyon —-------—---————————————————————————————-— 18

14. Photograph of interbedded laminated limestone and coarse-grained limestone unit in the upper part of the Roberts Mountains Formation ------------------------.--------------—————-————————-—————-———-——--———-—-—-— 23

15. Photomicrographs of laminated limestone interbedded with coarse-grained limestone unit at Bootstrap mine ———— 24

16-20. Maps showing distribution of types of rock deposited in north-central Nevada:

J.D. JLJuriii^ miQ." Xji3.iiQ.ovGri3.il time —•••-"——•••——----------.............................—._.................._......-_——.—...—.————... oo

j. i. xjuriiig^ 13 LC -Lji3HQ.ovGri3H time ————*——---------------——-—————————........———-——.—...._........_................— o4

i Q T3urin2r \Vfinlockifln timp ---"-«-««---«-««---—___....-.-............................................................-—-.__._....._...__________... Q P\

19. During latest Silurian and earliest Devonian time —————————————————————————————————— 36

--.—..—-.—..............—.——.—.—.——.——._._...._...————.....————.......... ^ ^
IV CONTENTS

TABLES

Page

TABLE 1. Silurian and Lower Devonian graptolite zones in Great Britain and central Europe —————————————————————— 25

2. Representative spectrographic analyses of limestone in the Roberts Mountains Formation and overlying Devonian for-
STRATIGRAPHY, PETROLOGY, AND SOME FOSSIL DATA OF THE 

ROBERTS MOUNTAINS FORMATION, NORTH-CENTRAL NEVADA

By THOMAS E. MULLENS1

ABSTRACT

Silty laminated very fine grained carbonate rock in the Roberts 

Mountains Formation is the host rock for the large gold-ore 

deposits at the Carlin and Cortez mines, north-central Nevada. Such 

rock forms the bulk of the Roberts Mountains Formation in northcentral Nevada, although the type section of the formation was 

established in an area of facies change where silty laminated very 

fine grained carbonate rock is subordinate to thick-bedded coarsegrained carbonate rock. The facies change is related to deposition of 

rocks in the north-trending Cordilleran geosyncline or miogeocline, 

where there was a west-to-east gradation of volcanic and siliceous 

rocks through shale to carbonate rocks during early Paleozoic time. 

Thrust faulting during the Antler orogeny at the end of the Devonian and beginning of the Mississippian moved the volcanic, 

siliceous, and shaly rocks eastward over the carbonate rocks. The 

Roberts Mountains Formation is restricted to the autochthon and it 

is exposed mainly in windows of the allochthon. Several windows expose the eastward gradation of laminated carbonate rock to 

massive carbonate rock, but no known window exposes a westward 

gradation of laminated carbonate rock to shaly, siliceous, or 

volcanic rocks. In nearly all windows on the western side of the area 

of study, the Roberts Mountains Formation is the youngest formation exposed, and so the westward relations of the formation to 

younger rocks are unknown.

At the type section, the Roberts Mountains Formation is about 

580 m (meters) thick and consists of four units. From bottom to top, 

these units are 2 m of cherty limestone, about 120 m of laminated 

limestone, about 175 m of interbedded laminated very fine grained 

carbonate rock and thin-bedded coarse-grained carbonate rock, and, 

at the top, about 275 m of thick-bedded to massive carbonate rock. 

The formation includes rocks of both Silurian and Devonian age in 

the type locality. Away from the type locality the Roberts Mountains Formation consists of a few to about 50 m of cherty limestone 

overlain by as much as 1,200 m of laminated silty carbonate rock. 

Only locally does the formation include an upper zone of interbedded laminated limestone and lenticular coarse-grained limestone. 

Part of the change in the dominant type of rock in the Roberts 

Mountains Formation away from the type section is related to 

facies changes, and part is related to nomenclature. Sequences of 

rock similar to the type locality occur in exposures to the southwest 

and northwest, but most thick-bedded coarse-grained carbonate 

rock in these sequences is assigned to other formations.

The basal cherty unit, locally as much as 50 m thick, is the only 

marker bed of regional extent. The basal unit is a relatively pure 

limestone that was partly silicified during diagenesis and is locally 

dolomitized. The overlying laminated rock, here called the 

laminated limestone unit, forms the bulk of the Roberts Mountains

'Deceased.

Formation. The laminated rock is a mixture of calcite, dolomite, 

quartz and feldspar silt, and clay minerals, and is black to very dark 

gray. The laminations form planes for platy weathering which are 

conspicuous and typical of weathered rock but not conspicuous in 

fresh rock.

The relative proportions of minerals in laminated limestone vary 

greatly from bed to bed, although the lower half of the laminated 

limestone unit generally contains more calcite than the upper half. 

The average mineralogic composition of about 120 samples of 

unaltered laminated limestone is about 45 percent calcite, 25 percent dolomite, 22 percent quartz and feldspar silt, and 8 percent 

clay minerals. The samples, however, do not cluster near this 

average. Instead they are uniformly distributed in a broad field that 

is roughly bounded by these parameters: 5-95 percent calcite, 0-50 

percent dolomite, 5-45 percent quartz and feldspar, and 1-15 percent clay minerals. Minor but ubiquitous components that generally 

form less than 1 percent of laminated limestone are carbonaceous 

material and pyrite in fresh rock, and iron oxide in weathered rock. 

Very fine grained (<0.020 mm) calcite generally forms the matrix of 

laminated limestone. Irregular grains to euhedral rhombs of 

dolomite that average about 0.045 mm and angular grains of quartz 

and feldspar that average about 0.055 mm are set in the matrix of 

calcite. Mixtures of these minerals occur in laminations that range 

in thickness from less than 0.05 to about 4 mm, averaging about 

0.2 mm. One set of a pair of laminations is generally marked in fresh 

rock by concentrations of carbonaceous material and pyrite and in 

weathered rock by iron oxide.

Locally, the upper part of the Roberts Mountains Formation contains as much as 185 m of laminated fine-grained limestone interbedded with coarse-grained limestone. The coarse-grained (0.2 

to>2.0 mm) limestone is composed of angular fragments of clear 

calcite, pellets of dirty very fine grained «0.005 mm) limestone, 

sparse dolomite rhombs, scattered silt-sized to fine grains of quartz, 

and veinlets of secondary quartz. At Bootstrap mine in western 

Elko County, some coarse-grained limestone beds assigned to the 

Roberts Mountains Formation have scour surfaces at the base and 

contain nonoriented fossils and angular fragments which decrease 

in size upward. These beds probably are debris flows from a reef. 

Similar beds occur in the type locality of the formation.

In most areas, strata similar to the massive carbonate rock in the 

upper part of the Roberts Mountains Formation at the type section 

are not included as part of the formation. The formation is 

restricted to include rocks from the base of the basal cherty unit upward to the base of a coarse-grained massive limestone.

The Roberts Mountains Formation contains fossils which indicate 

that it ranges in age from earliest Silurian into Early Devonian. 

Near Swales Mountain, the Roberts Mountains Formation seemingly is conformably overlain by Lower Mississippian rocks; this fact 

opens the possibility that locally the formation contains beds of 

Middle and Late Devonian age. The boundary between the Silurian
STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

and Devonian Systems is placed at the base of Monograptus uniformzs-bearing beds which do not form a mappable horizon.

A reef (coarse-grained limestone) and forereef (laminated finegrained limestone) environment of deposition is assumed for the 

Roberts Mountains Formation and equivalent rocks. The distribution of laminated fine-grained limestone and coarse-grained 

limestone indicates that by Late Silurian and Early Devonian time 

the reef line nearly enclosed a basin that was open to the northeast 

and probably had local openings to the west. The basinlike feature 

modified the general westward slope of the east side of the Cordilleran geosyncline or miogeocline. The source area for the silt in 

the laminated limestone is not known, but the silt is assumed to 

have been brought in from the north by longshore currents. The texture of the dolomite, and the presence of carbonaceous material and 

pyrite in the laminated limestone are interpreted as indicating that 

the basin was partly barred.

The Roberts Mountains Formation grades eastward into the Lone 

Mountain and Laketown Dolomites and south and southwestward 

into the Lone Mountain Dolomite. North and westward, equivalents 

of the Roberts Mountains Formation are present in both 

autochthon and allochthon of the Antler thrust system; those in the 

autochthon are assigned to other formations and no direct correlation can be made between the Roberts Mountains Formation and 

allochthonous units.

Laminated limestone in the upper part of the Roberts Mountains 

Formation is the host rock for large gold deposits at the Carlin and 

Cortez gold mines. In unoxidized ore the gold is associated mainly 

with small (<0.005 mm) grains of epigenetic arsenic-bearing pyrite. 

The small size of the gold-bearing pyrite is probably related to a 

stratigraphic control, which is the abundant microporosity along 

laminations that furnished permeability for the mineralizing solutions.

INTRODUCTION

PURPOSE

Silty laminated very fine grained carbonate rock in 

the Roberts Mountains Formation is the host rock for 

the large gold-ore deposits at the Carlin and Cortez 

mines, north-central Nevada. Such rock forms the bulk 

of the Roberts Mountains Formation, but the formation also includes a thin cherty unit at the base and 

locally it contains thick-bedded coarse-grained carbonate rock. Regional stratigraphic, geochemical, and 

petrographic studies of the Roberts Mountains and 

related formations were started in 1968 as part of the 

Heavy Metals Program of the U.S. Geological Survey. 

Regional study of the Roberts Mountains Formation 

was intended to furnish a framework for detailed 

studies of the gold deposits. During 1968-71 the 

Roberts Mountains and related formations were 

studied at more than 40 localities in north-central 

Nevada. This report presents the stratigraphic, 

petrographic, and paleontologic information obtained, 

gives data on trace elements in the samples collected, 

and presents a theory as to why the silty laminated 

carbonate rock is a favorable host for a specific type of 

gold ore. Details of the mineralogy and chemistry of individual samples are available in tabular form 

(Mullens, 1979); these details should be consulted by 

those interested in the composition of impure carbonate rock. This report is concerned mainly with the 

distribution and general composition of the laminated 

silty carbonate rock, which is hereafter called 

laminated limestone and which is locally as much as 

1,200 m thick. The cherty unit and coarse-grained carbonate rock in the Roberts Mountains Formation 

received less attention than the laminated limestone, 

but these units are important in determining 

stratigraphic relations, age, and nomenclature problems associated with the Roberts Mountains Formation.

An outcrop map of the Roberts Mountains Formation is shown on plate 1. The general composition, correlation, and thickness of the Roberts Mountains and 

its relations to adjacent rocks are shown on plate 2. 

These plates reflect the isolated nature of the outcrops, 

the general lack of complete sections, and the unknown 

relations to overlying rocks in places where the 

laminated limestone is the upper unit exposed below 

thrust faults. The only conspicuous zone of regional extent is the basal cherty unit. Therefore, interpretations 

about stratigraphy and regional trends given in this 

report are based on sparse and inconclusive lithologic 

data. The lack of lithologic data is somewhat mitigated 

by paleontologic data which allow correlations and interpretations that could not be made on lithologic data 

alone.

ACKNOWLEDGMENTS

I gratefully acknowledge the assistance of W. H. 

Pierce, who dissolved rocks, prepared heavy mineral 

grain mounts, and made X-ray diffractograms for both 

whole rock and insoluble residue of samples collected 

in 1968 and 1969. Without his assistance, the work on 

the project would have been much delayed. The contributions and assistance of the following people are 

also greatly appreciated: M. A. Murphy of the University of California at Riverside graciously made 

available to me the results of several years' study of 

the Roberts Mountains Formation at and near the type 

section. W. B. N. Berry of the University of California 

promptly identified all graptolites collected during the 

study. G. L. Essington of Carlin Gold Mines and P. 

West of Newmont Mining Co. contributed much information about the Carlin gold mine and surrounding 

area. U.S. Geological Survey colleagues F. G. Poole, J. 

H. Stewart, C. W. Merriam, E. H. McKee, J. D. Wells, 

J. G. Evans, L. D. Cress, K. B. Ketner, J. F. Smith, Jr., 

H. W. Dodge, and C. L. Rogers guided me to exposures 

of the Roberts Mountains Formation and gave me the 

benefit of their years of experience in north-central 

Nevada. I would also like to express my appreciation 

for the assistance of three U.S. Geological Survey colleagues: J. Huddle, who identified conodonts from bulk 

samples collected during the study; I. C. Frost, who
GEOLOGIC SETTING OF THE ROBERTS MOUNTAINS FORMATION

determined the organic carbon and sulfur content of 

many samples; and L. Hedricks, who photographed all 

the hand specimens and thin sections shown in this 

report.

GEOLOGIC SETTING OF THE 

ROBERTS MOUNTAINS FORMATION

In gross pattern, Cambrian to Devonian rocks in 

north-central Nevada compose three contemporaneous 

sequences that are in thrust contact. The 

autochthonous sequence that contains the Roberts 

Mountains Formation is dominantly carbonate rock 

(about 90 percent of the total), although a little quartzite and shale are also present. The other two sequences 

are found mainly in the allochthon. One of the 

allochthonous sequences is mainly chert and siliceous 

clastic rocks, but it includes minor amounts of volcanic 

rocks and thin beds of limestone. The other 

allochthonous sequence comprises about equal 

amounts of chert, carbonate rock, and siliceous 

elastics; it is interpreted as transitional between the 

chert and siliceous clastic sequence and the carbonate 

sequence in the autochthon. These sequences, and their 

geologic implications, have been studied by many 

geologists (Merriam and Anderson, 1942; Nolan and 

others, 1956; Merriam, 1963; Roberts and others, 1958; 

Kay and Crawford, 1964; Roberts, 1964; Roberts, 

1968; Gilluly and Gates, 1965; Smith and Ketner, 

1968; Ketner, 1970; Smith and Ketner, 1975; Stewart 

and McKee, 1977; and Stewart and Poole, 1974). The 

rocks in the sequences have been interpreted by most 

of these geologists as representing deposition in the 

north-northeast-trending Cordilleran geosyncline, 

although Stewart and Poole (1974) interpreted the 

structure as a miogeocline where no major land mass 

or island is formed on the west side. Using terminology 

established by Kay (1951), the chert, siliceous clastic, 

and volcanic sequence is interpreted as having been 

deposited in a eugeosynclinal part of the geosyncline, 

which is west of the transitional rocks. The carbonate 

rock sequence is interpreted as having been deposited 

in a miogeosynclinal part of the geosyncline, which is 

east of the transitional sequence. Stewart and Poole 

(1974) recognized the same sequence of rocks, but they 

applied slightly different terminology in describing the 

areas of sedimentation. Exact locations of the boundaries between the sequences are not known because of 

oscillations of the sea and later structural complexities. At lat 40° N., most of the volcanic and siliceous 

sequence was deposited west of long 117 ° W. and most 

of the carbonate rock sequence was deposited east of 

long 117° W. (Roberts, 1968, fig. 6).

Roberts (1969) recognized six subfacies in the rocks. 

He divided the carbonate sequence into an easterly 

dolomite and limestone and a westerly limestone and

limy shale facies. The transition rocks are divided into 

an easterly limestone-shale and a westerly shale-chert 

subfacies. The siliceous and volcanic rocks are divided 

into a chert-shale easterly facies and a volcanic-quartzite-chert-shale westerly facies. The Roberts Mountains 

Formation falls mainly in the westerly limestone and 

limy shale subfacies of the carbonate sequence of 

Roberts (1969), although true shale is nearly absent 

and the formation contains thick-bedded coarsegrained carbonate rock that is assigned to the easterly 

dolomite and limestone subfacies along its eastern and 

southern margins.

The present distribution of the lower Paleozoic rocks 

is attributed mainly to thrust faulting during the 

Antler orogeny (Roberts, 1951), which spanned time 

from the end of the Devonian to the beginning of the 

Mississippian (Smith and Ketner, 1968; Ketner, 1970). 

During this orogeny, volcanic, siliceous, and shaly 

rocks were thrust 80-160 km east and over the carbonate rocks. The Roberts Mountains Formation is in 

the autochthon and most of the outcrops of the 

Roberts Mountains Formation are in windows of 

allochthonous rocks related to the Antler orogeny (pi. 

1). The only exposure east of the leading edge of Antler 

allochthon is in the Pequop Mountains, and this exposure is in a younger thrust plate (Thorman, 1970, pi. 

2, p. 2426). The windows in the allochthon are caused 

mainly by post-Antler movements that include 

folding, thrust faulting, and normal faulting. These 

movements range in age from Mississippian to Tertiary, but Tertiary basin-and-range folding and 

faulting are the major causes of the present distribution of windows exposing the Roberts Mountains Formation.

Some of the windows where the Roberts Mountains 

Formation is exposed are places where laminated silty 

limestone grades into the coarse-grained carbonate 

rocks to the east. No known window, however, exposes 

the gradation between laminated silty limestone and 

the western siliceous rocks. The Roberts Mountains 

Formation is the youngest formation that is exposed in 

several of the windows on the west side of the area of 

study. Therefore, information on which to base original 

thicknesses, relations to overlying rocks, and lateral 

relations with equivalent rocks deposited westward is 

lacking in much of the area of study.

The lateral gradations—eastward gradation of 

laminated limestone to coarse-grained carbonate and 

southeastward gradation of laminated limestone 

to laminated dolomite and coarse-grained 

dolomite—cause nomenclature problems. Because of 

the gradations, the use of the name Roberts Mountains 

Formation will be limited to an area that extends as far 

as the edge of laminated limestone to the east and as 

far as a change to less silty laminated dolomite to the
STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

south. In addition to the gradational boundaries, the 

units involved are time transgressive. At the eastern 

edge, laminated rock assigned to the Roberts Mountains is probably entirely of Silurian age, whereas in 

western exposures of the Roberts Mountains, 

laminated rock is Silurian and Devonian in age.

METHODS OF STUDY

The Roberts Mountains Formation was examined at 

all outcrop areas shown on plate 1, except in the Pequop Mountains and the isolated outcrop in the 

northern part of the Sulphur Spring Range. No detailed description or collection of samples was made 

in the area of the Roberts Mountains which M. A. 

Murphy has mapped in detail, because his data were 

available. At other places the Roberts Mountains Formation and related formations were described, sampled, and, where possible, measured, and a search was 

made for fossils.

The laminated limestone is difficult to study in the 

field because it is poorly exposed, it lacks marker beds, 

and the relative amounts of quartz silt, clay, calcite, 

and dolomite cannot be determined with consistent accuracy with a hand lens and acid. These limitations 

make it difficult to make regional correlations or to 

determine the local structure, which is generally complicated by faults. No measured sections are included 

in this report, but the general character and thickness 

of rocks measured are shown on plate 2.

Because the laminated limestone lacks marker beds, 

intensive efforts were made to collect graptolites. 

Some 60 graptolite collections were made, although no 

graptolites were collected in the Roberts Mountains 

area and only a few were collected at Coal Canyon, 

where Murphy (1969) and Berry (1969) had already 

determined the graptolite sequence. The graptolites, 

all studied by W. B. N. Berry, allow correlation of 

several zones in the Roberts Mountains Formation. 

These zones are correlated with the Llandoverian, 

Wenlockian, Ludlovian, Pridolian, Gedinnian, and 

Siegenian Stages of Europe.

About 50 samples, including both laminated 

limestone and coarser-grained material, were collected 

and submitted to John Huddle for recovery and identification of conodonts. All but one of the laminated 

limestone samples and many of the coarse-grained 

samples collected from the Roberts Mountains Formation are barren or lack diagnostic conodonts. Several 

collections from coarse-grained beds above and below 

the Roberts Mountains contain diagnostic conodonts 

that allow age limits of the Roberts Mountains to be 

established locally.

Localities where fossils were collected are shown on 

plate 1. Fossils identified from these localities and

some fossils collected by my colleagues are listed in the 

appendix.

A total of 246 samples of Roberts Mountains and 

related formations were collected to determine 

petrographic and chemical properties. Details of the 

mineralogy and chemistry of these samples are 

reported elsewhere (Mullens, 1979). The distribution of 

the samples collected is not uniform. A total of 89 

samples were collected at the Coal Canyon and Rattlesnake Canyon localities (pi. 1) where complete sections are present and where the Roberts Mountains 

Formation consists mainly of unaltered laminated 

limestone. Nineteen samples, chiefly of altered rock, 

were collected at the Carlin mine. The remaining 138 

samples were collected at 35 other localities.

The method of study used for the rock samples was 

as follows: All 246 samples were studied by spectrographic methods, and 228 were further studied by 

chemical, petrographic, and X-ray diffraction methods. 

Of the 228 samples studied in detail, rapid rock 

analyses (Shapiro and Brannock, 1962) were obtained 

for 82. In these analyses the major components were 

reported as oxides.

For the 228 samples studied in detail, part of each 

was retained as a hand sample from which a thin section was cut. The remainder was ground to minus-40 

mesh (the largest particle was about 0.62 mm, about 10 

times larger than the average grain size of the 

laminated limestone). Part of the ground sample was 

pulverized by mortar and pestle; this powder was used 

to make an acetate disk for X-ray diffraction. Fifty 

grams of the minus-40-mesh material was then dissolved in dilute hydrochloric acid (15 parts water and 1 

part concentrated hydrochloric acid) at room 

temperature. After bubbling ceased, the acid solution 

was heated to about 35 °C to insure that all dolomite 

dissolved. The insoluble residue was filtered, dried, 

and weighed to determine the present insoluble residue 

in the sample. A split of the insoluble residue was 

pulverized by mortar and pestle to make an acetate 

disk for X-ray diffraction. The remainder of the insoluble residue was centrifuged in bromoform (specific 

gravity about 2.89) to separate heavy minerals. The 

heavy minerals were then mounted in Canada balsam 

on a slide.

X-ray diffractograms of both whole rock and insoluble residue were made, so that the methods of 

Gulbrandsen (1960), Schultz (1964), and Diebold, 

Lemish, and Hiltrop (1963) for determining quantitative mineralogical composition could be used. All 

diffractograms were made on the same machine with 

Ni-filtered CuKa: radiation with high gain at 2 ° 26 per 

minute and a chart speed of 1 inch per minute. All 

samples were run from 4° to 60° 20. These settings 

were selected in an attempt to detect traces of minerals 

other than calcite, dolomite, quartz, feldspar, and clay.
STRATIGRAPHY AND PETROLOGY OF THE ROBERTS MOUNTAINS FORMATION

For the most part this procedure was unrewarding inasmuch as other minerals seldom occurred in sufficient 

quantities to produce identifiable X-ray peaks. A 

faster speed would have produced equally good results 

in half the machine time.

Thin sections and heavy mineral mounts were 

studied to determine the variety and relative amounts 

of minerals, and the fabric of the rock. Grain counts 

were made at 100 X magnification; details of texture 

and replacement were generally studied at 500 X. For 

the most part, thin-section study of the laminated 

limestone is difficult because of the small grain size 

and because most sections are smeared with carbonaceous material or iron oxides. The thin section 

data were integrated with the percent insoluble 

residue, X-ray diffractograms, spectrographic 

analysis, and oxide analyses to obtain the mineral composition.

For the 82 samples where rapid rock analyses are 

available, the actual amounts of calcite, dolomite, 

quartz, feldspar, and clay minerals are probably within 

2 percentage points of the amounts shown in Mullens 

(1979). X-ray diffraction traces of the whole rock and 

insoluble residue of these 82 samples were used as 

standards for comparing X-ray information on mineral 

composition of the other samples. For the samples 

where oxide analyses were not obtained, the accuracy 

is less. I estimate that the values are ±5 percentage 

points of the correct value, where a mineral exceeds 50 

percent. For values less than 50 percent, the probable 

error is greater and unbalanced. For minerals that 

form 15-50 percent of the rock, the probable error is 

within 5-10 percentage points of the correct value. For 

minerals that form less than 10 percent of the rock, the 

probable error is within 1-5 percentage points of the 

correct value.

The data for major components—calcite, dolomite, 

quartz, feldspar, and clay minerals—are calculated to 

100 percent of the rock for most samples (Mullens, 

1979). Only where pyrite, iron oxide, carbonaceous 

material, phosphatic material, or some alteration product exceeds 1 percent are the major components reduced below 100 percent. Water is ignored except to 

the extent that it is included in clay. The variety of 

clay recognized is based mainly on identification from 

X-ray diffraction studies. Kaolinite and montmorillonite were never positively identified in thinsection study.

STRATIGRAPHY AND PETROLOGY OF THE 

ROBERTS MOUNTAINS FORMATION

The Roberts Mountains Formation was defined by 

Merriam (1940, p. 11-12) for rocks exposed along the 

headwaters of Pete Kanson Creek in the north-central

part of T. 23 N., R. 50 E. (unsurveyed), Roberts Mountains, Eureka County, Nev. At the type section, the 

Roberts Mountains Formation includes Silurian and 

Devonian rocks, and is about 580 m thick. From bottom to top, it consists of 2 m of cherty limestone, about 

120 m of platy-weathering limestone, about 175 m of 

interbedded platy-weathering limestone and massive 

limestone, and 275 m of massive limestone and 

dolomite (M. A. Murphy, written commun., 1970). The 

Roberts Mountains Formation overlies dolomite and 

limestone of the Hanson Creek Formation, which Merriam believed to be entirely of Ordovician age, but 

which is now considered to be of Silurian age in the upper part (Mullens and Poole, 1972). The Roberts Mountains Formation, at the type section, is overlain by 

massive dolomite assigned to the restricted Lone 

Mountain Dolomite (Merriam, 1940, p. 13), which Merriam believed was of Late Silurian age, although he 

recognized the possibility that the Lone Mountain 

might contain beds of Early Devonian age.

The type section of the Roberts Mountains Formation, as established by Merriam, is in an area of abrupt 

facies changes. Winterer and Murphy (1960, p. 

119-122, figs. 1-4) and Murphy (1969) mapped the 

changes in detail; they assigned a maximum of about 

760 m of rock to the Roberts Mountains Formation 

and noted that as a mappable unit the formation 

ranges from a few meters to 760 m (Winterer and Murphy, 1960, p. 122). Merriam (1940, p. 11-12) assigned 

all rocks at the type section to the Silurian, but Murphy (1969), Klapper (1969), and Berry, Jaeger, and 

Murphy (1971) found that locally the upper part of the 

formation in the Roberts Mountains area is of Devonian age.

I did not study the type locality in detail; I have used 

the available literature, supplemented by written communications from M. A. Murphy (1968, 1969, and 

1970), in relating my work to the type locality.

Sequences of rock similar in age and composition to 

those in the type area of the Roberts Mountains Formation occur in the Shoshone, Toiyabe, Toquima, 

Monitor, and Sulphur Spring Ranges and in the Cortez, Simpson Park, and Tuscarora Mountains. In those 

ranges, rocks above the silty laminated limestone have 

been excluded from the Roberts Mountains Formation 

(Gilluly and Masursky, 1965; Johnson, 1965; Kay and 

Crawford, 1964; Evans, 1972a, b; and Stewart and 

McKee, 1977). In this report, some limits are established for the Roberts Mountains Formation away 

from the type area, to avoid placing mappable thickbedded and coarse-grained limestone of Devonian age 

in the upper part of the formation and to conform with 

previous work. The Roberts Mountains Formation 

away from the type area is subdivided in three parts: 

(1) a basal chert or cherty carbonate unit; (2) a
6 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

laminated limestone unit; and (3) locally, an upper interbedded laminated limestone and thick-bedded 

coarse-grained carbonate unit. The cherty unit is the 

only marker bed of regional extent; regional correlations of rocks within the formation are based mainly on 

fossils. Berry and Boucot (1970, p. 206) recognized 

only two facies of the Roberts Mountains Formation: a 

platy limestone facies and a thick-bedded facies. Their 

platy limestone facies included the basal cherty unit. 

Some of the rocks in the Tuscarora Mountains that 

they and Merriam and McKee (1976) included in their 

thick-bedded facies are here excluded from the Roberts 

Mountains Formation.

The thickness and distribution of the units in the 

Roberts Mountains Formation and the relations of the 

units to underlying, laterally equivalent, and overlying 

rocks are shown on plate 2. The only conspicuous unit 

of regional extent in the Roberts Mountains Formation is the basal 0-50 m of interbedded chert, 

limestone, and dolomite. This cherty unit was called 

the upper member of the Gatecliff Formation in the Toquima Range by Kay and Crawford (1964), and was 

called the upper member of the Happy Camp Formation in the Independence Mountains by Kerr (1962).

A laminated rock that weathers platy and that consists mainly of calcite, dolomite, quartz and feldspar 

silt, and clay minerals forms the bulk of the Roberts 

Mountains Formation. Minor, but ubiquitous, constituents, which generally form less than 1 percent of 

laminated rock, are carbonaceous material and pyrite 

in unoxidized rock and iron oxides in oxidized rock. 

The term "laminated limestone" is used to describe 

this rock although much of it contains less than 50 percent calcite. The rock is very fine grained (the average 

detrital grain size is large silt), and it fizzes with dilute 

acid. Relative proportions of calcite, dolomite, quartz, 

and clay cannot be determined with hand lens and acid. 

The laminated rock was called Masket Shale in the Toquima Range by Kay and Crawford (1964), and was 

called the Taylor Canyon Formation in the Independence Mountains by Kerr (1962).

The Roberts Mountains Formation in most areas is 

restricted to strata extending upward from the base of 

the cherty unit to the base of the lowest coarse-grained 

massive limestone that can be mapped for about 3 km. 

In a few places, lenticular coarse-grained limestone 

beds of less than 3 km in extent are interbedded with 

laminated limestone. In these places, the upper contact 

of the Roberts Mountains is placed where coarsegrained massive beds become more abundant than 

fine-grained laminated beds. Using this restriction, 

coarse-grained nonlaminated limestone and dolomite 

form a major part of the Roberts Mountains Formation only in the type area, near Bootstrap mine in the 

Tuscarora Mountains, Goat Peak window in the

Shoshone Range, and Petes Canyon in the Toquima 

Range, and at Miniature Grand Canyon in the Monitor 

Range.

The type locality of the Roberts Mountains Formation is near the west-to-east gradation of laminated 

limestone to massive dolomite and near a south and 

southeast gradation to laminated slightly silty 

dolomite. The massive dolomite has been assigned to 

the Lone Mountain Dolomite and was not studied. The 

laminated dolomite at Lone Mountain, Mahogany 

Hills, Hot Creek Canyon, and Rawhide Mountain, 

which I studied and sampled, is herein excluded from 

the Roberts Mountains Formation. Merriam (1973b, 

p. 12-17) has assigned the laminated dolomite at these 

places to his unit 1 of the Lone Mountain Dolomite.

The cherty carbonate rock at the base is present 

throughout the Roberts Mountains Formation. In 

most areas this unit overlies thick-bedded limestone or 

dolomite of Early Silurian or Late Ordovician age. 

Locally in the Shoshone, Toiyabe, and Toquima 

Ranges, the cherty unit overlies laminated or thinbedded limestone that ranges in age from Early Ordovician to Late Ordovician. The upper contact of the 

Roberts Mountains Formation away from the type 

area is generally placed at the change from laminated 

limestone to laminated limestone interbedded with 

massive coarse-grained carbonate rock, or at the 

change from laminated limestone to massive carbonate 

rock only. In most places studied, this contact is above 

the Monograptus uniformis Zone, which is here used to 

indicate the base of Devonian rocks although no 

lithologic change occurs at this fossil zone. As a mappable unit, the Roberts Mountains Formation includes 

both Silurian and Devonian rocks.

Use of the M. uniformis Zone to indicate the base of 

the Devonian follows a recommendation of the committee established by the International Union of 

Geological Sciences and chaired by D. W. McLaren to 

select a boundary between the Silurian and Devonian 

Systems. This boundary has been accepted by some 

geologists (Berry, 1970; Berry and Boucot, 1970, p. 16; 

Berry and others, 1971, p. 1969; Klapper and others, 

1970; and Berdan and others, 1969). Other geologists, 

notably C. W. Merriam (1973a, b; Merriam and McKee, 

1976), disagree with this boundary and would place it 

somewhat higher on the basis of rugose corals.

There are exceptions to the above generalization 

about the upper contact of Roberts Mountains Formation. In parts of the Crescent Valley-Grass Valley area 

coarse-grained carbonate rock is absent above the 

laminated limestone. In those places the contact of the 

Roberts Mountains and the overlying Devonian Wenban Limestone locally can be defined by a subtle 

change based more on weathering characters than on 

composition. The upper contact of the Roberts Moun-
STRATIGRAPHY AND PETROLOGY OF THE ROBERTS MOUNTAINS FORMATION

tains Formation at the Carlin mine is placed at the 

base of a reddish-brown silty zone that is 6-10 m thick. 

The reddish-brown zone is overlain by very fine 

grained limestone that contains many features of turbidites but little silt or dolomite. Laminated limestone 

assigned to the Roberts Mountains Formation near the 

Swales Mountain is seemingly conformably overlain 

by Lower Mississippian very fine grained limestone 

that contains abundant borings (Ketner, 1970).

BASAL CHERTY UNIT

The basal chert, limestone, and dolomite of the 

Roberts Mountains Formation constitute the only 

distinctive subdivision of regional extent in the formation (pi. 2, fig. 1). This unit is erratic in thickness and 

locally it is absent. Ranges in thickness in most of the 

outcrop bands are as follows:

Meters

Shoshone Range ....................................... 3.0-25

Toiyabe Range......................................... 0.0-30

Toquima Range (upper unit of Gatecliff Formation of Kay 

and Crawford, 1964).................................. 0.0-50

Monitor Range ........................................ 6.0-31

Cortez Mountains ...................................... 0.0-23

Roberts Mountains .................................... 0.3-12

Sulphur Spring Range .................................. 0.6- 6

Tuscarora Mountains .................................. 3.0-25

Independence Mountains (upper unit of Happy Camp Formation of Kerr, 1962)................................. 0.0-30

In both the Toquima Range (Kay and Crawford, 1964) 

and the Independence Mountains (Kerr, 1962), abrupt

DSrl

changes in thickness have been attributed to exposures being in different thrust plates.

Typically, the cherty unit contains about half chert 

and half carbonate rock in alternating beds 2.5-50 cm 

thick (fig. 2). The chert content, however, ranges from 

25 to 100 percent and, generally, the thinner the zone, 

the greater the relative chert content. Most chert is 

black or brown and weathers black or brown, but 

medium-gray chert that weathers medium to light 

gray is found locally. Some beds that are seemingly 

pure chert at outcrop will be found to contain 20-40 

percent carbonate several centimeters beneath the surface. In detail, the chert ranges from even beds 

through lenticular beds to nodules parallel to bedding, 

and in places veins of chert up to 5 cm thick cut across 

as much as 60 cm of beds. The contact with the interbedded carbonate rock ranges from sharp to gradational and most of the chert beds grade laterally into 

carbonate rock. Bedding in the chert zone ranges from 

gently lensed to wildly contorted. Where the bedding 

is only slightly lensed the chert beds are commonly 

laminated on a 0.5- to 4-mm scale. Locally the cherty 

beds are brecciated, and at many places distribution of 

the brecciated chert indicates that the breccia is 

diagenetic and not related to tectonic forces.

Carbonate rock interbedded with the chert is commonly dark to very dark gray, very fine grained (<0.02 

mm), and laminated on a 0.25- to 2-mrn scale; it contains little detrital silt or clay. The insoluble residue is 

generally less than 5 percent in places where the beds 

are not replaced by chert (Mullens, 1979, sample 8135, 

loc. 8; sample 9063, loc. 14; and sample 7001, loc. 25). 

This lack of insoluble residue is in contrast to the mixFIGURE 1.—Basal cherty unit of the Roberts Mountains Formation 

exposed on the west side of Copenhagen Canyon, Monitor Range, 

Eureka County, Nev. Basal beds of laminated limestone unit of 

Roberts Mountains Formation (DSrl) cap cliff. Basal cherty unit 

(Src) is 31 m thick and conformably overlies the Hanson Creek 

Forma tion(SOh).

FIGURE 2.—Basal cherty unit of the Roberts Mountains Formation 

exposed near the south end of South Ravenswood window, central 

Shoshone Range, Lander County, Nev. Thicker beds are completely silicified; thinner beds are partly silicified. White streaks 

and nodules are calcite.
8 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

ture of quartz silt, clay, calcite, and dolomite typical of 

the bulk of the Roberts Mountains Formation.

The following slightly condensed field description of 

the cherty unit at Copenhagen Canyon, Monitor 

Range, Eureka County, is typical of the entire cherty 

unit where it exceeds 6 m in thickness.

Limestone and chert are interbedded, 31 m thick. 

Limestone is dark gray to black, very fine to fine 

grained, and occurs in beds 5-20 cm thick. Limestone 

tends to be very fine grained, slightly dolomitic, and in 

beds 5-10 cm thick in lower 21 m; it is coarser (fine) 

grained, not dolomitic, and in beds 10-20 cm thick in 

upper 10 m. Chert is very dark gray to brown and occurs in beds 1-5 cm thick that are locally laminated, 

and in nodules which are up to 50 cm long and 10 cm 

thick and whose long dimension parallels bedding. 

Chert in lower 5 m is vitreous and smooth weathering, 

and contains no carbonate rock; chert above is definitely silicified carbonate rock as beds grade both 

laterally and vertically into carbonate rock that has 

sandy texture on the surface. Chert in upper 3 m is in 

small irregular lenses 1-5 cm thick and 0.6-3 m long 

and weathers grayish brown. All beds in unit are 

gently lensed, but the ends of some chert beds are contorted and have intruded as much as 50 cm of adjacent 

rock. No gradation of chert to carbonate rock is observed at the intruded ends of the chert. The contortions and the intrusive nature were seemingly caused 

by compaction during diagenesis as contortions disappear within 5-60 cm upward. Beds in upper third of 

unit are slightly more lenticular than in lower twothirds. The lower 3 m contains more than 60 percent 

chert, the next 15 m above is about 50 percent chert, 

and the upper 13 m is about 40 percent chert. Unit 

forms banded zone, and upper 15 m weathers to conspicuous cliff.

At Pablo Canyon in the Toiyabe Range and at Black 

Cliff Canyon and Petes Canyon in the Toquima Range, 

the cherty unit contains scattered 0.4- to 5-cm-thick 

beds that seemingly are silicified claystone instead of 

carbonate rocks.

Where the cherty unit is less than 3 m thick it is 

dominantly irregularly bedded chert that retains few 

characters to indicate that the chert is silicified carbonate rock.

STRATIGRAPHIC RELATIONS OF THE CHERTY UNIT

The cherty unit, as used here, includes the black 

chert unit that forms the upper part of the Gatecliff 

Formation of Kay and Crawford (1964) in the Toquima 

Range, and the upper member of the Happy Camp Formation of Kerr (1962, p. 446-447) in the Independence 

Mountains. In most of the east and northeast part of 

the area studied, the cherty unit conformably overlies

thick- to medium-bedded dolomite and limestone 

assigned to the Hanson Creek Formation of Ordovician and, locally, Early Silurian age. In parts of the 

Shoshone, Toquima, and Toiyabe Ranges, the cherty 

unit locally conformably overlies rocks assigned to the 

Hanson Creek Formation or the basal unit of the 

Gatecliff Formation of Kay and Crawford (1964). At 

Black Cliff Canyon in the Toquima Range the cherty 

unit overlies, in probable conformable contact, very 

dark gray to black, laminated, very fine grained 

limestone of Late Ordovician age. In other places in 

these ranges the chert unconformably overlies beds 

assigned to the Copenhagen Formation of Middle Ordovician age or to part of the Pogonip Group of Early 

Ordovician age (Stewart and McKee, 1977).

The Upper Ordovician laminated limestone at Black 

Cliff Canyon is typical of rocks assigned to the transitional facies of Roberts (1969); thus the cherty unit 

conformably overlies both transitional shaly limestone 

and coarse-grained carbonate rock deposited eastward, 

and shelf rocks of the geosyncline. Also, west of the 

area of probable conformable contact with uppermost 

Ordovician rocks, the chert unconformably overlies 

Middle and Lower Ordovician rocks. The cherty unit 

seemingly conformably underlies laminated limestone 

typical of the bulk of the Roberts Mountains Formation.

LAMINATED LIMESTONE UNIT

GENERAL CHARACTER AND COMPOSITION

A laminated limestone unit that weathers platy 

forms the bulk of the Roberts Mountains Formation. 

Locally the unit contains medium- to coarse-grained 

limestone in lenticular beds a few centimeters to a few 

meters thick and thin beds of chert and small chert 

nodules. Nowhere do these coarser grained beds and 

chert make up more than 2 percent of the unit, and no 

observed coarse-grained limestone or cherty zone extended for more than 1 km. Because the coarser 

limestone and chert form such a small part of the 

laminated limestone unit and because the gold ore 

deposits are in laminated limestone, the emphasis in 

this report is on the laminated rock.

In fresh exposures, the laminated limestone is black 

to very dark gray and appears massive. Slight 

weathering produces conspicuous partings and a 

medium-gray color (fig. 3); more extensive weathering 

produces flags and small plates that are gray, tan, pale 

red, and reddish brown and that disintegrate to soil 

(fig. 4). Typically, the end result is a smooth slope 

uninterrupted by ledges (fig. 5). The tan, pale-red, and 

reddish-brown colors of plates in the Roberts Mountains Formation locally serve to distinguish the formation from Ordovician or younger Devonian laminated
STRATIGRAPHY AND PETROLOGY OF THE ROBERTS MOUNTAINS FORMATION

:>% m-*9*£i3*^v.^ X..

^^ -" - "^ —^Bfc « « »t - -** '

^air^ v /. -**rs -- «f . \ ..L. • .> .j^dt1

FIGURE 3.—Laminated limestone unit in the Roberts Mountains 

Formation, north-central Nevada. A, Outcrop in Petes Canyon 

area, Toquima Range. B, Man-made exposure in roadcut in Maggie Creek Canyon, Eureka County.

limestones of other formations that tend to weather 

black and dark gray.

The weathering is along laminations which are not 

conspicuous in fresh rock but which are conspicuous in 

weathered rock and in thin sections. Figures 6 and 7 

show some details of these laminations. Most laminations are even and extend a few meters; some, however, 

are lenticular and contorted (fig. IB and D) and extend 

a few millimeters to a few centimeters. The lenticular 

and contorted laminations seem more abundant in the 

upper part of the laminated limestone unit in the 

Tuscarora and Roberts Mountains than elsewhere.

The laminations range in thickness from less than 

0.05 to about 4 mm, averaging about 0.2 mm. There 

seems to be no universal rhythmic composition control 

of the laminations. Concentrations of carbonaceous

*

FIGURE 4.—Weathered laminated limestone unit in the Roberts 

Mountains Formation, Nev. A, Slightly weathered; Petes Canyon 

area, Toquima Range. Zone shown is weathered phase of zone 

shown in figure 3A. B, Weathered; exposed along bulldozer cut, 

Coal Canyon area, northern Simpson Park Mountains.

material and extremely fine grained pyrite generally 

form one set in a pair of laminations in unoxidized 

rock, and concentrations of iron oxide generally form 

one set in a pair of laminations in oxidized rock. These 

types of laminations separate other laminations that 

range in composition from relatively pure calcite to 

quartz silt. Locally, carbonaceous material and iron 

minerals are absent and laminations of relatively pure 

calcite separate laminations that contain abundant 

detrital material. Laminations relatively rich in 

detrital material do not show graded bedding.

Triangular diagrams showing amounts of calcite, 

dolomite, insoluble residue, quartz and feldspar, clay 

minerals, and total carbonate for all unaltered 

laminated limestone samples from the Roberts Moun-
10 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

FIGURE 5.—Slope formed in laminated limestone unit of Roberts 

Mountains Formation, northeast side of Maggie Creek Canyon, 

Eureka County, Nev. Ledges shown in upper right part of 

photograph are lenticular beds of coarse-grained limestone within 

the laminated limestone unit. Shows about 150 m vertical relief.

FIGURE 6.—Fresh and weathered laminated limestone from the Roberts Mountains Formation, Nev. A, Hand sample of fresh 

limestone, Rattlesnake Canyon, Eureka County. White spots are 

places where rock has been powdered. Conspicuous laminations 

near top and bottom of specimen are formed by epigenetic pyrite 

(Mullens, 1979, sample 8082, loc. 2, table 1). B, Sawed sample of 

weathered limestone from upper part of formation 1.5 km west of 

Carlin mine (Mullens, 1979, sample 7003, loc. 28, table 1).

tains Formation are shown on figure 8. Rock is considered altered if it contains more than 10 percent 

epigenetic minerals or more than 10 percent diagenetic 

silica. Triangular diagrams that show similar features 

for all rocks collected at each locality listed on plate 2 

are shown on plate 3, which indicates that the wide 

spread in composition of laminated limestone shown in 

figure 8 is typical for most localities. The major exceptions to this general rule are in the southern Toiyabe 

and Toquima Ranges.

Laminated limestone in the southern Toiyabe and 

Toquima Ranges (pi. 3, nos. 32, 33, 34, and 36) is more 

dolomitic, tends to weather blocky instead of platy, 

and contains more silt and iron oxide than laminated 

limestone in other areas (pi. 3). The blocky weathering 

and high dolomite and silt content of rocks in the 

southern Toiyabe and Toquima Ranges reflect a facies 

change, but outcrops in those areas are so sparse, 

isolated, and complicated by faults that little detail of 

the change can be determined.

The average of all unaltered laminated limestone 

samples collected is about 70 percent total carbonate 

(45 percent calcite and 25 percent dolomite), and about 

30 percent insoluble residue (22 percent quartz and 

feldspar silt and 8 percent clay minerals). The samples 

do not cluster near the average, but show a nearly 

uniform distribution in a relatively wide range of composition. Parameters for this wide range are 5-95 percent calcite, 0-50 percent dolomite, 5-60 percent insoluble residue (fig. 8A); and 1-15 percent clay 

minerals, 40-95 percent carbonate, and 5-45 percent 

quartz and feldspar (fig. 8-B). Because the composition 

of the laminated limestone does not change greatly 

with geographic position, interpretations that relate 

composition to source and paleogeography are severely restricted.

Along with the wide range in composition, figure 8 

shows three features worthy of mention. First is the 

tendency for a vertical distribution in composition 

based on an arbitrary division of the laminated unit at 

each locality into two halves. Rocks in the lower half 

are more likely to contain 50 percent or more calcite (38 

of 66 samples) than rocks in the upper half (11 of 42 

samples). Second is the tendency for insoluble residue 

and dolomite to increase in about a 58:42 ratio as 

calcite decreases, and third is the tendency for quartz 

and feldspar, as compared to clay, to increase in a ratio 

of about 3:1 as total carbonate decreases.

DISTRIBUTION AND THICKNESS

The laminated limestone unit extends westward and 

northwestward from a probable wedge edge that is 

concealed in the valley between the Sulphur Spring 

Range and the Diamond Mountains. The unit is not 

present in the Pinon Range and its eastern extent is in
STRATIGRAPHY AND PETROLOGY OF THE ROBERTS MOUNTAINS FORMATION 11

FIGURE 7.—Thin sections of laminated limestone 

from the Roberts Mountains Formation, Nev. A, 

Evenly laminated fresh limestone from Rattlesnake Canyon section. Laminations conspicuous because of carbonaceous material. Irregular black lens is pyrite enclosed by secondary 

quartz and clay (Mullens, 1979, sample 8058, loc. 

2, table 1). B, Slightly unevenly laminated fresh 

limestone from Rattlesnake Canyon section. 

Laminations conspicuous because of carbonaceous material (Mullens, 1979, sample 8079, 

loc. 2, table 1). C, Weathered evenly laminated 

limestone. Lamination conspicuous because of 

iron oxide. Sample from 1.5 km west of Carlin 

mine (Mullens, 1979, sample 7003, loc. 28, table 

1). .D, Fresh irregularly laminated limestone. Gold 

ore from Carlin mine. Large white seam in lower 

part is where rock pulled apart (Mullens, 1979, 

sample 7006, loc. 3, table 1).

northern Pine Valley between the Pinon Range and 

Cortez Mountains. North of Pine Valley, the edge of 

the laminated limestone unit is inferred to trend eastnortheasterly to the Pequop Mountains, but the edge 

is not exposed. The laminated limestone unit disappears eastward and southward by grading laterally into laminated dolomite and coarse-grained dolomite. 

The original west, northwest, and southwest extent of 

the laminated limestone unit is not known, because of 

structural complications and lack of outcrop. The exposures at Wall, Pablo, and Black Cliff Canyons contain laminated to medium-bedded dolomite and are interpreted to be near the edge of the laminated 

limestone unit.

The known thickness and distribution of the 

laminated limestone (pi. 2) suggest two depocenters. 

These depocenters are based on sections that contain 

more than 700 m of laminated limestone that apparently is not repeated by faults. If these sections contain 

unrecognized faults, the interpretations made herein 

must be modified. One depocenter extends from near 

Swales Mountain to near Antelope Peak north of 

Wells. Near Swales Mountain, a diamond-drill core 

hole penetrated 823 m of seemingly unfaulted 

laminated limestone that is assigned to the Roberts 

Mountains (Ketner and others, 1968) without reaching 

the cherty unit or recognizable Ordovician beds. No 

fossils were found in the core and the assignment was 

made on the basis of lithologic similarity. The 

laminated limestone near Swales Mountain is seeming-
12 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

DOLOMITE

I

DOLOMITE

INSOLUBLE CALCITE 

RESIDUE

INSOLUBLE RESIDUE 50

A

CLAY MINERALS

I PI AV <;n.

CALCITE 

wi

MINERALS

QUARTZ CARBONATE

AND 

FELDSPAR

QUARTZ AND FELDSPAR CARBONATE

EXPLANATION

• Upper part of formation 

+ Lower part of formation 

X Stratigraphic position in formation not known

FIGURE 8.—Composition of unaltered laminated limestone samples from the Roberts Mountains Formation, Nev. A, Insoluble residue, calcite, and dolomite. B, Total carbonate, combined quartz and feldspar, and clay minerals.
STRATIGRAPHY AND PETROLOGY OF THE ROBERTS MOUNTAINS FORMATION 13

ly overlain conformably by Lower Mississippian rocks 

(Ketner, 1970; Evans and Ketner, 1971). Ketner (1970) 

believed that laminated limestone was deposited during both Silurian and Devonian time. About 760 m of 

laminated limestone overlies the cherty unit and 

underlies coarse-grained limestone at Antelope Peak 

reported by Peterson (1968) to be of Middle Devonian 

age. Peterson indicated in his text that in the Antelope 

Peak area the laminated limestone assigned to the 

Roberts Mountains is about 460 m thick whereas in his 

cross section he showed it to be about 760 m thick. 

Faults and poor exposures prohibit exact measurements at Antelope Peak but my measurements indicate that 760 m is more reasonable than 460 m. The 

depocenter extending from Swales Mountain to near 

Antelope Peak nearly coincides with a depocenter for 

Ordovician quartzite reported by Ketner (1968, fig. 3).

The other depocenter for laminated limestone is in 

the Crescent Valley-Grass Valley area. Gilluly and 

Masursky (1965, p. 25-38) separated autochthonous 

Silurian and Devonian rocks in the Crescent Valley 

area into the Roberts Mountains Formation and the 

overlying Wenban Limestone of Devonian age. Locally 

this division is based on thick-bedded coarse-grained 

limestone of Devonian age that is assigned to the Wenban Limestone. In other places, coarse-grained 

limestone is absent and laminated limestone assigned 

to the Wenban Limestone directly overlies laminated 

limestone in the Roberts Mountains Formation. At 

outcrop, the Wenban locally can be separated from the 

Roberts Mountains Formation because of its different 

weathering characteristics and the occurrence of Tentaculites and Styliolina in the Wenban. This contact 

probably cannot be detected in unweathered rock. A 

diamond drill hole, 670 m deep, in Mill Canyon east of 

Crescent Valley crossed the projected subsurface contact of the Roberts Mountains and Wenban, but I 

could detect no change in the core that could be used as 

a contact.

Stewart and McKee (1968) mapped as Roberts 

Mountains Formation about 1,200 m of laminated 

limestone that is partly altered to hornfels in Grass 

Valley. This is the youngest rock exposed beneath a 

thrust and Quaternary basin fill. I could find no faults 

that repeated the section nor could I find a method of 

dividing the rocks into the Roberts Mountains Formation and Wenban Limestone. I suspect, however, that 

the upper 600 m is a lateral equivalent to the Wenban 

exposed in the Crescent Valley area.

The depocenters for the thick laminated limestone 

unit may connect southeast of Maggie Creek Canyon. 

This possibility would involve a southeastward 

thickening of the laminated limestone unit in the direction in which I assume the laminated limestone grades 

into thick-bedded carbonate rock. I doubt that the

depocenters connect, but control points are not 

available to prove or refute this possibility. No control 

points are available to obtain the thickness of 

laminated limestone north and northwest of the 

Swales Mountain-Antelope Peak depocenter. The 

laminated limestone in the Grass Valley-Crescent 

Valley area seems to thin westward, northwestward, 

and southwestward. Several beds of coarse-grained 

carbonate of probable Late Silurian age occur about 

460 m above the basal cherty unit, just beneath upper 

plate rocks at Goat Peak window in the west side of the 

northern Shoshone Range. Thick-bedded pelletal 

limestone of Late Silurian age is interbedded with 

laminated limestone at Bootstrap mine, and the base 

of the Roberts Mountains Formation is not exposed; so 

the thickness of the laminated limestone unit that is 

presumably beneath the exposed section could not be 

obtained. Southwestward of Grass Valley, a coarsegrained limestone about 9 m thick and of Early Devonian age overlies about 460 m of laminated limestone 

at Point of Rocks. The upper 22 m of the laminated 

limestone unit at Point of Rocks contains thin beds of 

bioclastic limestone. I place the upper contact of the 

Roberts Mountains at the base of the 9-m bed, 

although Stewart and McKee (1977) placed the upper 

contact of the Roberts Mountains at the lowest 

bioclastic limestone.

At the type section of the Roberts Mountains Formation, the laminated limestone unit is about 120 m 

thick and entirely of Silurian age. Sixteen kilometers 

northwestward at Coal Canyon the laminated 

limestone is about 460 m thick and includes beds of 

Devonian age in the upper 155 m. At Rattlesnake Canyon, the laminated limestone unit is about 310 m thick 

and includes Devonian beds in the upper 30 m. The 

Rattlesnake section lies slightly west and presumably 

closer to the middle of the Cordilleran geosyncline; 

thus, in theory, the laminated limestone should be 

thicker than at Coal Canyon. Rattlesnake Canyon, 

however, is near the crest of the Cortez-Uinta axis of 

Roberts (1968), which I interpret as being high enough 

to have caused deposition of coarse-grained limestone 

instead of laminated limestone in this area during Early Devonian time. I also attribute the absence of 

laminated limestone in the Pinon Range to this slight 

positive zone.

At Maggie Creek Canyon and the Carlin mine area 

the laminated limestone is faulted (Evans, 1972a, 

Evans and Cress, 1972), so that accurate 

measurements cannot be obtained. Evans (oral commun., 1970) believed that there was about 460 m of 

laminated limestone in these areas. Near the Carlin 

mine and at Maggie Creek Canyon the upper part of 

the laminated limestone contains a few lenses of 

coarse-grained limestone as much as 3.5 m thick.
14 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

ALTERATION PETROGRAPHY OF THE EAMINATED LIMESTONE

Locally the laminated limestone is visibly altered; 

the degree of alteration ranges from a minor replacement by quartz, slight increase in clay content, and 

minor decrease in calcite content to complete silicification or conversion to hornfels. The dividing point between altered and unaltered rocks used here and in the 

tabulated data of mineral and chemical composition of 

the rocks (Mullens, 1979) is based on 10 percent 

epigenetic minerals, or more than 10 percent 

diagenetic silica. The laminated limestone is probably 

easy to metamorphose as traces of epigenetic amphibole are found in about half the samples that 

megascopically seemed to be unaltered. In addition, 

sepiolite is found in three samples and talc in one sample that seemed to be unaltered.

The most conspicuous altered zones are silicified 

zones that are as much as several meters thick and 

that range in length from a few hundred to several 

thousand meters. These zones roughly parallel bedding, and form ledges. In these zones, the megatexture and laminations are faithfully preserved, the 

replacement by silica is complete, the color changes to 

dark brown and pale red, and the rock does not weather 

to plates. These zones are most common in the line of 

outcrop from Maggie Creek Canyon to Bootstrap mine 

and possibly are related to thrust faults of the Antler 

orogeny. A second and less conspicuous alteration is 

incomplete silicification that changes the texture of 

the laminated limestone to a rock resembling siltstone 

or very fine grained sandstone, generally alters the color to pale reddish orange, but does not alter the platy 

weathering character of the rock. These zones are a few 

meters to about 100 m thick and are fairly lenticular 

(most are only about 200 m long). These zones commonly cannot be related directly to faults or intrusive 

rock. Both the Carlin and Cortez mines are associated 

with silicified zones in the Roberts Mountains Formation that contain features common to both of these 

types of silicification.

In addition to some silicification, the gold ore at the 

Carlin and Cortez mines is in rocks that have added 

clay and reduced calcite content; the southwest pit of 

the Carlin mine contains many iron-oxide Liesegang 

rings that cross laminations. The southwest pit is the 

only place observed where features associated with 

silicification commonly cross laminations.

Near intrusives, the laminated limestone is locally 

altered to scapolite-bearing rock and hornfels. The 

largest scapolite-bearing zone observed is along the 

east side of the Tuscarora Mountains (Evans, 1972a, 

b). The Grass Valley outcrop is mainly altered to hornfels.

The laminated limestone consists of varying 

amounts of angular quartz and feldspar silt and very 

fine sand, silt-sized irregular grains to euhedral 

rhombs of dolomite and calcite, and clay minerals all 

set in an extremely fine grained calcite matrix. Fresh 

rock contains disseminated grains and tiny stringers 

of pyrite; specks, films, and coatings of carbonaceous 

material; and minute inclusions of carbonaceous 

material and pyrite in the calcite matrix. Weathered 

rock contains grains and stringers of iron oxide. In 

general, a slice the size of a thin section, cut across "the 

laminations, is representative of the sample; but the 

sample is heterogeneous at a 1- to 2-mm scale (see figs. 

10, 11). Graded bedding, though extremely scarce in 

rocks collected during this study, is present in the 

laminated limestone in the Roberts Mountains area, 

according to Winterer and Murphy (1960, p. 123-124).

X-ray diffraction studies show that calcite and 

dolomite in the laminated limestone are nearly pure except in samples collected at Black Cliff Canyon in the 

southern Toquima Range. The calcite does not contain 

enough magnesium and the dolomite does not contain 

enough excess calcium to cause peak shifts in the 

4 °-60 ° 20 range. The amount of iron contained in the 

calcite and dolomite was not determined but is 

estimated from oxide analyses and X-ray diffraction 

studies to be less than 0.1 percent.

Information on chemical and mineralogical composition given in this report is a summary of integrated 

chemical, petrographic, and X-ray diffraction studies 

of individual samples collected. Amounts of the 

various minerals in individual samples collected are 

reported in detail elsewhere (Mullens, 1979). The 

amounts of two minor constituents, pyrite and iron oxide, are exceptions, based on point counts. Carbonaceous material, another minor constituent, was 

not determined although organic carbon, shown for 

most samples (Mullens, 1979), was determined by 

chemical methods. Chemical and X-ray diffraction 

studies are probably more accurate in determining the 

relative amounts of the major minerals than point 

counts on thin sections because of the fine-grained 

character and heterogeneous nature of the rock in the 

2-mm range.

Many of the samples collected contain veins and 

veinlets of epigenetic calcite, and a few contain 

veinlets of epigenetic quartz. For the most part the 

vein calcite is not separated from deposited calcite in 

data shown by Mullens (1979). Secondary quartz 

shown in the data (Mullens, 1979) is mainly diagenetic 

chert or epigenetic replacement of minerals by quartz; 

epigenetic quartz veins are excluded from the data.

Photomicrographs illustrating the range of textures
STRATIGRAPHY AND PETROLOGY OF THE ROBERTS MOUNTAINS FORMATION 15

^t^i^c '. fe. •*.>•? > -sir. '^ x. -

a.w*i-«:'-:A^v.^.^

' *'

FIGURE 9.—Photomicrographs of laminated limestone from Rattlesnake Canyon. Larger grains are labelled: C, calcite; D, 

dolomite; Q, quartz; F, feldspar; I, illite; Z, zircon. P, large 

opaque grain is pyrite partly altered to red iron oxide; rq, areas 

where calcite has replaced quartz; cm, film of pure carbonaceous material. All plain light. A, Matrix is mainly calcite; 

opaque grains are red iron oxide (Mullens, 1979, sample 8055, 

loc. 2, table 1). B, Fine-grained light-gray matrix is calcite; 

dark areas are mainly carbonaceous calcite (Mullens, 1979, 

sample 8058, loc. 2, table 1). C, Dark matrix is carbonaceous 

calcite (Mullens, 1979, sample 8079, loc. 2, table 1).

and composition of unaltered laminated limestone are 

shown in figures 9 to 12. The composition given for the 

samples includes information from chemical and X-ray 

data as well as point counts, and the photomicrographs are not necessarily representative of the entire 

sample. Figure 9A is a photomicrograph of a highcalcite (87 percent), and low-dolomite (5 percent), 

quartz (7 percent), and clay-mineral (1 percent) sample 

from the lower part of the laminated limestone unit at 

Rattlesnake Canyon. Megascopically the rock seems 

unoxidized but microscopic study discloses specks of 

red iron oxide. Figure 9B shows fresh rock that approaches the "average" composition (see p. 10); this 

rock contains 50 percent calcite, 22 percent dolomite, 

20 percent quartz, 2 percent potassium-feldspar, and 6 

percent clay minerals. Figure 9C also shows a 

near-"average" rock; it contains 40 percent calcite, 23
16 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

FIGURE 10.—Photomicrographs of laminated limestone from 1.5 km 

west of the Carlin mine. Plain light. A, Heterogeneity of rock at 

1- to 2-mm scale. B, Many discrete particles of iron oxide in the 

0.001- to 0.005-mm range. Matrix shown in B is mainly calcite and 

clay. Iron oxide grains not marked. Quartz (Q) and dolomite (D) 

form large grains (Mullens, 1979, sample 7003, loc. 28, table 1).

percent dolomite, 26 percent quartz of which 2 percent 

is secondary, 2 percent potassium-feldspar, and 9 percent clay minerals. Figure 10 shows a weathered sample that contains 37 percent calcite, 27 percent 

dolomite, 18 percent quartz, 5 percent potassiumfeldspar, and 12 percent clay minerals. Figure 11 

shows parts of two different laminations in a sample 

with 9 percent calcite, 52 percent dolomite, 27 percent 

quartz, 4 percent potassium-feldspar, and 7 percent 

clay minerals. Figure 12 is a photomicrograph of a section of one of the thin coarse-grained limestone beds 

that are sparsely interbedded with the laminated 

limestone at Rattlesnake Canyon.

Calcite is the most abundant mineral in most of the 

laminated limestone, and most of this calcite forms the 

matrix in which other minerals are set. The matrix has

f'B

Q

FIGURE 11.—Photomicrograph of laminated dolomite from Mill Canyon, Toquima Range. Laminations are in same thin section. 

Material between grains is mainly calcite, and opaque grains are 

red iron oxide. Note that dolomite approaches mosaic texture. D, 

dolomite; Q, quartz; C?, possible calcite. Plain light (Mullens 

1979, sample 9066, loc. 31, table 1). A, Lamination composed 

mainly of grains less than 0.04 mm across. B, Lamination that 

contains grains more than 0.1 mm across.

all gradations from near opaque, in which no grains can 

be observed, to slightly cloudy and composed of grains 

0.002 to 0.02 mm in size. Both end members can be 

found in most samples of laminated limestone, 

although the samples containing more than 70 percent 

calcite tend to be mainly mosaics of anhedral grains 

that are transparent or cloudy instead of nearly 

opaque. The near-opaque matrix can be determined as 

mainly a carbonate mineral under crossed nicols. 

Chemical and X-ray data indicate that the matrix is 

mainly calcite. The near-opaque calcite contains submicrometer specks of opaque material that is assumed 

to be mainly carbonaceous material and pyrite. The
STRATIGRAPHY AND PETROLOGY OF THE ROBERTS MOUNTAINS FORMATION 17

FIGURE 12.—Photomicrograph of coarse-grained limestone interbedded with laminated limestone at Rattlesnake Canyon section. 

Plain light. Rock is mainly calcite. Some quartz (Q) grains marked 

(Mullens, 1979, sample 8078, loc. 2, table 1).

cloudy matrix consists of tiny anhedral grains packed 

in a semimosaic pattern with submicrometer specks of 

opaque material along the grain boundaries. I interpret 

the semimosaic texture as slight recrystallizing of the 

calcite, although the texture may be due to original 

packing of tiny grains. Most laminated limestone 

samples also contain a minor amount of calcite in 

anhedral grains 0.03 to 0.15 mm in size. A few of the 

larger grains of calcite seem to be primary, others seem 

to be the result of "pinpoint" secondary crystallization, and some seem to be fragments of fossils. The 

larger grains are more abundant in areas where the 

laminated limestone grades into or is interbedded with 

coarse-grained limestone. In addition to the grains, 

calcite in quantitatively minor amounts but numerous 

occurrences replaces parts of quartz and feldspar 

grains. Generally this calcite is partly in continuity 

with matrix calcite; if the replacement is complete, the 

resulting grain of calcite cannot be identified definitely 

as replacement of a detrital grain. This partial replacement of quartz and feldspar by calcite is a fairly common phenomenon in laminated limestone, but in many 

of the sections examined, secondary quartz in tiny 

blebs and stringers has replaced calcite. Not uncommonly, both calcite replacement of detrital grains and 

quartz replacement of calcite are observed in the same 

section.

Dolomite is the second most abundant mineral in 

most samples of laminated limestone. Dolomite identified in thin sections occurred in irregular grains to 

euhedral rhombs that range in size from 0.02 to 0.12 

mm, averaging about 0.045 mm. Generally, identifiable dolomite in thin sections amounts to 80-90 percent of the dolomite indicated by chemical and X-ray 

studies. Part of this discrepancy is interpreted as indicating that some of the grains of dolomite were so 

small that they could not be separated from the calcite 

matrix; the remainder includes larger carbonate grains 

that could not be positively identified as dolomite instead of calcite. Staining techniques to determine the 

relative amounts of calcite and dolomite are of little 

use because of the small grain size and the iron oxide or 

carbonaceous smear on cut sections. The dolomite 

grains are set in a calcite matrix; however, textures 

that I would interpret to indicate that the dolomite 

had replaced calcite are absent. In laminations composed mainly of dolomite, euhedral rhombs seem to 

replace irregular dolomite grains. None of the dolomite 

observed is "mixed grained"; a mixture might have indicated a true detrital origin from a preexisting 

dolomite. In general, irregular grains of dolomite are 

relatively more abundant as compared to euhedral 

rhombs in rocks that contain 2-20 percent dolomite, 

whereas subhedral to euhedral rhombs far outnumber 

irregular grains in rocks that contain more than 25 percent dolomite. Zoned crystals are common in rocks 

that contain more than 25 percent dolomite. The irregular shape of dolomite grains is interpreted as mainly the result of solution or imperfect crystallization of 

rhombs rather than the result of abrading.

In the range of 4 °-60 ° 20, X-ray diffraction indicates 

that most dolomite in the laminated limestone is close 

to pure dolomite; peak distances are within 0.1 ° of pure 

dolomite in all but a few samples. The samples were 

not run past 60° 20, where Goldsmith and Graf (1958, 

fig. 1) showed that shift in peaks for impure carbonates 

was larger. In appearance and purity the dolomite is 

very similar to dolomite in Cretaceous marine sandstone which Sabins (1962) interpreted as primary 

dolomite. The texture of dolomite in the laminated 

limestone differs considerably from the mosaic texture 

of laterally equivalent laminated dolomite that contains little silt and is found at Lone Mountain, 

Mahogany Hills, and southern Monitor Range, and in 

the Hot Creek Range (fig. 13). Merriam (1973b, p. 

12-17) assigned the laterally equivalent laminated
18 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

dolomite to unit 1 of the Lone Mountain Dolomite. The 

rock shown on figure 13 is interpreted as secondary 

dolomite.

Detrital grains consisting mainly of quartz, but including minor amounts of potassium-feldspar and 

plagioclase feldspar, occur in all laminated limestone. 

The quartz and potassium-feldspar grains range in size 

from 0.02 to 0.15 mm, averaging about 0.055 mm. In 

most laminated rocks examined, the range is from 0.03 

to 0.08 mm and the number of grains tends to be 

skewed only moderately below the 0.055-mm average, 

which indicates that the weight percent of detrital 

grains is highly skewed toward the larger grains. I interpret the skewness to indicate that many of the small 

grains were completely dissolved during deposition or 

completely replaced during diagenesis. Laminated 

limestone with detrital grains larger than 0.1 mm and 

with the wider range is mainly from the east and south

FIGURE 13.—Photomicrograph of secondary dolomite from Hot 

Creek Canyon, containing some detrital quartz (Q) and zircon (Z) 

grains. Plain light. Rock is typical of laminated dolomite in the 

less silty laminated dolomite at Lone Mountain (Eureka County), 

Mahogany Hills, Hot Creek Range, and southern Monitor Range. 

Note mosaic texture. Such laminated dolomite is the lateral 

equivalent of laminated limestone in the Roberts Mountains Formation (Mullens, 1979, sample 6901, loc. 17, table 1).

sides of the laminated limestone unit, where the unit 

grades into or is interbedded with coarse-grained carbonate rock. The detrital grains are mainly angular, 

although some of the grains that are larger than 0.08 

mm are rounded or are fragments of rounded grains. In 

about half the samples, the quartz and potassiumfeldspar grains are slightly corroded to deeply embayed and many of the grains are partly replaced by 

calcite. Generally, minute stringers and blebs of 

secondary quartz occur in samples where the quartz 

grains are embayed, a feature interpreted as indicating 

that the dissolved silica was not moved far before 

being redeposited. Few detrital quartz grains show undulatory extinction under crossed nicols, indicating 

that most quartz was derived mainly from preexisting 

sediments instead of from plutonic igneous rock or 

metamorphic rocks (Blatt and Christie, 1963, p. 574).

Plagioclase feldspar is relatively scarce in laminated 

limestone; its presence is more likely to be noted on 

X-ray diffraction traces than in thin sections. These 

diffractograms indicate that the plagioclase feldspar is 

albite. Plagioclase grains observed average about 0.03 

mm and range from 0.01 to 0.08 mm. Most plagioclase 

feldspar grains are severely embayed. Their smaller 

average size, compared to the size of quartz and 

potassium-feldspar grains, is probably due to the 

relatively high solubility of plagioclase.

The quartz-feldspar (both potassium-feldspar and 

plagioclase) ratio ranges from about 3:1 to more than 

100:1 in the samples studied. Wide ranges in this ratio 

are found in different samples collected at the same 

locality, but an average for all unaltered laminated 

limestones is about 7:1. Considering only quartz and 

feldspar, and ignoring clay minerals, the 7:1 ratio of 

quartz to feldspar indicates that the detrital material 

is subarkose in the classification of Pettijohn (1957, p. 

291, table 48).

Clay minerals are present in most laminated 

limestone; all the clay recognized by optical methods 

was either illite or chlorite. Kaolinite and mont: 

morillonite are present in some samples according to 

X-ray data, but they were never identified definitely in 

thin section. Montmorillonite is possibly more abundant than indicated (see Mullens, 1979), as the method 

of treating the samples would have lessened the 

chances of recognizing montmorillonite in the insoluble residue by X-ray diffraction. Some of the illite is interpreted as detrital; most, however, is probably 

related to diagenetic changes in detrital montmorillonite and to depth of burial (Miiller, 1967, p. 

155-156). A little illite occurs along epigenetic quartz 

seams and such illite is also epigenetic. The illite is 

commonly concentrated along laminations, although 

the long dimension of many flakes forms angles of 

15°-90° with the laminations. The flakes are clear and
STRATIGRAPHY AND PETROLOGY OF THE ROBERTS MOUNTAINS FORMATION 19

colorless; they range in size from 0.01 X 0.03 mm to 

0.03 X 0.15 mm, averaging about 0.02 X 0.08 mm. The 

flakes are not observed in "books" and most have 2Vs 

in the 10°-20° range. For these reasons they are called 

illite instead of muscovite, although most flakes are 

larger than material generally considered as illite. 

When X-rayed, the flakes give diffraction patterns 

nearly identical to those of muscovite except that the 

peaks are not as sharp. Ketner (1969, p. B25) reported 

that illite separated from slightly metamorphosed Ordovician argillite in the Cordilleran geosyncline gave a 

diffraction pattern nearly identical to that of 

muscovite. Epigenetic amphibole, in widespread but 

trace amounts, in the laminated limestone indicates 

that the limestone is slightly metamorphosed, so the illite might have been changed slightly.

Chlorite occurs in about one-fourth of the samples 

studied. The chlorite flakes are pale green and have 

about the same size range as illite. Optically, they have 

small (0°-10°) 2Vs. Some samples have flakes that are 

optically positive; others have flakes that are negative, 

but mixtures of positive and negative flakes are never 

found in the same sample. A detrital and diagenetic 

origin for most chlorite is assumed; Miiller (1967, p. 

142-146) indicated that much detrital montmorillonite 

entering seawater was changed to chlorite during 

diagenesis. Some chlorite, however, may be epigenetic 

and related to low-grade metamorphism.

X-ray diffraction indicates that kaolinite is most 

abundant in altered rocks at the Carlin mine, and is 

fairly abundant at Bootstrap mine and Maggie Creek 

Canyon where altered rocks are relatively common. 

Otherwise, kaolinite seems to occur mainly in samples 

that contain more than average iron oxide and in 

samples from the less calcitic upper part of the 

laminated limestone. The association of kaolinite with 

altered and weathered rocks probably indicates that 

much of the kaolinite is epigenetic.

The amount of organic carbon in many samples was 

determined in order to obtain information on the 

presence of carbonaceous material in laminated 

limestone. The mean organic carbon content of all 

laminated limestone samples analyzed is about 0.30 

percent, but these samples include fresh as well as 

weathered and altered rocks. The average organic carbon content of samples that I consider mainly unoxidized and unaltered is about 0.35 percent and 

clustered in the 0.20- to 0.45-percent range. The range 

in organic carbon in seemingly unoxidized samples is 

from 0.18 to 1.34 percent. A general observation, not 

confirmed by extensive sampling, is that carbonaceous 

material is locally selectively concentrated in highly 

fractured zones and near intrusive rocks. 

Only three samples collected during this study contain 

more than 1.0 percent organic carbon. One of these

(Mullens, 1979, sample 8001), from the base of the 

laminated limestone at Coal Canyon, a very clayey 

sample that contains abundant carbonaceous 

fragments of graptolites, has 1.34 percent organic carbon; another (Mullens, 1979, sample 7005), from a 

highly fractured zone where carbonaceous material is 

seemingly enriched epigenetically at the Carlin mine, 

contains 1.24 percent; the third (Mullens, 1979, sample 

7105), from Grass Valley, is from an area where the 

laminated limestone is thermally metamorphosed. J. 

Fred Smith, Jr. (written commun., 1971) found 4.2 percent organic carbon in a sample of the Roberts Mountains Formation exposed in a fault slice in sec. 36, T. 29 

N., R. 52 E., Elko County, Nev. Only eight of the 

samples collected contain between 0.50 and 1.0 percent 

organic carbon.

Using a factor of 1.22 (Gehman, 1962, p. 886) to convert the 0.35 percent organic carbon to carbonaceous 

material, the laminated limestone contains an average 

of about 0.42 percent carbonaceous material. This compares with 0.24 percent carbonaceous material in 346 

limestone samples and 1.14 percent organic content for 

1,066 shales analyzed by Gehman (1962, p. 885, fig. 1).

The type, or types, of carbonaceous material in the 

laminated limestone is not determined. In thin section, 

the carbonaceous material appears coaly and occurs in 

flakes, specks, and coatings that adhere to grains, as 

well as in tiny inclusions in the calcite matrix. The lack 

of permeability of fresh rock and the coaly nature of 

the carbonaceous material hinder recovery of carbonaceous material in cold organic solvents such as 

benzene, acetone, and sodium hydroxide on rock 

ground to minus-40 mesh. The fact that I never 

liberated enough carbonaceous material from this size 

material to discolor sodium hydroxide indicates that 

the carbonaceous material is not humate. Carbonaceous material in seven samples was separated by 

treating the rock with hydrochloric acid to remove carbonate minerals, hydrofluoric acid to remove silicate 

minerals, and then nitric acid to remove pyrite. After 

such treatment a fine black powder was obtained from 

each sample. When X-rayed, this powder gives a single 

broad curve approximately 10 ° 20 wide that has a high 

point at 26.5° 20. The curve is so broad that the carbonaceous material is interpreted as nearly amorphous, although the high point of the curve corresponds closely with the major graphite peak.

Pyrite, in minor quantity, is ubiquitous in unoxidized laminated limestone. The amount of pyrite is 

highly variable, ranging from less than 0.1 to about 2.0 

percent, averaging an estimated 0.5 percent. The 

pyrite includes both syngenetic and epigenetic 

varieties. Most recognizable pyrite is in disseminated 

anhedral to euhedral crystals, although in some
20 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

samples irregular grains of pyrite are concentrated 

along laminations. Pyrite recognizable in thin section, 

using reflected light with a petrographic microscope, 

ranges from grains of about 0.005 mm to stringers 

about 3 mm in length. Pyrite locally lines minute vugs, 

occurs in minute irregular stringers as large as 0.15 X 

3 mm that roughly parallel laminations, and occurs as 

subhedral to euhedral crystals associated with quartz 

veinlets. Some pyrite in grains of 0.005-0.01 mm forms 

spheres. Polished sections indicate that some 

unaltered rock contains pyrite in grains of less than 

0.005 mm but that other unaltered rock does not contain such pyrite. In thin sections the very fine grained 

pyrite (less than 0.005 mm) cannot be identified 

separately from much of the fine-grained carbonaceous 

material.

The pyrite content of laminated limestone probably 

has a uniform distribution in the field of 0.2-1.0 percent and the content of individual samples does not 

cluster about an average. A guess on "average" content is made here because gold ore has epigenetic 

pyrite (Wells and Mullens, 1973; Radtke and others, 

1972), and a background value of syngenetic pyrite is 

needed for comparison. I estimate the syngenetic 

pyrite content of laminated limestone to be about 0.25 

percent and the epigenetic pyrite to be about 0.25 percent. A relatively high epigenetic pyrite content seems 

reasonable, as about half the places where rocks were 

collected locally contain silicified zones or intrusive igneous rocks and traces of epigenetic pyrite.

The pyrite cannot be determined consistently as 

syngenetic or epigenetic. Epigenetic pyrite can be identified if it occurs in fractures or associated with quartz 

veinlets. Otherwise, I know of no way of determining 

the origin of the pyrite. Pyrite along laminations cannot be considered as entirely syngenetic because rocks 

that contain epigenetic pyrite along fractures generally contain more epigenetic pyrite along laminations 

than other rocks.

Different methods of determining original pyrite in 

laminated limestone yield different results. Point 

counts of pyrite in seemingly unoxidized laminated 

limestone indicate a range of less than 0.1 to about 2.0 

percent pyrite, averaging about 0.2 percent. Point 

counts of iron oxide in oxidized rock indicate an 

average of about 0.5 percent pyrite if all iron oxide is 

considered as being derived from pyrite. The laminated 

limestone generally contains no sulfur-bearing 

minerals besides pyrite and very minor and erratically 

distributed barite, although the carbonaceous material 

probably contains a little sulfur. Sulfur content of 

many samples that include unoxidized, oxidized, and 

altered rocks was determined (Mullens, 1979) with the 

thought that most of the sulfur would be in pyrite or

would have been derived from pyrite. The average 

sulfur content of all the samples is less than 0.10 percent; and the average of relatively unoxidized and 

unaltered rock is about 0.15 percent. This would indicate about 0.3 percent pyrite in "average" unoxidized laminated limestone. This figure is about the 

same as pyrite content calculated from FeO content 

(Mullens, 1979). The 0.3 percent determined by sulfur 

and FeO content is slightly higher than pyrite content 

as determined by point count, but it is low by a factor 

of nearly 2 if most iron oxide observed was derived 

from pyrite. Thin- and polished-section study indicates 

that fresh pyrite is extremely scarce; most pyrite 

observed has iron oxide borders. Thus, the average 

content of pyrite based on sulfur and FeO content is 

probably low in comparison with pyrite originally in 

the rock.

Some of the very fine grained (less than 0.005 mm) 

pyrite forms black scum that accumulates at the top of 

dilute acid used to dissolve the laminated limestone. 

This pyrite cannot be distinguished optically from the 

fine-grained carbonaceous material that also accumulates in the black scum. Seven unoxidized 

laminated limestone samples were treated with 

hydrochloric and hydrofluoric acids. Visible pyrite was 

removed from the residue which consisted mainly of 

black powder. This powder was X-rayed and two of the 

seven X-ray diffractograms showed a strong pyrite 

pattern. The absence of pyrite in five residues does not 

indicate that those five rocks contain no ultra-finegrained pyrite. Some fine-grained pyrite can be dissolved in extremely dilute acid or in distilled water contaminated only by air (H. W. Lakin, oral commun., 

1970).

HEAVY MINERALS

Heavy minerals obtained by centrifuging the insoluble residue of 50 g of laminated limestone in 

bromoform (specific gravity about 2.89) include four 

types of minerals—detrital, syngenetic, diagenetic, 

and epigenetic. Weight of all heavy minerals obtained 

from 50 g of unaltered limestone ranged from 1.0 g (2 

percent) to less than 0.005 g (0.01 percent), and the median was about 0.15 g (0.3 percent). In general, samples 

above the median simply contain more syngenetic, 

diagenetic, or epigenetic iron minerals; samples below 

the median also consist mainly of iron minerals as true 

detrital heavy minerals never exceeded 0.10 percent of 

unaltered rock.

The median of 0.3 percent heavy minerals obtained 

by mineral separating in bromoform is low when compared to the amount of iron minerals determined by 

point count in thin section. The discrepancy seemingly 

reflects the solubility of very fine grained pyrite and 

red, yellow, and brown iron oxide, inasmuch as some
STRATIGRAPHY AND PETROLOGY OF THE ROBERTS MOUNTAINS FORMATION 21

rocks rich in iron oxide produce little heavy mineral 

concentrate. The solubility of iron minerals is easily 

detected because the dilute HC1 solution used to 

dissolve the rock turns green with iron chloride when 

heated to about 35 °C. Iron oxide also probably was not 

completely recovered because much of the iron oxide is 

extremely fine grained (see fig. 11), and some iron oxide that formed films on quartz was not recovered by 

centrifuging. Amounts of iron oxide and pyrite 

reported elsewhere (Mullens, 1979) are based on the 

study of thin sections instead of on iron minerals 

recovered in the heavy mineral concentrate.

Grain counts, based on area covered and converted 

to volume, indicate that pyrite and iron oxide derived 

from pyrite form 75-99+ percent of the total heavy 

mineral content in about 85 percent of the samples. 

The remaining 15 percent of the samples, where pyrite 

or iron oxide does not form the major part of the heavy 

minerals, are a diverse lot. In some samples a flood of 

epigenetic minerals reduced the iron minerals to less 

than 75 percent of the total. In some oxidized nearly 

pure carbonate rock only zircon and (or) tourmaline 

was recovered.

In addition to pyrite and iron oxide a few other 

syngenetic, diagenetic, and epigenetic minerals are 

common. Trace amounts of amphibole occur in about 

50 percent of seemingly unaltered samples, and amphibole is a major component of altered rocks collected 

in Grass Valley (Mullens, 1979, loc. 32). Epigenetic 

diopside and garnet form the bulk of heavy minerals in 

samples collected at South Ravenswood window 

(Mullens, 1979, loc. 8). Epigenetic(?) barite is relatively 

common in trace amounts, and in a few samples it 

forms the bulk of the concentrate. Phosphatic 

material, sparsely distributed in laminated limestone, 

apparently always dissolved in the dilute hydrochloric 

acid used to dissolve samples. A lenticular coarsegrained limestone near the base of the laminated 

limestone at Copenhagen Canyon (Mullens, 1979, sample 8151, loc. 14) contains about 15 percent collophane, 

but none of the collophane was recovered in the insoluble residue. Opaque minerals, probably magnetite and 

ilmenite, as inclusions in tiny veins of quartz are found 

in about 5 percent of the samples. Epigenetic white 

mica, chlorite, epidote, fluorite, and sphalerite, and 

leucoxene in samples that contain opaque minerals in 

quartz veins, are found in a few samples. Periclase is 

found in a sample of laminated dolomite that is a 

lateral equivalent of the laminated limestone in the 

Hot Creek Range.

The relative abundance of all minerals in the heavy 

mineral concentrates and the absolute amount of iron 

minerals are greatly influenced by the degree of oxidation; first, because pyrite is present in unoxidized

rocks and iron oxide is present in oxidized rocks; and 

second, because much of the iron oxide is soluble in 

dilute hydrochloric acid. For example, a concentrate of 

an unoxidized rock might contain 1 percent 

recoverable heavy minerals consisting of 90 percent 

pyrite, 5 percent zircon, and 5 percent tourmaline. An 

oxidized sample of the same rock might contain 0.5 

percent recoverable heavy minerals consisting of 80 

percent iron oxide and 10 percent each of zircon and 

tourmaline.

Detrital heavy minerals form 0.08-0.13 percent of 

the total detrital material in most laminated limestone 

but the percentage is generally higher in samples composed mainly of calcite. Zircon and tourmaline form 

about 99 percent of the detrital heavy minerals, but a 

few grains of detrital rutile and monazite are found in 

concentrates where the quartz and feldspar content exceeds 15 percent. Noteworthy is the fact that no 

detrital ilmenite, magnetite, or garnet is found. The 

dominance of zircon and tourmaline is expected for 

rocks as old as Silurian and Devonian (Pettijohn, 1957, 

p. 676, fig. 114) but the absence of garnet, magnetite, 

and ilmenite is probably due more to the pH and Eh of 

the environment of deposition than to removal by later 

intrastratal solution.

Zircon is slightly more abundant than tourmaline. 

When individual samples are compared, the zircontourmaline ratios have a range of two orders of 

magnitude—from 10:1 (10) to 1:10 (0.1) (Mullens, 

1979). At most places, the ratio is between 2:1 and 1:2; 

it averages nearly 1:1 at Maggie Creek Canyon, 

Bootstrap mine, Carlin mine, and Mill Canyon. The 

ratio is higher, about 5:1, in rocks in the lower part of 

the laminated limestone at Rattlesnake Canyon, and 

about 10:1 for a couple of unaltered samples at South 

Ravenswood window and for rocks near, but not at, the 

Carlin mine. I am unable to relate the high ratios to 

other features of the laminated limestone.

Considering all samples, 85 percent of the zircon is 

colorless or pale yellow, about 10 percent is deep 

yellow, and 5 percent is pale to deep purple. A few 

medium-brown euhedral crystals and broken 

fragments of euhedral crystals that seem to be 

metamict zircon are observed. These grains are opaque 

in transmitted light, and any angular or rounded 

fragments of such material are probably counted as 

iron oxide. The zircon occurs in grains that range from 

0.02 to 0.12 mm across, averaging about 0.045 mm. By 

number, about 5 percent of the zircon grains are well 

rounded and spherical and about 40 percent are 

euhedral crystals; the remainder range from subrounded to near-euhedral crystals that have slightly rounded 

edges. The relatively low proportion of rounded grains 

is probably a function of size inasmuch as grains above
22 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

0.06 mm tend to be rounded and euhedral crystals 

larger than 0.08 mm are scarce. Except for the brown 

opaque zircon, all concentrates contain zircon as 

described above, but relative proportions vary greatly. 

In a few of the high-calcite samples, zircon occurs 

mainly as medium silt-sized euhedral to slightly rounded euhedral crystals. Samples containing abundant 

detrital quartz and feldspar generally contain slightly 

larger and more rounded grains. The abundance of 

euhedral crystals <0.05 mm across would be favorable 

for solution of zircon in the postulated pH and Eh of 

the environment of deposition.

Study of the insoluble residue indicates that the 

average zircon content is about 0.06 percent, whereas 

counts on the thin sections indicate zircon forms less 

than 0.04 percent of the noncarbonate minerals. Zircon 

grains probably were selectively removed in preparing 

the thin sections, so estimates from the heavy mineral 

concentrates are assumed to be more accurate than zircon counts in thin sections. A method of approximating the amount of zircon by using spectrographic 

analyses of Zr (zirconium) gives results that are higher 

than my estimate of the amount of zircon in the 

laminated limestone. The "average" laminated 

limestone contains 22 percent quartz and feldspar silt 

and 100 ppm Zr to the nearest spectrographic step. If 

all Zr is placed in zircon, then the "average" rock contains about 0.02 percent zircon. For a rock composed 

entirely of detrital quartz, feldspar, clay, and zircon, 

the zircon content is calculated to be about 0.1 percent, 

considerably higher than my estimate of 0.06 percent 

for the insoluble residue. Ketner (1966, p. C56) also 

reported that spectrographic analyses indicated a 

higher zircon content in Ordovician quartzite from the 

Cordilleran geosyncline than he found in heavy mineral 

concentrates or thin sections of the quartzite. If excess 

Zr really exists, it may be in some form of hydrozircon, 

a Zr carbonate complex, or Zr hydroxide not recognized in the heavy mineral concentrate or thin section. 

Coleman and Erd (1961, p. C297-C300) reported 

hydrozircon in Wyoming, and Blumenthal (1958, p. 

37-39, 210-213) indicated that zircon was soluble and 

formed a stable Zr carbonate complex in slightly 

alkaline solutions. Such alkaline solutions are 

postulated for deposition of calcite and dolomite which 

form the major part of laminated limestone.

Tourmaline tends to occur in slightly larger grains 

than zircon and the proportion of rounded and 

subrounded grains to euhedral or splintery fragments 

of euhedral crystals is about 1:1, regardless of size. 

About 60 percent of the tourmaline is brown to 

brownish black, about 35 percent is green, about 5 percent is pink and yellow, and a trace is blue. Clear, colorless authigenic extensions of the long axis of broken 

euhedral tourmaline crystals and authigenic tourmaline overgrowths on angular fragments of tourmaline are fairly common in samples from Rattlesnake 

Canyon and from a locality 1.5 km south of Bootstrap 

mine. Scattered samples from other localities also contain clear authigenic tourmaline on detrital tourmaline 

grains. The authigenic tourmaline is similar to that 

shown by Krynine (1946, fig. 3e). Only a few rounded 

tourmaline grains that have authigenic overgrowths 

are observed in concentrates from the Roberts Mountains Formation, whereas Krynine (1946) commonly 

found overgrowths on rounded grains in Paleozoic 

rocks in the Appalachian region.

Euhedral crystals as well as rounded grains of tourmaline are relatively common in the 0.06 to 0.12 mm 

range, implying a primary igneous or metamorphic 

source for some of the tourmaline and a reworked 

sedimentary source for some. Euhedral crystals of zircon are not common in this range, but many of the 

smaller euhedral crystals of zircon could have been 

derived from the same source that supplied the larger 

tourmaline crystals.

The 0.08- to 0.13-percent heavy mineral content of 

the total detrital material in the laminated limestone is 

a seemingly low figure when compared to some sandstones. Cadigan (1967, table 13) reported that 266 

samples of the Salt Wash Member of the Jurassic Morrison Formation, collected throughout the Colorado 

Plateau, averaged 0.23 percent heavy minerals. 

Cadigan (1971, p. 34) further reported an average of 

0.26 percent for sandstone in the Moenkopi Formation. 

The figures given for the Morrison and Moenkopi sandstones reflect a high percentage of iron oxide minerals 

and authigenic minerals not considered in this study. 

The approximate ratio of opaque to nonopaque to 

authigenic heavy minerals in sandstone in the 

Moenkopi Formation is 15:3:1 (Cadigan, 1971, p. 34). 

This ratio indicates an approximate content of 0.04 

percent nonopaque heavy minerals in the Moenkopi 

sandstone. When considered in this manner, the 

nonopaque heavy mineral content of the laminated 

limestone is relatively high. And it is much higher than 

the <0.01 percent heavy mineral content that Ketner 

(1966, table 2) reported for Ordovician quartzites in the 

Cordilleran geosyncline. I suspect that the relatively 

high zircon and tourmaline contents are caused by zircon and tourmaline being more resistant to solution 

than quartz and feldspar in the environment where the 

laminated limestone was deposited.

INTERBEDDED LAMINATED LIMESTONE AND COARSEGRAINED LIMESTONE UNIT

DEFINITION AND DISTRIBUTION

The type section of the Roberts Mountains Formation at Pete Hanson Creek contains a zone of interbedded laminated limestone and coarse-grained carbonate
STRATIGRAPHY AND PETROLOGY OF THE ROBERTS MOUNTAINS FORMATION 23

extending from about 125 m to about 295 m above the 

base (M. A. Murphy, written commun., 1970). This 

zone is overlain by about 275 m of mainly coarsegrained carbonate rock also assigned to the Roberts 

Mountains Formation. Somewhat similar rocks of the 

same or slightly younger age also occur in the Simpson 

Park, Cortez, and Tuscarora Mountains, and in the 

Monitor, Toiyabe, and Shoshone Ranges. Away from 

the Roberts Mountains area these rocks have not been 

treated consistently by geologists. Merriam (1963, p. 

42-44) applied the name Rabbit Hill Limestone to thinbedded limestone of Early Devonian age in the 

Monitor Range. Johnson (1965) established his Windmill Limestone, interbedded laminated limestone, and 

coarse-grained limestone in the Simpson Park Mountains, as Devonian age. Gilluly and Masursky (1965, p. 

29-38) assigned the rocks in the Cortez area to the 

Devonian Wenban Limestone. Kay and Crawford 

(1964, p. 440) assigned Lower Devonian coarse-grained 

limestone and sparse beds of laminated limestone to 

the McMonnigal Limestone; these strata are underlain 

by laminated limestone which they assign to the 

Masket Shale in part of the Toquima Range. The 

Masket Shale is considered part of the Roberts Mountains Formation in this report. McKee, Merriam, and 

Berry (1972) found that the massive coarse-grained 

Tor Limestone also overlies laminated limestone of the 

Roberts Mountains Formation in the Toquima Range.

In this report, strata assigned to the Roberts Mountains Formation are restricted to rocks included in the 

zone extending from the base of the cherty unit to the 

base of the first coarse-grained limestone that is mappable for about 2 km. In several places the upper 

boundary is transitional and is placed where coarsegrained limestone dominates in an interbedded 

laminated limestone and coarse-grained limestone 

unit. Merriam and McKee (1977) assign overlying 

dominantly coarse-grained limestone to the Roberts 

Mountains Formation in a few places.

Places where I assign interbedded laminated 

limestone and coarse-grained limestone to the Roberts 

Mountains Formation include Miniature Grand Canyon, Petes Canyon, Goat Peak window, and Bootstrap 

mine. At Miniature Grand Canyon the section is 

faulted but about 80 m of interbedded laminated 

limestone and coarse-grained limestone is assigned to 

the Roberts Mountains Formation. Laminated 

limestone dominates in this zone, which is overlain by 

coarse-grained limestone that contains sparse beds of 

laminated limestone. The upper laminated limestone in 

rocks assigned to the Roberts Mountains Formation 

contains monograptids of probable Ludlovian age, and 

the overlying coarse-grained limestone contains conodonts of Early(?) Devonian age. In the Petes Canyon 

area, about 30 m of interbedded coarse-grained

limestone and laminated limestone occurs just beneath 

a thrust fault. According to Stewart and McKee (1977) 

the underlying laminated limestone contains 

monograptids of Silurian age in the upper couple of 

meters, and the basal coarse-grained limestone contains corals of Early Devonian age. Stewart and 

McKee (1977) placed the top of the Roberts Mountains 

at the base of the lowest coarse-grained limestone. At 

Goat Peak window, a zone 60-120 m thick of coarsegrained limestone interbedded with laminated 

limestone exposed just beneath a thrust fault is assigned to the Roberts Mountains. Conodonts indicate 

a probable Late Silurian age for the coarse-grained 

limestone.

About 460 m of Silurian and Devonian rocks is exposed beneath a thrust fault at Bootstrap mine. The 

basal 180 m, which is assigned to the Roberts Mountains, consists of mainly laminated limestone but includes abundant coarse-grained limestone in lenticular 

beds 0.3-10 m thick (fig. 14). The upper 26 m of the 

Roberts Mountains Formation is laminated limestone. 

Monograptus uniformisC!) occurs about 6 m below the 

top of the 26-m laminated limestone that caps the 

Roberts Mountains. The upper 280 m of rock exposed 

beneath the thrust is excluded from the Roberts Mountains Formation although Merriam and McKee (1976) 

include the rock in the Roberts Mountains. The rocks 

consist mainly of coarse-grained limestone, but include 

sparse laminated limestone in beds 0.1-2 m thick.

COMPOSITION AND PETROGRAPHY

Laminated limestone interbedded with coarsegrained limestone was collected from Miniature Grand 

Canyon, Bootstrap mine, and Birch Creek in the 

Roberts Mountains. These samples do not differ 

materially from those of the laminated limestone unit

FIGURE 14.—Interbedded laminated limestone and coarse-grained 

limestone unit in the upper part of the Roberts Mountains Formation, Bootstrap mine, Elko County, Nev.
24 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

described on pages 8-10, except that some contain 

quartz grains of up to 0.15 mm. Figure 15.4, shows a 

thin section of laminated limestone interbedded with 

coarse-grained limestone at Bootstrap mine. Note that 

the dolomite grains have the same habit as dolomite in 

the laminated limestone unit (figs. 11-13). Winterer 

and Murphy (1960, p. 123-124) reported that the 

calcite content of laminated limestone increased at the 

expense of silt and clay as the laminated units graded 

into coarse-grained units in the Roberts Mountains 

area. The single sample from Birch Creek (Mullens, 

1979, sample 8152, loc. 15, table 1) supports their 

observation.

The coarse-grained limestone occurs in beds as much 

as 12 m thick, but averaging only about 3 m. The beds 

are relatively lenticular; none found could be traced 

more than 1 km along strike although faults instead of 

pinchouts terminated many beds that I examined. The 

coarse-grained limestone consists of fragments of clear 

calcite, sparse silt to fine sand-sized grains of quartz

and feldspar, sparse silt-sized rhombs of dolomite, 

sparse crystals of pyrite or iron oxide pseudomorphs 

after pyrite, and pellets of very fine grained dirty 

calcite. Such rock is illustrated in figure 15.B. Pellets 

form more than 50 percent of the coarse-grained 

limestone at Bootstrap mine but are less common at 

Miniature Grand Canyon, Goat Peak window, and 

Petes Canyon. The pellets range in diameter from 

about 0.1 to 1.5 mm, averaging about 0.3 mm; they are 

rounded to angular, and some are locally deformed by 

compaction to irregular shapes. A few of the pellets 

show concentric lines and are true oolites, but most 

pellets do not have the concentric bands. The pellets 

commonly contain secondary quartz in irregular blebs 

0.02-0.10 mm long or in thin (0.02 mm) stringers of 

secondary quartz along the concentric rings. Secondary quartz in irregular blebs and stringers to 0.2 mm 

commonly form along fractures in both the clear 

calcite and the pellets. Euhedral crystals of authigenic 

quartz as much as 0.1 mm across are sparsely

FIGURE 15.—Photomicrographs of laminated limestone interbedded with coarse-grained limestone at Bootstrap mine. D, dolomite; Q, detrital quartz; sq, secondary quartz; CC, coarse-grained calcite; fc, fine-grained calcite; re, recrystallized calcite; F, potassium-feldspar; I, illite; rq, places where calcite has replaced quartz. Plain light. A, Matrix is mainly calcite (Mullens, 1979, sample 8129, loc. 6, table 1). B, 

Coarse-grained limestone is pelletal; most pinpoint-sized light spots in pellets are secondary quartz (Mullens, 1979, sample 8126, loc. 6, 

table 1).
AGE OF THE ROBERTS MOUNTAINS FORMATIONS 25

distributed in the coarse-grained limestone. The 

detrital quartz and feldspar grains are angular to 

rounded, some are deeply embayed, and some are partly replaced by calcite. The coarse-grained limestone 

generally contains several times as much authigenic 

quartz as laminated limestone.

At Bootstrap mine much of the pelletal coarsegrained limestone assigned to the Roberts Mountains 

Formation contains angular fragments of coarsegrained pelletal limestone and nonoriented corals and 

stromatoporoids, and has scour surfaces at the base of 

the beds. The fossils and fragments in these beds show 

graded bedding. These features are interpreted as indicating that some of the coarse-grained material was 

emplaced as debris flows or as a debris apron from a 

reef. Winterer and Murphy (1960, p. 126-127) believed 

that many breccia beds in the Roberts Mountains Formation in the type area originated in a similar manner. 

Mountjoy and Playford (1972) indicated that many of 

the thinner coarse-grained limestone beds interbedded 

with shale in the Devonian reef complex in Canada 

were debris flows. The isolated beds at Bootstrap 

mine, however, cannot be traced into a reef complex as 

can the breccia beds in the Roberts Mountains area 

and in Canada. Coarse-grained limestone at Miniature 

Grand Canyon, Petes Canyon, and Goat Peak has little 

breccia.

The coarse-grained limestone interbedded with 

laminated limestone and assigned to the Roberts 

Mountains Formation is very similar to coarse-grained 

limestone in overlying Lower Devonian formations.

AGE OF THE ROBERTS MOUNTAINS FORMATION

Most of the information about the age of the Roberts 

Mountains given in this report is based on graptolites 

identified by W. B. N. Berry, supplemented by conodonts identified by J. W. Huddle. Information given 

here fits well with the age of the Roberts Mountains 

Formation at the type section as reported by Murphy 

(1969), Berry (1969), and Klapper (1969). Graptolites 

indicate that the Roberts Mountains Formation contains Silurian beds of Llandoverian, Wenlockian, 

Ludlovian, and Pridolian ages and Early Devonian 

beds of Gedinnian and Siegenian ages. Merriam 

(1973a, b) and Merriam and McKee (1976) include most 

of the rocks assigned here to the Early Devonian 

Epoch in the Silurian Period. The stages of the European Silurian are used instead of stages of the 

American Silurian or Lower, Middle, and Upper Series 

in accord with the suggestion of Berry and Boucot 

(1970, p. 14-15). The stages of the Silurian and early 

part of the Devonian as well as the graptolite zones of 

Great Britain and central Europe are shown in table 1.

TABLE 1.—Silurian and Lower Devonian graptolite zones in Great 

Britain and central Europe

[British zones from Elles and Wood (1901-18) and central European zones modified from 

Berry (1969; and 1970, table 2].

SYSTEM

(ned) 

NVINOA3Q

Mwiumic 1 (Ved) [NvioiAoaao NVianils 

EUROPEAN 

STAGE 

OR SERIES

SIEGENIAN STAGE (part)

GEDINNIAN 

STAGE

PRIDOLI 

SERIES

LUDLOW 

SERIES

WENLOCK 

SERIES

tz

£ 

a.

3

LLANDOVERY

SERIES 

MIDDLE

a:

W

_i

ASHGILL SERIES

GRAPTOLITE 

ZONE

Monograptus 

hercynicus

Monograptus 

praehercynicus

Monograptus 

uniformis

Monograptus 

transgrediens

Monograptus 

dubius

36 Monograptus 

leintwardinensis

35 Monograptus 

tumescens

34 Monograptus 

scanicus

33 Monograptus 

nilssoni

32 Monograptus 

vulgaris

31 Cyrtograptus 

lundgreni

30 Cyrtograptus ellesi 

(= C. rigidus E & \N)

29 Cyrtograptus 

linnarssoni

28 Cyrtograptus rigidus 

(= C. symmetricus E & VW

27 Monograptus 

riccartonensis

26 Cyrtogreptus 

murchisoni

25 Monograptus 

crenulatus

24 Monograptus 

griestoniensis

23 Monograptus 

crispus

22 Monograptus 

turriculatus

21 Monograptus 

sedgwicki

20 Monograptus 

convolutus

19 Monograptus 

gregarius

18 Monograptus 

cyphus

17 Orthograptus 

vesiculosus

16 Akidograptus 

acuminatus

CENTRAL EUROPE

GREAT BRITAIN

The sequence of graptolites in the Llandoverian, 

Wenlockian, and Ludlovian parts of the formation fits 

the standard Silurian graptolite zones of Great Britain 

fairly well (Elles and Wood, 1901-18), and the graptolites in the upper part of the formation fit graptolite 

zones established for uppermost Silurian and lowermost Devonian rocks of central Europe (Berry, 1970, p. 

513-520). Merriam (1973), and Merriam and McKee 

(1976) established zones based on rugose coral for the 

coarse-grained carbonate rock of Silurian and Devonian age. Johnson and Boucot (1969) and Johnson, 

Boucot, and Murphy (1973) established brachiopod
26 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

zones for Silurian to Middle Devonian rocks in central 

Nevada. The laminated rocks that contain graptolites, 

correlated to central Europe, seem to grade into 

coarse-grained limestone which contains Merriam's 

Upper Silurian coral zone. Some of the information on 

graptolites collected in this study was included by 

Berry and Boucot (1970, p. 206-208).

Localities where fossils were collected are shown on 

plate 1; all fossils collected during this study and some 

fossils collected by other people are listed in the appendix to this report. Stratigraphic position and identification numbers for some of the fossils collected are 

indicated on the columnar sections shown on plate 2. 

The lists in the appendix are arranged in a geographic 

scheme based mainly on a west-to-east order of mountain ranges, and fossil localities within ranges are 

listed from south to north. Specific location and 

stratigraphic position, where known, are also included 

with the lists of fossils. Fossils are the chief means of 

correlating the isolated exposures in north-central 

Nevada and complete lists of fossils are needed so that 

the correlations can be evaluated. All fossil data are 

presented in a composite listing for the convenience of 

readers interested specifically in evaluating the correlations.

Graptolites are erratically distributed in the Roberts 

Mountains Formation; they are abundant in some 

areas and nearly absent in other areas. The manner of 

preservation is also erratic; some graptolites are well 

preserved as carbonaceous films, whereas others are 

only abraded impressions in the rock. Conodonts are 

found in some of the coarse-grained beds, but are nearly absent in the laminated limestone. Corals, 

brachiopods, algae, and ostracods locally are abundant 

in coarse-grained carbonate rock, but they were not 

collected extensively.

The only observed laminated limestone that contains 

relatively abundant brachiopods, all of a similar type, 

is in the upper part of the Roberts Mountains Formation, exposed in both the main and northeast pits at 

the Carlin mine. Boucot and Johnson (1972) identified 

the brachiopods in this bed as Callicalyptella empelia, 

n. gen., n. sp. This brachiopod is associated with 

Monograptus microdon and monograptids of the M. 

hercynicus group, which indicate an Early Devonian 

age for the bed. Except in the bed of Carlin mine, 

brachiopods are scarce in laminated limestone.

Poorly preserved corals were found in a laminated 

limestone in the upper half of the Roberts Mountains 

exposed along a bulldozer cut about 460 m south of the 

North Star mine in northern Eureka County. This 

limestone is slightly coarser grained and contains less 

silt and dolomite than most laminated limestone in the 

upper part of the formation.

Graptolites are used as time indicators in this section of the report although Berry and Boucot (1971) indicate that some of these graptolites may be related to 

water depth. In nearly all places where "a decrease in 

age" or "younger" are used, the phrases can also be interpreted as "a decrease in depth of water."

The basal cherty unit contains graptolites indicative 

of zones ranging from 16 to 24 (early, middle, and late 

Llandoverian) at Pablo Canyon in the Toiyabe Range, 

and Black Cliff, Wood, and Petes Canyons in the Toquima Range (USGS Coll. D304 SD, D305 SD, D306 

SD, D313 SD, D314 SD, D329 SD, D320 SD, D327 

SD, and D328 SD). Graptolites of these ages were first 

reported by Kay and Crawford (1964, p. 438) and were 

re-collected during this study. In addition conodonts 

from Wall Canyon in the Toiyabe Range (USGS Coll. 

8822 SD) indicate a Llandoverian Age for the cherty 

unit in that area. Graptolites from the uppermost 

limestone of the cherty unit exposed at Copenhagen 

Canyon in the Monitor Range include Glytograptus sp. 

and Dimorphograptus confertus (USGS Coll. D256 

SD), which, according to Berry, are indicative of zone 

18 of Great Britain; but as this is the only known occurrence of these graptolites in the Great Basin, 

the zone 18 assignment is not firm in north-central 

Nevada.

No graptolites or other fossils were found in the 

basal cherty unit except in the aforementioned 

localities. Other information on the age of the cherty 

unit is based on fossils collected just below and just 

above the unit.

In Eureka County the Hanson Creek Formation contains a quartz sand-bearing zone in the upper part 

(Mullens and Poole, 1972). Conodonts from samples 

collected at Copenhagen Canyon in the Monitor Range 

(USGS Coll. 8488 and 8989 SD) and near the Carlin 

mine in the Tuscarora Mountains (USGS Coll. 8823 

SD), identified by John Huddle, indicate that the part 

of the Hanson Creek above the quartz sand-bearing 

zone is early, but not earliest, Llandoverian in age. 

Thus, the cherty unit in Eureka County is probably not 

as old as the cherty unit in the Toquima and Toiyabe 

Ranges. Farther northeast, at Antelope Peak near 

Wells, Nev., the cherty unit overlies a couple of meters 

of sandstone that probably represents a greater accumulation of sand in the Hanson Creek; the cherty 

unit in that area probably is also younger than earliest 

Silurian. In the Knoll Mountain area northeast of 

Wells, a cherty unit near the base of the Noh Formation of Riva (1970) contains Monograptus spiralis according to Riva (1970, p. 2713). M. spiralis is indicative 

of zone 25 or uppermost Llandoverian, according to W. 

B. N. Berry (written commun., 1969). The cherty unit 

of the Noh Formation probably correlates with the
AGE OF THE ROBERTS MOUNTAINS FORMATION 27

basal cherty unit of the Roberts Mountains Formation. 

The information given above indicates a decrease in 

age of the cherty unit from the southwest to northeast 

exposures. Such a decrease was first postulated by 

Berry and Roen (1963).

The cherty unit is overlain by the laminated 

limestone unit which generally contains M. spiralis in 

the basal meter. The only area where M. spiralis is 

known to occur more than a few meters above the cherty zone is at Pablo Canyon, Toiyabe Range, where F. 

G. Poole found M. spiralis about 25 m above the top of 

the basal cherty unit (USGS Coll. D323 SD). The only 

extensive area of outcrop where graptolites are fairly 

common and where M. spiralis or other graptolites indicative of zone 25 were not found just above the chert 

is the Independence Mountains. M. spiralis or other 

late Llandoverian fossils were not found at Antelope 

Peak nor in the Sulphur Spring Range, although at 

these places graptolites are scarce and poorly preserved in beds just above the chert. The absence of M. 

spiralis in the Independence Mountains and the probable absence at Antelope Peak and the Sulphur 

Spring Range, coupled with the occurrence of M. 

spiralis well above the base of the laminated limestone 

unit at Pablo Canyon, are interpreted as indicating 

that the base of the laminated limestone becomes 

younger northeastward. This inference is strengthened 

by the occurrence of possible late Wenlockian graptolites collected 9 m above the base of the Roberts 

Mountains Formation in the Sulphur Spring Range 

(USGS Coll. D326 SD).

Early Wenlockian graptolites generally occur within 

a few centimeters above M. spiralis, indicating no 

significant break between Llandoverian and 

Wenlockian beds. Monograptus testis, used to indicate 

uppermost Wenlockian, is scarce in the Roberts Mountains Formation. It was found about 38 m above the 

basal cherty unit at Coal Canyon in the Simpson Park 

Mountains (M. A. Murphy, oral commun., 1968), 65 m 

above basal cherty unit 3.3 km southwest of the Carlin 

mine in the Tuscarora Mountains (USGS Coll. D253 

SD), and in float just above the basal cherty unit at 

Thomas- Jose Canyon in the Independence Mountains 

(USGS Coll. D235 SD). Little, then, can be inferred 

about Wenlockian beds except for the possibility that 

the top of the Wenlockian approaches the basal chert 

in the Independence Mountains. This relation 

strengthens the inference that the base of the 

laminated limestone unit becomes younger northeastward.

Graptolites and other fossils indicate that most of 

the laminated limestone is of Ludlovian, Pridolian, 

Gedinnian, and Siegenian ages. The Ludlovian and

younger graptolites occur in beds that, for the most 

part, grade eastward into and are overlain by coarsegrained limestone and dolomite in the area of study. 

This relation is interpreted as indicating westward 

regression of the sea and of deposition of laminated 

limestone during Late Silurian and Early Devonian 

time. Johnson (1971, p. 3265) noted that during late 

Early Devonian the extent of marine waters on the 

continent was at a minimum. The Llandoverian and 

Wenlockian beds seem to represent an eastward transgression during deposition of the basal cherty unit and 

of the lower part of the laminated limestone unit during Early Silurian time. If these interpretations are 

correct, then the general eastward migration of the 

Cordilleran geosyncline as postulated by Roberts 

(1968, fig. 6) was reversed in Late Silurian and Early 

Devonian time.

Zone markers in the Ludlovian and younger beds 

assigned to the Roberts Mountains Formation are fairly abundant, but few were found in complete sections 

where the distance above the base of the Roberts 

Mountains can be established. Monograptus uniformis, used here to mark the Silurian-Devonian boundary, occurs about 300 m above the base of the formation at Coal Canyon (W. B. N. Berry, oral commun., 

1970) and 150 m below the first mappable coarsegrained limestone. M. uniformisC!) is about 300 m 

above the base, just north of Rattlesnake Canyon in 

the Cortez Mountains (USGS Coll. D293 SD), and is 30 

m below a coarse-grained limestone assigned to the 

Wenban Limestone. At Bootstrap mine in the Tuscarora Mountains, M. uniformisCl) occurs in the interbedded laminated limestone and coarse-grained carbonate unit and about 175 m above the base of the exposed Roberts Mountains Formation (USGS Coll. 

D252 SD). It is about 6 m below a change to dominant 

coarse-grained limestone. M. uniformis has also been 

found at Willow Creek and Birch Creek (Berry and 

others, 1971, p. 1969-1971) in the interbedded 

limestone and coarse-grained carbonate unit on the 

north flank of the Roberts Mountains. None of the M. 

uniformis has been found at a contact that could be 

used to map lithologic units.

Monograptus praehercynicus group graptolites are 

335-430 m above the base and Monograptus hercynicus group graptolites are about 460 m above the 

base at Coal Canyon (W. B. N. Berry and M. A. Murphy, oral commun., 1970). The M. hercynicus beds are 

overlain by coarse-grained limestone. M hercynicus 

group graptolites were found at the Cortez and Carlin 

mines and about 1.5 km west of the Carlin mine (USGS 

Coll. D332 SD, D255 SD, and D254 SD); in the Toquima Range at Ikes Canyon beneath the McMonnigal
28 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

Limestone (USGS Coll. D310 SD) and beneath the Tor 

Limestone (McKee and others, 1972); in the Clear 

Creek area of the Toiyabe Range (Stewart and McKee, 

1977); at Brock Canyon in the Monitor Range (USGS 

Coll. D310 SD); at Maggie Creek Canyon (USGS Coll. 

D278 SD); and at Birch and Willow Creeks, on the 

north flank of the Roberts Mountains (Berry and 

others, 1971, p. 1969).

As far as has been determined in this study, all 

laminated limestone beds containing M. uniformis or 

M. hercynicus group graptolites are near gradations of 

laminated limestone to coarse-grained carbonate beds. 

The beds bearing those graptolites at Coal and Rattlesnake Canyons and the ones at the Cortez mine apparently grade eastward into coarse-grained rocks 

assigned to the Roberts Mountains Formation in the 

Roberts Mountains area or to the Lone Mountain 

Dolomite in the Sulphur Spring Range. The M. hercynicus group graptolites in laminated limestone at 

and near the Carlin mine seem to grade northwestward 

into coarse-grained rock at Bootstrap mine. The 

graptolite-bearing laminated limestone beds at Maggie 

Creek Canyon presumably grade eastward into coarsegrained Lone Mountain Dolomite in the Ruby Mountains and Wood Hills. The beds with hercynicus group 

graptolites in the southern Toquima and Toiyabe 

Ranges are assumed to grade southeastward into 

coarse-grained Lone Mountain Dolomite in the 

southern Monitor Range. The western equivalents of 

the hercynicus group beds at Rattlesnake and Coal 

Canyons, Cortez mine, and Toquima and Toiyabe 

Ranges are not known because of structural complexity and lack of outcrop.

The only megafossils other than graptolites collected 

from the laminated limestone unit and submitted for 

identification are brachiopods collected at Carlin mine 

(see p. 26) and Coal and Cortez Canyons, and corals collected near the North Star mine. Styliolina and Tentaculites are present in laminated limestone assigned 

to the Roberts Mountains Formation at the North Star 

mine, but they were not collected. These criconarids 

are common in laminated limestone interbedded with 

coarse-grained limestone overlying the Roberts Mountains Formation.

Several samples of laminated limestone from the 

Roberts Mountains Formation were collected for conodonts. All except one from Antelope Peak are barren. 

Conodonts in a medium-grained laminated limestone 

about 490 m above the base and 275 m below the top of 

the Roberts Mountains Formation at Antelope Peak 

(USGS Coll. 8824 SD) suggest a Devonian age for at 

least the upper 275 m of laminated limestone.

The coarse-grained beds in the Roberts Mountains

Formation were sampled for conodonts in a few places 

where graptolites could not be found and these conodonts furnish a little information about the age of the 

Roberts Mountains. No samples were collected in the 

type area of the Roberts Mountains Formation where 

Murphy (1969) and Klapper (1969) have studied the 

conodonts. These conodonts from the type area indicate that the upper part of the formation is of Early 

Devonian age. Away from the type area, however, 

coarse-grained limestone beds of equivalent age are 

generally assigned to formations other than the 

Roberts Mountains (p. 6). Coarse-grained beds of probable Silurian age assigned to the Roberts Mountains 

are conspicuous only at Miniature Grand Canyon in 

the Monitor Range (USGS Coll. 8435 SD), at Goat 

Peak window in the Shoshone Range (USGS Coll. 8809 

SD), and at Bootstrap mine in the Tuscarora Mountains (USGS Coll. 8219 SD), although thin coarsegrained beds of limestone that contained Silurian conodonts were found in a few other localities. Conodonts 

from thin coarse-grained beds in the upper part of the 

laminated limestone unit in the Roberts Mountains at 

Maggie Creek Canyon and Coal Canyon seem to straddle the Silurian-Devonian boundary. Conodonts from 

other samples suggest that the first mappable coarsegrained rock above the Roberts Mountains Formation 

is of Devonian age.

Several of the coarse-grained samples collected for 

conodonts contain corals and brachiopods that were 

identified by J. T. Dutro and W. A. Oliver. Their 

reports on the fossils are included in the appendix.

The conodont samples were primarily taken to solve 

a specific age problem related to the Roberts Mountains Formation. Only collections from exposures 

about 1.5 km south of the North Star mine in the 

Tuscarora Mountains were used to establish a detailed 

chronology for rocks above the Roberts Mountains 

Formation. Seven collections were made through a 

mappable, but faulted, unit about 460 m thick; this 

unit overlies the Roberts Mountains Formation and 

consists of coarse-grained limestone with thick (to 150 

m) interbeds of laminated limestone. Six of the seven 

collections contain conodonts and the beds range in 

age from Early to Late Devonian (USGS Coll. 8440 

SD-8445 SD).

The information given in this section indicates a 

general range in age from Early Silurian (early Llandoverian) to Early Devonian (Siegenian) for the 

Roberts Mountains Formation in north-central 

Nevada. The lack of fossils in the upper part of thick 

sequences of laminated limestone at Grass Valley and 

near Swales Mountain, however, prohibits putting an 

upper age limit on rocks assigned to the Roberts
CORRELATION OF THE ROBERTS MOUNTAINS FORMATION 29

Mountains Formation. Quaternary basin fill caps the 

Grass Valley exposure so that a meaningful minimum 

age cannot be determined. Near Swales Mountain, the 

laminated limestone is seemingly conformably 

overlain by Lower Mississippian rocks (Ketner, 1970, 

p. D18-D19). If the contact is truly conformable, rocks 

assigned to the Roberts Mountains probably include 

Middle and Upper Devonian units.

CORRELATION OF THE ROBERTS MOUNTAINS 

FORMATION

Most of the Roberts Mountains Formation is of 

Early Silurian to Early Devonian age, although it 

probably contains Middle and Late Devonian age 

rocks at Swales Mountain and in Grass Valley. Considering the maximum probable age and facies 

changes, the Roberts Mountains Formation is 

equivalent to all other Silurian and Devonian rocks 

that surround it. A more restricted view is that the 

Roberts Mountains Formation grades eastward from 

the type area into the Lone Mountain Dolomite. 

Southeast of Antelope Peak it grades into the 

Laketown Dolomite. Southward and southwestward it 

grades into laminated dolomite that forms unit 1 of the 

Lone Mountain Dolomite (Merriam, 1973b, p. 12-15).

The basal cherty unit seemingly correlates with the 

basal chert of the Noh Formation of Riva (1970, p. 

2693-2694) of the Knoll Mountain area in northeastern 

Nevada, northeast of the study area. The cherty unit is 

also the same as the basal chert of Silurian rocks exposed in the Nevada Test Site area in central Nye 

County (F. G. Poole, oral commun., 1968). The cherty 

unit may correlate with the chert and dolomite that 

Ross (1966, p. 27-29) included as the Late Ordovician 

upper member of the Ely Springs Dolomite in the Independence quadrangle, Inyo County, Calif., suggesting that the upper member may be Early Silurian 

in age. Eastward, into the shelf facies, a cherty zone 

near the base of the Laketown Dolomite probably correlates with the basal cherty unit of the Roberts Mountains Formation.

Chert and overlying laminated dolomite and 

limestone beneath the Lone Mountain Dolomite in the 

Bare Mountain quadrangle east of Beatty, in southern 

Nevada, were assigned to the Roberts Mountains by 

Cornwall and Kleinhampl (1961). Later work by F. G. 

Poole (oral commun., 1969) indicated that the chert 

and laminated rock near Bare Mountain did correlate 

with the Roberts Mountains Formation but that these 

rocks were more closely related lithologically with 

other Silurian rocks in southern Nevada than with the 

Roberts Mountains Formation. The Roberts Mountains Formation seems to correlate with the Vaughn

Gulch Limestone and its equivalent Sunday Canyon 

Formation in the Independence quadrangle, Inyo 

County, Calif. (Ross, 1966, p. 29-35), both of Silurian 

and Devonian(?) age.

R. J. Ross, Jr., and James Dover (written commun., 

1973) have assigned laminated limestone of 

Wenlockian age and an underlying cherty carbonate 

unit exposed along the east side of Wildhorse Creek in 

the Standhope Peak quadrangle, southern Custer 

County, central Idaho, to the Roberts Mountains Formation. These rocks are underlain by cherty dolomite 

that Ross assigns to the Hanson Creek Formation. According to R. J. Ross, the name Trail Creek Formation 

applied by C. P. Ross (1937, pi. 1) to strata along Malm 

Gulch in the Bayhorse area, central Custer County, 

central Idaho, also should be assigned to the Roberts 

Mountains Formation. The beds R. J. Ross assigns to 

the Roberts Mountains are considerably different from 

the impure quartzite at the type locality of the Trail 

Creek Formation in the Wood River region, Custer and 

Blaine Counties, central Idaho (Umpleby and others, 

1930, p. 23-24). Graptolites collected by R. J. Ross, 

James Dover, and S. W. Hobbs, and identified by W. 

B. N. Berry, indicate that the type locality of Trail 

Creek was deposited, in part, at the same time as the 

Roberts Mountains Formation. Seemingly, the Trail 

Creek and Roberts Mountains Formations in Idaho 

represent similar deposition in relation to the Cordilleran geosyncline, as do the allochthonous Silurian 

siliceous beds and autochthonous laminated limestone 

of the Roberts Mountains Formation in central 

Nevada.

Decker (1962, p. 18-21) described the Chellis and 

Storff Formations of probable Silurian age and the 

Van Duzer Limestone of probable Devonian age in 

autochthonous rocks exposed in the Bull Run 

quadrangle, northern Elko County, Nev. R. R. Coats 

(oral commun., 1973) found brachiopods in the upper 

part of the Van Duzer Limestone that Mackenzie Gordon, Jr., identified as indicating a probable Mississippian age for part of the Van Duzer. I examined the 

lower part of the Van Duzer Limestone and the Storff 

and Chellis Formations exposed on the south side of 

Pennsylvania Hill in the Bull Run quadrangle, but the 

following descriptions are paraphrased more from 

Decker (1962) than from my notes. The Chellis Formation is about 580 m thick and consists of laminated-tomassive finely crystalline limestone, and minor 

argillaceous dolomitic very fine grained limestone and 

thin beds of chert. The overlying Storff Formation is 

about 1,190 m thick and consists mainly of thinbedded phyllites, low-rank slates, and argillaceous 

limestone. The Van Duzer Limestone is locally more
30 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

than 2,200 m thick and consists of laminated-tomassive limestone. All three formations are slightly 

metamorphosed, are conformable, do not contain 

reeflike coarse-grained carbonate rocks, and are locally 

difficult to map separately. I could not determine a 

direct correlation of these rocks with the Roberts 

Mountains Formation. The Chellis and Storff Formations cannot be classified as volcanic and siliceous 

rocks, although they may be a transitional shale and 

carbonate rock assemblage between volcanic and 

siliceous rocks and carbonate rocks. These formations 

seem to represent deposition in a more central part of 

the Cordilleran geosyncline or miogeocline than the 

Roberts Mountains Formation. The thickness of 1,770 

m for the Chellis and Storff Formations of Decker 

greatly exceeds the thickness of known Silurian and 

Devonian carbonate rock exposed southward and 

eastward (Berry and Boucot, 1970; Poole and others, 

1967). If, however, the more than 825 m of laminated 

limestone near Swales Mountain is considered as indicating a northward thickening of Silurian and Devonian rocks toward a thick sequence of siliceous rocks, 

then the thickness of 1,770 m for the Storff and Chellis 

Formations plus an unknown thickness of part of the 

Van Duzer Limestone might represent a normal 

thickness for Silurian and Devonian rocks deposited in 

that part of the geosyncline or miogeocline.

Silurian and Lower Devonian rocks are common in 

the allochthon associated with the Antler orogeny. 

Because of structural complications and lack of faunal 

data in the allochthonous rocks, no coherent picture of 

the rocks has been obtained. General descriptions and 

location of rocks in the upper plate, rocks which are in 

part lateral equivalents of the Roberts Mountains Formation, are given in the following paragraphs. These 

rocks are believed to have been deposited west and 

northwest of the Roberts Mountains and moved by 

faults to the present location. The age of the rocks 

discussed is not firmly established; sequences more 

than 1,000 m thick have yielded fossils in only one or 

two places.

The Noh Formation of Riva (1970) crops out in the 

Knoll Mountain area of northeastern Nevada and is of 

Silurian age. According to Riva (1970, p. 2693-2694, 

2699) the Noh Formation consists of siltstone, shale, 

thin beds of limestone, and a cherty zone at the base. 

About 300 m of the Noh Formation is preserved, but 

the original thickness is not known. The Noh Formation is exposed in the upper plate that moved southsoutheastward along a thrust fault which is younger 

than the Antler orogeny (Riva, 1970, p. 2708-2709). 

The Noh Formation might have been part of the 

allochthon of the Antler thrust system before the later 

faulting. Gardner and Peterson (1969) described

Silurian age siltstone, sandstone, chert, and sparse 

limestone in the upper plate of an Antler thrust fault in 

the Antelope Peak area north of Wells. The Seetoya sequence of Kerr (1962, p. 449-450) is part of the Antler 

allochthon in the Independence Mountains. The 

Seetoya sequence consists of medium-bedded chert, 

poorly'bedded quartzite, minor siltstone, dark volcanic 

rocks, and at least one bed of black shale (Kerr, 1962, p. 

449). The thickness is not known but it probably exceeds 1,000 m. The bed of black shale, in the lower part 

of the sequence, contains graptolites along Water Pipe 

Canyon which indicate a middle to late Llandoverian 

age for the shale (Kerr, 1962, p. 448; Coll. D236 SD of 

this report). Upper and lower limits of age of the 

Seetoya sequence are not known. Lovejoy (1959, p. 

551, pi. 1) found monograptid-bearing siltstone in a 

thick sequence of shale and chert that also contains Ordovician graptolites near Lone Mountain in Elko County. Lovejoy did not give a thickness for this unit, but I 

estimate at least 300 m of Silurian and possibly Devonian rock to be present. The sequence of shale and 

chert is in the upper plate of an Antler system thrust 

(Lovejoy, 1959, p. 542). Evans (1972a, b) and Evans 

and Cress (1972) recognized shale, chert, quartzite, 

laminated limestone, and coarse-grained carbonate of 

Silurian and Devonian age in the upper plate rocks extending from Maggie Creek Canyon to Bootstrap 

mine. Probably a minimum of 1,000 m of Silurian and 

Devonian rocks is present, but complicated structure 

prohibits exact measurements. Smith and Ketner 

(1975) recognized black shale, sandstone, and sparse 

coarse-grained carbonate rocks in the Devonian 

Woodruff Formation, which is in the upper plate in the 

Carlin-Pinon Range area. The Woodruff is locally 

more than 1,000 m thick and it contains Monograptus 

hercynicus nevadensis (Berry, 1967).

Gilluly and Masursky (1965, p. 54-61) and Gilluly 

and Gates (1965, p. 35-42) mapped the Fourmile Canyon Formation and Elder Sandstone of Silurian age in 

allochthonous rocks exposed in the Cortez quadrangle 

and northern Shoshone Range. The Fourmile Canyon 

Formation is more than 2,000 m and consists of chert, 

siltstone, argillite, and scattered beds of sandstone, 

but contains no beds of carbonate (Gilluly and Masursky, 1965, p. 54-57). Monograptids indicative of an age 

somewhere between zones 16 and 21 of the British 

zones were found in the Fourmile Canyon Formation at 

one locality in Fourmile Canyon (Gilluly and Masursky, 1965, p. 57; Coll. D92 SD of this report). The Elder 

Sandstone is 600-1,200 m thick in the Shoshone Range 

and consists mainly of silty fine-grained feldspathic 

sandstone, but includes minor amounts of chert and 

shale, and possibly devitrified volcanic glass shards in 

the sandstone (Gilluly and Gates, 1965, p. 35).
ENVIRONMENT OF DEPOSITION OF THE ROBERTS MOUNTAINS FORMATION 31

Monograptids indicative of zones 19-22 of the British 

section were found at two localities in the Elder Sandstone in the Shoshone Range (Gilluly and Gates, 1965, 

p. 36).

Shale, chert, and coarse-grained carbonate beds of 

Silurian and Devonian age are known in allochthonous 

rocks in the region south and southeast of the northern 

Shoshone Range (J. H. Stewart and M. A. Murphy, 

oral commun., 1970). Since these rocks have not been 

studied in detail, the thicknesses and relative amounts 

of shale, chert, and carbonate rock are not known.

Except for the Noh Formation of Riva (1970) the 

rock types and stratigraphic sequence of the Silurian 

allochthonous units described above have little in common with the Roberts Mountains Formation and adjacent rocks. The Noh Formation contains a basal chert, 

and the overlying thin-bedded rocks slightly resemble 

rocks in the Roberts Mountains Formation. Possibly 

the Roberts Mountains grades directly into the Noh 

Formation. The other upper plate units probably were 

deposited several kilometers west and northwest of the 

westernmost rocks here assigned to the Roberts Mountains. These units may have been deposited within a 

few kilometers of rocks assigned to the Roberts Mountains, but there is no known evidence for such an 

abrupt facies change in rocks in either autochthon or 

allochthon.

Some rocks in a structural complex area at Goat 

Peak window in the northern Shoshone Range were 

mapped as Roberts Mountains by Gilluly and Gates 

(1965, pi. 1). I believe the only Roberts Mountains Formation present is in the first outcrop of lower plate 

rocks west of Goat Peak. Other rocks mapped as 

Roberts Mountains in the Goat Peak window are in different thrust plates according to Gilluly and Gates 

and, in my opinion, are more similar to Ordovician 

laminated limestone than to the laminated limestone 

in the Roberts Mountains Formation.

ENVIRONMENT OF DEPOSITION OF THE 

ROBERTS MOUNTAINS FORMATION

Lack of knowledge of lateral relations of equivalent 

rocks on the western and northwestern edges of the 

formation prohibits definite conclusions about the environment of deposition or the source of detrital 

material in the Roberts Mountains Formation. This 

lack of knowledge about the formation is further compounded by the apparent absence of current analogs to 

the environment of deposition assumed for the Roberts 

Mountains. The interpretations of environment of 

deposition given here are slanted to include shallow 

water to the east and, generally, somewhat deeper 

water to the west. Locally and occasionally reefs

formed in the deeper water to the west. These interpretations conflict slightly with the Silurian and Early 

Devonian parts of the Cordilleran geosyncline model as 

represented by Roberts (1968, p. 106-108, fig. 6) and 

Roberts and others (1958, fig. 4), or (and) with the 

model of the miogeocline postulated by Stewart and 

Poole (1974). Basically, I believe that the water in 

which the sediments were deposited was not as deep as 

indicated by their models and that reefs existed west 

of their westernmost reefs. Roberts (1968, fig. 6) indicated more than a kilometer of water in the area 

where the Roberts Mountains Formation was 

deposited during Middle Devonian time; and Stewart 

and Poole (1974, p. 45) postulated that the laminated 

limestone "* * * represents moderately deep water 

deposition on the outer shelf." This implies water 

about 200 m deep.

Lateral relations of rock types in the Roberts Mountains and underlying and overlying formations are 

shown on plate 2. The reef environment for coarsegrained rock and the fore-reef environment for the 

laminated limestone in the type area of the Roberts 

Mountains Formation postulated by Winterer and 

Murphy (1960) are accepted and extended north and 

northeast of the type area to near Wells, Nev. Only in 

the area northwest of Wells, however, does the 

laminated limestone seem to grade consistently into a 

more basinward zone. The evidence for this gradation 

is scanty as the Roberts Mountains cannot be directly 

related to the Storff and Chellis Formations which are 

assumed to represent deposition closer to the middle of 

the geosyncline (p. 29 of this report). South of the type 

area the laminated limestone grades to only slightly 

silty laminated carbonate rock that has been dolomitized. Westward and southwestward of the type area, 

the upper part of the laminated limestone seems to 

grade locally into coarse-grained reeflike carbonate 

rocks. The distribution and lateral relations of the 

rocks require some modification of a simple fore-reef 

grading to deeper water. In addition, these relations 

seemingly require an eastward curve in the reef line in 

the Carlin-Elko area where the trend of the edge of the 

Roberts Mountains Formation deviates from the 

northward trend of the Cordilleran geosyncline as 

postulated by Roberts (1968, fig. 5). Stewart and Poole 

(1974) attributed the eastward-curve to much later 

oroflexural bending.

The basal cherty unit of the Roberts Mountains Formation is inorganically precipitated calcite that was 

partly to completely silicified before it was lithified. 

The source of the silica that replaced the calcite is not 

known. Study of thin sections revealed no evidence for 

either volcanic glass or tests of siliceous organisms 

that could have furnished the silica. Possibly the silica
32 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

was derived from ash falls related to the volcanic rocks 

in the Seetoya sequence of Kerr (1962, p. 449) and to 

the shards in the Elder Sandstone (Gilluly and Gates, 

1965, p. 35). The Seetoya sequence and Elder Sandstone contains beds of about the same age as the cherty unit (p. 30 and 31), but no bentonite beds have been 

identified in the cherty unit. I believe the calcite 

formed in shallow water (a few meters deep) during a 

time when little detrital material was being supplied. 

The chert replacement of beds at the same stratigraphic position continues into coarse-grained 

carbonate rock in southern Nevada (F. G. Poole, oral 

commun., 1968), where the replaced beds contain pentamerid brachiopods that lived in relatively shallow 

water.

Where completely silicified, the cherty unit of the 

Roberts Mountains Formation resembles cherty units 

of the volcanic and siliceous assemblage of Roberts 

(1969) and Stewart and Poole (1974). These authors indicated that the volcanic and siliceous assemblage of 

the Cordilleran miogeosyncline formed in deep water 

(more than 200 m). They also considered the laminated 

limestone unit of the Roberts Mountains Formation to 

represent a transitional unit between rocks deposited 

in deep water and in fairly shallow water. No undoubted evidence exists that the siliceous assemblage 

was deposited in deep water. Goldstein and Hendricks 

(1953) postulated that some sediments of the Ouachita 

geosyncline in Arkansas and Oklahoma that are 

similar to the siliceous rocks in the Cordilleran 

geosyncline were deposited in shallow water to tidal 

flat environments. Folk (1973) gave evidence that the 

Devonian and Mississippian Caballos Novaculite of 

west Texas, also deposited in the Ouachita 

geosyncline, was deposited in a peritidal environment.

Wise (1972) reported that silica in the form of 

spherical aggregates 0.0025-0.003 mm in diameter occur in Cenozoic deep sea chalks deposited in the South 

Atlantic Ocean and Caribbean Sea. The silica in the 

chalk is presumed to be derived from volcanic glass or 

from tests of siliceous organisms. During lithification 

the movement of interstitial fluids could redistribute 

the silica so as to replace calcite and form deep sea 

chert. Similar processes might have been responsible 

for forming the cherty unit if it is really a deep sea 

deposit.

The laminated limestone probably was deposited in 

water not more than 100 m deep. That water was west 

of a major reef throughout the time of deposition, but 

east of a minor reef line formed in the Late Silurian and 

Early Devonian time in parts of the south and west

sides of the area of deposition. These relations modify 

the general concept of a uniform westward-sloping sea 

floor, by locally reversing the westward slope of the 

sea floor of the Cordilleran geosyncline or 

miogeosyncline to form a nearly closed basin in which 

laminated limestone was deposited in latest Silurian 

and earliest Devonian time.

The type and distribution of rocks being deposited in 

north-central Nevada at five times ranging from Early 

Silurian to Early Devonian are shown by figures 

16-20. The maps incorporate fossil data along with 

distribution of rocks; they are my interpretation of 

stratigraphic relations and relative depth of water during Silurian and Early Devonian. The change in rock 

type is interpreted as mainly representing changes in 

depth of water from a few meters to about 100 m. 

Coarse-grained fossiliferous carbonate rock is assumed 

to have been deposited in water a few meters deep and 

the laminated limestone in water a few tens of meters 

deep. The reasons for the changes in depth of water, 

which also changed the depositional pattern near the 

end of Silurian time, are not known. The relatively 

more abundant detrital material in the upper half of 

the laminated limestone unit suggests an elevated, or 

new, source of material near the end of Silurian time. 

Possibly the forces that altered the source of the 

detrital material also changed the configuration of the 

sea floor.

My interpretations about water depth are of the 

same order of magnitude as Ziegler (1965) postulated 

for some Silurian rocks in Great Britain. Ziegler defined five faunal zones, based on brachiopods. The 

areal distribution of these zones is roughly parallel and 

the zones are believed to represent changes in depth of 

water associated with the edge of the sea. The ranges 

between the zones are in tens instead of hundreds of 

feet according to Ziegler (1965), which I interpret to be 

several meters instead of possibly a hundred meters. 

Berry and Boucot (1971) believed monograptids in the 

Roberts Mountains Formation could be related directly to the lower four zones of Ziegler. To some extent, 

this association would invalidate the use of monograptids as time lines. The depth control of monograptids 

would, however, add strength to part of the interpretation given below because, according to Berry and 

Boucot (1971), Monograptus spiralis is associated with 

deeper water than the M. hercynicus group graptolites.

The presence of pyrite and organic material indicates 

that a reducing environment existed at the time of 

deposition of the laminated limestone. This reducing 

environment was probably toxic to boring organisms, 

as the laminations are preserved. The toxic conditions
CORRECTED PAGES

U.S. Geological Survey Professional Paper 1063, Stratigraphy, Petrology, and Some 

Fossil Data of the Roberts Mountains Formation, North-Central Nevada, by Thomas 

E. Mullens: U.S. Government Printing Office, Washington, D.C. 20402,1980, Stock 

Number 024-001-03264-3.

The patterned areas in figures 16 through 20 (pages 33 to 37) 

were positioned incorrectly when the report was printed. 

Reprinted pages with corrected illustrations are attached. 

Page 38 is also included in the reprinting for convenience; 

this page is not incorrect in the original printing.

ENVIRONMENT OF DEPOSITION OF THE ROBERTS MOUNTAINS FORMATION 33

120°

42° r--- 

WASHOE

'/' •// laminated dolomite equivalent to | 

•'-.'/•I."0 the Roberts Mountains Forma40°

\

38° Tonopah

Approximate eastern extent of 

laminated limestone in th6| 

Roberts Mountains Formation ,

\

ESMERALDA

\

\

3LN

PR

RC

SM

-1 SR

i SS

TJ

W

EXPLANATION 37°

LOCALITIES

Antelope Peak

Black Cliff Canyon

Brock Canyon

Bootstrap mine

Copenhagen Canyon

Coal Canyon

Clear Creek Mountain

Carlin mine

Goat Peak window

Grass Valley

Hot Creek Canyon

Ikes Canyon

Lone Mountain

Maggie Creek Canyon

Miniature Grand Canyon

Pablo Canyon

Petes Canyon

Pete Hanson Creek (type 

section of Roberts 

Mountains Formation)

Point of Rocks 

Rattlesnake Canyon 

Swales Mountain 

South Ravenswood window 

Sulphur Spring Range 

Thomas Jose Canyon 

Wood Canyon 

WC Wall Canyon

Very fine grained carbonate rock that 

was partly silicified during 

diagenesis—Part of the basal cherty 

unit of the Roberts Mountains Formation

Fine- to coarse-grained carbonate 

rock—Assigned to Hanson Creek 

Formation and correlative formations

CLARK

\

50

T 

100

100 MILES

_I

150 KILOMETERS 35°

FIGURE 16.—Type of rock deposited in north-central Nevada during mid-Llandoverian time. Approximately graptolite zone 20.
34 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

116° 115°

\ CHURCHILL :n~~-Approximate eastern extent of

/

' / laminated dolomite equivalent to 

(. the Roberts Mountains Forma- 

| X tion

!••'/ Eureka

Approximate eastern extent of 

laminated limestone in the 

Roberts Mountains Formation

EXPLANATION

LOCALITIES

Antelope Peak

Black Cliff Canyon

Brock Canyon

Bootstrap mine

Copenhagen Canyon

Coal Canyon

Clear Creek Mountain

Carlin mine

Goat Peak window

Grass Valley

Hot Creek Canyon

Ikes Canyon

Lone Mountain

Maggie Creek Canyon

Miniature Grand Canyon

Pablo Canyon

Petes Canyon

Pete Hanson Creek (type 

section of Roberts 

Mountains Formation)

Point of Rocks 

Rattlesnake Canyon 

Swales Mountain 

South Ravenswood window 

Sulphur Spring Range 

Thomas Jose Canyon 

Wood Canyon

1 WC Wall Canyon

Laminated carbonate rock—Part of 

major unit in Roberts Mountains 

Formation

Very fine grained carbonate rock that 

was partly silicified during 

diagenesis—Part of the basal cherty 

unit of the Roberts Mountains Formation

Fine- to coarse-grained carbonate 

rock—Assigned to Hanson Creek 

Formation and correlative formations

FIGURE 17.—Type of rock deposited in north-central Nevada during late Llandoverian time. Approximately graptolite zone 24.
ENVIRONMENT OF DEPOSITION OF THE ROBERTS MOUNTAINS FORMATION 35

120°

LOCALITIES

AP Antelope Peak

B Black Cliff Canyon

BC Brock Canyon

BM Bootstrap mine

C Copenhagen Canyon

CC Coal Canyon

CL Clear Creek Mountain

] CM Carlin mine

GP Goat Peak window

] GV Grass Valley

_l HC Hot Creek Canyon

/\J.' r. I

pH/.J%~Approximate eastern extent of | 1C Ikes Canyon 

/?:*i/4 laminated dolomite equivalent to |

• '.71 1 the Roberts Mountains Forma- LM Lone Mountain 

',•".. I & ? tion

LM|| j;^, MC Maggie Creek Canyon 

fiS$ Eureka I

I MG Miniature Grand Canyon

P Pablo Canyon 

PC Petes Canyon

J

PH Pete Hanson Creek (type 

section of Roberts 

Mountains Formation)

38°

ESMERALDA

. Tonopah

I

"Approximate eastern extent of 

laminated limestone in the| 

Roberts Mountains Formation ,

i

-\

PR Point of Rocks

RC Rattlesnake Canyon

SM Swales Mountain

SR South Ravenswood window

J SS Sulphur Spring Range

TJ Thomas Jose Canyon

W Wood Canyon

EXPLANATION 37°

WC Wall Canyon

Laminated limestone—Part of major 

unit in Roberts Mountains Formation

Laminated carbonate rock that was 

dolomitized—Equivalent to Roberts 

Mountains Formation

Coarse-grained carbonate rock— 

Assigned to the Laketown and Lone 

Mountain Dolomites

\

CLARK

r

^ \

\

100 MILES

100

~n~^ 

150 KILOMETERS

FIGURE 18.—Type of rock deposited in north-central Nevada during late Wenlockian time. Approximately graptolite zone 31.
36 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

120° 

42° r—--

WASHOE

41

40°

Approximate eastern extent of 

laminated limestone in the| 

Roberts Mountains Formation

Laminated carbonate rock — Part of 

major unit in Roberts Mountains 

Formation

Interbedded laminated and coarsegrained carbonate rock — Assigned 

to the Roberts Mountains Formation

Coarse-grained carbonate rock — 

Assigned to the Roberts Mountains 

Formation in the type area only

LOCALITIES

AP Antelope Peak

B Black Cliff Canyon

i BC Brock Canyon

BM Bootstrap mine

C Copenhagen Canyon

CC Coal Canyon

CL Clear Creek Mountain

! CM Carlin mine

GP Goat Peak window

1 GV Grass Valley

_j HC Hot Creek Canyon

iV-Approximate eastern extent of i 1C Ikes Canyon 

' laminated dolomite equivalent to .

the Roberts Mountains Forma- LM Lone Mountain 

;Sfc tion

MC Maggie Creek Canyon

I MG Miniature Grand Canyon

P Pablo Canyon

PC Petes Canyon

PH Pete Hanson Creek (type 

section of Roberts 

Mountains Formation)

PR Point of Rocks

RC Rattlesnake Canyon

I SM Swales Mountain

— SR South Ravenswood window

i SS Sulphur Spring Range

TJ Thomas Jose Canyon

W Wood Canyon

WC Wall Canyon

50 100

FIGURE 19.—Type of rock deposited in north-central Nevada during latest Silurian and earliest Devonian time. Approximately Monograptus uniformis Zone.
120°

ENVIRONMENT OF DEPOSITION OF THE ROBERTS MOUNTAINS FORMATION

116° 115°

37

|~j Approximate eastern extent ofj 1C 

: laminated dolomite equivalent to |

the Roberts Mountains Forma- LM 

X tion

LOCALITIES

Antelope Peak

Black Cliff Canyon

Brock Canyon

Bootstrap mine

Copenhagen Canyon

Coal Canyon

Clear Creek Mountain

Carlin mine

Goat Peak window

Grass Valley

Hot Creek Canyon

Ikes Canyon

Lone Mountain 

MC Maggie Creek Canyon 

MG Miniature Grand Canyon 

P Pablo Canyon

Petes Canyon

Pete Hanson Creek (type 

section of Roberts 

Mountains Formation)

38° Tonopah

Approximate eastern extent of 

laminated limestone in the| 

Roberts Mountains Formation ,

r

ESMERALDA

PR 

RC 

SM 

SR 

i SS

\

TJ 

W

Point of Rocks 

Rattlesnake Canyon 

Swales Mountain 

South Ravenswood window 

Sulphur Spring Range 

Thomas Jose Canyon 

Wood Canyon

EXPLANATION 37*

WC Wall Canyon

Laminated carbonate rock—Part of 

major unit in Roberts Mountains 

Formation

Interbedded laminated and coarsegrained carbonate rock—Locally assigned to the Roberts Mountains 

Formation

Coarse-grained carbonate rock— 

Generally excluded from Roberts 

Mountains Formation although 

some may be included in the Roberts 

Mountains Formation in the type 

area

\

CLARK

\

\

100 MILES

j

100

I 

150 KILOMETERS 35°

FIGURE 20.—Type of rock deposited in north-central Nevada during mid-Early Devonian time. Approximately Monograptus hercynicus

Zone.
38 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

and the reducing environment are interpreted to be in 

the mud bottom, but not necessarily in the water a few 

meters above. The composition, pH, and Eh of the 

water at and above the sea floor were favorable for 

precipitation of both very fine grained calcite and siltsized grains that became dolomite. At the sea floor, the 

pH was probably in the 7.9-8.2 range and the Eh was 

probably near —0.3 (Krumbein and Garrels, 1952, fig. 

8), but the Eh might have been higher a few meters 

above. The degree of toxicity of the water above the 

sea floor is not known, but probably the water supported algae that secreted no calcareous parts, graptolites, and a few corals and brachiopods. Anaerobic 

bacteria probably lived on and near the sea floor.

The mineral assemblage in laminated limestone is interpreted as containing two major components—detrital grains from preexisting rocks and 

chemical precipitates that formed in seawater above or 

at the sea floor. Detrital grains that were derived from 

preexisting rock include quartz, feldspar, some of the 

clay, and heavy minerals such as zircon, tourmaline, 

monazite, and rutile. Most carbonate in the laminated 

limestone is here interpreted as either having 

precipitated in the sea or having crystallized by nucleation at or slightly below the sea floor before the sediment was compacted. Minor components in the 

laminated limestone are of varied origin. Some angular 

grains of calcite as much as 0.2 mm across are probably fragments of fossils. The carbonaceous material is 

likely of two origins: most films and specks are interpreted as parts of graptolites or other organisms; the 

carbonaceous coatings adhering to quartz and 

dolomite grains, and carbonaceous inclusions in calcite 

are interpreted as derived from algae that secreted no 

hard parts or from anaerobic bacteria. The pyrite is interpreted as formed from iron derived from dissolving 

iron-bearing minerals and then combined with H2S at 

or slightly below the sea floor. Presumably, anaerobic 

bacteria and decaying organic matter had some role in 

producing the H2S needed to precipitate pyrite.

The coarse-grained limestone in the upper part of the 

Roberts Mountains Formation, as well as laterally 

equivalent coarse-grained carbonate rock assigned to 

other formations, are interpreted as deposited in water 

not more than several meters deep and as part of a reef 

complex. The reefs varied from long-lived major 

features where the Lone Mountain Dolomite was 

deposited (Winterer and Murphy, 1960) to short-lived 

patch reefs where only a few meters of limestone were 

deposited. At Bootstrap mine and near the type section, much of the coarse-grained limestone in the 

Roberts Mountains Formation might have been 

emplaced as debris flows from major reefs. At other 

places, the coarse-grained limestone in the Roberts 

Mountains seemingly accumulated in patch reefs that

existed only for short periods before being covered by 

laminated limestone.

The reef limestone is interpreted as mainly 

bioclastic. It probably formed in well-aerated water 

where currents were strong enough to remove silt, to 

transport fine to medium quartz grains, and to move 

limestone pellets as large as 2 mm in diameter.

Tenuous evidence indicates that laminated 

limestone in the upper part of the Roberts Mountains 

Formation was deposited in a nearly closed basin (figs. 

19 and 20). The interbedded coarse-grained limestone 

and laminated limestone at Bootstrap Hill, at Goat 

Peak, and at Miniature Grand Canyon, coupled with 

the Tor Limestone of Devonian age (Johnson and 

Boucot, 1970) and the McMonnigal Limestone, which 

is in part Early Devonian in age, in the Toquima 

Range, and the 10-m bed of coarse-grained Lower 

Devonian Limestone at Point of Rocks in the Toiyabe 

Range suggest that local to extensive reefs existed 

west and south of the main area of deposition of the 

laminated limestone during latest Silurian and earliest 

Devonian time. The lack of outcrops of equivalent 

rocks west of the Shoshone Range allows several interpretations of the distribution of these reefs. I believe 

that a reef probably extended from Bootstrap mine to 

Goat Peak window but that it probably did not extend 

far southward. Another reef, extending from Point of 

Rocks eastward through the Toquima Range to the 

Monitor Range, is also indicated. Probably this reef 

connected in Late Silurian and Early Devonian time 

with the Roberts Mountains area via Mahogany Hills. 

The laminated limestone that overlies the single bed of 

coarse-grained limestone at Point of Rocks indicates 

that the reef there did not persist long. Stewart and 

McKee (1977) found no extensive coarse-grained 

limestone of Devonian age in the area south of Austin.

The lack of interbeds of coarse-grained reeflike 

limestone in the laminated limestone at Swales Mountain and in Silurian and Lower Devonian rocks at 

Antelope Peak indicates that no reef line formed in 

rocks assigned to the Roberts Mountains Formation 

northwest of Wells, Nev. This interpretation is 

strengthened by the absence of reeflike carbonate 

rocks in presumed correlative autochthonous beds of 

the Chellis and Storff Formations, and of part of the 

Van Duzer Limestone of Decker (1962) in the Bull Run 

quadrangle (see p. 29).

The nearly enclosed basin outlined in figure 20 is 

about 200 km long and 30-80 km across. The size and 

open end of the basin approximate the Delaware basin 

in Texas and New Mexico (King, 1934, p. 704). The 

depth of water within the nearly closed basin where 

most of the rocks assigned to the Roberts Mountains 

Formation were deposited is not known. The maximum depth is assumed to have been about 100 m, but
ENVIRONMENT OF DEPOSITION OF THE ROBERTS MOUNTAINS FORMATION 39

it could have been as much as 4,500 m; this latter 

figure is the calcite compensation depth according to 

Berner (1965), although the compensation depth of 

calcite is not uniform (Heath and Culberson, 1970). The 

depth was less—probably less than 30 m—near the 

margin where laminated limestone, assumed to have 

been deposited in reducing and toxic water, graded into coarse-grained carbonate. Newell and others (1953, 

p. 96) noted that toxic and reducing conditions also 

prevailed near the foot of a growing reef in the Permian 

basin of Texas and New Mexico. The general evenness 

of the laminations cannot be used as indicating depth 

below wave base. Laminations are preserved in modern 

tidal and supratidal deposits (Reineck, 1972, p. 148, 

fig. 4; Lucia, 1972, table 1), in pools marginal to the sea 

(Friedman and others, 1972), in lagoonal deposits 

(Behrens and Land, 1972, p. 155, fig. 2), as well as in 

rocks presumably deposited below wave base (Rubey, 

1931, p. 40-43). If the interpreted depth is correct, 

then the sea floor had an extremely gentle slope that 

approached the slope that Irwin (1965, fig. 2) 

postulated for epeiric seas. As a corollary, the accumulation of laminated limestone probably is related 

to crustal subsidence rather than to filling of the sea.

In texture and composition the laminated limestone 

is similar to parts of the Paradox Member of the Hermosa Formation of eastern Utah (Peterson and Kite, 

1969, p. 892) and to the limy clastic basin deposits 

associated with the Permian reef complex in west 

Texas (King, 1948, pi. 10A; Newell and others, 1953; 

Albritton and Smith, 1965, fig. 5). These units are 

believed to have been deposited in barred basins (King, 

1934; Peterson and Kite, 1969, p. 893-894). The 

laminated limestone of the Roberts Mountains Formation is here interpreted to have been deposited in a 

partly barred basin although the location of the bar, or 

bars, is not known.

High salinity probably existed in the partly barred 

basin and extraction of Ca++ to form limestone in the 

reef areas caused the water to become relatively enriched in Mg++ and Cl~. Currents, probably of the 

longshore type, strong enough to transport clay, silt, 

and a little sand, and to mix waters of different composition, were also present. Near the reef line 

longshore currents are postulated, as the laminated 

limestone in these areas contains very fine to fine sand 

grains that are not found in the bulk of the laminated 

limestone.

The precipitation of fine-grained calcite in seawater 

upsets no established geologic dogma, but the 

precipitation of large amounts of nearly primary 

dolomite from subtidal water is controversial. A highmagnesian calcite can be precipitated in large amounts 

in a slightly restricted basin and the high-magnesian 

calcite can be changed to dolomite early in diagenesis.

Friedman and others (1972) reported high-magnesian 

calcite in highly carbonaceous modern sediments near 

the Red Sea. Muller and others (1972, p. 162-163) 

reported that high-magnesian calcite formed in 

lacustrine water with a 7-15:1 molecular ratio of Mg to 

Ca converts to dolomite. Dolomite is found in 

sediments of such lakes. Removal of Ca++ by 

precipitating calcite either by organic or inorganic 

methods would bring the magnesium-to-calcium ratio 

of seawater into this range. The high-magnesiancalcite converts to dolomite as the calcite acts as a 

matrix for dolomite nucleation; then further growth involves dissolution of the calcite with reprecipitation as 

dolomite. The dissolution probably takes place in the 

sediments of the lake floor (Muller and others, 1972, 

p. 163).

Possibly, however, much of the dolomite in the 

laminated limestone is a primary precipitate, since the 

texture and composition of the dolomite give no 

evidence that the dolomite evolved from a highmagnesian calcite. The texture of dolomite in the 

laminated limestone is very similar to that of the 

primary dolomite shown by Sabins (1962, fig. 5). X-ray 

diffraction studies indicate that the dolomite is pure, a 

feature Sabins (1962, table 1) found in dolomite he 

believed to be primary. I saw no undoubted evidence 

that dolomite grains had replaced any other mineral. 

The irregular shape of many of the grains is interpreted as solution of dolomite or incomplete 

crystallization instead of as abrasion by rolling on the 

sea floor. Gypsum precipitated by mixing brines shows 

the same range of irregular grains to perfect crystals 

(R. J. Kite, oral commun., 1972) as the dolomite in the 

laminated limestone. Even if the dolomite was 

precipitated as a high-magnesian calcite, the calcite 

was converted to dolomite before compaction, as the 

dolomite rhombs grew in an unconfined environment.

I do not believe that the laminated limestone was 

deposited on a supertidal flat where most undoubted 

primary dolomite has been reported. Behrens and 

Land (1972, p. 155-161) reported a bed of primary 

dolomite in anhedral to euhedral 0.005 mm rhombs in 

laminated subtidal lagoonal sediments in Baffin Bay, 

Tex. Raup (1970) has shown that halite can be 

precipitated by mixing brines of different composition 

and specific gravity without further loss of water by 

evaporation. R. J. Kite (oral commun., 1972) believed 

that the model used by Raup can be extrapolated to 

allow dolomite to precipitate in seawater if variable 

compositions are included. Such a condition might 

prevail in water depleted in Ca++ by inorganic deposition of calcite or organic deposition of calcite in a reef, 

slightly enriched in carbonaceous material and H2 S, 

and then mixed with normal seawater.

The dolomite grains seem to be in hydrologic
40 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

equilibrium with the quartz grains. The amount of 

dolomite in the laminated limestone also shows a good 

correlation with the increase in quartz, feldspar, and 

clay content (see fig. 8). These features seem to indicate that the dolomite, or its high-magnesian calcite 

precursor, acted like clastic grains, but the grains are 

so small that they would not be abraded by current 

action.

I interpret the eastward trend of the reef line from 

Carlin to Wells, shown on figures 19 and 20, to represent the original pattern of deposition caused by a 

curve in the basin of deposition. Stewart and Poole 

(1974, p. 45, fig. 12), however, related the eastward 

trend of the reef line from Carlin to Wells to later 

oroclinal folding. Although exact reasons for the curve 

are not known, I believe the basin of deposition had 

curves resembling modern ocean shores instead of being a linear trough. Part of the curve is interpreted as 

related to the Cortez-Uinta axis (Roberts, 1968, fig. 5) 

which, I believe, influenced the depositional pattern in 

northeastern Nevada during the Silurian and Early 

Devonian. Also, I interpret the work of Gilluly and 

Gates (1965), Gilluly and Masursky (1965), Webb 

(1958), and Ketner (1968) to indicate that the arch was 

high in part of Ordovician time, and the work of 

Yochelson and Fraser (1973) to indicate that the arch 

was active in Pennsylvanian and Permian time. Seemingly the arch was asymmetrical, the north side dipping steeper, during Silurian and Early Devonian time. 

Evidence that I interpreted to indicate that the arch influenced deposition during Silurian and Early Devonian time is found in the Pinon and Sulphur Spring 

Ranges and Cortez Mountains. The coarse-grained 

limestone extends farther west along the crest of the 

arch in these ranges than does the coarse-grained carbonate rock to the south. This relation is interpreted to 

indicate that the crest of the Cortez-Uinta axis influenced the depth of water and allowed the higher 

energy coarser grained material to be deposited.

The coarse-grained limestone interbedded with 

laminated limestone is not shown as connected from 

Rattlesnake Canyon to Goat Peak window on figure 

19, although these localities are along the axis. The 

reason for not connecting the localities and sealing off 

a basin is that a 670-m-deep drill hole in Mill Canyon 

east of Crescent Valley and only a few kilometers north 

of Rattlesnake Canyon did not penetrate coarsegrained carbonate rock.

SOURCE OF DETRITAL MATERIAL IN THE 

ROBERTS MOUNTAINS FORMATION

Berry and Boucot (1970, p. 63-65) examined the 

problem of source areas for detrital material in Silurian 

rocks in North America and found that, except in the

Appalachian region, no known areas are adequate to 

furnish detrital material for Silurian quartz-rich 

sediments. Study of the Roberts Mountains Formation 

does not modify their conclusions, as the source area of 

the detrital minerals in the formation and the method 

of transport are not known to me. The quantities of silt 

and feldspathic sandstone (p. 31-32) in equivalent 

rocks in the allochthon of the Antler orogeny suggest 

that a landmass existed west and northwest of the area 

of deposition of the Roberts Mountains Formation. 

The detrital material in the Roberts Mountains, which 

is mainly silt sized, could represent an eastern extent 

and dilution of the more clastic rocks deposited to the 

west. If so, the transport was probably by water currents. The size of the detrital material in the Roberts 

Mountains Formation indicates that air-current 

transport was also possible.

Any landmass that furnished sediments from the 

west or northwest seems now to be concealed by 

younger rocks or metamorphosed beyond recognition. 

Or, in view of plate tectonics, such a landmass could 

have been subducted or moved a great distance by 

transcurrent faults. As an alternative to coming from a 

westward landmass, the detrital material could have 

been transported by longshore currents from a source 

far removed to the north. The more abundant larger 

grains in laminated limestone closer to coarse-grained 

limestone lend support to transport by longshore currents. Ketner (1968, p. B174-B175) postulated that 

much of the quartz in Ordovician quartzite in the 

Cordilleran miogeosyncline was derived from the 

north. Possibly such a source existed into Silurian and 

Devonian time.

An eastern or southern source, in my opinion, is not 

plausible, as it would have required the transporting of 

the detrital material in the Roberts Mountains Formation across many kilometers of water in which coarsegrained carbonate rock of equivalent age was 

deposited.

The type of material in the source area is nearly as 

unknown as the location of the source area. The 

detrital minerals suggest a mixture of plutonic rocks 

and sedimentary rocks in the source area, but this mixture must be considered in view of the unknown type of 

weathering in the source area, the unknown method of 

transport from the source area, and the probable environment of deposition of the laminated limestone. 

The probable 7.9-8.2 range of pH and the probable Eh 

of about —0.3 of water needed for the deposition of carbonaceous and pyritic limestone (Krumbein and Garrels, 1952, fig. 8) possibly destroyed diagnostic 

minerals. Magnetite and ilmenite, if present in the 

source, were dissolved. Only the most resistant heavy 

minerals —zircon, tourmaline, rutile, and 

monazite—are preserved; much of the quartz and
TRACE ELEMENTS IN THE ROBERTS MOUNTAINS FORMATION 41

feldspar was partly to completely dissolved. The remaining quartz is dominantly nonundulatory quartz, 

which is more resistant than undulatory quartz (Blatt 

and Christie, 1963, p. 570-572). Seemingly, the only 

definite conclusion about the source rocks is that they 

did not include major amounts of Ordovician quartzite. 

Ketner (1966) found no feldspar in these quartzites and 

the heavy mineral content of the quartzites is an order 

of magnitude lower than that of the detrital material in 

the Roberts Mountains Formation.

TRACE ELEMENTS IN THE 

ROBERTS MOUNTAINS FORMATION

Spectrographic analyses were made on 246 samples 

of the Roberts Mountains Formation and related formations collected during this study. The object of the 

spectrographic analyses was to obtain information on 

the trace element content of the Roberts Mountains 

and related formations. Details of the spectrographic 

analyses are given elsewhere (Mullens, 1979). 

Representative spectrographic analyses of laminated 

limestone in the Roberts Mountains Formation and 

coarse-grained limestone from the Roberts Mountains 

and overlying Devonian formations are shown in table 

2. The laminated limestone seems to have the average 

elemental composition of a rock composed of about 80 

percent limestone and 20 percent shale when compared 

to the composition of carbonates and shale reported by 

Turekian and Wedepohl (1961, table 2). The elemental 

content of the coarse-grained limestone is close to that 

of carbonates reported by Turekian and Wedepohl. The 

major exception to the composition reported by 

Turekian and Wedepohl is that the manganese content 

is low in both the laminated limestone and coarsegrained limestone. The laminated limestone averages 

about 200 ppm manganese and the coarse-grained 

limestone averages about 100 ppm manganese. These 

numbers are low when compared to the 1,100 ppm 

manganese in carbonates and 850 ppm manganese in 

shale that Turekian and Wedepohl reported. The 

reason, or reasons, for the low manganese content in 

the Roberts Mountains and related formations was not 

determined. Possibly it is low because the rocks were 

deposited mainly in a reducing environment where 

manganese hydroxide remained in solution (Rankama 

and Sahama, 1950, p. 648).

A few trace elements in the laminated limestone 

show positive correlations with some major components of the rock. Boron generally correlates with 

the amount of clay; vanadium correlates mainly with 

organic carbon content, although it is abundant in 

some clay-rich samples and in rocks that contain traces

TABLE 2.—Representative spectrographic analyses of limestone 

in the Roberts Mountains Formation and overlying Devonian 

formations

Element Roberts Mountains Formation 

laminated limestone

Roberts Mountains Formation 

and overlying Devonian 

coarse-grained limestone

In percent

Fe 

Mg 

Ca 

Ti

1.5 

5

0.1

0.2 

0.2

0.02

In parts per million, except that N = not detected, and 

L = present, but below limit of detection

Mn

Ag 

As

Au

B

Ba

Be

Bi

Ca

Co

Cr

Cu

La

Mo

Nb

Ni

Pb

Sb

Sc

Sn

Sr

V

W

Y

Zn

Zr

200

N 

N

N

30

200

N

N

N

L

30

15

20

5

L

15

15

N

L

N

200-500

200

N

15

LtoN

100

100

N 

N

N

L

200

N

N

N

N

15

10

N

N

L

L

L

N

N

N

500

50

N

15

N

30

of collophane; and lanthanum and zirconium generally 

are related to the silt content. Yttrium is probably 

mainly related to the carbonate content of the rock 

(Rankama and Sahama, 1950, p. 528), although some 

may be in the zircon. Cobalt, chromium, nickel, and 

titanium are generally more abundant in rocks that 

have a relatively high iron content. The distribution of 

copper and zinc is erratic and some samples high in 

these elements contain epigenetic sulfide minerals.

The mercury and gold contents of many of the 

samples collected were determined by atomic absorption methods (Mullens, 1979). Mercury values are high, 

more than 0.2 ppm, in several areas, but mercury 

anomalies are common in Nevada and I cannot relate 

the high values to original sedimentary or 

stratigraphic features. The gold values are low, about 

0.01 ppm, except near known gold deposits which are 

only indirectly related to the sedimentary and 

stratigraphic features. The near absence of gold in the 

Roberts Mountains and related formations is interpreted as indicating that the gold deposits at Carlin 

and Cortez do not represent reconcentration of gold 

originally in the rocks.
42 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

GOLD DEPOSITS IN THE 

ROBERTS MOUNTAINS FORMATION

Laminated limestone in the Roberts Mountains Formation is the host rock for most ore at the Carlin and 

Cortez gold mines and for a small part of the ore at 

Gold Acres mine. These ore deposits do not contain 

visible gold in unoxidized ore nor are they known to 

contribute gold to placer deposits. For these reasons, 

they are commonly known as invisible gold deposits. 

The deposits are surrounded by a distinctive 

geochemical halo, but the halo and unoxidized goldbearing rock can be determined only by chemical 

analyses. Probably the "invisible" character of the 

gold and associated elements is due to a stratigraphic 

control, namely, the character of the permeability and 

porosity of laminated limestone. The source of gold 

and associated elements and the fractures that furnished the plumbing are assumed to have little effect 

on the character of the ore.

The occurrence of gold and geochemical halo at the 

Carlin deposit is described by Hausen (1967), Hausen 

and Kerr (1968), Akright, Radtke, and Grimes (1969), 

Radtke and Scheiner (1970), and Wells and Mullens 

(1973). These features have been studied at the Cortez 

deposit by Wells, Stoiser, and Elliott (1969), Wells and 

Elliott (1971), Wells and Mullens (1973), and Erickson 

and others (1966). The Gold Acres deposit was briefly 

described by Ketner (in Gilluly and Gates, 1965, p. 

134) and in more detail by Wrucke and Armbrustmacher (1975). The Gold Acres mine is structurally so complicated that few details about the Roberts 

Mountains Formation can be determined. The Getchell 

gold deposit in Humboldt County, Nev. (described in 

Joralemon, 1951), is in Cambrian rocks, but otherwise 

the deposit seems similar to the deposits in the 

Roberts Mountains Formation. A summary description of all these deposits is given by Roberts, Radtke, 

and Coats (1971).

Each of the gold deposits named has a characteristic 

suite of elements associated with the ore. Besides gold, 

these elements include arsenic, mercury, tungsten, antimony, nickel, copper, zinc, and lead (Akright and 

others, 1969, fig. 5; Wells and others, 1969, figs. 

13-14). Altered and non-ore samples collected from the 

Carlin mine and the only sample of gold ore collected 

during this study, sample 7006 from the Carlin mine, 

suggest that iron and sulfur should also be considered 

as part of the suite of elements associated with gold 

ore. Pyrite commonly is the only sulfide mineral that 

can be identified in unoxidized ore without recourse to 

polished section although orpiment and realgar are 

locally abundant at the Carlin mine. The only other 

sulfides identified in polished section are minor

amounts of pyrrhotite, arsenopyrite, and sphalerite. 

At the Carlin and Cortez mines, the ore is associated 

with rocks that have had most of the calcite removed 

and clay and quartz added (Wells and others, 1969; 

Wells and Mullens, 1973). The major part of the ore at 

both mines occurs in the upper and more silty part of 

the laminated limestone.

Radtke and Scheiner (1970) postulated that the gold 

at the Carlin mine occurred as a carbon complex. 

Microprobe study of unoxidized gold ore from both the 

Carlin and Cortez deposits, however, indicates that 

most of the gold and arsenic occures in tiny (< 0.005 

mm) grains of pyrite and in the rims of larger grains of 

pyrite disseminated in the ore (Wells and Mullens, 

1973). The tiny grains are abundant in ore but are 

relatively sparse in barren rock. The amount of pyrite 

in the ore, about 1-1.5 percent, exceeds by a factor of 

about 5 my estimate of syngenetic pyrite in unaltered 

laminated limestone (p. 19-20). The relative abundance 

of pyrite in the ore indicates that some pyrite has been 

added, but it is not possible, without isotope studies, 

to prove that most of the pyrite is epigenetic. Probably 

most of the syngenetic pyrite is in larger grains where 

only the edges contain gold. Although some of the 

pyrite may be syngenetic, all gold associated with the 

pyrite is interpreted as epigenetic. If pyrite in 

unaltered laminated limestone contained amounts of 

gold equivalent to the pyrite in the gold ore, then the 

unaltered rock would contain about 1-3 ppm gold, an 

amount easily detected by atomic absorption methods. 

No such gold was found in samples away from ore 

deposits.

I interpret the fine size of the gold- and arsenicbearing pyrite as due to the type of permeability in the 

laminated limestone. The typical weathering to platy 

material indicates that surface waters attack the 

limestone along laminations, although fresh rock is 

seemingly impervious (figs. 3-4). Mineralizing solutions, controlled basically by wide-spaced fractures, 

could also attack along laminations. If so, the surface 

area of rock exposed to mineralizing solutions is enormous, although movement of solutions is along a zone 

that approaches a plane. Thus, while the effective 

permeability is probably great, it is actually due to an 

enormous number of microscopic pores along laminations. The quartz and feldspar silt and the dolomite 

content of the laminated limestone are apparently 

great enough to prevent collapse of the rock as calcite 

along laminations is dissolved, and thereby to allow 

continued permeability in the altered limestone. The 

microscopic pores would control the size of mineral 

grains that filled open space, but not the site of 

minerals that replaced parts of the rock. The dissolving and precipitation of minerals could be related to
APPENDIX: FOSSIL DATA 43

some specific component of the rock or it could be 

related solely to the gross chemistry, pressure, and 

temperature of the hydrologic system.

The theory that the character of the ore is related to 

certain types of permeability and porosity suggests 

that all silty laminated limestone is a potential host for 

ore similar to that in the Carlin and Cortez mines. Such 

silty laminated limestone occurs in many formations 

other than the Roberts Mountains Formation in northcentral Nevada. Probably such formations will contain 

gold ore where they occur over a suitable fracture 

system and source of gold. Finding the gold, however, 

will be done only with chemical analyses, as the gold is 

too fine grained to form placer deposits.

APPENDIX

FOSSIL DATA

Many graptolites and samples to be examined for 

conodonts were collected while studying the Roberts 

Mountains and related formations. All graptolites 

were studied by W. B. N. Berry and all conodonts were 

studied by John W. Huddle. Sparse collections of 

brachiopods and corals were made and these collections were studied by J. T. Dutro, Jr., A. J. Boucot, J. 

G. Johnson, and W. A. Oliver. Jean M. Berdan identified ostracodes from several samples originally submitted for conodonts. Fossils collected during this 

study and a few collected by colleagues are listed in the 

following pages. The lists of fossils were reviewed in 

late 1973 by R. J. Ross, Jr., J. W. Huddle, J. T. Dutro, 

Jr., W. A. Oliver, and J. M. Berdan.

The fossils are listed by localities arranged generally 

by a west-to-east grouping of mountain ranges and a 

south-to-north grouping within the mountain ranges. 

The localities are shown on plate 1. Identification 

numbers, such as 8220 SD, indicate that the fossils are 

part of the permanent collection of the U.S. Geological 

Survey. Field numbers such as TM-F-4-70 show the 

year the collection was made. Most of the graptolites 

and some of the conodonts and brachiopods are tied to 

the Great Britain and Central Europe stages shown in 

table 1.

SHOSHONE RANGE

South Ravenswood window, Shoshone Range, Lander County, Nev. 

About sec. 9, T. 20 N., R. 42 E. (unsurveyed), Mount Airy Mesa 

quadrangle.

USGS Coll. D231 SD (TM-F-24-68). Graptolites collected from 

laminated limestone unit within 1.3 m of the top of the basal 

cherty unit of the Roberts Mountains Formation.

Monograptus priodon (Bronn)

Monograptus spiralis (Geinitz)

Monograptus variabilis (Perner)?

Monograptus sp. (of theM. vomerinus type)

Monograptus sp. (possibly M pandus (Lapworth))

Retiolites geinitzianus Barrande

Age: late Llandoverian—this is an association typical of zone 1 of 

the Silurian-Devonian faunizones outlined by Berry in abstract 

for Tucson meetings of GSA. It is the approximate correlative 

of the late Llandoverian zones of Monograptus griestoniensis 

and M. crenulatus of Elles and Wood.

William B. N. Berry 

November 8, 1968

USGS Coll. D261 SD (TM-F-60-69) Graptolites 0.3-0.6 m above 

basal cherty unit of Roberts Mountains Formation. Same location 

and zone as TM-F-24-68. Re-collected to include better 

specimens.

Cyrtograptus lapworthi (Tullberg) 

Monograptus spiralis (Geinitz) 

Monograptus priodon (Bronn)

Monograptus vomerinus cf. var. gracilis Elles and Wood 

Monograptus sp. (d streptograptid) 

Age: late Llandoverian M. spiralis Zone

William B. N. Berry 

January 5, 1970

Horse Mountain window, northern Shoshone Range, Lander County, Nev. NWV4 sec. 24, T. 28 N., R. 44 E. (unsurveyed) Mt. Lewis 

quadrangle

USGS Coll. D259 SD (TM-F-58-69) Graptolites from laminated 

limestone float, poorly preserved, meager collection, about 46 m 

above base of Roberts Mountains Formation. 

Cyrtograptus sp. 

Monograptus flemingii (Salter) 

Age: Wenlockian

William B. N. Berry 

January 5, 1970

Mill Creek window, northern Shoshone Range, SEViSW1/* sec. 4, T. 

28 N., R. 45 E., Lander County, Nev. Mt. Lewis quadrangle 

USGS Coll. D260 SD (TM-F-59-69) Graptolites from Roberts 

Mountains Formation, stratigraphic position not known, basal 

and upper parts of exposure bounded by faults. 

Gothograptus nassa (Holm) 

Monograptus sp. (of the M. dubius group) 

Monograptus sp.

Age: in span of late Wenlockian-early Ludlovian; could be "dubius/nassa interregnum of Jaeger" which is at Wenlockian-Ludlovian border

William B. N. Berry 

January 5, 1970

Goat Peak window, northern Shoshone Range, sec. 28, T. 29 N., R. 

45 E., Lander County, Nev., Mt. Lewis quadrangle 

USGS Coll. D303 SD (TM-F-15-70) Extremely poorly preserved 

graptolites. Mainly about 15 m above base of Roberts Mountains 

Formation WJ/2 sec. 28, T. 29 N., R. 45 E.

Monograptus flemingi (Salter) 

Age: Wenlockian

William B. N. Berry 

August 12, 1970

USGS Coll. 8809 SD (TM-F-16-70) Coarse-grained limestone, upper 

part of Roberts Mountains Formation, SVfeSE^SWVi sec. 28, T. 

29 N., R. 45 E., at the 7200-ft contour, 605 m east and 60 m north 

of the SW corner of sec. 28, Mt. Lewis quadrangle. About 60 m 

below rocks in upper plate of thrust.

Hindeodella sp. 6 

Icriodus sp. 1
44 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

Neoprioniodus excavatus (Branson and Mehl) 1 

Panderodus sp. 3 

Plectospathodus sp. 2 

Spathognathodus inclinatus Rhodes 22 

Spathognathodus sp. 1 

Age: I am not sure of the age of this sample. There is nothing 

diagnostic and the conodonts are altered. The S. inclinatus 

looks like the subspecies S. inclinatus posthamatus Walliser. 

This has been reported only from rocks of Ludlovian Age and on 

this basis I suggest that this may be Silurian in age rather than 

Devonian.

John W. Huddle 

January 18, 1971

TOIYABE RANGE

Wall Canyon, southern Toiyabe Range, Nye County, Nev. About 

sec. 35, T. 10 N., R. 42 E. (unsurveyed), Pablo Canyon Ranch 

quadrangle

USGS Coll. D2144 Co-supplement (69-FP-102-AF) Basal Roberts 

Mountains Formation chert exposed on south side of Wall Canyon. Collected by F. G. Poole. 

Climacograptus cf. C. scalaris Hisinger 

Climacograptus sp. 

Age: probably early Llandoverian (Early Silurian)

William B. N. Berry 

January 11, 1971

USGS Coll. 8822 SD (TM-70-20-F) Laminated limestone in basal 

cherty unit and 2.4 m above the base of the Roberts Mountains 

Formation. Same location as 69-FP-102-AF. 

Distacodus cf. D. obliquicostatus Branson and Mehl 11 

D. sp. 4 

Distimodus sp. 4 

Ligonodina sp. 1 

Trichonodella sp. 1 

Age: These specimens are altered and fragile and therefore difficult to identify. Probably this is an Early Silurian collection 

because it contains forms common in the Early Silurian of the 

Cincinnati arch area.

John W. Huddle 

February 25, 1971

Pablo Canyon, southern Toiyabe Range, Nye County, Nev. About

sec. 22, T. 10 N., R. 42 E. (unsurveyed), Pablo Canyon Ranch

quadrangle

USGS Coll. D323 SD (70 FP-517F) SWV4 sec. 22, T. 10 N., R. 42 E. 

(unsurveyed). Large coiled graptolites from measured section A 

on south side of Pablo Canyon about 3.2 km WNW of Pablo Canyon Ranch. Collected from float in a 6-m interval between 45 and 

52 m above base of Roberts Mountains Formation and 18 to 25 m 

above basal cherty unit. Collected by F. G. Poole. 

Monograptus spiralis (Geinitz) 

Monograptus sp. (cf. M. vomerinus var. gracilis) 

Age: Silurian-late Llandoverian, Monograptus spiralis Zone

USGS Coll. D324 SD (70 FP-518F) SWV* sec. 22, T. 10 N., R. 42 E. 

(unsurveyed). Graptolites from measured section A on south side 

of Pablo Canyon about 3.2 km WNW of Pablo Canyon Ranch. Collected from float in a 12-m interval between 40 and 52 m above 

base of Roberts Mountains Formation, and 15 to 28 m above 

basal cherty unit. Collected by F. G. Poole.

Cyrtograptus sp.

Monograptus priodon (Bronn)

Monograptus spiralis (Geinitz)

Monograptus cf. M. vomerinus var. gracilis Elles and Wood 

Retiolites geinitzianus Barrande 

Age: Silurian-late Llandoverian, Monograptus spiralis Zone

William B. N. Berry 

October 23, 1970

USGS Coll. D304 SD (TM-F-22-70) In-place collection 10 m above 

base of 25-m-thick basal cherty unit of Roberts Mountains Formation on south side of and 3.2 km above mouth of Pablo Canyon. 

(Cherty unit is about 25 m thick.)

Climacograptus sp. (of the C. Medius-C. rectangularis type)

diplograptid

Monograptus convolutus Hisinger

Monograptus sp. (of the M. triangulatus type) 

Age: Silurian-early-early middle Llandoverian, probably about

zone 20.

In-place graptolites from about llm above base of basal cherty unit 

of Roberts Mountains Formation and 0.4 km east of collection.

Climacograptus sp.

Monograptus sp. (of the M. triangulatus type) 

Age: Silurian-early-early middle Llandoverian, possibly about

zone 19-21

USGS Coll. D305 SD Float collection just above cherty unit of Roberts Mountains Formation on south side and 3.2 km above mouth 

of Pablo Canyon.

Climacograptus sp. (similar to C. mediusl)

Monograptus convolutus Hisinger

Monograptus jaculum Lapworth

Monograptus sp. (of the M. triangulatus type)

Monograptus sp. (hooked thecae—somewhat similar to M.

sedgwicki)

Retiolites geinitzianus Barrande 

Age: Silurian-Llandoverian, overall association indicates age in

span of zone 20-22 or 23

USGS Coll. D306 SD (TM-F-24-70) Float collection from base to 

top of basal cherty unit of Roberts Mountains Formation on 

south side and about 3.2 km above mouth of Pablo Canyon. Collected at exposures where D304 SD was collected and at another 

exposure 0.4 km east. 

Eastern collection:

Climacograptus sp.

Monograptus convolutus Hisinger

Monograptus sp. (hooked thecae and similar toM sedgwicki) 

Age: Silurian-Llandoverian, in span of zones 20-22 

Western collection:

Climacograptus sp.

Monograptus convolutus Hisinger

Monograptus clinganit

Monograptus regularis?

Monograptus revolutus Kurck 

Age: Silurian-Llandoverian, in span of zones 19-20

William B. N. Berry 

January 11, 1971

Clear Creek, Toiyabe Range, Lander County, Nev. Sec. 11 (unsurveyed), T. 15 N., R. 43 E., Millet Ranch quadrangle 

USGS Coll. D249 SD (12349-18J). Roberts Mountains Formation, 

or equivalent, 0.8 km north of Clear Creek, east side of Toiyabe 

Range, east central part of sec. 11 (unsurveyed). Collected by J. 

H. Stewart. 

Monograptus sp. (This fragment appears to be a good mono-
APPENDIX: FOSSIL DATA 45

graptid and the thecal form appears to be most similar to that 

in M. scanicus) 

Age: Silurian—possibly early Ludlovian (latest Middle Silurian)

USGS Coll. D250 SD (12349-25J). Roberts Mountains Formation, 

1.2 km north of Clear Creek, NE part of sec. 11 (unsurveyed) 

(about 460 m north of 12345-18J). Collected by J. H. Stewart. 

Monograptus sp. (appears to have uncinate thecae—could be a

member of the M. hercynicus group)

Age: Late Silurian or Early Devonian, probably in the span of 

Ludlovian- Gedinnian

William B. N. Berry

Point of Rocks, SE'/i sec. 36 (unsurveyed), T. 17 N., R. 42, E., 

Lander County, Austin quadrangle

USGS Coll. D246 SD (14052-6J). Roberts Mountains Formation, 

probably near middle. Collected by J. H. Stewart. 

Monograptus sp. (hooked thecae) 

monograptid or cyrtograptid fragments 

Age: Silurian(?) (could be Devonian)

USGS Coll. D247 SD (14052-6JA). Roberts Mountains Formation, 

about 15 m below top as mapped. Collected by J. H. Stewart. 

Monograptus sp. (a monograptid of the M. hercynicus group 

very similar to M. yukonensis—it may be that form or something closely related to it) 

linograptid fragments

Age: Early Devonian, probably in the span of late Siegenian-Emsian

USGS Coll. D248 SD (14052-6JB). Roberts Mountains Formation, 

about 15 m below top but 90 m west of 6JA. Collected by J. H. 

Stewart.

Monograptus aff. M. kodymi Boucek 

Monograptus sp. (has simple tubular thecae) 

Age: Silurian, in span of late Llandoverian-Wenlockian and probably latest Llandoverian

William B. N. Berry 

October 15, 1969

Silver Creek, west side of Toiyabe Range, Lander County, Nev. 

About sec. 21, T. 21 N., R. 44 E. Vigus Butte NE quadrangle. 

USGS Coll. D258 SD (TM-F-57-69) Graptolites from Roberts 

Mountains Formation, float, stratigraphic position not 

known—thrust faults at base and top of exposure. Unit in thrust 

contact—both above and below—with rocks mapped as Ordovician Antelope Valley Limestone by Stewart and McKee (1970). 

Monograptus nilssoni (Barrande) 

Monograptus sp. (of theM. scanicus type) 

Age: early Ludlovian

William B. N. Berry 

January 5, 1970

USGS Coll. 6918 CO (TM-F-6-69) Fine-grained blue-gray limestone near crest of ridge. About 120 m above thrust fault and 

from unit mapped as Antelope Valley Limestone. 

Oepikodus sp. 2 

Belodellat sp. 1 

Age: This is probably Ordovician in age, but these species are new 

tome.

John W. Huddle 

February 19, 1970

Grass Valley between Toiyabe Range and Simpson Park Mountains, Lander County, Nev. Sec. 13, T. 21 N., R. 46 E., Mt. 

Callaghan quadrangle.

USGS Coll. D330 SD (TM-F-71-6) Scrap graptolites, all float from 

basal 23 m of Roberts Mountains Formation, NWViSW'/i sec. 13, 

T.21N., R. 46 E. 

Monograptus sp. (appear to be monograptids of the M. vomerinus and priodon groups) 

Age: Silurian, probably in span of late Llandoverian-Wenlockian

USGS Coll. D331 SD (TM-F-71-7) Three poorly preserved fragments of monograptids and a couple of plates with odd possibly 

organic markings. Collected just east of prospect in south part of 

sec. 13, T. 21 N., R. 46 E. Rocks have more of a Wenban 

Limestone look (gray nonplaty weathering) than most of the 

Roberts Mountains Formation. If no faults are present, the collection is about 610 m above base of Roberts Mountains and about 

610 m below top of exposed laminated limestone, 

linograptid?

Monograptus sp. (could beM dubius type) 

Age: probably in span of Late Silurian-Early Devonian

William B. N. Berry 

June 16, 1971

TOQUIMA RANGE

Black Cliff Canyon (informal name), central Toquima Range, Nye 

County, Nev. About sec. 8, T. 12 N., R. 46 E. (unsurveyed), lat 

38°53' N., long 116°50' W., Northumberland Pass quadrangle 

USGS Coll. D2214 CO (TM-F-31-70) Graptolites in place in laminated limestone about 1 m below top Perkins Canyon Formation 

(Ordovician) of Kay and Crawford (1964) about 1.6 km above 

mouth of canyon just south of East Northumberland Canyon. 

Dicellograptus complanatus ornatus Elles and Wood 

Dicellograptus complanatus arkansasensis Ruedemann 

Climacograptus supernus Elles and Wood 

Diplograptus cf. D. crassitestus 

Orthograptus truncatus abbreviatus Elles and Wood 

Age: latest Ordovician, zone 15 (D. complanatus ornatus Zone) 

One piece in the collection does not bear any of the above listed species but instead bears the following: 

Leptograptus sp. 

Pleurograptus? sp.

Climacograptus sp. (similar to C. styloideus) 

Age: This association of forms suggests a zone 14 age. (See USGS 

Coll. D2277 CO).

USGS Coll. D313 SD (TM-F-32-70) Graptolites from greenish-gray 

silicified claystone in place 35 m above base of basal cherty unit of 

Roberts Mountains Formation (cherty unit is 50 m thick) exposed 

1.6 km above mouth of canyon just south of East Northumberland Canyon.

Monograptus convolutus Hisinger

Monograp tus jaculum?

Monograptus lobiferus?

Monograptus sp. (of the M. priodon type)

Retiolites geinitzianus Barrande 

Age: Silurian-Llandoverian, about zone 22-23

USGS Coll. D314 SD (TM-F-33-70) Float collection from upper 15 m 

of the basal cherty unit in the Roberts Mountains Formation, 

Black Cliff Canyon, same location as D313 SD.

Monograptus sp. (of theM spiralis type)

Monograptus sp. (of the M. priodon type)

Monograptus cf. M. crispus Lapworth

Retiolites geinitzianus Barrande

plegmatograptid
46 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

Age: Silurian-Llandoverian, probably about zones 23-24

William B. N. Berry 

January 11,1971

USGS Coll. D2277 CO (TM-F-71-4) Graptolites. Perkins Canyon 

Formation of Kay and Crawford (1964). Collected in laminated 

black limestone 4.5 m below top and 3.2 m below D2214 CO. 

Climacograptus hvalross Ross and Berry 

Dicellograptus complanatus var. ornatus Elles and Wood 

Orthograptus truncatus var. abbreviates Elles and Wood 

Age: Ordovician, zone 15 without question (all but one piece in 

D2214 CO had the same zone graptolites and the graptolites on 

that one piece were so highly smeared that precise identification 

to species was not possible, hence the suggested zone 14 age for 

it was highly questionable—and a suggestion that perhaps zone 

14 material was present in the section)

USGS Coll. D329 SD (TM-F-71-5) Scraps of graptolites from float 

of silicified claystone below M. convolutus Zone in basal chert of 

the Roberts Mountains Formation, Black Cliff Canyon. 

Climacograptus sp. 

Diplograptusl 

GlyptograptusTW

Age: in span of Late Ordovician-Early Silurian. The climacograptid seems similar to species known from the Early Silurian such 

as C. rectangularis and C. medius.

William B. N. Berry 

June 16, 1971

Wood Canyon, east side of Toquima Range, Nye County, Nev. 

About sec. 4, T. 12 N., R. 46 E. (unsurveyed), Northumberland Pass 

quadrangle.

USGS Coll. D320 SD (TM-F-43-70) Graptolites from about 8 m 

above base of Roberts Mountains Formation, basal cherty unit 

north side of Wood Canyon, and about 2.4 km above mouth. 

Cherty unit is about 35m thick. Collected by E. H. McKee. 

Climacograptus cf. C. scalaris Hisinger 

Climacograptus sp. (similar to C. medius) 

Age: Silurian-Early Llandoverian, about zones 16-19

William B. N. Berry 

January 11, 1971

USGS Coll. D327 SD (TM-F-71-2) Sparse collection of graptolites 

from about 15 m above base of Roberts Mountains Formation, 

north side of Wood Canyon and about 2.4 km above mouth. Same 

locality as D320 SD.

Climacograptus sp. (C. medius-C. rectangularis type) 

Pseudoclimacograptus hughesi (Nicholson) 

Monograptus sp. (cf. M. revolutus Kurck) 

Age: Silurian-Llandoverian, approximately zone 18 or 19

William B. N. Berry 

June 16, 1971

USGS Coll. D242 SD (E8FP-170F). Graptolites from south side of 

Wood Canyon and about 2.4 km above mouth. From basal cherty 

unit of Roberts Mountains Formation. Collected by F. G. Poole. 

Climacograptus of C. scalaris (Hisinger) (Linne?) 

Climacograptus sp. 

Diplograptus sp.

Monograptus sp. (fragments have the aspect of M. revolutus) 

Rhaphidograptusl sp.

Age: Silurian-Llandoverian, probably in the span of zone 18 

(Monograptus cyphus) and 19 (Monograptus gregarius)

William B. N. Berry 

April 16, 1969

West Northumberland Canyon, Toquima Range. Land not surveyed. About lat 39°00' N., long 116°53' W., near border of Jet Spring 

and Wildcat Peak quadrangle

USGS Coll. D237 SD (TM-F-30-68). North side of West Northumberland Canyon. About 0.4 km upstream from Badwater Canyon. 

Single graptolite from float just above basal cherty unit of 

Roberts Mountains Formation. Graptolite is not well preserved.

cyrtograptid cladial fragment? (Only a fragment is present) 

Age: inasmuch as this fragment has plain thecae and may be a 

part of a cyrtograptid—or perhaps it may be a piece of a long, 

slender rhabdosome with plain thecae—it is Silurian in age and 

probably falls within a late Llandoverian-Wenlockian span

William B. N. Berry 

November 8, 1968

USGS Coll. D307 SD (TM-F-25-70) Float collection of graptolites 

from just above basal cherty unit of Roberts Mountains Formation on west side of mouth of Badwater Canyon at West Northumberland Canyon.

Monograptus vomerinus cf. var. gracilis Elles and Wood 

cyrtograptid scrap? 

Age: in span of late Llandoverian-Wenlockian

William B. N. Berry 

January 11,1971

Mill Canyon, Toquima Range, Nye County, Nev. About lat 39°01' 

N., long 116°47' W., Wildcat Peak quadrangle 

USGS Coll. D308 SD (TM-F-26-70) Float collection from just above 

base of Roberts Mountains Formation (no basal chert) from east 

side and about 1.2 km up first major fork at Mill Canyon. 

Monograptus colonus Barrande 

Monograptus dubius Suess 

Monograptus nilssoni Barrande 

Age: Silurian-early Ludlovian, Monograptus nilssoni Zone

USGS Coll. D309 SD (TM-F-27-70) Float collection about 23 m 

above base of Roberts Mountains Formation. Same location as 

D308 SD

Monograptus bohemicus Barrande 

Monograptus colonus Barrande 

Monograptus nilssoni Barrande 

Monograptus uncinatus? 

Age: Silurian-early Ludlovian, Monograptus nilssoni Zone

William B. N. Berry 

January 11, 1971

Ikes Canyon, Toquima Range, Nye County, Nev. About sec. 13, T. 

14 N., R. 46 E. (unsurveyed), Dianas Punch Bowl quadrangle 

USGS Coll. D310 SD (TM-F-28-70) Graptolites in place but distance above base of Roberts Mountains Formation not 

known—probably about 115 m above base and 3 m below top. 

Just below basal bed of McMonnigal Limestone. About 0.4 km 

south of Ikes Cabin and on south side of and 1.8 km above the 

mouth of Ikes Canyon. 

Monograptus sp. (M. hercynicus group—could be M. angustidens)

Monograptus sp. (uncinate thecae—could beM bouceki) 

Monograptus sp. (appears similar toM. transgrediens) 

Age: in span of latest Silurian-earliest Devonian, possibly latest 

Silurian

USGS Coll. D311 SD (TM-F-29-70) Float collection of graptolites. 

All about 8 m above base of Roberts Mountains Formation (no 

basal chert) exposed along ridge that extends southwest from 

mouth of Ikes Canyon. Possibly Roberts Mountains Formation is 

in fault contact with underlying rocks and an unknown thickness 

of basal Roberts Mountains is missing.
APPENDIX: FOSSIL DATA 47

Monograptus bohemicus Barrande 

Monograptus colonus Barrande 

Monograptus dubius Suess 

Monograptus scanicusl 

Age: Silurian-early Ludlovian, Monograptus nilssoni Zone (?)

USGS Coll. D312 SD (TM-F-30-70) Float collection of graptolites. 

Three fragments about 85 m above base of Roberts Mountains 

Formation, and two fragments about 105 m above base which is 

probably a fault instead of a sedimentary contact. About 100 m 

southwest of D311 SD on ridge that extends southwest from 

mouth of Ikes Canyon. 

85m:

Monograptus sp. (of the M. dubius type) 

Monograptus nilssoni? Barrande 

105m:

Monograptus nilssonit 

Age: Silurian, probably Ludlovian

William B. N. Berry 

January 11, 1971

Petes Canyon area, Toquima Range, Lander County, Nev. Sec. 10, 

T. 16 N., R. 46 E., Wildcat Peak quadrangle and sec. 5, T. 16 N., R. 

46 E., Spencer Hot Springs quadrangle.

USGS Coll. D232 SD (TM-F-25-68) Sec. 10, T. 16 N., R. 46 E., 

Graptolites collected from the lower part of the Roberts Mountains Formation at Petes Canyon window.

Bag 1—Graptolites in chert float near base of basal cherty unit of 

Roberts Mountains Formation.

Monograptus sp. (of the M. priodon group)

Monograptus sp. (plain tubular thecae) 

Age: in the span of late Llandoverian-Wenlockian 

Bag 2—Sparse collection of graptolites that are either from within 

the upper part of the lower cherty unit of the Roberts Mountains 

Formation or within the lower 0.3 m of rock that overlies the 

chert.

Cyrtograptus cf. C. Solaris Boucek

Monograptus spiralis (Geinitz)

Retiolites geinitzianus Barrande 

Age: late Llandoverian, this association is typical of zone 1 of the

Silurian-Devonian faunizones outlined by Berry (1969). It is the

approximate correlative of the late Llandoverian zones of

Monograptus griestoniensis and M. crenulatus of Elles and

Wood.

Bag 3—Float of straight graptolites that could have been in the 

upper meter of the chert or in the lower 3 m of rock that overlie 

the chert.

Cyrtograptus sp. (of the C. lapworthi type)

Monograptus priodon (Bronn)

Monograptus sp. (of the M. vomerinus group) 

Age: probably late Llandoverian (could be early Wenlockian). The

presence of a cyrtograptid close to C. lapworthi is suggestive

that this collection is more likely of late Llandoverian age. 

Bag 4—Graptolites that occur 23-35 m above the base of the 

Roberts Mountains Formation.

Monograptus sp. (of the M. dubius group)

Monograptus sp. (fragment appears to be a monograptid of the

M. vomerinus type)

Age: in the span of late Llandoverian-Wenlockian 

Bag 5—Graptolites collected from float at the top of the basal 

cherty unit of the Roberts Mountains Formation in sec. 5, T. 16 

N., R. 46 E.

Cyrtograptus sp. (of the C. lapworthi type)

Monograptus priodon (Bronn)

Stomatograptus grandis Suess

Age: late Llandoverian, the presence of S. grandis is indicative of 

a latest Llandoverian age

William B. N. Berry 

November 8, 1968

USGS Coll. D299 SD (TM-F-11-70) Single fragment of graptolite 

collected about 150 m above basal cherty unit of Roberts Mountains Formation at Petes Canyon area, sec. 10. Probably float 

from older Roberts Mountains exposed across fault to south.

Monograptus sp.—M dubius group? 

Age: in the span of late Llandoverian-Pridoli

William B. N. Berry 

August 12, 1970

USGS Coll. D328 SD (TM-F-71-3) Very sparse float collection of 

graptolites in lower 23 m of basal cherty unit of the Roberts 

Mountains Formation, north-central sec. 10, T. 16 N., R. 46 E. 

Chert is about 43 m thick if not faulted. Chert is across normal 

fault from D232 SD. 

In place collection: about 23 m above base of chert

Climacograptus sp.

Retiolites geinitzianus angustidens Elles and Wood

Monograptus convolutus (Hisinger) 

Age: Silurian-Llandoverian, about zone 22 or 23 

Float collection: float below in place collection

Climacograptus sp.

Diplograptus sp.?

Monograp tusl

Orthograptusl 

Age: Silurian-early part of the Llandoverian, in span of zones

18-23 or 24

William B. N. Berry 

June 16, 1971

MONITOR RANGE

Clear Creek Mountain (informal name), Monitor Range, Nye County, Nev. About sec. 31, T. 12 N., R. 49 E. (unsurveyed), Danville 

quadrangle

USGS Coll. D262 SD (TM-F-61-69) Sparse collection of monograptids from laminated dolomite float in lower 15 m of beds 

equivalent to the Roberts Mountains Formation. 

Cyrtograptus? sp.

Monograptus sp. (of the M. vomerinus type?) 

Age: in span of late Llandoverian-Wenlockian

William B. N. Berry 

January 5, 1970

USGS Coll. 8222 SD (TM-F-14-68) Grab sample of medium-grained

light-gray massive dolomite. About 30 m above laminated

dolomite that is equivalent to the Roberts Mountains Formation

at Miniature Grand Canyon a few miles north T. 12 N., R. 49 E.

Acodus sp. 2

Belodella sp. 1

Prioniodina sp. 1

Icriodusl fragment

Icriodus woschmidtit Ziegler 1

Hindeodella sp. 1

Age: probably Early Devonian based on the I. woschmidtil I

would need a larger collection to be sure of this identification.

John W. Huddle 

April 4, 1969

USGS Coll. 8485 SD (69FP-237F) Brown medium-grained 4.5-mthick dolomite cliff-former estimated to be about 60 m above top 

of Ely Springs Dolomite or Hanson Creek Formation interbedded
48 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

with laminated dolomite beds equivalent to the Roberts Mountains Formation. Collected by F. G. Poole.

Ligonodona sp. 1 

Prioniodina sp. 1 

Spathognathodus exiguus Phillip 1 

Age: S. exiguus has been reported from Lower Devonian rocks 

in Nevada, Canada, and Australia.

USGS Coll. 8486 SD (69FP-238F) Coarse-grained dolomite about

15m above 8485 SD. Collected by F. G. Poole. 

Belodella sp. 1 

Ozarkodina sp. 1 

O. cf. O. media Walliser 1 

Panderodus sp. 3 

Plectospathodus sp. 1 

Spathognathodus sp. 2

Age: This collection could be Silurian or Early Devonian in age. 

Nothing diagnostic but there is nothing inconsistent with a 

Devonian age indicated by the samples above and below.

USGS Coll. 8487 SD (69 FP-239F) Coarse-grained dolomite probably equivalent to the Lone Mountain Dolomite and 15 m above 

8486 SD. Collected by F. G. Poole.

Diplododella sp. 1 

Hindeodella sp. 10 

Ozarkodina denkmanni Ziegler 9 

Panderodus sp. 6 

Plectospathodus sp. 1 

Spathognathodus remscheidensis Ziegler 20 

Age: The conodonts in this collection are fractured and most specimens are broken. The identification of S. remscheidensis is 

doubtful but this seems to be an Early Devonian fauna.

John W. Huddle 

September 18, 1970

Miniature Grand Canyon, Monitor Range. About sec. 32, T. 13 N., 

R. 49 E. and sec. 5, T. 12 N., R. 49 E. Stargo Creek quadrangle, Nye 

County, Nev.

USGS Coll. D257 SD (TM-F-56-69) About sec. 32, T. 12 N., R. 49 E. 

Graptolites probably about 60 m above base of exposed Roberts 

Mountains Formation, but base of exposure of Roberts Mountains is at a fault. Collected above second coarse-grained 

fossiliferous limestone exposed just east of fault. Between 8435 

SD and 8436 SD.

Monograptus chimaera (Barrande)? 

Monograptus colonus (Barrande) 

Monograptus dubius (Suess) 

Monograptus nilssoni (Barrande) 

Monograptus otM. praedubius (Boucek) 

Age: early Ludlovian

William B. N. Berry 

January 5, 1970

USGS Coll. 8435 SD (TM-F-3-69) Basal coarse-grained limestone 

in zone of interbedded laminated limestone and coarse-grained 

limestone unit of the Roberts Mountains Formation. Below D257 

SD.

Belodella cf. B. resimus Philip 1 

Hindeodella sp. 6 

Neoprioniodus excavatus (Branson and Mehl) 3 

Ozarkodina sp. 1 

Panderodus sp. 31 

Plectospathodus sp. 1 

Ozarkodina sp. 1 

Prioniodina sp. 1

Spathognathodus inclinatus inclinatus Rhodes 16 

S. sp. 3 

Trichonodella sp. 1 

' 'Oneotodus '' beckmanni Bischof f and Sanneman 1 

Age: There is nothing in this fauna restricted to the Silurian or 

Lower Devonian. It could be as old as early Ludlovian or as 

young as Emsian.

John W. Huddle 

February 19, 1970

pentameroid brachiopod, probably Rhipidium 

Coelospira sp. 

atrypid fragment, indet.

Age: The presence of a probable Rhipidium suggests a Late Silurian (Ludlovian) rather than a Devonian age.

J. T. Dutro, Jr. 

September 27, 1971

Alveolites sp. 

Cladopora sp. 

Coenites sp. 

Favosites*!

Undetermined rugose corals, 8 + species 

Age: Silurian or Devonian

William A. Oliver, Jr. 

September 14, 1971

USGS Coll. 8436 SD (TM-F-4-69) Unnamed Devonian beds. 

Coarse-grained limestone 15m above the base of the interbedded 

coarse-grained limestone and silty limestone that overlies the 

laminated silty limestone in the Roberts Mountains Formation 

where D257 SD was collected.

Belodella cf. B. resimus Philip 1 

Bryantodus sp. 1 

Hindeodella sp. 10 

Neoprioniodus excavatus (Branson and Mehl) 5 

Ozarkodina denckmanni (Ziegler) 1 

O. media Walliser 18 

O. robustus (Bischoff and Sannemann) 3 

Panderodus sp. 1 

Plectospathodus extensus (Rhodes) 11 

Scolopodus devonicus Bischoff and Sannemann 2 

Spathognathodus remscheidensis (Ziegler) 23 

S. wurmi Bischoff and Sannemann 38 

Age: This collection appears to be Early Devonian in age. The 

presence of O. denckmanni, S. remscheidensis, B. cf. resimus, 

and S. devonicus all suggest an Early Devonian age but a Late 

Silurian age is not impossible.

John W. Huddle 

February 19, 1970

Machaerarial sp. 

Atrypinacf. A. simpsoni Johnson 

brachiopod fragments, indet.

Age: This most likely represents the Early Devonian Quadrithyris Zone.

J. T. Dutro, Jr. 

September 27, 1971

Cladopora sp. 

Coenites sp. 

Favosites sp. 

Age: Silurian or Devonian

William A. Oliver, Jr. 

September 14, 1971
APPENDIX: FOSSIL DATA 49

Stargo Spring area, Monitor Range, Nye County, Nev. About sec. 

20, T. 13 N., R. 49 E. (unsurveyed), Stargo Creek quadrangle. 

USGS Coll. D300 SD (TM-F-12-70) Graptolites from laminated 

limestone about 15 m above basal chert of Roberts Mountains 

Formation, but there is a fault of unknown displacement between 

graptolite-bearing rocks and top of basal cherty unit. Sparse float 

collection from isolated outcrop a few hundred meters east of 

main collection. 

Monograptus dubius Suess 

Monograptus "praedeubeli" 

Age: latest Wenlockian, M. dubius/G. nassa Zone 

Float—M. dubius and M. scanicus.

William B. N. Berry 

August 12, 1970

Copenhagen Canyon, Monitor Range, Eureka County, Nev. SWVi 

sec. 36 T. 16 N., R. 49 E., Horse Heaven Mountain quadrangle. 

USGS Coll. D234 SD (TM-F-27-68) Collection includes one bag of 

graptolites from laminated limestone float collected just above 

the basal cherty unit and 35 m above base of Roberts Mountains 

Formation, one bag from float extending 35 to 85 m above base; 

and one bag from 100 m above base.

Graptolites from laminated limestone float near top of the basal 

cherty unit and 35 m above base of the Roberts Mountains Formation.

Cyrtograptus sp.

Monograptus priodon (Bronn) 

Age: in the span of late Llandoverian-early Wenlockian

Graptolites in float 35 to 85 m above base of the Roberts Mountains Formation.

Cyrtograptus sp.

Monograptus flemingii (Salter) 

Age: probably Wenlockian

Graptolites from 100 m above base of the Roberts Mountains 

Formation.

Monograptus dubius (Suess)

Monograptus uncinatus Tullberg

Gothograptus spinosus Wood 

Age: early Ludlovian, Monograptus nilssoni-M. Scanicus Zone

William B. N. Berry 

November 8, 1968

USGS Coll. D256 SD (TM-F-55-69)

Bag A—Graptolites from upper 0.3 m of basal limestone and 

chert unit (31 m thick) of Roberts Mountains Formation.

Climacograptus of C. rectangularis (McCoy)

Dimorphograptus confertus of var. Swanstoni (Lapworth)

Glyptograptus sp.

Age: early Llandoverian, zone 18 of Elles and Wood 

Bag B—Graptolites, mainly float, at 120 m above base of Roberts 

Mountains Formation.

Monograptus bohemicus (Barrande)

Monograptus colonus (Barrande)

Monograptus of M. crinitus (Wood)

Monograptus micropoma (Jaekel) 

Age: early Ludlovian

Bag C—Graptolites, mainly float, at 150 m above base of the 

Roberts Mountains Formation.

Monograptus bohemicus (Barrande)

Monograptus colonus (Barrande)

Monograptus of M. crinitus (Wood)

Monograptus dubius (Suess)

Monograptus micropoma (Jaekel)

Monograptus nilssoni (Barrande)

Monograptus of M. praedubius (Boucek)

Monograptus scanicus (Tullberg) 

Age: early Ludlovian

Bag D—Graptolites in float 150-185 m above base of Roberts 

Mountains Formation.

185 m—Monograptus sp. (of the M. dubius type) 

175 m—Monograptus bohemicus (Barrande) 

Age: Ludlovian

William B. N. Berry 

January 5, 1970

USGS Coll. D297 SD (TM-F-9-70) Two meager float collections of 

graptolites from Roberts Mountains Formation. 

Bag A—From about 230 m above base and bag B from about 245 

to 305 m above base if no faults crossed.

Age: Monograptus of the M. dubius group—age is in span of late 

Llandoverian-Pridoli; Monograptus sp. with uncinate 

thecae—possibly Pridoli or Early Devonian

William B. N. Berry 

August 12, 1970

USGS Coll. 8214 SD (TM-F-15-68) Thin beds of bioclastic limestone 120 m above base of Roberts Mountains Formation. 

"Neoprioniodus'" excavatus (Branson and Mehl) 1 

Ozarkodina media Walliser 1 

Panderodus sp. 12 

Plectospathodus extensus Rhodes 4 

Plectospathodus sp. 1 

Spathognathodus inclinatus Rhodes 2 

S. remscheidensis! Ziegler 1 

"Synprioniodina" siluricaf Walliser 1 

Trichonodella sp. 1 

S. remscheidensis and S. inclinatus occur in Upper Silurian and

lower Devonian rocks. 

Age: Late Silurian or Early Devonian

John W. Huddle 

March 4, 1969

Collection contains a number of silicified fragments of brachiopods, including Resserettal, Salopina, Atrypa and pentameroids 

(at least one specimen of Conchidium or Kirkidium). 

Age: most likely Late Silurian (Ludlovian)

J. T. Dutro, Jr. 

March 9, 1972

USGS Coll. 8304 SD (TM-F-15-68) Thin beds of medium-grained 

limestone 190 m above base of Roberts Mountains Formation. 

Hindeodella sp. 1 

Panderodus sp. 4 

Ozarkodina aff. O. ziegleri Walliser 1 

Spathognathodus inclinatus Rhodes 5 

S. sp. 1 

Age: Late Silurian or Early Devonian

John W. Huddle 

March 4, 1969

USGS Coll. 8304 SD (TM-F-15-68) Same location as 8214 SD, 

190 m above base of Roberts Mountains Formation. 

Collection contains scraps of orthoids (perhaps Salopina), A trypa

and costate pentameroids (perhaps Kirkidium). 

Age: most likely Late Silurian (Ludlovian)

J. T. Dutro, Jr. 

March 9, 1972

USGS Coll. 8449 SD (TM-F-16-69) Platy weathering fine-grained 

limestone about 180 m above the base of the Roberts Mountains 

Formation. 1.6 m above 8304 SD.
50 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

Ancyrognathus? sp. 2 

Hindeodella sp. 2 

Drepanodus sp. 1 

Ozarkodina sp. 1 

Panderodus sp. 1 

Plectospathodus extensus Rhodes 2 

Polygnathoides emarginatus (Branson and Mehl) 1 

Prioniodina sp. 1 

Spathognathodus inclinatus Rhodes 2 

Age: If I am correct in my identification of P. emarginatus, from a 

single specimen, this collection is Late Silurian.

John W. Huddle 

March 13, 1970

USGS Coll. 8488 SD (69FP-246F) About 5 m below top of Hanson 

Creek Formation. Collected by F. G. Poole.

Icriodina cf. /. stenolopata Rexroad 1 

Age: If this identification is correct the age is Early Silurian. The

species was described from the Brassfield Formation. More

specimens needed to be sure.

USGS Coll. 8489 SD (69FP-247F) About 1 m below top of Hanson 

Creek Formation. Collected by F. G. Poole.

Acodus unicostatus Branson 1 

Drepanodus sp. 2 

Panderodus sp. 2 

Paltodus cf. P. dyscritus Rexroad 2 

Except for the Drepanodus, these species occur in the Brassfield Formation of Kentucky. 

Age: probably Early Silurian

John W. Huddle 

September 18, 1970

Brock Canyon, Monitor Range, Eureka County, Nev. About 

sec. 25, T. 17 N., R. 48 E. (unsurveyed), Hickison Summit 

quadrangle.

USGS Coll. D315 SD (TM-F-34-70) Float collection of graptolites 

from base of cherty unit (about 9 m thick) to 45 m above base of 

Roberts Mountains Formation at Brock Canyon. 

Monograptus bohemicus (Barrande) 

Monograptus colonus (Barrande) 

Monograptus nilssoni (Barrande) 

Monograptus uncinatus? 

Age: Silurian-early Ludlovian, Monograptus nilssoni Zone

USGS Coll. D316 SD (TM-F-35-70) Float collection of graptolites 

from about 60 to 140 m above base of Roberts Mountains Formation, Brock Canyon.

Monograptus colonus (Barrande)

Monograptus dubius Suess

Monograptus scanicus Tullberg 

Age: Silurian-early Ludlovian, Monograptus scanicus Zone

USGS D317 SD (TM-F-36-70) In place collection of graptolites 

from about 185 m above base of Roberts Mountains Formation, 

Brock Canyon, and a float collection 100 m southeast of in-place 

collection.

Monograptus sp. (M. hercynicus group) 

Age: Early Devonian(?)

William B. N. Berry 

January 11, 1971

SIMPSON PARK MOUNTAINS

Coal Canyon, northern Simpson Park Mountains, Eureka County, 

Nev. SE J/4 sec. 17 and N1^ sec. 20, T. 25 N., R. 49 E. Horse Creek 

Valley quadrangle.

USGS Coll. 8218 SD (TM-F1-68) Laminated limestone just above 

chert at base of Roberts Mountains Formation in SWVi sec. 17. 

Monograptus griestoniensis (Nicol) 

Monograptus sp. 

Stomatograptus grandis (Suess) 

Age: latest Llandoverian

USGS Coll. 8218A SD Roberts Mountains Formation—float from 

60 m above base. SWVi sec. 17

Fragments of graptoloids, slender, two pieces with plain thecae

and one with slightly hooked thecae. These could be parts of cyrtograptids.

Age: Silurian, possibly Wenlockian.

USGS Coll. 8218B SD 105 m above base of Roberts Mountains Formation at SWVi sec. 17.

Monograptus bohemicus cf. var. tenuis Boucek 

Monograptus uncinatus Tullberg 

Age: Ludlovian, probably early Ludlovian

William B. N. Berry 

March 17, 1969

USGS Coll. D228 SD (TM-F-21-68) Central part NV* sec. 20, T. 25 

N., R. 49 E. Poorly preserved graptolites from about 380 m above 

the base of the Roberts Mountains Formation of the Coal Canyon 

section.

Monograptus praehercynicus Jaeger

Monograptus cf. M. praehercynicus Jaeger (This is a thin form 

commonly found to occur in the M. uniformis Zone and to 

range upwards to occur with M. praehercynicus in the M. 

praehercynicus Zone.)

Age: Devonian, Monograptus praehercynicus Zone—this is a probable correlative of the late Gedinnian

William B. N. Berry 

November 8, 1968

USGS Coll. 8216 SD (TM-F-2-68) Roberts Mountains Formation 

across fault and about 67 m above creek on east side of Coal Canyon, SE :/4 sec. 17, T. 25 N., R. 49 E.

Belodella devonicus (Stauffer) 3 

B. n. sp. 7 

Hindeodella sp. 11 

Icriodina? sp. 1 

Kockelella variabilis Walliser 1 

Lonchodina walliseri Ziegler 1 

Neoprioniodus excavatus (Branson and Mehl) 2 

Ozarkodina denkmanni Ziegler 2 

O. gaertnerif Walliser 1 

O. media Walliser 14 

O. typica Branson and Mehl 2 

Neoprioniodus multiformis? Walliser 5 

Paltodus n. sp. 1 

Panderodus sp. 1 

Plectospathodus extensus Rhodes 12 

P. aff. P. alternatus Walliser 10 

Scolopodus devonicus Bischoff and Sannemann 2 

Spathognathodus dubius (Ethington and Furnish) 26 

S. eosteinhornensis (Walliser) 14 

Synprioniodina sp. 1 

Age: The fauna is probably Late Silurian, Ludlovian in age. The
APPENDIX: FOSSIL DATA 51

Late Silurian age is based primarily on the presence of S. eosteinhornensis. O. gaertneri, Icriodina and Kockelella should not 

occur with O. denkmanni, S. eosteinhornensis and O. typica. 

Perhaps this is a mixed or contaminated sample.

John W. Huddle 

April 4, 1969

Collection contains:

echinoderm debris, indet.

favositid and horn corals, indet.

ramose bryozoans, indet.

orthoid brachiopods, indet.

Leptaenal sp.

Gypidula aff. G. pelagica (Barrande)

Cyrtina sp.

Atrypa sp. 

Age: probably earliest Devonian (Gedinnian)

J. T. Dutro, Jr. 

March 9, 1972

CORTEZ MOUNTAINS

Rattlesnake Canyon (informal name), Cortez Mountains, Eureka 

County, Nev. Includes sees. 4 and 9, T. 26 N., R. 48 E., Cortez 

quadrangle.

USGS Coll. D229 SD (TM-F-22-68) NWVi sec. 9, T. 26 N., R. 48 E. 

Only graptolites found in place in section measured at Rattlesnake Canyon. They are 8 m above base of Roberts Mountains 

Formation. One specimen of a Monograptus spiralis found at base 

of Roberts Mountains Formation 0.8 km south of section. 

Monograptus cf. M. praedubius Boucek 

Monograptus priodon (Bronn) 

Monograptus riccartonensis Lapworth 

Possible cyrtograptid cladia 

fragments of monograptids that may be of the M. vomerinus

group

Age: early Wenlockian, probably Monograptus riccartonensis 

Zone. The presence of a Monograptus spiralis at the base of the 

formation is indicative of a slightly older age—a latest Llandoverian age—for the beds bearing it.

William B. N. Berry 

November 8, 1968

USGS Coll. D293 SD (TM-F-5-70) Meager collection of graptolites from laminated limestone about 300 m above base of Roberts 

Mountains Formation and 30 m below lowest coarse-grained 

limestone assigned to the Wenban Limestone. SEViSWVi sec. 4. 

About 0.8 km north of section measured in Rattlesnake Canyon.

Monograptus uniformist—a hercynicus group form anyway. 

Age: Early Devonian

William B. N. Berry

Cortez mine, Lander County, Nev., Cortez quadrangle. Land not 

surveyed. Approximately lat 40°11'30" N., long 116°37'00" W. 

USGS Coll. D289 SD (TM-F-1-70) Poorly preserved iron-stained 

graptolitesf?), Roberts Mountains Formation; stratigraphic position not known. From gold ore float, 1550-m level, high wall on 

south side of west pit. 

?'Monograptus flemingii

USGS Coll. D290 SD (TM-F-2-70) Poorly preserved graptolites 

and a leaf-shaped marking on bedding surface. Roberts Mountains Formation; stratigraphic position not known. From gold 

ore, 5200-ft level, west end of east pit. 

Monograptids, but not identifiable as to genus

USGS Coll. D291 SD (TM-F-3-70) Extremely poorly preserved 

graptolitesl?), Roberts Mountains Formation; stratigraphic position not known. From 1550-m level, west end of east pit.

Monograptus sp. of theM dubis group

Age: These three collections indicate an age in the span of late 

Llandoverian to Pridoli

William B. N. Berry 

August 12, 1970

USGS Coll. D332 SD (TM-F-8-71) Two collections from float of

Roberts Mountains Formation. 1550-m bench, north side of

southeast pit.

Bag 1 contains graptolites and possible Styliolina or Tentaculites; bag 2 contains different graptolites from other float. 

Stratigraphic position in Roberts Mountains Formation not 

known.

Bag I: Monograptus cf. M. praehercynicus Jaeger

Age: Early Devonian—probably late Gedinnian.

Bag 2: Monograptus aff. M. praehercynicus (a new species)

Age: Early Devonian—this is the M. hercynicus group monograptid cited by Berry (1970) as being indicative of the M. uniformis 

Zone in central Nevada; thus an Early Devonian-early Gedinnian age is suggested for the blocks bearing it.

It appears that these rocks from the Cortez mine area are Early 

Devonian in age and that two graptolite zones—M. uniformis 

and M. praehercynicus—are represented.

William B. N. Berry 

June 16, 1971

Cortez Canyon, Lander County, Nev. Land not surveyed. Approximately lat 40°11' N., long 116°38' W., Cortez quadrangle. Collections made across contact of Roberts Mountains Formation and 

Wenban Limestone as mapped by Gilluly and Masursky (1965, pi. 1) 

about 0.5 km above mouth of Cortez Canyon. 

USGS Coll. 8220 SD (TM-F-13-68) Float from the upper 15 m of 

the Roberts Mountains Formation.

Age: A number of specimens of Strophochonetes and poor scraps 

of a possible Leptocoelia. If latter is actually that genus, age is 

Early Devonian. It could be a similar-looking genus, however, 

and age range would be Late Silurian-Early Devonian.

USGS Coll. 8220A SD (TM-F-13-68) Same locality as 8220 SD. 

Float from the lower 30 m of the Wenban Limestone. 

Collection contains indeterminate brachiopod fragments, a possible Leptocoelia, and several partial trilobites, probably 

phacopids. 

Age: probably Early Devonian

J. T. Dutro, Jr. 

March 9, 1972

Icriodusl sp. 

Age: probably Devonian

John W. Huddle 

April 4, 1969

Fourmile Canyon, Cortez quadrangle. About lat 40°13'N., long 

116°32'30" W.

USGS Coll. D92 SD Supplemental collection by TEM-Fourmile 

Canyon Formation, about 2.5 km above mouth and on north side of 

Fourmile Canyon, Cortez Mountains, Eureka County, Nev. Supplement to collection F 20A made by Gilluly and Masursky (1965, pi. 2 

and table 2).

Climacograptus sp. of the C. scalaris type

Monograptus sp.
52 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

Age: early Llandoverian

William B. N. Berry 

August 12, 1970

SULPHUR SPRING RANGE

Sulphur Spring Range, Eureka County, Nev. Unnamed canyon 

about NEViNEtt sec. 27, T. 25 N., R. 52 E. (unsurveyed), Mineral 

Hill quadrangle.

USGS Coll. D326 SD (TM-F-1-71) Sparse collection of monograptids in laminated limestone from 9 m above base of Roberts 

Mountains Formation. 

Cyrtograptusl

Monograptus retroflexus Tullberg 

Monograptus sp. (M. dubius group) 

Monoclimacis flumendosae Gortani 

Monoclimacis sp. 

Age: Silurian-Wenlockian, possibly later part of Wenlockian

William B. N. Berry 

June 16, 1971

MAGGIE CREEK CANYON

Maggie Creek Canyon, Eureka County, Nev. Sees. 24, 26, and 27, T. 

34 N., R. 51 E., Schroeder Mountain quadrangle. 

USGS Coll. D230 SD (TM-F-23-68). Stratigraphic position in Roberts Mountains Formation not known.

Graptolite from float from Roberts Mountains Formation high on 

south side of Maggie Creek Canyon, NWV4 sec. 26.

Monograptus bohemicus (Barrande) 

Age: Ludlovian

In-place collection from Roberts Mountains Formation exposed in 

roadcut, south side of Maggie Creek Canyon, NE'/i sec. 26. 

Monograptus bohemicus (Barrande) (thin form) 

Monograptus dubius (Suess) 

Monograptus micropoma (Jaekel) 

Monograptus sp. (of the M colonus type?)

Age: early Ludlovian, probably Monograptus nilssoni-M. scanicus Zone

William B. N. Berry 

November 8, 1968

USGS Coll. 8227 SD (TM-F-7-68) Basal coarse-grained limestone 

in Roberts Mountains Formation northeast side of Maggie Creek 

Canyon (unit 2 of measured section), NWViNEVi sec. 26. 

Hindeodellaequidentata Rhodes 16 

"Neoprioniodus " excavatus (Branson and Mehl) 7 

Ozarkodina media Walliser 14 

Plectospathodus extensus Rhodes 26 

Spathognathodus inclinatus Rhodes 33 

Trichonodella excavatus (Branson and Mehl) 10 

The conodont elements listed above are thought to belong in a 

single conodont-bearing animal, Apparat H of Walliser (1964). 

Panderodus sp. 26 

Ligonodina sp. 2 

Icriodella? sp. 1 

Spathognathodus sp. 1 

Prioniodina sp. 1 

Age: Walliser (1964) says that Apparat H ranges from Late Silurian to Early Devonian (Emsian) and this whole fauna falls in 

that range. If it were Devonian, I would expect to see other 

genera present and I think that this collection is probably Late 

Silurian. To be sure of the age we would need a suite of samples 

through the whole section.

John W. Huddle 

January 29, 1969

USGS Coll. 8217 SD (TM-F-8-68) Bioclastic limestone lens, Roberts Mountains Formation, NWV4NEV4 sec. 26, about 40 m above 

8227 SD.

Hindeodellaequidentata Rhodes 1 

Ozarkodina media Walliser 1 

Panderodus sp. 4 

Paltodus sp. 2 

Spathognathodus inclinata Rhodes 2 

Apparently the same fauna as 8214 SD [Copenhagen Canyon, 

Monitor Range] and 8227 SD [Maggie Creek Canyon].

John W. Huddle 

January 29, 1969

USGS Coll. D277 SD (69CM-179A) Basal platy limestone in Roberts Mountains Formation, SEJ/i sec. 27. Collected by L. D. Cress. 

Cyrtograptus sp. 

Monograptus spiralis (Geinitz) 

Monograptus sp. (of the M. priodon group) 

Stomatograptus grandis (Suess)

Age: Silurian-late Llandoverian, beds are approximately correlative with Elles and Wood zones 24-25

USGS Coll. D278 SD (69CM-192). Upper part of Roberts Mountains Formation, SWV4 sec. 24. Collected by L. D. Cress. 

Monograptus sp. (of the M. hercynicus group—cf. M. praehercynicus (Jaeger)) 

Age: Devonian-Gedinnian, possibly M. praehercynicus Zone.

USGS Coll. D279 SD (69CM-193). Roberts Mountains Formation, 

SWV4 sec. 24. Collected by L. D. Cress. 

Monograptus sp. (of the M. colonus type)

Monograptus sp. (with simple, tubular thecae—possibly a fragment of M. bohemicus) 

Age: Silurian-early Ludlovian

William B. N. Berry 

December 30, 1969

TUSCARORA MOUNTAINS

Carlin mine area, including sees. 14, 15, 23, and 27, T. 35 N., R. 50 

E., and sec. 30, T. 35 N., R. 51 E., Rodeo Creek NE quadrangle, 

Eureka County, Nev.

USGS Coll. 8221 SD (TM-F-5-68) Lowest massive coarse-grained 

limestone at Carlin gold mine, 160 m above base of Popovich Formation of Hardie (1966) and about 30 m below thrust fault near 

top of Popovich Hill. NE1/* sec. 14, T. 35 N., R. 50 E., Eureka 

County, Nev.

Belodella triangularis Stauffer 1 

Hibbardella sp. 1 

Hindeodella sp. 1 

Nothognathella sp. 5 

Polygnathus asymmetricus asymmetricus B & Z 20 

P. a. ovalis Ziegler and Klapper 4 

P. cristatus Hinde 5 

P. decorosus Stauffer 14 

P. normalis? Miller and Youngquist 1 

Spathognathodus sp. 2 

Age: this fauna is early Late Devonian (Frasnian, lower P. asymmetricus Zone)

John W. Huddle 

January 29, 1969

USGS Coll. D255 SD (TM-F-54-69) About sec. 14, T. 35 N., R. 50 E. 

Graptolites from altered, laminated limestone (gold ore) in upper 

part of Roberts Mountains Formation at survey marker TT-451,
APPENDIX: FOSSIL DATA 53

main pit, Carlin gold mine. Graptolites just below bed that contains Tentaculites. 

Dendrograptus sp. 

Monograptus hercynicus Perner 

Monograptus praehercynicus Jaeger? 

Age: Early Devonian, probably Siegenian

William B. N. Berry 

January 5, 1970

USGS Coll. D294 SD (TM-F-6-70) Graptolites, poorly preserved. 

From ore zone at base of main pit, Carlin mine, NWViSE 1A sec. 14, 

T. 35 N., R. 50 E. This collection is from the same zone as 

69-FP-269-F which contained a new kind of brachiopod (Boucot 

and Johnson, 1972). The beds containing the graptolites strike so 

as to be just under the M. hercynicus beds (D254 SD), but a dikefilled fault separates the localities. Displacement along fault not 

known, but interpreted as minor.

Monograptus microdonl

Monograptus of the M. hercynicus group 

Age: Early Devonian

USGS Coll. D296 SD (TM-F-8-70) Two bags. Poorly preserved 

graptolites. From gold ore, 6440 bench, east pit of Carlin mine. 

NE'/aSEtt sec. 14, T. 35 N., R. 50 E. Graptolites probably are 

from the same beds as D294 SD, but several faults and a lot of 

cover make it impossible to be exact. They should be Late Silurian 

or Devonian unless there is a thrust fault. 

Monograptus of the M. hercynicus group—probably M. praehercynicus. 

Age: Early Devonian

USGS Coll. D301 SD (TM-F-13-70) Poorly preserved graptolite 

from Roberts Mountains Formation exposed above measured section but probably across a fault, SE'/iNW1/* sec. 27.

Monograptus sp.—M. priodon type?? 

Age: might be Wenlockian but could be younger.

USGS Coll. D302 SD (TM-F-14-70) Graptolites-fairly well preserved. Collected by G. L. (Mel) Essington, geologist at Carlin 

mine. From 1950-m level, east pit of the Carlin mine. Essington 

believes this collection was made a little lower (6-10 m) 

stratigraphically than D296 SD. 

Monograptus microdonl 

Monograptus of the M. hercynicus group—possibly M. uniformis 

Age: Early Devonian

William B. N. Berry 

August 12, 1970

USGS Coll. 8724 SD (TM-F-17-70) is from the NW1/* sec. 30, T. 35 

N., R. 51 E. The fossils, a well-preserved coral and ostracodes, 

were collected by G. L. (Mel) Essington. The fossils are from interbedded fine- and coarse-grained limestone that Evans (1972a) 

has assigned to the upper part of the Roberts Mountains Formation, but these rocks correlate with the Popovich Formation of 

Hardie (1966). The fossils are from beds just below a thrust that 

contains western assemblage rocks in the upper plate. 

Age: The single coral in this collection is referred to Lyrielasma. 

In eastern North America the genus ranges from the uppermost 

Silurian (Pridoli) through the Lower Devonian although its 

known range elsewhere is Lower to lower Middle Devonian. 

Similarly, the presumably related forms are common in the Middle Devonian. The earlier Lyrielasma are characterized by morphologic features not present in the specimen at hand and this

new specimen is almost certainly from the Lower Devonian.

William A. Oliver, Jr. 

September 14, 1971

This collection contains the following ostracodes: 

Aechmina sp. aff. A. longispina Coryell and Cuskley, 1934 

Aechmina sp. 

Aechminaria! sp. 

Ulrichia sp. 

Hanaites sp. 

Abditoloculina sp. 

Parabolbina sp. 

Tetrasacculus sp. 

Psilokirkbyellal sp.

Neothlipsura bispinosa(McClean, 1973) 

Geisinid ostracodes 

Berounella sp.

Bairdia sp. cf. B. leguminoides Ulrich, 1891 

Birdsallella sp. 

smooth ostracodes, indet.

This ostracode assemblage has definite Appalachian affinities and 

resembles that of the Port Ewen Limestone of New York. According to Johnson (1970, p. 50-51) the first influx of Appalachian elements is in his Spinoplasia Zone, which he also correlates with the Port Ewen. These ostracodes probably belong 

in the Spinoplasia Zone and the rocks containing them may be 

equivalent to at least a part of the Rabbit Hill Limestone.

Jean M. Berdan 

February 16, 1972

TM-F-18-70 A sparse collection of brachiopods from an altered 

zone in the east wall of the west pit of the Carlin mine. NEViSW1/* 

sec. 14, T. 35 N., R. 50 E. On lithologic correlation, these 

brachiopods seem to be above the M. hercynicus Zone in the main 

pit and in rocks assigned to the Popovich Formation of Hardie 

(1966), but cover, faults, and altered rocks make lithologic correlations between pits risky.

Leptocoelina squamosa Johnson

Spinoplasia roeni Johnson 

Age: Spinoplasia Zone, Siegenian

TM-F-19-70 A sparse collection of poorly preserved brachiopods 

from the 1950-m level, west pit of the Carlin mine, NW'^SWVi 

sec. 14, T. 35 N., R. 50 E. These brachiopods seem to be from less 

altered rocks in the same zone as TM-F-18-70.

Leptocoelia? sp. 

Age: probable Siegenian or Emsian

J. G. Johnson 

A. J. Boucot 

July 16, 1970

USGS Coll. D253 SD (TM-F-52-69) Sec. 27, T. 35 N., R. 50 E. About 

3.2 km southwest of Carlin gold mine.

Bag A—Graptolites from in place and from float in zone extending from top bed of basal chert to 1.5 m above basal chert of 

Roberts Mountains Formation.

Cyrtograptus lapworthi Tullberg

Monograptus spiralis (Geinitz)

Monograptus sp. (M. priodon group)

Retiolites geinitzianus var. angustidens (Elles and Wood) 

Age: late Llandoverian, M. spiralis Zone 

Bag B—Graptolites from float 12 to 16 m above basal cherty unit.

Cyrtograptus sp.

Monograptus cf. M. praedubius (Boucek)

Monograptus vomerinus cf. var. gracilis (Elles and Wood)
54 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

Age: Wenlockian

Bag C—Graptolites from in place and float 65 m above basal 

cherty unit. 

Cyrtograptus sp. 

Monograptus testis (Barrande) 

Monograptus sp. (of theM. dubius group) 

Age: late Wenlockian, M. testis Zone

William B. N. Berry 

January 5, 1970

USGS Coll. 8823 SD (TM-F-21-70) Upper 1.5 m of the Hanson 

Creek Formation, SE'/tNEVi sec. 23, T. 35 N., R. 50 E. 

Drepanodus cf. D. aduncus Nicoll and Rexroad 2 

Hindeodella sp. 1 

Icriodina irregularis Branson and Branson 1 

Ligonodina cf. L. kentuckyensis Branson and Branson 9 

Neoprioniodus sp. 3 

OzarkodJaa sp. 2 

Paltodus dyscritus Rexroad 17 

Panderodus sp. 60 

Synprioniodina sp. 1 

Trichonodella aff. T. papilo Nicoll and Rexroad 2 

Age: early Silurian

John W. Huddle 

February 25, 1971

USGS Coll. D254 SD (TM-F-53-69) About sec. 15, T. 35 N., R. 50 

E., about 1.5 km west of Carlin gold mine. Highest graptolites 

found in Roberts Mountains Formation and about 30 m below 

change to interbedded laminated limestone and coarse-grained 

limestone unit. 

Linograptus sp.

Monograptus sp. (of theM. hercynicus group) 

Tentaculitid 

Age: early Devonian

William B. N. Berry 

January 5, 1970

USGS Coll. 8446 SD (TM-F-15a-69) About sec. 15, T. 35 N., R. 50

E. Gray medium- to coarse-grained partly pelletal limestone bed

0.3 m thick in upper part of Roberts Mountains Formation. About

12 m above the highest graptolites found (D254 SD).

Acodina sp. 1

Belodella triangularis (Stauffer) 1

Hindeodella 3

Icriodus pesavis Bischoff and Sannemann 1

Panderodus sp. 3

Age: The presence of /. pesavis suggests that this collection is

Early Devonian, Siegenian in age (Quadrithyris Zone).

John W. Huddle 

March 13, 1970

USGS Coll. 8447 SD (TM-F-15b-69) Same location as 8446 SD. 

Gray coarse-grained partly pelletal limestone about 6 m above 

base of zone with dominant coarse-grained limestone and about 

60 m above 8446 SD. Unnamed Devonian limestone that pverlies 

Roberts Mountains Formation.

Acodusl sp. 1 

Hindeodella sp. 10 

Icriodus sp. 2 

Ligonodina sp. 2 

Lonchodina cristagalli Ziegler 4 

L. greilingi? Walliser 3 

L. walliseri? Ziegler 1 

Neoprioniodus excauatus (Branson and Mehl) 2

"Oneotodus " beckmanni Bischoff and Sannemann

Ozarkodina denckmanni Ziegler

O. cf. O. fundementata Walliser

O. media Walliser

O. cf. O. ortus Walliser

Panderodus sp.

Plectospathodus extensus Rhodes

P. sp.

Spathognathodus boucoti Klapper

S. remscheidensis Ziegler

Trichonodella symmetrica (Branson and Mehl)

1

3

1

8

8

34

1

2

9

7

3

Age: S. boucoti is confined to the Icrodus pesauis-S. boucoti Zone 

in the Early Devonian Seigenian rocks in western North 

America. This collection is probably Early Devonain in age, 

although some of the species have not been reported from rocks 

of this age previously.

John W. Huddle 

March 13, 1970

USGS Coll. 8448 SD (TM-F-15c-69) Dark-gray coarse-grained partly pelletal limestone 125-150 m above 8847 SD. Unnamed Devonian limestone.

Belodella sp. 2 

Hindeodella species 2 

Ozarkodina denckmanni Ziegler 2 

O. sp. 1 

Plectospathodus sp. 1 

Spathognathodus remscheidensis Ziegler 10 

Age: Early Devonian, but there is nothing in the conodont fauna 

to date it more precisely.

John W. Huddle 

March 13, 1970

North Star mine area includes WVz sec. 4 and NVfe sec. 9, T. 35 N., R. 

50 E., Eureka County, Nevada, Rodeo Creek NE quadrangle 

69 FP-265F, Limestone float from basal coarse-grained limestone 

that overlies laminated limestone assigned to the Roberts Mountains Formation on east flank of hill 0.8 km south-southwest of 

North Star mine SWVi sec. 4, T. 35 N., R. 50 E. Collected by F. G. 

Poole. Bed possible equivalent of bed where 8440 SD collected 1.5 

km south. 

Gypidula? sp. 

Cyrtina? sp. 

indet. brachiopods 

Age: probably Devonian, based on the presence of Cyrtina? sp.

J. G. Johnson

A. J. Boucot

January 21, 1971

USGS Coll. 8433 SD (TM-F-1-69). Unnamed Devonian bioclastic 

limestone, medium- to coarse-grained, about 15m above the sandstone bed that overlies the Roberts Mountains Formation. 

Belodella sp. 1 

Hindeodella sp. 1 

Icriodus sp. 2 

Silicified bryozoa

Age: probably Early Devonian based on the presence of Icriodus

John W. Huddle 

February 19, 1970

USGS Coll. 8434 SD (TM-F-2-69) Fine-grained limestone and interbedded silty laminated limestone in Roberts Mountains Formation. About 460 m south of the North Star mine, WVfc sec. 4.
APPENDIX: FOSSIL DATA 55

About 120 m below the sandstone that overlies the Roberts

Mountains Formation.

Belodella cf. B. resimus Philip 1 

Hindeodella sp. 6 

Neoprioniodus excavatus (Branson and Mehl) 5 

Ozarkodina media Walliser 7 

O. sp. B of Philip 2 

O. sp. 2 

Plectospathodus extensus (Rhodes) 111 

Prioniodina sp. 1 

Spathognathodus remscheidensis? Ziegler 5 

S. cf. S. transitans n. subsp. 4 

S. wurmi Bischoff and Sannemann 22 

S. sp. 2 

Trichonodella inconstans Walliser 3 

T. symmetrica (Branson and Mehl} 2

Age: This fauna includes elements that are found in the Lower 

Devonian of Alaska and Australia. Most of the species range 

from the Upper Silurian through the Lower Devonian. S. 

remscheidenses and S. wurmi suggest an Early Devonian age, 

but it could be Silurian in age.

John W. Huddle 

February 19, 1970

Emmonsia sp. Upper Silurian to Middle Devonian.

William A. Oliver, Jr. 

September 14, 1971

The following six collections were made on a line extending 

southwest from the east flank of a minor hill in NE 1/^ sec. 9 to hill 

6052 in NWVi sec. 9. They were collected to obtain an age for a few 

hundred meters of coarse-grained limestone and laminated 

limestone that overlies the Roberts Mountains Formation. The upper two collections are across a fault that seems to repeat lower part 

of unit.

USGS Coll. 8440 SD (TM-F-14a-69) Sec. 9, T. 35 N., R. 50 E., about 

1.5 km south of North Star mine. Coarse-grained limestone at 

base of 120-m unit of coarse-grained limestone interbedded with 

and underlain and overlain by laminated limestone. Base of unit 

forms mapping contact of Roberts Mountains Formation and 

overlying unnamed Devonian beds.

Acodina sp. 2 

Spathognathodus remscheidensis (Ziegler) 8 

"Oneotodus " beckmanni Bischoff and Sannemann 10 

Age: probably Early Devonian. This is indicated by the presence 

of S. remscheidensis and "O." beckmanni. "O. " beckmanni may 

not be a conodont but it has been found in the United States, 

Australia, and Germany in Lower Devonian rocks and is not 

known from the Silurian.

John W. Huddle 

March 13, 1970

Strepulal sp.

Aparchitellina? sp.

Saccarchites sp.

Alaskabolbinal sp.

Hypotetragona sp.

Marginia sp. aff. M. sculpta multicostata Polenova, 1952

Aechmina sp.

Tubulibairdial sp.

Newsomites? sp.

Bairdiocypris sp.

Praepilatina sp. aff. praepilata sibiriea Polenova, 1972

Bairdia sp. cf. B. leguminoides Ulrich, 1891 

Camdenidea sp. 

Bashkirina sp.

Silus sp. cf. S. acclivis Polenova, 1968 

Miraculum sp. aff. M. simplex Polenova, 1960 

Tricornina sp.

alate podocope, new genusaff. "Beecherella" angularis Ulrich, 

1891

Age: This association of ostracodes is new, but is almost certainly 

Early Devonian. Possibly it is Gedinnian, as Miraculum sp. aff. 

M. simplex, Bairdia sp. cf. B. leguminoides and Saccarchites sp. 

also occur in collection USNM 12323 made by A. J. Boucot, 

which he described as float from beds of Gedinnian Age in the 

Roberts Mountains Formation. It is interesting that six of the 

ostracodes listed above are related to species described from the 

Devonian of Siberia.

Jean M. Berdan 

September 4, 1969

USGS Coll. 8441 SD (TM-F-14b-69) Coarse-grained limestone.

Same locality as 8440 SD, but 60 m stratigraphically above 8440

SD. Unnamed Devonian limestone.

Belodella sp. 1 

Hindeodella sp. 7 

Neoprioniodus excavatus (Branson and Mehl) 4 

Ozarkodina media Walliser 3 

Plectospathodus extensus Rhodes 8 

Spathognathodus inclinatus wurmi? Bischoff and Sanneman 7 

S. johnsoni (Klapper) 1 

S. sp. 2 

Trichonodella symmetrica (Branson and Mehl) 1

Age: The two species of Spathognathodus indicate an Early Devonian age. S. johnsoni has been reported from the Quadrithyris 

Zone at Coal Canyon, Nevada, and from the Royal Creek section, Yukon Territory, Canada, by Klapper (1969) and is regarded as early Seigenian.

John W. Huddle 

March 13, 1970

USGS Coll. 8442 SD (TM-F-14c-69) Same locality as 8440 SD, base 

of a sandy, coarse-grained limestone overlying a 150-m laminated 

limestone with Styliolina in the upper part. Somewhere between 

180 and 250 m above 8441 SD, if no faults are present. Devonian 

limestone probably above Popovich Formation of Hardie (1966) at 

Carlin mine.

Belodella triangularis (Stauffer) 8 

Hindeodella sp. 6 

Icriodus sp. 2 

Panderodus sp. 1 

Plectospathodus sp. 1 

Polygnathus linguiformis linguiformis Hinde 8 

Po. sp. 2 

Synprioniodina sp. 2 

Age: probably Middle Devonian. Polygnathus linguiformis linguiformis ranges from late Emsian to early Late Devonian. All 

the other species have longer ranges. The collection is probably 

older than 8221 SD (TM-F-12-68) from 167 m above the base of 

the Popovich Formation at Carlin mine.

John W. Huddle 

March 13, 1970

USGS Coll. 8443 SD (TM-F-14e-69) About 50 m above 8442 SD, 

same locality, dark-gray medium-grained partly pelletal 

limestone. Unnamed Devonian limestone.
56 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

Ancyrodella rotundiloba rotundiloba (Bryant) 1 

Hindeodella sp. 4 

Ozarkodina sp. 1 

Polygnathus decorosus Stauffer 2 

Synprioniodina sp. 1 

Age: early Late Devonian, lower or middle asymmetrica Zone

John W. Huddle 

March 13, 1970

USGS Coll. 8444 SD (TM-F-14f-69) Dark-gray, partly pelletal medium-grained limestone. Same general locality as 8443-SD, but 

there is a fault between 8443 SD and 8444 SD. Fault is in swale 

just east of hill 6052 in NW1/^ sec. 9. Unnamed Devonian 

limestone.

Belodella triangularis (Stauffer) 1 

Icriodus cf. /. pesavis Bischoff and Sannemann 4 

Ligonodina sp. 3 

Neoprioniodus bicurvatus (Branson and Mehl) 1 

Ozarkodina denckmanni Ziegler 12 

O. aff. O. fundementala Walliser 3 

Spathognathodus cf. S. sagitta (Walliser) 29 

Age: S. sagitta and O. fundementala suggest a Silurian age while 

the /. pesavis and O. denckmanni suggest an Early Devonian 

age. /. pesavis is confined to beds of early Siegenian age in Coal 

Canyon, Nevada, and Royal Creek, Yukon Territory, Canada. I 

think the collection is Early Devonian.

John W. Huddle 

March 13, 1970

USGS Coll. 8445 SD (TM-F-14g-69) Dark-gray, coarse-grained

pelletal limestone. Same locality about 6 m stratigraphically

above 8444 SD. Unnamed Devonian limestone.

Icriodus sp. 1

Neoprioniodus bicurvatus (Branson and Mehl) 1

Spathognathodus cf. S. remscheidensis (Ziegler) 1

"Oneotodus " beckmanni Bischoff and Sannemann 22

Age: probably Early Devonian. "Oneotodus" has been found in

rocks of Early Devonian age in Europe, Australia, and the

United States and is not known from rocks of other ages.

John W. Huddle 

March 13, 1970

Strepulaf sp. 

Camdenidea sp. 

Silus sp.

These ostracodes are few and broken, but appear to represent 

about the same horizon as 8440 SD.

Jean M. Berdan 

September 4, 1969

Bootstrap mine, western Tuscarora Mountains approx. sees. 10 and 

15, T. 36 N., R. 49 E. (unsurveyed). Rodeo Creek NW quadrangle, 

Elko and Eureka Counties, Nevada, and McDermitt 1°X2° quadrangle (mine not shown on 1 °X2 ° quadrangle). About 460 m of rock 

is exposed beneath a thrust fault at Bootstrap mine. The lower 180 

m is assigned to the Roberts Mountains Formation and the base of 

the Roberts Mountains is not exposed. The upper 280 m are in an 

unnamed Devonian formation.

USGS Coll. D233 SD (TM-F-26-68) Sec. 10. Sparse collection of 

graptolites in float 45 m above base of exposure and three 

fragments of graptolites from float 85 m above base of exposure. 

Graptolites from 45 m above base of exposure:

Monograptus sp. (plain thecae)

Monograptus sp. (fragment could be M. uncinatus Tullberg)

Monograptus sp. (specimen appears to have thecae with spines

similar to those in M. chimaera)

Age: Ludlovianf?)— the presence of a fragment with uncinate thecae is suggestive of the Ludlovian as is the presence of a 

specimen with what appear to be spines similar to those in M. 

chimaera.

Monograptids from float 85 m above base of exposed rock: 

Monograptus sp. (of theM dubius type?)

Monograptus sp. (thecae appear to be similar to those in M. uncinatus}

Age: possibly Late Silurian-Ludlovian or Pridoli—the presence 

of a specimen with thecae similar to those in M. uncinatus is 

suggestive of a Late Silurian age

William B. N. Berry 

November 8, 1968

USGS Coll. D252 SD Sec. 10.

Bag A—Graptolites from 175 m above base of exposure of 

Roberts Mountains Formation and 6 m below change from 

dominantly laminated limestones to dominantly coarse grained 

limestone above. Coarse-grained limestone is probably Rabbit 

Hill Limestone equivalent. 

Monograptus angustidens Pribyl 

Monograptus uniformis Pribyl 

Age: earliest Devonian-Gedinnian

Bag B—Graptolites from 20 m above base of exposure of Roberts 

Mountains Formation 

Monograptus sp. (of theM dubius group) 

Monograptus sp. (M. uncinatus Tullberg?) 

Monograptus sp. (an M. vomerinusl or possibly M. micropoma

mannopoma Jaeger) 

Age: in span of late Llandoverian-early Ludlovian

William B. N. Berry 

January 5, 1970

USGS Coll. D319 SD (TM-F-42-70) One specimen from float about 

9 m above M. uniformis Zone of D252 SD.

Monograptus uniformis Pribyl 

Age: Early Devonian-Gedinnian, Monograptus uniformis Zone

William B. N. Berry 

January 11, 1971

USGS Coll. 8228 SD (TM-F-9-68) From coarse-grained limestone 

in Roberts Mountains Formation in lowest 15 m of rock exposed 

at Bootstrap mine, sec. 10. The following conodonts were found in 

the residue of 5000 grams of rock:

Hindeodella sp. 1 

"Neoprioniodus"excavatus (Branson and Mehl) 1 

Ozarkodina media Walliser 5 

Plectospathodus extensus Rhodes 3 

Age: Silurian or Early Devonian, probably Late Silurian

USGS Coll. 8219 SD (TM-F-10-68) 37 m above base of exposed 

section, west side of Bootstrap mine, sec. 10. 

Belodella devonicus (Stauffer) 1 

Hindeodella sp. 8 

"Neoprioniodus" excavatus Walliser 2 

Ozarkodina aff. O. media Walliser 5 

O. ziegleri Walliser 1 

Paltodus aff. P. migratus Rexroad 2 

Paltodus sp. 1 

Panderodus sp. 19 

Plectospathodus extensus Rhodes 2 

Spathognathodus eosteinhornensis (Walliser) 2
APPENDIX: FOSSIL DATA 57

S. inclinatus (Rhodes) 5 

S. primus (Branson and Mehl) 1 

Age: Most of these species occur in Upper Silurian and Lower 

Devonian rocks. I think that this collection is Late Silurian but 

it is little more than a guess, based on the absence of Icriodus 

woschmidti (a rare form in this area) and the species of 

Spathognathodus present.

John W. Huddle 

April 4, 1969

Collection contains echinoderm debris, indeterminate fragments 

of strophomenoid and orthoid brachiopods and one fair pentameroid, probably Kirkidium or Conchidium. 

Age: Late Silurian

J. T. Dutro, Jr. 

March 9, 1972

USGS Coll. 8219A SD (TM-F-10A-68) Same locality as 8219 SD 

coarse-grained limestone in Roberts Mountains Formation. 120 m 

above base of outcrop.

Belodella devonicus (Stauffer) 2 

"Neoprioniodus " excavatus (Branson and Mehl) 1 

Ozarkodina gaertneri Walliser 1 

Paltodus aff. P. migratus Rexroad 1 

Panderodus sp. 17 

Spathognathodus ranuliformis (Walliser) 7 

S. sp. 1 

Age: O. gaertneri and S. ranuliformis are reported only from the 

amorphognathoides Zone (Valentian and Wenlockian in 

Europe); probably Middle Silurian

John W. Huddle 

April 4, 1969

USGS 8215 SD (TM-F-11-68) Coarse-grained limestone 245 to 267 m

above base of outcrop at Bootstrap mine. Unnamed Devonian

limestone above Roberts Mountains Formation.

Icriodusl sp. 4

Prioniodina sp. 1

Ozarkodina sp. 1

Trichonodella incons tans Walliser 1

Spathognathodus primus (Branson and Mehl) 1

Age: these species range from Middle Silurian to Early Devonian

John W. Huddle

April 4, 1969 

Collection contains:

orthoid, indet. 

strophomenoid, indet. 

Leptaenasp.

Gypidula cf. G. pelagica (Barrande) 

Age: probably earliest Devonian (Gedinnian)

J. T. Dutro, Jr. 

March 9, 1972

USGS Coll. D292 SD (TM-F-4-70) Graptolites from Roberts Mountains Formation. NW1/4 SE 1/4 sec. 15, T. 36 N., R. 49 E. About 1.6 

km south of measured section at Bootstrap mine. In complexly 

faulted area and stratigraphic position in the Roberts Mountains 

Formation not known. 

Monograptus colonus (Barrande) 

Monograptus dubiust 

Monograptus nilssoni (Barrande) 

Monograptus uncinatusl 

Age: early Ludlovian, Monograptus nilssoni Zone

William B. N. Berry 

August 12, 1970

INDEPENDENCE MOUNTAINS

Water Pipe Canyon, Elko County, Nev. NE'/4 sec. 19, T. 39 N., R. 53 

E., Tuscarora quadrangle

USGS Coll. D236 SD. Graptolites from black shale from adit on 

north side of Water Pipe Canyon. Graptolites from Silurian upper 

plate (western facies) first reported by Kerr (1962). 

Climacograptus hughesi Nicholson

Climacograptus sp. (of the C. medius-C. rectangularis type) 

Glyptograptus sp. (of the G. tamariscus Nicholson group) 

Monograptus sp. (fragment of distal part of rhabdosome—a 

monograptid similar to M. argutus Lapworth and M. atavus 

Jones)

Monograptus cf. M. lobiferus (M'Coy) 

Monograptus triangulatus (Harness)

Age: middle Llandoverian, falls in the span of Elles and Wood 

British zones 19 (Monograptus gregarius Zone) and 20 (Monograptus convolutus Zone)

William B. N. Berry 

November 8, 1968

Thomas Jose Canyon, Elko County, Nev. Sees. 6 and 7, T. 39 N., R. 

53 E., Tuscarora quadrangle

USGS Coll. D235 SD (TM-F-28-68) All graptolites from float just 

above basal cherty unit of Roberts Mountains Formation. Float is 

from the base of the Taylor Canyon Formation of J. W. Kerr 

(1962) which is equivalent to the Roberts Mountains Formation 

above the basal cherty unit. 

Cyrtograptus hamatus (Baily) 

Cyrtograptus sp. 

Monograptus flemingii (Salter) 

Monograptus testis Barrande 

Monograptus sp. (of theM vomerinus group) 

Age: late Wenlockian. This association is indicative of zone 4 of 

the Silurian-Devonian graptolite faunizones outlined by Berry 

(1969). It is the approximate correlative of the Cyrtograptus 

lundgreni Zone of Elles and Wood.

William B. N. Berry 

November 8, 1968

USGS Coll. D263 SD (TM-F-62-69) In place collection probably 

15-30 m above basal cherty unit of Roberts Mountains Formation, but low-angle faults separate the graptolite-bearing rocks 

from the cherty unit. NWVi sec. 7.

Monograptus bohemicus (Barrande)

Monograptus chimaera (Barrande)?

Monograptus dubius (Suess)

Monograptus fritschi (Perner)

Monograptus scanicus (Tullberg)

Monograptus uncinatus (Tullberg) 

Age: early Ludlovian

William B. N. Berry

USGS Coll. D295 SD. Graptolites, poorly preserved. Isolated exposures in a faulted area, but collected above the M. 

bohemicus-M. dubius Zone of D263 SD. 

Monograptus bohemicus (Barrande) 

Monograptus colonus (Barrande) 

Monograptus dubius Suess 

Age: early Ludlovian, Monograptus nilssoni Zone

William B. N. Berry 

August 12, 1970
58 STRATIGRAPHY, PETROLOGY, FOSSIL DATA OF ROBERTS MOUNTAINS FORMATION

ANTELOPE PEAK, ELKO COUNTY NEVADA

About NEy4 sec. 32, T. 40 N., R. 62 E., Summer Camp quadrangle. 

USGS Coll. 8824 SD (TM-F-41-70) Medium-grained laminated 

dark-gray limestone about 490 m above base of Roberts Mountains Formation. The limestone is slightly coarser grained and 

contains less silt than laminated limestone beds above and below. 

Hindeodella sp. 1 

Neoprioniodus excavatus (Branson and Mehl) 1 

Panderodus sp. 5 

Pelekysgnathus furnishil Klapper 1 

Prioniodina sp. 1 

Spathognathodus inclinatus Rhodes 3 

P. furnishi has previously been reported from the Emsian of 

Royal Creek, Yukon Territory, but its range is not known.

John W. Huddle 

February 25, 1971

HOT CREEK CANYON

Sec. 19, T. 8 N., R. 50 E., Nye County, Nev., Little Fish Lake 

quadrangle. From rocks equivalent to Roberts Mountains Formation but probably should be assigned to unit 1 of the Lone Mountain 

Dolomite (Merriam, 1973b, p. 9-17)

USGS Coll. 8437 SD. Fine-grained, dark-gray dolomite 10 m above 

the basal cherty unit.

Acontiodus sp. 1 

A?sp. 3 

Acodus sp. 1 

Hindeodella sp. 6 

Ligonodina sp. 1 

Lonchodina cf. L. greylingi Walliser 2 

Neoprioniodus bicurvatus (Branson and Mehl) 1 

Ozarkodina media Walliser 4 

Panderodus sp. 6 

Plectospathodus extensus Rhodes 4 

Spathognathodus inclinatus inclinatus Rhodes 12 

Trichonodella symmetrica (Branson and Mehl) 3 

Age: Most of these forms range from Silurian (Ludlovian) to Devonian (Emsian). On the basis of the lack of other species of 

Spathognathodus and Icriodus it seems probable that this is 

Silurian but nothing here demonstrates a Silurian age.

USGS Coll. 8438 SD (TM-F-10-69) Fine-grained, dark-gray dolomite with silicified fossil fragments. 33 m above basal cherty unit. 

Ozarkodina sp. 1 

Panderodus sp. 4 

Spathognathodus inclinatus Rhodes 1 

Trichonodella symmetrica (Branson and Mehl) 1 

Age: Late Silurian or Early Devonian

John W. Huddle 

February 19, 1970

Cladopora sp. 

Favositesl sp. 

Age: Silurian or Devonian

William A. Oliver, Jr. 

September 14, 1971

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INDEX

[Italic pages numbers indicate major references]

	Page 

abbreviatus, Orthograptus truncatus ......... 45

Abditoloculina sp. .......................... 53

acclivis, Silus .............................. 55

Acodina sp. ................................ 54, 55

Acodus unicostatus ......................... 50

sp. ................................... 47, 54, 58

Acontiodus sp. ............................. 58

aduncus, Drepanodus ....................... 54

Aechmina longispina ....................... 53

sp...................................... 53, 55

Aechminaria sp. ............................ 53

Age ....................................... 25

fossil. See Zones.

Alaskabolbina sp. ........................... 55

Albite ..................................... 18

Algae...................................... 26

Allochthon ................................. 3, 30

Antler thrust system .................... 30, 40

Alteration, laminated limestone .............. 14

alternatus, Plectospathodus ................. 50

Alveolites sp. .............................. 48

Amorphognathoides Zone ................... 57

Amphibole ................................. 21

epigenetic .............................. 19

Ancyrodella rotundiloba rotundiloba ......... 56

Ancyrognathus sp. ......................... 49

angustidens, Monograptus .................. 56

Retiolites geinitzianus .................. 47, 53

Antelope Peak ............................ 13, 26, 38

conodonts .............................. 28

fossil data .............................. 58

Antelope Valley Limestone .................. 45

Antimony.................................. 42

Antler orogeny ............................. 3, 30, 40

Aparchitellina sp............................ 54

Apparat H ................................. 52

Area....................................... 4

Argillite ................................... 19, 30

argutus, Monograptus ...................... 57

arkansasensis, Dicellograptus complanatus ... 45

Arsenic .................................... 42

Arsenopyrite ............................... 42

Asymmetrica Zone ......................... 56

asymmetricus, Polygnathus asymmetricus .... 52

asymmetricus, Polygnathus ............. 52

ovalis, Polygnathus ..................... 52

atavus, Monograptus ....................... 57

Atrypa .................................... 49

sp...................................... 50

A trypina simpsoni.......................... 48

Austin quadrangle.......................... 45

Authigenic minerals, Moenkopi Formation .... 22

Autochthon ................................ 3

B

Bairdia leguminoides ....................... 53, 55

Bairdiocypris sp. ........................... 55

Bare Mountain quadrangle .................. 29

Barite ..................................... 20, 21

Bashkirina sp. .............................. 55

beckmanni, Oneotodus ..................... 48, 54, 55

Belodella devonicus ......................... 50, 56

resimus ................................ 48, 55

triangularis ........................... 52, 54, 55

sp................................. 45, 47, 54, 55

Page 

Berounella sp. .............................. 53

Bibliography ............................... 58

bicurvatus, Neoprioniodus ................... 56, 58

Birch Creek ............................... 23, 27, 28

Birdsallella sp. ............................. 53

bispinosa, Neothlipsura ..................... 53

Black Cliff Canyon ...................... 8, 11, 14, 45

graptolites ............................. 26

bohemicus, Monograptus ......... 46, 49, 50, 51, 52, 57

tenuis, Monograptus .................... 50

Bootstrap mine ............... 13, 23, 24, 27, 28, 38, 56

kaolinite ............................... 18

stratigraphy ........................... 6

zircon-tourmaline ratio .................. 21

Borings .................................... 7

Boron ..................................... 41

boucoti, Spathognathodus ................... 54

Brachiopods .............................. 26, 28, 32

Brassfield Formation ....................... 49, 50

Brock Canyon .............................. 28, 50

Bryantodus sp. ............................. 48

Bull Run quadrangle ........................ 29, 38

Caballos Novaculite......................... 32

Calcite ............ 6, 9, 10, 14, 16, 18, 24, 32, 37, 38, 39

Callicalyptella empelia ...................... 26

Camdenidea sp. ............................ 55, 56

Carbon, organic ............................ 79, 41

Carbonaceous material.................... 6, 9, 14, 79

Carlin mine ................. 2, 4, 13, 19, 27, 28, 41, 42

brachiopods ............................ 26

conodonts .............................. 26

gold ................................... 2, 13

iron oxide Liesegang rings ............... 13

kaolinite ............................... 18

zircon-tourmaline ratio .................. 21

Carlin-Pinon Range ......................... 30

Chellis Formation .......................... 29, 38

Chemical precipitates ....................... 38

chimaera, Monograptus .................... 48, 56, 57

Chlorite.................................... 79, 21

Chromium ................................. 41

Cladopora sp. .............................. 48, 58

Clay ...................................... 14,18, 38

minerals .......................... 6, 9,10, 14, 18

Claystone .................................. 8

Clear Creek ................................ 28, 44

Clear Creek Mountain ....................... 47

Climacograptus hughesi..................... 57

hvalross ............................... 45

medius ................................. 44, 46

rectangularis ........................... 44, 49

scalaris ............................... 44, 46, 51

styloideus .............................. 45

supernus ............................... 45

sp. ............................. 44, 45, 46, 47, 57

clingani, Monograptus ...................... 44

Coal Canyon ............................ 4, 19, 27, 50

Cobalt ..................................... 41

Coelospira sp. .............................. 48

Coenites sp. ................................ 48

Collophane ................................. 41

Copenhagen Canyon .................... 21

colonus. Monograptus ......... 46, 48, 49, 50, 51, 52, 57

Colorado Plateau ........................... 22

Page

complanatus arkansasensis, Dicellograptus ... 45 

ornatus, Dicellograptus .................. 45

Conchidium ................................ 49, 57

confertus. Dimorphograptus ................. 26, 49

convolutus, Monograptus .................. 44, 45, 47

Copenhagen Canyon ....................... 26, 48, 52

Collophane ............................. 21

conodonts .............................. 26

graptolites ............................. 26

Copenhagen Canyon Formation .............. 8

Copper .................................... 41, 42

Corals .................................. 6, 23, 26, 28

favositid ............................... 51

horn ................................... 51

Correlation................................. 29

Cortez Canyon ............................. 51

Cortez mine ...................... 2, 14, 27, 41, 42, 51

gold ................................... 2, 14

Cortez Mountains ......................... 23, 27, 40

Cortez Canyon.......................... 51

Cortez mine ................... 2, 14, 27, 41, 42, 51

fossil data .............................. 51

Fourmile Canyon ....................... 51

Rattlesnake Canyon ................. 4, 13, 28, 51

thickness .............................. 7

Cortez quadrangle .......................... 30, 51

Cortez Uinta axis ........................... 13, 40

Correlation................................. 29

crassitestus, Diplograptus ................... 45

crenulatus, Monograptus .................... 43, 47

Crescent Valley-Grass Valley area ........... 6, 13

Criconarids ................................ 28

crinitus, Monograptus ...................... 49

crispus, Monograptus ....................... 45

cristagalli, Lonchodina ...................... 54

cristatus, Polygnathus ...................... 52

Crystals, anhedral .......................... 20

euhedral .............................. 20, 22, 25

zoned .................................. 17

cyphus, Monograptus ....................... 46

Cyrtina sp. ................................. 51, 54

Cyrtograptid cladial fragment ............... 46

Cyrtograptid scrap ......................... 46

Cyrtograptus hamatus ...................... 57

lapworthi ............................. 43, 47, 53

lundgreni Zone ......................... 57

Solaris ................................. 47

sp. ................... 43, 44, 47, 49, 52, 53, 54, 57

D

Danville quadrangle ........................ 47

decorosus, Polygnathus ..................... 52, 56

Delaware basin ............................. 38

denckmanni, Ozarkodina ................ 48, 50, 51, 54

Dendrograptus sp. .......................... 53

Depocenters, laminated limestone ............ 11

Detrital grains ............................. 17, 38

Detrital material........................ 9, 22, 32, 40

Detrital minerals ........................... 21

devonicus, Belodella ........................ 50, 56

Scolopodus ............................. 48, 50

Diagenetic minerals......................... 21

Dianas Punch Bowl quadrangle .............. 46

Dicellograptus complanatus arkansasensis .... 45

complanatus ornatus .................... 45

Dimorphograptus confertus ................. 26, 49

Diopside, South Ravenswood window ........ 21

63
64 INDEX

Diplododella sp.

Diplograptus ...

crassitestus

sp.

Distacodus obliquicostatus ..................

sp......................................

Distimodus sp. .............................

Dolomite .......... 6, 9, 10, 14, 17. 24, 29, 30, 37,

Ely Springs ............................

Laketown ..............................

Lone Mountain ............. 5, 6, 28, 29, 38,

Drepanodus aduncus ........................

sp. .....................................

dubius. Monograptus ...... 43, 45, 46, 48, 49, 50,

Spathognathodus .......................

dyscritus, Paltodus .........................

E

Page

48

46

45

46, 47

44

44

44

39, 42

29,47

29

47,58

54

49, 50

51,57

50

50, 54

East Northumberland Canyon, Toquima Range 45 

Echinoderm debris.......................... 51

Elder Sandstone ............................ 30, 32

Elements, trace............................. 41

Ely Springs Dolomite ....................... 29, 47

emarginatus, Polygnathoides ................ 50

Emmonsia sp. .............................. 55

empelia, Callicalyptella ...................... 26

eosteinhornensis, Spathognathodus .......... 50, 56

Epidote.................................... 21

Epigenetic amphibole ....................... 19

Epigenetic minerals ......................... 14, 21

Epigenetic pyrite ........................... 19, 42

equidentata, Hindeodella .................... 52

excavatus, Neoprioniodus .............. 43, 48, 49, 50,

52,54,55,56,57 

Trichonodella........................... 52

exiguus, Spathognathodus .................. 47

extensus. Plectospathodus .............. 48, 49, 50, 52,

54,55,56,58

Faulting ................................... 3

Faults, transcurrent ........................ 40

Favosites .................................. 48

sp...................................... 48, 58

Favositid coral ............................. 51

Feldspar ............................ 9, 22, 38, 39, 40

Feldspar silt......................... 6, 10, 22, 24, 42

flemingii, Monograptus ................. 43, 49, 51, 57

flumendosae, Monoclimacis .................. 52

Fluorite.................. .................. 21

Forereefs .................................. 31

Formations, Antelope Valley Limestone ...... 44

Brassfield .............................. 49, 50

Chellis ................................. 29, 38

Copenhagen Canyon .................... 8

Elder Sandstone ........................ 30, 32

Fourmile Canyon ....................... 30, 51

Gatecliff ................................. 6, 7, 8

Hanson Creek .................. 5, 8, 26, 29, 47, 50

Happy Camp ............................. 6, 7, 8

Hermosa ............................... 39

McMonnigal Limestone ................ 23, 27, 38

Moenkopi .............................. 22

Morrison ............................... 22

Noh .................................. 26, 29, 30

Perkins Canyon......................... 45

Popovich ............................... 52, 53

Port Ewen Limestone ................... 53

Rabbit Hill Limestone ................... 23, 56

Storff .................................. 29. 38

Sunday Canyon ......................... 29

Taylor Canyon ........................... 6, 8, 57

Tor Limestone ......................... 23, 28, 38

Trail Creek ............................. 29

Van Duzer Limestone ................... 29, 38

Vaughn Gulch Limestone ................ 29

Wenban Limestone .................. 6, 13, 23, 51

Windmill Limestone .................... 23

Woodruff .............................. 30

Page

......... 58

......... 51

......... 58

......... 57

......... 52

......... 47

......... 43

......... 50

......... 52

......... 44

......... 45

......... 52

......... 51

Fourmile Canyon Formation ................. 30, 51

fritschi, Monograptus ....................... 57

furnish!, Pelekysgnathus .................... 58

Fossil data, Antelope Peak ...

Cortez Mountains........

Hot Creek Canyon .......

Independence Mountains .

Maggie Creek Canyon ....

Monitor Range ..........

Shoshone Range .........

Simpson Park Mountains.

Sulphur Spring Range....

Toiyabe Range ..........

Toquima Range..........

Tuscarora Mountains .... 

Fossil zones. See Zones. 

Fourmile Canyon ............

gaertneri, Ozarkodina .......................

Garnet, South Ravenswood window ..........

Gatecliff Formation...........................

geinitzianus. Retiolites ................. 43, 44

angustidens, Retiolites ..................

Geisinid ostracodes .........................

Geologic setting ............................

Getchell gold deposit........................

Glytograptus...............................

tamariscus .............................

sp.

.. 6,13, 

28,31

50, 57

21

6,7,8

45,47

47,53

53

3

42

26, 46

57

49, 57

23, 24,

, 38, 43

41,42

2, 13

2, 14

42

42

42

2,8

43

49

46,53

47

26

28,45

46

54

58

47, 50

51, 57

54

39

Goat Peak window, Shoshone Range .

Gold.......................................

Carlin mine.............................

Cortez mine ............................

Gold Acres mine ............................

Gold deposits ..............................

Getchell.................................

Gold-ore deposits ...........................

Gothograptus nassa ........................

spinosus ...............................

gracilis, Monograptus vomerinus ........ 43, 44

grandis, Stomatograptus ....................

Graptolites, Copenhagen Canyon ............

Grass Valley .................... 13, 14, 19, 21,

gregarius, Monograptus .....................

greilingi, Lonchodina .......................

greylingi, Lonchodina .......................

griestoniensis, Monograptus ............... 43,

Gypidula pelagica ..........................

sp......................................

Gypsum ...................................

H

Halite ..................................... 39

hamatus, Cyrtograptus...................... 57

Hanaites sp. ............................... 53

Hanson Creek .............................. 26

Hanson Creek Formation ........... 5, 8, 26, 29, 47, 50

Happy Camp Formation ....................... 6, 7,8

Heavy Metals Program, Roberts Mountains

Formation ............................. 2

Heavy minerals ............................ 20, 38, 41

hercynicus, Monograptus ......... 27, 32, 44, 45, 52, 53

nevadensis, Monograptus ............... 30

Hermosa Formation ........................ 39

Hibbardella sp. ............................. 52

Hickison Summit quadrangle ................ 50

Hindeodella equidentata .................... 52

sp. ................ 43, 47, 48, 50, 52, 54. 55, 56, 58

Horn coral ................................. 51

Horse Creek Valley quadrangle .............. 50

Horse Heaven Mountain quadrangle ......... 49

Horse Mountain window, Shoshone Range .... 43

Hot Creek Canyon, fossil data ............... 58

Hot Creek Range ........................... 17

periclase ............................... 21

hughesi, Climacograptus .................... 57

Pseudoclimacograptus .................. 46

hvalross, Climacograptus . 

Hypotetragona sp. .......

Page 

45 

55

Icriodella sp. .......

Icriodina irregularis

stenolopata ....

sp..............

Icriodus ...........

.................. 52

.................. 54

.................. 50

.................. 49

.................. 47

pesavis ................................ 54, 56

pesavis-Spathognathodus boucoti Zone ... 54

woschmidti ............................ 47, 57

sp. ............................. 43, 51, 54, 56, 57

Ikes Canyon ............................... 27, 46

Illite....................................... 18

Ilmenite ................................... 21, 40

inclinatus, Spathognathodus ......... 43, 49, 52, 57, 58

inclinatus .......................... 48, 58

inclinatus, Spathognathodus ............. 48, 58

posthamatus, Spathognathodus .......... 43

wurmi, Spathognathodus ................ 55

inconstans, Trichonodella ................... 55, 57

Independence Mountains .................... 30

fossil data .............................. 57

graptolites ............................. 27

Happy Camp Formation ................. 6, 7, 8

Taylor Canyon Formation ................ 6, 8, 57

thickness .............................. 7

Thomas Jose Canyon .................... 27,57

Water Pipe Canyon ..................... 30, 57

Independence quadrangle ................... 29

Iron ....................................... 42

Iron minerals............................... 20

Iron oxide ...................... 6, 9, 13, 14, 19, 20, 22

Liesegang rings, Carlin mine ............. 13

irregularis, Icriodina ........................ 54

J, K

jaculum, Monograptus ...................... 44, 45

Jet Spring quadrangle ...................... 46

johnsoni, Spathognathodus .................. 55

Kaolinite .................................. 18

kentuckyensis, Ligonodina .................. 54

Kirkidium ................................. 49, 57

Knoll Mountain ........................... 26, 29, 30

Kockelella variabilis ........................ 50

kodymi, Monograptus ....................... 45

Laketown Dolomite ......................... 29

Lanthanum ........................ ....... 41

lapworthi. Cyrtograptus .................... 43, 47, 53

Lead ...................................... 42

leguminoides, Bairdia ....................... 53, 55

Leptaena sp. ............................... 51, 57

Leptocoelia ................................ 51

sp...................................... 53

Leptocoelina squamosa ..................... 53

Leptograptus sp. ........................... 45

Leucoxene ................................. 21

Ligonodina kentuckyensis ................... 54

sp. .......................... 44,47, 52, 54, 56, 58

Limestone, bioclastic ....................... 13

coarse-grained .......................... 22, 41

laminated ............................. 2, 6, S, 41

depocenters ........................ 11

interbedded ........................ 22

petrography ........................ 14

linguiformis, Polygnathus linguiformis ....... 55

linguiformis, Polygnathus ............... 55

Linograptid fragments ...................... 45

Linograptus sp. ............................ 54

Little Fish Lake quadrangle ................. 58

lobiferus, Monograptus ..................... 45, 57

Lonchodina cristagalli ...................... 54

greilingi ............................... 54

greylingi ............................... 54, 58

walliseri ............................... 50, 54
INDEX 65

Page 

Lone Mountain, dolomite .................... 17

graptolites ............................. 30

Lone Mountain Dolomite ........ 5, 6, 28, 29, 38, 47, 58

longispina, Aechmina ....................... 53

Lyrielasma................................. 53

M

Machaeraria sp. ............................ 48

Maggie Creek Canyon .................. 13, 28, 30, 52

fossil data .............................. 52

kaolinite ............................... 18

zircon-tourmaline ratio .................. 21

Magnetite ................................. 21, 40

Mahogany Hills ............................ 38

dolomite ............................... 17

Malm Gulch................................ 29

Manganese ................................ 41

mannopoma, Monograptus micropoma ....... 56

Marginia sculpta multicostata ............... 55

sp...................................... 55

Masket Shale, Toquima Range ............... 6, 23

Matrix calcite .............................. 14

McDermitt 1 ° X 2° quadrangle .............. 56

McMonnigal Limestone .................... 23, 27, 38

media, Ozarkodina ............ 48, 49, 50, 52, 55, 56, 58

medius, Climacograptus ..................... 44, 46

Member, Paradox .......................... 39

Salt Wash .............................. 22

Mercury ................................... 41, 42

Mica, white ................................ 21

microdon, Monograptus ..................... 53

micropoma, Monograptus ................... 49, 52

mannopoma, Monograptus .............. 56

migratus, Paltodus ......................... 57

Mill Canyon ............................... 13, 40, 46

zircon-tourmaline ratio .................. 21

Mill Creek window, Shoshone Range.......... 43

Millet Ranch quadrangle .................... 44

Mineral Hill quadrangle ..................... 52

Minerals, clay ......................... 6, 9, 10, 14, 18

detrital ................................ 21

diagenetic .............................. 21

epigenetic .............................. 14, 21

iron ................................ 21

heavy ................................. 20, 38, 41

opaque................................. 21

syngenetic ............................. 21

Mines, Bootstrap ............. 13, 23, 24, 27, 28, 38, 56

Carlin ................ 2, 4, 7, 13, 19, 27, 28, 41, 42

Cortez ........................ 2, 14, 27, 41, 42, 51

Getchell................................ 42

Gold Acres ............................. 42

North Star ............................. 28

Miniature Grand Canyon, Monitor Range .... 6, 23, 24,

28, 38, 48 

Miraculum simplex ......................... 55

Moenkopi Formation ....................... 22

Monazite ................................. 21, 38, 40

Monitor Range ............................. 23

Brock Canyon .......................... 28, 50

Clear Creek Mountain ................... 47

Copenhagen Canyon .................... 26, 48

dolomite ............................... 17

fossil data .............................. 47

Lone Mountain Dolomite .... 5, 6, 28, 29, 38, 47, 58

Miniature Grand Canyon ...... 6, 23, 24, 28, 38, 48

stratigraphy........................ 6

Rabbit Hill Limestone ................... 23, 56

Stargo Spring .......................... 49

thickness .............................. 7

Monoclimacis flumendosae .................. 52

sp. ..................................... 52

Monograptids ............................. 23, 30, 32

Monograptus............................... 47

angustidens ............................ 56

argutus ................................ 57

atauus ................................. 57

bohemicus ................... 46, 49, 50, 51, 52, 57

bohemicus-Monograptus dubius Zone .... 57

tenuis .............................. 50

Monograptus—Continued Page 

chimaera .............................. 48, 56, 57

clingani ................................ 44

colonus .................. 46, 48, 49, 50, 51, 52, 57

convolutus ............................ 44, 45, 47

Zone ............................... 57

crenulatus .............................. 43, 47

crinitus ................................ 49

crispus ................................. 45

cyphus ................................. 46

dubius ................ 43, 45, 46, 48, 49, 50, 51, 57

flemingii ........................... 43, 49, 51, 57

fritschi ................................. 57

gregarius .............................. 46

Zone ............................... 57

griestoniensis ......................... 43, 47, 50

hercynicus .................. 27, 32, 44, 45, 52, 53

Zone ............................... 53

nevadensis ......................... 30

jaculum ................................ 44, 45

kodymi ................................ 45

lobiferus ............................... 45, 57

microdon ............................... 53

micropoma ............................. 49, 52

mannopoma ........................ 56

nilssoni ..................... 45, 46, 48, 49, 50, 57

Zone ............................... 57

nilssoni-Monograptus scanicus Zone ..... 49, 52

pandus................................. 43

praedeubeli............................. 49

praedubius ......................... 48, 49, 51,53

praehercynicus ..................... 27, 50, 51, 53

Zone ............................... 50

priodon .................. 43, 44, 45, 47, 49, 51, 53

retroflexus ............................. 52

reuolutus ............................... 44, 46

riccartonensis .......................... 51

Zone ............................... 51

scanicus ........................ 44, 45, 47, 49, 57

sedgwicki .............................. 44

spiralis ............... 26, 32, 43, 44, 47, 51, 52, 53

Zone ............................... 53

testis ................................. 27, 54, 57

Zone ............................... 54

triangulatus ............................ 44, 57

uncinatus .......................... 49, 50, 56, 57

uniformis ............................. 23, 51, 56

Zone ......................... 6, 27, 28,51, 56

variabilis ............................... 43

vomerinus ...................... 43, 44, 45, 47, 51

gracilis ........................ 43, 44, 46, 53

yukonensis ............................. 45

sp.............................. 43, 44, 47, 56, 57

Montmorillonite ............................ 18

Morrison Formation ........................ 22

Mount Airy Mesa quadrangle ................ 43

Mt. Callaghan quadrangle ................... 45

Mt. Lewis quadrangle ....................... 43

multicostata, Marginia sculpta ............... 55

N

nassa, Gothograptus ........................ 43

Neoprioniodus bicurvatus ................... 56, 58

excauatus ......... 43, 48, 49, 50, 52, 54, 55, 56, 57

sp. ..................................... 54

Neothlipsura bispinosa ...................... 53

Nevada Test Site ........................... 29

nevadensis, Monograptus hercynicus ......... 30

Newsomites ................................ 55

Nickel ..................................... 41, 42

nilssoni, Monograptus ............ 45, 46, 48, 49, 50, 57

Noh Formation ............................ 26, 29, 30

Non-opaque minerals ....................... 22

normalis, Polygnathus ...................... 52

North Star mine ............................ 28

Northumberland Pass quadrangle ............ 45, 46

Nothognathella sp. ......................... 52

O

obliquicostatus, Distacodus ................. 44

Oepikodus sp............................... 45

Page 

Oneotodus beckmanni ..................... 48, 54, 55

Oolites .................................... 25

Opaque minerals ........................... 21, 22

ornatus, Dicellograptus complanatus ......... 45

Orpiment .................................. 42

Orthograptus .............................. 47

truncatus abbreviatus ................... 45

Orthoid .................................... 57

brachiopods ............................ 51

ortus, Ozarkodina........................... 54

Ostracodes, Geisinid ........................ 53

Ostracodes................................. 26

Ouachita geosyncline ....................... 32

ovalis, Polygnathus asymmetricus ........... 52

Ozarkodina denckmanni................ 48, 50, 51, 54

gaertneri ............................... 50, 57

media .................... 48, 49, 50, 52, 55, 56, 58

ortus .................................. 54

robustus ............................... 48

typica ................................. 50, 51

ziegleri ................................. 49, 56

sp........................... 47, 48, 54, 55, 56, 57

sp.B................................... 55

Pablo Canyon ........................ 8, 11, 26, 27, 44

graptolites ............................. 26

Ranch quadrangle ...................... 44

Paltodus dyscritus .......................... 50, 54

migratus ............................... 57

sp.................................... 50, 52, 56

Panderodus sp. ..... 43, 47, 48, 49, 50, 52, 54, 55, 56, 57

pandus, Monograptus ....................... 43

papilo, Trichonodella........................ 54

Parabolbina sp. ............................. 53

Paradox Member ........................... 39

pelagica, Gypidula .......................... 51, 57

Pelekysgnathus furnishi .................... 58

Pennsylvania Hill .......................... 29

Pentameroids .............................. 49

Pequop Mountains.......................... 3

Periclase, Hot Creek Range .................. 21

Perkins Canyon Formation .................. 45

Permian basin .............................. 39

pesavis, Icriodus ........................... 54, 56

Pete Hanson Creek ......................... 5, 22

Petes Canyon ...................... 6, 8, 23, 24, 26, 47

graptolites ............................. 26

Petrography ............................... 14,23

Pine Valley, laminated limestone ............. 11

Pinon Range ............................... 40

Plagioclase feldspar......................... 18

Plectospathodus alternatus .................. 50

extensus .............. 48, 49, 50, 52, 54, 55, 56, 58

sp........................... 43, 47, 48, 49, 54, 55

Plegmatograptid ........................... 45

Pleurograptus sp. ........................... 45

Pogonip Group ............................. 8

Point of Rocks ............................ 13, 38, 45

Polygnathoides emarginatus ................ 50

Polygnathus asymmetricus asymmetricus .... 52

ovalis .............................. 52

Zone ............................... 52

cristatus ............................... 52

decorosus .............................. 52, 56

linguiformis linguiformis ................ 55

normalis ............................... 52

Popovich Formation ........................ 52, 53

Port Ewen Limestone ....................... 53

posthamatus, Spathognathodus inclinatus .... 43

Potassium feldspar ......................... 18

praedeubeli, Monograptus ................... 49

praedubius, Monograptus ............... 48, 49, 51, 53

praehercynicus Monograptus ............ 27, 50, 51, 53

praepilatas sibiriea, Praepilatina ............. 55

Praepilatina praepilatas sibiriea .............. 55

priodon, Monograptus ........ 43, 44, 45, 47, 49, 51, 53

Prioniodina sp. ............... 47, 48, 50, 52, 55, 57, 58

primus, Spathognathodus ................... 56

Pseudoclimacograptus hughesi .............. 46
66 INDEX

Page 

Psilokirkbyella sp. .......................... 53

Pyrite ................ 6, 9, 14, 16, 19, 20, 24, 32, 38, 42

epigenetic .............................. 19, 42

syngenetic ............................. 19

Pyrrhotite ................................. 42

Quadrangles, Austin ........................ 45

Bare Mountain ......................... 29

Bull Run ............................... 29, 38

Cortez ................................. 30, 51

Danville ............................... 47

Dianas Punch Bowl..................... 46

Hickison Summit ....................... 50

Horse Creek Valley ..................... 50

Horse Heaven Mountain ................ 49

Independence .......................... 29

Jet Spring.............................. 46

Little Fish Lake ........................ 58

McDermitt 1° X 2° ..................... 56

Millet Ranch ........................... 44

Mineral Hill ............................ 52

Mount Airy Mesa ....................... 43

Mt. Callaghan .......................... 45

Mt. Lewis .............................. 43

Northumberland Pass ................... 45, 46

Pablo Canyon Ranch .................... 44

Rodeo Creek NW ....................... 56

Schroeder Mountain .................... 52

Spencer Hot Springs .................... 47

Standhope Peak ........................ 29

Stargo Creek ........................... 48, 49

Summer Camp.......................... 58

Tuscarora .............................. 57

Vigus Butte NE ........................ 45

Wildcat Peak ........................... 46

Quadrithyris Zone ......................... 48, 54, 55

Quartz ..... 6, 9, 10, 14, 16, 17, 18, 22, 24, 38, 39, 40, 42

Quartzite .................................. 22

R

Rabbit Hill Limestone ......................

Ramose bryozoans ..........................

ranuliformis, Spathognathodus ..............

Rattlesnake Canyon .................. 4, 13, 15,

zircon-tourmaline ratio ..................

rectangularis, Climacograptus ...............

Red Sea ....................................

remscheidensis, Spathognathodus ....... 48, 49,

resimus, Belodella ..........................

Resserella ..................................

Retiolites geinitzianus .................. 43, 44,

angustidens ........................

retroflexus, Monograptus ...................

revolutus, Monograptus .....................

Rhaphidograptus sp. ........................

Rhipidium .................................

riccartonensis, Monograptus .................

Roberts Mountains, thickness ...............

robustus, Ozarkodina .......................

Rodeo Creek NW quadrangle ................

roeni, Spinoplasia ...........................

rotundiloba^ Ancyrodella rotundiloba .........

rotundiloba, Ancyrodella ................

Ruby Mountains ...........................

Rugose corals ..............................

Rutile .................................... 21,

Saccarchites sp. .........

sagitta, Spathognathodus 

Salinity .................

Salopina .................

23, 56

51

57

28,51

21

42

44, 49

39

54,55

48, 55

49

45,47

47, 53

52

44, 46

46

48

51

7

48

56

53

56

56

28

6

38,40

Page 

Salt Wash Member ......................... 22

scalaris, Climacograptus ................... 44, 46, 51

scanicus, Monograptus .............. 44, 45, 47, 49, 57

Schroeder Mountain quadrangle ............. 52

Scolopodus devonicus ....................... 48, 50

sculpta multicostata, Marginia ............... 55

sedgwicki, Monograptus .................... 44

Seetoya sequence ........................... 30, 32

Sepiolate .................................. 14

Setting, geologic............................ 3

Shoshone Range .......................... 6, 8, 23, 30

fossil data .............................. 43

Goat Peak window ...... 6, 13, 23, 24, 28, 31, 38, 43

stratigraphy........................ 6

Horse Mountain window ................ 43

Mill Creek window ...................... 43

South Ravenswood window .............. 21, 43

thickness .............................. 7

sibiriea^ Praepilatina praepilatas ............. 55

Silica ...................................... 32

silurica, Synprioniodina ..................... 49

Silus acclivis ............................... 55

sp...................................... 55

Silver Creek ................................ 45

simplex, Miraculum ......................... 55

Simpson Park Mountains ................... 23

Coal Canyon ........................ 4, 19, 27, 50

fossil data .............................. 50

Windmill Limestone .................... 23

simpsoni, Atrypina ......................... 48

Solaris, Cyrtograptus ....................... 47

South Ravenswood window .................. 21, 43

Spathognathodus boucoti ................... 54

dubius ................................. 50

eosteinhornensis ........................ 50, 56

exiguus ................................ 47

indinatus ....................... 43, 49, 52, 57, 58

inclinatus .......................... 48, 58

posthamatus ....................... 43

wurmi .............................. 55

johnsoni ............................... 55

primus ................................. 56

ranuliformis ............................ 57

remscheidensis ..................... 48, 49, 54, 55

sagitta ................................. 56

wurmi ................................. 48

sp.................................... 43, 47, 52

Spencer Hot Springs quadrangle ............. 47

Sphalerite.................................. 21, 42

Spinoplasia roeni ........................... 53

Zone ................................... 53

spinosus, Gothograptus ..................... 49

spiralis. Monograptus ..... 26, 32, 43, 44, 47, 51, 52, 53

squamosa, Leptocoelina ..................... 53

Standhope Peak quadrangle ................. 29

Stargo Creek quadrangle .................... 48, 49

Stargo Spring .............................. 49

stenoloptata, Icriodina ...................... 50

Stomatograptus grandis .................... 47

Storff Formation ........................... 29, 38

Stramatoporoids ........................... 26

Stratigraphy ............................... 5

Strepula sp. ................................ 55, 56

Strophochonetes............................ 51

Strophomenoid ............................. 57

Styliolina ................................. 13, 28, 51

styloideus, Climacograptus .................. 45

Subfacies .................................. 3

Sulfur ..................................... 20, 42

Sulphur Spring Range ...................... 40

fossil data .............................. 52

graptolites ............................. 27

Lone Mountain Dolomite .... 5,6, 28, 29, 38, 47, 58

thickness .............................. 7

Summer Camp quadrangle .................. 58

Sunday Canyon Formation .................. 29

supernus, Climacograptus ................... 45

Swales Mountain .......................... 13, 28, 38

Antelope Peak depocenter ............... 13

Page

symmetrica, Trichonodella ................. 54, 55, 58

Syngenetic minerals ........................ 21

pyrite .................................. 42

Synprioniodina silurica ..................... 49

sp................................. 50, 54, 55, 56

Talc ....................................... 14

tamariscus, Glyptograptus .................. 57

Taylor Canyon Formation .................... 6, 8, 57

Tentaculites ........................... 13, 28, 51, 53

Tentaculitid................................ 53

tenuis, Monograptus bohemicus ............. 50

testis, Monograptus ....................... 27, 54, 57

Tetrasacculus sp. ............................ 53

Thomas Jose Canyon ....................... 27, 57

Thrust faulting............................. 3

Titanium .................................. 41

Toiyabe Range ........................... 6, 8, 10, 28

Clear Creek ............................. 28, 44

fossil data .............................. 44

Grass Valley ................. 13, 14, 19, 21, 28, 45

Pablo Canyon .................... 8, 11, 26, 27, 44

Point of Rocks ......................... 13, 38, 45

Silver Creek ............................ 45

southern ............................... 10

thickness .............................. 7

Wall Canyon .......................... 11, 26, 44

Toquima Range .......................... 6, 8, 10, 28

Black Cliff Canyon ............... 8, 11, 14, 26, 45

East Northumberland Canyon ........... 45

fossil data .............................. 45

Gatecliff Formation ..................... 6, 8

Ikes Canyon ............................ 27, 46

Masket Shale ........................... 6, 23

McMonnigal Limestone ................ 23, 27, 38

Mill Canyon ........................... 13, 40, 46

Petes Canyon .................. 6, 8, 23, 24. 26, 47

stratigraphy........................ 6

thickness .............................. 7

Tor Limestone ......................... 23, 28, 38

West Northumberland Canyon ........... 46

Wood Canyon .......................... 26, 46

Tor Limestone ............................ 23, 28, 38

Tourmaline ............................ 21, 22, 38, 40

Rattlesnake Canyon .................... 22

Toxicity ................................... 38

Trace elements ............................. 41

Trail Creek Formation ...................... 29

triangularis, Belodella ..................... 52, 54, 55

triangulatus, Monograptus .................. 44, 57

Trichonodella excavatus .................... 52

inconstans ............................. 55, 57

papilo .................................. 54

symmetrica ........................... 54, 55, 58

sp.................................... 44, 48, 49

Tricornina sp. .............................. 55

truncatus abbreviatus, Orthograptus ......... 45

Tubulibairdia sp. ........................... 55

Tungsten .................................. 42

Turbidites ................................. 7

Tuscarora Mountains .................... 9, 14, 23, 28

Bootstrap mine ........... 13, 23, 24, 27, 28, 38, 56

stratigraphy ........................ 6

Carlin mine ............ 2, 4, 7, 13, 19, 27, 28, 41, 42

fossil data .............................. 52

thickness .............................. 7

Tuscarora quadrangle....................... 57

typica, Ozarkodina .......................... 50, 51

U, V

Ulrichia sp. ................................ 53

uncinatus, Monograptus ................ 49, 50, 56, 57

unicostatus, Acodus ........................ 50

uniformis, Monograptus ................... 23, 51, 56

Van Duzer Limestone ....................... 29, 38
INDEX 67

Page

41

50

43

29

45

Vanadium .................................

variabilis, Kockelella ........................

Monograptus ...........................

Vaughn Gulch Limestone ...................

Vigus Butte quadrangle .....................

vomerinus, Monograptus ............ 43, 44, 45, 47, 51

gracilis, Monograptus ............... 43, 44, 46, 53

W

Wall Canyon .............................. 11, 26, 44

conodonts .............................. 26

walliseri, Lonchodina ....................... 50, 54

Water Pipe Canyon ......................... 30, 57

Weathering ................................ 8, 9

Wenban Limestone ...................... 6, 13, 23, 51

West Northumberland Canyon ............... 46

White mica................................. 21

Wildcat Peak quadrangle.................... 46

Page 

Wildhorse Creek ............................ 29

Willow Creek ............................... 27, 28

Windmill Limestone 

Wood Canyon ......

graptolites .....

Wood Hills .........

Wood River region . . Woodruff Formation

23

26, 46

26

28

29

30

Y, Z

Yttrium ................

yukonensis, Monograptus

Page 

Zircon ................................. 21, 38, 40, 41

Zirconium .................................. 22, 41

Zones, Amorphognathoides .................. 57

Asymmetrica ........................... 56

Cyrtograptus lundgreni ................. 57

Icriodus pesavis-Spathognathodus boucoti 54 

Monograptus convolutus ................ 57

gregarius ........................... 57

hycernicus ......................... 53

nilssoni ............................ 57

nilssoni-Monograptus scanicus ...... 49, 52

praehercynicus ..................... 50

riccartonensis ...................... 51

spiralis ............................. 53

testis .............................. 54

uniformis .................... 6, 27, 28, 51, 56

Polygnathus asymmetricus .............. 52

Quadrithyris .......................... 48, 54, 55

Zoned crystals ............................. 17